The canon extender ef 1.4x iii extends 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.