The cactus is a world first a wireless flash transmitter compatible with any camera with a hotshoe or pc sync port able to control the power output of nikon canon and pentax flashes olympus and panasonic now added via firmware update or any combination of them simultaneously its an inventive design and great value for money to boot you need a minimum of two v6 units one to act as a transmitter and a second as a receiver to trigger and remote power control of one flash unit unless