Optical path deflecting prism for endoscope, oblique-viewing endoscope optical system having the same and endoscope

An optical path deflecting prism for endoscope which is used for observing an object in an oblique direction, includes a first prism and a second prism, and the first prism and the second prism are cemented. The first prism has a first polished surface and a second polished surface. The first reflecting surface is a mirror surface having a mirror coating applied to a polished surface of a flat plate, and is fixed by gluing to the fifth polished surface of the second prism upon adjusting an angle so as to correct an optical-axis shift which occurs due to a manufacturing error of the first prism and the second prism.

BACKGROUND

Technical Field

The present disclosure relates to an optical path deflecting prism for endoscope, an oblique-viewing endoscope optical system having the same and an endoscope.

Description of the Related Art

As for endoscopes for observing various parts inside a body cavity, oblique-viewing endoscopes having an optical path deflecting prism group for directing a visual-field direction in a predetermined direction have been proposed in Japanese Patent Application Laid-open Publication No. Hei 09-123411 and U.S. Pat. No. 4,138,192 Specification for example.

Moreover, a visual-field direction changing optical system has been proposed in Japanese Patent Application Laid-open Publication No. Hei 09-288240.

SUMMARY

An optical path deflecting prism for endoscope according to at least some embodiments of the present disclosure is an optical path deflecting prism for endoscope which is used for observing an object in an oblique direction.

The optical path deflecting prism for endoscope includesa first prism, anda second prism, whereinthe first prism and the second prism are cemented,the first prism has a first polished surface and a second polished surface,the first polished surface is perpendicular to an oblique direction and has a first light-beam incident surface for light incident on the optical path deflecting prism for endoscope,

the second polished surface is disposed at an angle with respect to the first polished surface, and is a cemented surface with the second prism,the second prism has a third polished surface, a fourth polished surface, and a fifth polished surface,the third polished surface is a cemented surface with the first prism,the fourth polished surface is perpendicular to an optical axis of a lens group disposed on an emergence side of the optical path deflecting prism for endoscope, and is a last light-beam emergence surface for light emerged from the optical path deflecting prism for endoscope,the fifth polished surface is disposed at an angle with respect to the third polished surface,a first reflecting surface reflects first time a light beam incident on the optical path deflecting prism for endoscope, and exists on the fifth polished surface of the second prism,a second reflecting surface reflects second time a light beam incident on the optical path deflecting prism for endoscope, and exists on any one of the second polished surface of the first prism and the third polished surface of the second prism,the first reflecting surface is a mirror surface having a mirror coating applied to a polished surface of a flat plate, andthe first reflecting surface is fixed by gluing to the fifth polished surface of the second prism upon adjusting an angle so as to correct an optical-axis shift which occurs due to a manufacturing error of the first prism and the second prism.

Moreover, an oblique-viewing endoscope optical system according to at least some embodiments of the present disclosure includes the abovementioned optical path deflecting prism for endoscope, and an optical system which is disposed on an emergence side of the optical path deflecting prism for endoscope.

Furthermore, an endoscope according to at least some embodiments of the present disclosure includes the abovementioned oblique-viewing endoscope optical system.

DETAILED DESCRIPTION

Reasons for and effects of adopting such arrangements for an optical path deflecting prism for endoscope according to the present embodiment, an oblique-viewing endoscope optical system having the optical path deflecting prism for endoscope, and an endoscope will be described below by using the accompanying diagrams. However, the present invention is not restricted to the embodiments described below.

First Embodiment

FIG.1Ais a perspective view of a first prism PR1in an optical path deflecting prism for endoscope10according to a first embodiment.FIG.1Bis a perspective view of a second prism PR2in the optical path deflecting prism for endoscope10according to the first embodiment.FIG.1Cis a cross-sectional view of the optical path deflecting prism for endoscope10according to the first embodiment.

