Objective lens system for an endoscope

Claim 2

An objective lens system for an endoscope comprising a front lens unit, a rear lens unit, and a stop located between said front and rear lens units, said front lens unit comprising a negative meniscus lens component convex toward the object side arranged that the surface on the object side thereof is formed as an aspherical surface having portions whose curvature is made gradually stronger as they are farther from the optical axis, and said rear lens unit comprising a plurality of lens components including a positive cemented doublet, one of said lens components being arranged so that the surface of the object side thereof is formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis, the air space between the surface on the extreme image side of said front lens and said stop being constant.

Claim 3

An objective lens system for an endoscope according to claim 1, fulfilling the following conditions: A.sub.F.A.sub.R <0 0.01<|A.sub.F /A.sub.R |<10 where, reference symbol A F represents the sum of coefficients of astigmatism of said aspherical surfaces provided in said front lens unit, and reference symbol A R represents the sum of coefficients of astigmatism of said aspherical surfaces provided in said rear lens unit.

Claim 4

An objective lens system for an endoscope according to claim 2, wherein said front lens unit has negative refractive power, said rear lens unit has positive refractive power and said stop located between said front and rear lens units in the vicinity of the front focal point.

Claim 5

An object lens system for an endoscope according to claim 3 wherein said rear lens unit comprises a positive meniscus lens component convex toward the image side, a positive lens component, each of said aspherical surfaces is expressed by the formula shown below when the optical axis is designated as the x axis and a straight line perpendicular to the optical axis and passing the intersecting point between said aspherical surface and optical axis is designated as the y axis and, moreover, each of said aspherical surfaces fulfills the condition shown below: ##EQU5## where, reference symbol f represents the focal length of the lens system as a whole, reference symbol C represents the inverse number of the radius of curvature of the aspherical surface which is in contact with said aspherical surface on the optical axis, reference symbol P represents a parameter representing the shape of said aspherical surface, and reference symbols B, E, F, G, . . . respectively represent the aspherical surface coefficients of the second power, fourth power, sixth power, eighth power and so on.

Claim 6

An objective lens system for an endoscope according to claim 4 further fulfilling the following conditions: |f.sub.1 |<2.5f D<1.8f where, reference symbol f 1 represents the focal length of said front lens unit, and reference symbol D represents the distance from the rearmost surface of said front lens unit to the foremost surface of said rear lens unit.

Claim 7

An objective lens system for an endoscope according to claim 5 wherein the surface on the object side of said cemented doublet in said rear lens unit is formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis.

Claim 8

An objective lens system for an endoscope according to claim 5 wherein the surface on the object side of said rearmost positive lens component in said rear lens unit is formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis.

Claim 9

An objective lens system for an endoscope according to claim 7 having the following numerical data: ______________________________________ r.sub.1 = 6.3984 (aspherical surface) d.sub.1 = 0.5595 n.sub.1 = 1.51633 ν.sub.1 = 64.15 r.sub.2 = 0.6778 d.sub.2 = 0.9092 r.sub.3 = ∞ (stop) d.sub.3 0.2098 r.sub.4 = 5.5166 d.sub.4 1.2588 n.sub.2 = 1.58913 ν.sub.2 = 61.11 r.sub.5 = -1.5634 d.sub.5 = 0.1399 r.sub.6 = 29.9814 d.sub.6 = 1.2588 n.sub.3 = 1.58913 ν.sub.3 = 61.11 r.sub.7 = -4.3416 d.sub.7 = 0.1399 r.sub.8 = 2.8491 d.sub.8 = 2.0980 n.sub.4 = 1.61800 ν.sub.4 = 63.38 r.sub.9 = -2.3590 d.sub.9 = 0.4755 n.sub.5 = 1.84666 ν.sub.5 = 23.90 r.sub.10 = -148.8749 d.sub.10 = 0.2114 r.sub.11 = 1.7587 (aspherical surface) d.sub.11 = 1.1277 n.sub.6 1.51633 ν.sub.6 64.15 r.sub.12 = ∞ f = 1, 2ω = 119.986° aspherical surface coefficient of 1st surface P = 1, E = 0.35094 × 10.sup.-1 F = -0.35734 × 10.sup.-2 aspherical surface coefficient of 11th surface P = 1, E = -0.11938 F = 0.11557 × 10.sup.-2 A.sub.F = -0.01539, A.sub.R = 0.04461 A.sub.F /A.sub.R = -0.34499 f.sub.1 = -1.519, D.sub.1 = 1.119 ______________________________________ where, reference symbols r 1 , r 2 , . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 , d 2 , . . . respectively represent thicknesses of respective lenses and airspaces between respective lens, reference symbols n 1 , n 2 , . . . respectively represent refractive indices of respective lenses, and reference symbols ν 1 , ν 2 , . . . respectively represent Abbe's numbers of respective lenses.

Claim 10

An objective lens system for an endoscope according to claim 8 wherein said front lens unit comprises two negative lens components each having a concave surface on the image side, said rear lens unit comprises a positive lens component, a positive lens component, a positive cemented doublet, and a positive lens component having a convex surface on the object side, each of said aspherical surfaces is expressed by the formula shown below when the optical axis is designated as the x axis and a straight line perpendicular to the optical axis and passing the intersecting point between said aspherical surface and optical axis is designated as the y axis and, moreover, each of said a spherical surfaces fulfills the conditions shown below: ##EQU6## where, reference symbol f F represents the focal length of said front lens group, reference symbol f represents the focal length of the lens system as a whole, reference symbol C represents the inverse number of the radius of curvature of the spherical surface which is in contact with said aspherical surface on the optical axis, reference symbol P represents a parameter representing the shape of said aspherical surface, and reference symbols B, E, F, G, . . . respectively represent the aspherical surface coefficients of the second power, fourth power, sixth power eighth power and so on.

Claim 11

An objective lens system for an endoscope according to claim 9 wherein the surface on the object side of said rearmost positive lens component in said rear lens unit is formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis.

Claim 12

An objective lens system for an endoscope according to claim 10 having the following numerical data: ______________________________________ r.sub.1 = 16.1623 (aspherical surface) d.sub.1 = 0.7273 n.sub.1 = 1.49109 ν.sub.1 = 57.00 r.sub.2 = 1.6598 d.sub.2 = 1.2510 r.sub.3 = 19.6061 d.sub.3 = 1.1736 n.sub.2 = 1.78800 ν2 .sub. = 47.43 r.sub.4 = 1.9317 d.sub.4 = 1.0628 r.sub.5 = ω (stop) d.sub.5 = 0.1119 r.sub.6 = 14.1042 d.sub.6 = 1.2096 n.sub.3 = 1.58913 ν.sub.3 = 60.97 r.sub.7 = -2.9033 d.sub.7 = 0.6212 r.sub.8 = -17.7424 d.sub.8 = 1.1115 n.sub.4 = 1.58913 ν.sub.4 = 60.97 r.sub.9 = -3.1102 d.sub.9 = 0.1372 r.sub.10 = 6.4185 d.sub.10 = 2.1674 n.sub.5 = 1.61800 ν.sub.5 = 63.38 r.sub.11 = -2.2840 d.sub.11 = 0.2467 n.sub.6 = 1.84666 ν.sub.6 = 23.90 r.sub.12 = -8.1806 d.sub.12 = 0.6832 r.sub.13 = 2.5389 (aspherical surface) d.sub.13 = 2.5050 n.sub.7 = 1.49109 ν.sub.7 = 57.00 r.sub.14 = ∞ f = 1 , 2ω = 116.002° aspherical surface coefficient of 1st surface P = 1 , E = 0.79514 × 10.sup.-2 , F = 0 aspherical surface coefficient of 13th surface P = 1 , E = 0.79514 × 10.sup.-2 , F = 0 A.sub.F = -0.01083 , A.sub.R = -0.03888 A.sub.F /A.sub.R = -0.27855 , f.sub.F = -1.251 ______________________________________ where, reference symbols r 1 , r 2 , . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 , d 2 , . . . respectively thicknesses of respective lenses and airspaces between respective lens, reference symbols n 1 , n 2 , . . . respectively represent refractive indices of respective lenses, and reference symbols ν 1 , ν 2 , . . . respectively represent Abbe's numbers of respective lenses.

