Objective optical system, imaging device, and endoscope

Abstract

Provided is an objective optical system, an imaging device, and an endoscope that can ensure the stroke of lens movement at the time of focus adjustment, suppress the effects of center shift and degradation of optical performance caused by manufacturing errors, and set the base length of a left-eye objective optical system and a right-eye objective optical system shorter at the time of 3D observation. The objective optical system includes, in order from the object side, a front group FG, an aperture stop S, and a rear group RG, the front group FG includes a first lens L1 having a negative refractive power with a concave surface facing the image side, a second lens L2 having a negative refractive power, and a third lens L3 having a positive refractive power, the rear group RG includes a fourth lens L4 having a positive refractive power and a fifth lens L5 having a positive refractive power, the fifth lens L5 is a cemented lens, and the objective optical system satisfies the following conditional expression (1): 2.3 < f3 / f5 < 20 (1), where f3 is the focal length of the third lens L3 and f5 is the focal length of the fifth lens L5.

Description

Technical Field

[0001] This invention relates to objective lens optical systems, imaging devices, and endoscopes. Background Technology

[0002] In the field of medical electronic endoscopy, skills related to treatment and diagnosis are constantly improving. Electronic endoscopes are inserted into living organisms to detect and assess even smaller lesions. 2D electronic endoscopes provide planar (2D) observation, while 3D electronic endoscopes provide stereoscopic (3D) observation. In both 2D and 3D observation, precise focus adjustment of the imaging plane of the camera element is required during the manufacture of the objective lens optics system. Furthermore, the endoscopic objective lens optics system must be close to the lesion for observation during treatment or diagnosis. Therefore, with a large distance between the optical axes of the left and right eye objective lens optics systems (i.e., a large baseline length), the parallax between the left and right eye images also increases. Consequently, observers are prone to eye strain during 3D observation. Therefore, endoscopic objective lens optics systems for 3D observation need to have a shorter baseline length. Furthermore, stereoscopic observation may become difficult when the position of the obtained image is offset relative to the position suitable for 3D observation due to the eccentricity of the objective optical systems for the left and right eyes.

[0003] As a conventional objective lens optical system, for example, Patent Document 1 discloses a five-group structure with refractive power configurations arranged sequentially from the object side as negative, negative, positive, aperture, positive, and junction (positive and negative).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2018-159853 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] Here, Patent Document 1 discloses an objective lens optical system that uses a single imaging element to acquire images for both the left and right eyes. To adjust the focus during the manufacturing of the objective lens optical system, the imaging element is moved along the optical axis, causing the focus positions of both the left and right eye objective lens optical systems to change simultaneously, and a bonding lens is moved along the optical axis. This allows for independent focus adjustment of one of the two objective lens optical systems used for 3D observation (left and right eyes). Furthermore, the objective lens optical system of Patent Document 1 takes into account the refractive power of the lens (bonding lens) to ensure the lens travel, i.e., the movement interval, during focus adjustment during the manufacturing of the objective lens optical system.

[0009] However, in this objective optical system, although the lens travel during focus adjustment during manufacturing is ensured, the center shift and aberration performance degradation caused by lens eccentricity during 3D observation are not fully considered.

[0010] The present invention was made in view of the following problems, and its object is to provide an objective lens optical system, a camera device and an endoscope that can ensure the travel of the lens movement during focus adjustment and suppress the effects of center shift and aberration performance degradation during 3D observation caused by manufacturing errors, by setting the baseline length of the left eye objective lens optical system and the right eye objective lens optical system for 3D observation to be shorter.

[0011] means for solving problems

[0012] To solve the above problems and achieve the objective, the objective lens optical system of at least several embodiments of the present invention includes, from the object side, a front group, an aperture stop, and a rear group in sequence. The front group includes: a first lens with negative refractive power, the concave surface of which faces the image side; a second lens with negative refractive power; and a third lens with positive refractive power. The rear group includes: a fourth lens with positive refractive power; and a fifth lens with positive refractive power, the fifth lens being a conjoined lens. The objective lens optical system satisfies the following conditional expression (1):

[0013] 2.3 <f3 / f5<20 (1)

[0014] Where f3 is the focal length of the third lens and f5 is the focal length of the fifth lens.

[0015] Furthermore, the imaging device of at least a few embodiments of the present invention has an objective lens optical system and an imaging element disposed on an image plane. The imaging element has an imaging plane and converts the image formed on the imaging plane by the objective lens optical system into an electrical signal. The objective lens optical system is the objective lens optical system described above.

[0016] Furthermore, the endoscopes of at least a few embodiments of the present invention have the aforementioned imaging device.

