Endoscope objective lenses and endoscopes

Abstract

The present invention provides an endoscope objective lens that allows for independent magnification and focusing, and that can suppress the increase in the diameter of the endoscope, as well as an endoscope equipped with this endoscope objective lens. [Solution] The objective lens for the endoscope consists of four or fewer lens groups, including a first fixed lens group that remains stationary during magnification and focusing, a first movable lens group, and a second movable lens group, arranged in order from the object side. During magnification, the first movable lens group and the second movable lens group move along different trajectories. During focusing, at least one of the first movable lens group and the second movable lens group moves. The amount of movement of the lens group that moves during focusing is different from the amount of movement during magnification from the wide-angle end state at the furthest point to the telephoto end state at the furthest point, and the amount of movement during focusing from the wide-angle end state at the furthest point to the wide-angle end state at the nearest point.

Description

Technical Field

[0001] The technology of the present disclosure relates to an objective lens for an endoscope and an endoscope.

Background Art

[0002] Conventionally, as an objective lens that can be used for an endoscope, the lens system described in Patent Document 1 below is known.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In an endoscope, in order not to overlook a lesion, in addition to wide-area observation, magnified observation of the lesion is also required. Conventionally, an objective lens for an endoscope that enables magnified observation of a lesion by changing the focal length during focusing has been proposed. However, in such an objective lens for an endoscope, since zooming and focusing are performed simultaneously, the field of view range fluctuates during focusing, or the focus position fluctuates during zooming, and there is a concern of losing sight of the lesion. In order to eliminate this concern, it is preferable to perform zooming and focusing independently. However, if this is done, the number of lens groups to be moved increases, the lens movement mechanism becomes complicated, and there is a risk that the endoscope becomes thicker in diameter.

[0005] The present disclosure provides an objective lens for an endoscope that can perform zooming and focusing independently and can suppress an increase in the outer diameter of the endoscope, and an endoscope including this objective lens for an endoscope.

Means for Solving the Problems

[0006] An objective lens for an endoscope according to one aspect of this disclosure comprises four or fewer lens groups, including a first fixed lens group having refractive power, a first movable lens group having refractive power, and a second movable lens group having refractive power, arranged in order from the object side to the image side. When changing magnification from the wide-angle end state at the furthest point observation to the telephoto end state at the furthest point observation, the first movable lens group and the second movable lens group move on different trajectories. When focusing from the wide-angle end state at the furthest point observation to the wide-angle end state at the nearest point observation, at least one of the first movable lens group and the second movable lens group moves. The amount of movement of the lens group that moves when focusing is different from the amount of movement when changing magnification from the wide-angle end state at the furthest point observation to the telephoto end state at the furthest point observation. The first fixed lens group is fixed to the image plane during magnification and focusing. 0 <YFw / (fFw×tanωFw)<0.5 (1) The condition (1) expressed by the equation is satisfied. Here, YFw is the maximum image height at the wide-angle end when observing at the farthest point. ωFw is the maximum half-angle at the wide-angle end when observing at the farthest point. fFw is the focal length of the entire system at the wide-angle end when observing at the farthest point.

[0007] The objective lens for endoscopes in the above-described embodiment is: 0.02 <YFw / (fFw×tanωFw)<0.3 (1-1) It is preferable that the conditional expression (1-1) represented by is satisfied, 0.04 <YFw / (fFw×tanωFw)<0.2 (1-2) It is more preferable to satisfy the condition expressed in equation (1-2).

[0008] The first moving lens group and the second moving lens group may be configured to move along different trajectories when focusing from the wide-angle end state at the furthest point to the wide-angle end state at the nearest point.

[0009] The first and second moving lens groups may be configured to move together when focusing from the wide-angle end state at the furthest point to the wide-angle end state at the nearest point.

[0010] The system may be configured to include a second fixed lens group between the first and second movable lens groups, which is fixed to the image plane during magnification and focusing, and which has refractive power.

[0011] The second movable lens group may be configured to include a second fixed lens group on the image side, which is fixed to the image plane during magnification and focusing, and which has refractive power.

[0012] When ωFt is the maximum half-angle of view at the telephoto end when observing the furthest point, the objective lens for the endoscope in the above embodiment is: 1.2 < ωFw / ωFt < 3 (2) It is preferable that the condition (2) expressed by is satisfied.

[0013] If ωCw is the maximum half-angle of view at the wide-angle end during nearest-nearest point observation, then the endoscopic objective lens of the above embodiment is: 0.5 < ωFw / ωCw < 2 (3) It is preferable that the condition expressed in equation (3) is satisfied, 0.9 < ωFw / ωCw < 1.2 (3-1) It is more preferable to satisfy the condition expressed in equation (3-1).

[0014] When D0Fw is the distance along the optical axis from the furthest point in the wide-angle end state during furthest point observation to the surface of the first fixed lens group closest to the object, fCw is the focal length of the entire system in the wide-angle end state during nearest point observation, and D0Cw is the distance along the optical axis from the nearest point in the wide-angle end state during nearest point observation to the surface of the first fixed lens group closest to the object, then the objective lens for endoscopes in the above embodiment is: -0.1<(fCw-fFw) / (D0Fw-D0Cw)<0.1 (4) It is preferable that the condition expressed in equation (4) is satisfied, -0.01<(fCw-fFw) / (D0Fw-D0Cw)<0.01 (4-1) It is more preferable to satisfy the condition expressed in equation (4-1).

[0015] The first fixed lens group includes, in order from the object side to the image side, a first negative lens, a second negative lens, and a first positive lens, and it is preferable that the second negative lens and the first positive lens are joined to each other.

[0016] It is preferable that the lens surface on the object side of the first negative lens is a flat surface.

[0017] When the focal length of the first negative lens is fL1, the objective lens for an endoscope of the above aspect is 0.5 < |fL1 / fFw| < 5 (5) preferably satisfies the conditional expression (5) represented by 0.7 < |fL1 / fFw| < 3 (5-1) more preferably satisfies the conditional expression (5-1) represented by 0.8 < |fL1 / fFw| < 2 (5-2) even more preferably satisfies the conditional expression (5-2) represented by

[0018] When the focal length of the first fixed lens group is f1 and the focal length of the most image-side lens group of the objective lens for an endoscope is fE, the objective lens for an endoscope of the above aspect is 0.05 < |f1| / fE < 2.3 (6) preferably satisfies the conditional expression (6) represented by 0.15 < |f1| / fE < 1.2 (6-1) more preferably satisfies the conditional expression (6-1) represented by

[0019] Another aspect of the present disclosure is an endoscope including the objective lens for an endoscope of the above aspect.

[0020] In addition, the "consisting of" and "comprising" in this specification are intended to mean that, in addition to the listed components, lenses having substantially no refractive power, optical elements other than lenses such as diaphragms, filters, and cover glasses, and lens flanges, lens barrels, imaging elements, etc. may be included.

[0021] In this specification, "a group of lenses having positive refractive power" means that the group as a whole has positive refractive power. Similarly, in this specification, "a group of lenses having negative refractive power" means that the group as a whole has negative refractive power. "A lens having positive refractive power" and "a positive lens" are synonymous. "A lens having negative refractive power" and "a negative lens" are synonymous. A "lens group" is not limited to a configuration consisting of multiple lenses, but may also consist of a single lens.

[0022] In this specification, the number of lenses refers to the number of constituent lenses. For example, in a cemented lens formed by joining multiple single lenses of different materials, the number of lenses is expressed as the number of single lenses that make up the cemented lens. However, a composite aspherical lens (a lens in which a lens (e.g., a spherical lens) and an aspherical film formed on that lens are integrally constructed and function as a single aspherical lens as a whole) is not considered a cemented lens and is treated as a single lens. Unless otherwise specified, the sign and surface shape of the refractive power for lenses including aspherical surfaces shall be those of the paraxial region.

[0023] In this specification, "including ~ and ~ in order from the object side to the image side" includes both cases where the components are included in a continuous order and cases where the components are included in a discontinuous order. For example, in this specification, "including A and B in order from the object side to the image side" means that A and B may be placed continuously, or another component may be placed between A and B, as long as B is placed on the image side of A.

[0024] In this specification, "entire system" refers to the objective lens for the endoscope. The "focal length" used in the conditional equations is the paraxial focal length. Unless otherwise specified, the "distance on the optical axis" used in the conditional equations is the geometric distance. The values ​​used in the conditional equations are values ​​with respect to the d line. "~lens group" may include optical elements other than lenses, such as parallel plates and / or apertures. Regarding the movement of the lens group, "moving on mutually different trajectories" is synonymous with "moving while changing the distance between them."

