The caustic surface, which is the locus of the sagittal and tangential focal points for general skew rays, is shown to be given by the Coddington equations for the special case of meridional rays reflected or refracted by a spherical surface.
© 1976 Optical Society of America
David L. Shealy, "Caustic surface and the Coddington equations," J. Opt. Soc. Am. 66, 76-77 (1976)