Objective lens system for endoscope

• US 5,703,724 A
• Filed: 05/16/1996
• Issued: 12/30/1997
• Est. Priority Date: 05/16/1995
• Status: Expired due to Fees

• Current Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Original Assignee: Fuji Photo Film Co Limited (Fujifilm Holdings Corporation), Fuji Photo Optical Co. Ltd (Fujifilm Holdings Corporation)
• Inventors: Miyano, Hitoshi
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): Lester, Evelyn A.
• Application Number:
  US08/653,599
• Time in Patent Office: 593 Days
• Field of Search: 359/656-660, 359/643, 359/644, 359/737, 359/739, 359/783
• US Class Current: 359/660
• CPC Class Codes: G02B 23/243 Objectives for endoscopes
• CPC Class Codes: G02B 9/34 having four components only

Abstract

An objective lens system for an endoscope comprises from the subject end to the image end a meniscus lens element of negative optical power having a concave image side surface, a plano-convex lens element of positive optical power having a convex subject side surface, an aperture element, a plano-convex lens element of positive optical power having a convex image side surface and a biconvex lens element of positive optical power.

Claims

1. An objective lens system for an endoscope comprising from the subject end to the image end a meniscus lens element of negative optical power having a concave image side surface, a plano-convex lens element of positive optical power having a convex subject side surface, an aperture element, a plano-convex lens element of positive optical power having a convex image side surface and a biconvex lens element of positive optical power, said objective lens systems satisfying the following relations:

Bf'"'"'>

1.5f'"'"'

1.80<

D/R2<

2.40

μ

₂ >

45.0

μ

₃ >

50.0

μ

₄ >

50.0

where Bf'"'"' designates the back focal length of the objective lens system, f'"'"' designates the overall focal length of the objective lens system, D designates the value of d₂₃ +(d₃₄ /n₂)+d_4S, where d₂₃, d₃₄ and d_4S are the axial distance between the second and third lens surfaces, the third and fourth lens surfaces and the fourth lens surface and the image side surface of the aperture element, respectively, and n₂ is the index of refraction of the second lens element, R2 is the radius of curvature of the second lens surface, and μ

₂, μ

₃ and μ

₄ are the dispersion of the second, third and fourth lens elements as measured by the Abbe number, respectively.

2. An objective lens system as defined in claim 1, and further comprising a rectangular prism disposed behind the fourth lens element.

3. An objective lens system as defined in claim 1, wherein said aperture element is formed as a light shield layer coated on a subject side surface of the third lens element.

4. An objective lens system as defined in claim 1 substantially as described:

space="preserve" listing-type="tabular">______________________________________ Radius of Axial distance Element Curvature Between Surfaces nd ν

d ______________________________________ R1 = 2.8333 L1 0.2141 1.83500 42.6 R2 = 0.3576 0.1224 R3 = 2.8359 L2 0.9461 1.80518 25.4 R4 = ∞

S 0.0306 R5 = ∞

L3 0.3670 1.69680 55.6 R6 = -0.6338 0.0314 R7 = 2.3497 L4 0.3670 1.69680 55.6 R8 = -6.5207 ______________________________________

where the objective lens system comprises lens elements L1 to L4 having surfaces R1 to R8 and an aperture element S, the index of refraction in relation to d-line is given by nd, the dispersion μ

d is measured by the Abbe number.

5. An objective lens system as defined in claim 4, and further comprising a rectangular prism disposed at a distance of 1.2 mm behind the fourth lens element from the fourth lens element.

6. An objective lens system as defined in claim 5, wherein said rectangular prism has an axial distance of 1.2 mm between surfaces intersecting at a right angle, the index of refraction of 1.55920 and a dispersion of 53.9 as measured by the Abbe number.

7. An objective lens system as defined in claim 4, wherein said aperture element is formed as a light shielding layer coated on a subject side surface of the third lens element.

8. An objective lens system as defined in claim 1 substantially as described:

space="preserve" listing-type="tabular">______________________________________ Radius of Axial distance Element Curvature Between Surfaces nd ν

d ______________________________________ R1 = ∞

L1 0.2486 1.83500 42.6 R2 = 0.3816 0.1422 R3 = 3.3087 L2 1.0044 1.80518 25.4 R4 = ∞

S 0.0355 R5 = ∞

L3 0.4263 1.69680 55.6 R6 = -0.7028 0.0711 R7 = 2.3647 L4 0.4263 1.69680 55.6 R8 = -9.3143 ______________________________________

where the objective lens system comprises lens elements L1 to L4 having surfaces R1 to R8 and an aperture element S, the index of refraction in relation to d-line is given by nd, the dispersion μ

d is measured by the Abbe number.

9. An objective lens system as defined in claim 8, and further comprising a rectangular prism disposed behind the fourth lens element.

10. An objective lens system as defined in claim 8, wherein said aperture element is formed as a light shielding layer coated on a subject side surface of the third lens element.

11. An objective lens system as defined in claim 1 substantially as described:

space="preserve" listing-type="tabular">______________________________________ Radius of Axial distance Element Curvature Between Surfaces nd ν

d ______________________________________ R1 = 11.9586 L1 0.2072 1.88300 41.0 R2 = 0.3380 0.1189 R3 = 4.1222 L2 0.9816 1.80518 25.4 R4 = ∞

S 0.0296 R5 = ∞

L3 0.3558 1.69680 55.6 R6 = -0.6681 0.0602 R7 = 2.8365 L4 0.3560 1.62041 60.3 R8 = -4.0220 ______________________________________

where the objective lens system comprises lens elements L1 to L4 having surfaces R1 to R8 and an aperture element S, the index of refraction in relation to d-line is given by nd, the dispersion μ

d is measured by the Abbe number.

12. An objective lens system as defined in claim 11, and further comprising a rectangular prism disposed behind the fourth lens element.

13. An objective lens system as defined in claim 11, wherein said aperture element is formed as a light shielding layer coated on a subject side surface of the third lens element.

14. An objective lens system as defined in claim 1 substantially as described:

space="preserve" listing-type="tabular">______________________________________ Radius of Axial distance Element Curvature Between Surfaces nd ν

d ______________________________________ R1 = 19.2005 L1 0.2501 1.88300 41.0 R2 = 0.3785 0.2302 R3 = 111.4488 L2 1.0768 1.80518 25.4 R4 = ∞

S 0.0357 R5 = ∞

L3 0.4623 1.69680 55.6 R6 = -0.7769 0.0948 R7 = 3.2396 L4 0.4535 1.69680 55.6 R8 = -6.6209 ______________________________________

where the objective lens system comprises lens elements L1 to L4 having surfaces R1 to R8 and an aperture element S, the index of refraction in relation to d-line is given by nd, the dispersion μ

d is measured by the Abbe number.

15. An objective lens system as defined in claim 14, and further comprising a rectangular prism disposed at a distance of 0.5 mm behind the fourth lens element from the fourth lens element.

16. An objective lens system as defined in claim 15, wherein said rectangular prism has an axial distance of 1.5 mm between surfaces intersecting at a right angle, the index of refraction of 1.55920 and a dispersion of 53.9 as measured by the Abbe number.

17. An objective lens system as defined in claim 14, wherein said aperture element is formed as a light shielding layer coated on a subject side surface of the third lens element.