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Publication numberUSRE33689 E
Publication typeGrant
Application numberUS 07/346,909
Publication dateSep 10, 1991
Filing dateMay 3, 1989
Priority dateFeb 15, 1984
Also published asUS4662725
Publication number07346909, 346909, US RE33689 E, US RE33689E, US-E-RE33689, USRE33689 E, USRE33689E
InventorsKimihiko Nishioka
Original AssigneeOlympus Optical Co., Ltd.
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Objective lens system for endoscopes
US RE33689 E
Abstract
An objective lens system for endoscopes having favorably corrected distortion. Said lens system comprising a front lens group having negative refractive power and a rear lens group having positive refractive power, arranged in said front lens group is a lens component having an aspherical surface having portions whose curvature is increased as they are farther from the optical axis or decreases as they are farther from the optical axis.
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Claims(23)
I claim:
1. 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.
2. 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.
3. 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.
4. 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:
______________________________________r1 = 6.1789     d1 = 0.7129                   n1 = 1.8830                              ν1 = 40.76r2 = 3.8110     d2 = 0.5704r3 = 16.0271     (aspherical surface)     d3 = 0.6654                   n2 = 1.49109                              ν2 = 57.00r4 = 2.2192     d4 = 1.1407r5 = 9.5060     d5 = 0.9506                   n3 = 1.80518                              ν3 = 25.43r6 = -9.5060     d6 = 0.3802                   n4 = 1.77250                              ν4 = 49.66r7 = 4.3058     d7 = 2.6617r8 = -1.3401     d8 = 0.9506                   n5 = 1.80610                              ν5 = 40.95r9 = 1.7300     d9 = 0.3327r10 =  ∞     (stop)     d10 = 0.0570r11 = -6.6171     d11 = 1.2358                   n6 = 1.58913                              ν6 = 60.97r12 = -1.2320     d12 = 1.1882                   n7 = 1.66998                              ν7 = 39.32r13 = -4.3271     d13 = 1.5381r14 = 40.6961     d14 = 1.0932                   n8 = 1.80610                              ν8 = 40.95r15 = -4.9754     d15 = 0.1426r16 = 4.0439     d16 = 1.8061                   n9 = 1.60311                              ν9 = 60.70r17 = -4.0439     d17 = 0.5704                   n10 = 1.80518                              ν10 = 25.43r18 = 6.7198     d18 = 2.3689r19 = ∞     d19 = 0.6654                   n11 = 1.56384                              ν11 = 60.69r20 = ∞f = 1, FNO = 2.544, image height = 0.97436P = 1.0000, B = 0, E = 0.70488  10-2F = 0.17289 10-3, G = 0______________________________________
wherein the reference symbols r1 through r20 represent radii of curvature on the surfaces of the respective lens elements, the reference symbols d1 through d19 designate thicknesses of the respective lens elements and airspaces reserved therebetween, the reference symbols n1 through n11 denote refractive indices of the respective lens elements, and the reference symbols ν1 through ν11 represent Abbe's numbers of the respective lens elements.
5. 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:
______________________________________r1 = 4.4865     d1 = 0.5982                   n1 = 1.88300                              ν1 = 40.76r2 = 2.0438     d2 = 0.5483r3 = ∞     (aspherical surface)     d3 = 1.1066                   n2 = 1.49109                              ν2 = 57.00r4 = 1.0614     d4 = 1.7035r5 = 1.7161     d5 = 0.2157                   n3 = 1.78590                              ν3 = 44.18r6 = 1.4071     d6 = 0.6995r7 = -1.5783     d7 = 0.5555                   n4 = 1.80610                              ν4 = 40.95r8 = -1.4248     d8 = 0.0014r9 = ∞     (stop)     d9 = 0.0598r10 = -6.9401     d10 = 1.2961                   n.sub. 5 = 1.58913                              ν5 = 60.97r11 = -1.2921     d11 = 1.2462                   n6 = 1.66998                              ν6 = 39.32r12 = -4.5483     d12 = 1.6131r13 = 43.6826     d13 = 1.1465                   n7 = 1.80610                              ν7 = 40.95r14 = -5.2183     d14 = 0.1495r15 = 4.2412     d15 = 1.8943                   n8 = 1.60311                              ν8 = 60.70r16 = -4.2412     d16 = 0.5982                   n9 = 1.80518                              ν9 = 25.43r17 = 7.0478     d17 = 2.4845r18 = ∞     d18 = 0.6979                   n10 = 1.56384                              ν10 = 60.69r19 = ∞f = 1, FNO = 2.588, image height = 1.0219P = 1.0000, B = 0.16225  10-1, E = 0.50809  10-1F = 0.34471  10-7, G = 0______________________________________
wherein the reference symbols r1 through r19 represent radii of curvature on the surraces of the respective lens elements, the reference symbols d1 through d18 designate thicknesses of the respective lens elements and airspaces reserved therebetween, the reference symbols n1 through n10 denote refractive indices of the respective lens elements, and the reference symbol ν1 through ν10 represent Abbe's numbers of the respective lens elements.
6. 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:
______________________________________r1 = ∞     (aspherical surface)     d1 = 0.6186                   n1 = 1.49109                              ν1 = 57.00r2 = 1.6347     d2 = 0.8247r3 = 5.4807     d3 = 0.5155                   n2 = 1.88300                              ν2 = 40.76r4 = 2.6388     d4 = 1.9166r5 = ∞     d5 = 0.5155                   n3 = 1.78590                              ν3 = 44.18r6 = ∞     d6 = 0.5826r7 = -1.5709     d7 = 1.1340                   n4 = 1.80610                              ν4 = 40.95r8 = -1.9679     d8 = 0.0014r9 = ∞     (stop)     d9 = 0.0617r10 = -7.1548     d10 = 1.3362                   n5 = 1.58913                              ν5 = 60.97r11 = -1.3321     d11 = 1.2848                   n6 = 1.66998                              ν6 = 39.32r12 = -4.6787     d12 = 1.6630r13 = 44.0027     d13 = 1.1820                   n7 = 1.80610                              ν7 = 40.95r14 = -5.3797     d14 = 0.1542r15 = 4.3724     d15 = 1.9529                   n8 = 1.60311                              ν8 = 60.70r16 = -4.3724     d16 = 0.6167                   n9 = 1.80518                              ν9 = 25.43r17 = 7.2658     d17 = 2.5614r18 = ∞     d18 = 0.7195                   n10 = 1.56384                              ν10 = 60.69r19 = ∞f = 1, F.sub. NO = 2.531, image height 1.0535P = 1.0000, B = 0, E = 0.13075  10-1F = 0, G = 0______________________________________
wherein the reference symbols r1 through r19 represent radii of curvature on the surfaces of the respective lens elements, the reference symbols d1 through d18 designate thicknesses of the respective lens elements and airspaces reserved therebetween, the reference symbols n1 through n10 denote refractive indices of the respective lens elements, and the reference symbols ν1 through ν10 represent Abbe's numbers of the respective lens elements.
