YONGNUO YN600EX-RT II Wireless HSS TTL Flash Speedlite Plus YN-E3-RT Speedlite Transmitter for Canon DSLR Cameras One YN600EX-RT can be used as on-camera master unit and remote slave unit of Canons RT system,and supports Gr grouping mode. One YN600EX-RT can respectively receive the wireless signal of master unit YN600EX-RTYN-E3-RTCanons 600EX-RT/ST-E3-RT, realizing remote TTLM and Gr flash. High Guide Number, Supports High-speed Sync GN60@ISO100200mm;supports high-speed sync TTL, manual flash, Gr grouping flash, the highest synchronous speed can reach 1/8000s The YN600EX-RT equipped with the USB interface, supports firmware upgrade, the users can download the upgrade firmware through the Yongnuo official website to upgrade the flash. Settings Save Automatically, Supports Custom Settings (Fn) The parameters on the flash will automatically save when the flash turned off; the users can customize setting the flash function as needed.