The optical path deflecting prism for endoscope10according to the first embodiment is used for observation of an object (not shown in the diagram) in an oblique direction. The optical path deflecting prism for endoscope10is formed by cementing the first prism PR1and the second prism PR2. The first prism PR1has a first polished surface11awhich is a first light-beam incident surface for light incident on the optical path deflecting prism for endoscope10, perpendicular to an oblique direction AX1(FIG.2), and a second polished surface lib which is disposed at an angle with respect to the first polished surface11a, and is a cemented surface with the second prism PR2. The second prism PR2has a third polished surface11cwhich is a cemented surface with the first prism PR1. The second prism PR2has a fourth polished surface11dwhich is perpendicular to an optical axis AX2of a lens group100(FIG.2) disposed on an emergence side of the optical path deflecting prism for endoscope10, and is a last light-beam emergence surface for light emerged from the optical path deflecting prism for endoscope10. The second prism PR2has a fifth polished surface11ewhich is disposed at an angle with respect to the third polished surface11c. A first reflecting surface RF1at which a light beam incident on the optical path deflecting prism for endoscope10is reflected first time, exists on the fifth polished surface11eof the second prism PR2. A second reflecting surface RF2at which a light beam incident on the optical path deflecting prism for endoscope10is reflected second time, exists on any one of the second polished surface lib of the first prism PR1and the third polished surface11cof the second prism PR2. The following conditional expressions (1) and (2) are satisfied,
14.5≤A(°)≤23  (1)
62≤B(°)≤66  (2)

A denotes a first angle made by the first reflecting surface RF1and the second reflecting surface RF2with each other (FIG.2), and

B denotes a second angle made by a normal direction N of the second reflecting surface RF2and a direction of the optical axis AX2of the lens group100disposed on an emergence side of a light beam of the optical path deflecting prism for endoscope10(FIG.2).

A surface S1of the first prism PR1shown inFIG.1Aand a surface S2of the second prism PR2shown inFIG.1Bare cemented. Accordingly, the optical path deflecting prism for endoscope10shown inFIG.1Cis formed.

FIG.2is a cross-sectional view of a lens arrangement in an oblique-viewing endoscope optical system200having the optical path deflecting prism for endoscope10. A lens L0is cemented to a surface of incidence of a light beam on the optical path deflecting prism for endoscope10. An image of an object in an oblique direction (direction of the optical axis AX1) is formed on an image pickup surface of an image sensor IMG disposed on an emergence (image plane) side of the oblique-viewing endoscope optical system200.

Moreover, it is desirable that the present embodiment satisfies conditional expression (1). Conditional expression (1) regulates an appropriate range of the first angle A.

When conditional expression (1) is satisfied, in a case in which the first angle A=15° (FIG.3B) for example, it is possible to pass a thick light beam of an endoscope optical system with a large NA (a large numerical aperture, NA) through the optical path deflecting prism for endoscope10without an occurrence of vignetting.

When a value falls below a lower limit value of conditional expression (1), in a case in which the first angle A=12° (FIG.3B) for example, or more specifically, when the first angle A made by the first reflecting surface RF1and the second reflecting surface RF2is adjusted to 12° on a premise of not changing a path length in glass of the optical path deflecting prism for endoscope10and be constant as it has been, an optical axis transmitted through the first polished surface11ais drawn excessively toward an edge portion. Consequently, vignetting of a light ray occurs in the optical path deflecting prism for endoscope10.

When an upper limit value of conditional expression (1) is exceeded, in a case in which the first angle A=25° (FIG.3C) for example, or more specifically, when the first angle A made by the first reflecting surface RF1and the second reflecting surface RF2is adjusted to 25° on a premise of not changing the path length in glass of the optical path deflecting prism for endoscope10, a distance between a point through which the optical axis passes through the third polished surface11cand a point at which the optical axis is reflected at the third polished surface11cbecomes excessively close. Consequently, in the optical path deflecting prism for endoscope10, overlapping of light beams occurs and as a result, the vignetting of the light ray occurs.

Moreover, it is desirable that the present embodiment satisfies conditional expression (2). Conditional expression (2) regulates an appropriate range of the second angle B.

When conditional expression (2) is satisfied, in a case in which the second angle B=65° for example (FIG.4B), it is possible to pass a thick light beam of the endoscope optical system with a large NA through the optical path deflecting prism for endoscope10without an occurrence of vignetting.

