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03-29-2013, 11:21 AM   #1
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How can I check if my Tamron 17-50 is front-focussing/back-focussing and needs repair

My Tamron 17-50 does not seem to get subjects in sharp focus at F2.8.

I found out however that if I focused a little bit (about 1ft) in front of the subject standing 10 ft away from me, the subject turned out sharper in the picture than if I focussed on the subject. I don't have any samples, but would like to confirm if there is a scientific test to determine issues.

03-29-2013, 11:28 AM - 1 Like   #2
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This article explains how to test your lens:
Fixing Front and Back Focus - Introduction - PentaxForums.com

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03-29-2013, 12:55 PM   #3
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There is supposed to be a cheaper way to do this. See thread below. I have not used it myself. I am planning to try it sometime:

https://www.pentaxforums.com/forums/photographic-technique/216496-anybody-tri...inetuning.html
03-30-2013, 06:57 PM   #4
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focus issue

If your lens is still under warranty send it back to Tamron. Just got my 70-200 f2.8 back from service . Lens was brand new and I was going crazy to get focus right but something was not right . 2.8 was unuseable and live view would not focus correctly. Tamron adjusted and it seems fine now . Actually got a call from service and talked to a real person ! Give them a call they were very helpful.

03-30-2013, 07:23 PM   #5
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QuoteOriginally posted by jeffw Quote
If your lens is still under warranty send it back to Tamron. Just got my 70-200 f2.8 back from service . Lens was brand new and I was going crazy to get focus right but something was not right . 2.8 was unuseable and live view would not focus correctly.
That sounds bad, since with my 17-50/2.8 on a K-x.
live view has always been a reliable standby for critical focusing.
It's not fast, but it's accurate.
03-30-2013, 07:51 PM   #6
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QuoteOriginally posted by StDevious Quote
I don't have any samples, but would like to confirm if there is a scientific test to determine issues.
For my Sigma 30, I shot a cement walkway wide open at an angle, focusing on a crack with some short grass. Made it easy to see where it was focusing, and after a couple shots, dialed it in at +5.
03-31-2013, 03:58 PM   #7
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I recently purchased this lens, and haven't been able to detect any consistent focus issues with either of my bodies. Occasionally it focus does seem to miss, and of course the lens has the notorious field curvature at the wider focal lengths. However I think the biggest problem with bf/ff is that it can be different at each focal length and distance setting. So can many lens defects - centering, for example. So it might be that the best solution is to try the lens as best you can in the manner you'd most likely use it, and examine the results. In my case I was able to compare it to the results from the 16-45DA, so at least I know it's better than my available alternative.

Paul
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