Objective optical system, endoscope, and imaging device

Abstract

The optical lens includes, in order from the object side, a first lens group having negative refractive power, a second lens group having positive refractive power, and a third lens group having positive refractive power. Focusing is performed by movement of the second lens group. The first lens group is composed of two lenses, namely a first lens as a negative lens and a second lens as a negative lens having a concave surface facing the image side. The second lens group is configured from one positive meniscus lens having a convex surface facing the object side. The third lens group has, in order from the object side, a single lens having a positive refractive power and a cemented lens comprising a positive lens and a negative lens. When L1Rr is the curvature radius of the image side surface of the first lens and L2Rr is the curvature radius of the image side surface of the second lens, 0.01 < L1Rr / L2Rr < 0.95 is satisfied.

Description

Technical Field

[0001] The present invention relates to an objective optical system, an endoscope, and an imaging device. Background Art

[0002] Endoscopes are widely used as medical equipment for technicians, doctors and other users to inspect, treat and dispose of lesions while directly observing the image of the lesion of the subject. Since the insertion portion of the endoscope is inserted from the outside of the subject's body into the body, it is preferred that the overall length of the objective optical system provided in the insertion portion is short and the diameter of the objective optical system is small. In addition, in order to improve the inspection accuracy of the lesion, etc., it is preferred that the objective optical system can be used to capture a narrow range with high resolution. In the past, objective optical systems that can be provided in endoscopes with a short overall length, a small diameter and high resolution have been proposed, thereby achieving high image quality of the obtained images (for example, refer to patent documents 1 to 5).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent No. 4819969

[0006] Patent Document 2: Japanese Patent No. 5930257

[0007] Patent Document 3: Japanese Patent No. 4819969

[0008] Patent Document 4: Japanese Patent Application Laid-Open No. 2017-219783

[0009] Patent Document 5: International Publication No. 2020 / 217443 Summary of the Invention

[0010] Problems to be solved by the invention

[0011] The objective optical systems disclosed in Patent Documents 1 to 5 are capable of observing an object at a predetermined magnification by focusing on a distant object point, and are capable of magnifying the object by focusing on a close object point. For example, in the objective optical systems disclosed in Patent Documents 1, 3, and 4, the first to third lens groups are arranged sequentially from the object side to the image side, and only the second lens group moves when focusing. The objective optical system disclosed in Patent Document 2 is configured sequentially from the object side to include a first lens with negative refractive power, a second meniscus lens, a third meniscus lens, a lens group with positive refractive power, and a cemented lens, and the third meniscus lens moves when focusing.

[0012] In the objective optical system of the past represented by the objective optical system disclosed in patent documentation 1 to patent documentation 5, along with the high resolution and the high image quality when being assembled in the camera, the depth of field becomes shallow, and can't obtain enough depth of field. In addition, for example, in the objective optical system disclosed in patent documentation 1 to patent documentation 4, the shortening of the total length of the optical system, the taper are also insufficient. In addition, for example, in the objective optical system disclosed in patent documentation 5, if want to cope with autofocus, then the movable space of lens group is sometimes insufficient.

[0013] The present invention has been completed in view of the above-mentioned problems, and its object is to provide an objective optical system with a small diameter and high performance, the objective optical system having a focusing function, capable of handling autofocus, and capable of fully ensuring a depth of field and a movable range along the optical axis of the lens group. Furthermore, the present invention is to provide an endoscope and an imaging device having the above-mentioned objective optical system.

[0014] Means for solving problems

[0015] The objective optical system of the present invention includes, from the object side, in order: a first lens group with negative refractive power, a second lens group with positive refractive power, and a third lens group with positive refractive power. Focusing from a distant object point to a close object point is performed by moving the second lens group from the object side to the image side. The first lens group is composed of two lenses: a first lens as a negative lens and a second lens as a negative lens with the concave surface facing the image side. The second lens group is composed of a positive meniscus lens with the convex surface facing the object side. The third lens group has, from the object side, a single lens with positive refractive power and a cemented lens composed of a positive lens and a negative lens. The objective optical system of the present invention satisfies the following conditional formula (1),

[0016] 0.01 <L1_Rr / L2_Rr<0.95···(1)

[0017] Wherein, L1_Rr is the curvature radius of the image-side surface of the first lens, and L2_Rr is the curvature radius of the image-side surface of the second lens.

[0018] The endoscope of the present invention comprises: a front end portion which accommodates the above-mentioned objective optical system; an extension portion which is connected to the base end of the front end portion and is capable of bending; and an operating portion which is connected to the base end of the extension portion on the opposite side of the front end connected to the front end portion and has a handle for freely changing the axial shape of the extension portion.

[0019] An imaging device according to the present invention includes: the endoscope described above; and an imaging element that converts an image acquired by the objective optical system into an electrical signal.

[0020] Effects of the Invention

[0021] According to the objective optical system of the present invention, when focusing from a distant object point to a close object point, the second lens group with positive refractive power moves, thereby having a focusing function, being able to cope with autofocus, being able to fully ensure the depth of field and the movable area of ​​the lens group, and achieving miniaturization. In addition, according to the objective optical system of the present invention, the first lens of the first lens group satisfies the above-mentioned conditional formula (1), thereby being able to ensure the depth of field and reduce the diameter, and achieving a balance of various aberrations generated as a whole, being well corrected, and achieving high performance. Furthermore, according to the present invention, an endoscope and a camera device having the above-mentioned objective optical system can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a cross-sectional view of the objective optical system of Example 1.

[0023] Figure 2 This is a cross-sectional view of the objective optical system of Example 2.

[0024] Figure 3 This is a cross-sectional view of the objective optical system of Example 3.

[0025] Figure 4 This is a cross-sectional view of the objective optical system of Example 4.

[0026] Figure 5 This is a cross-sectional view of the objective optical system of Example 5.

[0027] Figure 6 This is a cross-sectional view of the objective optical system of Example 6.

[0028] Figure 7 This is a cross-sectional view of the objective optical system of Example 7.

[0029] Figure 8 1 and 2 are aberration diagrams of the objective optical system of Example 1.

[0030] Figure 9 This is an aberration diagram of the objective optical system of Example 2.

[0031] Figure 10 1 and 2 are aberration diagrams of the objective optical system of Example 3.

[0032] Figure 11 This is an aberration diagram of the objective optical system of Example 4.

[0033] Figure 12 This is an aberration diagram of the objective optical system of Example 5.

[0034] Figure 13 This is an aberration diagram of the objective optical system of Example 6.

[0035] Figure 14This is an aberration diagram of the objective optical system of Example 7.

[0036] Figure 15 This is a schematic diagram of an endoscope and an imaging device according to one embodiment of the present invention. DETAILED DESCRIPTION

[0037] Below, with reference to the accompanying drawings, the embodiment of the objective optical system, endoscope and imaging device of mode of the present invention is described. In addition, when specifying the effect of this embodiment, show specific example and describe, but similarly with the embodiment described later, the embodiment of illustration is a part for the mode that the present invention comprises. In the embodiment of illustration, there are a plurality of modifications. Therefore, the present invention is not limited to the embodiment of illustration.

[0038] The objective optical system of this embodiment is, for example, assembled into an endoscope and used to observe the lesion of an endoscope subject. In the objective optical system of this embodiment, it is possible to automatically focus on a close object point that is relatively close to the optical system and a distant object point that is farther than the close object point. By focusing on the close object point, the observation object can be further magnified relative to a specified magnification for observation. In addition, by focusing on the distant object point, the observation object can be observed at a specified magnification.

