Canon 650D - Manual (Page 234)

234
When [Flash mode] is set to [E-TTL II], flash exposure compensation
can be set. The flash exposure compensation settings (see below)
which can be set will differ depending on the [Wireless func.] and
[Firing group] settings.
[Flash exp. comp.]
The flash exposure compensation is
applied to the built-in flash and all
external Speedlites.
[2 exp. comp.]
The flash exposure compensation is
applied to the built-in flash.
[1 exp. comp.]
The flash exposure compensation is
applied to all external Speedlites.
If [Flash mode] is set to [E-TTL II], you can press the <A> button to
perform FE lock.
Other Settings
Flash Exposure Compensation
FE Lock
COP
Y