JP2006039259A - Endoscope objective optical system and imaging apparatus using the system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low cost endoscope objective optical system, particularly a video endoscope objective optical system with which a wide angle is provided, distortion is made small, image surface curve is made small and only spherical lenses are used to construct the system. <P>SOLUTION: The endoscope objective optical system is made of a first group G1 which is made of a negative meniscus lens whose convex face is facing toward an object side, a brightness diaphragm S, a second group G2 which is made of a positive lens whose flat surface is facing toward the object point side, a third group G3 which includes a refractive surface, that has at least one concave surface, and has a positive refractive power as a whole and a fourth group G4 which is made of a joint lens of a negative meniscus lens and a biconvex lens and has a positive refractive power. In the system, an image is formed on an imaging element I through the first group G1 to the fourth group G4 and the main optical line is refracted to the direction separating from the optical axis at the convex surface of the positive lens of the second group G2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an endoscope objective optical system and an imaging apparatus using the same, and more particularly to a video endoscope objective optical system and an electronic endoscope.

  In an endoscope, particularly in the medical field, it is desirable to have a wide-angle visual field for the purpose of easily detecting lesions in a body cavity and preventing oversight of treatment. When used in the abdominal cavity, the viewing angle needs to be at least about 70 °.

  The endoscope optical system is preferably a telecentric optical system in which a chief ray is incident perpendicular to the image transmission means in order to increase transmission efficiency. A wide-angle, telecentric optical system is a negative focus group, stop, and positive back group retrofocus optical system that can be achieved by matching the stop position with the front focus position of the rear group. As a basic configuration, negative distortion occurs due to the positive refracting power behind the stop, and the negative distortion is large.

  If the distortion is large, the difference between the real object and the image is large, which is inconvenient for the operator and is not preferable.

  As a means for reducing distortion, as shown in Patent Document 1 and a cross-sectional view in FIG. 37, as shown in a cross-sectional view, an endoscope objective lens with a small distortion aberration of a retrofocus type in which the front group is constituted by a positive lens and one negative meniscus lens. Is described.

  Patent Document 2 describes a technique for correcting distortion using an aspheric lens.

  Furthermore, Patent Document 3 describes a technique for reducing the occurrence of distortion without using an aspheric lens.

  However, in the device described in Patent Document 1, the convex lens placed on the object side is arranged on the object side relative to the concave lens, the distance is larger than the stop, and the light beam is increased by the action of the front group concave lens. It must be. Since the endoscope is an insertion device, an increase in the outer diameter of the objective optical system installed at the distal end portion is not preferable because the insertion portion is enlarged.

  Patent Document 4 describes an example of an objective optical system for a rigid endoscope in which the curvature of field is positively excessively corrected. When a relay lens is used as the image transmission means, it is known that a positive curvature of field is generated in the objective lens arranged on the object side of the relay lens in order to cancel the negative curvature of field generated in the relay lens. However, as shown in the astigmatism diagram of FIG. 38 (Patent Document 4 FIG. 6), the objective optical system described in Patent Document 4 is of this type. An example of an optical system that needs to form an image on a plane such as a videoscope that forms an image on a solid-state image sensor or a fiberscope that uses an image guide, that is, an optical system that corrects curvature of field to almost zero There is no.

  Furthermore, the type using an aspherical lens as described in Patent Document 2 has a remarkable effect of removing distortion, but the production of the aspherical lens generally has a drawback that the cost tends to increase.

  Further, the one described in Patent Document 3 uses a plurality of lenses in the front group, which increases the number of lenses, which similarly increases the cost and is not preferable.

  The objective optical system with less distortion and less curvature of field is suitable for endoscopic surgery. Endoscopic surgery is a procedure in which a small hole is made in the body and a video scope is inserted to secure a visual field, and forceps are inserted to perform surgery and treatment. There is an advantage that the burden on the patient is small, and it is mainly applied to gallbladder excision and lung resection such as spontaneous pneumothorax.

  Endoscopic surgery is not performed directly by an operator, but is performed by watching a video image through a television monitor. Therefore, an image with small distortion and curvature of field is preferable so as not to burden the operator. In endoscopic surgery, a rigid videoscope with good insertability is often used, and a perspective optical system having a visual field direction obliquely forward with respect to the longitudinal direction is preferred. Furthermore, there is a need to easily secure a surgical field of view in a perspective optical system. FIG. 39 shows the appearance of such a scope (rigid endoscope). When the operation knob K is rotated, for example, by 90 ° as shown by an arrow, the visual field shown in FIG. After the rotation, it becomes as shown in FIG.

  FIG. 41 (a) shows a monitor image under a surgical operation using an endoscope. When the entire scope is rotated, as shown in FIG. 41 (b), the top and bottom are in the direction of gravity. The direction of the biopsy forceps handled by the operator on the monitor does not match the top and bottom. This makes it very difficult to perform endoscopic surgery or the like that requires precise work.

  Therefore, as shown in FIGS. 42 (a) to (c), as a means for converting the visual field direction without changing the operator's top and bottom direction, the video scope itself has a rotation function. As shown in FIG. 43 (FIG. 1 of Patent Document 5), a technique for correcting image rotation by rotating the imaging surface 9 of the optical system is disclosed.

However, as in the case of Patent Document 5, if the CCD imaging surface 9 is fixed to the tip of the shaft 11 and rotated integrally, so-called play occurs due to manufacturing errors of interior parts and clearance between parts, and the shaft 11 is moved. When it is rotated, as shown in FIG. 44, the center of the visual field on the monitor moves so as to draw an arc, thereby inducing a problem that it is difficult to see on observation.
Japanese Patent Laid-Open No. 60-80816 US Pat. No. 4,867,546 US Pat. No. 6,618,207 Japanese Patent Publication No. 5-85884 US Pat. No. 6,464,631

  The present invention has been made in view of such a situation of the prior art, and its purpose is a low-cost endoscope objective optical system that is wide-angle, has little distortion, has little curvature of field, and includes only a spherical lens. In particular, it aims to provide a video endoscope objective optical system.

  Further, the present invention provides an eccentricity of the center of the visual field on the observation surface even when the visual field direction is changed by rotating in a perspective optical system capable of rotating the visual field direction in a desired direction with respect to the longitudinal direction of the endoscope. An object of the present invention is to provide an imaging system such as an electronic endoscope suitable for observation on a television monitor by providing an optical system in which generation is suppressed.

  In order to solve the above problems, an endoscope objective optical system according to the present invention includes, in order from the object side, a first group of negative meniscus lenses having a convex surface facing the object side, an aperture stop, and a flat surface on the object point side. A second lens unit having a positive refractive power, a third lens unit including at least one concave refracting surface and having a positive refractive power as a whole, and a positive refractive power composed of a cemented lens of a negative meniscus lens and a biconvex lens. An objective optical system that forms an image on the image sensor from the first group through the fourth group, and the principal ray is emitted from the convex surface of the positive lens in the second group. It is refracted in a direction away from the axis.

In this case, the lens thickness of the positive lens of the second group is t ₂ , the focal length is f ₂ , the refractive index is n ₂ , and the focal lengths of the negative meniscus lens of the first group and the entire optical system are f ₁ , respectively. , F, the Petzval sum due to the concave refractive surface of the third group is PS3, the Abbe numbers on the d-line basis of the positive lens and negative lens of the fourth group are νp and νn, respectively, and the focal length of the fourth group is f _{When 4} , it is desirable to satisfy the following conditional expression.

(1) 2 <f ₂ (n ₂ −1) / t ₂ <6
(2) -2.3 <f ₁ /F<-0.9
(3) -0.6 <PS3 <-0.2
(4) νp> 50, νn <30
(5) 2.3 <f ₄ / F
In addition, an imaging apparatus according to the present invention includes the above-described endoscope objective optical system and a solid-state imaging device disposed on an image plane thereof, and includes a front group from the first group, the brightness stop, and the second group. The rear group is composed of the third group and the fourth group, and the rear group and the solid-state imaging device are mechanically integrated, and the imaging device longitudinal direction with respect to the front group And an angle of incidence of an on-axis marginal ray incident on the rear group from the front group is substantially parallel to the rotation axis. It is characterized by being.

  Another imaging apparatus according to the present invention includes, in order from the object side, an endoscope objective optical system including a front group including a negative lens, a stop, and a positive lens, and a rear group including a positive refractive power as a whole, A solid-state imaging device disposed on an image plane, wherein the rear group and the solid-state imaging device are mechanically integrated, and rotate relative to the front group about the longitudinal direction of the imaging device. It is configured so that an incident angle of an on-axis marginal ray incident on the rear group from the front group is configured to be substantially parallel to the rotation axis. is there.

In the above imaging apparatus, when the focal length of the negative lens in the front group is f ₁ , the focal length of the positive lens in the front group is f ₂ , and the focal length of the entire endoscope objective optical system is F, It is desirable to satisfy the following conditional expressions.

(6) −0.3 <(f ₂ − | f ₁ |) / F <1.5
Further, a prism can be provided in the front group of the endoscope objective optical system to form a perspective optical system.

  Below, the reason and effect | action which take the said structure in this invention are demonstrated.

  When the retrofocus type is applied to the endoscope objective optical system, it is conceivable to place a convex lens in front of the concave lens on the object point side in order to correct distortion, but this is not possible due to outer diameter restrictions. . Therefore, in the present invention, attention is paid to a convex lens placed immediately after the stop. In order to form an image, a relatively strong convex action is necessary in the vicinity of the stop, but it is generally considered that a strong negative curve occurs in paraxial manner.

  FIG. 1B is a diagram showing the principal ray having the maximum image height as a thin lens system in the conventional optical system (FIG. 37). The chief ray intersects the optical axis at the aperture stop AS, refracts at the convex lens (second lens) L2 immediately after the stop AS, and thereafter forms an image by repeating refraction. Since the distance between the aperture stop AS and the convex lens L2 behind the aperture stop AS is relatively long, the light beam height becomes high. As a result, the refracting action (inside the circle in FIG. 1B) at the convex lens L2 immediately after the stop AS is bent in the direction approaching the optical axis, and negative distortion occurs.

