Endoscope objective lens and endoscope

Abstract

To provide an endoscope objective lens which offers a focusing function and maintains good optical performance in an observation over an entire object distance range from the farthest point to the nearest point, and to provide an endoscope having the same.SOLUTION: An endoscope objective lens is provided, comprising a first lens group having positive refractive power and a second lens group having positive refractive power arranged in order from the object side to the image side. Only the second lens group moves while focusing. The first lens group includes a single lens having negative refractive power on the most object side. The endoscope objective lens satisfies predetermined conditional expressions involving a maximum image height, a focusing length of the entire system, a maximum half angle, a focusing length of the first lens group, a focusing length of the second lens group, and a focusing length of the single lens of the first lens group.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Conventionally, the objective lenses described in the following Patent Documents 1, 2, 3, 4, and 5 are known as objective lenses used in endoscopes. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2022-033521 [Patent Document 2] JP 2011-075915 A [Patent Document 3] JP 2002-028126 A [Patent Document 4] International Publication No. 2019 / 163744 [Patent Document 5] JP 2001-091832 A Summary of the Invention [Problem to be solved by the invention]

[0004] There is a demand for an objective lens for an endoscope that has a focusing function and maintains good optical performance in observation over the entire range of object distances from the farthest point to the nearest point. This demand level is increasing year by year.

[0005] The present disclosure has been made in consideration of the above-mentioned circumstances, and aims to provide an objective lens for an endoscope that has a focusing function and maintains good optical performance during observation over the entire range of object distances from the farthest point to the nearest point, and an endoscope equipped with this objective lens for an endoscope. [Means for solving the problem]

[0006] An objective lens for an endoscope according to one embodiment of the present disclosure includes, in order from the object side to the image side, a first lens group having positive refractive power and a second lens group having positive refractive power, and when focusing from a farthest object to a nearest object, the first lens group is fixed with respect to the image plane and only the second lens group moves along the optical axis, and the first lens group includes a single lens having negative refractive power closest to the object side, 0 <Y / (fF×tanωf)<0.6 (1) 0 <f1 / f2<0.25 (2) -1.2 <fL1 / fF<0 (3) The conditional expressions (1), (2), and (3) expressed by the following are satisfied. The symbols in each conditional expression are defined as follows. The maximum image height is Y. The focal length of the entire system when focused on the farthest object is fF. The maximum half angle of view when focused on the farthest object is ωf. The focal length of the first lens group is f1. The focal length of the second lens group is f2. The focal length of the above-mentioned single lens in the first lens group is fL1.

[0007] When the F-number in a state where the farthest object is focused is taken as FNof, the objective lens for endoscopes of the above-mentioned embodiment has the following F-number: 0 <FNof / tanωf<2 (4) It is preferable to satisfy conditional expression (4) expressed as follows:

[0008] The objective lens for endoscopes according to the above aspect is 0 <fF / f1<2 (5) It is preferable to satisfy conditional expression (5) expressed as follows:

[0009] The objective lens for endoscopes according to the above aspect is 0 <fF / f2<0.5 (6) It is preferable to satisfy conditional expression (6) expressed as follows:

[0010] The objective lens for endoscopes according to the above aspect is -1.5 <fL1 / f1<0 (7) It is preferable to satisfy conditional expression (7) expressed as follows:

[0011] It is preferable that the object-side lens surface of the single lens in the first lens group is a flat surface.

[0012] In a configuration in which the first lens group is composed of, in order from the object side to the image side, a 1a lens group having positive refractive power, an aperture stop, and a 1b lens group having positive refractive power, and the focal length of the 1a lens group is f1a, the objective lens for endoscopes of the above aspect has the following characteristics: 0 <fF / f1a<1 (8) It is preferable to satisfy conditional expression (8) expressed as follows:

[0013] In a configuration in which the first lens group is composed of, in order from the object side to the image side, a 1a lens group having positive refractive power, an aperture stop, and a 1b lens group having positive refractive power, and the focal length of the 1a lens group is f1a, the objective lens for endoscopes of the above aspect has the following characteristics: 0 <f1 / f1a<1 (9) It is preferable to satisfy conditional expression (9) expressed as follows:

[0014] In a configuration in which the first lens group is composed of, in order from the object side to the image side, a 1a lens group having positive refractive power, an aperture stop, and a 1b lens group having positive refractive power, and the focal length of the 1b lens group is f1b, the objective lens for endoscopes of the above aspect has the following characteristics: 0 <fF / f1b<1 (10) It is preferable to satisfy conditional expression (10) expressed as follows:

[0015] In a configuration in which the first lens group is composed of, in order from the object side to the image side, a 1a lens group having positive refractive power, an aperture stop, and a 1b lens group having positive refractive power, and the focal length of the 1b lens group is f1b, the objective lens for endoscopes of the above aspect has the following characteristics: 0 <f1 / f1b<1 (11) It is preferable to satisfy conditional expression (11) expressed as follows:

[0016] When the distance that the second lens group moves when focusing from the farthest object to the nearest object is M, the paraxial imaging magnification of the entire system when focused on the farthest object is βf, and the paraxial imaging magnification of the entire system when focused on the nearest object is βn, the objective lens for endoscopes of the above aspect has the following characteristics: 0.01<(fF / |M|)×(βf / βn)<1 (12) It is preferable to satisfy conditional expression (12) expressed as follows:

[0017] In a configuration in which the first lens group consists of, in order from the object side to the image side, a 1a lens group having positive refractive power, an aperture stop, and a 1b lens group having positive refractive power, it is preferable that the 1a lens group includes a cemented lens in which at least one negative lens and at least one positive lens are cemented together.

