WO2017183371A1 - Endoscopic system - Google Patents

Abstract

The purpose of the present invention is to provide an endoscopic system with which it is possible to obtain good image quality from a center area to a peripheral area of a screen. This endoscopic system includes: an objective optical system OBL; an optical path splitting unit 20 for splitting, using two prisms, a subject image obtained by the objective optical system OBL into two optical images having different focus points; one imaging element 22 for acquiring the two optical images; and an image synthesis processing unit 23 for selecting, in a prescribed region, an image having a relatively high contrast among the acquired two optical images to generate a synthesized image. The endoscopic system is characterized in that the two prisms are bonded with a bonding agent interposed therebetween such that bonding surfaces are substantially parallel to each other, and the bonding surfaces and the optical axis of the objective optical system OBL form a 45-degree angle and satisfy the following conditional expression (1). (1): -10<d×sin(θ'-45)/(cosθ'×im_pitch)<10

Description

Endoscope system

The present invention relates to an endoscope system, and more particularly to a depth-of-field endoscope system.

Generally, it is known that in an apparatus including an endoscope system and other devices including an imaging device, the depth of field becomes narrower as the number of pixels of the imaging device increases. That is, when the pixel pitch (the vertical and horizontal dimensions of one pixel) is reduced in order to increase the number of pixels in the imaging device, the permissible circle of confusion is also reduced accordingly, and the depth of field of the imaging device is reduced.

In order to increase the depth of field, for example, Patent Documents 1, 2, and 3 disclose a configuration in which a self-portrait is divided and formed, and the acquired images are combined by image processing to increase the depth. . This configuration is superior in that the self-portrait is divided and imaged, and the acquired images are combined by image processing to increase the depth.

International Publication No. 2013/061819 JP 2008-99746 A Japanese Patent No. 4226235

However, the configurations of Patent Documents 1, 2, and 3 are not preferable because a plurality of image sensors are required and the cost increases.

The present invention has been made in view of the above, and in an endoscope system using a depth expansion technique in self-portrait division using a prism, it is possible to obtain good image quality from the center region to the peripheral region of the screen. An object is to provide an endoscope system.

In order to solve the above-described problems and achieve the object, the present invention provides the following means.
One aspect of the endoscope system according to the present invention is as follows.
An objective optical system;
An optical path dividing unit that divides a subject image obtained by the objective optical system into two optical images with different focus using two prisms;
One image sensor for acquiring two optical images;
An endoscopic system having an image composition processing unit that selects an image having relatively high contrast between two acquired optical images in a predetermined region and generates a composite image,
The two prisms are bonded so that the bonding surfaces are substantially parallel with each other through a bonding agent,
The adhesive surface and the optical axis of the objective optical system form an angle of 45 degrees and satisfy the following conditional expression (1). The unit of the angle is degrees −10 <d × sin (θ′−45) / (cos θ ′ × im_pitch) <10 (1)
here,
im_pitch is the pixel pitch of the image sensor,
θ ′ is the refraction angle of the light ray incident on the adhesive surface,
d is the thickness of the bonding agent,
It is.

INDUSTRIAL APPLICABILITY The present invention has an effect of providing an endoscope system that can obtain a good image quality from the center region to the peripheral region of a screen in an endoscope system using a depth expansion technique in self-portrait division using a prism. .

It is a figure which shows the cross-sectional structure of the objective optical system which the endoscope system which concerns on one Embodiment of this invention, an optical path division part, and an image pick-up element. It is a schematic block diagram of the optical path division part and imaging device which the endoscope system which concerns on embodiment of this invention has. It is a schematic structure figure of an image sensor which an endoscope system concerning an embodiment of the present invention has. It is a figure which shows the structure of the adhesive agent vicinity of an optical path division part. (A) is a spot diagram of an optical system in which the x-direction shift is corrected. (B) is a spot diagram of an optical system in which an x-direction shift occurs. It is a functional block diagram which shows the structure of the endoscope system which concerns on embodiment of this invention. It is a flowchart which shows the flow in the case of synthesize | combining two optical images in the endoscope system which concerns on embodiment of this invention. In the endoscope system according to the embodiment of the present invention, it is a diagram showing an imaging state when an image is formed on an imaging device after an odd number of reflections by a beam splitter. It is a figure which shows the cross-sectional structure of the objective optical system which the endoscope system which concerns on Example 1 of this invention, an optical path division | segmentation part, and an image pick-up element, (a) is sectional drawing in a normal observation state, (b) is a proximity observation. It is sectional drawing in a state. (A), (b), (c), and (d) are spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC) in the normal observation state of Example 1, respectively. (E), (f), (g), and (h) respectively show spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC) in the close-up observation state. FIG.

