Yongnuo Upgrade RF-603 II C1 Flash Trigger/Wireless Shutter Release Transceiver Kit for Canon Rebel 300D/350D/400D/450D/500D/550D/1000D Series 1, Higher sync speed than the first generation --- The highest flash sync speed up to 1/320 second (some of models may only reach to 1/250s or less, difference combination of models of flash and camera using may achieved difference flash sync speed). 2, Adding the Locking rings 3, Improved Flash / Shutter control Buttons 4, Working for more non Canon/Nikon cameras and single firing pin cameras --- ALL Standard Hot shoe DSLR Camera except Sony and Minolta. 5, Adding the power switch for single transmitter --- Set the power switch on TX (single transmit) or TRX (transmit-receive automatic switch) state according to different shooting requirement. When it used as wireless triggering transmitter and flash testing, set to "TX"; When it used as wireless triggering receiver, using shutter release or other extended functions, set to "TRX". set to OFF means turn off the power.