Claim 13

An objective lens system for an endoscope according to claim 10 having the following numerical data: ______________________________________ r.sub.1 = 5.8227 (aspherical surface) d.sub.1 = 0.6155 n.sub.1 = 1.88300 ν.sub.1 = 40.78 r.sub.2 = 1.7026 d.sub.2 - 1.0434 r.sub.3 = 2.3876 d.sub.3 = 0.4505 n.sub.2 = 1.78800 ν.sub.2 = 47.43 r.sub.4 = 0.9653 d.sub.4 = 0.8366 r.sub.5 = ∞ (stop) d.sub.5 = 0.122 r.sub.6 = -7.1626 d.sub.6 - 1.1660 n.sub.3 - 1.58913 ν.sub.3 = 60.97 r.sub.7 = -1.5456 d.sub.7 = 0.6796 r.sub.8 = -5.6290 d.sub.8 = 1.1942 n.sub.4 = 1.58913 ν.sub.4 = 60.97 r.sub.9 = -2.7189 d.sub.9 = 0.1287 r.sub.10 = 3.58785 d.sub.10 = 2.0335 n.sub.5 = 1.61800 ν.sub.5 = 63.38 r.sub.11 = -2.1429 d.sub.11 = 0.3520 n.sub.6 = 1.84666 ν.sub.6 = 23.90 r.sub.12 = 20.9041 d.sub.12 = 0.5519 r.sub.13 = 2.1991 (aspherical surface) d.sub.13 = 2.2863 n.sub.7 = 1.49109 ν.sub.7 = 57.00 r.sub.14 = ∞ f = 1, 2ω = 112.91° aspherical surface coefficient of 1st surface P = 1, E = 0.96277 × 10.sup.-2, F = 0 aspherical surface coefficient of 13th surface P = 1, E = -0.32235 × 10.sup.-1, F = 0 A.sub.F = -0.01292 , A.sub.R = 0.03088 A.sub.F /A.sub.R = -0.41389 , f.sub.F = -1.044 ______________________________________ where, reference symbols r 1 , r 2 , . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 , d 2 , . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 , n 2 , . . . respectively represent refractive indices of respective lenses, and reference symbols ν 1 , n 2 , . . . respectively represent Abbe's numbers of respective lenses.

Claim 14

An objective lens system for an endoscope according to claim 1, wherein a meniscus lens component concave toward the image side is arranged on the extreme object side of said front lens unit, a meniscus lens component concave toward the object side is arranged on the extreme image side of said rear lens unit, a positive lens component is arranged on the extreme image side of said front lens unit, a positive lens component is arranged on the extreme object said of said rear lens units, and a stop is arranged between said positive lenses arranged in front lens unit and rear lens unit.

Claim 15

An objective lens system for an endoscope according to claim 13 wherein said front lens unit comprises a negative lens component having a concave surface on the image side, and a positive cemented doublet, said rear lens group comprises a positive cemented doublet, and a meniscus lens component convex toward the image side, each of said aspherical surfaces is expressed by the formula shown below when the optical axis is designated as the x axis and a straight line perpendicular to the optical axis and passing the intersecting point between said aspherical surface and optical axis is designated as the y axis and, each of said aspherical surfaces fulfills the condition shown below: ##EQU7## where, reference symbol f represents the focal length of the lens system as a whole, reference symbol C represents the inverse number of the radius of curvature of the spherical surface which is in contact with said aspherical surface on the optical axis, reference symbol P represents a parameter representing the shape of said aspherical surface, and reference symbols B, E, F, G, respecively represent the aspherical coefficients of the second power, fourth power, sixth power, eighth power and so on.

Claim 16

An objective lens system for an endoscope comprising a front lens unit, a rear lens unit, and a stop located between said front and rear units, said front lens unit comprising a negative lens component concave toward the image side arranged so that the surface on the object side thereof is formed as an aspherical surface having portions whose curvature is made gradually stronger as they are farther from the optical axis, and said rear lens unit comprising a plurality of lens components including a positive cemented doublet one of said lens components being arranged so that the surface on the image side thereof is formed as an aspherical surface having portions whose curvature is made gradually stronger as they are farther from the optical axis, the air space between the surface on the extreme image side of said front lens unit and said stop being constant.

Claim 17

An objective lens system for an endoscope comprising a front lens unit, a rear lens unit, and a stop located between said front and rear units, said front lens unit comprising a negative lens component concave toward the image side arranged so that the surface on the object side thereof is formed as an aspherical surface having portions whose curvature is made gradually stronger as they are farther from the optical axis, and said rear lens unit comprising a plurality of lens components including a positive cemented doublet one of said lens components being arranged so that the surface on the image side thereof is formed as an aspherical surface having portions whose curvature is made gradually stronger as they are farther from the optical axis, the air space between the surface on the extreme image side of said front lens unit and said stop being constant.

Claim 18

An objective lens system for an endoscope according to claim 15 fulfilling the following conditions: A.sub.F.A.sub.R <0 0.01<|A.sub.F/A.sbsb.R.sub.|<10 where, reference symbol A F represents the sum of coefficients of astigmatism of said aspherical surfaces provided in said front lens unit, and reference symbol A R represents the sum of coefficients of astigmatism of said aspherical surfaces provided in said rear lens unit.

Claim 19

An objective lens system for an endoscope according to claim 16, wherein said front lens unit has negative refractive power, said rear lens unit has positive refractive power and said stop located between said front and rear lens unit in the vicinity of the front focal point.

Claim 20

An objective lens system for an endoscope according to claim 17 wherein said negative lens component in said front lens unit is a negative meniscus lens convex toward the object side, said rear lens unit comprises a positive meniscus lens component convex toward the image side, a positive lens component, a positive cemented doublet, and a positive lens component, each of said aspherical surfaces is expressed by the formula shown below when the optical axis is designed as the x axis and a straight line perpendicular to the optical axis and passing the intersecting point between said aspherical surface and optical axis is designated as the y axis and, moreover, each of said aspherical surfaces fulfills the condition shown below. ##EQU8## where, reference symbol f represents the focal length of the lens system as a whole, reference symbol C represents the inverse number of the radius of curvature of the aspherical surface which is in contact with said aspherical surface on the optical axis, reference symbol P represents a parameter representing the shape of said aspherical surface, and reference symbols B, E, F, G, . . . respectively represent the aspherical surface coefficients of the second power, fourth power, sixth power, eighth power and so on.

Claim 21

An objective lens system for an endoscope according to claim 18 fulfilling the following conditions: |f.sub.1 |<2.5f D<1.8f where, reference symbol f 1 represents the focal length of said front lens unit, and reference symbol d represents the distance from the rearmost surface of said front lens unit to the foremost surface of said rear lens unit.

Claim 22

An objective lens system for an endoscope according to claim 19 wherein the surface on the image side of said cemented doublet in said rear lens unit is formed as an aspherical surface having portions whose curvature is made gradually stronger as they are farther from the optical axis.

