Telephoto zoom lens system

Claim 2

A telephoto zoom lens system comprising: a first lens group arranged on the extreme object side, consisting of a positive lens and a negative lens, and having positive refractive power as a whole; a second lens group having negative refractive power; a third lens group arranged on the extreme image side, and including a first subgroup having positive refractive power and a second subgroup having negative refractive power arranged consecutively from the object side with a substantial airspace reserved therebetween; said first subgroup including a cemented doublet, said second subgroup including a negative lens, said airspace reserved between the first and second subgroups being fixed, a stop being fixedly spaced a distance from any lens in the third lens group, and the first lens group, the third lens group and the stop being moved in the same direction for varying the focal length of the telephoto zoom lens system.

Claim 3

A telephoto zoom lens system according to claim 1 wherein said second lens group is kept fixed in respect to the image surface at the time of zooming.

Claim 4

A telephoto zoom lens system according to claim 2 fulfilling the conditions (1) through (4) shown below: 0.4<f.sub.1 /f.sub.T <0.8 (1) 0.15<|f.sub.2 |/f.sub.T <0.25 (2) 0.1<Δnd (3) 15<Δνd<30 (4) where, reference symbol f T represents the focal length of the lens system as a whole in the teleposition, reference symbols f 1 and f 2 respectively represent the focal lengths of the first lens group and the second lens group, reference symbol Δnd represents the difference between the refractive indices of the positive lens and the negative lens constituting the first lens group, and reference symbol Δνd represents the difference between Abbe's numbers of the positive lens and the negative lens constituting the first lens group.

Claim 5

A telephoto zoom lens system according to claim 3 wherein said second lens group comprises a cemented doublet, which consists of a positive lens element and a negative lens element, and a negative lens component, and said third lens group comprises a cemented doublet, which consists of a positive lens element and a negative lens element, a positive lens component, a positive lens component, a negative lens component and a positive lens component, said telephoto zoom lens system having the following numerical data: ______________________________________ f = 72.45˜193.00, F/3.5˜F/4.5 ______________________________________ r.sub.1 = 79.567 d.sub.1 = 2.30 n.sub.1 = 1.80518 ν.sub.1 = 25.43 r.sub.2 = 44.857 d.sub.2 = 10.00 n.sub.2 = 1.58267 ν.sub.2 = 46.33 r.sub.3 = -285.287 d.sub.3 = D.sub.1 r.sub.4 = 337.164 d.sub.4 = 5.01 n.sub.3 = 1.80518 ν.sub.3 = 25.43 r.sub.5 = -36.739 d.sub.5 = 1.45 n.sub.4 = 1.66755 ν.sub.4 = 41.93 r.sub.6 = 48.075 d.sub.6 = 5.10 r.sub.7 = -35.811 d.sub.7 = 1.03 n.sub.5 = 1.69680 ν.sub.5 = 55.52 r.sub.8 = -414.819 d.sub.8 = D.sub.2 r.sub.9 = 135.589 d.sub.9 = 7.05 n.sub.6 = 1.67003 ν.sub.6 = 47.25 r.sub.10 = -26.431 d.sub.10 = 1.01 n.sub.7 = 1.80518 ν.sub.7 = 25.43 r.sub.11 = -91.828 d.sub.11 = 0.28 r.sub.12 = 34.838 d.sub.12 = 6.34 n.sub.8 = 1.61375 ν.sub.8 = 56.36 r.sub.13 = 131.591 d.sub.13 = 30.37 r.sub.14 = 291.464 d.sub.14 = 2.77 n.sub.9 = 1.83400 ν.sub.9 = 37.16 r.sub.15 = -97.825 d.sub.15 = 6.31 r.sub.16 = -24.343 d.sub.16 = 1.06 n.sub.10 = 1.77250 ν.sub.10 = 49.66 r.sub.17 = -75.409 d.sub.17 = 0.10 r.sub.18 = 168.973 d.sub.18 = 3.89 n.sub.11 = 1.66755 ν.sub.11 = 41.93 r.sub.19 = -247.956 ______________________________________ f D.sub.1 D.sub.2 ______________________________________ 72.45 1.514 27.451 118.14 20.771 14.400 193.00 37.865 1.200 ______________________________________ f.sub.1 = 139.437, f.sub.2 = -38.702 f.sub.T = 193.00, f.sub.1 /f.sub.T = 0.72, |f.sub.2 |/f. sub.T = 0.20 Δn.sub.d = 0.22, Δν.sub.d = 20.9 ______________________________________ where, reference symbols r 1 through r 19 respectively represent radii of curvautre of respective lens surfaces, reference symbols d 1 through d 18 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 11 respectively represent refractive indices of respective lenses, reference symbols ν 1 through ν 11 respectively represent Abbe's numbers of respective lenses, and reference symbol ν represents the focal lengthof the lens sysem as a whole.