[0039] The objective optical system of this embodiment comprises a first lens group with negative refractive power, a second lens group with positive refractive power, and a third lens group with positive refractive power. The first, second, and third lens groups are arranged sequentially from the object side to the image side. Focusing from a distant object point to a close object point is achieved by moving the second lens group from the object side to the image side. Furthermore, when focusing the objective optical system of this embodiment, only the second lens group moves; the first and third lens groups remain fixed.

[0040] In the objective optical system of this embodiment, the first lens group comprises a first lens, which is a negative lens, and a second lens, which is a negative lens with its concave surface facing the image side. The second lens group consists of a single positive meniscus lens with its convex surface facing the object side. The third lens group comprises a single lens with positive refractive power and a cemented lens consisting of a positive lens and a negative lens. In the third lens group, the single lens and the cemented lens are arranged in order from the object side.

[0041] The objective optical system of this embodiment has multiple lens groups from the first lens group to the third lens group, thereby suppressing the diameter of the entire system within a plane perpendicular to the optical axis, and forming the second lens group as a movable group. In addition, in the objective optical system of this embodiment, the first lens group has the first lens and the second lens as negative lenses, thereby shortening the focal length of the entire system and ensuring the depth of field. Moreover, by having two negative lenses in the first lens group, chromatic aberration and coma can be corrected compared to the case where only one negative lens is used to shorten the focal length of the entire system. In other words, if the first lens group only has one negative lens, if the focal length of the entire system is to be shortened, chromatic aberration and coma will be significantly generated, and a high-performance objective optical system with good aberration performance cannot be obtained.

[0042] In order to achieve a smaller diameter of the objective optical system and ensure the movable area of ​​the second lens group when focusing, the movable area on the object side of the second lens group is required, and it is necessary to expand the maximum distance between the image side of the lens of the first lens group that is arranged closest to the image side and the object side of the lens of the second lens group that is arranged closest to the object side. The lenses of each lens group and optical elements other than the lenses are held by a holding member such as a lens barrel from the radial outside in a plane perpendicular to the optical axis. Therefore, in the plane perpendicular to the optical axis, in the portion relatively located radially outside, it is necessary to ensure the maximum distance between the air area on the object side of the second lens group, that is, the image side closest to the first lens group and the object side closest to the second lens group. In addition, it is necessary to ensure space for the configuration of the third lens group and the back focal length for adjusting the focus position.

[0043] In addition, in this specification, the interval refers to the air interval, which refers to the separation distance in air between one surface and another surface in a direction parallel to the optical axis. Unless otherwise specified, the interval refers to the separation distance on the optical axis between one surface and another surface in an objective optical system.

[0044] In the objective optical system of this embodiment, since the second lens group is composed of a positive meniscus lens with its convex surface facing the object side, the principal points of the lenses constituting the second lens group can be positioned on the object side of the second lens group. This ensures that the movable range of the second lens group in the objective optical system of this embodiment, as well as the space on the object side of the second lens group, i.e., the space between the first lens group and the second lens group, can be secured.

[0045] In order to shorten the total length of the objective optical system, it is preferred that the number of lenses constituting the objective optical system is small. In the objective optical system of the present embodiment, the second lens group is composed of a positive meniscus lens, so the length of the second lens group can be shortened, resulting in a shortened total length. In addition, in this specification, a lens refers to an optical element other than a parallel flat plate having a surface on the object side and a surface on the image side parallel to a flat surface perpendicular to the optical axis, such as a single lens or a cemented lens. The surface on either side of the object side and the image side of the lens includes a curved surface. The object side and the image side of the single lens and the cemented lens are in contact with air.

[0046] Furthermore, in an objective optical system, it is preferable to ensure a larger movable area on the image side of the second lens group. However, in an objective optical system comprising three lens groups, for example, if only the image side space of the second lens group is shortened, aberrations generated in the first and second lens groups may not be corrected, and aberrations may remain on the imaging plane. Shortening the image side space of the second lens group refers to increasing the maximum distance between the image side surface of the lens of the second lens group positioned closest to the image side and the object side surface of the lens of the third lens group positioned closest to the object side.

[0047] The third lens group of the objective optical system of this embodiment comprises at least a single lens with positive refractive power and a cemented lens composed of a positive lens and a negative lens. Therefore, even if the diameter and total length of the entire system of the objective optical system of this embodiment are restricted and need to be suppressed within a specified range, aberrations can be well corrected, and in particular, spherical aberration and chromatic aberration can be well maintained. As a result, an objective optical system with good aberration performance can be obtained.

[0048] In the objective optical system of the present embodiment, preferably in the third lens group, a lens with positive refractive power is configured at intervals from the image side of the cemented lens to the cemented lens. This lens plays the role of a cover glass that contacts the imaging surface from the object side. That is, the imaging surface of the imaging element, i.e., the object side, can also be configured with a lens with positive refractive power to replace the cover glass as a parallel plate. According to such a structure, the alignment of the image plane of the objective optical system with respect to the imaging surface is carried out by adjusting the interval between the cemented lens and the lens with positive refractive power configured on the imaging surface of the imaging element. In addition, the region on the image side of the objective optical system of the present embodiment, i.e., the region close to the imaging surface, plays a role of positive refractive power, so the error sensitivity of the alignment of the image plane becomes lower. Therefore, when the alignment of the image plane in the objective optical system of the present embodiment, the positional offset of the image plane can be suppressed.

[0049] In the objective optical system of this embodiment, an aperture diaphragm may be arranged in a space closer to the object side than the single lens of the third lens group that is arranged closest to the object side. However, in the space between the second lens group and the third lens group, no matter where the aperture diaphragm is arranged in a direction parallel to the optical axis, the brightness and optical performance of the image of the objective optical system will not change significantly. Therefore, the position of the aperture diaphragm arranged between the second lens group and the third lens group is determined based on the shape of the lens barrel used to hold the various lenses of the objective optical system and the aperture diaphragm. In addition, the aperture diaphragm may also be configured to be arranged in a space closer to the image side than the positive meniscus lens of the second lens group, so that it can move in conjunction with the second lens group when focusing and can move integrally with the second lens group.

[0050] The objective optical system of this embodiment satisfies the following conditional expression (1).

[0051] 0.01 <L1_Rr / L2_Rr<0.95···(1)

[0052] In conditional expression (1), L1_Rr is the curvature radius of the image side surface of the first lens as a negative lens in the first lens group, and L2_Rr is the curvature radius of the image side surface of the second lens as a negative lens in the first lens group.

[0053] Conditional expression (1) is a conditional expression regarding an appropriate ratio between the radius of curvature of the image side surface of the first lens and the radius of curvature of the image side surface of the second lens in the first lens group. The first lens is the single lens disposed closest to the object side among the multiple single lenses in the first lens group. The second lens is disposed at a position closer to the image side than the first lens among the multiple lenses in the first lens group, for example, in a space closer to the image side than the first lens.

[0054] In order to realize the structure of the reverse telephoto type by the objective optical system of this embodiment, the first lens of the first lens group needs a relatively strong negative refractive power. However, if the negative refractive power of the first lens is too strong, there is a situation where aberrations such as chromatic aberration and coma aberration are deteriorated. Therefore, in order to appropriately set the negative refractive power of the first lens, it is preferably to appropriately set the radius of curvature. In addition, since sometimes only adjusting the negative refractive power of the first lens cannot properly correct aberrations, it is difficult to realize an objective optical system with a deeper depth of field. Therefore, it is necessary to make the second lens have a negative refractive power. Therefore, in order to appropriately set the negative refractive power of the second lens, it is preferably to appropriately set the radius of curvature of each side of the first lens and the second lens.