7. 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:
______________________________________r1 = 10.3716     d1 = 0.7992                   n1 = 1.88300                              ν1 = 40.76r2 = 17.9820     d2 = 0.0999r3 = 12.0112     (aspherical surface)     d3 = 0.6993                   n2 = 1.49109                              ν2 = 57.00r4 = 4.9950     d4 = 0.3996                   n3 = 1.80610                              ν3 = 40.95r5 = 2.4975     d5 = 0.7992r6 = 19.2639     d6 = 0.3996                   n4 = 1.88300                              ν4 = 40.76r7 = 1.9843     d7 = 2.3429r8 = 15.5038     d8 = 0.5455                   n5 = 1.78590                              ν5 = 44.18r9 = -84.2272     d9 = 0.5669r10 = - 1.9200     d10 = 1.0992                   n6 = 1.80610                              ν6 = 40.95r11 = -2.3493     d11 = 0.3497r12 = ∞     (stop)     d12 = 0.0599r13 = -6.9540     d13 = 1.2987                   n7 = 1.58913                              ν7 = 60.97r14 = -1.2947     d14 = 1.2488                   n8 = 1.66998                              ν8 = 39.32r15 = -4.5475     d15 = 1.6164r16 = 42.7682     d16 = 1.1489                   n9 = 1.80610                              ν9 = 40.95r17 = -5.2288     d17 = 0.1499r18 = 4.2498     d18 = 1.8981                   n10 = 1.60311                              ν10 = 60.70r19 = -4.2498     d19 = 0.5994                   n11 = 1.80518                              ν11 = 25.43r20 = 7.0619     d20 = 2.4895r21 = ∞     d21 = 0.6993                   n12 = 1.56384                              ν12 = 60.69r22 = ∞f = 1, FNO = 2.581, image height = 1.0240P = 1.0000, B = 0, E = 0.92329  10-2F = -0.22743  10-3, G = 0______________________________________
wherein the reference symbols r1 through r22 represent radii of curvature on the surfaces of the respective lens elements, the reference symbols d1 through d21 designate thicknesses of the respective lens elements and airspaces reserved therebetween, the reference symbols n1 through n12 denote refractive indices of the respective lens elements, and the reference symbols ν1 through ν12 represent Abbe's numbers of the respective lens elements.
8. 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:
______________________________________r1 = 8.8295     d1 = 0.8048                   n1 = 1.88300                              ν1 = 40.76r2 = 18.1087     d2 = 0.1006r3 = 6.3299     (aspherical surface)     d3 = 0.6036                   n2 = 1.80610                              ν2 = 40.95r4 = 2.4397     d4 = 0.9054r5 = 9.6935     d5 = 0.4024                   n3 = 1.88300                              ν3 = 40.76r6 = 1.8280     d6 = 2.4161r7 = 50.2371     d7 = 0.5505                   n4 = 1.78590                              ν4 = 44.18r8 = 24.9036     d8 = 0.5712r9 = -1.9359     d9 = 1.1101                   n5 = 1.80610                              ν5 = 40.95r10 = - 2.2035     d10 = 0.3521r11 = ∞     stop     d11 = 0.0604r12 = -7.0030     d12 = 1.3078                   n6 = 1.58913                              ν6 = 60.97r13 = -1.3038     d13 = 1.2575                   n7 = 1.66998                              ν7 = 39.32r14 = -4.5795     d14 = 1.6278r15 = 43.0694     d15 = 1.1569                   n8 = 1.80610                              ν8 = 40.95r16 = -5.2656     d16 = 0.1509r17 = 4.2797     d17 = 1.9115                   n9 = 1.60311                              ν9 = 60.70r18 = -4.2797     d18 = 0.6036                   n10 = 1.80518                              ν10 = 25.43r19 = 7.1117     d19 = 2.5070r20  = ∞     d20 = 0.7042                   n11 = 1.56384                              ν11 = 60.69r21 = ∞f = 1, FNO = 2.617, image height = 1.0312P = 1.0000, B = 0, E = 0.86037  10-2F = -0.38814  103, G = -0.27509  10-11______________________________________
wherein the reference symbols r1 through r2 represent radii of curvature on the surfaces of the respective lens elements, the reference symbols d1 through d20 designate thicknesses of the respective lens elements and airspaces reserved therebetween, the reference symbols n1 through n11 denote refractive indices of the respective lens elements, and the reference symbols ν1 through ν11 represent Abbe's numbers of the respective lens elements.
9. 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=Aω3 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.
10. 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.
11. 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.
12. 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.
13. 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:
______________________________________r1 = 7.0140       d1 = 0.7515                  n1 = 1.88300                              ν1 = 40.76r2 = 3.9221       d2 = 0.8617r3 = 5.5110       d3 = 0.7014                  n2 = 1.49109                              ν2 = 57.00r4 = 1.5917       (aspherical surface)       d4 = 1.0521r5 = 4.0080       d5 = 1.1022                  n3 = 1.80518                              ν3 = 25.43r6 = -10018.9980       d6 = 0.4008                  n4 = 1.77250                              ν4 = 49.66r7 = 3.0749       d7 = 3.3019r8 = -1.4028       d8 = 1.0020                  n5 = 1.80610                              ν5 = 40.95r9 = -1.8511       d9 =  0.3507r10 = ∞       (stop)       d10 = 0.0601r11 = -6.9749       d11 = 1.3026                  n6 = 1.58913                              ν6 = 60.97r12 = -1.2986       d12 = 1.2525                  n7 = 1.66998                              ν7 = 39.32r13 = -4.5611       d13 = 1.6212r14 = 42.8966       d14 = 1.1523                  n8 = 1.80610                              ν8 = 40.95r15 = -5.2445       d15 = 0.1503r16 = 4.2625       d16 = 1.9038                  n9 = 1.60311                              ν9 = 60.70r17 = -4.2625       d17 = 0.6012                  n10 = 1.80518                              ν10 = 25.43r18 = 7.0831       d18 = 2.4970r19 = ∞       d.sub. 19 = 0.7014                  n11 = 1.56384                              ν11 = 60.69r20 = ∞f = 1, FNO = 2.561, image height = 1.02705P = 0, B = 0, E = -0.13727  10-2F = 0.25809  10-3, G = 0______________________________________
wherein the reference symbols r1 through r20 represent radii of curvature on the surfaces of the respective lens elements, the reference symbols d1 through d19 designate thicknesses of the respective lens elements and airspaces reserved therebetween, the reference symbols n1 through n11 denote refractive indices of the respective lens elements, and the reference symbols ν1 through ν11 represent Abbe's numbers of the respective lens elements.
