With the Speedlite 550EX and the Speedlite Transmitter ST-E2, it is now possible to use multiple Speedlites under full E-TTL control and without the need for any interconnecting wires. Developed in conjunction with the Speedlite 550EX and the EOS-3 camera, this master control device for a wireless Speedlite flash system meets professional and advanced amateur standards. Its dedicated transmitter controls up to 3 Canon 550EX Speedlites as slave units 33ft. away outdoors and 49.5ft. away indoors. It is mounted as a clip-on with shoe lock lever and locking pin.
Compatable with:
EOS 20D
EOS-1D Mark II N
EOS-1Ds Mark II
PowerShot G3
PowerShot G5
PowerShot G6
PowerShot G7
PowerShot G9
PowerShot Pro 1
Speedlite 420EX
Speedlite 430EX
Speedlite 430EX II
Speedlite 550EX
Speedlite 580EX
Speedlite 580EX II