Canon EOS Rebel T1i EOS REBEL T1i/EOS 500D Instruction Manual - Page 65

E: Changing the AF ModeN If focus cannot be achieved, the focus confirmation light in the viewfinder will blink. If this occurs, a picture cannot be taken even if the shutter button is pressed completely. Recompose the picture and try to focus again. Or see "When Autofocus Fails" (p.192). If the [1 Beep] menu is set to [Off], the beeper will not sound when focus is achieved. AI Servo AF for Moving Subjects This AF mode is for moving subjects when the focusing distance keeps changing. While you hold down the shutter button halfway, the subject will be focused continuously. The exposure is set at the moment the picture is taken. When the AF point selection (p.66) is automatic, the camera first uses the center AF point to focus. During autofocusing, if the subject moves away from the center AF point, focus tracking continues as long as the subject is covered by another AF point. With AI Servo AF, the beeper will not sound even when focus is achieved. Also, the focus confirmation light in the viewfinder will not light. AI Focus AF for Automatic Switching of AF Mode AI Focus AF switches the AF mode from One-Shot AF to AI Servo AF automatically if the still subject starts moving. After the subject is focused in the One-Shot AF mode, if the subject starts moving, the camera will detect the movement and change the AF mode automatically to AI Servo AF. When focus is achieved in the AI Focus AF mode with the Servo mode active, the beeper will sound softly. However, the focus confirmation light in the viewfinder will not light. 65