Canon EOS 6D Manual De Instrucciones página 63

A Full Auto Techniques (Scene Intelligent Auto)
Recomposing the Shot
Depending on the scene, position the subject toward the left or right to
create a balanced background and good perspective.
In the <A> mode, while you press the shutter button halfway to focus
a still subject, the focus will be locked. You can then recompose the
shot and press the shutter button completely to take the picture. This is
called "focus lock". Focus lock is also possible in other Basic Zone
modes (except <5> Sports).
Shooting a Moving Subject
In the <A> mode, if the subject moves (distance to camera changes)
while or after you focus, AI Servo AF will take effect to focus the subject
continuously. (The beeper will continue beeping softly.) As long as you
keep aiming the AF point on the subject while pressing the shutter
button halfway, the focusing will be continuous. When you want to take
the picture, press the shutter button completely.
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