PK-Tether mcro focus adjustment issue

AlessandroB · 06-25-2012, 05:23 AM

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

lightsleuth · 07-02-2012, 08:29 AM

Bump. Would like to hear some other experiences with this before I adjust mine.

thanks,
Steve.

**jbinpg** · 07-02-2012, 10:53 AM

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

06-25-2012, 05:23 AM	#1
AlessandroB New Member Join Date: Dec 2011 Location: New York, NY Photos: Gallery Posts: 11	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

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07-02-2012, 08:29 AM	#2
lightsleuth Junior Member Join Date: Jul 2010 Location: Winnipeg Posts: 33	Bump. Would like to hear some other experiences with this before I adjust mine. thanks, Steve.

07-02-2012, 10:53 AM	#3
jbinpg Site Supporter Join Date: Mar 2008 Location: Prince George, BC Photos: Gallery \| Albums Posts: 3,546	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