The Canon CM-V1 EF Cinema Lock Mount incorporates the EF mount electronic contacts and allows you to mount virtually any Canon EF mount lens, either the stills variety or the cinema lens variety, on your camera. The kit includes the locking EF mount and a shim kit for precisely adjusting the mount on your camera to ensure the correct flange distance. Many of the zoom Cinema lenses require the distance from lens to the image plane be precise for the best optical and mechanical performance. This is where this Cinema lock mount comes into play.