Reproducing objective for video disks

Claim 2

A reproducing objective for video disks comprising a first, second and third lenses, said first lens being a biconvex lens, said second lens being a negative meniscus lens, said third lens being a positive meniscus lens, said reproducing objective for video disks satisfying the following conditions: (1) -1.65f<r 3 <-1.00f (2) 0.42f<r 5 <0.56f (3) f 3 <0.8f (4) 0.7f<d 4 <1.0f (5) 1.4f<f 1 <1.7f (6) 0.1f<d 5 <0.19f wherein reference symbol r 3 represents the radius of curvature of the surface on the first lens side of the second lens, reference symbol r 5 represents the radius of curvature of the surface on the second lens side of the third lens, reference symbol d 4 represents the airspace between the second and third lenses, reference symbol d 5 represents the thickness of the third lens, reference symbol f 1 represents the focal length of the first lens, reference symbol f 3 represents the focal length of the third lens, 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: ______________________________________ r.sub.1 = 1.7571 d.sub.1 = 0.294 n.sub.1 = 1.77861 ν.sub.1 = 25.7 r.sub.2 = -2.9694 d.sub.2 = 0.129 r.sub.3 = -1.2488 d.sub.3 = 0.235 n.sub.2 = 1.51462 ν.sub.2 = 64.2 r.sub.4 = -2.6100 d.sub.4 = 0.848 r.sub.5 = 0.5044 d.sub.5 = 0.118 n.sub.3 = 1.77861 ν.sub.3 = 25.7 r.sub.6 = 3.9556 f = 1 N.A. = 0.4 W.D. = 0.259 β = -0.05X f.sub.3 = 0.7318 f.sub.1 = 1.458 ______________________________________ wherein reference symbols r 1 through r 6 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 5 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 , n 2 and n 3 respectively represent refractive indices of respective lenses at λ=632.8 nm, reference symbols ν 1 , ν 2 and ν 3 respectively represent Abbe's numbers of respective lenses for d-line, reference symbol f represents the focal length of the lens system as a whole, reference symbols f 1 and f 3 respectively represents focal lengths of the first and third lenses, reference symbol N.A. represents the numerical aperture, reference symbol W.D. represents the working distance, and reference symbol β represents magnification.

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 = 1.3306 d.sub.1 = 0.232 n.sub.1 = 1.77861 ν.sub.1 = 25.7 r.sub.2 = -8.0103 d.sub.2 = 0.131 r.sub.3 = -1.6152 d.sub.3 = 0.335 n.sub.2 = 1.51462 ν.sub.2 = 64.2 r.sub.4 = -3.5690 d.sub.4 = 0.751 r.sub.5 = 0.4414 d.sub.5 = 0.119 n.sub.3 = 1.77861 ν.sub.3 = 25.7 r.sub.6 = 1.4929 f = 1 N.A. = 0.4 W.D. = 0.245 β = -0.05X f.sub.3 = 0.7672 f.sub.1 = 1.483 ______________________________________ wherein reference symbols r 1 through r 6 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 5 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 , n 2 and n 3 respectively represent refractive indices of respective lenses at λ=632.8 nm, reference symbols ν 1 , ν 2 and ν 3 respectively represent Abbe's numbers of respective lenses for d-line, reference symbol f represents the focal length of the lens system as a whole, reference symbols f 1 and f 3 respectively represents focal lengths of the first and third lenses, reference symbol N.A. represents the numerical aperture, reference symbol W.D. represents the working distance, and reference symbol β represents magnification.

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 = 2.6586 d.sub.1 = 0.377 n.sub.1 = 1.77861 ν.sub.1 = 25.7 r.sub.2 = -2.4267 d.sub.2 = 0.129 r.sub.3 = -1.0082 d.sub.3 = 0.274 n.sub.2 = 1.51462 ν.sub.2 = 64.2 r.sub.4 = -1.3662 d.sub.4 = 0.923 r.sub.5 = 0.5442 d.sub.5 = 0.183 n.sub.3 = 1.77861 ν.sub.3 = 25.7 r.sub.6 = 5.2755 f = 1 N.A. = 0.4 W.D. = 0.259 β = -0.05X f.sub.3 = 0.7667 f.sub.1 = 1.683 ______________________________________ wherein reference symbols r 1 through r 6 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 5 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 , n 2 and n 3 respectively represent refractive indices of respective lenses at λ=632.8 nm, reference symbols ν 1 , ν 2 and ν 3 respectively represent Abbe's numbers of respective lenses for d-line, reference symbol f represents the focal length of the lens system as a whole, reference symbols f 1 and f 3 respectively represents focal lengths of the first and third lenses, reference symbol N.A. represents the numerical aperture, reference symbol W.D. represents the working distance, and reference symbol β represents magnification.