Canon EOS 90D DSLR Camera with 18-135mm Lens - Manual (Page 317)

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Movie Servo AF
With this function enabled, the camera focuses on the subject continuously
during movie recording.
1 Select [ z : Movie Servo AF].
2 Select [Enable].
 When [Enable] is set:

The camera focuses on the subject continuously even when you are
not pressing the shutter button halfway.

To keep the focus at a specifi c position, or if you prefer not to record
mechanical sounds from the lens, you can temporarily stop Movie
Servo AF by touching [
Z
] in the lower left of the screen.

When Movie Servo AF is paused, if you return to movie recording after
operations such as pressing the <
M
> or <
x
> button or changing
the AF method, Movie Servo AF will resume.
 When [Disable] is set:

Press the shutter button halfway or press the <
p
> button to
focus.