Objective lens for endoscope

• US 6,956,703 B2
• Filed: 05/28/2004
• Issued: 10/18/2005
• Est. Priority Date: 05/30/2003
• Status: Active Grant

• Current Assignee: Olympus Corporation
• Original Assignee: Olympus Corporation
• Inventors: Saito, Shinichi
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): HASAN, MOHAMMED A
• Application Number:
  US10/855,484
• Publication Number:
  US 20040240081A1
• Time in Patent Office: 508 Days
• Field of Search: 359/660, 359/782, 359/783, 359/659, 359/763, 359/770
• 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 for endoscopes comprises a front lens unit component and a rear lens unit component, between which a stop is located, wherein a front lens unit component comprises, in order from the object side, a first lens having a negative refractive power and a second lens having a positive refractive power which directs a surface of the small radius of curvature toward the object side; wherein a rear lens unit component comprises a third lens having a positive refractive power which directs a surface of the small radius of curvature toward the image side, a fourth lens having a positive refractive power and a fifth lens having a negative refractive power; and wherein the fourth lens and the fifth lens are cemented, and satisfying the following condition:
2.0<|f₃/f|<3.0
where f is the composite focal length of the total system and f₃ is the focal length of the third lens.

Claims

1. An objective lens for endoscopes comprises a front lens unit component and a rear lens unit component, between which a stop is located, wherein the front lens unit component comprises, in order from the object side, a first lens having a negative refractive power, and a second lens having a positive refractive power which directs a surface of the small radius of curvature toward the object side;

wherein the rear lens unit component comprises a third lens having a positive refractive power which directs a surface of the small radius of curvature toward the image side, a fourth lens having a positive refractive power, and a fifth lens having a negative refractive power; and

wherein the fourth lens and the fifth lens are cemented, and satisfying the following condition;

2.0<

|f₃/f|<

3.0

where f is the composite focal length of the total system and f₃ is the focal length of the third lens.

2. An objective lens for endoscopes according to claim 1, satisfying the following condition:

1.0<

|d_F/f|<

1.8

0.8<

IH/f<

1.2

where d_F is the distance from a top surface of the large radius of curvature of the first lens to the stop (an air-converted length) and IH is the maximum image height on the imaging surface.

3. An objective lens for endoscopes according to claim 2, satisfying the following condition:

3.0<

|f₂/f|<

10.0

where f₂ is a focal length of the second lens.

4. An objective lens for endoscopes according to claim 2, satisfying the following condition:

n₂<

1.6 and ν

₂>

50

where n₂ is the d-line refractive index of the second lens and ν

₂ is the d-line Abbe'"'"'s number of the second lens.

5. An objective lens for endoscopes according to claim 2, satisfying the following condition:

1.2<

d₂₃/f<

1.7

where d₂₃ is the distance from a top surface of the small radius of curvature of the second lens to that of the third lens (an air-converted length).

6. An objective lens for endoscopes according to claim 1, satisfying the following condition:

3.0<

|f₂/f|<

3.0

where f₂ is a focal length of the second lens.

7. An objective lens for endoscopes according to claim 1, satisfying the following condition:

n₂<

1.6, ν

₂>

50

where n₂ is the d-line refractive index of the second lens and ν

₂ is the d-line Abbe'"'"'s number of the second lens.

8. An objective lens for endoscopes according to claim 1, satisfying the following condition:

1.2<

d₂₃/f<

1.7

where d₂₃ is the distance from a top surface of the small radius of curvature of the second lens to that of the third lens (an air-converted length).

9. An objective lens for endoscopes according to claim 5, satisfying the following condition:

1.3<

d₂₃/f<

1.6

where d₂₃ is the distance from a top surface of the small radius of curvature of the second lens to that of the third lens (an air-converted length).

10. An objective lens for endoscopes according to claim 8, satisfying the following condition:

1.3<

d₂₃/f<

1.6

where d₂₃ is the distance from a top surface of the small radius of curvature of the second lens to that of the third lens (an air-converted length).

11. An objective lens for endoscopes according to claim 2, wherein the surface of the object side of the third lens is flat.

12. An objective lens for endoscopes according to claim 11, wherein the stop is closely fixed on the third lens.