The Canon EF 2X II Extender teleconverter that doubles the effective focal length of a compatible lens. For instance, attaching it to a 200mm lens increases its reach to 400mm. These high-performance accessories are compatible with select EF lenses, including the EF 70-200mm f/2.8L USM, EF 70-200mm f/2.8L IS USM, EF 70-200mm f/4L, EF 100-400mm f/4.5-5.6L USM, EF 400mm f/4 DO IS USM, and fixed-length L-series lenses with focal lengths of 135mm or higher.