Canon EOS 650D Instruction Manual page 197

Cautions when [Movie servo AF] is set to [Enable]
Shooting conditions that make focusing difficult

A fast-moving subject approaching or moving away from the camera.

A subject moving at a close distance in front of the camera.

Also refer to "Shooting conditions that make focusing difficult" on page
159.
• Since using Movie Servo AF will consume battery power, the number of
possible shots and the possible movie shooting time will be reduced.
• During zooming or image magnification, Movie Servo AF operation will be
stopped momentarily.
• During movie shooting, if a subject approaches / moves away, or if During movie shooting, if a subject approaches / moves away, or if During movie shooting, if a subject approaches / moves away, or if
the camera is moved vertically or horizontally (panning) the recorded the camera is moved vertically or horizontally (panning) the recorded the camera is moved vertically or horizontally (panning) the recorded
movie image may momentarily expand or contract (change in image movie image may momentarily expand or contract (change in image movie image may momentarily expand or contract (change in image
magnification).
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