WO2021049000A1 - Endoscopic objective optical system, imaging device, and endoscope - Google Patents

Abstract

An endoscopic objective optical system (1) is provided with, in order from an object side to an image side, a first lens group (G1) having a negative refractive power and a second lens group (G2) including a positive lens (3) having a positive refractive power. The first lens group (G1) includes a simple lens (2) that has a concave surface (2a) on the image side and has a negative refractive power. The image-side surface of the simple lens (2) is provided with a reflection part (6) for reflecting light incident from the image side. The reflection part (6) is arranged radially outside of the optical path of the luminous flux that forms the image (I) of the object.

Description

Endoscope objective optical system, imaging device and endoscope

The present invention relates to an endoscope objective optical system, an imaging device, and an endoscope.

Conventionally, an endoscopic objective optical system including a first lens group having a negative refractive power and a second lens group having a positive refractive power is known in order to secure a wide angle of view (for example,). See Patent Document 1.). The eccentricity between the optical axis of the first lens group and the optical axis of the second lens group is a large source of coma aberration. Patent Document 1 proposes a method for manufacturing an endoscopic objective optical system capable of simultaneously suppressing coma aberration and image plane tilt. Specifically, in Patent Document 1, the first lens group and the second lens group are fixed to each other in advance, and then the units of the first lens group and the second lens group are optical axes with respect to the units of other lenses. The image quality is adjusted so that the image plane tilt is reduced by shifting in the direction orthogonal to.

International Publication No. 2018/186100

In recent years, 4K or 8K high pixel image sensors have also been used in endoscopes. When a high-pixel image sensor is used, the deterioration of the image, which was not a problem when the conventional image sensor is used, appears remarkably in the image, so that high optics capable of forming a higher-definition object image can be formed. A performance endoscopic optical system is desired.
In order to achieve high optical performance, it is necessary to adjust the shift of the first lens group after adjusting the angle of the optical axis of the first lens group with respect to the optical axis of the second lens group. However, the manufacturing method of Patent Document 1 does not solve this problem. If an error in the angle of the optical axis of the first lens group with respect to the optical axis of the second lens group remains, various aberrations such as coma and astigmatism and image plane tilt cannot be sufficiently reduced. Therefore, in order to achieve high optical performance, it is necessary to accurately adjust the angle of the optical axis of the first lens group with respect to the optical axis of the second lens group.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an endoscope objective optical system, an imaging device, and an endoscope having high optical performance in which aberration and image plane tilt are suppressed. And.

In order to achieve the above object, the present invention provides the following means.
One aspect of the present invention includes a first lens group having a negative refractive force and a second lens group including a positive lens having a positive refractive force in this order from the object side to the image side. One lens group includes a single lens having a concave surface on the image side and having a negative refractive force, and a reflecting portion for reflecting light incident from the image side is provided on the image side surface of the single lens. , The reflecting portion is an endoscopic objective optical system arranged outside the radial direction of the optical path of a light beam forming an image of an object.

Light from an object is collected by the first lens group and collected by the positive lens of the second lens group to form an image. In order to obtain an image in which aberration and image plane tilt are suppressed, it is necessary to accurately adjust the angle in addition to the position of the optical axis of the first lens group with respect to the optical axis of the second lens group. According to this aspect, the angle of the optical axis of the first lens group with respect to the optical axis of the second lens group can be accurately adjusted by utilizing the reflection portion provided on the single lens of the first lens group. Therefore, it is possible to achieve high optical performance in which aberration and image plane tilt are suppressed.

Specifically, light is incident on the second lens group and the first lens group from the image side, and the reflected light from the reflecting portion is measured on the image side of the second lens group. The measurement position of the reflected light changes in response to a change in the angle of the optical axis of the first lens group with respect to the optical axis of the second lens group. Therefore, the angle of the optical axis of the first lens group can be accurately adjusted based on the measurement position of the reflected light.