14. 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:
______________________________________r1 = 7.5512       d1 = 0.8091                  n1 = 1.88300                              ν1 = 40.76r2 = 4.2225       d2 = 0.9277r3 = 5.9331       d3 = 0.7551                  n2 = 1.49109                              ν2 = 57.00r4 = 1.7136       (aspherical surface)       d4 = 1.1327r5 = 4.3150       d5 = 1.1866                  n3 = 1.80518                              ν3 = 25.43r6 = -10786.4078       d6 = 0.4315                  n4 = 1.77250                              ν4 = 49.66r7 = 3.3104       d7 = 3.5548r8 = -1.5102       d8 = 1.0787                  n5 = 1.80610                              ν5 = 40.95r9 = -1.9929       d9 =  0.3776r10 = ∞       (stop)       d10 = 0.7704                  n6 = 1.51633                              ν6 = 64.15r11 = ∞       d11 = 1.5410r12 = -23.2120       d12 = 0.6164                  n7 = 1.78472                              ν7 = 25.71r13 = 7.7327       d13 = 1.5410                  n8 = 1.69680                              ν8 = 55.52r14 = -4.6245       d14 = 0.3082r15 = 5.0791       d15 = 2.0032                  n9 = 1.58913                              ν9 = 60.57r16 = -3.6013       d16 = 0.6164                  n10 = 1.78472                              ν10 = 25.71r17 = -7.7928f = 1, FNO = 2.374, image height = 1.1057P = 0, B = 0, E = -0.11001  10-2F = 0.17844  10-3, G = 0______________________________________
wherein the reference symbols r1 through r17 represent radii of curvature on the surfaces of the respective lens elements, the reference symbols d1 through d16 designate thicknesses of the respective lens elements and airspaces reserved therebetween, the reference symbols n1 through n10 denote refractive indices of the respective lens elements, and the reference symbols ν1 through ν10 represent Abbe's numbers of ν the respective lens elements.
15. 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:
______________________________________r1 = 3.8648     d1 = 0.4533                   n1 = 1.88300                              ν1 = 40.76r2 = 1.7120     d2 = 0.5359r3 = -261.1516     d3 = 0.4946                   n2 = 1.49109                              ν2 = 57.00r4 = 1.2965     (aspherical surface)     d4 = 2.2278r5 = 15.9398     d5 = 0.8254                   n3 = 1.80518                              ν3 = 25.43r6 = -2.5723     d6 = 0.3875                   n4 = 1.56873                              ν4 = 63.16r7 = -138.3595     d7 = 0.2887r8 = ∞     stop     d8 = 0.0495r9 = -5.7387     d9 = 1.0717                   n5 = 1.58913                              ν5 = 60.97r.sub. 10 = -1.0684     d10 = 1.0305                   n4 = 1.66998                              ν6 = 39.32r11 = -3.7527     d11 = 1.3339r12 = 35.2935     d12 = 0.9481                   n7 = 1.80610                              ν7 = 40.95r13 = -4.3149     d13 = 0.1237r14 = 3.5070     d14 = 1.5664                   n8 = 1.60311                              ν8 = 60.70r15 = -3.5070     d15 = 0.4946                   n9 = 1.80518                              ν9 = 25.43r16 = 5.8277     d16 = 2.0544r17 = ∞     d17 = 0.5771                   n10 = 1.56384                              ν10 = 60.69r18 = ∞f = 1, FNO = 3.714, image height = 0.8450P = - 4.0000, B = 0, E = 0, F = 0, G = 0______________________________________
wherein the reference symbols r1 through r18 represent radii of curvature on the surfaces of the respective lens elements, the reference symbols d1 through d17 designate thicknesses of the respective lens elements and airspaces reserved therebetween, the reference symbols n1 through n10 denote refractive indices of the respective lens elements, and the reference symbols ν1 through ν10 represent Abbe's numbers of the respective lens elements.
16. 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=Aω3 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.
17. 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.
18. 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).
19. 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=Aω3 Hσ: ##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.
20. 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:
______________________________________r1 = 6.1379     d1 = 0.7082                   n1 = 1.88300                              ν1 = 40.76r2 = 2.8682     d2 = 0.9443r3 = 7.7708     (aspherical surface)     d3 = 0.6610                   n2 = 1.49109                              ν2 = 57.00r4 = 2.4614     (aspherical surface)     d4 = 1.1331r5 = 9.4429     d5 = 0.9943                   n3 = 1.80518                              ν3 = 25.43r6 = -9.4429     d6 = 0.3777                   n4 = 1.77250                              ν4 = 49.66r7 = 7.1863     d7 = 2.6440r8 = -1.2695     d8 = 0.9443                   n5 = 1.80610                              ν5 = 40.95r9 = -1.6981     d9 = 0.3305r10  = ∞     (stop)     d10 = 0.0567r11 = -6.5732     d11 = 1.2276                   n6 = 1.58913                              ν6 = 60.97r12 = -1.2238     d12 = 1.1804                   n7 = 1.66998                              ν7 = 39.32r13 = -4.2984     d13 = 1.5279r14 = 40.4259     d14 = 1.0859                   n8 = 1.80610                              ν8 = 40.95r15 = -4.9424     d15 = 0.1416r16 = 4.0170     d16 = 1.7941                   n9 = 1.60311                              ν9 = 60.70r17 = -4.0710     d17 = 0.5666                   n10 = 1.80518                              ν10 = 25.43r18 = 6.6752     d18 = 2.3532r19 = ∞     d19 = 0.6610                   n11 = 1.6384                              ν11 = 60.69r20 = ∞f = 0, FNO = 2.543, image height = 0.9679third surface     P = 1.0000, B = 0, E = 0.2254  10-2     F = 0.15533 = 10-3, G = 0fourth surface     P = 1.0000, B = 0, E = -0.95012  10-2     F = 0.26639  10-2, G = 0______________________________________
wherein the reference symbols r1 through r20 represent radii of curvature on the surfaces of the respective lens elements, the reference symbols d1 through d19 designate thicknesses of the respective lens elements and airspaces reserved therebetween, the reference symbols n1 through n11 denote refractive indices of the respective lens elements, and the reference symbols ν1 through ν11 represent Abbe's numbers of the respective lens elements.
21. 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=Aω3 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.
22. 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
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.
Description
BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to an objective lens system for endoscopes using optical fiber bundles or relay lenses as an image transmission optical system, and more specifically to an objective lens system having favourably corrected distortion.

