Objective optical system for endoscope

Patent metadata

Field	Value
Publication number	US-10018827-B2
Application number	US-201715678791-A
Country	US
Kind code	B2
Filing date	Aug 16, 2017
Priority date	Jun 18, 2015
Publication date	Jul 10, 2018
Grant date	Jul 10, 2018

Abstract

An objective optical system for endoscope includes, in order from an object side, a front lens group having a negative refractive power as a whole, an aperture stop, and a rear lens group having a positive refractive power as a whole. The front lens group includes, in order from the object side, a single first lens having a negative refractive power and a single second lens having a positive refractive power. The rear lens group includes a single third lens having a positive refractive power, and a cemented lens of a fourth lens having a positive refractive power and a fifth lens having a negative refractive power. An object-side surface of the first lens is a flat surface, the second lens has a meniscus shape having a convex surface directed toward an image side, and the third lens has a biconvex shape.

First claim

What is claimed is:

1. An objective optical system for an endoscope, the objective optical system consisting of, in order from an object side:
a front lens group having a negative refractive power as a whole;
an aperture stop; and
a rear lens group having a positive refractive power as a whole,
wherein:
the front lens group consists of, as lenses having a refractive power, in order from the object side, a first lens which is a single lens having a negative refractive power and a second lens which is a single lens having a positive refractive power,
the rear lens group includes a third lens which is a single lens having a positive refractive power, and a cemented lens of a fourth lens having a positive refractive power and a fifth lens having a negative refractive power,
an object-side surface of the first lens is a flat surface,
the second lens has a meniscus shape having a convex surface directed toward an image side,
the third lens has a biconvex shape, and
the objective optical system for endoscope satisfies the following conditional expressions (1) and (2)
−2.0≤ f 1 /Ih≤−1.39  (1)

−0.2≤SF 3 ≤0.61  (2)

where,
f 1 denotes a focal length of the first lens,
Ih denotes the maximum image height of the objective optical system for endoscope, and
SF 3 denotes a shape factor which is expressed by SF 3 =(R 3L +R 3R )/(R 3L −R 3R ), when a radius of curvature of an object-side surface of the third lens is let to be R 3L and a radius of curvature of an image-side surface of the third lens is lens to be R 3R .

2. The objective optical system for endoscope according to claim 1 , wherein the objective optical system satisfies the following conditional expression (3)
−0.27≤SF 34 ≤0.37  (3)

where,
SF 34 denotes a shape factor which is expressed by SF 34 =(R 3R +R 4L )/(R 3R −R 4L ), when a radius of curvature of an image-side surface of the third lens is let to be R 3R and a radius of curvature of an object-side surface of the fourth lens is let to be R 4L .

3. The objective optical system for endoscope according to claim 1 , wherein the objective optical system satisfies the following conditional expression (4)
0.15≤(1/Fno)×( f 1 /f 5 )≤0.3  (4)

where,
Fno denotes an effective F-number of the objective optical system for endoscope,
f 1 denotes the focal length of the first lens, and
f 5 denotes the focal length of the fifth lens.

4. The objective optical system for endoscope according to claim 1 , wherein the second lens and the third lens are arranged in this order from the object side to the image side with a fixed spacing therebetween and with no intervening refractive optical elements therebetween, and
wherein the objective optical system satisfies the following conditional expression (5)
− 2 . 0 ≤ f 23 /f 5 ≤−1.0  (5)

where,
f 23 denotes a combined focal length of the second lens and the third lens, and
f 5 denotes a focal length of the fifth lens.

5. The objective optical system for endoscope according to claim 1 , wherein the objective optical system for endoscope satisfies the following conditional expression (6)
−1.1≤ f 1 /f 4 ≤−0.7  (6)

where,
f 1 denotes the focal length of the first lens, and
f 4 denotes the focal length of the fourth lens.

6. The objective optical system for endoscope according to claim 1 , wherein the objective optical system for endoscope satisfies the following conditional expression (7)
0.25≤ R 1R /R 4L ≤0.7  (7)

where,
R 1R denotes a radius of curvature of an image-side surface of the first lens, and
R 4L denotes a radius of curvature of an object-side surface of the fourth lens.

7. The objective optical system for endoscope according to claim 1 , wherein the objective optical system for endoscope satisfies the following conditional expression (8)
−0.3≤ R 1R /R 5R ≤0  (8)

where,
R 1R denotes a radius of curvature of an image-side surface of the first lens, and
R 5R denotes a radius of curvature of an image-side surface of the fifth lens.

8. The objective optical system for endoscope according to claim 1 , wherein the objective optical system for endoscope satisfies the following conditional expression (9)
ω≥62°  (9)

where,
ω denotes a half angle of view of the objective optical system for endoscope.

Assignees

• Olympus Corp

Inventors

• Ushio Yasuaki

Classifications

• A61B1/00163

  Optical arrangements (A61B1/002, A61B1/06 take precedence) · CPC title

• G02B9/58

  arranged - + + - · CPC title

• G02B9/34

  having four components only · CPC title

• G02B23/243 Primary

  Objectives for endoscopes · CPC title

• A61B1/00096

  Optical elements · CPC title