The Canon 2X EF Extender II is a professional grade teleconverter designed exclusively for use with select Canon brand L-Series lenses (focal lengths over 135mm). Doubling the lens focal length, Extender EF 2X II incorporates incorporates careful lens placement and anti-reflective coatings for high quality optical performance. The converter also features a built-in microcomputer for seamless communication between camera body, lens, and extender. Extender EF 2X II maintains high standards not only optically, but also in terms of the rugged weather resistant construction outdoor pros want. Often an integral part of a professional’s kit, Extender EF 2X II is a very practical complement to compatible telephoto lenses.