Variable focal length lens system

Claim 2

A highly efficient variable focal length lens system composed of seven lenses divided in two groups, the first group nearest the object consisting of three lenses forming a negative lens and the second group nearest the image consisting of the remaining four lenses and forming a positive lens, said first group of said lenses including in succession in the direction from the object to the image a first lens L1 in the form of a negative meniscus lens concave to the image side of said lens system, a second negative lens L2 of which both surfaces are concave, and a third lens L3 in the form of a positive double convex lens with the more convex surface directed toward the object, said second group of said lenses including in succession in the direction from the object to the image a fourth lens L4 in the form of a positive double convex lens, a fifth lens L5 in the form of a positive meniscus lens concave to the image, a sixth lens L6 in the form of a thick negative lens, and a seventh lens L7 in the form of a positive lens, the spacing between said first group and said second group being variable.

Claim 3

The lens system of claim 1 wherein __________________________________________________________________________ F = 36 - 68.5 F.sub.1 = -72.18 Radius of Lens Thickness Refractive Abbe's Lens Curvature r or Distance d Index n No. ν __________________________________________________________________________ r.sub.1 = 61.498 L.sub.1 d.sub.1 = 1.98 n.sub.1 = 1.81600 ν.sub.1 = 46.8 r.sub.2 = 28.292 d.sub.2 = 10.19 r.sub.3 = -115.896 L.sub.2 d.sub.3 = 1.4 n.sub.2 = 1.69680 ν.sub.2 = 56.5 r.sub.4 = 77.925 d.sub.4 = 3.3 r.sub.5 = 54.580 L.sub.3 d.sub.5 = 5.01 n.sub.3 = 1.77551 ν.sub.3 = 37.8 r.sub.6 = - 1879.350 d.sub.6 = 45.989 -0.782 r.sub.7 = 54.200 L.sub.4 d.sub.7 = 4.99 n.sub.4 = 1.69680 ν.sub.4 = 56.5 r.sub.8 = -159.222 d.sub.8 = 2.00 r.sub.9 = 35.335 L.sub.5 d.sub.9 = 6.49 n.sub.5 = 1.81600 ν.sub.5 = 46.8 r.sub.10 = 81.154 d.sub.10 = 2.60 r.sub.11 = -131.435 L.sub.6 d.sub.11 = 13.24 n.sub.6 = 1.80518 ν.sub.6 = 25.4 r.sub.12 = 26.491 d.sub.12 = 4.19 r.sub.13 = 99.329 L.sub.7 d.sub.13 = 3.80 n.sub.7 = 1.75700 ν.sub.7 = 47.9 r.sub.14 = -48.129. __________________________________________________________________________

Claim 4

The lens system of claim 1 wherein __________________________________________________________________________ F = 36 - 68.5 F.sub.1 = -73.78 Radius of Lens Thickness Refractive Abbe's Lens Curvature r or Distance d Index n No. ν __________________________________________________________________________ r.sub.1 = 71.093 L.sub.1 d.sub.1 = 1.98 n.sub.1 = 1.75700 ν.sub.1 = 47.9 r.sub.2 = 28.420 d.sub.2 = 9.85 r.sub.3 = -119.378 L.sub.2 d.sub.3 = 1.40 n.sub.2 = 1.69350 ν.sub.2 = 50.8 r.sub.4 = 79.402 d.sub.4 = 3.21 r.sub.5 = 54.563 L.sub.3 d.sub.5 = 4.99 n.sub.3 = 1.77551 ν.sub.3 = 37.8 r.sub.6 = - 1111.494 d.sub.6 = 47.085 -0.784 r.sub.7 = 52.129 L.sub.4 d.sub.7 = 5.0 n.sub.4 = 1.72600 ν.sub.4 = 53.6 r.sub.8 = -187.526 d.sub.8 = 2.0 r.sub.9 = 35.850 L.sub.5 d.sub.9 = 6.41 n.sub.5 = 1.79500 ν.sub.5 = 45.2 r.sub.10 = 83.058 d.sub.10 = 2.59 r.sub.11 = -122.606 L.sub.6 d.sub.11 = 13.33 n.sub.6 =1.80518 ν.sub.6 = 25.4 r.sub.12 = 26.523 d.sub.12 = 3.78 r.sub.13 = 101.957 L.sub.7 d.sub.13 = 3.80 n.sub.7 = 1.75700 ν.sub.7 = 47.9 r.sub.14 = -47.120 __________________________________________________________________________