The Canon ST-E3-RT Speedlite Transmitter can help you take full advantage of all the latest features on Canon's top-of-the-line 600EX-RT flash. The ST-E3-RT makes complex lighting setups simple by facilitating radio-controlled, two-way wireless transmission up to 30m away, among up to five groups or fifteen individual Speedlites. It has controls similar to the new 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.

Features:

• 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 30m, all at a 360 degree angle.
• Up to 5 groups, or 15 individual flashes can be controlled via 1 transmitter.
• Supports E-TTL II flash, manual flash, stroboscopic and auto external flash metering.
• Dot matrix LCD panel displays all pertinent information simultaneously and backlit control panel means easy operation.
• 8 types of custom functions, 3 types of personal functions.
• Improved hot shoe contacts for more reliable information transmission and operation.
• Slave operation confirmation: 
• Green Light--Lit: Radio Transmissions Okay
• Red Light--Lit: Not Connected, Blinking: Transmission Error/ Too many units (Master units + slave units = more than 16 units)
• Orange Light--Lit: Sub-master transmission, Blinking: Receiving remote release shooting, linked shooting signal
• Not compatible with earlier Speedlite models such as 580EX II

• Canon ST-E3-RT Speedlite Transmitter 
• Softcase