Attaching this high-performance Extender to a 135mm or longer lens or to the EF 70-200mm f/2.8L boosts the focal length by 2 times. With seven elements in five lens groups, it preserves the prime lens image quality.

With the Extender attached, the f-number decreases by two stops. Autofocusing is possible with lenses whose maximum aperture is f/2.8 or faster.