In the above aspect, it is preferable that the light reflectance of the reflecting portion is 20% or more.
According to this configuration, the intensity of the reflected light can be ensured and the measurement accuracy of the reflected light can be improved.
In the above embodiment, at least a part of the reflecting portion on the object side may be provided with a light-shielding portion that shields light incident from the object side.
According to this configuration, the light shielding portion prevents the light from entering the reflecting portion from the object. This makes it possible to prevent the generation of unnecessary light due to the light incident on the reflecting portion when observing the object. In order to reliably prevent the generation of unnecessary light, the light transmittance of the light-shielding portion is preferably 5% or less.

In the above aspect, the single lens may have a notch on the object side of the reflecting portion.
According to this configuration, the incident of light from the object to the reflecting portion is prevented by the notch. This makes it possible to prevent the generation of unnecessary light due to the light incident on the reflecting portion when observing the object.

In the above aspect, the second lens group may have at least one prism.
According to this configuration, the optical axis is deflected by the prism of the second lens group. Such a configuration is suitable for a perspective type or side view type endoscope.

Another aspect of the present invention is an imaging device including an imaging element and an objective optical system, wherein the objective optical system is a first lens group having a negative refractive force in order from the object side to the image side. The first lens group includes a single lens having a concave surface on the image side and having a negative refractive power, and the single lens includes a second lens group including a positive lens having a positive refractive power. In an imaging device, a reflecting portion for reflecting light incident from the image side is provided on the surface on the image side, and the reflecting portion is arranged on the radial outside of the optical path of the light beam forming the image of the object. is there.

Another aspect of the present invention is an endoscope including an image pickup element and an objective optical system, and the first lens group in which the objective optical system has a negative refractive force in order from the object side to the image side. And a second lens group including a positive lens having a positive refractive power, and the first lens group includes a single lens having a concave surface on the image side and having a negative refractive power. A reflecting portion that reflects light incident from the image side is provided on the surface on the image side of the lens, and the reflecting portion is arranged on the radial outside of the optical path of the light beam forming the image of the object. It is a mirror.

According to the present invention, it is possible to achieve high optical performance in which aberration and image plane tilt are suppressed.

It is an overall block diagram of the endoscope objective optical system which concerns on one Embodiment of this invention. It is sectional drawing of the negative lens of the 1st lens group. It is a rear view of the negative lens of FIG. 2A seen from the image side, and is the figure which shows an example of the arrangement of the reflecting part. It is a figure explaining the method of adjusting the angle of the optical axis of the 1st lens group. It is sectional drawing of the negative lens provided with the light-shielding part. It is sectional drawing of the negative lens provided with a notch. It is the whole block diagram of the modification of the endoscope objective optical system. It is an overall block diagram of another modification of an endoscope objective optical system. It is a figure explaining the method of adjusting the angle of the optical axis of the 1st lens group. It is a front view of the brightness diaphragm of the endoscope objective optical system of FIG.

Hereinafter, the endoscope objective optical system 1, the image pickup apparatus, and the endoscope according to the embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a rigid mirror (endoscope) 30 including an endoscope objective optical system 1 and a relay optical system 20 as an application example of the endoscope objective optical system 1 according to the present embodiment. .. As shown in FIG. 1, the endoscopic objective optical system 1 includes a first lens group G1 having a negative refractive power and a positive lens 3 having a positive refractive power in this order from the object side to the image side. It is composed of a second lens group G2 including the third lens group G3 and a third lens group G3. In the reference drawing, the left side is the object side and the right side is the image side. The endoscope objective optical system 1 is a direct view type, and the optical axes of the three lens groups G1, G2, and G3 are arranged on the same straight line.

