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01-14-2013, 09:19 AM   #1
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My observation on K5 AF issue

Maybe it is a bit late to discuss it since K5 is now discontinued. But...here's what I found:

My K5 has lastest firmware 1.13. Lenses are wide open in testing.
In low light condition, AF adjustment is set 0 and it is spot on for all my AF lenses (including FA43).
However, under good lighting (outdoor), I need AF adjustment +7 and it is spot on for all my AF lenses.
It is such a heachache.

My observation is Pentax didn't fix the K5 AF issue in firmware 1.13 (1.03). They just simply tweaked it so that in low light it is more accurate but sacrificed good lighting case. Any way, we are more likely to discern AF error in low light due to wider aperture used. For good lighting, lens is more likely to be close down to make the error less noticeable.

This is what I feel about Pentax's K5 AF and its fix. What do you think?

Thanks.

01-14-2013, 09:53 AM   #2
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So the AF calibration is 0 when indoors and +7 when outdoors?

This is sort of weird, I have also a K-5 at 1.13, so far, have not seen this behavior. What sort of subjects are you using for a test?
01-14-2013, 10:02 AM   #3
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i shoot everything outdoors so i cannot comment on low light conditions...i have 2 k5s...one i put the 1.13 version and the other does not have it...i noted that both cameras shifted this summer...one is +5 and the other +8 and they are consistent with all lens...i felt it kind of odd that they both suddenly changed about the same time...assumed that it was the hot weather but now that it is cold they are still at the same focus adjustment...sorry i can't help on your topic but i did feel the adjustment was odd but as long as it doesn't change again then i am fine...i periodically recheck in bright light conditions just to make sure or if my focus doesn't seem to be where i want it...amy
01-14-2013, 10:04 AM   #4
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I used various methods including comparing PDAF with Live View AF - by enlarging pics and checking lens distance marks. I didn't use standard target but various flat cardboards with texts and patterns. I also used various real outdoor objects, like mailbox, trees, brickwalls to confirm which AF adjustment value gets me the best focus in general. They all seemed to point to +7 outdoor for my K5.

I normally observe this problem easily with lens set at largest apertures, i.e. 1.4, 1.9, or 1.8, and for 50-135, 2.8. Thanks.


Last edited by hyyz; 01-14-2013 at 10:11 AM.
01-14-2013, 10:35 AM   #5
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Sounds very much like something I had going on with several K-5's I tried over last summer. In the end (after twice having unsuccessfully sent the camera in for repairs) I was offered a full refund or exchange with some other item(s) from them shop - I then went on with K-30 and been happy since.

I started a thread about it as well back then: https://www.pentaxforums.com/forums/general-technical-troubleshooting/191214-...ocus-rant.html
01-14-2013, 02:02 PM   #6
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Thanks!

I'm afraid I have the same problem. I also guess it is related to hardware, not software. If this is true, sending for repair won't solve the problem. I do have 3 year warranty on mine though.

A workaround for my case: set to +7 for outdoor use and when it comes to low light, change to 0. Well, I guess if I can do this, Pentax should have the fix in software, right:-)?
01-14-2013, 02:21 PM   #7
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QuoteOriginally posted by hyyz Quote
A workaround for my case: set to +7 for outdoor use and when it comes to low light, change to 0. Well, I guess if I can do this, Pentax should have the fix in software, right:-)?
"Should"

I do not have a technical understanding about all this but at the end I realized different colors (wave lengths, I suppose) was what affected the AF. I believe deep red was worst with every single camera. Even a small red spot such as red streetlight at a distance could through AF way off. Green would be fine - more or less, the different K-5's I tried behaved slightly different to eachother, but overall the basic behavior.

In everyday life it means if you are out for a walk during sunset or rise, you'd have to adjust the camera several times within a short period of time. It also means while 0 might work for you at home or where ever you tried, you'd need to find a different value under different sorts of artificial lighting. This was unacceptable to me.
01-14-2013, 02:51 PM   #8
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I'm currently trying to replicate the issue. Haven't had any success thou...probably because their is no sun in Houston right now. I tried taking a picture of a book page (with a vertical object on top of it, a USB drive, as my focus point) under 4 F40T12 fluorescents, then I cover up the "subject" and myself with a black trash bag, until I can barely see it on the viewfinder. I have my K-5 (-8 calibration, center AF point) with a Sigma 50mm f/1.4, it hunts a bit when dark...but so far I haven't seen significant front or back focus.

I was reading Zafar's other thread, and it's sort of interesting...

01-14-2013, 04:30 PM   #9
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Give this a try (follow the link): https://www.pentaxforums.com/forums/pentax-k-5/211883-k-5-front-focus-woes.html#post2240783
01-14-2013, 08:11 PM   #10
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QuoteOriginally posted by HSV Quote
I have my K-5 (-8 calibration, center AF point) with a Sigma 50mm f/1.4, it hunts a bit when dark...but so far I haven't seen significant front or back focus.
So, with this combo under outdoor lighting and -8 calibration you won't see FF or BF either , right?

Try a cereal box as it is larger and with texture. Make it vertical and directly focus on it. See if you can get clear picture both lightings.

Last edited by hyyz; 01-14-2013 at 08:19 PM.
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