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03-03-2011, 10:22 AM   #286
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JeffJS is right but conducting tests with the lens not fully mounted could be difficult.

QuoteOriginally posted by Ray Pulley Quote
You might be right now that I think about it, or at least a non-A lens, as the aperture lever of the A lenses is held wide open mechanically once attached to the camera.

Thanks for pointing that out.

Ray
Also K and M-series lenses are mechanically held wide open (by the aperture lever) when attached to a camera.

QuoteOriginally posted by Duplo Quote
The aperture level is only controlling the aperture if you set the aperture ring in the "A" position.
No. the aperture lever is held wide open just the same when a manual aperture setting is selected.

03-03-2011, 10:32 AM   #287
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Well, you're obviously not going to perform any AF tests with the lens rotated on the mount. You May be able to decide where a particular lens gives a proper AF confirm however. My last post was specifically about the question of the aperture ring actually operating the blades before the shutter release is pressed.

03-03-2011, 10:44 AM   #288
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Might Work

QuoteOriginally posted by JeffJS Quote
Well, you're obviously not going to perform any AF tests with the lens rotated on the mount. You May be able to decide where a particular lens gives a proper AF confirm however. My last post was specifically about the question of the aperture ring actually operating the blades before the shutter release is pressed.

The manual AF confirm was the intent.

I no longer have any M42 or non-A lenses so I cannot check, but the rotation of the lens does seem to work on the FA 50 f1.4.

Ray
03-04-2011, 12:14 AM   #289
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that there has not been a firmware fix YET, is a bit of a worry frankly.

03-04-2011, 12:31 AM   #290
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i think they have their hands full, they need to do it right
03-04-2011, 01:25 AM   #291
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From other threads it seems that there is a low tungsten light FF problem with the K-r as well. If the K-5 issue is about a problem with the colorimetric reading, K-r's problem/fix would have to be different as it does not have such a sensor.
03-04-2011, 01:41 AM   #292
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Yes, I think that the SAFOX IX AF module (shared by the K5, Kr and 645D) may be more sensitive to color temp shifts than the previous SAFOX VIII...

After all, it was presented as being more sensitive and more spread out, so I would not be surprised if it was one of the culprits here.

One encouraging point is that the 645D does not seem to suffer from FF, so the '+' sensor may be working as expected in this case.

On the other hand, I'd not expect 645D users to try those low-light handheld casual shots every day...
03-04-2011, 03:39 AM - 1 Like   #293
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QuoteOriginally posted by jolepp Quote
From other threads it seems that there is a low tungsten light FF problem with the K-r as well. If the K-5 issue is about a problem with the colorimetric reading, K-r's problem/fix would have to be different as it does not have such a sensor.
Since my girlfriend has a K-r, I asked the Swedish Pentax repair company about this on the phone. The guy confirmed that the K-r also has FF issues, "significantly worse than the K-5, actually", so there you go.

HOWEVER, he said that while K-5's cannot really be fixed at the moment, they have had success in calibrating K-r cameras to be more accurate. I have no idea what they're doing exactly, but since he asked what lenses she had it is likely that they are doing a global adjustment that will work with some lenses and not with others. It is not just the in-camera fine tuning, though.

03-04-2011, 05:29 AM   #294
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QuoteOriginally posted by jolepp Quote
From other threads it seems that there is a low tungsten light FF problem with the K-r as well. If the K-5 issue is about a problem with the colorimetric reading, K-r's problem/fix would have to be different as it does not have such a sensor.
Are the kr's issues different from past camera's front focusing in tungsten lighting? I haven't read nearly as much about this issue and I know for a fact that the K20 and before did front focus to a certain extent in tungsten lighting situations. But, since my understanding was the camera could not detect tungsten light temperature, there was no fixing the problem.
03-04-2011, 06:07 AM   #295
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QuoteOriginally posted by Rondec Quote
Are the kr's issues different from past camera's front focusing in tungsten lighting? I haven't read nearly as much about this issue and I know for a fact that the K20 and before did front focus to a certain extent in tungsten lighting situations. But, since my understanding was the camera could not detect tungsten light temperature, there was no fixing the problem.
It could be that the k-r just has the typical tungsten light FF and this would even seem like the most likely thing IMO as anything else is kind of hard to explain. Then again this managing to get through with the K-5 with the premise that Pentax was making a specific attempt to improve AF performance in the kind of light of which tungsten would seem to be the most common case seems odd and could mean that the issue still is more clever than us and Pentax combined .
03-04-2011, 06:17 AM   #296
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I don't think the FF issue of Kr is this typical FF issue, but one much severe. I believe it's a Safox9 issue, with or without + sensor. The coincidence is too big that both K5 and Kr have so severely FF.

