Objective lens system for endoscopes

Claim 2

A retrofocus-type objective for endoscopes comprising a front lens group having negative refractive power, a rear lens group having positive refractive power in the order from object side, and a stop arranged between said front and rear lens groups, said front lens group comprising a negative lens element having a concave surface having a selected curvature which is strong and a positive lens element, and said rear lens group having at least two positive lens components, one of said positive lens components being a cemented doublet having a positive lens element and negative lens element the cemented surface of which is convexed to the image side, and at least one of the lens components in said front lens group having an aspherical surface on the object side thereof including portions whose curvature is gradually increased as the distance thereof increases from the optical axis.

Claim 3

An objective lens system for endoscopes according to claim 1 wherein said aspherical surface is expressed by the following formula when the optical axis is taken as the x axis, and the straight line passing through the top of said aspherical surface and is perpendicular to the x axis is taken as the y axis: ##EQU10## wherein the reference symbol C represents an inverse number of the radius of a circle in contact with said aspherical surface in the vicinity of the optical axis, the reference symbol P designates a parameter representing shape of said aspherical surface, and the reference symbols B, E, F, G, . . . denote the second power, fourth power, sixth power, eighth power aspherical surface coefficients respectively.

Claim 4

An object lens system for endoscopes according to claim 2 wherein said system includes a factor A and wherein factor A satisfies the following formula when degree of deflection angle K for the principal ray is expressed as ##EQU11## wherein the reference symbol 2ω represents angle of view, the reference symbol H designates correction ratio and σ denotes a value of -1 when said aspherical surface is arranged on the object side of said lens component.

Claim 5

An objective lens system for endoscopes according to claim 3 wherein said front lens group comprises a negative meniscus lens component, a negative meniscus lens component, a cemented doublet and a meniscus lens component, said rear lens group comprises a cemented doublet, a positive lens component, a cemented doublet and a cover glass, and the object side surface of the second negative meniscus lens component as counted from the object side in said front lens group is designed as the aspherical surface, said objective lens system having the following numerical data: ______________________________________ r.sub.1 = 6.1789 d.sub.1 = 0.7129 n.sub.1 = 1.8830 ν.sub.1 = 40.76 r.sub.2 = 3.8110 d.sub.2 = 0.5704 r.sub.3 = 16.0271 (aspherical surface) d.sub.3 = 0.6654 n.sub.2 = 1.49109 ν.sub.2 = 57.00 r.sub.4 = 2.2192 d.sub.4 = 1.1407 r.sub.5 = 9.5060 d.sub.5 = 0.9506 n.sub.3 = 1.80518 ν.sub.3 = 25.43 r.sub.6 = -9.5060 d.sub.6 = 0.3802 n.sub.4 = 1.77250 ν.sub.4 = 49.66 r.sub.7 = 4.3058 d.sub.7 = 2.6617 r.sub.8 = -1.3401 d.sub.8 = 0.9506 n.sub.5 = 1.80610 ν.sub.5 = 40.95 r.sub.9 = 1.7300 d.sub.9 = 0.3327 r.sub.10 = ∞ (stop) d.sub.10 = 0.0570 r.sub.11 = -6.6171 d.sub.11 = 1.2358 n.sub.6 = 1.58913 ν.sub.6 = 60.97 r.sub.12 = -1.2320 d.sub.12 = 1.1882 n.sub.7 = 1.66998 ν.sub.7 = 39.32 r.sub.13 = -4.3271 d.sub.13 = 1.5381 r.sub.14 = 40.6961 d.sub.14 = 1.0932 n.sub.8 = 1.80610 ν.sub.8 = 40.95 r.sub.15 = -4.9754 d.sub.15 = 0.1426 r.sub.16 = 4.0439 d.sub.16 = 1.8061 n.sub.9 = 1.60311 ν.sub.9 = 60.70 r.sub.17 = -4.0439 d.sub.17 = 0.5704 n.sub.10 = 1.80518 ν.sub.10 = 25.43 r.sub.18 = 6.7198 d.sub.18 = 2.3689 r.sub.19 = ∞ d.sub.19 = 0.6654 n.sub.11 = 1.56384 ν.sub.11 = 60.69 r.sub.20 = ∞ f = 1, F.sub.NO = 2.544, image height = 0.97436 P = 1.0000, B = 0, E = 0.70488 × 10.sup.-2 F = 0.17289 10.sup.-3, G = 0 ______________________________________ wherein the reference symbols r 1 through r 20 represent radii of curvature on the surfaces of the respective lens elements, the reference symbols d 1 through d 19 designate thicknesses of the respective lens elements and airspaces reserved therebetween, the reference symbols n 1 through n 11 denote refractive indices of the respective lens elements, and the reference symbols ν 1 through ν 11 represent Abbe's numbers of the respective lens elements.

