D300 lens AF fine tuning is FANTASTIC!!!!!

Started Nov 27, 2007 | Discussions thread
Peter Davis Senior Member • Posts: 1,171
Re: Why I think infinity isn't a problem....

dylanear wrote:

I think that the adjustment is a certain distance, a small distance,
like 6 inches at most. So subtract that from infinity and your still
pretty much OK.

Infinity minus 6 inches is still infinity, but that's unfortunately not how lenses work. The adjustment is not a percentage either, but more likely a factor in an equation modeling the nonlinear physical optics.

Maybe we can think of it as turning the focus ring a little bit left or right of where it would normally be. It's easy to see that focused close up, turning 5 ticks to the right has a much smaller effect, distance-wise, than it does at infinity.

I'd guess that what it really affects is the desired offset between the two images projected by the split prism in the focusing sensor itself. Normally if the lens is focused, the split images align perfectly, but if it is front or back focusing, then for perfect focus, you actually need imperfect alignment one way or the other.

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