When a value falls below a lower limit value of conditional expression (2), in a case in which the second angle B=60° for example (FIG.4A), or more specifically, when the second angle B made by the normal N direction of the second reflecting surface RF2and the direction of the optical axis AX2of the lens group100disposed on the emergence side of a light ray of the optical-axis deflecting prism for endoscope10(FIG.2) is adjusted to 60° on a premise of not changing a path length in glass of the optical path deflecting prism for endoscope10, a distance between a point through which the optical axis passes through the third polished surface11cand a point at which the optical axis is reflected at the third polished surface11cbecomes excessively close. In the optical path deflecting prism for endoscope10, as a result of an occurrence of overlapping of light beams, the vignetting of the light ray occurs.

When an upper limit value of conditional expression (2) is exceeded, in a case in which the second angle B=70° for example (FIG.4C), or more specifically, when the second angle B made by the normal N direction of the second reflecting surface RF2and the direction of the optical axis AX2of the lens group disposed on the emergence side of a light ray of the optical path deflecting prism10for endoscope is adjusted to 70° on a premise of not changing the path length in glass of the optical path deflecting prism for endoscope10, an optical axis transmitted through the first polished surface11ais drawn excessively toward the edge portion. Consequently, vignetting of a light ray occurs in the optical path deflecting prism for endoscope10.

Second Embodiment

FIG.5Ais a perspective view of a first prism in an optical path deflecting prism for endoscope20according to a second embodiment.FIG.5Bis a perspective view of a second prism in the optical path deflecting prism for endoscope20according to the second embodiment.FIG.5Cis a cross-sectional view of the optical path deflecting prism for endoscope20according to the second embodiment. Same reference numerals are assigned to components that are same as in the first embodiment, and repetitive description thereof is omitted.

Moreover, in the optical path deflecting prism for endoscope20according to the present embodiment, it is desirable that the first reflecting surface RF1is a mirror surface having a mirror coating applied to a polished surface of a plane parallel plate PP, and is fixed by gluing on the fifth polished surface11eof the second prism PR2upon adjusting an angle so as to correct an optical-axis shift which occurs due to a manufacturing error of the first prism PR1and the second prism PR2.

As shown inFIG.5B, a surface S3of the second prism PR2and a surface S4of the plane parallel plate PP are cemented. The first reflecting surface RF1is formed on a cemented-side surface of the plane parallel plate PP.

As shown inFIG.5C, the first reflecting surface RF1formed on the plane parallel plate PP is cemented to the fifth polished surface11eafter having adjusted the angle to cancel the manufacturing error of the first prism PR1and the second prism PR2. A process for cementing the plane parallel plate PP after adjusting the angle will be described later.

FIG.6is a cross-sectional view of an optical path deflecting prism for endoscope30according to an example 1. In diagrams of other examples, a straight line which is an elongation of a second reflecting surface RF2is LN1. A straight line which is an elongation of a first reflecting surface RF1is LN2.

Various data for the present example is shown below.refractive index n for a d-line of a first prism PR1and a second prism PR2is, n=1.88first angle A 15°second angle B 65°length d1=1.45length d2=2.11length d3=4.09length d4=8.04length d5=7.50Each angle is shown in the diagram.

The present example satisfies conditional expressions (1) and (2). Moreover, with such configuration, even a thick light beam of an endoscope objective optical system with a high NA can also be transmitted through without an occurrence of vignetting.

Consequently, it is possible to provide a high-quality optical path deflecting prism for endoscope and an oblique-viewing endoscope optical system having a high NA.

FIG.7is a cross-sectional view of an optical path deflecting prism for endoscope40according to an example 2.

Various data of the present example is shown below.refractive index n for a d-line of a first prism PR1and a second prism PR2is, n=1.88first angle A 22.5°second angle B 65°length d1=1.33length d2=1.93length d3=4.36length d4=8.07length d5=7.50Each angle is shown in the diagram.

The present example satisfies conditional expressions (1) and (2). Moreover, with such configuration, even a thick light beam of an endoscope optical system with a high NA can also be transmitted through without an occurrence of vignetting. Consequently, it is possible to provide a high-quality optical path deflecting prism for endoscope and an oblique-viewing endoscope optical system having a high NA.

FIG.8is a cross-sectional view of an optical path deflecting prism for endoscope50according to an example 3.

