Falk Lumo

Wiesn Girls in dirndl

2011-10-03T02:15:00.000+02:00

A girl at Oktoberfest 2011 München (aka Wiesn). Wiesn girl #1

A trademark of Wiesn (the original Oktoberfest) are girls wearing dirndl for showing off their (sometimes remarkable) décolletage also known as cleavage. Dirndl are a traditional dress in Bavaria. It used to be worn by poorer working girls in the past. But more recently, it became rather popular at Oktoberfest because of its figure-hugging qualities. It even appears that the dirndl currently makes new friends all over the world. A fashion trend made in Munich.

So, all of this theoretically provides for ample of photo opportunities like in a giant fashion show. Except that Wiesn is a very crowded party zone and nobody would want to make it easy for you. On the other hand, taking photos is a tolerated sports as long as they are serious and don't show up in the internet without permission (which is why I omitted the face of people I have no permission from). Nevertheless, good décolletage photos are rare (except from prominent people posing to be photographed) and I made a test of what can be achieved.

Equipment wise, I used a Pentax K-5 with the DA* 60-250mm/4 using AF and a Pentax K-x with a DA 15mm/4. I fixed the latter to f/8 and 1.4m manual focus with SR turned off to have sub-second reaction time to take photos in the crowd. No photo bag to keep a low profile. This turned out to be quite a capable combination.

Actually, the girl in the opening image is taken from a video I took with the K-5 at 250mm using manual focus while she walked up the staircase to the Bavaria monument at Wiesn. The manual focus was difficult to maintain (and is not perfect). But I still like the result as a photo I may not have been able to shoot as a still.

Below is this staircase in the background.

Bavaria monument

Below, I'll show impressions from Wiesn 2011. Note that many images are heavily cropped. Also, some post-processing was applied to reduce some hard shadows from the sunny day.

Wiesn girl #2

Wiesn girl #3 (note the cleavage)

Wiesn girls #739.347 to #968.567

Wiesn girl #4 ("Awaiting him while being looked at")

Wiesn girl #5

Wiesn girl #6

Wiesn girl #7

Wiesn girl #8

I'd like to know from any comments if you like the fashion trend at Oktoberfest. It definitely provides for some nice eye catchers. If you have any favourites in this mini series, post a comment. I'd like to know your taste too :)

Thanks for stopping bye and I hope you enjoyed your stay.

Falk

A hypothetical Pentax DFA* 500mm F5.6 ED(IF) SDMii

2011-04-26T20:43:00.001+02:00

Goshawk  

Young goshawk in the wild near our garden.  The 35mm-equivalent focal length is 2600 mm. Shot with a Pentax K-5 and Pentax 1.7x AF converter using a 500mm lens. Cropped to half size.

The Pentax system as great as it is does still lack a super tele lens option from Pentax which is in production. This made me wonder which lens exactly Pentax should do to both fill the empty space and to attract new photographers into their system.

Pentax once was famous for optically great and affordable super tele lenses such as the Pentax FA* 600mm F4 or gorgeous 645 600mm F5.6 etc. It is a shame they take so long to revive their tradition of great long glass.

To my big surprise, the answer which lens to start with was pretty easy:
A Pentax DFA* 500mm F5.6 ED(IF) SDMii.

Before I'll dig into details, let me explain why. First, shorter lenses don't make sense with a popular DA* 300 F4 or DA* 60-250 F4. After all, digital cameras are crop machines and need larger steps between lens options to make sense. But an even faster or longer lens becomes too expensive to be a smooth enough upgrade (as detailed below, a 600/5.6 would have to be 80%, a 500/4.5 100% more expensive). Same goes for a very long zoom lens which would become too heavy and too expensive too. Moreover, f/5.6 is really fast enough with the advent of great sensors such as the one in the Pentax K-5.

However, it must not be slower than f/5.6 (or maybe f/5.4) because then the Pentax AF system wouldn't work anymore in conjunction with an 1.4x tele converter. Yes, it does work with f/5.6 or f/7.8 effective. How do I know? Well, the above photo was shot with a Sigma 500mm f/4.5 APO manual lens and the Pentax 1.7x tele AF converter which is f/7.7 effective. The AF works flawlessly and fast! Heck, the K-5 even gives me a stabilized 850 mm autofocus lens this way :)

A 500/5.6 lens really is the sweet spot between long enough, fast enough, not too heavy and not too expensive. And it is the missing option from Sigma, Sony, Canon and Nikon! Their product suites are all so 2000-ish! Optimized to be fast, expensive and heavy rather than the versatile resolution super weapons modern sensors need so much.

Pentax DFA* 500mm F5.6 ED(IF) SDMii details

I compared a couple super tele primes from Sigma and Canon (Canon MSRP prices divided by 1.34 to meet Sigma MSRPs, e.g., for the 800/5.6). The following two formulas are the best description to predict weight and price:

Weight [kg] = D[mm]^2.20 /12000 (typical error is +/- 15%)

Price [MSRP in USD] = D[mm]^3.26 /1177 (typical error is +/- 25%, street price shouldn't be higher)

D is the diameter = focal length / f-stop number.

D^2 is the expected term describing how glass surface grows with diameter. 2.2 accounts for increasing thickness, I guess. Price should be proportional to weight but isn't. It has an extra factor D probably accounting for increasing rareness and hand-made production steps. Anyway, the above formula allows to describe the lens in fairly accurate terms:

Lens: Pentax DFA* 500mm F5.6 ED(IF) SDMii
Mount: Pentax KAF
Price: 1940 USD (MSRP)
Weight: 1630 g
Filter size (front): 91 mm
Length: 300 mm
Close distance: 4 m
Lens elements / groups: ~12 / ~11 (e.g., like the Pentax A* 645 600mm F5.6).
Stabilized: Yes (in body)
Autofocus: Yes (SDM, version 2 (ring motor); screw drive supported; focus limiter in firmware)
Teleconverter: Yes, optomized to support Pentax DFA 1.4x SDM converter (tba ;) )
Image circle: 43mm (full frame)
Weather-sealed: Yes
MTF characteristics: Blur widths below 2px in the center, similiar to DA*300, outresolving the sensor x2 ("made for cropping" (tm)).

Option:

Pentax DFA 1.4x SDM converter
700 mm, F7.8, phase AF supported in daylight.

I am pretty sure that this lens would sell in a volume high enough to make it an economically viable option for Pentax. And drag new users into the Pentax system. And keep existing users happy as well ;)

Pentax, where is your pre-order page? :)

LumoLabs: Pentax K-5 low light focus with firmware upgrade 1.03

2011-03-27T03:53:00.001+02:00

Fig.1: "Caribbean Sunset".
Why doing measurements is no substitute to taking photos (taken while I type) ;)

The current story is continued from the blog article Pentax K-5 low light focus after Pentax has published the version 1.03 firmware upgrade officially featuring an improvement of focus operation in low light.

When the 1.03 update was released, many users reported positive findings. So, I was optimistic to find that the low light focus issues are a thing of the past. Unfortunately, this isn't what I eventually found.

Please refer to the updated version of the complete paper for my findings:

www.falklumo.com/lumolabs/articles/k5focus (HTML version)
www.falklumo.com/lumolabs/articles/k5focus/K5Focus.pdf
(PDF version for download and offline reading)

Summary:

Basically, I find no significant difference between firmware versions 1.02 and 1.03 when using my testing scenarios. This means that there is no significant improvement if:

The background is white
The target has high contrast
The AF assist light is disabled

Under the above circumstances, the K-5 auto focus starts to lock focus in a false front focus position at tungsten light levels below 0 EV for a fast lens (like f/1.8) or below about 2-4 EV for slower lenses. This did not change at all with release 1.03. Note that the above light level values would read 2-3 steps higher with a target like a Caucasian skin (18% gray).
Moreover, I found that at low enough light levels, the 1.03 firmware seems to rely more than 1.02 on color information outside the direct selected AF spot. With a uniform color distribution, this can lead to somewhat improved results in the vicinity of the focus shift transition. OTOH, the focus system is more easily fooled by features with a singular color. Overall, the advantages may dominate and the effect is small anyway. Version 1.03 still doesn't seem to make use of white balance information, either manually or automatic.

If I believe that Pentax improved the low light focus situation for many users of the 1.03 firmware, then the progress must be bound to any of the following:

AF assist light engages more actively (not tested by myself).
Focus improved in the presence of dark backgrounds (not tested by myself).
Focus improved with low contrast or dim focus features (not tested by myself).

As I don't have a version 1.02 K-5 anymore, I cannot find it out. But any progress brought by the 1.03 firmware upgrade is limited rather than universal.

As much as I applaud Pentax to having addressed the problem, as much I am a bit disappointed they didn't dig deep enough to address the root problem: that the K-5 AF subsystem locks focus even in a situation where the colorimetric sensor(s) fails to determine the light color. It simply shouldn't lock focus at all then. Or ask for user assistance like a priming shot. The light-sensitive AF system of the K-5 has too strong a color dependency to autofocus if the color of the focus feature remains unknown.

A better workaround than 1.03 in firmware is feasible and should stay on Pentax' agenda.

Please, read the full paper linked above if you have further questions and come back here to leave comments or questions. General comments about the issue should still go to the general (earlier) article while firmware release 1.03 comments should go here. Thank You.

LumoLabs: Pentax K-5 low light focus

2011-02-23T01:12:00.002+01:00

Note: I updated the article to version 1.3.
2011, March 27.

Note: I updated the article to version 1.1.

I think, the feedback and experiments done after version 1.0 helped to understand the observed focus behaviour rather well and version 1.1 takes this into account.

An important (new) aspect is a description how low key studio photography, esp. when combined with an f/4 lens (or slower), can lead to inaccurate focus.

2011, March 07.

Fig.1: Accuracy of the Pentax K-5 phase detect AF vs. luminosity in EV. The above chart includes all measurements, i.e. various lenses, light colors, distances and apertures. The accuracy is measured as deviation of the focal plane from the sensor plane, in µm.

In modern times, each new release of a digital SLR camera seems to be accompanied by teething troubles. This applies to all makes across the board. Sometimes, they are fixed quickly by the vendor, like the “Green Line Syndrome” video issue in the Pentax K-7, the “Hot Pixel” video issue in the Nikon D7000 or the “String of Pearls” stain issue in the K-5. Sometimes, they aren't like the shutter-induced blur issue with the K-7 which LumoLabs succeeded to document in this blog.

Currently, there are two remaining teething troubles for the K-5 which are widely reported: wrong PTTL exposure with external flashes in some situations (confirmed in writing by 3rd party flash makers, even for Pentax' own flashes). And a systematic wrong lock of autofocus in low (tungsten) light.

Therefore, LumoLabs has decided to have a closer look at the issue. After careful evaluation and many hundred test shots we found the issue to be real. Pentax has unofficially reported to work on the issue. The pressure is on them to address the issue and the author hopes that our findings may contribute to their efforts. Buyers of the K-5 must be able to be confident that the issue is fixed sooner than later.

A preliminary copy of the paper was provided to Pentax earlier this week and the head of Pentax Europe officially receives a printed copy today. I have been told that Pentax engineering will receive a copy too.

The study

The results are too complex to be presented in the scope of a blog. Fig.1 above provides a first idea of our work.

Please refer to the complete paper for our findings:

www.falklumo.com/lumolabs/articles/k5focus (HTML version)
www.falklumo.com/lumolabs/articles/k5focus/K5Focus.pdf
(PDF version for download and offline reading)

You'll gain a deeper understanding of Fig.1 too ;)

In a nutshell, this is what we find:

The K-5 as it presently ships indeed has a flaw in its phase detect autofocus module or software which causes it to front focus in low light below a lens-dependent threshold in EV.
If it does, it seems to consistently focus ≈ 255 µm behind the sensor plane (although with a significant ± 75 µm scatter of results which is about twice as large as the normal scatter of result).
Faster lenses seem to keep working in lower light but of course, are prone to more blur when the front focus does eventually happen. Slower lenses can already start to front focus at light levels metering as 4 EV or 6 EV even. A fast lens may work down to 0 EV in white light.
Light sources other than daylight emphasize this problem as they simply appear darker to the AF module. Moreover, it seems to be moderately color blind for red which further emphasizes the effect in deep tungsten light.
The effect is real and can negatively impact the daily work of a photographer. On the other hand, it is possible to run into a low light tungsten situation without the problem.
The paper clarifies conditions to hit or avoid the issue. White light (halogen is not white enough though) and a wide lens stopped down help to work around the problem. AF assist light typically doesn't help though. But an LED flash light does. ;)

It may be interesting to note what we did not find: There seems to be no strong dependency on the light color. Except that colored light causes the transition to happen earlier as it means less usable light for the AF module. It seems to have a somewhat low sensitivity esp. for red light. Moreover, there seems to be no dependency on actual aperture or distance.

Move focal plane by 0xFF µm? Yes, do it so! :)

This may describe what's going on behind the curtain: a µm-valued variable becomes 0xFF (255) and causes a false shift of the focus plane by 255 µm. I call it the +0xFFµm hypothesis. :)
- Is it likely? No.
- Is it possible? Yes.

Please, read the full paper linked above if you have further questions and come back here to leave comments or questions. Thank You.

LumoLabs: Pentax K-5 shutter

2010-12-01T23:08:00.001+01:00

Total blur widths as a function of shutter speed for a Pentax K-7 camera (red) and a Pentax K-5 camera (green).

Our recent study of shutter-induced blur for the Pentax K-7 SLR camera has created a lot of buzz in the Pentax community. We are now actually watching to see similiar work been done for cameras of other vendors too.

Meanwhile of course I have been more than curious to see how the Pentax K-5 camera performs in this regard. I am glad to say that the lab work is done and a report is published. You may access it here (HTML and PDF):

www.falklumo.com/lumolabs/articles/k5shutter/

In a nutshell: Pentax may not have changed much. But the little they changed helped. The increase of blur due to shutter operation (the amount which the image blur increases by at certain shutter speeds) is almost halved with respect to a K-7, at least at the most critical speed around 1/80s.

You may see this from the chart as depicted above as well. On average, the K-5 shutter induces a pixel blur increase by less than a pixel which should not be noticeable in day to day work. Normally, the increase is less due to other sources of softness or by not shooting at the shutter speed where the effect is largest.

Also note that every camera with a focal plane shutter (every SLR) will exhibit a certain amount of shutter blur for physical reasons.

We are not surprised to see the issue of shutter-induced blur for Pentax mitigated in the K-5. After all, the previous study for the K-7 was in reaction to numerous complaints and for the K-5, the first user feedback is very positive, incl. sharpness at the critical shutter speeds.

The conclusion cited from the white paper is this:

The shutter-induced blur in the Pentax K-5 is measurable but it should be small enough to be of no concern in day to day photography. The absolute magnitude of the effect sits halfway in between a K20D which has almost no measurable effect and a K-7 which exhibits an effect large enough to make some people notice in their work.

The matter may now have reached a satisfactory state with the K-5. But there remains work to be done for Pentax to fully understand and eliminate any unnecessary effects which compromise image sharpness.

It would be interesting to test another camera with fast shutter (like a D300s) to compare the absolute magnitude of the shutter blur effect which is never zero. Esp. at ~1/160 s. Ideally, vendors would measure it and make part of their cameras' shutter specification.

Pentax K-5 Preview

2010-09-28T23:32:00.004+02:00

A cut model of the Pentax K-5 as shown at Photokina 2010
"The engineering masterpiece" (photo © 2010 Falk Lumo)

The Photokina 2010 has just closed its doors and I am compiling my findings regarding Pentax into this article. I posted my first impressions a week ago.

Pentax K-5

The most exciting part (besides trying out the 645D) certainly was to find out about the new K-5 camera. I gathered a lot of material from various sources and wrote a full Pentax K-5 hands-on preview report. A short blog article turned out to be the wrong format and therefore, I posted it on my website. Here you go:

-> Pentax K-5 hands-on preview

Don't miss the exciting news. Moreover, I tried to answer as many questions I received as possible in the report and to skip as much redundant info as possible too.

However, a small number of questions didn't fit the K-5 context so I am putting them here:

Lens questions:

DA 35mm f/2.4:

The new DA 35/2.4 introduced short before Photokina is specified here:

DA 35/2.4 press release by Pentax Japan (English version)

The production capacity is 2/3 of that of the 18-135 lens and will be available as a kit lens for the K-5. Early reports about the 35/2.4 have been very positive (sharpness wide open, bokeh, very fast focussing, maybe 35mm image circle) and as a kit, may have a very attractive pricing.
The kit will be black only and non-black versions are said to be unavailable (at least outside Japan).

DA 18-135mm f/3.5-5.6:

This lens was announced together with the K-5 at Photokina and is specified here:

DA 18-135 press release by Pentax Japan (English version)

The lens was received with much interest and will be offered as a kit lens for the K-5 too. A number of features I could clarify:

The aperture ranges are as follows:
18-19 mm f/3.5
20-29 mm f/4.0
30-79 mm f/4.5
80-135 mm f/5.6
DC focus motor:
"DC" stands for direct current according to one source, and for dual current according to another. That needs further clarification although my bet is with the direct current camp ;)
Focus motor noise:
The focus motor almost certainly is not ultrasonic. I tried to listen despite the show's background noise. It sounds different than an ultrasonic motor (it's more motor-like, less twitter-like) but isn't necessarily (much) noisier.
Focus motor speed:
The focus motor appeared to be about as fast as a DA*16-50mm ultrasonic motor. Which isn't fast exactly. The DA 18-55 WR kit lens is a lot faster!
Pentax missed a chance to deliver a higher speed focus motor (e.g. ring type) rather than a lower production cost one.
Image quality:
I don't know. From the specs, it could be better than that of a usual floating aperture lens.

Teleconverters:

Pentax showed its 1.4x autofocus teleconverter at Photokina 2 years ago. It has disappeared. I asked what happened to it. The response I obtained was hard to accept: Pentax Germany requests production of the teleconverter but Japan denies saying that teleconverters aren't required anymore in the digital age. Pentax Germany tried to explain that a digital magnification may actually have a negative impact on image quality (as we all know) but obviously it did not help much. What shall I say...?

Post Photokina Pentax strategy (as I guess it):

Overall, Pentax is a bold performer in 2010: 645D, K-5 and K-r seem to be 3 winners. And the company itself is making profit. So what else should it take to make a Pentaxian a happy Pentaxian? Not much should one think. Esp. as an Olympus E-5 (good-bye gift?), Canon 60D (downgrade?) and Nikon D7000 (Pentax clone?) are not particularly exciting. But the grass never is green enough ;)

It's because many Pentaxians are addicted to their hobby. They want to invest further in their system and are imaginative enough to foresee "their" camera and lenses in one or two years time.

Therefore, it's a bit irritating that all signs emanating from Pentax at Photokina (foremost but not only from Pentax Germany staff) cry out: we're not going upstream with the K mount. Not now. The 645D digital medium format is as professional as one may actually desire. "Unfortunately" however, cameras in the tradition of the *istD or the higher end film bodies attracted quite a few rather professional photographers into Pentax. Over the last couple years, their fraction is shrinking though and this Photokina won't halt it. It's no fortunate coincidence either that no new Star-lenses are announced and FA Ltds. are tagged "end of life" (whatever that means...) in Germany. Personally, I also don't expect a revival of non-standard lenses (like 85/1.4, 135/1.8, 300/2.8, 600/4, maybe not even a 400/5.6), based on a statement that the rarer lenses aren't currently profitable for Pentax to make. And I hear a bold "no" to full frame. Pentax doesn't see their enthusiast user base go full frame.

To be fair, nobody knows about the future prospect of mirrored cameras. On the other hand, Pentax seems still to be in an evaluation phase with respect to mirrorless cameras and meanwhile anticipates to sell the K-r against mirrorless cameras from other vendors. This worked out fine in the past (with the K-x) but Pentax may start to realize that this won't continue for too long. So, it may be understandable that in this atmosphere of change, Pentax may not invest in the $1500+ segment in order to re-establish their share in that market segment. On the other hand, Pentax learns that what was the $1500 segment (K-7, D300) now is the $1200 segment (D7000) and soon will be in a region with aggressive price competition. As will be mirrorless cameras.

So, some kind of either upstream or innovation strategy was expected and missed from Pentax at this year's Photokina. That's the one complaint. But I hear it from many, from Pentaxians and all over the press watching the market: "where is Pentax heading?".

As a side note, there has been staff from Hoya visiting Pentax and Photokina. E.g., Ned Bunnell was spotted at Photokina and Eguchi Kazumichi (head of marketing imaging systems division) gave an interview. So, if anybody (not me) had a chance to meet with Hoya Int'l management at Photokina and exchange some ideas, please drop a comment... ;)

Summary and verdict:

K-5: Very solid and satisfying performance. (as known so far)
Hoya Pentax: In good shape but tight on resources. Communication skills leave some room for improvement.

P.S.
I activated some ads on my blog. It enables a certain guy to pay reparations:) (just joking!)

Photokina 2010: First impressions

2010-09-20T13:14:00.005+02:00

Marie showing the Pentax K-r.

This morning, I made a first tour across Photokina opening tomorrow in Cologne. It is already open to the press and most booths are still under construction. I'll report more about Photokina later today and this week. Nevertheless, I have a couple first impressions to share.

Pentax

Pentax K-5

Pentax officially launched the K-5 which is the successor to the K-7. A body is still on its way to Cologne and I'll have more about it soon. The press kit is out though and these are the specs:

Same specs as the Pentax K-7 which it succeeds, except:
New CMOS sensor with integrated A/D converter and 16.3 MP (4928 x 3264).
Noise reduction configurable per ISO.
New prime II four channel processing (but I believe K-7 had prime II too).
7.0 fps.
New SAFOX IX+ 11 point autofocus with higher light sensitivity (larger light intake).
"Complete rehaul and faster and more accurate".
ISO 80 to 51.200 (standard is 100 to 12.800).
Sensor position is adjustable in order to tune to lens (whatever this means, I will clarify).
Full HD video with 1920x1080 25fps.
HDR with image alignment and adjustable equalizing parameter.
Golden rule grid and scale grid in LV.
Electronic horizon for roll (old) and pitch (new).
670g body only w/o batteries.
German list price body only €1.459,- which includes 19% VAT.
Available in October 2010.