Claim 23

An objective lens system for an endoscope according to claim 20 having the following numerical data: ______________________________________ r.sub.1 = 6.1180 (aspherical surface) d.sub.1 = 0.5298 n.sub.1 = 1.51633 ν.sub.1 = 64.15 r.sub.2 0.6522 d.sub.2 = 0.8609 r.sub.3 = ∞ (stop) d.sub.3 = 0.1987 r.sub.4 = -5.6100 d.sub.4 = 1.1921 n.sub.2 = 1.58913 ν.sub.2 = 61.11 r.sub.5 = -1.4817 d.sub.5 = 0.1325 r.sub.6 = 197.8841 d.sub.6 = 1.1921 n.sub.3 = 1.58913 ν.sub.3 = 61.11 r.sub.7 = -4.2546 d.sub.7 = 0.1325 r.sub.8 = 2.4509 d.sub.8 = 1.9868 n.sub.4 1.61800 ν.sub.4 = 63.88 r.sub.9 = -2.4826 d.sub.9 = 0.4503 n.sub.5 = 1.84666 ν.sub.5 - 23.90 r.sub.10 = -50.0313 (aspherical surface) d.sub.10 = 0.2181 r.sub.11 = 2.5823 d.sub.11 = 1.0680 n.sub.6 = 1.51633 ν.sub.6 = 64.15 r.sub.12 = ∞ f = 1, 2ω = 105.004° aspherical surface coefficient of 1st surface P = 1, E = 0.58449 × 10.sup.-1 F = -0.2063f3 × 10.sup.-2 aspherical surface coefficient of 10th surface P = 1, E = 0.49349 × 10 .sup.-1 F = 0.11654 × 10.sup.-1 A.sub.F = -0.01847, A.sub.R = 0.0294 A.sub.F /A.sub.R = -.062823 f.sub.1 = -1.462, D.sub.1 = 1.06 ______________________________________ where, reference symbols r 1 , r 2 , . . . respectively represent radii of curvature of respective lens surfaces, references symbols d 1 , d 2 , . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 , n 2 , . . . respectively represent refractive indices of respective lenses, and reference symbols ν 1 , ν 2 , . . . respectively represent Abbe's numbers of respective lenses.

Claim 24

An objective lens system for an endoscope according to claim 20 having the following numerical data: ______________________________________ r.sub.1 = 4.2490 (aspherical surface) d.sub.1 = 0.4310 n.sub.1 1.51633 ν.sub.1 = 64.15 r.sub.2 = 0.5336 d.sub.2 = 0.7004 r.sub.3 = ∞ (stop) d.sub.3 = 0.1616 r.sub.4 = -5.1135 d.sub.4 = 0.9698 n.sub.2 1.58913 ν.sub.2 = 61.11 r.sub.5 = -1.1946 d.sub.5 = 0.1078 r.sub.6 = 431.8244 d.sub.6 -0.9698 n.sub.3 = 1.58913 ν.sub.3 = 61.11 r.sub.7 = -3.3672 d.sub.7 = 0.1078 r.sub.8 = 2.4551 d.sub.8 = 1.6164 n.sub.4 = 1.61800 ν.sub.4 = 63.38 r.sub.9 = -1.6551 d.sub.9 = 0.3664 n.sub.5 1.84666 ν.sub.5 = 23.90 r.sub.10 = 10.7060 (aspherical surface) d.sub.10 = 0.3668 r.sub.11 = 1.7661 d.sub.11 1.0237 n.sub.6 = 1.51633 ν.sub.6 = 64.15 r.sub.12 = ∞ f = 1, 2ω= 104.908° aspherical surface coefficient of 1st surface P = 1, E = 0.38819 × 10.sup.-1 F = -0.23129 × 10.sup.-2 aspherical surface coefficient of 10th surface P = 1, E = 0.42299 × 10.sup.-1 F = -0.15892 × 10.sup.-1 A.sub.F = -0.00364, A.sub.R = 0.00995 A.sub.F /A.sub.R = -0.36583 f.sub.1 = -1.231, D1 - 0.862 ______________________________________ where, reference symbols r 1 , r 2 , . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 , d 2 , . . . respectively represent thickness of respective lenses and airspaces between respective lenses, reference symbols n 1 , n 2 , . . . respectively represent refractive indices of respective lenses, and reference symbols ν 1 , ν 2 , . . . respectively Abbe's numbers of respective lenses.

Claim 25

An objective lens system for an endoscope according to claim 17 wherein said negative lens component in said front lens unit is a negative meniscus lens convex toward the object side, said rear lens unit comprises a positive lens component, and a cemented doublet, each of said aspherical surfaces is expressed by the formula shown below when the optical axis is designed as the x axis and a straight line perpendicular to the optical axis and passing the intersecting point between said aspherical surface and optical axis is designated as the y axis and, moreover, each of said aspherical surfaces fulfills the condition shown below: ##EQU9## where, reference symbol f represents the focal length of the lens system as a whole, reference symbol C represents the inverse number of the radius of curvature of the spherical surface which is in contact with said aspherical surface on the optical axis, reference symbol P represents a parameter representing the shape of said aspherical surface, and reference symbols B, E, F, G, . . . respectively represent the aspherical surface coefficients of the second power, fourth power, sixth power, eighth power and so on.

Claim 26

An objective lens system for an endoscope according to claim 23 further fulfilling the following conditions: |f.sub.1 |>1.8f D>1.5f where, reference symbol f 1 represents the focal length of said front lens unit, and reference symbol D represents the distance from the rearmost surface of said front lens unit to the foremost surface of said rear lens unit.

Claim 27

An objective lens system for an endoscope according to claim 24 wherein the surface on the image side of said cemented doublet in said rear lens is formed as an aspherical surface having portions whose curvature is made gradually stronger as they are farther from the optical axis.

Claim 28

An objective lens system for an endoscope according to claim 25 having the following numerical data: ______________________________________ r.sub.1 = 6.8768 (aspherical surface) d.sub.1 = 0.7795 n.sub.1 = 1.88300 ν.sub.1 = 40.78 r.sub.2 = 1.9045 d.sub.2 = 4.2438 r.sub.3 = ∞ (stop) d.sub.3 = 0.6058 r.sub.4 = -18.35668 d.sub.4 = 0.8762 n.sub.2 = 1.69680 ν.sub.2 = 55.52 r.sub.5 = -3.5516 d.sub.5 = 0.3341 r.sub.6 = 2.4922 d.sub.6 = 1.5367 n.sub.3 = 1.64000 ν.sub.3 = 60.09 r.sub.7 = -1.7814 d.sub.7 0.4454 n.sub.4 = 1.84666 ν.sub.4 = 23.88 r.sub.8 = -3.4576 (aspherical surface) f 1, 2ω = 95.0° aspherical surface coefficient of 1st surface P = 1, E = 0.63687 × 10.sup.-2 F = -0.12992 × 10.sup.-3 aspherical surface coefficient of 8th surface P = 1, E = 0.22882 × 10.sup.-1 F = -0.38644v × 10.sup.-2 A.sub.F = -.00116, A.sub.R = 0.01893 A.sub.F /A.sub.R = -0.06128 f.sub.1 = -3.22, D.sub.1 = 4.85 ______________________________________ where, reference symbols r 1 , r 2 , . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 , d 2 , . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 , n 2 , . . . respectively represent refractive indices of respective lenses, and reference symbols ν 1 , ν 2 , . . . respectively represent Abbe's numbers of respective lenses.

