Reproducing objective for video disks

Claim 2

A reproducing objective for video disks comprising a first, second, third and fourth lenses in the order from the reproducing light source side to the video disk side, said first lens being a positive lens, said second lens being a negative meniscus lens, said third lens being a positive lens, said fourth lens being a positive meniscus lens, at least one of said lenses being arranged as a plastic lens, said reproducing objective for video disks fulfilling the following conditions: (1) 2.1f<f 1 <3.2f (2) -55f<f 2 <-3.9f (3) 1.3f<f 4 <2.4f (4) f<r 8 <2.3f (5) d 2 <0.1f (6) 0.5f<d 4 wherein reference symbols f 1 , f 2 and f 4 respectively represent focal lengths of the first, second and fourth lenses, reference symbol r 8 represents the radius of curvature of surface on the video disk side of the fourth lens, reference symbol d 2 represents the airspace between the first and second lenses, reference symbol d 4 represents the airspace between the second and third lenses, and reference symbol f represents the focal length of the lens system as a whole.

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: ______________________________________ NA = 0.45 WD = 0.534 β = -1/18.5 r.sub.1 = 3.0032 d.sub.1 = 0.2322 n.sub.1 = 1.59119 ν.sub.1 = 57.8 r.sub.2 = -2.6218 d.sub.2 = 0.0580 r.sub.3 = -1.1963 d.sub.3 = 0.3250 n.sub.2 = 1.49819 ν.sub.2 = 57.8 r.sub.4 = -2.4894 d.sub.4 = 0.7545 r.sub.5 = 2.1883 d.sub.5 = 0.2322 n.sub.3 = 1.59119 ν.sub.3 = 57.8 r.sub.6 = -3.1827 d.sub.6 = 0.0116 r.sub.7 = 0.7015 d.sub.7 = 0.1857 n.sub.4 = 1.59119 ν.sub.4 = 57.8 r.sub.8 = 2.1531 t = 0.15 n.sub.t = 1.50 f.sub.1 = 2.405 f.sub.2 = -5.044 f.sub.3 = 2.229 f.sub.4 = 1.680 f = 1 ______________________________________ wherein reference symbols r 1 through r 8 repsectively 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, reference symbols ν 1 , 84 2 , ν 3 and ν 4 respectively represent Abbe's numbers of respective lenses at λ=6328 A, reference symbol t represents the thickness of cover glass, reference symbol t n represents the refractive index of cover glass, reference symbol NA represents the numerical aperture, reference symbol WD represents the working distance, reference symbol β represents magnification, and reference symbol f represents the focal length of the lens system as a whole.

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: ______________________________________ NA = 0.45 WD = 0.460 β = -1/18.5 r.sub.1 = 2.0547 d.sub.1 = 0.2300 n.sub.1 = 1.4902 ν.sub.1 = 57.8 r.sub.2 = 2.2681 d.sub.2 = 0.0575 r.sub.3 = -1.2145 d.sub.3 = 0.3220 n.sub.2 = 1.4902 ν.sub.2 = 57.8 r.sub.4 = -2.2457 d.sub.4 = 0.8165 r.sub.5 = 1.2677 d.sub.5 = 0.2300 n.sub.3 = 1.4902 ν.sub.3 = 57.8 r.sub.6 = -3.7974 d.sub.6 = 0.0115 r.sub.7 = 0.5727 d.sub.7 = 0.1380 n.sub.4 = 1.4902 ν.sub.4 = 57.8 r.sub.8 = 1.7107 t = 0.15 n.sub.t = 1.50 f.sub.1 = 2.238 f.sub.2 = -6.013 f.sub.3 = 1.968 f.sub.4 = 1.689 f = 1 ______________________________________ 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, reference symbols ν 1 , ν 2 , ν 3 and ν 4 respectively represent Abbe's numbers of respective lenses at λ=6328 A, reference symbol t represents the thickness of cover glass, reference symbol t n represents the refractive index of cover glass, reference symbol NA represents the numerical aperture, reference symbol WD represents the working distance, reference symbol β represents magnification, and reference symbol f represents the focal length of the lens system as a whole.