  Therefore, in the present invention, as shown in FIG. 1A, when the stop AS is disposed immediately before the second lens (convex lens) L2, the refraction action of the off-axis principal ray on the curved surface of the second lens L2 is as shown in FIG. Like the inside of the circle in 1 (a), it is bent in the light direction away from the optical axis, and the second lens L2 is a convex lens, but can generate positive distortion. With the rear group (the third lens L3 and the fourth lens L4) having a convex configuration, it is possible to provide an effect of correcting negative distortion caused by the concave lens L1 of the front group.

  Conditional expression (1) is a conditional expression related to the ability to correct distortion and lens workability, and relates to the aperture stop of the optical system, the refractive index of the second lens L2 (second group positive lens), and the focal length. It is. If the stop position is on the image plane side from the center of curvature of the curved surface of the second lens L2, the principal ray is refracted in the direction away from the optical axis on the curved surface of the second lens L2. If the lower limit of 2 of the conditional expression (1) is not reached, off-axis rays cannot be raised in the direction away from the optical axis on the convex surface of the second lens L2, and positive distortion cannot be generated and there is no correction effect. When the upper limit of 6 is exceeded, the lens thickness of the second lens L2 becomes very small, which is not preferable in terms of lens processing.

  Conditional expression (2) is a conditional expression relating to the viewing angle, and relates to the focal length of the entire optical system and the focal length of the first lens unit L1 (negative meniscus lens). If the upper limit of -0.9 of conditional expression (2) is exceeded, the wide angle will be unfavorably large, but if it falls below the lower limit of -2.3, a viewing angle of 70 ° or more suitable for an endoscope will be obtained. It is not preferable because it cannot be secured.

  Further, in the present invention, the rear group is divided into the third group and the fourth group, and the third group is provided with a relatively strong concave surface having an air contact surface, and the fourth group is provided with a concave surface of the air contact surface. First, the positive lens and the meniscus lens are combined to have a positive refractive power as a whole. Accordingly, it is possible to achieve an optical system that corrects distortion and does not cause excessive curvature of field. Conditional expression (3) embodies these. When the Petzval sum due to the concave surface of the third lens group falls below the lower limit of −0.6, curvature of field and distortion become insufficiently corrected, and the upper limit − If it exceeds 0.2, the field curvature becomes excessive and the flatness of the image plane cannot be satisfied. Examples of a conventional endoscope optical system with little distortion include Examples 1 and 2 of Patent Document 4 described above, which are PS3 = −0.09 and −0.04, respectively. Conditional expression (3) is not satisfied (Table 1).

  Conditional expression (4) relates to the fourth group of bonding glass materials. In the fourth group, since the light ray height is highest in the rear group, the effect of correcting chromatic aberration at the cemented surface is high. In conditional expression (4), if the lower limit of 50 and the upper limit of 30 are exceeded, chromatic aberration of magnification becomes large, which is not preferable.

  Conditional expression (5) relates to the power arrangement of the fourth group, and is a conditional expression for controlling the light incident angle on the imaging surface. If the lower limit of 2.3 is not reached, the refractive power of the fourth group becomes large, the exit pupil cannot be further separated from the imaging surface, and the light incident angle cannot be reduced.

  Next, the present invention for a rotating optical system that enables the imaging surface to rotate will be described. In order to perform image rotation correction, the optical system must be structured to be mechanically separated into a front group and a rear group. As a result, a fitting portion is formed between the front group and the rear group, and naturally a clearance is required, and relative eccentricity is generated between the front group and the rear group. In the present invention, as shown in FIG. 2, the relationship between the front group (first lens L1 and second lens L2) and the rear group (third lens L3 and fourth lens L4) is substantially afocal. As a result, the exit pupil of the rear group becomes substantially infinite, and even if the front group is displaced in the direction perpendicular to the longitudinal direction of the endoscope, no deviation of the imaging position occurs in a paraxial manner. Furthermore, even if the front group and the rear group rotate relatively, it is possible to suppress the deviation of the center of the visual field.

Since the object plane is sufficiently larger than the focal length of the entire optical system, the on-axis marginal ray am from the object plane is incident as substantially parallel light, as shown in FIG. Bounced up by the concave action of the first lens L1, restricted by the aperture stop AS, and refracted in the optical axis direction by the convex action of the second lens L2. In order to make this marginal ray parallel to the optical axis (rotation axis), the rear focal position of the first lens L1 and the front focal position of the second lens L2 may be matched. The relationship between the focal lengths f ₁ and f _{2 of} the first lens L1 and the second lens L2 and the interval t ₁ between them is as follows:
t ₁ = f ₂ − | f ₁ |
It becomes. The axial afocal configuration between the front group and the rear group can be substantially achieved if the above relational expression is satisfied, but in reality, a prism that changes the viewing direction is required in the perspective optical system, and there is a value of t _1. Subject to certain restrictions. Conditional expression (6) shows the relationship between the focal lengths f ₁ and f ₂ due to the restriction between the optical path length of the prism and the outer diameter of the tip lens. When the upper limit of 1.5 is exceeded, the first lens L1 This increases the light beam height, increases the outer diameter of the cover glass having no refractive power at the tip, which leads to an increase in the diameter of the endoscope. Further, if the lower limit of −0.3 is not reached, the optical path length for twice reflection inside the prism becomes insufficient, and the viewing direction cannot be changed by one reflection, and an inverted image and a rear image (mirror image). It is not preferable.

  In the present invention, when the incident angle of the on-axis marginal ray incident from the front group to the rear group is made substantially parallel to the rotation axis, it is set within ± 3 °. means.

  According to the present invention described above, an endoscope objective optical system, particularly a video endoscope objective optical system, and an endoscope having a wide angle, a small distortion, a small curvature of field, and a relatively small number of lenses using only a spherical lens. It is possible to provide a perspective optical system that can rotate the visual field direction in a desired direction with respect to the mirror longitudinal direction. In addition, observation is performed even when the endoscope is rotated to change the visual field direction so that the desired visual field can be entered. An optical system that suppresses the occurrence of decentering of the field center on the surface can be provided, and in particular, an electronic endoscope suitable for observation on a television monitor can be realized.

  Examples 1 to 15 of the endoscope objective optical system according to the present invention will be described below.

Example 1
FIG. 4 shows an optical path diagram of the endoscope objective optical system according to the first embodiment of the present invention. FIG. 22 is an aberration diagram showing spherical aberration, astigmatism, lateral chromatic aberration, distortion aberration, and coma aberration of the endoscope objective optical system of Example 1. Here, “FNO” indicates the F number, and “I.H” indicates the image height. The same applies to the aberration diagrams of the following examples. The endoscope objective optical system according to this embodiment includes, in order from the object side, a first glass group G1 including a cover glass C of the objective optical system, a negative meniscus lens having a convex surface facing the object side, a parallel plate P, an aperture S, and an object. A second lens group G2 having a positive surface facing the side, a third lens group G3 comprising a cemented lens of a concave plano-negative lens and a plano-convex positive lens, a negative meniscus lens having a biconvex positive lens and a convex surface facing the image surface side And an object image is formed on the imaging surface I via the infrared cut filter F and the cover glass G of the CCD.

  The principal ray on the convex surface of the convex lens (second group G2) immediately after the stop S is refracted in the direction away from the optical axis, as is apparent from FIG. Further, the cemented surface of the fourth group G4 has a negative refractive power, and the principal ray is also refracted in the direction away from the optical axis to correct the distortion on this surface having a high ray height. The incident angle of the CCD onto the imaging surface I is about 3 ° at the maximum image height.

  The concave surface of the third lens group G3 corrects the curvature of field. The refractive power of the entire fourth lens group G4 is weak, and coma, astigmatism, and lateral chromatic aberration are mainly corrected.

  Since the plano-convex lens (second lens, second group G2) immediately after the stop S refracts the chief ray immediately after the stop S, when the tilt occurs, the chief ray above and below the optical axis is asymmetrically refracted. Cause blurring on the image plane.

  In order to prevent this, the inclination can be prevented by setting the plane side to the object-side parallel plate P as in the present embodiment. In addition, the plane-parallel plate P placed between the first lens (first group G1) and the second lens (second group G2) is used for a prism when the optical system of this embodiment is a perspective optical system. It is an optical path. If this is omitted, astigmatism and chromatic aberration worsen. When the direct-viewing optical system and the perspective optical system are composed of the same lens, it is desirable to put a parallel plate P for the prism optical path length in the direct-viewing optical system.

  Lens data of this example will be described later. The same applies to the following embodiments.

(Example 2)
FIG. 5 shows an optical path diagram of the endoscope objective optical system according to the second embodiment of the present invention. FIG. 23 is an aberration diagram similar to FIG. 22 of the endoscope objective optical system according to Example 2. The second group G2 is the same as in Example 1, and the third group G3 is composed of a convex plano-positive lens with a convex surface facing the object side, a biconcave negative lens, and a plano-convex positive lens with a convex surface facing the image surface side. The fourth group G4 is composed of a cemented lens of a negative meniscus lens having a convex surface facing the object surface and a biconvex positive lens. An object image is captured on the imaging surface I through an infrared cut filter F and a cover glass G of the CCD. Form an image.

  The refraction of the chief ray on the convex surface of the second lens (second group G2) immediately after the stop S is in a direction away from the optical axis, generates a positive distortion, and particularly an image of the negative lens in the third group G3. The distortion on the side surface is corrected positively, and the distortion is very small at about -6.4% at the maximum image height. Distortion and chromatic aberration of magnification are corrected by the negative action of the joint surface of the fourth group G4. The two plano-convex positive lenses in the third group G3 are of the same type and are convenient in terms of cost, and the curvatures of the biconcave negative lenses are equal, which is convenient because there is no discrimination of the direction during assembly. In addition, a flare stop FS is provided between the biconcave negative lens of the third group G3 and the planoconvex positive lens on the image plane side in order to remove ghost light by reflection from the CCD imaging surface. Further, the biconcave negative lens of the third lens group G3 is provided with a flat surface on the concave surface and faces the imaging surface side plano-convex positive lens, thereby suppressing the occurrence of eccentricity due to the tilt in the machine frame.

