Gradient index lens system

Claim 2

A gradient index lens system for use as a pick-up lens for an optical disc, in which spherical aberration and coma are well corrected and which has an excellent imaging performance, said lens system comprising: a first gradient index lens of a convergent refractive power having a gradient index rotationally symmetrical with respect to the optical axis thereof and having a refractive index which continuously decreases as the radius from the optical axis increases until the periphery is reached, and a second gradient index lens of a convergent refractive power having a gradient index rotationally symmetrical with respect to the optical axis thereof and having a refractive index which continuously decreases as the radius from the optical axis increases until the periphery is reached, the gradient index of said first gradient index lens being different from that of said second gradient index lens, and the gradient index of said first and second gradient index lenses being so determined that spherical aberration and coma of said lens system are compensated, wherein when the gradient index n 1 of said first gradient index lens and the gradient index n 2 of said second gradient index lens are expressed by ##EQU14## the following conditions are satisfied:

Claim 3

0<h 41 <5.0 -1.5<h.sub.61 <0 -5.0<h.sub.42 <-0.5 1.0<h.sub.62 <8.0 where n 0 is the center refractive index, r is the radial distance from the optical axis, g is a parameter indicative of the degree of refractive index gradient, h 4 and h 6 are the coefficients of the fourth order term and the sixth order term as the high order terms of gradient index, and subscript numbers 1 and 2 mean that the gradient indices are the amounts regarding said different first and second gradient index lenses.

Claim 4

0<h 41 <5.0 -1.5<h.sub.61 <0 -5.0<h.sub.42 <-0.5 1.0<h.sub.62 <8.0 where n 0 is the center refractive index, r is the radial distance from the optical axis, g is a parameter indicative of the degree of refractive index gradient, h 4 and h 6 are the coefficients of the fourth order term and the sixth order term as the high order terms of gradient index, and subscript numbers 1 and 2 mean that the gradient indices are the amounts regarding said different first and second gradient index lenses.

Claim 5

A gradient index lens system according to claim 1, wherein numerical data are as follows: ______________________________________ NA = 0.45, WD = 2.55, Maximum image height: 0.07 mm n.sub.01 = n.sub.02 = 1.7 g.sub.1 = g.sub.2 = 0.243 r.sub.0 = 1.6 mm ______________________________________ h.sub.41 = 2.381 h.sub.61 = -0.325 z.sub.1 = 1.57 h.sub.42 = -2.591 h.sub.62 = 3.655 z.sub.2 = 1.57 ______________________________________ where n 0 is the center refractive index, r 0 is the effective diameter of a lens, g is a parameter indicative of the degree of refractive index gradient, h 4 and h 6 are the coefficients of the fourth order term and the sixth order term as the high order terms of gradient index, z is a lens length, and subscript numbers 1 and 2 mean that the gradient indices are the amounts regarding said different first and second gradient index lenses.

Claim 6

A gradient index lens system according to claim 1, wherein numerical data are as follows: ______________________________________ NA = 0.45, WD = 2.55 mm, Maximum image height: 0.083 mm n.sub.01 = n.sub.02 = 1.66666 g.sub.1 = g.sub.2 = 0.1974 r.sub.0 = 1.8 mm ______________________________________ h.sub.41 = 2.124 h.sub.61 = -0.325 z.sub.1 = 2.215 h.sub.42 = -2.476 h.sub.62 = 4.055 z.sub.2 = 2.215 ______________________________________ where n 0 is the center refractive index, r 0 is the effective diameter of a lens, g is a parameter indicative of the degree of refractive index gradient, h 4 and h 6 are the coefficients of the fourth order term and the sixth order term as the high order terms of gradient index, z is a lens length, and subscript numbers 1 and 2 mean that the gradient indices are the amounts regarding said different first and second gradient index lenses.

Claim 7

A gradient index lens system according to claim 1, wherein numerical data are as follows: ______________________________________ NA = 0.45, WD = 2.55 mm, Maximum image height: 0.07 mm n.sub.01 = n.sub.02 = 1.66666 g.sub.1 = g.sub.2 = 0.145 r.sub.0 = 2.2 mm ______________________________________ h.sub.41 = 1.860 h.sub.61 = -0.322 z.sub.1 = 3.52 h.sub.42 = -2.445 h.sub.62 = 5.057 z.sub.2 = 3.52 ______________________________________ where n 0 is the center refractive index, r 0 is the effective diameter of a lens, g is a parameter indicative of the degree of refractive index gradient, h 4 and h 6 are the coefficients of the fourth order term and the sixth order term as the high order terms of gradient index, z is a lens length, and subscript numbers 1 and 2 mean that the gradient indices are the amounts regarding said different first and second gradient index lenses.

