JP6764813B2 - Objective optics and endoscope - Google Patents

Description

The present invention relates to objective optics, particularly endoscopic objective optics for 2D or 3D observation.

In the medical field of electronic endoscopes, skills related to treatment and diagnosis are becoming more sophisticated. An electronic endoscope is inserted into a living body to detect and detect smaller lesions. An electronic endoscope for 2D observation performs planar (two-dimensional) observation. An electronic endoscope for 3D observation performs three-dimensional (three-dimensional) observation.

Accurate focusing is essential for both observations. For 3D observation, a configuration is known in which an image for the right eye and an image for the left eye are acquired by one image sensor. In this configuration, if one image sensor is moved along the optical axis for focus adjustment, the focus positions of both the right eye image and the left eye image change at the same time. Therefore, when the image sensor is moved, it is not possible to focus only one of the two parallax images.

Further, it is desirable that the distance (space) from the final lens to the imaging surface can be secured in both the optical system of the objective optical system of the electronic endoscope for 2D observation and the objective optical system of the electronic endoscope for 3D observation. .. As a result, it is possible to secure a space for arranging the prism or the like on the object side of the imaging surface.

As a conventional objective optical system, for example, Patent Documents 1, 2, 3, and 4 have a five-group configuration having negative, negative, positive, aperture, positive, and positive (junction lens) power arrangements in order from the object side. It is disclosed.

Here, in particular, in the objective optical system for 3D observation, the focus can be adjusted as described above, the distance (space) from the final lens to the imaging surface is secured, and the lens having the most negative refractive power on the object side is used. It is desirable that the parallax between the right-eye optical system and the left-eye optical system can be set small by lowering the light beam height. Further, in the objective optical system for 2D observation, as described above, the space for arranging the prism or the like on the object side of the imaging surface is secured, and the light beam height of the lens having the negative refractive power on the object side is lowered. It is desirable to reduce the size of the objective optical system.

Japanese Unexamined Patent Publication No. 2016-85282 Japanese Patent No. 5930257 Japanese Patent No. 4934233 International Publication No. 2016/157623

In the optical systems of Patent Documents 1, 2, 3, and 4, it is not possible to secure an adjustment stroke (space) for moving the lens to adjust the focus in the optical system for 3D observation. Further, it is difficult to secure a small parallax of about 1 mm in the optical system for 3D observation. Further, it is difficult to miniaturize the optical system for 2D observation.

The present invention has been made in view of the above, and in the objective optical system for 3D observation, when the lens is moved to adjust the focus, an adjustment stroke (space) can be secured, and further, about 1 mm. It is an object of the present invention to provide an objective optical system capable of ensuring a small parallax and reducing the size of the objective optical system for 2D observation.
Another object of the present invention is to provide an endoscope having the above-mentioned objective optical system.

In order to solve the above-mentioned problems and achieve the object, the objective optical system according to at least some embodiments of the present invention is used.
In order from the object side has a first lens of a single lens having a negative refractive power with a concave surface facing the image side, a second lens of a single lens having a negative refractive power with a concave surface facing the object side, a positive refractive power It consists of a third single lens , a brightness aperture, a fourth single lens having positive refractive power, and a fifth lens that is a junction lens having positive refractive power.
It is characterized by satisfying the following conditional expressions (1 ' ) and (2).
2.5 <f45 / f ≤ 4 (1 ' )
| F12 | / f3 <0.18 (2)
here,
f45 is the combined focal length of the 4th lens and the 5th lens.
f is the focal length of the entire objective optical system,
f12 is the combined focal length of the first lens and the second lens.
f3 is the focal length of the third lens,
Is.
Further, the endoscope according to at least some embodiments of the present invention is characterized by having the above-mentioned objective optical system.

In the objective optical system for 3D observation, the present invention can secure an adjustment stroke (space) when the lens is moved to adjust the focus, and further, parallax can be secured, and is used for 2D observation. The objective optical system has the effect of being able to provide an objective optical system that can reduce the size of the optical system.

