Schwarz is a catoptric (i.e. containing only mirrors) system often used as a microscope objective. The system shows the use of reflective imaging surfaces, as well as the use of a star command to enter data for a common system. The Schwarzschild objective is a convex-concave mirror system in which the mirrors are approximately concentric, with the long conjugate on the convex mirror side. Originally intended as a microscope objective, the design is widely used in a variety of two-mirror relay systems. The archetype Schwarzschild system can be designed analytically (there is a star command *schwarz that does this), but for practical use, variations are usually required. The design included here is a basic system designed using the *schwarz star command. The ray analysis below shows that the third-order spherical and coma aberrations are corrected, but there is high-order over-corrected spherical. This can be corrected by perturbing the design. Also, the obscuration can be decreased, usually at the expense of increased coma.