(b) Description of the Prior Art

As the conventional objective lens systems for endoscopes of the retrofocus type as shown in FIG. 1, there has already been known, for example, the one disclosed by Japanese published unexamined patent application No. 121547/74.

This objective lens system for endoscopes of retrofocus type comprises a lens group I having negative refractive power and a rear lens group II having positive refractive power which are arranged on the object side and image side respectively with a stop S interposed therebetween. This objective lens system is so designed as to obtain a wide angle by strongly refracting the principal ray P with the negative lens group I arranged before the stop S. Further, the positive lens group II arranged after the stop S functions to make the principal ray P incident on the image surface in parallel with the optical axis.

The objective lens system is so designed as to minimize loss of light in the image guide G by making the principal ray P emerging from the objective lens incident perpendicularly on the end surface of the image guide G.

When the objective lens system of this type is to be applied to an endoscope equipped with relay lenses, the principal ray P is made perpendicular to the image surface O' as shown in FIG. 2 to minimize loss of rays in the relay lenses R.

The conventional objective lens system for endoscopes of retrofocus type satisfies two requirements for an objective lens system for endoscopes, i.e., a wide angle and perpendicular incidence of the principal ray on the image surface. However, there still remains a defect that negative distortion is remarkable in the objective lens system for endoscopes.

In the objective lens system for endoscopes shown in FIG. 1, for example, distortion is -21% at ω=37 (2ω=angle of view). In addition, negative distortion is remarkable in the other conventional objective lens systems of retrofocus type as is seen from the relationship between angle of view and distortion listed in Table 1:

              TABLE 1______________________________________ω  20            30                      40                            50                                    60______________________________________Distortion    -6%     -13.5%    -23%  -36%    -50%______________________________________

In order to correct the negative distortion, it is contrived to arrange an aspherical surface in the objective lens system. As an example of objective lens systems having distortion nd other aberrations corrected with an aspherical surface, there have been known the one disclosed by Japanese published unexamined patent application No. 173810/82. However, distortion is not corrected sufficiently in this objective lens system though it has a narrow angle of view (2ω) of 56.

SUMMARY OF THE INVENTION

A general object of the present invention is to provide a wide-angle objective lens system for endoscopes comprising a negative front lens group and a positive rear lens group, and having distortion minimized by arranging at least one lens component having aspherical surface in said negative front lens group.

The objective lens system for endoscopes according to the present invention has the composition, for example, shown in FIG. 3. Speaking concretely, the objective lens system according to the present invention comprises a lens group I (front lens group) having negative refractive power, a lens group II (rear lens group) having positive refractive power and a stop S arranged in the vicinity of the front focal point of said lens group II. One of the lens components arranged in said front lens group I has an object side surface (for example, the surface R1 shown in FIG. 3) which is designed as an aspherical surface having portions whose curvature gradually increases as they are farther from the optical axis. Alternately, the objective lens system for endoscopes according to the present invention has the composition shown in FIG. 4, and comprises a negative front lens group I, a positive rear lens group II and a stop S arranged in the vicinity of the front focal point of said lens group II, one of the lens components arranged in said front lens group I having portions whose curvature gradually decreases as they are farther from the optical axis. The aspherical surfaces of these lenses are symmetrical with regard to the optical axis, like the other types of lenses.

The objective lens system for endoscopes according to the present invention is so designed as to correct negative distortion sufficiently by arranging the aspherical surface having the shape described above.

The negative distortion can be corrected by arranging the aspherical surface having above-described shape for the reason described below:

As reverse tracing of the principal ray from the image side clarifies, the conventional objective lens system for endoscopes having the composition shown in FIG. 1 produces remarkable negative distortion because the principal ray is refracted, as image height increases, in such a direction as to widen angle of view by the front and rear lens groups I and II which are arranged before and after the stop S.

Therefore, it is possible to correct the remarkable negative distortion by arranging a lens component having a surface including at least an aspherical surface including portions whose refractive power for the principal ray is continuously weakened as they are it is farther from the opical axis.

It is therefore sufficient to design one of the lens components in the front lens group I arranged before the stop S so as to have an object side surface having portions whose curvature is gradually increased as they are farther from the optical axis as shown in FIG. 3, or one of the lens components in the front lens group I so as to have an image side surface having portions whose curvature is gradually decreased as they are farther from the optical axis as shown in FIG. 4.

The above mentioned surface having portions whose curvature is gradually increased as they are farther from the optical axis can include the aspherical surfaces having shapes shown in FIG. 5 and FIG. 6. "Curvature" used herein should be interpreted as a term including positive or negative sign. Speaking concretely, curvature at a point should be considered as negative when center of curvature of a spherical surface in contact with the lens surface at an optional point on said lens surface is located on the object side or positive when the center of curvature is located on the image side. Accordingly, the aspherical surface shown in FIG. 5 is an example having curvature increasing as it is farther from the optical axis (increasing from negative curvature of concavity on the object side to positive curvature of convexity on the object side), whereas the aspherical surface shown in FIG. 6 is an example having curvature increasing and then decreasing as it is farther from the optical axis.

The aspherical surface shown in FIG. 6 is also effective to correct the distortion because undulation of distortion curve as shown in FIG. 7 poses no practical problem and because the peripherical portions of the aspherical surface shown in FIG. 6 has no relation to correction of distortion since the lower ray passes through the peripheral portions but the principal ray does not.

The aspherical surface having portions whose curvature is decreased as they are farther from the optical axis includes the examples shown in FIG. 8 and FIG. 9.

The aspherical surface arranged in the objective lens system for endoscopes according to the present invention is, when it is designed as an object side surface of a lens component, a surface having curvature gradually increasing at least on its portions including the surfaces shown in FIG. 5 and FIG. 6. When the aspherical surface is designed as an image side surface of a lens component, it is a surface having curvature gradually decreasing at least on its portions including the surfaces shown in FIG. 8 and FIG. 9. A lens system including at least one aspherical surface of this type can correct distortion favourably.

Now, shape of the aspherical surface required for correcting distortion will be described quantitatively.

