Canon EOS 90D DSLR Camera with 18-135mm Lens - Manual (Page 188)

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Wireless Flash Photography Using Optical Transmission
Advanced Wireless Flash Photography
 Flash exposure compensation
Available when [Flash mode] is set to [E-TTL II] . Note that the setting items
available for fl ash exposure compensation (see below) vary depending on
[Wireless func.] and [Firing group] setting details.
Flash exposure compensation

The same amount of fl ash exposure
compensation is set for the built-in fl ash
and all external Speedlites.
2 Flash exposure compensation
 Set fl ash exposure compensation for the
sender.
1 Flash exposure compensation

The same amount of fl ash exposure
compensation is set for all receivers.
 FE lock
You can lock the fl ash exposure (FE Lock, = 167) by pressing the <
A
>
button.