[0017] Invention Effects

[0018] According to the present invention, an objective lens optical system, a camera device, and an endoscope can be provided, which can ensure the travel of the lens movement during focus adjustment when manufacturing the objective lens optical system, and in the case of an objective lens optical system for 3D observation, can suppress the effects of center shift and aberration performance degradation caused by manufacturing errors of the left-eye objective lens optical system and the right-eye objective lens optical system, and can set the baseline length of the left-eye objective lens optical system and the right-eye objective lens optical system for 3D observation to be shorter. Attached Figure Description

[0019] Figure 1These are cross-sectional views of the lens of the objective optical system and the imaging device of the embodiment.

[0020] Figure 2 (a) is a cross-sectional view of the lens of the objective optical system of Embodiment 1 of the present invention. Figure 2 (b), (c), (d), and (e) are aberration diagrams representing spherical aberration (SA), astigmatism (AS), distortion aberration (DT), and chromatic aberration (CC) in Example 1, respectively.

[0021] Figure 3 (a) is a cross-sectional view of the lens of the objective optical system of Embodiment 2 of the present invention. Figure 3 (b), (c), (d), and (e) are aberration diagrams representing spherical aberration (SA), astigmatism (AS), distortion aberration (DT), and chromatic aberration (CC) in Example 2, respectively.

[0022] Figure 4 (a) is a cross-sectional view of the lens of the objective optical system of Embodiment 3 of the present invention. Figure 4 (b), (c), (d), and (e) are aberration diagrams representing spherical aberration (SA), astigmatism (AS), distortion aberration (DT), and chromatic aberration (CC) in Example 3, respectively.

[0023] Figure 5 (a) is a cross-sectional view of the lens of the objective optical system of Embodiment 4 of the present invention. Figure 5 (b), (c), (d), and (e) are aberration diagrams representing spherical aberration (SA), astigmatism (AS), distortion aberration (DT), and chromatic aberration (CC) in Example 4, respectively.

[0024] Figure 6 (a) is a cross-sectional view of the lens of the objective optical system of Embodiment 5 of the present invention. Figure 6 (b), (c), (d), and (e) are aberration diagrams representing spherical aberration (SA), astigmatism (AS), distortion aberration (DT), and chromatic aberration (CC) in Example 5, respectively.

[0025] Figure 7 (a) is a cross-sectional view of the lens of the objective optical system of Embodiment 6 of the present invention. Figure 7 (b), (c), (d), and (e) are aberration diagrams representing spherical aberration (SA), astigmatism (AS), distortion aberration (DT), and chromatic aberration (CC) in Example 6, respectively.

[0026] Figure 8 (a) is a cross-sectional view of the lens of the objective optical system of Embodiment 7 of the present invention. Figure 8(b), (c), (d), and (e) are aberration diagrams representing spherical aberration (SA), astigmatism (AS), distortion aberration (DT), and chromatic aberration (CC) in Example 7, respectively.

[0027] Figure 9 This is a cross-sectional view of the objective optical system for 3D observation according to Embodiment 8 of the present invention.

[0028] Figure 10 This is a schematic structural diagram of the endoscope of Embodiment 9 of the present invention. Detailed Implementation

[0029] Before describing the embodiments, the effects of one embodiment of the present invention will be explained. Furthermore, specific examples will be shown when specifically describing the effects of this embodiment. However, as with the embodiments described later, these illustrative methods are merely a part of the methods included in the present invention, and many variations exist within these methods. Therefore, the present invention is not limited to the illustrative methods.

[0030] Figure 1 This is a cross-sectional view of the lens of the objective optical system according to the embodiment. This embodiment has a structure with one optical axis Ax for 2D observation. Furthermore, the objective optical system constitutes an imaging device by including an imaging element IMG.

[0031] Figure 9 It is to put 2 Figure 1 The diagram shows a side-by-side objective lens optical system. This is a 3D observation objective lens optical system that uses two objective lens optical systems, one for the right eye and one for the left eye.

[0032] Figure 1 The objective lens optical system of this embodiment shown includes, from the object side, a front group FG, an aperture stop S, and a rear group RG. The front group FG includes a first lens L1 with negative refractive power and a second lens L2 with negative refractive power and a third lens L3 with positive refractive power, with the concave surface facing the image side. The rear group RG includes a fourth lens L4 with positive refractive power and a fifth lens L5 with positive refractive power. The fifth lens L5 is a combination lens L51 and L52, satisfying the following conditional expression (1).

[0033] 2.3 <f3 / f5<20 (1)

[0034] Here, f3 is the focal length of the third lens L3, and f5 is the focal length of the fifth lens L5.

[0035] Additionally, filter F1, which is a parallel flat plate, is disposed on the front group FG. Furthermore, filter F2 is bonded to the object-side surface of the glass cover CG of the imaging element IMG.

[0036] As is common knowledge in the field of technology, even if a parallel plate, such as a filter or lens group, which has almost no refractive power is added to the objective optical system of this embodiment, it will not affect the optical performance achieved by the objective optical system in principle.

