Canon 580EXII Instruction Manual page 22

Auto Zoom for Image Size
EOS DIGITAL cameras have one of three image sizes. The lens'
effective focal length will differ depending on the camera's image size.
The Speed lite automatically recognizes the EOS DIGITAL camera's
image size and automatically sets the flash coverage for lens focal
lengths from 24mm to 105mm.
When the Speed lite is attached to a compatible camera, <§> will
appear on the Speed lite's LCD panel.
ETTL
Zoom Sam
§
F-
s.
-------
0.50.7 1 1.5 2 3 4 6 9 13 18 m
Auto zoom can be disabled. (C.Fn-09
----j-
p.27)
21