Canon Speedlite 600EX II-RT Manual (en)

Flash Control from the Camera’s Menu Screen
Flash firing
To perform flash photography, set to [Enable]. To use the flash's AF-
assist beam only, set to [Disable].
E-TTL II flash metering
For normal exposures, set it to [Evaluative]. If [Average] is set, the 
flash exposure will be averaged for the entire scene metered by the 
camera. Flash exposure compensation may be necessary 
depending on the scene. This setting is for advanced users.
Flash synchronization speed in Av mode
You can set the flash synchronization speed when shooting in <f> 
aperture-priority AE mode with flash.
Flash mode
You can select the flash mode from [E-TTL II], [Manual flash], 
[MULTI flash], [AutoExtFlash], and [Man.ExtFlash] to suit your 
desired flash photography.
Shutter sync settings
You can select the flash firing timing/method from [1st curtain], [2nd 
], or [High-speed synchronization]. To perform normal flash 
photography, set [1st curtain].
Flash exposure compensation
With a similar procedure as exposure compensation, you can adjust 
the flash output. The flash exposure compensation amount can be 
set up to ±3 stops in 1/3-stop increments.
You can take three shots while automatically changing the flash 
output. The settable range is up to ±3 stops in 1/3-stop increments.