[0037] In this embodiment, a retrofocus optical system is constructed by sequentially arranging negative, negative, positive, aperture stop, positive, and positive refractive forces from the object side. Furthermore, in the objective lens optical system for 2D observation, a large space is formed between the image plane (camera plane) I and the fifth lens L5. Therefore, sufficient travel for focus adjustment during manufacturing can be ensured.

[0038] In addition, in the objective lens optical system used for 3D observation, such as Figure 9 As shown, the two objective lens optical systems are arranged side by side, and the fifth lens L5 is moved to adjust the focus during the manufacturing of the objective lens optical system. As described later in Example 8, this ensures that the adjustment... Figure 9 The travel distance of the fifth lens L5 shown.

[0039] Condition (1) specifies the ratio of the focal length of the third lens L3 to the focal length of the fifth lens L5.

[0040] If the value exceeds the upper limit of condition (1), the focal length of the fifth lens L5 becomes smaller. Therefore, it is difficult to ensure the travel of the fifth lens L5 used for focus adjustment.

[0041] If the focal length is lower than the lower limit of condition (1), the focal length of the third lens L3 becomes relatively smaller than that of the fifth lens L5. In the objective lens optical system for 3D observation, the images for the right eye and the left eye experience a center shift in the vertical direction (roughly perpendicular to the direction connecting the left and right eyes) due to eccentricity, making stereoscopic observation difficult. In addition, if the focal length of the third lens L3 becomes relatively smaller than that of the fifth lens L5, aberration performance such as image plane curvature is easily degraded.

[0042] Thus, in this embodiment, the lens movement stroke during focus adjustment during the manufacturing of the objective lens optical system can be ensured. Furthermore, in the case of an objective lens optical system for 3D observation, the effects of center shift and aberration performance degradation caused by manufacturing errors in the left-eye and right-eye objective lens optical systems can be suppressed by setting the baseline lengths of the left-eye and right-eye objective lens optical systems to be shorter.

[0043] Furthermore, according to a preferred embodiment of this invention, in order to adjust the focus of the objective lens optical system, it is desirable for the fifth lens L5 to move along the optical axis Ax.

[0044] Therefore, the travel of the fifth lens L5 was ensured during the manufacture of the objective lens optical system, making focus adjustment easy.

[0045] In addition, in the preferred embodiment of this invention, the following condition (2) is preferably satisfied.

[0046] 0.8 < |g2 / g1| < 2.6 (2)

[0047] Here, g1 is the focal length of the front group FG, and g2 is the focal length of the rear group RG.

[0048] Condition (2) specifies the ratio of the focal length of the front group FG to the focal length of the rear group RG.

[0049] If the value exceeds the upper limit of condition (2), the symmetry between the front group FG and the rear group RG before and after the aperture stop S is disrupted. As a result, chromatic aberration and image plane curvature become insufficiently corrected.

[0050] If the value is lower than the lower limit of condition (2), the focal length of the front group FG increases, and the height of the light rays in the first lens L1 increases. Therefore, it is difficult to set the baseline length of the right-eye objective optical system and the left-eye objective optical system of the 3D objective optical system to be short.

[0051] In addition, in the preferred embodiment of this invention, the following condition (3) is preferably satisfied.

[0052] 1.0 < |g1 / f| < 4.0 (3)

[0053] Here, g1 is the focal length of the front group FG, and f is the focal length of the objective lens optical system as a whole.

[0054] Condition (3) specifies the ratio of the focal length of the front group FG to the focal length of the entire objective lens optical system.

[0055] If the value exceeds the upper limit of condition (3), the focal length of the front group FG becomes larger, i.e., the refractive power becomes smaller. As a result, it is impossible to miniaturize the first lens L1, so it is not preferred.

[0056] If the value is lower than the lower limit of condition (3), the focal length of the front lens group FG becomes smaller, i.e., the refractive power becomes larger. As a result, the error sensitivity during the manufacture of the front lens group FG increases. Therefore, when the lens is shifted in the direction of the optical axis of the objective lens optical system or in a direction perpendicular to the optical axis, the field of view changes, which easily produces a deflection angle. The "deflection angle" refers to the angle between the optical axis and the central axis of the field of view.

[0057] In addition, in the preferred embodiment of this invention, the following condition (4) is preferably satisfied.

[0058] f2 / f1<100 (4)

[0059] Here, f2 is the focal length of the second lens L2, and f1 is the focal length of the first lens L1.

[0060] Condition (4) specifies the ratio of the focal length of the first lens L1 to the focal length of the second lens L2.

[0061] If the value exceeds the upper limit of condition (4), the focal length of the first lens L1 becomes smaller. Therefore, it is difficult to suppress the unilateral blur caused by the relative eccentricity between the first lens L1 and the second lens L2.

[0062] In addition, in the preferred embodiment of this invention, the following condition (5) is preferably satisfied.

[0063] 3.0 <f4 / f<6.0 (5)

[0064] Here, f4 is the focal length of the fourth lens L4, and f is the focal length of the objective lens optical system as a whole.