(Example 3)
FIG. 6 shows an optical path diagram of the endoscope objective optical system according to the third embodiment of the present invention. FIG. 24 is an aberration diagram similar to FIG. 22 of the endoscope objective optical system according to Example 3. The second group G2 is the same as in the first and second embodiments, and the third group G3 is composed of a cemented lens of a biconvex positive lens and a biconcave negative lens. Comprises a cemented lens of a negative meniscus lens having a convex surface facing the object side and a biconvex positive lens, and forms an object image on the imaging surface I through the cover glass G of the CCD.

  The function of the second lens is the same as in Examples 1 and 2, and the distortion and lateral chromatic aberration are corrected by the negative action of the air contact surface of the third group G3. The distortion is -8.8% at the maximum image height. Further, the third group G3 and the parallel plate immediately after the third group G3 are bonded, and the edge (lens outer peripheral length) is lengthened to suppress the eccentricity due to the inclination. Between the third group G3 and the absorption filter F, a stop FS for preventing flare caused by reflection from the CCD imaging surface is inserted. The infrared absorption filter F may be provided with a YAG laser (wavelength 1076 nm) cut coat, a semiconductor laser (wavelength 805 nm) cut coat, or the like in addition to a normal antireflection coating. In that case, considering the characteristics of the interference filter, it is preferable that the incident angle is 25 ° or less because the shift of the cut wavelength is small and laser cut can be achieved.

  In general, an imaging optical system includes an infrared cut filter for cutting off unnecessary infrared light. These include an interference filter using a multilayer film and an absorption type that is cut by the material itself, but the interference type has drawbacks such as a limited incident angle, flare, and ghosting. Often used. Infrared absorption filters have a larger coefficient of thermal expansion than general optical glass, so if they are pasted and bonded to a CCD imaging surface, etc., the adhesive surface will peel off when sterilized at high temperatures. There is. In order to prevent such inconvenience, an absorption filter is not bonded to the CCD, and it is preferable to arrange it inside the optical system as in this embodiment.

  As described above, in conventional endoscopes, a telecentric optical system is suitable for preventing a reduction in light amount. By adjusting and arranging the microlens installed in the lens, it is possible to tilt the incident angle from which the light quantity does not decrease from the vertical. Nowadays, even if the incident angle is up to about 20 °, a light amount that does not cause a decrease in the amount of light is realized. In this embodiment, the incident angle of the chief ray on the imaging surface is 11 °.

Example 4
FIG. 7 shows an optical path diagram of the endoscope objective optical system according to the fourth embodiment of the present invention. FIG. 25 is an aberration diagram similar to FIG. 22 of the endoscope objective optical system according to Example 4. In this embodiment, a prism Pr is provided at the tip of the optical system, and the front perspective is 30 °. From the object side, through the cover glass C, the first lens constituting the first group G1, the first prism Pr1, and the second prism Pr2, it is reflected by the aluminum coat Al on the bottom surface of the second prism Pr2, and further the second prism Pr2 Of the first prism Pr1 is totally reflected and emitted toward the second lens constituting the second group G2. The configuration after the second group G2 is the same as that of the first embodiment.

  In this prism Pr, the transmitted light beam and the reflected light beam are separated on the side surface of the first prism Pr1 of the second prism Pr2, the vignetting of the light beam due to the aluminum coat Al does not occur, and the illuminance on the image surface I becomes constant. Is good.

  There is an air layer between the first prism Pr1 and the second prism Pr2, and total reflection within the second prism Pr2 is achieved.

In order to increase the critical angle of this total reflection, it is preferable to increase the refractive index of the second prism Pr2. In this embodiment, n _d = 1.883 and the critical angle is about 32 °. . The angle of the on-axis marginal ray between the second group G2 and the third group G3 is about −2.2 ° with respect to the optical axis, and the front group (up to the second group G2) and the rear group (third group). The movement of the image center on the image plane I is less with respect to the eccentricity of G3 and thereafter.

  Furthermore, it is desirable that the distance between the front group and the rear group be set to some extent in order to cope with variations due to mechanical fitting and rotation of the movable part. If this distance is narrow, the lens may collide during assembly and damage the lens surface, which is not preferable. In the endoscope objective optical system of this embodiment, the focal length is standardized, but in actual assembly, the interval between the front group and the rear group is set to 1 mm.

(Example 5)
FIG. 8 shows an optical path diagram of the endoscope objective optical system according to the fifth embodiment of the present invention. FIG. 26 is an aberration diagram similar to FIG. 22 of the endoscope objective optical system according to Example 5. In this embodiment, the path passing through the first prism Pr1 and the second prism Pr2 is the same as in the first embodiment, but the total reflection is performed on the bottom surface of the second prism Pr2, and the first prism Pr1 of the second prism Pr2 is used. After the aluminum coat Al is provided on the side surface and reflected, the light enters the second lens constituting the second group G2. Unlike the fourth embodiment, this type of prism eliminates the need for an air layer for total reflection between the first prism Pr1 and the second prism Pr2, and therefore an asymmetrical aberration (particularly astigmatism due to the wedge effect of the air layer). (Aberration) does not occur, which is convenient. The glass material of the prism preferably has a large refractive index in order to increase the total reflection critical angle, n _d = 1.883, and the critical angle is about 32 °. The configuration after the second group G2 is the same as that of the second embodiment. Further, the angle of the on-axis marginal ray between the second group G2 and the third group G3 is about −0.7 ° with respect to the optical axis and is substantially afocal, so that the front group (second group The image plane movement can be suppressed with respect to the eccentricity of the rear group (up to G2) and the rear group (third group G3 and later).

  FIGS. 9A and 9B respectively show an optical system having a structure in which the front group FG and the rear group RG of the present embodiment are fitted and the rear group RG and the CCD unit IU are rotated together, and a patent. In the optical system of the structure which rotates CCD unit IU like literature 5, it is the figure which showed the behavior of the on-axis light beam when a movable part was shifted +0.1 mm in the direction perpendicular | vertical (↑) with respect to an optical axis. is there. FIG. 9B shows a structure as in Patent Document 5 in which only the CCD unit IU is moved, and the optical axis center moves downward by 0.1 mm, which is the same amount as the shift amount of the CCD unit IU, with respect to the CCD imaging surface. To do. FIG. 9A shows the present embodiment. When the rear group RG and the CCD unit IU are moved in the same manner, the optical axis movement relative to the CCD imaging surface is only 0.02 mm. It can be seen that rotating the rear group RG including the CCD unit IU effectively reduces the image eccentricity by making the optical system division portion (between the front group FG and the rear group RG) substantially afocal.

(Example 6)
FIG. 10 shows an optical path diagram of the endoscope objective optical system according to the sixth embodiment of the present invention. FIG. 27 is an aberration diagram similar to FIG. 22 of the endoscope objective optical system according to Example 6. In this embodiment, the path passing through the first prism Pr1 and the second prism Pr2 is the same as in the fifth embodiment, and the glass material of the prism is also the same. The configuration after the second group G2 is the same as that of the third embodiment. The angle of the on-axis marginal ray between the second group G2 and the third group G3 is approximately −1.8 ° with respect to the optical axis, and is substantially afocal, with respect to the eccentricity of the front group and the rear group. The movement of the image center on the image plane is reduced.

  Here, in common with Examples 4 to 6, the relationship between the optical system and the machine frame will be described. FIG. 11 shows a cross-sectional view of the internal structure of the rigid endoscope insertion portion of FIG. FIG. 12 is an enlarged view of the tip (arrow part in FIG. 11). The meniscus lens 21 (G1), the prism 22 (Pr), and the plano-convex lens 23 (G2) at the tip are housed in a frame 24 (hereinafter referred to as a “part 1”). The assembly 1 is bonded to the exterior tube 25, and the exterior space 25 extends to the endoscope operation section and is integrated with the operation knob K in FIG.

  On the other hand, the third group and the fourth group are integrally mounted on the frame 26, and are fitted and integrated with the frame 27 in which the CCD is mounted (hereinafter referred to as a set 2). The part set 1 and the part set 2 are not bonded, and the part set 1 is relatively rotatable about the center in the longitudinal direction of the part set 2 and the center of the CCD imaging surface. Then, as shown in FIGS. 42A to 42C, the image is converted into a desired visual field direction. It is desirable to make the fitting length as long as possible so that a relative inclination between the frame 24 and the frame 26 does not occur.

  Furthermore, when there is a visual field direction rotation correction mechanism, the illumination means must also be able to rotate following the visual field direction (FIG. 42). In this embodiment, the light guide is built in the outer tube 25 and is configured to be rotatable together with the front group. The light guide is not fixed at the proximal portion of the endoscope and can be moved by a turning operation. The light guide is bent and formed at the distal end of the endoscope so as to illuminate the visual field direction.

(Examples 7 to 15)
13 to 21 show optical path diagrams of the endoscope objective optical systems of Examples 7 to 15, respectively. FIGS. 28 to 36 show aberration diagrams similar to FIG. 22 of the endoscope objective optical systems of Examples 7 to 15, respectively.

  Although details of these examples are omitted, Examples 7 to 9 (FIGS. 13 to 15) have the same configuration as that of Example 2 (FIG. 5).

  Examples 10 to 13 (FIGS. 16 to 19) have the same configuration as that of Example 1 (FIG. 4).

  Examples 14-15 (FIGS. 20-21) are the same as the structure of Example 3 (FIG. 6).

  In addition, although all the endoscope objective optical systems of the above Examples 1 to 15 are standardized with a focal length of 1 for simplicity, the focal length is about 1 to 3 mm as the endoscope objective optical system. The image height is desirably about 0.5 to 2 mm.