An aspherical surface can generally be expressed by the following formula (1): ##EQU1## wherein the reference symbols x and y represent values on coordinates on which the optical axis is traced as x axis taking the image direction as positive and y axis is traced perpendicularly to the x axis taking the intersect between the aspherical surface and optical axis as origin O, the reference symbol C designates a curvature of a spherical surface in contact with the aspherical surface in the vicinity of the optical axis, reference symbol P denotes a parameter representing shape of the aspherical surface, and the reference symbols E, F, G, . . . represent the second power, fourth power, sixth power, eighth power aspherical surface coefficients respectively.

Now, let us consider a circle which is in contact on the optical axis with the aspherical surface expressed by the formula (1). A spherical surface having C as an inverse number of its radius is generally expressed by the following formula: ##EQU2##

In case of C≠0 and B=0 in the formula (1), the spherical surface in contact on the optical axis with the aspherical surface can be expressed by the following formula (2): ##EQU3##

In case of C=0 in the formula (1), the spherical surface in contact on the optical surface with the aspherical surface can be expressed by the following formula (3): ##EQU4##

Distortion is corrected by properly adjusting difference Δ between the aspherical surface expressed by the formula (1) and the spherical surface expressed by the formula (2) or (3). That is to say, distortion is corrected by properly adjusting Δ expressed by the following formula (4):

Δ=x-xs                                          ( 4)

Speaking more strictly, distortion is corrected by properly adjusting deflection angle K of the principal ray caused by Δ, i.e., K given by the following formula (5): ##EQU5## wherein the reference symbol n represents refractive index of the constituent substance of the aspherical surface lens component and the reference symbol yc designates height of the principal ray having the maximum image height on the aspherical surface, yc is smaller than 0 at a point before the stop.

Now, let us define correcting ratio of distortion as expressed by the following formula (6): ##EQU6##

In this formula (6), the reference symbol D represents distortion remaining in a lens system whose distortion is corrected with an aspherical surface and the reference symbol Ds designates distortion in the same lens system composed only of spherical surface lens components without using an aspherical surface. Ds can be determined, for example, directly or by interpolation from the Table 1 summarizing the data on the conventional examples.

According to the aberration theory, it is already known that distortion increases in proportion to cube of the angle ω (2ω=angle of view) of objective lens system. Hence, the above-mentioned deflection angle K of the principal ray produced by aspherical surface is approximately expressed by the following formula (7):

K=Aω3 Hσ    (7)

wherein the reference symbol A represents a proportional constant which is variable depending on degree of distortion correctable with lens surfaces other than the asphercal surface. A has a small value when distortion is corrected to a high degree with lens surfaces other than the aspherical surface, and vice versa. Further, when the principal ray P incident on the image surface forms a negative angle θ deviating from 0 with the image surface as shown in FIG. 11, A has a value smaller than its value at θ=0. In addition, let us assume that σ has a value of -1 when the aspherical surface is arranged on the object side of a lens component, or a value of 1 when the aspherical surface is arranged on the image side of a lens component. Moreover, let us assume that ω has a value within a range of ω>0 expressed in unit of degree.

When a plural number N of aspherical surfaces are arranged within an objective lens system, K has a value equal to total of values on the respective surfaces. That is, K is expressed by the following formula (8): ##EQU7##

In case of C=0 in the formula (5), the square root in the formula (1) or (2) has a negative value when value of Yc exceeds radius of contact circle R=1/C, i.e., in a range of yc ≦R. In such a case, let us select a value of yc within the range defined below and calculate H by using the formula (6) at the angle ω corresponding to the value of Yc :

0.6R<yc <0.75R

In the foregoing descriptions, A should desirably have a value within the range defined below when other aberrations, etc. are taken into consideration:

A<10-5                                                ( 9)

If the limit is exceeded, the meridional image plane will be undercorrected, thereby resulting in undesirable effect to produce remarkable astigmatic difference.

The upper limit of value of A is variable depending also on F number of lens systems. When image quality is taken into consideration, upper limit of value of A for an optional F number is defined as follows: ##EQU8##

Therefore, it is possible to obtain an objective lens system for endoscopes having little distortion and excellent imaging performance by determining shape of aspherical surface so as to satisfy the formula (10).

In addition, an objective lens system which is a little low in its imaging performance but has favourably corrected distortion may be desired for practical use. When this point is taken into consideration, the range defined by the formula (10) can be widened to that expressed by the following formula (11): ##EQU9##

Further, curvature of field produced by a single lens surface is generally proportional to square of height of ray, whereas distortion is proportional to cube of height of ray. Therefore, higher ray is more desirable to correct distortion only without varying curvature of field. For this reason, it is desirable to design a lens surface having a high transmitting section for the principal ray, for example, the first object side surface in the lens system shown in FIG. 3, as an aspherical surface. That is to say, an objective lens system having high imaging performance can be obtained by designing the first object side surface so as to satisfy the formula (11).

As is understood from the foregoing descriptions, it is possible to determine a shape of aspherical surface capable of favourably correcting distortion without affecting the other aberrations by selecting value of A within the range defined by the formula (11).

As a process to manufacture a lens component having the aspherical surface described above, molding of plastic or glass material is advantageous from the viewpoint of manufacturing cost.

The objective lens system is usable not only with endoscopes using optical fiber bundles and relay lenses for transmitting images but also with endoscopes using solid state image pick-up device. When the objective lens system is designed for use with endoscopes using solid state image pick-up device. A has a small value since θ is not equal to 0 and may be smaller than 0. However, formula (9) and formula (10) are still satisfied in such a case.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 and FIG. 2 show sectional views illustrating the compositions of the conventional objective lens systems for endoscopes;

FIG. 3 and FIG. 4 show sectional views illustrating compositions of the objective lens system for endoscopes according to the present invention;

FIG. 5 and FIG. 6 show sectional views of lens components having aspherical surfaces to be used in the objective lens system according to the present invention;

FIG. 7 shows a curve exemplifying correcting condition of distortion;

FIG. 8 and FIG. 9 show sectional views illustrating other examples of aspherical surfaces to be used in the objective lens system according to the present invention;

FIG. 10 shows a diagram illustrating a coordinates system for expressing formulae defining aspherical surfaces;

FIG. 11 shows a diagram descriptive of deflection angle of the principal ray;

FIG. 12 through FIG. 20 show sectional views illustrating Embodiments 1 through 9 of the objective lens system according to the present invention; and

FIG. 21 through FIG. 29 show curves illustrating aberration characteristics of said Embodiments 1 through 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, numerical data will be clarified as preferred embodiments of the objective lens system for endoscopes according to the present invention described above.