Claim 8

A gradient index lens system according to claim 1, wherein numerical data are as follows: ______________________________________ NA = 0.33, WD = 2.55, Maximum image height: 0.07 mm n.sub.01 = n.sub.02 = 1.66666 g.sub.1 = g.sub.2 = 0.36 r.sub.0 = 1.0 mm ______________________________________ h.sub.41 = 2.607 h.sub.61 = -0.726 z.sub.1 = 0.81 h.sub.42 = -2.551 h.sub.62 = 3.040 z.sub.2 = 0.81 ______________________________________ where n 0 is the center refractive index, r 0 is the effective diameter of a lens, g is a parameter indicative of the degree of refractive index gradient, h 4 and h 6 are the coefficients of the fourth order term and the sixth order term as the high order terms of gradient index, z is a lens length, and subscript numbers 1 and 2 mean that the gradient indices are the amounts regarding said different first and second gradient index lenses.

Claim 9

A gradient index lens system for use as a pick-up lens for an optical disc, in which spherical aberration and coma are well corrected and which has an excellent imaging performance, said lens system comprising: a first gradient index lens of a convergent refractive power having a gradient index rotationally symmetrical with respect to the optical axis thereof, said first gradient index lens extending continuously from its optical axis to its periphery and having a refractive index which continuously decreases as the radius from the optical axis increases until the periphery is reached, and a second gradient index lens of a convergent refractive power having a gradient index rotationally symmetrical with respect to the optical axis thereof, said second gradient index lens extending continuously from its optical axis to its periphery and having a refractive index which continuously decreases as the radius from the optical axis increases until the periphery is reached, the optical axes of said first and second gradient index lenses being collinear, the radius of the first gradient index lens being substantially the same as the radius of the second gradient index lens, the gradient index of said first gradient index lens being different from that of said second gradient index lens, and the gradient index of said first and second gradient index lenses being so determined that spherical aberration and coma of said lens system are compensated.

Claim 10

A gradient index lens system for use as a pick-up lens for an optical disc, in which spherical aberration and coma are well corrected and which has an excellent imaging performance, said lens system comprising: a first gradient index lens of a convergent refractive power having a gradient index rotationally symmetrical with respect to the optical axis thereof, said first gradient index lens extending continuously from its optical axis to its periphery and having a refractive index which continuously decreases as the radius from the optical axis increases until the periphery is reached, and a second gradient index lens of a convergent refractive power having a gradient index rotationally symmetrical with respect to the optical axis thereof, said second gradient index lens extending continuously from its optical axis to its periphery and having a refractive index which continuously decreases as the radius from the optical axis increases until the periphery is reached, the optical axes of said first and second gradient index lenses being collinear, the radius of the first gradient index lens being substantially the same as the radius of the second gradient index lens, the gradient index of said first gradient index lens being different from that of said second gradient index lens, and the gradient index of said first and second gradient index lenses being so determined that spherical aberration and coma of said lens system are compensated.

Claim 11

A gradient index lens system for use as a pick-up lens for an optical disc, in which spherical aberration and coma are well corrected and which has an excellent imaging performance, said lens system comprising: a divergent gradient index lens component of a divergent refractive power having a gradient index rotationally symmetrical with respect to the optical axis thereof, said divergent gradient index lens component extending continuously from its optical axis to its periphery and having a refractive index which continuously increases as the radius from the optical axis increases until the periphery is reached, and a convergent gradient index lens component of a convergent refractive power having a gradient index rotationally symmetrical with respect to the optical axis thereof, said convergent gradient index lens component extending continuously from its optical axis to its periphery and having a refractive index which continuously decreases as the radius from the optical axis increases until the periphery is reached, the optical axes of said divergent gradient index lens component and said convergent gradient index lens component being collinear, the radius of the divergent gradient index lens component being substantially the same as the radius of the convergent gradient index lens component, said divergent gradient index lens component of a divergent refractive power decreasing the Petzval sum of the lens system, and the gradient index of said divergent and convergent gradient index lens components being so determined that spherical aberration and coma of said lens system are compensated.

