Lens for use with an optical disk

Claim 2

A lens system for use with an optical disk comprising, in order from the side of a light source, a front unit composed of a cemented lens made up of positive and negative lenses, and a rear unit composed of at least a single positive lens, said lens system satisfying the following conditions: ν.sub.+ >50, ν.sub.- <35; (1) and ΔN.sub.+ /ΔN.sub.- <0.5, ΔN.sub.- >0 (2) where ν + is the Abbe number of a positive lens, ν - is the Abbe number of a negative lens, ΔN + is the temperature coefficient of the refractive index of a positive lens, and ΔN - is the temperature coefficient of the refractive index of a negative lens.

Claim 3

The lens system according to claim 1, further satisfying the following chart: ______________________________________ Surface No. r.sub.i d.sub.i N.sub.i ν.sub.i ΔN.sub.i ______________________________________ 1 1.2763 0.1304 1.67790 55.3 0.8 2 -0.7173 0.0815 1.78472 25.7 9.4 3 ∞ 0.4638 4 0.6735 0.0815 1.61800 63.4 -3.5 5 5.1964 ______________________________________ wherein r i =the radius of curvature of the surface at the i-th position as counted from the surface closest to the light source; d i =the thickness of the lens at the i-th position as counted from the lens closest to the light source or the aerial distance between the i-th and (i+1)th lenses; N i =the refractive index of the i-th lens as counted from the lens closest to the light source; V i =the Abbe number of the i-th lens as counted from the lens closest to the light source; and ΔN i =the temperature coefficient unit: 10 -6 /°C. of refractive index of the i-th lens as counted from the lens closest to the light source.

Claim 4

The lens system according to claim 1, further satisfying the following chart: ______________________________________ Surface No. r.sub.i d.sub.i N.sub.i ν.sub.i ΔN.sub.i ______________________________________ 1 1.1117 0.2121 1.61800 63.4 -3.5 2 -0.9001 0.2026 1.80518 25.4 10.1 3 -4.5069 0.9328 4 0.4082 0.1158 1.61800 63.4 -3.5 5 1.6515 ______________________________________ wherein r i =the radius of curvature of the surface at the i-th position as counted from the surface closest to the light source; d i =the thickness of the lens at the i-th position as counted from the lens closest to the light source or the aerial distance between the i-th and (i+1)th lenses; N i =the refractive index of the i-th lens as counted from the lens closest to the light source; V i =the Abbe number of the i-th lens as counted from the lens closest to the light source; and ΔN i =the temperature coefficient unit: 10 -6 /°C. of refractive index of the i-th lens as counted from the lens closest to the light source.

Claim 5

The lens system according to claim 1, further satisfying the following chart: ______________________________________ Surface No. r.sub.i d.sub.i N.sub.i ν.sub.i ΔN.sub.i ______________________________________ 1 1.3076 0.2405 1.61800 63.4 -3.5 2 -0.8732 0.2105 1.76182 26.6 8.3 3 -4.4001 1.0489 4 0.3419 0.1372 1.57099 50.8 0.0 5 1.3792 ______________________________________ wherein r i =the radius of curvature of the surface at the i-th position as counted from the surface closest to the light source; d i =the thickness of the lens at the i-th position as counted from the lens closest to the light source or the aerial distance between the i-th and (i+1)th lenses; N i =the refractive index of the i-th lens as counted from the lens closest to the light source; V i =the Abbe number of the i-th lens as counted from the lens closest to the light source; and ΔN i =the temperature coefficient unit: 10 -6 /°C. of refractive index of the i-th lens as counted from the lens closest to the light source.