[0025] The terms "d-line," "C-line," "F-line," and "h-line" used herein refer to emission lines, with the wavelength of the d-line being 587.56 nm (nanometers), the wavelength of the C-line being 656.27 nm (nanometers), the wavelength of the F-line being 486.13 nm (nanometers), and the wavelength of the h-line being 404.66 nm (nanometers). [Effects of the Invention]

[0026] According to this disclosure, it is possible to provide an endoscope objective lens that can independently perform magnification and focusing, and that can suppress the increase in diameter of the endoscope, and an endoscope equipped with this endoscope objective lens. [Brief explanation of the drawing]

[0027] [Figure 1] This is a cross-sectional view corresponding to the objective lens for endoscopes in Example 1, showing the configuration of an objective lens for endoscopes according to one embodiment. [Figure 2] This is a cross-sectional view showing the configuration and light beam of each state of the endoscope objective lens of Example 1. [Figure 3] These are aberration diagrams of the endoscope objective lens of Example 1. [Figure 4] This is a cross-sectional view showing the configuration of the objective lens for the endoscope in Example 2. [Figure 5] These are aberration diagrams of the endoscope objective lens used in Example 2. [Figure 6] This is a cross-sectional view showing the configuration of the objective lens for the endoscope in Example 3. [Figure 7] These are aberration diagrams of the objective lens for the endoscope in Example 3. [Figure 8] This is a cross-sectional view showing the configuration of the objective lens for the endoscope in Example 4. [Figure 9] These are aberration diagrams of the endoscope objective lens of Example 4. [Figure 10] This is a cross-sectional view showing the configuration of the objective lens for the endoscope in Example 5. [Figure 11] These are aberration diagrams of the endoscope objective lens of Example 5. [Figure 12] This is a cross-sectional view showing the configuration of the objective lens for the endoscope in Example 6. [Figure 13] These are aberration diagrams of the endoscope objective lens of Example 6. [Figure 14] This is a cross-sectional view showing the configuration of the objective lens for the endoscope in Example 7. [Figure 15] These are aberration diagrams of the endoscope objective lens used in Example 7. [Figure 16] This is a cross-sectional view showing the configuration of the objective lens for the endoscope in Example 8. [Figure 17] These are aberration diagrams of the endoscope objective lens of Example 8. [Figure 18] This is a cross-sectional view showing the configuration of the objective lens for the endoscope in Example 9. [Figure 19] These are aberration diagrams of the endoscope objective lens of Example 9. [Figure 20] This is a cross-sectional view showing the configuration of the endoscope objective lens in Example 10. [Figure 21] These are aberration diagrams of the endoscope objective lens of Example 10. [Figure 22] This is a cross-sectional view showing the configuration of the objective lens for the endoscope in Example 11. [Figure 23] These are aberration diagrams of the endoscope objective lens used in Example 11. [Figure 24] This is a cross-sectional view showing the configuration of the objective lens for the endoscope in Example 12. [Figure 25] These are aberration diagrams of the endoscope objective lens used in Example 12. [Figure 26] This is a cross-sectional view showing the configuration of the objective lens for the endoscope in Example 13. [Figure 27] These are aberration diagrams of the endoscope objective lens used in Example 13. [Figure 28] This is a schematic diagram of an endoscope according to one embodiment. [Modes for carrying out the invention]

[0028] Embodiments of this disclosure will be described below with reference to the drawings.

[0029] In the following terms, "farthest point observation" refers to the state where the endoscopic objective lens is focused on the farthest point, and "nearest point observation" refers to the state where the endoscopic objective lens is focused on the nearest point. Furthermore, "farthest point" refers to the point that is furthest from the object-side surface of the endoscopic objective lens among the points that the endoscopic objective lens can focus on. "Nearest point" refers to the point that is closest to the object-side surface of the endoscopic objective lens among the points that the endoscopic objective lens can focus on.

[0030] Figure 1 shows the configuration of an endoscope objective lens in a cross-section including the optical axis Z according to one embodiment of the present disclosure. Figure 2 shows the configuration and cross-sectional view of the light beam in each state of the endoscope objective lens of Figure 1. In Figure 2, the top row labeled "Farthest Point Wide Angle End" shows the wide-angle end state when observing the furthest point, the second row from the top labeled "Farthest Point Telephoto End" shows the telephoto end state when observing the furthest point, the third row from the top labeled "Nearest Point Wide Angle End" shows the wide-angle end state when observing the nearest point, and the bottom row labeled "Nearest Point Telephoto End" shows the telephoto end state when observing the nearest point. In Figure 2, the axial light beam and the light beam of the maximum half-angle of view in each state are shown as the light beam. In Figures 1 and 2, the left side is the object side and the right side is the image side. The examples shown in Figures 1 and 2 correspond to Embodiment 1 described later.

[0031] As an example, the objective lens for the endoscope in Figure 1 consists of four lens groups, arranged in order from the object side to the image side: the first lens group G1, the second lens group G2, the third lens group G3, and the fourth lens group G4. As an example, each group in the example in Figure 1 is configured as follows: The first lens group G1 consists of lens L11, optical element P1, lens L12, and lens L13, arranged in order from the object side to the image side. The second lens group G2 consists of lens L21 and lens L22, arranged in order from the object side to the image side. The third lens group G3 consists of lens L31, lens L32, and aperture diaphragm St, arranged in order from the object side to the image side. The fourth lens group G4 consists of lens L41, lens L42, and lens L43, arranged in order from the object side to the image side. Optical element P1 is intended to be a filter or the like, and is a member that does not have refractive power with an incident surface and an exit surface that are parallel. In Figure 1, the aperture diaphragm St indicates its position on the optical axis, not its size or shape.

[0032] In the example shown in Figure 1, an optical component PP with parallel incident and exit surfaces is placed between the endoscopic objective lens and the image plane Sim. The optical component PP is a component that is envisioned to be a prism, filter, or cover glass. The optical component PP is a component that does not possess refractive power. A configuration without the optical component PP is also possible.

[0033] In the example shown in Figure 1, the first lens group G1 corresponds to the first fixed lens group of this disclosure, the second lens group G2 corresponds to the first movable lens group of this disclosure, the third lens group G3 corresponds to the second movable lens group of this disclosure, and the fourth lens group G4 corresponds to the second fixed lens group of this disclosure.

[0034] The endoscope objective lens of this disclosure comprises four or fewer lens groups, including a first fixed lens group with refractive power, a first movable lens group with refractive power, and a second movable lens group with refractive power, all arranged in order from the object side to the image side along the optical axis Z. When changing magnification from the wide-angle end state at the furthest point observation to the telephoto end state at the furthest point observation, the first movable lens group and the second movable lens group move along different trajectories. When focusing from the wide-angle end state at the furthest point observation to the wide-angle end state at the nearest point observation, at least one of the first movable lens group and the second movable lens group moves. The amount of movement of the lens group that moves when focusing is different from the amount of movement when changing magnification from the wide-angle end state at the furthest point observation to the telephoto end state at the furthest point observation, and different from the amount of movement when focusing from the wide-angle end state at the furthest point observation to the wide-angle end state at the nearest point observation. In this context, "amount of displacement" refers to a negative value for displacement toward the object and a positive value for displacement toward the image, and the sign is also considered.

[0035] As described above, the technology of this disclosure allows the lens group that moves during focusing to also move during magnification, thereby minimizing the number of moving lens groups. This prevents complexity of the movement mechanism and, consequently, suppresses the need to increase the diameter of the endoscope. Furthermore, in the technology of this disclosure, the lens groups that move during magnification and focusing are configured to have different movement trajectories during magnification and focusing. In other words, the objective lens for endoscopes of this disclosure can perform magnification and focusing independently. This suppresses fluctuations in the field of view during focusing and fluctuations in the focusing position during magnification, thereby reducing concerns about losing sight of the lesion during focusing and / or magnification.

[0036] On the other hand, if one attempts to independently perform magnification and focusing with conventional endoscope objective lenses, at least two lens groups are required to move during magnification, and at least one lens group is required to move during focusing, resulting in a total of three or more moving lens groups. Having so many moving lens groups complicates the lens movement mechanism and may lead to an increase in the diameter of the endoscope. An increase in the diameter of the endoscope increases the physical burden on the patient during examination, which is undesirable.

