40D -- contrasty background, not so contrasty subject. How to compensate?

Suppose you're using your 40D to track, in AI Servo, a moving subject that doesn't itself have all that much in the way of contrasty detail to lock onto (example: a martial arts instructor in the appropriate attire), while the background which is only a few feet behind him has plenty of contrasty edges to lock onto (example: a wall with printed logos and such).

Seems that even if you are tracking the subject from an area which lacks the kind of contrasty detail that the eventual background has (and thus can easily establish a relatively predictable trend), if you either use all focus points or, alternatively, manage to even temporarily move your single active autofocus off the subject and onto the background, the focus system will decide that the background looks much more interesting and will focus on it instead of your subject, even though that would imply that your subject managed to transit the distance between himself and the background in an instant.

The only technique I've come up with to reliably deal with that situation is to ask my subject to stand roughly where he will be when he gets to the point in the action that I want to capture, manually focus onto him, and wait for him to arrive in that location before actually shooting.

[I manually focused onto him because the autofocus system, even in one shot, thinks the background is much more interesting than my subject even if my single active focus point is centered on a relatively high contrast area of my subject. Sometimes the autofocus system will actually focus on my subject also, but not reliably enough for me to be able to depend on it, and the viewfinder isn't good enough to allow me to tell the difference]

Needless to say, I find that behaviour quite limiting in such situations.

Are there any techniques I can employ to reduce or eliminate this issue? Is this an issue that a 1D series camera would have, or are its autofocus points precise enough that they won't even care about the background unless they've been hovering over the background for a relatively long while?

You can do one of two things:

1) Use only the center focus spot (in AI Servo) and keep that on your subject
2) Manually "pre focus" at where your subject will be when you want to make the exposure and disable the auto focus so it doesn't grab something else in the frame.

FlyingPhotog wrote in post #5992194
You can do one of two things:

1) Use only the center focus spot (in AI Servo) and keep that on your subject

Yep. Tried that. Seems you have to keep it on the subject without fail. Guess for that it's now just a matter of practice...

Which is exactly what I ended up doing.

I was hoping there was some other magic technique that might work.

I guess the good photographers just get really good at following the subject precisely!

Of these two options, I often use the third (!):

Set the camera to foucs only when AF-ON (or *) is depressed. Set camera to Servo AF, so you can shoot regardless of whether the active point is in focus or not.
Now, when the subject is where you want to capture the action, and you have the center focus point on the subject, press AF-ON. You can keep pressed to update focus as long as movements are such that you can keep the focus point on the subject. When things start flying around, let go of the AF-ON and take your pictures. Assuming you have full time manual focus on your lens, you can now also easily update the focus manually, or just press AF-ON to update using autofocus.

This is the principle I'm using when taking photos of people running in the woods, where high-contrast branches from trees often present far more interesting targets to the AF chip than the runners themselves. From your desription, it seems your situation is equivalent, albeit very different.

apersson850 wrote in post #5992297
Of these two options, I often use the third (!):

Set the camera to foucs only when AF-ON (or *) is depressed. Set camera to Servo AF, so you can shoot regardless of whether the active point is in focus or not.
Now, when the subject is where you want to capture the action, and you have the center focus point on the subject, press AF-ON.

I might be inclined to do this, but my reaction time just isn't fast enough to allow me to do that and track the target precisely all at the same time. If I don't start tracking my subject well before I start taking shots, I won't be able to track him at all.

I do have my camera set up that way (use AF-ON for focusing and the shutter button for activating the shutter), though...

It sounds like my best bet is to get really good at keeping the sole active autofocus point on my subject.

Is the 1DmkIII (or mkII) significantly better in this regard than the 40D?