Canon EOS 90D DSLR Camera with 18-135mm Lens - Manual (Page 265)

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Continuous AF (Live View Shooting)
This function keeps subjects generally in focus in Live View shooting. The
camera is ready to focus immediately when you press the shutter button
halfway.
1 Select [ z : Continuous AF].
2 Select [Enable].
o
Enabling this function reduces the number of shots available, because the
lens is driven continuously and battery power is consumed.