AI Servo and One Shot AF definitely behave differently on the 7D, as already touched upon earlier in this thread.
If you try to do a test where you aim at one subject and then at a second subject that has a drab flat lighting indoors and only moderate contrast the AI Servo will pretty much refuse to ever switch focus to the second object even if you hold it over it for like 4 seconds, sometimes after lot of coaxing it will it will eventually grab it.
In one shot mode it grabs it though (although occasionally it might still pause for a second).
20D,40D,50D,5D2 don\'t act like that at all and lock onto the second subject in AI Servo no matter what (unless it is impossible to AF on of course).
Doing a test like that, going back and forth between the two objects in AI Servo, it took the 5D2/50D about 20 seconds and the 20D about 30 seconds to do it a given number of times and the 7D about infinity haha.
In many real world scenarios this might be good since the 7D will really avoid anything it maybe thinks is washed out drab background but maybe it explains those having trouble tracking brown deer against brown woods under drab lighting? Maybe it is awesome for sports, on average, but occasionally terrible for birds/nature while other times being great for that? I tried all sensitivities and custom functions and it didn\'t seem to ever make it grab focus on the second target.
Switching to a second subject with a bit sharper contrast and using a 135L to flip focus back and forth between each in AI servo as fast as possible (7D tracking to fast mode) with subjects only about 3\' apart the 7D and 5D2 seemed to do it in pretty much the same amount of time, actually the 5D2 a tiny bit faster perhaps. So the \'slow\' 5D2 didn\'t seem any slower than the 50D or 7D in this sort of test. However, part of it may be the 7D has much stronger logic trying to remain on target. OTOH at the ballpark i thought the 5D2 might\'ve been a little slower to get first grab on a player than the 7D.
Anyway, this test wasn\'t really setup like most action photography,
but I think it definitely shows that there is some very different AI Servo logic between the two cameras and the 7D seem to try to avoid stuff it thinks is junk is think or shouldn\'t appear next in a sequence of tracking. It doesn\'t like jumping to targets at different distances with one outside the DOF of the first if the second one is kinda low contrast compared to the other even when sensitivity is set to high. This might be better in real world usage, although I\'m sure there will be the rare time where it causes a real mess.
I am quite curious to see how it would do on the football or soccer field. I wonder if it will really lock onto a target and really nail the tracking with frame after crisp frame and still allow quick jumping, when needed, in realistic scenarios.
I predict that it will either do much worse, much better or about the same or somewhere in between those choices.
(side note: I did some AI servo on a leaf on a branch that was blowing up and down about 4\' and the 5D2 tracked right on the leaf, at f/2 and 135mm pretty well)
Oct 07, 2009 at 10:33 PM
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