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01-31-2016, 11:50 AM   #1
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Trouble with DA 60-250 Focusing Accuracy (Advice Requested)

Hey guys,

I got a new DA 60-250 in recently, and I'm trying to check and calibrate the auto-focus with the fine adjustment tool.

I followed this blog post to set up the testing: Jeffrey Friedl's Blog (I made a 0% gray version because i could focus on even the 5% gray!)

I noticed that at 60mm, the lens front-focuses, and at 200mm+ it back-focuses. In general though, it's also fairly inconsistent. Thinking it might be the camera (this was my first big AF tuning venture), I tried out my FA77 and DFA100 - both needed small adjustments, but they were both rock solid on consistency. So - it's not the camera. The only other factor that might have been affecting things was that my battery was getting quite low (red).

So my questions:

1) Is a front-focus at 60mm and back-focus at 200mm+ correctable besides at a repair shop?
2) Is SDM affected by low battery (more-so than the in-body motor used with FA77 and DFA100)?
3) Side question: When making AF fine adjustments, does the "all" offset affect lenses that have individual offsets set? E.g., if my DFA100 has "all" set to -3 and "individual" set to +2, is the camera doing -1 or +2?

Thanks guys!

01-31-2016, 12:02 PM   #2
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AF fine tune on zooms is always an issue because the different focal lengths might need different focus adjustments.
Either set it to the best focus at the focal length you use the most or find an average that works.
01-31-2016, 12:33 PM   #3
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In practice, are you getting soft images? Since the 60-250 is not that fast, minor inaccuracies might not be noticeable.
01-31-2016, 12:47 PM - 1 Like   #4
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I've grown not to trust shooting an angled target because the AF sensor area is known to be a larger circle than implied by the AF indicator in the viewfinder. This can result in the "calibrated" focus point being forward of where it should be. I instead, with camera on tripod, focus on a tree trunk or some other high contrast item that is generally parallel with the plane of the camera sensor and located a fair distance away. Then I compare PDAF (through viewfinder focus) with liveview focus, making adjustments until they perform similarly. If after you've done this, you see inconsistencies for 60mm versus 250mm, you'll need to make a judgement call whether to pick one over the other or find a "happy medium" based on your shooting needs/preferences. I would probably calibrate for the long end because the DOF is shallower there, making inaccurate focus more apparent compared to shorter focal lengths.
Daryl

01-31-2016, 02:36 PM   #5
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Thanks guys for the feedback. Sounds like the AF has to be balanced on one side or the other. My other option is to exchange it, since I just bought it from B&H.

As for the AF sensor area - I took that into account. The test sheet I'm using does not allow focus to lock on anything other than what I intend it to. This worked great on the FA77 and DFA100, so I don't think that's the problem.
01-31-2016, 04:52 PM   #6
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Exchanging it would only help if this issue was with only your copy. In my experience all zooms show this to some degree. So no guarantee a replacement would be any different.
As Adam says this is an f/4 lens, minor inaccuracies will not show.
if the adjustment is large that is different of course.
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