Claim 6

A telephoto zoom lens system according to claim 3 wherein said second lens group comprises a cemented doublet, whick consists of a positive lens element and a negative lens element, and a negative lens component, and said third lens group comprises a cemented doublet, which consists of a positive lens element and a negative lens element, a positive lens component, a positive lens component, said telephoto zoom lens system having the following numerical data: ______________________________________ f ==72.45˜193.00, F/3.5˜F/4.5 ______________________________________ r.sub.1 = 89.814 d.sub.1 = 2.30 n.sub.1 = 1.75520 ν.sub.1 = 27.51 r.sub.2 = 44.870 d.sub.2 = 9.00 n.sub.2 = 1.62012 ν.sub.2 = 49.66 r.sub.3 = -315.702 d.sub.3 = D.sub.1 r.sub.4 = -361.172 d.sub.4 = 5.02 n.sub.3 = 1.75520 ν.sub.3 = 27.51 r.sub.5 = -34.939 d.sub.5 = 1.50 n.sub.4 = 1.65160 ν.sub.4 = 58.52 r.sub.6 = 57.174 d.sub.6 = 5.10 r.sub.7 = -38.884 d.sub.7 = 1.30 n.sub.5 = 1.69680 ν.sub.5 = 55.52 r.sub.8 = -367.947 d.sub.8 = D.sub.2 r.sub.9 = 687.627 d.sub.9 = 7.05 n.sub.6 = 1.67003 ν.sub.6 = 47.25 r.sub.10 = -25.677 d.sub.10 = 1.50 n.sub.7 = 1.78470 ν.sub.7 = 26.22 r.sub.11 = -96.353 d.sub.11 = 0.68 r.sub.12 = 54.591 d.sub.12 = 4.00 n.sub.8 = 1.51633 ν.sub.8 = 64.15 r.sub.13 = 519.787 d.sub.13 = 0.39 r.sub.14 = 44.054 d.sub.14 = 4.00 n.sub.9 = 1.51742 ν.sub.9 = 52.41 r.sub.15 = 175.567 d.sub.15 = 34.17 r.sub.16 = 70.338 d.sub.16 = 3.00 n.sub.10 = 1.80610 ν.sub.10 = 40.95 r.sub.17 = -370.425 d.sub.17 = 6.67 r.sub.18 = -29.087 d.sub.18 = 1.20 n.sub.11 = 1.77250 ν.sub.11 = 49.66 r.sub.19 = -105.273 ______________________________________ f D.sub.1 D.sub.2 ______________________________________ 72.45 1.514 24.038 118.14 23.824 13.117 193.00 41.312 1.200 ______________________________________ f.sub.1 = 136.715, f.sub.2 = -36.372 f.sub.T = 193.00, f.sub.1 /f.sub.T = 0.71, |f.sub.2 |/f. sub.T = 0.19 Δn.sub.d = 0.14, Δν.sub.d = 22.15 ______________________________________ where, reference symbols r 1 through r 19 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 18 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 11 respectively represent refractive indices of respective lenses, reference symbols ν 1 through ν 11 respectively represent Abbe's numbers of respective lenses, and reference symbol f represents the focal length of the lens system as a whole.