Hereinafter, the reason and operation of the endoscope system according to this embodiment will be described with reference to the drawings. In addition, this invention is not limited by the following embodiment.

As shown in FIG. 1, the endoscope system according to the present embodiment divides an object optical system OBL and a subject image obtained by the objective optical system OBL into two optical images with different focus using two prisms. An image combining process for generating a composite image by selecting an image having a relatively high contrast between the acquired two optical images in a predetermined region The two prisms are bonded so that the bonding surfaces are substantially parallel to each other with a bonding agent interposed between the bonding surface and the objective optical system OBL. The optical axis forms an angle of 45 degrees and satisfies the following conditional expression (1). The unit of angle is degrees.
−10 <d × sin (θ′−45) / (cos θ ′ × im_pitch) <10 (1)
here,
im_pitch is the pixel pitch of the image sensor 22,
θ ′ is the refraction angle of the light ray incident on the bonding surface 21h,
d is the thickness of the bonding agent 21g,
It is.

The configuration of the optical path splitting unit 20 will be described. FIG. 2 is a diagram illustrating a schematic configuration of the optical path splitting unit 20.

The light emitted from the objective optical system OBL enters the optical path dividing unit 20.

The optical path splitting unit 20 includes a polarizing beam splitter 21 that splits a subject image into two optical images with different focus, and an image sensor 22 that captures two optical images and acquires two images.

As shown in FIG. 2, the polarization beam splitter 21 includes a first prism 21b, a second prism 21e, a mirror 21c, and a λ / 4 plate 21d. Both the first prism 21b (object-side prism) and the second prism 21e (image-side prism) have beam split surfaces having an inclination of 45 degrees with respect to the optical axis AX.

A polarization splitting film 21f is formed on the beam splitting surface of the first prism 21b. The first prism 21b and the second prism 21e constitute the polarization beam splitter 21 by bringing the beam split surfaces into contact with each other via the polarization separation film 21f.

The mirror 21c is provided near the end face of the first prism 21b via a λ / 4 plate 21d. An image sensor 22 is attached to the end face of the second prism 21e via a cover glass CG.

The subject image from the objective optical system OBL is separated into a P-polarized component (transmitted light) and an S-polarized component (reflected light) by the polarization separation film 21f provided on the beam splitting surface in the first prism 21b, and the reflected light side And an optical image on the transmitted light side are separated into two optical images.

The optical image of the S-polarized component is reflected to the imaging element 22 by the polarization separation film 21f, passes through the A optical path, passes through the λ / 4 plate 21d, is reflected by the mirror 21c, and is folded back to the imaging element 22 side. It is. The folded optical image is transmitted through the λ / 4 plate 21d again to rotate the polarization direction by 90 °, passes through the polarization separation film 21f, and forms an image on the imaging device 22.

The optical image of the P-polarized component passes through the polarization separation film 21f, passes through the B optical path, and is reflected by a mirror surface provided on the opposite side of the beam splitting surface of the second prism 21e that folds vertically toward the image sensor 22. The image is formed on the image sensor 22. At this time, a prism glass path is set so that a predetermined optical path difference of, for example, about several tens of μm is generated between the A optical path and the B optical path, and two optical images with different focus are received on the light receiving surface of the image sensor 22. To form an image.

That is, the first prism 21b and the second prism 21e can be separated into two optical images having different focus positions so that the optical path length (glass path length) on the transmitted light side to the imaging element 22 in the first prism 21b can be separated. The optical path length on the reflected light side is short (small).

As shown in FIG. 3, the image sensor 22 receives two optical images with different focus positions and individually receives and captures two optical regions (effective pixels) in the entire pixel area of the image sensor 22. Regions) 22a and 22b are provided.

The light receiving regions 22a and 22b are arranged so as to coincide with the image planes of these optical images in order to capture two optical images. In the image sensor 22, the light receiving area 22a is relatively shifted (shifted) to the near point side with respect to the light receiving area 22b, and the light receiving area 22b is in focus with respect to the light receiving area 22a. The position is relatively shifted to the far point side. Thereby, two optical images with different focus are formed on the light receiving surface of the image sensor 22.

