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04-19-2010, 07:48 PM   #1
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How does AF adjustment work?

Just curious what it does.

Does it change some parameters for the AF algorithm?
Does it physically move the AF sensor?
Does it physically move the sensor?
Or ....

04-20-2010, 03:18 AM   #2
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I think all it does is simply add a modifier value to the af calculations. Something like: when you've reached focus, move the lens another + or - value.
04-20-2010, 08:33 PM   #3
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I have no idea how it works, but IMO, AF adjustment may be the single most valuable feature on my new K-7. I did not realize how sharp my lenses could be until I calibrated them properly with the Lens Align system. I am certain that they were all backfocusing slightly on my K10D. I wonder how many tests of cameras and lenses that are published in print or on the web have been done without proper AF adjustment.

Rob
04-21-2010, 01:33 AM   #4
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QuoteOriginally posted by robgo2 Quote
I have no idea how it works, but IMO, AF adjustment may be the single most valuable feature on my new K-7. I did not realize how sharp my lenses could be until I calibrated them properly with the Lens Align system. I am certain that they were all backfocusing slightly on my K10D. I wonder how many tests of cameras and lenses that are published in print or on the web have been done without proper AF adjustment.

Rob
Rob, why not calibrate your K10D as well?
Have a look at: Welcome to Pentax Hack
It will help to enter the K10D's debug mode and do the same as with your K-7.
I often use my K10D next to my K-7 (one wide and tele), it will give you the best with both camera's.

- Bert

04-21-2010, 01:38 AM   #5
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It simply adds this value into focus plane shift calculations.
Phase detection AF system always knows where focus plane should be and what difference is between it and current focus position. So this value just corrects equation.

PS: There are also other parameters in this equation. They are setuped during AF calibration process. (It is seen in service manuals as selecting peaks of three diagrams in service software)
04-21-2010, 04:51 AM   #6
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Original Poster
Thanks for the replies. i know that the second option taht I gave was not a very likely one but did not want to exclude it.

So it's a plain software (algorithm/parameter) thing.
04-21-2010, 12:20 PM   #7
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QuoteOriginally posted by bymy141 Quote
Rob, why not calibrate your K10D as well?
Have a look at: Welcome to Pentax Hack
It will help to enter the K10D's debug mode and do the same as with your K-7.
I often use my K10D next to my K-7 (one wide and tele), it will give you the best with both camera's.

- Bert
I was too chicken to try anything like that. Besides, the K-7 is a much better camera in many ways. I have already sold my K10D. It did give me some great images, I must say. In its day, it was a fine camera.

Rob
05-08-2010, 01:29 AM   #8
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QuoteOriginally posted by VF-19 Quote
Something like: when you've reached focus, move the lens another + or - value.
Although I don't know for sure, I believe that's not the way it is implemented.

AF phase detection works very similar to the traditional split image focusing aid. I presume that an AF adjustment value is used as a phase shift. In other words, the AF system doesn't adjust focus until the two images are aligned but until they shifted against each other by the adjustment value.

One way to support the above hypothesis is to check whether the AF adjustment also affects the focus confirmation in MF mode. One forum member confirmed that this happens, but I haven't tried it myself.

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