YONGNUO YN600EX-RT-II Wireless Flash Speedlite TTL Master for Canon DSLR 70D 60D 50D 40D 30D w/EACHSHOT Diffuser Comes with one EACHSHOT Brand diffuser. Supports RT System: One YN600EX-RT II can be used as on-camera master unit and remote slave unit of Canon's RT system, and supports Gr grouping mode. High Guide Number, Supports High-speed Sync: GN60@ISO100, 200mm; supports high-speed sync TTL, manual flash, Gr grouping flash; the highest synchronous speed can reach 1/8000s. Supports USB Firmware Upgrade: The YN600EX-RT II equipped with the USB interface, supports firmware upgrade, the users can download the upgrade firmware through the Yongnuo official website to upgrade the flash. Supports Wireless Optical Slave function: The YN600EX-RT II supports YONGNUO, Canon's and Nikon's wireless optical master signal, supports S1 and S2 pre flash cancel mode.