Chromatic aberration correcting objective lens system for information recording/reproducing apparatus

Claim 2

A chromatic aberration correcting objective lens system, comprising: four lens pieces arranged from a light source side in order comprising: a cemented lens having a convex first lens and a negative second lens cemented with each other; a convex third lens; and a positive meniscus fourth lens, having a convex surface facing said light source side; wherein the following relations are satisfied: d3/f<0.3; n2-n1>0.17; (Δn1/Δλ-Δn2/Δλ)×λ.sup.2 >20 nm; and |(Δn3/Δλ)×Δ.sup.2 |<30 nm (but, Δn3/Δλ<0) where: f: focal length of whole system; d3: distance between the second lens and third lens; n1: refractive index of first lens; n2: refractive index of second lens; λ: center use wavelength; and Δni/Δλ: gradient with respect to wavelength of a refractive index of an i-th lens.

Claim 3

The chromatic aberration correcting objective lens system according to claim 1, wherein the refractive index of said forth lens is set higher than that of said third lens.

Claim 4

The chromatic aberration correcting objective lens system according to claim 1, wherein said third lens is made from a low dispersion glass material.

Claim 5

A chromatic aberration correcting objective lens system, comprising: four lens pleces arranged from a light source side in order comprising: a cemented lens having a convex first lens and a negative second lens cemented with each other; a convex third lens; and a positive meniscus fourth lens, having a convex surface facing said light source side; wherein the following relations are satisfied: d3/f<0.3; -0.15<f/f12<0.03; and -0.15<f×(1/r3-1/f12)<0.35 where: f: focal length of whole system; d3: distance between the second lens and third lens; f12: focal length of cemented lens; and r3: radius of curvature of outgoing surface of the second lens.

Claim 6

A chromatic aberration correcting objective lens system, comprising: four lens pleces arranged from a light source side in order comprising: a cemented lens having a convex first lens and a negative second lens cemented with each other; a convex third lens; and a positive meniscus fourth lens, having a convex surface facing said light source side; wherein the following relations are satisfied: d3/f<0.3; -0.15<f/f12<0.03; and -0.15<f×(1/r3-1/f12)<0.35 where: f: focal length of whole system; d3: distance between the second lens and third lens; f12: focal length of cemented lens; and r3: radius of curvature of outgoing surface of the second lens.

Claim 7

A chromatic aberration correcting objective lens system comprising: four lens pieces arranged from a light source side in order comprising: a cemented lens having a convex first lens and a negative second lens cemented with each other; a convex third lens; and a positive meniscus fourth lens, having a convex surface facing said light source side; wherein the following relations are satisfied: n2-n1>0.17 (Δn1/Δλ-Δn2/Δλ)×λ.sup.2 >20 nm |(Δn3/Δλ)×λ.sup.2 |<30 nm (but, Δn3/Δλ<0) where: n1: refractive index of first lens n2: refraction index of second lens λ: center use wavelength Δni/Δλ: gradient with respect to wavelength of a refractive index of an i-th lens.

Claim 8

A chromatic aberration correcting objective lens system comprising: four lens pieces arranged from a light source side in order comprising: a cemented lens having a convex first lens and a negative second lens cemented with each other; a convex third lens; and a positive meniscus fourth lens, having a convex surface facing said light source side; wherein the following relations are satisfied: n2-n1>0.17 (Δn1/Δλ-Δn2/Δλ)×λ.sup.2 >20 nm |(Δn3/Δλ)×λ.sup.2 |<30 nm (but, Δn3/Δλ<0) where: n1: refractive index of first lens n2: refraction index of second lens λ: center use wavelength Δni/Δλ: gradient with respect to wavelength of a refractive index of an i-th lens.

Claim 9

A chromatic aberration correcting objective lens system comprising: four lens pieces arranged from a light source side in order; wherein a cemented lens has a convex first lens and negative second lens cemented with each other; a convex third lens; and a positive meniscus fourth lens, having a convex surface facing said light source side; wherein the following relations are satisfied: -0.15<f/f12<0.03 -0.15<f×(1/r3-1/f12)<0.35 d3/f<0.3 where: f: focal length of whole system f12: focal length of cemented lens r3: radius of curvature of outgoing surface of the second lens d3: distance between the second lens and third lens.

