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12-30-2010, 03:40 AM   #301
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Are all the K-5 actually affected by the AF issue, or only some batches ?

12-30-2010, 04:49 AM   #302
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You know Falconeye has the right idea here i think. I never thought about open source before for cameras. but It would certainly help Pentax. There are many smart people out there that would tackle the problem. Spot on...
12-30-2010, 05:49 PM   #303
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QuoteOriginally posted by Aku Ankka Quote
Though, if one is tracking a subject and shooting continously, there should be some benefit because of constantly availablle information for the AF unit.
You are right when it comes to AF.C. The original question was one about accuracy which I translated to be about AF.S.

The SLT system was made primarily with video and EVF in mind. But it could have an edge at AF.C. If it is paired with a very capable AF module and algoruthm, of course.
12-30-2010, 08:51 PM   #304
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This is getting off the OP. But is there a thread on shutter blur for the k-x? I tried to read falconeyes article on the subject for the k-5 and k-7 but do not understand other than a .6 pixel blur for the k-5 between certian shutter speeds. I think????

I suspect I am getting very bad shutter blur with the k-x. As i crop heavily. It is apparent i think... I can hold my hand over the lens and really stabalize it and it helps but i think it is a problem for me with the k-x. Especially with a 1.4 tc. connected...

12-31-2010, 03:46 PM   #305
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Some Tests

QuoteOriginally posted by falconeye Quote
That's not true. It depends but in a complex way.

I did one more test to rule out or confirm another possible explaination. The tests have been around 1EV which is above the threshold AF assist light is triggered. ISO100, 2s, f/1.8 to be precise.

First with tungsten, a bit brighter: focus almost ok.
Next with halogen: focus miss.

So I thought, it may be the flicker from artificial AC light. So, I tried my battery-powered headlight positioned to give indirect light, even a stop less:

So, next with 3LEDs: focus hit!

I thought this is it, it is the flicker the battery doesn't cause. My battery-powered headlight has two more settings: mini tungsten bulb and 1LED. And it rules it out:

Next with battery tungsten: focus miss (luminosity between the 3 and 1 LED cases)
Next with 1LED: focus hit!

At the last position, the AF assist light wanted to come on 3/4 of times. I report the result without it.

The difference between battery powered tungsten and LED is spectrum only, ruling out the difference in luminosity and flicker.

So, daylight and LED are best, tungsten is worse and halogen is worst. A non-monotone dependency on color temperature.

My best guess still is a simple software error where correction factors are running off. Reminds me of the flash situation actually where the distance-dependent correction factor seems to run off too (following some discussion in Germany). I wouldn't be surprised to learn it is the same engineer to blame here...

To Pentax, I advise a code review of the critical sections of the firmware. One of the advantages of open source actually...


And anybody who likes to think it is a hardware bug: Maybe. But the likelyhood of software is much larger comparing the design complexities involved. Always stick to Occam's razor...
Hi Falk,

I did some tests today and the results are interesting and somewhat puzzling at the same time.

I am too lazy to post all the results again here, but you can check out my posts on the K5 low light focus thread at the other forum.

A summary:

I tested a K20D and a K5 and a focus test target (many thanks to Yvon Bourque!) using my FA 50 f1.4.

I shot test shots of the chart illuminated solely by tungsten light.

I measured the incident light at the target position with my Sekonic L-358 meter.

I shot 3 images of my WhiBal cards, one through my stack of ND filters (3 x .9 or 9 stops reduction).

I then focused the camera on the test chart and took a normal image.

I added the ND stack and re-focused and took another image.

The focus shifted to the front significantly.

Using the color dropper tool in ACR, the color temp for the non-ND shots was 2900K. The temp changed just a bit to 2800K with the filters on.

I shot the same test in bright sunlight.

The focus also shifted to FF with the ND stack on.

Color temps were 5000K, 4950K with no filters and 4750K with the ND stack on.

Here is the surprise of the day:

The K20D also shifted to FF under the same conditions, but the K5 shift was bigger.

Here are some quick videos I shot of the shift on both cameras with and without the filter stack:

K5 -


K20 -


Same lens, same lighting, same target, ND on/off.

I cannot say 100% what is going on, but I am more convinced than ever that it is not color temp related, or at least that color temp is not the main problem.

The shift occurs on both cameras in low color temp light and also in full daylight and all that is required to force a shift is a reduction in light level.

Note that at no time did I test below the metering range even though I did find that the K5 will lock well under the camera's ability to meter. It's just that it locks at a FF position.

Ray

Last edited by Ray Pulley; 12-31-2010 at 03:49 PM. Reason: Typo
01-01-2011, 12:22 PM   #306
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QuoteOriginally posted by Ray Pulley Quote
I cannot say 100% what is going on, but I am more convinced than ever that it is not color temp related, or at least that color temp is not the main problem.

The shift occurs on both cameras in low color temp light and also in full daylight and all that is required to force a shift is a reduction in light level.
Ray, thanks for your extensive testing.

The post I found most useful was this: Re: Low light level and focussing for K-5: Pentax SLR Talk Forum: Digital Photography Review

You demonstrate that there is a threshold where the camera misses focus. For both tungsten and daylight. However, I didn't find a test where you studied how this threshold depends on color temperature.

Maybe I missed it as the discussion in the other thread is rather confusing with various theories and actual results mixed.

I've seen Gordon's theory now (a failure to measure color temperature) and it isn't my preferred one. It's not impossible but not very plausible. Color temperature can normally be measured more accurately than focus because you normally have a larger light sensitive surface per measured number. OTOH, I don't know how the +-sensor is implemented. So, Gordon's theory is a possibility.

