Canon MARK IV User Manual (en)

 Setting the Flash
While the flash output is changed automatically, three flash shots are 
taken. For details, see the instructions for FEB (Flash Exposure 
Bracketing) in your Speedlite’s instruction manual.
Flash exposure compensation
The same setting as “Flash exposure compensation” on page 119 
can be done.
For normal flash exposures, set it to [Evaluative].
If [Average] is set, the flash exposure will be averaged for the entire 
metered scene as with an external metering flash. Since flash 
exposure compensation may be necessary depending on the scene, 
this setting is for advanced users.
You can adjust the Speedlite’s flash coverage. Normally, set this to 
[Auto] so that the camera will automatically set the flash coverage to 
match the lens focal length.
Wireless setting
Wireless flash (with multiple flash units) is possible. For details, see 
your Speedlite’s instruction manual about wireless flash.
Flash firing
To enable flash photography, set [Enable]. To enable only the AF-
assist beam to be emitted, set [Disable].
When using 2nd-curtain sync, set the shutter speed to 1/50 sec. or slower. If 
the shutter speed is 1/60 sec. or faster, 1st-curtain sync will be applied even 
if [2nd curtain] is set.
If flash exposure compensation has already been set with the Speedlite, 
you cannot use the camera’s <Q> button or Flash function settings 
menu to set flash exposure compensation. If it is set with both the 
camera and Speedlite, the Speedlite’s setting overrides the camera’s.
The flash function’s [E-TTL II] setting will work together with C.Fn II -5 
(p.215). And [Flash firing] will work with C.Fn II -7 (p.216).