Lens is a curved piece of ground and polished or molded material, usual glass, used for the refraction of light. It always consist of one or more pieces of optical glass with surfaces curved (always spherical) that they serve to converge or diverge the transmitted rays from an object, thus forming a real or virtual image of that object. The application range from the simple collection of the scanning of laser beams to precise imaging and image transfer. Lenses are classified as singlet lenses, cylindrical lenses and achromatic lenses according to their different applications.