Hans Wolter - a pioneer of applied optics
  Applied optics was one of the major topics Hans Walter was engaged in during his scientific life. He contributed to the understanding of optical properties of thin films, which could be used to design coating layers to improve the properties of optical and other surfaces. He developed the theoretical description of the basic principles of phase-contrast, schlieren and interference optics applied to enhance low contrast details and to increase the resolution in studies of biological samples. And last, but not least, Hans Wolter proposed an optical system of two grazing--incidence mirrors for use in an X--ray imaging microscope. A microscope using such an optics never was put into practice, but the optical design turned out to be well suited for telescopes. 
Andreas Schrimpf
physics.hist-ph