Lens system for optical disks

Claim 2

A lens system for optical disks comprising a single lens element, one surface of said lens element being formed as an aspherical one expressed by the formula shown below wherein the standard radius of curvature of said surface is r, the distance from a point on the lens surface to the tangential plane which is tangential to said surface at the vertex thereof is x, and the distance from said point to the optical axis is y, said lens system being arranged to satisfy the conditions (1) and (2) shown below: ##EQU2## (1) 0.1<n-2 r1/f<0.5 (2) 0.25<d/f<0.75 where B, E, F, G, H, I, J, ... respectively represent the 2nd-, 4th-, 6th-, 8th-, 10th-, 12th-, 14th-, ... order coefficients of the aspherical surface, k represents the constant of cone, r1 represents the radius of curvature of the first surface (the standard radius of curvature thereof if aspherical), d represents the thickness of said lens element, n represents the refractive index of said lens element, and f represents the focal length of said lens system.

Claim 3

A lens system for optical disks according to claim 1, the first surface of said lens element being aspherical and the second surface thereof being spherical.

Claim 4

A lens system for optical disks according to claim 2, wherein said lens system for optical disks has the following numerical data: ______________________________________ r1 = 0.8282 (aspherical) d = 0.6522 n = 1.89502 r2 = 6.9675 f = 1, WD = 0.4632, t = 0.2609 k = -0.543, B = 0, E = 0.21273 × 10.sup.-1 F = 0.1284 × 10.sup.-2, G = -0.59402 × 10.sup.-2 H = -0.12514 × 10.sup.-1, I = 0.94836 × 10.sup.-9 J = -0.72672 × 10.sup.-8, n -- 2 r1/f ≈ 0.24 ______________________________________ where r1 represents the standard radius of curvature of the first surface, r2 represents the radius of curvature of the second surface, n represents the refractive index of said lens element at 800 nm wavelength, WD represents the working distance, and t represents the thickness of a cover glass.

Claim 5

A lens system for optical disks according to claim 2, wherein said lens system for optical disks has the following numerical data: ______________________________________ r1 = 0.7586 (aspherical) d = 0.5217 n = 1.76825 r2 = 42.1426 f = 1, WD = 0.5364, t = 0.2609 k = 1.2248, B = 0, E = 0.20071 F = 0.15674 × 10.sup.-1, G = -0.81498 × 10.sup.-2 H = -0.12911 × 10.sup.-1, I = 0.14655 × 10.sup.-8 J = 0.53678 × 10.sup.-13, n -- 2 r1/f ≈ 0.25 ______________________________________ where r1 represents the standard radius of curvature of the first surface, r2 represents the radius of curvature of the second surface, n represents the refractive index of said lens element at 800 nm wavelength, WD represents the working distance, and t represents the thickness of a cover glass.

Claim 6

A lens system for optical disks according to claim 2, wherein said lens system for optical disks has the following numerical data: ______________________________________ r1 = 0.6796 (aspherical) d = 0.5435 n = 1.60838 r2 = -4.0499 f = 1, WD = 0.5326, t = 0.2609 k = 1.678, B = 0, E = 0.40592 F = -0.23739, G = -0.8318 × 10.sup.-2 H = -0.12906 × 10.sup.-1, I = 0.14642 × 10.sup.-8 J = 0.53203 × 10.sup.-13, n -- 2 r1/f ≈ 0.25 ______________________________________ where r1 represents the standard radius of curvature of the first surface, r2 represents the radius of curvature of the second surface, n represents the refractive index of said lens element at 800 nm wavelength, WD represents the working distance, and t represents the thickness of a cover glass.

Claim 7

A lens system for optical disks according to claim 2, wherein said lens system for optical disks has the following numerical data: ______________________________________ r1 = 0.6022 (aspherical) d = 0.5217 n = 1.48423 r2 = -1.7734 f = 1, WD = 0.5525, t = 0.2609 k = 0.2721, B = 0, E = -0.30981 F = -0.68736, G = -0.80047 H = -0.21653 × 10, I = 0.11728 × 10.sup.-7 J = 0.11148 × 10.sup.-10, n -- 2 r1/f ≈ 0.28 ______________________________________ where r1 represents the standard radius of curvature of the first surface, r2 represents the radius of curvature of the second surface, n represents the refractive index of said lens element at 800 nm wavelength, WD represents the working distance, and t represents the thickness of a cover glass.

Claim 8

A lens system for optical disks according to claim 1, the first surface of said lens element being spherical and the second surface thereof being aspherical.

Claim 9

A lens system for optical disks according to claim 7, further satisfying the condition (3) shown below: (3) 0.7<r1/f<0.85

Claim 10

A lens for optical disks according to claim 8, further satisfying the condition (4) shown below: (4) 1.8<n

Claim 11

A lens system for optical disks according to claim 9, wherein said lens system for optical disks has the following numerical data: ______________________________________ r1 = 0.775 d = 0.2826 n = 1.89502 r2 = 4.7846 (aspherical) f = 1, WD = 0.66288, t = 0.2609 k = 39.1393, B = 0, E = 0.2887 F = -0.19998, G = 0.35833 H = -0.65269, I = 0.18261 × 10.sup.-1 J = 0.21333 × 10.sup.-3, n -- 2 r1/f ≈ 0.35 ______________________________________ where r1 represents the radius of curvature of the first surface, r2 represents the standard radius of curvature of the second surface, n represents the refractive index of said lens element at 800 nm wavelength, WD represents the working distance, and t represents the thickness of a cover glass.

Claim 12

A lens system for optical disks according to claim 9, wherein said lens system for optical disks has the following numerical data: ______________________________________ r1 = 0.7578 d = 0.2826 n = 1.82199 r2 = 8.0779 (aspherical) f = 1, WD = 0.6668, t = 0.2609 k = -151.7316, B = 0, E = 0.25648 F = -0.278, G = 0.31784 H = -0.65269, I = 0.18261 × 10.sup.-1 J = 0.21333 × 10.sup.-3, n -- 2 r1/f ≈ 0.31 ______________________________________ where r1 represents the radius of curvature of the first surface, r2 represents the standard radius of curvature of the second surface, n represents the refractive index of said lens element at 800 nm wavelength, WD represents the working distance, and t represents the thickness of a cover glass.