JP2001147382A - Objective optical system for endoscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an objective optical system having an adequate parallax and size of an image, without increasing the diameter of an endoscope in the measurement of a small diameter in particular and a stereoscopic endoscope. SOLUTION: This objective optical system has a pair of negative lens groups 1, a pair of positive lens groups 2, brightness diaphragms 3, second positive lens groups 4 and one image pickup element 8 arrayed successively from the object side. The second position lens groups 4 include a pair of positive lenses decentered more toward the respective optical axes on the object side than toward the brightness diaphragms 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an objective optical system for an endoscope.

[0002]

2. Description of the Related Art Conventionally, endoscopes for observing by inserting an elongated insertion portion into a cavity or a human body cavity have been widely used in the industrial field and the medical field. In recent years, in the industrial field, there has been an increasing need for measuring the size and depth of scratches and cracks, and in the medical field, there is a growing need for performing a surgical operation using an endoscope. Observation using a stereoscopic image capable of recognizing depth information in an observation unit. Is desired.

Conventionally, as an endoscope capable of stereoscopic observation, an optical system described in, for example, Japanese Patent Application Laid-Open No. Hei 8-29701 is known. This is composed of two objective lens systems arranged in parallel at the end of the endoscope insertion section as shown in FIG.
The stereoscopic vision is made possible by obtaining the image shift, that is, the parallax, due to the difference in the position of. An optical system in which an image is captured by two CCDs as described above is effective in improving the image quality of a three-dimensional image and improving measurement accuracy.
Arranging two CCDs in parallel goes against the need for observing a narrower area than before and the trend toward less invasive medical use, and makes it difficult to miniaturize the endoscope.

Therefore, as an example in which an image having parallax is formed on one CCD, for example, Japanese Patent Laid-Open No. 7-359
No. 89 has proposed an optical system. In this optical system, as shown in FIG. 7, there is one CCD on an extension of the optical axis of two objective optical systems arranged in parallel with each other,
Two images are formed. Incidentally, the optical axis interval of the objective optical system affects parallax, which is important for stereoscopic vision, and accuracy in measurement. In this case, if the distance between the optical axes at the tip of the objective optical system (the part closest to the object) is small, the parallax will be small, and it will be difficult to obtain information in the depth direction when stereoscopically viewed. The error increases.

Conversely, as the distance between the optical axes at the tip of the objective optical system increases, the parallax increases, which is advantageous in terms of measurement accuracy. However, there is a problem that the tip of the endoscope becomes large. In stereoscopic vision, the parallax may be too large to make observation difficult. Parallax depends not only on the optical axis interval at the tip of the objective optical system but also on the object distance to be observed. In other words, the parallax increases as the object distance decreases, and the parallax decreases as the object distance increases. Based on the above, in a stereoscopic endoscope, in order to obtain an appropriate parallax required for measurement and observation according to the observation distance and to prevent the endoscope from being enlarged, Of the optical axis is determined.

On the other hand, in recent years, the size of a CCD tends to be reduced. However, the optimal optical axis interval at the tip of the objective optical system is determined as described above, and CC
When the image is formed on D, if the CCD is small as shown in FIG. 8, the center of the image is closer to the edge of the CCD, and the image of the common area on the left and right which is shaded in the figure is reduced. The measurement will be hindered. Conversely, assuming that the size of the CCD to be used is determined from the specification of the thickness of the endoscope and the optimum center interval of the image on the CCD is determined, the center interval of the image on the CCD is determined as shown in FIG. In the case of the optical axis interval at the tip of the objective optical system, there is a possibility that parallax required for measurement and stereoscopic vision cannot be obtained. Therefore, in order to obtain an appropriate parallax necessary for measurement and stereoscopic vision and an image of an area common to the left and right,
The distance between the optical axis of the objective optical system and the center of the image on the CCD is
You have to change it as needed.

