Canon EOS 90D DSLR Camera with 18-135mm Lens - Manual (Page 126)

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Selecting the AF Operation
AI Focus AF (Viewfi nder Shooting) for Automatic Switching
of AF Operation
AI Focus AF switches the AF operation from One-Shot AF to AI Servo AF
automatically if a still subject starts moving.

After the camera uses One-Shot AF to focus on a subject, if it detects
subject movement, a change in distance, or similar changes, it switches
to AI Servo AF and continues to track the moving subject.
o The camera continues beeping quietly when subjects are in focus using the
servo.
o The focus indicator <
o
> in the viewfi nder does not light up when subjects are
in focus using the servo.
o Shooting with the focus locked is not possible when the servo is used.
o In <
A
> mode in Live View shooting, AI Focus AF is used to focus. Note that
Servo AF is used to focus on moving subjects. When focus is achieved, the
AF point will turn blue. Note that the camera will not switch to Servo AF if the
subject moves during continuous shooting.
AF-Assist Beam

In viewfi nder shooting, the built-in fl ash can emit an AF-assist beam to
make autofocusing easier under low light or in other conditions where
autofocusing is diffi cult. The AF-assist beam will be emitted as needed
after you press the <
I
> button to raise the fl ash and press the shutter
button halfway.

The AF-assist beam is not emitted in Live View shooting, even if the built-
in fl ash is raised.
o The fl ash does not emit an AF-assist beam when AF operation is set to
[AI Focus AF] or [AI Servo AF] .
o To disable AF-assist beam fi ring, set [ z : AF-assist beam fi ring] to [Disable] .