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01-08-2007, 01:57 PM   #46
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K10D Front Focus - All Lenses

Hi all,

I have been using my K10D now for about 3 weeks and it exhibits consistent front focus on every Pentax lens I have tested to date:

FA 31mm LTD
FA 50mm F1.4
F 50mm F1.7
DA 40mm f2.8 Pancake
DA 16-45 f4.0
DA 18-55


I first noticed this when shooting indoors at wide apertures with the DA 16-45.

I have tested it with tungsten, a color balanced (5000K) bulb, and daylight, and it front focuses no matter what.

I changed the battery for a freshly charged unit - no difference.

SR on/off - no difference.

I have tested each focus point individually and they all front focus equally.

I carefully re-focused manually using DA lenses with and I noted that there is considerable range where the green light is on, indicating focus confirmation, but this is always front focused on my K10D. I noted also that the "beep" of focus confirmation comes on just when the green light lights up, but you can adjust the lens focus to show the green light and not have the "beep". It did not matter if I stopped on the "beep" or at the furthest range where the green light was lit, the image was still front focused.

I have have repeated all of my tests on my K100D body, and it is spot on in every case (no problem).

I have several non-Pentax lenses that I have yet to test, which I will do as soon as I get a chance (one 28-70 Tamron f2.8, one Sigma 70-200 f2.8, one Tamron 90mm macro).

I suspect that the body is simply out of calibration based upon the above tests.

I have spent almost 30 years manufacturing electronics goods, almost all of which needed calibration much like this (including high precision optics, digital cameras, digital scales, and so on) and variation or tolerance is always a possibility, as is human error, and of course, there is design choice as well as design error.

However, given that the K100D performs perfectly in the same conditions, and it uses what I presume to be the same focusing technology, I think design issues can be ruled out. If the "Front Focus in Tungsten Light due to IR" theory were valid, why does my K100D focus properly in the same light?

I can live with small differences due to lens variations and lighting, after all, physics are physics and it is rare that one design can fit all conditions, especially within a limited budget. As it is, I have a hard time getting a sharp image from my K10D with any lens unless I stop down considerably, and that is unacceptable, especially when shooting with such good glass as the 31mm LTD.

I have contacted Pentax for a repair, but have yet to receive a response.

I will re-post If I learn anything more.

Ray

01-23-2007, 04:41 PM   #47
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Credit to training_editor at dpreview for discovering this, but apparently the K10D firmware update has corrected the lighting-dependent front focus problem. I tested my 50/1.4 again (skeptically) with a number of shots which previously caused front-focus problems. All gone. It focuses perfectly. I'm not sure why Pentax didn't mention this fix in the firmware documentation. Maybe it was unintentional? Maybe it's in my head? I don't really care either way. My 50/1.4 works flawlessly now and I'm thrilled.
01-24-2007, 05:43 AM   #48
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Location: Hong Kong
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Wishfull thinking symptom, maybe.. :-)

QuoteOriginally posted by Evolution Quote
Credit to training_editor at dpreview for discovering this, but apparently the K10D firmware update has corrected the lighting-dependent front focus problem. I tested my 50/1.4 again (skeptically) with a number of shots which previously caused front-focus problems. All gone. It focuses perfectly. I'm not sure why Pentax didn't mention this fix in the firmware documentation. Maybe it was unintentional? Maybe it's in my head? I don't really care either way. My 50/1.4 works flawlessly now and I'm thrilled.
I had similar experience, each time Pentax released a new firmware for my *ist D, I hoped that the firmware "secretly" correct something which were very annoying but actually those correction were not officially announced (and of course for Pentax in the past), e.g. the underexposure symptom as well as the yellow light FF problem, etc.

Once or a few times, I found that something seem to be improved and then I post my little inital findings in forums when I just found a little of the few samples which are believed to be correctly made. However, later on, when time goes by, again, I found that actually there *nothing* was changed. The times I saw the "improvement" were just coincidence as the camera was actually behaving quite inconsistently - well, sometimes it could do it close to right but the sucessfull rate is not that high, i.e., most of the other time, it behaved "typically" for typical situations which it didn't work!

My experience is that when we had a great desire to see something happened, sometimes we cannot see thing correctly as our mind has been blockened somehow! :-)

All above are my true experience..

I know that training_editor told that he did repeated comparison and experiment, however, actually, his test samples have not been posted. So, pls be aware that what I experienced in the past may happen again in this case.

Well, I am not saying firmly the possiblity cannot be true, but I think it is very *unlikely* (if Pentax have corrected a problem that they have never been able to re-solved since their first DSLR, why not told this great news in the firmware update annoucement? Do note at least they mention about banding and B mode battery indication, etc.)
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