[0037] In contrast, the endoscopic objective lens of this disclosure has only two moving lens groups, and can independently perform magnification and focusing. Therefore, the movement mechanism can be simplified compared to conventional endoscopic objective lenses, enabling miniaturization and reduction of the optical system diameter. In other words, the endoscopic objective lens of this disclosure allows for both wide-area observation and magnified observation, while reducing concerns about losing sight of the lesion during focusing and magnification. Furthermore, it prevents the endoscope from becoming larger in diameter due to the complexity of the movement mechanism.

[0038] Specifically, in the example shown in Figure 1, during magnification, the second lens group G2 and the third lens group G3 move along different trajectories, while the other lens groups remain fixed relative to the image plane Sim. Also, in the example shown in Figure 1, during focusing, only the second lens group G2 moves, while the other lens groups remain fixed relative to the image plane Sim.

[0039] In Figure 1, brackets and solid arrows are shown below the lens groups that move during magnification. These solid arrows indicate the approximate direction of movement of each lens group when changing magnification from the wide-angle end state at the farthest point to the telephoto end state at the farthest point. Also in Figure 1, brackets and white arrows are shown below the lens groups that move during focusing. These white arrows indicate the direction of movement of each lens group when focusing from the wide-angle end state at the farthest point to the wide-angle end state at the nearest point.

[0040] The method of illustrating the moving lens group described above is the same in the diagrams of other embodiments described later. In addition, in the drawings of this application, multiple components enclosed in a single bracket accompanying an arrow indicating movement indicate that they move as a single unit. "Moving as a single unit" means moving simultaneously in the same direction and by the same amount.

[0041] In the example shown in Figure 1, the first lens group G1 and the fourth lens group G4 are fixed to the image plane Sim during magnification and focusing. In the technology of this disclosure, the first fixed lens group, which is positioned closest to the object, is fixed to the image plane Sim during magnification and focusing. Fixing the lens group closest to the object in this way is advantageous for ensuring airtightness. In endoscopes, the endoscopic objective lens is often mounted on the endoscope without protective members, and the lens closest to the object among the endoscopic objective lenses also functions as an optical window. In such cases, maintaining airtightness is required, so a configuration in which the first fixed lens group is immovable is advantageous.

[0042] The example shown in Figure 1 is just one example, and the endoscopic objective lens of this disclosure can be modified in various ways without departing from the spirit of the technology of this disclosure. For example, the number of lenses included in each lens group may be different from the example in Figure 1. Also, the configuration of the lenses included in each lens group may be different from the example in Figure 1. Furthermore, the lens group that moves during magnification and the lens group that moves during focusing may also be configured differently from the example in Figure 1.

[0043] For example, in the example shown in Figure 1, only one lens group moves during focusing. However, in the technology of this disclosure, the first moving lens group and the second moving lens group may be configured to move on different trajectories when focusing from the wide-angle end state at the furthest point to the wide-angle end state at the nearest point. This configuration is advantageous in ensuring better optical performance across the entire range of magnification and focusing.

[0044] Alternatively, the first and second moving lens groups may be configured to move together when focusing from the wide-angle end state at the furthest point to the wide-angle end state at the nearest point. In this case, it is advantageous to simplify the movement mechanism while ensuring better optical performance throughout the entire range of magnification and focusing.

[0045] The endoscope objective lens of this disclosure may be configured to include a second fixed lens group between the first movable lens group and the second movable lens group, which is fixed to the image plane Sim during magnification and focusing and has refractive power. In this case, it is advantageous to ensure better optical performance throughout the entire range of magnification and focusing.

[0046] Alternatively, the endoscopic objective lens of this disclosure may be configured such that the image side of the second moving lens group includes a second fixed lens group that is fixed to the image plane Sim during magnification and focusing and has refractive power. In this case, it is advantageous to ensure better optical performance throughout the entire range of magnification and focusing.

[0047] Alternatively, the endoscope objective lens of this disclosure may be configured to consist of three lens groups: a first fixed lens group, a first movable lens group, and a second movable lens group. This configuration is advantageous for miniaturizing the lens system.

[0048] The first fixed lens group may be configured to include, in order from the object side to the image side, a first negative lens having negative refractive power, a second negative lens having negative refractive power, and a first positive lens having positive refractive power. The second negative lens and the first positive lens may be configured to be joined together. In this case, it is advantageous to suppress axial chromatic aberration and lateral chromatic aberration from the visible range to the short wavelength range around 400 nm (nanometers) while performing wide-angle observation.

[0049] It is preferable that the object-side surface of the first negative lens be flat. This is advantageous in suppressing an increase in the outer diameter of the first negative lens and also in improving the manufacturability of the first negative lens. The first negative lens may be positioned closest to the object, in which case, by making the object-side surface of the first negative lens flat, the adhesion of liquids, etc., to the object-side surface of the first negative lens can be reduced. The term "flat" as used herein includes the tolerance range that is generally accepted in the technical field.

[0050] The first moving lens group may be configured to include two or fewer lenses. This configuration is advantageous for miniaturizing the lens system and simplifying the moving mechanism. When the first moving lens group includes two lenses, these two lenses may be configured as a negative lens and a positive lens joined together. This configuration is advantageous for suppressing fluctuations in chromatic aberration during magnification.

[0051] The second moving lens group may be configured to include a cemented lens in which a positive lens and a negative lens are joined together. This configuration is advantageous in suppressing fluctuations in chromatic aberration during magnification.

[0052] Next, preferred configurations relating to the conditional formulas for the endoscope objective lens of this disclosure will be described. In the following explanation of the conditional formulas, the same symbols will be used for terms with the same definition to avoid redundant explanations, and redundant explanations of symbols will be omitted. Also, in the following, to avoid redundant explanations, "the endoscope objective lens of this disclosure" will also simply be referred to as "the endoscope objective lens."

[0053] The objective lens for an endoscope preferably satisfies the following conditional expression (1). Here, the maximum image height in the wide-angle end state during the farthest point observation is defined as YFw. The maximum half angle in the wide-angle end state during the farthest point observation is defined as ωFw. The overall focal length in the wide-angle end state during the farthest point observation is defined as fFw. Tan represents the tangent. As an example, FIG. 2 shows the above maximum image height YFw and maximum half angle ωFw. Regarding the lower limit of the conditional expression (1), since YFw>0, fFw>0, and tanωFw>0, 0<YFw / (fFw×tanωFw) holds. By ensuring that the corresponding value of the conditional expression (1) does not exceed the upper limit value, it becomes easier to increase the magnification near the center of the imaging region while performing wide-angle field observation. 0<YFw / (fFw×tanωFw)<0.5 (1)

[0054] The objective lens for an endoscope more preferably satisfies the following conditional expression (1-1). By ensuring that the corresponding value of the conditional expression (1-1) does not fall below the lower limit value, an increase in the outer diameter of the lens can be suppressed. Also, in order to obtain better characteristics, the objective lens for an endoscope preferably satisfies the following conditional expression (1-2). 0.02<YFw / (fFw×tanωFw)<0.3 (1-1) 0.04<YFw / (fFw×tanωFw)<0.2 (1-2)

[0055] When the maximum half angle in the telephoto end state during the farthest point observation is defined as ωFt, the objective lens for an endoscope preferably satisfies the following conditional expression (2). As an example, FIG. 2 shows the above maximum half angle ωFt. By ensuring that the corresponding value of the conditional expression (2) does not fall below the lower limit value, it becomes easier to magnify and observe a lesion part or the like during zooming. By ensuring that the corresponding value of the conditional expression (2) does not exceed the upper limit value, an increase in the outer diameter and / or overall length of the lens can be suppressed. 1.2<ωFw / ωFt<3 (2)

[0056] When the maximum half-angle of view at the wide-angle end during nearest-nearest-point observation is denoted as ωCw, it is preferable that the endoscopic objective lens satisfies the following condition (3). As an example, Figure 2 shows the above maximum half-angle of view ωCw. By satisfying condition (3), the field of view does not change significantly when focusing, making it easier to observe the object without losing sight of it. 0.5 < ωFw / ωCw < 2 (3)

[0057] To obtain better characteristics, it is preferable that the endoscopic objective lens satisfies the following condition (3-1). 0.9 < ωFw / ωCw < 1.2 (3-1)

