Canon EOS 1DS MARK II 9443A009 Instruction Manual (en)

C.Fn-03 is unused. 
Custom Function Settings
Viewfinder display during exposure
1:  Displays the exposure information and number of remaining shots 
during continuous shooting. 
Shutter release without card
1:  The shutter button will not work without a memory card in the 
camera. This prevents shooting without a memory card. 
If there is no memory card and you press the shutter button, 
Card” will blink on the top LCD panel and in the viewfinder. It 
indicates that C.Fn-02-1 is in effect. 
Shutter button/AE lock button
1:  You can focus at one location and obtain AE lock at another 
location in the scene. Press the <
> button to autofocus and 
press the shutter button halfway to attain AE lock. 
2:  In the AI Servo AF mode, you can press the <
> 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:  This is useful for subjects which keep moving and stopping 
repeatedly. In the AI Servo AF mode, you can press the <
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.153) 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