Canon EOS REBEL T7i Instruction Manual page 119

One-Shot AF for Still Subjects
AF point
Focus indicator
While you hold down the shutter button halfway, the focus will be

locked. You can then recompose the shot if desired.
If focus cannot be achieved, the focus indicator <o> in the viewfinder

will blink. If this occurs, the picture cannot be taken even if the shutter
button is pressed completely. Recompose the shot or see "Subjects
Difficult to Focus on" (p.139) and try to focus again.
If [53: Beep] is set to [Disable], the beeper will not sound when focus is

achieved.
After achieving focus with One-Shot AF, you can lock the focus on a

subject and recompose the shot. This is called "focus lock". This is useful
when you want to focus on a peripheral subject not covered by the Area
AF frame.
When a lens equipped with an electronic manual focusing function is

used, see page 122.
f: Changing the Autofocus OperationN
Suited for still subjects. When you
press the shutter button halfway, the
camera will focus only once.
The AF point that achieves focus is

displayed, and the focus indicator
<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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