Master control device for a wireless Speedlite flash system.

Features
-Use multiple 550EX Speedlites under full E-TTL control without need for any interconnecting wires
-Dedicated transmitter controls up to 3 Canon 550EX Speedlites as slave units 33 ft. away outdoors and 49.5 ft. away indoors
-Mounted as a clip-on with shoe lock lever and locking pin
-For use with EOS 20D, EOS Digital Rebel XT, EOS Digital Rebel, EOS 10D, EOS-1D Mark II, EOS D60, EOS-1Ds, EOS-1D and PowerShots Pro1, G6 and G5