AF fine tune and focus shift for fast lenses

Started Sep 12, 2016 | Discussions thread
Ferguson
Ferguson Senior Member • Posts: 1,826
Re: Great idea

JF69 wrote:

Ferguson wrote:

I need to go back now and experiment with the 85/1.4. I used a D800 to do my initial testing, I'll give it a go with the D5.

Great idea.....please do come back with your findings.

I'm completely confused now.

It has been some time since I tested the 85 with the D800, but it had a distinct focus shift. Now I cannot see it. It has been repaired, twice, since then for other things, but among the repairs they also "adjust focus". The 85 has never been in the shop.

I tried it as (1) focusing at F1.4, then shooting successive shots at F2, F2.8 and F4 without refocus, and (2) focusing at each of those f-stops for each shot.

Interestingly, there is almost no difference that I can see between the refocus and no-refocus, certainly within the range of AF variation. This would seem to imply there is no innate correction for AF Focus shift. Though interestingly, there does not seem to be any significant shift either.

So I tried the D5 and did the same thing. And got the same results. No difference in refocus/not, and no focus shift.

The test is quite subjective, interpreting exactly where the focus area is (my green z's). I put these into two collages, one for each camera, so people can interpret themselves. The actual focus target is vertical and a bit right of the edge of each segment in the collage, the crops are on the ruler which is at a shallow angle, maybe 30 degrees from horizontal.

I KNOW the 85 didn't do this a couple years ago, as you went through F2.8 the DOF front edge would be very near the target, now it is not.

I put the F4 versions adjacent so you can see how they compare, but the full res shots are there if someone wants to re-crop to put others adjacent.

Frankly I do not know what to conclude from this. Unless it's actually focusing when I do not adjust the focus button, there is no visible indication of a correction for aperture, but then again there's no evident focus shift either. And this lens is definitely known for one.

Very confusing. Perhaps just a failed test.

By the way, I set the AF Fine Tune to zero for each -- what I was looking for was not whether it was correctly tuned but changes between aperture.

Linwood

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Sony a7R IV Sony a9 II Sony FE 24-70mm F2.8 GM Sony FE 70-200mm F2.8 GM OSS Sony FE 85mm F1.4 GM +2 more
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