Up to 5 groups, or 15 individual flashes can be controlled via 1 transmitter
The Speedlite Transmitter ST-E3-RT facilitates radio controlled, two-way wireless transmission up to 98.4 feet, for a reliable and robust connection among sender and receiver units. Communicating on 2.4 GHz frequencies, the Speedlite Transmitter ST-E3-RT does not have the same directional limitations of traditional wireless optical transmitters. Where other wireless signals can be interrupted by physical obstacles, radio controlled systems excel. Fifteen transmission channels are available, selectable manually or automatically, and radio transmission IDs can be set to prevent misfiring in the event of signal interference on the same channel. With the extended, more reliable range afforded by radio transmission, ambitious photography is made easier.

Supports E-TTL II Flash, manual flash, stroboscopic and auto external flash metering
With the Speedlite Transmitter ST-E3-RT, up to fifteen flashes in five groups can be controlled via a single unit. Each group can be set to a different flash mode, enabling multiple configurations for creative photography. For example, with the Speedlite Transmitter ST-E3-RT, some flashes can be directed to operate according to the cameras meter reading, others can be set manually; groups can be set to overexposure or underexpose, and much, much more. With up to fifteen flashes under the control of one transmitter, wirelessly, complex lighting setups normally reserved for the studio are a breeze.

Dot matrix LCD panel displays all pertinent information simultaneously and backlit control panel means easy operation
The Speedlite Transmitter ST-E3-RT features an all-new dot matrix LCD panel (172 x 104 dots). This new LCD displays Flash status, flash settings and wireless configuration with more detailed information in comparison to previous systems. With its new screen combined with backlit operation buttons and even an internal sound emitter, the Speedlite Transmitter ST-E3-RT is as easy to operate in the dark as in daylight.

8 types of custom functions, 3 types of personal functions
To accommodate the demands of a number of different shooting situations, the Speedlite Transmitter ST-E3-RT can be configured with eight types of custom and three types of personal functions. Custom functions include: auto power off, modeling flash controls, sound, illumination and more. Personal functions include display contrast and LCD panel illumination color for both sender and receiver flashes.

Improved hot shoe contacts for more reliable information transmission and operation
The Speedlite Transmitter ST-E3-RT is built to the standards one would expect from professional Canon camera systems. A newly updated hot shoe contact ensures reliable communication between camera and transmitter. Dust and water resistance is excellent as well: all moving parts and areas surrounding the transmitters display and buttons are sealed for uninterrupted performance in harsh conditions. A new dust and water resistant adapter for the mounting foot creates a dust and water resistant seal between camera and flash. Compact and lightweight, the Speedlite Transmitter ST-E3-RT is approx. 2.65 (w) x 2.42 (H) x 3.05 (D) in.