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08-20-2010, 01:04 AM   #1
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Tamron 17-50mm f/2.8 focusing problem

Hi, I just got a brand new Tamron 17-50mm f/2.8 XR DI-II LD for my K-x, (got it from TheCameraBox), was very excited until ran a series of improvized tests against my 18-55 Pentax kit lens. At first, I thought smth is wrong with my tests, as the kit lens was consistently sharper on some of the shots. I made tests more and more controlled, until I pinpointed the problem.

For some reason, in 100% of trials, my k-x + tammy lens auto-focuses slightly ahead of the subject starting exactly at 5.6. So, 5.0 focal point is dead on target, 5.6 is ~2% ahead, which obviously makes it blurred. I see the effect at all focal lengths, but its most destructive at longer end, obviously.

Any ideas? Would this be a lens' fault, or is it the k-x/firmware?

Thanks,
Greg

08-20-2010, 03:03 AM   #2
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You might be interested in checking out these threads: https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/44118-tamron-1...-focusing.html
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/44702-tamron-1...-part-2-a.html

Sounds like the lens itself might be at fault.

Adam
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08-20-2010, 03:36 AM   #3
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I think I have noticed similar issues with slight FF with my Tamron 28-75. Pentax lenses seem to be more accurate on my K-x. Perhaps this is something hard to avoid with 3rd party lenses
08-20-2010, 04:01 AM   #4
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had a problem with this tamron, took it back to the store for focus calibration, works perfectly after that.

good luck, janko

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