[0018] When the average Abbe number based on the d-line of all the positive lenses included in the cemented lens of the 1a lens group is v1p and the average Abbe number based on the d-line of all the negative lenses included in the cemented lens of the 1a lens group is v1n, the objective lens for endoscopes of the above aspect has the following properties: 0<|ν1p-ν1n|<40 (13) It is preferable to satisfy condition (13) expressed by the following formula (13):

[0019] The second lens group preferably includes a cemented lens in which at least one negative lens and at least one positive lens are cemented together.

[0020] The second lens group may be configured to include one cemented lens in which at least one negative lens and at least one positive lens are cemented together.

[0021] When the average value of the Abbe numbers based on the d-line of all the positive lenses included in the cemented lens of the second lens group is v2p and the average value of the Abbe numbers based on the d-line of all the negative lenses included in the cemented lens of the second lens group is v2n, the objective lens for endoscopes of the above aspect has the following properties: 25<|ν2p-ν2n|<85 (14) It is preferable to satisfy conditional expression (14) expressed as follows:

[0022] The endoscope of the present disclosure includes the objective lens for an endoscope of the present disclosure.

[0023] In addition, in this specification, "consisting of" and "consisting of" are intended to mean that in addition to the listed components, the invention may also include a lens having substantially no refractive power, as well as optical elements other than lenses such as an aperture, a filter, and a cover glass, as well as a lens flange, a lens barrel, an image sensor, etc.

[0024] In this specification, "a group having positive refractive power" means that the group as a whole has positive 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. The "lens group" is not limited to a configuration consisting of multiple lenses, and may be a configuration consisting of only one lens.

[0025] "Single lens" means a single lens that is not cemented. However, a compound aspheric lens (a lens that is integrally constructed with a lens (e.g., a spherical lens) and an aspheric film formed on the spherical lens, and functions as a single aspheric lens as a whole) is not considered a cemented lens, but is treated as a single lens. The sign of the refractive power and the surface shape of a lens that includes an aspheric surface are those in the paraxial region, unless otherwise specified.

[0026] In this specification, "whole system" means an objective lens for an endoscope. The "focal length" used in the conditional expressions is the paraxial focal length. The values ​​used in the conditional expressions are values ​​based on the d-line. The "d-line," "C-line," "F-line," and "h-line" described in this specification are emission lines, and the wavelength of the d-line is treated as 587.56 nm (nanometers), the wavelength of the C-line is 656.27 nm (nanometers), the wavelength of the F-line is 486.13 nm (nanometers), and the wavelength of the h-line is 404.66 nm (nanometers). Effect of the Invention

[0027] According to the present disclosure, it is possible to provide an objective lens for an endoscope that has a focusing function and maintains good optical performance during observation over the entire range of object distances from the farthest point to the nearest point, and an endoscope equipped with this objective lens for an endoscope. [Brief description of the drawings]

[0028] [Figure 1] 2 is a cross-sectional view showing a configuration and a light beam of an endoscope objective lens according to one embodiment, which corresponds to the endoscope objective lens of Example 1. FIG. [Diagram 2] 1 is a cross-sectional view showing a configuration of an objective lens for an endoscope according to a first embodiment. [Diagram 3] 3A to 3C are diagrams showing various aberrations of the objective lens for an endoscope according to Example 1. [Figure 4] FIG. 11 is a cross-sectional view showing the configuration of an objective lens for an endoscope according to a second embodiment. [Diagram 5] 5A to 5C are diagrams showing various aberrations of the objective lens for an endoscope according to Example 2. [Figure 6] FIG. 11 is a cross-sectional view showing the configuration of an objective lens for an endoscope according to a third embodiment. [Figure 7] 11A to 11C are diagrams showing various aberrations of the objective lens for an endoscope according to Example 3. [Figure 8] FIG. 11 is a cross-sectional view showing the configuration of an objective lens for an endoscope according to a fourth embodiment. [Figure 9] 11A to 11C are diagrams showing various aberrations of the objective lens for an endoscope according to Example 4. [Figure 10] FIG. 11 is a cross-sectional view showing the configuration of an objective lens for an endoscope according to a fifth embodiment. [Figure 11] 11A to 11C are diagrams showing various aberrations of the objective lens for an endoscope according to Example 5. [Figure 12] 1 is a schematic configuration diagram of an endoscope according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0030] In endoscopes, there are two demands: one is to observe a wide range in its entirety, and the other is to observe an affected area or the like found during the overall observation in detail. To observe a wide range in its entirety, an optical system with a wide angle of view is used to observe the object to be observed from a distance, which corresponds to a far-point observation state. On the other hand, to observe an affected area or the like in detail, an endoscope is brought closer to the object to be observed, which corresponds to a near-point observation state. In order to satisfy the above two demands, an objective lens for an endoscope is required to have a focusing function so that the entire range of object distances from the farthest point to the nearest point can be observed well. Hereinafter, a state in which the objective lens for an endoscope is focused on the farthest object is referred to as the farthest point observation state, and a state in which the objective lens is focused on the nearest object is referred to as the nearest point observation state.

