Interfit Strobies STR129 i sync 4 Receiver for STR130 (Black) Optical triggering: It is similar to your in built sync cell on your studio flash heads and can allow a greater distance to be used when using Infrared triggers such as the Interfit INT411 or receiving white light from a second head. Wireless triggering: When used with the radio trigger on your camera allows out of sight flash triggering or around walls and most obstacles up to a maximum distance of 30 mtrs (100 feet).