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02-26-2013, 06:56 PM   #1
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Tamron lens and teleconverter MF issue

I have the Tamron 18-250 lens and the Tamron 1.4x Pz-AF MC4 teleconverter. My problem is that I am unable to use normal MF on the Tamron with the teleconverter. I say "normal MF" because I can focus manually, but there is a fair amount of resistance, like I'm actually turning the AF motor. Without the teleconverter the MF on the Tamron feels normal without resistance. I simply switch to MF on my K-5. The lens does not have a AF/MF switch. However, with the teleconverter I switch to MF on the K-5 and the focusing has quite a bit of resistance. The resistance makes me think I should not use MF under these conditions because this is not normal. I found another thread that said to push the teleconverter's lens release button down for MF under different circumstances and this does work for me too, thus removing the resistance. So it does appear that I'm turning something inside the camera without this trick. I appreciate any help on this issue.

02-26-2013, 07:05 PM   #2
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You are turning the gears in the TC. As long as the camera body is set to MF, it shouldn't be turning the gears in the body itself. Still probably should be avoided...you can put a piece of tape or something over the screw-drive bit on the TC that couples with the lens screw-drive so it doesn't engage. (And make sure camera stays on MF.)
02-26-2013, 07:38 PM   #3
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Is it different with the TC and lens when not mounted? Maybe the AF screw drive is getting caught and not releasing
02-26-2013, 07:48 PM   #4
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QuoteOriginally posted by Lowell Goudge Quote
Is it different with the TC and lens when not mounted? Maybe the AF screw drive is getting caught and not releasing
The TC has no way to disengage its own screw-drive pass-through mechanism and that is not a quick-shift lens -- if the focus ring is moving, the screw-drive is moving. So yes if you take it off the body but with TC attached to lens it should be easy to see that the screw is spinning on the TC when you turn focus ring. I've got the same lens (Pentax version) and noticed the same thing on my TC that has screw-drive pass-through...

02-26-2013, 07:50 PM   #5
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The resistance is the same when the TC is not mounted to the camera, and I've confirmed that the camera screw drive is recessed in the camera body when the camera is set to MF. So it does appear to be due to the resistance in the TC alone. Thanks for the quick help.
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