Compact zoom lens

Claim 2

A compact zoom lens comprising: a first lens group which has a positive refractive power and consists of a positive lens formed by joining a negative lens and a positive lens together and a positive meniscus lens, the first lens group being movable for focusing; a second lens group which has a negative refractive power and is disposed in the rear of the first lens group on the axis thereof, the second lens group consisting of a negative lens and another negative lens formed by joining a negative lens and a positive lens together, the second lens group being movable for variation; a third lens group which has a positive refractive power and is disposed in the rear of the second group on the axis thereof, the third group consisting of a positive lens formed by joining a negative lens and a positive lens together, the third lens group being movable for compensation concurrently with the second lens group, the locus of the movement of the third group being in a concave shape as viewed from the side of an photographing object; and an image forming lens group which has a positive refractive power and is disposed in the rear of the third lens group on the axis thereof, the image forming lens group consisting of a front sub-group and a rear sub-group, the front sub-group having a positive refractive power and being composed of two positive lenses each having a convex face on the object side and a negative lens being disposed apart from these two lenses on their axis, the rear sub-group being composed of a positive lens, a negative lens having a concave face on the object side; and a positive lens having a convex face on the object side.

Claim 3

A compact zoom lens according to claim 1 wherein the positive lens disposed on the image side in the front sub-group and the negative lens in the same sub-group are spaced on the axis thereof at an interval of more than 0.070 time and less than 0.091 times the focal length of said image forming lens group.

Claim 4

A compact zoom lens according to claim 1 wherein the focal length of said front sub-group is more than 0.95 times and less than 1.05 times the focal length of said image forming lens group.

Claim 5

A compact zoom lens according to claim 1 wherein the composite focal length of the two positive lenses in said front sub-group is more than 0.50 times and less than 0.59 times the focal length of said image forming lens group.

Claim 6

A compact zoom lens according to claim 1 wherein one of the two positive lenses in said front sub-group is formed by joining a negative meniscus lens and a positive meniscus lens together.

Claim 7

A compact zoom lens according to claim 1 wherein said front sub-group consists of two positive miniscus lenses having their convex faces directed to the object and a biconcave lens disposed apart from these two lenses on the axis thereof; and said rear sub-group consists of a biconvex lens, a negative lens which has a concave face directed to the object and the radius of curvature of its lens face on the object side of the object is less than the radius of curvature of its face on the image side and a positive lens which has a convex face directed to the object.

Claim 8

A compact zoom lens according to claim 6 wherein the positive meniscus lens of said front sub-group disposed nearer to the image is formed by joining a negative meniscus lens and a positive meniscus lens together.

Claim 9

A compact zoom lens according to claim 6 wherein: f = 71.4 - 195.99 F1:4.0 ______________________________________ No. r d vd nd ______________________________________ 1 285.967 3.00 25.4 1.80518 2 96.160 7.65 61.1 1.58913 3 -222.868 0.10 1. 4 84.085 5.04 61.1 1.58913 5 495.029 d.sub.5 = variable 1. 6 -331.765 1.40 53.9 1.71300 7 55.672 3.27 1. 8 -70.157 1.40 53.9 1.71300 9 37.045 3.85 25.4 1.80518 10 271.395 d.sub.10 = variable 1. 11 93.287 1.60 33.8 1.64769 12 32.468 5.82 61.1 1.58913 13 -142.576 d.sub.13 = variable 1. 14 38.375 5.96 64.1 1.51633 15 165.946 0.85 1. 16 44.267 2.77 64.1 1.51633 17 76.858 10.57 1. 18 3072.885 1.78 28.3 1.74000 19 83.148 29.87 1. 20 193.897 3.11 49.3 1.60729 21 -82.538 5.65 1. 22 -24.269 1.95 50.9 1.65844 23 -435.335 0.06 1. 24 68.442 3.71 49.3 1.60729 25 -149.072 41.91 1. ______________________________________ Variable distance: f 71.40 118.29 195.99 d.sub.5 3.23 28.19 43.26 d.sub.10 41.54 26.47 1.51 d.sub.13 12.00 2.11 12.00 ______________________________________

Claim 10

in the above table, r representing the radius of lens face curvature; d either lens thickness or an air gap; and vd and Abbe's number; and nd a refractive index.

Claim 11

in the above table, r representing the radius of lens face curvature; d either lens thickness or an air gap; and vd and Abbe's number; and nd a refractive index.

Claim 12

A compact zoom lens according to claim 6 wherein: f = 81.00 - 194.44 F1:4.0 ______________________________________ No. r d vd nd ______________________________________ 1 299.582 3.00 25.4 1.80518 2 99.340 6.40 61.1 1.58913 3 -223.035 0.10 1. 4 85.752 4.89 61.1 1.58913 5 535.718 d.sub.5 =variable 1. 6 -303.748 1.60 53.9 1.71300 7 58.079 2.97 1. 8 -74.086 1.60 53.9 1.71300 9 39.082 4.19 25.4 1.80518 10 321.421 d.sub.10 =variable 1. 11 102.994 1.60 33.8 1.64769 12 35.328 6.44 61.1 1.58913 13 -129.625 d.sub.13 =variable 1. 14 38.933 4.44 64.1 1.51633 15 196.503 0.20 1. 16 50.668 2.52 64.1 1.51633 17 88.204 9.11 1. 18 -649.191 9.79 28.3 1.74000 19 87.775 30.01 1. 20 150.725 3.36 49.3 1.60729 21 -65.259 3.59 1. 22 -26.416 1.50 53.3 1.69350 23 223.506 0.10 1. 24 62.316 3.97 49.3 1.60729 25 -144.433 1. ______________________________________ Variable distance: f 81.00 126.00 194.44 d.sub.5 3.540 25.760 39.840 d.sub.10 37.346 23.061 1.332 d.sub.13 12.000 4.065 11.713 in the above table, r representing the radius of lens face curvature; d either lens thickness or an air gap; vd an Abbe's number; and nd a refractive index.

Claim 13

A compact zoom lens according to claim 6 wherein: f = 81.01 - 194.46 F1:4.0 ______________________________________ No. r d vd nd ______________________________________ 1 302.521 3. 25.4 1.80518 2 99.734 6.034 61.1 1.58913 3 -276.288 0.1 1. 4 87.859 4.89 61.1 1.58913 5 1521.034 d.sub.5 =variable 1. 6 -249.143 1.6 53.9 1.713 7 58.335 2.97 1. 8 -75.382 1.6 53.9 1.713 9 40.008 4.19 25.4 1.80518 10 370.374 d.sub.10 =variable 1. 11 104.198 1.6 33.8 1.64769 12 36.579 6.44 61.1 1.58913 13 -129.164 d.sub.13 =variable 1. 14 36.673 6.94 64.1 1.51633 15 188.364 0.6 1. 16 54.993 1.46 33.8 1.64769 ra 31.252 3.85 53.6 1.54739 17 144.658 8.71 1. 18 -158.414 2.39 40.9 1.80610 19 114.916 33.17 1. 20 388.587 2.42 49.3 1.60729 21 -95.805 4.48 1. 22 -24.88 1.32 57.0 1.6228 23 -60.604 0.3 1. 24 49.996 2.95 53.6 1.54739 25 126.851 1. ______________________________________ f 81.01 126.01 194.46 d.sub.5 3.923 26.143 40.223 d.sub.10 37.211 22.925 1.196 d.sub.13 12.000 4.065 11.714 ______________________________________ in the above table, r representing the radius of lens face curvature; d either lens thickness or an air gap; vd an Abbe's number; and nd a refractive index.