Dreadful AI Servo from my Mark III
Updates below.
My IIn is in for repairs, so I thought this might be a good time to roll the dice and see if I could latch onto a quality Mark III body. I recently picked up a low time Mark III that had been back to Canon for all updates and was advertised as free of focus defects. After a couple of bright, sunny days playing with it at Crex Meadows in Wisconsin I've come to the conclusion that it has the worst AI Servo focusing that I've ever seen. My 5D runs rings around it. Heck, I have point and shoots that are far better. I've put a lot of miles on a Mark II and a IIn, and they are in a different league entirely. Use it in one shot mode, and it's a dream. Accurate, fast, beautiful images. But in Ai Servo . . . oh, my. It can't focus dependably on static objects. If the object is pretty close, it can sometimes get a sharp image, but that's just luck -- I can sat and watch the focus jitter back and forth to an astonishing degree. And if the target is moving, it gets worse. It can't focus on targets with busy backgrounds, can't focus on anything in the sky, can't handle even moderate back lit situations. This body makes Galbraith's bodies look like the best focusing cameras in the universe. Yesterday's low point came when it couldn't focus on a pickup truck moving slowly and laterally in front of me. 10 frames with a 500/1.4x and not one of them even close.
It's so bad that I've thought I must be doing something wrong and I've been through the set up menus more times than I can count. I've tried everything and gotten my best results with single point, no helpers, focus point priority. But when I say "best" I'm saying those settings aren't quite as awful as the other settings.
Quite frankly, I'm stunned. I heard all the horror stories and I knew I was taking a chance, but never in my wildest dreams did I expect this. I'm leaning toward keeping it, because AI Servo aside it's a wonderful piece of gear. I'll probably send it in and give Canon another shot at it. But I won't be selling my IIn anytime soon, I can tell you that.
Update: Just came in from some more testing, shooting cars coming toward me on a busy street, and the Mark III was splendid. I set the tracking sensitivity to max and enabled the center assist points. Light over my shoulder, bright sun, cars doing 30-40 mph. 90 percent keepers. Whuh?
Update, Again: Tracked some airliners coming into MPLS/St. Paul airport. Nailed them with the same setup. This was the same experiment it failed dismally at yesterday when tracking sandhill cranes and blue herons moving at similar relative speed to me (center point, only).