The press kit is full of errors and I'll have to verify a number of other details first. E.g., I doubt that the camera ships June 2009 ;) Meanwhile, I verified and it ships next month already! They fixed a number of other errors too.

The price hints at a US list price of $1,399.- which is only $100 more than the D7000 and means that both cameras will have an equal street price.

Let me repeat: The K-5 is not more expensive than the D7000!

... updated and continued from the break ...

Two points I have run a quick test for are (i.e., I may have missed a hidden custom function): no manual control in video (merde) and almost certainly no f/2.8 center AF sensor. However, the AF box on the bottom of the mirror box changed indeed. I took a photograph of it. The AF feels faster too.

"Sensor position is adjustable in order to tune to lens" and "New prime II processor" are two questions Pentax has to call back Japan to find out what this actually means ...

I'll have more about the K-5 in a separate blog article.

Pentax DA 18-135mm f/3.5-5.6 ED WR new kit lens

This lens has the additional "DC" designation. I asked. It stands for a new, faster ultrasonic focus motor. Pentax could not answer the question if this implies a ring type motor. The list price is 799.- € incl. 19% VAT.

Pentax 645D

Pentax introduces the applauded 645D medium format digital camera in the Europen market. It is the same model as in the Japanese market and will be available January 2011 for 10,000.- € incl. 19% VAT list price. Add another 1,000.- € incl. 19% VAT list price for the 55/2.8 lens.

The positioning is straightforward: best image quality for both the entire range of outdoor as well as indoor photography. What a well defined positioning ;)

I heard people say that the backlog of orders in Japan is slowly decreasing now and this is why delivery outside Japan has become possible. In other words, it was sold out which is why we haven't seen more gray imports actually.

The 645D press announcement contains no mention about a creation of a professional support network. I heard that this is under consideration though. Strange.

For anybody visiting Photokina: Pentax has one single 645D in the business area behind the public area of their booth. This is an restricted area. You normally have to be press or a business partner to enter. But insist a bit, maybe refer to my blog, and I think you will be able to do a quick test. Bring an SD card because you can put your own card if you don't ask ;)

Fuji Finepix X100

Fuji announced a camera in development, the Finepix X100. They showed a prototype and it is awesome. It is the perfect blend between a rangefinder and an EVIL camera. Well, almost because its lens isn't interchangeable.

It is an APS-C camera with a an "exceptional resolution" 23mm f/2 fixed prime lens and a very rangefinder-like viewfinder: It is both optical and electronic! You switch between optical and electronic. Additionally, the optical viewfinder may display an electronic overlay for additional information. And so, it is no surprise the camera looks like a rangefinder.

I asked why not with a lens mount? Answer: We want see how this one sells first. I asked: but you know that if this version does not sell it may be because it has no mount? Answer: no, is it so...?

Obviously, the X100 was made to compete against the Leica X1. With the optical viewfinder as its bonus. I asked if its cheaper than Leica X1. Answer was hesitant. Eventually they gave me "1000" as a ballpark number which would be about 2/3 of a Leica X1.

The Finepix X100 was one of the positive surprises of the Photokina.

More colors

Who says that Pentax is the only company with colorful bodies?

An Olympus P&S embedded into a frozen block of melting ice. Marie is behind the block though :)

Ah yes, Olympus showed the E-5 of course and a concept camera which is said to compete against the Panasonic LX5 with a high resolution Zuiko lens. They denied to answer questions about its sensor size. However to my eye, the camera looked larger than an LX5.

Lomographical bodies in various colors.

I'll update my blog with more articles about the Pentax K-5 as soon as possible. Enjoy the read for the time being.

Photokina 2010, Pentax and the full frame mystery

2010-08-06T18:07:00.020+02:00

Only a few days left until Photokina 2010

Or why at this year's 2010 Photokina exhibition, Pentax may not get
away with ignoring the full frame conumdrum.

Many users of digital SLR cameras may not be aware that the sensor in their
camera is smaller than it used to be in the era of 35mm film. Most dSLR cameras
use an APS-C sized sensor which does only have about 40% of the surface of
a "full
35mm film frame", or "full frame" in short.
Of course, this is expressed by the crop factor and users actually do know
about this. They simply ignore this. And they have reason to do so: the image
quality exceeds that of full frame film cameras and therefore, there seems
to be no reason to care about the detail of sensor size for a dSLR camera.

But as always, there is a school of photograhers who do not agree. It can
be shown that a larger sensor -- when combined with lenses which fully exploit
the design options offered by a larger sensor -- delivers superior image quality.
Independent on how great it was in the first place. After all, it's the reason
of digital medium format cameras to exist. Moreover, the lens mount of all dSLRs
with an APS-C sized sensor is desgned for full frame lenses (lenses with an
image circle large enough to use the entire surface of a full frame sized sensor).
Simply because those mounts are from the 35mm film era. And because it is the
mount (diameter and registration distance) which determines the majority of
the size of an SLR camera, a full frame dSLR wouldn't need to be (significantly)
heavier
or
bulkier
than
an APS-C
dSLR.
Four-Third sized SLR cameras are an exception as their mount isn't full frame
capable. But we can savely ignore it after the impact of this sensor size on
the SLR market has almost vanished after the introduction of Micro Four-Third.

The opening photo is that of a Pentax APS-C dSLR certainly bulkier
than any full frame Pentax film SLR has ever been. Actually, the famous 30+
year old Pentax MX full frame film SLR is smaller than any digital SLR on the
market today, whatever small be its sensor. A full frame dSLR could certainly
be made more compact than the APS-C dSLR shown on the photo above.

So after dismissing the size disadvantage, we are left with only three arguments against a full frame camera which
all disappear on closer inspection, too:

Full frame sensors are too expensive and only pros
can afford it. Right?

Well, from public cost models I computed upper bounds
for
2010 manufacturing costs for APS-C and full frame sensrs and the difference is
less than $100 (*) ! Of course, semiconductor vendors will
add significantly different margins as long as this
market doesn't heat up.
(*) Note: for all claims made in this article, look up the "Furter reading" section at the end of the article for further reference.

The lenses are too expensive, bulky and heavy. Right?

Well, equivalent lenses (different lenses but such that
they provide equivalent image quality for different
sized sensors) have the same size and weight for APS-C
and full frame. And are a bit less expensive
for full frame! Which is easy to explain by looking
at lp/mm resolution requirements.

One needs longer, heavier, more expensive tele lenses
because one looses the crop factor. Right?

Well, about heavier and more expensive, read above. About
longer, that's actually a function of the pixel pitch,
not the crop factor. There is no reason why a full frame
camera should have a larger pixel pitch than an APS-C
camera. Currently and for cost reasons only, most actually
do indeed. Although the difference is already as small as 5µm vs. 6µm. And it is going away. Read about the cost factor above.

So, we are left with a situation where a full frame SLR
should be a no brainer. But as always, things aren't as
simple as they appear.

Market segmentation

Because full frame cameras can deliver better image quality
they appeal to a higher segment of the market. The so-called
enthusiast and professional photographer markets. There
is a hidden consensus between Japanese camera makers (with
maybe the exception of Sony) to draw excessive margins
from the full frame market. Therefore, full frame dSLRs
are either prohibitively expensive (Nikon D3X, Canon 1DsMkIII) or crippled
in one way or another. Sometimes not voluntariliy (Sony).
And they are all bulky and ugly because they have to show
"full frame inside", right? ;)

But despite all the artificial barriers to keep the
markets segmented, more popular models like Canon 5DmkII
or Nikon D700 have risen to 2-3% unit market share each
(estimated from BCN figures). Adding the many professional models from
Canon
and Nikon and the very affordable Sony A850 we have
a unit market share of full frame dSLRs of 5-10%.
Of couse, each new model sends shock waves thru this segmentation
and an upgrade to the D700 is expected
later this year. The figures do also mean that full frame
dSLRs create a significant portion of the vendor's overall
margins,
possibly in excess of 30%.

Overall, the dSLR market is in a state like a supercooled
fluid: the right perturbation and the segmentation will
implode and all but the entry-level SLRs go full frame
(the entry-level SLRs go mirrorless Single Lens Digital
(SLD) anyway...). Think of a full frame Canon 7D or Pentax
K-7 in terms of ergonomics and speed, for well below $1800
settled street price ...

Pentax and the Full Frame mystery

Pentax is an interesting special case. They have not offered
a full frame dSLR yet and always denied any plans to launch
such a camera. On the other hand, Pentax is the brand of
the image quality perfectionist and landscape photographers.
Pentax was the first trying to launch an enthusiast full
frame dSLR, back in the year 2000 (the famous 6MP Pentax
MZ-D), three years before they launched their APS-C dSLR.
They were the first to promote weather sealed bodies and
lenses
for outdoor photography, the first to offer a 15MP APS-C
dSLR (the Pentax K20D) and they are even first to offer
an enthusiast digital medium format SLR below $10,000
(the Pentax 645D). So, they shoud be predestined to offer
the
first
ergonomic
outdoor 20MP+ full frame dSLR in the enthusiast market
segment (~$1200 to ~$1800). This could make
their market share explode.

But there are problems: Pentax burned fingers when trying
to be full frame in 2000. And they burned bridges when
later launching their APS-C only line of dSLRs. Because
for 5 years, they developped APS-C lenses
only and assured the market that their lens investments
are safe because full frame cameras won't come back. In
mid 2008 though, they seem to have changed direction again
and almost no new lenses have been introduced. Two new
lenses, introduced in 2008/2009, the DA*300 and the
DA*60-250/4, are patented as full
frame lenses, actually. So, who knows ... But at least
officially, Pentax is now short in full frame lenses. And
because they never left the decision between APS-C and
full frame to their customers, any announcement about a
forthcoming full frame camera could stall their on-going
business. Well, Pentax may even fear to cannibalize their
new digital medium format business which seems to have
a bright future.

Most importantly though and because they burned fingers
once, Pentax may be convinced that their share of the full
frame market is simply too small, like 5% of 5% or 0.25%
only.

And if deciding to divert development resources, they
may as well decide to invest into the SLD market to protect
their cash cow.

So, when looking at the current or past situation, there
is no reason for Pentax to launch a full frame dSLR camera.
But what about when looking into the future?

This is were the community of Pentax photographers (called
Pentaxians by Pentax) comes into play.

Pentax and the year 2011

2011 will be the year where everybody sells SLD cameras,
Pentax included. Everybody. Pentax will have a genuine
SLD camera. As will Canon and Nikon. But where are buyers
coming from? Well, mostly upgraders from the dying point
& shoot market (in majority shifting to cell phones) and
migraters from equally priced (i.e., entry-level) dSLR.
So, to launch an SLD camera is vital to preserve a market
share in the $400 - $800 segment. Exactly where the Pentax
K-x attracted new buyers to Pentax in the year 2009. But
all
of this doesn't help to preserve the enthusiast (Pentaxian)
market which is the $900 - $1800 segment.

One may argue that the enthusiast market isn't that important
for Pentax from a point of view of turnover. But according
to my own analysis, K-x, K-7 and 645D each create about
the same amount of earnings. Simply because
the mass markets are always small in margin. But most importantly,
blogging Pentaxians are the most influential group: they
are opinion leaders in forums where magazine authors and
store managers draw their opinion from and recommend some
products or not. Unlike in previous years, this group
of opinion leaders has expressed very clearly that they
either expect to see Pentax going full frame in the enthusiast
segment, or leave the brand. I refer to bloggers like LanceB,
once selected "Pentaxian of the year" and who now test
drives a D700 before taking final action.

Pentax is already seeing that Pentaxians put themselves
onto "hold and wait": The sale of expensive DA lenses has
declined while the market for used (full frame) FA and
A lenses is still healthy. This isn't only due to a lack
of new DA* lenses. It is mostly due to the fact that the
enthusiast market drives lens sales and Pentaxians now
assume that the "never be full frame" claim of Pentax lost
its
credibility (due to technical arguments as outlined above).
After all, purchasing a lens is much more kind of an investment
than purchasing a camera which is known to deprecate
fast. The full frame conundrum is already destroying half
of Pentax' business.

So, what would be the right actions to be taken by Pentax
in 2011? Well, first, join the P&S and part of the SLR
team into a new SLD department, delivering the world's
first water-proof SLD and making sure a K-mount adapter
with AF support exists. Drop the P&S division. Pentax'
SLD mount should look as close as possible to Sony's E-mount,
allowing
for
future
35mm SLD cameras. Possibly allowing to sell Pentax lenses
for the E-mount too. I assume the E-mount uses an encrypted
communication protocol. But at least mechanically, there
should be fit.

Second though, form a team from remaining SLR and
645D developers for enthusiast cameras. Their first product
shall be a 24-35MP full frame SLR with Exmor HD
sensor in a K-5* body. Third, release new full frame lenses,
like the DFA 100/Macro relaunched earlier this year.

One may argue that this is infeasible. At least for the
second "enthusiast" team, I don't think so. Assuming Sony
would share their full frame Exmor sensor with Pentax,
all the rest is routine work for Pentax engineers. Moreover,
in June 2008, a Pentax manager said in an interview
that the development of a full frame camera is in its planning
stage. So, if that project wasn't cancelled, it should
be ready to deliver by 2011. Even taking into account that
K-7 and 645D diverted valuable resources in the first 2
years of the 3 year period. Surprisingly, the "leaked"
full frame project coincides with a rush of completed APS-C
DA lenses (2008) and a complete halt to new APS-C
only lens releases from then on and until now (with the
exception of the DA15 lens). Therefore, I guess that Pentax
would have enough full frame lenses to accompany the release
of the camera: FA31, FA43, FA77, DA*55, DA*60-250, DFA100,
DA*200, DA*300. With only 4 additional lenses (DFA28-80
kit zoom, a DFA~18 wideangle prime and two f/2.8 DFA* zooms
(24-70
and
70-200)), the lens line up would be fairly complete. Four
lenses developped or optimized in 3 years, why not?

Pentax and Photokina 2010

Photokina 2010 starts September 21 in Cologne, Germany.
It is the event and everybody is watching
Pentax there (if at all). The internet's rumor mill has
a pretty detailed prediction about what Pentax is going
to reveal: A K-x successor (with focus indicators) and
a new camera positioned above the K-7 but not replacing
it. The first camera named K-r, the second K-5. The K-5
would be APS-C but with a 16MP Sony Exmor sensor, faster
fps (7?) and faster AF system in a body similiar or identical
to that of the K-7. At a price spot at the lower end of
the enthusiast market segment. No full frame. No SLD.

But I sincerely fear that this doesn't suffice. Starting
at Photokina 2010, Pentaxians need a roadmap to full frame
and corresponding lenses in order to be able continue to
invest into their system. They have harvested enough money
now to either invest or migrate elsewhere. And Photokina
2010 will be the checkpoint for many to take action.

To stay silent at Photokina on the full frame front may
imply suicide for Pentax in the mid term.

Pentax can wait until 2011 to say anything about SLD.
People waiting for SLD aren't the opinion leaders so letting
them wait doesn't hurt. Moreover, they can buy any other
SLD w/o leaving the Pentax system. But to disappoint the
enthusiasts now is more dangerous than it ever has been
before. Up to the point that a K-5 would only sell if the
roadmap to full frame is sufficiently clear. Which sounds
paradox but isn't. It's all about psychology and the comfort
zone for what appears to be a hobby for most Pentaxians.
Pentax has to make Pentaxians believe into the brand. That's
part of their job, actually!

So, these are my recommended action items for Pentax at
Photokina 2010:

Announce K-5

Launch K-r

Publish a road-map to full frame, with a first delivery
in 2011.

Launch new lenses, maybe one for APS-C and two for
full frame.

Keep the SLD project a secret.

This article may be read as an open letter to Pentax.
Pentax has no plan to say anything about full frame. Which
is a severe mistake. Seize your chance. If you're too late
to the party, there may
be nobody
left
to become
enthusiast
about
;)
So, keep
people dancing ...

Further reading:

Leaked
information about Pentax K-r and Pentax K-5 ff.

Leaked information about Pentax SLD project.

Full
frame patent of DA*300/4.

Full
frame patent of DA*60-250/4 (note: on full
frame, the 60-250 has slight vignetting and drop of
corner
sharpness
at the tele end
which can be cured in post-processing; work tba).

2008
leak of planned full frame project (by Shibata,
Chi Ho).

Suitability
of various Pentax lenses labelled DA for full frame.

Release
date gap for APS-C only DA lenses.

True
manufacturing cost of a full-frame sensor out of fab.

About lens equivalence, article endorsed by LumoLabs.

BCN
market share by camera model in H1/2010 (no full
frame releases in this period).

note: no information received in private communication
has been made public in this article!

You may use the commenting section to express your endorsement.
Thanks for reading!

LumoLabs: Shutter-induced blur with an SLR camera

2010-07-21T17:00:00.003+02:00

A recent observation made by us and others was that shake reduction efficiency for the Pentax K-7 camera seemed to have a weak spot around about 1/100s and less. Something nobody could really understand and not everybody was able to confirm.

Therefore, we decided to try to answer an old and fundamental question for SLR photography: To which extent does the mechanical focal plane shutter and the mirror slap negatively influence image sharpness? Especially in the digital age with its theoretically rather high image resolution. We, this means two friends (Henning and Rüdiger) and myself (Falk). And of course, we decided to focus our study to the Pentax K-7 SLR camera in order to provde an answer to the observation mentioned above.

The short story is that we managed to find the answers. All our findings are written down in detail in a LumoLabs White paper:

-> http://www.falklumo.com/lumolabs/articles/k7shutter/index.html.

Please refer to this document to actually understand the work we have done. In the following, we will summarize our findings without explaining how we got there. However, note that 4 different camera bodies, data from 4 testers, 8 lenses and two firmware versions have been used. More than thousand test shots and several thousand accurate blur data measurements have been aggregated. High speed video, acoustic recording and acceleration measurements complement the data. So, we assure that the result describe the general behaviour of a Pentax K-7 SLR camera. Pentax has obtained a copy of the paper to be used at their discretion.

We will make no statement about how the results relate to other SLR cameras. Except for a quantitative comparison with one Pentax K20D SLR camera.

Results:

The mechanical focal plane shutter indirectly can increase the blur in an image. The exact amount of additional blur depends on the direction in the image. It is zero at a vertical contrast edge (aka yaw blur, blur due to yaw movement). And it is up to 11 µm (on average) at a horizontal contrast edge (aka nick blur, blur due to nick movement).

The exact amount of average blur is shown in the opening figure of this article. It has its maximum for shutter speeds of about 1/100s to 1/80s. It is less than 5 µm for 1/25s and slower. Or 1/250s and faster.

Note that any single image can be affected more or less. Add or subtract +/-50% to get an idea of variation from image to image.

Note that one pixel is 5 µm large and the blur effect is only visible if all other sources of blur are very well under control (sharpening, defocus, shake, subject blur, lens abberation, noise etc.). Normally, these other sources mask the effect. Nevertheless, if you want tack sharp images then you need to understand the shutter blur effect.
The effect for the Pentax K-7 is larger than for the Pentax K20D. About 2 - 3x larger.
Mirror slap or shake reduction have no negative or positive impact on the effect. Shake reduction works as advertized but cannot counteract the perturbation from the focal plane shutter as it is too fast really. Mirror slap is very well dampened in the K-7 camera and has no negative impact on image resolution except on a weak tripod.

There is a delay of about 10 ms between end of mirror slap and begin of shutter operation which suffices to keep the mirror slap perturbation out of the image.
The blur effect is an indirect one:

First, the moving masses of the shutter (curtain etc.) make the body move (with surprising speed and acceleration of its stiff body!).

Second, the body movements cause a classical blur effect lasting as long as the shutter works. The K-7 shutter is faster and stronger than that of the K20D probably increasing the effect by some 60% or so.

Third, the body accelerations cause additional vibrations in the imaging sensor which last a bit longer than the first shutter curtain operates and which magnify the effect by another 60% or so.

Preventing the first from happening (which requires a heavy and sturdy tripod) will kill the effect. There is no "loose" magnetically held imaging sensor and no negative direct impact from shutter curtain or mirror slap causing air flow in the mirror box or whatever.
In practice, you'll only see any effect with wide angle lenses.

At about 1/100s you would normally have blur due to free-hand shake (we can ignore the case of a tripod as only weak tripods would cause any trouble with the shutter). At 50 mm and longer, the shutter blur will be masked and at 30 mm it will have comparable magnitude. It is at 10-20 mm that the effect will be noticeable most.

In these cases, we highly recommend to shoot at 1/25s (or slower) and to enable shake reduction as it is highly efficient at such exposure speeds. The images will be sharper than at 1/100s!
Early efficiency tests of the K-7 shake reduction suggested that it may be ineffective at fast shutter speeds as required for long focal lengths. This was a preliminary conclusion we proved to be wrong.

The Pentax shake reduction is effective even at 1/500s! It just cannot prevent the shutter blur at about 1/100s. We may soon publish an update to our SR guide reflecting this.

So, here you have it in a nutshell. Please, refer to the full paper before asking questions. The paper is available as HTML and PDF (linked from the top of the paper). It is recommended to download and read the White Paper on "Understanding Image Sharpness" first.

UPDATE (2010 July, 28):

We checked if the new firmware release 1.10.00.25 released earlier today brought an improvement. The answer is NO.

We've run a number of measurements and within the limits of our very good measurement accuracy (about 0.10 to 0.15 pixels error margins) we cannot see an improvement.

[end of update]

Frequently Asked Questions:

Q: Did you study the K-x, do you know if it has a similar effect?
A: No. But anybody is invited to replicate our study for the Penatx K-x :)

Q: Is the shutter blur in the Pentax K-7 a defect?
A: No, any SLR shutter for any make causes blur to some degree. We just wished for the Pentax K-7 that it would be as small as it is for the K20D. We publish this partly to remind all camera makers that we watch their work ;)

Q: Does switching off shake reduction lead to sharper images?
A: No.