[0058] The objective lens for the endoscope preferably satisfies the following condition (4). Here, D0Fw is the distance along the optical axis from the furthest point in the wide-angle end state during furthest point observation to the surface of the first fixed lens group closest to the object. fCw is the focal length of the entire system in the wide-angle end state during nearest point observation. D0Cw is the distance along the optical axis from the nearest point in the wide-angle end state during nearest point observation to the surface of the first fixed lens group closest to the object. By satisfying condition (4), it becomes easier to focus over a wider area without significantly changing the field of view. -0.1<(fCw-fFw) / (D0Fw-D0Cw)<0.1 (4)

[0059] To obtain better characteristics, it is preferable that the objective lens for the endoscope satisfies the following condition (4-1). -0.01<(fCw-fFw) / (D0Fw-D0Cw)<0.01 (4-1)

[0060] In a configuration where the first fixed lens group includes a first negative lens, a second negative lens, and a first positive lens in order from the object side to the image side, it is preferable that the endoscopic objective lens satisfies the following condition (5). Here, the focal length of the first negative lens is set to fL1. Ensuring that the corresponding value of condition (5) does not fall below the lower limit is advantageous in ensuring good optical performance across the entire range of magnification and focusing. Ensuring that the corresponding value of condition (5) does not exceed the upper limit is advantageous in suppressing the increase in size of the lens system. 0.5 < |fL1 / fFw| < 5 (5)

[0061] To obtain better characteristics, the endoscopic objective lens preferably satisfies the following condition (5-1), and more preferably satisfies the following condition (5-2). 0.7 < |fL1 / fFw| < 3 (5-1) 0.8 < |fL1 / fFw| < 2 (5-2)

[0062] It is preferable that the objective lens for the endoscope satisfies the following condition (6). Here, the focal length of the first fixed lens group is defined as f1. The focal length of the lens group closest to the image on the endoscope objective lens is defined as fE. By ensuring that the corresponding value in condition (6) does not fall below the lower limit, it is advantageous to shorten the overall optical length. By ensuring that the corresponding value in condition (6) does not exceed the upper limit, it is possible to suppress excessive correction of spherical aberration. 0.05 < |f1| / fE < 2.3 (6)

[0063] To obtain better characteristics, the endoscopic objective lens preferably satisfies the following condition (6-1), and more preferably satisfies the following condition (6-2). 0.15 < |f1| / fE < 1.2 (6-1) 0.25 < |f1| / fE < 0.8 (6-2)

[0064] The preferred and possible configurations described above, including the configurations related to conditional expressions, can be combined in any way within the bounds of consistency, and it is preferable to selectively adopt them as appropriate according to the required specifications.

[0065] As an example, a preferred embodiment of the endoscope objective lens of this disclosure comprises four or fewer lens groups, including a first fixed lens group with refractive power, a first movable lens group with refractive power, and a second movable lens group with refractive power, arranged in order from the object side to the image side, wherein when changing magnification from the wide-angle end state at the furthest point observation to the telephoto end state at the furthest point observation, the first movable lens group and the second movable lens group move on different trajectories from each other, from the wide-angle end state at the furthest point observation When focusing to the wide-angle end state at the nearest point of observation, at least one of the first movable lens group and the second movable lens group moves, and the amount of movement of the lens group that moves when focusing is different from the amount of movement when changing magnification from the wide-angle end state at the farthest point of observation to the telephoto end state at the farthest point of observation, and the amount of movement when focusing from the wide-angle end state at the farthest point of observation to the wide-angle end state at the nearest point of observation, and the first fixed lens group is fixed with respect to the image plane Sim at both the time of magnification and focusing, satisfying the above condition (1).

[0066] Next, embodiments of the endoscope objective lenses of this disclosure will be described with reference to the drawings. Note that the reference numerals assigned to the lenses and lens groups in the cross-sectional views of each embodiment are used independently for each embodiment to avoid complexity in the explanation and drawings due to the increasing number of digits in the reference numerals. Therefore, even if the same reference numerals are assigned to different embodiments, the configurations are not necessarily the same.

[0067] [Example 1] Cross-sectional views showing the configuration of the endoscope objective lens of Example 1 are shown in Figures 1 and 2, and the method of illustration is as described above, so some redundant explanations will be omitted here. The endoscope objective lens of Example 1 consists of four lens groups, in order from the object side to the image side: a first lens group G1 having negative refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having positive refractive power.

[0068] The first lens group G1 corresponds to the first fixed lens group, the second lens group G2 corresponds to the first movable lens group, the third lens group G3 corresponds to the second movable lens group, and the fourth lens group G4 corresponds to the second fixed lens group.

[0069] When changing magnification from the wide-angle end to the telephoto end, the second lens group G2 moves towards the image side and then towards the object side, the third lens group G3 moves towards the object side, and the other lens groups remain fixed relative to the image plane Sim. When focusing from the furthest point observation to the nearest point observation, the second lens group G2 moves towards the object side, and the other lens groups remain fixed relative to the image plane Sim.

[0070] Table 1 shows the basic lens data for the endoscopic objective lens of Example 1, and Table 2 shows the specifications and variable plane spacing.

[0071] The basic lens data table is as follows: The "Sn" column shows the surface number, with the surface closest to the object being designated as the 1st surface and the number increasing by one as you move towards the image side. The "R" column shows the radius of curvature of each surface. The "D" column shows the interplanar spacing on the optical axis between each surface and the surface adjacent to it on the image side. The "Nd" column shows the refractive index of each lens with respect to the d line. The "νd" column shows the Abbe number of each lens based on the d line. The "Material" column shows the material name of each lens before the period. "OHARA" after the period in the "Material" column indicates that the manufacturer of that material is Ohara Corporation.

[0072] In the basic lens data table, the sign of the radius of curvature of a surface with a convex shape facing the object is positive, and the sign of the radius of curvature of a surface with a convex shape facing the image is negative. In the column for the surface number of the surface corresponding to the aperture diaphragm St, the surface number and the phrase (St) are entered. The value in the bottom column of column D in the table is the distance between the image-side surface in the table and the image plane Sim. For variable surface spacing, the symbol DD[ ] is used, and the object-side surface number for this spacing is placed inside the [ ] and entered in the surface spacing column.

[0073] Table 2 shows the object distance, magnification ratio, focal length, F-number, maximum field of view, maximum image height, and variable plane spacing relative to the d-line. The object distance is the distance along the optical axis from the furthest point to the lens surface closest to the object when observing at the furthest point, and the distance along the optical axis from the nearest point to the lens surface closest to the object when observing at the nearest point. The maximum field of view is twice the maximum half-field of view. The [°] in the maximum field of view column indicates that the unit is degrees. In Table 2, the "Farthest Point / Wide Angle End" column shows the values ​​in the wide-angle end state when observing at the furthest point, the "Farthest Point / Telephoto End" column shows the values ​​in the telephoto end state when observing at the furthest point, the "Nearest Point / Wide Angle End" column shows the values ​​in the wide-angle end state when observing at the nearest point, and the "Nearest Point / Telephoto End" column shows the values ​​in the telephoto end state when observing at the nearest point.

[0074] In the data in each table, degrees are used as the unit for angles and millimeters (mm) as the unit for lengths. However, since optical systems can be used with proportional magnification or reduction, other appropriate units can also be used. Furthermore, the values ​​in the tables below are rounded to a predetermined number of decimal places.

[0075] [Table 1]

[0076] [Table 2]

[0077] Figure 3 shows the aberration diagrams for the objective lens of the endoscope in Example 1. From left to right in Figure 3, the diagrams are shown as follows: spherical aberration, astigmatism, distortion, and chromatic aberration. In Figure 3, the top row labeled "Farthest Point / Wide Angle End" shows the aberration diagrams at the wide-angle end during furthest point observation; the second row from the top labeled "Farthest Point / Telephoto End" shows the aberration diagrams at the telephoto end during furthest point observation; the third row from the top labeled "Nearest Point / Wide Angle End" shows the aberration diagrams at the wide-angle end during nearest point observation; and the bottom row labeled "Nearest Point / Telephoto End" shows the aberration diagrams at the telephoto end during nearest point observation. In Figure 3, the object distance is shown in millimeters (mm) to the right of "Object Distance:". In the spherical aberration diagram, the aberrations along the d, C, F, and h lines are shown as solid lines, long dashed lines, short dashed lines, and dashed lines, respectively. In the astigmatism diagram, the aberration along the d line in the sagittal direction is shown by a solid line, and the aberration along the d line in the tangential direction is shown by a short dashed line. In the distortion diagram, the aberration along the d line is shown by a solid line. In the chromatic aberration diagram, the aberrations along the C line, F line, and h line are shown by a long dashed line, a short dashed line, and a dashed-dotted line, respectively. In the spherical aberration diagram, the F number value for each state is shown after "FNo.=". In other aberration diagrams, the value of the maximum half-angle of view for each state is shown after "ω=".