In addition, by changing the refractive indexes of the glass materials of the first prism 21b and the second prism 21e, the optical path length to the image sensor 22 is changed so that the focus position with respect to the light receiving regions 22a and 22b is relatively shifted. Also good.

Further, around the light receiving areas 22a and 22b, a correction pixel area 22c for correcting a geometric shift of the optical image divided into two is provided. In the correction pixel region 22c, manufacturing errors are suppressed, and correction by image processing is performed by an image correction processing unit 23b (FIG. 6) described later, thereby eliminating the geometrical deviation of the optical image described above. It has become.

The second lens group G2 of the present embodiment described above is a focusing lens and can be selectively moved to two positions in the direction of the optical axis. The second lens group G2 is driven by an actuator (not shown) so as to move from one position to the other position and from the other position to one position between two positions.

In the state where the second lens group G2 is set to the front side (object side) position, the second lens group G2 is set so as to focus on the subject in the observation area when performing far-field observation (normal observation). Further, in the state where the second lens group G2 is set to the rear side position, it is set to focus on the subject in the observation region when performing close-up observation (magnification observation).

Note that, as in the present embodiment, when the polarization beam splitter 21 is used for the polarization separation, the brightness of the separated image is different unless the polarization state of the light to be separated is a circular polarization. Regular brightness differences are relatively easy to correct in image processing. However, if brightness differences occur locally and under viewing conditions, they cannot be corrected completely, resulting in uneven brightness in the composite image. May end up.

The subject observed with the endoscope may have uneven brightness in the relatively peripheral part of the visual field of the composite image. It should be noted that the brightness unevenness with the polarization state broken is conspicuous when the subject has a relatively saturated brightness distribution.

In the peripheral part of the visual field, the endoscope often sees the blood vessel running and the mucous membrane structure of the subject image relatively close to each other, and there is a high possibility that the image will be very troublesome for the user.
Therefore, for example, as shown in FIG. 2, it is preferable to arrange the λ / 4 plate 21a closer to the object side than the polarization separation film 21f of the optical path splitting unit 20 so as to return the polarization state to the circularly polarized state. .

It should be noted that a half mirror that splits the intensity of incident light can be used instead of the polarizing beam splitter as described above.

The optical path splitting unit 20 in this embodiment will be further described. FIG. 4 shows a configuration in the vicinity of the bonding agent 21 g of the optical path splitting unit 20. The first prism 21b and the second prism 21e are bonded so that the bonding surfaces 21h and 21i are substantially parallel to each other with a bonding agent 21g interposed therebetween. The bonding surface 21h and the optical axis AX of the objective optical system OBL form an angle of 45 degrees. The angle formed by the adhesive surface 21h and the optical axis AX of the objective optical system OBL may be approximately 45 degrees.

The light beam AL traveling along the optical axis AX enters the bonding surface 21h of the first prism 21b at an incident angle θ = 45 °. The normal line of the bonding surface 21h is indicated by N. The light beam AL is refracted in the direction of the angle θ ′ on the bonding surface 21h.

In an optical system that splits the optical path using two 45 degree prisms, the light beam is refracted by the difference between the refractive index of the prism and the refractive index of the bonding agent. This refraction occurs on the surface including the 45 slope of the prism (x direction in FIG. 4), but does not occur in the vertical direction (y direction in FIG. 4). The distance between the light beam AL that has traveled without being refracted and the light beam AL 'that has traveled after being refracted is referred to as x-direction shift x-sht (see FIG. 4). Note that the x-direction shift occurs in both the optical paths A and B in the prism.

In the configuration of FIG. 4, the following law of refraction (A) is established.
Nd_Pr01 × sin θ = Nd_CE × sin θ ′ (A)
here,
Nd_Pr01 is the refractive index at the d-line of the first prism 21b on the object side,
Nd_CE is the refractive index of the bonding agent 21g at the d-line,
θ is the incident angle of the light beam AL incident on the bonding surface 21h,
θ ′ is the refraction angle of the light beam AL incident on the bonding surface 21h,
It is.

Further, when the thickness of the bonding agent 21g is d, the following formula (B) is established.
α = d / cos θ ′ (B)

From the expressions (A) and (B), the x-direction shift x-sht is expressed by the following expression.
x-sht = α × sin (θ′−θ)
= D × sin (θ′−θ) / cos θ ′
Therefore, conditional expression (1) can be obtained by setting θ = 45 (°) and dividing x-direction shift x-sht by im_pitch.

