Objective optical system for endoscopes

• US 5,619,380 A
• Filed: 04/28/1995
• Issued: 04/08/1997
• Est. Priority Date: 05/25/1992
• Status: Expired due to Term

• Current Assignee: Olympus Optical Corporation Limited (Olympus Corporation)
• Original Assignee: Olympus Optical Corporation Limited (Olympus Corporation)
• Inventors: Mori, Takao, Yokota, Akira, Ogasawara, Syuichiro
• Primary Examiner(s): Epps, Georgia Y.
• Assistant Examiner(s): Lester, Evelyn A.
• Application Number:
  US08/430,254
• Time in Patent Office: 711 Days
• Field of Search: 359/717, 359/708, 359/691, 359/739, 359/740, 359/793, 359/661, 359/656
• US Class Current: 359/661
• CPC Class Codes: G02B 23/243 Objectives for endoscopes
• CPC Class Codes: G02B 9/10 one + and one - component

Abstract

An objective optical system for endoscopes consisting, in order from the object side, of a front lens unit having a negative refractive power, and a rear lens unit which is composed of a single lens component and has a positive refractive power. This objective optical system comprises a small number of lens components, has favorably corrected aberrations and satisfies the following condition:

CJ<8IH

Claims

1. An objective optical system for endoscopes consisting of, in order from an object side:

a front lens unit consisting of a single lens component having a negative refractive power;

an aperture stop; and

a rear lens unit consisting of a single lens component having a positive refractive power;

wherein said objective optical system satisfies the following conditions;

CJ<

8IH

D₂ <

2f

wherein said reference symbol CJ represents a distance as measured from a first surface of said objective optical system to a paraxial image surface thereof, said reference symbol IH designates a maximum image height, said reference symbol D₂ represents a distance as measured from an image side surface of said negative single lens component to said aperture stop, and said reference symbol f designates a focal length of said objective optical system as a whole.

2. An objective optical system for endoscopes according to claim 1, wherein said single lens component of said rear lens unit consists of a single converging lens element.

3. An objective optical system for endoscopes according to claim 1, wherein said single lens component of said rear lens unit is a cemented lens component consisting of:

a diverging lens element having a concave surface on an image side; and

a biconvex converging lens element.

4. An objective optical system for endoscopes according to claim 2, wherein an absolute value of a radius of curvature on an object side surface of said rear lens unit is larger than an absolute value of a radius of curvature on an image side surface of said rear lens unit.

5. An objective optical system for endoscopes according to claim 1, wherein said system satisfies the following condition:

space="preserve" listing-type="equation">ν

.sub.1 >

40

wherein the reference symbol ν

₁ represents an Abbe'"'"'s number of a lens component disposed on said object side of said objective optical system.

8. An objective optical system for endoscopes according to claim 1, wherein said front lens unit has a convex surface on an object side thereof.

9. An objective optical system for endoscopes according to claim 2, wherein said system satisfies the following condition:

space="preserve" listing-type="equation">0.3<

|f.sub.2 /f.sub.1 |<

2

wherein said reference symbol f₁ represents a focal length of said front lens unit and said reference symbol f₂ designates a focal length of said rear lens unit.

10. An objective optical system for endoscopes according to claim 2, wherein said system satisfies the following condition:

space="preserve" listing-type="equation">ν

.sub.2 >

40

wherein said reference symbol ν

₂ represents an Abbe'"'"'s number of a lens component in said rear lens unit.

11. An objective optical system for endoscopes according to claim 3, wherein said system satisfies the following condition:

space="preserve" listing-type="equation">ν

.sub.2d <

ν

.sub.3d

wherein said reference symbol ν

_2d represents an Abbe'"'"'s number of a first lens element of said rear lens unit and said reference symbol ν

_3d designates an Abbe'"'"'s number of a second lens element of said rear lens unit.

12. An objective optical system for endoscopes according to claim 3, wherein said system satisfies the following condition:

space="preserve" listing-type="equation">ν

.sub.2d <

35

wherein said reference symbol ν

_2d represents an Abbe'"'"'s number of a first lens element of said rear lens unit.

13. An objective optical system for endoscopes according to claim 11, comprising at least one aspherical surface.

14. An objective optical system for endoscopes according to claim 13, wherein said aspherical surface satisfies the following condition:

space="preserve" listing-type="equation">E.sub.i '"'"'(n.sub.i-1 -n.sub.i)>

0

wherein said reference symbols n_i-1 and n_i represent refractive indices of media located on an object side and an image side respectively of said aspherical surface, and said reference symbol E_i '"'"' designates an aspherical surface coefficient of a fourth order of said aspherical surface.

15. An objective optical system for endoscopes according to claim 13, wherein said aspherical surface satisfies the following condition:

space="preserve" listing-type="equation">Δ

x(h.sub.m)·

(n.sub.i-1 -n.sub.i)>

0

wherein said reference symbols n_i-1 and n_i represent refractive indices of media located on an object side and an image side respectively of said aspherical surface, and said reference symbol Δ

x(h_m) designates a departure of said aspherical surface from a reference sphere thereof as measured at a height of h_m of a marginal ray on said aspherical surface.

16. An objective optical system for endoscopes according to any one of claims 14 or 15, wherein said aspherical surface is used as an image side surface of said rear lens unit.

