The Yongnuo YN-E3-RT Speedlite Transmitter is directly compatible with the Canon 600EX-RT flash, Canon 430EX III-RT, and the Yongnuo YN600EX-RT flash unit with in-built wireless receiver. It has all the features of the Canon ST-E3-RT, as well as a few additional features.

It’s a 16 channel, 5 group wireless triggering device with a 100m working range. The transmitter offers E-TTL II/E-TTL auto-flash, manual flash, stroboscopic flash, auto external flash metering modes as well as 1:8 flash ratio control

Other features include flash exposure lock, AF beam focus assist, modeling lamp functionality and 9 custom functions. The YN-E3-RT transmitter will run for 10 hours of continuous use on AA/LR6 alkaline batteries. A power saving function shuts the unit down after being idle for 5 minutes to conserve battery power.

It acts as a transmitter for wireless flash shooting. It can control up to 5 groups (15 units) of speedlites that have wireless multiple flash shooting functionality through the use of radio transmission. The transmitter also has dust and water resistance features, equivalent to EOS-1D series cameras. 

Compatible with Canon Speedlite 600EX II-RT via firmware update. 

It includes all the features of the Canon ST-E3-RT, as well as few more important features:

• AF Focus Assist light.
• USB port for firmware updates
• Second curtain sync (in manual only)
• Full GR Group Mode functionality has also now been added for pre 2012 model cameras
• Slave flash charge status does not stop other flashes from firing 

Main Features:

• Two-way 2.4G radio communication, fully compatible with ST-3E-RT/600EX-RT
• 5 Physical Channels, 1 Auto Channel, Up to 10,000 customisable photographer ID
• Transmission Range: 100M
• Multi YN-E3-RT can share slave flashes
• Display group/charge status of slave flashes
• Firmware can be upgraded via USB
• High resolution Dot-Matrix LCD, Backlight for LCD/keys
• Fast lock mechanism
• Built-in AF assist beam emitter, buzzer
• Remote shutter release, Linked Shot (Need extra shutter cable for cameras released before 2012)
• Flash Mode: ETTL/M/Multi/GR 4 flash modes
• A/B/C/D/E 5 groups
• Supports 1st Curtain, 2nd Curtain (Only in M mode), High speed Sync
• Supports ETTL Ratio, Flash Exposure Compensation, Flash Exposure Lock, Flash Exposure Bracket, Modeling Flash
• 9 Custom Functions
• Settings saved automatically