A conventional example in which the distance between the optical axes of the objective optical system and the center of the image on the CCD is different is disclosed in, for example,
There is an optical system described in JP-A-215221. In this example, as shown in FIG. 10, a parallel plane refraction element is sandwiched between a pair of optical systems to reduce the distance between the optical axes of the objective optical system and to guide it to the center of the image on the CCD. I have. Such an optical system is effective when the amount of narrowing the optical axis is relatively larger than the thickness of the light beam at the position where the parallel-plane refraction element is arranged. When the amount of narrowing is small and the size of the parallel plane refraction element is small, it is necessary to consider a place where the parallel plane refraction element is arranged, and there is a problem that processing becomes difficult.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art.
The objective is to achieve the objective parallax and image size required for measurement and stereoscopic vision, especially for small-diameter measurement and stereoscopic endoscopes, without increasing the diameter of the endoscope. Is to provide a system.

[0009]

In order to achieve the above object, an objective optical system of an endoscope according to the present invention comprises a pair of negative lens groups arranged in order from the object side as shown in FIG. A pair of positive lens groups, a brightness stop, a second positive lens group, and one image pickup device, wherein the second positive lens group is configured such that each light on the object side with respect to the pair of brightness stops. It includes a pair of positive lens groups that are eccentric with respect to the axis.

The objective optical system for an endoscope according to the present invention comprises, as shown in FIG. 3 viewed from the side, at least one view direction changing prism arranged in order from the object side, and a pair of negative lens groups. , A pair of positive lens groups, a brightness stop, a second positive lens group, and one image sensor, wherein the second positive lens group is configured such that each light on the object side with respect to the brightness stop is It includes a pair of positive lenses that are eccentric with respect to the axis. Accordingly, aberrations such as spherical aberration and curvature of field are suppressed while the angle of view is determined by the negative lens group and the positive lens group on the object side of the aperture stop. Then, the optical axis of the second positive lens group is shifted after the light beam is stopped down by the brightness stop, so that the influence of aberration due to decentering is reduced.

Further, according to the present invention, the pair of positive lenses closer to the image pickup device than the aperture stop are decentered inward by the same amount in the horizontal direction of the screen with respect to each optical axis on the object side of the aperture stop. ing. In stereoscopic endoscopes, it is important to minimize the deviation of the aberration between the left and right images, but by making the amount of eccentricity symmetrical in this way, the design balance of the left and right images is balanced. .

Further, according to the present invention, the following conditional expression (1) is satisfied. 0.2 ≦ x / d ≦ 0.9 (1) where, d: optical axis interval on the object side from the aperture stop x: optical axis interval on the image sensor side from the aperture stop The lens system before and after the aperture stop Decentering is, of course, disadvantageous in terms of assembly and performance of the optical system compared to an optical system without eccentricity. Therefore, when the value exceeds the upper limit of this equation, considering that the amount of decentering is small, the optical system is not decentered, and the optical axis interval on the object side from the aperture stop or the optical axis on the image sensor side It is thought that it is possible to cope without eccentricity by balancing the intervals, so the upper limit was set. On the other hand, when approaching the lower limit of this equation, it means that the optical axis interval on the object side is larger than the optical axis interval on the image sensor side than the aperture stop, that is, the lens diameter on the object side is larger. Therefore, if the lower limit is exceeded, the endoscope cannot be made thinner even if a small-sized imaging device is used, so that the merit of the small-sized imaging device cannot be used. Therefore, the lower limit was set. At present, as an image pickup device, an image pickup device having a size of about 2 mm in length and about 2.5 mm in width is manufactured, but in the near future, the size of the image will be reduced to half or less with the same number of pixels both vertically and horizontally. Because of such momentum, the present invention assumes a size of 2 mm × 2.5 mm or less.

According to the present invention, the following conditional expression (2) is satisfied.
It is configured to satisfy. 0.03L <d <2L (2) where L is the best observation distance of the endoscope. The lower limit of this formula is a condition necessary for obtaining parallax and further obtaining accuracy required for measurement. As shown in FIG. 1, when the best observation distance is L, it is considered that an inward angle θ of about 1 ° <θ is necessary. Here, the best observation distance means the best imaging object distance. When the inward angle θ is 1 ° or less, the parallax decreases, and it becomes difficult to obtain information in the depth direction when stereoscopically viewed, and a measurement error increases when measuring the shape of an object. Further, the upper limit value of the above equation (2) suppresses the tip of the endoscope from becoming large, and at the same time, prevents the parallax from being too strong and making it difficult to observe.