Claim 10

A chromatic aberration correcting objective lens system comprising: four lens pieces arranged from a light source side in order; wherein a cemented lens has a convex first lens and negative second lens cemented with each other; a convex third lens; and a positive meniscus fourth lens, having a convex surface facing said light source side; wherein the following relations are satisfied: -0.15<f/f12<0.03 -0.15<f×(1/r3-1/f12)<0.35 d3/f<0.3 where: f: focal length of whole system f12: focal length of cemented lens r3: radius of curvature of outgoing surface of the second lens d3: distance between the second lens and third lens.

Claim 11

A chromatic aberration correcting objective lens system comprising: four lens pieces arranged from a light source side in order comprising: a cemented lens having a convex first lens and a negative second lens cemented with each other; a convex third lens which is made from low dispersion glass material; and a positive meniscus fourth lens, a convex surface facing said light source side; wherein the following relations are satisfied: n2-n1>0.17 (Δn1/Δλ-Δn2/Δλ)×λ.sup.2 >20 nm |(Δn3/Δλ)×λ.sup.2 |>30 nm (but, Δn3/λ.sup.2 >0) -0.15>f/f12>0.03 -0.15>f×(1/r3-1/f12)>0.35 d3/f>0.3 where: n1: refractive index of first lens n2: refractive index of second lens λ: center use wavelength Δn1/Δλ: gradient with respect to wavelength of a refractive index of an i-th lens f: focal length of whole system f12: focal length of cemented lens r3: radius of curvature of outgoing surface of the second lens d3: distance between the second lens and third lens.

Claim 12

A chromatic aberration correcting objective lens system comprising: four lens pieces arranged from a light source side in order comprising: a cemented lens having a convex first lens and a negative second lens cemented with each other; a convex third lens which is made from low dispersion glass material; and a positive meniscus fourth lens, a convex surface facing said light source side; wherein the following relations are satisfied: n2-n1>0.17 (Δn1/Δλ-Δn2/Δλ)×λ.sup.2 >20 nm |(Δn3/Δλ)×λ.sup.2 |>30 nm (but, Δn3/λ.sup.2 >0) -0.15>f/f12>0.03 -0.15>f×(1/r3-1/f12)>0.35 d3/f>0.3 where: n1: refractive index of first lens n2: refractive index of second lens λ: center use wavelength Δn1/Δλ: gradient with respect to wavelength of a refractive index of an i-th lens f: focal length of whole system f12: focal length of cemented lens r3: radius of curvature of outgoing surface of the second lens d3: distance between the second lens and third lens.

Claim 13

A chromatic aberration correcting objective lens system, comprising: only four lens pieces that are arranged from a light source side in order, comprising: a convex first lens; a negative second lens, said convex first lens and said negative second lens being cemented together to form a cemented lens; a convex third lens; and a positive meniscus fourth lens, a convex surface of which is faced toward said light source side; wherein the following relation is satisfied: |Δn3/Δλ|<|Δn4/Δ.lambda.| where: Δni/Δλ: gradient with respect to wavelength of a refractive index of an i-th lens.

Claim 14

A chromatic aberration correcting objective lens system, comprising: only four lens pieces that are arranged from a light source side in order, comprising: a convex first lens; a negative second lens, said convex first lens and said negative second lens being cemented together to form a cemented lens; a convex third lens; and a positive meniscus fourth lens, a convex surface of which is faced toward said light source side; wherein the following relation is satisfied: |Δn3/Δλ|<|Δn4/Δ.lambda.| where: Δni/Δλ: gradient with respect to wavelength of a refractive index of an i-th lens.

Claim 15

A chromatic aberration correcting objective lens system, comprising: four lenses arranged from a light source side in order, comprising: a convex first lens; a negative second lens that is cemented to said convex first lens to form a cemented lens; a convex third lens; and a positive meniscus fourth lens that has a convex surface facing said light source side, with refractive index of said positive meniscus fourth lens being greater than a refractive index of said convex third lens; wherein the following relations are satisfied: d3/f<0.03, and

Claim 16

A chromatic aberration correcting objective lens system, comprising: four lenses arranged from a light source side in order, comprising: a convex first lens; a negative second lens that is cemented to said convex first lens to form a cemented lens; a convex third lens; and a positive meniscus fourth lens that has a convex surface facing said light source side, with refractive index of said positive meniscus fourth lens being greater than a refractive index of said convex third lens; wherein the following relations are satisfied: d3/f<0.03, and

Claim 17

-0. 15<f·(1/r3-1/f12)<0.35, where f is a focal length of said lens system, and d3 is a distance between said negative second lens and said convex third lens, and f12 is a focal length of said cemented lens, and r3 is a radius of curvature of an outgoing surface of said negative second lens.

