ENDOSCOPE AND OBJECTIVE LENS FOR THE SAME

• US 20110002052A1
• Filed: 07/06/2010
• Published: 01/06/2011
• Est. Priority Date: 07/06/2009
• Status: Active Grant

• Current Assignee: Hoya Corporation
• Original Assignee: Hoya Corporation
• Inventors: NASU, Sachiko
• Granted Patent: US 8,164,839 B2
• Time in Patent Office: Days
• US Class Current: 359/717
• CPC Class Codes: G02B 23/2438 Zoom objectives

Abstract

An objective lens for an endoscope, including a negative front lens group and a positive rear lens group arranged such that an aperture stop is positioned therebetween, wherein the front lens group has at least a front-side negative lens and a front-side positive lens arranged in this order from an object side, and the rear lens group has at least a rear-side positive lens and a cemented lens arranged in this order from the object side, the cemented lens being configured by cementing together negative and positive lenses. The objective lens satisfies following conditions: −4.5≦f_F/f≦−2.0 and 1.5≦f_RP/f≦2.5, where f_F (unit: mm) represent of the front lens group, f (unit: mm) represents a total focal length of the front lens group and the rear lens group, and f_RP (unit: mm) represents a focal length of the rear-side positive lens.

Claims

1. An objective lens for an endoscope, comprising:

a front lens group having a negative power; and

a rear lens group having a positive power arranged such that an aperture stop is positioned between the front lens group and the rear lens group,

wherein;

the front lens group comprises at least a front-side negative lens and a front-side positive lens arranged in this order from an object side;

the rear lens group comprises at least a rear-side positive lens and a cemented lens arranged in this order from the object side, the cemented lens being configured by cementing together a negative lens and a positive lens; and

the objective lens satisfies following conditions;

−

4.5≦

f_F/f≦

−

2.0  

 

(1); and

1.5≦

f_RP/f≦

2.5  

 

(2)

where f_F (unit;

mm) represents a focal length of the front lens group, f (unit;

mm) represents a total focal length of the front lens group and the rear lens group, and f_RP (unit;

mm) represents a focal length of the rear-side positive lens.

2. The objective lens according to claim 1,

wherein:

an object side surface of the front-side positive lens is a convex surface formed to be an aspherical surface; and

the objective lens satisfies a condition;

−

1.5≦

f_FP/f_F≦

−

0.5  

 

(3)

where f_FP (unit;

mm) represents a focal length of the front-side positive lens.

3. The objective lens according to claim 1,

wherein:

an image side surface of the rear-side positive lens is a convex surface formed to be an aspherical surface; and

the objective lens satisfies a condition;

−

0.9≦

f_RP/f_F≦

−

0.4  

 

(4)

where f_RP (unit;

mm) represents a focal length of the rear-side positive lens.

4. The objective lens according to claim 1,

wherein:

an image side surface of the front-side negative lens is formed to be a concave surface; and

the front-side positive lens is configured such that an object side surface thereof is a convex surface and an image side surface thereof is a flat surface.

5. The objective lens according to claim 1,

wherein:

the rear-side positive lens is configured such that an object side surface thereof is one of a flat surface and a concave surface and an image side surface thereof is a convex surface; and

the negative lens of the cemented lens is a negative meniscus lens whose object side surface is formed to be a convex surface.

6. The objective lens according to claim 1,

wherein the objective lens satisfies a condition:

0.2≦

D_F/D_R≦

0.5  

 

(5).

where D_F (unit;

mm) represents a distance in air from an object side surface of the front-side positive lens to a surface of the aperture stop, and D_R (unit;

mm) represents a distance in air from the surface of the aperture stop to an image side surface of the rear-side positive lens.

7. The objective lens according to claim 1, wherein the objective lens has an angle of view larger than or equal to 130°

.

8. An endoscope, comprising:

an elastic insertion unit; and

an objective lens arranged at a tip part of the elastic insertion unit,

wherein the objective lens comprises;

a front lens group having a negative power; and

a rear lens group having a positive power arranged such that an aperture stop is positioned between the front lens group and the rear lens group,

wherein;

the front lens group comprises at least a front-side negative lens and a front-side positive lens arranged in this order from an object side;

the rear lens group comprises at least a rear-side positive lens and a cemented lens arranged in this order from the object side, the cemented lens being configured by cementing together a negative lens and a positive lens; and

the objective lens satisfies following conditions;

−

4.5≦

f_F/f≦

−

2.0  

 

(1); and

1.5≦

f_RP/f≦

2.5  

 

(2)

where f_F (unit;

mm) represents a focal length of the front lens group, f (unit;

mm) represents a total focal length of the front lens group and the rear lens group, and f_RP (unit;

mm) represents a focal length of the rear-side positive lens.

9. The endoscope according to claim 8,

wherein:

an object side surface of the front-side positive lens is a convex surface formed to be an aspherical surface; and

the objective lens satisfies a condition;

−

1.5≦

f_FP/f_F≦

−

0.5  

 

(3)

where f_FP (unit;

mm) represents a focal length of the front-side positive lens.

10. The endoscope according to claim 8,

wherein:

an image side surface of the rear-side positive lens is a convex surface formed to be an aspherical surface; and

the objective lens satisfies a condition;

−

0.9≦

f_RP/f_F≦

−

0.4  

 

(4)

where f_RP (unit;

mm) represents a focal length of the rear-side positive lens.

11. The endoscope according to claim 8,

wherein:

an image side surface of the front-side negative lens is formed to be a concave surface; and

the front-side positive lens is configured such that an object side surface thereof is a convex surface and an image side surface thereof is a flat surface.

12. The endoscope according to claim 8,

wherein:

the rear-side positive lens is configured such that an object side surface thereof is one of a flat surface and a concave surface and an image side surface thereof is a convex surface; and

the negative lens of the cemented lens is a negative meniscus lens whose object side surface is formed to be a convex surface.

13. The endoscope according to claim 8,

wherein the objective lens satisfies a condition:

0.2≦

D_F/D_R≦

0.5  

 

(5).

where D_F (unit;

mm) represents a distance in air from an object side surface of the front-side positive lens to a surface of the aperture stop, and D_R (unit;

mm) represents a distance in air from the surface of the aperture stop to an image side surface of the rear-side positive lens.

14. The endoscope according to claim 8, wherein the objective lens has an angle of view larger than or equal to 130°

.