Canon EOS REBEL T7i Instruction Manual page 121

AF Points Lighting Up in Red
By default, the AF points light up in red when focus is achieved in low-
light conditions or on a dark subject. In Creative Zone modes, you can
set whether to have the AF points light up in red when focus is achieved
(p.394).
AF-Assist Beam with the Built-in Flash
Under low-light conditions, when you press the shutter button halfway,
the built-in flash may fire a brief burst of flashes. This illuminates the
subject to help autofocusing.
AF-assist beam will not be emitted from the built-in flash in <7>, <3>,

<5>, or <8: C> modes, or when [Built-in flash firing] is set to
<b> in <A>, <C>, <2>, <4>, <8: qPF>, or <v:
GWXZHc> modes.
The AF-assist beam will not be emitted with AI Servo AF operation.

The built-in flash makes a sound when firing continuously. This is normal

and not a malfunction.
The effective range of the AF-assist beam emitted by the built-in flash is

approx. 4 meters / 13.1 feet.
In Creative Zone modes, when you raise the built-in flash with the <D>

button, the AF-assist beam will be emitted as necessary. Note that
depending on the setting for [5: AF-assist beam firing] under [54:
Custom Functions (C.Fn)], AF-assist beam will not be emitted (p.392).
f: Changing the Autofocus OperationN
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