The Hahnel Viper Wireless Flash Trigger means that you can individually control up to three groups of Canon dedicated flashguns, or studio lights (with optional cable), from your Canon EOS DSLR, with each of those groups comprising of one or more flashes. The easy to use LCD panel means that you can control each of these groups, turning the power on or off, adjusting the output or setting it to Manual allowing the output from the light source to override the Viper. Both the transmitter & receiver are powered by two AA batteries & additional receivers are available for multiple flash set ups