______________________________________Embodiment 1______________________________________r1 = 6.1789     d1 = 0.7129                   n1 = 1.8830                              ν1 = 40.76r2 = 3.8110     d2 = 0.5704r3 = 16.0271     (aspherical surface)     d3 = 0.6654                   n2 = 1.49109                              ν2 = 57.00r4 = 2.2192     d4 = 1.1407r5 = 9.5060     d5 = 0.9506                   n3 =1.80518                              ν3 = 25.43r6 = -9.5066     d6 = 0.3802                   n4 = 1.77250                              ν4 = 49.66r7 = 4.3058     d7 = 2.6617r8 = -1.3401     d8 = 0.9506                   n5 = 1.80610                              ν5 = 40.95r9 = -1.7300     d9 = 0.3327r.sub. 10 = ∞     stop     d10 = 0.0570r11 = -6.6171     d11 = 1.2358                   n6 = 1.58913                              ν6 = 60.97r12 = -1.2320     d12 = 1.1882                   n7 = 1.66998                              ν7 = 39.32r13 = -4.3271     d13 = 1.5381r14 = 40.6961     d14 = 1.0932                   n8 = 1.80610                              ν8 = 40.95r15 = -4.9754     d15 = 0.1426r16 = 4.0439     d16 = 1.8061                   n9 = 1.60311                              ν9 = 60.70r17 = -4.0439     d17 = 0.5704                   n10 = 1.80518                              ν10 = 25.43r18 = 6.7198     d18 = 2.3698r19 = ∞     d19 =  0.6654                   n11 = 1.56384                              ν11 = 60.69r20 = ∞f = 1, FNO = 2.544, image height = 0.97436P = 1.0000, B = 0, E = 0.70488  10-2F = 0.17289  10-3, G = 0______________________________________

______________________________________Embodiment 2______________________________________r1 = 4.4865     d1 = 0.5982                   n1 = 1.88300                              ν1 = 40.76r2 = 2.0438     d2 = 0.5483r3 = ∞     (aspherical surface)     d3 = 1.1066                   n2 = 1.49109                              ν2 = 57.00r4 = 1.0614     d4 = 1.7035r5 = 1.7151     d5 = 0.2157                   n3  1.78590                              ν3 = 44.18r6 = 1.4071     d6 = 0.6995r7 = -1.5783     d7 = 0.5555                   n4 = 1.80610                              ν4 = 40.95r8 = -1.4248     d8 = 0.0014r9 = ∞     stop     d9 = 0.0598r10 = -6.9401     d10 =  1.2961                   n5 = 1.58913                              ν5 = 60.97r11 = -1.2921     d11 = 1.2462                   n6 = 1.66998                              ν6 = 39.32r12 = -4.5383     d12 = 1.6131r13 = 42.6826     d13 = 1.1465                   n7 = 1.80610                              ν7 = 40.95r14 = -5.2183     d14 = 0.1495r15 = 4.2412     d15 = 1.8943                   n8 = 1.60311                              ν8 = 60.70r16 = -4.2412     d16 = 0.5982                   n9 = 1.80518                              ν9 = 25.43r17 = 7.0478     d17 = 2.4845r18 = ∞     d18 = 0.6979                   n10 = 1.56384                              ν10 = 60.69r19 = ∞f =  1, FNO = 2.588, image height = 1.0219P = -1.0000, B = 0.16225  10-1E = 0.50809  10-1, F = 0.34471  10-7, G =______________________________________

______________________________________Embodiment 3______________________________________r1 = ∞     (aspherical surface)     d1 = 0.6186                   n1 = 1.49109                              ν1 = 57.00r2 = 1.6347     d2 = 0.8247r3 = 5.4807     d3 = 0.5155                   n2 = 1.88300                              ν2 = 40.76r4 = 2.63388     d4 = 1.9166r5 = ∞     d5 = 0.5155                   n1 = 1.78590                              ν1 = 44.18r6 = ∞     d6 = 0.5826r7 = -1.5709     d7 = 1.1340                   n4 = 1.80610                              ν4 = 40.95r8 = 1.9679     d8 = 0.0014r9 = ∞     stop     d9 = 0.6017r10 = -7.1548     d10  = 1.3362                   n5 = 1.58913                              ν5 = 60.97r11 = -1.3321     d11 = 1.2848                   n6 = 1.66998                              ν6 = 39.32r12 = -4.6787     d12 = 1.6630r13 = 44.0027     d13 = 1.1820                   n7 = 1.80610                              ν7 = 40.95r14 = -5.3797     d14 = 0.1542r15 = 4.3724     d15 = 1.9529                   n8 = 1.60311                              n8 = 60.70r16 = -4.3724     d16 = 0.6167                   n9 = 1.80518                              ν9 = 25.43r17 = 7.2658     d17 = 2.5614r18 = ∞     d18 = 0.7195                   n10 = 1.56384                              ν10 = 60.69r19 = ∞f =  1, FNO = 2.531, image height = 1.0535P = -1.000, B = 0, E = 0.13075  10-1F = 0, G = 0______________________________________

______________________________________Embodiment 4______________________________________r1 = 7.0140       d1 = 0.7515                  n1 = 1.88300                              ν1 = 40.76r2 = 3.9221       d2 = 0.8617r3 = 5.5110       d3 = 0.7014                  n2 = 1.49109                              ν2 = 57.00r4 = 1.5917       (aspherical surface)       d4 = 1.0521r5 = 4.0080       d5 = 1.1022                  n3 = 1.80518                              ν3 = 25.43r6 = -10018.9980       d6 = 0.4008                  n4 = 1.77250                              ν4 = 49.66r7 = 3.0749       d7 = 3.3019r8 = -1.4028       d8 = 1.0020                  n5 = 1.80610                              ν5 = 40.95r9 = -1.8511       d9 = 0.3507r10 = ∞       stop       d10 = 0.0601r11 = -6.9749       d11 = 1.3026                  n6 = 1.58913                              ν6 = 60.97r12 = -1.2986       d12 = 1.2525                  n7 = 1.66998                              ν7 = 39.32r13 = -4.5611       d13 = 1.6212r14 = 42.8966       d14 = 1.1523                  n8 = 1.80610                              ν8 = 40.95r15 = -5.2445       d15 = 0.1503r16 = 4.2625       d16 = 1.0938                  n9 = 1.60311                              ν9 = 60.70r17 = -4.2625       d17 = 0.6012                  n10 = 1.80518                              ν10 = 25.43r18 = 7.0831       d18 = 2.4970r19 =  ∞       d19 = 0.7014                  n11 = 1.56384                              ν11 = 60.69r20 = ∞f = 1, FNO = 2.561, image height = 1.02705P = 0, B = 0, E = -0.13727  10-2F = 0.25809  10-3 , G = 0______________________________________