Claim 12

A gradient index lens system for use as a pick-up lens for an optical disc, in which spherical aberration and coma are well corrected and which has an excellent imaging performance, said lens system comprising: a divergent gradient index lens component of a divergent refractive power having a gradient index rotationally symmetrical with respect to the optical axis thereof, said divergent gradient index lens component extending continuously from its optical axis to its periphery and having a refractive index which continuously increases as the radius from the optical axis increases until the periphery is reached, and a convergent gradient index lens component of a convergent refractive power having a gradient index rotationally symmetrical with respect to the optical axis thereof, said convergent gradient index lens component extending continuously from its optical axis to its periphery and having a refractive index which continuously decreases as the radius from the optical axis increases until the periphery is reached, the optical axes of said divergent gradient index lens component and said convergent gradient index lens component being collinear, the radius of the divergent gradient index lens component being substantially the same as the radius of the convergent gradient index lens component, said divergent gradient index lens component of a divergent refractive power decreasing the Petzval sum of the lens system, and the gradient index of said divergent and convergent gradient index lens components being so determined that spherical aberration and coma of said lens system are compensated.

Claim 13

A gradient index lens system for use as a pick-up lens for an optical disc, in which spherical aberration and coma are well corrected and which has an excellent imaging performance, said lens system comprising: a divergent gradient index lens component of a divergent refractive power having a gradient index rotationally symmetrical with respect to the optical axis thereof and having a refractive index which continuously increases as the radius from the optical axis increases until the periphery is reached, and a convergent gradient index lens component of a convergent refractive power having a gradient index rotationally symmetrical with respect to the optical axis thereof and having a refractive index which continuously decreases as the radius from the optical axis increases until the periphery is reached, said divergent gradient index lens component of a divergent refractive power decreasing the Petzval sum of the lens system, and the gradient index of said divergent and convergent gradient index lens components being so determined that spherical aberration and coma of said lens system are compensated, wherein when the refractive index n n of said divergent gradient index lens component and the refractive index n p of said convergent gradient index lens component are respectively expressed by ##EQU15## and said two lens components are cemented together, the following conditions are satisfied:

Claim 14

A gradient index lens system for use as a pick-up lens for an optical disc, in which spherical aberration and coma are well corrected and which has an excellent imaging performance, said lens system comprising: a divergent gradient index lens component of a divergent refractive power having a gradient index rotationally symmetrical with respect to the optical axis thereof and having a refractive index which continuously increases as the radius from the optical axis increases until the periphery is reached, and a convergent gradient index lens component of a convergent refractive power having a gradient index rotationally symmetrical with respect to the optical axis thereof and having a refractive index which continuously decreases as the radius from the optical axis increases until the periphery is reached, said divergent gradient index lens component of a divergent refractive power decreasing the Petzval sum of the lens system, and the gradient index of said divergent and convergent gradient index lens components being so determined that spherical aberration and coma of said lens system are compensated, wherein when the refractive index n n of said divergent gradient index lens component and the refractive index n p of said convergent gradient index lens component are respectively expressed by ##EQU15## and said two lens components are cemented together, the following conditions are satisfied:

Claim 15

1<g p <0.3 0.1<g.sub.n <0.3 where n 0 is the center refractive index, r is the radial distance from the optical axis, g is a parameter indicative of the degree of refractive index gradient, h 4 and h 6 are the coefficients of the fourth order term and the sixth order term as the high order terms of the gradient index, subscript n means an amount regarding said divergent gradient index lens component, and subscript p means an amount regarding said convergent gradient index lens component.

Claim 16

1<g p <0.3 0.1<g.sub.n <0.3 where n 0 is the center refractive index, r is the radial distance from the optical axis, g is a parameter indicative of the degree of refractive index gradient, h 4 and h 6 are the coefficients of the fourth order term and the sixth order term as the high order terms of the gradient index, subscript n means an amount regarding said divergent gradient index lens component, and subscript p means an amount regarding said convergent gradient index lens component.

Claim 17

A gradient index lens system according to claim 8, wherein said divergent gradient index lens component and said convergent gradient index lens component further satisfy the following conditions: 0<h.sub.4p <1.0 -1.0<h.sub.6p <1.5 0<h.sub.4n <10.0 -1.0<h.sub.6n <15.0.

