Objective lens and endoscope using the same

• US 8,300,325 B2
• Filed: 10/04/2011
• Issued: 10/30/2012
• Est. Priority Date: 04/07/2010
• Status: Active Grant

• Current Assignee: Olympus Corporation
• Original Assignee: Olympus Medical Systems Corporation (Olympus Corporation)
• Inventors: Katahira, Yuko
• Primary Examiner(s): Collins, Darryl J
• Application Number:
  US13/252,588
• Publication Number:
  US 20120127598A1
• Time in Patent Office: 392 Days
• Field of Search: 359749-756, 359/761, 359/763, 359/770, 600101-183
• US Class Current: 359/770
• CPC Class Codes: G02B 13/004 having four lenses
• CPC Class Codes: G02B 13/006 at least one element being a compound optical element, e.g. cemented elements
• CPC Class Codes: G02B 23/2423 of the distal end
• CPC Class Codes: G02B 9/34 having four components only
• CPC Class Codes: G02B 9/60 having five components only

Abstract

Provided is a simple-structured endoscope objective lens suitable for a compact, high-resolution image acquisition element. Provided is an objective lens constituted of a first negative lens, a second positive lens, an aperture stop, a third positive lens, and a joined lens arranged in that order from an object side, the joined lens being formed of a fourth positive lens and a fifth negative lens and satisfying the expressions (1) and (2), and the objective lens satisfies the expression (3):
nn≧2.0  (1)
12<(νp−νn)<34  (2)
1.52<(f23/fl)<1.75  (3)
where nn, νp, νn, f23 and fl denote a refractive index at d-line of the fifth lens, an Abbe number of the fourth lens, an Abbe number of the fifth lens, a combined focal length of the second lens and the third lens, and a focal length of the entire, respectively.

Claims

1. An objective lens comprising a first negative lens, a second positive lens, an aperture stop, a third positive lens, and a joined lens arranged in order from an object side, the joined lens being formed of a fourth positive lens and a fifth negative lens that are joined together,

wherein the joined lens satisfies conditional expressions (1) and (2), and the objective lens satisfies conditional expression (3):

nn≧

2.0 

 

(1)

12<

(ν

p−

ν

n)<

34 

 

(2)

1.52<

(f23/fl)<

1.75 

 

(3)

where nn denotes a refractive index with respect to a d-line of the fifth lens, ν

p denotes an Abbe number of the fourth lens, ν

n denotes an Abbe number of the fifth lens, f23 denotes a combined focal length of the second lens and the third lens, and fl denotes a focal length of the entire system.

2. The objective lens according to claim 1, wherein the first lens satisfies conditional expression (4):

n1≧

2.0 

 

(4)

where n1 denotes a refractive index with respect to a d-line of the first lens.

3. The objective lens according to any one of claim 1, wherein the second lens satisfies conditional expression (5):

n2≧

2.00 

 

(5)

where n2 denotes a refractive index with respect to a d-line of the second lens.

4. The objective lens according to claim 1, wherein the third lens satisfies conditional expression (6):

(R3b+R3a)/(R3b−

R3a)≧

−

1.0 

 

(6)

where R3a denotes a radius of curvature of an object-side surface of the third lens, and R3b denotes a radius of curvature of an image-side surface of the third lens.

5. The objective lens according to claim 1, further comprising at least one positive lens between a rear end of the joined lens and an image surface.

6. The objective lens according to claim 1, wherein at least the first lens is composed of a material having a tolerance to sterilization and/or a tolerance to chemicals, and

wherein the material is sapphire, zirconia, yttrium-stabilized zirconia, synthetic quartz, light-transmissive YAG, or spinel.

7. The objective lens according to claim 1, further comprising an optical-path changing element between a rear end of the joined lens and an image surface.

8. An endoscope comprising the objective lens according to claim 1.