Last edited by ursamajor; 03-04-2011 at 08:16 AM.
03-04-2011, 08:16 AM   #297
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One Wonders

QuoteOriginally posted by ursamajor Quote
I don't think the FF issue of Kr is this typical FF issue, but one much severe. I believe it's a Safox9 issue, with or without + sensor. The coincidence is too big that both K5 and Kr have so severely ff.
I would agree with this observation.

It makes one wonder what part or process is shared by the Kr and the K5 that might be at fault?

I will soon have a K7 and it will be interesting to see if it is closer to the K20 or the K5 in terms of focusing accuracy in low light.

Ray
03-05-2011, 10:07 PM   #298
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Another Interesting Patent

QuoteOriginally posted by falconeye Quote
Ray,
thanks a lot for the link. I must have missed it when it was first posted

I'll have a deeper look at it. But one thing seems to be pretty clear:

The AF+ system assumes a colorimetric sensor (#17 in the patent) which is located on top of the eyepiece and exposure meter (#16 in the patent). However, #16+17 require an aspherical condenser lens in front of them (#15 in the patent) which the K-5 lacks. It is very similiar otherwise.

As I said, I now believe Pentax merged #17 and 16 into a metering CCD and made #15 spherical. Which means the colorimetric sensor sees the focussing screen image. Which in turn means a Katzeye may affect focus beyond exposure

The sensor #17 in the patent is describes as a global light color sensor. That's a bad idea anyway because such a system makes the hidden assumption that overall light color and edge color are the same. That's not always true though.


Nevertheless, I herewith promote hypothesis to theory: The focus shift is caused by a low reading of the colorimetric sensor which is hosted above the eyepiece and performs proportionally to the max. aperture of the lens which, in turn is proportional to the focus screen image overall brightness rather than edge brightness.

I am allowed to do so because the hypothesis predicted the +sensor to be outside the AF module and the patent (which I wasn't aware of) now confirms it.


This means that the fix shouldn't be very hard: If the reported calorimetric signal (brightness) falls below a given limit then it must not be trusted anymore.


There is an interesting corollary for studio shooters: a low key situation with a dark background may not send much light to the calorimetric sensor, even if the required EV value is high.

Therefore, studio shooters should currently not use the K-5 phase AF for low key photography except if combined with primes faster than f/2.8 and/or an external daylight focus assist light.

In retrospect, this explains what I see in the studio myself. Most of my studio AF misses are low key with a zoom.

A well lit feature makes the AF lock focus confidently but a dark overall illumination makes the colorimetric sensor send it off 250 um. Theoretically, it should then be possible to construct a scenery which front focusses at almost any EV value.
Samsung, applied for 2009, issued 2010:

WAVELENGTH DETECTING APPARATUS AND FOCUS DETECTING APPARATUS HAVING THE SAME

I suspect that this is a bit closer to what is in the K5 than the older Hoya patent. The layout even looks very much like the K5 in the prism area above the eyepiece.

Note that the color or wavelength sensor is described as also being the metering system.

The focal length shift versus wavelength is graphed, which you might find interesting relative to your calculations and tests.

At least we are getting to the bottom of the longstanding "yellow light" AF errors. I suppose that other brands could have more corrected optical layouts for the AF module, but otherwise, the shift has to be reasonably similar for most AF systems that do not employ an active correction system. Maybe others apply a correction based upon the WB or AWB calculation?

Ray
03-06-2011, 02:54 AM   #299
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AWB is out of the equation, as it is computed afterwards from the image taken...
A manually selected WB could be used, but I doubt it...
03-06-2011, 08:44 AM   #300
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Maybe, maybe not

QuoteOriginally posted by dlacouture Quote
AWB is out of the equation, as it is computed afterwards from the image taken...
A manually selected WB could be used, but I doubt it...
Not if it is done by a second sensor which is mentioned in the patent.

Ray
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