[0055] By satisfying conditional expression (1), in an objective optical system having a relatively small F-number like the objective optical system of the present embodiment, it is possible to achieve a good balance of overall aberrations and realize a compact objective optical system with a deep depth of field.

[0056] If the value falls below the lower limit of conditional expression (1), the negative refractive power of the first lens of the first lens group becomes stronger, which easily causes chromatic aberration, coma, etc., and is therefore not preferred. In addition, if the value falls below the lower limit of conditional expression (1), the negative refractive power of the second lens of the first lens group cannot be ensured, and the depth of field of the objective optical system becomes shallow. As a result, the diameter of the first lens and the entire system becomes larger, resulting in an increase in the size of the objective optical system of this embodiment, which is not preferred.

[0057] When the upper limit of conditional expression (1) is exceeded, the negative refractive power of the first lens of the first lens group cannot be ensured, and the depth of field of the objective optical system cannot be deepened, and the diameter of the first lens becomes large, which is not preferable. In addition, when the upper limit of conditional expression (1) is exceeded, the amount of aberration generated by the second lens of the first lens group becomes excessively large, and in particular, coma aberration and lateral chromatic aberration worsen. In the second lens group and the third lens group arranged at a stage further back than the first lens group, it is difficult to correct the aberrations worsened in the first lens group as described above.

[0058] The objective optical system of this embodiment preferably satisfies the following conditional expression (2).

[0059] 0.136 <L1 / L2<0.95···(2)

[0060] In the conditional expression (2), L1 is the focal length of the first lens in the first lens group, and L2 is the focal length of the second lens.

[0061] Conditional expression (2) is a conditional expression for an appropriate ratio between the negative refractive power of the first lens of the first lens group and the negative refractive power of the second lens. By satisfying conditional expression (2), various aberrations of the objective optical system of this embodiment can be well corrected, and a small-diameter objective optical system with a deep depth of field can be realized.

[0062] If the value falls below the lower limit of conditional expression (2), the negative refractive power of the first lens in the first lens group becomes strong, the Petzval sum becomes large, and the field curvature is overcorrected, which is not preferable. Furthermore, if the value falls below the lower limit of conditional expression (2), the negative refractive power of the second lens in the first lens group becomes too weak, making it impossible to shorten the focal length of the entire system, making it difficult to ensure the depth of field of the objective optical system of this embodiment.

[0063] When the upper limit of conditional expression (2) is exceeded, the negative refractive power of the first lens of the first lens group becomes weak, the height of the light incident on the first lens becomes larger, and the diameter of the first lens becomes larger, which is not preferable. In addition, when the upper limit of conditional expression (2) is exceeded, the negative refractive power of the second lens of the first lens group becomes too strong, and the position of the principal point moves toward the image side. As a result, the total length of the objective optical system becomes longer, making it difficult to achieve miniaturization of the objective optical system of this embodiment.

[0064] The objective optical system of this embodiment preferably satisfies the following conditional expression (3).

[0065] 0.2 <L2_SF<1.85···(3)

[0066] In the conditional expression (3), L2_SF is the shape factor of the second lens of the first lens group.

[0067] The shape factor of the second lens of the first lens group is expressed by the following formula (4).

[0068] L2_SF=(L2_Lr-L2_Rr) / (L2_Lr+L2_Rr)···(4)

[0069] In equation (4), L2_Lr is the radius of curvature of the object-side surface of the second lens in the first lens group, and L2_Rr is the radius of curvature of the image-side surface of the second lens.

[0070] Conditional expression (3) is a conditional expression related to the shape of the second lens of the first lens group. By satisfying conditional expression (3), it is possible to maintain the small diameter of the objective optical system of this embodiment, well correct astigmatism, and realize an objective optical system with a deep depth of field.

[0071] If the lower limit of conditional expression (3) is exceeded, the curvature radius of the second lens of the first lens group becomes too large, the negative refractive power of the second lens cannot be maintained, and the depth of field becomes shallow, which is not preferable.

[0072] If the upper limit of conditional expression (3) is exceeded, the curvature radius of the second lens of the first lens group becomes too small, and astigmatism worsens, making it difficult to ensure the aberration performance of the objective optical system of this embodiment.

[0073] The objective optical system of this embodiment preferably satisfies the following conditional expression (5).

[0074] -0.4 <L1 / f2<-0.145···(5)

[0075] In the conditional expression (5), L1 is the focal length of the first lens in the first lens group, and f2 is the focal length of the second lens group.

[0076] Conditional equation (5) relates to an appropriate ratio between the negative refractive power of the first lens in the first lens group and the positive refractive power of the second lens group. By satisfying conditional equation (5), various aberrations of the objective optical system can be well corrected, and a compact objective optical system with a deep depth of field can be realized.

[0077] When the lower limit of conditional expression (5) is exceeded, the negative refractive power of the first lens of the first lens group becomes weak, the focal length cannot be shortened, and it is difficult to ensure the depth of field. In addition, when the lower limit of conditional expression (5) is exceeded, the positive refractive power of the second lens group becomes too strong, and the performance degradation corresponding to the decentering of the frame member holding the positive meniscus lens of the second lens group relative to the frame member holding the first lens becomes significant, making it difficult to ensure the optical performance of the objective optical system when focusing.

[0078] When the upper limit of conditional expression (5) is exceeded, the negative refractive power of the first lens of the first lens group becomes weak, the Petzval sum becomes large, and thus the field curvature is easily overcorrected, which is not preferable. In addition, when the upper limit of conditional expression (5) is exceeded, the positive refractive power of the second lens group becomes too weak, which can reduce the error sensitivity corresponding to the decentering of the frame member holding the positive meniscus lens relative to the frame member holding the first lens. On the other hand, the movement amount of the second lens group becomes large, and the objective optical system of this embodiment becomes large, which is not preferable.

[0079] The objective optical system of this embodiment preferably satisfies the following conditional expression (6).

[0080] -3 <L1 / fw<-0.955···(6)

[0081] In conditional expression (6), L1 is the focal length of the first lens of the first lens group, and fw is the focal length of the entire objective optical system of this embodiment when focusing on a distant object point.

[0082] Conditional equation (6) relates to an appropriate ratio between the negative refractive power of the first lens of the first lens group and the refractive power of the entire objective optical system. By satisfying conditional equation (6), various aberrations of the objective optical system can be well corrected, and a compact objective optical system with a deep depth of field can be realized.

[0083] If the lower limit of conditional expression (6) is exceeded, the negative refractive power of the first lens of the first lens group becomes too weak, making it difficult to shorten the total length of the objective optical system of this embodiment.

[0084] If the upper limit of conditional expression (6) is exceeded, the negative refractive power of the first lens of the first lens group becomes too strong, and coma and astigmatism are likely to occur and become larger, which is not preferable. In addition, if the upper limit of conditional expression (6) is exceeded, the curvature radius of the image side surface of the first lens becomes too small, and the error sensitivity corresponding to decentering of the first lens with respect to the optical axis is likely to increase, which is not preferable.

[0085] The objective optical system of this embodiment preferably satisfies the following conditional expression (7).

[0086] -3 <f1 / fw<-1.06···(7)

[0087] In the conditional expression (7), f1 is the focal length of the first lens group, and fw is the focal length of the entire objective optical system of the present embodiment when focusing on a distant object point.

[0088] Conditional expression (7) relates to an appropriate ratio between the refractive power of the first lens group and the refractive power of the entire objective optical system. By satisfying conditional expression (7), various aberrations can be corrected well, and the objective optical system of this embodiment can be miniaturized.

[0089] If the lower limit of conditional expression (7) is exceeded, the negative refractive power of the first lens group becomes too weak, the ray height of light incident on the first lens of the first lens group increases, and the diameter of the first lens increases, which is not preferable.