Next, show lens data of Examples 1 to 15 of the present invention, the symbols used in the respective lens data, out of the, F is the focal length of the entire optical system, F _NO is the F-number, Ih Is the maximum image height at the image plane, 2ω is the viewing angle, D is the distortion at the maximum image height, α is the incident angle of the principal ray to the maximum image height of the image plane, r ₁ , r ₂ . The curvature radii, d ₁ , d ₂ ... _Are the distances between the lens surfaces, n _d1 , n _d2 ... _Are the refractive indices of the d-line of each lens, and ν _d1 , ν _d2 . R ₀ is the object plane, and d ₀ is the object distance.

Example 1
r ₀ = ∞ (object) d ₀ = 14.4568
r ₁ = ∞ d ₁ = 0.2754 n _d1 = 1.76820 ν _d1 = 71.79
r ₂ = ∞ d ₂ = 0.2065
r ₃ = 2.5155 d ₃ = 0.2065 n _d2 = 1.88300 ν _d2 = 40.76
r ₄ = 0.7993 d ₄ = 0.2341
r ₅ = ∞ d ₅ = 1.9276 n _d3 = 1.80610 ν _d3 = 40.95
r ₆ = ∞ d ₆ = 0.0000
r ₇ = ∞ (aperture) d ₇ = 0.0207
r ₈ = ∞ d ₈ = 0.3442 n _d4 = 1.88300 ν _d4 = 40.76
r ₉ = -1.4918 d ₉ = 0.6884
r ₁₀ = -1.5696 d ₁₀ = 0.2134 n _d5 = 1.84666 ν _d5 = 23.78
r ₁₁ = ∞ d ₁₁ = 0.6884 n _d6 = 1.88300 ν _d6 = 40.76
r ₁₂ = -1.4918 d ₁₂ = 0.0688
r ₁₃ = 3.6989 d ₁₃ = 0.8261 n _d7 = 1.51633 ν _d7 = 64.14
r ₁₄ = -1.0884 d ₁₄ = 0.2065 n _d8 = 1.84666 ν _d8 = 23.78
r ₁₅ = -2.4102 d ₁₅ = 0.3373
r ₁₆ = ∞ d ₁₆ = 1.1015 n _d9 = 1.51399 ν _d9 = 75.00
r ₁₇ = ∞ d ₁₇ = 0.0138 n _d10 = 1.51000 ν _d10 = 63.00
r ₁₈ = ∞ d ₁₈ = 0.3442 n _d11 = 1.51633 ν _d11 = 64.14
r ₁₉ = ∞ d ₁₉ = 0.0207
r ₂₀ = ∞ (image plane)

F = 1.00
F _NO = 6.058
Ih = 0.627
2ω (°) = 69.425
D (%) = -9.475
α (°) = 3.038.

Example 2
r ₀ = ∞ (object) d ₀ = 14.9395
r ₁ = ∞ d ₁ = 0.2988 n _d1 = 1.76820 ν _d1 = 71.79
r ₂ = ∞ d ₂ = 0.2134
r ₃ = 4.5420 d ₃ = 0.1921 n _d2 = 1.88300 ν _d2 = 40.76
r ₄ = 0.8204 d ₄ = 0.1921
r ₅ = ∞ d ₅ = 2.5610 n _d3 = 1.88300 ν _d3 = 40.76
r ₆ = ∞ (aperture) d ₆ = 0.0128
r ₇ = ∞ d ₇ = 0.4695 n _d4 = 1.72916 ν _d4 = 54.68
r ₈ = -1.7253 d ₈ = 0.2988
r ₉ = 1.6404 d ₉ = 0.5976 n _d5 = 1.88300 ν _d5 = 40.76
r ₁₀ = ∞ d ₁₀ = 0.2134
r ₁₁ = -1.5832 d ₁₁ = 0.6701 n _d6 = 1.75520 ν _d6 = 27.51
r ₁₂ = 1.5832 d ₁₂ = 0.1067
r ₁₃ = ∞ d ₁₃ = 0.5976 n _d7 = 1.88300 ν _d7 = 40.76
r ₁₄ = -1.6404 d ₁₄ = 0.0427
r ₁₅ = 2.4889 d ₁₅ = 0.2134 n _d8 = 1.84666 ν _d8 = 23.78
r ₁₆ = 1.0321 d ₁₆ = 0.6360 n _d9 = 1.48749 ν _d9 = 70.23
r ₁₇ = -2.8462 d ₁₇ = 0.2220
r ₁₈ = ∞ d ₁₈ = 0.6829 n _d10 = 1.51400 ν _d10 = 75.00
r ₁₉ = ∞ d ₁₉ = 0.0085 n _d11 = 1.51000 ν _d11 = 63.00
r ₂₀ = ∞ d ₂₀ = 0.2134 n _d12 = 1.51633 ν _d12 = 64.14
r ₂₁ = ∞ d ₂₁ = 0.0128
r ₂₂ = ∞ (image plane)

F = 1.00
F _NO = 7.925
Ih = 0.643
2ω (°) = 69.016
D (%) = -6.353
α (°) = 5.468.

Example 3
r ₀ = ∞ (object) d ₀ = 14.5912
r ₁ = ∞ d ₁ = 0.2918 n _d1 = 1.76820 ν _d1 = 71.79
r ₂ = ∞ d ₂ = 0.2084
r ₃ = 2.7707 d ₃ = 0.2084 n _d2 = 1.88300 ν _d2 = 40.76
r ₄ = 0.7158 d ₄ = 0.1751
r ₅ = ∞ d ₅ = 0.0125
r ₆ = ∞ d ₆ = 2.2929 n _d3 = 1.88300 ν _d3 = 40.76
r ₇ = ∞ (aperture) d ₇ = 0.0125
r ₈ = ∞ d ₈ = 0.3669 n _d4 = 1.78800 ν _d4 = 47.37
r ₉ = -1.3111 d ₉ = 0.2918
r ₁₀ = 1.4770 d ₁₀ = 0.5420 n _d5 = 1.88300 ν _d5 = 40.76
r ₁₁ = -2.5901 d ₁₁ = 0.2501 n _d6 = 1.74077 ν _d6 = 27.79
r ₁₂ = 0.8288 d ₁₂ = 0.1876
r ₁₃ = ∞ d ₁₃ = 0.2501 n _d7 = 1.51800 ν _d7 = 74.60
r ₁₄ = ∞ d ₁₄ = 0.0417
r ₁₅ = 3.2188 d ₁₅ = 0.2084 n _d8 = 1.84666 ν _d8 = 23.78
r ₁₆ = 1.2428 d ₁₆ = 0.6253 n _d9 = 1.51633 ν _d9 = 64.14
r ₁₇ = -1.4479 d ₁₇ = 0.1876
r ₁₈ = ∞ d ₁₈ = 0.4211 n _d10 = 1.51633 ν _d10 = 64.14
r ₁₉ = ∞ d ₁₉ = 0.4169 n _d11 = 1.61350 ν _d11 = 50.20
r ₂₀ = ∞ d ₂₀ = 0.0000
r ₂₁ = ∞ (image plane)

F = 1.00
F _NO = 8.925
Ih = 0.679
2ω (°) = 72.785
D (%) = -8.913
α (°) = 11.358.

Example 4
r ₀ = ∞ (object) d ₀ = 14.4592
r ₁ = ∞ d ₁ = 0.2754 n _d1 = 1.76820 ν _d1 = 71.79
r ₂ = ∞ d ₂ = 0.2066
r ₃ = 2.5159 d ₃ = 0.2066 n _d2 = 1.88300 ν _d2 = 40.76
r ₄ = 0.7994 d ₄ = 0.2341
r ₅ = ∞ d ₅ = 0.3305 n _d3 = 1.88300 ν _d3 = 40.76
r ₆ = ∞ d ₆ = 0.0392
r ₇ = ∞ d ₇ = 0.4462 n _d4 = 1.88300 ν _d4 = 40.76
r ₈ = ∞ d ₈ = 0.6094 n _d5 = 1.88300 ν _d5 = 40.76
r ₉ = ∞ d ₉ = 0.5508 n _d6 = 1.88300 ν _d6 = 40.76
r ₁₀ = ∞ (aperture) d ₁₀ = 0.0207
r ₁₁ = ∞ d ₁₁ = 0.3443 n _d7 = 1.88300 ν _d7 = 40.76
r ₁₂ = -1.4921 d ₁₂ = 0.6885
r ₁₃ = -1.5699 d ₁₃ = 0.2134 n _d8 = 1.84666 ν _d8 = 23.78
r ₁₄ = ∞ d ₁₄ = 0.6885 n _d9 = 1.88300 ν _d9 = 40.76
r ₁₅ = -1.4921 d ₁₅ = 0.0689
r ₁₆ = 3.6995 d ₁₆ = 0.8262 n _d10 = 1.51633 ν _d10 = 64.14
r ₁₇ = -1.0886 d ₁₇ = 0.2066 n _d11 = 1.84666 ν _d11 = 23.78
r ₁₈ = -2.4106 d ₁₈ = 0.3374
r ₁₉ = ∞ d ₁₉ = 1.1017 n _d12 = 1.51399 ν _d12 = 75.00
r ₂₀ = ∞ d ₂₀ = 0.0138 n _d13 = 1.51000 ν _d13 = 63.00
r ₂₁ = ∞ d ₂₁ = 0.3443 n _d14 = 1.51633 ν _d14 = 64.14
r ₂₂ = ∞ d ₂₂ = 0.0207
r ₂₃ = ∞ (image plane)

F = 1.00
F _NO = 6.058
Ih = 0.627
2ω (°) = 69.406
D (%) = -9.428
α (°) = 3.037.

