Canon SPEEDLITE EL-1 Advanced User's Manual page 177

Note
The flash coverage of the sender unit and receiver unit is set to 24 mm. You can
also set the flash coverage manually.
It can also fire a flash on the sender ( ).
You can press the depth-of-field preview button on the camera to fire the modeling
flash ( ).
If the receiver unit's auto power off takes effect, press the sender unit's test flash
button to turn on the receiver unit.
You cannot use the test flash when operating the flash timer, etc. on the camera
end.
You can change the time until the receiver unit's auto power off takes effect
(C.Fn-10).
You can disable the blinking of the AF-assistant beam emitter when the receiver
unit is fully charged (C.Fn-23).
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