Catadioptric system with a gradient-index corrector plate

Sands showed the equivalence of the third-order aspheric surface contribution of the aberration polynomial to the third-order inhomogenous surface contribution. This fact is exemplified by the substitution of an axial gradient for the aspheric surface of the Schmidt corrector plate. It is shown that a gradient-index corrector plate system is limited in its off-axis performance by fifth-order oblique spherical aberration just as the conventional Schmidt system is.