The Canon EF 2x II Extender is a high-quality teleconverter that preserves the image quality of the lens it's mounted to and multiplies its focal length by 2x. When combined with pro level EOS cameras & EF supertelephoto lenses with image stabilization, near imperviousness to weather extremes is achieved thanks to rubber gasket seals. Improved antireflective internal coatings also increase transmissivity & performance in backlit conditions.
The 2x extender (also known as a teleconverter) will multiply the focal length of the existing lens by 2x, and will cut back the amount of light by 2 f/stops. For example, using a 2x teleconverter with a 300mm lens will effectively increase the focal length to 600mm. A lens set to f/2.8 will now be f/5.6. Teleconverters are best used with longer telephoto lenses and are not recommended for lenses wider than 50mm, e.g. 28-105mm (35mm format).
Note: Autofocus is possible with any EOS body if the lens has an f/2.8 or faster maximum aperture, and compatible Image Stabilization lenses maintain the IS feature when used with any current EOS camera.
Preserves the image quality of the lens it's mounted to