The Canon Speedlite Transmitter ST-E2 is compatible with Type A EOS cameras (E-TTL, auto flash) and Type B EOS cameras (manual flash). The ST-E2 is designed to control slaved Canon 550 EX flashes, enabling simultaneous flash use in professional settings. The wireless controller has a flash ratio control, allowing for several different A:B ratios, 1:8 to 8:1 in half-step increments, as well as slave confirmation via a test transmission button, which sets off slave A, followed by slave B, at 1/64 output.
Wireless flash controller for the Canon 420EX and 550EX and other Canon flashes.
Indoor transmission range of approximately 40 to 50 feet
Outdoor transmission range of approximately 26 to 33 feet