US5936778A
Expired / Lapsed
US
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Objective lens for endoscope
Assignee: Fujinon Corp
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Filing: 1998-03-09
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Granted: 1999-08-10
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Expires: 2018-03-09
Abstract
Abstract In a retro-focus type objective lens for an endoscope, its front-group concave lens system is constituted by two concave lenses, and a predetermined conditional expression is satisfied, so as to secure a sufficient length of back focus, while fully favorably correcting chromatic aberration in magnification. A four group lens configuration having five lenses comprising a front-group concave lens system composed of two concave lenses L 1 and L 2 , a rear convex lens system composed of lenses L 3 and L 5 , with an aperture stop interposed therebetween, in order to secure a long back focus at least three times the composite focal length of the whole system, satisfied is the following conditional expression: dx≧3.0×|f.sub.F | (1) wherein f F is a composite focal length of the front-group concave lens system, and dx is a distance between a rear-side principal point of the front-group concave lens system and a front-side principal point of the rear-group convex lens system.
Inventors
- 👤 Hitoshi Miyano
- 👤 Chikara Yamamoto
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 15:33
CPC Classifications
G; G02; G02B; G02B9/00; G02B9/34; G02B23/00; G02B23/24; G02B23/2407; G02B23/2423; G02B23/243
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
93 words
An objective lens for an endoscope, said objective lens comprising a front-group concave lens system, a rear-group convex lens system, and an aperture stop disposed therebetween; wherein said front-group concave lens system is constituted by two concave lenses; and wherein said objective lens satisfies the following conditional expression (1): dx≧3.0×|f.sub.F | (1) wherein f F is a composite focal length of said front-group concave lens system; and dx is a distance between a rear-side principal point of said front-group concave lens system and a front-side principal point of said rear-group convex lens system.
Claim 2
Dependent Claim
93 words
An objective lens for an endoscope, said objective lens comprising a front-group concave lens system, a rear-group convex lens system, and an aperture stop disposed therebetween; wherein said front-group concave lens system is constituted by two concave lenses; and wherein said objective lens satisfies the following conditional expression (1): dx≧3.0×|f.sub.F | (1) wherein f F is a composite focal length of said front-group concave lens system; and dx is a distance between a rear-side principal point of said front-group concave lens system and a front-side principal point of said rear-group convex lens system.
Claim 3
Dependent Claim
91 words
An objective lens for an endoscope according to claim 1, further satisfying the following conditional expressions (2) and (3): νd>50×(2.6-n.sub.d) (2) 2.0<f.sub.2 /f.sub.1 <4.0 (3) wherein νd is an Abbe number of the second lens in said front-group concave lens system; nd is a refractive index of the second lens in said front-group concave lens system at d-line; f 1 is a focal length of the first lens in said front-group concave lens system; and f 2 is a focal length of the second lens in said front-group concave lens system.
Claim 4
Dependent Claim
69 words
An objective lens for an endoscope according to claim 2, wherein said rear-group convex lens system comprises, successively from the object side, a third convex lens having a surface with a small radius of curvature directed onto the image surface side, and a cemented lens composed of fourth and fifth lenses one of which is constituted by a convex lens while the other is constituted by a concave lens.
Claim 5
Dependent Claim
123 words
An objective lens for an endoscope, and objective lens comprising a front-group concave lens system, a rear-group convex lens system, and an aperture stop disposed therebetween; wherein said front-group concave lens system is constituted by two concave lenses; and wherein said objective lens satisfies the following conditional expressions (4) and (5): νd>50×(2.6-nd) (4) 2.0<f.sub.2 /f.sub.1 <4.0 (5) wherein νd is an Abbe number of the second lens in said front-group concave lens system; nd is a refractive index of the second lens in said front-group concave lens system at d-line; f 1 is a focal length of the first lens in said front-group concave lens system; and f 2 is a focal length of the second lens in said front-group concave lens system.
Claim 6
Dependent Claim
123 words
An objective lens for an endoscope, and objective lens comprising a front-group concave lens system, a rear-group convex lens system, and an aperture stop disposed therebetween; wherein said front-group concave lens system is constituted by two concave lenses; and wherein said objective lens satisfies the following conditional expressions (4) and (5): νd>50×(2.6-nd) (4) 2.0<f.sub.2 /f.sub.1 <4.0 (5) wherein νd is an Abbe number of the second lens in said front-group concave lens system; nd is a refractive index of the second lens in said front-group concave lens system at d-line; f 1 is a focal length of the first lens in said front-group concave lens system; and f 2 is a focal length of the second lens in said front-group concave lens system.
