Canon 40D AI Servo Mode issues

Has anyone had good success with the 40D in AI Servo mode? I find that the focus with my 40D is generally spot on for static subjects, but I rarely get crisp shots when in Servo mode. I rented a 135mm f/2 over the weekend and hoped that getting the f/2.8 middle AF sensor going would help, but found the same results as with my 70-200 f/4. In general the focus seems a little behind the subject. I tend to use the central AF point only, or the auto select (all AF sensors). This is a typical shot from a series -the focus point is in the middle of his shirt, but the sharp part of the photo is his sleeve, earand back shoe. I also shoot in the 3fps mode, rather than 5fps, thinking that this gives it more time to lock focus...


I don't see how micro AF adjustment would help since images are sharp when not moving at similar subject distances. Any suggestions or advice? Am I expecting too much from the xxD series?


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ISO 200, 1/800s, f2.2

I lived in AF Servo on my 40, works just fine. The trick is to set one focus point and not all the points.

Maybe I'm just not getting the center point where it needs to be. When I look at this shot again maybe my center point is just off the body and onto the arm. Next time I'll try an off center focusing point or keep the centre on his face. I suppose that at f/2.2 the body and face probably aren't in the same plane either - especially if I'm standing and looking down a little bit...

How often do you use AI Servo? To succesfully use AI Servo AF you need a lot of practice. The 40D's AI Servo AF has served me well in the past 2 years, I've made a lot of sharp images using just this AF mode.

If the picture above is the whole picture, I could imagine that the center point found the contrast between the arm and the background to be the best target, and focused there.


You have to let the Servo AF start working half a second or so before you take the picture, if the subject is moving. Also, don't let go of the button in between shots, even if you halt continuous shooting for a while. This keeps AF active and tracking.


Using all points in automatic mode can work well, under some circumstances. Not any distracting, high contrast targets in the background, no irrelevant items passing in the front of the subject and the subject being big enough to cover two points at the same time, then you can use all points very well. But if these conditions aren't met, it will be trickier.


There are some runners here, for example. Most of these images are taken with the 40D.

I'm not quite that successful either. I'm going to test it out some more tonight.

I'm not quite that successful either. I'm going to test it out some more tonight. I

I'm not quite that successful either. I'm going to test it out some more tonight. I test

WOW!! I don't know what happened there. Anyhow, I'm going to test it out tonight on my 70-200 2.8 IS and the 24-70 2.8

Thanks for the replies.


This is the whole picture, and I think you are right about the focus point. I chose this particular one as it is the worst, but probably had the worst point of focus. Seems like I need to really to spend some time working on tracking in AF Servo, I haven't spent a lot of time with it... I'd tried using all focus points, but you don't really know where it is picking. In a situation like this, am I better to switch to an edge AF point and track using it, or shift the center point to the face and crop later?