Q: Does mirror lookup work around shutter blur?
A: No.

Q: Does a tripod work around shutter blur?
A: Sometimes. If it is rock solid. A normal tripod most likely won't help much.

Q: Why does a longer exposure time work around shutter blur?
A: Because during the majority of the exposure, the shutter won't move and what you get is an average blur.

Q: Why does a shorter exposure time work around shutter blur?
A: Partly, because there simply is less time for anything to blur. Partly, because stimulated vibrations cause no harm after the shutter already closed.

Q: May I ask questions without reading the White paper?
A: No.

Q: But I don't understand the White paper!
A: How do you know without reading it? ;)

Q: Will you win a Nobel price for this crazy shit of work?
A: No. Alfred Nobel forgot photographers ;)

Further reading:

Enjoy the read ;)

Philipp Lahm Wedding

2010-07-14T20:00:00.009+02:00

Philipp Lahm is team captain of German national FIFA football team, who just scored third place at the FIFA world championship in South Africa.

First thing he did when he came back to Munich was to marry his bride, Claudia Schattenberg. And as luck would have it he selected the St. Emmeran church of Kleinhelfendorf to do so. Just some of hundred meters away from where my studio is located.

So, I decided to play paparazzo and see what I could grab as a photo.

No question that about hundred true paparazzi were blocking my sight and -- as the number of them exceeded the population of Kleinhelfendorf ;) -- theirs as well. I can only say:

Bring your own ladder!

I am glad I don't have to earn my money this way. As soon as the bride entered the church, they started to run each other over in an attempt to be first to upload the photo. Of course, the 3G/UMTS infrastructure of Kleinhelfendorf wasn't really meant for this use case. To see scores of paparazzi left in frustration is a priceless experience :)

Also, chatting with some of the photographers, TV teams and moderators was interesting. I now have a better idea of the amount of money changing hands on events like this. Needless to say that the right to officially take photos was sold exclusively upfront.

Despite the competition for sight, I tried my luck and here is what I managed to achieve. Enjoy :)

(Click on the images to enlarge. All photos © 2010 Falk Lumo. No reprint or linking without permission. All and more photos available in high resolution.)

Just a closing remark after you have seen the images... I used my mountain bike to be ahead of the horse drawn wedding carriage on its path thru small and rural roads. After a few kilometers only I've seen no more paparazzi photographers. They don't try as hard as one would imagine... ;)

LumoLabs: Understanding Image Sharpness

2010-06-17T17:30:00.008+02:00

We have prepared our first White Paper. It shall serve as a base to better understand our methodologies to measure image resolution and more importantly, it is meant to help understand what factors can prevent an image from turning out tac-sharp.

LumoLabs website

We changed the layout of our site too.

LumoLabs is now at www.falklumo.com/lumolabs and hosts a repository of articles.

Therefore, we will use the blog to announce new articles or important updates to followers and interested parties. And to enable their discussion.

The actual articles are not posted as a blog article as its format was deemed unsuitable. But you'll find links to both the online article and a printable PDF version. If possible, we always recommend to download and read the PDF version. The PDF version does update more frequently too ;)

Understanding Image Sharpness

(Sample chart form the article)
Hint: The article image URLs actually open as larger images as they appear embedded in the article.

This article is a recommended read for anybody loving to dig into technology and who isn't afraid of a bit of math.

It's abstract and table of contents is:

Abstract
This White Paper is one in a series of articles discussing various aspects in obtaining sharp photographs such as obtaining sharp focus, avoiding shake and motion blur, possible lens resolution etc. This paper tries to provide a common basis for a quantitative discussion of these aspects.

Table of Content
1. Measures
1.1. Modular Transfer Function
1.2. Blur
1.2.1. The hard pixel
1.2.2. The perfect pixel
1.2.3. The real pixel, sharp and soft
1.3. More realistic resolution measures
1.4. Combining blur
2. Sources of blur
2.1. Defocus
2.1.1. Ability of deconvolution operators to reduce defocus blur
2.2. Bayer matrix and anti aliasing
2.3. Diffraction
2.4. Lens aberrations
2.4.1. Defocus, Spherical aberration, Coma, Astigmatism
2.5. Shake
2.5.1. Measuring shake
2.5.2. Expected shake
2.5.3. Empirical results
2.5.4. Tripod classification
2.6. Motion blur
2.7. Noise
2.8. Atmospheric perturbations
2.9. Precision and calibration
3. Practical considerations and examples

Please, proceed here:

Online article (same as click onto blog title)
PDF print version

Apple iPhone 4 camera specs

2010-06-10T01:56:00.005+02:00

On 2010, June 7 His Steveness has introduced the Apple iPhone 4 which features a new camera module. Two actually but I am going to talk about the main camera (on its rear side) only. And only about its still photography capabilities (it records 720p 30fps HD video as well).

It is typically hard to figure out the exact camera specification for cell phones and to compare them with a P&S camera. E.g., the HTC EVO 4G is said to have an 8 megapixel camera but little else is known. Images shot with the EVO all lack the significant EXIF information!

However, I think I managed to extract the full iPhone 4 camera specs now.

First, the pixels are 1.75 µm (according to Job's keynote) and we may assume that this is the pixel pitch. Sample images are 2592x1936 pixels (5.0 MP, 4.02:3). This makes a 4.54 x 3.39 mm^2 chip (5.67 mm diagonal) which corresponds to a 35mm film camera crop factor of 7.64.

In a P&S, this would be called a 1/3.2" sensor and P&S sensors range between 1/3.8" and 1/1.5" (crop factors between 8.6 and 3.9). So, it is an imaging sensor at the lower end of the P&S range, but it is in the P&S range and with a reasonable number of pixels and a back-illuminated sensor like the Sony Exmor R sensor. Here is a sample image from Apple's web site:

(click on the image for the sample in original size; hosted on apple.com)

Gizmodo.de has published the full EXIF data for exactly this sample photo (it is magically absent from the web sample though ...):

Aperture: 2.97
Color space: Uncalibrated
Date and time: 2010/05/07 15:14
Exposure: Auto exposure
Exposure time: 1/887
Flash: Flash did not fire, auto mode
FNumber: 2.8
Focal length: 3.85
ISO speed rating: 80
Metering mode: Spot
Sharpness: Hard
White balance: Auto

So, the lens is a 3.85 mm f/2.8 lens.

This corresponds to 35mm film camera equivalent lens of 29.4mm f/21.4.

I should note that even an aperture this small is not restricted by diffraction yet (limit at f/2.8 is at 54% of pixel width). This is a good value. But one really shouldn't stop down beyond f/4 and it seems the iPhone 4 has an f/3 fixed aperture lens anyway.

Summary

iPhone 4 main camera:

5.0 Mpixels (2592 x 1936)
1/3.2" back-illuminated CMOS sensor
4:3 aspect ratio
35 mm film camera crop factor: 7.64
Low ISO 80 (or better)
3.85 mm lens focal length
f/2.8 lens aperture
Autofocus: tap to focus

Equivalent 35mm film camera and lens:

30 mm f/22

So, don't throw away your FourThird, APS-C or full frame SLR ;)

Besides the deep depth of field, an f/21.4 aperture at ISO 80 produces as much noise as an f/8 lens at ISO 570 (for a given shutter speed). Where 35mm film camera f/8 and APS-C f/5.6 produce the same level of noise.

Conclusion

The iPhone 4 seems to have a camera which should deliver an image quality on par with the lower segment of P&S cameras. It's field of view (no zoom!) corresponds to a 30mm lens (on a 35mm film camera) and it captures as much light (produces as much noise) as a system camera with a lens aperture between f/11 (FourThird) and f/22 (35mm film).

Pentax shake reduction revisited

2010-04-14T15:31:00.024+02:00

Update (April 18, 2010) Breaking News

The entire blog article may only apply to Pentax K-7 with firmware up to 1.00.02.xx with yet to be determined xx. Rüdiger from a German forum has done more measurements with 1.03 which seem to indicate this. I'll keep you updated.

End of Update.

This is a first for me. Because I am going to write about results obtained by others.

Nevertheless, I hope to be able to shed some new light onto an old question: How well does the Pentax shake reduction system work? The result may be surprising which is why I post this article.

1. Information sources

1.1 First and foremost, the admirable work by P. Smith for the Pentax K-7:
- Study of the Effectiveness of Shake Reduction in the Pentax K7
- Discussion of the above original work

1.2 Article by German magazines:
- ColorFoto 7/2008 "8 Bildstabilisatoren von 8 Herstellern"
- Pentax measurement chart contained therein
- ColorFoto 1/2010 "14 Bildstabilisatoren" (only available as print, pp.26-32).

1.3 Own work:
- Quick tests with my K-7
- Re-evaluation of data originally published by P.Smith
- Proposed mathematical model

Let me add that all data I am using (except my own quick tests) are based on a careful examination of edge blur widths (and their variation). Note that edge blur widths can be computed with high subpixel accuracy using the slanted edge method as all sources above do. They compare the shake (motion blur) with static blur caused by the sensor and lens too. Comparisons based on "percentage of useful shots" are not meaningful enough and therefore, haven't been used.

The work of P. Smith uses the Smith shake device aka as his body. The work of ColorFoto uses Steve aka Stabilization Evaluation Equipment which is an apparatus build exclusively for ColorFoto magazine. It was set to a mean shake frequency of 4 Hz and 0.2° amplitude. AFAIK, the shake isn't harmonic which is good.

2. Scope of the work

Aquiring a better understanding of the Pentax SR system. I am not in the boat to examine the 1/100s "SR bug" some report for the K-x and others deny. However, my article may help decide what is a bug and what isn't. My article will also help understand the performance differences of a sensor based system vs. an optical system.

3. A little background

Pentax uses sensor shift-based image stabilization (SR aka shake reduction). It is based on two (or three) angular velocity (gyro) sensors. More about the sensors:
- maRata Gyrostar ENC-03R

The measured angular velocities means that the body knows how the lens pointing direction is shaking and can shift the sensor to compensate. Unlike in-lens systems, it can even compensate for rotations around the axis which are not to be neglected. P. Smith has compiled a number of documents from the Pentax patent application:
- Pentax patents collected by P. Smith

Vendors with sensor-shift based image stabilization include Olympus, Pentax and Sony. Vendors with lens-tilt based image stabilization include Nikon, Canon and Sigma. A few lenses with lens-based stabilization for Pentax exist from Sigma. All systems are actively powered.

It is commonly accepted that neither system is superior to the other. I'll spend a few words on this later. No existing system works in the macro range. Canon has filed a patent requiring additional sensors to address this.

4. A fresh look at existing data

© 2010: measurement data: P. Smith; chart: F. Lumo.

This plot shows the blur width (in pixels) due to shake induced motion blur as a function of exposure time (in milli seconds; e.g., 1/125s = 8ms). The data is taken from the work by P. Smith as cited above. The red curve above is without shake reduction, the green curve is with shake reduction enabled. The thin lines denote upper and lower error margins (based on standard deviation and N=10 sample size). The dashed lines denote a fitted linear line thru the origin.

The camera used (Pentax K-7) has 5 µm pixels and the lens (Sigma 50/2.8 Macro) has 50 mm focal length.

This plot is the same as above with both axes in logarithmic scale. The green dashed line shows a linear line thru zero blur at 44 ms.

It turns out that all data by P. Smith are (within margins of statistical and systematic errors) compatible with the following formula (dotted lines in the above log-log plot):

b = a f |t - t0|

where b be the blur width (e.g., in µm),
a and t0 are constants,
and f be the focal length (e.g., in mm)
and t be the exposure time (e.g., in ms).

and where values are as follows:

SR OFF:
t0 = 0
a = 1 / (280 s)
(of course, a as above is a measurement of P. Smith's body tremor ;) )

SR ON:
t0 = 44 ms
a = 1 / (1200 s)

and b_SRON actually is the minimum of the above formula and b_SROFF. The crossover where b_SRON actually becomes b_SROFF is at t=8ms or 1/125s. For faster shutter speeds, the SR system has no effect (at 50mm focal speed).

The standard deviation of blur width is about the same size as the blur width itself, for both SR on and off.

This corresponds to an advantage of 2.1 stops within a nice range and actually better (~4 stops) around 1/20s - 1/25s. Persons with stronger tremor may see a better reduction.

The nice things about this formula is that we can compute the range of permissable shutter speeds, given a blur width and focal length.

5. Claim

The Pentax formula above holds true for all focal lengths.

6. Backing it up

Wait a second! If true, this claim means that the Pentax SR mechanism isn't able to help aquiring tac-sharp images with long focal lengths! Because below 1/125s, SR basically won't help anymore. It does help aquiring accepable images at maybe 1/50s and 200mm. But not tac-sharp at maybe 1/150s and 200mm. This may then require 1/400s actually, where SR on or off wouldn't matter anyway.

Because this claim is not to be made light-heartedly, I will use more sources to confirm it.

First, my own informal tests involving a visual inspection of images taken with a 300mm lens, at 1/320s, 1/160s, 1/100s, 1/25s, SR ON and OFF: the blur doesn't seem to depend on SR on or off with 1/320s, 1/160s, 1/100s. Blur was less at 1/25s with SR on but still a little bit more than at 1/160s with SR on or off.

Because this quick test isn't academic enough, I consult two additional sources: The ColorFoto tests from 2008 (K20D) and 2010 (K-7). The former measurement chart is online and I try to embedd it here (if it doesn't display, follow the link in the sources section):

© 2008 ColorFoto

We need to look at the second chart here, taken at 130mm and 1/125s. The red bar is with SR off and the dark blue bar to the right is with SR on. As you can see, both bars are roughly of same height, i.e., ColorFoto found SR ineffective at 130mm and 1/125s with the K20D. They actually found blur to be less at 1/15s than at 1/125s...

Now in 2010, I have the paper source for the same test with the K-7 and DA60-250 at 130mm at my disposition. Result: SR on (compared to SR off) has a positive effect of only 10% at 1/200s and maybe 20% at 1/100s. In a range of 1/200s to 1/13s, it remains at about 1 to 1.5 pixels as opposed to 0.5 pixels with tripod. Which is excellent at 1/13s but not so good at 1/200s. Their same curve at 23mm focal length reveals contant, tripod-like blur between 1/30s and 1/8s and even at 1s, only 2px blur. Their result is a little bit less irritating than the earlier K20D result in so far as shorter exposure times didn't lead to more blur.

These are two independent measurements basically coming to the same result: The Pentax SR is designed "to kick in" at exposures longer than about 1/50s.

This leads me to make my claim above.

7. Compared to the competition

In their 2010 study, ColorFoto compared the following SR systems, both at 35mm equivalent and 200mm equivalent focal lengths (FT and APS-C sensors).

35mm: (improvement in stops vs. 1/30s):
Nikon 18-200 VR II: 5
Olympus E3: 5
Panasonic GH1: 3
Sigma 18-50: 3
Pentax K-7: 3 (*)
Canon 18-135: 1
Sony A380: 1
Tamron 17-50: 0

200mm:
Olympus E3: 3
Panasonic GH1: 2
Canon 18-135: 1
Nikon 18-200 VR II: 1
Tamron 18-270: 1
Sony 70-300: 1
Canon 100: 0
Nikon 70-200 VR: 0
Sigma 70-300: 0
Pentax K-7: 0 (*)

(*) I define the number of stops improvement by the time where blur becomes more than 120% compared to a tripod shot, using the 1/focal-s rule to define the 0 stop point. The K-7 had more published shake without SR than the others which can only mean that the higher resolution wasn't corrected for. So, it was ok to add 1 stop to Pentax results (and avoid a -1 stop improvement listing ;) ).

So, all vendors have a common problem already at 100mm (FT) and 130mm (APS-C) focal lengths. At the long end, the best and the worst result are from sensor-shift based systems. At the wide end, they are mixed as well. So, differences are always due to the particular implementation details and not the principle as such.

Looking at results in more detail, I can see the "kick in effect" for the following systems: Tamron 18-270, Nikon 70-200 VR, Canon 100, Sigma 70-300 and Pentax K-7. So, it isn't a system-immanent effect.

8. Pentax SR usage guide

One can compile a usage guide of good exposure times based on the formula given above. This is possible because we can now assume that it holds true for all focal lengths.

The above is a 2D plot of ranges of good combinations of exposure time and focal length. The bright green (tack-sharp) represents 1 µm extra blur due to shake or better (0.2 pixels), the red (blurry) represents 20 µm blur or worse (4 pixels). The two darker shades of green (sharp and soft) represent degrees of blur, which are bearly or clearly noticeable at the 100% crop level.

The border between the two darker green regions represents the standard 135-format 1/f rule (1/(1.5*f) in APS-C land).

The blue or lilac region (blurred) represents a region where blur is obvious but not ruining the shot when looked at from the normal viewing distance: 20µm or 0.02mm is the traditional circle of confusion diameter for depth of field calculations.

One may think that the level of DoF-kind of sharpness be good enough. It depends on the subject. Because a crop from a shorter focal length would have done as well then. Sometimes, the longer focal length would still be the better choice because it collects more light (less noise than the crop) and allows for better focussing.

(Note: the chart and chart description was updated 2010, April 16.)

As can be seen, for focal lengths larger than 100mm, it is getting increasingly difficult or impossible to obtain the required sharpness from the SR mechanism and one has to use the good old rule of thumb. Nevertheless, if one shoots at 200mm and is accepting 1 pixel motion blur, then the avaible range is extended down from about 1/150s to 1/25s or 1/15s even, with the region around 1/100s to be avoided!

One may think that adding a tele lens from Sigma with lens-based stabilization could deliver more headroom for long range tele photo shots. In theory, this may be true. But it remains to be seen if the image stabilization mechanism made by Sigma can deliver for longer focal lengths. It may well be limited to the wide end as well. Additional tests would be required to answer this question.

9. Conclusion

Pentax delivers a capable shake reduction system able to provide up to 4 stops stabilization. However, it is designed to work best at exposure time around 1/20s and therefore, is most useful for normal and wide angle lenses used at low light or in video. Starting at around 100mm focal length, it is increasingly unlikely to see a positive effect from the SR system and beyond 200mm, the SR system cannot be used anymore to produce tac-shap images at lower than usual exposure times.

Olympus shows that this isn't a principle limitation of sensor-shift by delivering best stabilization for longer focal lengths (as far as I am aware of tests). So, there is hope that a future installment of the Pentax SR system is more useful for long focal lengths.

I call it "Tele-SR" and say to Pentax: I want it and I want it now :)

Thanks for stopping by.

LumoLabs: HowTo long range telephoto shots

2010-04-05T17:30:00.004+02:00

It all started when I shot the sunset panorama below from one of the locations where I work. It shows a horizontal field of view comparable to a 60mm lens on a 35mm film camera. There is nothing exceptional about this panorama except maybe that it shows -- on the righthand side -- the Zugspitze which happens to be Germany's highest mountain.

The Zugspitze is 2962 m (or 9718 Ft) high and from the point where the photo was taken, exactly 83.39 km (or 52 miles) away. So, I thought it may be a good idea to crop into that image and look what guys are doing up there on mountain top ;)

Theoretically, such a crop should be feasible because the image actually was stitched from several images taken with the FA* 300mm f/4.5 lens on the Pentax K-7 each. So, a pixel corresponds to as little as 1.4 m up there on mountain top and this excellent lens clearly outresolves the sensor.

Below is what the crop (100% pixel level and corresponding to a 2000mm lens on 35mm film) looks like:

Really looks blurry as if it were out of focus or having motion blur. Actually, razor-sharp trees in 300 m distance point out that this may play a role as well. Because 300 m isn't within hyperfocal distance for 5µm at f/8. But as we'll see, we can actually ignore this little detail.

Lesson #1: Focus on something about 1-2 miles away (i.e., which is within hyperfocal distance for a 5µm circle of confusion) because infinity may be too blurry to focus at and more nearby objects may be, well too nearby.

As it turns out, the real problem actually is that large distance objects look blurry indeed (no wonder the auto focus didn't properly lock on them).

So, I ask myself the question how sharp to expect an object at a given distance to appear?

There is scientific literature about this but I couldn't find anything accessible to photographers. So, I decided to compile a little How To guide. Starting now ...

1. Possible optical resolutions for long range tele photographs taken in the atmosphere

Of course, photos taken outside the atmosphere aren't the most important category for most people reading this ;)

Another category are photos taken from the atmosphere into outer space (astro photography) and a common figure one is finding is to expect resolutions of up to 1 arcsec resolution but no better. In nights with very low atmospheric turbulence aka as excellent "Seeing". When the stars blink less than they usually do ;) This is related to the Fried parameter r0 which is about 5cm (sea level) to 20cm (in the mountains at a very good night) large. It isn't possible to achieve better resolution than with a diffraction-limited lens with diameter r0.

A lens with diameter 300mm/8 or 38mm (<r0) isn't limited by atmospheric turbulences. However, the turbulences vary at a time scale of t0 = 0.3 r0 / v_wind and with typical values of v_wind = 2 m/s (10 m above ground) we obtain t0 ~ 1/125s.

For anything slower than t0, we effectively smear out the turbulent perturbations and decrease the resolution.

Lesson #2: Shoot at 1/125s or less, even when on a tripod :)

Of course, I wasn't aware of this and used 1/25s. But as we shall see, this isn't a big problem either. Because for excellent results, we need extremely low noise (lower than at ISO 100) and will need a long effective exposure time.

One way would be to adaptively restore turbulent distortion using a parameterized grid and stacking many restored image frames. Which is nothing but applying adaptive optics.

Another and more practically feasible way is to accept the loss in resolution due to atmospheric turbulence. But how large is it?