Claim 18

A gradient index lens system according to claim 9 wherein numerical data are as follows: ______________________________________ NA = 0.464, WD = 2.6 mm, r.sub.0 = 1.53 mm Maximum image height: 0.185 mm Focal length: 3.3 mm Divergent Convergent lens L.sub.n lens L.sub.p ______________________________________ Lens length Z 2.60 7.67 Center refractive index 1.56 1.66666 g 0.2 0.18 h.sub.4 0.988 0.287 h.sub.6 0.886 0.053 ______________________________________ where r 0 is the effective diameter of a lens, g is a parameter indicative of the degree of refractive index gradient and h 4 and h 6 are coefficients of the fourth order term and the sixth order term as the high order terms of gradient index, and subscript n means an amount regarding said divergent gradient index lens.

Claim 19

A gradient index lens system according to claim 9 wherein numerical data are as follows: ______________________________________ NA = 0.464 WD = 2.6 mm r.sub.0 = 1.53 mm Maximum image height: 0.185 mm Focal length: 3.3 mm Divergent Convergent lens L.sub.n lens L.sub.p ______________________________________ Lens length Z 4.49 5.69 Center refractive 1.56 1.66666 index n.sub.0 g 0.12 0.2 h.sub.4 3.835 0.256 h.sub.6 8.487 0.029 ______________________________________ where r 0 is the effective diameter of a lens, g is a parameter indicative of the degree of refractive index gradient, and h 4 and h 6 are coefficients of the fourth order term and the sixth order term as the high order terms of gradient index, and subscript n means an amount regarding said divergent gradient index lens.

Claim 20

A gradient index lens system according to claim 9, wherein numerical data are as follows: ______________________________________ NA = 0.4 WD = 2.6 mm r.sub.0 = 1.15 mm Maximum image height: 0.185 mm focal length 2.5 mm Divergent Convergent lens L.sub.n lens L.sub.p ______________________________________ Lens length Z 3.67 5.13 Center refractive index n.sub.0 1.56 1.66666 g 0.2 0.24 h.sub.4 1.441 0.286 h.sub.6 1.669 0.022 ______________________________________ where r 0 is the effective diameter of a lens, g is a parameter indicative of the degree of refractive index gradient and h 4 and h 6 are coefficients of the fourth order term and the sixth order term as the high order terms of gradient index, and subscript n means an amount regarding said divergent gradient index lens.

Claim 21

A gradient index lens system according to claim 9 wherein numerical data are as follows: ______________________________________ NA = 0.4 WD = 2.6 mm r.sub.0 = 1.15 mm Maximum image height: 0.185 mm Focal length: 2.5 mm Divergent Convergent lens L.sub.n lens L.sub.p ______________________________________ Lens length Z 2.47 4.71 Center refractive index n.sub.0 1.56 1.666666 g 0.26 0.26 h.sub.4 1.045 0.255 h.sub.6 0.830 0.061 ______________________________________ where r 0 is the effective diameter of a lens, g is a parameter indicative of the degree of refractive index gradient and h 4 and h 6 are coefficients of the fourth order term and the sixth order term as the high order terms of gradient index, and subscript n means an amount regarding said divergent gradient index lens.

Claim 22

A gradient index lens system according to claim 9, wherein said convergent gradient index lens component includes a first gradient index lens of a convergent refractive power having a gradient index rotationally symmetrical with respect to the optical axis thereof and having a refractive index which continuously decreases as the radius from the optical axis increases until the periphery is reached, and a second gradient index lens of a convergent refractive power having a gradient index rotationally symmetrical with respect to the optical axis thereof and having a refractive index which continuously decreases as the radius from the optical axis increases until the periphery is reached, the gradient index of said first gradient index lens being different from that of said second gradient index lens.

Claim 23

A gradient index lens system according to claim 14, wherein numerical data are as follows: ______________________________________ NA = 0.464 WD = 2.6 mm r.sub.0 = 1.53 mm Maximum image height: 0.185 mm Focal length: 3.3 mm 1st 2nd Divergent convergent convergent lens L.sub.n lens L.sub.p1 lens L.sub.p2 ______________________________________ Lens length Z 1.96 2.56 2.56 Center refractive 1.56 1.66666 1.66666 index n.sub.0 g 0.2 0.22 0.22 h.sub.4 2.898 -0.547 0.740 h.sub.6 2.115 1.089 -0.851 ______________________________________ where r 0 is the effective diameter of a lens, g is a parameter indicative of the degree of refractive index gradient and h 4 and h 6 are coefficients of the fourth order term and the sixth order term as the high order terms of gradient index.

