Canon EOS 20D EOS 20D Instruction Manual - Page 142

3 Custom Function SettingsN 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 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 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 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-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. 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. 142