Confusion between AF and Exposure

It could possibly lock both, depending on some factors.

If you have AF set to One Shot or potentially AI Focus, it will lock the focus when you press the shutter halfway dwn, but if it is set to AI Servo or possbily AI Focus, then it will take the focus once you open the shutter.

On a 300D here's the Short Version (I'm sure other Canons are about the same):
Pressing the shutter halfway down locks the focus. It also takes an exposure reading at the same time. Recomposing will keep the same focus if you hold the shutter down, but the exposure reading will change as you recompose.

Pressing the AE Lock button when you press the shutter down locks the exposure. Now you can keep the same original focus and exposure during recomposing OR you hold the AE lock button down and take a series of pictures. The original exposure is kept as long as you hold that button down but you can change the focus point between shots.

Goofup - excellent explanation, I had the jist of it, but this totally clears things up with me. Thanks so much!

Thanks Goofup, I think that covers it.

Canon: = Enjoy! Digital SLR camera =
http://www.canon.co.jp​/Imaging/enjoydslr/ind​ex.html

As with all things, what the cam thinks is the "correct" exposure isn't (usually) the right exposure? Too many factors come into it to let some programming geek at Canon try to figure it out for me. So I usually shoot on "M" & make my own MiSTeaKs?

Gray card: Why your meter may be lying to you!
I found something that I didn't expect!

Gray Card…White Paper. What’s best?
What’s best for exposure, Gray cards, white paper, expensive attachments for the lens?

Need an exposure crutch?
Don’t have a gray or white card, or hand held meter with you? “Film tricks” can help you out.

RE: "MiSTeaKs" When I screw up...
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