The optical difference is that a Schmidt uses a concave spherical mirror and a 'flat' correcting lens but the result is that at the focus, the image plane is strongly curved, requiring that the film be bent to cancil out the center to edge distortion. This is a photographic instrument only. The Maksutov design has a spherical primary mirror and a secondary mirror and correcting lens that are also spherical surfaces. Maksutovs, unlike Schmidts, can be used as visual instruments. As photographic instruments, I believe that Schmidts are superior because they have no coma, no spherical aberration and only slight astigmatism and chromatic aberration.