The Canon ST-E3-RT Speedlite Transmitter can help you take full advantage of all the features on Canon's Speedlite 600EX-RT and 430EX III-RT flashes. The ST-E3-RT makes complex lighting setups simple by facilitating radio-controlled, two-way wireless transmission up to 98.4' away, among up to five groups or fifteen individual Speedlites. It has controls similar to the Speedlite 600EX-RT, including multiple flash metering options, and a variety of flash modes. Compact design with highly reliable construction combined with a clearly laid-out information panel and buttons with back lighting make this an indispensible tool for advanced professional flash photography. The ST-E3-RT represents the next generation in wireless flash systems.
Note: Because it does not have an optical transmission function, the Speedlite Transmitter ST-E3-RT is not compatible with earlier Speedlite models such as 580EX II.