Claim 6

The lens system according to claim 1, further satisfying the following chart: ______________________________________ Surface No. r.sub.i d.sub.i N.sub.i ν.sub.i ΔN.sub.i ______________________________________ 1 1.0571 0.1852 1.60311 60.7 2.7 2 -1.2986 0.1684 1.78472 25.7 9.4 3 23.5690 0.9891 4 0.4190 0.1536 1.61800 63.4 -3.5 5 -21.7503 0.0084 6 -1.6475 0.1578 1.78472 25.7 9.4 7 -5.560 ______________________________________ wherein r i =the radius of curvature of the surface at the i-th position as counted from the surface closest to the light source; d i =the thickness of the lens at the i-th position as counted from the lens closest to the light source or the aerial distance between the i-th and (i+1)th lenses; N i =the refractive index of the i-th lens as counted from the lens closest to the light source; V i =the Abbe number of the i-th lens as counted from the lens closest to the light source; and ΔN i =the temperature coefficient unit: 10 -6 /°C. of refractive index of the i-th lens as counted from the lens closest to the light source.

Claim 7

The lens system according to claim 1, further satisfying the following chart: ______________________________________ Surface No. r.sub.i d.sub.i N.sub.i ν.sub.i ΔN.sub.i ______________________________________ 1 1.3933 0.1873 1.61800 63.4 -3.5 2 -0.9801 0.1158 1.80518 25.4 10.1 3 -8.9403 0.9289 4 0.5263 0.1683 1.61800 63.4 -3.5 5 -2.2460 0.1053 6 -0.7985 0.1158 1.80518 25.4 10.1 7 -1.4138 ______________________________________ wherein r i =the radius of curvature of the surface at the i-th position as counted from the surface closest to the light source; d i =the thickness of the lens at the i-th position as counted from the lens closest to the light source or the aerial distance between the i-th and (i+1)th lenses; N i =the refractive index of the i-th lens as counted from the lens closest to the light source; V i =the Abbe number of the i-th lens as counted from the lens closest to the light source; and ΔN i =the temperature coefficient unit: 10 -6 /°C. of refractive index of the i-th lens as counted from the lens closest to the light source.

Claim 8

The lens system according to claim 1, further satisfying the following chart: ______________________________________ Surface No. r.sub.i d.sub.i N.sub.i ν.sub.i ΔN.sub.i ______________________________________ 1 0.9745 0.2391 1.48749 70.2 -0.9 2 -0.7939 0.2632 1.80518 25.4 10.1 3 -2.8116 0.4103 4 0.5906 0.2632 1.48749 70.2 -0.9 5 -1.0826 0.1622 6 -0.4663 0.1158 1.805181 25.4 10.1 7 -0.6962 ______________________________________ wherein r i =the radius of curvature of the surface at the i-th position as counted from the surface closest to the light source; d i =the thickness of the lens at the i-th position as counted from the lens closest to the light source or the aerial distance between the i-th and (i+1)th lenses; N i =the refractive index of the i-th lens as counted from the lens closest to the light source; V i =the Abbe number of the i-th lens as counted from the lens closest to the light source; and ΔN i =the temperature coefficient unit: 10 -6 /°C. of refractive index of the i-th lens as counted from the lens closest to the light source.

Claim 9

The lens system according to claim 1, further satisfying the following chart: ______________________________________ Surface No. r.sub.i d.sub.i N.sub.i ν.sub.i ΔN.sub.i ______________________________________ 1 1.3465 0.1826 1.61800 63.4 -3.5 2 -1.0557 0.1189 1.76182 26.6 8.3 3 -9.6129 0.9436 4 0.4711 0.2632 1.57099 50.8 0.0 5 -2.5348 0.0084 6 -1.3349 0.1368 1.805181 25.4 10.1 7 -3.0344 ______________________________________ wherein r i =the radius of curvature of the surface at the i-th position as counted from the surface closest to the light source; d i =the thickness of the lens at the i-th position as counted from the lens closest to the light source or the aerial distance between the i-th and (i+1)th lenses; N i =the refractive index of the i-th lens as counted from the lens closest to the light source; V i =the Abbe number of the i-th lens as counted from the lens closest to the light source; and ΔN i =the temperature coefficient unit: 10 -6 /°C. of refractive index of the i-th lens as counted from the lens closest to the light source.

Claim 10

The lens system according to claim 1, wherein said rear unit is composed of a positive lens and a negative lens.