The first lens group G1 is composed of a negative lens (single lens) 2 having a negative refractive power. As shown in FIGS. 2A and 2B, the negative lens 2 is composed of a single concave lens having a concave surface 2a on the image side, and is a concave meniscus lens in the reference drawing. The negative lens 2 has an annular flat surface 2b that surrounds the concave surface 2a and is perpendicular to the optical axis of the negative lens 2 on the image side.
The second lens group G2 is composed of a positive lens 3 having a positive refractive power. The positive lens 3 is composed of a single rod lens, has a flat surface perpendicular to the optical axis of the positive lens 3 on the object side, and has a convex surface on the image side.
The third lens group G3 is composed of, for example, two sets of junction lenses 4 and 5.

The endoscope objective optical system 1 and the relay optical system 20 are fixed in the cylindrical lens frames 11 and 12 as shown in FIG. Specifically, the second lens group G2 and a part of the lenses 4 of the third lens group G3 are fixed in the first lens frame 11, and the remaining lens 5 of the third lens group G3 and the relay optical system 20. Is fixed in the second lens frame 12. The first lens group G1 is fixed to the flat surface of the second lens group G2 on the object side of the positive lens 3.
Light from an object is collected by a first lens group G1 having a negative refractive power, collected by a second lens group G2 having a positive refractive power, passes through a third lens group G3, and forms an image I. To do. The image I is relayed to an image sensor (not shown) by the relay optical system 20 and photographed by the image sensor. The endoscope objective optical system 1 may be provided as an image pickup apparatus including the endoscope objective optical system 1, the relay optical system 20, and the image pickup element.

The endoscope objective optical system 1 further includes a reflecting unit 6 provided on the negative lens 2.
As shown in FIG. 2A, the reflecting portion 6 is provided on the flat surface 2b and reflects the light incident on the reflecting portion 6 from the image side. The reflecting portion 6 is, for example, a metal film, and the light reflectance of the reflecting portion 6 is preferably 20% or more. As shown in FIG. 2B, for example, the reflecting portion 6 is provided at only one place on the flat surface 2b or at a plurality of places, or is provided over the entire circumference of the flat surface 2b.

Image I is formed by the luminous flux that has passed through the concave surface 2a. Since the flat surface 2b is arranged on the radial outside of the concave surface 2a, the reflecting portion 6 is arranged on the radial outside of the optical path of the light flux forming the image I. The radial direction is a direction orthogonal to the optical axis. That is, the reflecting unit 6 is arranged at a position that does not interfere with the light traveling from the object to the image plane when observing the object, and the reflecting unit 6 is prevented from affecting the image I.

Next, a method of manufacturing the endoscope objective optical system 1 will be described.
First, the second lens group G2 and a part of the lenses 4 of the third lens group G3 are inserted into the first lens frame 11 and fixed to the first lens frame 11. Further, the other lens 5 of the third lens group G3 and the relay optical system 20 are inserted into the second lens frame 12 and fixed to the second lens frame 12.

Next, the position and angle of the optical axis of the first lens group G1 with respect to the optical axis of the second lens group G2 are adjusted. Specifically, by arranging the negative lens 2 on the flat surface of the positive lens 3 and shifting the negative lens 2 in the radial direction, the light of the first lens group G1 with respect to the optical axis of the second lens group G2. Align the shaft radially. Further, the angle of the optical axis of the first lens group G1 with respect to the optical axis of the second lens group G2 is adjusted by using the reflection unit 6 provided on the negative lens 2.

FIG. 3 shows a method of adjusting the angle of the optical axis of the first lens group G1. As shown in FIG. 3, in adjusting the angle of the optical axis of the first lens group G1, the incident light L is directed from the image side of the second lens group G2 toward the reflecting portion 6 of the negative lens 2 toward the second lens group. It is incident on G2. The incident light L is convergent light that is incident on the reflecting portion 6 from the second lens group G2 as parallel light parallel to the optical axis of the second lens group G2. In the example of FIG. 3, two incident lights L corresponding to the two reflecting portions 6 are incident on the endoscope objective optical system 1 via the relay optical system 20.