Example 5
r ₀ = ∞ (object) d ₀ = 14.9395
r ₁ = ∞ d ₁ = 0.2988 n _d1 = 1.76820 ν _d1 = 71.79
r ₂ = ∞ d ₂ = 0.2134
r ₃ = 4.5420 d ₃ = 0.1921 n _d2 = 1.88300 ν _d2 = 40.76
r ₄ = 0.8204 d ₄ = 0.1921
_{r 5 = ∞ d 5 = 0.7022} n d3 = 1.88300 ν d3 = 40.76
r ₆ = ∞ d ₆ = 0.4930 n _d4 = 1.88300 ν _d4 = 40.76
r ₇ = ∞ d ₇ = 0.8537 n _d5 = 1.88300 ν _d5 = 40.76
r ₈ = ∞ d ₈ = 0.5122 n _d6 = 1.88300 ν _d6 = 40.76
r ₉ = ∞ (aperture) d ₉ = 0.0128
r ₁₀ = ∞ d ₁₀ = 0.4695 n _d7 = 1.72916 ν _d7 = 54.68
r ₁₁ = -1.7253 d ₁₁ = 0.2988
r ₁₂ = 1.6404 d ₁₂ = 0.5976 n _d8 = 1.88300 ν _d8 = 40.76
r ₁₃ = ∞ d ₁₃ = 0.2134
r ₁₄ = -1.5832 d ₁₄ = 0.6701 n _d9 = 1.75520 ν _d9 = 27.51
r ₁₅ = 1.5832 d ₁₅ = 0.1067
r ₁₆ = ∞ d ₁₆ = 0.5976 n _d10 = 1.88300 ν _d10 = 40.76
r ₁₇ = -1.6404 d ₁₇ = 0.0427
r ₁₈ = 2.4889 d ₁₈ = 0.2134 n _d11 = 1.84666 ν _d11 = 23.78
r ₁₉ = 1.0321 d ₁₉ = 0.6360 n _d12 = 1.48749 ν _d12 = 70.23
r ₂₀ = -2.8462 d ₂₀ = 0.2220
r ₂₁ = ∞ d ₂₁ = 0.6829 n _d13 = 1.51400 ν _d13 = 75.00
r ₂₂ = ∞ d ₂₂ = 0.0085 n _d14 = 1.51000 ν _d14 = 63.00
r ₂₃ = ∞ d ₂₃ = 0.2134 n _d15 = 1.51633 ν _d15 = 64.14
r ₂₄ = ∞ d ₂₄ = 0.0128
r ₂₅ = ∞ (image plane)

F = 1.00
F _NO = 7.925
Ih = 0.643
2ω (°) = 69.016
D (%) = -6.353
α (°) = 5.468.

Example 6
r ₀ = ∞ (object) d ₀ = 20.8169
r ₁ = ∞ d ₁ = 0.2914 n _d1 = 1.76820 ν _d1 = 71.79
r ₂ = ∞ d ₂ = 0.2082
r ₃ = 2.7670 d ₃ = 0.2082 n _d2 = 1.88300 ν _d2 = 40.76
r ₄ = 0.7149 d ₄ = 0.1874
r ₅ = ∞ d ₅ = 0.6245 n _d3 = 1.88300 ν _d3 = 40.76
r ₆ = ∞ d ₆ = 0.4413 n _d4 = 1.88300 ν _d4 = 40.76
_{r 7 = ∞ d 7 = 0.7619} n d5 = 1.88300 ν d5 = 40.76
r ₈ = ∞ d ₈ = 0.4580 n _d6 = 1.88300 ν _d6 = 40.76
r ₉ = ∞ (aperture) d ₉ = 0.0125
r ₁₀ = ∞ d ₁₀ = 0.3664 n _d7 = 1.78800 ν _d7 = 47.37
r ₁₁ = -1.3094 d ₁₁ = 0.2914
r ₁₂ = 1.4751 d ₁₂ = 0.5412 n _d8 = 1.88300 ν _d8 = 40.76
r ₁₃ = -2.5867 d ₁₃ = 0.2498 n _d9 = 1.74077 ν _d9 = 27.79
r ₁₄ = 0.8277 d ₁₄ = 0.1874
r ₁₅ = ∞ d ₁₅ = 0.2498 n _d10 = 1.51800 ν _d10 = 74.60
r ₁₆ = ∞ d ₁₆ = 0.0416
_{r 17 = 3.2145 d 17 = 0.2082} n d11 = 1.84666 ν d11 = 23.78
r ₁₈ = 1.2411 d ₁₈ = 0.6245 n _d12 = 1.51633 ν _d12 = 64.14
r ₁₉ = -1.4459 d ₁₉ = 0.1874
r ₂₀ = ∞ d ₂₀ = 0.4205 n _d13 = 1.51633 ν _d13 = 64.14
r ₂₁ = ∞ d ₂₁ = 0.4163 n _d14 = 1.61350 ν _d14 = 50.20
r ₂₂ = ∞ d ₂₂ = 0.0000
r ₂₃ = ∞ (image plane)

F = 1.00
F _NO = 8.885
Ih = 0.678
2ω (°) = 72.715
D (%) = -8.621
α (°) = 11.358.

Example 7
r ₀ = ∞ (object) d ₀ = 14.6532
r ₁ = ∞ d ₁ = 0.2931 n _d1 = 1.76820 ν _d1 = 71.79
r ₂ = ∞ d ₂ = 0.2093
r ₃ = 4.3378 d ₃ = 0.1884 n _d2 = 1.88300 ν _d2 = 40.76
r ₄ = 0.8191 d ₄ = 0.1884
r ₅ = ∞ d ₅ = 2.5120 n _d3 = 1.88300 ν _d3 = 40.76
r ₆ = ∞ (aperture) d ₆ = 0.0126
r ₇ = ∞ d ₇ = 0.4605 n _d4 = 1.72916 ν _d4 = 54.68
r ₈ = -1.6417 d ₈ = 0.2931
r ₉ = 1.5032 d ₉ = 0.4187 n _d5 = 1.77250 ν _d5 = 49.60
r ₁₀ = ∞ d ₁₀ = 0.2093
r ₁₁ = -3.3253 d ₁₁ = 0.4187 n _d6 = 1.75520 ν _d6 = 27.51
r ₁₂ = 1.9014 d ₁₂ = 0.1758
r ₁₃ = ∞ d ₁₃ = 0.5382 n _d7 = 1.72916 ν _d7 = 54.68
r ₁₄ = -2.1251 d ₁₄ = 0.0837
r ₁₅ = 6.2758 d ₁₅ = 0.6238 n _d8 = 1.51823 ν _d8 = 58.90
r ₁₆ = -0.7299 d ₁₆ = 0.2093 n _d9 = 1.71736 ν _d9 = 29.52
r ₁₇ = -2.9131 d ₁₇ = 0.0937
r ₁₈ = ∞ d ₁₈ = 0.6699 n _d10 = 1.51400 ν _d10 = 75.00
r ₁₉ = ∞ d ₁₉ = 0.0084 n _d11 = 1.51000 ν _d11 = 63.00
r ₂₀ = ∞ d ₂₀ = 0.2093 n _d12 = 1.51633 ν _d12 = 64.14
r ₂₁ = ∞ d ₂₁ = 0.0126
r ₂₂ = ∞ (image plane)

F = 1.00
F _NO = 4.634
Ih = 0.631
2ω (°) = 68.610
D (%) = -8.317
α (°) = 8.899.

Example 8
r ₀ = ∞ (object) d ₀ = 14.4134
r ₁ = ∞ d ₁ = 0.2883 n _d1 = 1.76820 ν _d1 = 71.79
r ₂ = ∞ d ₂ = 0.2059
r ₃ = 5.1056 d ₃ = 0.1853 n _d2 = 1.88300 ν _d2 = 40.76
r ₄ = 0.7598 d ₄ = 0.1854
r ₅ = ∞ d ₅ = 2.4709 n _d3 = 1.88300 ν _d3 = 40.76
r ₆ = ∞ (aperture) d ₆ = 0.0124
r ₇ = ∞ d ₇ = 0.2059 n _d4 = 1.72916 ν _d4 = 54.68
r ₈ = -1.4755 d ₈ = 0.2883
r ₉ = 1.5871 d ₉ = 0.4375 n _d5 = 1.77250 ν _d5 = 49.60
r ₁₀ = ∞ d ₁₀ = 0.2059
r ₁₁ = -4.0713 d ₁₁ = 0.4118 n _d6 = 1.75520 ν _d6 = 27.51
r ₁₂ = 1.8879 d ₁₂ = 0.1730
r ₁₃ = ∞ d ₁₃ = 0.5294 n _d7 = 1.72916 ν _d7 = 54.68
r ₁₄ = -2.1561 d ₁₄ = 0.0824
r ₁₅ = 7.1108 d ₁₅ = 0.6136 n _d8 = 1.51823 ν _d8 = 58.90
r ₁₆ = -0.7292 d ₁₆ = 0.2059 n _d9 = 1.71736 ν _d9 = 29.52
r ₁₇ = -3.4414 d ₁₇ = 0.1140
r ₁₈ = ∞ d ₁₈ = 0.6589 n _d10 = 1.51400 ν _d10 = 75.00
r ₁₉ = ∞ d ₁₉ = 0.0082 n _d11 = 1.51000 ν _d11 = 63.00
r ₂₀ = ∞ d ₂₀ = 0.2059 n _d12 = 1.51633 ν _d12 = 64.14
r ₂₁ = ∞ d ₂₁ = 0.0124
r ₂₂ = ∞ (image plane)

F = 1.00
F _NO = 5.060
Ih = 0.621
2ω (°) = 67.792
D (%) = -8.808
α (°) = 10.508.

