Zoom lens system

Claim 2

A zoom lens system comprising a first fixed lens group, a first movable lens group, a second movable lens group and a second fixed lens group arranged in this order from front to rear, wherein a stop is located at the center of the whole lens system and the first fixed lens group and the second fixed lens group are located symmetrically with respect to the stop, and the first movable lens group and the second movable lens group are located symmetrically with respect to the stop, and the first movable lens and the second movable lens are asymmetrically moved with respect to the stop when the magnification of the system is varied.

Claim 3

A zoom lens system as defined in claim 1 wherein the structure of said first fixed and movable lens group is the same as that of said second fixed and movable lens groups, respectively.

Claim 4

A zoom lens system as defined in claim 1 wherein the focal length of said lens system f 1 .0 when the magnification is unity and the focal length of the movable lens group f v satisfy the condition of 2.0<f.sub. 1.0 /|f v |< 3.0.

Claim 5

A zoom lens system as defined in claim 1 having the following constructional data wherein the radii of curvature of the refracting surfaces, the axial air separations or thicknesses of lenses, the refractive indices for the d-line and the Abbe dispersion numbers are respectively designated at R, d, N and ν numbered respectively by subscripts in order from front to rear, __________________________________________________________________________ R.sub.1 = 190.495 .sup.-d.sub.1 = 6.00 N.sub.1 =1.78472 ν.sub.1 =25.7 R.sub.2 = 113.337 .sup.-d.sub.2 =20.00 N.sub.2 =1.62041 ν.sub.2 =60.3 R.sub.3 =-1254.7 .sup.-d.sub.3 = 1.00 R.sub.4 = 154.416 .sup.-d.sub.4 =10.00 N.sub.3 =1.62041 ν.sub.3 =60.3 R.sub.5 = 506.725 .sup.-d.sub.5 = variable R.sub.6 = 1013.4 .sup.-d.sub.6 = 3.94 N.sub.4 =1.71700 ν.sub.4 =47.9 R.sub.7 = 127.044 .sup.-d.sub.7 =11.80 R.sub.8 =- 304.601 .sup.-d.sub.8 = 3.94 N.sub.5 =1.51633 ν.sub.5 =64.0 R.sub.9 = 146.785 .sup.-d.sub.9 = 9.85 N.sub.6 =1.68893 ν.sub.6 =31.1 R.sub.10 = 2845.8 .sup.-d.sub.10 = variable stop .sup.-d.sub.10 *= variable R.sub.11 =-2845.8 .sup.-d.sub.11 = 9.85 N.sub.7 =1.68893 ν.sub.7 =31.1 R.sub.12 =-146.785 .sup.-d.sub.12 = 3.94 N.sub.8 =1.51633 ν.sub.8 =64.0 R.sub.13 = 304.601 .sup.-d.sub.13 =11.80 R.sub.14 =- 127.044 .sup.-d.sub.14 = 3.94 N.sub.9 =1.71700 ν.sub.9 =47.9 R.sub.15 =-1013.4 .sup.-d.sub.15 = variable R.sub.16 =- 506.725 .sup.-d.sub.16 =10.00 N.sub.10 =1.62041 ν.sub.10 =60.3 R.sub.17 =- 154.416 .sup.-d.sub.17 = 1.00 R.sub.18 = 1254.7 .sup.-d.sub.18 =20.00 N.sub.11 =1.62041 ν.sub.11 =60.3 R.sub.19 =-113.337 .sup.-d.sub.19 = 6.00 N.sub.12 =1.78472 ν.sub.12 =25.7 R.sub.20 =- 190.495 __________________________________________________________________________ where d 5 , d 10 , d 10 * and d 15 are 17.21, 3,68, 6.80 and 14.09 when the magnification is -2.0; 11.92, 8.97, 10.28 and 10.61 when the magnification is -1.4; 10.0, 10.89, 10.98 and 9.91 when the magnification is -1.0; 10.73, 10.16, 9.11 and 11.78 when the magnification is -0.7; and 14.25, 6.64, 4.01 and 16.88 when the magnification is -0.5, respectively.

Claim 6

A zoom lens system as defined in claim 1 having the following constructional data wherein the radii of curvature of the refracting surfaces, the axial air separations or thicknesses of lenses, the refractive indices for the d-line and the Abbe dispersion numbers are respectively designated at R, d, N and ν numbered respectively by subscripts in order from front to rear, __________________________________________________________________________ R.sub.1 = 194.211 .sup.-d.sub.1 = 5.03 N.sub.1 =1.68893 ν.sub.1 =31.1 R.sub.2 = 95.877 .sup.-d.sub.2 =16.06 N.sub.2 =1.62041 ν.sub.2 =60.3 R.sub.3 =12588.9 .sup.-d.sub.3 = 0.60 R.sub.4 = 103.135 .sup.-d.sub.4 = 9.10 N.sub.3 =1.71300 ν.sub.3 =53.9 R.sub.5 = 1150.4 .sup.-d.sub.5 = variable R.sub.6 = 4085.8 .sup.-d.sub.6 = 3.88 N.sub.4 =1.70154 ν.sub.4 =41.1 R.sub.7 = 87.991 .sup.-d.sub.7 = 9.84 R.sub.8 =- 580.450 .sup.-d.sub.8 = 3.88 N.sub.5 =1.51633 ν.sub.5 =64.0 R.sub.9 = 111.224 .sup.-d.sub.9 = 8.05 N.sub.6 =1.68893 ν.sub.6 =31.1 R.sub.10 = 572.600 .sup.-d.sub.10 = variable stop .sup.-d.sub.10 *= variable R.sub.11 =- 572.600 .sup.-d.sub.11 = 8.05 N.sub.7 =1.68893 ν.sub.7 =31.1 R.sub.12 =- 111.224 .sup.-d.sub.12 = 3.88 N.sub.8 =1.51633 ν.sub.8 =64.0 R.sub.13 = 580.450 .sup.-d.sub.13 = 9.84 R.sub.14 =- 87.991 .sup.-d.sub.14 = 3.88 N.sub.9 =1.70154 ν.sub.9 =41.1 R.sub.15 =-4085.8 .sup.-d.sub.15 = variable R.sub.16 =-1150.4 .sup.-d.sub.16 = 9.10 N.sub.10 =1.71300 ν.sub.10 =53.9 R.sub.17 =- 103.135 .sup.-d.sub.17 = 0.60 R.sub.18 =-12588.9 .sup.-d.sub.18 =16.06 N.sub.11 =1.62041 ν.sub.11 =60.3 R.sub.19 =- 95.877 .sup.-d.sub.19 = 5.03 N.sub.12 =1.68893 ν.sub.12 =31.1 R.sub.20 =- 194.211 __________________________________________________________________________ where d 5 , d 10 , d 10 * and d 15 are 4.70, 9.61, 9.66 and 4.66 when the magnification is -1.0; 5.15, 9.16, 8.69 and 5.63 when the magnification is -0.74; and 5.85, 8.47, 7.82 and 6.50 when the magnification is -0.65, respectively.