Canon Speedlite 600 EX-RT User Manual (en, zh)

Troubleshooting Guide
You were too close to the subject. Move away from the subject.
When shooting within 1 m (3.3 ft.) of the subject, set the bounce 
position down by 7°.
Remove the lens hood if attached.
Set the flash coverage to the automatic setting (p.29).
When using the manual setting for the flash coverage, set a flash 
coverage that is wider than the shooting angle of view (p.30).
Check that C.Fn-21-1 is not set (p.100).
When the shooting mode is set to <W> and the scene is dark, slow 
sync is enabled automatically (the shutter speed becomes slower). Use 
a tripod, or set the shooting mode to <V> or fully automatic mode 
(p.19). Note that you can also set the sync speed in [Flash sync. 
speed in Av mode
] (p.44).
Insert the mounting foot into the camera’s hot shoe all the way, slide the 
lock lever to the right, and secure the Speedlite to the camera (p.15).
Set the flash coverage to <L> (Automatic) (p.29).
The bottom of the picture looks dark.
The picture periphery looks dark.
The picture is very blurred.
The flash coverage is not set automatically.