Claim 7
Dependent Claim
69 words
An objective lens for an endoscope according to claim 4, wherein said rear-group convex lens system comprises, successively from the object side, a third convex lens having a surface with a small radius of curvature directed onto the image surface side, and a cemented lens composed of fourth and fifth lenses one of which is constituted by a convex lens while the other is constituted by a concave lens.
Claim 8
Dependent Claim
135 words
An objective lens for an endoscope, said objective lens comprising a front-group concave lens system, a rear-group convex lens system, and an aperture stop disposed therebetween; wherein said front-group concave lens system is constituted by two concave lenses; wherein said objective lens satisfies the following conditional expression (1): dx≧3.0×|f.sub.F | (1) wherein f F is a composite focal length of said front-group concave lens system; and dx is a distance between a rear-side principal point of said front-group concave lens system and a front-side principal point of said rear-group convex lens system; and further satisfying the following conditional expression (2): νd>50×(2.6-nd) (2) wherein νd is an Abbe number of the second lens in said front-group concave lens system; nd is a refractive index of the second lens in said front-group concave lens system at d-line.
Claim 9
Dependent Claim
135 words
An objective lens for an endoscope, said objective lens comprising a front-group concave lens system, a rear-group convex lens system, and an aperture stop disposed therebetween; wherein said front-group concave lens system is constituted by two concave lenses; wherein said objective lens satisfies the following conditional expression (1): dx≧3.0×|f.sub.F | (1) wherein f F is a composite focal length of said front-group concave lens system; and dx is a distance between a rear-side principal point of said front-group concave lens system and a front-side principal point of said rear-group convex lens system; and further satisfying the following conditional expression (2): νd>50×(2.6-nd) (2) wherein νd is an Abbe number of the second lens in said front-group concave lens system; nd is a refractive index of the second lens in said front-group concave lens system at d-line.
Claim 10
Dependent Claim
138 words
An objective lens for an endoscope, said objective lens comprising a front-group concave lens system, a rear-group convex lens system, and an aperture stop disposed therebetween; wherein said front-group concave lens system is constituted by two concave lenses; wherein said objective lens satisfies the following conditional expression (1): dx≧3.0×|f.sub.F | (1) wherein f F is a composite focal length of said front-group concave lens system; and dx is a distance between a rear-side principal point of said front-group concave lens system and a front-side principal point of said rear-group convex lens system; and further satisfying the following conditional expression (2): 2.0<f.sub.2 /f.sub.1 <4.0 (2) wherein f 1 is a focal length of the first lens in said front-group concave lens system; and f 2 is a focal length of the second lens in said front-group concave lens system.
Claim 11
Dependent Claim
138 words
An objective lens for an endoscope, said objective lens comprising a front-group concave lens system, a rear-group convex lens system, and an aperture stop disposed therebetween; wherein said front-group concave lens system is constituted by two concave lenses; wherein said objective lens satisfies the following conditional expression (1): dx≧3.0×|f.sub.F | (1) wherein f F is a composite focal length of said front-group concave lens system; and dx is a distance between a rear-side principal point of said front-group concave lens system and a front-side principal point of said rear-group convex lens system; and further satisfying the following conditional expression (2): 2.0<f.sub.2 /f.sub.1 <4.0 (2) wherein f 1 is a focal length of the first lens in said front-group concave lens system; and f 2 is a focal length of the second lens in said front-group concave lens system.
Claim 12
Dependent Claim
69 words
An objective lens for an endoscope according to claim 6, wherein said rear-group convex lens system comprises, successively from the object side a third convex lens having a surface with a small radius of curvature directed onto the image surface side, and a cemented lens composed of fourth and fifth lenses one of which is constituted by a convex lens while the other is constituted of a concave lens.
Claim 13
Dependent Claim
69 words
An objective lens for an endoscope according to claim 7, wherein said rear-group convex lens system comprises, successively from the object side a third convex lens having a surface with a small radius of curvature directed onto the image surface side, and a cemented lens composed of fourth and fifth lenses one of which is constituted by a convex lens while the other is constituted of a concave lens.
Claim 14
Dependent Claim
69 words
An objective lens for an endoscope according to claim 1, wherein said rear-group convex lens system comprises, successively from the object side a third convex lens having a surface with a small radius of curvature directed onto the image surface side, and a cemented lens composed of fourth and fifth lenses one of which is constituted by a convex lens while the other is constituted of a concave lens.
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