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06-08-2012, 06:55 AM   #1
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K5 focus varies with temperature

We're having a cold spell.
This morning it was 5C, and my DA*55 lens was having difficulty with focus, needing a +8 focus correction.
By the middle of the day, the temperature had risen to 15C, and the DA*55 only needed a focus correction of +2

I checked and rechecked the focus accuracy with other lenses (Sigma 85mm/1.4, FA 77 limited) and noted similar variance.

The only sensible conclusion is that my K5/lenses seems to have temperature related focus issues.

Has anyone else noticed this behaviour?

Cheers

Jack.

06-08-2012, 07:05 AM   #2
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i have never had to change the focus adjustment on any lens..i'm wondering if i am missing something or am i just lucky...i live in va so the temps don't go to extremes
06-08-2012, 07:20 AM   #3
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Pentax has a recent publication describing how to solve this problem (which also admits that this is a problem, though not a Pentax particular problem).

https://www.pentaxforums.com/forums/pentax-news-rumors/160585-sony-style-auto-focus-coming.html
06-08-2012, 07:34 AM   #4
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We had a pretty mild winter this year, so I don't have any really cold data. 5C isn't cold, though, and I had mine out well below freezing and it worked without trouble. The pictures I found on my quick look at snowy days on my Flickr stream shows only about -6C as the cold days.

I know my K10 operated easily at -15C, and likely lower.


Last edited by TER-OR; 06-08-2012 at 07:47 AM. Reason: edited temp
06-08-2012, 09:06 AM   #5
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I live in Canada and use my K-5 at -10C and never saw that phenomenon. I do not believe this is the case
06-08-2012, 09:33 AM   #6
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i used mine in minus 20 and plus 20 C one week between without isues
06-08-2012, 10:06 AM   #7
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In theory, it makes perfect sense, since the cause of an problem would be AF sensors at a different distance from the focal point of the lens than the imaging sensor, and temperature changes could cause shifts in the body shape that would affect this. Whether the magnitude of this effect would be enough to see it over the measurement error is another matter.
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