Canon 580EXII Instruction Manual page 42

Flash Ratio with E-TTL II
With one master unit and one slave unit or two slave groups, you can
set the flash ratio for E- TTL II autoflash shooting.
The example below has two slave units and the master unit disabled
from firing.
Indoors
12m (39.4ft.)
Setting the Slave Units
Two slave units can be assigned to different slave groups by setting the
slave 10.
ETTL ailZoom 2Ymm
Set the wireless mode to
<a,'·S!4_>.
(p.36)
Press the
<ZOOM/~>
button
so that
<A>
blinks.
41