Conditional expression (1) relates to x-direction shift. FIG. 5A is a diagram showing a spot diagram of the optical system in which the x-direction shift is corrected in the present embodiment. FIG. 5B is a spot diagram of an optical system in which an x-direction shift occurs in the conventional configuration. As described above, due to the x-direction shift of the light beam AL, even if the objective optical system OBL is an ideal lens without aberration, a circular object at the center of the screen becomes elliptical on the image plane. For this reason, the resolution is deteriorated, which is not preferable.

Satisfying conditional expression (1) makes it possible to reduce the x-direction shift, so that good optical performance can be obtained.

If the upper limit value of conditional expression (1) is exceeded or less than the lower limit value, the maximum value of the x-direction shift becomes larger than the pixel pitch of the image sensor. For this reason, since optical performance will deteriorate, it is not preferable.

Note that it is desirable to satisfy the following conditional expression (1) ′ instead of conditional expression (1).
−5 <d × sin (θ′−45) / (cos θ ′ × im_pitch) <5 (1) ′
Furthermore, it is desirable to satisfy the following conditional expression (1) ″ instead of conditional expression (1).
-2 <d × sin (θ′−45) / (cos θ ′ × im_pitch) <2 (1) ”

Moreover, according to the preferable aspect of this embodiment, it is desirable to satisfy the following conditional expressions (2) and (3).
0.7 <Nd_Pr01 / Nd_CE <1.3 (2)
0.7 <Nd_Pr02 / Nd_CE <1.3 (3)
here,
Nd_Pr01 is the refractive index at the d-line of the first prism 21b on the object side,
Nd_Pr02 is a refractive index at the d-line of the second prism 21e on the image side,
Nd_CE is the refractive index of the bonding agent 21g at the d-line,
It is.
The refractive index Nd_Pr01 of the first prism 21b and the refractive index Nd_Pr02 of the second prism 21e are desirably the same value.

Conditional expression (2) relates to an appropriate ratio between the refractive index of the first prism 21b and the refractive index of the bonding agent 21g. Satisfying the conditional expression (2) is preferable because the amount of refraction of the light beam AL at the interface between the first prism 21b and the bonding agent 21g becomes small.

When the upper limit value of conditional expression (2) is exceeded or below the lower limit value, the amount of refraction of the light beam AL at the interface between the first prism 21b and the bonding agent 21g increases. This is not preferable because the x-direction shift becomes too large.

Conditional expression (3) relates to an appropriate ratio of the refractive indexes of the second prism 21e and the bonding agent 21g. Satisfying the conditional expression (3) is preferable because the amount of refraction of the light beam AL at the interface between the second prism 21e and the bonding agent 21g becomes small.

If the upper limit value of conditional expression (3) is exceeded or below the lower limit value, the amount of light refraction at the interface between the second prism 21e and the bonding agent 21g increases. This is not preferable because the x-direction shift becomes too large.

It should be noted that the following conditional expressions (2) ′ and (3) ′ are preferably satisfied instead of conditional expressions (2) and (3).
0.8 <Nd_Pr01 / Nd_CE <1.2 (2) ′
0.8 <Nd_Pr02 / Nd_CE <1.2 (3) ′
Furthermore, it is desirable to satisfy the following conditional expressions (2) "and (3)" instead of the conditional expressions (2) and (3).
0.9 <Nd_Pr01 / Nd_CE <1.11 (2) "
0.9 <Nd_Pr02 / Nd_CE <1.11 (3) "

Moreover, according to the preferable aspect of this embodiment, it is desirable to satisfy the following conditional expressions (4) and (5).
0.001 <d × sin (θ′−45) / (cos θ ′ × fw) <5 (4)
0.001 <d × sin (θ′−45) / (cos θ ′ × ih) <3 (5)
here,
d is the thickness of the bonding agent 21g,
θ ′ is the refraction angle of the light ray incident on the bonding surface 21h,
fw is the focal length in the normal observation state of the objective optical system,
ih is the image height,
It is.

Conditional expression (4) relates to an appropriate ratio between the x-direction shift and the focal length of the objective optical system. By satisfying conditional expression (4), it is possible to suppress an appropriate shift in the x direction, so that the resolving power does not deteriorate greatly.