Various data of the present example is shown below.refractive index n for a d-line of a first prism PR1and a second prism PR2is, n=1.88first angle A 22.5°second angle B 65°length d1=1.61length d2=1.94length d3=4.10length d4=8.04length d5=7.50Each angle is shown in the diagram.

The present example satisfies conditional expressions (1) and (2). Moreover, with such configuration, even a thick light beam of an endoscope optical system with a high NA can also be transmitted through without an occurrence of vignetting. Consequently, it is possible to provide a high-quality optical path deflecting prism for endoscope and an oblique-viewing endoscope optical system having a high NA.

FIG.9Ais a perspective view of a cemented state of a first prism PR1and a second prism PR2in an optical path deflecting prism for endoscope60according to an example 4, andFIG.9Bis a perspective

view of the second prism PR2in the optical path deflecting prism for endoscope60according to the example 4.

In the present example, a first reflecting surface RF1is a mirror surface having a mirror coating applied to a polished surface formed on the plane parallel plate PP. The first reflecting surface RF1formed on the plane parallel plate PP is cemented to a fifth polished surface11eafter having adjusted the angle to cancel the manufacturing error of the first prism PR1and the second prism PR2. A process for cementing the plane parallel plate PP after adjusting the angle will be described later.

FIG.10Ais a cross-sectional view of the cemented state of the first prism PR1and the second prism PR2in the optical path deflecting prism for endoscope60according to an example 4.FIG.10Bis a diagram showing an arrangement for adjusting the optical path deflecting prism for endoscope60according to the example 4.

InFIG.10B, an adjustment at the time of gluing the plane and parallel plate PP will be described. By using an autocollimator AC, an adjustment of tilting of the plane parallel plate PP is carried out so that, return light LI2from a first polished surface11aand return light LI1from a fourth polished surface11dare aligned. An angle adjuster ADJ carries out an adjustment of angle (adjustment of tilting) of the plane parallel plate PP. Moreover, in a state of the return lights LI1and LI2aligned, the plane parallel plate PP is cemented to a fifth polished surface11e. Accordingly, it is possible to cancel the manufacturing error of the first prism PR1and the second prism PR2.

FIG.11Ais a cross-sectional view of the optical path deflecting prism for endoscope60according to the example 4 obtained through the abovementioned process.FIG.11Bis a perspective view of the optical path deflecting prism for endoscope60according to the example 4.FIG.11Cis a perspective view in which the optical path deflecting prism for endoscope60according to the example 4 is processed to a circular cylindrical shape.

The optical path deflecting prism for endoscope60is cut to a circular cylindrical shape having a desired radius indicated by dashed lines inFIG.11B.FIG.11Cshows an optical path deflecting prism for endoscope60awhich has assumed a circular cylindrical shape after cutting.

More specifically, the optical path deflecting prism for endoscope60ais circular cylindrical shaped, having a first prism PR1a, a second prism PR2a, and a plane parallel plate PP.

FIG.12Ais a cross-sectional view of an arrangement of the optical path deflecting prism10according to the abovementioned example for instance. In the examples, an optical path deflecting prism for endoscope70is formed by gluing two prisms. However, without restricting to such arrangement, it is possible to form the optical path deflecting prism for endoscope70by cementing the first prism PR1, a second prism PR2, and a third prism PR3.

Moreover, an oblique-viewing endoscope optical system according to the present embodiment, according to another aspect of the present disclosure, includes the abovementioned optical path deflecting prism for endoscope, and an optical system which is disposed on the emergence side of the optical path deflecting prism for endoscope.

FIG.13is a cross-sectional view of a lens arrangement of an oblique-viewing endoscope optical system210according to an example 5. The oblique-viewing endoscope optical system210includes an optical path deflecting prism for endoscope80, and a lens group110.

The oblique-viewing endoscope optical system210includes in order from an object side, a plane parallel plate L1, a negative meniscus lens L2having a convex surface directed toward the object side, the optical path deflecting prism for endoscope80, and the lens group110. In the cross-sectional view of the lens arrangement, the optical path deflecting prism for endoscope80is shown as a rectangular parallelepiped body in an unfolded state. A planoconvex lens L5having a flat surface directed toward the object side is cemented to an image-side surface of the optical path deflecting prism for endoscope80. The lens group110further includes in order from the object side, a negative meniscus lens L6having a convex surface directed toward the object side, a biconvex positive lens L7, a planoconvex positive lens L8having a flat surface directed toward the object side, and a biconvex positive lens L9. In order from the object side, the negative meniscus lens L6and the biconvex positive lens L7are cemented. The planoconvex positive lens L8and the biconvex positive lens L9are cemented. An

imaging plane (image pickup surface) I is on an image side of the lens group110.

