Canon EOS Rebel SL2 EOS 200D Instruction Manual page 115

One-Shot AF for Still Subjects
AF point
Focus indicator
While you keep holding 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.121) 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.
When a lens equipped with an electronic manual focusing function is
used, see page 118.
f: Changing the Autofocus OperationN
Suited for still subjects. When you
press the shutter button halfway, the
camera will focus only once.
The dot inside the AF point achieving
focus lights up briefly in red, 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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