Claim 7

A telephoto zoom lens system according to claim 3 wherein said second lens group comprises a cemented doublet, which consists of a positive lens element and a negative lens element, and a negative lens component, and said third lens group comprises a cemented doublet, which consists of a positive lens element and a negative lens element, a positive lens component, a negative lens component, a positive lens component and a negative lens component, said telephoto zoom lens system having the following numerical data: ______________________________________ f = 72.45˜193.00, F/3.5˜F/4.5 ______________________________________ r.sub.1 = 89.490 d.sub.1 = 2.30 n.sub.1 = 1.75520 ν.sub.1 = 27.51 r.sub.2 = 44.643 d.sub.2 = 9.00 n.sub.2 = 1.62012 ν.sub.2 = 49.66 r.sub.3 = -309.685 d.sub.3 = D.sub.1 r.sub.4 = -970.005 d.sub.4 = 5.01 n.sub.3 = 1.75520 ν.sub.3 = 27.51 r.sub.5 = -37.775 d.sub.5 = 1.50 n.sub.4 = 1.65160 ν.sub.4 = 58.52 r.sub.6 = 51.873 d.sub.6 = 5.10 r.sub.7 = -38.194 d.sub.7 = 1.30 n.sub.5 = 1.69680 ν.sub.5 = 55.52 r.sub.8 = -206.631 d.sub.8 = D.sub.2 r.sub.9 = 176.622 d.sub.9 = 7.05 n.sub.6 = 1.67003 ν.sub.6 = 47.25 r.sub.10 = -27.963 d.sub.10 = 1.50 n.sub.7 = 1.78470 ν.sub.7 = 26.22 r.sub.11 = -78.566 d.sub.11 = 0.65 r.sub.12 = 31.596 d.sub.12 = 6.50 n.sub.8 = 1.51454 ν.sub.8 = 54.69 r.sub.13 = -329.451 d.sub.13 = 2.01 r.sub.14 = -151.835 d.sub.14 = 2.00 n.sub.9 = 1.80518 ν.sub.9 = 25.43 r.sub.15 = 421.122 d.sub.15 = 26.41 r.sub.16 = 90.256 d.sub.16 = 2.91 n.sub.10 = 1.74950 ν.sub.10 = 35.27 r.sub.17 = -116.777 d.sub.17 = 6.78 r.sub.18 = -26.214 d.sub.18 = n.sub.11 = 1.77250 ν.sub.11 = 49.66 r.sub.19 = -73.163 ______________________________________ f D.sub.1 D.sub.2 ______________________________________ 72.45 1.514 26.713 118.18 21.057 14.167 193.00 37.860 1.200 ______________________________________ f.sub.1 = 135.754, f.sub.2 = -38.165 f.sub.T = 193.00, f.sub.1 /f.sub.T = 0.70, |f.sub.2 |/f. sub.T = 0.20 Δn.sub.d = 0.14, Δν.sub.d = 22.15 ______________________________________ where, reference symbols r 1 through r 19 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 18 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 11 respectively represent refractive indices of respective lenses, reference symbols ν 1 through ν 11 respectively represent Abbe's nubmers of respective lenses, and reference symbol f represnets the focal length of the lens system as a whole.