[0078] The symbols, meanings, methods of description, and methods of illustration for each data point in Example 1 described above are the same in the following examples unless otherwise specified, so redundant explanations will be omitted below.

[0079] [Example 2] Figure 4 shows a cross-sectional view of the configuration of the endoscope objective lens of Example 2. The endoscope objective lens of Example 2 consists of four lens groups, arranged in order from the object side to the image side: a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having negative refractive power, and a fourth lens group G4 having positive refractive power.

[0080] The first lens group G1 consists of, in order from the object side to the image side, lens L11, optical element P1, lens L12, and lens L13. The second lens group G2 consists of, in order from the object side to the image side, lens L21, lens L22, and aperture diaphragm St. The third lens group G3 consists of, in order from the object side to the image side, lens L31 and lens L32. The fourth lens group G4 consists of, in order from the object side to the image side, lens L41, lens L42, and lens L43. Optical element P1 is intended to be a filter or the like, and is a component that does not have refractive power with its incident and exit surfaces parallel.

[0081] The first lens group G1 corresponds to the first fixed lens group, the second lens group G2 corresponds to the first movable lens group, the third lens group G3 corresponds to the second movable lens group, and the fourth lens group G4 corresponds to the second fixed lens group.

[0082] When changing magnification from the wide-angle end to the telephoto end, the second lens group G2 and the third lens group G3 move toward the object along different trajectories, while the other lens groups remain fixed relative to the image plane Sim. When focusing from the farthest point to the nearest point, the third lens group G3 moves toward the image, while the other lens groups remain fixed relative to the image plane Sim.

[0083] For the endoscopic objective lens of Example 2, the basic lens data is shown in Table 3, the specifications and variable plane spacing are shown in Table 4, and the aberration diagrams are shown in Figure 5.

[0084] [Table 3]

[0085] [Table 4]

[0086] [Example 3] Figure 6 shows a cross-sectional view of the configuration of the endoscope objective lens of Example 3. The endoscope objective lens of Example 3 consists of four lens groups, arranged in order from the object side to the image side: a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having negative refractive power, and a fourth lens group G4 having positive refractive power.

[0087] The first lens group G1 consists of, in order from the object side to the image side, lens L11, optical element P1, lens L12, and lens L13. The second lens group G2 consists of, in order from the object side to the image side, aperture diaphragm St, lens L21, and lens L22. The third lens group G3 consists of, in order from the object side to the image side, lens L31 and lens L32. The fourth lens group G4 consists of, in order from the object side to the image side, lens L41, lens L42, and lens L43. Optical element P1 is intended to be a filter or the like, and is a component that does not have refractive power with its incident and exit surfaces parallel.

[0088] The first lens group G1 corresponds to the first fixed lens group, the second lens group G2 corresponds to the first movable lens group, the third lens group G3 corresponds to the second movable lens group, and the fourth lens group G4 corresponds to the second fixed lens group.

[0089] When changing magnification from the wide-angle end to the telephoto end, the second lens group G2 moves toward the object, the third lens group G3 moves toward the image, and the other lens groups remain fixed relative to the image plane Sim. When focusing from the furthest point to the nearest point, the second lens group G2 and the third lens group G3 move toward the image together, and the other lens groups remain fixed relative to the image plane Sim.

[0090] For the endoscopic objective lens of Example 3, the basic lens data is shown in Table 5, the specifications and variable plane spacing are shown in Table 6, and the aberration diagrams are shown in Figure 7.

[0091] [Table 5]

[0092] [Table 6]

[0093] [Example 4] Figure 8 shows a cross-sectional view of the configuration of the endoscope objective lens of Example 4. The endoscope objective lens of Example 4 consists of four lens groups, arranged in order from the object side to the image side: a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having negative refractive power, and a fourth lens group G4 having positive refractive power.

[0094] The first lens group G1 consists of, in order from the object side to the image side, lens L11, optical element P1, lens L12, and lens L13. The second lens group G2 consists of, in order from the object side to the image side, lens L21, lens L22, and aperture diaphragm St. The third lens group G3 consists of, in order from the object side to the image side, lens L31 and lens L32. The fourth lens group G4 consists of, in order from the object side to the image side, lens L41, lens L42, and lens L43. Optical element P1 is intended to be a filter or the like, and is a component that does not have refractive power with its incident and exit surfaces parallel.

[0095] The first lens group G1 corresponds to the first fixed lens group, the second lens group G2 corresponds to the first movable lens group, the third lens group G3 corresponds to the second movable lens group, and the fourth lens group G4 corresponds to the second fixed lens group.

[0096] When changing magnification from the wide-angle end to the telephoto end, the second lens group G2 moves toward the object, the third lens group G3 moves toward the image, and the other lens groups remain fixed relative to the image plane Sim. When focusing from the furthest point to the nearest point, the second lens group G2 and the third lens group G3 move toward the image along different trajectories, and the other lens groups remain fixed relative to the image plane Sim.

[0097] For the endoscopic objective lens of Example 4, the basic lens data is shown in Table 7, the specifications and variable plane spacing are shown in Table 8, and the aberration diagrams are shown in Figure 9.

[0098] [Table 7]

[0099] [Table 8]

[0100] [Example 5] Figure 10 shows a cross-sectional view illustrating the configuration of the endoscope objective lens of Example 5. The endoscope objective lens of Example 5 consists of four lens groups, arranged in order from the object side to the image side: a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having negative refractive power, and a fourth lens group G4 having positive refractive power.

[0101] The first lens group G1 consists of lens L11, optical element P1, lens L12, and lens L13, in order from the object side to the image side. The second lens group G2 consists of lens L21. The third lens group G3 consists of lens L31, lens L32, and aperture diaphragm St, in order from the object side to the image side. The fourth lens group G4 consists of lens L41, lens L42, and lens L43, in order from the object side to the image side. Optical element P1 is intended to be a filter or the like, and is a component that does not have refractive power with its incident and exit surfaces parallel.

[0102] The first lens group G1 corresponds to the first fixed lens group, the second lens group G2 corresponds to the first movable lens group, the third lens group G3 corresponds to the second fixed lens group, and the fourth lens group G4 corresponds to the second movable lens group.

[0103] When changing magnification from the wide-angle end to the telephoto end, the second lens group G2 moves toward the image, the fourth lens group G4 moves toward the object, and the other lens groups remain fixed relative to the image plane Sim. When focusing from the farthest point to the nearest point, the second lens group G2 moves toward the image, and the other lens groups remain fixed relative to the image plane Sim.

[0104] For the endoscopic objective lens of Example 5, the basic lens data is shown in Table 9, the specifications and variable plane spacing are shown in Table 10, and the aberration diagrams are shown in Figure 11.

[0105] [Table 9]

[0106] [Table 10]

[0107] [Example 6] Figure 12 shows a cross-sectional view illustrating the configuration of the endoscope objective lens of Example 6. The endoscope objective lens of Example 6 consists of four lens groups, arranged in order from the object side to the image side: a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having negative refractive power, and a fourth lens group G4 having positive refractive power.

[0108] The first lens group G1 consists of, in order from the object side to the image side, lens L11, optical element P1, lens L12, and lens L13. The second lens group G2 consists of, in order from the object side to the image side, lens L21 and lens L22. The third lens group G3 consists of, in order from the object side to the image side, lens L31, lens L32, and aperture diaphragm St. The fourth lens group G4 consists of, in order from the object side to the image side, lens L41, lens L42, and lens L43. Optical element P1 is intended to be a filter or the like, and is a component that does not have refractive power with its incident and exit surfaces parallel.

[0109] The first lens group G1 corresponds to the first fixed lens group, the second lens group G2 corresponds to the first movable lens group, the third lens group G3 corresponds to the second fixed lens group, and the fourth lens group G4 corresponds to the second movable lens group.

[0110] When changing magnification from the wide-angle end to the telephoto end, the second lens group G2 and the fourth lens group G4 move toward the object along different trajectories, while the other lens groups remain fixed relative to the image plane Sim. When focusing from the farthest point to the nearest point, the fourth lens group G4 moves toward the object, while the other lens groups remain fixed relative to the image plane Sim.