If the upper limit value of conditional expression (4) is exceeded, the x-direction shift becomes too large and the resolution is deteriorated, which is not preferable.

If the lower limit value of conditional expression (4) is not reached, the x-direction shift almost does not exist, so the problem of the present application itself does not occur.

Conditional expression (5) relates to an appropriate ratio between x-direction shift and image height. By satisfying conditional expression (5), an appropriate x-direction shift can be achieved, so that the resolving power does not deteriorate significantly.

If the upper limit value of conditional expression (5) is exceeded, the x-direction shift becomes too large, and the resolution is deteriorated.

If the lower limit of conditional expression (5) is not reached, there is almost no x-direction shift, so the problem of the present application itself does not occur.

It should be noted that the following conditional expressions (4) ′ and (5) ′ are preferably satisfied instead of conditional expressions (4) and (5).
0.0015 <d × sin (θ′−45) / (cos θ ′ × fw) <1 (4) ′
0.0015 <d × sin (θ′−45) / (cos θ ′ × ih) <0.5 (5) ′
Furthermore, it is desirable to satisfy the following conditional expressions (4) "and (5)" instead of the conditional expressions (4) and (5).
0.0016 <d × sin (θ′−45) / (cos θ ′ × fw) <0.1 (4) ”
0.0016 <d × sin (θ′−45) / (cos θ ′ × ih) <0.1 (5) ”

In a preferred aspect of the present embodiment, it is desirable that the first negative lens is provided on the most object side of the objective optical system and the following conditional expressions (6) and (7) are satisfied.
0.7 <Nd_L01 / Nd_CE <1.5 (6)
0.7 <Nd_L01 / Nd_Pr01 <1.5 (7)
here,
Nd_L01 is a refractive index at the d-line of the negative first lens L1,
Nd_CE is the refractive index of the bonding agent 21g at the d-line,
Nd_Pr01 is the refractive index at the d-line of the object-side prism 21b,
It is.

Conditional expression (6) relates to an appropriate ratio between the refractive index of the negative first lens L1 and the refractive index of the bonding agent 21g.

If the upper limit of conditional expression (6) is exceeded, the refractive index of the bonding agent 21g becomes too small, making it difficult to obtain materials, which is not preferable.

If the lower limit of conditional expression (6) is not reached, the refractive index of the negative first lens L1 is too small, and a sufficient negative power cannot be obtained.

Conditional expression (7) relates to an appropriate ratio between the refractive index of the negative first lens L1 and the refractive index of the first prism 21b.

If the upper limit of conditional expression (7) is exceeded, the refractive index of the first prism 21b becomes too small, making it difficult to obtain the material, which is not preferable.

If the lower limit of conditional expression (7) is not reached, the refractive index of the negative first lens L1 is too small, and a sufficient negative power cannot be obtained.

In addition, it is desirable to satisfy the following conditional expressions (6) ′ and (7) ′ instead of the conditional expressions (6) and (7).
0.8 <Nd_L01 / Nd_CE <1.4 (6) ′
0.8 <Nd_L01 / Nd_Pr01 <1.3 (7) ′
Furthermore, it is desirable to satisfy the following conditional expressions (6) "and (7)" instead of the conditional expressions (6) and (7).
0.95 <Nd_L01 / Nd_CE <1.3 (6) "
0.95 <Nd_L01 / Nd_Pr01 <1.2 (7) "

Next, the synthesis of two acquired images will be described with reference to FIG.

The image processor 23 reads an image relating to two optical images captured by the image sensor 22 and has different focus positions, and an image for performing image correction on the two images read by the image reading unit 23a. The image processing apparatus includes a correction processing unit 23b and an image composition processing unit 23c that performs image composition processing for compositing two corrected images.

The image correction processing unit 23b corrects the images related to the two optical images formed on the light receiving regions 22a and 22b of the image sensor 22 so that the differences other than the focus are substantially the same. That is, the two images are corrected so that the relative positions, angles, and magnifications in the optical images of the two images are substantially the same.

When the subject image is separated into two and formed on the image sensor 22, geometrical differences may occur. That is, each optical image formed on the light receiving regions 22a and 22b of the image sensor 22 may have a relative displacement, a displacement, an angle, that is, a displacement in the rotation direction, and the like.

Although it is difficult to completely eliminate these differences at the time of manufacturing or the like, if the amount of misalignment increases, the composite image becomes a double image or unnatural brightness unevenness occurs. Therefore, the above-described geometric difference and brightness difference are corrected by the image correction processing unit 23b.

