Yongnuo RF-603C3-INT Wireless Remote Flash Trigger for Canon 1D 1DS 5D 5DII LF239 (Discontinued by Manufacturer) Works as a wireless shutter release control to trigger your camera Transceiver System - works as a wireless flash trigger and receiver Each RF-603 is designed to work as trigger and as receiver Compatible with Canon 1D/5D/7D/50D/40D/30D/20D/10D Series cameras for shutter release control Includes (2) RF-603 transeivers (1) C3 shutter release cord