Attaches to 9xi's hot shoe, emits any of 4 infrared control signals which start and stop an off-camera 3500xi or 5400xi that is in remote/wireless flash mode. Allows for a 2:1 ratio from off-camera flashes. Provides off-camera flash control to as close as 7.9" from subject--the minimum working range for the AF 50mm f/2.8 Macro lens--without affecting exposure.