Canon EOS 70D Instruction Manual page 89

One-Shot AF for Still Subjects
AF point
Focus confirmation light
While you hold down the shutter button halfway, the focus will be
locked. You can then recompose the shot if desired.
AI Servo AF for Moving Subjects
This AF operation is suited for moving subjects when the focusing
distance keeps changing. While you hold down the shutter button
halfway, the subject will be focused continuously.
The exposure is set at the moment the picture is taken.
When the AF area selection mode is set to 19-point automatic
selection AF (p.91), the camera first uses the manually-selected AF
point to focus. During autofocusing, if the subject moves away from
the manually-selected AF point, focus tracking continues as long as
the subject is covered by the Area AF frame.
f: Selecting the AF OperationN
Suited for still subjects. When you
press the shutter button halfway, the
camera will focus only once.
When focus is achieved, the AF point
that achieved focus will be displayed,
and the focus confirmation light <o>
in the viewfinder will also light up.
With evaluative metering, the
exposure setting will be set at the
same time focus is achieved.
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