Well, I managed to find a formula in the scientific literature and adapt it for an optical path with constant atmospheric conditions:

MTF_turbulence(f) = exp (-21.57 f^(5/3) lambda^(-1/3) Cn^2 L)

where:

MTF: Atmospheric modular transfer function
for turbulent distortions along a horizontal path [%].
f: angular spatial frequency [cycles/rad].
Cn^2: (refractive-index structure coefficient),
typically between 10^-15 and 10^-13 [m^(-2/3)].
lambda: wavelength e.g. 0.55 [µm].
L: pathlength e.g. 83.39 [km].

Source: R. E. Hufnagel and N. R. Stanley, "Modulation transfer function through turbulent media", J. Opt. Soc. Am. 54, 52–61 (1964).

A public online source (i.e., free of charge) discussing this formula is I. Dror and N. S. Kopeika, "Experimental comparison of turbulence modulation transfer function and aerosol modulation transfer function through the open atmosphere", (1995).

Be f = L / (2 x) where x is the size of the smallest resolved detail. Then I derive that the limiting resolving power (i.e. where MTF drops to 5.0%) is reached where

x = (L / L1)^1.6

where L1 = (1.633 * (Cn^2)^0.6 * lambda^-0.2)^(-5/8) is the distance where a 1m-sized detail can be resolved. Typical values are:

L1 = 50,000 [m^0.375] for weak turbulences (good seeing),
L1 = 20,000 [m^0.375] for normal turbulences,
L1 = 10,000 [m^0.375] for strong turbulences.

This formula as it stands is my own work and I hope it may be of good use for fellow photographers. The L1 values are slightly rounded (~10%) from the results using the typically rounded values for Cn^2 as given above. However, my table below uses L1 values as computed from the rounded Cn^2 values.

MTF jumps from 5% to about 40% for details twice as large (2x) and drops to below 0.01% for details half the size (x/2). So, there really isn't a reason to use more than one pixel per detail x and the maximum useful focal length can be computed from the above. The following table does so and assumes 5µm large pixels:

Distance [m]	max. focal [mm] (5 µm pixel)
Seeing:	good	normal	bad
1	171.410	43.056	10.815
2	113.088	28.406	7.135
5	65.261	16.393	4.118
10	43.056	10.815	2.717
20	28.406	7.135	1.792
50	16.393	4.118	1.034
100	10.815	2.717	682
200	7.135	1.792	450
500	4.118	1.034	260
1.000	2.717	682	171
2.000	1.792	450	113
5.000	1.034	260	65
10.000	682	171	43
20.000	450	113	28
50.000	260	65	16
100.000	171	43	11
200.000	113	28	7

This means that you don't have to care about atmospheric turbulence if you shoot shorter than 200 m only (assuming your longest lens is 500mm).

In all other cases, turbulence may be of concern. Typically, it may not be useful to shoot more far than 1 mile away. Because you would be tempted to use your longer than 500mm which then resolves worse than 500mm.

Lesson #3: Don't shoot your 20+ Gigapixel panorama at a day with just "normal" atmospheric turbulences.

Lesson #4: Wildlife photographers wanting to resolve 1mm at a bad Seeing condition day (like in Africa) either approach to at least 100m or use 1000mm f/22 (r0!) 1/250s (t0!) which applying the Sunny 16 rule, means a tripod and ISO 400...

2. Possible optical contrast for long range tele photographs taken in the atmosphere

So far, we looked at a loss of resolution due to atmospheric turbulences. While being the strongest enemy for astro photography (besides light pollution), it isn't for long range tele photographs. While crystal-clear days exist where it is possible to view 200 km far away (on a mountain), other days clearly exist where vision is limited to a few meters only (fog).

The normal is somewhere in between where aerosol particles (due to condensed water, smoke etc.) scatter light along its path thru the atmosphere and dramatically lower the MTF with distance. The effect is much more dependent on distance than on detail size which is why we tend to not even see the object at all. Nevertheless, if we see a distant object it may be at very low contrast only. Formulas exist for MTF due to atmospheric aerosol scattering. They only mean that the useful range of tele photo lenses is limited even more.

To make things more fun, turbulence and aerosol scattering counteract each other. Dry air normally means less aerosol scattering but more turbulences too due to the heat which dried the air in the first place.

Low contrast is of double concern. Because we may wish to reconstruct missing detail which is only possible for high signal to noise ratios.

3. Improving long range tele photographs

We will apply a three step procedure to improve our tele photographs. Note that this will only be applicable for static subjects, though.

Step 1: Improve the signal to noise ratio

I took 16 images and selected the best 10 of them. Then, I used PhotoAcute to align and stack them into a "superresolved" image with a signal to noise ratio corresponding to ISO 10:

If you click onto the photo and select "Original size", you'll see that the image is twice as large. But not sharp. PhotoAcute's superresolution technique actually works for images which are sharp in the first place. Here, we only used it to boost the signal to noise ratio. Parameters used are a Nikon D40 camera with Sigma 30mm/1.4 lens, a combination I found particlarly neutral, i.e., PhotoAcute doesn't try to deconvolve for lens aberrations too much ;)

Step 2: Sharpening

The next step is a restauration of image sharpness using a deconvolution technique. FocusMagic seems to deliver best results, even in the case here where the defocus' point spread function doesn't strictly apply.

The sharpness is clearly improved. I used a blur radius of 6 pixels (after scaling the image back to 50% size). And "Forensic" regularization, made feasible by the stacking in the prior step. There is a window reflecting the sun. And because being 83 km away, it should be a perfect point. The ring artefact is a sign that a different deconvolution kernel would have yielded better results.

Step 3: Contrast enhancement

The last step is boosting the contrast within the given area. All tone values are typically within just a small range and the first step is clipping. The remaining tone mapping may be done using a gamma correction and a dose of clarity.

This resulting image may not be the most beautiful image of the top of the Zugspitze mountain. Nevertheless, from 83 km away, it not only shows a radio emmitter pole which is 4 m wide at its base and 2 m wide at its middle portion. It even shows (in the background on the right side at a 45° angle) the steel cables of the Austrian side funicular. It doesn't resolve the individual cables. But imaging them at all from more than 50 miles away is ... well, interesting ;)

Lesson #5: Burst enough images to be able to boost contrast.

Lesson #6: Stock up on a bunch of capable post-processing tools.

I hope you enjoyed the read.

4. Links

Lumolabs: Sensors of Nikon D700, D5000 and Pentax K-x

2009-12-11T17:44:00.016+01:00

(Photo ©2009 Karsten Pawlik.)

After the interesting findings about the relatively good dynamic range properties of the Pentax K-x (cf. Lumolabs: Pentax K-x sensor quality), many have requested to publish a comparison with some other well known camera models.

Well, I am happy to announce that a great photographer and dear friend of mine, Karsten Pawlik (kafenio.org) shares my passion and we could spend some time in studio together in order to compile this comparison.

Most of the photos (e.g., all Nikon photos) presented in this article are © Karsten Pawlik. The opening photo shows two Pentax K-x with the gorgeous Pentax FA 31/1.8 Limited lens, in both black and silver color.

It is interesting to compare the K-x with these two cameras from Nikon for the following reasons:

Nikon D5000 and Pentax K-x may share the same Sony Exmor sensor which is supposed to be found in the Sony A500 too. (well, maybe not: DxO measures that the A500 has a different sensor)
Nikon D700 is a full frame camera and captures 1.2 stops more light than both the Nikon D5000 and Pentax K-x which are both APS-C only. It is interesting to see if this advantage shows in images.

1. ISO Noise

(please click on the photo above (and all others) for better readable versions)

The above chart summarizes the noise levels for 18% gray patches (2800 °K tungsten) at various values for ISO: 100, 1600 and 12800, measured as a signal to noise ratio (SNR [dB]). Please read Lumolabs: Welcome and testing methodology for details about how we measure these values. Towards the end of this article, you'll find links to all original test shots suitable for further examination.

Within this article, I will ignore the fact that the D5000 delivered the best SNR at ISO 100. AT ISO1600, we see the expected result: About 3dB or 1 f-stop (1EV) advantage for the full frame D700 with respect to both D5000 and K-x.

At ISO 12800, the K-x manages to match the result of the D700 while the D5000 behaves as expected. However, the SNR should decrease by at least 9dB when going from ISO 1600 to 12800 while it only decreases by only about 6dB for the K-x. This is a sign for raw file noise reduction at work for the Pentax and I believe that all SNR values for Pentax K-x should be reduced by 3dB for ISO values of 3200 or higher.

(Note: The D5000 has no native setting of ISO 12800. It was emulated using ISO 6400 and exposing like for ISO 12800, pushing 1 stop in postprocessing.)

In summary, we confirm the 1 stop advantage for the full frame sensor as far as high iso gray level noise is concerned.

2. Dynamic range

The situation turns out to be more complicated when we study the respective dynamic ranges. Let's start with the full SNR curves for all cameras.

Look first at the three red (D700 full frame), blue (D5000) and green (K-x) curves in the middle of the graph: These are the ISO 1600 curves for the three camera models and the red line lying above the others shows the full frame advantage we have been talking about above. The curves show how the signal-to-noise ratio decreases (relative noise increases) towards the shadows (the lower luminosities towards the left). At ISO 1600, the full frame advantage remains significant throughout all luminosities spanning 7 stops (1%). Note that the curves at ISO12800 may be "polluted" by noise reduction tricks for the APS-C sensors.

Most important for the determination of dynamic range are the SNR curves at lowest ISO (i.e., ISO 100). In order to measure deepest shadow noise, we made three shots at ISO100: normal, underexposed by -5EV and underexposed by -10EV! Patches from all three shots were analyzed to compile an SNR curve spanning 13 stops (down to 0.02% luminosity (which is RGB 0.05/255 and sRGB 0.6/255 aka perfect black)).

The surprising result is that at deepest shadows, the D5000 outperform the D700 by 2 dB and the K-x by even 5 dB. This should translate to about 0.5 EV more dynamic range for the D5000, and about 1.5 EV more dynamic range for the K-x, when compared to the D700. DxO does indeed confirm more dynamic range for the D5000 (12.5EV) compared to D700 (12.2EV). In combination, this is a confirmation for the "13EV or better" dynamic range claim I made in my earlier blog article.

3. Dynamic range (revisited)

I decided that this isn't the full story. Numeric results of measurements of noise are one thing. Plausibility checks are another.

(you must click the image and then select "O" (original size) to use this chart!)

The above chart contains various (small) noise patches from all cameras and ISO values. I even added some Pentax K-7 patches for comparison (Note: the K-7 has more pixels). Towards the end of this article, you'll find links to all original test shots suitable for further examination.

A quick examination of the patches at ISO 100 and -10EV shows that the D700 wins hands-down: better color accuracy, better readability of letters and better contrast. It sure looks slightly more busy (more noise) but the noise looks more fine grain too. More fine grain? Yes, the noise from the D5000 and K-x look coarser than the noise from the D700 or K-7. But noise should be statistically uncorrelated and look always fine grain (except for pattern noise).

Good detail note: all three cameras have no visible pattern noise.

Obviously, the sensor of the Nikon D5000 and Pentax K-x (and I guess it is the sensor rather than the firmware) plays some tricks with the signal in deepest shadows: there seems to be some sort of deep shadow noise reduction at work (like binning dark pixels) which leads to softer detail and a lower noise measurement.

Therefore, I conclude that the excellent dynamic range measurements of the D5000 and K-x are partly due to sophisticated signal processing, possibly on the sensor itself.

However, even taking this disclaimer into account, we can say that the deepest shadow reproduction of all three cameras play in one league: e.g., look at the 153 letters in the -10EV samples and compare to the K-7 (-9EV only) where the letters aren't legible anymore.

I conclude that by dynamic range, taking all information into account, the cameras rank as follows:

Nikon D700 (#3 by lab test)
Pentax K-x (#1 by lab test) and
Nikon D5000 (#2 by lab test)

and are all very close.

The ISO12800 patches roughly confirm the numeric lab results. A K-x at ISO12800 and a K-7 at ISO6400 do roughly have the same noise while the K-7 keeps a slight resolution advantage even at such high ISO values.

4. Conclusion

Traditionaly, there is a one stop difference between full frame and APS-C. Temporarily, this sensor (Nikon D5000, Pentax K-x, supposed to be a Sony Exmor sensor) fills the gap (towards a Nikon D700) with respect to dynamic range while the difference remains with respect to high ISO noise.

This means that the D5000/K-x sensor has the same sensitivity to light as usual (as the D700) but has significantly reduced read-out noise.

The Pentax K-x may have a slight advantage over the Nikon D5000, esp. at very high ISO values. At the same time, this sensor (or firmware library) seems to include raw data alteration which makes the numerical analysis even more difficult, even when done in the DxO way. The time for true signal measurements has come, defining random noise as the sample variations of the signal and fixed pattern noise as the difference of the mean value with the ideal signal.

Lab tests (our own and the ones published by DxO) make the D5000/K-x have better dynamic range than the D700. But this is due to the limited testing methodology. D700 still has the better dynamic range, but by a small margin only.

5. Further reading

Access to full sample shot material:

Enjoy! :)

Lumolabs: Pentax K-x vs. K-7, sensor and video

2009-10-28T23:03:00.007+01:00

Pentax has recently released a new SLR, the Pentax K-x. And while it is positioned at the entry-level market and very competitively priced, it is yet rumoured to have a very good noise performance.

After having done all my lab tests, I may say that the rumors are not true.

The truth is that the K-x may be the 35mm SLR camera which has the best high ISO noise and dynamic range performance to date. This isn't "very good". This is outstanding!

This is my concluding summary which is based on the following individual articles:

Noise and Dynamic Range comparison:

At the top of the article is a compilation of various gray sample patches for both cameras, for direct comparison. The patches are from linear raw files (cf. "further reading" at the end of the article).

The resulting 18% gray level chart is like this:

Signal to noise ratio of 18% gray luminosity and color temperature 2900°K (halogen tungsten). Using manufacturer ISO stops 100, 200, 400, 800, 1600, 3200, 6400, 12800. The interpretation of results is the same as for the corresponding graphs on dxomark.com. E.g., print-normalization is for 8 megapixels. The dotted lines indicate the slope for pure photon shot noise.

Obviously, the K-x has no true ISO 100 and both cameras reduce noise even in RAW at ISO 3200 and higher. The ISO sensitivity of the K-x seems to be slightly higher, like at ISO 100, true ISO were more like 87 for the K-7 (DxO's value for the K20D) and 105 for the K-x. However, the above curves have not been left/right-shifted to take this into account.

Gray level noise at ISO 1600/3200 for the K-x is about the same as at ISO 1000 for the K-7. While gray level noise at ISO 1600 and 3200 are about the same for the K-x, there is a minimal loss of resolution when looking at the pattern part in the full test charts. Nothing serious, though.

Signal to noise ratio (SNR) for the Pentax K-7 and K-x. Full measurement for various luminosities and ISO settings at color temperature 2900°K. Measurement similiar to dxomark.com. The dotted lines indicate the slope for pure photon shot noise. The flattening at 30% gray and brighter is believed to be due to systematic measurement errors like imperfect gray patches. The dashed curves for the K-x have been properly normalized to match the higher sensor resolution of the K-7.

The curve for K-7 only and test images are at:
Full SNR Pentax K-7

The curve for K-x only and test images are at:
Full SNR Pentax K-x

The K-x/ISO 200 and K-7/ISO 100 curves are almost identical down to 1% luminosity.

The full SNR graph clearly exhibits the true strength of the K-x sensor: it maintains the good SNR at low luminosity levels. This is an indication that the read-out noise from this sensor is very low.

Therefore, the K-x sensor outperforms the K-7 in low light situations whereas the K-7 outperforms the K-x in good light. This is further confirmed by the better resolution and more artifact-free images from the K-7.

Video:

The quality from HD video is very good. The resolution is as high as the 720p mode allows. It somewhat more moiré and color moiré artifacts than the K-7 and therefore, may not exactly match its analog and film-like quality in 720p mode. But it is very good nevertheless.

Conclusion:

The Pentax K-x has a sensor which rivals the best. That Pentax makes it available in the entry-level class is a good thing. On the other hand, the Pentax K-7 excells in many respects and even its noise performance isn't bad. It is in line with the rest of the competition which is beaten by the K-x in this respect now.

Pentax K-x: "Editor's choice" (entry level, available light)
Pentax K-7: "Editor's choice" (semi professional)

Further reading: Lumolabs testing methodology.

Lumolabs: Pentax K-x sensor quality

2009-10-28T21:55:00.006+01:00

The Pentax K-x is an incredible machine for an entry level SLR. Here, I will look at the image quality which its sensor can produce.

In my lumolab testings, I will not report about ergonomics or lack of features etc. The internet is full of this easily obtained information and I will refrain from duplicating it here.

Test chart results:

The photo at the top of the article is an ISO test shot taken at ISO 1600 and color temperature 2900°K. It is a linearly converted RAW file (cf. "further reading" at the end of the article). Go to the gallery (click the image) to have a look at all test shots, available at original full size.

ISO resolution test chart using FA 31 Ltd. at f/4.5. The inner part is 4x. The Nyquist limit is at "7.1" in the inner part. Watch the original at 100% size.

The K-x resolves down to the Nyquist limit. However, it exhibits color moiré and false demosaicing at the limit frequency. The anti alias filter is very weak or absent as it allows for moiré down to three times the Nyquist limit. Color moiré is visible for textures at the Nyquist frequency.

E.g., note that the "7" patch has false demosaicing and strong color moiré. The same is visible from the zone plate chart. The K-7 doesn't show this in comparison.

Zone plate test chart using FA 31 Ltd. at f/4.5. The big circles have a resolution limit of 1280 LW/PH. The smaller ones are 2x and 4x. The 4x circles at above ~4000 LW/PH have uncolored printing moiré. The Nyquist limit is at 2848 LW/PH which is about 55% into the smallest circle. Watch the original at 100% size.

The zone plate chart of the K-x has false colors (fringing) already at half the Nyquist frequency and "green blobs" at three-quarter of the Nyquist frequency, followed by heavy color moiré at the Nyquist frequency exactly. The latter two effects are limited in spatial frequency space but the fringing is kind of disappointing.

While most testers will not notice the effect and welcome "the good resolving power of the K-x", which "leaves no resolution advantage to the K-7" (anticipated quotes from future pseudo tests), I personally would have preferred a stronger anti alias filter.

Numerical lab result:

The numerical evaluation of all noise charts (the full SNR plot) is as follows:

Signal to noise ratio (SNR) for the Pentax K-x. Full measurement for various luminosities and ISO settings at color temperature 2900°K. Measurement similiar to dxomark.com. The dotted lines indicate the slope for pure photon shot noise.

It is possible to derive both dynamic range and noise from the graph. If extrapolating the 0db point for ISO 100 at luminosity 0.01%, then the resulting dynamic range is 13.3 EV (print-normalized to 13.6 EV). E.g., DxO tests the print-normalized dynamic range of the K20D to be 11.05 EV and of the outstanding Nikon D3X to be 13.65. The flattening at 30% gray and brighter is believed to be due to systematic measurement errors like imperfect gray patches.

The theoretical photon noise separation between neighboring ISO lines is 3dB. There are three effects which can be observed:

- The SNR at ISO 100 is reduced for luminance levels above ~3% and drops to the ISO 200 values. A sign that ISO 100 is no native IO value for this sensor. On the other hand, it is exceptionally high for luminance levels below ~3%, with a boost more like ISO 75 than ISO 100.

- The ISO 3200 line is only 0.5 dB separated from the ISO 1600 line. DxO labs found that this is due to noise reduction applied to RAW data at ISO 3200 and higher. Without such noise reduction, the SNR would obviously be about 2.5 dB lower. This smoothing is even stronger than for the K-7.

Overall, the gray level noise (the SNR at luminosity 18.00%) is very close to the competition (worse at ISO 100, same at ISO 200 and better beyond) while the black level noise (the SNR at luminosity 0.10%) is very small. The ISO 1600 curve provides about the same black signal than ISO 100 pushed +4EV.

I have not measured SNR for luminance below 0.04%. But from extrapolation one may deduce that the K-x has a dynamic range of about 13.6 EV which would be even an excellent value for a full frame camera.

Update - The K-x "bump" at 2%, ISO 100 (2009, October 29):

Because of the importance of the ISO 100 SNR curve at low luminosities for the outstanding dynamic range claim made for the K-x, I have evaluated available testing material again, with special emphasis on this bump.

Signal to noise ratio (SNR) for the Pentax K-x. Full measurement for various luminosities and ISO 100 at color temperature 2900°K. Measurement similiar to dxomark.com. The dotted lines indicate the slope for pure photon shot noise.

This graph is meant to study the "bump" at about luminosity 2% in the ISO 100 curve of the full SNR graph (cf. above). The full 12 EV test chart is compiled from two parts: one exposed normally, another underexposed by 5 stops.

The above plot is a reexamination of both parts, now separately evaluated. There indeed is a discontinuous step (by +1.8 dB) when going from the normal to the -5EV curve which I cannot currently explain. The flattening of the brightest parts looks the same and could indeed be due to imperfect bright print patches. This would imply an underestimation of the "bump" by another 1.7 dB leading to a possible overall overestimation of SNR by +3.5 dB in the dark part.

Even taking this correction into account though, the above plot still confirms an extrapolated 0 dB SNR point at 0.01% luminosity. Therefore, the conclusions made in the other sesctions are not altered by this detail examination.

(end of update)

Conclusion:

- Resolution: Full Nyquist 12.2 Mpixel resolution, some moiré, some color moiré, some demosaicing artifacts. Very weak or absent anti alias filter.

- Noise: Gray level 40.0 dB at ISO 100, 31.6 dB at ISO 1600, dynamic range (print-normalized) >13 EV.

The image quality is good at low ISO values and very good if shadows are pushed-processed. It is outstanding at high ISO values and sets the bar for 2010. I haven't tested the Nikon D700 but from the known results, I say that the Pentax K-x is seriously challenging the D700 in terms of high ISO noise and dynamic range. With a much smaller body, a smaller sensor and a much smaller price tag ... and video ;)

I award the Pentax K-x the following title:

"Dynamic range champion 2009 in the 35 mm body class".

Further reading:
- Lumolabs: Pentax K-7 sensor quality
- Lumolabs testing methodology.

