Canon EOS 20D - Manual (Page 142)

3 Custom Function SettingsN
142
C.Fn-04 Shutter button/AE lock button
0: AF/AE lock
1: AE lock/AF
Convenient when you want to focus and meter separately. Press the <
A>
button to autofocus and press the shutter button halfway to attain AE lock.
2: AF/AF lock, no AE lock
In the AI Servo AF mode, you can press the <
A> button to stop
the AF operation momentarily. This prevents the AF from being
thrown off by any obstacle passing between the camera and
subject. The exposure is set at the moment the picture is taken.
3: AE/AF, no AE lock
This is useful for subjects which keep moving and stopping
repeatedly. In the AI Servo AF mode, you can press the <
A> button
to start or stop the AI Servo AF operation. The exposure is set at the
moment the picture is taken. Thus, the focusing and exposure will
always be at the optimum point as you wait for the decisive moment.
C.Fn-05 AF-assist beam
You can set the AF-assist beam to be emitted from the camera or EOS-dedicated Speedlite.
0: Emits
1: Does not emit
AF-assist beam not emitted.
2: Only ext. flash emits
When an EOS-dedicated Speedlite is used, the AF-assist beam is emitted only
when necessary. When the built-in flash is used, the AF-assist beam is not emitted.
C.Fn-06 Exposure level increments
0: 1/3-stop
1: 1/2-stop
Sets 1/2-stop increments for the shutter speed, aperture, exposure
compensation, AEB, etc.
C.Fn-04 and C.Fn-17-0, 1, 2 (p.146) both have AF start/stop and AE lock
functions. If you have set both these Custom Functions and you execute
both Custom Function operations, the latter operation will not work. The only
exception will be when AF stop is executed after AF start.