Canon EOS REBEL T6i Instruction Manual page 101

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.110) and try to focus again.
If [z1: 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
convenient when you want to focus on a peripheral subject not covered
by the Area AF frame.
When a lens equipped with electronic manual focusing function is used,

after achieving focus, you can focus manually by turning the lens
focusing ring while pressing the shutter button halfway.
f: Changing the Autofocus OperationK
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 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.
101