Lumolabs: Pentax K-7 sensor quality

2009-10-28T20:04:00.006+01:00

I have previously reported about the image quality from the Pentax K-7.

The corresponding blog articles are here:

Here, I will set a level playing ground for future comparisons of the image quality obtained from various cameras.

In my lumolab testings, I will not report about ergonomics or lack of features etc. The internet is full of this easily obtained information and I will refrain from duplicating it here.

Test chart results:

The photo at the top of the article is an ISO test shot taken at ISO 1600 and color temperature 2900°K. It is a linearly converted RAW file (cf. "further reading" at the end of the article). Go to the gallery (click the image) to have a look at all test shots, available at original full size.

ISO resolution test chart using FA 31 Ltd. at f/4.5. The inner part is 4x. The Nyquist limit is at "7.8" in the inner part. Watch the original at 100% size.

The K-7 resolves down to the Nyquist limit with very little color moiré and false demosaicing. The anti alias filter is rather weak as it allows for moiré down to twice the Nyquist limit. Color moiré is under control though.

Zone plate test chart using FA 31 Ltd. at f/4.5. The big circles have a resolution limit of 1280 LW/PH. The smaller ones are 2x and 4x. The 4x circles at above ~4000 LW/PH have uncolored printing moiré. The Nyquist limit is at 3104 LW/PH which is about 61% into the smallest circle. Watch the original at 100% size.

The transition at the Nyquist limit is rather smooth (the printing moiré being stronger than the sensor moiré) with almost no color moiré.

Numerical lab result:

The numerical evaluation of all noise charts (the full SNR plot) is as follows:

Signal to noise ratio (SNR) for the Pentax K-7. Full measurement for various luminosities and ISO settings at color temperature 2900°K. Measurement similiar to dxomark.com. The dotted lines indicate the slope for pure photon shot noise.

It is possible to derive both dynamic range and noise from the graph. If extrapolating the 0db point for ISO 100 at luminosity 0.07%, then the resulting dynamic range is 10.5 EV (print-normalized to 10.9 EV). E.g., DxO tests the print-normalized dynamic range of the K20D to be 11.05 EV which is about the same. The flattening at 30% gray and brighter is believed to be due to systematic measurement errors like imperfect gray patches.

The theoretical photon noise separation between neighboring ISO lines is 3dB. There are two effects which can be observed:

- The SNR drops faster than required by photon shot noise at gray levels under about 1%. This reduces the dynamic range. Gordon B Good found that this is due to a rather large read-out noise caused by the variable gain amplifiers (VGA) integrated into the CMOS sensor chip.

- The ISO 3200 line is only 1 dB separated from the ISO 1600 line. DxO labs found that this is due to noise redauction applied to RAW data at ISO 3200 and higher. Without such noise reduction, the SNR would obviously be about 2 dB lower.

Overall, the gray level noise (the SNR at luminosity 18.00%) is very close to the competition while the black level noise (the SNR at luminosity 0.10%) is rather large. This is of concern if brightness needs to be pushed in post processing. Interestingly, the ISO 1600 curve provides a better black signal than ISO 100 pushed +4EV.

Conclusion:

- Resolution: Full Nyquist 14.6 Mpixel resolution, weak moiré, very weak color moiré, nearly no demosaicing artifacts.

- Noise: Gray level 40.5 dB at ISO 100, 28.1 dB at ISO 1600, dynamic range (print-normalized) 10.9 EV.

The image quality is excellent at low ISO values and if shadows aren't pushed-processed, good at low ISO values otherwise and in line with the 2008 competition at high ISO values.

Further reading: Lumolabs testing methodology.

Lumolabs: Pentax K-x HD video quality

2009-10-28T19:23:00.004+01:00

The Pentax K-x is an incredible machine for an entry level SLR. Here, I will look at the quality one can expect to obtain from its 720p@24Hz HD video capture mode.

In my lumolab testings, I will not report about ergonomics or lack of features etc. The internet is full of this easily obtained information and I will refrain from duplicating it here.

The above is a frame from a dumb sample video, available here:

Test chart results:

Video frame from 720p HD mode. ISO resolution test chart using FA 31 Ltd. at f/4.5. The inner part is 4x. The 720p Nyquist limit is at "8.5" in the outer part.

Watch the original at 100% size.

Zone plate test chart. The big circles have a resolution limit of 1080 LW/PH. The smaller ones are 2x and 4x. The Nyquist limit is at 720 LW/PH which is about 67% into the big circle. Watch the original at 100% size. The sampling frequency is clearly visible by the position of the four false color disks positioned at an 70% radius. The false color at and remaining artefacts beyond the sampling frequency is due to a missing video anti alias filter.

Note that the false color artifacts are significantly more intense than from the K-7, overall and esp. at 45°.

A similiar image for the Canon 5DmkII is visible here: Canon 5DmkII zone plate test.

Rolling Shutter Test:

Panning left and right to evaluate the rolling shutter effect.

Note that the sensor of the Pentax K-x is read out in the opposite direction than that of the Pentax K-7, like bottom-up rather than top-down.

In comparing with the K-7, please note that the panning speed is not exactly equal. The magnitude of the rolling shutter effect is proportional to the panning speed. Also note that the K-x video has slightly more blur. Lightning condition and aperture has been the same, though.

Some testers have stated that the K-x has a stronger rolling shutter effect than other cameras. I cannot confirm this. Maybe, the opposite direction of skew disturbed the viewing habits of video testers ...

Conclusion:

The Pentax K-x delivers very good HD video quality. It has color moiré artifacts close to the Nyquist frequency which are due to subsampling without an anti alias filter. The artifacts are strong and not so nicely confined to a close neighborhood around the sampling frequency. So, in real footage one has to expect to see some textures with color moiré. This is a problem of all SLRs though, specifically those sampling at natively 720p.

The effect seems to be about that of a Pentax K-7 along horizontal and vertical lines. But the K-7 has no such artifacts along diagonal lines which may point to the fact that it uses more and differently aligned pixels in its subsampling procedure. Obviously, the K-7 scans 1024 lines (using 864 in 16:9 format) whereas the K-x only scans 720 lines.

Interestingly and unlike the K-7, the K-x has no magenta/green fringing and no double seam effect along near vertical lines. The subjective effective resolution in 16:9 is about 1350x717 or 1.0 MPixel. This is an excellent value not achieved by consumer HD camcorders. It even surpasses the 1280 limit ;) The K-7 has slightly less resolution in the horizontal direction but much better resolution along diagonal lines.

Further reading:
- Lumolabs: Pentax K-7 HD video quality
- Lumolabs testing methodology.

Lumolabs: Pentax K-7 HD video quality

2009-10-28T18:26:00.010+01:00

I have previously reported about the HD video mode in the Pentax K-7.

The corresponding blog articles are here:

As a movie camera -- Part I, Part II, Part III

Here, I will set a level playing ground for future comparisons of the video image quality obtained from various cameras.

In my lumolab testings, I will not report about ergonomics or lack of features etc. The internet is full of this easily obtained information and I will refrain from duplicating it here.

The above is a frame from a dumb sample video, available here:
Bavarian Camels (K-7 version).

Test chart results:

Video frame from 720p HD mode. ISO resolution test chart using FA 31 Ltd. at f/4.5. The inner part is 4x. The 720p Nyquist limit is at "8.5" in the outer part. The 1024p Nyquist limit is at "10.0" in the outer part. The color moiré shows that the 720p frames are downsampled from 1024p video frames.

Watch the original at 100% size!

Video frame from 1536x1024p HD mode. The 1024p Nyquist limit is at "10.0" in the outer part and "2.5" in the inner part. The resolved parts with distinct lines is about "8.0" in horizontal and "8.5" in vertical direction, corresponding to 1200x850 pixels in 3:2 or about 1200x717p pixels in 16:9 mode.

Video frame from 720p HD mode. The big circles have a resolution limit of 1080 LW/PH. The smaller ones are 2x and 4x. The Nyquist limit is at 720 LW/PH which is about 67% into the big circle. The Nyquist limit of the 1024p sampling is at 864 LW/PH which is 80% into the big circle. Watch the original at 100% size.
The sampling frequency is clearly visible by the position of the four false color disks positioned at an 80% radius. The false color at and remaining artefacts beyond the sampling frequency is due to a missing video anti alias filter.

A similiar image for the Canon 5DmkII is visible here: Canon 5DmkII zone plate test.

Rolling Shutter Test:

Panning left and right to evaluate the rolling shutter effect.

Note that the sensor of the Pentax K-7 is read out in the opposite direction compared to that of the Pentax K-x, like top-down rather than bottom-up.

Conclusion:

The Pentax K-7 delivers stunning HD video quality, specifically in 720p. It has color moiré artifacts close to the Nyquist frequency which are due to subsampling without an anti alias filter. The artifacts are strong but seem to be nicely confined to a close neighborhood around the sampling frequency. So, in real footage one has to really hit the "wrong" texture to see the effect.

The effect seems to be about that of a Canon 5DmkII along horizontal lines. But the Canon has no such artifacts along vertical lines, pointing to supersampling within lines and line skipping. The Pentax K-7 does line and row skipping. Obviously, the 5DmkII scans 1053 lines whereas the K-7 only scans 1024 lines.

Moreover, in 1024p along nearly vertical edges (cf. the 1024p resolution test chart), one can see the magenta/green fringing and a double seam effect. This is much less visible in 720p though. Additionally, it may be possible to cure it in post processing. The subjective effective resolution in 16:9 is about 1200x717 or 0.9 MPixel. This is a good value actually not achieved by consumer HD camcorders.

Due to its supersampling applied to 720p video, footage from the K-7 looks more cinema-like and analog than footage from entry-level dSLRs.

Further reading: Lumolabs testing methodology.

Lumolabs: Welcome and testing methodology

2009-10-28T09:00:00.003+01:00

Welcome to Lumolabs.

I never was really satisfied with the big lab tests (dxomark.com and dpreview.com) and really was disappointed by print magazine and other ezine tests. So, I decided to set up my own testing laboratory, based on experience as a photographer, insight as a physicist, software writing and image processing skills and patience.

For the time being, I am not challenging the big labs and confine my ambitions to the following areas:

1. RAW file image quality, in particular noise, dynamic range and resolution.
2. Video frame image quality, in particular resolution and artifacts.
3. Pentax.

I am not looking into color accuracy (not even chrominance noise...) or the camera's JPG engine. Or autofocus, ergonomy, build quality, etc. I may do lens tests and other vendors later as well.

Let me provide you with a short summary of my testing methodology:

RAW file treatment

I use the RAW file from the camera (DNG preferred) and use Adobe Lightroom 2.4 (LR) to do the demosaicing. The standard settings must be altered in the follwing ways to get a neutral demosaiced 16Bit sRGB TIFF file:

- Gray card calibrated white balance (I use 2900°K halogen tungsten light).
- Blacks 0 (changed from 5)
- Brightness 0 (changed from 50)
- Contrast 0 (changed from 25)
- Sharpening 0 (changed from 25)
- Noise reduction Color 0 (changed from 25)

I then read the resulting 16Bit sRGB TIFF file into my own lumolabs software. I properly convert the sRGB response curve (which isn't exactly a gamma curve) into linear colors and 18% gray is RGB 117.6/255.

Taking test chart photos

I then take test chart photos with controlled manual settings, including manual focus. About the slowest shutter speed is 1/15s.

Some think that noise test shots must be taken in low tungsten light. I agree for the tungsten part and I use it. I disagree for the low light part, though. A short exposure is a perfect approximation to low light because the read-out time of the sensor is longer than 0.1 seconds anyway whatever fast be the shutter. So, only if I wanted to study exposure time longer than, say 1/5s would low light be able to have an influence. In consequence, I don't publish exposure times shorter than 1/10s. Additionally, except for initial focus, I avoid using live view in noise tests to not overheat the sensor.

One of my test charts is the zone plate chart useful to evaluate anti alias filter and Bayer mosaic filter artifacts. It is shown in the beginning of the article. It is allowed to download it for own testing purposes, providing proper credit is given.

Other testing charts are an ISO-12233 resolution chart which I modified to include inner parts of 4x the resolution. Another chart is the noise testing chart with defined gray and color patches. All charts are printed on A2 paper using a high end photo printer. There are minimal printing artifacts visible at and beyond 4000 LW/PH (line widths per picture height). They do not disturb the testing results though.

The density range of the printed noise test chart is about 7 EV. So, I take a second shot at -5EV and obtain a combined test chart of about 12 EV dynamic range (luminance range 0.02% to 100%). Which immediateley turned out to be outperformed by the recent Pentax K-x ;)

My software will search for patches of minimal variance to exclude the effect of scratches and the like which may be present on the printed test chart. I am not sure though that there aren't some invisible defects below the -40dB range. They do not disturb the testing results though, except maybe for very bright patches.

SNR, noise and dynamic range

I am unrelated to DxO Labs, Boulogne, France. However, whereever I found their methodology to be appropriate (cf. dxomark.com), I adopted it. I disagree on some of their methodologies but some are best practise to be followed. My biggest concern with DxO is their lack of examination of influence of spatial frequency dependencies. They only "correct" their results for resolution effects as to be expected from pure photon shot noise. IMHO, this isn't good enough. I am currently working at a new testing methodology to overcome this. For the time being though, I am happy to adopt DxO's pixel-level measure methodologies.

It is therefore important to understand the SNR [dB] figure. It is explained here: SNR.

Another important detail is the print normalization: Noise, dynamic range etc. are all improved by downsizing an image. Still, measures take place at the varying resolution of the sensor. Like DxO, I use a "print-normalization" calibrated to a 8 MPixel resolution. The normalization formulae are here: print-normalization.

SNR [dB] can be easily understood by using the follwing hints:
- A patch of basically random pixels has an SNR of 0 dB.
- A decrease of light by 1 EV, doubling the ISO, going to a 50% darger region in an image or doubling the number of pixels all amount to a change of SNR by -3dB.
- Going from 1.53 crop APS-C to full frame amounts to a change of SNR by +3.7dB. So, 3dB is a lot ...

My full SNR curves can be directly compared with the DxO mark tab "Full SNR". Note however that DxO uses noise patches made from glass, has a different light source most importantly at a different color temperature and uses a different raw converter. Also, in derived measures, I don't include ISO sensitivity variance and possible raw data noise reduction (smoothing).

The dynamic range is the luminance level where SNR reaches 0dB, converted to f-stops and normalized for resolution. Note that the 0dB level is arbitrarily choosen by DxO and is resolution dependent. They formula-correct for resolution dependency but fail to understand that the full dynamic range must be measured at a much lower resolution. I plan to address this issue.

Video frame tests

The video frames studied in the video section are extracted using the Quicktime Pro "export as an image" feature. Because the video uses the camera's JPG engine, here are the parameters:

- Pentax: WB manual (2900°K), "Natural color profile preset", all other parameters at default values (like noise reduction and sharpness -1).

Enjoy the tests :)

Pentax K-7 in German magazine test

2009-08-19T06:14:00.005+02:00

I don't normally copy/cite content from other sources. But I am going to make an exception now. I cite numeric test results which were recently published by German photo magazine ColorFoto (ColorFoto 9/2009). I do so because there are so few sources around which offer a comparison of the K-7 image quality when brought to lab tests.

You may read more about the K-7 test done by ColorFoto by fetching a printed copy. You may probably be able to download the full text after the printed copy went out of stores, by going here: www.colorfoto.de.

So, besides citing their numeric image quality test results, I am only going to say this much: They liked the K-7 a lot!

Cited test results:

Test (ISO)	Pentax K-7	Pentax K20D	Nikon D300	Canon D50	Olympus E-3
Resolution 100 [LP/PH]	1327	1310	1253	1327	1146
Resolution 400 [LP/PH]	1325	1294	1248	1326	1113
Resolution 800 [LP/PH]	1318	1302	1189	1286	1052
Resolution 1600 [LP/PH]	1295	1287	1144	1191	1053
Texture loss 100	0.0	0.0	0.2	1.1	0.7
Texture loss 400	0.0	0.0	0.2	1.2	0.7
Texture loss 800	0.0	0.1	0.3	1.0	0.9
Texture loss 1600	0.1	0.2	0.3	0.9	1.1
Noise 100 [VN]	0.8	0.8	0.7	0.6	0.9
Noise 400 [VN]	1.5	1.5	0.8	0.9	1.7
Noise 800 [VN]	2.6	2.4	0.9	1.2	2.7
Noise 1600 [VN]	2.7	4.1	1.3	1.5	3.6
Dynamic range 100 [EV]	8.5	8.5	10.5	9.5	8.5
Dynamic range 400 [EV]	7.5	7.5	9.5	9.5	8.0
Dynamic range 800 [EV]	7.0	7.0	10.5	9.5	7.0
Dynamic range 1600 [EV]	6.5	6.0	9.0	9.0	6.5
AF + shutter latency at ~10 EV [ms]	390	280	270	280	360
AF + shutter latency at ~3.5 EV [ms]	580	1060	470	260	730

Notes:
Lenses used (image quality test / AF test):

Pentax DFA 100 f2.8 Macro / DA 18-55 f3.5-5.6 AL II
Nikon AF 60 f2.8 Macro / AF-S 27-70 f2.8 G ED
Canon EF 50 f2.5 Macro / EF 24-70 f2.8 L USM
Olympus ED Digital 50 f2.0 Macro / ED 12-60 f2.8-4.0 SWD

Light values (EV) in AF tests are computed from quoted 3000/30 lx figures by myself.

The image tests have been run from the JPGs produced out of camera. The default setting of the K-7 (as used in the test) applies noise reduction starting at over ISO 800 only which explains the relatively good values at ISO 1600. Most other brands obviously already apply noise reduction at ISO 800 or below.

The ColorFoto lab tests may be unique in that they provide a measurement of the loss of texture (typically caused by aggressive noise reduction algorithms).

Therefore, one may have a careful look at the "texture loss" measurements. Pentax has none, Nikon has it somewhat under control and Canon is more like a mess. So, depending on how you weight noise vs. texture, either Nikon or Pentax would win in the noise/texture department. Dynamic range when measured from JPGs does always include the tone curve applied. As there are plenty of tone curve parameters to play with, esp. on the K-7, I don't know how useful the corresponding measure is. I included it for the sake of completeness of citation.

More interestingly though, the K-7 sensor seems to have no significant difference to the K20D sensor (to be confirmed by raw file lab tests though) and the K-7 JPG engine seems to offer subtle improvement in resolution and noise/texture. This is in line with what I found out myself (cf. my other blog articles). And, this test sharply contradicts another blog article ricing high concerns...

Another figure being noteworthy of course is the AF measurement. In low light, the K20D AF.S figures were last in the field. The K-7 now seems to be more comparable to Nikon or Olympus with Canon still winning the competition. But the results are to be taken with a grain of salt: The difference of figures in full light between K-7 and K20D showcase errors in the measurements.

Conclusion

The first lab test of the K-7 image quality I am aware of confirms my early impression: image quality is on par with K20D or better. The JPG engine still produces a lot of noise but preserves a lot of texture detail too, compared to its direct competition.

LumoLabs: Busting the alignment myth

2009-07-28T23:30:00.010+02:00

This will be a special feature for hard core falconeye followers ;)

It all started with the exciting new feature of the Pentax K-7 camera which can produce true HDR images in-camera (it takes 3 shots, 3 exposure values apart from each other, and creates a single, tone-mapped or blended image from the sequence). It does it so well, esp. in the medium setting (as opposed to strong) that a limitation of the feature does actually hurt: you require a tripod to use the function.

The general opinion why Pentax left out the alignment step from their HDR function is that it is a processing power-hungry computation not easily done in-camera.

Not my opinion, though. I felt that Pentax has left out 10% of the implementation which reduces 90% of the functionality. Shouldn't it be the other way round?

Now, opinion isn't proof.

So, I implemented my own alignment operator, benchmarked it and compared its quality against the state-of-the-art in HDR.

The algorithm

The implementation is based on an algorithm whose computing time increases linearly with image size and is constant with amount of distortion. Note that I did not attempt to cope with the alignment problem known in panorama stitching, i.e., I don't do SIFT key extraction, I don't correct for lens distortion, I don't project onto a sphere before alignment, etc. pp. However, what I do is correct for shift and rotations which is a mathematical first order approximation to the latter and rather exact for small shifts and rotations.

The implementation uses a monochrome quad tree and high bit depth. The coding is in Java. It isn't based on anybody else's intellectual property.

The benchmark

I benchmarked the algorithm with a 5 image HDR from Munich Siegestor. It had distortions of up to 20 pixels and needed rotation as well. The source images haven't been ideally sharp (e.g., 1/25s and wide open with 15mm). And no program created a perfect alignment. So, I considered this example be adequate. The images were 14.6 MPixel JPG images.

The processing times on a Mac Mini (Early 2009), one processor used, are as follows:

Single alignment: 175 ms
Alignment of all HDR images: 700 ms
Reading of all images from disk into Java heap: 16 s
Shift-turn and write images to disk: 34 s
Total, disk to disk (70 MB transferred), 5 images: 50 s

The K-7 has a dedicated image DSP and can certainly rival this. E.g., it can JPG-compress a 14.6 MPixel image in about 100 ms only!

Because the HDR function within K-7 already has created the required image structures in its 2 GB memory, it would be conclusive to assume that addition of an auto-alignment feature to the HDR function would add less than an extra 1/2 second to overall operation time.

If processing speed isn't the reason, so maybe it is quality? This must be looked at. In particular as some of the alignment operators I compared with took several to nearly 10 minutes to complete.

The quality

I've run several alignment operators and come up with the following ranking:

Photoshop CS3; PhotoAcute ("normal alignment")
Falk Lumo Operator (as of this blog article); PhotoMatix 3 ("by matching features")
PhotoMatix 3 ("by matching features"; "reduce ghosting")
PhotoMatix 3 ("by correcting horizontal and vertical shifts")
No alignment

All pre-aligned images have been read into Adobe Photoshop CS3, either by HDR merge (without further alignment) or by opening the 32 Bit .hdr-file written by PhotoMatix. Tonemapping was done in Photoshop CS3, using the "Equalize Histogram" method. The latter isn't best but as it has no parameters, I thought it would make for a good option in a comparative study. Finally, the result was studied to derive the above ranking. Which is entirely subjective!