Example 9
r ₀ = ∞ (object) d ₀ = 14.8973
r ₁ = ∞ d ₁ = 0.2979 n _d1 = 1.76820 ν _d1 = 71.79
r ₂ = ∞ d ₂ = 0.2128
r ₃ = 3.0953 d ₃ = 0.1915 n _d2 = 1.88300 ν _d2 = 40.76
r ₄ = 0.9805 d ₄ = 0.1916
r ₅ = ∞ d ₅ = 2.3800 n _d3 = 1.88300 ν _d3 = 40.76
r ₆ = ∞ (aperture) d ₆ = 0.0128
r ₇ = ∞ d ₇ = 0.6385 n _d4 = 1.72916 ν _d4 = 54.68
r ₈ = -1.8937 d ₈ = 0.2979
r ₉ = 2.0182 d ₉ = 0.4522 n _d5 = 1.77250 ν _d5 = 49.60
r ₁₀ = ∞ d ₁₀ = 0.2128
r ₁₁ = -2.5538 d ₁₁ = 0.4256 n _d6 = 1.75520 ν _d6 = 27.51
r ₁₂ = 3.5902 d ₁₂ = 0.1787
r ₁₃ = ∞ d ₁₃ = 0.5472 n _d7 = 1.72916 ν _d7 = 54.68
r ₁₄ = -1.3625 d ₁₄ = 0.0851
r ₁₅ = 3.3306 d ₁₅ = 0.6342 n _d8 = 1.51823 ν _d8 = 58.90
r ₁₆ = -0.7834 d ₁₆ = 0.2128 n _d9 = 1.71736 ν _d9 = 29.52
r ₁₇ = -5.2313 d ₁₇ = 0.1146
r ₁₈ = ∞ d ₁₈ = 0.6810 n _d10 = 1.51400 ν _d10 = 75.00
r ₁₉ = ∞ d ₁₉ = 0.0085 n _d11 = 1.51000 ν _d11 = 63.00
r ₂₀ = ∞ d ₂₀ = 0.2128 n _d12 = 1.51633 ν _d12 = 64.14
r ₂₁ = ∞ d ₂₁ = 0.0128
r ₂₂ = ∞ (image plane)

F = 1.00
F _NO = 8.885
Ih = 0.641
2ω (°) = 68.037
D (%) = -4.880
α (°) = 4.876.

Example 10
r ₀ = ∞ (object) d ₀ = 14.2337
r ₁ = ∞ d ₁ = 0.2711 n _d1 = 1.76820 ν _d1 = 71.79
r ₂ = ∞ d ₂ = 0.2033
r ₃ = 2.1480 d ₃ = 0.2033 n _d2 = 1.88300 ν _d2 = 40.76
r ₄ = 0.8544 d ₄ = 0.2304
r ₅ = ∞ d ₅ = 1.8978 n _d3 = 1.80610 ν _d3 = 40.95
r ₆ = ∞ d ₆ = 0.0000
r ₇ = ∞ (aperture) d ₇ = 0.0203
r ₈ = ∞ d ₈ = 0.3389 n _d4 = 1.88300 ν _d4 = 40.76
r ₉ = -1.7259 d ₉ = 0.6778
r ₁₀ = -2.0622 d ₁₀ = 0.2101 n _d5 = 1.84666 ν _d5 = 23.78
r ₁₁ = ∞ d ₁₁ = 0.6778 n _d6 = 1.88300 ν _d6 = 40.76
r ₁₂ = -1.5631 d ₁₂ = 0.0678
r ₁₃ = 2.2179 d ₁₃ = 0.8134 n _d7 = 1.51633 ν _d7 = 64.14
r ₁₄ = -1.2429 d ₁₄ = 0.2033 n _d8 = 1.84666 ν _d8 = 23.78
r ₁₅ = -3.6966 d ₁₅ = 0.1105
r ₁₆ = ∞ d ₁₆ = 1.0845 n _d9 = 1.51399 ν _d9 = 75.00
r ₁₇ = ∞ d ₁₇ = 0.0136 n _d10 = 1.51000 ν _d10 = 63.00
r ₁₈ = ∞ d ₁₈ = 0.3389 n _d11 = 1.51633 ν _d11 = 64.14
r ₁₉ = ∞ d ₁₉ = 0.0203
r ₂₀ = ∞ (image plane)

F = 1.00
F _NO = 5.522
Ih = 0.617
2ω (°) = 68.239
D (%) = -8.977
α (°) = 3.029.

Example 11
r ₀ = ∞ (object) d ₀ = 14.2786
r ₁ = ∞ d ₁ = 0.2720 n _d1 = 1.76820 ν _d1 = 71.79
r ₂ = ∞ d ₂ = 0.2040
r ₃ = 2.2075 d ₃ = 0.2040 n _d2 = 1.88300 ν _d2 = 40.76
r ₄ = 0.9147 d ₄ = 0.2312
r ₅ = ∞ d ₅ = 1.9038 n _d3 = 1.80610 ν _d3 = 40.95
r ₆ = ∞ d ₆ = 0.0000
r ₇ = ∞ (aperture) d ₇ = 0.0204
r ₈ = ∞ d ₈ = 0.6799 n _d4 = 1.88300 ν _d4 = 40.76
r ₉ = -1.5496 d ₉ = 0.6799
r ₁₀ = -1.9256 d ₁₀ = 0.2108 n _d5 = 1.84666 ν _d5 = 23.78
r ₁₁ = ∞ d ₁₁ = 0.6799 n _d6 = 1.88300 ν _d6 = 40.76
r ₁₂ = -1.5467 d ₁₂ = 0.0680
r ₁₃ = 2.4495 d ₁₃ = 0.7354 n _d7 = 1.51633 ν _d7 = 64.14
r ₁₄ = -1.1536 d ₁₄ = 0.2040 n _d8 = 1.84666 ν _d8 = 23.78
r ₁₅ = -3.4560 d ₁₅ = 0.2473
r ₁₆ = ∞ d ₁₆ = 0.6799 n _d9 = 1.51399 ν _d9 = 75.00
r ₁₇ = ∞ d ₁₇ = 0.0136 n _d10 = 1.51000 ν _d10 = 63.00
r ₁₈ = ∞ d ₁₈ = 0.3400 n _d11 = 1.51633 ν _d11 = 64.14
r ₁₉ = ∞ d ₁₉ = 0.0204
r ₂₀ = ∞ (image plane)

F = 1.00
F _NO = 5.275
Ih = 0.619
2ω (°) = 68.000
D (%) = -7.990
α (°) = 1.974.

Example 12
r ₀ = ∞ (object) d ₀ = 14.4872
r ₁ = ∞ d ₁ = 0.2759 n _d1 = 1.76820 ν _d1 = 71.79
r ₂ = ∞ d ₂ = 0.2070
r ₃ = 2.2610 d ₃ = 0.2070 n _d2 = 1.88300 ν _d2 = 40.76
r ₄ = 0.9179 d ₄ = 0.2346
r ₅ = ∞ d ₅ = 1.9316 n _d3 = 1.80610 ν _d3 = 40.95
r ₆ = ∞ d ₆ = 0.0000
r ₇ = ∞ (aperture) d ₇ = 0.0207
r ₈ = ∞ d ₈ = 0.2759 n _d4 = 1.88300 ν _d4 = 40.76
r ₉ = -1.8035 d ₉ = 0.6899
r ₁₀ = -2.1647 d ₁₀ = 0.2139 n _d5 = 1.84666 ν _d5 = 23.78
r ₁₁ = ∞ d ₁₁ = 0.6899 n _d6 = 1.88300 ν _d6 = 40.76
r ₁₂ = -1.4993 d ₁₂ = 0.0690
r ₁₃ = 2.3066 d ₁₃ = 0.8251 n _d7 = 1.51633 ν _d7 = 64.14
r ₁₄ = -1.1486 d ₁₄ = 0.2070 n _d8 = 1.84666 ν _d8 = 23.78
r ₁₅ = -3.3278 d ₁₅ = 0.2910
r ₁₆ = ∞ d ₁₆ = 0.6899 n _d9 = 1.51399 ν _d9 = 75.00
r ₁₇ = ∞ d ₁₇ = 0.0138 n _d10 = 1.51000 ν _d10 = 63.00
r ₁₈ = ∞ d ₁₈ = 0.3449 n _d11 = 1.51633 ν _d11 = 64.14
r ₁₉ = ∞ d ₁₉ = 0.0207
r ₂₀ = ∞ (image plane)

F = 1.00
F _NO = 5.270
Ih = 0.628
2ω (°) = 68.744
D (%) = -8.104
α (°) = 2.765.

Example 13
r ₀ = ∞ (object) d ₀ = 14.2860
r ₁ = ∞ d ₁ = 0.2721 n _d1 = 1.76820 ν _d1 = 71.79
r ₂ = ∞ d ₂ = 0.2041
r ₃ = 2.2591 d ₃ = 0.2041 n _d2 = 1.88300 ν _d2 = 40.76
r ₄ = 0.9705 d ₄ = 0.2313
r ₅ = ∞ d ₅ = 1.9048 n _d3 = 1.80610 ν _d3 = 40.95
r ₆ = ∞ d ₆ = 0.0000
r ₇ = ∞ (aperture) d ₇ = 0.0204
r ₈ = ∞ d ₈ = 0.6803 n _d4 = 1.88300 ν _d4 = 40.76
r ₉ = -1.6399 d ₉ = 0.6803
r ₁₀ = -2.0669 d ₁₀ = 0.2109 n _d5 = 1.84666 ν _d5 = 23.78
r ₁₁ = ∞ d ₁₁ = 0.6803 n _d6 = 1.88300 ν _d6 = 40.76
r ₁₂ = -1.5413 d ₁₂ = 0.0680
r ₁₃ = 2.5467 d ₁₃ = 0.7196 n _d7 = 1.51742 ν _d7 = 52.43
r ₁₄ = -1.1240 d ₁₄ = 0.2041 n _d8 = 1.84666 ν _d8 = 23.78
r ₁₅ = -2.9600 d ₁₅ = 0.2406
r ₁₆ = ∞ d ₁₆ = 0.6803 n _d9 = 1.51399 ν _d9 = 75.00
r ₁₇ = ∞ d ₁₇ = 0.0136 n _d10 = 1.51000 ν _d10 = 63.00
r ₁₈ = ∞ d ₁₈ = 0.3401 n _d11 = 1.51633 ν _d11 = 64.14
r ₁₉ = ∞ d ₁₉ = 0.0204
r ₂₀ = ∞ (image plane)

F = 1.00
F _NO = 5.082
Ih = 0.620
2ω (°) = 68.000
D (%) = -7.702
α (°) = 0.838.

