The Zeikos 58mm High Quality 4.5X Telephoto Lens is an auxiliary lens that magnifies your existing lens by a factor of 4.5x. For example, when this auxiliary lens is attached to a 50mm lens, the lens will have an angle of view of a 225mm lens. This multicoated optical glass auxiliary lens attaches to the front of an existing lens with a 58mm filter thread. For lenses with a 52mm thread a step-up ring is included. Using this "auxiliary" telephoto lens is an economical alternative to buying expensive lenses.