Canon Speedlite Transmitter ST-E2
Wireless controller for the E-TTL wireless autoflash system. It can control up to two Speedlite 550EX slave groups in one of four channels. The flash ratio between the two groups can also be controlled. The wireless transmitter range is about 15-20 m/49-66 ft. indoors and 8-10 m/33 ft. outdoors at a vertical angle of ± 39°. Under low-light or low-contrast conditions it emits an AF-assist beam linked to the EOS-3's 45 focusing points.