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03-14-2012, 04:01 PM   #1
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FF and BF oddity?

Just got a K-5 and have been trying to get my AF lenses dialed in. I've noticed on my Tamron 70-200 that at say 20ft. it will FF, and at say 6ft. it will BF. So far I've only tested this at 200mm, but I don't recall anyone ever mentioning an issue like this. I've done my best to rule out it focusing on the wrong subject by making sure what I'm shooting fills the frame. Thoughts?

03-14-2012, 05:00 PM   #2
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Theoretically this is possible, and it does happen with zoom lenses, but are you 100% sure you're getting FF and the lens isn't actually simply focusing elsewhere than you had expected?

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03-14-2012, 06:09 PM   #3
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99% positive as the subject fills almost the entire frame. Still want to keep at it, but will wait for sunlight instead of trying to do it indoors under tungsten.
03-14-2012, 09:32 PM   #4
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I experienced the same issue with Fa 77 and my new K-5. After "wow" effect faded a bit, I found that it has severe backfocus with that lens. At first I tried a very contrast target - a white box with black printing on it and performed tests from 1-1.5m distance. Testing showed that even +10 is not enough I entered into debug-mode through PK_tether and dialed AF to +110. Now 1-1.5 m subject was in focus but when I tried to take pictures of some real objects I found that at 2-3m distance I got front-focus. I was pretty upset and decided to wait for good lighting conditions. Next day I was lucky with sunny morning, I first tried real-life subjects (my wife and cat ) at 2-3m distance and then re-tested on 1-1.5m distance. Now AF in debug mode was set to +70 and AF fine adjustment set to 0. Both, distant subjects and close-ups were perfectly in focus even with low ambient light conditions and tungsten lamp.


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