It is a lens sectional view of the objective optical system which concerns on embodiment. In the objective optical system according to the first embodiment, (a) is a cross-sectional view of the lens in a designed state, and (b) and (c) are cross-sectional views of the lens when the image plane position is changed. (A), (b), (c), and (d) are aberration diagrams showing spherical aberration (SA), astigmatism (AS), distortion (DT), and chromatic aberration of magnification (CC) of Example 1, respectively. Is. (A) is a cross-sectional view of a lens of an objective optical system according to a second embodiment of the present invention. (B), (c), (d), and (e) are aberration diagrams showing spherical aberration (SA), astigmatism (AS), distortion (DT), and chromatic aberration of magnification (CC) of Example 2, respectively. Is. (A) is a cross-sectional view of a lens of an objective optical system according to a third embodiment of the present invention. (B), (c), (d), and (e) are aberration diagrams showing spherical aberration (SA), astigmatism (AS), distortion (DT), and chromatic aberration of magnification (CC) of Example 3, respectively. Is. It is a lens sectional view of the objective optical system for 3D observation which concerns on Example 4 of this invention.

Hereinafter, the objective optical system according to the embodiment will be described in detail with reference to the drawings. The present invention is not limited to this embodiment.

FIG. 1 is a cross-sectional view of a lens of an objective optical system according to an embodiment. This embodiment has a configuration having one optical axis Ax for 2D observation. Further, FIG. 6 is a configuration in which two objective optical systems shown in FIG. 1 are arranged in parallel, and is an objective optical system for 3D observation used as an optical system for the right eye and an optical system for the left eye.

In this embodiment, in order from the object side, the first lens L1 having a negative refractive power with the concave surface facing the image side, the second lens L2 having the negative refractive power with the concave surface facing the object side, and the positive refractive power are applied. The third lens L3, the brightness aperture S, the fourth lens L4 having a positive refractive power, and the fifth lens L5, which is a junction lens having a positive refractive power, are composed of the following conditional expression (1). It is characterized by satisfying (2).
2.5 <f45 / f (1)
| F12 | / f3 <0.18 (2)
here,
f45 is the combined focal length of the fourth lens L4 and the fifth lens L5.
f is the focal length of the entire objective optical system,
f12 is the combined focal length of the first lens L1 and the second lens L2.
f3 is the focal length of the third lens L3,
Is.

Further, the filter F1 which is a parallel flat plate is arranged on the image side of the third lens L3. Further, the filter F2 is adhered to the object side surface of the cover glass CG of the image sensor (not shown).

In this embodiment, the retrofocus optical system is formed by arranging negative, negative, positive, brightness diaphragm, positive, and positive power in order from the object side. Then, a space can be secured before and after the fifth lens L5 (see FIG. 2A).

The effect on the objective optical system for 2D observation will be described. Since a wide space is created between the position of the image plane I and the fifth lens L5, the effect that a prism or the like can be arranged can be obtained.

Moreover, the effect in the objective optical system for 3D observation will be described. Two objective optical systems are arranged in parallel, and the fifth lens L5 is moved to adjust the focus. For example, as will be described later as Example 1, the position of the image plane I can be changed by changing the positions of the fourth lens L4 and the fifth lens L5 by ± 0.26 mm as shown in FIGS. 2 (b) and 2 (c). (Focus position) can be adjusted.

Next, the conditional expression will be described. By setting the lower limit of the conditional expression (1) to 2.5 or more, the focal length of the fourth lens L4 to the fifth lens L5 becomes longer, and the distance to the position of the image plane I can be increased. it can. As a result, a space is secured before and after the fifth lens L5 (see FIG. 2A).

Further, by setting the upper limit value of the conditional expression (2) to less than 0.18, the negative focal length of the first lens L1 to the second lens L2 is shortened. As a result, the following effects (a), (b), and (c) are obtained.
(A) It becomes a strong retrofocus, and the distance to the position of the image plane I represented by the conditional expression (1) can be set farther.
(B) Since the light beam height of the first lens L1 can be reduced, the size of the first lens L1 can also be reduced.
(C) By combining the conditional expression (1) and the conditional expression (2), the power arrangement of the entire objective optical system is optimized, and good optical performance as shown in FIG. 3 can be obtained.

Further, according to the preferred embodiment of the present embodiment, it is desirable to satisfy the following conditional expression (3).
4 <f5 / f (3)
here,
f5 is the focal length of the 5th lens,
Is.

By making the lower limit of the conditional expression (3) larger than 4, the focal length of the fifth lens L5 can be set longer. As a result, deterioration of optical performance due to a position error of the fifth lens L5 can be reduced. For example, in the case of an objective optical system for 3D observation, the influence of the lens position error on the position of the image plane I can be reduced.