Below are the two samples from category #2. Please, visit the gallery to view the other samples, too. Note that all sample images have been resized to 6 MPixel.

Fig.1 No alignment

Fig.2 PhotoMatix

Fig.3 Falk Lumo Alignment Operator (as decribed here)

Take me to the gallery

Conclusion

The myth is busted. There is no reason to not include auto-alignment into the next firmware release of the K-7 HDR feature. In less than an extra second of processing time, about PhotoMatix quality can be provided. Make it so!

K-7 Barbecue

2009-07-22T16:07:00.008+02:00

K-7 Grillen

In order to celebrate the end of the Pentax K-7 alpha test, another tester from Munich and myself organized a little barbecue.

I've cut a little movie from files found on my K-7 and some shots from friends (in German language).

K7Grillen (K-7 Barbecue) from falconeye on Vimeo.

Enjoy :)

Btw, the green light at the end is the K-7's AF assist light.

Pentax K-7 Concluding Review Report

2009-07-03T01:00:00.017+02:00

Fig. K-7 getting wet feet while recording a movie (aperture blades stopped down).

This is my concluding review report about the Pentax K-7 dSLR camera hitting stores next week (last week in Japan).

It is based on my experience throughout the past month, after Pentax Germany was so kind to ask me to test their new flagship camera. It is today that I have to return the camera :(

You may read about my detailed findings in my various blog articles found here:

Again, I am not going to repeat the spec sheet of the camera. Please, go to

to get the full list of features. Here, I'll just share my opinion about the product. First, I am going to break up my impression with various "use cases" in mind.

1. General comments

The Pentax K-7 is in a class with only five competitors (*). It is Nikon D5000, D90, D300, Canon EOS 50D, and Pentax K-7. The price range covers 730$ (D5000), 950$ (D90), 1200$ (50D), 1300$ (K-7), 1700$ (D300). However, as the K-7 is at launch price now, it is expected that the street price of the K-7 is to drop below 1000$ later this year and would be priced roughly like the D90.

So, let me quickly compare the K-7 against the other four models:

K-7 vs. D5000
Pro: Better LCD, Faster/better shutter, much better VF, SR, WR, metal body, 15MP
Con: Heavier, no tilt LCD

K-7 vs. D90
Pro: Faster/better shutter, slightly better VF, SR, WR, full metal body, 15MP
Con: none

K-7 vs. 50D
Pro: Slightly better VF, video, SR, WR
Con: 1/180X, no double cross center AF sensor, no tethering

K-7 vs. D300
Pro: Lighter, video, SR, 15MP
Con: slower and no 150k shutter, 1/180X, no 51 AF points (11), no 1005 zone metering (77), no tethering

_____
(*) defined by dSLR, 12+ MPixel APS-C, LiveView, ISO3200+, 3.5+ fps
SR: in-body stabilization (shake reduction)
WR: sealed body and kit lenses for weather resistance

This little list is not meant to rank the competition ;) But it shows that the K-7 is very interestingly positioned. Let's say that the D5000 seems to be an interesting camera but is positioned below the D90 which is a more serious competitor, but still somewhat below the class of the K-7. The only true matches in class are 50D and D300, where D300 actually is somewhat above. However, if video or in-body stabilization or bad weather-resistance are required then there simply is no match for the K-7. The only thing we need to check out is whether K-7 delivers on its promise. If it does then it has no real competition (yet).

Having said this, I'll leave the feature list comparison for a more meaningful consideration of strong or weak fields of application. Each of the following fields gets a score within 1 to 5 stars (category for digital 35mm mount SLR).

Throughout, this is based on the following judgements:
- High ISO noise performance is on par with the current state-of-the-art for APS-C (ignoring differences of a 1/3 stop). The K-7 will look both more noisy and more detailed at the pixel level compared to the competition above. Some think that this renders more beautiful images when printed. Others think that buttery images at high ISO are better. I think that the differences aren't significant enough to be important but I prefer to keep noise and detail for later processing. Full frame delivers one full additional stop though.
- Autofocus is significantly improved compared to previous models from Pentax and at or above average. But still no match for the best in its class (D300).
- 15 MP resolution is fully applicable when using good glass.
- Everything what you can read in the separate articles as given above.

2. Landscape / Cityscape photography
★★★★★
Actually, the K-7 is a stellar performer here and K20D already scores high. The relatively lightweight body, stellar image quality at low ISO in combination with available stunning prime lenses makes this the best choice short of a (heavier) full frame 20+ MP camera. A function for automatic horizon just makes it perfect.

3. Wildlife
★★★☆☆
It scores high like for landscape, but I remove two stars for the following reasons:
- fast and/or long glass is extremely rare and expensive, and a tele converter is lacking.
- AF.C autofocus is good (and much better than in previous Pentax cameras) but may still miss a shot in action-loaden situations (flying birds, predator attack).
Note that the first point is not a weakness of the camera itself.

4. Sports and Action
★★★☆☆
Same rationale as for wildlife. Also, there are faster, machine gun type bodies.

5. Wedding
★★★★☆
The K-7 is the perfect APS-C body for this kind of shootings and additionally can provide stunning HD footage. It is a robust tool and sufficiently fast, too. However, in situations where light is not optimal, a full frame body with fast glass can be a better option.

6. Family
★★★★☆
Much like wedding. But ease of use and the fact that full frame would be overkill adds a star. Very young active kids or pets can still be challenging though and costs a star.

Btw, I don't agree with some other reviewers that the K-7 underexposes. If I would, I would subtract another star here. I agree that K-7 tends to expose darker than what is seen in other cameras, but for a reason. Easily studied with its live histogram. E.g., a burned highlight in the extreme quarter decreases exposure from 1/25s to 1/30s. So, it isn't true that K-7 underexposes to rescue irrelevant highlights. It just takes into account that bright levels clip where dark levels don't. Just work with +1/3EV if you never adjust levels.

7. Street and People Photography
★★★★★
Can't be beaten. Light-weight un-obstrusive and able to cope with almost every foreseeable situation. A smaller camera (like K-m or non SLR) may be interesting but would be less rugged. The improved metering performance with highlights and with flash are important improvements coming with the K-7 (for night life).

8. Travel
★★★★★
Same rationale as above. Just keep an eye on your stuff, though. An SLR may not always be the best option. Depending on your priorities.

9. Portrait and Studio
★★★★☆
The K-7 is almost perfect. The lack of a tethering option costs a star, though.

10. Movies
★★★☆☆
I judge the K-7 to be the second most interesting SLR offering video (with Canon 5DmkII being no.1 which would get 4 stars). The missing 2 stars are:
- No supersampling of full 15MP down to 1080p
- No videographer form factor/controls/EVF available with working Contrast AF
(taking the strengths (ISO, DoF etc.) into account.)

What sets it apart from other offerings are a "better than 720p" mode @30fps, uncropped 3:2 video, stereo, bearable jello effect, some manual control (aperture, EV compensation, exposure lock), no motion-compression artifacts. Of course, full manual control, electronic viewfinder and a fast contrast AF are all missing.

11. HDR and panoramas
★★★★★
The built-in HDR feature makes any other camera score 4 stars or less only. But Pentax missed the chance to align the images in-camera which would have been straightforward to do. The feature works great, otherwise. Moreover, the K-7 offers perfect control to do HDR panoramas. Live view with grid, exposure bracket and horizon control are an additional help.

12. Macro photography
★★★★☆
Perfect control available. A higher resolution LV would be an improvement but doesn't currently exist on the market. I subtract a star because an automatic focus series for focus stacking would be great. AFAIK, it doesn't currently exist on the market for no reason.

13. Astro photography
★★★☆☆
LiveView is of great help and controls are perfect. Missing though:
- Tethering option.
- Dark frame subtraction shut off for exposures > 30s not possible.
- Crop of FoV compared to full frame, depending on the type (FoV) of telescope.

14. Final Verdict
Four stars is the average and my conclusive score. If you look at my criteria, there probably will be no camera scoring at 5 stars (smarter beats bigger). Certainly not its direct competitors, the 50D and D300. I like both cameras as well and they have different weaknesses and strenghts. But I like the K-7 better. A contender for 5 stars would be Nikon's D3X, if it were 1/3 lighter and had video.

So, the K-7 not only feels like a lot of fun to use, it is a very good proposition on the current market. The best ever made by Pentax and a bigger step forward for Pentax than they did whith the (already very good) K20D. Compared to the K-7, the K20D feels old already.

So it does deliver on its promise indeed which means:

Pentax K-7

★★★★☆

Editor's Choice

"APS-C SLR camera"

(5 stars not assigned in category; as of 2009, July 1st)

A sunny sunday

2009-06-29T19:39:00.002+02:00

Enough testing. The Alpha Test is going to end anyway soon. Just relax, sit outside in the garden and have a good time. Which doesn't mean that I cannot press the shutter once in a while ;)

And then I saw a red balloon in the distance.

Shot freehand with a Pentax K-7 and a FA* 300/4.5 lens. You may click on the image above to view it in original size and see that the opening image actually is nothing but a 100% crop from this very image. You actually can see heads more than 3 km or 2 miles away (as I later computed).

Enjoy ;)

K-7 and ergonomics

2009-06-28T10:12:00.004+02:00

This is just a short essay about 5 ergonomic details in the K-7 which may create worries.

1. The omission of the Shake Reduction button

The K20D has a clearly visible SR button which is missing in the K-7. The following sequence is required in the K-7 to switch SR on or off. First, lets define how I call the buttons around the OK button: "8", "4", "5", "6", "2", like on a numeric keypad, with "5" being the OK-button itself ("8" is the drive button on top of "5").

[INFO] -> [2]/[6]{0-6} -> [RearDialClick]

{0-6} means that the button must be pressed 0 to 6 times, depending on where it was before. Assuming you only switch SR, it is just two buttons, [INFO] -> [RearDialClick]

Because SR is switched off automatically, e.g., on a tripod with remote control, this omission is no big deal.

2. The omission of the exposure bracket button

The K20D has an exposure bracket button which serves to quickly enable exposure bracket using the two dials to set #images and EV distance in between.

Assuming you always use the same exposure bracket (e.g., 5 exposures 2EV apart), the enabling sequence is as follows:

enable: [8] -> [4] -> [4] -> [5]
disable: [8] -> [6] -> [6] -> [5]

So, it is 4 button presses to activate and de-activate. If used often, one can live withit. But it is a lot less fun to set than with the K20D. Again, this omission is no deal breaker though.

3. Pressing OK for AF selection

Not being a heavy user of AF point selection, I can live with pressing OK prior to AF point selection. A user which relies on AF point selection however, will not understand why the logics isn't inverted as soon as you dial into AF point "SEL" mode. Because now, a change of AF point is much more frequent than, e.g., a change of drive mode.

So I really hope that Pentax adds a custom setting which makes AF selection the default in "SEL" AF point mode where pressing OK acts like Fn.

-- UPDATE --
As of today (July 29, 2009), Pentax has released a firmware update (v.1.01) which adds exactly the behaviour as described above as an option. Now, AF point selection can be used like with a K20D (i.e., the OK button will act as mode switch, not as middle AF point selector).

Pentax, thank you for listening!
-- END of UPDATE --

4. The mode dial lock button (mdlb)

The mode dial of the K-7 on the left side controls mode such as P, Av etc. In order to prevent that it can be changed inadvertently, it got a button in the middle to lock it. It must be pressed in order to turn the dial.

I developped a technique using three fingers from my left hand: the index finger presses the lock while the two neighboring fingers (one is the thumb) turn. Any other technique including using two hands (the obvious choice) turned out to create headaches.

There are two problems with the mdlb:

Engaging it will more probably lead to an inadverted change of the exposure meter mode (the level right underneath!) than the mode would change w/o the mdlb. And this inadverted change passes unnotices most of the time!
Therefore, adding the mdlb and not removing the exposure meter mode level is a clear engineering mistake.
They've put the video button as a mode
So all of a sudden, mode changes are frequent. While it was ok to stay in Av mode for ages with, e.g., a K20D, you now have to always switch between video and Av modes. If you seriously use video, you'll soon do it blindly -- and change exposure meter mode sooner or later.

So, you better regularly check your exposure meter mode, and EXIF for photos said underexposed ;)

I consider the mdlb to be a real nuisance. Pentax, please, take it back! Or make it toggle so we can leave it unlocked permanently.

And by the way, making the video button a mode is a schnapsidee (crazy idea) ...

5. Focal length info

The info screen has changed. It is more useful now. But I found no way anymore to display the focal length of a zoom lens prior to a shot.

Overall

With the exception of the mdlb, I like the new interface. And I didn't want to discuss the RAW button ;) The info button grants easy access to many quick changes. So, despite some weak points, I consider the overall button ergonomics of the K-7 even better than that of the K20D. Anyway, I really like the ergonomics of Pentax, in particular their hyperprogram and manual focus shift philosophy.

K-7 as a movie camera -- PART III: Sample video

2009-06-24T02:13:00.010+02:00

-> Link to part I

After all the preparation, I would like to share a short and uninspired video with you. And some thoughts about post processing ...

This is a short video sequence shot at 1536 x 1024 with a Pentax K-7 during an oldtimer car meeting earlier this year near Munich.

Pentax K-7 movie in 1080p from falconeye on Vimeo.

This video is nothing special. But I will use it to illustrate

Options for post-processing

1. The form factor.

720p video is 1280x720, 1080p video is 1920x1080, both in 16:9 aspect ratio. The native video capture is in 1536x1024 or 3:2 aspect ratio.

1536x1024 -> 720p: magnify by 83.33%, crop 8.00% from upper and lower edge each.

1536x1024 -> 1080p: magnify by 125%, crop 7.81% (100px) from upper and lower edge each.

There is no benefit in recording in 720p directly, except for a better control of framing (16:9 framing on rear display) and smaller file sizes. For 720p, the camera does the same supersampling to 83% size one would do in post-processing otherwise. On the other side, keeping the 1536x1024 material provides some more options for post-processing.

1536x1024 material is not suitable for direct presentation. Here, 720p is a better option.

2. Recoding.

Most video editing software will directly open the AVI file stored on SD card. Additionally, Apple Quicktime will open the file and Quicktime Pro allows to extract individual or all frames as images. Or to recode the movie, e.g., to MP4 AVC H.264.

Photoshop CS3/CS4 can open the AVI file directly as well and you get a video layer. There, you can do many image operations like you do for still images and recode, e.g., again to MP4.

After touching up the raw material, I used Adobe Premiere Elements for more video-oriented editing. On the Apple, MacOSX has something similiar on board, called iMovie.

3. Quality.

The K-7 captures stunning video quality. But it isn't good enough to justify the extra size coming with 1080p, compared to 720p. At least not without further touching up the quality.

Below, you'll see two frame images from the short clip above. The first is as out of the camera.

The second image is post-processed using my K-7 video IQ master (a program which I developed to defeat the "768-aliasing artifact"). The K-7 video IQ master is work in progress and yet unpublished. The basic idea is to use the insight about the submatrix as described in part I and try to correct some of the weaknesses in the original algorithm as built into the camera.

You may have to click onto the images to see the original size to study the difference. According to several opinions, the filtered footage has less fringing and less jaggy lines while still gaining (or at least maintaining) on overall detail (read: without becoming softer). It was used to create the 1080p clip in the opening of the article.

I hope that a forthcoming version of the K-7 video IQ master will be good enough to render 1080p footage to the same stunning quality we now see in 720p footage. And further improve on 720p quality. Btw, I very much welcome any comments on this topic.

As a side note. It is no problem to add motion blur to frames belonging to a panning action. Or tilt to remove the skew. Just open the corresponding video sequence in CS3.

Conclusion:

This shall conclude my three part article about the video capabilities of the Pentax K-7.

The video mode in the Pentax K-7 looks like a very promising proposition. It can produce stunning video quality, esp. in 720p. However, Pentax made a number of trade-offs to keep the camera affordable as a still camera (and it is a high spec camera already w/o video). Therefore, to achieve maximum possible quality in movies, a number of tweaks applied during capture and in post-processing are of help.

Enjoy your moving images :)

Further reading:

Ned Bunnell's blog article about using a stereo microphone
Disussion thread about K-7 video quality
Discussion thread about K-7 and an external microphone (dosdan's posts starting at #11)

K-7 as a movie camera -- PART II: Controlling video recording

2009-06-23T23:19:00.013+02:00

In part I, we have discussed the technical implementation of the video feature in the Pentax K-7.

Now, let's see how to make good use of it. Again, I'm not going to repeat the specification or user's guide.

At first glance, it seems to be very straight-forward: Turn the mode dial to movie and press the shutter! Ok, done this, been there. Now, for the more serious fun: how do we control shooting parameters?

The official answer by Pentax is: you don't! There is almost no manual over shooting parameters. But as always, there are back doors :)

Things to know:

You can set global parameters like pixel format, quality, shake reduction in the "video" menu (press the menu button when in video mode) and is not affected by all the nice settings you may have tweaked. E.g., forget about your Auto-ISO range ;)

Autofocus, aperture and E/V-compensation can be set prior to a recording. All three are defunct while recording. Of course, the camera won't complain if you change aperture or focus manually (read: mechanically). The focus in video mode is contrast autofocus by default. But you can switch to phase autofocus which is faster.

The exposure (with all its parameters) can be locked/unlocked before and during a recording, using the AE-L button.

EV values in video and still image modes seem to be the same.

Controlling exposure

Knowing the video exposure response curve is key in determinig and manually controlling an exposure in a K-7 video. It isn't published by Pentax but I researched them to be this:

Assuming an aperture is preset to a given value:

Light value [EV] at f/										Shutter	Sensitivity
1.4	2.0	2.8	4.0	5.6	8.0	11	16	22	32	[s]	[ISO]
0	1	2	3	4	5	6	7	8	9	underexposure	blng red
1	2	3	4	5	6	7	8	9	10	1/30	3200
2	3	4	5	6	7	8	9	10	11	1/30	1600
3	4	5	6	7	8	9	10	11	12	1/30	800
4	5	6	7	8	9	10	11	12	13	1/30	400
5	6	7	8	9	10	11	12	13	14	1/30	200
6	7	8	9	10	11	12	13	14	15	1/30	100
7	8	9	10	11	12	13	14	15	16	1/60	100
8	9	10	11	12	13	14	15	16	17	1/125	100
9	10	11	12	13	14	15	16	17	18	1/250	100
10	11	12	13	14	15	16	17	18	19	1/500	100
11	12	13	14	15	16	17	18	19	20	1/1000	100
12	13	14	15	16	17	18	19	20	21	1/2000	100
13	14	15	16	17	18	19	20	21	22	1/4000	100
14	15	16	17	18	19	20	21	22	23	overexposure	blng red

How to read the table: Look up the aperture in the upper left (e.g., f/5.6, marked in bold), search the measured light value in the corresponding column (e.g., EV 10) and look up shutter speed and ISO in the same row (e.g., 1/30s, ISO 100).

I didn't research much how aperture would be controlled if set to AUTO. But it will choose a combination from the diagonal line of constant EV in the table above. In AUTO, the aperture is controlled live and you can hear the aperture blades moving! IMHO, this is a cool feature for a dSLR with a legacy SLR lens!

(Update) I had another look at this.

In video recording with aperture set to AUTO, I illuminated the sensor with a torch and observed the lens aperture's reaction. This is what happened:

Without extra light: wide open (f/2.4)
With medium extra light (torch into lens): shut down (f/5.6) (*)
With full extra light (torch fully aligned and directly in front of lens): closed down (f/11) (*)

(*) estimated from diameter left open by aperture blades, as seen thru the front lens element.

There are really only these 3 steps. With a f/5.6 lens, this reduces to really only two steps. If it changes aperture, it does so by jumping 2EV, at least. Of course, it causes a visible jump in brightness in the video then being compensated afterwards. Therefore, manually shifting aperture creates a much smoother effect. (end of update)

Note: The above table may not be fully accurate. E.g., the sweet spot shutter speed (1/30s) may be shorter, like 1/50s, actually. Note that many videographers prefer a shutter speed of 1/30s or 1/50s (i.e., the motion blur from it) for 30fps footage to minimize a stuttering effect in panning action. Also note that all this is from my own research. Pentax doesn't disclose the information given above and the recorded video contains no useful meta information.

Now, using the response curve above, you can meter any subject, set the required aperture, use E/V-compensation to hit the required EV value, switch to movie mode (E/V compensation stays active!), lock exposure with AE-L and you successfully manually controlled your video parameters!

It is possible. But I agree that it is awkward in many if not most circumstances. If you need longer shutter times at daylight without wanting to stop down then you need to use a gray filter like you maybe would use for water still photography. Note that for video, you can stop fully down without loosing sharpness in the resulting video.

However, what I did find very easy to use is the following trick: In video mode, before starting to record, I observe the live histogram on the rear display when pointing to different subjects which will emerge during a scene. Then I point to a "typical" histogram and lock exposure. Eventually, I record using these parameters.

Controlling focus

Autofocus stays inactive during recording (it was enabled up to firmware release 0.20). However, it is so slow and badly implemented that it wouldn't be useful in actual footage anyway. If you need to refocus using the autofocus, the fastest would be to set live view autofocus to phase detect and stop a recording (press the shutter again and wait ~2s), press the AF button (~1s) and start recording again (~1s). If there is no time for a ~5s break, then you must control focus manually. Unfortunately, magnifying live view is inactive during recording as well (and the view finder stays dark, of course).

Fortunately, the quality of the rear screen with its 640x480 resolution allows an approximate focus. If the DoF effect isn't required, then shooting with fixed focus at hyperfocal distance is a viable option. The DoF calculations as obtained for an APS-C sensor do still apply. If you need to pixel peep, set circle of confusion to 0.015 mm.

