Objective optical system for endoscopes

• US 7,773,318 B2
• Filed: 04/03/2009
• Issued: 08/10/2010
• Est. Priority Date: 04/04/2008
• Status: Active Grant

• Current Assignee: Olympus Corporation
• Original Assignee: Olympus Medical Systems Corporation (Olympus Corporation)
• Inventors: Takato, Hideyasu
• Primary Examiner(s): Harrington; Alicia M
• Application Number:
  US12/417,637
• Publication Number:
  US 20100091388A1
• Time in Patent Office: 494 Days
• Field of Search: 359/793, 359/794, 348/65
• US Class Current: 359/794
• CPC Class Codes: G02B 23/243 Objectives for endoscopes

Abstract

An objective optical system for endoscopes is characterized by comprising, in order from its object side, a stop, a first lens and a second lens. The first lens comprises a positive meniscus lens concave on its object side and the second lens comprises a positive lens convex on its object side. The following conditions (1), (2), (3) and (4) are satisfied:
−1.2<r1/f<−0.8  (1)
−1.0<r2/f<−0.6  (2)
2.1<f2/f<4.2  (3)
nd1>1.65  (4)
where r1 is the radius of curvature of the object-side surface of the first lens, r2 is the radius of curvature of the image-side surface of the first lens, f is the focal length of the whole optical system, f2 is the focal length of the second lens, and nd1 is the d-line refractive index of the first lens.

Claims

1. An objective optical system for endoscopes, characterized by comprising, in order from its object side, a stop, a first lens and a second lens, wherein the first lens comprises a positive meniscus lens concave on its object side and the second lens comprises a positive lens convex on its object side, with satisfaction of the following conditions (1), (2), (3) and (4):

−

1.2<

r1/f<

−

0.8 

 

(1)

−

1.0<

r2/f<

−

0.6 

 

(2)

2.1<

f2/f<

4.2 

 

(3)

nd1>

1.65 

 

(4)

where r1 is a radius of curvature of an object-side surface of the first lens,

r2 is a radius of curvature of an image-side surface of the first lens,

f is a focal length of the whole optical system,

f2 is a focal length of the second lens, and

nd1 is a d-line refractive index of the first lens.

2. The objective optical system for endoscopes according to claim 1, characterized by being located substantially vertically to a direction of insertion of an end of the endoscope.

3. The objective optical system for endoscopes according to claim 1, characterized by satisfying the following conditions (5), (6), (7) and (8):

1.0<

r3/f<

1.8 

 

(5)

3.2<

lt/ih<

5.2 

 

(6)

5<

|ν

2−

ν

1|<

35 

 

(7)

2w>

85°

 

 

(8)

where r3 is a radius of curvature of an object-side surface of the second lens,

lt is a total lens length (from a first surface to an imaging plane),

ih is a maximum image height,

ν

1 is an Abbe constant of the first lens,

ν

2 is an Abbe constant of the second lens, and

2w is a maximum angle of view.

4. The objective optical system for endoscopes according to claim 1, characterized by satisfying the following conditions (9), (10) and (11):

1.3<

f2/f1<

2.5 

 

(9)

0.37<

d1/f1<

0.55 

 

(10)

0.12<

d2/f2<

0.24 

 

(11)

where f1 is a focal length of the first lens,

d1 is a thickness of the first lens,

d2 is a thickness of the second lens, and

f2 is a focal length of the second lens.

5. The objective optical system for endoscopes according to claim 1, characterized by satisfying the following conditions (12) and (13):

0.34<

d2/r3<

1.0 

 

(12)

0.2<

d3/f<

0.6 

 

(13)

where d2 is a thickness of the second lens,

r3 is a radius of curvature of an object-side surface of the second lens,

d3 is a distance from the second lens to a CCD'"'"'s cover glass, and

f is a focal length of the whole optical system.