Claim 6

An object lens system for endoscopes according to claim 3 wherein said front lens group comprises a negative meniscus lens component, a negative meniscus lens component, a nemiscus lens component and a meniscus lens component, said rear lens group comprises a cemented doublet, a positive lens component, a cemented doublet and a cover glass, and the object side surface of the second negative meniscus lens component as counted on from the object side in said front lens group is designed as an aspherical surface, said objective lens system having the following numerical data: ______________________________________ r.sub.1 = 4.4865 d.sub.1 = 0.5982 n.sub.1 = 1.88300 ν.sub.1 = 40.76 r.sub.2 = 2.0438 d.sub.2 = 0.5483 r.sub.3 = ∞ (aspherical surface) d.sub.3 = 1.1066 n.sub.2 = 1.49109 ν.sub.2 = 57.00 r.sub.4 = 1.0614 d.sub.4 = 1.7035 r.sub.5 = 1.7161 d.sub.5 = 0.2157 n.sub.3 = 1.78590 ν.sub.3 = 44.18 r.sub.6 = 1.4071 d.sub.6 = 0.6995 r.sub.7 = -1.5783 d.sub.7 = 0.5555 n.sub.4 = 1.80610 ν.sub.4 = 40.95 r.sub.8 = -1.4248 d.sub.8 = 0.0014 r.sub.9 = ∞ (stop) d.sub.9 = 0.0598 r.sub.10 = -6.9401 d.sub.10 = 1.2961 n.sub. 5 = 1.58913 ν.sub.5 = 60.97 r.sub.11 = -1.2921 d.sub.11 = 1.2462 n.sub.6 = 1.66998 ν.sub.6 = 39.32 r.sub.12 = -4.5483 d.sub.12 = 1.6131 r.sub.13 = 43.6826 d.sub.13 = 1.1465 n.sub.7 = 1.80610 ν.sub.7 = 40.95 r.sub.14 = -5.2183 d.sub.14 = 0.1495 r.sub.15 = 4.2412 d.sub.15 = 1.8943 n.sub.8 = 1.60311 ν.sub.8 = 60.70 r.sub.16 = -4.2412 d.sub.16 = 0.5982 n.sub.9 = 1.80518 ν.sub.9 = 25.43 r.sub.17 = 7.0478 d.sub.17 = 2.4845 r.sub.18 = ∞ d.sub.18 = 0.6979 n.sub.10 = 1.56384 ν.sub.10 = 60.69 r.sub.19 = ∞ f = 1, F.sub.NO = 2.588, image height = 1.0219 P = 1.0000, B = 0.16225 × 10.sup.-1, E = 0.50809 × 10.sup.-1 F = 0.34471 × 10.sup.-7, G = 0 ______________________________________ wherein the reference symbols r 1 through r 19 represent radii of curvature on the surraces of the respective lens elements, the reference symbols d 1 through d 18 designate thicknesses of the respective lens elements and airspaces reserved therebetween, the reference symbols n 1 through n 10 denote refractive indices of the respective lens elements, and the reference symbol ν 1 through ν 10 represent Abbe's numbers of the respective lens elements.

Claim 7

An objective lens system for endoscopes according to claim 3 wherein said front lens group comprises a negative meniscus lens component, a negative meniscus lens component, a plane parallel plate and a meniscus lens component, said rear lens group comprises a cemented doublet, a positive lens component, a cemented doublet and a cover glass, and the extreme object side surface is designed as an aspherical surface, said objective lens system having the following numerical data: ______________________________________ r.sub.1 = ∞ (aspherical surface) d.sub.1 = 0.6186 n.sub.1 = 1.49109 ν.sub.1 = 57.00 r.sub.2 = 1.6347 d.sub.2 = 0.8247 r.sub.3 = 5.4807 d.sub.3 = 0.5155 n.sub.2 = 1.88300 ν.sub.2 = 40.76 r.sub.4 = 2.6388 d.sub.4 = 1.9166 r.sub.5 = ∞ d.sub.5 = 0.5155 n.sub.3 = 1.78590 ν.sub.3 = 44.18 r.sub.6 = ∞ d.sub.6 = 0.5826 r.sub.7 = -1.5709 d.sub.7 = 1.1340 n.sub.4 = 1.80610 ν.sub.4 = 40.95 r.sub.8 = -1.9679 d.sub.8 = 0.0014 r.sub.9 = ∞ (stop) d.sub.9 = 0.0617 r.sub.10 = -7.1548 d.sub.10 = 1.3362 n.sub.5 = 1.58913 ν.sub.5 = 60.97 r.sub.11 = -1.3321 d.sub.11 = 1.2848 n.sub.6 = 1.66998 ν.sub.6 = 39.32 r.sub.12 = -4.6787 d.sub.12 = 1.6630 r.sub.13 = 44.0027 d.sub.13 = 1.1820 n.sub.7 = 1.80610 ν.sub.7 = 40.95 r.sub.14 = -5.3797 d.sub.14 = 0.1542 r.sub.15 = 4.3724 d.sub.15 = 1.9529 n.sub.8 = 1.60311 ν.sub.8 = 60.70 r.sub.16 = -4.3724 d.sub.16 = 0.6167 n.sub.9 = 1.80518 ν.sub.9 = 25.43 r.sub.17 = 7.2658 d.sub.17 = 2.5614 r.sub.18 = ∞ d.sub.18 = 0.7195 n.sub.10 = 1.56384 ν.sub.10 = 60.69 r.sub.19 = ∞ f = 1, F.sub. NO = 2.531, image height 1.0535 P = 1.0000, B = 0, E = 0.13075 × 10.sup.-1 F = 0, G = 0 ______________________________________ wherein the reference symbols r 1 through r 19 represent radii of curvature on the surfaces of the respective lens elements, the reference symbols d 1 through d 18 designate thicknesses of the respective lens elements and airspaces reserved therebetween, the reference symbols n 1 through n 10 denote refractive indices of the respective lens elements, and the reference symbols ν 1 through ν 10 represent Abbe's numbers of the respective lens elements.

