Lens system

A lens system comprising:

• a primary mirror having a spherical reflecting surface;
• a secondary mirror having a spherical reflecting surface and being arranged to receive light reflected from said primary mirror, said primary and secondary mirrors having a common center of curvature;
• image receiving means situated on or adjacent to the focal plane of a mirror system defined by said primary and secondary mirrors;
• and
• optical relay means comprising a spherical mirror having a curvature and operable to perform a focusing function and a plurality of corrector elements located on the incident side of said spherical mirror, each of said corrector elements having surfaces concentric with said curvature of said spherical mirror and being operable to correct for spherical aberration and chromatic aberration induced by at least one of said corrector elements and said spherical mirror.

A lens system comprising:

• a primary mirror having a spherical reflective surface;
• a secondary mirror having a spherical reflecting surface and being arranged to receive light reflected from said primary mirror, said primary and secondary mirrors having a common center of curvature;
• image receiving means situated on or adjacent to the focal plane of a mirror system defined by said primary and secondary mirrors;
• and
• optical relay means comprising a spherical reflecting surface, optical correcting means located on the incident side of said spherical reflecting surface and being operable to correct for primary spherical aberration, said optical correcting means comprising refractive elements having surfaces concentric with said spherical reflecting surface, said spherical reflecting surface and said refractive elements being symmetrical about a common axis of symmetry.