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04-27-2016, 01:54 PM   #1
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K20d Autofocus Issue

Hello all,

So, for the past few years I have been all work and no play, and my gear has been sitting in its cabinet rarely used. A couple of months ago I pulled out my K20d and pentax 50mm f/1.4 lens to take my nephew's college graduation portraits. It had been maybe 6 months since the last time I used that combo with no issues.
I noticed immediately that it was focusing behind where I intended it to consistently, but not enough to matter at the sizes I intended to print. I chalked it up to just not doing much pixel peeping before and not noticing, and also using the lens almost wide open. One thing that struck me as odd is the autofocus was bang on when using the far left and right focus points, the non cross type.
On to last weekend. Same body and lens. My son asked if I would do his senior portraits and I agreed. It was a mess. I turned on and adjusted the lens correction all the way to -10 I believe and I still couldn't get the autofocus dead on. Never thought to try the far left/right focus points. Finished up by manually focusing. After that was done it was really bugging me so I pulled out another lens, sigma 24-60 f/2.8 with the same results. pentax 18-55 same results also. Got out the old K100d and mounted up all 3 lenses with no issues autofocus-wise.
So, I guess my question is is my autofocus module or whatnot bad? Any fixes I can try? I would really like to get it focusing properly if I can, if not time to save up for a K-3II.

Thanks guys,
Marcus

04-27-2016, 02:01 PM   #2
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QuoteOriginally posted by marcusjtaylor Quote
Hello all,

So, for the past few years I have been all work and no play, and my gear has been sitting in its cabinet rarely used. A couple of months ago I pulled out my K20d and pentax 50mm f/1.4 lens to take my nephew's college graduation portraits. It had been maybe 6 months since the last time I used that combo with no issues.
I noticed immediately that it was focusing behind where I intended it to consistently, but not enough to matter at the sizes I intended to print. I chalked it up to just not doing much pixel peeping before and not noticing, and also using the lens almost wide open. One thing that struck me as odd is the autofocus was bang on when using the far left and right focus points, the non cross type.
On to last weekend. Same body and lens. My son asked if I would do his senior portraits and I agreed. It was a mess. I turned on and adjusted the lens correction all the way to -10 I believe and I still couldn't get the autofocus dead on. Never thought to try the far left/right focus points. Finished up by manually focusing. After that was done it was really bugging me so I pulled out another lens, sigma 24-60 f/2.8 with the same results. pentax 18-55 same results also. Got out the old K100d and mounted up all 3 lenses with no issues autofocus-wise.
So, I guess my question is is my autofocus module or whatnot bad? Any fixes I can try? I would really like to get it focusing properly if I can, if not time to save up for a K-3II.

Thanks guys,
Marcus
If the camera focuses behind the subject, don't you need to apply a positive adjustment? In other words, but inputting -10, you've inadvertently made the problem worse

Also, adjustment values will vary from lens to lens. Since the K20D only has a global adjustment (AFAIK), you'll need to change it for each lens. Other lenses may or may not require an adjustment.

I would also recommend that you use an AF calibration chart (minimally one that you print out yourself) to conduct tests in a controlled manner:
Fixing Front and Back Focus - The Remedy - In-Depth Articles

Finally, if the camera hasn't been in use for a while, but sure to use a blower (not compressed air) to clean the mirror box, in case dust has settled on the mirror.

Adam
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04-27-2016, 02:08 PM   #3
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Hmm. I will have to play around with the corrections again tonight and post the results. I wrongly assumed a negative would bring the focus back toward me. I hope its that easy! Thank you!
04-27-2016, 02:19 PM   #4
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QuoteOriginally posted by Adam Quote
Also, adjustment values will vary from lens to lens. Since the K20D only has a global adjustment (AFAIK)
You can adjust for multiple lenses on the K20D.

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