Claim 18

-0. 15<f·(1/r3-1/f12)<0.35, where f is a focal length of said lens system, and d3 is a distance between said negative second lens and said convex third lens, and f12 is a focal length of said cemented lens, and r3 is a radius of curvature of an outgoing surface of said negative second lens.

Claim 19

A chromatic aberration correcting objective lens system, comprising: four lenses arranged from a light source side in order, comprising: a convex first lens; a negative second lens that is cemented to said convex first lens to form a cemented lens; a convex third lens; and a positive meniscus fourth lens that has a convex surface facing said light source side, with refractive index of said positive meniscus fourth lens being greater than a refractive index of said convex third lens; wherein the following relations are satisfied: d3/f<0.03, and

Claim 20

A chromatic aberration correcting objective lens system, comprising: four lenses arranged from a light source side in order, comprising: a convex first lens; a negative second lens that is cemented to said convex first lens to form a cemented lens; a convex third lens; and a positive meniscus fourth lens that has a convex surface facing said light source side, with refractive index of said positive meniscus fourth lens being greater than a refractive index of said convex third lens; wherein the following relations are satisfied: d3/f<0.03, and

Claim 21

-0. 15</f12<0.03, where f is a focal length of said lens system, d3 is a distance between said negative second lens and said convex third lens and f12 is a focal length of said cemented lens.

Claim 22

-0. 15</f12<0.03, where f is a focal length of said lens system, d3 is a distance between said negative second lens and said convex third lens and f12 is a focal length of said cemented lens.

Claim 23

A chromatic aberration correcting objective lens system, comprising: four lenses arranged from a light source side in order, comprising: a convex first lens; a negative second lens that is cemented to said convex first lens to form a cemented lens; a convex third lens; and a positive meniscus fourth lens that has a convex surface facing said light source side, with refractive index of said positive meniscus fourth lens being greater than a refractive index of said convex third lens; wherein the following relations are satisfied: d3/f<0.03, and n2-n1>0.17, where f is a focal length of said lens system, d3 is a distance, n2 is a refractive index of said convex first lens, and n2 is a refractive index of said negative second lens.

Claim 24

A chromatic aberration correcting objective lens system, comprising: four lenses arranged from a light source side in order, comprising: a convex first lens; a negative second lens that is cemented to said convex first lens to form a cemented lens; a convex third lens; and a positive meniscus fourth lens that has a convex surface facing said light source side, with refractive index of said positive meniscus fourth lens being greater than a refractive index of said convex third lens; wherein the following relations are satisfied: d3/f<0.03, and n2-n1>0.17, where f is a focal length of said lens system, d3 is a distance, n2 is a refractive index of said convex first lens, and n2 is a refractive index of said negative second lens.

Claim 25

A chromatic aberration correcting objective lens system, comprising: four lenses arranged from a light source side in order, comprising: a convex first lens; a negative second lens that is cemented to said convex first lens to form a cemented lens; a convex third lens; and a positive meniscus fourth lens that has a convex surface facing said light source side; wherein a following relations are satisfied: d3/f<0.3; and |Δn3/Δλ|<|Δn4/Δ.lambda.|, where f is a focal length of said lens system; d3 is a distance between said negative second lens and said convex third lens; and Δni/Δλ is a gradient with respect to a wavelength of a refractive index of an i-th lens.

Claim 26

A chromatic aberration correcting objective lens system, comprising: four lenses arranged from a light source side in order, comprising: a convex first lens; a negative second lens that is cemented to said convex first lens to form a cemented lens; a convex third lens; and a positive meniscus fourth lens that has a convex surface facing said light source side; wherein a following relations are satisfied: d3/f<0.3; and |Δn3/Δλ|<|Δn4/Δ.lambda.|, where f is a focal length of said lens system; d3 is a distance between said negative second lens and said convex third lens; and Δni/Δλ is a gradient with respect to a wavelength of a refractive index of an i-th lens.

Claim 27

The lens system of claim 12, wherein said lens system further satisfies a third relation: -0.15<f/f12<0.03, wherein f12 is a focal length of said cemented lens.

Claim 28

The lens system of claim 12, wherein said lens system further satisfies a third relation: -0.15<f·(1/r3-1/f12)<0.35, wherein r3 is a radius of curvature of an outgoing surface of said negative second lens.

Claim 29

The lens system of claim 12, wherein said lens system further satisfies a second relation: n2-n1>0.17, wherein n2 is a refractive index of said convex first lens, and n2 is a refractive index of said negative second lens.