The 420EX's flash head zooms automatically to provide adequate flash coverage for the lens focal length in use. Flash coverage is provided for the 24mm to 105mm focal lengths. The corresponding autozoom position indicator on the Speedlite lights

When a zoom lens is used, the flash coverage changes automatically to suit the focal length you zoom to

Press the shutter button halfway The autozoom position indicator for the corresponding lens focal length lights.

! If a lens focal length shorter than 24mm is used, the pictures periphery will look dark

• When the flash coverage changes, the Speedlite's Guide No. also changes. See the Guide No. table to see how the Guide No. change
• If the lens focal length is 105mm or longer, the 105 autozoom position indicator lights
• When the wireless selector is set to <SLAVE> the flash coverage is set automatically to 24mm