Hereinafter, each embodiment will be described.

(Example 1)
The objective optical system according to the first embodiment will be described. FIG. 2A is a cross-sectional view of the lens of the objective optical system in the designed state. FIG. 2B is a cross-sectional view of the lens when the value (air spacing) of d11 on the eleventh surface r11 is changed from 0.437 to 0.177 and the position of the image plane I is changed. FIG. 2C is a cross-sectional view of the lens when the value (air spacing) of d11 on the eleventh surface r11 is changed from 0.437 to 0.697 and the position of the image plane I is changed.

The objective optical system of the first embodiment has a plano-concave first lens L1 having a negative refractive power with a concave surface facing the image side and a meniscus shape having a negative refractive power with the concave surface facing the object side in order from the object side. The second lens L2, the plano-convex third lens L3 having a positive refractive power with the plane facing the image side, the filter F1 which is a parallel flat plate, the brightness aperture S, and the plane facing the object side. A plano-convex fourth lens L4 having a positive refractive power, a fifth lens L5 which is a junction lens having a positive refractive power in which a biconvex positive lens and a negative meniscus lens with a convex surface facing the image side are joined, Has. This embodiment has the same lens configuration as the above-described embodiment.

Further, the object side of the infrared absorption filter F1 is coated with a YAG laser cut, and the image side is coated with an LD laser cut. Further, the filter (cover glass) F2 and the CCD cover glass CG are joined. d16 is an adhesive layer.

3 (a), (b), (c), and (d) show spherical aberration (SA), astigmatism (AS), distortion (DT), and chromatic aberration of magnification (CC) of this embodiment.

Aberration diagrams are shown for each wavelength of 656.27 nm (C line), 587.56 nm (d line), 486.13 nm (F line) and 435.84 nm (g line). In each figure, FNO indicates an F number and IH indicates a maximum image height. Hereinafter, the same applies to the aberration diagram. In each aberration diagram, the horizontal axis represents the amount of aberration. For spherical aberration, astigmatism, and Magnification aberration, the unit of aberration amount is mm. For distortion, the unit of aberration is%. In addition, IH is the image height, the unit is mm, and FNO is the F number.

(Example 2)
FIG. 4A is a cross-sectional view of the lens of the objective optical system according to the second embodiment.

The objective optical system of the second embodiment has a plano-concave first lens L1 having a negative refractive power with a concave surface facing the image side and a meniscus shape having a negative refractive power with the concave surface facing the object side in order from the object side. The second lens L2, the plano-convex third lens L3 having a positive refractive power with the plane facing the image side, the filter F1 which is a parallel flat plate, the brightness aperture S, and the plane facing the object side. A plano-convex fourth lens L4 having a positive refractive power, a fifth lens L5 which is a junction lens having a positive refractive power in which a biconvex positive lens and a negative meniscus lens with a convex surface facing the image side are joined, Has.

This embodiment is an example in which the distance between the fourth lens L4 and the fifth lens L5 is longer than that of the first embodiment. Further, the value (air interval) of d11 on the 11th surface r11 is changed from 0.437 to 0.52. As a result, the value of the conditional expression (1) also increases to 3.15.

The conditional expression (1) is preferably 4 or less. When it becomes 4 or more, the position of the fifth lens L5 becomes too far, and the light ray height in the fifth lens L5 becomes large. This makes miniaturization difficult.

Further, the object side of the infrared absorption filter F1 is coated with a YAG laser cut, and the image side is coated with an LD laser cut. Further, the filter (cover glass) F2 and the CCD cover glass CG are joined. d16 is an adhesive layer.

4 (b), (c), (d), and (e) show spherical aberration (SA), astigmatism (AS), distortion (DT), and chromatic aberration of magnification (CC) of this embodiment.

(Example 3)
FIG. 5A is a cross-sectional view of the lens of the objective optical system according to the third embodiment.

