Canon Speedlite 600EX II-RT Manual (en)

a: Fully Automatic Wireless Flash Photography
During radio transmission wireless shooting, the master unit’s LCD 
panel illuminates or turns off according to the charge status of the 
master unit and slave units (firing groups).
The master unit’s LCD panel illuminates if the master unit and slave units 
are not fully charged. When the master unit and slave units are fully 
charged, the LCD panel illumination will turn off after approx. 12 sec.
When the charge of the master unit and slave units becomes 
insufficient as you take pictures, the master unit’s LCD panel will be 
illuminated again.
When you need more flash output or you 
want to perform lighting more easily, you 
can increase the number of slave units 
and fire them as a single flash.
To add slave units, perform the same 
procedure as “Autoflash Shooting Using 
One Slave Unit” (p.68). Set the firing 
group to A, B, or C (p.73). The flash will 
not fire if it is set to D or E.
When the number of slave units is increased or master flash firing is set 
to ON, automatic control is performed to fire all flashes at the same 
flash output and to ensure that the total flash output results in the 
standard exposure.
LCD Panel Illumination
Autoflash Photography Using Multiple Slave Units
If the master unit or any of the slave units (firing group) are not fully charged, 
<G> will be displayed on the master unit’s LCD panel. Make sure to 
take the picture after checking either that the <G> icon is not 
displayed on the LCD panel or the LCD panel is not illuminated.