Improvements relating to optical systems comprising a concave spherical mirror and a meniscus-shaped correcting lens

摘要

804,769. Optical systems. OPTISCHE INDUSTRIE DE OUDE DELFT N.V. Jan. 4, 1957 [Jan. 6, 1956], No. 485/57. Class 97(1) An optical system corrected for spherical aberration comprises a concave mirror and a meniscus shaped correcting lens having spherical external surfaces whose centres of curvature lie near that of the mirror and which is formed of a positive and negative element cemented together, the positive element having a refractive index at least 0.05 higher than that of the negative element and the radius being such that the internal surface is transversed approximately perpendicularly by rays from an axial object point whilst an image of the centre of curvation of one external surface of the meniscus lens is formed by the internal surface at a position situated at or near the centre of curvature of the other external surface. Further correction for spherical aberration can be achieved by adding to the system a conical lens as described in Specification 732,427 whilst correction of the slight chromatic aberration present can be effected by adding to the system a colour correction plate as described in Specification 784,435. Numerical data are given for one example of the system shown which comprises a colour correction plate 16, a'meniscus correcting lens 13 and a concave mirror 15 which forms an image at 17 after reflection in a plane mirror 14. Numerical data are also given for one example of a system, as in Fig. 5, in which the plate 16 and mirror 14 are omitted, and for one example of such a modified system in which the meniscus lens 13 is concave towards the concave mirror 15. Specification 637,645 also is referred to.