title: Dummy lens for the computer optimization of autostigmatic null correctors.
abstract: The computer optimization of an autostigmatic null corrector can be simplified by using a plano-convex lens as a dummy element. The lens is placed in contact with the aspheric surface and rays traced from star space. The exact shape of the convex surface is found parametrically for an arbitrary aspheric surface or as an accurate approximation for a conicoid with a focal ratio >2; in the latter case the refractive index of the lens must be 2 regardless of the wavelength that we use.
authors.forename: J E
authors.initials: JE
authors.lastname: Landgrave
authors.forename: J R
authors.initials: JR
authors.lastname: Moya