[0031] Fig. 1 shows a configuration and light beams in a cross section including an optical axis Z of an objective lens for an endoscope according to an embodiment of the present disclosure. The example shown in Fig. 1 corresponds to Example 1 described later. In Fig. 1, the left side is the object side and the right side is the image side. In Fig. 1, the farthest point observation state is shown in the upper part, and the nearest point observation state is shown in the lower part. In Fig. 1, as light beams, an axial light beam and a light beam with a maximum half angle of view ωf in the farthest point observation state, and an axial light beam and a light beam with a maximum half angle of view ωn in the nearest point observation state are shown.

[0032] The objective lens for endoscopes according to the present disclosure comprises, in order from the object side to the image side along the optical axis Z, a first lens group G1 having positive refractive power and a second lens group G2 having positive refractive power. This configuration is advantageous in ensuring good optical performance in observation over the entire range of object distances from the farthest point to the nearest point.

[0033] As an example, each group in the example of FIG. 1 is configured as follows. The first lens group G1 is composed of, in order from the object side to the image side, a lens L11, an optical member P1, a lens L12, a lens L13, an aperture stop St, a lens L14, and a lens L15. The second lens group G2 is composed of, in order from the object side to the image side, a lens L21 and a lens L22. The optical member P1 is intended to be a filter or the like, and is a member with no refractive power whose entrance surface and exit surface are parallel. The aperture stop St in FIG. 1 does not indicate the size or shape, but indicates the position on the optical axis.

[0034] In the example of Fig. 1, an optical member PP whose entrance and exit surfaces are parallel is disposed between the lens L22 and the image plane Sim. The optical member PP is a member assumed to be a prism, a filter, a cover glass, etc. The optical member PP is a member that does not have a refractive power, and a configuration in which the optical member PP is omitted is also possible.

[0035] The objective lens for endoscopes of the present disclosure has a focusing function. When focusing from the farthest object to the nearest object, the first lens group G1 is fixed with respect to the image plane Sim, and only the second lens group G2 moves along the optical axis Z. That is, in the present disclosure, a rear focus type configuration is adopted in which only one lens group moves during focusing. According to the configuration of the present disclosure, the structure required for focusing can be simplified compared to the type in which multiple lens groups move during focusing and the inner focus type. Also, as in the present disclosure, when focusing, the first lens group G1, which is the lens group closest to the object, is immovable, which is advantageous for ensuring airtightness. In endoscopes, the objective lens for endoscopes is often mounted on the endoscope without a protective member, and the lens closest to the object among the objective lenses for endoscopes is often made to function as an optical window. In that case, it is required to maintain airtightness, so a configuration in which the first lens group G1 is immovable is advantageous.

[0036] As an example, in the example of Fig. 1, when focusing from the farthest object to the nearest object, the second lens group G2 moves toward the object side. Fig. 2 shows a cross-sectional view of the configuration of the objective lens for an endoscope in Fig. 1. The basic illustration method of Fig. 2 is the same as that of Fig. 1. However, in Fig. 2, the light beam is not shown, and an arrow indicating the general movement direction of the second lens group G2 when focusing from the farthest object to the nearest object is written between the upper and lower rows.

[0037] The first lens group G1 includes a single lens having negative refractive power and is closest to the object. This configuration is advantageous for achieving both a wide angle and a compact lens system.

[0038] It is preferable that the object-side lens surface of the single lens having negative refractive power closest to the object side of the first lens group G1 is flat. In this case, it is advantageous to prevent the outer diameter of the single lens having negative refractive power closest to the object side from becoming large. In addition, it is possible to improve the manufacturability of this single lens and reduce adhesion of liquids, etc. to the object-side surface of this single lens.

[0039] It is preferable that the first lens group G1 comprises, in order from the object side to the image side, a 1a lens group G1a having positive refractive power, an aperture stop St, and a 1b lens group G1b having positive refractive power, which is advantageous in ensuring good optical performance in observation over the entire range of object distances from the farthest point to the nearest point.

[0040] As an example, in the example of Figure 1, the 1a lens group G1a consists, in order from the object side to the image side, of a lens L11, an optical member P1, a lens L12, and a lens L13, and the 1b lens group G1b consists, in order from the object side to the image side, of a lens L14 and a lens L15.

[0041] It is preferable that the 1a-th lens group G1a includes a cemented lens in which at least one negative lens and at least one positive lens are cemented together, which is advantageous in suppressing axial chromatic aberration and lateral chromatic aberration from the visible range to the short wavelength range around 400 nm.

[0042] The second lens group G2 preferably includes a cemented lens in which at least one negative lens and at least one positive lens are cemented together. In this case, it is advantageous for suppressing axial chromatic aberration and lateral chromatic aberration from the visible range to the short wavelength range near a wavelength of 400 nm.

