Canon Speedlite 600EX-RT Mode D'emploi page 79

Wireless Multiple Flash Shooting
You can divide the slave units into two or three groups and perform
E-TTL II/E-TTL autoflash shooting while changing the flash ratio
(factor).
Autoflash Shooting with Two Slave Groups
Autoflash Shooting with Three Slave Groups
Before shooting, perform a test flash (p.16) and test shooting.
To avoid interfering with transmission, do not place any obstacles
between the master unit and slave units.
:Optical Transmission Wireless Flash Shooting
A
C
A
(p.85)
B
(p.86)
B
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