[0065] Condition (5) specifies the ratio of the focal length of the fourth lens L4 to the focal length of the overall objective lens optical system.

[0066] If the value exceeds the upper limit of condition (5), the focal length of the fourth lens increases, meaning the refractive power decreases. Consequently, the correction for image plane curvature is insufficient.

[0067] If the value is lower than the lower limit of condition (5), the focal length of the fourth lens L4 becomes smaller, that is, the refractive power becomes larger. As a result, it is difficult to correct the magnification chromatic aberration caused by the relative eccentricity between the fourth lens L4 and the fifth lens L5.

[0068] Furthermore, the imaging device of this embodiment has an objective lens optical system and an imaging element (IMG) disposed on the image plane. The imaging element has an imaging plane and converts the image formed on the imaging plane by the objective lens optical system into an electrical signal. The objective lens optical system is the objective lens optical system described above.

[0069] Therefore, it is possible to provide a camera device that can ensure the travel of the lens movement during focus adjustment when manufacturing the objective lens optical system, and in the case of an objective lens optical system for 3D observation, can suppress the effects of center shift and aberration performance degradation caused by manufacturing errors of the left-eye and right-eye objective lens optical systems, and can set the baseline length of the left-eye and right-eye objective lens optical systems to be shorter.

[0070] Furthermore, the endoscope of this embodiment has the aforementioned camera device.

[0071] Therefore, an endoscope can be provided that ensures the travel of the lens movement during focus adjustment when manufacturing the objective lens optical system, and in the case of an objective lens optical system for 3D observation, can suppress the effects of center shift and aberration performance degradation caused by manufacturing errors of the left-eye and right-eye objective lens optical systems, and can set the baseline length of the left-eye and right-eye objective lens optical systems to be shorter.

[0072] Furthermore, in a preferred embodiment, the first lens L1 is preferably a plano-concave shape with a concave surface facing the image side and having negative refractive power.

[0073] In endoscopy, when mucus or blood from inside organs adheres to the lens surface and obstructs observation, water or air is sprayed from a nozzle located at the tip of the endoscope to clean the lens surface. In this case, if the object side of the first lens L1 is convex, cleaning performance is easily reduced; if it is concave, water droplets easily accumulate on the lens surface. Especially in the convex shape, when the tip of the endoscope is impacted during transport or cleaning, the lens surface is easily damaged or broken. By making the first lens L1 a plano-concave shape with the concave side facing the image side and having negative refractive power, a structure can be created that ensures both cleanliness and drainage of the lens surface, and is less prone to damage or breakage due to impact.

[0074] Furthermore, in a preferred embodiment, the second lens L2 is preferably a meniscus shape with a convex surface facing the image side and having negative refractive power.

[0075] Therefore, even if the relative eccentricity of the first lens L1 and the second lens L2 is caused by manufacturing errors within the tolerance range of the lens or frame components, it can still be a structure that easily suppresses unilateral blurring.

[0076] Furthermore, in a preferred embodiment of this invention, in the objective lens optical system for 3D observation, the first lens L1 is preferably a single lens having two spherical segments spaced apart by a baseline length, and the first lens L1 is shared in both the left-eye objective lens optical system and the right-eye objective lens optical system.

[0077] Therefore, compared to the case where different first lenses are configured in the left-eye objective optical system and the right-eye objective optical system, the outer diameter of the front end of the objective optical system can be reduced, and the baseline length can be set to be shorter. Because the baseline length can be shortened, even when close to the subject, the parallax between the left-eye image obtained by the left-eye optical system and the right-eye image obtained by the right-eye optical system can be reduced, thus suppressing eye fatigue during 3D viewing.

[0078] The following describes each embodiment.

[0079] (Example 1)

[0080] The objective lens optical system of Example 1 will be described. Figure 2 (a) is a cross-sectional view of the objective lens optical system of Embodiment 1. The objective lens optical system, from the object side, comprises a front group FG, an aperture stop S, and a rear group RG. The front group FG includes: a first lens L1 with a plano-concave shape and negative refractive power, with its concave surface facing the image side; a second lens L2 with a meniscus shape and negative refractive power, with its convex surface facing the image side; a third lens L3 with a plano-convex shape and positive refractive power, with its convex surface facing the object side; and a filter F1. The rear group RG includes: a fourth lens L4 with a plano-convex shape and positive refractive power, with its convex surface facing the image side; a biconvex positive lens L51; a meniscus shape L52 with negative refractive power, with its convex surface facing the image side; a glass cover F2; and a CMOS glass cover CG. The aperture stop S is positioned between the front group FG and the rear group RG. An image plane I is located on the image side of the glass cover CG.

[0081] Lens L51 and lens L52 are combined to form a combined lens with positive refractive power, namely the fifth lens L5.

[0082] Alternatively, a band-limiting coating for restricting infrared light can be applied to the surfaces of filters F1 and F2, which are parallel flat plates. Alternatively, a multilayer film for band limiting can be applied to the surface of the glass cover CG. d16 is the adhesive layer.