When correcting the difference in brightness between two images, the lower one of the two images or images or the image or image having the lower luminance at the relatively same position of the two images or images is used as a reference. It is desirable to make corrections.

The image composition processing unit 23c selects a relatively high contrast image in a corresponding region between the two images corrected by the image correction processing unit 23b, and generates a composite image. That is, by comparing the contrast in each spatially identical pixel area in two images and selecting a pixel area having a relatively higher contrast, a composite image as one image synthesized from the two images Is generated.

When the contrast difference in the same pixel area of the two images is small or substantially the same, a composite image is generated by a composite image process in which the pixel area is added with a predetermined weight.

Further, the image processor 23 performs subsequent image processing such as color matrix processing, contour enhancement, and gamma correction on one image synthesized by the image synthesis processing unit 23c. The image output unit 23d outputs an image that has been subjected to subsequent image processing. The image output from the image output unit 23d is output to the image display unit 24.

Further, the first prism 21b and the second prism 21e are made of different glass materials according to the near point optical path and the far point optical path leading to the image sensor 22, and the refractive index is made different so that the relative focus position is relatively increased. It may be shifted.

Thereby, it is possible to obtain images related to two optical images with different focus and to synthesize these images by the image composition processing unit 23c to obtain a combined depth of field. Far-field observation is suitable for screening a wide range by endoscopy, and close-up observation is suitable for observing or diagnosing the details of a lesion.

By adopting such a configuration, it becomes possible to expand the depth of field without reducing the resolving power even when using an image sensor having a larger number of pixels. Furthermore, since there is a focusing mechanism, it is possible to freely switch the observation range and perform high-quality endoscope observation and diagnosis.

Next, in the present embodiment, the flow when two optical images are combined will be described with reference to the flowchart of FIG.

In step S101, the image correction processing unit 23b performs a correction process on two images, that is, the image related to the far point image and the image related to the near point image acquired by the image sensor 22 in the image correction unit 22b. That is, according to a preset correction parameter, the two images are corrected so that the relative position, angle, and magnification in the optical images of the two images are substantially the same, and the corrected images are combined. The data is output to the processing unit 23c. In addition, you may correct | amend the brightness and color difference of 2 images as needed.

In step S102, the two images that have undergone the correction processing are combined by the image combining processing unit 23c. At this time, contrast values are calculated and compared in the corresponding pixel regions of the two perspective images.

In step S103, it is determined whether or not there is a difference in the compared contrast values. If there is a difference in contrast, the process proceeds to step S105, where a region having a high contrast value is selected and synthesized.

Here, if the difference in the contrast value to be compared is small or almost the same, it becomes an unstable factor in processing which of the two perspective images is selected. For example, if there are fluctuations in a signal such as noise, a discontinuous region may be generated in the composite image, or a problem may occur that the originally resolved subject image is blurred.

Therefore, the process proceeds to step S104 and weighting is performed. In step S104, if the contrast values of the two images are substantially the same in the pixel region to be subjected to the contrast comparison, weighting is performed, and the image weighted in the next step S105 is added to perform image selection. The instability is resolved.

As described above, according to the present embodiment, in both the close-up observation and the far-field observation, the field of view is prevented while preventing a discontinuous region from being generated in the composite image or the optical image from being blurred due to noise or the like. An image with an increased depth can be acquired.

In addition, since the two images are captured by the same imaging device, the manufacturing cost is reduced and the depth of field is increased without increasing the size of the device as compared with a device including a plurality of imaging devices. Can be obtained.

Also, a desired depth of field can be obtained, and degradation of resolution can be prevented.

In the case of the polarizing beam splitter 21 shown in FIG. 2 described above, an optical image is formed on the image sensor 22 after being reflected once, that is, an odd number of times. For this reason, one of the images is brought into an image formation state (mirror image) as shown in FIG.

Since the correction of the mirror image by the optical even number of reflections may increase the size of the objective optical system and the cost of the prism, the mirror image correction by the odd number of reflections may be reversed by the image correction processing unit 23b. It is preferable to carry out by.

In addition, when the imaging element 22 has a long shape in the endoscope longitudinal direction, it is preferable to appropriately rotate the composite image in consideration of the aspect ratio of the image display unit 24.

