Canon EOS 90D DSLR Camera with 18-135mm Lens - Manual (Page 185)

185
Wireless Flash Photography Using Optical Transmission
Autofl ash With Multiple Receivers
Multiple receivers can be treated as a single fl ash unit or, if you prefer to
adjust the fl ash ratio, as separate groups.
Basic settings are as follows.
Set these basic settings.
Flash mode : E-TTL II
Wireless functions :
0
Channel : (same as receiver)
 [
1
All] Firing multiple receivers as a single fl ash unit
All fl ash units fi re at the same output,
and the total, combined output is
automatically controlled to provide
standard exposure.
Set [Firing group] to [ 1 All].