Canon Speedlite 580EX II Instruction Manual page 44

The flash ratio range of 8:1 - 1:1 - 1:8 is equivalent to 3:1 - 1:1 - 1:3 in
stops (1/2-stop increments).
The flash ratio under the Z mark is shown in parentheses below the scale.
(5.6:1) (2.8:1) (1.4:1) (1:1.4) (1:2.8) (1:5.6)
Wireless Flash with Three Slave Groups
Indoors
Outdoors
You can have slave groups A and B and also add slave group C. You can use
slave groups A and B to obtain the standard flash exposure of the subject,
and slave group C to illuminate the background to eliminate shadows.
C
10m (32.8ft.)
A
Set the slave units.
1
See "Setting the Slave Units" on page
41 to set the slave unit's ID to <1>,
<2>, or <3>.
For slave <3>, also set the flash
exposure compensation as necessary.
15m (49.2ft.)
B
8m (26.2ft.)
o
80
12m (39.4ft.)
43