Canon EOS 7D - Manual (Page 90)

90
f : Selecting the AF ModeN
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.
Under low-light conditions, when you press the shutter button halfway,
the built-in flash fires a brief burst of flashes. It illuminates the subject to
enable easier autofocusing.
AI Focus AF for Automatic Switching of AF Mode
AF-Assist Beam with the Built-in Flash
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
<o> in the viewfinder will not light.
The built-in flash’s AF-assist beam is effective up to about 4 meters/13.1
feet.
In the d/s/f/a/F shooting modes, press the <I> button to pop-
up the built-in flash. Then it will fire the AF-assist beam when necessary.