Canon EOS50D EOS 50D Instruction Manual - Page 178

3 Custom Function SettingsN C.Fn III: Autofocus/Drive C.Fn III -1 Lens drive when AF impossible If autofocus is executed, but focus cannot be achieved, the camera can either keep trying to focus or stop. 0: Focus search on 1: Focus search off Prevents the camera from becoming grossly out of focus as it attempts to focus again. Especially convenient with super telephoto lenses which can become extremely out of focus. C.Fn III -2 Lens AF stop button function * The AF stop button is provided only on super telephoto IS lenses. 0: AF stop 1: AF start AF operates only while the button is pressed. While the button is pressed, AF operation with the camera is disabled. 2: AE lock When the button is pressed, AE lock is applied. Convenient when you want to focus and meter at different parts of the picture. 3: AF point: M 9 Auto/Auto 9 center In the manual AF point selection mode, the button instantly switches to automatic AF point selection only while you hold it down. This is convenient in the AI Servo AF mode when you can no longer track the subject with the manually-selected AF point. In the automatic AF point selection mode, the button selects the center AF point only while you hold it down. 4: ONE SHOT z AI SERVO In the One-Shot AF mode, the camera switches to AI Servo AF mode only while you hold down the button. And in the AI Servo AF mode, the camera switches to One-Shot AF mode only while you hold down the button. Convenient when you need to keep switching between One-Shot AF and AI Servo AF for a subject which keeps moving and stopping. 5: IS start With the lens' IS switch already , the Image Stabilizer operates when you press the button. With setting 5, the Image Stabilizer will not operate when you press the shutter button halfway. 178