Canon EOS 80D - Manual (Page 77)

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Depending on the scene, position the subject toward the left or right to
create a balanced background and good perspective.
In the mode, pressing the shutter button halfway to focus on a
still subject will lock the focus on that subject. Recompose the shot
while keeping the shutter button pressed halfway, and then 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>
).
In the mode, if the subject moves (distance to camera changes)
during or after focusing, AI Servo AF will take effect to focus on the
subject continuously. (The beeper will continue beeping softly.) As long
as you keep the Area AF frame positioned over 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.
A
Full Auto Techniques (Scene Intelligent Auto)
Recomposing the Shot
Shooting a Moving Subject