Canon SPEEDLITE EL-1 Advanced User's Manual page 105

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
Before shooting, perform a test flash (
The transmission distance may be shorter depending on the conditions such as
the positioning of the flashes, the surrounding environment, and weather
conditions.
Note
Using the mini stand provided with the receiver unit, position the receiver unit.
) and test shooting.
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