GB548253A - Improvements in or relating to photographic objectives - Google Patents

Abstract

548,253. Lenses. KODAK, Ltd. (Eastman Kodak Co.). March 27, 1941, No. 4155. [Class 97 (i)] In a photographic objective having focal length F and consisting of two outer positive components and two inner meniscus components highly concave to a diaphragm between them, the third component is a cemented triplet having successive surfaces with radii R 6 ... R 9 , R 6 being negative and numerically between 0.3 F and 3 F, R 7 being positive and greater than 0.5 F, R 8 being positive and between 0.3 F and 3 F, and R 9 being negative and numerically between 0.25 F and 0.75 F; the refractive index of the middle element is at least 0.15 greater than that of the front element, and its dispersive index may be at least 20 less. The refractive index of the rear element of the triplet may be between those of the other elements, and the indices, from front to rear, may be, respectively, 1.46, 1.72 and 1.6. The radii of the surfaces of the first and second components may be, respectively, R, between 0.3 F and F, R, numerically greater than F and positive or negative, R 3 greater than 0.3 F and less than 0.6 F, and R 5 between 0.2 F and 0.5 F. The cemented surface of the second component may have a radius R, equal to infinity or - 3 F. Data for three examples are set out in the Specification. Specifications 548,252, 548,254, and 548,256 are referred to.