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: ______________________________________ NA = 0.45 WD = 0.459 β = -1/18.5 r.sub.1 = 2.3631 d.sub.1 = 0.2296 n.sub.1 = 1.49819 ν.sub.1 = 57.8 r.sub.2 = -2.6102 d.sub.2 = 0.0919 r.sub.3 = -1.1435 d.sub.3 = 0.3215 n.sub.2 = 1.49819 ν.sub.2 = 57.8 r.sub.4 = -1.7398 d.sub.4 = 0.9186 r.sub.5 = 1.1498 d.sub.5 = 0.2067 n.sub.3 = 1.49819 ν.sub.3 = 57.8 r.sub.6 = -3.8750 d.sub.6 = 0.0115 r.sub.7 = 0.5679 d.sub.7 = 0.1378 n.sub.4 = 1.49819 ν.sub.4 = 57.8 r.sub.8 = 1.4233 t = 0.15 n.sub.t = 1.50 f.sub.1 = 2.528 f.sub.2 = -8.160 f.sub.3 = 1.805 f.sub.4 = 1.800 f = 1 ______________________________________ 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 indices of respective lenses, reference symbols ν 1 , ν 2 , ν 3 and ν 4 respectively represent Abbe's numbers of respective lenses at λ=6328 A, reference symbol t represents the thickness of cover glass, reference symbol t n represents the refractive index of cover glass, reference symbol NA represents the numerical aperture, reference symbol WD represents the working distance, reference symbol β represents magnification, and reference symbol f represents the focal length of the lens system as a whole.

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: ______________________________________ NA = 0.45 WD = 0.460 β = -1/18.5 r.sub.1 = 2.2811 d.sub.1 = 0.2302 n.sub.1 = 1.49819 ν.sub.1 = 57.8 r.sub.2 = -2.6068 d.sub.2 = 0.0575 r.sub.3 = -1.1867 d.sub.3 = 0.3222 n.sub.2 = 1.49819 ν.sub.2 = 57.8 r.sub.4 = -1.8606 d.sub.4 = 0.8977 r.sub.5 = 1.1534 d.sub.5 = 0.2302 n.sub.3 = 1.49819 ν.sub.3 = 57.8 r.sub.6 = -3.9686 d.sub.6 = 0.0115 r.sub.7 = 0.5731 d.sub.7 = 0.1381 n.sub.4 = 1.49819 ν.sub.4 = 57.8 r.sub.8 = 1.4170 t = 0.15 n.sub.t = 1.50 f.sub.1 = 2.481 f.sub.2 = -7.818 f.sub.3 = 1.821 f.sub.4 = 1.832 f = 1 ______________________________________ 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, reference symbols ν 1 , ν 2 , ν 3 and ν 4 respectively represent Abbe's numbers of respective lenses at λ=6328 A, reference symbol t represents the thickness of cover glass, reference symbol t n represents the refractive index of cover glass, reference symbol NA represents the numerical aperture, reference symbol WD represents the working distance, reference symbol β represents magnification, and reference symbol f represents the focal length of the lens system as a whole.

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: ______________________________________ NA = 0.45 WD = 0.460 β = -1/18.5 r.sub.1 = 2.3727 d.sub.1 = 0.2298 n.sub.1 = 1.49819 ν.sub.1 = 57.8 r.sub.2 = -2.5701 d.sub.2 = 0.0919 r.sub.3 = -1.1415 d.sub.3 = 0.3218 n.sub.2 = 1.49819 ν.sub.2 = 57.8 r.sub.4 = -1.7673 d.sub.4 = 0.8963 r.sub.5 = 1.1733 d.sub.5 = 0.2298 n.sub.3 = 1.49819 ν.sub.3 = 57.8 r.sub.6 = -3.7409 d.sub.6 = 0.0115 r.sub.7 = 0.5716 d.sub.7 = 0.1379 n.sub.4 = 1.49819 ν.sub.4 = 57.8 r.sub.8 = 1.4758 t = 0.15 n.sub.t = 1.50 f.sub.1 = 2.515 f.sub.2 = -7.805 f.sub.3 = 1.821 f.sub.4 = 1.782 f = 1 ______________________________________ 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, reference symbols ν 1 , ν 2 , ν 3 and ν 4 respectively represent Abbe's numbers of respective lenses at λ=6328 A, reference symbol t represents the thickness of cover glass, reference symbol t n represents the refractive index of cover glass, reference symbol NA represents the numerical aperture, reference symbol WD represents the working distance, reference symbol β represents magnification, and reference symbol f represents the focal length of the lens system as a whole.

