GB690405A - Improvements in or relating to optical objectives - Google Patents

Abstract

690,405. Optical objectives. COOK, G. H., and TAYLOR, TAYLOR, & HOBSON, Ltd. Jan. 30, 1952 [Feb. 15, 1951], No. 3685/51. Class 97 (i). In an objective corrected to cover a semiangular field not greater than 30 degrees and comprising two convergent simple components located between two divergent doublet components each having an outer convergent element and an inner divergent element, all four components being meniscii concave towards a diaphragm between the two simple components, the Petzval curvature of the objective is between 0.08 and 0.16 times the equivalent optical power of the objective, and the arithmetic mean between the curvatures of the internal contacts (cemented or broken) in the doublets (a curvature being reckoned for this purpose as positive when the surface is concave towards the diaphragm) is less than 3.5 times the equivalent optical power of the objective and is greater than 2(10x-1)/(10x+1) times such equivalent power, where x is the positive value of the difference between the arithmetic mean of the mean refractive indices of the materials of the convergent elements of the two doublets, and the arithmetic mean of the mean refractive indices of the materials of the two divergent elements. Numerical data are given for five examples of the objective shown, for one example in which the contact R9 of the rear doublet is broken, and for one example in which the contacts R2, R9 are both convex to the diaphragm. Specification. 690,404 is referred to.