The Canon Speedlite Transmitter ST-E2 is a wireless transmitter that can control up to two Speedlite 550EX groups set as slaves. The transmitting range is about 12 to 15 meters / 39.4 to 49.2 ft indoors and 8 to 10 meters / 26.2 to 32.8 ft outdoors. With Type A cameras, the ST-E2 can execute various operations through wireless control, including autoflash, high-speed sync, FE lock, flash exposure compensation, manual flash, and multi-flash firing. With Type H cameras, the ST-E2 can only be used for manual flash and multi-flash photography.