[0083] Figure 2 (b), (c), (d), and (e) are aberration diagrams representing spherical aberration (SA), astigmatism (AS), distortion aberration (DT), and chromatic aberration (CC) in Example 1, respectively.

[0084] These aberration diagrams represent wavelengths of 546.07 nm (e-line), 656.27 nm (C-line), and 486.13 nm (F-line). In each diagram, FNO represents the F-number, and FIY represents the maximum image height. The same applies to the aberration diagrams below. In each aberration diagram, the horizontal axis represents the aberration amount. For spherical aberration, astigmatism, and magnification aberration, the unit of aberration amount is mm. For distortion aberration, the unit of aberration amount is %. The unit of image height is mm.

[0085] (Example 2)

[0086] The objective lens optical system of Example 2 will be described. Figure 3(a) is a cross-sectional view of the objective lens optical system of Embodiment 2. The objective lens optical system, from the object side, comprises a front group FG, an aperture stop S, and a rear group RG. The front group FG includes: a first lens L1 with a plano-concave shape and negative refractive power, with its concave surface facing the image side; a second lens L2 with a meniscus shape and negative refractive power, with its convex surface facing the image side; a third lens L3 with a meniscus shape and positive refractive power, with its convex surface facing the image side; and a filter F1. The rear group RG includes: a fourth lens L4 with a plano-convex shape and positive refractive power, with its convex surface facing the image side; a biconvex positive lens L51; a meniscus shape L52 with negative refractive power, with its convex surface facing the image side; a glass cover F2; and a CMOS glass cover CG. The aperture stop S is positioned between the front group FG and the rear group RG. An image plane I is located on the image side of the glass cover CG.

[0087] Lens L51 and lens L52 are combined to form a combined lens with positive refractive power, namely the fifth lens L5.

[0088] Alternatively, a band-limiting coating for restricting infrared light can be applied to the surfaces of filters F1 and F2, which are parallel flat plates. Alternatively, a multilayer film for band limiting can be applied to the surface of the glass cover CG. d16 is the adhesive layer.

[0089] Figure 3 (b), (c), (d), and (e) are aberration diagrams representing spherical aberration (SA), astigmatism (AS), distortion aberration (DT), and chromatic aberration (CC) in Example 2, respectively.

[0090] (Example 3)

[0091] The objective lens optical system of Example 3 will be described. Figure 4 (a) is a cross-sectional view of the objective lens optical system of Embodiment 3. The objective lens optical system, from the object side, comprises a front group FG, an aperture stop S, and a rear group RG. The front group FG includes: a first lens L1 with a plano-concave shape and negative refractive power, with its concave surface facing the image side; a second lens L2 with a meniscus shape and negative refractive power, with its convex surface facing the image side; a third lens L3 with a plano-convex shape and positive refractive power, with its convex surface facing the object side; and a filter F1. The rear group RG includes: a fourth lens L4 with a plano-convex shape and positive refractive power, with its convex surface facing the image side; a biconvex positive lens L51; a meniscus shape L52 with negative refractive power, with its convex surface facing the image side; a glass cover F2; and a CMOS glass cover CG. The aperture stop S is positioned between the front group FG and the rear group RG. An image plane I is located on the image side of the glass cover CG.

[0092] Lens L51 and lens L52 are combined to form a combined lens with positive refractive power, namely the fifth lens L5.

[0093] Alternatively, a band-limiting coating for restricting infrared light can be applied to the surfaces of filters F1 and F2, which are parallel flat plates. Alternatively, a multilayer film for band limiting can be applied to the surface of the glass cover CG. d16 is the adhesive layer.

[0094] Figure 4 (b), (c), (d), and (e) are aberration diagrams representing spherical aberration (SA), astigmatism (AS), distortion aberration (DT), and chromatic aberration (CC) in Example 3, respectively.

[0095] (Example 4)

[0096] The objective lens optical system of Example 4 will be described. Figure 5 (a) is a cross-sectional view of the objective lens optical system of Embodiment 4. The objective lens optical system, from the object side, comprises a front group FG, an aperture stop S, and a rear group RG. The front group FG includes: a first lens L1 with a plano-concave shape and negative refractive power, with its concave surface facing the image side; a second lens L2 with a meniscus shape and negative refractive power, with its convex surface facing the image side; a third lens L3 with a plano-convex shape and positive refractive power, with its convex surface facing the object side; and a filter F1. The rear group RG includes: a fourth lens L4 with a plano-convex shape and positive refractive power, with its convex surface facing the image side; a biconvex positive lens L51; a meniscus shape L52 with negative refractive power, with its convex surface facing the image side; a glass cover F2; and a CMOS glass cover CG. The aperture stop S is positioned between the front group FG and the rear group RG. An image plane I is located on the image side of the glass cover CG.

[0097] Lens L51 and lens L52 are combined to form a combined lens with positive refractive power, namely the fifth lens L5.