Claim 8

An objective lens system for endoscopes according to claim 3 wherein said front lens group comprises a positive meniscus lens component, a cemented doublet, a negative meniscus lens component, a positive lens component and a meniscus lens component, said rear lens group comprises a cemented doublet, a positive lens component, a cemented doublet and a cover glass, and the object side surface of the second cemented doublet as counted from the object side in said front lens group is designed as an aspherical surface, said objective lens system having the following numerical data: ______________________________________ r.sub.1 = 10.3716 d.sub.1 = 0.7992 n.sub.1 = 1.88300 ν.sub.1 = 40.76 r.sub.2 = 17.9820 d.sub.2 = 0.0999 r.sub.3 = 12.0112 (aspherical surface) d.sub.3 = 0.6993 n.sub.2 = 1.49109 ν.sub.2 = 57.00 r.sub.4 = 4.9950 d.sub.4 = 0.3996 n.sub.3 = 1.80610 ν.sub.3 = 40.95 r.sub.5 = 2.4975 d.sub.5 = 0.7992 r.sub.6 = 19.2639 d.sub.6 = 0.3996 n.sub.4 = 1.88300 ν.sub.4 = 40.76 r.sub.7 = 1.9843 d.sub.7 = 2.3429 r.sub.8 = 15.5038 d.sub.8 = 0.5455 n.sub.5 = 1.78590 ν.sub.5 = 44.18 r.sub.9 = -84.2272 d.sub.9 = 0.5669 r.sub.10 = - 1.9200 d.sub.10 = 1.0992 n.sub.6 = 1.80610 ν.sub.6 = 40.95 r.sub.11 = -2.3493 d.sub.11 = 0.3497 r.sub.12 = ∞ (stop) d.sub.12 = 0.0599 r.sub.13 = -6.9540 d.sub.13 = 1.2987 n.sub.7 = 1.58913 ν.sub.7 = 60.97 r.sub.14 = -1.2947 d.sub.14 = 1.2488 n.sub.8 = 1.66998 ν.sub.8 = 39.32 r.sub.15 = -4.5475 d.sub.15 = 1.6164 r.sub.16 = 42.7682 d.sub.16 = 1.1489 n.sub.9 = 1.80610 ν.sub.9 = 40.95 r.sub.17 = -5.2288 d.sub.17 = 0.1499 r.sub.18 = 4.2498 d.sub.18 = 1.8981 n.sub.10 = 1.60311 ν.sub.10 = 60.70 r.sub.19 = -4.2498 d.sub.19 = 0.5994 n.sub.11 = 1.80518 ν.sub.11 = 25.43 r.sub.20 = 7.0619 d.sub.20 = 2.4895 r.sub.21 = ∞ d.sub.21 = 0.6993 n.sub.12 = 1.56384 ν.sub.12 = 60.69 r.sub.22 = ∞ f = 1, F.sub.NO = 2.581, image height = 1.0240 P = 1.0000, B = 0, E = 0.92329 × 10.sup.-2 F = -0.22743 × 10.sup.-3, G = 0 ______________________________________ wherein the reference symbols r 1 through r 22 represent radii of curvature on the surfaces of the respective lens elements, the reference symbols d 1 through d 21 designate thicknesses of the respective lens elements and airspaces reserved therebetween, the reference symbols n 1 through n 12 denote refractive indices of the respective lens elements, and the reference symbols ν 1 through ν 12 represent Abbe's numbers of the respective lens elements.

