The Speedlite 90EX from Canon is a featherweight (1.76 oz) shoe mount flash that's ideal for the Canon mirrorless EOS M digital camera. It has a guide number of 30' and provides coverage for lenses as wide as 24mm (35mm format equivalent).
Many functions can be controlled effortlessly through the camera’s menu system, such as the AF assist beam (used to ensure accurate AF in low light situations), Canon’s amazing E-TTL II flash metering, FE lock and flash exposure compensation. Even color temperature information can be transmitted back to the camera.
A wireless master function (optical) is built-in that allows multiple flash units to be controlled for creative lighting effects. Through 4-channel optical light pulse transmission, the 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. Best of all, the 90EX has a standard Canon hot shoe mount that makes it compatible with all Canon EOS SLR cameras.