Example 14
r ₀ = ∞ (object) d ₀ = 14.0174
r ₁ = ∞ d ₁ = 0.2803 n _d1 = 1.76820 ν _d1 = 71.79
r ₂ = ∞ d ₂ = 0.2002
r ₃ = 2.3752 d ₃ = 0.2002 n _d2 = 1.88300 ν _d2 = 40.76
r ₄ = 0.6814 d ₄ = 0.1682
r ₅ = ∞ d ₅ = 0.0120
r ₆ = ∞ d ₆ = 2.2027 n _d3 = 1.88300 ν _d3 = 40.76
r ₇ = ∞ (aperture) d ₇ = 0.0120
r ₈ = ∞ d ₈ = 0.2465 n _d4 = 1.72916 ν _d4 = 54.68
r ₉ = -1.1787 d ₉ = 0.2803
r ₁₀ = 1.3151 d ₁₀ = 0.5206 n _d5 = 1.88300 ν _d5 = 40.76
r ₁₁ = -1.9499 d ₁₁ = 0.2403 n _d6 = 1.74077 ν _d6 = 27.79
r ₁₂ = 0.7230 d ₁₂ = 0.1802
r ₁₃ = ∞ d ₁₃ = 0.2403 n _d7 = 1.51800 ν _d7 = 74.60
r ₁₄ = ∞ d ₁₄ = 0.0400
r ₁₅ = 3.0872 d ₁₅ = 0.2002 n _d8 = 1.92286 ν _d8 = 18.90
r ₁₆ = 1.0404 d ₁₆ = 0.6007 n _d9 = 1.51633 ν _d9 = 64.14
r ₁₇ = -1.0701 d ₁₇ = 0.1802
r ₁₈ = ∞ d ₁₈ = 0.4045 n _d10 = 1.51633 ν _d10 = 64.14
r ₁₉ = ∞ d ₁₉ = 0.4005 n _d11 = 1.61350 ν _d11 = 50.20
r ₂₀ = ∞ d ₂₀ = 0.0000
r ₂₁ = ∞ (image plane)

F = 1.00
F _NO = 9.075
Ih = 0.652
2ω (°) = 68.305
D (%) = -5.000
α (°) = 11.146.

Example 15
r ₀ = ∞ (object) d ₀ = 13.7201
r ₁ = ∞ d ₁ = 0.2744 n _d1 = 1.76820 ν _d1 = 71.79
r ₂ = ∞ d ₂ = 0.1960
r ₃ = 1.9900 d ₃ = 0.1960 n _d2 = 1.88300 ν _d2 = 40.76
r ₄ = 0.6323 d ₄ = 0.1646
r ₅ = ∞ d ₅ = 0.0118
r ₆ = ∞ d ₆ = 2.1560 n _d3 = 1.88300 ν _d3 = 40.76
r ₇ = ∞ (aperture) d ₇ = 0.0118
r ₈ = ∞ d ₈ = 0.2413 n _d4 = 1.72916 ν _d4 = 54.68
r ₉ = -1.1327 d ₉ = 0.2744
r ₁₀ = 1.3801 d ₁₀ = 0.5096 n _d5 = 1.88300 ν _d5 = 40.76
r ₁₁ = -2.7705 d ₁₁ = 0.2352 n _d6 = 1.74077 ν _d6 = 27.79
r ₁₂ = 0.7895 d ₁₂ = 0.1764
r ₁₃ = ∞ d ₁₃ = 0.2352 n _d7 = 1.51800 ν _d7 = 74.60
r ₁₄ = ∞ d ₁₄ = 0.0392
r ₁₅ = 3.2999 d ₁₅ = 0.1960 n _d8 = 1.92286 ν _d8 = 18.90
r ₁₆ = 1.5997 d ₁₆ = 0.5880 n _d9 = 1.51633 ν _d9 = 64.14
r ₁₇ = -1.7023 d ₁₇ = 0.1764
r ₁₈ = ∞ d ₁₈ = 0.3959 n _d10 = 1.51633 ν _d10 = 64.14
r ₁₉ = ∞ d ₁₉ = 0.3920 n _d11 = 1.61350 ν _d11 = 50.20
r ₂₀ = ∞ d ₂₀ = 0.0021
r ₂₁ = ∞ (image plane)

F = 1.00
F _NO = 9.281
Ih = 0.639
2ω (°) = 67.945
D (%) = -7.009
α (°) = 12.606.

  Next, the values of conditional expressions (1) to (6) of Examples 1 to 15 are shown below together with the corresponding values of the conventional example.

Conditional expression (1) (2) (3) (4) (5) (6)
νp νn Example 1 4.33 -1.41 -0.29 64.14 23.78 5.28 0.28
Example 2 4.45 -1.16 -0.54 70.23 23.78 5.88 1.20
Example 3 4.00 -1.15 -0.51 64.14 23.78 2.86 0.52
Example 4 4.33 -1.41 -0.29 64.14 23.78 5.28 0.28
Example 5 4.45 -1.16 -0.54 70.23 23.78 5.88 1.20
Example 6 4.00 -1.15 -0.51 64.14 23.78 2.86 0.52
Example 7 3.57 -1.17 -0.36 58.90 29.52 16.04 1.08
Example 8 7.17 -1.03 -0.33 58.90 29.52 66.91 0.99
Example 9 3.14 -1.70 -0.29 58.90 29.52 2.49 0.90
Example 10 5.09 -1.73 -0.22 64.14 23.78 4.98 0.22
Example 11 2.28 -1.91 -0.24 64.14 23.78 5.72 -0.16
Example 12 6.54 -1.89 -0.21 64.14 23.78 5.11 0.16
Example 13 2.41 -2.08 -0.22 52.43 23.78 5.03 -0.22
Example 14 4.78 -1.15 -0.53 64.14 18.90 2.48 0.47
Example 15 4.69 -1.13 -0.54 64.14 18.90 3.09 0.43

Example 1 of Patent Document 4 0.61 -0.71 -0.09 47.37 26.55 -55.72 1.96
Example 2 0.63 -0.79 -0.04 47.37 26.55 -31.28 3.11
.

  In addition, although the perspective direction of the Example demonstrated above is 30 degrees, you may make it a direct view or a 30 degrees or more perspective.

  Furthermore, although it is CCD used for an imaging surface, it is preferable to use a CCD with a small eccentricity between the CCD imaging center and the CCD exterior. Endoscope insertion parts are usually generally cylindrical, and if the CCD exterior and the center of the imaging surface are decentered, the trajectory when rotated is large, which is not preferable because the outer diameter of the endoscope increases. Because.

  As described above, an endoscope objective optical system, particularly a video endoscope objective optical system, and an endoscope having a wide angle, a small distortion, a small curvature of field, and a relatively small number of lenses using only a spherical lens. In a perspective optical system that can rotate the visual field direction in a desired direction with respect to the longitudinal direction, the visual field on the observation surface is also changed when the endoscope is rotated and the visual field direction is changed to enter the desired visual field. An optical system that suppresses the occurrence of decentering at the center is achieved, and an electronic endoscope suitable for observation on a television monitor is realized.

  The above-described endoscope objective optical system of the present invention and an image pickup apparatus using the same can be configured as follows, for example.

    [1] In order from the object side, a first group of negative meniscus lenses having a convex surface facing the object side, an aperture stop, a second group of positive lenses having a plane facing the object point side, and at least one surface And a third group having a positive refractive power as a whole and a fourth group having a positive refractive power made up of a cemented lens of a negative meniscus lens and a biconvex lens. An endoscope objective optical system that forms an image on an image pickup device through four groups, wherein the principal ray is refracted in a direction away from the optical axis by the convex surface of the positive lens of the second group. Mirror objective optical system.

[2] The lens thickness of the positive lens in the second group is t ₂ , the focal length is f ₂ , the refractive index is n ₂ , and the focal lengths of the negative meniscus lens in the first group and the entire optical system are f ₁ , respectively. F, Petzval sum due to the concave refracting surface of the third group is PS3, Abbe numbers on the d-line basis of the positive lens and negative lens of the fourth group are νp and νn, respectively, and the focal length of the fourth group is f ₄ The endoscope objective optical system according to 1 above, wherein the following conditional expression is satisfied:

(1) 2 <f ₂ (n ₂ −1) / t ₂ <6
(2) -2.3 <f ₁ /F<-0.9
(3) -0.6 <PS3 <-0.2
(4) νp> 50, νn <30
(5) 2.3 <f ₄ / F
[3] The endoscope objective optical system according to 1 or 2 described above and a solid-state imaging device disposed on an image plane thereof, and the front group includes the first group, the aperture stop, and the second group The rear group is constituted by the third group and the fourth group, and the rear group and the solid-state imaging device are mechanically integrated, and the longitudinal direction of the imaging device is axially oriented with respect to the front group. And the angle of incidence of the axial marginal ray incident on the rear group from the front group is substantially parallel to the rotation axis. An imaging apparatus characterized by the above.

    [4] In order from the object side, an endoscope objective optical system including a front group including a negative lens, a stop, and a positive lens, and a rear group including a positive refractive power as a whole, and a solid disposed on the image plane The rear group and the solid-state image sensor have a mechanically integrated structure, and are configured to be rotatable relative to the front group about the longitudinal direction of the imaging device, An imaging apparatus, wherein an incident angle of an axial marginal ray incident on the rear group from the front group is substantially parallel to the rotation axis.

[5] the focal distance f ₁ of the negative lens of the front group, the focal length f ₂ of the front group of the positive lens, and a focal length of the endoscope objective optical system as a whole system was F, the following conditional expression The imaging apparatus according to 3 or 4 above, wherein:

(6) −0.3 <(f ₂ − | f ₁ |) / F <1.5
[6] The imaging apparatus according to any one of [3] to [5], wherein a prism is provided in a front group of the endoscope objective optical system to form a perspective optical system.

