The EF-42 Shoe Mount Flash is a lightweight, portable on-camera flash with a 138' (42 m) guide number @ ISO 100. It has auto zoom that automatically matches the focal length of the lens (24-105mm in 35mm format), and can be set for APS-C or full-frame 35mm use. Light output is adjustable from full power all the way down to 1/64 power. Exposure compensation of +/-1.5 EV in 1/2-stop steps helps you further refine your lighting. The flash head rotates 90°vertically, 180°to the left, and 120°to the right for total flexibility in directing your light.