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06-30-2014, 07:40 AM   #1
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Weird off-focus issue between MF and AF lenses

My K-5 has a serious Back Focus issue with ALL my auto-focus lenses, but not with my manual focus lenses.

It doesn't make sense: With both types of lenses, the same phase-detection system is used.

* When I use a MF lens (A* 2.8 300mm or A 1.7 50mm), the focus detection (using the center AF point) is spot-on with zero AF correction.
* When I use a AF lens (DA 18-135 WR, DA* 16-50, DA 1.8 50 AL, DA 2.4 35 AL, FA 2.0 35), the focus consistently needs about +160-170Ám correction (I use the DEBUG mode for this, because the normal "C.26 AF Fine Adjustment" isn't going far enough).

I check the focus both using a Katzeye split prism focusing screen and by manifying the recorded images. I've taken 100s of test images, both on flat high- and low-contrast targets (such as a printed test sheet and printed colored images). Always at max aperture. The result is consistent.

Even comparing the DA 50/1.8 to the A 50/1.7, both having nearly the same wide aperture, and same focal length, their phase-detection AF is 160Ám apart. How can this be? And can this be fixed?

Has anyone else seen something like this?

Oh, I forgot to point out that I see this issue only with my K-5 but not with my K-3: There, both types of lenses are spot-on. So it's not a lens issue in itself, but maybe something related to the K-5 handling MF lenses differently in phase-detection focusing (why, though?).


Last edited by tempelorg; 06-30-2014 at 08:14 AM. Reason: adds note that K-3 doesn't show this issue
06-30-2014, 08:36 AM   #2
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Are you talking about when the red dot confirmation comes on? I get slightly different results depending on when I start from infinity or from close in. Silly question - you are not using live view, right?
06-30-2014, 08:45 AM   #3
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QuoteOriginally posted by HenrikDK Quote
Are you talking about when the red dot confirmation comes on? I get slightly different results depending on when I start from infinity or from close in. Silly question - you are not using live view, right?
correct, I am using the camera's AF red dot confirmation and catch-in-focus for manual focus lenses.
06-30-2014, 08:54 AM   #4
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Yes, what aleonx3 says

BTW, using the "Reset" (Setup menu, 3rd page) doesn't help either - this reset operation doesn't even reset the focus adjustment made via the Debug menu, so this isn't a true "factory reset", either.

06-30-2014, 09:40 AM   #5
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Didn't read this article closely, but does refer to the issue that you can get different results depending on whether the lens originally is focused before or after the subject.
Dpreview article

Not sure why there would be any difference between manual and auto focus, though... In short I have no answer for the OP.
06-30-2014, 09:48 AM   #6
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HenrikDK, I am aware of the issue you mentioned and have taken care to rule that out as a reason for my issue.
06-30-2014, 10:34 AM   #7
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I have a similar issue with my K10. All of my AF lenses have varying AF adjustment values. My MF lenses require a -40 adjustment value for confirmation to work. I leave my K10 in debug mode to facilitate the adjustment value change when I change lenses.

The firm that converted the camera to IR manually adjusted the AF detection module.
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