Generic various branded automatic tele-convertor for Pentax M42 threaded mount. Also known as Universal Screw mount fits Praktica, Pentax, Contax, Fujica, Olympus, Yashica, Zenit, Hanimex, Mamiya, Ricoh, Petri, Sears, M42 threaded camera mounts. Japanese made lens. Good like new condition. Use for extension of your camera lens for macro shooting or doubling the focal length of your lens to capture distant shots. Fun to extend your lens without purchase of new lens. Will need that stability of a tripod to stop lens shake, with the addition of a 2X teleconverter as it is only using 25% of your front lens, there is decreased light and will need slower shutter speeds. Explore photo possibilities with a 2X extender. Try stacking 2 of these extenders, it works. Your 200mm lens doubles twice to becomes a 800mm lens. Teleconverters are popular with birders because they provide an affordable ““ and relatively space-saving ““ way to achieve very long effective focal lengths without buying or carrying new heavy equipment.