Dave Evans , Jun 06, 1999; 05:29 a.m.
Spherical lenses have surfaces, which are defined by the radius of a given sphere. They are relatively easy to manufacture using equipment, which can generate that consistent curve on the surface of the lens through grinding and polishing.
Aspheric lenses have a surface curve, which is not spherical. They are usually made up of a series of convex and concave curves. These lenses are difficult to make via grinding and polishing. Today most of them are made through a molding process.
One aspheric lens can often take the place of three spherical lenses in a lens design, saving weight and space. They can also be used to reduce certain kinds of distortion.