YONGNUO YN024 YN600EX-RT Wireless Flash Speedlite 2 Piece Plus YN-E3-RT Radio Transmitter for Canon DSLR Cameras YN600EX-RT can be used as on-camera master unit and remote slave unit of Canon's RT system and supports Gr grouping mode 2.YN600EX-RT can be used as master unit to trigger another YONGNUO YN600EX-RT or Canon's 600EX-RT and live display the flash groupings of slave unit and recycling information.. 3.GN60@ISO100,200mm,supports high-speed sync TTL, manual flash, Gr grouping flash, the highest synchronous speed can reach 1/8000s 4.YN600EX-RT not only supports YONGNUO, Canon's and Nikon's wireless optical master signal, but also supports S1 and S2 pre flash cancel mode 5. 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