GB548256A - Improvements in or relating to photographic objectives - Google Patents

Abstract

548,256. Lenses. KODAK, Ltd. (Eastman Kodak Co.). March 27, 1941, No. 4158. [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 towards a diaphragm between them, the rear component is compound and has a cemented surface of radius R 10 between - 0.5 F and - 5 F, the refractive index of the element in front of it being at least 0.04 greater than that of the element behind it. The element in front of the surface may be positive and that behind it negative, the radius R 9 of the front surface of the positive element lying between 0.5 F and 5 F and the radius R 11 of the rear surface of the negative element being negative and numerically greater than 0.5 F. If the rear component is a doublet, the radii may be : R 9 between 0.6 F and F, R 10 between -0.75 F and -2 F, and R 11 numerically greater than R 10 , and the difference of refractive index may be at least 0.07. The refractive index of the element in front of the cemented surface may be greater than 1.7, and that of each of the other elements of the objective may be greater than 1.6. The ratio between the radii R 5 and Re, and between R, and R 9 , may be between <SP>2</SP>/ 5 and <SP>4</SP>/ 5 and preferably between ¢ and ¥, the signs associated with the radii being neglected. Complete data for two examples are set out in the Specification. Specifications 548,251, 548,252, 548,253, and 548,255 are referred to.