Designed to extend a lenses focal length by a factor of 2x, the redesigned Canon Extender EF 2X III delivers optical performance on par with the finest Canon super telephoto lenses. It features a built-in microcomputer for seamless communication among camera body, lens & extender, features careful lens placement & coatings to minimize ghosting, flare & chromatic aberration, & even has a new Fluorine coating that keeps soiling, smears, fingerprints to a minimum. Extending a lenses focal length by 2x Perfect complement to super telephoto lens Minimal chromatic aberration