[0111] For the endoscopic objective lens of Example 6, the basic lens data is shown in Table 11, the specifications and variable plane spacing are shown in Table 12, and the aberration diagrams are shown in Figure 13.

[0112] [Table 11]

[0113] [Table 12]

[0114] [Example 7] Figure 14 shows a cross-sectional view illustrating the configuration of the endoscope objective lens of Example 7. The endoscope objective lens of Example 7 consists of four lens groups, arranged in order from the object side to the image side: a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having negative refractive power, and a fourth lens group G4 having positive refractive power.

[0115] The first lens group G1 consists of, in order from the object side to the image side, lens L11, optical element P1, lens L12, and lens L13. The second lens group G2 consists of, in order from the object side to the image side, lens L21 and lens L22. The third lens group G3 consists of lens L31. The fourth lens group G4 consists of, in order from the object side to the image side, aperture diaphragm St, lens L41, lens L42, lens L43, and lens L44. Optical element P1 is intended to be a filter or the like, and is a component that does not have refractive power with its incident and exit surfaces parallel.

[0116] The first lens group G1 corresponds to the first fixed lens group, the second lens group G2 corresponds to the first movable lens group, the third lens group G3 corresponds to the second fixed lens group, and the fourth lens group G4 corresponds to the second movable lens group.

[0117] When changing magnification from the wide-angle end to the telephoto end, the second lens group G2 moves towards the object and then towards the image, the fourth lens group G4 moves towards the object, and the other lens groups remain fixed relative to the image plane Sim. When focusing from the farthest point to the nearest point, the second lens group G2 and the fourth lens group G4 move towards the image on different trajectories, and the other lens groups remain fixed relative to the image plane Sim.

[0118] For the endoscopic objective lens of Example 7, the basic lens data is shown in Table 13, the specifications and variable plane spacing are shown in Table 14, and the aberration diagrams are shown in Figure 15.

[0119] [Table 13]

[0120] [Table 14]

[0121] [Example 8] Figure 16 shows a cross-sectional view illustrating the configuration of the endoscope objective lens of Example 8. The endoscope objective lens of Example 8 consists of three lens groups, arranged in order from the object side to the image side: a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having positive refractive power.

[0122] The first lens group G1 consists of, in order from the object side to the image side, lens L11, optical element P1, lens L12, lens L13, lens L14, and lens L15. The second lens group G2 consists of, in order from the object side to the image side, lens L21, lens L22, and aperture diaphragm St. The third lens group G3 consists of, in order from the object side to the image side, lens L31, lens L32, and lens L33. Optical element P1 is intended to be a filter or the like, and is a component that does not have refractive power with its incident and exit surfaces parallel.

[0123] The first lens group G1 corresponds to the first fixed lens group, the second lens group G2 corresponds to the first movable lens group, and the third lens group G3 corresponds to the second movable lens group.

[0124] When changing magnification from the wide-angle end to the telephoto end, the second lens group G2 moves towards the object and then towards the image, the third lens group G3 moves towards the object, and the other lens groups remain fixed relative to the image plane Sim. When focusing from the farthest point to the nearest point, the second lens group G2 moves towards the image, and the other lens groups remain fixed relative to the image plane Sim.

[0125] For the endoscopic objective lens of Example 8, the basic lens data is shown in Table 15, the specifications and variable plane spacing are shown in Table 16, and the aberration diagrams are shown in Figure 17.

[0126] [Table 15]

[0127] [Table 16]

[0128] [Example 9] Figure 18 shows a cross-sectional view illustrating the configuration of the endoscope objective lens of Example 9. The endoscope objective lens of Example 9 consists of three lens groups, arranged from the object side to the image side: a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power.

[0129] The first lens group G1 consists of, in order from the object side to the image side, lens L11, optical element P1, lens L12, lens L13, aperture diaphragm St, lens L14, and lens L15. The second lens group G2 consists of, in order from the object side to the image side, lens L21 and lens L22. The third lens group G3 consists of, in order from the object side to the image side, lens L31, lens L32, and lens L33. Optical element P1 is intended to be a filter or the like, and is a component that does not have refractive power with its incident and exit surfaces parallel.

[0130] The first lens group G1 corresponds to the first fixed lens group, the second lens group G2 corresponds to the first movable lens group, and the third lens group G3 corresponds to the second movable lens group.

[0131] When changing magnification from the wide-angle end to the telephoto end, the second lens group G2 and the third lens group G3 move toward the image on different trajectories, while the other lens groups remain fixed relative to the image plane Sim. When focusing from the farthest point to the nearest point, the third lens group G3 moves toward the object, while the other lens groups remain fixed relative to the image plane Sim.

[0132] For the endoscopic objective lens of Example 9, the basic lens data is shown in Table 17, the specifications and variable plane spacing are shown in Table 18, and the aberration diagrams are shown in Figure 19.

[0133] [Table 17]

[0134] [Table 18]

[0135] [Example 10] Figure 20 shows a cross-sectional view illustrating the configuration of the endoscope objective lens of Example 10. The endoscope objective lens of Example 10 consists of three lens groups, arranged in order from the object side to the image side: a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power.

[0136] The first lens group G1 consists of, in order from the object side to the image side, lens L11, optical element P1, lens L12, lens L13, lens L14, lens L15, and aperture diaphragm St. The second lens group G2 consists of, in order from the object side to the image side, lens L21 and lens L22. The third lens group G3 consists of, in order from the object side to the image side, lens L31, lens L32, and lens L33. Optical element P1 is intended to be a filter or the like, and is a component that does not have refractive power with its incident and exit surfaces parallel.

[0137] The first lens group G1 corresponds to the first fixed lens group, the second lens group G2 corresponds to the first movable lens group, and the third lens group G3 corresponds to the second movable lens group.

[0138] When changing magnification from the wide-angle end to the telephoto end, the second lens group G2 moves towards the image side and then towards the object side, the third lens group G3 moves towards the object side, and the other lens groups remain fixed relative to the image plane Sim. When focusing from the furthest point observation to the nearest point observation, the second lens group G2 and the third lens group G3 move together towards the object side, and the other lens groups remain fixed relative to the image plane Sim.

[0139] For the endoscopic objective lens of Example 10, the basic lens data is shown in Table 19, the specifications and variable plane spacing are shown in Table 20, and the aberration diagrams are shown in Figure 21.

[0140] [Table 19]

[0141] [Table 20]

[0142] [Example 11] Figure 22 shows a cross-sectional view illustrating the configuration of the endoscopic objective lens of Example 11. The endoscopic objective lens of Example 11 consists of three lens groups, arranged in order from the object side to the image side: a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having positive refractive power.

[0143] The first lens group G1 consists of, in order from the object side to the image side, lens L11, optical element P1, lens L12, and lens L13. The second lens group G2 consists of lens L21. The third lens group G3 consists of, in order from the object side to the image side, aperture diaphragm St, lens L31, lens L32, lens L33, lens L34, and lens L35. Optical element P1 is intended to be a filter or the like, and is a component that does not have refractive power with its incident and exit surfaces parallel.

[0144] When changing magnification from the wide-angle end to the telephoto end, the second lens group G2 and the third lens group G3 move toward the object along different trajectories, while the other lens groups remain fixed relative to the image plane Sim. When focusing from the furthest point to the nearest point, the second lens group G2 and the third lens group G3 move toward the image along different trajectories, while the other lens groups remain fixed relative to the image plane Sim.

[0145] For the endoscopic objective lens of Example 11, the basic lens data is shown in Table 21, the specifications and variable plane spacing are shown in Table 22, and the aberration diagrams are shown in Figure 23.

[0146] [Table 21]

[0147] [Table 22]

[0148] [Example 12] Figure 24 shows a cross-sectional view illustrating the configuration of the endoscope objective lens of Example 12. The endoscope objective lens of Example 12 consists of three lens groups, arranged in order from the object side to the image side: a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having positive refractive power.

[0149] The first lens group G1 consists of, in order from the object side to the image side, lens L11, optical element P1, lens L12, and lens L13. The second lens group G2 consists of lens L21. The third lens group G3 consists of, in order from the object side to the image side, aperture diaphragm St, lens L31, lens L32, lens L33, lens L34, and lens L35. Optical element P1 is intended to be a filter or the like, and is a component that does not have refractive power with its incident and exit surfaces parallel.

