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. Note: This lens is only compatible with fixed focal length L-series lenses 135mm and over, as well as the Ef 70-200/2.8L, Ef 70-200/2.8L Is, Ef 70-200/4L, and Ef 100-400/4.5-5.6L. Additionally, please see the lens and/or camera body manual for full compatibility information with the Extender Ef 2x Iii.