Claim 29

An objective lens system for an endoscope according to claim 25 having the following numerical data: ______________________________________ r.sub.1 = 9.3756 (aspherical surface) d.sub.1 = 0.8621 n.sub.1 = 1.88300 ν.sub.1 = 40.78 r.sub.2 = 2.0517 d.sub.2 = 4.8958 r.sub.3 = ∞ (stop) d.sub.3 = 0.8554 r.sub.4 = 15.9800 d.sub.4 0.9690 n.sub.2 = 1.69680 ν.sub.2 = 55.52 r.sub.5 = -5.9752 d.sub.5 = 0.3695 r.sub.6 = 3.4698 d.sub.6 = 1.6374 n.sub.3 = 1.64000 ν.sub.3 = 60.09 r.sub.7 = -1.7857 d.sub.7 = 0.4926 n.sub.4 = 1.84666 ν.sub.4 = 23.88 r.sub.8 = -2.9875 (aspherical surface) f = 1, 2ω = 94.424° aspherical surface coefficient of 1st surface P = 1, E = 0.41954 × 10.sup.-2 F = 0.52825 × 10.sup.-4 aspherical surface coefficient of 8th surface P = 1, E = 0.18885 × 10.sup.-1 F = -0.24735 ×10.sup.-2 A.sub.F = -0.00001, A.sub.r = 0.00003 A.sub.F /A.sub.R = -0.33333 f.sub.1 = -3.148, D.sub.1 = 5.751 ______________________________________ where, reference symbols r 1 , r 2 , . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 , d 2 , . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, references symbols n 1 , n 2 , . . . respectively represent refractive indices of respective lenses, and reference symbols ν 1 , ν 2 , . . . respectively represent Abbe's numbers of respective lenses.

Claim 30

An objective lens system for an endoscope according to claim 17 wherein said front lens unit comprises two negative lens components each having a concave surface on the image side, said rear lens unit comprises a positive lens component, a positive lens component, a positive cemented doublet, and a positive lens component having a convex surface on the object side, each of said aspherical surfaces is expressed by the formula shown below when the optical axis is designated as the x axis and a straight line perpendicular to the optical axis and passing the intersecting point between said aspherical surface and optical axis is designated as the y axis and, moreover, each of said aspherical surfaces fulfills the conditions shown below: ##EQU10## where, reference symbol f F represents the focal length of said front lens group, reference symbol f represents the focal length of the lens system as a whole, reference C represents the inverse number of the radius of curvature of the spherical surface which is in contact with said aspherical surface on the optical axis, reference symbol P represents a parameter representing the shape of said aspherical surface, said reference symbols B, E, F, G, . . . respectively represent the aspherical surface coefficients of the second power, fourth power, sixth power eighth power and so on.

Claim 31

An objective lens system for an endoscope according to claim 16, wherein a meniscus lens component concave toward the image side is arranged on the extreme object side of said front lens unit, a meniscus lens component concave toward the object side is arranged on the extreme image side of said rear lens unit, a positive lens component is arranged on the extreme image side of said front lens unit, a positive lens component is arranged on the extreme object side of said rear lens unit, and stop is arranged between said positive lenses arranged in the front lens unit and rear lens unit.

Claim 32

An objective lens system for an endoscope according to claim 29 wherein said front lens unit comprises a negative lens component having a concave surface on the image side, and a positive cemented doublet, said rear lens group comprises a positive cemented doublet, and a meniscus lens component convex toward the image side, each of said aspherical surfaces is expressed by the formula shown below when the optical axis is designated as the x axis and a straight line perpendicular to the optical axis and passing the intersecting point between said aspherical surface and optical axis is designated as the y axis and, moreover, each of said spherical surfaces fulfills the condition shown below: ##EQU11## where, reference symbol f represents the focal length of the lens system as a whole, reference symbol C represents the inverse number of the radius of curvature of the spherical surface which is in contact with said aspherical surface on the optical axis, reference symbol P represents a parameter representing the shape of said aspherical surface, and reference symbols B, E, F, G, . . . respectively represent the aspherical the aspherical surface coefficients of the second power, fourth power, sixth power, eighth power and so on.

Claim 33

An objective lens system for an endoscope according to claim 30 wherein the surface on the image side of said meniscus lens component in said rear lens unit is formed as an aspherical surface having portions whose curvature is made gradually stronger as they are farther from the optical axis.

Claim 34

An objective lens system for an endoscope according to claim 31 further fulfilling the following condition: f.sub.4 <5f where, reference symbol f 4 represents the focal length of said meniscus lens component constituting said rear lens unit.

Claim 35

An objective lens system for an endoscope according to claim 31 further fulfilling the following condition: f.sub.4 <-3f where, reference symbol f 4 represents the focal length of said meniscus lens component constituting said rear lens unit.

Claim 36

An objective lens system for an endoscope according to claim 32 having the following numerical data: ______________________________________ r.sub.1 = ∞ (aspherical surface) d.sub.1 = 0.2681 n.sub.1 = 1.51633 ν.sub.1 = 64.15 r.sub.2 = 1.0400 d.sub.2 = 1.4189 r.sub.3 = 2.1359 d.sub.3 = 0.5362 n.sub.2 = 1.59270 ν.sub.2 = 35.29 r.sub.4 = -1.5405 d.sub.4 = 0.2145 n.sub.3 = 1.83400 ν.sub.3 = 37.16 r.sub.5 = -3.9303 d.sub.5 = 0.0536 r.sub.6 = ∞ (stop) d.sub.6 = 0.0536 r.sub.7 = 3.1352 d.sub.7 = 0.5898 n.sub.4 = 1.62041 ν.sub.4 = 60.27 r.sub.8 = -0.6278 d.sub.8 = 0.2145 n.sub.5 = 1.80518 ν.sub.5 = 25.43 r.sub.9 = -1.2322 d.sub.9 = 0.8609 r.sub.10 = -2.2697 d.sub.10 = 0.2681 n.sub.6 = 1.84666 ν.sub.6 = 23.88 r.sub.11 = -1.9100 (aspherical surface) f = 1, 2ω= 100.0° aspherical surface coefficient of 1st surface P = 1, E = 0.39752 × 10.sup.-2 aspherical surface coefficient of 11th surface P = 1, E = 0.25509 A.sub.F = -.00044, A.sub.R = 0.01371 A.sub.f /A.sub.R = -0.03209, E.sub.F = 0-.003975 E.sub.B = 0.25509, E.sub.B /E.sub.F = 64.17 f.sub.4 = 10.608 ______________________________________ where, reference symbols r 1 , r 2 , . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 , d 2 , . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbol n 1 , n 2 , . . . respectively represent refractive indices of respective lenses, and reference symbols ν 1 , ν 2 , . . . respectively represent Abbe's numbers of respective lenses.

Claim 37

An objective lens system for an endoscope according to claim 32 having the following numerical data: ______________________________________ r.sub.1 = ∞ (aspherical surface) d.sub.1 = 0.2772 n.sub.1 = 1.51633 ν.sub.1 = 64.15 r.sub.2 = 0.8565 d.sub.2 = 1.5573 r.sub.3 = 2.4166 d.sub.3 = 0.5543 n.sub.2 = 1.59270 ν.sub.2 = 35.29 r.sub.4 = -2.1023 d.sub.4 = 0.2217 n.sub.3 = 1.83400 ν.sub.3 = 37.16 r.sub.s = -3.7245 d.sub.s = 0.0554 r.sub.6 = ∞ (stop) d.sub.6 = 0.0554 r.sub.7 = 3.1854 d.sub.7 = 0.6098 n.sub.4 = 1.62041 ν.sub.4 = 60.27 r.sub.8 = -0.6391 d.sub.8 = 0.2217 n.sub.s = 1.80518 ν.sub.s = 25.43 r.sub.9 = -1.2642 d.sub.9 = 0.8900 r.sub.10 = -1.7084 d.sub.10 = 0.2772 n.sub.6 = 1.84666 ν.sub.6 = 23.88 r.sub.11 = -2.1791 (aspherical surface) f = 1, 2ω = 50.006° aspherical surface coefficient of 1st surface P = 1, E = 0.25013 × 10.sup.-1 aspherical surface coefficient of 11th surface P = 1, E = 0.11723, F = 0.11906 A.sub.F - -0.00283, A.sub.R = 0.00718 A.sub.F /A.sub.F = -0.39415, E.sub.F = 0.02501 E.sub.B = 0.1172, E.sub.B /E.sub.R = 4.686 f.sub.4 = -12.795 ______________________________________ where, reference symbols r 1 , r 2 , . . . respectively represent radii of curvature of respective lens surfaces, reference symbol d 1 , d 2 , . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 , n 2 , . . . respectively represent refractive indices of respective lenses, and reference symbols ν 1 , ν 2 , . . . respectively represent Abbe's numbers of respective lenses.

