Gary Fong explains how to setup your Canon 580exII to be either an on-camera “silent” master transmitter, or an off-camera slave for multiple light or off-camera flash situations. Note that to use this system, all of the flashes must have their red front panels visible to each other with no obstructions. If there is anything in the way (going around walls, etc.) then a Radio is recommended. Since the button sequence is tricky, this is a good guide.