[0043] The second lens group G2 may be configured to consist of one cemented lens in which at least one negative lens and at least one positive lens are cemented together. In this case, it is advantageous for suppressing axial chromatic aberration and lateral chromatic aberration from the visible range to the short wavelength range near a wavelength of 400 nm while suppressing an increase in the size of the lens system. The second lens group G2 may be configured to consist of one cemented lens in which one negative lens and one positive lens are cemented together. In this case, in addition to the above effects, it is advantageous for reducing the size of the lens system.

[0044] Next, a preferred configuration and a possible configuration regarding the conditional expressions of the objective lens for an endoscope of the present disclosure will be described. In the following description of the conditional expressions, in order to avoid redundant explanations, the same symbols are used for those having the same definitions, and the redundant explanations of the symbols are omitted. Further, hereinafter, in order to avoid redundant explanations, "the objective lens for an endoscope of the present disclosure" is also simply referred to as "the objective lens for an endoscope".

[0045] The objective lens for an endoscope preferably satisfies the following conditional expression (1). Here, the maximum image height is denoted as Y. The focal length of the entire system in a state of being focused on the farthest object is denoted as fF. The maximum semi-field angle in a state of being focused on the farthest object is denoted as ωf. Tan represents the tangent. As an example, FIG. 1 shows the maximum image height Y and the above-described maximum semi-field angle ωf. Regarding the lower limit of the conditional expression (1), since Y > 0, fF > 0, and tan ωf > 0, 0 < Y / (fF × tan ωf) holds. By ensuring that the corresponding value of the conditional expression (1) does not exceed the upper limit value, it is advantageous for increasing the magnification near the center of the imaging region while performing wide-field observation. 0 < Y / (fF × tan ωf) < 0.6 (1)

[0046] In addition, the objective lens for an endoscope preferably satisfies the following conditional expression (1-1). By preventing the corresponding value of the conditional expression (1-1) from falling below the lower limit value, an increase in the outer diameter of the lens can be suppressed. 0.2 < Y / (fF × tan ωf) < 0.6 (1-1)

[0047] In order to obtain better characteristics, it is more preferable that the upper limit values of the conditional expression (1) and the conditional expression (1-1) be 0.4. For example, it is more preferable that the objective lens for an endoscope satisfies the following conditional expression (1-2). 0.2 < Y / (fF × tan ωf) < 0.4 (1-2)

[0048] When the focal length of the first lens group G1 is f1 and the focal length of the second lens group G2 is f2, the objective lens for an endoscope preferably satisfies the following conditional expression (2). Regarding the lower limit of the conditional expression (2), since f1 > 0 and f2 > 0 because both the first lens group G1 and the second lens group G2 are groups having positive refractive powers, 0 < f1 / f2. By satisfying the conditional expression (2), it becomes easy to maintain a good balance of each aberration, which is advantageous for ensuring good optical performance in the observation over the entire object distance range from the farthest point to the nearest point. 0 < f1 / f2 < 0.25 (2)

[0049] In order to obtain better characteristics, it is preferable that the objective lens for an endoscope satisfies the following conditional expression (2-1). 0 < f1 / f2 < 0.22 (2-1)

[0050] When the focal length of the single lens having the most negative refractive power on the object side of the first lens group G1 is fL1, the objective lens for an endoscope preferably satisfies the following conditional expression (3). By preventing the corresponding value of the conditional expression (3) from falling below the lower limit value, it is advantageous for achieving both wide-angle conversion and miniaturization of the lens system. Regarding the upper limit of the conditional expression (3), since fL1 < 0 and fF > 0, fL1 / fF < 0. -1.2 < fL1 / fF < 0 (3)

[0051] In addition, the objective lens for an endoscope preferably satisfies the following conditional expression (3-1). By ensuring that the corresponding value of the conditional expression (3-1) does not exceed the upper limit value, it is advantageous for ensuring good optical performance in the observation over the entire object distance range from the farthest point to the nearest point. -1.2 < fL1 / fF < -0.8 (3-1)

[0052] To obtain better characteristics, the lower limit values of the conditional expression (3) and the conditional expression (3-1) are more preferably set to -1.1. For example, the objective lens for an endoscope more preferably satisfies the following conditional expression (3-2). -1.1 < fL1 / fF < -0.8 (3-2)

[0053] When the F-number in the state of focusing on the farthest point object is FNof, the objective lens for an endoscope preferably satisfies the following conditional expression (4). Regarding the lower limit of the conditional expression (4), since FNof > 0 and tanωf > 0, 0 < FNof / tanωf. By ensuring that the corresponding value of the conditional expression (4) does not exceed the upper limit value, it is advantageous for widening the angle of view of the lens system while ensuring a small F-number. 0 < FNof / tanωf < 2 (4)

[0054] In addition, the objective lens for an endoscope preferably satisfies the following conditional expression (4-1). By ensuring that the corresponding value of the conditional expression (4-1) does not fall below the lower limit value, it is advantageous for ensuring good optical performance in the observation over the entire object distance range from the farthest point to the nearest point. 0.6 < FNof / tanωf < 2 (4-1)