[0150] When changing magnification from the wide-angle end to the telephoto end, the second lens group G2 moves towards the object and then towards the image, the third lens group G3 moves towards the object, and the other lens groups remain fixed relative to the image plane Sim. When focusing from the farthest point to the nearest point, the second lens group G2 moves towards the image, and the other lens groups remain fixed relative to the image plane Sim.

[0151] For the endoscopic objective lens of Example 12, the basic lens data is shown in Table 23, the specifications and variable plane spacing are shown in Table 24, the aspheric coefficient is shown in Table 25, and the aberration diagrams are shown in Figure 25.

[0152] In the basic lens data, the aspherical surface number is marked with an asterisk (*), and the column for the radius of curvature of the aspherical surface lists the value of the paraxial radius of curvature. In Table 25, the row labeled Sn shows the aspherical surface number, and the rows labeled KA and Am show the aspherical coefficient values ​​for each aspherical surface. Note that m in Am is an integer greater than or equal to 3 and varies depending on the surface. For example, in the 14th surface of Example 12, m = 3, 4, 5, 6, ... 12. The "E±n" (n: integer) value of the aspherical coefficient in Table 25 is "×10 ±n This means "[...]. KA and Am are the aspheric coefficients in the aspheric equation expressed by the following formula. Zd = C × h 2 / {1+(1-KA×C 2 ×h 2 ) 1 / 2}+ΣAm×h m however, Zd: Aspherical depth (length of the perpendicular line drawn from a point on the aspherical surface at height h to a plane perpendicular to the optical axis Z to which the aspherical surface tangent is located). h: Height (distance from the optical axis Z to the lens surface) C: Reciprocal of the radius of paraxial curvature KA, Am: Aspherical coefficients Therefore, the Σ in the aspherical formula represents the summation with respect to m. The same method of describing aspherical surfaces described above will be used in the examples described later.

[0153] [Table 23]

[0154] [Table 24]

[0155] [Table 25]

[0156] [Example 13] Figure 26 shows a cross-sectional view illustrating the configuration of the endoscope objective lens of Example 13. The endoscope objective lens of Example 13 consists of four lens groups, arranged in order from the object side to the image side: a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having negative refractive power, and a fourth lens group G4 having positive refractive power.

[0157] The first lens group G1 consists of lens L11, optical element P1, lens L12, and lens L13, in order from the object side to the image side. The second lens group G2 consists of lens L21. The third lens group G3 consists of lens L31, lens L32, and aperture diaphragm St, in order from the object side to the image side. The fourth lens group G4 consists of lens L41, lens L42, and lens L43, in order from the object side to the image side. Optical element P1 is intended to be a filter or the like, and is a component that does not have refractive power with its incident and exit surfaces parallel.

[0158] The first lens group G1 corresponds to the first fixed lens group, the second lens group G2 corresponds to the first movable lens group, the third lens group G3 corresponds to the second fixed lens group, and the fourth lens group G4 corresponds to the second movable lens group.

[0159] When changing magnification from the wide-angle end to the telephoto end, the second lens group G2 moves towards the object and then towards the image, the fourth lens group G4 moves towards the object, and the other lens groups remain fixed relative to the image plane Sim. When focusing from the farthest point to the nearest point, the second lens group G2 moves towards the image, and the other lens groups remain fixed relative to the image plane Sim.

[0160] For the endoscopic objective lens of Example 13, the basic lens data is shown in Table 26, the specifications and variable plane spacing in Table 27, the aspheric coefficient in Table 28, and the aberration diagrams in Figure 27. For the materials "N231. Glass", "N181. Glass", "N200. Glass", and "N216. Glass" shown in Table 26, the glass described on pages 40-42 of the proceedings of the 49th Optical Symposium (held June 20-21, 2024, organized by the Optical Society of Japan) can be used.

[0161] [Table 26]

[0162] [Table 27]

[0163] [Table 28]

[0164] Table 29 shows the corresponding values ​​for conditional formulas (1) to (6) of the endoscope objective lenses in Examples 1 to 13. The values ​​in Table 29 are based on the d-line. The corresponding values ​​for the examples shown in Table 29 may be used as the upper or lower limits of the conditional formulas to set a preferred range for the formulas.

[0165] [Table 29]

[0166] The endoscope objective lenses of Examples 1 to 13 enable both wide-area observation and magnified observation. By limiting the number of moving lens groups to two or less and differentiating the behavior of the moving lens groups during magnification and focusing, magnification and focusing can be performed independently. Furthermore, the endoscope objective lenses of Examples 1 to 13 maintain high optical performance with aberrations well corrected in all four states shown in the respective aberration diagrams.

[0167] Next, an endoscope according to an embodiment of the present disclosure will be described. Figure 28 shows a schematic overall configuration diagram of an endoscope according to one embodiment of the present disclosure. The endoscope 100 shown in Figure 28 mainly comprises an operating unit 102, an insertion unit 104, and a universal cord 106 connected to a connector unit (not shown). Most of the insertion unit 104 is a flexible unit 107 that bends in any direction along the insertion path, and a bending unit 108 is connected to the tip of the flexible unit 107, and a tip unit 110 is connected to the tip of the bending unit 108. The bending unit 108 is provided to direct the tip unit 110 in a desired direction, and bending operation is possible by rotating a bending operation knob 109 provided on the operating unit 102. An endoscope objective lens 1 according to an embodiment of the present disclosure and an image sensor 2 are arranged at the inner tip of the tip unit 110. For example, a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) can be used as the image sensor 2. The image sensor 2 is positioned so that its imaging surface coincides with the image plane of the endoscope objective lens 1. Figure 28 conceptually shows the endoscope objective lens 1 and the image sensor 2.

[0168] Although the technology of this disclosure has been described above with reference to embodiments and examples, the technology of this disclosure is not limited to the above embodiments and examples, and various modifications are possible. For example, the radius of curvature, interplanar spacing, refractive index, and Abbe number of each lens are not limited to the values ​​shown in the above numerical examples, but can take other values.