The objective optical system of the third embodiment has a plano-concave first lens L1 having a negative refractive power with a concave surface facing the image side and a meniscus shape having a negative refractive power with the concave surface facing the object side in order from the object side. 2nd lens L2, a meniscus-shaped third lens L3 having a positive refractive power with a convex surface facing the object side, a brightness aperture S, a filter F1 which is a parallel flat plate, and positive refraction with a flat surface facing the object side. A fifth lens having a positive refractive power, which is a combination of a plano-convex fourth lens L4 having a force, a biconvex positive lens, and a meniscus-shaped lens having a negative refractive power with a convex surface facing the image side. It has a lens L5 and.

This embodiment is an example in which the distance between the fourth lens L4 and the fifth lens L5 is shorter than that of the first embodiment. The value (air interval) of d11 on the eleventh surface r11 is changed from 0.437 to 0.29.
As a result, the value of the conditional expression (1) is also as small as 2.8. The conditional expression (1) is preferably 2.7 or more. If it is 2.7 or more, a space near the fifth lens L5 can be secured.

Further, the object side of the infrared absorption filter F1 is coated with a YAG laser cut, and the image side is coated with an LD laser cut. Further, the filter (cover glass) F2 and the CCD cover glass CG are joined. d16 is an adhesive layer.

5 (b), (c), (d), and (e) show spherical aberration (SA), astigmatism (AS), distortion (DT), and chromatic aberration of magnification (CC) of this embodiment.

(Example 4)
FIG. 6 is a cross-sectional view of the lens of the objective optical system for 3D observation according to the fourth embodiment. For example, the objective optical system according to the first embodiment has a configuration in which a right eye optical system having an optical axis Ax1 and a left eye optical system having an optical axis Ax2 are arranged in parallel. The distance between the optical axis Ax1 and the optical axis Ax2 is defined as parallax. In this embodiment, the parallax is 1.1 mm. L11 and L12 are concave surfaces.

Here, the fifth lens L5 performs a so-called D-cut in which a part of the circular lens is linearly cut. The focus adjustment of the objective optical system for 3D observation needs to be performed independently for the left eye optical system and the right eye optical system. In this embodiment, one objective optical system moves the position of the image sensor to adjust the focus, and the other objective optical system moves the fifth lens L5 to adjust the focus. Therefore, in this embodiment, a space is provided in front of and behind the fifth lens L5 for the movement of the fifth lens L5.

That is, this embodiment has all of the following configurations.
(Structure 1) Since the focus is adjusted by moving the fifth lens L5 (positive junction lens) in the optical axis direction, an adjustment stroke is secured.
(Structure 2) A configuration in which parallax can be secured by lowering the height of light rays on a concave surface with the first lens L1.
(Structure 3) A configuration in which the refractive power of the fifth lens L5 (positive junction lens) is reduced to reduce the focus adjustment sensitivity. Preferably, it is desirable to reduce the deterioration of optical performance due to the eccentricity of the first lens L1 to the third lens L3.

The numerical data of each of the above examples is shown below. The symbols are r is the radius of curvature of each lens surface, d is the distance between each lens surface, ne is the refractive index of the e-line of each lens, νd is the Abbe number of each lens, and Fno is the F number. The diaphragm is a brightness diaphragm.

Numerical Example 1
Unit mm

Surface data Surface number rd ne νd
1 ∞ 0.35 1.88815 40.76
2 0.592 0.564 1
3 -1.522 0.46 1.85504 23.78
4 -2.406 0.04 1
5 4.079 0.63 1.85504 23.78
6 ∞ 0.03 1
7 ∞ 0.4 1.49557 75.00
8 ∞ 0.38 1
9 (Aperture) ∞ 0.03 1
10 ∞ 0.42 1.75453 35.33
11 -1.717 0.437 1
12 1.381 0.82 1.69979 55.53
13 -0.907 0.36 1.93429 18.90
14 -4.334 0.38 1
15 ∞ 0.5 1.51825 64.14
16 ∞ 0.01 1.515 64.00
17 ∞ 0.35 1.507 63.26
Image plane ∞

