GB559228A - Improvements in or relating to telephoto objectives - Google Patents

Abstract

559,228. Telephoto objectives. KODAK, Ltd. June 1, 1942, No. 15314/43. Convention date, Aug. 28, 1941. Divided out of 559,203. [Class 97 (i)] The rear, negative, member of a telephoto objective having a compound, positive, front member, comprises a negative element and a positive element, the refractive index of the negative element exceeding that of the positive element by at least .05, and the sum of the dispersive index of the negative element plus 200 times its refractive index exceeding the sum of these quantities for the positive element by at least 28. The front member may comprise more than two elements and include a negative element cemented to the front of a positive element, the refractive index of each negative element thereof exceeding that of each positive element by more than .05; the rear member may be meniscus and be spaced from the rear principal point of the front member by more than the axial thickness of either member and by less than .85 times the focal length of the front member, the focal length of the rear member being numerically less than 1.05 times that of the front member. The front member may consist of an element of one sign cemented between two elements of the opposite sign, and the Figure shows a front member consisting of a positive element 2 cemented between two negative elements 1, 3, wherein the sum of the dispersive index of the positive element plus 60 times its refractive index exceeds the sum of the average of the dispersive indices of the negative elements plus 20 times their average refractive index by less than 78. Complete data for this and another example are included in the Specification. Specification 559,203 is referred to.