Wide angle reading lens system

Claim 2

A wide-angle reading lens system which comprises, in order from the object side, a first lens element which is a negative meniscus lens having its convex surface directed toward the object side, a second lens element which is a positive lens having a strong convex surface directed toward the object side, a third lens element which is a negative lens, and a fourth lens element which is a positive lens having a strong convex surface directed toward the image side, said lens system satisfying the following conditions: -2.0f≦f.sub.1 ≦-0.75f (1) ##EQU3## d.sub.1-7 ≦0.85f (3) where f denotes the overall focal length of the system; f 1 is the focal length of the first lens element; n i is the refractive index of an ith lens at the d-line; ν i is the abbe number of the ith lens; and d 1-7 signifies the distance from the surface of the first lens element on the object side to the surface of the fourth lens element on the image side.

Claim 3

The system according to claim 1 which further satisfies the following additional conditions: d.sub.2 ≦0.20f (4) 0.3f≦r.sub.3 ≦0.8f (5) n.sub.1 <1.60 (6) ν.sub.3 <30 (7) where d 2 signifies the aerial distance between the first and the second lens elements, and r 3 is the curvature of radius of the surface of the second lens element on the object side.

Claim 4

The system according to claim 1 which further satisfies the following chart: ______________________________________ f = 100.0 F.sub.NO = 1:5.6 M = -0.12 × ______________________________________ Surface No. r d n ν ______________________________________ 1 61.778 7.04 1.51633 64.1 2 33.566 15.08 3 41.283 10.64 1.77250 49.7 4 -939.456 9.98 5 -120.137 6.34 1.80518 25.4 6 49.507 6.99 7 206.799 16.34 1.77250 49.7 8 -57.608 93.80 9 ∞ 4.93 cover glass 10 ∞ ______________________________________ f.sub.1 = -155.74 d.sub.1-7 = where f signifies the overall focal length of the lens system, F NO is the aperture ratio, M is the magnification, r is the curvature of radius of an individual lens surface, d is the thickness of an individual lens or the aerial distance between lenses, n is the refractive index of an individual lens at the d-line, and ν is the Abbe number of an individual lens.

Claim 5

The system according to claim 1 which further satisfies the following chart: ______________________________________ f = 100.0 F.sub.NO = 1:5.6 M = -0.112 × ______________________________________ Surface No. r d n ν ______________________________________ 1 72.805 8.11 1.51633 64.1 2 30.179 14.35 3 50.442 14.67 1.77250 49.7 4 -159.578 7.21 5 -81.889 8.11 1.80518 25.4 6 73.776 2.89 7 -485.667 15.98 1.77250 49.7 8 -42.859 109.90 9 ∞ 6.31 cover glass 10 ∞ ______________________________________ f.sub.1 = -106.746 d.sub.1-7 = 71.317 ______________________________________ where f signifies the overall focal length of the lens system, F NO is the aperture ratio, M is the magnification, r is the curvature of radius of an individual lens surface, d is the thickness of an individual lens or the aerial distance between lenses, n is the refractive index of an individual lens at the d-line, and ν is the Abbe number of an individual lens.

Claim 6

The system according to claim 1 which further satisfies the following chart: ______________________________________ f = 100.0 F.sub.NO = 1:4.5 M = -0.112 × ______________________________________ Surface No. r d n ν ______________________________________ 1 75.126 8.08 1.51633 64.1 2 35.907 13.38 3 52.334 12.93 1.80400 46.6 4 -224.991 7.18 5 -58.483 8.08 1.80518 25.4 6 82.585 1.71 7 -1141.508 17.24 1.80400 46.6 8 -42.253 106.70 9 ∞ 6.28 cover glass 10 ∞ ______________________________________ f.sub.1 = -143.260 d.sub.1-7 = 68.582 ______________________________________ where f signifies the overall focal length of the lens system, F NO is the aperture ratio, M is the magnification, r is the curvature of radius of an individual lens surface, d is the thickness of an individual lens or the aerial distance between lenses, n is the refractive index of an individual lens at the d-line, and ν is the Abbe number of an individual lens.

Claim 7

The system according to claim 1 which further satisfies the following chart: ______________________________________ f = 100.0 F.sub.NO = 1:5.0 M = -0.112 × ______________________________________ Surface No. r d n ν ______________________________________ 1 40.567 10.09 1.48749 70.1 2 23.822 13.65 3 59.624 12.60 1.79952 42.2 4 -138.198 6.02 5 -83.782 4.04 1.84666 23.9 6 83.782 2.02 7 -114.198 17.97 1.77250 49.7 8 -36.178 110.40 9 ∞ 2.83 cover glass 10 ∞ ______________________________________ f.sub.1 = -147.541 d.sub.1-7 = 66.379 ______________________________________ where f signifies the overall focal length of the lens system, F NO is the aperture ratio, M is the magnification, r is the curvature of radius of an individual lens surface, d is the thickness of an individual lens or the aerial distance between lenses, n is the refractive index of an individual lens at the d-line, and ν is the Abbe number of an individual lens.

Claim 8

The system according to claim 1 which further satisfies the following chart: ______________________________________ f = 100.0 F.sub.NO = 1:4.5 M = -0.112 × ______________________________________ Surface No. r d n ν ______________________________________ 1 53.917 8.09 1.49186 57.4 2 29.100 15.50 3 62.324 12.09 1.83481 42.7 4 -199.026 7.19 5 -71.520 8.09 1.80518 25.4 6 89.391 2.06 7 -228.900 15.74 1.80400 46.6 8 -40.249 110.09 9 ∞ 6.29 cover glass 10 ∞ ______________________________________ f.sub.1 = -144.015 d.sub.1-7 = 68.768 ______________________________________ where f signifies the overall focal length of the lens system, F NO is the aperture ratio, M is the magnification, r is the curvature of radius of an individual lens surface, d is the thickness of an individual lens or the aerial distance between lenses, n is the refractive index of an individual lens at the d-line, and ν is the Abbe number of an individual lens.