Sigma 18-35 dock AF adjust - Issues & resolution.

Been swapping gear around. Got a used 7D II body and some lenses including a brand new Sigma 18-35 f/1.8 with the dock. I went through the micro focus adjust dance with all the lenses saving the Sigma for last.

I dialed the Sigma in at the 3 close distances and was able to get it spot on. Very reliable, very repeatable. Beautiful. But infinity was totally terrible. The lens would grossly back focus then front focus at infinity. Totally not repeatable. I figured I'd have to exchange it for another.

Then I had an idea. What if I first adjusted the W and T micro-focus settings in the 7D II and then used the dock to fine tune it from there?

Much to my surprise, the lens was terribly inconsistent at infinity until I found the right micro-focus setting. Then it settled down and behaved like a normal lens. After getting the W and T values dialed in on the 7D II then went back to the dock.

Dock values were different this time but again, the lens was stunningly consistent and repeatable. It was pretty easy to get it all dialed in for the 3 close distances. I went outside and shot some infinity pics, making sure I had stuff in the foreground to find any front-focus. Sure enough, the lens was repeatable and front-focused at 18mm. Back to the Sigma dock and dial in some FF correction and that did the trick. Sharp images at infinity!!!

What was so shocking to me was how random AF was until I got the in-camera MFA values set. Now, mind you the lens is not 100%. I still get some infinity pics that are not in focus but the number is probably in the 10% or less category rather than the 80% to 90% that it was.

welcome to sigma!

Lucky that my copy was good out of the box without the need for dock.

I got nervous about AF accuracy for the lens so I bought a used EF-S 17-55 think I'd ship the Sigma back.

I dialed in the micro-focus on the EF-S and then did a walkabout with both lenses, shooting the same scene at the same settings to compare the lenses. After some 50 shots each, I found the AF accuracy of the Sigma at f/2.8 equaled the Canon wide open at f/2.8. They both had 20+ accurate focus events and only one miss.

At f/1.8 the in-focus rate for the Sigma was worse but it still hit focus more times than it missed. I suspect I could improve the infinity f/1.8 performace by some more attention to the MFA settings in the camera.

While the EF-S 17-55 f/2.8 IS USM is a great lens the Sigma is a more interesting lens. It can do the shallower DoF that you don't get on a crop sensor at f/1.8 and it produces crisper sunstars at f/16. At the mid aperatures, the Sigma and Canon are both sharp but the Sigma is sharper at the edges & corners, especially toward the telephoto end of their range.

So which do I keep?

Both, of course

From experience, I would not use AI servo when using the Sigma.
If accuracy is required, I would use the live view - Dual Pixel CMOS AF which the 7Dii has.

It would be better to change a new copy if your copy don't work consistently.

I've always found myself to have been extremely lucky with Sigma stuff - dozens of lenses, and probably just as many bodies (hundreds of possibilities)
ever since adjustments were available in-camera, I either didn't have to change a thing, or the changes were minimal and quick.
Then the global line came out, with the dock, and same thing... minimal if anything, and quick to do

Until I got the 1D IV..... actually, until a friend decided to mount the Sig35A to my 1D4.... in-camera would not adjust it at all - would come close, but not close enough!
I never noticed because, to me, the 35 on a crop isn't a thing I want to do all that much...
Every other Sig lenses I could throw at it is just fine.

I haven't bothered taking it through the dock to make it better - if I'm using the 35, it would be on a full frame

n1as wrote in post #18916626
Been swapping gear around. Got a used 7D II body and some lenses including a brand new Sigma 18-35 f/1.8 with the dock. I went through the micro focus adjust dance with all the lenses saving the Sigma for last.

I dialed the Sigma in at the 3 close distances and was able to get it spot on. Very reliable, very repeatable. Beautiful. But infinity was totally terrible. The lens would grossly back focus then front focus at infinity. Totally not repeatable. I figured I'd have to exchange it for another.

Then I had an idea. What if I first adjusted the W and T micro-focus settings in the 7D II and then used the dock to fine tune it from there?

Much to my surprise, the lens was terribly inconsistent at infinity until I found the right micro-focus setting. Then it settled down and behaved like a normal lens. After getting the W and T values dialed in on the 7D II then went back to the dock.

Dock values were different this time but again, the lens was stunningly consistent and repeatable. It was pretty easy to get it all dialed in for the 3 close distances. I went outside and shot some infinity pics, making sure I had stuff in the foreground to find any front-focus. Sure enough, the lens was repeatable and front-focused at 18mm. Back to the Sigma dock and dial in some FF correction and that did the trick. Sharp images at infinity!!!

What was so shocking to me was how random AF was until I got the in-camera MFA values set. Now, mind you the lens is not 100%. I still get some infinity pics that are not in focus but the number is probably in the 10% or less category rather than the 80% to 90% that it was.

That is interesting because I did something similar with my Sigma 18-35 on my 7D Mark II. I adjusted the camera's lens micro adjustment first and then fine tuned the settings using the dock.