Annular-aperture wide-field camera.
An annular-aperture wide-field camera, consisting of a spherical mirror and an annular aperture stop at its center of curvature (essentially a correctorless Schmidt camera), has been shown through analysis and laboratory tests to be a useful imaging device in the far and extreme UV, where the efficiencies of conventional refractive correctors and of reflective mirror coatings are relatively low.
Carruthers
G R
GR