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: ______________________________________ NA = 0.45 WD = 0.578 β = -1/18.5 r.sub.1 = 3.7269 d.sub.1 = 0.2312 n.sub.1 = 1.49819 ν.sub.1 = 57.8 r.sub.2 = -2.3833 d.sub.2 = 0.0925 r.sub.3 = -1.0641 d.sub.3 = 0.2081 n.sub.2 = 1.49819 ν.sub.2 = 57.8 r.sub.4 = -1.6543 d.sub.4 = 0.9249 r.sub.5 = 1.5397 d.sub.5 = 0.2081 n.sub.3 = 1.49819 ν.sub.3 = 57.8 r.sub.6 = -3.1801 d.sub.6 = 0.0116 r.sub.7 = 0.7601 d.sub.7 = 0.1387 n.sub.4 = 1.72309 ν.sub.4 = 28.46 r.sub.8 = 1.8463 t = 0.15 n.sub.t = 1.50 f.sub.1 = 2.955 f.sub.2 = -6.782 f.sub.2 = 2.113 f.sub.4 = 1.696 f = 1 ______________________________________ 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, reference symbols ν 1 , ν 2 , ν 3 and ν 4 respectively represent Abbe's numbers of respective lenses at λ=6328 A, reference symbol t represents the thickness of cover glass, reference symbol t n represents the refractive index of cover glass, reference symbol NA represents the numerical aperture, reference symbol WD represents the working distance, reference symbol β represents magnification, and reference symbol f represents the focal length of the lens system as a whole.

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: ______________________________________ NA = 0.45 WD = 0.580 β = -1/18.5 r.sub.1 = 3.9264 d.sub.1 = 0.2321 n.sub.1 = 1.49819 ν.sub.1 = 57.8 r.sub.2 = -2.4314 d.sub.2 = 0.0928 r.sub.3 = -1.0479 d.sub.3 = 0.2089 n.sub.2 = 1.49819 ν.sub.2 = 57.8 r.sub.4 = -1.6446 d.sub.4 = 0.8704 r.sub.5 = 1.6841 d.sub.5 = 0.2321 n.sub.3 = 1.49819 ν.sub.3 = 57.8 r.sub.6 = -2.9405 d.sub.6 = 0.116 r.sub.7 = 0.8141 d.sub.7 = 0.1741 n.sub.4 = 1.77861 ν.sub.4 = 25.71 r.sub.8 = 1.8989 t = 0.15 n.sub.t = 1.50 f.sub.1 = 3.051 f.sub.2 = -6.561 f.sub.3 = 2.186 f.sub.4 = 1.710 f = 1 ______________________________________ 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, reference symbols ν 1 , ν 2 , ν 3 and ν 4 respectively represent Abbe's numbers of respective lenses at λ=6328 A, reference symbol t represents the thickness of cover glass, reference symbol t n represents the refractive index of cover glass, reference symbol NA represents the numerical aperture, reference symbol WD represents the working distance, reference symbol β represents magnification, and reference symbol f represents the focal length of the lens system as a whole.

Claim 10

A reproducing objective for video disks according to claim 1, in which said reproducing objective for video disks has the following numerical data: ______________________________________ NA = 0.45 WD = 0.530 β = -1/18.5 r.sub.1 = 2.7135 d.sub.1 = 0.2304 n.sub.1 = 1.49819 ν.sub.1 = 57.8 r.sub.2 = -2.3475 d.sub.2 = 0.0922 r.sub.3 = -1.1732 d.sub.3 = 0.2074 n.sub.2 = 1.49819 ν.sub.2 = 57.8 r.sub.4 = -2.2729 d.sub.4 = 0.9102 r.sub.5 = 2.3475 d.sub.5 = 0.2304 n.sub.3 = 1.49819 ν.sub.3 = 57.8 r.sub.6 = -2.7135 d.sub.6 = 0.0115 r.sub.7 = 0.7232 d.sub.7 = 0.1728 n.sub.4 = 1.77861 ν.sub.4 = 25.71 r.sub.8 = 1.8951 t = 0.15 n.sub.t = 1.50 f.sub.1 = 2.565 f.sub.2 = -5.193 f.sub.3 = 2.565 f.sub.4 = 1.411 f = 1 ______________________________________ 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, reference symbols ν 1 , ν 2 , ν 3 and ν 4 respectively represent Abbe's numbers of respective lenses at λ=6328 A, reference symbol t represents the thickness of cover glass, reference symbol t n represents the refractive index of cover glass, reference symbol NA represents the numerical aperture, reference symbol WD represents the workding distance, reference symbol β represents magnification, and reference symbol f represents the focal length of the lens system as a whole.

