Aspheric lenses are any lenses whose surface angles and profiles are neither part of a sphere nor part of a cylinder. Conventional or non-aspheric lenses have the same curve across their entire surface, like a ping-pong ball. Aspheric lenses accomplish the same amount of refraction but are flatter and slimmer.
Aspheric lenses are commonly used in photography, as well as in eyeglasses and contact lenses. In the context of photography, the complex surface profiles of aspheric lenses can eliminate the distortion of certain types of lines, when compared to a conventional lens. A single aspheric lens sometimes has the ability to take the place of a more complex system of multiple lenses. This allows lens systems to be smaller and lighter, in addition to sometimes costing less.