[0055] To obtain better characteristics, the upper limit values of the conditional expression (4) and the conditional expression (4-1) are more preferably set to 1.6. For example, the objective lens for an endoscope more preferably satisfies the following conditional expression (4-2). 0.6 < FNof / tanωf < 1.6 (4-2)

[0056] The objective lens for an endoscope preferably satisfies the following conditional expression (5). Regarding the lower limit of the conditional expression (5), since fF>0 and f1>0, 0<fF / f1 holds. By ensuring that the corresponding value of the conditional expression (5) does not exceed the upper limit value, it is advantageous for ensuring good optical performance in the observation over the entire object distance range from the farthest point to the nearest point. 0<fF / f1<2 (5)

[0057] Also, the objective lens for an endoscope preferably satisfies the following conditional expression (5-1). By ensuring that the corresponding value of the conditional expression (5-1) does not fall below the lower limit value, it is advantageous for suppressing the enlargement of the lens system. 0.5<fF / f1<2 (5-1)

[0058] To obtain better characteristics, it is more preferable that the upper limit values of the conditional expression (5) and the conditional expression (5-1) be 1. For example, the objective lens for an endoscope more preferably satisfies the following conditional expression (5-2). 0.5<fF / f1<1 (5-2)

[0059] The objective lens for an endoscope preferably satisfies the following conditional expression (6). Regarding the lower limit of the conditional expression (6), since fF>0 and f2>0, 0<fF / f2 holds. By ensuring that the corresponding value of the conditional expression (6) does not exceed the upper limit value, it is advantageous for ensuring good optical performance in the observation over the entire object distance range from the farthest point to the nearest point. 0<fF / f2<0.5 (6)

[0060] Also, the objective lens for an endoscope preferably satisfies the following conditional expression (6-1). By ensuring that the corresponding value of the conditional expression (6-1) does not fall below the lower limit value, it is advantageous for suppressing the enlargement of the lens system. 0.1<fF / f2<0.5 (6-1)

[0061] In order to obtain better characteristics, it is more preferable that the upper limit values ​​of conditional expressions (6) and (6-1) be set to 0.2. For example, it is more preferable that the objective lens for an endoscope satisfies the following conditional expression (6-2). 0.1 <fF / f2<0.2 (6-2)

[0062] It is preferable that the objective lens for an endoscope satisfies the following conditional formula (7). Since fL1<0 and f1>0, the upper limit of conditional formula (7) is fL1 / f1<0. By ensuring that the corresponding value of conditional formula (7) is not equal to or smaller than the lower limit, it is advantageous in preventing the lens system from becoming large. -1.5 <fL1 / f1<0 (7)

[0063] Moreover, it is preferable that the endoscope objective lens satisfies the following conditional formula (7-1): By making sure that the corresponding value of conditional formula (7-1) is not equal to or greater than the upper limit, it is advantageous to ensure good optical performance in observation over the entire range of object distances from the farthest point to the nearest point. -1.5 <fL1 / f1<-0.6 (7-1)

[0064] In order to obtain better characteristics, it is more preferable that the lower limit values ​​of conditional expressions (7) and (7-1) be set to −0.9. For example, it is more preferable that the objective lens for an endoscope satisfies the following conditional expression (7-2). -0.9 <fL1 / f1<-0.6 (7-2)

[0065] In a configuration in which the first lens group G1 is composed of, in order from the object side to the image side, a 1a lens group G1a having positive refractive power, an aperture stop St, and a 1b lens group G1b having positive refractive power, it is preferable that the endoscope objective lens satisfies at least one of the following conditional expressions (8), (9), (10), and (11). Here, the focal length of the 1a lens group G1a is f1a. The focal length of the 1b lens group G1b is f1b. 0 <fF / f1a<1 (8) 0 <f1 / f1a<1 (9) 0 <fF / f1b<1 (10) 0 < f1 / f1b < 1 (11)

[0066] Regarding the lower limit of conditional expression (8), since fF > 0 and f1a > 0, 0 < fF / f1a holds. By ensuring that the corresponding value of conditional expression (8) does not exceed the upper limit value, it is advantageous for ensuring good optical performance in the observation over the entire object distance range from the farthest point to the nearest point.

[0067] Also, the objective lens for an endoscope preferably satisfies the following conditional expression (8-1). By ensuring that the corresponding value of conditional expression (8-1) does not fall below the lower limit value, it is advantageous for suppressing the enlargement of the lens system. 0.005 < fF / f1a < 1 (8-1)

[0068] To obtain better characteristics, it is more preferable that the upper limit values of conditional expression (8) and conditional expression (8-1) be 0.6. For example, the objective lens for an endoscope more preferably satisfies the following conditional expression (8-2). 0 < fF / f1a < 0.6 (8-2)

[0069] Regarding the lower limit of conditional expression (9), since f1 > 0 and f1a > 0, 0 < f1 / f1a holds. By ensuring that the corresponding value of conditional expression (9) does not exceed the upper limit value, it is advantageous for ensuring good optical performance in the observation over the entire object distance range from the farthest point to the nearest point.