Claim 11

A reproducing objective for video disks according to claim 1, in which said reproducing objective for video disks has the following numerical data: ______________________________________ NA = 0.45 WD = 0.531 β = -1/18.5 r.sub.1 = 2.4705 d.sub.1 = 0.2306 n.sub.1 = 1.49819 ν.sub.1 = 57.8 r.sub.2 = -2.3810 d.sub.2 = 0.0922 r.sub.3 = -1.1846 d.sub.3 = 0.2075 n.sub.2 = 1.49819 ν.sub.2 = 57.8 r.sub.4 = -2.4965 d.sub.4 = 0.8647 r.sub.5 = 2.3810 d.sub.5 = 0.2306 n.sub.3 = 1.49819 ν.sub.3 = 57.8 r.sub.6 = -2.4705 d.sub.6 = 0.0115 r.sub.7 = 0.7225 d.sub.7 = 0.1729 n.sub.4 = 1.77861 ν.sub.4 = 25.71 r.sub.8 = 1.7879 t = 0.15 n.sub.t = 1.50 f.sub.1 = 2.473 f.sub.2 = 4.776 f.sub.3 = 2.473 f.sub.4 = 1.454 f = 1 ______________________________________ 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, reference symbols ν 1 , ν 2 , ν 3 and ν 4 respectively represent Abbe's numbers of respective lenses at λ=6328 A, reference symbol t represents the thickness of cover glass, reference symbol t n represents the refractive index of cover glass, reference symbol NA represents the numerical aperture, reference symbol WD represents the working distance, reference symbol β represents magnification, and reference symbol f represents the focal length of the lens system as a whole.

Claim 12

A reproducing objective for video disks according to claim 1, in which said reproducing objective for video disks has the following numerical data: ______________________________________ NA = 0.45 WD = 0.531 β = -1/18.5 r.sub.1 = 2.3500 d.sub.1 = 0.2306 n.sub.1 = 1.49819 ν.sub.1 = 57.8 r.sub.2 = -2.4361 d.sub.2 = 0.0923 r.sub.3 = -1.1911 d.sub.3 = 0.2076 n.sub.2 = 1.49819 ν.sub.2 = 57.8 r.sub.4 = -2.6000 d.sub.4 = 0.8418 r.sub.5 = 2.3500 d.sub.5 = 0.2306 n.sub.3 = 1.49819 ν.sub.3 = 57.8 r.sub.6 = -2.4361 d.sub.6 = 0.0115 r.sub.7 = 0.7255 d.sub.7 = 0.1730 n.sub.4 = 1.77861 ν.sub.4 = 25.71 r.sub.8 = 1.7739 t = 0.15 n.sub.t = 1.50 f.sub.1 = 2.440 f.sub.2 = -4.639 f.sub.3 = 2.440 f.sub.4 = 1.470 f = 1 ______________________________________ 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, reference symbols ν 1 , ν 2 , ν 3 and ν 4 respectively represent Abbe's numbers of respective lenses at λ=6328 A, reference symbol t represents the thickness of cover glass, reference symbol t n represents the refractive index of cover glass, reference symbol NA represents the numerical aperture, reference symbol WD represents the working distance, reference symbol β represents magnification, and reference symbol f represents the focal length of the lens system as a whole.

Claim 13

A reproducing objective for video disks according to claim 1, in which said reproducing objective for video disks has the following numerical data: ______________________________________ NA = 0.45 WD = 0.519 β = -1/18.5 r.sub.1 = 2.0414 d.sub.1 = 0.2306 n.sub.1 = 1.49819 ν.sub.1 = 57.8 r.sub.2 = -2.4915 d.sub.2 = 0.0922 r.sub.3 = -1.2311 d.sub.3 = 0.2079 n.sub.2 = 1.49819 ν.sub.2 = 57.8 r.sub.4 = -3.2939 d.sub.4 = 0.7955 r.sub.5 = 2.0414 d.sub.5 = 0.2306 n.sub.3 = 1.49819 ν.sub.3 = 57.8 r.sub.6 = -2.4915 d.sub.6 = 0.0115 r.sub.7 = 0.7239 d.sub.7 = 0.1729 n.sub.4 = 1.77861 ν.sub.4 = 25.71 r.sub.8 = 1.6673 t = 0.15 n.sub.t = 1.50 f.sub.1 = 2.291 f.sub.2 = -4.083 f.sub.3 = 2.291 f.sub.4 = 1.521 f = 1 ______________________________________ 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, reference symbols ν 1 , ν 2 , ν 3 and ν 4 respectively represent Abbe's numbers of respective lenses at λ=6328 A, reference symbol t represents the thickness of cover glass, reference symbol t n represents the refractive index of cover glass, reference symbol NA represents the numerical aperture, reference symbol WD represents the working distance, reference symbol β represents magnification, and reference symbol f represents the focal length of the lens system as a whole.