When the optical axis of the negative lens 2 is parallel to the optical axis of the second lens group G2 and the flat surface 2b is perpendicular to the optical axis of the second lens group G2, the incident light L is vertically incident on the reflecting portion 6. The reflected light from the reflecting unit 6 returns along the path of the incident light L. Therefore, on the image side of the endoscope objective optical system 1, the reflected light is measured at the same position as the incident light L. On the other hand, when the optical axis of the negative lens 2 is tilted with respect to the optical axis of the second lens group G2, the reflected light from the reflecting portion 6 returns along a path different from the path of the incident light L. Therefore, on the image side of the endoscope objective optical system 1, the reflected light is measured at a position different from the incident light L.

Next, the position of the reflected light is measured on the image side of the second lens group G2 (in the example of FIG. 3, the side opposite to the object of the relay optical system 20), and the position of the reflected light coincides with the position of the incident light L. As such, the angle of the optical axis of the negative lens 2 with respect to the optical axis of the second lens group G2 is adjusted. At this time, the position of the reflected light changes in response to a change in the angle of the optical axis of the negative lens 2. Therefore, based on the position of the reflected light, the angle of the optical axis of the negative lens 2 can be accurately adjusted so that the optical axis of the negative lens 2 is parallel to the optical axis of the second lens group G2.
After adjusting the position and angle, the negative lens 2 is fixed to the positive lens 3 with an adhesive or the like.
For the measurement of the incident light L incident on the endoscope objective optical system 1 and the reflected light, for example, an autocollimator or an autocollimator combined with a lens system such that the reflecting portion 6 produces parallel light is used. Will be done.

Next, the first lens frame 11 and the second lens frame 12 are mutually positioned in the optical axis direction, and the first unit composed of the lenses 2, 3 and 4 and the first lens frame 11 is attached to the lens 5 and the relay optical system. By shifting in the radial direction with respect to the second unit including the 20 and the second lens frame 12, the first unit is positioned in the radial direction with respect to the second unit so that the image plane tilt is reduced. Then, the first lens frame 11 and the second lens frame 12 are fixed to each other with an adhesive or the like.

As described above, in the manufacture of the endoscope objective optical system 1, the position of the optical axis of the first lens group G1 with respect to the optical axis of the second lens group G2 is adjusted prior to the correction of the image plane tilt due to the shift of the first unit. By doing so, the eccentricity between the optical axis of the first lens group G1 and the optical axis of the second lens group G2 can be suppressed to be small. Further, when adjusting the position of the optical axis of the first lens group G1, the angle of the optical axis of the first lens group G1 with respect to the optical axis of the second lens group G2 is also accurately adjusted by using the reflecting portion 6 of the negative lens 2. It is possible to suppress the tilt of the optical axis of the first lens group G1 with respect to the optical axis of the second lens group G2, which causes various errors such as coma aberration and non-point aberration and image plane tilt. As a result, it is possible to manufacture the endoscope objective optical system 1 having high optical performance in which aberration and image plane tilt are suppressed.

As shown in FIG. 4, it is preferable that the negative lens 2 is further provided with a light-shielding portion 7 that covers the object side of the reflecting portion 6 and shields the light from the object side.
The light-shielding portion 7 is arranged on the object side of at least a part of the reflecting portion 6, and is preferably arranged on the object side of the entire reflecting portion 6. The light-shielding portion 7 is, for example, a surface coated on the flat surface 2b and having a black paint, a filter for absorbing light, or a surface having roughness interposed between the flat surface 2b and the reflecting portion 6. The light transmittance of the light-shielding portion 7 is preferably 5% or less.

When the light-shielding portion 7 is not provided, a part of the light incident on the negative lens 2 from the object is incident on the reflecting portion 6. The light incident on the reflecting unit 6 from the object may affect the image I as unnecessary light as a result of reflection by the reflecting unit 6 and refraction by the negative lens 2. By providing the light-shielding portion 7 on the negative lens 2, it is possible to prevent the generation of unnecessary light when observing an object.