[0090] When the upper limit of conditional expression (7) is exceeded, the negative refractive power of the first lens group becomes too strong, and the focus of the first lens group approaches itself, that is, the object side. As a result, the total length of the objective optical system of this embodiment becomes longer, which is not preferable.

[0091] The objective optical system of this embodiment preferably satisfies the following conditional expression (8).

[0092] 0.25 <thi_3g_L1 / thi_3g_air<1.5···(8)

[0093] In the conditional expression (8), thi_3g_L1 is the thickness of the single lens of the third lens group on the optical axis, and thi_3g_air is the air space between the single lens and the cemented lens in the third lens group on the optical axis.

[0094] Conditional expression (8) is a conditional expression for the ratio of the thickness of the first single lens from the object side of the third lens group on the optical axis to the distance between the single lens and the cemented lens in the third lens group on the optical axis. By satisfying conditional expression (8), the third lens group can be miniaturized, thereby achieving miniaturization of the objective optical system of this embodiment.

[0095] If the lower limit of conditional expression (8) is exceeded, the distance between the single lens and the cemented lens in the third lens group becomes large, so the total length of the objective optical system of this embodiment becomes long, which is not preferable.

[0096] If the upper limit of conditional expression (8) is exceeded, the single lens of the third lens group becomes larger, and thus the total length of the objective optical system of this embodiment becomes longer, which is not preferable.

[0097] The objective optical system of this embodiment preferably satisfies the following conditional expression (9).

[0098] 0.325 <v / fw<0.6···(9)

[0099] In conditional expression (9), v is the amount of movement of the second lens group from focusing on a distant object point to focusing on a close object point, and fw is the focal length of the entire objective optical system of this embodiment when focusing on a distant object point.

[0100] Conditional expression (9) is a conditional expression for the amount of movement of the positive meniscus lens of the second lens group on the optical axis. In order to realize the miniaturization and high performance of the objective optical system having a movable group as in the objective optical system of this embodiment, it is important to appropriately suppress the amount of movement of the movable group. By satisfying conditional expression (9), the amount of movement of the second lens group as the movable group of the objective optical system of this embodiment on the optical axis can be appropriately set according to the focal length of the entire system of the objective optical system of this embodiment when focusing on a distant object point, thereby realizing the miniaturization and high performance of the objective optical system of this embodiment.

[0101] If the lower limit of conditional expression (9) is exceeded, the error sensitivity of the image plane position in the objective optical system of this embodiment with respect to the movement amount of the positive meniscus lens in the second lens group becomes high, which is not preferable.

[0102] When the upper limit value of conditional expression (9) is exceeded, the distance between the first lens group and the second lens group becomes larger, which can ensure the movement amount of the second lens group, but the total length of the objective optical system of this embodiment becomes longer, making it difficult to miniaturize the objective optical system of this embodiment.

[0103] The objective optical system of this embodiment preferably satisfies the following conditional expression (10).

[0104] -0.4 <G3_L1_SF<0.4···(10)

[0105] In the conditional expression (10), G3_L1_SF is the shape factor of the single lens of the third lens group.

[0106] The shape factor of the single lens of the third lens group is expressed by the following equation (11).

[0107] G3_L1_SF=(G3_L1_Lr+G3_L1_Rr) / (G3_L1_Lr-G3_L1_Rr)···(11)

[0108] In equation (11), G3_L1_Lr is the radius of curvature of the object-side surface of the single lens in the third lens group, and G3_L1_Rr is the radius of curvature of the image-side surface of the single lens.

[0109] Conditional expression (10) is a conditional expression related to the shape of the single lens of the third lens group. By satisfying conditional expression (10), the objective optical system of this embodiment can be miniaturized and spherical aberration and coma aberration can be corrected well.

[0110] If the lower limit of conditional expression (10) is exceeded, the curvature radius of either the object-side surface or the image-side surface of the single lens in the third lens group becomes too small, making it difficult to correct spherical aberration and coma.

[0111] Even if the upper limit of conditional expression (10) is exceeded, the curvature radius of either the object-side surface or the image-side surface of the single lens in the third lens group becomes too small, making it difficult to correct spherical aberration and coma.

[0112] The objective optical system of this embodiment preferably satisfies the following conditional expression (12).

[0113] -1.5 <G3_Lce_SF<-0.2···(12)

[0114] In the conditional expression (12), G3_Lce_SF is the shape factor of the cemented lens of the third lens group.

[0115] The shape factor of the cemented lens of the third lens group is expressed by the following formula (13).

[0116] G3_Lce_SF=(G3_Lce_Lr+G3_Lce_Rr) / (G3_Lce_Lr-G3_Lce_Rr)···(13)

[0117] In equation (13), G3_Lce_Lr is the radius of curvature of the object-side surface of the cemented lens of the third lens group, that is, the radius of curvature of the object-side surface of the lens disposed on the object side of the cemented lens and having positive refractive power. In equation (13), G3_Lce_Rr is the radius of curvature of the image-side surface of the cemented lens of the third lens group, that is, the radius of curvature of the image-side surface of the lens disposed on the image side of the cemented lens and having negative refractive power.

[0118] Conditional expression (12) is a conditional expression related to the shape of the cemented lens of the third lens group. By satisfying conditional expression (12), astigmatism and coma aberration in the objective optical system of this embodiment can be corrected well.

[0119] If the value falls below the lower limit of conditional expression (12), the radius of curvature of the object side surface of the cemented lens of the third lens group becomes too small, which easily causes coma aberration, and is therefore not preferable. Furthermore, if the value falls below the lower limit of conditional expression (12), the coma aberration and astigmatism generated by the image side surface of the cemented lens are insufficiently corrected, which is also not preferable.

[0120] When the upper limit of conditional expression (12) is exceeded, the radius of curvature of the object side surface of the cemented lens of the third lens group becomes too large, and the refractive power of the cemented lens cannot be maintained. The total length of the objective optical system of this embodiment becomes longer, which is not preferable. Moreover, when the upper limit of conditional expression (12) is exceeded, the radius of curvature of the image side surface of the cemented lens becomes too small, and coma and astigmatism are easily overcorrected, which is not preferable.

[0121] The endoscope of this embodiment is characterized in that it comprises: a front end portion which accommodates the objective optical system of this embodiment; an extension portion which is connected to the base end of the front end portion and is capable of bending; and an operating portion which is connected to the base end on the opposite side of the front end of the extension portion connected to the front end portion and has a handle for freely changing the axial shape of the extension portion.

[0122] The imaging device of the present embodiment is characterized in that it includes: the endoscope of the present embodiment; and an imaging element that converts an image acquired by the objective optical system of the present embodiment into an electrical signal.

[0123] The present invention provides an endoscope and an imaging device, which have a small-diameter and high-performance objective lens optical system that can cope with autofocus and fully ensure the depth of field and movable area. As a result, the observation object can be observed with high precision through simple operation, and the lesion part of the observation object can be diagnosed.

[0124] Regarding the above-mentioned conditional expressions (1) to (3), (5) to (10), and (12), at least one of the lower limit value and the upper limit value may be changed as follows. By changing in this way, the effect of satisfying each conditional expression is further enhanced.

[0125] Conditional expression (1) is as follows.

[0126] The lower limit is more preferably 0.1, and further preferably 0.335.

[0127] The upper limit is more preferably set to 0.9, and further preferably to 0.795.

[0128] Conditional expression (2) is as follows.

[0129] The lower limit is more preferably 0.2, and further preferably 0.25.

[0130] The upper limit is more preferably set to 0.8, and further preferably to 0.625.

