Canon ST-E3-RT-V2 Manual page 17

' Wireless Flash Shooting
Wireless Multiple Flash Shooting
You can divide the receiver units into two or three groups and perform
E-TTL II/E-TTL autoflash shooting while changing the flash ratio
(factor). In addition, you can set and shoot with a different flash mode
for each firing group, for up to 5 groups.
 Autoflash Shooting with Two Receiver Groups
(p.32)
A
B
 Autoflash Shooting with Three Receiver Groups
(p.33)
C
A
B
17