Claim 14

A reproducing objective for video disks according to claim 1, in which said reproducing objective for video disks has the following numerical data: ______________________________________ NA = 0.45 WD = 0.466 β = -1/18.5 r.sub.1 = 1.4004 d.sub.1 = 0.3362 n.sub.1 = 1.49819 ν.sub.1 = 57.8 r.sub.2 = ∞ d.sub.2 = 0.0815 r.sub.3 = -1.1768 d.sub.3 = 0.6990 n.sub.2 = 1.49819 ν.sub.2 = 57.8 r.sub.4 = -1.4754 d.sub.4 = 0.5296 r.sub.5 = 1.4004 d.sub.5 = 0.3362 n.sub.3 = 1.49819 ν.sub.3 = 57.8 r.sub.6 = ∞ d.sub.6 = 0.0125 r.sub.7 = 0.5856 d.sub.7 = 0.1398 n.sub.4 = 1.77861 ν.sub.4 = 25.71 r.sub.8 = 1.0622 t = 0.15 n.sub.t = 1.50 f.sub.1 = 2.811 f.sub.2 = -52.675 f.sub.3 = 2.811 f.sub.4 = 1.485 f = 1 ______________________________________ 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, reference symbols ν 1 , ν 2 , ν 3 and ν 4 respectively represent Abbe's numbers of respective lenses at λ=6328 A, reference symbol t represents the thickness of cover glass, reference symbol t n represents the refractive index of cover glass, reference symbol NA represents the numerical aperture, reference symbol WD represents the working distance, reference symbol β represents magnification, and reference symbol f represents the focal length of the lens system as a whole.

Claim 15

A reproducing objective for video disks according to claim 1, in which said reproducing objective for video disks has the following numerical data: ______________________________________ NA = 0.45 WD = 0.518 β = -1/18.5 r.sub.1 = 2.1493 d.sub.1 = 0.2304 n.sub.1 = 1.49020 ν.sub.1 = 57.8 r.sub.2 = -2.4314 d.sub.2 = 0.0922 r.sub.3 = -1.2120 d.sub.3 = 0.2074 n.sub.2 = 1.49020 ν.sub.2 = 57.8 r.sub.4 = -2.9160 d.sub.4 = 0.8296 r.sub.5 = 2.1493 d.sub.5 = 0.2304 n.sub.3 = 1.49020 ν.sub.3 = 57.8 r.sub.6 = -2.4314 d.sub.6 = 0.0115 r.sub.7 = 0.7141 d.sub.7 = 0.1728 n.sub.4 = 1.77861 ν.sub.4 = 25.71 r.sub.8 = 1.6709 t = 0.15 n.sub.t = 1.50 f.sub.1 = 2.366 f.sub.2 = -4.408 f.sub.3 = 2.366 f.sub.4 = 1.484 f = 1 ______________________________________ 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, reference symbols ν 1 , ν 2 , ν 3 and ν 4 respectively represent Abbe's numbers of respective lenses at λ=6328 A, reference symbol t represents the thickness of cover glass, reference symbol t n represents the refractive index of cover glass, reference symbol NA represents the numerical aperture, reference symbol WD represents the working distance, reference symbol β represents magnification, and reference symbol f represents the focal length of the lens system as a whole.

Claim 16

A reproducing objective for video disks according to claim 1, in which said reproducing objective for video disks has the following numerical data: ______________________________________ NA = 0.45 WD = 0.518 β = -1/18.5 r.sub.1 = 2.0987 d.sub.1 = 0.2304 n.sub.1 = 1.49020 ν.sub.1 = 57.8 r.sub.2 = -2.7034 d.sub.2 = 0.0922 r.sub.3 = -1.2295 d.sub.3 = 0.2074 n.sub.2 = 1.49020 ν.sub.2 = 57.8 r.sub.4 = -2.7034 d.sub.4 = 0.8259 r.sub.5 = 2.0987 d.sub.5 = 0.2304 n.sub.3 = 1.49020 ν.sub.3 = 57.8 r.sub.6 = -2.7034 d.sub.6 = 0.0115 r.sub.7 = 0.7206 d.sub.7 = 0.1728 n.sub.4 = 1.77861 ν.sub.4 = 25.71 r.sub.8 = 1.7740 t = 0.15 n.sub.t = 1.50 f.sub.1 = 2.449 f.sub.2 = -4.824 f.sub.3 = 2.449 f.sub.4 = 1.454 f = 1 ______________________________________ 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, reference symbols ν 1 , ν 2 , ν 3 and ν 4 respectively represent Abbe's numbers of respective lenses at λ=6328 A, reference symbol t represents the thickness of cover glass, reference symbol t n represents the refractive index of cover glass, reference symbol NA represents the numerical aperture, reference symbol WD represents the working distance, reference symbol β represents magnification, and reference symbol f represents the focal length of the lens system as a whole.