[0131] Conditional expression (3) is as follows.

[0132] The lower limit is more preferably 0.3, and further preferably 0.55.

[0133] The upper limit is more preferably set to 1.7, and further preferably to 1.5.

[0134] Conditional expression (5) is as follows.

[0135] The lower limit is more preferably -0.35, and further preferably -0.25.

[0136] The upper limit is more preferably -0.15, and further preferably -0.16.

[0137] Conditional expression (6) is as follows.

[0138] The lower limit is more preferably -2.8, and even more preferably -2.5.

[0139] The upper limit is more preferably -1.0, and even more preferably -1.5.

[0140] Conditional expression (7) is as follows.

[0141] The lower limit is more preferably -2.0, and even more preferably -1.6.

[0142] The upper limit is more preferably -1.1, and even more preferably -1.2.

[0143] Conditional expression (8) is as follows.

[0144] The lower limit is more preferably 0.3, and further preferably 0.4.

[0145] The upper limit is more preferably set to 1.4, and further preferably to 1.25.

[0146] Conditional expression (9) is as follows.

[0147] More preferably, the lower limit is set to 0.35.

[0148] More preferably, the upper limit is set to 0.55.

[0149] Conditional expression (10) is as follows.

[0150] The lower limit is more preferably -0.35, and even more preferably -0.3.

[0151] The upper limit is more preferably set to 0.3, and further preferably to 0.25.

[0152] Conditional expression (12) is as follows.

[0153] The lower limit is more preferably -1.4, and even more preferably -1.3.

[0154] The upper limit is more preferably -0.3, and further preferably -0.35.

[0155] Next, examples of the objective optical system of this embodiment will be described. However, the present invention is not limited to the following examples.

[0156] Figures 1 to 7 1 is a cross-sectional view of the objective optical system of Example 1 to Example 7. Figures 1 to 7 In each figure, (a) is a cross-sectional view when the focus is achieved at a distant object point, and (b) is a cross-sectional view when the focus is achieved at a close object point. Figures 1 to 7 In (b) of each figure, for reference, the position of the meniscus lens of the second lens group when focusing on a distant object point is indicated by a two-dot chain line.

[0157] Figures 8 to 14 It is the aberration diagram of the objective optical system of Example 1 to Example 7. Figures 1 to 7 In each figure, (a), (b), (c), and (d) are aberration diagrams when the focus is achieved at a distant object point (denoted as "near" in the figure), and (e), (f), (g), and (h) are aberration diagrams when the focus is achieved at a close object point (denoted as "far" in the figure). Figures 1 to 7 In the figures, (a) and (e) are diagrams of spherical aberration (SA in the figures). (b) and (f) are diagrams of astigmatism (AS in the figures). (c) and (g) are diagrams of distortion (DT in the figures). (d) and (h) are diagrams of lateral chromatic aberration (CC). In Figures (a), (d), (e), and (h), the g line represents the aberrations at a wavelength of 435.84 nm, and the C line represents the aberrations at a wavelength of 656.27 nm. In (a) and (e), the d line represents the aberrations at a wavelength of 587.56 nm. In (b) and (f), ΔM represents the aberration on the d line relative to the meridional image plane, and ΔS represents the aberration on the d line relative to the sagittal image plane.

[0158] exist Figures 1 to 7 In the figure, the first lens group of the objective optical system of each embodiment is represented by G1, the second lens group is represented by G2, the third lens group is represented by G3, the infrared filter is represented by CF, the aperture is represented by AS, the cover glass is represented by CG, and the image plane, i.e., the imaging plane, is represented by I.

[0159] like Figures 1 to 7 As shown, each objective optical system of Examples 1 to 7 includes, from the object side, a first lens group G1 with negative refractive power, a second lens group G2 with positive refractive power, and a third lens group G3 with positive refractive power.

[0160] In each objective optical system of Examples 1 to 7, when focusing from a distant object point to a close object point, the second lens group G2 moves from the object side to the image side, while the first lens group G1 and the third lens group G3 are fixed. At this time, the infrared filter F is fixed in the same manner as the first lens group G1. The aperture stop P moves along the optical axis in conjunction with the second lens group G2. The cover glass C is fixed in the same manner as the third lens group G3.

[0161] In each of the objective optical systems of Examples 1 to 7, an aspherical surface is provided on the object-side surface of the meniscus lens L3 of the second lens group G2.

[0162] The detailed structure of each objective optical system of Examples 1 to 7 will be described below.

[0163] (Example 1)

[0164] like Figure 1 As shown, in the objective optical system of Example 1, the first lens group G1 is composed of a negative-power plano-concave lens L1 and a negative-power plano-concave lens L2, arranged in order from the object side. Plano-concave lens L1 corresponds to the "first lens" described in the claims below. Plano-concave lens L2 corresponds to the "second lens" described in the claims below. The concave surfaces of plano-concave lenses L1 and L2 face the image side. In other words, the object-side surfaces of plano-concave lenses L1 and L2 are flat surfaces perpendicular to the optical axis. The image-side surfaces of plano-concave lenses L1 and L2 are concave surfaces that are concave toward the object side. An infrared filter F is arranged in the first lens group G1, specifically, in a space closer to the image side than plano-concave lens L2. The object-side and image-side surfaces of the infrared filter F are flat surfaces perpendicular to the optical axis.

[0165] The second lens group G2 consists of a single positive meniscus lens, meniscus lens L3. Meniscus lens L3 corresponds to the "positive meniscus lens" described in the claims below. The convex surface of meniscus lens L3 faces the object side. In other words, the object-side and image-side surfaces of meniscus lens L3 are concave, concave toward the object.

[0166] The third lens group G3 is composed of a biconvex lens L4 with positive refractive power, a biconvex lens L5 as a positive lens, a meniscus lens L6 as a negative meniscus lens, and a plano-convex lens L7 with positive refractive power, which are arranged in order from the object side. The aperture stop P is arranged in the third lens group G3, and more specifically, in a space closer to the object side than the biconvex lens L4. An opening with the optical axis as the center and a diameter smaller than that of the biconvex lens L4 is formed in the aperture stop P. The biconvex lens L4 is equivalent to the "single lens" described in the claims described below. The object side surfaces of the biconvex lenses L4 and L5 are convex surfaces protruding toward the object side. The image side surfaces of the biconvex lenses L4 and L5 are convex surfaces protruding toward the image side. The object side surface of the meniscus lens L6 is a concave surface recessed toward the image side. The image side surface of the meniscus lens L6 is a convex surface protruding toward the image side. The biconvex lens L5 and the meniscus lens L6 are bonded to each other to form a bonded lens L C That is, the image side surface of the biconvex lens L5 and the object side surface of the meniscus lens L6 are in contact with each other. C This corresponds to the “cemented lens” described in the claims below.

[0167] The object-side surface of plano-convex lens L7 is a convex surface protruding toward the object. The image-side surface of plano-convex lens L7 is a flat surface perpendicular to the optical axis. Cover glass C is positioned closer to the image side than third lens group G3. Both the object-side and image-side surfaces of cover glass C are flat surfaces perpendicular to the optical axis. The image-side surface of cover glass C serves as image plane I, or the imaging surface, of the objective optical system. The image-side surface of plano-convex lens L7 and the object-side surface of cover glass C are in contact with each other.

[0168] Tables 1 to 5 show the numerical data for Example 1. The numerical data for Examples 1 to 7 are common. In the surface data, r is the radius of curvature of each surface, d is the distance between the surfaces, nd is the refractive index of each lens at a wavelength of 587.56 nm, i.e., the d-line, and νd is the Abbe number of each lens. The unit of each value is millimeter (mm). * indicates an aspherical surface. AS represents the aperture stop.

