GB559203A - Improvements in or relating to telephoto objectives - Google Patents

Abstract

559,203. Telephoto objectives. KODAK, Ltd. June 1, 1942, No. 7391. Convention date, Aug. 28, 1941. [Class 97 (i)] The front, positive member of a telephoto objective comprises more than two elements and includes 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 0.05 ; the rear member is meniscus, and is spaced from the rear principal point of the front member by more than the axial thickness of either member and by less than 0.85 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 opposite sign, or of two cemented doublets of which the front one is composed of a negative element in front of a positive element and the rear one of a positive element in front of a negative element. Desirable relations between refractive and dispersive indices are set out. The Figure shows a front member consisting of a negative element II cemented between positive elements I, III and of a single element IV. The rear member consists of a front negative element V cemented to a positive element VI. Complete data for this and two other examples are included in the Specification. Specification 559,228 is referred to.