EOS DIGITAL cameras have one of three image sensor sizes. The lens' effective focal length will differ depending on the camera's image sensor size. The Speedlite automatically recognizes the EOS Digital camera's sensor size and automatically set the flash coverage for lens focal lengths from 24mm to 105mm.
When the Speedlite is attached to a compatible camera will appear on the Speedlite's LCD panel.
C.Fn - Auto Zoom can be disabled - C.Fn-09