Get some extra versatility from your telephoto L-Series lens with this precision-designed 1.4X extender. Your 300mm lens, for example, will gain 40% more reach, with a resulting focal length of 420mm (on full-frame cameras) or 672mm (on APS-C sensor cameras) once this extender has been placed in the light path. And it will only give up one stop of light sensitivity in the process. It's like getting two lenses out of your kit bag when this extender is standing at the ready.
A built-in microcomputer facilitates communication between lens, extender, and camera body, and provides fully integrated exposure and focus control on many Canon lenses. Not all lenses will be fully compatible though, so you should check your manuals and the Canon website to make sure of your lens's compatibility with this extender.
Fluorine coatings on the extender's optical elements will keep soils, smearing and fingerprints to a minimum. And it features rugged dustproof and water-resistant construction.