Canon EOS REBEL T6i Instruction Manual page 374

Troubleshooting Guide
Even though I set a decreased exposure compensation,
the image comes out bright.
Set [z2: Auto Lighting Optimizer] to [Disable]. When [Low],

[Standard], or [High] is set, even if you set a decreased exposure
compensation or flash exposure compensation, the image may come
out bright (p.136).
When I use the <f> mode with flash, the shutter speed
becomes slow.
If you shoot at night when the background is dark, the shutter speed
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automatically becomes slow (slow-sync shooting) so that both the
subject and background are properly exposed. To prevent a slow
shutter speed, under [z1: Flash control], set [Flash sync. speed in
Av mode] to [1/200-1/60sec. auto] or [1/200 sec. (fixed)] (p.174).
The built-in flash rises by itself.
In shooting modes (<A> <C> <2> <4> <C> <6>) whose

default setting is <a> (Auto flash), the built-in flash will be raised
automatically when necessary.
In the <x> and <G> modes, when you press the shutter button

halfway under low-light conditions, the built-in flash may be raised
automatically and emit the AF-assist beam.
The built-in flash does not fire.
If you use the built-in flash too often in too short a period of time, the

flash may stop firing for a while to protect the light-emitting unit.
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