Canon SPEEDLITE EL-1 Advanced User's Manual page 162

Automatic Flash Photography with Receivers divided into Groups
( , )
You can divide the receiver units into two or three groups and perform E-TTL II / E-TTL
autoflash shooting while changing the flash ratio (flash output rate).
(1) 2 (A, B) groups
(2) 3 (A, B, C) groups
Caution
If you shoot with firing group C pointing directly toward the main subject,
overexposure may result.
Before shooting, perform a test flash (
To avoid interfering with transmission, do not place any obstacles between the
sender unit and receiver unit.
Note
Using the mini stand provided with the receiver unit, position the receiver of the
receiver unit towards the sender unit.
When shooting indoors, the transmission may be reflected off the wall, which
may cause the camera to be activated even when the layout is still preliminary.
) and test shooting.
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