Canon 420EX - Manual (Page 16)

Flash Coverage
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.
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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 picture's periphery will look
dark.
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When the flash coverage changes, the Speedlite's Guide No. also changes.
See the Guide No. table on page 50 to see how the Guide No. changes.
If the lens focal length is 105mm or longer, the 105 autozoom position indicator
lights.
When the wireless selector is set to <5LAVE> (^page 42), the flash coverage
is set automatically to 24mm.
AF-Assist Beam
If where you focus lacks sufficient light or contrast, the 420EX's AF-assist
beam is emitted automatically so that the camera can autofocus. The AF-
assist beam can cover the focusing points of the EOS 30/ELAN 7E and
almost all other EOS cameras. The AF-assist beam is effective from 0.7 to
7 m/2.3 to 23ft. at the center focusing point.
AF-Assist Beam Preconditions
The preconditions for the AF-assist beam to be emitted are explained on
page 51.
16