As shown in FIG. 5, a notch 8 may be provided in the negative lens 2 instead of the light-shielding portion 7. The notch 8 is provided on the object side of the reflecting portion 6. The notch 8 may have an arbitrary shape as long as it can prevent light from entering the reflecting portion 6 from the object. For example, the notch 8 may be formed on the surface of the negative lens 2 on the object side over the entire circumference, or may be formed only in the region of the reflecting portion 6 on the object side.
The light-shielding portion 7 and the notch 8 are formed on the radial side of the optical path of the light flux forming the image I, similarly to the reflecting portion 6, so as not to affect the image I of the object.

In the above embodiment, the second lens group G2 may have at least one prism.
FIG. 6 shows an endoscope objective optical system 101 for a perspective type rigid mirror (endoscope) 40 using two prisms 91 and 92. The two prisms 91 and 92 are arranged between the negative lens 2 and the positive lens 3, and by reflecting the incident light beam on the prism surface, the optical axis of the negative lens 2 is set with respect to the optical axis of the second lens group G2. And bias. In the modified example of FIG. 6, the negative lens 2 may be provided with a light-shielding portion 7 instead of the notch 8.

In the conventional manufacturing method of the perspective type endoscope objective optical system, the negative lens 2 is arranged on the incident surface 91a of the prism 91 on the object side, and the negative lens 2 is shifted along the incident surface 91a to obtain the second negative lens 2. The optical axis of the negative lens 2 was aligned with the optical axis of the lens group G2.
Here, in order to form the incident surface 91a perpendicular to the optical axis of the prism 91, high-precision processing is required. When the incident surface 91a is deviated from the direction perpendicular to the optical axis, the optical axis of the negative lens 2 is tilted with respect to the optical axis of the second lens group G2. It is difficult to control the trouble. In order to suppress aberration and image plane tilt, it is necessary to suppress the deviation of the incident surface 91a from the vertical, for example, to 5 minutes or less.

According to the endoscope objective optical system 101 of FIG. 6, the second lens is based on the reflected light from the reflecting portion 6 provided on the negative lens 2, regardless of the deviation of the incident surface 91a from the vertical with respect to the optical axis. The angle of the optical axis of the negative lens 2 with respect to the optical axis of the group G2 can be adjusted accurately. That is, the inclination of the optical axis of the negative lens 2 due to the manufacturing variation of the prism 91 can be easily corrected. Therefore, high-precision processing of the prisms 91 and 92 and complicated adjustment when joining the negative lens 2 to the prism 91 are not required, and an endoscope objective with high optical performance in which aberration and image plane tilt are suppressed. The optical system 101 can be easily manufactured.

In the above embodiment, the endoscope objective optical system 1 is applied to the rigid mirror 30, but instead, it may be applied to an endoscope other than the rigid mirror. The lens configuration of the endoscope objective optical system 1 may be changed according to the application of the endoscope objective optical system 1.

FIG. 7 shows an example of an endoscope objective optical system 102 for a flexible endoscope and an imaging device 50 including the endoscopic objective optical system 102. The image pickup device 50 includes an endoscope objective optical system 102 and an image pickup device 14. The endoscope objective optical system 102 includes a first lens group G1 composed of a negative lens 2, a second lens group G2 composed of a positive lens 3, and a third lens group composed of a set of junction lenses. It is composed of G3 and. Reference numeral 13 is a parallel flat plate. In the modified example of FIG. 7, the negative lens 2 may be provided with a notch 8 instead of the light-shielding portion 7. The relay optical system 20 is not arranged between the endoscope objective optical system 102 and the image pickup element 14, and the endoscope objective optical system 102 forms an image on the image pickup surface of the image pickup element 14.

When the endoscope objective optical system 102 is not combined with the relay optical system 20, the endoscope objective optical system 102 is provided with a brightness diaphragm 10. As shown in FIG. 8, the region corresponding to the reflecting portion 6 of the brightness aperture 10 is shown in FIG. 9 so that the light from the image side reaches the reflecting portion 6 when the optical axis of the negative lens 2 is adjusted. As described above, the window 10a through which the incident light L and the reflected light pass is provided.