[0169] The following additional information is disclosed regarding the above embodiments and examples. [Note 1] It consists of four or fewer lens groups, including a first fixed lens group with refractive power, a first movable lens group with refractive power, and a second movable lens group with refractive power, arranged in order from the object side to the image side. When changing magnification from the wide-angle end state to the telephoto end state at the furthest point observation, the first movable lens group and the second movable lens group move along different trajectories. When focusing from the wide-angle end state at the furthest point to the wide-angle end state at the nearest point, at least one of the first movable lens group and the second movable lens group moves. The lens group that moves during focusing has different amounts of movement when changing magnification from the wide-angle end state at the furthest point to the telephoto end state at the furthest point, and when focusing from the wide-angle end state at the furthest point to the wide-angle end state at the nearest point. The first fixed lens group is fixed to the image plane during magnification and focusing. YFw is the maximum image height at the wide-angle end when observing at the farthest point. ωFw is the maximum half-angle at the wide-angle end when observing at the farthest point. If the focal length of the entire system at the wide-angle end during observation at the farthest point is fFw, 0 <YFw / (fFw×tanωFw)<0.5 (1) An endoscope objective lens that satisfies the condition (1) represented by . [Note 2] The endoscopic objective lens described in Appendix 1, wherein when focusing from the wide-angle end state during observation of the furthest point to the wide-angle end state during observation of the nearest point, the first movable lens group and the second movable lens group move on different trajectories from each other. [Note 3] The endoscopic objective lens described in Appendix 1, wherein the first movable lens group and the second movable lens group move together when focusing from the wide-angle end state during observation of the furthest point to the wide-angle end state during observation of the nearest point. [Note 4] The endoscopic objective lens according to Appendix 1 or Appendix 2, comprising a second fixed lens group between the first movable lens group and the second movable lens group, which is fixed to the image plane during magnification and focusing and has refractive power. [Note 5] An endoscope objective lens according to any one of Appendix 1 to 3, comprising a second fixed lens group on the image side of the second movable lens group, which is fixed to the image plane during magnification and focusing and has refractive power. [Note 6] If ωFt is the maximum half-angle of view at the telephoto end when observing at the farthest point, 1.2 < ωFw / ωFt < 3 (2) An endoscope objective lens described in any one of Appendix 1 to Appendix 5 that satisfies the conditional expression (2) represented by . [Note 7] If ωCw is the maximum half-angle of view at the wide-angle end when observing the nearest point, 0.5 < ωFw / ωCw < 2 (3) An endoscope objective lens described in any one of the appendices 1 to 6 that satisfies the conditional expression (3) represented by . [Note 8] D0Fw is the distance along the optical axis from the furthest point in the wide-angle end state during observation at the furthest point to the surface of the first fixed lens group closest to the object. The focal length of the entire system at the wide-angle end during nearest-point observation is fCw. When D0Cw is the distance along the optical axis from the nearest point in the wide-angle end state during nearest-point observation to the surface of the first fixed lens group closest to the object, -0.1<(fCw-fFw) / (D0Fw-D0Cw)<0.1 (4) An endoscope objective lens described in any one of the appendices 1 to 7 that satisfies the conditional expression (4) represented by . [Note 9] The first fixed lens group includes, in order from the object side to the image side, a first negative lens, a second negative lens, and a first positive lens. The endoscopic objective lens described in any one of the appendices 1 to 8, wherein the second negative lens and the first positive lens are joined together. [Note 10] The objective lens for endoscopes as described in Appendix 9, wherein the object-side lens surface of the first negative lens is flat. [Note 11] When the focal length of the first negative lens is fL1, 0.5 < |fL1 / fFw| < 5 (5) An endoscope objective lens as described in Appendix 9 or Appendix 10 that satisfies the conditional expression (5) represented by . [Note 12] The focal length of the first fixed lens group is f1, If the focal length of the lens group closest to the image source of the aforementioned endoscope objective lens is denoted as fE, 0.05 < |f1| / fE < 2.3 (6) An endoscope objective lens described in any one of the appendices 1 to 11 that satisfies the conditional expression (6) represented by . [Note 13] 0.02 <YFw / (fFw×tanωFw)<0.3 (1-1) An endoscope objective lens described in any one of the appendices 1 to 12 that satisfies the conditional expression (1-1) represented by . [Note 14] 0.04 <YFw / (fFw×tanωFw)<0.2 (1-2) An endoscope objective lens described in any one of the appendices 1 to 12 that satisfies the conditional expression (1-2) represented by . [Note 15] 0.9 < ωFw / ωCw < 1.2 (3-1) An endoscope objective lens as described in Appendix 7 that satisfies the conditional expression (3-1) represented by . [Note 16] -0.01<(fCw-fFw) / (D0Fw-D0Cw)<0.01 (4-1) An endoscope objective lens as described in Appendix 8 that satisfies the conditional expression (4-1) represented by . [Note 17] 0.7 < |fL1 / fFw| < 3 (5-1) An endoscope objective lens as described in Appendix 11 that satisfies the conditional expression (5-1) represented by . [Note 18] 0.8 < |fL1 / fFw| < 2 (5-2) An endoscope objective lens as described in Appendix 11 that satisfies the conditional expression (5-2) represented by . [Note 19] 0.15 < |f1| / fE < 1.2 (6-1) An endoscope objective lens as described in Appendix 12 that satisfies the conditional expression (6-1) represented by . [Note 20] An endoscope equipped with an endoscopic objective lens as described in any one of the items from Appendix 1 to Appendix 19. [Explanation of Symbols]

[0170] 1 Endoscope Objective Lens 2 Image sensors 100 Endoscopes 102 Operation section 104 Insertion section 106 Universal Code 107 Soft part 108 Curved section 109 Curved operating knob 110 Tip G1 First Lens Group G2 2nd lens group G3 3rd lens group G4 4th lens group L11~L44 Lenses P1 Optical component PP optical components Sim image plane St aperture diaphragm YFw Maximum image height Z optical axis ωCw Maximum half-angle ωFt Maximum half-angle ωFw Maximum half-angle

Claims

1. It consists of four or fewer lens groups, including a first fixed lens group with refractive power, a first movable lens group with refractive power, and a second movable lens group with refractive power, arranged in order from the object side to the image side. When changing magnification from the wide-angle end state to the telephoto end state at the furthest point observation, the first moving lens group and the second moving lens group move along different trajectories. When focusing from the wide-angle end state at the furthest point to the wide-angle end state at the nearest point, at least one of the first movable lens group and the second movable lens group moves. The lens group that moves during focusing has different amounts of movement when changing magnification from the wide-angle end state at the furthest point to the telephoto end state at the furthest point, and when focusing from the wide-angle end state at the furthest point to the wide-angle end state at the nearest point. The first fixed lens group is fixed to the image plane during magnification and focusing. YFw is the maximum image height at the wide-angle end when observing at the farthest point. The maximum half-angle at the wide-angle end when observing at the farthest point is ωFw. If the focal length of the entire system at the wide-angle end during observation at the farthest point is fFw, 0<YFw / (fFw×tanωFw)<0.5 (1) An endoscope objective lens that satisfies the condition (1) represented by .

2. The objective lens for endoscopes according to claim 1, wherein when focusing from the wide-angle end state at the furthest point to the wide-angle end state at the nearest point, the first movable lens group and the second movable lens group move on different trajectories from each other.

3. The objective lens for endoscopes according to claim 1, wherein the first movable lens group and the second movable lens group move integrally when focusing from the wide-angle end state during observation of the furthest point to the wide-angle end state during observation of the nearest point.

4. The objective lens for endoscopes according to claim 1, further comprising a second fixed lens group between the first movable lens group and the second movable lens group, which is fixed to the image plane during magnification and focusing and has refractive power.

5. The objective lens for endoscopes according to claim 1, further comprising a second fixed lens group on the image side of the second movable lens group, which is fixed to the image plane during magnification and focusing and has refractive power.

6. If ωFt is the maximum half-angle of view at the telephoto end when observing at the farthest point, 1.2<ωFw / ωFt<3 (2) An endoscope objective lens according to claim 1 that satisfies the conditional expression (2) represented by .

7. If ωCw is the maximum half-angle of view at the wide-angle end when observing the nearest point, 0.5<ωFw / ωCw<2 (3) An endoscope objective lens according to claim 1 that satisfies the conditional expression (3) represented by .

8. D0Fw is the distance along the optical axis from the furthest point in the wide-angle end state during observation at the furthest point to the surface of the first fixed lens group closest to the object. Let fCw be the focal length of the entire system at the wide-angle end during nearest-point observation. When D0Cw is the distance along the optical axis from the nearest point in the wide-angle end state during nearest-point observation to the surface of the first fixed lens group closest to the object, -0.1<(fCw-fFw) / (D0Fw-D0Cw)<0.1 (4) An endoscope objective lens according to claim 1 that satisfies the conditional expression (4) represented by .

9. The first fixed lens group includes, in order from the object side to the image side, a first negative lens, a second negative lens, and a first positive lens. The objective lens for endoscopes according to claim 1, wherein the second negative lens and the first positive lens are joined together.

10. The objective lens for endoscopes according to claim 9, wherein the object-side lens surface of the first negative lens is flat.

11. When the focal length of the first negative lens is fL1, 0.5<|fL1 / fFw|<5 (5) The objective lens for an endoscope according to claim 9, satisfying the conditional expression (5) represented by .

12. The focal length of the first fixed lens group is f1, If the focal length of the lens group closest to the image source of the aforementioned endoscope objective lens is denoted as fE, 0.05<|f1| / fE<2.3 (6) An endoscope objective lens according to claim 1 that satisfies the conditional expression (6) represented by .

13. 0.02<YFw / (fFw×tanωFw)<0.3 (1-1) An endoscope objective lens according to claim 1 that satisfies the conditional expression (1-1) represented by .

14. 0.04<YFw / (fFw×tanωFw)<0.2 (1-2) An endoscope objective lens according to claim 1 that satisfies the conditional expression (1-2) represented by .

15. 0.9<ωFw / ωCw<1.2 (3-1) An endoscope objective lens according to claim 7 that satisfies the conditional expression (3-1) represented by .

16. -0.01<(fCw-fFw) / (D0Fw-D0Cw)<0.01 (4-1) An endoscope objective lens according to claim 8 that satisfies the conditional expression (4-1) represented by .

17. 0.7<|fL1 / fFw|<3 (5-1) The objective lens for an endoscope according to claim 11, satisfying the conditional expression (5-1) represented by .

18. 0.8<|fL1 / fFw|<2 (5-2) The objective lens for an endoscope according to claim 11, satisfying the conditional expression (5-2) represented by .

19. 0.15<|f1| / fE<1.2 (6-1) The objective lens for an endoscope according to claim 12, satisfying the conditional expression (6-1) represented by .

20. An endoscope comprising an objective lens for endoscopes according to any one of claims 1 to 19.

Images