K-7: DA* 16-50 & DA* 50-135 Focus Tests - Comments/Advice?

Started Feb 6, 2010 | Discussions thread
Rhombuss
New MemberPosts: 12
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Focus Test with 16-50 - Seems like a back-focus problem?
In reply to Rhombuss, Feb 7, 2010

Okay, did a focus chart test with the 16-50 first. Shots taken on tripod with 2-second shutter timer.

With default AF adjustment correction, this is the result at 16mm focal length.

Seems quite back-focused, so I changed the AF adjustment to -10 and this is the result...

Looks a lot better, not sure about the overall "sharpness" of the lens, but at least it seems that the back-focus problem has been corrected.

Just as a check, I took another sample shot at the telephoto end (50mm) with the same -10 AF adjustment. Here's the sample:

Overall it looks okay, albeit with some minor front-focus. Perhaps the -10 is an overcompensation in the AF correction. Is it possible that the lens changes from inherent back-focus at the wide end to slightly more front-focus at th telephoto end? To me, the -10 adjustment looks bang-on at the wide end, but slightly front-focused at the telephoto end, so I'm not sure how to reconcile this variation.

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