[0169] In addition, the numerical data in Examples 1 to 7 are the same. When the direction parallel to the optical axis of the objective optical system is set to z, a direction perpendicular to the optical axis is set to y, the cone coefficient is set to k, and the aspheric coefficient is set to A4, A6, A8, and A10, the aspheric shape is expressed by the following formula.

[0170] z=(y 2 / r) / [1+{1-(1+k)(y / r) 2} 1 / 2 ]+A4y 4 +A6y 6 +A8y 8 +A10y 10

[0171] [Numerical Example 1]

[0172] [Table 1]

[0173] Polygon data

[0174]

[0175] [Table 2]

[0176] Aspheric surface data

[0177]

[0178] [Table 3]

[0179] Zoom data

[0180]

[0181] [Table 4]

[0182] Focal length of each lens group

[0183] First lens group -0.7521

[0184] The second lens group 6.3591

[0185] The third lens group 1.8713

[0186] [Table 5]

[0187] Corresponding value of the conditional

[0188]

[0189] from Figure 8 It can be seen that in the objective optical system of Example 1, various aberrations such as spherical aberration, astigmatism, distortion, and lateral chromatic aberration are corrected, and good aberration characteristics are obtained in the visible wavelength region.

[0190] (Example 2)

[0191] like Figure 2 As shown, in Example 2, the first lens group G1 is composed of a negative-power plano-concave lens L1 and a negative-power plano-concave lens L2, arranged in this order from the object side. In each Example 2 and subsequent Examples, lenses of the same type as those in the previously described Examples are denoted by the same reference numerals, and descriptions of the object-side and image-side surfaces of these lenses are omitted. An infrared filter F is positioned within a space closer to the image side than the plano-concave lens L2.

[0192] The second lens group G2 is composed of a single meniscus lens L3 which is a positive meniscus lens.

[0193] The third lens group G3 is composed of a biconvex lens L4 with positive refractive power, a biconvex lens L5 as a positive lens, a meniscus lens L6 as a negative meniscus lens, and a plano-convex lens L7 with positive refractive power, which are arranged in this order from the object side. The aperture stop P is arranged in the space closer to the object side than the biconvex lens L4. The biconvex lens L5 and the meniscus lens L6 constitute a cemented lens L C The cover glass C is disposed in a space closer to the image side than the third lens group G3.

[0194] Tables 6 to 10 show the numerical data of Example 2.

[0195] [Numerical Example 2]

[0196] [Table 6]

[0197] Polygon data

[0198]

[0199] [Table 7]

[0200] Aspheric surface data

[0201]

[0202] [Table 8]

[0203] Zoom data

[0204]

[0205] [Table 9]

[0206] Focal length of each lens group

[0207] First lens group -0.7577

[0208] Second lens group 6.3019

[0209] The third lens group 1.8942

[0210] [Table 10]

[0211] Corresponding value of the conditional

[0212]

[0213] from Figure 9 It can be seen that in the objective optical system of Example 2, various aberrations such as spherical aberration, astigmatism, distortion, and lateral chromatic aberration are also corrected, and good aberration characteristics can be obtained in the visible wavelength region.

[0214] (Example 3)

[0215] like Figure 3As shown, in Example 3, the first lens group G1 is composed of a negative plano-concave lens L1 and a negative plano-concave lens L2 arranged in this order from the object side. An infrared filter F is arranged in a space closer to the image side than the plano-concave lens L2.

[0216] The second lens group G2 is composed of a single meniscus lens L3 which is a positive meniscus lens.

[0217] The third lens group G3 is composed of a biconvex lens L4 with positive refractive power, a biconvex lens L5 as a positive lens, a meniscus lens L6 as a negative meniscus lens, and a plano-convex lens L7 with positive refractive power, arranged in this order from the object side. The aperture stop P is arranged in the space closer to the object side than the biconvex lens L4. The biconvex lens L5 and the meniscus lens L6 constitute a cemented lens L C The cover glass C is disposed in a space closer to the image side than the third lens group G3.

[0218] Tables 11 to 15 show the numerical data of Example 3.

[0219] [Numerical Example 3]

[0220] [Table 11]

[0221] Polygon data

[0222]

[0223] [Table 12]

[0224] Aspheric surface data

[0225]

[0226] [Table 13]

[0227] Zoom data

[0228]

[0229] [Table 14]

[0230] Focal length of each lens group

[0231] First lens group -0.7090

[0232] The second lens group 5.8841

[0233] The third lens group 1.9368

[0234] [Table 15]

[0235] Corresponding value of the conditional

[0236]

[0237] from Figure 10 It can be seen that in the objective optical system of Example 3, various aberrations such as spherical aberration, astigmatism, distortion, and lateral chromatic aberration are also corrected, and good aberration characteristics are obtained in the visible wavelength region.

[0238] (Example 4)

[0239] like Figure 4 As shown, in Example 4, the first lens group G1 is composed of a negative-power plano-concave lens L1 and a negative-power plano-concave lens L2, arranged in this order from the object side. An infrared filter F is arranged in a space closer to the image side than the plano-concave lens L2.

[0240] The second lens group G2 is composed of a single meniscus lens L3 which is a positive meniscus lens.

[0241] The third lens group G3 is composed of a biconvex lens L4 with positive refractive power, a biconvex lens L5 as a positive lens, a meniscus lens L6 as a negative meniscus lens, and a plano-convex lens L7 with positive refractive power, arranged in this order from the object side. The aperture stop P is arranged in the space closer to the object side than the biconvex lens L4. The biconvex lens L5 and the meniscus lens L6 constitute a cemented lens L C The cover glass C is disposed in a space closer to the image side than the third lens group G3.

[0242] Tables 16 to 20 show the numerical data of Example 4.

[0243] [Numerical Example 4]

[0244] [Table 16]

[0245] Polygon data

[0246]

[0247] [Table 17]

[0248] Aspheric surface data

[0249]

[0250] [Table 18]

[0251] Zoom data

[0252]

[0253] [Table 19]

[0254] Focal length of each lens group

[0255] First lens group -0.7013

[0256] The second lens group 6.1245

[0257] The third lens group 1.9282

[0258] [Table 20]

[0259] Corresponding value of the conditional

[0260]

[0261] from Figure 11 It can be seen that in the objective optical system of Example 4, various aberrations such as spherical aberration, astigmatism, distortion, and lateral chromatic aberration are also corrected, and good aberration characteristics are obtained in the visible wavelength region.

[0262] (Example 5)

[0263] like Figure 5 As shown, in Example 5, the first lens group G1 is composed of a negative plano-concave lens L1 and a negative plano-concave lens L2, which are arranged in this order from the object side. An infrared filter F is arranged in a space closer to the image side than the plano-concave lens L2.

[0264] The second lens group G2 is composed of a single meniscus lens L3 which is a positive meniscus lens.

[0265] The third lens group G3 is composed of a biconvex lens L4 with positive refractive power, a biconvex lens L5 as a positive lens, a meniscus lens L6 as a negative meniscus lens, and a parallel plate PP1, which are arranged in this order from the object side. The aperture stop P is arranged in a space closer to the object side than the biconvex lens L4. The biconvex lens L5 and the meniscus lens L6 constitute a cemented lens L. C The object-side and image-side surfaces of the parallel plate PP1 are flat surfaces perpendicular to the optical axis. The cover glass C is positioned closer to the image side than the third lens group G3. The image-side surface of the parallel plate PP1 and the object-side surface of the cover glass C are in contact with each other.

[0266] Tables 21 to 25 show the numerical data of Example 5.

