The Viper Wireless Group Flash Trigger for Canon Cameras from channel provides multi-group wireless flash control to Canon cameras. It operates with a 2.4 GHz frequency with a range of 328'. The system uses Digital Channel Matching to quickly and reliably connect the receivers and transmitter and avoid interference from other devices. Also, it can manage up three different flash groups. Flash output can be set via the transmitter for each group from 1/1 to 1/128 with intermediate stops of ±0.3 and ±0.7 for more exacting control over your lighting. This is all shown on the backlit LCD display. Additionally, a manual mode is available for setting options on the flash itself and there is a pass-through hot shoe on the transmitter for TTL control of a mounted flash. The receiver features both 2.5mm and Mini-USB ports for connecting to flash units and the Mini-USB ports on both units can be used for external power or firmware updates. For general use, each unit runs on two AA batteries whose level is shown on the display.