If you need more control over the focus, using either a field monitor or an enlarging eye piece looking at the rear screen may be an option. The K-7 outputs live view and life audio via HDMI in 480p, 576p, 720p or 1080p. The image at the top of this article shows a K-7 hooked up to an HDMI 1.3 type C cable. However, the video data will always be 480p only, possibly enlarged to match the HDMI protocol.

K-7 videographing its own live view from falconeye on Vimeo.

The video above shows how the live feed from the K-7 behaves. In particular, you can assess the latency between reality and HDMI output. I guess it is about 1/3 s.

There are field monitors one can connect via HDMI and mount to the hot shoe or flash bar. The flash bar however, may be the better choice if a microphone is already mounted to the hot shoe ;) Because the feed is always 480p only, there would be no additional benefit in getting a 800x600 or 720p field monitor (this notice may not hold true for the Samsung GX30). A 5-6" 480p field monitor with HDMI input will do it. Avoid monitors with A/V analog input only.

Field monitors may have a headphone jack for audio playback as well.

And of course, for proper framing and smooth operation, you'll definitely want a video rig :)

Controlling shake

The K-7 features electro-mechanical sensor stabilization which proves very efficient in video capture. Note however that it is designed to work for still photography. So, it cannot compensate all the shake during a longer take. Because wide angle requires the anti shake to compensate less and is more stable in the first place, it is best to use wide angle (and tele lenses on a tripod). Or a rig again ;)

Note that a wide angle lens has a closer hyperfocal distance and produces smoother panning as well. So, I just adopted wider lenses as my standard when videographing.

Controlling audio

The built-in mono microphone is very sensitive to environmental noise like wind. So, using an external (stereo) microphone is a much better option (or use external sound recording and a take board). I tried the RØDE Stereo VideoMic connected to the flash hot shoe and it produces excellent results. The recorded quality is definitely more than sufficient for voice and sound. For music one may want to record externally.

Btw, there is no control of volume. But the recording level is relatively low and I didn't have any problems with either oversteer or noise floor.

Now, let's go out and have fun with video. I.e., it is time for part III.

-> Continue to part III

K-7 as a movie camera -- PART I: The technical foundation

2009-06-22T19:08:00.019+02:00

One of the more exciting features of the K-7 is its ability to record video in HD.

I will not repeat the specifications here. But it has an excellent 720p@30Hz recording mode and a 1536x1024p@30Hz mode which is almost full HD and can be used to create FullHD footage. In practice, it writes MJPEG at about 50 MBit/s and therefore can often outperform video recorded in AVCHD.

Many would think that Nikon D90 was the first dSLR sporting HD video. But this is only true 50%. The earlier Pentax K20D already included the ability to record video at 1024p@21Hz, although limited to clips of 5.6s each. So, the video funtion in the K-7 is regarded as already being version 2 by many Pentaxians.

My article about video will come in three parts:

The technical foundation (this part)

Controlling video recording in practice

Samples videos

PART I: The technical foundation

I am the kind of person who needs to look under the hood. Driving is fun. But seeing and grabbing the engine underneath is fun too ;) Read what I've found out.

First of all, video from a dSLR isn't a trivial thing to implement. Of course, one could read out all 14.6 raw million pixels 30 times a second (or at least 24) and construct the corresponding video frames, ideally by supersampling pixels into the smaller size, and compressing to a video codec. But this implies a tremendous processing load (i.e., processing 6.53 GBit/s raw input data in real time!). Implementing it this way (and I think Canon does it this way in their 5DmkII) makes the camera significantly more expensive than would have been required by still photography alone.

Pentax choose to implement it in a way which doesn't increase cost at all. The sensor of the K20D can be read out at a rate of 750+ MBit/s, or 375+ MBit/s per each of its two channels. This is exactly enough to support 3.3 fps at full resolution. In order to support 5.2 fps with the K-7 (seemingly 6.0 fps in the Samsung GX30), Pentax/Samsung doubled the number of channels to four and the K-7 sensor can be read out at a rate of 1.5 GBit/s. As staggering as this figure may seem, it is still only ~20% of what would be required following the approach above. It would have been somewhat easier with a 6 MPixel camera though ;)

Therefore, Pentax created a special subsampling mode where only every 6th raw pixel value is read out from the sensor at 30 Hz. This special signal is always used to create live view, zoomed live view and HD video frames, for all of Pentax K20D (21 Hz), Pentax K-7, Samsung GX20 (21 Hz), Samsung GX30 and Samsung NX' electronic view finder.

Because an HD video has only 2 MPixels (or less) which is about only 1/6th of pixels of a 16:9 still image, this means that at the same ISO step, pixel noise from a video frame and from a still image will look very similiar. Of course, using only every 6th pixel looses 2.5 EV stops in low light performance compared to ambitious supersampling approach. However, even 1/6th of the surface of an APS-C sensor is still a lot larger than the combined surface in dedicated 3 chip HD camcorders. So, videos in low light will look good. It is just that they could look even better.

The subsampling matrix

How are colors reconstructed if only every 6th pixel is read? This is a problem because standard demosaicing techniques as known from a Bayer matrix don't apply. Rather, color is constructed from picking values out of the Bayer matrix with a given color filter. Below is one variant of possible locations where color values are picked from:

(note: if you click onto the image, you can find another variant which most likely would yield better results.)

As you can see, the submatrix forms a pattern repeating every 6x6 pixels. Only 6 pixel values are picked from such a 6x6 area, producing 2 RGB pixels, e.g., as outlined by the black boundaries.

To tell the truth, Pentax applies a little bit of demosaicing magic and produces 4 RGB pixels from the information of 6 raw pixels. However, it does it in a rather bad way leading to the (arti)fact that two horizontally adjacent RGB pixels have very similiar values, almost reducing the advertized resolution of 1536x1024 down to 768x1024. In part three, however, we will see that part of the information is still there. We'll call this effect the "768-aliasing artifact".

Another problem with the subsampling matrix is that colors are spatially translated, i.e., the green channel sits left of the red+blue (=purple) channels within the subsampling matrix. This leads to green fringe where contrast changes from bright to dark (left to right), and purple fringe where contrast changes from dark to bright. You can see the effect in the following image:

(400% crop of a video frame, left from the K-7, right from the K20D)

You can see the fringe effect which is exactly as wide as the 6x3 subsampling matrix (2 pixels in horizontal direction). Also, K20D and K-7 share almost the same subsampling matrix, with a bit less of the "768-aliasing artifact" in the K-7.

There is a simple experiment that demosaicing of the subsampling matrix is very rudimentary indeed: Pierce a tiny hole into a black cardboard, position the K-7 on a tripod ~10 m away and zoom into the hole image using 10x zoomed live view. With a sharp lens, at most a single raw pixel in the subsampling matrix is hit only. What you see on the rear screen, is an image of the hole which is either dim or bright, in an arbitrary color, depending on minor movements of the camera. The hole is dim if a raw pixel which doesn't take part in the subsampling matrix is hit.

So, to summarize, some fringe (false colors) and jaggy edges are artifacts resulting from the way video frames are extracted from the sensor. Note that the effects are much less visible in 720p which is supersampled from the 1526x1024 feed. The K-7's 720p video quality is stunning.

You may look at the 1536x1024 recording quality as being the "raw image equivalent" for 720p final images. Needing post-processing but retaining extra headroom.

Rolling shutter

Another common problem with video in dSLRs is the rolling shutter. Because the mechanical shutter is too slow for 30 fps, it stays open all the time and an electronic shutter is used. In the K-7, the sensor is read-out line by line in progressive order, bottom edge first, within a period of ~1/30s. Because the image is projected head down, the lines at the top of a final image have been read-out earlier than the lines further down. If the camera is panned, e.g., left to right, then vertical lines become slightly skewed, e.g., tilted anti-clockwise. Therefore, this effect is called skewing effect or jello effect as well.

The jello effect does actually bend non-horizontal straight lines if they are rotating with respect to the camera (so, avoid tilting the camera when recording). It can produce funny images with rotating structures, like propellers, actually :)

As for the K-7, this effect is very well controlled. The skew is exact and without extra jagginess. I.e., the read-out is uninterrupted. Very good! If combined with a bit of motion blur, it becomes almost invisible. I would say that the rolling shutter is almost a non-issue with the K-7. Combine this with the lack of motion-compression artifacts and a gray filter maybe, and the K-7 can produce really stunning panning action.

Video compression codec

Another strong point is the selection of high bitrate MJPEG as the compression codec. Not being an amateur's first choice, it offers greater headroom for post-processing. Individual frames are JPEG-compressed and about 200 KBytes large. The JPEG compression artifacts are visible on larger than 100% inspection but don't disturb. Also, MJPEG is an easy format for post-production. And, it doesn't cause extra burden on the in-camera processing engine.

The container is "Motion JPEG OpenDML AVI" and can be opened on all platforms, e.g., using Apple Quicktime. Of course, for long-term archival, MJPEG needs to be recoded (e.g., to MP4 AVC) to save space.

Audio

The K-7 has a built-in mono microphone capturing a clear sound in the absence of any wind.

It does have a plug for a stereo microphone too. I tried the RØDE Stereo VideoMic connected to the flash hot shoe and it produces excellent results.

It plays back audio over the built-in speaker which is really bad, though ;) For decent audio in the field, one would require an HDMI-capable field monitor with a headphone jack. Yes, I checked that audio is played back via HDMI.

The audio quality seems to be good too. The format is 1 or 2 channels of 16 Bit, 32 kHz PCM.

Temperature

After 5 - 30 minutes of continued video recording, a red thermometer pops up on the rear screen and informs about increasing temperature. I didn't have any recording stopped by temperature alert. But it may be a concern in very hot regions, full sun shine and for extended scene recording.

(Update) I've test-driven continuous video recording at 27°C ambient temperature for 40 minutes. The red thermometer appeared after about 15 minutes. But the camera didn't interrupt. The camera felt warm and burned one out of three battery marks.

A still image shot at the end was ISO 800 and 40°C. It shows a very faint vertical line in the middle, about as pronounced as the ISO800 noise and only visible against a uniform background at 100%, invisible in normal photography. Even invisible against the uniform background are additional vertical lines exactly 256 pixels apart. I don't consider this hot temperature banding to be significant considering it is from a pre-production sensor.

Other observations: right after movie recording with temperature alert, the camera refuses to enter LV but still enters movie mode and continues recording movies (or allows still images using the viewfinder). Only 20s after movie recording, it accepts LV again, incl. the red thermometer. After 2 minutes, the red thermometer has disappeared.

I think at below 30°C ambient temperature, it won't emergency-break a movie recording. (end of update)

This shall conclude Part I. Next will be a discussion about making the K-7 video feature more accessible for real projects.

-> Continue to part II

Catwalk in Glockenbach quarter, Munich

2009-06-20T22:00:00.007+02:00

On my way back home today, I ran into the preparation for a public catwalk in the streets of Munich. More precisely, Glockenbach quarter which is pretty known for cool events like this.

For the curious: the fashion designer and store owner is Svenja Jander, a cool new designer.

Great, so I grabbed "my" K-7, two limiteds and a flash and hurried back for prime time :)

People having shot catwalks may know that it is harder than it appears. The models run fast, and in this particular case, daylight was already low and artificial light provided was sparse (well, one lamp exactly lighting up the models passing by, for 1/2s maybe ;) ). My fill flash helped a bit, just a bit though. Nevertheless, compared to earlier experience with the K20D, I had a much higher rate of keepers this time. I like to use the DA 40 Ltd. in events like these and today was no exception. Unfortunately, I had no opportunity to mount the 70mm. When I was ready to change subject, the show was over, already :(

I didn't shoot burst and therefore, the higher number of keepers is mainly accounted for by a better and faster autofocus. I was quite pleased except for the fact maybe that I still got out-of-focus shots ;) Seems, the K-7 cannot produce wonders but it was a reliable tool indeed. And if you are wondering if others can produce wonders, here is a comment from a photographer shooting Nikon at the event: "Oh oh, the models ran sooo fast ..." :)

Looking at some of the missed photos again, many have motion blur actually. Despite flash and 1/100 - 1/180s ... If you look at some of the photos below, you can feel the motion, actually.

Another photographer shooting Pentax K20D, K100D, with triggers and big flash lighting box, got a big smile when he saw me and a Pentax in my hands. And he got pretty shocked to read "K-7" printed on it. He had never heard of it! ;)

One more comment about the photos you're going to see below ... They are all (sometimes heavily) processed and/or cropped and (except for one unprocessed original). My aim was not to reproduce what I saw! The photos are not meant for measurbation (if spelled correctly). I present them more as an illustration of what I could artistically achieve with a K-7, a DA40, a Sigma flash and little preparation. Others may do better.

Here you go ...

Nymph
A 100% crop (when clicked) of the photograph above.

A nice walk

Shine, baby shine

(Please, click on the photos for enlargement, select size from the toolbar. Please, respect the copyright.)

If you enjoyed the images, then you may be interested to visit the entire gallery here:

Catwalk Glockenbachviertel Jahnstreet

Enjoy,
Falk

Comparative resolution study K-7 vs. K20D

2009-06-19T23:00:00.008+02:00

This blog article was initially meant to be part of the noise article. However, the matter turned out to be much more intricate than I thought (and somehow, it still is). So, I made it a separate article again owned by falconeye.

I would have loved to make it a short answer. However, I am going to tell you a story instead. I am sorry that Falk Lumo will have to wait with his catwalk beauties ;)

In the top of the article, you see a (synthetic -- more on this later) resolution test shot for the K-7. Please, click on it and open it in original size, and scroll to make the center visible. Note that what you see is the inner part of a special edition of the ISO 12233 test chart. Special because it contains insets of 4x resolution. I made this edition to be able to measure today's dSLRs. It is printed in A2 size and the printer's dots start to form Moiré at figure "8.5" in the chart insets, i.e., between "8" and "9". No big deal, just something to keep in mind.

For more information about the ISO 12233 test chart, you may want to visit this link:
http://www.imatest.com/docs/sfr_instructions.html

Also, note that the test chart only fills 86.7% of the picture height. As a consequence, the chart figures have to be multiplied by 460 (rather than 100) to yield LW/PH (line widths / picture height). Read, the K-7's Niquist limit is at chart figure "6.7". There shouldn't be any structure beyond this number.

Now, look at fields labelled "7" or "8" (we ignore "9" and higher for the reason given above). There still is structure but it is just Moiré, not the proper line pattern which is printed. So the lens plus AA (anti-alias) filter outresolve the sensor and we pick up a pseudo pattern which basically is a sampling error (which is what is called a Moiré pattern). Would lens plus AA filter be at the sensor resolution or below, than we would have uniform gray fields labelled "7" or "8".

First result:

The K-7 has an AA filter which allows to outresolve the sensor. It better has :)

Now comes the tricky part. Because we want to compare with the K20D which we must assume does have an AA filter which allows to outresolve the sensor, too. How on earth shall we measure a resolution beyond the sensors' capabilities? If I a had the accuracy and software of a testing lab at my disposal, I would extract these numbers from subtle details in the respective MTF figures; but I don't.

First, let's verify that the K20D is close indeed. Here is the corresponding synthetic resolution test shot for the K20D:

Oh yeah, just as nice :)
(About 3 visible fine white rings in the center circle.)

Ok, let me get serious now (which means that most likely, you're gonna run away before the end of the article -- just make sure to join in for the verdict ;) ). In order to study the AA filter's effects, I will apply a technique called superresolution. This technique involves taking multiple test shots (16 in this case) and creating a synthetic image at twice the native resolution, i.e., an 58 MPixel image! In order to construct this image, a "kernel" (deconvolution with a native pixel's PSF (point spread function)) is involved. By pure accident, I happen to have a kernel which rendered me good service with my K20D. Let me call this kernel "Falk1". I refrain from describing the exact procedure here... Let's just accept that, by some miracle, we now have test images at twice the resolution.

Because they are so large, I will only present crops (200% crops = 100% crops of superresolved image). Let's call them supercrops. First, for the K-7, next for the K20D.

Now, we see 5 rings and we suddenly see a difference, too! However, let's be cautious. The K-7 image has some artifacts. In the K-7 supercrop, the lines have more false color and more interestingly, the end of lines have a bubble artifact. E.g. look at the "5". From my experience with the superresolution method, this is a strong hint that the kernel (Falk1) overcorrected (similiar to the artifacts from oversharpening). While undercorrection just leaves some softness, overcorrection can have more funny effects ;) The assumed PSF was too wide. With a narrower PSF (Falk2, to be developped now ;) ), the supercrop would have looked better.

Second result:

From this, I am going to conclude that the AA filter in the K-7 is a tad weaker than in the K20D. This would also easily explain the pick-up of some false color in the demosaicing process.

But let's assure that this is a very subtle effect. Just any microscopic change in focus will add the softness required to make K-7 supercrops look like K20D supercrops. Here is an example from an earlier (premature) series I shot while doing the noise tests. Now, the difference is gone.

The images are with a Pentax DA 70mm Ltd. at f/5.0. Except for the last, shot with a Zeiss 50mm at f/4.0. And I did verify that a Zeiss 50mm at f/4.0 produces the same bubble artifacts when in precise focus.

One last thing ...

The images shown so far have all been synthetic. I.e., they are downsampled from the superresolved images. Here are three unaltered sample resolution images as shot:

Unaltered resolution test shot, K-7 + DA 70mm Ltd. @ f/5.0
(Note: underexposed on purpose)

Unaltered resolution test shot, K20D + DA 70mm Ltd. @ f/5.0

Unaltered resolution test shot, K-7 + Zeiss 50mm @ f/4.0 (from "premature series", 4.5% larger)

Interestingly, the unaltered sample image from the K-7 looks just a tad softer than from the K20D. Which is why I showed a third sample (with the Zeiss) to verify that this is within a range of insignificant variation. This is the reason why I consider the matter to be intricate still. Some samples tell a different story than other samples ... But it is all in the subtle details, anyway.

Verdict:

Pentax K-7 and K20D both have an AA filter of very similiar strength. It is pretty hard to say which one is weaker. I take my bet and say the K-7 has the weaker AA filter.

But by just so little that in almost all normal shooting conditions, I expect to see no significant difference in practice. The above image summarizes the data this verdict is based upon.

These and more test images are in the following image gallery:
Resolution and Noise of K-7 vs. K20D
Please, visit for further details.

Still here?

Well, one more last thing ...

Myself (and I know of at least one other alpha tester as well) have been wondering why the images on the rear screen, when magnified after the shot, don't look as crisp as with some other makes. One could think that the images are a bit soft. So, I made a test and compared the magnified image on the rear screen with a 1:1 crop as developed by Lightroom with default settings.

As you can see, the image on the rear screen, when magnified after the shot, does indeed look a bit soft. Even if it is perfectly crisp on a computer screen. I verified that this holds true for in-camera JPGs as well (to a slightly lesser extent). I think that this is something to keep in mind when working with the K-7. Even though it has a VGA screen and goes up to 32x magnification, it never shows the pixels. Probably a feature rather than a bug;) This may have been part of early rumors that the K-7 produces softer images than the K20D. My tests have not been able to confirm this.

Still here?

Then you must be waiting for the catwalk models ;)
Thanks for your patience and interest.

Comparative noise study K-7 vs. K20D

2009-06-18T23:06:00.007+02:00

Today, I found the time to shoot images from a K-7 and a K20D side by side. In this article, I will highlight the differences in noise between the two cameras.

This is particularly interesting because Pentax used a 2nd generation version of the sensor used in the K20D, a 14.6 MPixel APS-C sensor now famous for its beautiful images when used with an excellent lens.

I am not interested to compare the advances in the camera's built-in JPG engine and its noise reduction (NR) algorithms. I am sure they are significant. I am interested in the best quality I can get from the camera, i.e. from RAW.

Test methodology:

- Almost constant lighting, although not perfect (indirect sun light)
- Constant setup:
- My "special" 400% ISO test chart on a wall.
- Constant exposure at EV 9.
- Again, underexposed by ~ -0.7 EV to exhibit more visible noise (to make it "gray").
- Second image underexposed by ~ -1.7 EV (EV 10).
- Tripod, K-7 MLU and K20D 3s timer, both via remote control.
- Zeiss 50mm/1.4 at f/4.0, manually focussed using magnified live view. (The Zeiss 50 is sharper in the center at f/4.0 than f/5.6.)
- Focus series for a resolution test (pending).
- Late sun and wood floor made a nice 3900 Kelvin color temperature.
- Shot in RAW (K20D: PEF, K-7: DNG) and exported by Lightroom using default settings.

Caveats:

- No colors.
- Focus was only almost perfect in the noise test.
- Only one camera of each type tested.
- My camera is a preproduction unit (with final firmware) which may give slightly inferior results to a production camera. Therefore, subtle differences may not be significant.

-- Begin of update --
Clarification:
The interpretation as authorized by Pentax is as follows: Tests carried out with preproduction units and final firmware are allowed to be taken representative of final quality. There won't be a noticeable difference when just inspecting photographs. However, there may be numeric differences when tests are carried out by a quantitative lab test, and if so, in favour of the production cameras. Therefore and because I didn't publish test figures, this blog article must not be considered premature.
-- End of update --

Results:

All results are presented as 100% crops prepared for easy inspection here:

Resolution and Noise of K-7 vs. K20D

Please, have a look before joing my conclusion (note that you'll see snippets magnified by 15x!).

Verdict:

The noise from the K-7 and the K20D almost look the same. If there is a slight advantage, then it would go to the K20D. But the difference is so marginal that I say:

There is no significant difference in noise from black & white subjects in raw files from the K-7 and the K20D.

The K-7 produces excellent results up to ISO 1600, and ISO 6400 remains reserved for smaller image sizes. It is however remarkable how much detail is preserved in even ISO 6400!
This is what Pentax is known for: Details rule over noise!

K-7 final firmware and tungsten high iso noise

2009-06-17T22:26:00.006+02:00

I have just received the final firmware v1.00 and wanted to make available some samples shot at ISO 400-6400 in tungsten light (2900/2950 K, using Auto WB). Shot with the kit lens and AF focussing onto the SD card in the center.