Further, the endoscope objective optical system according to the present invention comprises:
In an optical system including a pair of positive lens groups closer to the image sensor than the aperture stop and forming an image on one image sensor, at least one eccentric optical axis after the aperture stop near the aperture stop. Includes optical elements. The reason why the optical element to be decentered is located near the aperture stop is that when using a small image pickup element, considering that the magnitude of the amount of decentering becomes relatively small, the size of the optical element also becomes small.
This is because it is desirable to dispose it near the aperture stop having a low ray height. Here, the vicinity of the aperture stop refers to an area including the aperture stop within 0.5 mm before and after the aperture stop or inside the optical element. Further, in this configuration, it is more preferable that the optical element for decentering the optical axis is one optical element for decentering the optical axis of one of the optical systems in the horizontal direction of the screen. This is because, in a small-diameter endoscope, if there are two optical elements that decenter the optical axis as in the conventional example,
This is because each optical element becomes smaller and processing becomes more difficult. Also, in the above configuration, it is desirable that the above-described expressions (1) and (2) are satisfied for the same reason as described above.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below based on illustrated embodiments. In each embodiment, substantially the same optical members are denoted by the same reference numerals. (First Embodiment) FIG. 1 shows the basic configuration of the first embodiment. In the present embodiment, a pair of negative lens groups 1 are arranged in order from the object side.
, A pair of positive lens groups 2, a brightness stop 3, a positive lens group 4, an infrared cut filter 5, a cover glass 6,
7 and one image sensor 8. The positive lens group 4 on the image sensor 8 side from the aperture stop 3 includes a pair of positive lenses decentered with respect to each optical axis on the object side from the aperture stop 3. Contains. The pair of negative lens groups 1 is a plano-concave lens having a concave surface facing the image plane side, and the pair of positive lens groups 2 behind it is composed of a cemented lens having irregularities, and the aperture stop 3 has two openings. Made of things. The positive lens group 4 closer to the image pickup device 8 than the aperture stop 3 has a pair of object-side convex surfaces decentered inward in the screen horizontal direction by the same amount with respect to each optical axis on the object side of the aperture stop 3. , And a central portion indicated by reference numeral A is cut so that the lenses do not interfere with each other. Behind that, an infrared cut filter 5 common to the left and right optical systems, cover glasses 6 and 7, and one image sensor 8 are arranged. This embodiment has a so-called tip AD (adapter) type structure that can be cut in the direction of the arrow at the position of the dashed line, and the rear portion is an endoscope-side portion including the cover glass 7 and the imaging element 8. I have. Therefore, by replacing the AD portion, it is possible to arbitrarily change an angle of view, a viewing angle, an inward angle that affects parallax, and the like of the endoscope.

The values and lens data corresponding to the above-mentioned conditional expressions are as follows. x = 0.886 d = 1.599 L = 13.69 0.2 ≦ x / d = 0.62 ≦ 0.9 0.03L <d = 0.12L <2L Object distance 13.6896 r ₁ = ∞ d ₁ = 0.04381 n ₁ = 1.88300 v ₁ = 40.78 r ₂ = 0.8436 d ₂ = 0.2409 r ₃ = ∞ d ₃ = 0.4275 r ₄ = 1.9713 d ₄ = 0 0.6727 n ₄ = 1.86666 v ₄ = 23.78 r ₅ = 0.9857 d ₅ = 1.3142 n ₅ = 1.51633 v ₅ = 64.14 r ₆ = −1.3015 d ₆ = 0. 7051 r ₇ = ∞ (aperture) d ₇ = 0.1095 r ₈ = 2.2431 d ₈ = 0.8785 n ₈ = 1.78800 v ₈ = 47.37 r ₉ = ｄ d ₉ = 0.0329 r ₁₀ = ∞d ₁₀ = 1.3142 n ₁₀ = 1.51400 ν ₁₀ = 75.00 r ₁₁ = ∞d _{1 1 = 0.0329 r 12 = ∞ d} 12 = 0.4381 n 12 = 1.88300 ν 12 = 40.76 r 13 = ∞ d 13 = 0.2190 r 14 = ∞ d 14 = 0.8761 n 14 = 1.88300 ν ₁₄ = 40.76 r ₁₅ = ∞ d ₁₅ = 0.3286 n ₁₅ = 1.49700 ν ₁₅ = 81.61 r ₁₆ = ∞ d ₁₆ = 0.0329 r ₁₇ = ∞Eccentricity of each convex lens 4 Amount = horizontal direction 0.3356 FIG. 2 is a cross-sectional view including the frame of the AD portion, and has a structure in which a cover glass 9 is incorporated at the tip to be watertight.

