Reproducing objective for video disks

Claim 2

A reproducing objective for video disks comprising a first, second, third and fourth lenses, said first lens being a plano-convex lens, said second lens being a plano-concave lens, said third lens being a positive lens, said fourth lens being a positive meniscus lens, said reproducing objective for video disks satisfying the following conditions: (1) 1.7f>f 1 >2.1f (2) -4.3f>f 2 >-3.5f (3) 1.4f>f 4 >1.9f (4) r 2 =∞ (5) r 4 =∞ (6) 0.5f>r 8 >1.7f (7) d 2 >0.1f (8) 0.6f>d 4 wherein reference symbol f represents the focal length of the lens system as a whole, reference symbols f 1 , f 2 and f 4 respectively represent the focal lengths of the first, second and fourth lenses, reference symbol r 2 represents the radius of curvature of the surface on the disk side of the first lens, reference symbol r 4 represents the radius of curvature of the surface on the disk side of the second lens, reference symbol r 8 represents the radius of curvature of the surface on the disk side of the fourth lens, reference symbol d 2 represents the airspace between the first and second lenses, and reference symbol d 4 represents the airspace between the second and third lenses.

Claim 3

A reproducing objective for video disks according to claim 1, in which said reproducing objective for video disks has the following numerical data: ______________________________________ r.sub.1 = 1.5200 d.sub.1 = 0.2372 n.sub.1 = 1.77861 ν.sub.1 = 25.71 r.sub.2 = ∞ d.sub.2 = 0.0593 r.sub.3 = -1.9855 d.sub.3 = 0.1186 n.sub.2 = 1.51462 ν.sub.2 = 64.15 r.sub.4 = ∞ d.sub.4 = 1.0081 r.sub.5 = 1.5602 d.sub.5 = 0.1779 n.sub.3 = 1.77861 ν.sub.3 = 25.71 r.sub.6 = -5.9979 d.sub.6 = 0.0119 r.sub.7 = 0.5087 d.sub.7 = 0.1542 n.sub.4 = 1.77861 ν.sub.4 = 25.71 r.sub.8 = 0.6823 W.D = 0.3914 t = 0.1305 n.sub.t = 1.51 f = 1 β = -1/14 N.A(disk side) = 0.45 f.sub.1 = 1.9522 f.sub.2 = -3.8583 f.sub.3 = 1.6067 f.sub.4 = 1.8500 Σd = 1.7672 ______________________________________ wherein reference symbols r 1 through r 8 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 7 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 , n 2 , n 3 and n 4 respectively represent refractive indices of respective lenses at the wavelength of 632.8 nm, reference symbols ν 1 , ν 2 , ν 3 and ν 4 respectively represent Abbe's numbers of respective lenses for d-line, reference symbol W.D. represents the working distance, reference symbol t represents the thickness of the cover glass, reference symbol n t represents the refractive index of the cover glass, reference symbol f represents the focal length of the lens system as a whole, reference symbols f 1 , f 2 , f 3 and f 4 respectively represent the focal length of the first, second, third and fourth lenses, reference symbol β represents magnification, reference symbol N.A. represents the numerical aperture on the image side, and reference symbol Σd represents the overall length of lens system.

