(From company literature) This tele extender can be used with fixed focal length lenses 135mm and longer (except the 135mm ƒ/2.8 Softfocus lens), and the EF 70-200 ƒ/2.8L, 70-200 ƒ/2.8L IS, 70-200 ƒ/4.0L, and 100-400 ƒ/4.5-5.6L IS zoom lenses. Superb optically, it preserves the image quality of the lens it's mounted to and multiplies its focal length 1.4x. Effective aperture is reduced by one f-stop; autofocus is possible on any EOS camera when combined with a lens having an ƒ/4 or faster maximum aperture. The new version II maintains the outstanding optics of the previous version, and adds enhanced weather-resistant construction, and improved anti-reflective surfaces in the barrel.
