Canon Speedlite 600EX II-RT Manual (en)

Set the power switch to <K>. 
The flash recharge starts.
During recharging, <G> is 
displayed on the LCD panel. When 
flash recharge is complete, this 
indicator disappears.
Check that the flash is ready. 
The status of the flash-ready lamp 
changes from off to green (Quick 
flash ready) to red (fully charged).
You can press the test flash button 
(flash-ready lamp) to fire a test flash.
The Quick flash function enables flash photography when the flash-
ready lamp is lit green (before the flash is fully charged). Quick flash is 
available regardless of the camera’s drive mode setting. Although the 
flash output will be approx. 1/2 to 1/6 of the full output, it is useful for
shooting with a shorter firing interval.
During manual flash photography, this function is available when the 
flash output is set to 1/4 to 1/128. Note that you cannot use Quick flash 
during stroboscopic flash and wireless flash photography.
Turning on the Power
Flash-ready lamp
(Test flash button)
Quick Flash
When Quick flash is fired during continuous shooting, underexposure 
may occur since the flash output decreases.
A test flash cannot be fired when the camera’s 3/1/o/7/2 
timer is active.
For the display of <G> when set as the master unit during radio 
transmission wireless shooting, see page 71.