[0070] Also, the objective lens for an endoscope preferably satisfies the following conditional expression (9-1). By ensuring that the corresponding value of conditional expression (9-1) does not fall below the lower limit value, it is advantageous for suppressing the enlargement of the lens system. 0.005 < f1 / f1a < 1 (9-1)

[0071] To obtain better characteristics, it is more preferable that the upper limit values of conditional expression (9) and conditional expression (9-1) be 0.7. For example, the objective lens for an endoscope more preferably satisfies the following conditional expression (9-2). 0 < f1 / f1a < 0.7 (9-2)

[0072] Regarding the lower limit of conditional expression (10), since fF > 0 and f1b > 0, 0 < fF / f1b holds. By ensuring that the corresponding value of conditional expression (10) does not exceed the upper limit value, it is advantageous for ensuring good optical performance in the observation over the entire object distance range from the farthest point to the nearest point.

[0073] Also, the objective lens for an endoscope preferably satisfies the following conditional expression (10-1). By ensuring that the corresponding value of conditional expression (10-1) does not fall below the lower limit value, it is advantageous for suppressing the enlargement of the lens system. 0.1 < fF / f1b < 1 (10-1)

[0074] To obtain better characteristics, it is more preferable that the upper limit values of conditional expression (10) and conditional expression (10-1) be 0.3. For example, the objective lens for an endoscope more preferably satisfies the following conditional expression (10-2). 0.1 < fF / f1b < 0.3 (10-2)

[0075] Regarding the lower limit of conditional expression (11), since f1 > 0 and f1b > 0, 0 < f1 / f1b holds. By ensuring that the corresponding value of conditional expression (11) does not exceed the upper limit value, it is advantageous for ensuring good optical performance in the observation over the entire object distance range from the farthest point to the nearest point.

[0076] Also, the objective lens for an endoscope preferably satisfies the following conditional expression (11-1). By ensuring that the corresponding value of conditional expression (11-1) does not fall below the lower limit value, it is advantageous for suppressing the enlargement of the lens system. 0.1 < f1 / f1b < 1 (11-1)

[0077] To obtain better characteristics, it is more preferable that the upper limit values of conditional expression (11) and conditional expression (11-1) be 0.4. For example, the objective lens for an endoscope more preferably satisfies the following conditional expression (11-2). 0.1 < f1 / f1b < 0.4 (11-2)

[0078] In a configuration in which the first lens group G1 is composed of, in order from the object side to the image side, a 1a lens group G1a having positive refractive power, an aperture stop St, and a 1b lens group G1b having positive refractive power, and the 1a lens group G1a includes a cemented lens in which at least one negative lens and at least one positive lens are cemented together, it is preferable that the endoscope objective lens satisfies the following conditional formula (13). Here, the average value of the Abbe numbers based on the d-line of all the positive lenses included in the cemented lens of the 1a lens group G1a is v1p. The average value of the Abbe numbers based on the d-line of all the negative lenses included in the cemented lens of the 1a lens group G1a is v1n. The lower limit of the conditional formula (13) is 0<|v1p-v1n|, since |v1p-v1n| is an absolute value. By ensuring that the corresponding value of conditional expression (13) is not equal to or greater than the upper limit, excessive correction of the axial chromatic aberration and the lateral chromatic aberration can be suppressed, which is advantageous for optimal control of the axial chromatic aberration and the lateral chromatic aberration. 0<|ν1p-ν1n|<40 (13)

[0079] Moreover, it is preferable that the endoscope objective lens satisfies the following conditional formula (13-1): By making sure that the corresponding value of conditional formula (13-1) is not equal to or smaller than the lower limit, it is advantageous to suppress axial chromatic aberration and lateral chromatic aberration from the visible range to the short wavelength range around 400 nm. 5.5<|ν1p-ν1n|<40 (13-1)

[0080] In order to obtain better characteristics, it is more preferable that the upper limit values ​​of conditional expressions (13) and (13-1) be set to 37. For example, it is more preferable that the objective lens for an endoscope satisfies the following conditional expression (13-2). 5.5<|ν1p-ν1n|<37 (13-2)

[0081] In a configuration in which the second lens group G2 includes a cemented lens in which at least one negative lens and at least one positive lens are cemented together, it is preferable that the endoscope objective lens satisfies the following conditional formula (14). Here, the average value of the Abbe numbers based on the d-line of all the positive lenses included in the cemented lens of the second lens group G2 is ν2p. The average value of the Abbe numbers based on the d-line of all the negative lenses included in the cemented lens of the second lens group G2 is ν2n. By making the corresponding value of the conditional formula (14) not equal to or less than the lower limit, it is advantageous to suppress the axial chromatic aberration and the lateral chromatic aberration from the visible range to the short wavelength range around the wavelength of 400 nm. By making the corresponding value of the conditional formula (14) not equal to or more than the upper limit, it is possible to suppress the amount of correction of the axial chromatic aberration and the lateral chromatic aberration from becoming excessive, which is advantageous to optimally control the axial chromatic aberration and the lateral chromatic aberration. 25<|ν2p-ν2n|<85 (14)