Claim 38

An objective lens system for an endoscope according to claim 32 having the following numerical data: ______________________________________ r.sub.1 = ∞ (aspherical surface) d.sub.1 = 0.2743 n.sub.1 = 1.51633 ν.sub.1 = 64.15 r.sub.2 = 0.8373 d.sub.2 = 1.5683 r.sub.3 = 4.2174 d.sub.3 = 0.5485 n.sub.2 = 1.59270 ν.sub.2 = 35.29 r.sub.4 = -10.5058 d.sub.4 = 0.2194 n.sub.3 = 1.83400 ν.sub.3 = 37.16 r.sub.s = -3.4706 d.sub.s = 0.0549 r.sub.6 = ∞ (stop) d.sub.6 = 0.0549 r.sub.7 = 2.6304 d.sub.7 = 0.6034 n.sub.4 = 1.62041 ν.sub.4 = 60.27 r.sub.8 = -0.7752 d.sub.8 = 0.2194 n.sub.5 = 1.80518 ν.sub.5 = 25.43 r.sub.9 = -1.4995 d.sub.9 = 0.8795 r.sub.10 = -2.2103 d.sub.10 = 0.2743 n.sub.6 = 1.84666 ν.sub.6 = 23.88 r.sub.11 = -4.1560 (aspherical surface) f = 1, 2δ = 99.978° aspherical surface coefficient of 1st surface P = 1, E = 0.15461 × 10.sup.-1 F = 0.13610 × 10.sup.-2 aspherical surface coefficient of 11th surface P = 1, E = 0.14239, F = 0.19039 A.sub.F = -0.00158, A.sub.R = 0.00701 A.sub.F /A.sub.F = -0.22539, E.sub.F = 0.01546 E.sub.B = 0.1424, E.sub.B /E.sub.F = 9.211 f.sub.4 = -5.961 ______________________________________ where, reference symbols r 1 , r 2 , . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 , d 2 , . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 , n 2 , . . . respectively represent refractive indices of respective lenses, and reference symbols ν 1 , ν 2 , . . . respectively represent Abbe's numbers of the respective lenses.

Claim 39

An objective lens system for an endoscope according to claim 32, wherein said front lens unit has negative refractive power, said rear lens unit has positive refractive power and said stop located between said front and rear lens units in the vicinity of the front focal point.

Claim 40

An objective lens system for an endoscope according to claim 37 wherein said front lens unit comprises a negative meniscus lens component convex toward the object side, said rear lens unit comprises a positive meniscus lens component convex toward the image side, a positive lens component, a positive cemented doublet, and a positive lens component, each of said aspherical surfaces is expressed by the formula shown below when the optical axis is designated as the x axis and a straight line perpendicular to the optical axis and passing the intersecting point between said aspherical surface and optical axis is designated as the y axis and, moreover, each of said aspherical surfaces fulfills the condition shown below: ##EQU12## where, reference, symbol f represents the focal length of the lens system as a whole, reference symbol f, represents the focal length of said front lens unit, reference symbol D represents the distance form the rearmost surface of said front lens unit to the foremost surface of said rear lens unit, reference symbol C represents the inverse number of the radius of curvature of the aspherical surface which is in contact with said aspherical surface on the optical axis, reference symbol P represents a parameter representing the shape of said aspherical surface, and reference symbols B, E, F, G, . . . respectively represent the aspherical surface coefficients of the second power, fourth power, sixth power, eighth power and so on.

Claim 41

An objective lens system for an endoscope according to claim 37 wherein said front lens unit comprises a negative meniscus lens component convex toward the object side, said rear lens unit comprises a positive lens component, and a cemented doublet, each of said aspherical surfaces is expressed by the formula shown below when the optical axis is designated as the x axis and a straight line perpendicular to the optical axis and passing the intersecting point between said aspherical surface and optical axis is designated as the y axis and, moreover, each of said aspherical surfaces fulfills the condition shown below: ##EQU13## where, reference symbol f represents the focal length of the lens system as a whole, reference symbol f, represents the focal length of said front lens unit, reference symbol D represents the distance from the rearmost surface of said front lens unit to the foremost surface of said rear lens unit, reference symbol O represents the inverse number of the radius of curvature of the aspherical surface which is in contact with said aspherical surface on the optical axis, reference symbol P represents a parameter representing the shape of said aspherical surface, and reference symbols B, E, F, G, . . . respectively represent the aspherical surface coefficients of the second power, fourth power, sixth power, eighth power and so on.

Claim 42

An objective lens system for an endoscope according to claim 37 wherein said front lens unit comprises two negative lens components each having a concave surface on the image side, said rear lens unit comprises a positive lens component, a positive lens component, a positive cemented doublet, and a positive lens component having a convex surface on the object side, each of said aspherical surfaces is expressed by the formula shown below when the optical axis is designated as the x axis and a straight line perpendicular to the optical axis and passing the intersecting point between said aspherical surface and optical axis is designated as the y axis and, moreover, each of said aspherical surfaces fulfills the conditions shown below: ##EQU14## where, reference symbol f F represents the focal length of said front lens group, reference symbol f represents the focal length of the lens system as a whole, reference symbol c represents the inverse number of the radius of curvature of the aspherical surface which is in contact with said aspherical surface on the optical axis, reference symbol P represents a parameter repesenting the shape of said aspherical surface, and reference symbols B, E, F, G, . . . respectively represent the aspherical surface coefficients of the second power, fourth power, sixth power eighth power and so on.

Claim 43

An objective lens system for an endoscope comprising a front lens unit, a rear lens unit, and a stop located between said front and rear lens units, said front lens unit comprising a negative lens component concave toward the image side arranged so that the surface on the image side thereof is formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis, and said rear lens unit comprising a plurality of lens component including a positive cemented doublet one of said lens components being arranged so that the surface on the image side thereof is formed as an aspherical surface having portions whose curvature is made gradually stronger as they are farther from the optical axis, the air space between the surface on the extreme image side of said front lens unit and said stop being constant.

Claim 44

An objective lens system for an endoscope comprising a front lens unit, a rear lens unit, and a stop located between said front and rear lens units, said front lens unit comprising a negative lens component concave toward the image side arranged so that the surface on the image side thereof is formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis, and said rear lens unit comprising a plurality of lens component including a positive cemented doublet one of said lens components being arranged so that the surface on the image side thereof is formed as an aspherical surface having portions whose curvature is made gradually stronger as they are farther from the optical axis, the air space between the surface on the extreme image side of said front lens unit and said stop being constant.

Claim 45

An objective lens system for an endoscope according to claim 41 fulfilling the following conditions: A.sub.F.A.sub.R <0 0.01<|A.sub.F /A.sub.R |<10 where, reference symbol A F represents the sum of coefficients of astigmatism of said aspherical surfaces provided in said front lens unit, and reference symbol A R represents the sum of coefficients of astigmatism of said aspherical surfaces provided in said rear lens unit. optical axis, reference symbol P represents a parameter representing the shape of said aspherical surface, and reference symbols B, E, F, G, . . . respectively represent the aspherical surface coefficients of the second power, fourth power, sixth power eighth power and so on.