______________________________________Embodiment 5______________________________________r1 = 7.5512       d1 = 0.8091                  n1 = 1.88300                              ν1 = 40.76r2 = 4.2225       d2 = 0.9277r3 = 5.9331       d3 = 0.7551                  n2 = 1.49109                              ν2 = 57.00r4 = 1.7136       (aspherical surface)       d4 = 1.1327r5 = 4.3150       d5 = 1.1866                  n3 = 1.80518                              ν3 = 25.43r6 = -10786.4078       d6 = 0.4315                  n4 = 1.77250                              ν4 = 49.66r7 = 3.3104       d7 = 3.5548r8 = -1.5102       d8 = 1.0787                  n5 = 1.80610                              ν5 = 40.95r9 = -1.9929       d9 = 0.3776r10 = ∞       (stop)       d10 = 0.7704                  n6 = 1.51633                              ν6 = 64.15r11 = ∞       d11 = 1.5410r12 = -23.2120       d12 = 0.6164                  n7 = 1.78472                              ν7 = 25.71r13 = 7.7327       d13 = 1.5410                  n8 = 1.69680                              ν8 = 55.52r14 = -4.6245       d14 = 0.3082r15 = 5.0791       d15 = 2.0032                  n9 = 1.58913                              ν9 = 60.97r16 = -3.6013       d16 = 0.6164                  n10 =1.78472                              ν10 = 25.71r17 = -7.7928f = 1, FNO = 2.374, image height = 1.1057P = 0, B = 0, E =  -0.11001  10-2F = 0.17844  10-3 , G = 0______________________________________

______________________________________Embodiment 6______________________________________r1 = 3.8648     d1 = 0.4533                   n1 = 1.88300                              ν1 = 40.76r2 = 1.7120     d2 = 0.5359r3 = -261.1516     d3 = 0.4946                   n2 = 1.49109                              ν2 = 57.00r4 = 1.2965     (aspherical surface)     d4 = 2.2278r5 = 15.9398     d5 = 0.8254                   n3 = 1.80518                              ν3 = 25.43r6 = -2.5723     d6 = 0.3875                   n4 = 1.56873                              ν4 = 63.16r7 = -138.3595     d7 = 0.2887r8 = ∞     (stop)     d8 = 0.0495r9 = -5.7387     d9 = 1.0717                   n5 = 1.58913                              ν5  = 60.97r10 = -1.0684     d10 = 1.0305                   n6 = 1.66998                              ν6 = 39.32r11 = -3.7527     d11 = 1.3339r12 = 35.2935     d12 = 0.9481                   n7 = 1.80610                              ν7 = 40.95r13 = -4.3149     d13 = 0.1237r14 = 3.5070     d14 = 1.5664                   n8 = 1.60311                              ν8 = 60.70r15 = -3.5070     d15 = 0.4946                   n9 = 1.80518                              ν9 = 25.43r16 = 5.8277     d16 = 2.0544r17 = ∞     d17 = 0.5771                   n10 = 1.56384                              ν10 = 60.69r18 = ∞f = 1, FNO = 3.714, image height = 0.8450P = -4.0000, B = 0, E = 0, F = 0, G = 0______________________________________

______________________________________Embodiment 7______________________________________r1 = 6.1379     d1 = 0.7082                   n1 = 1.88300                              ν1 = 40.76r2 = 2.8682     d2 = 0.9443r3 = 7.7708     (aspherical surface)     d3 = 0.6610                   n2 = 1.49109                              ν2 = 57.00r4 = 2.4614     (aspherical surface)     d4 = 1.1331r5 = 9.4429     d5 = 0.9443                   n3 = 1.80518                              ν3 = 25.43r6 = -9.4429     d6 = 0.3777                   n4 = 1.77250                              ν4 = 49.66r7 = 7.1863     d7 = 2.6440r8 = -1.2695     d8 = 0.9443                   n5 = 1.80610                              ν5 = 40.95r9  = -1.6981     d9 = 0.3305r10 = ∞     stop     d10 = 0.0567r11 = -6.5732     d11 = 1.2276                   n6 = 1.58913                              ν6 = 60.97r12 = -1.2238     d12 = 1.1804                   n7 = 1.66998                              ν7 = 39.32r13 = -4.2984     d13 = 1.5279r14 = 40.4259     d14 = 1.0859                   n8 = 1.80610                              ν8 = 40.95r15 = -4.9424     d15 = 0.1416r16 = 4.0170     d16 = 1.7941                   n9 = 1.60311                              ν9 = 60.70r17 = -4.0170     d17 = 0.5666                   n10 = 1.80518                              ν10 = 25.43r18 =  6.6752     d18 = 2.3532r19 = ∞     d19 = 0.6610                   n11 = 1.56384                              ν11 = 60.69r20 = ∞f = 1, FNO = 2.543, image height = 0.9679third surface      P = 1.0000, B = 0, E = 0.22454  10-2      F = 0.15533  10-3, G = 0fourth surface      P = 1.0000, B = 0, E = 0.95012  10-2      F = -0.26639  10-2, G = 0______________________________________

______________________________________Embodiment 8______________________________________r1 = 10.3716     d1 = 0.7992                   n1 = 1.88300                              ν1 = 40.76r2 = 17.9820     d2 = 0.0999r3 = 12.0112     (aspherical surface)     d3 = 0.6993                   n2 = 1.49109                              ν2 = 57.00r4 = 4.9950     d4 = 0.3996                   n3 = 1.80610                              ν3 = 40.95r5 = 2.4975     d5 = 0.7992r6 = -19.2639     d6 = 0.3996                   n4 = 1.88300                              ν4 = 40.76r7 = 1.9643     d7 = 2.3429r8 = 15.5038     d8 = 0.5455                   n5 = 1.78590                              ν5 = 44.18r9 = -84.2272     d9 = 0.5669r.sub. 10 = -1.9200     d10 = 1.0992                   n6 = 1.80610                              ν6 = 40.95r11 = -2.3493     d11 = 0.3497r12 = ∞     stop     d12 = 0.0599r13 = -6.9540     d13 = 1.2987                   n7 = 1.58913                              ν7 = 60.97r14 = 1.2947     d14 = 1.2488                   n8 = 1.66998                              ν8 = 39.32r15 = -4.5475     d15 = 1.6164r16 = 42.7682     d16 = 1.1489                   n9 = 1.80610                              ν9 = 40.95r17 = -5.2288     d17 = 0.1499r18 = 4.2498     d18 = 1.8981                   n10 = 1.60311                              ν10 = 60.70r19 = -4.2498     d19 =  0.5994                   n11 = 1.80518                              ν11 = 25.43r20 = 7.0619     d20 = 2.4895r21 = ∞     d21 = 0.6993                   n12 = 1.56384                              ν12 = 60.69r22 = ∞f = 1, FNO = 2.581, image height = 1.0240P = 1.000, B = 0, E = 0.92329  10-2F = -0.22743  10-3, G = 0______________________________________

