The world's 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 and a practical solution for those times when it is not possible or desirable to carry an extra telephoto lens with you.