Canon Speedlite 600EX II-RT Manual (en)

m Bounce
When you position the flash head down 
by 7° while pressing the <z> 
button, you can shoot subjects at a short 
distance in a range of approx. 0.5 to 2 m 
/ 1.6 to 6.6 ft.
When the flash head is positioned down 
by 7°, the display changes to <n>.
n Short Distance Flash Photography
If the ceiling or wall to bounce the flash light on is too far away, shooting 
with the appropriate exposure may not be possible since the bounced 
flash may be too weak.
If the picture appears dark, use a larger aperture opening (smaller f/
number) and try again. You can also increase the ISO speed when using 
a digital camera.
The ceiling or wall to bounce the flash light on should be plain white for 
high reflectance. If the bounce surface is not white, shooting with the 
appropriate exposure may not be possible, since a color cast may result 
in the picture or the bounced flash may be too weak.
When Quick flash is fired with bounce flash, underexposure may occur 
since the flash output decreases.