    [7] The imaging apparatus according to any one of [3] to [6], wherein the center of the imaging surface and the center of the exterior of the solid-state imaging device are substantially coincident.

    [8] The imaging apparatus according to any one of the above 3 to 6, wherein the center of the scope outer tube and the center of the imaging surface of the imaging element are substantially coincident with each other.

    [9] The endoscope objective optical system according to the above 1 or 2, or any one of the above 3 to 8, wherein an interference filter for cutting wavelengths in the infrared region is installed before the fourth group The imaging apparatus according to 1.

    [10] The endoscope objective optical system according to 1 or 2 above, or any one of 3 to 8 above, wherein an absorption type infrared cut filter is installed in the endoscope objective optical system The imaging apparatus according to 1.

    [11] The endoscope objective optical system or the imaging device according to [9], wherein an incident angle of a principal ray incident on the interference filter is 25 ° or less.

    [12] The endoscope objective optical system according to any one of the above 1, 2, 9 to 11, wherein the asymmetry of the image plane is kept in balance by adjusting the lens closest to the object side, or The method for assembling the imaging device according to any one of 3 to 11 above.

    [13] The structure according to any one of 1, 2, 9 to 11, wherein the front group and the rear group are assembled separately, the optical core is adjusted, and then the front group and the rear group are combined. Method for assembling an endoscope objective optical system.

    [14] The centering method for the front group is characterized in that the optical center is centered on the rear group after the optical center is adjusted to an allowable amount or less in advance. Assembly method of an endoscope objective optical system.

    [15] The illumination optical system arranged together with the objective optical system at the endoscope front-end image portion is rotated in a manner to follow the objective optical system when the visual field direction is converted by the image rotation mechanism and directed in the endoscope visual field direction. 12. The imaging apparatus according to any one of 3 to 11, wherein the imaging apparatus has a movable structure.

    [16] The endoscope objective optical system as set forth in any one of [1], [2] and [9] to [11], wherein a distance between the front group and the rear group is 0.5 mm or more.

It is explanatory drawing about the refraction | bending of the off-axis principal ray of the endoscope objective optical system of this invention, and the off-axis principal ray of the conventional endoscope objective optical system. It is explanatory drawing about the refraction | bending of an axial marginal ray of the endoscope objective optical system of this invention. It is explanatory drawing regarding the focal distance and space | interval of the 1st group of the endoscope objective optical system of this invention, and a 2nd group. It is an optical path figure of the endoscope objective optical system of Example 1 of the present invention. It is an optical path figure of the endoscope objective optical system of Example 2 of the present invention. It is an optical path figure of the endoscope objective optical system of Example 3 of the present invention. It is an optical path figure of the endoscope objective optical system of Example 4 of the present invention. It is an optical path figure of the endoscope objective optical system of Example 5 of this invention. It is explanatory drawing regarding the shift | offset | difference of the image center with respect to the visual field center when the movable part of Example 5 (a) and the prior art example (b) is shifted to the orthogonal | vertical direction with respect to an optical axis. It is an optical path figure of the endoscope objective optical system of Example 6 of this invention. It is sectional drawing of the internal structure of the rigid endoscope insertion part for demonstrating the relationship between an optical system and a machine frame to Examples 4-6. It is the figure which expanded the front-end | tip part of the rigid endoscope insertion part of FIG. It is an optical path figure of the endoscope objective optical system of Example 7 of this invention. It is an optical path figure of the endoscope objective optical system of Example 8 of the present invention. It is an optical path figure of the endoscope objective optical system of Example 9 of this invention. It is an optical path figure of the endoscope objective optical system of Example 10 of this invention. It is an optical path figure of the endoscope objective optical system of Example 11 of this invention. It is an optical path figure of the endoscope objective optical system of Example 12 of this invention. It is an optical path figure of the endoscope objective optical system of Example 13 of this invention. It is an optical path figure of the endoscope objective optical system of Example 14 of this invention. It is an optical path figure of the endoscope objective optical system of Example 15 of this invention. FIG. 3 is an aberration diagram showing spherical aberration, astigmatism, lateral chromatic aberration, distortion aberration, and coma aberration of the endoscope objective optical system according to Example 1. FIG. 23 is an aberration diagram similar to FIG. 22 of the endoscope objective optical system according to Example 2. FIG. 23 is an aberration diagram similar to FIG. 22 of the endoscope objective optical system according to Example 3. FIG. 23 is an aberration diagram similar to FIG. 22 of the endoscope objective optical system according to Example 4. FIG. 23 is an aberration diagram similar to FIG. 22 of the endoscope objective optical system according to Example 5. FIG. 23 is an aberration diagram similar to FIG. 22 of the endoscope objective optical system according to Example 6. FIG. 23 is an aberration diagram similar to FIG. 22 of the endoscope objective optical system according to Example 7. FIG. 23 is an aberration diagram similar to FIG. 22 of the endoscope objective optical system according to Example 8. FIG. 23 is an aberration diagram similar to FIG. 22 of the endoscope objective optical system according to Example 9. FIG. 23 is an aberration diagram similar to FIG. 22 of the endoscope objective optical system according to Example 10. FIG. 23 is an aberration diagram similar to FIG. 22 of the endoscope objective optical system according to Example 11. FIG. 23 is an aberration diagram similar to FIG. 22 of the endoscope objective optical system according to Example 12. FIG. 23 is an aberration diagram similar to FIG. 22 of the endoscope objective optical system according to Example 13. FIG. 23 is an aberration diagram similar to FIG. 22 of the endoscope objective optical system according to Example 14; FIG. 23 is an aberration diagram similar to FIG. 22 of the endoscope objective optical system according to Example 15; It is sectional drawing which shows the structure of the conventional endoscope objective lens of an example. It is an aberration diagram of another objective optical system of the conventional example. It is a figure which shows the external appearance of a rigid video endoscope. It is a figure which shows the visual field before (a) and after rotation (b) of the rigid video endoscope of FIG. It is a figure which shows the monitor image before (a) of rotation under a surgical operation using an endoscope, and (b) after rotation. It is a figure for demonstrating conversion of the visual field direction of a videoscope. It is a figure which shows the prior art example which correct | amends image rotation by rotating the imaging surface of an optical system. It is a figure for demonstrating the malfunction by the prior art example of FIG.

Explanation of symbols

AS ... Aperture L1 ... First lens (negative meniscus lens)
L2 ... Second lens (convex lens)
L3 ... 3rd lens L4 ... 4th lens G1 ... 1st group G2 ... 2nd group G3 ... 3rd group G4 ... 4th group P ... Parallel plate S ... Diaphragm F ... Infrared cut filter, infrared absorption filter G ... CCD cover glass I ... imaging surface C ... cover glass FS ... flare stop Pr ... prism Pr1 ... first prism Pr2 ... second prism Al ... aluminum coat FG ... front group RG ... rear group IU ... CCD unit K ... control knob am ... On-axis marginal ray 21 ... Meniscus lens (G1)
22 ... Prism (Pr)
23 ... Plano-convex lens (G2)
24 ... Frame 25 ... Exterior pipe 26 ... Frame 27 ... Frame

Claims (6)

In order from the object side, a first lens unit composed of a negative meniscus lens having a convex surface facing the object side, an aperture stop, a second lens unit composed of a positive lens having a plane facing the object point side, and at least one concave surface A third group including a refracting surface and having a positive refractive power as a whole; and a fourth group having a positive refractive power composed of a cemented lens of a negative meniscus lens and a biconvex lens. An endoscope objective optical system that forms an image on an image pickup device via an optical path, wherein the principal ray is refracted in a direction away from the optical axis by the convex surface of the positive lens in the second group. system. The positive lens of the second group has a lens thickness of t ₂ , a focal length of f ₂ , a refractive index of n ₂ , a negative meniscus lens of the first group, and the focal length of the entire optical system f ₁ , F, the Petzval sum according to the refractive surface of the concave of the third group PS3, the fourth group of positive lenses, respectively the Abbe number of d-line based negative lens vp, .nu.n, when the focal length of the fourth group was f ₄ The endoscope objective optical system according to claim 1, wherein the following conditional expression is satisfied.
(1) 2 <f ₂ (n ₂ −1) / t ₂ <6
(2) -2.3 <f ₁ /F<-0.9
(3) -0.6 <PS3 <-0.2
(4) νp> 50, νn <30
(5) 2.3 <f ₄ / F The endoscope objective optical system according to claim 1 or 2 and a solid-state imaging device disposed on an image plane thereof, wherein the front group is configured from the first group, the brightness stop, and the second group, A rear group is configured by the third group and the fourth group, and the rear group and the solid-state imaging device are mechanically integrated, and are relative to the front group with the longitudinal direction of the imaging device as an axis. And an angle of incidence of an on-axis marginal ray incident on the rear group from the front group is substantially parallel to the rotation axis. An imaging device. In order from the object side, an endoscope objective optical system composed of a front group consisting of a negative lens, a stop, and a positive lens, and a rear group consisting of a positive refractive power as a whole, and a solid-state imaging device disposed on the image plane The rear group and the solid-state imaging device are mechanically integrated, and are configured to be rotatable relative to the front group about the longitudinal direction of the imaging device. The imaging apparatus is configured such that an incident angle of an axial marginal ray incident on the rear group is substantially parallel to the rotation axis. When the focal length of the negative lens in the front group is f ₁ , the focal length of the positive lens in the front group is f ₂ , and the focal length of the entire endoscope objective optical system is F, the following conditional expression is satisfied. The imaging apparatus according to claim 3 or 4, wherein
_{(6) -0.3 <(f 2} - | f 1 |) / F <1.5 6. The imaging apparatus according to claim 3, wherein a prism is provided in a front group of the endoscope objective optical system to form a perspective optical system.

Images