Extending a lenses focal length by a factor of 1.4x, Extender EF 1.4X III incorporates phenomenal optical performance with minimal chromatic aberration & is a perfect complement to many of 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 & even has a new Fluorine coating that keeps soiling, smears & fingerprints to a minimum. An integral part of many professional systems, Extender EF 1.4X III maintains high standards not only optically, but also in terms of rugged, dustproof & water resistant construction. Focal Length & Maximum Aperture Magnification: 1.4x Lens Construction 7 elements in 3 groups Max. Diameter x Length, Weight 2.8 x 1.1 in, 7.9 oz. / 72.0 x 27.2