Overall though, I think we're speculating far too much (in that other thread).


I still think we at least have to conduct the following experiments before jumping to speculations:

1. Amount of defocus as a function of illumination (your test).
2. Amount of defocus as a function of illumination for another color temperature (your test).
3. Derivation of color temperature dependency (my test shows that this dependency is large too). One could do a test in red, green and blue light...
4. A test with a second body to study sample variation.


Personally though, I rather wait for Pentax doing their homework and will observe the results with interest
01-01-2011, 02:07 PM   #307
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QuoteOriginally posted by falconeye Quote
I've seen Gordon's theory now (a failure to measure color temperature) and it isn't my preferred one. It's not impossible but not very plausible. Color temperature can normally be measured more accurately than focus because you normally have a larger light sensitive surface per measured number. OTOH, I don't know how the +-sensor is implemented. So, Gordon's theory is a possibility.
Well did Volleybal in a sportsvenue and my K-5 was a little of in colourtemperature. So that could still be one of the problems.

Jpeg from my K-5 with AWB:
01-01-2011, 06:35 PM   #308
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I don't think the color temp sensor in the AF module and the AWB have any correlation. AFAIK, AWB works entirely independently from the AF module.

01-02-2011, 04:23 AM   #309
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QuoteOriginally posted by falconeye Quote
I don't think the color temp sensor in the AF module and the AWB have any correlation. AFAIK, AWB works entirely independently from the AF module.
Ok thats clear to me. But can the color temp sensor in the AF module just not make the same mistake? The picture I took with the cards is an easy target to get it good, but it didn't.
01-02-2011, 05:21 AM   #310
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QuoteOriginally posted by RonHendriks1966 Quote
Ok thats clear to me. But can the color temp sensor in the AF module just not make the same mistake? The picture I took with the cards is an easy target to get it good, but it didn't.
Actually, it isn't a mistake. How should the camera guess that the little gray patch is gray actually? There is so much green that the camera opted for a bit more blue, .i.e., there was no way for the camera to guess it is tungsten light.

The AF module's sensor only must measure the color of the contrast edge which is focused, not the illuminating light source's temperature. That's much easier because it doesn't involve any guessing. It's as easy as doing a manual white balance on a gray card which I'm sure your K-5 has no trouble with.
01-02-2011, 06:56 AM   #311
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QuoteOriginally posted by RonHendriks1966 Quote
Ok thats clear to me. But can the color temp sensor in the AF module just not make the same mistake? The picture I took with the cards is an easy target to get it good, but it didn't.
Actually, the picture you took of the cards is pretty well impossible for an AWB to get right because of the predominance of one colour (sucky green).
In my photo lab days we called that a colour failure, and it was caused by a predominance of one colour throwing off the white balance of the printer.
AWB depends on an "average" scene type to work properly, the farther you get away from that, the less likely AWB is going to hit the mark.
01-02-2011, 08:26 AM   #312
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I've been using my K-5 under a wide variety of conditions, including atrociously dim lighting and light predominantly from tungsten and halogen lighting.
In fact, a fair bit of lighting under which I wouldn't even have tried to use any previous Pentax camera.

I'm sorry to say I find the OP's statement on the K-5 quote "disability to autofocus in dim and tungsten lighting conditions" really an unfair assessment of the camera's performance.
I find the K-5 does autofocus in both dim and tungsten lighting conditions.

Like every dSLR I've ever used (including Canons and Nikons) it exhibits a degradation in AF performance and accuracy as the light grows really dim , and somewhat worse if that dim light is yellowish. At some level of dimness AF either shuts down totally or its no longer accurate.
Nothing abnormal or that surprising. dSLR AF isn't magic.
Maybe there is individual body variation involved, but my experience with the K-5 has been nothing really abnormal about its AF performance.
01-02-2011, 09:03 AM   #313
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Strange tests

I have not seen any similar issues like in K20D, K5 is ok in dim or tungsten light. I have sit in physics lab quite a lot an see the testing methods used here are not accurate nor the conclusions.

If the problem is corrected, the CaniKon marketing people still repeat the same pattern and fool people of course will believe it. Everyone can look tests how K5 performs against D7000 and it is not lacking behind much.

I am using DA*55, DA*50-135 amd DA 16-45 quite often, when I shoot 150 photos I get may be 10 misses and this is normal to any camera.

Tungsten shift is totally different issue and this is present with K-x,Kr,K20 and I see it in my K20D, this is systematic error and quite large.

In your test you have to take account that K5 AF areas are quite wide.
01-02-2011, 09:11 AM   #314
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To some degree my K-7 had the same problem, just not that big as in the K-5 I've here.

K-7 with DA*55 at f2.0


So it's not totally new.
01-02-2011, 09:23 AM   #315
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QuoteOriginally posted by kittykat46 Quote
I'm sorry to say I find the OP's statement on the K-5 quote "disability to autofocus in dim and tungsten lighting conditions" really an unfair assessment of the camera's performance.
You speak about general consistancy of AF at hard conditions. We have based our statment on more or less scientific and absolutely repeatable expieriences... including targetting at contrasty subject like af test charts etc. At least in case of myself, i dont want to claim that high expactation reg Pentax k5 AF means k5 failed. Its not about k5 sometimes showing up AF issues... its about AF is not able give to us consistent results within its range... its about some obvious fault at design stage
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