[0098] Alternatively, a band-limiting coating for restricting infrared light can be applied to the surfaces of filters F1 and F2, which are parallel flat plates. Alternatively, a multilayer film for band limiting can be applied to the surface of the glass cover CG. d16 is the adhesive layer.

[0099] Figure 5 (b), (c), (d), and (e) are aberration diagrams representing spherical aberration (SA), astigmatism (AS), distortion aberration (DT), and chromatic aberration (CC) in Example 4, respectively.

[0100] (Example 5)

[0101] The objective lens optical system of Example 5 will be described. Figure 6(a) is a cross-sectional view of the objective lens optical system of Embodiment 5. The objective lens optical system, from the object side, comprises a front group FG, an aperture stop S, and a rear group RG. The front group FG includes: a first lens L1 with a plano-concave shape and negative refractive power, with its concave surface facing the image side; a second lens L2 with a meniscus shape and negative refractive power, with its concave surface facing the image side; a third lens L3 with a plano-convex shape and positive refractive power, with its convex surface facing the object side; and a filter F1. The rear group RG includes: a fourth lens L4 with a plano-convex shape and positive refractive power, with its convex surface facing the image side; a biconvex positive lens L51; a meniscus shape L52 with negative refractive power, with its convex surface facing the image side; a glass cover F2; and a CMOS glass cover CG. The aperture stop S is positioned between the front group FG and the rear group RG. An image plane I is located on the image side of the glass cover CG.

[0102] Lens L51 and lens L52 are combined to form a combined lens with positive refractive power, namely the fifth lens L5.

[0103] Alternatively, a band-limiting coating for restricting infrared light can be applied to the surfaces of filters F1 and F2, which are parallel flat plates. Alternatively, a multilayer film for band limiting can be applied to the surface of the glass cover CG. d16 is the adhesive layer.

[0104] Figure 6 (b), (c), (d), and (e) are aberration diagrams representing spherical aberration (SA), astigmatism (AS), distortion aberration (DT), and chromatic aberration (CC) in Example 5, respectively.

[0105] (Example 6)

[0106] The objective lens optical system of Example 6 will be described. Figure 7 (a) is a cross-sectional view of the objective lens optical system of Embodiment 6. The objective lens optical system, from the object side, comprises a front group FG, an aperture stop S, and a rear group RG. The front group FG includes: a first lens L1 with a plano-concave shape and negative refractive power, with its concave surface facing the image side; a second lens L2 with a meniscus shape and negative refractive power, with its convex surface facing the image side; a third lens L3 with a plano-convex shape and positive refractive power, with its convex surface facing the object side; and a filter F1. The rear group RG includes: a fourth lens L4 with a plano-convex shape and positive refractive power, with its convex surface facing the image side; a biconvex positive lens L51; a meniscus shape L52 with negative refractive power, with its convex surface facing the image side; a glass cover F2; and a glass cover CG for the CCD. The aperture stop S is positioned between the front group FG and the rear group RG. An image plane I is located on the image side of the glass cover CG.

[0107] Lens L51 and lens L52 are combined to form a combined lens with positive refractive power, namely the fifth lens L5.

[0108] Alternatively, a band-limiting coating for restricting infrared light can be applied to the surfaces of filters F1 and F2, which are parallel flat plates. Alternatively, a multilayer film for band limiting can be applied to the surface of the glass cover CG. d16 is the adhesive layer.

[0109] Figure 7 (b), (c), (d), and (e) are aberration diagrams representing spherical aberration (SA), astigmatism (AS), distortion aberration (DT), and chromatic aberration (CC) in Example 6, respectively.

[0110] (Example 7)

[0111] The objective lens optical system of Example 7 will be described. Figure 8 (a) is a cross-sectional view of the objective lens optical system of Embodiment 7. The objective lens optical system, from the object side, comprises a front group FG, an aperture stop S, and a rear group RG. The front group FG includes: a first lens L1 with a plano-concave shape and negative refractive power, with its concave surface facing the image side; a second lens L2 with a meniscus shape and negative refractive power, with its concave surface facing the image side; a third lens L3 with a plano-convex shape and positive refractive power, with its convex surface facing the object side; and a filter F1. The rear group RG includes: a fourth lens L4 with a plano-convex shape and positive refractive power, with its convex surface facing the image side; a biconvex positive lens L51; a meniscus shape L52 with negative refractive power, with its convex surface facing the image side; a glass cover F2; and a CMOS glass cover CG. The aperture stop S is positioned between the front group FG and the rear group RG. An image plane I is located on the image side of the glass cover CG.

[0112] Lens L51 and lens L52 are combined to form a combined lens with positive refractive power, namely the fifth lens L5.

[0113] Alternatively, a band-limiting coating for restricting infrared light can be applied to the surfaces of filters F1 and F2, which are parallel flat plates. Alternatively, a multilayer film for band limiting can be applied to the surface of the glass cover CG. d16 is the adhesive layer.

