The sigma 20x tc 2001 teleconverter has been developed exclusively for sigmas global vision lenses such as the art sports and contemporary range by mounting it in between a telephoto lens and a camera the offered magnification of focal length is 2x the special low dispersion glass elements offer aberration correction while the dust proof and splash proof construction increases its longevity the tc 2001offers full communication between the lens and camera and will support autofocus at f8