Claim 8

A telephoto zoom lens system according to claim 3 wherein said second lens group comprises a cemented doublet, which consists of a positive lens element and a negative lens element, and a negative lens component, and said third lens group comprises a cemented doublet, which consists of a positive lens element and a negative lens element, a positive lens component, a negative lens component, a positive lens component and a negative lens component, said telephoto zoom lens system having the following numerical data: ______________________________________ f = 72.45˜193.00, F/3.5˜F/4.5 ______________________________________ r.sub.1 = 96.453 d.sub.1 = 2.30 n.sub.1 = 1.80518 ν.sub.1 = 25.43 r.sub.2 = 46.644 d.sub.2 = 10.00 n.sub.2 = 1.66892 ν.sub.2 = 44.98 r.sub.3 = -302.593 d.sub.3 = D.sub.1 r.sub.4 = -143.955 d.sub.4 = 5.01 n.sub.3 = 1.80518 ν.sub.3 = 25.43 r.sub.5 = -35.535 d.sub.5 = 1.45 n.sub.4 = 1.65160 ν.sub.4 = 58.52 r.sub.6 = 83.960 d.sub.6 = 5.10 r.sub.7 = -45.391 d.sub.7 = 1.03 n.sub.5 = 1.69680 ν.sub.5 = 55.52 r.sub.8 = 355.038 d.sub.8 = D.sub.2 r.sub.9 = 143.478 d.sub.9 = 7.05 n.sub.6 = 1.66892 ν.sub.6 = 44.98 r.sub.10 = -26.171 d.sub.10 = 1.01 n.sub.7 = 1.80518 ν.sub.7 = 25.43 r.sub.11 = -81.941 d.sub.11 = 0.50 r.sub.12 = 35.182 d.sub.12 = 6.22 n.sub.8 = 1.51633 ν.sub.8 = 64.15 r.sub.13 = -1674.665 d.sub.13 = 5.04 r.sub.14 = -384.037 d.sub.14 = 1.35 n.sub.9 = 1.80518 ν.sub.9 = 25.43 r.sub.15 = 1056.083 d.sub.15 = 23.64 r.sub.16 = 129.285 d.sub.16 = 3.03 n.sub.10 = 1.74950 ν.sub.10 = 35.27 r.sub.17 = -97.985 d.sub.17 = 6.56 r.sub.18 = -26.752 d.sub.18 = 1.06 n.sub.11 = 1.77250 ν.sub.11 = 49.66 r.sub.19 = -63.835 ______________________________________ f D.sub.1 D.sub.2 ______________________________________ 72.45 1.514 25.114 118.14 22.250 13.606 193.00 38,809 1.200 ______________________________________ f.sub.1 = 132.056, f.sub.2 = -36.326 f.sub.T = 193.00, f.sub.1 /f.sub.T = 0.68, |f.sub.2 |/f. sub.T = 0.19 Δn.sub.d = 0.14, Δν.sub.d = 19.55 ______________________________________ where, reference symbols r 1 through r 19 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 18 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 11 respectively represent refractive indices of respective lenses, reference symbols ν 1 through ν 11 respectively represent Abbe's numbers of respective lenses, and reference symbol f represents the focal length of the lens system as a whole.

Claim 9

A telephoto zoom lens system according to claim 1 wherein said first lens group and said third lens group are integrally moved at the time of zooming.

Claim 10

A telephoto zoom lens system according to claim 8 fulfilling the conditions (1) through (4) shown below: 0.4<f.sub.1 /f.sub.T <0.8 (1) 0.15<|f.sub.2 |/f.sub.T <0.25 (2) 0.1<Δnd (3) 15<Δνd<30 (4) where, reference symbol f T represents the focal length of the lens system as a whole in the teleposition, reference symbols f 1 and f 2 respectively represent the focal lengths of the first lens group and the second lens group, reference sybmol Δnd represents the difference between the refractive indices of the positive lens and the negative lens constituting the first lens group, and reference symbol Δνd represents the difference between Abbe's numbers of the positive lens and the negative lens constituting the first lens group.

