The RF mount adds 12-pin communication for high-speed data transfer between the camera and the lens, which enables faster autofocus and the addition of a new Combination IS system. In this Combination IS system, the electronic IS of the camera and the optical IS of an RF lens work co-operatively to give a greater level of image stabilisation.
RF lenses share the same large 54mm internal diameter as EF lenses, but at just 20mm, the flange distance from the mount to the camera sensor is less than half the distance required by the EF mount. Being able to position the rear element closer to the sensor brings an exceptional level of corner-to-corner sharpness with minimal light falloff. The combination of a large diameter and short flange distance also permits the design of faster, brighter lenses with larger maximum apertures.