dave_p wrote in post #15243070
When you say "I think I'm in a good spot now", what do you mean? How did you "work around" this issue? I'm not attempting to be confrontational...I am genuinely interested to know what you've done or how you've made peace with it on your lenses where you've noticed the issue.
I literally had to throw out otherwise good shots from a shoot I did for an agency. This was with an 85 1.8 from about 10 feet away. And, as I said, my subsequent testing showed that the keeper rate was less than 50% with the outer most middle focus point (right hand side). So from a "real world" perspective, I might as well have a 5Dc or 5D2 because I no longer feel comfortable with anything but the center point on my 5D3. Certainly not trying to say you or anyone else isn't "real world", just trying to emphasize that when I need acceptable photos for my purposes, I can't trust the outer AF points on a 5D3. Because 50% is not acceptable. Not even close.
I've not done testing at middle apertures (say, 5.6ish to 11) such that my DoF is larger. Maybe the outer points are trustable once DoF increases enough.
I had front-focusing issues. In the course of testing I concluded that the issue really only showed up to any noticeable extent with the 35L. It was ok at close distance but pretty bad at medium to long distance with the right outer points. I thought the 85L was spot on at first but the more I tested it the more I saw it not quite nail focus either using the right outer points--not nearly as badly as the 35L but it had some problems. Note that both lenses seemed ok at close distance, but at medium distances the misfocus was obvious. The 135L didn't seem to have any of those issues, which gave me hope that it wasn't a tilted AF sensor array or something awful requiring Canon service to intervene.
So I tested all my lenses and applied AFMA as needed, slowly chipping away at any softness I was seeing. I tested at close and medium distances, used the center and right center (upper center in portrait orientation) AF points. I also made a point to test in good light to avoid additional issues stemming from lack of light--my first round of tests were indoors at night which, although real world, doesn't do the camera any favors. The testing was a bit haphazard and by the seat of my pants--handheld, shooting a human target instead of a static, flat surface, etc.--but I eventually settled on +10 for the 35L and +4 for the 85L. This is what looked the best to me using the center and outer AF points.
I can't explain why I saw a discrepancy in right vs. center and left points at first but no longer do after AFMA. It still eats at me that the discrepancy has disappeared. I hate not knowing for sure what's going on and have no sensible theories to explain it. I went as far as going back to my original test setup indoors at night and still don't see the point-to-point discrepancy I saw before AFMA. Could be that my center point is now not as sharp as it was before, but it looks plenty good to me so I feel that that's not the answer.
Admittedly there were a lot of variables at play, which is why I only "think" I'm in a good spot. I'll know for sure after I've used it more particularly for jobs and have a better feel for it. Bottom line is I'm confident that I've got it calibrated to an acceptably good point but still need to work out any kinks with real shooting. I would use my 85L and 135L with total confidence even in portrait orientation using the outer cross-type AF points, but again the caveat is that I haven't really used the camera in anger. I'll be keeping a close eye on the 35L and won't use it at medium/long distance in portrait orientation with the outer AF points for critical shots until I feel more confident in it. That's the main area that still gives me pause. Otherwise I'm feeling pretty good with the understanding that I reserve the right to change my mind if results turn out poorly.
I don't know if any of that helped. I considered getting FoCal to do more scientific testing but decided not to since I was able to achieve good calibration after all. I still might though eventually, and I would recommend it as a valuable tool for anybody needing utmost AF performance and in need of a way to fully document their AF issues.
I'll say this: I have test shots with the 85L from about 10 feet away that are razor sharp at f/2 in portrait orientation, so you should be able to nail shots with the 85mm f/1.8 from that distance too. If you aren't getting the results you need with all the AFMA in the world then I'd lean toward a trip to Canon service.