GB696902A - Improvements relating to optical lenses - Google Patents

Abstract

696,902. Optical objective. WRAY (OPTICAL WORKS), Ltd., and WYNNE, C. G. Oct. 12, 1951 [July 15, 1950], No. 17752/50. Class 97 (i). An objective of a relative aperture of f/1.0 or larger comprises a convergent front part, an intermediate compound meniscus convex towards the front and a convergent rear part having a front surface convex to the front, the front part consists of at least two convergent components one of which is a meniscus doublet convex towards the front and formed of a convergent element and a divergent element, the former of which has a refractive index not less than 0.04 lower than that of the divergent element, the intermediate compound meniscus has an axial thickness greater than 0.4 of the focal length f of the objective and is formed of a convergent element and a divergent element, the former of which has a refractive index not less than 0.04 lower than that of the divergent element, and the convergent rear part has a total axial thickness greater than 0.35f; the convergent front part and the intermediate compound meniscus up to but not including its rear surface is substantially corrected for spherical aberration and coma, the uncorrected field curvature and astigmatism of that forward part of the lens is corrected by selecting the curvatures and positions of the rear surface of the intermediate compound meniscus and of the front surface of the rear convergent part and the resulting loss of convergence is substantially restored by providing the rear convergent part with a rear surface of a larger radius of curvature and placed not more than one-tenth of the focal length away from the focal plane. Optical data are given for the objective shown. The total axial thickness of the convergent front part, which consists of the lens A and doublet B1, B2 is preferably greater than 0.35F. Preferably also, the radius of curvature r8 of the rear surface of the intermediate compound meniscus C1, C2 is greater than that of the front surface r9 of the convergence rear part D1, D2 and r8 may lie between 0.5 and 0.33 of the distance lc between that surface and the point P at which a paraxial ray PR intersects the optical axis. The convergent elements in the objective may be made of a rare earth oxide glass having a refractive index not less than 1.65 and an AbbÚ value not less than 40, the divergent elements of the convergent front part and of the meniscus doublet preferably being made of an extra dense flint glass having a refractive index not less than 1.65 and an AbbÚ number less than 35.