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11-25-2010, 06:51 PM   #16
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QuoteOriginally posted by Kubicide Quote
Looks like there are three areas for potential focus errors:

1. Lens mount/rear optical element distance to focal plane
2. AF focus sensor distance to focal plane
3. Focus screen/sensor distance to focal plane

The AF focus adjustment in the menus will take care of #1 and #2. Shims added to the focus screen will fix #3 (so that it correctly 'shows' being in focus when the lens + sensor actually are in
focus).

On my K5 I needed the same "-3" AF fine tune offset for four primes and one zoom lens which suggests item #2 was the issue. Different numbers would suggest the lens(es) were off, and it can happen. Why do lenses have BF or FF issues? Manufacturing tolerances of camera or lens, damage, grease viscosity in moving bits, etc., anything that can cause optical elements to move affecting the focus point of the rays.
Thanks, this brought it all into focus (sorry for the pun) I can now see how it works.
Joe

11-25-2010, 09:25 PM   #17
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And I just adjusted one more new prime lens on the same K5 - this one needed "+6" and is the oddball of the bunch. But its focus is razor sharp now!
11-26-2010, 10:55 PM   #18
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QuoteOriginally posted by Kubicide Quote
Looks like there are three areas for potential focus errors:

1. Lens mount/rear optical element distance to focal plane
2. AF focus sensor distance to focal plane
3. Focus screen/sensor distance to focal plane

The AF focus adjustment in the menus will take care of #1 and #2. Shims added to the focus screen will fix #3 (so that it correctly 'shows' being in focus when the lens + sensor actually are in focus).

On my K5 I needed the same "-3" AF fine tune offset for four primes and one zoom lens which suggests item #2 was the issue. Different numbers would suggest the lens(es) were off, and it can happen. Why do lenses have BF or FF issues? Manufacturing tolerances of camera or lens, damage, grease viscosity in moving bits, etc., anything that can cause optical elements to move affecting the focus point of the rays.

You have pretty well covered things in this post.

I too had to adjust most of my lenses to +1 and 2 were -1


cheers

Neil
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