Canon EF - Manual (Page 72)

• When using the CAT System with the EF camera,
the shutter speed dial must be set at "125," the CAT
switch set to the "
^
" position, and the aperture
ring set at the green "O." With all other types of
flash, the switch may be left at its "NORMAL"
position, but the aperture ring has to be set
manually.
• At present, the CAT System may be used with
four Canon lenses: two standard 50mm lenses, the
f/1.4 and f/1.8and two 35mm wide-angle lenses, the
f/2 and f/3.5.
• Normal AE photography may be performed at
any time when using the CAT System by returning
the CAT switch to the "NORMAL" position.
• Two electronic flash units, one direct-mounting
type inserted in the flash hot shoe and another using
a PC cord plugged into the sync terminal, cannot be
used simultaneously on the EF. When a PC cord is
plugged into the sync terminal, the flash hot shoe is
automatically disconnected.