Example 1
Next, an objective optical system included in the endoscope system according to Example 1 will be described.
FIGS. 9A and 9B are diagrams showing a cross-sectional configuration of the objective optical system. Here, FIG. 9A is a diagram showing a cross-sectional configuration of the objective optical system in a normal observation state (a long distance object point). FIG. 2B is a diagram showing a cross-sectional configuration of the objective optical system in the close-up observation state (short-distance object point).

The objective optical system according to the present example includes, in order from the object side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a third lens group G3 having a positive refractive power. , Is composed of. The aperture stop S is disposed between the second lens group G2 and the third lens group G3. The second lens group G2 moves on the optical axis AX to the image side, and corrects the change in the focal position accompanying the change from the normal observation state to the close observation state.

The first lens group G1 includes, in order from the object side, a plano-concave negative lens L1 having a plane facing the object side, a parallel flat plate L2, a biconcave negative lens L3, and a plano-convex positive lens L4 having a plane facing the image side. And consist of Here, the negative lens L3 and the positive lens L4 are cemented. The second lens group G2 includes a positive meniscus lens L5 having a convex surface directed toward the object side. The third lens group G3 includes, in order from the object side, a biconvex positive lens L6, a negative meniscus lens L7 with a convex surface facing the image side, a planoconvex positive lens L8 with a plane facing the object side, and a biconvex positive lens. L9 and a negative meniscus lens L10 having a convex surface facing the image side. Here, the positive lens L6 and the negative meniscus lens L7 are cemented. The positive lens L9 and the negative meniscus lens L10 are cemented.

The optical path splitting unit 20 described above is disposed on the image side of the third lens group G3. In the prism in the optical system, the optical path is bent. The parallel flat plate L2 is a filter provided with a coating for cutting a specific wavelength, for example, 1060 nm of a YAG laser, 810 nm of a semiconductor laser, or an infrared region.

FIGS. 10A, 10B, 10C, and 10D show spherical aberration (SA), astigmatism (AS), distortion aberration (DT), and lateral chromatic aberration (CC) in the normal observation state of this embodiment. ).
10E, 10F, 10G, and 10H show spherical aberration (SA), astigmatism (AS), distortion aberration (DT), and lateral chromatic aberration (CC) in the close-up observation state of this example. ).
These aberration diagrams are shown for wavelengths of 656.27 nm (C line), 587.56 nm (d line), and 435.84 nm (g line). In each figure, “ω” indicates a half angle of view.

The numerical data of each of the above examples is shown below. Symbols r are the radius of curvature of each lens surface, d is the distance between the lens surfaces, nd is the refractive index of the d-line of each lens, νd is the Abbe number of each lens, FNO is the F number, and ω is the half field angle It is. The back focus fb represents the distance from the most image-side optical surface to the paraxial image surface in terms of air. The total length is obtained by adding back focus to the distance (not converted to air) from the lens surface closest to the object side to the optical surface closest to the image side.

Numerical example 1
Unit mm

Surface data Surface number r d nd νd
1 ∞ 0.48 1.88300 40.76
2 1.647 1.49
3 ∞ 0.55 1.52 100 65.12
4 ∞ 0.34
5 -7.955 0.96 1.88300 40.76
6 1.999 1.37 1.84666 23.78
7 ∞ variable
8 1.962 0.85 1.48749 70.23
9 2.080 Variable 10 (Aperture) ∞ 0.07
11 3.615 1.10 1.64769 33.79
12 -1.551 0.32 2.00330 28.27
13 -9.523 0.04
14 ∞ 0.78 1.69895 30.13
15 -2.831 0.04
16 11.007 0.92 1.48749 70.23
17 -2.335 0.34 1.92286 18.90
18 -5.022 4.48
Image plane ∞

Data Normal observation state Proximity observation state Focal length 1.00 1.00
Effective FNO. 3.58 3.54
Angle of view 2ω 145.01 139.17
fb (in air) 4.44 4.35
Total length (in air) 16.18 16.18

d7 0.45 1.17
d10 1.60 0.88

Each group focal length
f1 = -1.21 f2 = 21.02 f3 = 3.23

The numerical values of conditional expressions (1) to (7) in Example 1, Example 2, and Example 3 are shown below. The specification values of the objective optical system OBL (Numerical Example 1) are common to the three examples.