This is a preliminary article and my evaluation of noise is pending. Also, the subject is not ideal (colors missing, no gray card). I was in a hurry. The ball's surface has a subtle texture looking like noise but not being noise (in iso 400)! So, this may be used to compare denoising artifacts.

The camera was set to "natural" (default is "bright") and default settings otherwise (i.e., sharpness -1, NR medium, NR start iso800).

The images are here (out of camera or Lightroom standard settings):

K-7 Tungsten high iso noise

And the DNG raw files are here:

http://www.file-upload.eu/download-1709906/IMGP0006.DNG.html
http://www.file-upload.eu/download-1709919/IMGP0007.DNG.html
http://www.file-upload.eu/download-1709926/IMGP0008.DNG.html
http://www.file-upload.eu/download-1709937/IMGP0009.DNG.html
http://www.file-upload.eu/download-1709948/IMGP0010.DNG.html

Disclaimer:
Preliminary test, firmware is final but the sensor in my preproduction camera is said by Pentax to be different from the final one!

This is very warm tungsten (below 3000 Kelvin). In daylight, the noise would be much less. Also, ISO6400 is not a fully advertized feature.

K-7 and its precision autofocus

2009-06-16T19:51:00.021+02:00

Pentax claims to have improved the autofocus system in the K-7. It is now called SAFOX VIII+ and has an additional sensor to improve accuracy in tungsten light. So, I had a close look at the autofocus system in AF.S mode, the mode normally used to achieve highest precision.

A thing which I didn't do: I did not look into automatic selection of AF points. I've always used the center AF point (the K-7 has 11 AF points, which 9 are cross sensor of).

In order to have a scale of reference, I quantitatively compared with the Pentax K-m which is rumored to have a snappier AF over the earlier K20D. I also played with a Nikon D300 in similiar low light situations to get a better feeling about what I see...

1. Raw technical improvement

The K-7 turns the screw drive focus motor faster than the K-m. A complete drive-thru for the kit lens at 55mm is only 0.18s! This is 40% faster then the 0.25s of the K-m which is fast already (cf. table given below, first row). A overall cycle of the autofocus hunting for impossible focus is 0.81s (down from 0.94s). Interestingly, the K-7 still waits for the exact same 0.45s before hunting back (0.81s = 2 x 0.18s + 0.45s).

So, the K-7 has a stronger focus motor to start with. It will not have a big impact in most situations where the focus won't travel much. And SDM lenses with their built-in ultrasonic motor won't see the difference anyway.

2. Accuracy

I have been extremely pleased with the accuracy in AF.S mode (e.g., in the focus series we are going to talk about below, all images are perfectly sharp). I did comparisons between manual live view in 10x magnification, contrast AF and phase detect AF with a DA 70mm Ltd. and I wasn't able to beat phase detect AF accuracy by manual focussing. Contrast AF and manual live view in 10x magnification have been very close, though and would be a good option with a less evident subject than a test chart ;)

When going from 6x to 8x/10x magnification in live view (only possible with manual focussing), the quality of the magnified image is enhanced (e.g., less noise!) and visibly outperforms the quality known from the K20D.

Other lenses like 40mm, 18-55mm kit lens, 16-50mm, 300mm have all been focussed to "the point". At least for my test camera (which may have been manually adjusted, of course) I have been very happy with accuracy. This includes shots in tungsten light which produced correct focus as well.

Note that many Pentax users are more keen in exact focus rather than fast focus because this is what renders the ultimate image quality the K-7 with its almost 15 mega pixels is capable of if combined with some of the good glass Pentax is known for.

The only caveat is the rear display which will not create the illusion of overly sharp images except if taken with very high contrast. It requires a bit of experience to verify focus. However, the quick view zoom is fast and this is not a big issue at all.

Side note:
Sometimes, the contrast AF achieves focus where the phase AF doesn't and vice versa. E.g., the contrast AF is able to focus onto a white wall or a computer screen displaying a white surface only. Obviously, it is able to find sufficient micro contrast there! Phase detect AF systems are known to fail in these situations.

3. Low light and speed

In order to measure the speed one has to define the amount of light a scene is lit with. It is a knwon fact that below a certain threshold, phase detect AF systems cease to work. Therefore, they may feature an AF assist light illuminating a very dark scene. The K-7 has a green one and it is bright enough to disturb if used towards people. Fortunately, the K-7 only uses it in very dark situations, a lot darker where a Nikon D300 would already invoke its own assist light. In all my tests below, I switched it off!

When comparing to a K-m it becomes obvious that the AF algorithm is almost the same, only faster. It would still focus in 1, 2, or 3 tiny steps to aquire perfect focus.

I've made tests in five different situations of lighting:

3 LED torch behind flash diffusor in 1m distance to target
12 LED torch behind flash diffusor in 1m distance to target
Dim tungsten
Indoor with indirect daylight
Outdoor with subject in shadow

The table below will give exact light values (LV) and temperatures of the lighting, in the same order. You can read more about light values here: Wikipedia on LV .

At ISO 100, exposure values EV and light values LV are the same. LV 0 is very dark and not normally met indoors. I measured LV by spot-metering a white sheet of paper (the target) and adding 2.47 stops to adjust for 100% rather than 18% gray. The correctness of exposure was verified by inspection of the histogram. Color temperature as given where 5500 Kelvin is daylight and less is warmer.

The subject was a white sheet (A4) of paper about covering the frame, with a big cross in the middle painted by a 0.5mm wide black marker. The lens was the 18-55mm WR kit lens at f/5.6. I didn't check if the new WR kit lens is faster (has a shorter AF screw) than the previous kit lens.

The AF speed was measured by analyzing the audio recording and taking the time from start of focus motor (the half button press is inaudible) till focus confirmation beep. The actual shutter noise you hear on the audio tapes is from the full button press at some arbitrary later time.

-- Begin of update --

I have decided to measure the latency between the shutter button press and begin of focus motor activity. I've activated the shutter with a little hammer (button was shielded ;) ). So, one can hear shutter press as well. Below is the sound at 9 EV, daylight. The big sound at the beginning is the shutter button being hit ;)

mp3 audio (shutter press to shutter release)

As one can see, the focus motor delay is 135 ms and complete operation (shutter button to shutter release) is 515 ms (0.38s after focus motor activity). focus motor delay is unnoticeable in practice. In all following figures, the additional (short) delay before focus motor activity is ignored. Add 0.14s to all figures if you need the complete release latency.

-- End of update --

In all experiments, the lens was manually focussed to 35cm prior to first AF operation, then twice from the respective previous position. In all timings marked "~0s", there was no activation of the focus motor. The timings from such a series of up to 3 AF operations are separated by a semicolon (;) in the table below. Timings separated by comma (,) are for the same operation, but from different series. The subject was 1m (or more) away.

For every result, you find a link to an audio tape of the sample, always exactly starting at the first button half press. The amplitude in those samples has been normalized. Don't use to compare shutter noise.

Table of results:

LV	Kelvin	Pentax K-7	Pentax K-m
	Hunt	0.18s / 0.45s / 0.81s	0.25s / 0.44s / 0.94s
0.4	5800	1.71s ; ~0s ; 9.42s mp3 audio	-fail- mp3 audio
1.8	7600	0.81s ; ~0s ; ~0s mp3 audio	0.96s ; 0.45s ; ~0s mp3 audio
2.1	2500	1.47s mp3 audio	0.99s mp3 audio
5.4	5400	0.42s, 0.48s ; 0.29s mp3 audio	0.38s, 0.35s mp3 audio
10.2	5500	0.40s mp3 audio	0.53s mp3 audio

Discussion:

Most remarkably, the K-7 was able to focus at 0.4 LV without focus assist light! It also seems to be about its limit as can be seen by the second refocus operation which succeeded (sharp image) but took almost 10s ;) The K-m couldn't focus at so low light and it seemed to need a full stop more light.

At about 2 LV, AF was already quick and snappy needing about 1s for both cameras.

In normal lighting conditions, AF was even faster, requiring about 0.4s where K-7 was somewhat more consistent. Overall however, it wasn't faster than the K-m.

In normal lighting conditions and when the previous focus position is near the required one (the typical situation), the AF time goes down to a mere 0.3s and feels very quick and snappy.

In available night bar light (~2 LV) I got the impression that both K-7 and Nikon D300 would need about 1s to confirm focus. I didn't take exact measures. The D300 "felt" more reliable though because it didn't noticeably re-adjust focus in the operation.

Conclusion

My conclusion is that the new SAFOX VIII+ as deployed in the K-7 is a significant improvement over the previous installment (the K-m). The 40% faster focus motor and 1 stop extra performance in low light are well balanced with the overall improvement in the K-7 which has a faster shutter and 50% faster burst. The improved accuracy in tungsten light was asked for by many and as it seems, has now been delivered in the K-7.

The K-7 auto focus isn't the revolutionary step some had hopes for. I.e., you will still be able to miss shots ;) But when actually shooting with the K-7, it certainly feels much better than just an evolutionary step. Numbers don't tell the whole story.

K-7 and its continuous autofocus -- PART II

2009-06-15T17:53:00.004+02:00

This second part of the article about AF.C in the Pentax K-7 is based on experience in general and from a less controlled test situation.

To speak in general terms, the continous autofocus in the K-7 is significantly improved over, e.g., the K20D. However, so far I know of no autofocus which is fool proof in very difficult situations, like nearby kids running around you wildly. This would require focus latencies well less than 0.1s. I estimate focus latencies for AF.S in the K-7 to be 0.3 to 0.5s, and AF.C may be about 0.2 to 0.3s.

So, I decided to find out just how badly AF.C would fail in such difficult situations. I asked a friend to run "eights" around me, as close and fast as possible. I tried to make as many shots (hi burst) and counted how many good ones and acceptable ones I got. I used the kit lens at 55mm, f/5.6. To tell the truth, I missed to have the subject in center in a couple of shots and I had the AF set to use center point only.

Because of the awkward testing situation, I decided to count as "good" what looked sharp at 1600x1200 resolution. And "acceptable" what looked sharp at 800x600 resolution. "Excellent" would be sharp at full 4650x3100 resolution. The photo at the beginning of the article shows one of the "good" examples from the K-7. I did the experiment with both, a K-7 and a K20D.

Results from random run:

K-7:
35 images in 23 s (1.5 fps)
4 excellent, 5 good, 12 acceptable, 14 fail.

K20D:
24 images in 21 s (1.1 fps)
0 excellent, 2 good, 6 acceptable, 16 fail.

Esp. comparing the excellent/good ones we see that the K-7 could actually capture some of the moments which the K20D couldn't. But it is certainly not fool-proof as well.

Results from straight run:

I made another experiment, with the same setting, where I made the person running straight towards me, as fast as possible, starting from 25m away.

K-7:
17 images
3 excellent, 12 good, 1 acceptable, 1 fail.

K20D:
13 images
6 excellent, 2 good, 2 acceptable, 3 fail.

With ~90% good images, the K-7 looks like a real winner. Of course, I found it a bit cumbersome that only 3 out of 15 good images have been tack sharp (less than from the K20D). Seems like the AF.C in the K-7 has a bit more shutter priority than in the K20D. Nevertheless, with only 60% good images, the K20D was no match for the K-7.

This confirms my general observation with the K-7: in most situations, i.e. in situations where it would be straightforward to keep a moving subject in center will most images turn out sharp. If this is difficult and if one would have to rely on automatic AF field selection then the AF.C in the K-7 will most likely run into trouble too.

Overall, the AF.C in the K-7 is a good match for its improved speed which is a ~70% improvement over the previous K20D.

K-7 and its continuous autofocus -- PART I

2009-06-14T19:00:00.003+02:00

Probably the most often criticised feature with a Pentax dSLR is the speed of its SAFOX VIII autofocus system. Interestingly, its accuracy is believed to be very good (which matters most for many situations). But two domains remained to be improved:

Speed and availability of low light autofocus (AF-S).
Speed and hit rate of continous autofocus (AF-C) for fast moving subjects (aka action or sports).

In this blog post, I'll study the latter: AF-C. This will be a two part article:

PART I: A car moving towards the photographer

I decided to follow the methodology of a test which was carried out about a year ago by German magazine fotoMAGAZIN (published in issue 5/2008). At the time, I posted a summary about this here:

Magazine Review: K20D/SDM AF.C performance vs. 8 competitors

The method is as follows:

Continous shots (burst, continous AF aka AF.C) of an approaching white Chrysler LeBaron, tripod mounted and panned centering onto radiator grill. Photograph besides road. Road straight. Test done on a straight highway.
Original: red Chrysler PT cruiser, closed military airport.
Controlled speed: 100 km/h (62 mph). Starting photo burst at 100m distance (109 yards, 328 ft). Stopping when passing by. Time to drive through 100m: 3.6s.
Focal length: 35mm equivalent of 200mm (DA 18-250 at 142.5mm/5.6).
Original: DA SDM 50-135/2.8 at 135mm/2.8
Aperture: f/5.6
Original: f/2.8
Shutter: 1/180 or shorter
Original: 1/320 or shorter
Light: Bavarian white blue sky. Changing conditions.
Original: Daylight overcast with grayness. Constant conditions.
Storage: JPEGs onto Sandisk Extreme III.
Statistics: 6 series, averaged.

So, some conditions had to be changed. Not necessarily in favour of the new setup (assuming that the DA SDM 50-135/2.8 is superior to the DA 18-250).

At f/5.6, depth of field (DoF) is larger than at f/2.8. E.g. at 50m distance, it is 15.7m for f/2.8 and 33.9m for f/5.6. This may look like a big difference. However, the AP-C circle of confusion (20µm) is 4 pixels large and watching for 2px wide sharp edges means that we can compensate for this. Let's just require that 100% crops look pretty sharp.

To have a point of calibration, I decided to test both, a K20D and a K-7.

Disclaimer: I later discovered that I made the following mistakes in running the test. It doesn't ruin the results but should be taken into account: Fine sharpness set to 3 (too high); ISO in some runs set to 1600 (too high), others to 200 (too low); JPG noise reduction not turned off; JPG quality set to 4 stars (too high); driver not driving exactly constant speed.

The problem with 4 star JPG quality is that not 38 (K20D) or 40 (K-7) images are shot in hi-burst but only about 17. The K-7 can (theoretically) shoot 19 images within the time a car needs to travel 100m (3.6s). More if one launches too early or the car is too slow.

Here are my results:

K20D results:

5 runs, per run (total=++/+/o/-):

13=8/3/2/0 too slow
12=6/4/1/1 too far (150m), speed ok)
13=7/0/6/0 too slow
12=9/2/1/0 little too slow and little too far
14=7/5/1/1 too slow and little too far

Fig.1: The 100% crop images for run #2 are all shown in the compound image above and these are the ratings: ++/+/++/++/++/+/++/++/+/+/o/- (last one was too near to have any chance, and last one is not a crop).

The magazine's original result was like

7.8=5.8/2 (meaning 5 or 6 good ones and always 2 bad ones; 25.6% bad; rank 9/9)

Taking run #2, discarding the first 4 images (farer than 100m) and counting 2/4/1/1 as 6/2 we would roughly get at the same result. So, I decide to count the first two qualities ++/+ as "good".

In an attempt to simplify my analysis, I then get my new result:

12.8=10.2/2.6 (20.3% bad; rank 8/9)

K-7 results:

Due to its higher speed, the K-7 fires away 14 to 20 shots. It slows down towards the end. Maybe because of AF.C needing more time, maybe because the buffer fills up (after ~17 shots in 4 star quality). In another test I could verify that a busy AF.C can indeed slow down the burst speed. Fortunately, I did run #5 over 50m/2sec and the K-7 still took 7 images :)

7 runs, per run (total=++/+/o/-/(subject out of frame):

20=13/3/3/0/(1) too slow
16=11/3/1/1 little too slow and little to far
14=13/0/0/1 correct speed and distance!
17=15/1/0/1 little too fast and too far
7=5/0/1/0/(1) correct speed and 50m (run #5 is not counted!)
20=19/0/0/1 correct speed and too far
16=15/0/1/0 too slow and too short

Run #3 are 7% bad images only. And to quote a comparison: 13 good images is what the D300 delivered in the original test (rank 6/9)!

Fig.2: The 100% crop images for run #2 are all shown in the compound image above and these are the ratings: +/++(8x)/+/++(3x)/o/+/- (last one was too near to have any chance, and last one is not a crop).

In the same attempt to simplify my analysis, I get this result (counting out of frame as bad):

17.2=15.5/1.7 (9.9% bad; rank 4/9 -- about same as D300)

Summary and verdict:

The K-7 makes about 50% more good images and about 50% less bad images than the K20D in this test. This looks like a lot. But believe me: when I first saw the images, I thought ... "where the hell is the difference"? Both cameras for sure can capture driving cars except when they are very nearby. The difference is subtle more than evident. But on the other hand, it is significant enough to score side by side with a D300. Seems others also put their pants on one leg at a time. In practical terms, the AF.C will still fail in many situations when one would wish otherwise...

Additionally, the systematic errors in my test are large. So, let's me say it this way then:

The AF.C on the K-7, compared to the K20D, is an improvement making it significantly coming closer to the performance of a D300. How close exactly it comes, I don't know. Could be very close, or not.

This concludes PART I. The next part will study, in a just a bit less formal way, what happens with people running randomly around you ...

-> Continue to Part II

K-7 and the moskito

2009-06-13T20:29:00.005+02:00

Today, when I looked out of the window, I saw a moskito on the other side.

Well, a good opportunity to try out the K-7 with the DA 35mm Ltd. macro lens. What a wonderful lens!

The image below is taken at ISO1600 and was overexposed (I overexposed manually) and later post-processed for better contrast. It is a freehand shot but I used the window glass to rest parts of the camera body. Light is daylight in the shadow. The moskito was alive :)

I noticed that autofocus starts to have trouble when exceeding about 3:1 magnification. I think this is normal because with the DA35, the distance of front lens to subject starts to change dramatically as well. So, I used live view to focus manually and actually had to magnify to 10x and shift the region of interest on the rear screen (I couldn't get the moskito into the center of frame). This worked out nicely. The full 640x480 resolution of the display certainly is a benefit.

Below, I add a 100% crop too. It is from the unprocessed original.

Note that the moskito eye segments are very small, maybe only 25µm. The ISO is 1600 and the firmware is pre-production. So, please don't do noise analysis from it;)

Enjoy the image.

Falk

K-7 in the rain

2009-06-06T15:32:00.012+02:00

The saturday after fetching my K-7 was a rainy day. I.e., a perfect day to go out and do some test shots! This allowed me to get aquainted to the K-7 more and also enjoy shooting in bad weather conditions.

The K-7 is not only sealed for the worst of weather conditions; but its kit lens(es) is/are too! Needless to say that the K-7 really liked to get wet and for the first time ever, I didn't have any bad emotions seeing it getting wet :)

First impressions:

As noted by many on the web already, it is a real pleasure to hold and handle the K-7. In comparison, the K20D feels older than the core technical data would suggest. It feels solid, almost unbreakable and seems to offer timeless value. Of course, no dSLR can offer this with progress in semiconductor physics being this fast. Nevertheless, the K-7 just feels "right" -- as a serious photographer's tool. I like its size. It is rather small for what it does (smallest APS-C semi-pro body in the industry, look up the technical specs) but does not feel small because of the excellent grip. I could carry it around just holding its grip, for hours ... With its steel magnesium alloy body, it definitely feels solid rather than hollow; giving a nice balance to most lenses.

The first observations jumping to mind are: It does focus fast, it does shoot fast, and it does it in stealth mode (all compared to, e.g., a Pentax K20D or K-m). The shutter and mirror slap are so quick, silent and damped that it one wants to press the shutter in burst mode just for the joy of it (and my girl friend likes it too). Also, the live view (LV) operations are now fast enough to actually be useful. The K-7 is a lot faster to operate though without LV. Of course, for most discrete usage, the constant mirror up during LV, combined with SDM or manual focus, is an added benefit. Unfortunately, the mirror will unlock after a while, in some way or another.

Also, on first inspection, the image quality is very good. With the excellent image quality of the K20D, this is no surprise. I cannot yet tell if it is better or worse, though.

In the next couple of blog postings, I will study a number of details, e.g.:

Continous autofocus
Autofocus
Image resolution
Noise (when final firmware is out)
Experience with tethering, both USB and HDMI
Video
How to have fun with the camera

In general, I'll try to add to what has been posted already and not repost too much.

For a product description, go here:

Pentax Imaging's K-7 page

Pentaxforum's K-7 page

DP Review's K-7 page

Some more photos in the rain ...
Note: all photos as shown here are post processed. The gallery contains the original images, too.

Black drops

Red drops

Better stay dry

Very green

Unexpected flower

Peace

Please, visit the gallery page to access full size sample images. All original images have been taken with the camera's factory settings, in DNG raw format, and been converted to JPG in Lightroom with standard settings. You may download and print the original files but please note that the photos carry my copyright.

This blog post's gallery page

I am Pentax K-7 Alpha Tester :)

2009-06-05T17:08:00.017+02:00

When I returned to my office today, I found a yellow delivery note from UPS on my desk. Labeled: Sent by Pentax. Uuhh! Could this be related to the K-7 test action Pentax was calling alpha testers for? http://www.pentax.de/de/news/1160/foto_news.php

I got no notice and had almost forgotten about it but indeed: the package contains a kind letter from Pentax asking me to test the K-7 (also in the box); and this implies that I must be one of ten selected alpha testers for Germany. Of course, I felt very lucky immediately :)

So, I am now preparing to meet Karsten (kafenio's K-7 blog), another K-7 alpha tester in Munich to exchange first impressions. And I am now setting up my webspace (falklumo.com) so everything can be linked together and cited for further reference. Which is the real reason why this blog is born today, actually ...

After I got out and shot some photos, of course. The Pentax K-7 is too tempting to resist :)

http://www.pentaximaging.com/slr/K-7/

Stay tuned for further info ...