Canon EOS REBEL T2I Instruction Manual page 7

Custom Function Settings*
0: Disable
1: Enable
Improves the highlight detail The dynamic range is expanded from the
standard 18% gray to bright highlights. The gradation between the grays
and higMighte becomes smoother.
_ With setting 1, the [Disable] settin£ automatically laKes effect for the
Auto Lighting Optimizer U:.103) and it cannot be changed.
With setting 1, noise may eecome shghtiy more pronounced tiqan usual.
With sett qg 1, the settable ISO speed range will be 200 6480.
Also. the <De-> icon wili be displayed on the LCD monitor and in the
viewfinder when highlight tone priority is enabled.
CoFn Ill: AutofocuslDrive
The AF-assist beam can be emitted by the camera's built-in flash or by an
external, EOS-dedieated Speediite.
O: EnabJe
1: Disable
The AF-assist beam is not emitted.
2: Enable external flash only
If an external, EOS-dedicated Speedlite is attached, it wil! emit the AF-
assist beam when necessary. The camera's built-in flash will not fire the
AF-assist beam.
3: IR AF assist beam only
Among EOS=dedicated Speedlites, only those which have an infrared
AF-assist beam will be able to emit the beam. This prevents any
Speedlite which uses a series of smal! flashes (like the built=in flash)
from firing the AF=assist beam=
If the externa !, EOS_dedieated speed!ite!s [AF-ass!st beam firing] Custom
Function is set to [Disabled], the Speedlite w!!l not emit the AF-ass!st bea m
even if the camerals 0.Fn-7-0t2/3 is set,
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