[0114] Figure 8 (b), (c), (d), and (e) are aberration diagrams representing spherical aberration (SA), astigmatism (AS), distortion aberration (DT), and chromatic aberration (CC) in Example 7, respectively.

[0115] The numerical data for the above embodiments are shown below. The symbol r represents the radius of curvature of each lens surface, d represents the spacing between the lens surfaces, ne represents the refractive index of the e-line of each lens, νd represents the Abbe number of each lens, and Fno represents the F-number. Additionally, the aperture stop is the aperture stop.

[0116] Numerical Example 1

[0117] Unit mm

[0118] Surface data

[0119]

[0120]

[0121] Various data

[0122] Numerical Example 2: Unit mm Surface Data

[0123]

[0124] Various data

[0125] Numerical Example 3: Unit mm Surface Data

[0126]

[0127] Various data

[0128] Numerical Example 4: Unit mm Surface Data

[0129]

[0130] Various data

[0131] Numerical Example 5: Unit mm Surface Data

[0132]

[0133] Various data

[0134] Numerical Example 6: Unit mm Surface Data

[0135]

[0136] Various data

[0137] Numerical Example 7: Unit mm Surface Data

[0138]

[0139] Various data

[0141] The following shows the corresponding values ​​for each conditional expression in various embodiments.

[0142]

[0143]

[0144] The following shows the preferred values ​​for the upper and lower limits of each condition.

[0145] The following condition (1') is preferred to replace condition (1).

[0146] 3.5 <f3 / f5<15(1')

[0147] Moreover, it is preferable to replace condition (1) with the following condition (1”).

[0148] 4.9 <f3 / f5<10(1”)

[0149] The following condition (2') is preferred to replace condition (2).

[0150] 1.0<|g2 / g1|<2.0(2')

[0151] Moreover, it is preferable to replace condition (2) with the following condition (2”).

[0152] 1.5 < |g2 / g1| < 1.8(2”)

[0153] The following condition (3') is preferred to replace condition (3).

[0154] 1.2<|g1 / f|<3.2(3')

[0155] Moreover, it is preferable to replace condition (3) with the following condition (3”).

[0156] 1.5 < |g1 / f| < 2.2(3”)

[0157] The following condition (4') is preferred to replace condition (4).

[0158] f2 / f1<50(4')

[0159] Moreover, it is preferable to replace condition (4) with the following condition (4”).

[0160] f2 / f1<30(4”)

[0161] The following condition (5') is preferred to replace condition (5).

[0162] 3.5 <f4 / f<5.5(5')

[0163] Moreover, it is preferable to replace condition (5) with the following condition (5”).

[0164] 4.3 <f4 / f<5.2(5”)

[0165] The aforementioned objective lens optical system can also simultaneously satisfy multiple structures. This is preferred in terms of obtaining a good objective lens optical system. Furthermore, the preferred combination of structures is arbitrary. Additionally, regarding each conditional expression, only the upper or lower limit of the numerical range of the further defined conditional expressions can be specified.

[0166] (Example 8)

[0167] Figure 9 This is a cross-sectional view of the lens of the objective optical system for 3D observation in Embodiment 8. For example, the objective optical system of Embodiment 8 is a structure in which a right-eye optical system having optical axis Ax1 and a left-eye optical system having optical axis Ax2 are arranged side by side. The distance between optical axis Ax1 and optical axis Ax2 is defined as the baseline length.

[0168] Here, the fifth lens L5 undergoes a so-called D-cut, which involves linearly cutting a portion of the circular lens. Focus adjustment of the objective lens optical system for 3D observation needs to be performed independently in the left-eye and right-eye optical systems. In this embodiment, one objective lens optical system moves the position of the imaging element (not shown) to adjust the focus, while the other objective lens optical system moves the fifth lens L5 to adjust the focus. In this embodiment, to allow for the movement of the fifth lens L5, it is configured with space in front of and behind the fifth lens L5.

[0169] Furthermore, in this embodiment, the first lens L1 is shared in both the left-eye and right-eye optical systems. The light height at the concave surface is reduced in the first lens L1, thereby ensuring a shorter baseline length for both the left-eye and right-eye objective lens optical systems. This, in turn, reduces the refractive power of the fifth lens L5 (the positive conjoint lens), minimizing aberration performance degradation during focus adjustment.

[0170] Figure 10This diagram illustrates a schematic structure of the endoscope 10 of Embodiment 9. The endoscope 10 comprises an electronic endoscope 100 and a biological extracorporeal device 200. The electronic endoscope 100 includes a scope body 100a and a connecting cable portion 100b. The biological extracorporeal device 200 includes: a power supply; a video processor (not shown) that processes image signals from the electronic endoscope 100; and a display unit 204 that monitors and displays the image signals from the video processor. The scope body 100a corresponds to the intracorporeal device.