[0082] In order to obtain better characteristics, it is more preferable that the lower limit of conditional expression (14) be set to 26. Also, it is more preferable that the upper limit of conditional expression (14) be set to 70. For example, it is more preferable that the objective lens for an endoscope satisfy the following conditional expression (14-1). 26<|ν2p-ν2n|<70 (14-1)

[0083] It is preferable that the objective lens for endoscopes satisfies the following conditional expression (12). Here, the distance that the second lens group G2 moves when focusing from the farthest object to the nearest object is M. The paraxial imaging magnification of the entire system when focused on the farthest object is βf. The paraxial imaging magnification of the entire system when focused on the nearest object is βn. βf and βn use horizontal magnifications, not vertical magnifications. As an example, FIG. 1 shows the above distance M. By making the corresponding value of conditional expression (12) not equal to or less than the lower limit, it is advantageous to suppress the enlargement of the lens system. By making the corresponding value of conditional expression (12) not equal to or more than the upper limit, it is advantageous to improve the ease of focusing, since it is possible to suppress the sharpening of the focusing sensitivity when the second lens group G2 moves. 0.01<(fF / |M|)×(βf / βn)<1 (12)

[0084] In order to obtain better characteristics, it is more preferable that the lower limit value of the conditional expression (12) is 0.15. Also, it is more preferable that the upper limit value of the conditional expression (12) is 0.5. For example, it is more preferable that the objective lens for an endoscope satisfies the following conditional expression (12-1). 0.15 < (fF / |M|)×(βf / βn) < 0.5 (12-1)

[0085] Note that the example shown in FIG. 1 is just an example, and various modifications are possible within the scope not departing from the gist of the technology of the present disclosure. For example, the number of lenses included in each lens group may be different from the example in FIG. 1. Also, the configuration of the lenses included in each lens group can be different from the example in FIG. 1.

[0086] For example, the first a lens group G1a may be configured to include, in order from the object side to the image side, a single lens having a negative refractive power with a plane facing the object side, a negative lens, and a positive lens. Or, the first a lens group G1a may be configured to include, in order from the object side to the image side, a single lens having a negative refractive power with a plane facing the object side, a single lens having a positive refractive power, a negative lens, and a positive lens. When the first a lens group G1a includes a cemented lens in which at least one negative lens and at least one positive lens are cemented, this cemented lens may be disposed adjacent to the object side of the aperture stop St.

[0087] The first b lens group G1b may be configured to include, in order from the object side to the image side, a positive lens and a negative lens. In this case, the positive lens and the negative lens of the first b lens group G1b may be cemented to each other. The first b lens group G1b may be configured to consist of one cemented lens. Or, the first b lens group G1b may be configured to consist of one positive lens.

[0088] The second lens group G2 may be configured to include a cemented lens in which a negative lens and a positive lens are cemented together in that order from the object side, or the second lens group G2 may be configured to include a cemented lens in which a positive lens and a negative lens are cemented together in that order from the object side.

[0089] The above-mentioned preferred and possible configurations, including those relating to the conditional expressions, can be arbitrarily combined within a range not causing any contradiction, and it is preferable that they are appropriately and selectively adopted according to the required specifications.

[0090] As an example, a preferred embodiment of the objective lens for endoscopes of the present disclosure comprises, in order from the object side to the image side, a first lens group G1 having positive refractive power and a second lens group G2 having positive refractive power, and when focusing from the farthest object to the nearest object, the first lens group G1 is fixed with respect to the image plane Sim and only the second lens group G2 moves along the optical axis Z, and the first lens group G1 includes a single lens having negative refractive power closest to the object, and satisfies the above conditional expressions (1), (2), and (3).

[0091] Next, examples of the objective lens for endoscopes according to the present disclosure will be described with reference to the drawings. The reference symbols given to the lenses and groups in the cross-sectional views of each example are used independently for each example to avoid the explanation and the drawings becoming complicated due to the increase in the number of digits of the reference symbols. Therefore, even if common reference symbols are given in the drawings of different examples, they do not necessarily have the same configuration.

[0092] [Example 1] The cross-sectional views showing the configuration of the objective lens for an endoscope of Example 1 are shown in Figures 1 and 2, and the method of illustration is as described above, so some overlapping explanations will be omitted here. The objective lens for an endoscope of Example 1 is composed of, in order from the object side to the image side, a first lens group G1 having positive refractive power and a second lens group G2 having positive refractive power. When focusing from the farthest object to the nearest object, the first lens group G1 is fixed with respect to the image surface Sim, and the second lens group G2 moves toward the object side. The first lens group G1 is composed of, in order from the object side to the image side, a 1a lens group G1a having positive refractive power, an aperture stop St, and a 1b lens group G1b having positive refractive power. The above is an overview of the objective lens for an endoscope of Example 1.

[0093] Each group of the objective lens for an endoscope in Example 1 is configured as follows. The 1a lens group G1a is composed of, in order from the object side to the image side, a lens L11, an optical member P1, a lens L12, and a lens L13. The 1b lens group G1b is composed of, in order from the object side to the image side, a lens L14 and a lens L15. The second lens group G2 is composed of, in order from the object side to the image side, a lens L21 and a lens L22. The lens L12 and the lens L13 are cemented together. The lens L14 and the lens L15 are cemented together. The lens L21 and the lens L22 are cemented together. The lens L11 is a single lens.

