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| A2C2 (AFMA Array Color Chart) produced by FoCal for a Nikon D800E with Nikkor 24-70/2.8G lens at 24mm f/2.8 at 1.2m distance. |
Showing posts with label test. Show all posts
Showing posts with label test. Show all posts
September 13, 2012
LumoLabs: Using FoCal for testing of an AF sensor array
March 16, 2012
Apple iPad 3: A first screen evaluation
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| Screen comparison of The new iPad (iPad 3, left) and the original iPad (iPad 1, right) The image is shot in tungsten ambient light. White balance is set such that a white background on the iPad 1 appears white. Both devices show a page in iBooks using the Sepia theme. Image (c) 2012 Falk Lumo |
Please click onto the image to see the full size image exhibiting the physical pixel structure of each device.
As you can see, the new iPad has a much higher resolution (Apple says 2048 x 1536). Apple also claims the new iPad to have "44 percent greater color saturation". Photos definitely are displayed with incredible detail. There certainly are photos which looked ok on older devices or even a computer screen but are ugly on the new iPad. Especially artefacts from too strong a noise reduction are very visible on the new iPad. Therefore, the new iPad sets a new proof reading reference for photographers.
However, I must say that I am a bit concerned that on the new iPad, the "Sepia" iBook theme certainly doesn't appear Sepia at all. It has a definite greenish color cast. You may look at the image above to see what I mean. To be fair, in that image the white balance was calibrated to a white iPad 1 background. However, the image shows exactly what my subjective impression was too. And objectively, the iPad 3 is more Greenish and less Reddish than the iPad 1. The iPad 3 is a production device delivered today.
One may think that the difference is in color temperature only. However, if I calibrate for white balance of the new iPad or the iPad 1, they both calibrate to the same color temperature. It is the so-called "tint" which is different. Therefore, one or both of the iPads have a color cast.
So, I am wondering what is going on here?
Does the iPad 3 lack a color profile that it certainly would need?
And if this is the case, does it make the new iPad obsolete as a serious tool for photographers?
I hope that Apple will soon issue a statement of clarification.
UPDATE 10 days later:
In the Apple support forums, a minority of users expressed the opinion that the cause for the yellow/green tint is glue which just has to dry. So, letting the screen burn in would resolve the issue.After a bit over 10 days with most of the time powered on at full display brightness, I am sorry to report that the effect of burn in is zero. It is NOT a glue problem (for the new iPad). See for yourself:
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| Screen comparison of The new iPad (iPad 3, left) and the original iPad (iPad 1, right) -- After ten days of continuous burn in of the iPad3's display -- The image is shot in tungsten ambient light. White balance is set such that a white background on the iPad 1 appears white. Both devices show a page in iBooks using the Sepia theme. Image (c) 2012 Falk Lumo |
Moreover, I carried my sample of the iPad3 to my local Apple Store. I showed it to a store manager. Without hesitance, he confirmed that there is a problem. I then looked at three other iPad3 devices the store had on display. They all had the yellow/green tint if compared to an iPad2. Although to a lesser extent than mine and one device, I would have deemed acceptable. Therefore, there are better iPad3 devices out there. Nevertheless, the device shown in my blog article is still quite typical of what to expect in any individual case.
The store manager advised to mark my sample as defect if it is engraved and returned. I asked how Apple could ever repair it if all devices have the same problem to some extent. He meant he has no clue but I should contact a genius :)
End of UPDATE
Thanks for having stopped by,
Falk
March 27, 2011
LumoLabs: Pentax K-5 low light focus with firmware upgrade 1.03
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
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 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.
February 23, 2011
LumoLabs: Pentax K-5 low light focus
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:
In a nutshell, this is what we find:
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.
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)
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. ;)
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.
December 1, 2010
LumoLabs: Pentax K-5 shutter
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):
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.
September 28, 2010
Pentax K-5 Preview
A cut model of the Pentax K-5 as shown at Photokina 2010
"The engineering masterpiece" (photo © 2010 Falk Lumo)
Pentax K-5
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:
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:
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!)
July 21, 2010
LumoLabs: Shutter-induced blur with an SLR camera
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:
- Understanding Image Sharpness White Paper
- Understanding Image Sharpness White Paper PDF
- Shutter-induced blur with an SLR camera White Paper (this work)
- Shutter-induced blur with an SLR camera White Paper (this work) PDF
- Why the lens has little effect: Theory of pitch and shift of a camera+lens combination in reaction to moving shutter mass (PDF)
Enjoy the read ;)
June 17, 2010
LumoLabs: Understanding Image Sharpness
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:
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
April 14, 2010
Pentax shake reduction revisited
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):
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.
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).
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.
December 11, 2009
Lumolabs: Sensors of Nikon D700, D5000 and Pentax K-x
(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:
- Pentax K-x test shots (full size)
- Nikon D700 test shots (full size)
- Nikon D5000 test shots (full size)
- Lumolabs: Welcome and testing methodology
Enjoy! :)
October 28, 2009
Lumolabs: Pentax K-x sensor quality
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
I have previously reported about the image quality from the Pentax K-7.
The corresponding blog articles are here:
- Tungsten high iso noise
- Comparative noise study K-7 vs. K20D
- Comparative resolution study K-7 vs. K20D
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-7 HD video quality
I have previously reported about the HD video mode in the Pentax K-7.
The corresponding blog articles are here:
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
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 :)
August 19, 2009
Pentax K-7 in German magazine test
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:
Notes:
Lenses used (image quality test / AF test):
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.
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.
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