(Second Embodiment) FIG. 3 shows a basic configuration of a second embodiment. In this embodiment, the cover glass 9
The first embodiment differs from the first embodiment in that the camera and the field-of-view conversion prism 10 are disposed to enable side viewing. That is, in order from the object side, a viewing direction conversion prism 10, a pair of negative lens groups 1, a pair of positive lens groups 2, a brightness stop 3, a positive lens group 4, an infrared cut filter 5, a cover A pair of positive lenses 4 composed of glasses 6 and 7 and one image pickup device 8, which are closer to the image pickup device 8 than the aperture stop 3 are decentered with respect to each optical axis on the object side of the aperture stop 3. Includes positive lens. At the tip of the viewing direction conversion prism 10,
A left and right common cover glass 9 is arranged, and the viewing direction changing prism 10 is also formed of one 90 ° side-viewing right-angle prism common to the left and right. This embodiment also has a tip AD type structure, and the portion on the imaging element 8 side is common to that of the first embodiment. Therefore, it is possible to obtain direct vision and side vision by replacing the AD of the first embodiment. It becomes possible.

The values and lens data corresponding to each of the above conditional expressions are as follows. x = 0.856 d = 1.635 L = 10.167 0.2 ≦ x / d = 0.52 ≦ 0.9 0.03L <d = 0.16L <2L Object distance 10.1672 r ₁ = ∞ d ₁ = 0.3804 n ₁ = 1.88300 ν ₁ = 40.76 r ₂ = ∞ d ₂ = 0.1902 r ₃ = ｄ d ₃ = 2.2580 n ₃ = 1.88300 ν ₃ = 40.76 r ₄ = ∞d ₄ = 0.1303 r ₅ = ∞d ₅ = 0.3804 n ₅ = 1.88300 ν ₅ = 40.78 r ₆ = 0.8526 d ₆ = 0.2092 r ₇ = ｄ d ₇ = 0.3215 r ₈ = 1.7120 d ₈ = 0.4990 n ₈ = 1.86666 ν ₈ = 23.78 r ₉ = 0.8560 d ₉ = 1.413 n ₉ = 1.51633 ν ₉ = 64 _{.14 r 10 = -1.1315 d 10 =} 0.7160 r 11 = ∞ ( stop) d ₁₁ = 0.09 _{51 r 12 = 2.0201 d 12 =} 0.7630 n 12 = 1.78800 ν 12 = 47.37 r 13 = ∞ d 13 = 0.0285 r 14 = ∞ d 14 = 1.1413 n 14 = 1. _{51400 ν 14 = 75.00 r 15 =} ∞ d 15 = 0.0285 r 16 = ∞ d 16 = 0.3804 n 16 = 1.88300 ν 16 = 40.76 r 17 = ∞ d 17 = 0.1902 r _{18 = ∞ d 18 = 0.7609 n} 18 = 1.88300 ν 18 = 40.76 r 19 = ∞ d 19 = 0.2853 n 19 = 1.49700 ν 19 = 81.61 r 20 = ∞ d 20 = 0.0285 r ₂₁ = ∞ eccentricity of each convex lens 4 = 0.39 in the horizontal direction

(Third Embodiment) FIG. 4 shows a basic configuration of a third embodiment. In this embodiment, the positive lens group 4 closer to the image pickup device 8 than the aperture stop 3 has a point that the optical axis interval is narrower with respect to each optical axis on the object side than the aperture stop 3 and the optical axis is inclined in an oblique direction. Is different from the first embodiment. That is,
In order from the object side, a pair of negative lens group 1, a pair of positive lens group 2, a brightness stop 3, a positive lens group 4, an infrared cut filter 5, cover glasses 6, 7, and one image pickup The positive lens group 4 composed of the element 8 and located closer to the imaging element 8 than the aperture stop 3 includes a pair of positive lenses that are decentered with respect to each optical axis on the object side of the aperture stop 3. This embodiment also has a structure of the tip AD system.

