Yongnuo YN-E3-RT is a professional transmitter for speedlites with the RT system support - a superior copy of the original Canon ST-E3-RT. The transmitter is fully compatible with Canon Speedlite 600 EX-RT and Yongnuo YN600EX-RT II Speedlite. Main Features Autofocus assist light Second-curtain sync (in M mode only) Wireless E-TTL support High-speed sync support (HSS/FP) Controls up to 5 "slave" groups Main frequency: 500 Hz Maximum working distance: up to 100 m (300') Firmware update possible via USB Package Includes Yongnuo YN-E3-RT Speedlite Transmitter Case for storage User manual