Claim 24

A gradient index lens system according to claim 14, wherein numerical data are as follows: ______________________________________ NA = 0.46 WD = 2.6 mm r.sub.0 = 1.15 mm Maximum image height: 0.185 mm Focal length: 2.5 mm 1st 2nd Divergent convergent convergent lens L.sub.n lens L.sub.p1 lens L.sub.p2 ______________________________________ Lens length Z 2.82 4.79 4.21 Center refrac- 1.56 1.66666 1.66666 tive index n.sub.0 g 0.26 0.18 0.18 h.sub.4 0.440 0.586 0.197 h.sub.6 0.381 -0.273 0.335 ______________________________________ where r 0 is the effective diameter of a lens, g is a parameter indicative of the degree of refractive index gradient, h 4 and h 6 are the coefficients of the fourth order term and the sixth order term as the high order terms of gradient index.

Claim 25

A gradient index lens system for use as a pick-up lens for an optical disc, in which spherical aberration and coma are well corrected and which has an excellent imaging performance, said lens system comprising: a divergent gradient index lens component of a divergent refractive power having a gradient index rotationally symmetrical with respect to the optical axis thereof and having a refractive index which continuously increases as the radius from the optical axis increases until the periphery is reached, and a convergent gradient index lens component of a convergent refractive power having a gradient index rotationally symmetrical with respect to the optical axis thereof and having a refractive index which continuously decreases as the radius from the optical axis increases until the periphery is reached, said divergent gradient index lens component of a divergent refractive power decreasing the Petzval sum of the lens system, and the gradient index of said divergent and convergent gradient index lens components being so determined that spherical aberration and coma of said lens system are compensated, wherein when the refractive index n n of said divergent gradient index lens component and the refractive index n p of said convergent gradient index lens component are respectively expressed by ##EQU16## and said two lens components are separated from each other by a spacing Z 0 , the following conditions are satisfied:

Claim 26

A gradient index lens system for use as a pick-up lens for an optical disc, in which spherical aberration and coma are well corrected and which has an excellent imaging performance, said lens system comprising: a divergent gradient index lens component of a divergent refractive power having a gradient index rotationally symmetrical with respect to the optical axis thereof and having a refractive index which continuously increases as the radius from the optical axis increases until the periphery is reached, and a convergent gradient index lens component of a convergent refractive power having a gradient index rotationally symmetrical with respect to the optical axis thereof and having a refractive index which continuously decreases as the radius from the optical axis increases until the periphery is reached, said divergent gradient index lens component of a divergent refractive power decreasing the Petzval sum of the lens system, and the gradient index of said divergent and convergent gradient index lens components being so determined that spherical aberration and coma of said lens system are compensated, wherein when the refractive index n n of said divergent gradient index lens component and the refractive index n p of said convergent gradient index lens component are respectively expressed by ##EQU16## and said two lens components are separated from each other by a spacing Z 0 , the following conditions are satisfied:

Claim 27

1<g p <0.3 0.1<g.sub.n <0.3 0≦Z.sub.0 <3.0 where n 0 is the center refractive index, r is the radial distance from the optical axis, g is a parameter indicative of the degree of refractive index gradient, h 4 and h 6 are the coefficients of the fourth order term and the sixth order term as the high order terms of the gradient index, subscript n means an amount regarding said divergent gradient index lens component, and subscript p means an amount regarding said convergent gradient index lens component.

Claim 28

1<g p <0.3 0.1<g.sub.n <0.3 0≦Z.sub.0 <3.0 where n 0 is the center refractive index, r is the radial distance from the optical axis, g is a parameter indicative of the degree of refractive index gradient, h 4 and h 6 are the coefficients of the fourth order term and the sixth order term as the high order terms of the gradient index, subscript n means an amount regarding said divergent gradient index lens component, and subscript p means an amount regarding said convergent gradient index lens component.

Claim 29

A gradient index lens system according to claim 17, wherein said divergent gradient index lens and said convergent gradient index lens further satisfy the following conditions: 0<h.sub.4p <1.0 -1.0<h.sub.6p <1.5 0<h.sub.4n <10.0 -1.0<h.sub.6n <15.0.