Claim 46

An objective lens system for an endoscope according to claim 42, wherein a meniscus lens component concave toward the image side is arranged on the extreme object side of said front lens unit, a meniscus lens component concave toward the object side is arranged on the extreme image side of said rear lens unit, a positive lens component is arranged on the extreme image side of said front lens unit, a positive lens component is arranged on the extreme image side of said front lens unit, a positive lens component is arranged on the extreme object side of said rear lens unit, and a stop is arranged between said positive lenses arranged in front lens unit and rear lens unit.

Claim 47

An objective lens system for an endoscope according to claim 43 wherein said front lens unit comprises a negative lens component having a concave surface on the image side, and a positive cemented doublet, said rear lens group comprises a positive cemented doublet, and a meniscus lens component convex toward the image side, each of said aspherical surfaces is expressed by the formula shown below when the optical axis is designated as the x axis and a straight line perpendicular to the optical axis and passing the intersecting point between said aspherical surface and optical axis is designated as the y axis and, moreover, each of said aspherical surfaces fulfills the condition shown below: ##EQU15## where, reference symbol f represents the focal length of the lens system as a whole, reference symbol c represents the inverse number of the radius of curvature of the spherical surface which is in contact with said aspherical surface on the optical axis, reference symbol P represents a parameter representing the shape of said aspherical surface, and reference symbols B, E, F, G, . . . respectively represent the aspherical surface coefficients of the second power, fourth power, sixth power, eighth power and so on.

Claim 48

An objective lens system for an endoscope according to claim 44 wherein the surface on the image side of said meniscus lens component in said rear lens unit is formed as an aspherical surface having portions whose curvature is made gradually stronger as they are farther from the optical axis.

Claim 49

An objective lens system for an endoscope according to claim 45 further fulfilling the following condition: f.sub.4 <-3f where, reference symbol f 4 represents the focal length of said meniscus lens component constituting said rear lens unit.

Claim 50

An objective lens system for an endoscope according to claim 44 having the following numerical data: ______________________________________ r.sub.1 = -10.5764 d.sub.1 = 0.2644 n.sub.1 = 1.51633 ν.sub.1 = 64.15 r.sub.2 = 0.8576 (aspherical surface) d.sub.2 = 1.4849 r.sub.3 = 4.0495 d.sub.3 = 0.5887 n.sub.2 = 1.5927 ν.sub.2 = 35.29 r.sub.4 = -3.11 d.sub.4 = 0.015 r.sub.4 = ∞ (stop) d.sub.s = 0.0017 r.sub.6 = 2.5394 d.sub.6 = 0.5817 n.sub.3 = 1.62041 ν.sub.3 = 60.27 r.sub.7 = -0.783 d.sub.7 = 0.2115 n.sub.4 = 1.80518 ν.sub.4 = 25.43 r.sub.8 = -1.4395 d.sub.8 = 0.7633 r.sub.9 = -2.2144 d.sub.9 = 0.2712 n.sub.5 = 1.84666 ν.sub.5 = 23.88 r.sub.10 = -3.4775 (aspherical surface) f = 1, 2ω = 105.97° aspherical surface coefficient and 2nd surface P = 1, E = -0.6762 × 10.sup.-1 F = -0.98299 × 10.sup.-1 aspherical surface coefficient of 10th surface P = 1, E = 0.28784 F = -0.63525 × 10.sup.-1 A.sub.F = -0.00404, A.sub.F = 0.01655 A.sub.F /A.sub.F = -0.2441, E.sub.F = -0.06762 E.sub.B = 0.28784, |E.sub.B /E.sub.F | = 4.257 f.sub.4 = -7.987 ______________________________________ where, reference symbols r 1 , r 2 , . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 , d 2 , . . . respectively represent thickness of respective lenses and airspaces between respective lenses, reference symbols n 1 , n 2 , . . . respectively represent refractive indices of respective lenses, and reference symbols ν 1 , ν 2 , . . . respectively represent Abbe's numbers of respective lenses.

Claim 51

An objective lens system for an endoscope comprising a front lens unit, a rear lens unit, and a stop located between said front and rear lens units, said front lens unit comprising a negative meniscus lens component convex toward the object side arranged that the surface of the image side thereof is formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis, and said rear lens unit comprising plurality of lens components including a positive cemented doublet one of said lens components being arranged so that the surface on the object side thereof is formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis, the air space between the surface on the extreme image side of said front lens unit and said stop being constant.

Claim 52

An objective lens system for an endoscope comprising a front lens unit, a rear lens unit, and a stop located between said front and rear lens units, said front lens unit comprising a negative meniscus lens component convex toward the object side arranged that the surface of the image side thereof is formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis, and said rear lens unit comprising plurality of lens components including a positive cemented doublet one of said lens components being arranged so that the surface on the object side thereof is formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis, the air space between the surface on the extreme image side of said front lens unit and said stop being constant.

Claim 53

An objective lens system for an endoscope according to claim 48 fulfilling the following conditions: A.sub.F ·A.sub.R <0 0.01<|A.sub.F /A.sub.R |<10 where, reference symbol A F represents the sum of coefficients of astigmatism of said aspherical surfaces provided in said front lens unit, and reference symbol A R represents the sum of coefficients of astigmatism of said aspherical surfaces provided in said rear lens unit.

Claim 54

An objective lens system for an endoscope according to claim 49, wherein said front lens unit has negative refractive power, said rear lens unit has positive refractive power and said stop located between said front and rear lens units in the vicinity of the front focal point.

Claim 55

An objective lens system for an endoscope according to claim 50 wherein said rear lens unit comprises a positive meniscus lens component convex toward the image side, a positive lens component, a positive cemented doublet, and a positive lens component, each of said aspherical surfaces is expressed by the formula shown below when the optical axis is designated as the x axis and a straight line perpendicular to the optical axis and passing the intersecting point between said aspherical surface and optical axis is designated as the y axis and, moreover, each of said aspherical surfaces fulfills the condition shown below: ##EQU16## where, reference symbol f represents the focal length of the lens system as a whole, reference symbol f 1 represents the focal length of said front lens unit, reference symbol D represents the distance from the rearmost surface of said front lens unit to the foremost surface of said rear lens unit reference symbol C represents the inverse number of the radius of curvature of the aspherical surface which is in contact with said aspherical surface on the optical axis, reference symbol P represents a parameter representing the shape of said aspherical surface, and reference symbols B, E, F, G, . . . respectively represent the aspherical surface coefficients of the second power, fourth power, sixth power, eighth power and so on.

Claim 56

An objective lens system for an endoscope according to claim 50 wherein said rear lens unit comprises a positive lens component, and a cemented doublet, each of said aspherical surfaces is expressed by the formula shown below when the optical axis is designated as the x axis and a straight line perpendicular to the optical axis and passing the intersecting point between said aspherical surface and optical axis is designated as the y axis and, moreover, each of said aspherical surfaces fulfills the conditions shown below: ##EQU17## where, reference symbol f represents the focal length of the lens system as a whole, reference symbol O represents the inverse number of the radius of curvature of the spherical surface which is in contact with said aspherical surface on the optical axis, reference symbol P represents a parameter representing the shape of said aspherical surface, and reference symbols B, E, F, G, . . . respectively represent the aspherical surface coefficients of the second power, fourth power, sixth power, eighth power and so on.

Claim 57

An objective lens system for an endoscope according to claim 52 further fulfilling the following conditions: |f.sub.1 |>1.8f D>1.5f where, reference symbol f 1 represents the focal length of said front lens unit, and reference symbol D represents the distance from the rearmost surface of said front lens unit to the foremost surface of said rear lens unit.

