Canon ST-E3-RT Speedlite Transmitter Newly designed wireless system uses 2-way radio wave communication for enhanced communication among master and slave units. Achieves a transmission distance of up to 98.4 ft. / 30m, all at a 360 degree angle. Up to 5 groups, or 15 individual flashes can be controlled via 1 transmitter; 8 types of custom functions, 3 types of personal functions. Supports E-TTL II flash, manual flash, strobe and external flash metering. Dot matrix LCD panel displays all pertinent information simultaneously and backlit control panel means easy operation. It even features an internal sound emitter.