______________________________________Embodiment 9______________________________________r1 = 8.8295     d1 = 0.8048                   n1 = 1.88300                              ν1 = 40.76r2 = 18.1087     d2 = 0.1006r3 = 6.3299     (aspherical surface)     d3 = 0.6036                   n2 =1.80610                              ν2 = 40.95r4 = 2.4397     d4 = 0.9054r5 = 9.6935     d5 = 0.4024                   n3 = 1.88300                              ν3 = 40.76r6 = 1.8280     d6 = 2.4161r7 = 50.2371     d7 = 0.5505                   n4 = 1.78590                              ν4 = 44.18r8 = 24.9036     d8 = 0.5712r9 = -1.9359     d9 = 1.1101                   n5 = 1.80610                              ν5 = 40.95r10 = -2.2035     d10 = 0.3521r11 = ∞     stop     d11 = 0.0604r12 = -7.0030     d12 = 1.3078                   n6 = 1.58913                              ν6 = 60.97r13 = -1.3038     d13 = 1.2575                   n7 = 1.66998                              ν7 = 39.32r14 = -4.5795     d14 = 1.6278r15 = 43.0694     d15 = 1.1569                   n8 = 1.80610                              ν8 = 40.95r16 = -5.2656     d16 = 0.1509r17 = 4.2797     d17 = 1.9115                   n9 = 1.60311                              ν9 = 60.70r18 = -4.2797     d18 = 0.6036                   n10 = 1.80518                              ν10 = 25.43r19 = 7.1117     d19 =  2.5070r20 = ∞     d20 = 0.7042                   n11 = 1.56384                              ν11 = 60.69r21 = ∞f = 1, FNO = 2.617 image height = 1.0312P = 1.0000, B = 0, E = 0.86037  10-2F = -0.38814  10-3, G = -0.27509  10-11______________________________________

wherein the reference symbols r1, r2, . . . represent radii of curvature on the surfaces of the respective lens elements, the reference symbols d1, d2, . . . designate thicknesses of the respective lens elements and airspaces reserved therebetween, the reference symbols n1, n2, . . . denote refractive indices of the respective lens elements, and the reference symbols ν1, ν2, . . . represent Abbe's numbers of the respective lens elements.

The Embodiments 1 through 9 mentioned above are objective lens systems having the compositions shown in FIG. 12 through FIG. 20 respectively.

In Embodiments 1, 2, 8 and 9 out of the embodiments mentioned above, the object side surface of the second lens component as counted from the object side is designed as an aspherical surface having portions whose curvature is increased as they are farther from the optical axis.

In the Embodiment 3, the extreme object side surface is designed as an aspherical surface having a shape similar to that of the aspherical surface used in the Embodiment 1, etc. described above.

In the Embodiments 4 through 6, the image side surface of the second lens components as counted from the object side is designed as an aspherical surface having portions whose curvature is decreased as they are farther from the optical axis.

In the Embodiment 7, the object side surface of the second lens component as counted from the object side is designed as an aspherical surface including portions whose curvature is increased as they are farther from the optical axis, and the image side surface of said second lens component is designed as an aspherical surface including portions whose curvature is decreased as they are farther from the optical axis.

The shapes of the aspherical surfaces adopted by respective embodiments described above are defined by the formula (1) and values of their aspherical surface coefficients, etc. are as listed in the numerical data. Values of yc, k etc. adopted for the individual embodiments are as listed in Table 2. As is clear from Table 2, all the values of A are selected within the range defined by the formula (11).

                                  TABLE 2__________________________________________________________________________Embodiment   Yc  K     ω()                D(%) D3 (%)                         H  σ                                A__________________________________________________________________________1       -2.616       -0.3103             45                -5.62                     -29.3                         1.19                            -1  2.857  10-62       -1.475       -0.332             45                 0.01                     -29.3                         1.000                            -1  3.644  10-63       -2.422       -0.3649             45                 2.0 -29.3                         1.07                            -1  3.749  10-64       -1.127       0.1472             2699                 1.86                     -10.9                         1.17                            1   6.396  10-65       -1.228       0.1538             2823                 1.83                     -11.9                         1.15                            1   5.921  10-66       -0.773       0.1767             40                 -0.003                     -23.4                         0.999                            1    2.76  10-6third7       -2.233       0.3032               -1    surfacefourth   -1.848       0.2870               1    surface       0.5902             45                -5.73                     -29.3                         0.805   8.05  10-68       -2.87       -0.2983             4515                -3.42                     -29.5                         0.884                            1    3.67  10-69       -2.68       -0.2748             45                -3.38                     -29.3                         0.885                            1    3.41  10-6__________________________________________________________________________

As is understood from the foregoing descriptions, the present invention has succeeded in designing a wide-angle objective lens system for endoscopes having favorably corrected distortion by arranging an aspherical lens surface having the above-described shape in the front lens group. This fact is clear from the aberration characteristic curves of the individual embodiments shown in FIG. 21 through FIG. 29.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US4059344 *Feb 14, 1977Nov 22, 1977Olympus Optical Co., Ltd.Retrofocus-type objective for endoscopes
US4300817 *Sep 5, 1979Nov 17, 1981U.S. Precision Lens IncorporatedProjection lens
US4400064 *Jul 8, 1981Aug 23, 1983Canon Kabushiki KaishaZoom lens
JPS49121547A * Title not available
JPS57173810A * Title not available
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US5828498 *Oct 29, 1997Oct 27, 1998Asahi Kogaku Kogyo Kabushiki KaishaObjective lens of endoscope
US7441909 *Jan 20, 2005Oct 28, 2008Hewlett-Packard Development Company, L.P.Optical assembly for a projection system
Classifications
U.S. Classification359/708
International ClassificationG02B13/18, G02B23/24, G02B13/04
Cooperative ClassificationG02B13/18, G02B23/243
European ClassificationG02B23/24B2B, G02B13/18