AF system speed, says Canon, is similar to the 50D, but changes have been made to the 7D's AF algorithms to allow the camera to better track irregular movement, plus the camera will more intelligently cope with a bad AF system reading in the middle of a sequence.
During light-duty shooting over a couple of days with a beta 7D, mostly of static subjects and a good portion of it in foggy outdoor conditions, we noticed the following:
* Static autofocus was excellent, using Spot AF, various AF points, AI Servo (we almost never use One Shot) and a small batch of different lenses. With the EF 16-35mm f/2.8L II, EF-S 15-85mm f/3.5-5.6 IS (also introduced today), EF 70-200mm f/4L IS, EF 200mm f/2L IS and EF 800mm f/5.6L IS, photos were simply in focus. We also used the EF 85mm f/1.2L II, and focus was all over the place. The same lens exhibited the same unstable AF on an EOS 5D Mark II, suggesting the problem was more a function of the lens than the camera.
* Continuous focus using Spot AF, centre AF point, AI Servo and the EF 200mm f/2L IS, tracking a soccer player for a few minutes in fading light, the results showed promise but were ultimately inconclusive: through about 200 frames, the camera was able to hang onto focus properly for portions of several sequences, better than we've ever seen from the 50D, as well as deal with the AF point moving off the subject briefly. But it would also lose focus for several frames for no apparent reason, even when the AF point was right on the mark and the subject was moving at an easy pace.
* Continuous focus using Zone AF, nine points in the centre, AI Servo and the EF 800mm f/5.6L IS, tracking distant seagulls in semi-overcast light, the results were pretty good. The camera-to-subject distance wasn't changing too rapidly, but the position of the bird within the AF point group was changing constantly, and the camera handled this just fine.
* Continuous focus using Zone AF, nine points in the centre, AI Servo and the EF 200mm f/2L IS, tracking a running dog in fading light, the results were terrible. Over about 80 frames the camera got almost nothing usably in focus. If this result is representative of Zone AF, then Zone AF will be the way wrong choice for fast-moving subjects. We had better luck tracking the same dog with Spot AF.
Based on our experience with the new camera's AF system so far, it's likely that focus on static subjects is going to be solid. We'll need to give the camera more of a continuous focus workout than this, however, to see if it will be right for peak action sports.
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