Canon Speedlite 90EX Instruction Manual page 13

Flash Sync Speeds and Apertures Used
Set automatically (1/X sec. - 1/60 sec.)
V
X
Set automatically (1/X sec. - 30 sec.)
W
q Set manually (1/X sec. - 30 sec., Bulb)
1/X sec. is the camera's maximum flash sync speed.

Shutter Speed Setting
Set manually (1/X sec. - 30 sec.)
Aperture Setting
Automatic
Automatic
Manual
Manual
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