Claim 9

An objective lens system for endoscopes according to claim 3 wherein said front lens group comprises a positive meniscus lens component, a negative meniscus lens component a negative meniscus lens component, a meniscus lens component and a meiscus lens component, said rear lens group comprises a cemented doublet, a positive lens component, a cemented doublet and a cover glass, and the object side surface of the second lens component as counted from the object side in said front lens group is designed as an aspherical surface, said objective lens system having the following numerical data: ______________________________________ r.sub.1 = 8.8295 d.sub.1 = 0.8048 n.sub.1 = 1.88300 ν.sub.1 = 40.76 r.sub.2 = 18.1087 d.sub.2 = 0.1006 r.sub.3 = 6.3299 (aspherical surface) d.sub.3 = 0.6036 n.sub.2 = 1.80610 ν.sub.2 = 40.95 r.sub.4 = 2.4397 d.sub.4 = 0.9054 r.sub.5 = 9.6935 d.sub.5 = 0.4024 n.sub.3 = 1.88300 ν.sub.3 = 40.76 r.sub.6 = 1.8280 d.sub.6 = 2.4161 r.sub.7 = 50.2371 d.sub.7 = 0.5505 n.sub.4 = 1.78590 ν.sub.4 = 44.18 r.sub.8 = 24.9036 d.sub.8 = 0.5712 r.sub.9 = -1.9359 d.sub.9 = 1.1101 n.sub.5 = 1.80610 ν.sub.5 = 40.95 r.sub.10 = - 2.2035 d.sub.10 = 0.3521 r.sub.11 = ∞ stop d.sub.11 = 0.0604 r.sub.12 = -7.0030 d.sub.12 = 1.3078 n.sub.6 = 1.58913 ν.sub.6 = 60.97 r.sub.13 = -1.3038 d.sub.13 = 1.2575 n.sub.7 = 1.66998 ν.sub.7 = 39.32 r.sub.14 = -4.5795 d.sub.14 = 1.6278 r.sub.15 = 43.0694 d.sub.15 = 1.1569 n.sub.8 = 1.80610 ν.sub.8 = 40.95 r.sub.16 = -5.2656 d.sub.16 = 0.1509 r.sub.17 = 4.2797 d.sub.17 = 1.9115 n.sub.9 = 1.60311 ν.sub.9 = 60.70 r.sub.18 = -4.2797 d.sub.18 = 0.6036 n.sub.10 = 1.80518 ν.sub.10 = 25.43 r.sub.19 = 7.1117 d.sub.19 = 2.5070 r.sub.20 = ∞ d.sub.20 = 0.7042 n.sub.11 = 1.56384 ν.sub.11 = 60.69 r.sub.21 = ∞ f = 1, F.sub.NO = 2.617, image height = 1.0312 P = 1.0000, B = 0, E = 0.86037 × 10.sup.-2 F = -0.38814 × 10.sup.3, G = -0.27509 × 10.sup.-11 ______________________________________ wherein the reference symbols r 1 through r 2 represent radii of curvature on the surfaces of the respective lens elements, the reference symbols d 1 through d 20 designate thicknesses of the respective lens elements and airspaces reserved therebetween, the reference symbols n 1 through n 11 denote refractive indices of the respective lens elements, and the reference symbols ν 1 through ν 11 represent Abbe's numbers of the respective lens elements.

Claim 10

A retrofocus-type objective for endoscopes according to claim 3 wherein factor A further satisfies the following formula when degree of deflection angle K for the principal ray is expressed as K=Aω 3 Hσ: ##EQU12## wherein the reference symbol 2ω represents angle of view, the reference symbol H designates correction ratio and σ denotes a value of -1 when said aspherical surface is arranged on the object side of said lens component.

Claim 11

A retrofocus-type objective for endoscopes comprising a front lens group having negative refractive power, a rear lens group having positive refractive power in the order from object side, and a stop arranged between said front and rear lens groups, said front lens group comprising a negative lens element having a concave surface having a selected curvature which is strong and a positive lens element, and said rear lens group having at least two positive lens components, one of said positive lens components being a cemented doublet having a positive lens element and negative lens element the cemented surface of which is convexed to the image side, and at least one of the lens components in sid front lens group having an aspherical surface on the image side thereof including portions whose curvature gradually decreases as the distance thereof decreases from the optical axis.

Claim 12

A retrofocus-type objective for endoscopes comprising a front lens group having negative refractive power, a rear lens group having positive refractive power in the order from object side, and a stop arranged between said front and rear lens groups, said front lens group comprising a negative lens element having a concave surface having a selected curvature which is strong and a positive lens element, and said rear lens group having at least two positive lens components, one of said positive lens components being a cemented doublet having a positive lens element and negative lens element the cemented surface of which is convexed to the image side, and at least one of the lens components in sid front lens group having an aspherical surface on the image side thereof including portions whose curvature gradually decreases as the distance thereof decreases from the optical axis.