The values and lens data corresponding to the above-mentioned conditional expressions are as follows. x = 0.902 d = 1.382 L = 12.537 0.2 ≦ x / d = 0.65 ≦ 0.9 0.03L <d = 0.11L <2L Object distance 12.5367 r ₁ = ∞ d ₁ = 0.4012 n ₁ = 1.88300 v ₁ = 40.78 r ₂ = 0.6887 d ₂ = 0.2206 r ₃ = ∞ d ₃ = 0.9186 r ₄ = 1.6840 d ₄ = 1 .0029 n ₄ = 1.86666 ν ₄ = 23.78 r ₅ = 0.7463 d ₅ = 1.415 n ₅ = 1.51633 ν ₅ = 64.14 r ₆ = −0.9984 d ₆ = 0. 0501 r ₇ = ∞ (aperture) d ₇ = 0.1003 r ₈ = 3.41212 d ₈ = 1.5044 n ₈ = 1.78800 v ₈ = 47.37 r ₉ = 4.5675 d ₉ = 0.3009 _{r 10 = ∞ d 10 = 1.2035} n 10 = 1.51400 ν 10 = 75.00 r _{11 = ∞ d 11 = 0.0301 r} 12 = ∞ d 12 = 0.4012 n 12 = 1.88300 ν 12 = 40.76 r 13 = ∞ d 13 = 0.2006 r 14 = ∞ d 14 = 0. _{8024 n 14 = 1.88300 ν 14 =} 40.76 r 15 = ∞ d 15 = 0.3009 n 15 = 1.49700 ν 15 = 81.61 r 16 = ∞ d 16 = 0.0301 r 17 = ∞ each Eccentricity of convex lens 4 (angle α in FIG. 4) = 15 °

(Fourth Embodiment) FIG. 5 shows a basic configuration of a fourth embodiment. In this embodiment, the brightness stop 3
Is composed of two apertures, and a pair of positive lens groups on the image sensor 8 side from the aperture stop 3 are a pair of convex meniscus lenses 11 whose concave surfaces face the image side in order from the aperture stop 3.
And a pair of positive lenses 12 having infrared cut filters with convex surfaces facing the object side, and cover glasses 6 and 7. In one optical system on the object side of the aperture stop 3, one parallelogram prism 13 for decentering the optical axis after the aperture stop 3 is disposed, and in the other optical system, The eccentricity is not particularly made only because the parallel plate 14 is arranged. In a conventional optical system, for example, FIG.
Although a pair of prisms are arranged as shown in FIG. 5, in this embodiment, since the amount of eccentricity is relatively small, the optical element for decentering the optical axis is arranged on only one side, so that a fine prism processing is not performed. I have to. In this embodiment, a prism element is used. However, two opposite mirrors may be arranged to perform the same eccentricity. And also in this embodiment,
It has the structure of the advanced AD method.

The values and lens data corresponding to the above-mentioned conditional expressions are as follows. x = 0.833 d = 1.351 L = 10.094 0.2 ≦ x / d = 0.62 ≦ 0.9 0.03L <d = 0.13L <2L Object distance 10.0937 r ₁ = ∞ d ₁ = 1.0372 n ₁ = 1.88300 v ₁ = 40.76 r ₂ = (aperture) d ₂ = 0.0926 r ₃ = -0.6631 d ₃ = 0.9568 n ₃ = 1.88300 ν ₃ = 40.76 r ₄ = -0.8176 d ₄ = 0.0926 r ₅ = 1.6107 d ₅ = 0.9260 n ₅ = 1.51400 ν ₅ = 75.00 r ₆ = ｄd ₆ = 0.3704 n ₆ = 1.88300 v ₆ = 40.76 r ₇ = ∞ d ₇ = 0.1852 r ₈ = ∞ d ₈ = 0.7408 n ₈ = 1.88300 v ₈ = 40.76 r ₉ = _{∞ d 9 = 0.4630 n 10 =} 1.49700 ν 10 = 81.54 r 10 = ∞ d 10 = 0.0 _{78 r 11 = ∞ d 11 =} 0.0037 r 12 = eccentricity in ∞ parallelogram prism 13 = 0.518 in the horizontal direction