Claim 58

An objective lens system for an endoscope according to claim 53 wherein the surface on the object side of said positive cemented doublet constituting said rear lens unit is formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis.

Claim 59

An objective lens system for an endoscope according to claim 54 having the following numerical data: ______________________________________ r.sub.1 = 4.1406 d.sub.1 = 0.8005 n.sub.1 = 1.88300 ν.sub.1 = 40.76 r.sub.2 = 1.1345 (aspherical surface) d.sub.2 = 4.1302 r.sub.3 = ∞ (stop) d.sub.3 = 0.3680 r.sub.4 = 6.9159 d.sub.4 = 0.8469 n.sub.2 = 1.69680 ν.sub.2 = 55.52 r.sub.5 = -4.1736 d.sub.5 = 1.7075 r.sub.6 = 2.8187 (aspherical surface) d.sub.6 = 1.9723 n.sub.3 = 1.64000 ν.sub.3 = 60.09 r.sub.7 = -1.4348 d.sub.7 = 0.5801 n.sub.4 = 1.84666 ν.sub.4 = 23.88 r.sub.8 = -4.0238 f = 1, 2ω = 66.482° aspherical surface coefficient of 2nd surface P = 1, E = -0.92345 × 10.sup.-1 F = 0.33387 × 10.sup.-1 aspherical surface coefficient of 6th surface P = 1, E = -0.79246 × 10.sup.-2 F = 0.36822 × 10.sup.-2 A.sub.F = -0.01433, A.sub.R = 0.00246 A.sub.F /A.sub.R = -5.8252 f.sub.1 = -2.002, D.sub.1 = 4.498 ______________________________________ where, reference symbols r 1 , r 2 , . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 , d 2 , . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 , n 2 , . . . respectively represent refractive indices of respective lenses, and reference symbols ν 1 , ν 2 , . . . respectively represent Abbe's numbers of respective lenses.

Claim 60

An objective lens system for an endoscope according to claim 50 wherein said front lens unit comprises two negative lens components each having a concave surface on the image side, said rear lens unit comprises a positive lens component, a positive lens component, a positive cemented doublet, and a positive lens component having a convex surface on the object side, each of said aspherical surfaces is expressed by the formula shown below when the optical axis is designated as the x axis and a straight line perpendicular to the optical axis and passing the intersecting point between said aspherical surface and optical axis is designated as the y axis and, moreover, each of said aspherical surfaces fulfills the conditions shown below: ##EQU18## where, reference symbol f F represents the focal length of said front lens group, reference symbol f represents the focal length of the lens system as a whole, reference symbol C represents the inverse number of the radius of curvature of the spherical surface which is in contact with said aspherical surface on the optical axis, reference symbol P represents a parameter representing the shape of said aspherical surface, and reference symbols B, E, F, G, . . . respectively represent the aspherical surface coefficients of the second power, fourth power, sixth power, eighth power and so on.

Claim 61

An objective lens system for an endoscope according to claim 56 wherein the surface on the object side of said rearmost lens component in said rear lens unit is formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis.

Claim 62

An objective lens system for an endoscope according to claim 57 having the following numerical data: ______________________________________ r.sub.1 = 13.333 d.sub.1 = 0.7333 n.sub.1 = 1.49109 ν.sub.1 = 57.00 r.sub.2 = 3.6471 (aspherical surface) d.sub.2 = 1.0730 r.sub.3 = 2240.3652 d.sub.3 = 2.1988 n.sub.2 = 1.78800 ν.sub.2 = 47.43 r.sub.4 = 1.2225 d.sub.4 = 1.0494 r.sub.5 = ∞ (stop) d.sub.5 = 0.1241 r.sub.6 = -77.6317 d.sub.6 = 1.2380 n.sub.3 = 1.58913 ν.sub.3 = 60.97 r.sub.7 = -1.9899 d.sub.7 = 0.7377 r.sub.8 = -6.0607 d.sub.8 = 1.3244 n.sub.4 = 1.58913 ν.sub.4 = 60.97 r.sub.9 = -2.7972 d.sub.9 = 0.1333 r.sub.10 = 4.3283 d.sub.10 = 2.1067 n.sub.5 = 1.61800 ν .sub.5 = 63.38 r.sub.11 = -2.2200 d.sub.11 = 0.4667 n.sub.6 = 1.84666 ν.sub.6 = 23.90 r.sub.12 = -16.4147 d.sub.12 = 0.9325 r.sub.13 = 2.0725 (aspherical surface) d.sub.13 = 1.9851 n.sub.7 = 1.49109 ν.sub.7 = 57.00 r.sub.14 = ∞ f = 1, 2ω = 115.9° aspherical surface coefficient of 2nd surface P = 1, E = -0.11242 × 10.sup.-1, F = 0 aspherical surface coefficient of 13th surface P = 1, E = -0.54135 × 10.sup.-1, F = 0 A.sub.F = -0.01753, A.sub.R = 0.05767 A.sub.F /A.sub.R = -0.30397, f.sub.F = -1.151 ______________________________________ where, reference symbols r 1 , r 2 , . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 , d 2 , . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 , n 2 , . . . respectively represent refractive indices of respective lenses, and reference symbols ν 1 , ν 2 , . . . respectively represent Abbe's numbers of respective lenses.

Claim 63

An objective lens system for an endoscope according to claim 50 wherein a meniscus lens component concave toward the image side is arranged on the extreme object side of said front lens unit, a meniscus lens component concave toward the object side is arranged on the extreme image side of said rear unit, a positive lens component is arranged on the extreme image side of said front lens unit, a positive lens component is arranged on the extreme object side of said rear lens unit, and a stop is arranged between said positive lenses arranged in front lens unit and rear lens unit.

Claim 64

An objective lens system for an endoscope according to claim 59 wherein said front lens unit comprises a negative lens component having a concave surface on the image side, and a positive cemented doublet, said rear lens group comprises a positive cemented doublet, and a meniscus lens component convex toward the image side, each of said aspherical surfaces is expressed by the formula shown below when the optical axis is designated as the x axis and a straight line perpendicular to the optical axis and passing the intersecting point between said aspherical surface and optical axis is designatedas the y axis and, moveover, each of said aspherical surfaces fulfills the condition shown below: ##EQU19## where, reference symbol f represents the focal length of the lens system as a whole, reference symbol C represents the inverse number of the radius of curvature of the spherical surface which is in contact with said aspherical surface on the optical axis, reference symbol P represents a parameter representing the shape of said aspherical surface, and reference symbols B, E, F, G, . . . respectively represent the aspherical surface coefficients of the second power, fourth power, sixth power, eighth power and so on.

Claim 65

An objective lens system for an endoscope comprising a front lens unit, a rear lens unit, and a stop located between said front and rear lens units, said front lens unit comprising a plane-parallel transparent plate on the object side of which a portion is provided at a distance from the optical axis which is aspherical in shape, the curvature of which is made gradually stronger as the distance increases from the optical axis, and said rear lens unit comprising two positive lens components arranged so that the lens surfaces facing each other are convex and the surface on the object side of the positive lens component on the image side thereof is formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis.

Claim 66

An objective lens system for an endoscope comprising a front lens unit, a rear lens unit, and a stop located between said front and rear lens units, said front lens unit comprising a plane-parallel transparent plate on the object side of which a portion is provided at a distance from the optical axis which is aspherical in shape, the curvature of which is made gradually stronger as the distance increases from the optical axis, and said rear lens unit comprising two positive lens components arranged so that the lens surfaces facing each other are convex and the surface on the object side of the positive lens component on the image side thereof is formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis.

