Canon EOS REBEL T4I Instruction Manual page 39

Other Settings
Setting the Flash Output Manually for Wireless Flash
When [Flash mode] is set to [Manual flash], flash exposure
compensation can be set. The flash output settings ([_ flash output],
[Group A output], etc.) that can be set will differ depending on the
[Wireless func.] setting (see below).
[W/ireless func. _]
_ [Firing group: %All]: The manual
flash output setting will be applied to
all the external Speedlites.
_ [Firing group: =_ (A:B)]: You can set
the flash output separately for slave
groups A and B.
[Wireless rune. _% + _,_ ]
_ [Firing group: %All and --_,]: The
flash output can be set separately for
the external Speedlite(s) and built-in
flash.
_ [Firing group: =_ (A:B)-_ ]: You can
set the flash output separately for
slave groups A and B. You can also
set the flash output for the built-in
flash.
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