Objective for video disks

Claim 2

An objective for video disks comprising a first and second lens components, said first lens component being a positive cemented oublet consisting of a positive lens and negative lens, said second lens component bieng a positive meniscus lens arranged concave toward the image side, said objective for video disks satisfying the following conditions: (1) -1.46/f<n 2 /n 1 ·1/r 2 <-1.1/f (2) 1.7f<(n 3 -1)r 5 <2.4f wherein reference symbol r 2 represents the radius of curvature of the cemented surface of the first lens component, reference symbol r 5 represents the radius of curvature of the surface on the image side of the second lens component, reference symbols n 1 , n 2 and n 3 respectively represent refractive indices of respective lenses at the wavelength of 632.8 nm, and reference symbol f represents the focal length of the lens system as a whole.

Claim 3

An objective for video disks according to claim 1, in which said objective for video disks has the following numerical data: ______________________________________ r.sub.1 = 2.605 d.sub.1 = 0.4070 n.sub.1 = 1.51462 ν.sub.1 = 64.1 r.sub.2 = -0.8514 d.sub.2 = 0.2581 n.sub.2 = 1.75607 ν.sub.2 = 26.6 r.sub.3 = -2.1127 d.sub.3 = 0.0233 r.sub.4 = 0.7804 d.sub.4 = 0.3256 n.sub.3 = 1.75607 ν.sub.3 = 26.6 r.sub.5 = 2.8579 f = 1 s = 0.5581 t = 0.2558 N.A. = 0.45 ______________________________________ wherein reference symbols r 1 through r 5 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 4 respectively represent thicknesses of respective lenses and airspace between lenses, reference symbols n 1 , n 2 and n 3 respectively represent refractive indices of respective lenses at the wavelength of 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 symbol s represents the working distance, reference symbol t represents the thickness of the cover glass and reference symbol N.A. represents the numerical aperture.

Claim 4

An objective for video disks according to claim 1, in which said objective for video disks has the following numerical data: ______________________________________ r.sub.1 = 2.5324 d.sub.1 = 0.4070 n.sub.1 = 1.51462 ν.sub.1 = 64.1 r.sub.2 = -0.8796 d.sub.2 = 0.2581 n.sub.2 = 1.77861 ν.sub.2 = 25.7 r.sub.3 = -2.1384 d.sub.3 = 0.0233 r.sub.4 = 0.7883 d.sub.4 = 0.3256 n.sub.3 = 1.77861 ν.sub.3 = 25.7 r.sub.5 = 2.7431 f = 1 s = 0.5581 t = 0.2558 N.A. = 0.45 ______________________________________ wherein reference symbols r 1 through r 5 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 4 respectively represent thicknesses of respective lenses and airspaces between lenses, reference symbols n 1 , n 2 and n 3 respectively represent refractive indices of respective lenses at the wavelength of 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 symbol s represents the working distance, reference symbol t represents the thickness of the cover glass and reference symbol N.A. represents the numerical aperture.

Claim 5

An objective for video disks according to claim 1, in which said objective for video disks has the following numerical data: ______________________________________ r.sub.1 = 2.744 d.sub.1 = 0.4070 n.sub.1 = 1.51462 ν.sub.1 = 64.1 r.sub.2 = -0.8073 d.sub.2 = 0.2581 n.sub.2 = 1.77861 ν.sub.2 = 25.7 r.sub.3 = -2.0591 d.sub.3 = 0.0233 r.sub.4 = 0.7685 d.sub.4 = 0.3256 n.sub.3 = 1.77861 ν.sub.3 = 25.7 r.sub.5 = 3.0267 f = 1 s = 0.5581 t = 0.2558 N.A. = 0.45 ______________________________________ wherein reference symbols r 1 through r 5 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 4 respectively represent thickeness of respective lenses and airspace between lenses, reference symbols n 1 , n 2 and n 3 respectively represent refractive indices of respective lenses at the wavelength of 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 symbol s represents the working distance, reference symbol t represents the thickness of the cover glass and reference symbol N.A. represents the numerical aperture.

Claim 6

An objective for video disks according to claim 1, in which said objective for video disks has the following numerical data: ______________________________________ r.sub.1 = 1.8224 d.sub.1 = 0.4067 n.sub.1 = 1.51462 ν.sub.1 = 64.1 r.sub.2 = -1.0188 d.sub.2 = 0.2580 n.sub.2 = 1.77861 ν.sub.2 = 25.7 r.sub.3 = -2.7232 d.sub.3 = 0.0232 r.sub.4 = 0.7560 d.sub.4 = 0.3254 n.sub.3 = 1.77861 ν.sub.3 = 25.7 r.sub.5 = 2.1852 f = 1 s = 0.5113 t = 0.2556 N.A. = 0.50 ______________________________________ wherein reference symbols r 1 through r 5 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 4 respectively represent thicknesses of respective lenses and airspace between lenses, reference symbols n 1 , n 2 and n 3 respectively represent refractive indices of respective lenses at the wavelength of 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 symbol s represents the working distance, reference symbol t represents the thickness of the cover glass and reference symbol N.A. represents the numerical aperture.