Claim 67

An objective lens system for an endoscope according to claim 61 wherein said front lens unit comprises a plane-parallel transparent plate on the object side of which is provided with a portion at a distance from the optical axis which is aspherical, said rear lens unit comprising a positive lens cemented on to the image side of said plane-parallel transparent plate, and a positive lens component having an aspherical surface on the object side, each of said aspherical surfaces being expressed by the formula shown below when the optical axis is designated as the x axis and a straight line perpendicular to the optical axis and passing the intersecting point between said aspherical surface and the optical axis is designated as the y axis and, moreover, each of said aspherical surfaces fulfills the condition shown below: ##EQU20## where, reference symbol f represents the focal length of the lens system as a whole, reference symbol C represents the inverse number of the radius of curvature of the spherical surface which is in contact with said aspherical surface on the optical axis, reference symbol P represents a parameter representing the shape of said aspherical surface, the reference symbols B, E, F, G, . . . respectively represent the aspherical surface coefficients of the second power, fourth power, sixth power, eighth power and so on.

Claim 68

An objective lens system for an endoscope according to claim 62 having the following numerical data: ______________________________________ r.sub.1 = ∞ (aspherical surface) d.sub.1 = 0.5725 n.sub.1 = 1.51633 ν.sub.1 = 64.15 r.sub.2 = ∞ (stop) d.sub.2 = 1.3991 n.sub.2 = 1.80610 ν.sub.2 = 40.95 r.sub.3 = -1.2000 d.sub.3 = 0.5436 r.sub.4 = 1.5780 (aspherical surface) d.sub.4 = 1.2126 n.sub.3 = 1.80610 ν.sub.3 = 40.95 r.sub.5 = ∞ f = 1, 2ω = 81.502° aspherical surface coefficient of 1st surface P = 1, E = 0.12374, F = 0 aspherical surface coefficient of 4th surface P = 1, E = -0.87329 × 10.sup.-1 F = -0.18044 × 10.sup.-1 A.sub.F = -0.00267, A.sub.R = 0.01139 A.sub.F /A.sub.R = -0.23442 ______________________________________ where, reference symbols r 1 , r 2 , . . . respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 , d 2 , . . . respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 , n 2 , . . . respectively represent refractive indices of respective lenses, and reference symbols ν 1 , ν 2 , . . . respectively represent Abbe's numbers of the respective lenses.

Claim 69

An objective lens system for an endoscope comprising a front lens unit, a rear lens unit, and a stop located between said front and rear lens units, and front lens unit comprising a negative lens component concave toward the image side and at least one lens surface of said front lens unit being formed as an aspherical surface having portions whose curvature is made gradually stronger as they are farther from the optical axis, and said rear lens unit comprising a plurality of lens components including a positive cemented doublet, one of said lens components being arranged so that the surface on the object side thereof is formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis, the air space between the surface on the extreme image side of said front lens unit and said stop being constant.

Claim 70

An objective lens system for an endoscope comprising a front lens unit, a rear lens unit, and a stop located between said front and rear lens units, and front lens unit comprising a negative lens component concave toward the image side and at least one lens surface of said front lens unit being formed as an aspherical surface having portions whose curvature is made gradually stronger as they are farther from the optical axis, and said rear lens unit comprising a plurality of lens components including a positive cemented doublet, one of said lens components being arranged so that the surface on the object side thereof is formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis, the air space between the surface on the extreme image side of said front lens unit and said stop being constant.

Claim 71

An objective lens system for an endoscope according to claim 64, wherein said negative lens component of said front lens unit is arranged that the surface on the object side thereof is formed as an aspherical surface having portions whose curvature is made gradually stronger as they are farther from the optical axis.

Claim 72

An objective lens system for an endoscope comprising a front lens unit, a rear lens unit, and a stop located between said front and rear lens units, said front lens unit comprising a negative lens component concave toward the image side and at least one lens surface of said front lens unit being formed as an aspherical surface having portions whose curvature is made gradually stronger as they are farther from the optical axis, and said rear lens unit comprising a plurality of lens components including a positive cemented doublet, one of said lens components being arranged so that the surface on the image side thereof is formed as an aspherical surface having portions whose curvature is made gradually stronger as they are farther from the optical axis, the air space between the surface on the extreme image side of said front lens unit and said stop being constant.

Claim 73

An objective lens system for an endoscope comprising a front lens unit, a rear lens unit, and a stop located between said front and rear lens units, said front lens unit comprising a negative lens component concave toward the image side and at least one lens surface of said front lens unit being formed as an aspherical surface having portions whose curvature is made gradually stronger as they are farther from the optical axis, and said rear lens unit comprising a plurality of lens components including a positive cemented doublet, one of said lens components being arranged so that the surface on the image side thereof is formed as an aspherical surface having portions whose curvature is made gradually stronger as they are farther from the optical axis, the air space between the surface on the extreme image side of said front lens unit and said stop being constant.

Claim 74

An objective lens system for an endoscope comprising a front lens unit, a rear lens unit, and a stop located between said front and rear lens units, said front lens unit comprising a negative lens component concave toward the image side and at least one lens surface of said front lens unit being formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis, and said rear lens unit comprising a plurality of lens components including a positive cemented doublet, one of said lens components being arranged so that the surface on the image side thereof is formed as an aspherical surface having portions whose curvature is made gradually stronger as they are farther from the optical axis, the air space between the surface on the extreme image side of said front lens unit and said stop being constant.

Claim 75

An objective lens system for an endoscope comprising a front lens unit, a rear lens unit, and a stop located between said front and rear lens units, said front lens unit comprising a negative lens component concave toward the image side and at least one lens surface of said front lens unit being formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis, and said rear lens unit comprising a plurality of lens components including a positive cemented doublet, one of said lens components being arranged so that the surface on the image side thereof is formed as an aspherical surface having portions whose curvature is made gradually stronger as they are farther from the optical axis, the air space between the surface on the extreme image side of said front lens unit and said stop being constant.

Claim 76

An objective lens system for an endoscope comprising a front lens unit, a rear lens unit, and a stop located between said front and rear lens units, said front lens unit comprising a negative lens components concave toward the image side and at least one lens surface of said front lens unit being formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis, and said rear lens unit comprising plurality of lens components including a positive cemented doublet, one of said lens components being arranged so that the surface on the object side thereof is formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis, the air space between the surface on the extreme image side of said front lens unit and said stop being constant.

Claim 77

An objective lens system for an endoscope comprising a front lens unit, a rear lens unit, and a stop located between said front and rear lens units, said front lens unit comprising a negative lens components concave toward the image side and at least one lens surface of said front lens unit being formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis, and said rear lens unit comprising plurality of lens components including a positive cemented doublet, one of said lens components being arranged so that the surface on the object side thereof is formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis, the air space between the surface on the extreme image side of said front lens unit and said stop being constant.

Claim 78

An objective lens system for an endoscope according to claim 68, wherein said negative lens component of said front lens unit is arranged that the surface of the image side thereof is formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis.

Claim 79

An objective lens system for an endoscope comprising a front lens unit, a rear lens unit, and a stop located between said front and rear lens units, said front lens unit comprising an optical element having an aspherical surface, the curvature of which is made gradually stronger as the distance increases from the optical axis, and said rear lens unit comprising two positive lens components arranged so that the lens surfaces facing each other are convex and at least one lens surface of said two positive lens components is formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis.

Claim 80

An objective lens system for an endoscope comprising a front lens unit, a rear lens unit, and a stop located between said front and rear lens units, said front lens unit comprising an optical element having an aspherical surface, the curvature of which is made gradually stronger as the distance increases from the optical axis, and said rear lens unit comprising two positive lens components arranged so that the lens surfaces facing each other are convex and at least one lens surface of said two positive lens components is formed as an aspherical surface having portions whose curvature is made gradually weaker as they are farther from the optical axis.