Canon EOS-5D Instruction Manual page 152

3 Custom Function SettingsN
C.Fn-04
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-04 and C.Fn-19-0, 1, 2 (p.157) 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.
C.Fn-05
Enables or disables the EOS-dedicated Speedlite's AF-assist beam.
0: Emits
The AF-assist beam is emitted when necessary.
1: Does not emit
C.Fn-06
0: 1/3-stop
1: 1/2-stop
Sets 1/2-stop increments for the shutter speed, aperture, exposure compensation, AEB, etc.
The exposure level will be displayed in the viewfinder and on the LCD panel as shown below.
152
Shutter/AE lock button
AF-assist beam
Exposure level increments