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D800 and 85/1.4G with Focal testing


Cape Coral, US
5701 posts

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Ferguson Silver Member Fellow Ribbon awarded for the generous sharing of his high level expertise in the spirit of Nikonians Nikonian since 19th Aug 2004
Sat 28-Jul-12 07:09 PM | edited Sat 28-Jul-12 07:10 PM by Ferguson

This is a continuation of a specific aspect of a now locked thread.

It is specifically about entry #203 and testing an 85/1.4G at different distances.


My thanks to Peter Beckett for doing that. I had mentioned a struggle with my 85 on the D800 and getting consistently good focus.

This image (rather large but I think more efficient than a pile of little ones) shows a series of tests run at different distances (top to bottom) and for one distance left and right focus points.

I am frankly not sure what to conclude, but here are some.

First, my camera definitely has a left focus problem, and I had not thought it so. Look at the dramatic shift in AF needed for the left focus point, in fact it is clear -20 is not even enough to achieve best focus. Not sure if it is bad enough to fix, but it is very clear (I want to try a few other lenses in this way).

Secondly, my combination of lens and D800 at the center point show more variation than Peter's. His was +/- 1, mine varies from +5 to -3 and not very predictably. The variation in shots at a given adjustment is also fairly significant (dot separation vertically). But the real quality difference over that whole range is not that great in terms of viewed image differences or quantitatively (example, at 4.6m with a -3 best, +5 at the other extreme is still about 90% as good by QOF score). But as I go even more distant it changes a lot more.

As I go to 30m, with a best of -1, the +5 point now has 65% as good by QOF.

If I used this only a portrait distances, it is pretty easy to pick some average (even zero) and get good results with the center focus point, but then at the left focus point I'm way off.

I tried to do an eyeball estimate of the best compromise of all this, and came up with -10. That's not a good blend at some distances, but does tend to average things out a bit even over the leftmost focus point. I've shown the -10 image at each scenario as well to see how they differ.

Do I understand why I had such bad luck in the real world? Not really. I'm right handed shooting without a grip, so when I use and off-center focus point for portraits, it is usually the rightmost not leftmost. Last session I had the AF set to -10, and tried -5 for a while. From all these plots it should have been pretty close.

Am wondering now if my failures were more technique. But also sadly now wonder if I need to get the left AF adjusted.

Comments welcomed on pictures: Http://captivephotons.com

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