Radio-controlled, two-way wireless transmission up to 98.4 feet, up to five groups or fifteen individual Speedlites, a dot matrix LCD with backlighting, intuitive controls, and more. The Canon Speedlite Transmitter ST-E3-RT (Ver.3) provides continued support for Canon DSLRs that feature a standard hot shoe (not compatible with multi-function shoe-equipped cameras). Many of the most popular features carry over to version 3, such as wireless rear curtain synchronization to capture ambient light trails and convey a sense of speed for moving subjects. Control Multiple Groups: With the Speedlite Transmitter ST-E3-RT (Ver.3), up to fifteen Canon RT-compatible Speedlites in five groups can be controlled from the camera, via a single transmitter An expansive minimum output range (down to 1/8192 power), and FE Memory as part of the radio transmitter so you can lock in an E-TTL flash exposure level, even in complex multi-flash set-ups, and continue to use it for the same scene or subject.