Claim 11

A telephoto zoom lens system according to claim 9 wherein said second lens group comprises a cemented doublet, which consists of a positive lens element and a negative lens element, and a negative lens component, and said third lens group comprises a cemented doublet, which consists of a positive lens element and a negative lens element, a positive lens component, a negative lens compoennt, a positive lens component and a negative lens component, said telephoto zoom lens system having the following numerical data: ______________________________________ f = 72.45˜193.00, F/3.5˜F/4.5 ______________________________________ r.sub.1 = 88.884 d.sub.1 = 2.30 n.sub.1 = 1.80518 ν.sub.1 = 25.43 r.sub.2 = 46.226 d.sub.2 = 9.00 n.sub.2 = 1.62374 ν.sub.2 = 47.10 r.sub.3 = -265.706 d.sub.3 = D.sub.1 r.sub.4 = 243.870 d.sub.4 = 5.01 n.sub.3 = 1.75520 ν.sub.3 = 27.51 r.sub.5 = -35.216 d.sub.5 = 1.50 n.sub.4 = 1.66672 ν.sub.4 = 48.32 r.sub.6 = 52.143 d.sub.6 = 5.27 r.sub.7 = -38.718 d.sub.7 = 1.30 n.sub.5 = 1.77250 ν.sub.5 = 49.66 r.sub.8 = -258.801 d.sub.8 = D.sub.2 r.sub.9 = 90.813 d.sub.9 = 7.05 n.sub.6 = 1.67003 ν.sub.6 = 47.25 r.sub.10 = -27.536 d.sub.10 = 1.50 n.sub.7 = 1.78470 ν.sub.7 = 26.22 r.sub.11 = -117.766 d.sub.11 = 0.10 r.sub.12 = 37.888 d.sub.12 = 6.52 n.sub.8 = 1.51823 ν.sub.8 = 58.96 r.sub.13 = -124.108 d.sub.13 = 1.56 r.sub.14 = -150.179 d.sub.14 = 1.96 n.sub.9 = 1.77250 ν.sub.9 = 49.66 r.sub.15 = 432.630 d.sub.15 = 31.67 r.sub.16 = 77.454 d.sub.16 = 2.85 n.sub.10 = 1.71736 ν.sub.10 = 29.51 r.sub.17 = -330.833 d.sub.17 = 6.62 r.sub.18 = -26.590 d.sub.18 = 1.20 n.sub.11 = 1.77250 ν.sub.11 = 49.66 r.sub.19 = -76.930 ______________________________________ f D.sub.1 D.sub.2 ______________________________________ 72.45 1.539 34.868 118.14 16.770 19.637 193.00 31.307 5.100 ______________________________________ f.sub.1 = 134.554, f.sub.2 = -41.115 f.sub.T = 193.00, f.sub.1 /f.sub.T = 0.70 , |f.sub.2 |/f .sub.T = 0.21 Δn.sub.d = 0.18144, Δν.sub.d = 21.67 ______________________________________ where, reference symbols r 1 through r 19 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 18 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 11 respectively represent refractive indices of respective lenses, reference symbols ν 1 through ν 11 respectively represent Abbe's numbers of respective lenses, and reference symbol f represents the focal length of the lens system as a whole.

Claim 12

A telephoto zoom lens system according to claim 9 wherein said second lens group comprises a cemented doublet, which consists of a positive lens element and a negative lens element, and a negative lens component, and said third lens group comprises a cemented doublet, which consists of a positive lens element and a negative lens element, a positive lens component, a negative lens component, a positive lens componennt, a negative lens component and a positive lens component, said telephoto zoom lens system having the following numerical data: ______________________________________ f = 72.45˜193.00, F/3.5˜F/4.5 ______________________________________ r.sub.1 = 83.619 d.sub.1 = 2.30 n.sub.1 = 1.80518 ν.sub.1 = 25.43 r.sub.2 = 44.971 d.sub.2 = 9.00 n.sub.2 = 1.62374 ν.sub.2 = 47.10 r.sub.3 = -328.662 d.sub.3 = D.sub.1 r.sub.4 = 212.498 d.sub.4 = 5.01 n.sub.3 = 1.75520 ν.sub.3 = 27.51 r.sub. 5 = -35.776 d .sub.5 = 1.50 n .sub.4 = 1.66672 ν.sub.4 = 48.32 r.sub.6 = 51.473 d.sub.6 = 5.44 r.sub. 7 = -40.460 d.sub. 7 = 1.30 n.sub.5 = 1.77250 ν.sub.5 = 49.66 r.sub.8 = -586.527 d.sub.8 = D.sub.2 r.sub.9 = 108.182 d.sub.9 = 8.00 n.sub.6 = 1.67003 ν.sub.6 = 47.25 r.sub.10 = -27.480 d.sub.10 = 1.50 n.sub.7 = 1.78470 ν.sub.7 = 26.22 r.sub.11 = -94.106 d.sub.11 = 0.10 r.sub.12 = 33.462 d.sub.12 = 6.51 n.sub. 8 = 1.51633 ν.sub.8 = 64.15 r.sub.13 = -154.544 d.sub.13 = 1.44 r.sub.14 = -139.853 d.sub.14 = 1.96 n.sub.9 = 1.77250 ν.sub.9 = 49.66 r.sub.15 = 477.511 d.sub.15 = 31.53 r.sub.16 = 242.882 d.sub.16 = 2.82 n.sub.10 = 1.69895 ν.sub.10 = 30.12 r.sub.17 = -129.338 d.sub.17 = 6.27 r.sub.18 = -22.322 d.sub.18 = 1.20 n.sub. 11 = 1.77250 ν.sub.11 = 49.66 r.sub.19 = -88.565 d.sub.19 = 0.10 r.sub.20 = 104.480 d.sub.20 = 4.07 n.sub.12 = 1.74950 ν.sub.12 = 35.27 r.sub.21 = -417.921 ______________________________________ f D.sub.1 D.sub.2 ______________________________________ 72.45 1.539 33.258 118.14 16.115 18.682 193.00 29.697 5.100 f.sub.1 = 134.062, f.sub.2 = -40.200 f.sub.T = 193.00, f.sub.1 /f.sub.T = 0.69, |f.sub.2 |/f.sub.T = 0.21 Δn.sub.d = 0.18144, Δν.sub.d = 21.67 ______________________________________ where, reference symbols r 1 through r 21 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 20 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 12 respectively represent refractive indices of respective lenses, reference symbols ν 1 through ν 12 respectively represent Abbe's numbers of respective lenses, and reference symbol f represents the focal length of the lens system as a whole.

