Wireless master function (optical) allows multiple flash units to be controlled for creative lighting effects
For a number of advanced lighting setups, the Speedlite 90EX can be used as a master transmitter to control multiple flash units - wirelessly! Through 4 channel optical light pulse transmission, the Speedlite 90EX can control up to three groups of slave-enabled flashes, controlling power from 8:1 to 1:8 in 1/2 stop increments. It can transmit up to approximately 16.4 ft. indoors, up to 23 ft. outdoors. With the Speedlite 90EX controlling each light source according to the specific parameters of a shot, the creative possibilities are endless!