Claim 13

An objective lens system for endoscopes according to claim 10 wherein said aspherical surface is expressed by the following formula when the optical axis is taken as the x axis, and the straight line passing through the top of said aspherical surface and is perpendicular to the x axis is taken as the y axis: ##EQU13## wherein the reference symbol C represents an inverse number of the radius of a circle in contact with said aspherical surface in the vicinity of the optical axis, the reference symbol P designates a parameter representing shape of said aspherical surface, and the reference symbols B, E, F, G, . . . denote the second power, fourth power, sixth power, eighth power aspherical surface coefficients respectively.

Claim 14

An objective lens system for endoscopes according to claim 11 wherein said system includes a factor A wherein factor A satisfies the following formula when degree of deflection angle K for the principal ray is expressed as ##EQU14## wherein the reference symbol 2ω represents angle of view, the reference symbol H designates correction ratio and σ denotes a value of +1 when said aspherical surface is arranged on the image side of said lens component.

Claim 15

An objective lens system for endoscopes according to claim 12 wherein said front lens group comprises a negative meniscus lens component, a negative meniscus lens component, a cemented doublet and a meniscus lens component, said rear lens group comprises a cemented doublet, a positive lens component, a cemented doublet aand a cover glass, and the image side surface of the second lens component as counted from the object side in said front lens group is designed as an aspherical surface, said objective lens system having the following numerical data: ______________________________________ r.sub.1 = 7.0140 d.sub.1 = 0.7515 n.sub.1 = 1.88300 ν.sub.1 = 40.76 r.sub.2 = 3.9221 d.sub.2 = 0.8617 r.sub.3 = 5.5110 d.sub.3 = 0.7014 n.sub.2 = 1.49109 ν.sub.2 = 57.00 r.sub.4 = 1.5917 (aspherical surface) d.sub.4 = 1.0521 r.sub.5 = 4.0080 d.sub.5 = 1.1022 n.sub.3 = 1.80518 ν.sub.3 = 25.43 r.sub.6 = -10018.9980 d.sub.6 = 0.4008 n.sub.4 = 1.77250 ν.sub.4 = 49.66 r.sub.7 = 3.0749 d.sub.7 = 3.3019 r.sub.8 = -1.4028 d.sub.8 = 1.0020 n.sub.5 = 1.80610 ν.sub.5 = 40.95 r.sub.9 = -1.8511 d.sub.9 = 0.3507 r.sub.10 = ∞ (stop) d.sub.10 = 0.0601 r.sub.11 = -6.9749 d.sub.11 = 1.3026 n.sub.6 = 1.58913 ν.sub.6 = 60.97 r.sub.12 = -1.2986 d.sub.12 = 1.2525 n.sub.7 = 1.66998 ν.sub.7 = 39.32 r.sub.13 = -4.5611 d.sub.13 = 1.6212 r.sub.14 = 42.8966 d.sub.14 = 1.1523 n.sub.8 = 1.80610 ν.sub.8 = 40.95 r.sub.15 = -5.2445 d.sub.15 = 0.1503 r.sub.16 = 4.2625 d.sub.16 = 1.9038 n.sub.9 = 1.60311 ν.sub.9 = 60.70 r.sub.17 = -4.2625 d.sub.17 = 0.6012 n.sub.10 = 1.80518 ν.sub.10 = 25.43 r.sub.18 = 7.0831 d.sub.18 = 2.4970 r.sub.19 = ∞ d.sub. 19 = 0.7014 n.sub.11 = 1.56384 ν.sub.11 = 60.69 r.sub.20 = ∞ f = 1, F.sub.NO = 2.561, image height = 1.02705 P = 0, B = 0, E = -0.13727 × 10.sup.-2 F = 0.25809 × 10.sup.-3, G = 0 ______________________________________ wherein the reference symbols r 1 through r 20 represent radii of curvature on the surfaces of the respective lens elements, the reference symbols d 1 through d 19 designate thicknesses of the respective lens elements and airspaces reserved therebetween, the reference symbols n 1 through n 11 denote refractive indices of the respective lens elements, and the reference symbols ν 1 through ν 11 represent Abbe's numbers of the respective lens elements.

