Volk 20D lens, Double Aspheric, Yellow Tinted, Perfect Condition, Made In USA.

As the name suggests, an aspheric lens is a lens with a shape other than that of a regular sphere or cylinder. These lenses, which come in a variety of shapes, are used to correct spherical aberration and enhance image quality. Spherical aberration is a type of defect that occurs when light passes through a spherical lens. Depending on how close to the edge it enters the lens, light focuses at different distances, creating a blurry image. In comparison, aspheric lenses focus light to a single point, regardless of where the light enters, to reduce or entirely eliminate blurriness from the image.