Continuously-variable-magnification afocal lens system

Claim 1

A continuously-variable-magnification afocal lens system comprising four lens group, a first group consisting of a cemented lens element consisting of a negative meniscus lens and a biconvex lens and a positive lens element, a second group consisting of a biconcave lens element and a cemented lens consisting of a biconcave lens and a positive meniscus lens, a third group consisting of a biconcave lens element, a fourth group consisting of a biconvex lens element, said lenses satisfying the following relations: r1 83.5 d1 2.0 n1 1.74077 V1 27.7 r2 30.0 d2 5.5 n2 1.60738 V2 56.7 r3 -940.0 d3 0.2 r4 34.5 d4 4.4 n3 1.51742 V3 52.2 r5 1100.0 d5 variable as mentioned below. r6 -65.8 d6 1.5 n4 1.74400 V4 44.9 r7 17.5 d7 2.5 r8 -78.0 d8 1.0 n5 1.69350 V5 53.4 r9 10.2 d9 4.0 n6 1.74077 V6 27.7 r10 102.8 d10 variable as mentioned below. r11 -98.0 d11 1.8 n7 1.78472 V7 25.7 r12 98.0 d12 variable as mentioned below. r13 41.8 d13 1.8 n8 1.69350 V8 53.4 r14 -41.8 d5 d10 d12 magnification shortest: 2.17 22.82 1.65 0.472 medium: 16.14 5.02 5.48 1.000 longest: 24.83 0.98 0.83 2.016 Where r with a numeral subscript indicates the radius of curvature of a surface identified by the subscript; d with a numerical subscript indicates the thickness of a lens or the distance of the air space along the optical axis identified by the subscript; n with a numerical subscript indicates the refractive index of a lens element identified by the subscript, the lenses being numbered consecutively from the front to the rear; and V with a numerical subscript indicates the reciprocal of the dispersive power of a lens identified by the subscript, the refractive index as well as the dispersive power being measured with the d-line of helium.