[0171] The endoscope body 100a is roughly divided into an operating section 140 and an insertion section 141. The insertion section 141 is composed of a slender, flexible component that can be inserted into the patient's body cavity. The user (not shown) can perform various operations using angle knobs or the like provided on the operating section 140.

[0172] Additionally, a connecting cable section 100b extends from the operation section 140. The connecting cable section 100b includes a universal cable 150. The universal cable 150 is connected to the extracorporeal device 200 via a connector 250.

[0173] Furthermore, the universal cable 150 communicates power supply voltage signals and CMOS drive signals from the power supply unit or video processor with the endoscope body 100a, and also communicates image signals from the endoscope body 100a with the video processor. Additionally, peripheral devices such as a VTR turntable (not shown) and a video printer can be connected to the video processor within the extracorporeal device 200. The video processor performs prescribed signal processing on the image signals from the endoscope body 100a, enabling the display of endoscopic images on the display screen of the display unit 204.

[0174] Furthermore, various modifications can be made to the present invention without departing from its spirit. Additionally, it is not necessarily limited to the shapes and number of lenses shown in the above embodiments. Furthermore, in the above embodiments, a glass cover may not be necessary. Additionally, lenses not shown in the above embodiments and which do not substantially have refractive power may be arranged inside or outside the lens spaces.

[0175] Industrial availability

[0176] As described above, the present invention is suitable for objective lens optical systems, imaging devices, and endoscopes that can ensure the travel of lens movement during focus adjustment and suppress the effects of center shift and optical performance degradation during 3D observation caused by manufacturing errors. In 3D observation, the baseline lengths of the left-eye objective lens optical system and the right-eye objective lens optical system can be set to be shorter.

[0177] Marker description

[0178] Ax, Ax1, Ax2 optical axes

[0179] L1-L5, L51, L52 lenses

[0180] F1 and F2 filters (parallel flat plates)

[0181] CG glass dome

[0182] I Image

[0183] IMG camera element

[0184] S-Aperture Stop

[0185] 10. Endoscope

[0186] 100 Electronic Endoscopes

[0187] 100a Mirror body part

[0188] 100b Connecting cable section

[0189] 140 Operations Department

[0190] 141 Insertion section

[0191] 150 General Purpose Cable

[0192] 200 biological extracorporeal devices

[0193] 204 display units

[0194] 250 connector

Claims

1. An objective lens optical system for 3D observation, said objective lens optical system comprising a left-eye optical system and a right-eye optical system, characterized in that, The optical system for the left eye and the optical system for the right eye, starting from the object side, consist of a front group, an aperture stop, and a rear group, respectively. The front group consists of a first lens with negative refractive power and its concave surface facing the image side; a second lens in the shape of a meniscus and its convex surface facing the image side, also having negative refractive power; and a third lens with positive refractive power. The rear group consists of a fourth lens with positive refractive power and a fifth lens with positive refractive power. The fifth lens is a combined lens with positive refractive power, formed by joining a biconvex positive lens and a meniscus lens with negative refractive power whose convex surface faces the image side. The objective lens optical system satisfies the following conditions (1) and (2): 2.38≤f3 / f5<20 (1) 0.8 < |g2 / g1| < 2.6 (2) Wherein, f3 is the focal length of the third lens, f5 is the focal length of the fifth lens, g1 is the focal length of the front group, and g2 is the focal length of the rear group. The fifth lens is subjected to a D-cut, which involves cutting a portion of a circular lens in a straight line. The D-cut involves removing at least one pair of opposite sides of the circular lens that are parallel to the optical axis, forming a lens with a cross-section resembling the letter "D". The first lens is shared by the left-eye optical system and the right-eye optical system, and the light height of the concave surface is reduced in the first lens.

2. The objective lens optical system according to claim 1, wherein, In order to adjust the focus of the objective lens optical system, the fifth lens moves along the optical axis.

3. The objective lens optical system according to claim 1, wherein, The objective lens optical system satisfies the following condition (3): 1.0 < |g1 / f| < 4.0 (3) Wherein, g1 is the focal length of the front group, and f is the focal length of the entire objective lens optical system.

4. The objective lens optical system according to claim 1, wherein, The objective lens optical system satisfies the following condition (4): f2 / f1<100 (4) Where f2 is the focal length of the second lens and f1 is the focal length of the first lens.

5. The objective lens optical system according to claim 1, wherein, The objective lens optical system satisfies the following condition (5): 3.0 <f4 / f<6.0 (5) Where f4 is the focal length of the fourth lens, and f is the focal length of the objective lens optical system as a whole.

6. A camera device comprising: an objective lens optical system; and an imaging element disposed on an image plane, characterized in that, The imaging element has an imaging surface, and converts the image formed on the imaging surface by the objective lens optical system into an electrical signal. The objective lens optical system is the objective lens optical system for 3D observation as described in claim 1.

7. An endoscope, characterized in that, The endoscope has the imaging device as described in claim 6.

Images