Canon Speedlite 600EX II-RT Manual (en)

a: Fully Automatic Wireless Flash Photography
Since the following functions set on the master unit will be set 
automatically to the slave units with this wireless system, you do not 
need to operate the slave unit(s). For this reason, you can perform 
wireless flash photography in the same way as normal flash 
You can designate two or more master units. By preparing multiple 
cameras with master units attached, you can change cameras while 
keeping the same lighting (slave units) during wireless flash 
Note that when using two or more master units, the color of the <D> 
lamp will change depending on the order in which the master setting 
was performed. The first master (main master) is green, and the second 
and subsequent masters (sub-masters) are orange.
Advanced Shooting with Fully Automatic Wireless Flash
• Flash exposure compensation
• High-speed sync
• FEB 
• Manual flash
• FE  lock
• Stroboscopic flash
Master Units
You can also directly operate the slave unit to separately set flash exposure 
compensation and flash coverage on each slave unit.
If the <D> lamp is red, the connection has not been established. After 
checking the transmission channel and wireless radio ID, turn each 
master unit off and on again.
During radio transmission wireless shooting, limit the total number of 
masters and slaves up to 16 units.
You can take pictures even when the master flash is set as a sub-master.