Color corrected optical system containing a concave spherical mirror and a meniscus lens

Claim 1

AN OPTICAL SYSTEM COMPRISING A CONCAVE SPHERICAL MIRROR AND A COMPOUND SPHERICAL ABERRATION CORRECTING MENISCUS LENS OF NEGATIVE POWER IN OPERATIVE OPTICAL ALIGNMENT AXIALLY AIR SPACED FROM SAID MIRROR AND HAVING ITS CONCAVE SIDE TURNED TOWARDS THE CENTER OF CURVATURE OF SAID MIRROR, A COLOR CORRECTION PLATE HAVING PLANE EXTERNAL SURFACES AND AN INTERNAL SPHERICAL SURFACE LOCATED SUBSTANTIALLY AT THE CENTER OF CURVATURE OF SAID MIRROR, SAID INTERNAL SURFACE SEPARATING MATERIALS HAVING SUBSTANTIALLY EQUAL REFRACTIVE INDICES FOR LIGHT OF AN INTERMEDIATE WAVE-LENGTH BUT DIFFERING IN DISPERSION, WHEREBY SAID SYSTEM IS ACHROMATIZED FOR LONG FOCAL LENGTH, SAID MENISCUS LENS BEING A DOUBLET HAVING A SPHERICAL INTERNAL SURFACE WHOSE RADIUS OF CURVATURE IS SUBSTANTIALLY GREATER THAN THE RADII OF CURVATURE OF ITS EXTERNAL SURFACES, SAID INTERNAL SURFACE OF SAID MENISCUS LENS SEPARATING MATERIALS OF SUBSTANTIALLY EQUAL REFRACTIVE INDICES FOR LIGHT OF AN INTERMEDIATE WAVE-LENGTH BUT DIFFERING IN DISPERSION.