GB1432641A - Wide angle lenses - Google Patents

Abstract

1432641 Wide angle objective lens CANON KK 4 July 1973 [4 July 1972] 31966/73 Heading G2J A large aperture wide angle objective lens of retro-focus type, of focal length f, has one refracting surface of a lens to the rear of the diaphragm aspheric, satisfying the equation. where the X-axis is the optical axis of the lens, the Y-axis is normal to the optical axis, B, C, D, E..... are constants, and Ri is the paraxial curvature radius at the principal point of the aspheric surface. The lens also satisfies: B (Ni<SP>1</SP> - Ni) < O, and C(Ni<SP>1</SP> - Ni)< O where Ni<SP>1</SP> and Ni are the refractive indices respectively of the media to the front and to the rear of the aspheric surface. The lens system also satisfies the following:- wherein Ni<SP>1</SP> represents reflective index of the medium to the rear of the aspheric surface and Ni represents refractive index to the front. As disclosed, the objective has three lens groups I, II, III. Group I is negative and comprises in order, a meniscus concave lens, a convex lens, and a meniscus concave lens which may be compound. Group II is positive and comprises a biconvex lens, which may be compound, and a concave lens, in either order. Group III is positive and comprises a compound meniscus concave lens having negative and positive lens elements, and whose rear surface is aspheric and two convex lenses. The embodiments satisfy where L is the total length of the objective, and f I , f II , f III are the focal lengths of groups I, II, III respectively, and also:- where R I convex and R II convex, are the curvature radii on the image side of the convex lenses of groups I and II respectively. Optical data are provided for four examples.