In each of the above embodiments, x, d, L
, And lens data are normalized by the focal length f ′ = 1, and r ₁ , r ₂ ,... Denote the radii of curvature of each lens surface, cover glass surface or prism surface, and d ₁ , d ₂ ,
.. Represents the thickness or air space of each lens, cover glass or prism, n ₁ , n ₂ ,... Represents the refractive index of each lens, cover glass or prism, ν ₁ , ν ₂ ,. ... is the number of each lens, cover glass or prism.
Each is represented.

As described above, the objective optical system for an endoscope according to the present invention has the following features in addition to the features described in the claims. (1) The second positive lens group includes a pair of positive lens groups that are decentered inward in the screen horizontal direction by the same amount with respect to each optical axis on the object side of the aperture stop. 3. The objective optical system for an endoscope according to 2.

(2) The objective optical system for an endoscope according to claim 3, wherein the optical element is one optical element that decenters the optical axis of one of the optical systems in the horizontal direction of the screen.

(3) When the distance between the optical axes on the object side from the aperture stop is d and the distance between the optical axes on the image sensor side from the aperture stop is x, the condition 0.2 ≦ x / d ≦ 0.9 is satisfied. The objective optical system for an endoscope according to any one of claims 1 to 3, or (1) or (2), which satisfies.

(4) When the best observation distance of the endoscope is L, the condition 0.03L <d <2L is satisfied.
The objective optical system for an endoscope according to any one of (1) to (3) or (1) or (2).

[0028]

As described above, according to the present invention, particularly in a small-diameter measuring and stereoscopic endoscope, an appropriate parallax and image necessary for measurement and stereoscopic vision can be obtained without increasing the diameter of the endoscope. It is possible to provide an objective optical system having a size of

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of a first embodiment of the present invention.

FIG. 2 is a sectional view of an AD portion of the first embodiment assembled in a frame.

FIG. 3 is a basic configuration diagram of a second embodiment of the present invention.

FIG. 4 is a basic configuration diagram of a third embodiment of the present invention.

FIG. 5 is a basic configuration diagram of a fourth embodiment of the present invention.

FIG. 6 is a basic configuration diagram of a conventional example of an endoscope objective optical system capable of stereoscopic viewing.

FIG. 7 is a basic configuration diagram of another conventional example of an endoscope objective optical system capable of stereoscopic viewing.

FIG. 8 is a diagram for explaining a problem of the conventional example shown in FIG. 7;

FIG. 9 is a diagram for explaining a problem of the conventional example shown in FIG. 7;

FIG. 10 is a basic configuration diagram of still another conventional example of an endoscope objective optical system capable of stereoscopic viewing.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 pair of negative lens group 2 pair of positive lens group 3 aperture stop 4 positive lens group 5 infrared cut filter 6, 7, 9 cover glass 8 image sensor 10 view conversion prism 11 convex meniscus lens 12 infrared cut filter A pair of positive lenses 13 Parallelogram prism 14 Parallel plate

Claims (3)

[Claims] A first lens group, a brightness stop, a second positive lens group, and one imaging element, which are arranged in order from the object side. An objective optical system for an endoscope, wherein the second positive lens group includes a pair of positive lens groups decentered with respect to each optical axis on the object side of the aperture stop. 2. At least one viewing direction changing prism arranged in order from the object side, a pair of negative lens groups,
The image pickup apparatus includes a pair of positive lens groups, a brightness stop, a second positive lens group, and one image sensor, and the second positive lens group is located on each optical axis on the object side of the brightness stop. An objective optical system for an endoscope including a pair of positive lenses that are decentered. 3. An endoscope objective optical system including a brightness stop, a pair of positive lens groups, and one image sensor, which are arranged in order from the object side.
An objective optical system for an endoscope, comprising: at least one optical element for decentering an optical axis on an image side of the aperture stop with respect to an optical axis on an object side of the aperture stop.