6. An objective optical system for endoscopes comprising, in order from an object side:

a front lens unit consisting of a single lens component having a negative refractive power;

an aperture stop; and

a rear lens unit consisting of a single lens component having a positive refractive power;

wherein said objective optical system satisfies the following conditions;

CJ<

8IH

D₂ <

2f

wherein said reference symbol CJ represents a distance as measured from a first surface of said objective optical system to a paraxial image surface thereof and said reference symbol IH designates a maximum image height, said reference symbol D₂ represents a distance as measured from an image side surface of said negative single lens component to said aperture stop and said reference symbol f designates a focal length of said objective optical system as a whole; and

wherein said front lens unit has a coating on a concave surface thereof which cuts off YAG laser light.

7. An objective optical system for endoscopes comprising, in order from an object side:

a front lens unit consisting of a single lens component having a negative refractive power;

an aperture stop; and

a rear lens unit consisting of a single lens component having a positive refractive power;

wherein said objective optical system satisfies the following conditions;

CJ<

8IH

D₂ <

2f

where said reference symbol CJ represents a distance as measured from a first surface of said objective optical system to a paraxial image surface thereof and said reference symbol IH designates a maximum image height, said reference symbol D₂ represents a distance as measured an image side surface of said negative single lens component to said aperture stop and said reference symbol f designates a focal length of said objective optical system as a whole; and

wherein said lens component of said rear lens unit is made of material which absorbs infrared light and is disposed immediately after said aperture stop.

17. An objective optical system for endoscopes comprising, from an object side:

a front lens unit consisting of a single lens component having a negative refractive power;

an aperture stop; and

a rear lens unit consisting of a single lens component consisting of a single converging lens element having a positive refractive power;

wherein said objective optical system satisfies the following conditions;

CJ<

8IH

D₂ <

2f

wherein said reference symbol CJ represents a distance as measured from a first surface of said objective optical system to a paraxial image surface thereof and said reference symbol IH designates a maximum image height, said reference symbol D₂ represents a distance as measured from an image side surface of said negative single lens component to said aperture stop and said reference symbol f designates a focal length of said objective optical system as a whole;

wherein said rear lens unit has an image side surface configured as an aspherical surface and said aspherical surface satisfies the following conditions;

space="preserve" listing-type="equation">E.sub.i '"'"'(n.sub.i-1 -n.sub.i)>

0

space="preserve" listing-type="equation">F.sub.i '"'"'(n.sub.i-1 -n.sub.i)>

0

wherein said reference symbols n_i-1 and n_i represent refractive indices of media located on an object side and an image side respectively of said aspherical surface, and said reference symbols E_i '"'"' and F_i '"'"' designate aspherical surface coefficients of a fourth order and a sixth order respectively of said aspherical surface.

18. An objective optical system for endoscopes comprising, in order from an object side:

a front lens unit consisting of a single lens component having a negative refractive power;

an aperture stop; and

a rear lens unit consisting of a single lens component consisting of a single converging lens element having a positive refractive power;

wherein said object optical system satisfies the following conditions;

CJ<

8IH

D₂ <

2f

wherein said reference symbol CJ represents a distance as measured from a first surface of said objective optical system to a paraxial image surface thereof and said reference symbol IH designates a maximum image height, said reference symbol D₂ represents a distance as measured from an image side surface of said negative single lens component to said aperture stop and said reference symbol f designates a focal length of said objective optical system as a whole;

wherein said rear lens unit has an image side surface configured as an aspherical surface and said aspherical surface satisfies the following conditions;

space="preserve" listing-type="equation">Δ

x(h.sub.m)·

(n.sub.i-1 -n.sub.i)>

0

space="preserve" listing-type="equation">F.sub.i '"'"'(n.sub.i-1 -n.sub.i)>

0

wherein said reference symbols n_i-1 and n_i represent refractive indices of media located on an object side and an image side respectively of said aspherical surface, said reference symbol Δ

x(h_m) designates a departure of said aspherical surface from a reference sphere thereof as measured at a height of h_m of a marginal ray on said aspherical surface and said reference symbol F_i '"'"' denotes an aspherical surface coefficient of a sixth order of said aspherical surface.

19. An objective optical system for endoscopes consisting of two only single lens components and an aperture stop, one of said lens components having a negative refractive power and the other of said lens components having a positive refractive power;

said aperture stop being between said single lens components and said single lens component having said negative refractive power being closest to an object side of said system; and

said objective optical system satisfying the following condition;

CJ<

8IH

D₂ <

2f

wherein said reference symbol CJ represents a distance as measured from a first surface of said objective optical system to a paraxial image surface thereof and said reference symbol IH designates a maximum image height, said reference symbol D₂ represents a distance as measured from an image side surface of said negative single lens component to said aperture stop, and said reference symbol f designates a focal length of said objective optical system as a whole.

20. An objective optical system for endoscopes comprising, in order from an object side:

a front lens unit consisting of a single lens component having a negative refractive power;

an aperture stop; and

a rear lens unit consisting of a single lens component having a positive refractive power, an absolute value of a radius of curvature on an object side surface of said rear lens unit being larger than an absolute value of a radius of curvature on an image side surface of said rear lens unit, and said single lens component of said rear lens unit is a cemented lens component consisting of;

a diverging lens element having a concave surface on an image side, and

a biconvex lens element;

said objective optical system satisfying the following conditions;

CJ<

8IH

D₂ <

2f

wherein said reference symbol CJ represents a distance as measured from a first surface of said objective optical system to a paraxial image surface thereof, said reference symbol IH designates a maximum image height, said reference symbol D₂ represents a distance as measured from an image side surface of said negative single lens component to said aperture stop, and said reference symbol f designates a focal length of said objective optical system as a whole.