i'd like to know what the "AF-ON" button adds - just spent a couple hours with the manual + trial and error to get the * button to work like my 20D and 5D
Canon is moving their pro and prosumer lines closer together in handling and operation. Not sure I like it, but I'm learning.
OK, on th 40-D, the new AF-On button acts just like the * button on the 20-D, 5-D, and the 1-series cameras. You can program it the same way, to use thumb focus. In Canon's thinking, this lets you use the * button as an AE-Lock button and as a flash-spot-meter button. (But keep reading -- you can change this.)
So under C Fn IV: Operation/Others, Function #1 Shutter Button/AF-ON Button, choose #2, Metering Start/Meter+AF Start. That makes the AF-ON button operate like the * button on the other cameras, PLUS hitting the button will wake up the camera (which it doesn't do on my 20-D to my ever-loving exasperation.)
NOW, here is the important part: In that same set of custom functions, go to Function 2: AF-ON/AE Lock Button Switch, and choose "Enable." You have just swapped out the function of the * button and the AE-ON button. That means the * button is your autofocus button and the AF-ON button is your AE lock/flash meter button.
Note that swapping these buttons means you have also swapped their functions in playback mode. You may zoom in and out of an image, or choose the single/four/nine view using the +/- buttons --
but realize that the AF-ON button is now your "-" (minus) button. Hitting the * button cancels playback mode and wakes up the camera for shooting.
Are we awake yet? <g> There will be a short quiz later.
Now I am sort-of happy, since the * button works properly, but I have gotten used to the two-button operation of the 1-series cameras, allowing me to use either the full 45 points for AF or choose a selected point with the second button (now called the AF-ON button). Argh.
Anyway, the 40-D is a nice little camera, and you should be able to set it up the way you want. Good luck.
--Ken