Claim 4

A reproducing objective for video disks according to claim 1, in which said reproducing objective for video disks has the following numerical data: ______________________________________ r.sub.1 = 1.5414 d.sub.1 = 0.2378 n.sub.1 = 1.77861 ν.sub.1 = 25.71 r.sub.2 = ∞ d.sub.2 = 0.0595 r.sub.3 = -1.9040 d.sub.3 = 0.1189 n.sub.2 = 1.51462 ν.sub.2 = 64.15 r.sub.4 = ∞ d.sub.4 = 0.9276 r.sub.5 = 1.9428 d.sub.5 = 0.1784 n.sub.3 = 1.77861 ν.sub.3 = 25.71 r.sub.6 = -4.9656 d.sub.6 = 0.0951 r.sub.7 = 0.5191 d.sub.7 = 0.1546 n.sub.4 = 1.77861 ν.sub.4 = 25.71 r.sub.8 = 0.7852 W.D = 0.3924 t = 0.1308 n.sub.t = 1.51 f = 1 β = -1/14 N.A(disk side) = 0.45 f.sub.1 = 1.9795 f.sub.2 = -3.6998 f.sub.3 = 1.8140 f.sub.4 = 1.5682 Σd = 1.7719 ______________________________________ wherein reference symbols r 1 through r 8 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 7 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 , n 2 , n 3 and n 4 respectively represent refractive indices of respective lenses at the wavelength of 632.8 nm, reference symbols ν 1 , ν 2 , ν 3 and ν 4 respectively represent Abbe's numbers of respective lenses for d-line, reference symbol W.D. represents the working distance, reference symbol t represents the thickness of the cover glass, reference symbol n t represents the refractive index of the cover glass, reference symbol f represents the focal length of the lens system as a whole, reference symbols f 1 , f 2 , f 3 and f 4 respectively represent the focal length of the first, second, third and fourth lenses, reference symbol β represents magnification, reference symbol N.A. represents the numerical aperture on the image side, and reference symbol Σd represents the overall length of lens system.

Claim 5

A reproducing objective for video disks according to claim 1, in which said reproducing objective for video disks has the following numerical data: ______________________________________ r.sub.1 = 1.4580 d.sub.1 = 0.2366 n.sub.1 = 1.77861 ν.sub.1 = 25.71 r.sub.2 = ∞ d.sub.2 = 0.0592 r.sub.3 = -1.9571 d.sub.3 = 0.1183 n.sub.2 = 1.51462 ν.sub.2 = 64.15 r.sub.4 = ∞ d.sub.4 = 0.9227 r.sub.5 = 1.6686 d.sub.5 = 0.1775 n.sub.3 = 1.77861 ν.sub.3 = 25.71 r.sub.6 = -5.3343 d.sub.6 = 0.0946 r.sub.7 = 0.4583 d.sub.7 = 0.1183 n.sub.4 = 1.77861 ν.sub.4 = 25.71 r.sub.8 = 0.6306 W.D = 0.3667 t = 0.1301 n.sub.t = 1.51 f = 1 β = -1/14 N.A(disk side) = 0.45 f.sub.1 = 1.8727 f.sub.2 = -3.8029 f.sub.3 = 1.6507 f.sub.4 = 1.6567 Σd = 1.7272 ______________________________________ wherein reference symbols r 1 through r 8 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 7 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 , n 2 , n 3 and n 4 respectively represent refractive indices of respective lenses at the wavelength of 632.8 nm, reference symbols ν 1 , ν 2 , ν 3 and ν 4 respectively represent Abbe's numbers of respective lenses for d-line, reference symbol W.D. represents the working distance, reference symbol t represents the thickness of the cover glass, reference symbol n t represents the refractive index of the cover glass, reference symbol f represents the focal length of the lens system as a whole, reference symbols f 1 , f 2 , f 3 and f 4 respectively represent the focal lengths of the first, second, third and fourth lenses, reference symbol β represents magnification, reference symbol N.A. represents the numerical aperture on the image side, and reference symbol Σd represents the overall length of lens system.

