The chapter deals with main optical properties of Schwarzschild and Head objectives from the point view of geometrical
optics. General approach in the study can be applied to both XUV and visible/IR optical instrumentation.
Igor A. Artyukov, Igor A. Artyukov,
"Schwarzschild objective and similar two-mirror systems", Proc. SPIE 8678, Short-Wavelength Imaging and Spectroscopy Sources, 86780A (11 December 2012); doi: 10.1117/12.2002118; https://doi.org/10.1117/12.2002118