I finally decided which UWA lens to get for my 5DM3 and took delivery yesterday of the Tokina 16-28. I made that decision based on the large number of positive reviews I'd read. I especially wanted it for its sharpness edge to edge, as I'm not getting that with my current widest lens, the 24-105 kit lens. The Tokina is a nice solid, heavy lens that appears to be well made. I took it out to my normal lens testing spot this morning, on a tripod, cable release, etc running a large number of shots at multiple apertures, focal lengths etc.
My problem is two-fold, which are probably related. In Live-View mode the lens just won't ever come to a focus - occasionally it appears to lock-on, but I can tell looking at the screen that it didn't lock on in-focus. It was a bright sunny day, so it isn't a lack of light issue. I don't use Live-View focusing that often, but wanted to compare the focus with the standard viewfinder focus, to see if any AFMA was going to be necessary. Since I couldn't get Live-View focus to work, I did the next best thing, which was to use the Live-View mode, go to 10X magnification and manually focus. The Tokina has a unique method of switching the lens from AF to MF - you slide a ring on the lens. What I found has me stumped. I was focusing on a rock outcrop probably 50 or more yards away in the center of the shot. Both the manual and autofocus were in pretty good agreement in the center of the image, although the widest-aperture shots, 2.8 and 4.0, were better in manual focus, suggesting some minor AFMA is going necessary. The problem is with the sides of the image. Regardless of focal length, or aperture, the left side of the image would be blurry using manual focus, and the right side would be sharp, the AF images were just reversed, ie the left would be sharp and the right would be blurry. It isn't a depth of field issue (at 16mm most everything at f8.0 should be in focus), and the out of focus sides are both near and far objects in both cases. I had my old trusty t2i along with me so did the same set of tests with it. Same problem in that it would never focus itself using Live-View. Again comparing Live View zoomed manual focus vs viewfinder focus, one side is sharp and one fuzzy, with the sides flip-flopping depending on focus method. It's almost as if there is a out of alignment element that gets moved out of alignment the opposite direction when shifting from MF to AF.
Has anyone who owns this lens seen this sort of problem? I'm pretty sure I'm going to send this back and see if I just got a bad copy, unless someone here has a suggestion in the next day or two.