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06-13-2010, 09:36 AM   #1
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Testing a new lens: good or bad copy?

Just purchased a new lens (DA 15mm F4 Ltd) and will probably get one or two other primes/zooms fairly soon. I have read a lot about people receiving a "bad copy" of a lens and then returning it for a "good copy." How can a non-pro (like me) determine if I have a bad copy? I know how to use a focus chart to test the FF or BF of the auto focus system, but is there another test or two I should try? I am not really a pixel-peeper because I would not know what to look for. Any advice for us amateurs out here?

Thanks in advance.

06-13-2010, 10:51 AM   #2
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Well, I am not really much of an expert on this, but ... you could take sample pictures of things with lots of horizontal and vertical lines and detail (e.g. brick walls, building fronts etc) and see whether the sharpness / image attributes are symmetrical ... left vs. right, top vs. bottom, corners (may help notice any de-centering issues) ... center vs. corners ... and check this with what is typically expected / reviewed for the said lens (eg. at

Along with the (often tedious) FF/BF checks ... and the above ... you could also add physical inspection ... whether you hear any rattle sounds etc if you shake the lens a bit ... any wobble when you zoom ... whether the zoom and focus rings turn smoothly ...

I am sure you'd also get more expert advice soon

Last edited by rkt; 06-13-2010 at 10:52 AM. Reason: typo
06-13-2010, 10:17 PM   #3
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When checking for rattles, hold the aperture lever with one finger. It rattles because it is a movable piece of the lens.
06-13-2010, 10:30 PM   #4
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Well if in doubt you can post sample images here and I'm sure plenty would be glad to help you out.


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