I am trying to find out if Canon flashes (550EX, 580EX II) can be set up to fire in response to another flash going off. Example: Shooting a Yashica FX-D w/Yashica CS-220 flash in Auto mode. Can I set up my Canon's for fill/BG and have them auto-fire when the the camera-mounted 220 fires? I'm thinking not.
Do other units do this?