Claim 6

A reproducing objective for video disks according to claim 1, in which said reproducing objective for video disks has the following numerical data: ______________________________________ r.sub.1 = 1.4482 d.sub.1 = 0.1779 n.sub.1 = 1.77861 ν.sub.1 = 25.71 r.sub.2 = ∞ d.sub.2 = 0.0474 r.sub.3 = -2.1026 d.sub.3 = 0.1186 n.sub.2 = 1.51462 ν.sub.2 = 64.15 r.sub.4 = ∞ d.sub.4 = 0.9834 r.sub.5 =0 2.0859 d.sub.5 = 0.1779 n.sub.3 = 1.77861 ν.sub.3 = 25.71 r.sub.6 = -5.2958 d.sub.6 = 0.0119 r.sub.7 = 0.5147 d.sub.7 = 0.1542 n.sub.4 = 1.77861 ν.sub.4 = 25.71 r.sub.8 = 0.7703 W.D = 0.3913 t = 0.1305 n.sub.t = 1.51 f = 1 β = -1/14 N.A(disk side) = 0.45 f.sub.1 = 1.8599 f.sub.2 = -4.0858 f.sub.3 = 1.9425 f.sub.4 = 1.5759 Σd = 1.6713 ______________________________________ wherein reference symbols r 1 through r 8 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 7 respectively represent thickness of respective lenses and airspaces between respective lenses, reference symbols n 1 , n 2 , n 3 and n 4 respectively represent refractive indices of respective lenses at the wavelength of 632.8 nm, reference symbols ν 1 , ν 2 , ν 3 and ν 4 respectively represent Abbe's numbers of respective lenses for d-line, reference symbol W.D. represents the working distance, reference symbol t represents the thickness of the cover glass, reference symbol n t represents the refractive index of the cover glass, reference symbol f represents the focal length of the lens system as a whole, reference symbols f 1 , f 2 , f 3 and f 4 respectively represent the focal length of the first, second, third and fourth lenses, reference symbol β represents magnification, reference symbol N.A. represents the numerical aperture on the image side, and reference symbol Σd represents the overall length of lens system.

Claim 7

A reproducing objective for video disks according to claim 1, in which said reproducing objective for video disks has the following numerical data: ______________________________________ r.sub.1 = 1.3664 d.sub.1 = 0.2369 n.sub.1 = 1.77861 ν.sub.1 = 25.71 r.sub.2 = ∞ d.sub.2 = 0.0474 r.sub.3 = -2.0923 d.sub.3 = 0.1184 n.sub.2 = 1.51462 ν.sub.2 = 64.15 r.sub.4 = ∞ d.sub.4 = 0.9237 r.sub.5 = 2.3052 d.sub.5 = 0.1776 n.sub.3 = 1.77861 ν.sub.3 = 25.71 r.sub.6 = -5.0286 d.sub.6 = 0.0545 r.sub.7 = 0.4654 d.sub.7 = 0.1776 n.sub.4 = 1.77861 ν.sub.4 = 25.71 r.sub.8 = 0.6590 W.D = 0.3079 t = 0.1303 n.sub.t = 1.51 f = 1 β = -1/14 N.A(disk side) = 0.45 f.sub.1 = 1.7550 f.sub.2 = -4.0658 f.sub.3 = 2.0519 f.sub.4 = 1.4519 Σd = 1.7361 ______________________________________ wherein reference symbols r 1 through r 8 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 7 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 , n 2 , n 3 and n 4 respectively represent refractive indices of respective lenses at the wavelength of 632.8 nm, reference symbols ν 1 , ν 2 , ν 3 and ν 4 respectively represent Abbe's numbers of respective lenses for d-line, reference symbol W.D. represents the working distance, reference symbol t represents the thickness of the cover glass, reference symbol n t represents the refractive index of the cover glass, reference symbol f represent the focal length of the lens system as a whole, reference symbols f 1 , f 2 , f 3 and f 4 respectively represent the focal lengths of the first, second, third and fourth lenses, reference symbol β represents magnification, reference symbol N.A represents the numerical aperture on the image side, and reference symbol Σd represents the overall length of lens system.

