Your 70-200 not long enough? Add the 1.4x extender for that extra reach. Adding extender reduces the f/stop on your lens by one full stop. I.E.: f/2.8 to f/4.0
Extending a lens's focal length by a factor of 1.4x, the 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.