Retrofocus type wide angle photographic lens

Abstract

Abstract PURPOSE: To simplify the constitution while maintaining the back focus Bf of more than focal length (f), angle of view of 60° or more, and F-number of 2.0W1.8, by requiring special conditions in the specifications of each lens in five group constitution. CONSTITUTION: The lens system consists of, sequentially from the object side, the first group L 1 of negative meniscus lens with the convex side directed to the object side, the second group L 2 of biconvex positive lens, the third group L 3 of biconcave negative lens, the fourth group L 4 of positive meniscus lens with the convex side directed to the image side, and the fifth group L 5 of biconvex positive lens. Supposing (f) as the composite focal length of the entire system, R as the radius of curvature each lens plane, (d) as the central interval of each lens plane, and subscripts as the sequence of group numbers from the object side, conditions (1)W(5) are satisfied. Besides, when the fifth group is divided into two positive lenses, a large aperture ratio of F-number 1.8 may be possible, and the focusing may be possible by moving the positive lenses integrally, or by moving only the one at the object side. COPYRIGHT: (C)1980,JPO&Japio

Inventors

• 👤 Yukio Mori

Bibliographic Details