Claim 8

A reproducing objective for video disks according to claim 1, in which said reproducing objective for video disks has the following numerical data: ______________________________________ r.sub.1 = 1.4173 d.sub.1 = 0.2376 n.sub.1 = 1.77861 ν.sub.1 = 25.71 r.sub.2 = ∞ d.sub.2 = 0.0475 r.sub.3 = -2.0160 d.sub.3 = 0.1188 n.sub.2 = 1.51462 ν.sub.2 = 64.15 r.sub.4 = ∞ d.sub.4 = 0.9265 r.sub.5 = 2.0045 d.sub.5 = 0.1782 n.sub.3 = 1.77861 ν.sub.3 = 25.71 r.sub.6 = -4.8085 d.sub.6 = 0.0950 r.sub.7 = 0.4644 d.sub.7 = 0.1782 n.sub.4 = 1.77861 ν.sub.4 = 25.71 r.sub.8 = 0.6161 W.D = 0.3088 t = 0.1307 n.sub.t = 1.51 f = 1 β = -1/14 N.A(disk side) = 0.45 f.sub.1 = 1.8204 f.sub.2 = -3.9173 f.sub.3 = 1.8381 f.sub.4 = 1.6001 Σd = 1.7818 ______________________________________ wherein reference symbols r 1 through r 8 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 7 respectively represent thicknesses of respective lenses and airspaces and airspaces between respective lenses, reference symbols n 1 , n 2 , n 3 and n 4 respectively represent refractive indices of respective lenses at the wavelength of 632.8 nm, reference symbols ν 1 , ν 2 , ν 3 and ν 4 respectively represent Abbe's numbers of respective lenses for d-line, reference symbol W.D. represents the working distance, reference symbol t represents the thickness of the cover glass, reference symbol n t represents the refractive index of the cover glass, reference symbol f represents the focal length of the lens system as a whole, reference symbols f 1 , f 2 , f 3 and f 4 respectively represent the focal lengths of the first, second, third and fourth lenses, reference symbol β represents magnification, reference symbol N.A. represents the numerical aperture on the image side, and reference symbol Σd represents the overall length of lens system.

Claim 9

A reproducing objective for video disks according to claim 1, in which said reproducing objective for video disks has the following numerical data: ______________________________________ r.sub.1 = 1.5493 d.sub.1 = 0.2077 n.sub.1 = 1.77861 ν.sub.1 = 25.71 r.sub.2 = ∞ d.sub.2 = 0.0554 r.sub.3 = -1.8552 d.sub.3 = 0.1154 n.sub.2 = 1.51462 ν.sub.2 = 64.15 r.sub.4 = ∞ d.sub.4 = 0.7603 r.sub.5 = 1.5493 d.sub.5 = 0.2077 n.sub.3 = 1.77861 ν.sub.3 = 25.71 r.sub.6 = ∞ d.sub.6 = 0.0162 r.sub.7 = 0.7581 d.sub.7 = 0.1788 n.sub.4 = 1.77861 ν.sub.4 = 25.71 r.sub.8 = 1.5862 W.D = 0.4535 t = 0.1500 n.sub.t = 1.50 f = 1 β = -1/14 N.A(disk side) = 0.45 f.sub.1 = 1.9897 f.sub.2 = -3.6050 f.sub.3 = 1.9897 f.sub.4 = 1.7039 Σd = 1.5415 ______________________________________ wherein reference symbols r 1 through r 8 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 7 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 , n 2 , n 3 and n 4 respectively represent refractive indices of respective lenses at the wavelength of 632.8 nm, reference symbols ν 1 , ν 2 , ν 3 and ν 4 respectively represent Abbe's numbers of respective lenses for d-line, reference symbol W.D. represents the working distance, reference symbol t represents the thickness of the cover glass, reference symbol n t represents the refractive index of the cover glass, reference symbol f represents the focal length of the lens system as a whole, reference symbols f 1 , f 2 , f 3 and f 4 respectively represent the focal lengths of the first, second, third and fourth lenses, reference symbol β represents magnification, reference symbol N.A represents the numerical aperture on the image side, and reference symbol Σd represents the overall length of lens system.