ABSTRACT
All optical components are bound by the combination of plane and curved surfaces. Due to ease of fabrication, the curved surfaces are spherical, though nonspherical and free-form surfaces are gaining importance in some sophisticated designs. The spherical surfaces need to be produced with tight tolerances on the surface curvature. The measurement of radius of curvature and focal length of lenses and mirrors is a very important activity in the production environment. For a concave surface, two positions can be found that give the point image on retro-reflection. The separation between these positions is the radius of curvature of the surface. For making measurement on the convex surface, an additional lens is required that must have focal length larger than the radius of curvature of the surface being measured. Gerchman and Hunter presented a method to measure long radius of curvature in which a cavity is formed between the concave surface under test and a plane surface.
