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04-19-2010, 05:36 PM   #1
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Af adjustment

I recently purchased a Da 15mm. But i seem to have problems with IQ not being sharp or at least not in focus. I adjustment AF to +10 and seemed to have solved the issue for close focus but not necessary true for far focusing. What is the best way to test for front / back focusing. If i need to adjust +10 does that mean it's a problems with the lens. Would i still have the same issue if i sent the lens back for replacement.

04-19-2010, 06:07 PM   #2
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QuoteOriginally posted by Alex00 Quote
I recently purchased a Da 15mm. But i seem to have problems with IQ not being sharp or at least not in focus. I adjustment AF to +10 and seemed to have solved the issue for close focus but not necessary true for far focusing. What is the best way to test for front / back focusing. If i need to adjust +10 does that mean it's a problems with the lens. Would i still have the same issue if i sent the lens back for replacement.
Near and far focusing can be different on many lenses, especially macros. I would be more inclined to have the lens focus accurately at far distances and use manual focusing for up close stuff where it is easier to accurately focus manually.
04-19-2010, 06:47 PM   #3
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I'm Doing allot of testing. AF is focusing differently every time. I have the camera on a tripod focusing on a steady object. When i hit autofocus, first time it goes a bit over 3ft. If i hit AF again it changes focus to a but further from 3ft, if i hit af again sometimes it goes under 3ft. Why is this happening. It shoudl focus equally everytime since i'm not changing distance. Is it a problem with the lens.
04-19-2010, 07:10 PM   #4
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I have similar results with my DA* 50-135. Seems to search for focus if the subject is too flat. Unless it's sure of the focus will re-try each time I press the shutter. Also focus is slower and seems less accurate with AF in auto so I generally use center focus and occationally select area.

04-19-2010, 07:31 PM   #5
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Are you using a focus test chart designed specifically for the purpose? most homemade attempts fail miserably, because there is more than thing the camera could legitimately choose to focus on. That's especially the case with wide angle lenses - it's actually fairly difficult to design a test in which you have complete control over where the camera focuses.
04-19-2010, 09:07 PM   #6
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QuoteOriginally posted by Alex00 Quote
I'm Doing allot of testing. AF is focusing differently every time. I have the camera on a tripod focusing on a steady object. When i hit autofocus, first time it goes a bit over 3ft. If i hit AF again it changes focus to a but further from 3ft, if i hit af again sometimes it goes under 3ft. Why is this happening. It shoudl focus equally everytime since i'm not changing distance. Is it a problem with the lens.
When it does this, are some of the resulting images sharper than others? Or does it not make much difference in reality?

When I focus on anything with my Sigma 17-70 at 17mm, there is a wide variation in where the focusing ring actually ends up every time (at long distances the variation can be quite big), and I concluded that because the depth of field is so great at that length (still more with the DA15), any of those positions produces a result that is acceptably in focus so far the camera is concerned. I wonder if you are asking too much of the AF system. And as Marc says with a wide angle there is the additional question of what the camera actually thinks it should focus on.
04-19-2010, 09:13 PM   #7
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Yes, you need to test by focusing on edges, so the AF can get a grip. And even a difference in the ambient lighting will make a difference. Obviously a tripod setup is also a prerequisite.
04-19-2010, 09:50 PM   #8
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QuoteOriginally posted by Lance B Quote
Near and far focusing can be different on many lenses, especially macros. I would be more inclined to have the lens focus accurately at far distances and use manual focusing for up close stuff where it is easier to accurately focus manually.
Should we really worry about far distance AF adjust. According to DOF calculator, if the focus subject is at least 10ft on 15mm f4, we should get focus to infinity.

04-20-2010, 03:36 PM   #9
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QuoteOriginally posted by Alex00 Quote
Should we really worry about far distance AF adjust. According to DOF calculator, if the focus subject is at least 10ft on 15mm f4, we should get focus to infinity.
Sorry, I should have made myself a little clearer. By far distance, I should have said it is lens dependant and so for a 15mm lens, I mean distances over, say, 30feet. For a 15mm lens, by close focus distances I mean under, say, 6 feet.
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