Claim 16

An objective lens system for endoscopes according to claim 12 wherein said front lens group comprises a negative meniscus lens component, a negative meniscus lens components, a cemented doublet and a meniscus lens component, said rear lens group comprises a plane parallel plate, a cemented doublet and a cemented doublet, and the image side surface of the second lens component as counted from the object side in said front lens group is designed as an aspherical surface, said objective lens system having the following numerical data: ______________________________________ r.sub.1 = 7.5512 d.sub.1 = 0.8091 n.sub.1 = 1.88300 ν.sub.1 = 40.76 r.sub.2 = 4.2225 d.sub.2 = 0.9277 r.sub.3 = 5.9331 d.sub.3 = 0.7551 n.sub.2 = 1.49109 ν.sub.2 = 57.00 r.sub.4 = 1.7136 (aspherical surface) d.sub.4 = 1.1327 r.sub.5 = 4.3150 d.sub.5 = 1.1866 n.sub.3 = 1.80518 ν.sub.3 = 25.43 r.sub.6 = -10786.4078 d.sub.6 = 0.4315 n.sub.4 = 1.77250 ν.sub.4 = 49.66 r.sub.7 = 3.3104 d.sub.7 = 3.5548 r.sub.8 = -1.5102 d.sub.8 = 1.0787 n.sub.5 = 1.80610 ν.sub.5 = 40.95 r.sub.9 = -1.9929 d.sub.9 = 0.3776 r.sub.10 = ∞ (stop) d.sub.10 = 0.7704 n.sub.6 = 1.51633 ν.sub.6 = 64.15 r.sub.11 = ∞ d.sub.11 = 1.5410 r.sub.12 = -23.2120 d.sub.12 = 0.6164 n.sub.7 = 1.78472 ν.sub.7 = 25.71 r.sub.13 = 7.7327 d.sub.13 = 1.5410 n.sub.8 = 1.69680 ν.sub.8 = 55.52 r.sub.14 = -4.6245 d.sub.14 = 0.3082 r.sub.15 = 5.0791 d.sub.15 = 2.0032 n.sub.9 = 1.58913 ν.sub.9 = 60.57 r.sub.16 = -3.6013 d.sub.16 = 0.6164 n.sub.10 = 1.78472 ν.sub.10 = 25.71 r.sub.17 = -7.7928 f = 1, F.sub.NO = 2.374, image height = 1.1057 P = 0, B = 0, E = -0.11001 × 10.sup.-2 F = 0.17844 × 10.sup.-3, G = 0 ______________________________________ wherein the reference symbols r 1 through r 17 represent radii of curvature on the surfaces of the respective lens elements, the reference symbols d 1 through d 16 designate thicknesses of the respective lens elements and airspaces reserved therebetween, the reference symbols n 1 through n 10 denote refractive indices of the respective lens elements, and the reference symbols ν 1 through ν 10 represent Abbe's numbers of ν the respective lens elements.

Claim 17

An objective lens system for endoscopes according to claim 12 wherein said front lens groups comprises a negative meniscus lens component, a negative lens component and a cemented doublet, said rear lens group comprises a cemented doublet, a positive lens component, a cemented doublet and a cover glass, and the image side surface of the second negative lens component as counted from the object side in said front lens group is designed as an aspherical surface, said objective lens system having the following numerical data: ______________________________________ r.sub.1 = 3.8648 d.sub.1 = 0.4533 n.sub.1 = 1.88300 ν.sub.1 = 40.76 r.sub.2 = 1.7120 d.sub.2 = 0.5359 r.sub.3 = -261.1516 d.sub.3 = 0.4946 n.sub.2 = 1.49109 ν.sub.2 = 57.00 r.sub.4 = 1.2965 (aspherical surface) d.sub.4 = 2.2278 r.sub.5 = 15.9398 d.sub.5 = 0.8254 n.sub.3 = 1.80518 ν.sub.3 = 25.43 r.sub.6 = -2.5723 d.sub.6 = 0.3875 n.sub.4 = 1.56873 ν.sub.4 = 63.16 r.sub.7 = -138.3595 d.sub.7 = 0.2887 r.sub.8 = ∞ stop d.sub.8 = 0.0495 r.sub.9 = -5.7387 d.sub.9 = 1.0717 n.sub.5 = 1.58913 ν.sub.5 = 60.97 r.sub. 10 = -1.0684 d.sub.10 = 1.0305 n.sub.4 = 1.66998 ν.sub.6 = 39.32 r.sub.11 = -3.7527 d.sub.11 = 1.3339 r.sub.12 = 35.2935 d.sub.12 = 0.9481 n.sub.7 = 1.80610 ν.sub.7 = 40.95 r.sub.13 = -4.3149 d.sub.13 = 0.1237 r.sub.14 = 3.5070 d.sub.14 = 1.5664 n.sub.8 = 1.60311 ν.sub.8 = 60.70 r.sub.15 = -3.5070 d.sub.15 = 0.4946 n.sub.9 = 1.80518 ν.sub.9 = 25.43 r.sub.16 = 5.8277 d.sub.16 = 2.0544 r.sub.17 = ∞ d.sub.17 = 0.5771 n.sub.10 = 1.56384 ν.sub.10 = 60.69 r.sub.18 = ∞ f = 1, F.sub.NO = 3.714, image height = 0.8450 P = - 4.0000, B = 0, E = 0, F = 0, G = 0 ______________________________________ wherein the reference symbols r 1 through r 18 represent radii of curvature on the surfaces of the respective lens elements, the reference symbols d 1 through d 17 designate thicknesses of the respective lens elements and airspaces reserved therebetween, the reference symbols n 1 through n 10 denote refractive indices of the respective lens elements, and the reference symbols ν 1 through ν 10 represent Abbe's numbers of the respective lens elements.