[0267] [Numerical Example 5]

[0268] [Table 21]

[0269] Polygon data

[0270]

[0271] [Table 22]

[0272] Aspheric surface data

[0273]

[0274] [Table 23]

[0275] Zoom data

[0276]

[0277] [Table 24]

[0278] Focal length of each lens group

[0279] First lens group -0.7311

[0280] The second lens group 5.5917

[0281] The third lens group 1.8626

[0282] [Table 25]

[0283] Corresponding value of the conditional

[0284]

[0285] from Figure 12 It can be seen that in the objective optical system of Example 5, various aberrations such as spherical aberration, astigmatism, distortion, and lateral chromatic aberration are also corrected, and good aberration characteristics are obtained in the visible wavelength region.

[0286] (Example 6)

[0287] like Figure 6 As shown, in Example 6, the first lens group G1 consists of a negative-power plano-concave lens L1 and a negative-power meniscus lens L8, arranged in this order from the object side. Meniscus lens L8 is a negative meniscus lens and corresponds to the "second lens" described in the claims below. The object-side surface of meniscus lens L8 is a convex surface that protrudes toward the object. The image-side surface of meniscus lens L8 is a concave surface that is recessed toward the object. An infrared filter F is positioned within the space on the image side of plano-concave lens L2.

[0288] The second lens group G2 is composed of a single meniscus lens L3 which is a positive meniscus lens.

[0289] The third lens group G3 is composed of a biconvex lens L4 with positive refractive power, a biconvex lens L5 as a positive lens, a biconcave lens L9 as a negative meniscus lens, and a plano-convex lens L7 with positive refractive power, which are arranged in this order from the object side. The aperture stop P is arranged in a space closer to the object side than the biconvex lens L4. The object side surface of the biconcave lens L9 is a concave surface that is concave toward the image side. The image side surface of the biconcave lens L9 is a concave surface that is concave toward the object side. The biconvex lens L5 and the biconcave lens L9 constitute a cemented lens L C That is, the image-side surface of the biconvex lens L5 and the object-side surface of the biconcave lens L9 are in contact with each other. The cover glass C is arranged in a space closer to the image side than the third lens group G3.

[0290] Tables 26 to 30 show the numerical data of Example 6.

[0291] [Numerical Example 6]

[0292] [Table 26]

[0293] Polygon data

[0294]

[0295] [Table 27]

[0296] Aspheric surface data

[0297]

[0298] [Table 28]

[0299] Zoom data

[0300]

[0301] [Table 29]

[0302] Focal length of each lens group

[0303] First lens group -0.6500

[0304] The second lens group 5.2044

[0305] The third lens group 1.9687

[0306] [Table 30]

[0307] Corresponding value of the conditional

[0308]

[0309] from Figure 13 It can be seen that in the objective optical system of Example 6, various aberrations such as spherical aberration, astigmatism, distortion, and lateral chromatic aberration are also corrected, and good aberration characteristics are obtained in the visible wavelength region.

[0310] (Example 7)

[0311] like Figure 7 As shown, in Example 7, the first lens group G1 is composed of a negative refractive power plano-concave lens L1 and a negative refractive power biconcave lens L2 arranged in this order from the object side. 10 Composition. Biconcave lens L 10 This corresponds to the "second lens" described in the claims below. 10 The object side of the lens is concave and concave toward the image side. 10The image side of the lens is concave toward the object. The infrared filter F is placed on a side that is slightly larger than the double concave lens L. 10 In the space on the image side.

[0312] The second lens group G2 is composed of a single meniscus lens L3 which is a positive meniscus lens.

[0313] The third lens group G3 is composed of a biconvex lens L4 with positive refractive power, a biconvex lens L5 as a positive lens, a biconcave lens L9 as a negative meniscus lens, and a plano-convex lens L7 with positive refractive power, which are arranged in this order from the object side. The aperture stop P is arranged in a space closer to the object side than the biconvex lens L4. The object side surface of the biconcave lens L9 is a concave surface that is concave toward the image side. The image side surface of the biconcave lens L9 is a concave surface that is concave toward the object side. The biconvex lens L5 and the biconcave lens L9 constitute a cemented lens L C That is, the image-side surface of the biconvex lens L5 and the object-side surface of the biconcave lens L9 are in contact with each other. The cover glass C is arranged in a space closer to the image side than the third lens group G3.

[0314] Tables 31 to 35 show the numerical data of Example 7.

[0315] [Numerical Example 7]

[0316] [Table 31]

[0317] Polygon data

[0318]

[0319] [Table 32]

[0320] Aspheric surface data

[0321] [Table 33]

[0322] Zoom data

[0323]

[0324] [Table 34]

[0325] Focal length of each lens group

[0326] First lens group -0.6908

[0327] The second lens group 5.9970

[0328] The third lens group 1.9368

[0329] [Table 35]

[0330] Corresponding value of the conditional

[0331]

[0332] from Figure 14 It can be seen that in the objective optical system of Example 7, various aberrations such as spherical aberration, astigmatism, distortion aberration and lateral chromatic aberration are corrected, and good aberration characteristics are obtained in the visible wavelength range.

[0333] Next, the endoscope and imaging device according to this embodiment will be described. Figure 15 It is a schematic diagram of the endoscope 100 and the imaging device 200 according to this embodiment.

[0334] like Figure 15 As shown, the endoscope 100 includes an insertion portion 110 and an operating portion 120. The insertion portion 110 is formed to be slender and can be inserted into a body cavity of a patient (not shown). The insertion portion 110 has an extension portion 112 and a front end portion 114. The extension portion 112 can be freely bent along the axis JX by operation of a user (not shown) using the operating portion 120. That is, the axial shape of the extension portion 112 along the axis JX can be freely changed, for example, along an anatomical passage inserted such as the stomach, duodenum, kidney, ureter, etc. The extension portion 112 is formed of a flexible material. The front end portion 114 is arranged at the front end 112a of the extension portion 112, has a diameter substantially the same as that of the extension portion 112, and is inserted into the anatomical passage integrally with the extension portion 112. That is, the front end 112a of the extension portion 112 is connected to the base end 114b of the front end portion 114.

[0335] Although not shown, the insertion portion 110 includes a plurality of extremely elongated functional components, such as a treatment instrument such as a choledochoscope, a light guide cable, an electrical cable, a fluid passage, a guide wire, and a puller wire, as well as a covering member that covers these functional components radially outward from the axis JX. The objective optical system of this embodiment is housed in the distal end portion 114 of the insertion portion 110.

[0336] The operating portion 120 is connected to the base end 112b of the extension portion 112 of the insertion portion 110. That is, the operating portion 120 is connected to the base end 112b on the opposite side of the front end 112a of the extension portion 112 that is connected to the front end portion 114. The operating portion 120 has a control knob 122 and a port 130. The control knob 122 is used for the user to manually move the insertion portion 110 forward and backward, change the axial shape of the extension portion 112 to bend it, or change the direction in which the front end portion 114 is facing. The control knob 122 is equivalent to the "handle" described in the claims described later. The port 130 is configured to enable a variety of functional components such as cables, guide wires, auxiliary probes, fluid tubes, etc. to be installed on the operating portion 120 so as to be connected to the insertion portion 110.

[0337] The imaging device 200 includes an endoscope 100 and a control device 150. The control device 150 includes a controller 152, an output device 154, an input device 156, a light source 160, a fluid source 170, and a suction pump 172. The controller 152 receives data related to the observation object from the endoscope 100 and sends data to the endoscope 100, and includes an imaging element 180. The operating unit 120 of the endoscope 100 is connected to the controller 152 via a connection unit 190 such as a universal cable. The imaging element 180 receives an image obtained by the objective optical system of this embodiment, that is, an image formed on the image plane I of the objective optical system, via the connection unit 190. The imaging element 180 performs image processing on the received image, converts it into an electrical signal, and sends it to the output device 154. The imaging element 180 is, for example, an image sensor such as a CMOS (complementary metal-oxide semiconductor) or a CCD (Charge Coupled Device).