Numerical data for each example is shown below. In surface data, r denotes a radius of curvature of each lens surface, d denotes a distance between two lens surfaces, nd denotes a refractive index for a d-line of each lens, and νd denotes Abbe's number for each lens. S denotes an aperture stop. ER denotes an effective diameter.

Moreover, an aspheric surface shape is expressed by the following expression when z is an optical axial direction, y is a direction orthogonal to an optical axis, k is a conical coefficient, and A4, A6, A8, and A10 are aspherical coefficients.
Z=(y2/r)/[1+{1−(1+k)(y/r)2}1/2]+A4y4+A6y6,+A8y8+A10y10

As mentioned above, it is possible to provide an oblique-viewing endoscope (endoscope) having installed an optical path deflecting prism for endoscope which does not allow vignetting of a light beam, a flare, and a ghost to occur even in an endoscope in which the numerical aperture is made high. Moreover, it is possible to provide an inexpensive oblique-viewing endoscope optical system having an inexpensive optical path deflecting prism for endoscope by providing an angle adjuster to one of reflecting surfaces of an optical path deflecting prism group for correcting an optical-path shift which occurs due to a manufacturing error (an angle error) of a prism in the optical path deflecting prism for endoscope.

Various embodiments of the present invention were described above. However, the present invention is not restricted only to the embodiments described heretofore, and embodiments in which the arrangements of these embodiments are appropriately combined without departing from the scope of the invention, are also within the scope of the present invention.

A disclosure of the following arrangements is derived from the examples described heretofore.

It is possible to obtain the abovementioned optical path deflecting prism for endoscope by a method of manufacturing as follows.

A method of manufacturing an optical path deflecting prism for endoscope for observing an object in an oblique direction, comprising steps of:cementing a first prism and a second prism of the optical path deflecting prism for endoscope;forming a first polished surface which is perpendicular to the oblique direction, and the first polished surface is a first light-beam incident surface for light incident on the optical path deflecting prism for endoscope, in the first prism;forming a second polished surface which is disposed at an angle with respect to the first polished surface, and the second polished surface is a cemented surface with the second prism;forming a third polished surface which is a cemented surface with the first prism;forming a fourth polished surface which is perpendicular to an optical axis of a lens group disposed on an emergence side of the optical path deflecting prism for endoscope, and the fourth polished surface is a last light-beam emergence surface for light emerged from the optical path deflecting prism for endoscope;forming a fifth polished surface which is disposed at an angle with respect to the third polished surface;making a first reflecting surface which reflects first time a light beam incident on the optical path deflecting prism for endoscope exist on the fifth polished surface of the second prism; andmaking a second reflecting surface which reflects second time a light beam incident on the optical path deflecting prism for endoscope exist on any one of the second polished surface of the first prism and the third polished surface of the second prism, whereint the following conditional expressions (1) and (2) are satisfied,
14.5≤A(°)≤23  (1)
62≤B(°)≤66  (2)where,A denotes a first angle made by the first reflecting surface and the second reflecting surface with each other, andB denotes a second angle made by a normal direction of the second reflecting surface and an optical axial direction of a lens group disposed on an emergence side of a light beam of the optical path deflecting prism for endoscope.

As described heretofore, the present disclosure is suitable for an optical path deflecting prism for endoscope which does not allow a ghost, a flare, and a vignetting of a light beam even in an endoscope in which the numerical aperture NA is made high, and an oblique-viewing endoscope optical system having the optical path deflecting prism for endoscope, and an endoscope.

According to the present disclosure, it is possible to provide an optical path deflecting prism for endoscope which does not allow a ghost, a flare, and a vignetting of a light beam even in an endoscope in which the numerical aperture NA is made high, and an oblique-viewing endoscope optical system having the optical path deflecting prism for endoscope, and an endoscope.