Spherical lenses are those in which both surfaces form the surface of a sphere. Depending on whether the curvature of the surface is convex, concave or planar (radius of an infinite circle), one can get convex, concave, plano-convex, negative meniscus and many other types of lenses. Most focusing systems use multiple lenses to correct for the aberrations in the final image.
Lenses can be used individually or as part of a focusing assembly including other lenses to create the right image and correct for aberrations or magnification. Lenses typically are coated with thin layers of dielectrics to generate the desired reflectivity and transmission.

Among the main areas of application for ball lenses are medical endoscopy and fiber optics. Ball lenses are extremely difficult to coat on both sides, however, lenses in fiber optics require a different coating on each side; as one side is typically matched to air while the other is matched to the fiber glass. Agniroth OPTIK specializes in the coating of even small ball lenses while providing a maximum clear aperture.