Canon SPEEDLITE EL-1 Advanced User's Manual page 36

Caution
You cannot use the test flash when operating the flash timer on the camera.
Note
The flash settings will remain in effect even after the power is turned off.
You can set the beep not to sound when charging is completed (P.Fn-06).
About the Quick Flash Function
The Quick flash function enables flash photography when the flash-ready lamp is flashing in
red (before the flash is fully charged). Quick flash is available regardless of the camera's
drive mode setting. Although the flash output will be approx. 1/2 to 1/6 of the full output, it is
useful for shooting with a shorter firing interval.
During manual flash photography, this function is available when the flash output is set to
1/4 to 1/8192. Note that you cannot use Quick flash during stroboscopic flash and wireless
flash shooting.
Caution
When Quick flash is fired during continuous shooting, underexposure may occur
since the flash output decreases.
Note
For more details on the <
wireless sender unit, see
You can disable Quick Flash (P.Fn-02).
> display when setting the radio transmission
"About the LCD Panel
36
Illumination".