Various data focal length 0.43
Maximum image height 0.429
Angle of view 163.4
Fno 3.77
Object distance 7.25

f12 = -0.60
f3 = 4.77
f45 = 1.25
f5 = 2.17

Numerical Example 2
Unit mm

Surface data Surface number rd ne νd
1 ∞ 0.35 1.88815 40.76
2 0.592 0.56 1
3 -1.5461 0.66 1.85504 23.78
4 -2.9761 0.043 1
5 3.4898 0.5353 1.85504 23.78
6 ∞ 0.03 1
7 ∞ 0.4 1.49557 75.00
8 ∞ 0.38 1
9 (Aperture) ∞ 0.03 1
10 ∞ 0.4771 1.75453 35.33
11 -1.8688 0.52 1
12 1.383 0.8779 1.69979 55.53
13 -0.8976 0.5955 1.93429 18.90
14 -4.0999 0.27 1
15 ∞ 0.5 1.51825 64.14
16 ∞ 0.01 1.515 64.00
17 ∞ 0.35 1.507 63.26
Image plane ∞

Various data focal length 0.43
Maximum image height 0.429
Angle of view 163
Fno 3.88
Object distance 7.25

f12 = -0.58
f3 = 4.08
f45 = 1.35
f5 = 2.18

Numerical Example 3
Unit mm

Surface data Surface number rd ne νd
1 ∞ 0.35 1.88815 40.76
2 0.592 0.54 1
3 -1.9637 0.76 1.85504 23.78
4-4.8559 0.0244 1
5 1.6123 0.3 1.85504 23.78
6 2.653 0.39 1
7 (Aperture) ∞ 0.03 1
8 ∞ 0.4 1.49557 75.00
9 ∞ 0.03 1
10 ∞ 0.48 1.75453 35.33
11 -1.6741 0.29 1
12 1.387 1.0241 1.69979 55.53
13 -0.896 0.446 1.93429 18.90
14 -4.6984 0.275 1
15 ∞ 0.5 1.51825 64.14
16 ∞ 0.01 1.515 64.00
17 ∞ 0.35 1.507 63.26
Image plane ∞

Various data focal length 0.43
Maximum image height 0.429
Angle of view 160
Fno 3.784
Object distance 7.25

f12 = -0.55
f3 = 4.24
f45 = 1.20
f5 = 2.24

The values corresponding to the conditional expressions of each embodiment are shown below.

Conditional expression Example 1 Example 2 Example 3
(1) f45 / f 2.91 3.15 2.80
(2) | f12 | / f3 0.13 0.14 0.13
(3) f5 / f 5.05 5.09 5.22

The above-mentioned objective optical system may satisfy a plurality of configurations at the same time. This is preferable in order to obtain a good objective optical system. Moreover, the combination of preferable configurations is arbitrary. Further, for each conditional expression, only the upper limit value or the lower limit value of the numerical range of the more limited conditional expression may be limited.

Although various embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and the embodiments are configured by appropriately combining the configurations of these embodiments without departing from the spirit of the present invention. The form is also within the scope of the present invention.

As described above, in the objective optical system for 3D observation, the present invention can secure an adjustment stroke (space) when the lens is moved to adjust the focus, and further, parallax can be secured. The objective optical system for 2D observation is useful for an objective optical system that can be miniaturized.

L1 to L5 Lens Ax, Ax1, Ax2 Optical Axis S Brightness Aperture F1 Filter (Infrared Absorption Filter)
F2 filter (cover glass)
CG CCD cover glass L11, L12 Concave surface

Claims (5)

From the object side , the first single lens having a negative refractive power with the concave surface facing the image side, and
A second single lens with a negative refractive power with a concave surface facing the object side,
A third single lens with positive refractive power and
Brightness aperture and
The fourth lens, which is a single lens with positive refractive power,
It consists of a fifth lens, which is a junction lens with positive refractive power.
An objective optical system characterized by satisfying the following conditional expressions (1 ' ) and (2).
2.5 <f45 / f ≤ 4 (1 ' )
| F12 | / f3 <0.18 (2)
here,
f45 is the combined focal length of the fourth lens and the fifth lens.
f is the focal length of the entire objective optical system,
f12 is the combined focal length of the first lens and the second lens.
f3 is the focal length of the third lens,
Is. The objective optical system according to claim 1, wherein the objective optical system satisfies the following conditional expression (3).
4 <f5 / f (3)
here,
f5 is the focal length of the fifth lens,
Is. The objective optical system according to claim 1, wherein the objective optical system satisfies the following conditional expression (1 ").
2.5 <f45 / f≤3.15 (1 ") The objective optical system according to claim 1, wherein the objective optical system satisfies the following conditional expression (3').
4 <f5 / f≤5.22 (3') An endoscope having the objective optical system according to any one of claims 1 to 4.

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