Claim 13

A telephoto zoom lens system according to claim 9 wherein said second lens group comprises a cemented doublet, which consists of a positive lens element and a negative lens element, and a negative lens component, and said third lens group comprises a cemented doublet, which consists of a positive lens element and a negative lens element, a positive lens component, a negative lens component, a positive lens component and a negative lens component, said telephoto zoom lens system having the following numerical data: ______________________________________ f = 72.45˜193.00, F/3.5˜F/4.5 ______________________________________ r.sub.1 = 98.030 d.sub.1 = 2.30 n.sub.1 = 1.80518 ν.sub.1 = 25.43 r.sub.2 = 49.206 d.sub.2 = 9.00 n.sub.2 = 1.62374 ν.sub.2 = 47.10 r.sub.3 = -217.810 d.sub.3 = D.sub.1 r.sub.4 = -785.453 d.sub.4 = 5.01 n.sub.3 = 1.76180 ν.sub.3 = 27.11 r.sub.5 = -34.617 d.sub.5 = 1.50 n.sub.4 = 1.65160 ν.sub.4 = 58.52 r.sub.6 = 63.100 d.sub.6 = 5.57 r.sub.7 = -37.019 d.sub.7 = 1.28 n.sub.5 = 1.74400 ν.sub.5 = 44.73 r.sub.8 = -240.280 d.sub.8 = D.sub.2 r.sub.9 = 211.096 d.sub.9 = 7.05 n.sub.6 = 1.65844 ν.sub.6 = 50.86 r.sub.10 = -29.039 d.sub.10 = 1.50 n.sub.7 = 1.78472 ν.sub.7 = 25.71 r.sub.11 = -70.499 d.sub.11 = 0.10 r.sub.12 = 35.714 d.sub.12 = 6.50 n.sub.8 = 1.51742 ν.sub.8 = 52.41 r.sub.13 = -434.751 d.sub.13 = 1.20 r.sub.14 = -164.868 d.sub.14 = 2.00 n.sub.9 = 1.80518 ν.sub.9 = 25.43 r.sub.15 = 901.042 d.sub.15 = 30.44 r.sub.16 = 80.736 d.sub.16 = 2.91 n.sub.10 = 1.74950 ν.sub.10 = 35.27 r.sub.17 = -115.426 d.sub.17 = 7.40 r.sub.18 = -30.425 d.sub.18 = 1.18 n.sub.11 = 1.74400 ν.sub.11 = 44.73 r.sub.19 = -135.183 ______________________________________ f D.sub.1 D.sub.2 ______________________________________ 72.45 1.501 25.912 118.14 14.969 12.445 193.00 26.416 0.998 f.sub.1 = 136.499, f.sub.2 = -38.719 f.sub.T = 193.00, f.sub.1 /f.sub.T = 0.71, |f.sub.2 |/f.sub.T = 0.20 Δn.sub.d = 0.18144, Δν.sub.d = 21.67 ______________________________________ where, reference symbols r 1 through r 19 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 18 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 11 respectively represent refractive indices of respective lenses, reference symbols ν 1 through ν 11 respectively represent Abbe's numbers of respective lenses, and reference symbol f represents the focal length of the lens system as a whole.