Objective lens for endoscopes and endoscope

Patent metadata

Field	Value
Publication number	US-9709796-B2
Application number	US-201615099672-A
Country	US
Kind code	B2
Filing date	Apr 15, 2016
Priority date	Apr 20, 2015
Publication date	Jul 18, 2017
Grant date	Jul 18, 2017

Abstract

An objective lens for endoscopes includes, in order from the object side: a front group; an aperture stop; and a positive rear group. The front group includes, in order from the object side, a negative first lens, in which the absolute value of the radius of curvature of the surface toward the image side is less than that of the surface toward the object side, and at least one plane parallel plate. The rear group includes, in order from the object side, a positive second lens, and a cemented lens formed by a positive third lens and a negative fourth lens. The coupling surface of the cemented lens is convex toward the image side. Conditional Formulae (1) through (3) concerning the plane parallel plates within the front group, the focal length of the first lens, the radius of curvature of the coupling surface of the cemented lens, etc., are satisfied.

First claim

What is claimed is:

1. An objective lens for endoscopes consisting of, in order from the object side to the image side:
a front group;
an aperture stop; and
a rear group having a positive refractive power as a whole;
the front group consisting of; in order from the object side to the image side, a first lens having a negative refractive power, in which the absolute value of the radius of curvature of the surface toward the image side thereof is less than the absolute value of the radius of curvature of the surface toward the object side thereof, and at least one plane parallel plate;
the rear group consisting of, in order from the object side to the image side, a second lens having a positive refractive power, a third lens having a positive refractive power, and a fourth lens having a negative refractive power;
the third lens and the fourth lens being cemented together to constitute a cemented lens;
the coupling surface of the cemented lens being convex toward the image side; and
all of Conditional Formulae (1) through (3) below being satisfied:

0.045
<

1
f

⁢

∑

i
=
1

k

⁢

⁢

ti
×

(

Ndi
-
1

)

vdi

<
0.15

(
1
)

-
0.9

<

f
⁢

/

⁢
fl

<

-
0.5

(
2
)

-
2.9

<

Dsc
⁢

/

⁢
RC

<

-
1

(
3
)

wherein f is the focal length of the entire lens system, k is the total number of plane parallel plates within the front group, i is a natural number within a range from 1 to k, ti is the thickness of an ith plane parallel plate from the object side within the front group, Ndi is the refractive index with respect to the d line of an ith plane parallel plate from the object side within the front group, vdi is the Abbe's number with respect to the d line of an ith plane parallel plate from the object side within the front group, fl is the focal length of the first lens, Dsc is the distance along the optical axis from the aperture stop to the coupling surface of the cemented lens, and RC is the radius of curvature of the coupling surface of the cemented lens.

2. An objective lens for endoscopes as defined in claim 1 , in which Conditional Formula (1-1) below is satisfied:

0.05
<

1
f

⁢

∑

i
=
1

k

⁢

⁢

ti
×

(

Ndi
-
1

)

vdi

<

0.12
.

(

1
⁢

-

⁢
1

)

3. An objective lens for endoscopes as defined in claim 1 , in which Conditional Formula (2-1) below is satisfied:
−0.8 <f /fl<−0.6  (2-1).

4. An objective lens for endoscopes as defined in claim 1 , in which Conditional Formula (3-1) below is satisfied:
−2.7 <Dsc /RC<−1.2  (3-1).

5. An endoscope equipped with an objective lens for endoscopes as defined in claim 1 .

6. An objective lens for endoscopes as defined in claim 1 , in which Conditional Formula (4) below is satisfied:

2.5
⁢

⁢
mm

<

∑

i
=
1

Assignees

• Fujifilm Corp

Inventors

• Harada Keisuke
• Cho Michio

Classifications

• G02B13/06

  Panoramic objectives; So-called "sky lenses" {including panoramic objectives having reflecting surfaces} · CPC title

• G02B23/243 Primary

  Objectives for endoscopes · CPC title