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06-25-2012, 05:23 AM   #1
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PK-Tether mcro focus adjustment issue

Hi,
after I bought a Tamron 17-50, which was front focusing more than I could compensate with the -10 setting in my k5, I decided to go with pk-tether debug mode and, considering that most of my lenses tend to front focus, I set the compensation to -90, and then recalibrated all my lenses.
All good, in the sense that now I genereally get perfect focus with all my FA limited primes and various zooms, at regular distances (everything but infinite), The issue is that, ad infinite, the autofocus simply doesn't lock, the lens focus get set to infinite but the green light keeps blinking, and I need to switch to manual focus, set to infinite and take the picture.
Has this ever been experienced by anybody?
My understanding of how the global adjustment would work is simply a value that is added (or removed) by the autofocus algorithm in order to decide how much the screw drive has to run to adjust the focus, so changing it should not affect the ability to focus per se, but maybe now it thinks it should still be able to keep going a little bit after infinite?
This happens regularly with the FA 77, the FA 43 and even with some zooms.
I can adjust the lens more to the positive side (for instance, with a +5 fine adjustment), but then it becomes front focused with close subjects (and yes, I know all about the size of the sensor, and I am testing that on reasonable subjects).

Thoughts?

Thanks
Alessandro


Last edited by AlessandroB; 06-28-2012 at 06:13 AM. Reason: double signature
07-02-2012, 08:29 AM   #2
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Bump. Would like to hear some other experiences with this before I adjust mine.

thanks,
Steve.
07-02-2012, 10:53 AM   #3
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IIRC, the PK-tether microfocus adjustment just re-defines the zero point for adjustment. For example, if the factory setting was zero for the
+-0 setting, then after using the debug facility and adjusting to taste, the zero point may have moved to what would have been +10 on the stock scale, whereas it will show up as 0 on the adjusted scale. A good idea to write down the vector of the adjustment you made in debug so you don't lose track of how you moved the zero point around.

Jack
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