Conditional expression
(1) d × sin (θ'-45) / (cosθ '× im_pitch)
(2) Nd_Pr01 / Nd_CE
(3) Nd_Pr02 / Nd_CE
(4) d × sin (θ'-45) / (cosθ '× fw)
(5) d × sin (θ'-45) / (cosθ '× ih)
(6) Nd_L01 / Nd_CE
(7) Nd_L01 / Nd_Pr01

Value corresponding to conditional expression Example 1 Example 2 Example 3
(1) 1.12 1.92 9.98
(2) 1.10 1.14 1.29
(3) 1.10 1.14 1.29
(4) 0.0017 0.0038 0.013
(5) 0.0017 0.004 0.0135
(6) 1.26 1.26 1.29
(7) 1.15 1.11 1.00

Parameter value The refractive index is the refractive index at the d-line.

Example 1 Example 2 Example 3
Nd_Pr01 1.63854 1.69895 1.883
Nd_Pr02 1.63854 1.69895 1.883
Nd_CE 1.49 1.49 1.46
d 0.01 0.015 0.015
θ '51.04 53.73 65.78
im_pitch (um) 1.5 2 1.3
fw 1 1 1
ih 0.959 0.959 0.959
Nd_L01 1.883 1.883 1.883

Although various embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and may be implemented 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, the present invention is useful for an endoscope system that can acquire a high-quality image in which the depth of field is enlarged and aberrations are corrected favorably.

DESCRIPTION OF SYMBOLS 10 Endoscope system 20 Optical path division | segmentation part 21 Polarization beam splitter 21a (lambda) / 4 board 21b 1st prism 21c Mirror 21d (lambda) / 4 board 21e 2nd prism 21f Polarization separation film 21g Bonding agent 21h, 21i Adhesive surface 22 Imaging element 22a, 22b Light receiving area 22c Correction pixel area 23 Image processor 23a Image reading section 23b Image correction processing section 23c Image composition processing section 23d Image output section 24 Image display section CG Cover glass OBL Objective optical system G1 First lens group G2 Second lens group G3 Third lens group S Brightness stop

Claims (4)

1. An objective optical system;
   An optical path dividing unit that divides a subject image obtained by the objective optical system into two optical images with different focus using two prisms;
   One image sensor for acquiring the two optical images;
   An endoscope system having an image composition processing unit that selects an image having a relatively high contrast between the obtained two optical images in a predetermined region and generates a composite image,
   The two prisms are bonded so that the bonding surfaces are substantially parallel with a bonding agent interposed therebetween,
   The endoscope system according to claim 1, wherein the adhesive surface and the optical axis of the objective optical system form an angle of 45 degrees and satisfy the following conditional expression (1).
   −10 <d × sin (θ′−45) / (cos θ ′ × im_pitch) <10 (1)
   here,
   im_pitch is the pixel pitch of the image sensor,
   θ ′ is the refraction angle of the light ray incident on the adhesive surface,
   d is the thickness of the bonding agent,
   It is.
2. The endoscope system according to claim 1, wherein the following conditional expressions (2) and (3) are satisfied.
   0.7 <Nd_Pr01 / Nd_CE <1.3 (2)
   0.7 <Nd_Pr02 / Nd_CE <1.3 (3)
   here,
   Nd_Pr01 is the refractive index at the d-line of the object-side prism,
   Nd_Pr02 is the refractive index at the d-line of the image side prism,
   Nd_CE is the refractive index of the bonding agent at the d-line,
   It is.
3. The endoscope system according to claim 1, wherein the following conditional expressions (4) and (5) are satisfied.
   0.001 <d × sin (θ′−45) / (cos θ ′ × fw) <5 (4)
   0.001 <d × sin (θ′−45) / (cos θ ′ × ih) <3 (5)
   here,
   d is the thickness of the bonding agent,
   θ ′ is the refraction angle of the light ray incident on the adhesive surface,
   fw is a focal length in a normal observation state of the objective optical system,
   ih is the image height,
   It is.
4. A negative first lens closest to the object side of the objective optical system;
   The endoscope system according to claim 2, wherein the following conditional expressions (6) and (7) are satisfied.
   0.7 <Nd_L01 / Nd_CE <1.5 (6)
   0.7 <Nd_L01 / Nd_Pr01 <1.5 (7)
   here,
   Nd_L01 is the refractive index of the negative first lens at the d-line,
   Nd_CE is the refractive index of the bonding agent at the d-line,
   Nd_Pr01 is the refractive index at the d-line of the object-side prism,
   It is.
   
   

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