In the above embodiment, the first lens group G1 and the second lens group G2 may be composed of a plurality of lenses, respectively. Further, the endoscope objective optical systems 1, 101 and 102 may be composed of only the first lens group G1 and the second lens group G2, or may be composed of four or more lens groups. Further, the endoscope objective optical systems 1, 101 and 102 may further include any optical element having no refractive power such as an optical filter.

1,101,102 Endoscope objective optical system G1 1st lens group G2 2nd lens group G3 3rd lens group 2 Negative lens (single lens)
2a Concave surface 2b Flat surface 3 Positive lens 4, 5 Joint lens 6 Reflection part 7 Light-shielding part 8 Notch 91,92 Prism 10 Brightness diaphragm 10a Window 14 Image sensor 20 Relay optical system 30,40 Rigid mirror (endoscope)
50 Imaging device

Claims (18)

A first lens group having a negative refractive power and a second lens group including a positive lens having a positive refractive power are provided in this order from the object side to the image side.
The first lens group includes a single lens having a concave surface on the image side and having a negative refractive power.
A reflecting portion for reflecting light incident from the image side is provided on the image side surface of the single lens.
An endoscopic objective optical system in which the reflecting portion is arranged radially outside the optical path of a luminous flux forming an image of an object. The endoscope objective optical system according to claim 1, wherein the light reflectance of the reflecting portion is 20% or more. The endoscopic objective optical system according to claim 1, wherein at least a part of the reflecting portion on the object side is provided with a light-shielding portion that shields light incident from the object side. The endoscope objective optical system according to claim 3, wherein the light transmittance of the light-shielding portion is 5% or less. The endoscope objective optical system according to claim 1, wherein the single lens has a notch on the object side of the reflecting portion. The endoscopic objective optical system according to claim 1, wherein the second lens group has at least one prism. An image pickup device including an image sensor and an objective optical system.
The objective optical system includes, in order from the object side to the image side, a first lens group having a negative refractive power and a second lens group including a positive lens having a positive refractive power.
The first lens group includes a single lens having a concave surface on the image side and having a negative refractive power.
A reflecting portion for reflecting light incident from the image side is provided on the image side surface of the single lens.
An imaging device in which the reflecting portion is arranged radially outside the optical path of a luminous flux forming an image of an object. The imaging device according to claim 7, wherein the light reflectance of the reflecting unit is 20% or more. The imaging device according to claim 7, wherein at least a part of the reflecting portion on the object side is provided with a light-shielding portion that shields light incident from the object side. The imaging device according to claim 9, wherein the light transmittance of the light-shielding portion is 5% or less. The imaging device according to claim 7, wherein the single lens has a notch on the object side of the reflecting portion. The imaging device according to claim 7, wherein the second lens group has at least one prism. An endoscope including an image sensor and an objective optical system.
The objective optical system includes, in order from the object side to the image side, a first lens group having a negative refractive power and a second lens group including a positive lens having a positive refractive power.
The first lens group includes a single lens having a concave surface on the image side and having a negative refractive power.
A reflecting portion for reflecting light incident from the image side is provided on the image side surface of the single lens.
An endoscope in which the reflecting portion is arranged radially outside the optical path of a luminous flux forming an image of an object. The endoscope according to claim 13, wherein the light reflectance of the reflecting portion is 20% or more. The endoscope according to claim 13, wherein at least a part of the reflecting portion on the object side is provided with a light-shielding portion that shields light incident from the object side. The endoscope according to claim 15, wherein the light transmittance of the light-shielding portion is 5% or less. The endoscope according to claim 13, wherein the single lens has a notch on the object side of the reflecting portion. The endoscope according to claim 13, wherein the second lens group has at least one prism.

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