Extending a lenses focal length by a factor of 1.4x, Extender EF 1.4X III incorporates phenomenal optical performance with minimal chromatic aberration and is a perfect complement to many of Canon super telephoto lenses. It features a built-in microcomputer for seamless communication among camera body, lens and extender; features careful lens placement and coatings to minimize ghosting and flare and even has a new Fluorine coating that keeps soiling, smears and 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 and water resistant construction. In other words, it's wicked awesome.
Please keep in mind that using this Tele-Converter "costs" one stop of light, so your 70-200 f/2.8 will become a 98-280 f/4.
Focal Length & Maximum Aperture
7 elements in 3 groups
Max. Diameter x Length, Weight
2.8 x 1.1 in, 7.9 oz. / 72.0 x 27.2mm, 225g