The Canon ST-E3-RT Speedlite Transmitter makes advanced remote flash photography simple. You can trigger up to 15 flashes simultaneously and control the settings from a distance, even if your line of sight is blocked by a corner. You can trigger up to 15 cameras at once from a distance of up to 30 meters for complex, synchronized shots. The transmitter is sealed against dust and moisture to the same degree as a professional EOS camera, allowing you to work outdoors without fear of damage. Finally, the backlit LCD screen is easy to read and operate.