Yongnuo RF-603C II is improved version of RF-603 flash trigger. It is a remote shutter release as well as a multi-functional flash trigger which can synchronously trigger flashes and studio strobes. This is the transceiver based system so each transceiver can be used flexibly as trigger or receiver. If you place it on camera, it will act as transmitter. If you mount it on flash speedlite, it will act as receiver. The 2.4 GHz wireless frequency is allowed in most countries and guarantees high speed, range and stability. Within capacious areas, the remote control distance may reach up to 100m. The synchronization speed can reach up to 1/320, depending on the situation.