Claim 30

A gradient index lens system according to claim 18, wherein numerical data are as follows: ______________________________________ NA = 0.464 WD = 2.6 mm r.sub.0 = 1.53 mm Maximum image height: 0.185 mm focal length: 3.3 mm Z.sub.0 = 1.8 mm Divergent Convergent lens L.sub.n lens L.sub.p ______________________________________ Lens length Z 0.91 4.36 Center refractive index n.sub.0 1.56 1.66666 g 0.2 0.22 h.sub.4 2.661 0.286 h.sub.6 4.133 0.006 ______________________________________ where r 0 is the effective diameter of a lens, g is a parameter indicative of the degree of refractive index gradient and h 4 and h 6 are coefficients of the fourth order term and the sixth order term as the high order terms of gradient index, and subscript n means an amount regarding said divergent gradient index lens.

Claim 31

A gradient index lens system in which spherical aberration and coma are well corrected and which has an excellent imaging performance, said lens system comprising: a first convergent gradient index lens and a second convergent gradient index lens, said second gradient index lens having a gradient index different from that of said first gradient index lens, and when the gradient indices n 1 and n 2 of said lenses are expressed by ##EQU17## the following conditions are satisfied:

Claim 32

A gradient index lens system in which spherical aberration and coma are well corrected and which has an excellent imaging performance, said lens system comprising: a first convergent gradient index lens and a second convergent gradient index lens, said second gradient index lens having a gradient index different from that of said first gradient index lens, and when the gradient indices n 1 and n 2 of said lenses are expressed by ##EQU17## the following conditions are satisfied:

Claim 33

0<h 41 <5.0 -1.5<h.sub.61 <0 -5.0<h.sub.42 <-0.5 1.0<h.sub.62 <8.0 where n 0 is the center refractive index, r is the radial distance from the optical axis, g is a parameter indicative of the degree of refractive index gradient, h 4 and h 6 are the coefficients of the fourth order term and the sixth order term as the high order terms of gradient index, and subscript numbers 1 and 2 mean that the gradient indices are the amounts regarding said different first and second gradient index lenses.

Claim 34

0<h 41 <5.0 -1.5<h.sub.61 <0 -5.0<h.sub.42 <-0.5 1.0<h.sub.62 <8.0 where n 0 is the center refractive index, r is the radial distance from the optical axis, g is a parameter indicative of the degree of refractive index gradient, h 4 and h 6 are the coefficients of the fourth order term and the sixth order term as the high order terms of gradient index, and subscript numbers 1 and 2 mean that the gradient indices are the amounts regarding said different first and second gradient index lenses.

Claim 35

A gradient index lens system in which spherical aberration and coma are well corrected and which has an excellent imaging performance, said lens system comprising: a convergent gradient index lens and a divergent gradient index lens, said divergent gradient index lens decreasing the Petzval sum so as to compensate curvature of field, wherein when the refractive index n n of said divergent gradient index lens and the refractive index n p of said convergent gradient index lens are respectively expressed by ##EQU18## the following conditions being satisfied:

Claim 36

A gradient index lens system in which spherical aberration and coma are well corrected and which has an excellent imaging performance, said lens system comprising: a convergent gradient index lens and a divergent gradient index lens, said divergent gradient index lens decreasing the Petzval sum so as to compensate curvature of field, wherein when the refractive index n n of said divergent gradient index lens and the refractive index n p of said convergent gradient index lens are respectively expressed by ##EQU18## the following conditions being satisfied:

Claim 37

1<g p <0.3 0.1<g.sub.n <0.3 where n 0 is the center refractive index, r is the radial distance from the optical axis, g is a parameter indicative of the degree of refractive index gradient, h 4 and h 6 are the coefficients of the fourth order term and the sixth order term as the high order terms of the gradient index, subscript n means an amount regarding said divergent gradient index lens, and subscript p means an amount regarding said convergent gradient index lens.

Claim 38

1<g p <0.3 0.1<g.sub.n <0.3 where n 0 is the center refractive index, r is the radial distance from the optical axis, g is a parameter indicative of the degree of refractive index gradient, h 4 and h 6 are the coefficients of the fourth order term and the sixth order term as the high order terms of the gradient index, subscript n means an amount regarding said divergent gradient index lens, and subscript p means an amount regarding said convergent gradient index lens.

Claim 39

A gradient index lens system according to claim 21, wherein said divergent gradient index lens and said convergent gradient index lens further satisfy the following conditions: 0<h.sub.4p <1.0 -1.0<h.sub.6p <1.5 0<h.sub.4n <10.0 -1.0<h.sub.6n <15.0.

Claim 40

A gradient index lens system according to claim 22, wherein said divergent gradient index lens and said convergent gradient index lens are separated from each other by a spacing Z 0 , and wherein the following condition is satisfied: 0≦Z.sub.0 <3.0.