Claim 18

A retrofocus-type objective for endoscopes according to claim 12 wherein factor A satisfies the following formula when degree of deflection angle K for the principal ray is expressed as K=Aω 3 Hσ: ##EQU15## wherein the reference symbol 2ω represents angle of view, the reference symbol H designates correction ratio and σ denotes a value of +1 when said aspherical surface is arranged on the image side of said lens component.

Claim 19

A retrofocus-type objective for endoscopes comprising a front lens group having negative refractive power, a rear lens group having positive refractive power in the order from object side, and a stop arranged between said front and rear lens groups, said front lens group comprising a negative lens element having a concave surface having a selected curvature which is strong and a positive lens element, and said rear lens group having at least two positive lens components, one of said positive lens components being a cemented doublet having a positive lens element and negative lens element the cemented surface of which is convexed to the image side, at least one of the lens components in said front lens group having an aspherical surface on the object side thereof including portions whose curvature is gradually increased as the distance thereof from the optical axis increases, and at least one of the lens components in said front lens group having an aspherical surface on the image side thereof including portions whose curvature is gradually decreased as the distance thereof from the optical axis increases.

Claim 20

A retrofocus-type objective for endoscopes comprising a front lens group having negative refractive power, a rear lens group having positive refractive power in the order from object side, and a stop arranged between said front and rear lens groups, said front lens group comprising a negative lens element having a concave surface having a selected curvature which is strong and a positive lens element, and said rear lens group having at least two positive lens components, one of said positive lens components being a cemented doublet having a positive lens element and negative lens element the cemented surface of which is convexed to the image side, at least one of the lens components in said front lens group having an aspherical surface on the object side thereof including portions whose curvature is gradually increased as the distance thereof from the optical axis increases, and at least one of the lens components in said front lens group having an aspherical surface on the image side thereof including portions whose curvature is gradually decreased as the distance thereof from the optical axis increases.

Claim 21

An objective lens system for endoscopes according to claim 17 wherein said aspherical surfaces are expressed by the following formula when the optical axis is taken as the x axis, and the straight line passing through the top of said aspherical surface and is perpendicular to the x axis is taken as the y axis: ##EQU16## wherein the reference symbol C represents an inverse number of the radius of a circle in contact with said aspherical surface in the vicinity of the optical axis, the reference symbol P designates a parameter representing shape of said aspherical surface, and the reference symbols B, E, F, G, . . . denote the second power, fourth power, sixth power, eighth power aspherical surface coefficients respectively and where A is a proportional constant 2ω is the view angle, H is the distortion correcting ratio and α=(-1).

Claim 22

An object lens system for endoscopes according to claim 18 wherein said system includes a factor A and wherein factor A satisfies the following formula when degree of deflection angle K for the principal ray is expressed as K=A·ω 3 ·H·σ: ##EQU17## wherein the reference symbol 2ω represents angle of view, the reference symbol H designates correction ratio and σ denotes a value of -1 when said aspherical surface is arranged on the object side of said lens component or +1 when said aspherical surface is arranged on the image side of said lens component.

