The worlds first teleconverter to incorporate an aspherical lens element for outstanding resolution and contrast the nikon tc 20e af s iii is teleconverter doubles the effective focal length of certain nikkor lenses without increasing the closest focusing distance for example using this teleconverter with a 200mm lens will effectively increase the focal length to 400mm and it will also cut out the amount of light by 2 f stops it is both compact and lightweight making it a cost effective an