Focus question about 40D

Okay, I just got my 40D and took it out today and noticed something that I don't know how to correct. You know how you push the shutter button halfway to lock focus and exposure, then recompose and push it the rest of the way to take the picture?
Well, it doesn't seem to be locking when I push it halfway down. When I recompose, it focuses on the new spot. I've read the manual, but I am unsure if there is a Custom Function that needs to be reset or what?
Anyone have any suggestions?

Do you have focus mode set to AI Servo?

I've tried it in AI Servo, AI Focus and One Shot, as well as trying on the Full Auto modes.

You must be in *one shot*, you can not do it in servo.

Well, it won't do it in one shot either.

Anyone?

Needs to be one-shot AF, and not one of the funky basic modes like green box or sports.
Maybe you're not holding the button down completely?

It could be a faulty camera, but operator error is more likely. My guess is you'll figure it out if you keep trying.

try changing focus to custom function 4, perhaps that will help?

See custom functions.. maybe?

Got there before me!

Okay, playing with it some more I realized that the focus is indeed locking but the exposure is not. It will keep the focus where I put it when I pushed the button halfway down, but unless it's on M, the exposure changes. Am I just an idiot? I can't figure this out.

Ship the camera to me, with the 300L-2.8 and I will set it up.

If you recompose your picture, your exposure might changed if you bring more white or dark toned pixel in the image. You can change that setting in the MENU. AF/AE lock.

sebmour wrote in post #3840433
If you recompose your picture, your exposure might changed if you bring more white or dark toned pixel in the image. You can change that setting in the MENU. AF/AE lock.

Okay...is this different from the 30D and the Rebel XT? Because with those, the exposure locks when I push the shutter button halfway down.
Also, where in the Menu would this be?

Let me be clear here: I know I can push the * button and lock auto-exposure. But I also know that on other cameras I have been able to set it so that when I spot-meter and lock focus on a subject, I can then recompose without shifting exposure and without having to push the * button, but I can't figure out how to do that on this camera and I can't find it in the manual.