Claim 23

An objective lens system for endoscopes according to claim 19 wherein said front lens group comprises a negative meniscus lens component, a negative meniscus lens component, a cemented doublet and a meniscus lens component, said rear lens group comprises a cemented doublet, a positive lens component, a cemented doublet and a cover glass, and both surfaces of the second negative meniscus lens component as counted from the object side in said front lens group are respectively designed as aspherical surfaces, said objective lens system having the following numerical data: ______________________________________ r.sub.1 = 6.1379 d.sub.1 = 0.7082 n.sub.1 = 1.88300 ν.sub.1 = 40.76 r.sub.2 = 2.8682 d.sub.2 = 0.9443 r.sub.3 = 7.7708 (aspherical surface) d.sub.3 = 0.6610 n.sub.2 = 1.49109 ν.sub.2 = 57.00 r.sub.4 = 2.4614 (aspherical surface) d.sub.4 = 1.1331 r.sub.5 = 9.4429 d.sub.5 = 0.9943 n.sub.3 = 1.80518 ν.sub.3 = 25.43 r.sub.6 = -9.4429 d.sub.6 = 0.3777 n.sub.4 = 1.77250 ν.sub.4 = 49.66 r.sub.7 = 7.1863 d.sub.7 = 2.6440 r.sub.8 = -1.2695 d.sub.8 = 0.9443 n.sub.5 = 1.80610 ν.sub.5 = 40.95 r.sub.9 = -1.6981 d.sub.9 = 0.3305 r.sub.10 = ∞ (stop) d.sub.10 = 0.0567 r.sub.11 = -6.5732 d.sub.11 = 1.2276 n.sub.6 = 1.58913 ν.sub.6 = 60.97 r.sub.12 = -1.2238 d.sub.12 = 1.1804 n.sub.7 = 1.66998 ν.sub.7 = 39.32 r.sub.13 = -4.2984 d.sub.13 = 1.5279 r.sub.14 = 40.4259 d.sub.14 = 1.0859 n.sub.8 = 1.80610 ν.sub.8 = 40.95 r.sub.15 = -4.9424 d.sub.15 = 0.1416 r.sub.16 = 4.0170 d.sub.16 = 1.7941 n.sub.9 = 1.60311 ν.sub.9 = 60.70 r.sub.17 = -4.0710 d.sub.17 = 0.5666 n.sub.10 = 1.80518 ν.sub.10 = 25.43 r.sub.18 = 6.6752 d.sub.18 = 2.3532 r.sub.19 = ∞ d.sub.19 = 0.6610 n.sub.11 = 1.6384 ν.sub.11 = 60.69 r.sub.20 = ∞ f = 0, F.sub.NO = 2.543, image height = 0.9679 third surface P = 1.0000, B = 0, E = 0.2254 × 10.sup.-2 F = 0.15533 = 10.sup.-3, G = 0 fourth surface P = 1.0000, B = 0, E = -0.95012 × 10.sup.-2 F = 0.26639 × 10.sup.-2, G = 0 ______________________________________ wherein the reference symbols r 1 through r 20 represent radii of curvature on the surfaces of the respective lens elements, the reference symbols d 1 through d 19 designate thicknesses of the respective lens elements and airspaces reserved therebetween, the reference symbols n 1 through n 11 denote refractive indices of the respective lens elements, and the reference symbols ν 1 through ν 11 represent Abbe's numbers of the respective lens elements.

Claim 24

A retrofocus-type objective for endoscopes according to claim 19 wherein factor A satisfies the following formula when degree of deflection angle K for the principal ray is expressed as K=Aω 3 Hσ: ##EQU18## wherein the reference symbol 2ω represents angle of view, the reference symbol H designates correction ratio and σ denotes a value of -when said aspherical surface is arranged on the object side of said lens component or +1 when said aspherical surface is arranged on the image side of said lens component. .Iadd.

Claim 25

A retrofocus-type objective for endoscopes comprising, a front lens group having negative refractive power, a rear lens group having positive refractive power in the order from the object side, and a stop arranged between said front and rear lens groups, said front lens group comprising at least one lens element, one of which is a negative lens element having a concave surface having a selected curvature which is strong, and said rear lens group having at least two positive lens components, and at least one lens element in said front lens group having an aspherical surface on the object side thereof including portions whose curvature is gradually increased as the distance thereof increases from the optical axis. .Iaddend. .Iadd.23. A retrofocus-type objective for endoscopes according to claim 22, one of said two positive lens components in said rear lens group being a cemented doublet having a positive lens element and negative lens element. .Iaddend. .Iadd.24. A retrofocus-type objective for endoscopes according to claims 22 or 23, wherein said front lens group includes a positive lens element. .Iaddend. .Iadd.25. A retrofocus-type objective for endoscopes comprising a front lens group having negative refractive power, a rear lens group having positive refractive power in the order from the object side, and a stop arranged between said front and rear lens groups, said front lens group comprising at least one lens element, one of which is a negative lens element having a concave surface having a selected curvature which is strong, and said rear lens group having at least two positive lens components, and at least one lens element in said front lens group having an aspherical suface on the image side thereof including portions whose curvature gradually decreases as the distance thereof increases from the optical axis. .Iaddend. .Iadd.26. A retrofocus-type objective for endoscopes according to claim 24, one of said two positive lens components in said rear lens group being a cemented doublet having a positive lens element and a negative lens element. .Iadd.27. A retrofocus-type objective for endoscopes according to claim 25 or 26, wherein said front lens group includes a positive lens element. .Iaddend. .Iadd.28. A retrofocus-type objective for endoscopes comprising a front lens group having negative refractive power, a rear lens group having positive refractive power in the order from the object side, and a stop arranged between said front and rear lens groups, said front lens group comprising at least one lens element, one of which is a negative lens element having a concave surface having a selected curvature which is strong, and said rear lens group having at least two positive lens components, at least one of the lens elements in said front lens group having an aspherical surface on the object side thereof including portions whose curvature is gradually increased as the distance thereof from the optical axis increases, and at least one of the lens elements in said front lens group having an aspherical surface on the image side thereof including portions whose curvature is gradually decreased as the distance

Claim 26

thereof from the optical axis increases. .Iaddend. .Iadd.29. A retrofocus-type objective for endoscopes according to claim 28, wherein said front lens group includes a positive lens element. .Iaddend. .Iadd.30. A retrofocus-type objective for endoscopes according to claims 28 or 29, wherein said front lens group includes a positive lens element.