[0338] The output device 154 outputs a plurality of information, including an image of an observation object and information about the observation object transmitted from the imaging element 180, information transmitted from the controller 152, and information about the operation of the endoscope 100. The output device 154 is, for example, a display capable of displaying the plurality of information transmitted to the output device 154 as described above. The input device 156 primarily inputs a plurality of information, including the operation of the endoscope 100 and information about the subject, to the controller 152. The output device 154 is, for example, a keyboard, but may also be a mouse or the like.

[0339] The light source 160 emits light for capturing an image of the object under observation. Light emitted from the light source 160 is directed from the distal end portion 114 toward the object under observation via an optical fiber link and a light guide cable inserted through the connection portion 190, the operating portion 120, and the insertion portion 110 of the endoscope 100. The fluid source 170 is configured to communicate with the controller 152 and supplies liquids such as air and treatment water to the endoscope 100 via the port 130. The suction pump 172 discharges fluid from the anatomical region into which the insertion portion 110 of the endoscope 100 is inserted, and includes, for example, a port for generating vacuum suction.

[0340] The endoscope 100 and the imaging device 200 of the present embodiment described above include the objective optical system of the present embodiment. Therefore, according to the endoscope 100 and the imaging device 200 of the present embodiment, it is possible to achieve miniaturization of the distal end portion 114 of the endoscope 100 and reduction in the diameter of the extension portion 112, and to observe an observation object such as a lesion at high resolution using the high-performance objective optical system, and to obtain a high-definition image of the observation object using the imaging element 180.

[0341] The endoscope 100 and imaging device 200 described above are examples of the endoscope and imaging device of this embodiment. Therefore, the structures of the endoscope and imaging device of this embodiment can be modified appropriately based on the structures of the endoscope 100 and imaging device 200. For example, the operating unit 120 of the endoscope 100 can accommodate a power supply, light source, imaging element, and various supply devices (not shown). Furthermore, for example, the imaging device 200 can omit the fluid source 170 and suction pump 172, or be provided with a video detector (not shown). Furthermore, the imaging device 200 can be connected to a storage device or communication terminal (not shown) via wired or wireless communication.

[0342] [Description of labels]

[0343] 100: Endoscope;

[0344] 110: insertion part;

[0345] 112: extension;

[0346] 114: front end;

[0347] 120: operation unit;

[0348] 180: camera element;

[0349] 200: camera device;

[0350] G1: first lens group;

[0351] G2: second lens group;

[0352] G3: third lens group;

[0353] L1: Plano-concave lens (first lens);

[0354] L2: Plano-concave lens (second lens);

[0355] L3: meniscus lens;

[0356] L4: biconvex lens (single lens);

[0357] L8: Meniscus lens (second lens);

[0358] L 10 : Biconcave lens (second lens);

[0359] L C : Cemented lens.

Claims

1. An objective optical system, wherein: The objective optical system is composed of a first lens group with negative refractive power, a second lens group with positive refractive power, and a third lens group with positive refractive power, which are arranged in order from the object side. The second lens group is moved from the object side to the image side to focus from a distant object point to a close object point. The first lens group is composed of two lenses: a first lens which is a negative lens and a second lens which is a negative lens with a concave surface facing the image side. The second lens group consists of a positive meniscus lens with its convex surface facing the object side. The third lens group includes, in order from the object side, a single lens with positive refractive power and a cemented lens consisting of a positive lens and a negative lens. The objective optical system satisfies the following conditional formula (1): 0.01 <L1_Rr / L2_Rr<0.95···(1) in, L1_Rr is the curvature radius of the image side surface of the first lens, L2_Rr is the curvature radius of the image-side surface of the second lens.

2. The objective optical system according to claim 1, wherein The objective optical system satisfies the following conditional formula (2): 0.136 <L1 / L2<0.95···(2) in, L1 is the focal length of the first lens, L2 is the focal length of the second lens.

3. The objective optical system according to claim 1, wherein: The objective optical system satisfies the following conditional formula (3): 0.2 <L2_SF<1.85···(3) in, L2_SF is the shape factor of the second lens, and the shape factor of the second lens is expressed by the following formula (4): L2_SF=(L2_Lr-L2_Rr) / (L2_Lr+L2_Rr)···(4) and, L2_Lr is the curvature radius of the object-side surface of the second lens, and L2_Rr is the curvature radius of the image-side surface of the second lens.

4. The objective optical system according to claim 1, wherein The objective optical system satisfies the following conditional formula (5): -0.4 <L1 / f2<-0.145···(5) in, L1 is the focal length of the first lens, f2 is the focal length of the second lens group.

5. The objective optical system according to claim 1, wherein: The objective optical system satisfies the following conditional formula (6): -3 <L1 / fw<-0.955···(6) in, L1 is the focal length of the first lens, Fw is the focal length of the entire objective optical system when focusing on a distant object point.

6. The objective optical system according to claim 1, wherein: The objective optical system satisfies the following conditional formula (7): -3 <f1 / fw<-1.06···(7) in, f1 is the focal length of the first lens group, fw is the focal length of the entire objective optical system when focusing on a distant object point.

7. The objective optical system according to claim 1, wherein: The objective optical system satisfies the following conditional formula (8): 0.25 <thi_3g_L1 / thi_3g_air<1.5···(8) in, thi_3g_L1 is the thickness of the single lens on the optical axis, thi_3g_air is the air space between the single lens and the cemented lens on the optical axis.

8. The objective optical system according to claim 1, wherein: The objective optical system satisfies the following conditional formula (9): 0.325 <v / fw<0.6···(9) in, v is the amount of movement of the second lens group from when it focuses on a distant object point to when it focuses on a close object point, and fw is the focal length of the entire objective optical system when it focuses on a distant object point.

9. The objective optical system according to claim 1, wherein: The objective optical system satisfies the following conditional formula (10): -0.4 <G3_L1_SF<0.4···(10) in, G3_L1_SF is the shape factor of the single lens, which is expressed by the following equation (11): G3_L1_SF=(G3_L1_Lr+G3_L1_Rr) / (G3_L1_Lr-G3_L1_Rr)···(11) and, G3_L1_Lr is the radius of curvature of the object side of the single lens, G3_L1_Rr is the curvature radius of the image-side surface of the single lens.

10. The objective optical system according to claim 1, wherein: The objective optical system satisfies the following conditional formula (12): -1.5 <G3_Lce_SF<-0.2···(12) in, G3_Lce_SF is the shape factor of the cemented lens, which is expressed by the following equation (13): G3_Lce_SF=(G3_Lce_Lr+G3_Lce_Rr) / (G3_Lce_Lr-G3_Lce_Rr)···(13) and, G3_Lce_Lr is the radius of curvature of the object side surface of the cemented lens, G3_Lce_Rr is the curvature radius of the image-side surface of the cemented lens.

11. An endoscope, wherein: The endoscope comprises: a front end portion accommodating the objective optical system according to claim 1; an extension portion connected to the base end of the front end portion and capable of bending; and An operating portion is connected to a base end of the extending portion on the opposite side of the distal end connected to the distal end portion and has a handle for changing the axial shape of the extending portion.

12. A camera device, wherein: The camera device comprises: The endoscope according to claim 11; and An imaging element converts an image acquired by the objective optical system into an electrical signal.

Images