Canon Speedlite 600EX II-RT Manual (en)

This section describes the basic fully 
automatic wireless shooting when using 
a 600EX II-RT attached to the camera 
(master) and a 600EX II-RT set as a 
slave unit.
Set the master unit.
Set the 600EX II-RT attached to the 
camera as the master unit (p.92).
You can also use a device equipped 
with the optical transmission wireless 
master function as the master unit.
Set the slave unit.
Set the 600EX II-RT to be controlled 
wirelessly from the master unit as the 
slave unit (p.92).
You can also use other EX-series 
Speedlites that are equipped with an 
optical transmission wireless slave 
You can use any of A, B, or C as the 
firing group.
Check the channel.
If the channels of the master unit and 
slave unit are different, set them to 
the same number (p.93).
a: Fully Automatic Wireless Flash Photography
Autoflash Photography Using One Slave Unit
Firing group