[0094] Regarding the objective lens for an endoscope in Example 1, basic lens data is shown in Table 1, and specifications and variable surface spacing are shown in Table 2.

[0095] The basic lens data table is written as follows. The "Sn" column shows the surface numbers, with the surface closest to the object being surface 1 and the numbers increasing by one as you move toward the image side. The "R" column shows the radius of curvature of each surface. The "D" column shows the surface spacing on the optical axis between each surface and its adjacent surface on the image side. The "Nd" column shows the refractive index for each lens with respect to the d line. The "νd" column shows the Abbe number for each lens based on the d line.

[0096] In the basic lens data table, the sign of the radius of curvature of a surface with a convex shape facing the object side is positive, and the sign of the radius of curvature of a surface with a convex shape facing the image side is negative. In Table 1, the surface number and the term (St) are entered in the column for the surface number corresponding to the aperture stop St. Table 1 also lists the optical member PP. The value in the bottom row of the D column in the table is the distance between the surface in the table closest to the image side and the image plane Sim. The symbol DD[ ] is used for the variable surface distance during focusing, and the surface number on the object side of this distance is entered in the [ ] in the surface distance column.

[0097] Table 2 shows the values ​​of focal length, back focus in air equivalent distance, F-number, maximum total angle of view, maximum image height, object distance, paraxial imaging magnification, and variable surface spacing for the farthest point observation state and the nearest point observation state. Note that the object distance is the distance on the optical axis from the object to the lens surface of the first lens group G1 closest to the object. The [°] in the maximum total angle of view column indicates that the unit is degrees. The values ​​shown in Table 2 are based on the d-line.

[0098] In the data in each table, the angle unit is degrees and the length unit is mm (millimeters), but since the optical system can be used with proportional enlargement or reduction, other appropriate units can also be used. Also, in each table shown below, values ​​are rounded to a predetermined number of decimal places.

[0099] [Table 1]

[0100] [Table 2]

[0101] FIG. 3 shows each aberration diagram of the objective lens for endoscopes of Example 1. In FIG. 3, from the left, spherical aberration diagram, astigmatism diagram, distortion aberration diagram, and lateral chromatic aberration diagram are shown. In FIG. 3, each aberration diagram in the farthest point observation state is shown in the upper part, and each aberration diagram in the nearest point observation state is shown in the lower part. In FIG. 3, the value of the object distance is shown to the right of "Distance:". In the spherical aberration diagram, the aberrations at the d-line, C-line, F-line, and h-line are shown by solid lines, long dashed lines, short dashed lines, and dashed lines, respectively. In the astigmatism diagram, the aberration at the d-line in the sagittal direction is shown by solid lines, and the aberration at the d-line in the tangential direction is shown by short dashed lines. In the distortion aberration diagram, the aberration at the d-line is shown by solid lines. In the lateral chromatic aberration diagram, the aberrations at the C-line, F-line, and h-line are shown by long dashed lines, short dashed lines, and dashed lines, respectively. In the spherical aberration diagram, the F-number value in each state is shown after "FNo.=". In the other aberration diagrams, the maximum half angle of view in each state is shown after "ω=".

[0102] The symbols, meanings, description methods, and illustration methods of each piece of data related to the above-mentioned Example 1 are the same in the following Examples unless otherwise specified, so duplicated explanations will be omitted below.

[0103] [Example 2] 4 shows a cross-sectional view of the configuration of the endoscope objective lens of Example 2. The endoscope objective lens of Example 2 has a similar configuration to the outline of the endoscope objective lens of Example 1.

[0104] Each group of the objective lens for an endoscope of Example 2 is configured as follows. The 1a lens group G1a is composed of, in order from the object side to the image side, a lens L11, an optical member P1, a lens L12, and a lens L13. The 1b lens group G1b is composed of, in order from the object side to the image side, a lens L14 and a lens L15. The second lens group G2 is composed of, in order from the object side to the image side, a lens L21 and a lens L22. The lens L12 and the lens L13 are cemented together. The lens L14 and the lens L15 are cemented together. The lens L21 and the lens L22 are cemented together. The lens L11 is a single lens.

[0105] Regarding the objective lens for an endoscope of Example 2, basic lens data is shown in Table 3, specifications and variable surface spacing are shown in Table 4, and each aberration diagram is shown in FIG.

[0106] [Table 3]

[0107] [Table 4]

[0108] [Example 3] 6 shows a cross-sectional view of the configuration of the endoscope objective lens of Example 3. The endoscope objective lens of Example 3 has a similar configuration to that of the endoscope objective lens of Example 1.

[0109] Each group of the objective lens for an endoscope of Example 3 is configured as follows. The 1a lens group G1a is composed of, in order from the object side to the image side, a lens L11, an optical member P1, a lens L12, and a lens L13. The 1b lens group G1b is composed of, in order from the object side to the image side, a lens L14 and a lens L15. The second lens group G2 is composed of, in order from the object side to the image side, a lens L21 and a lens L22. The lens L12 and the lens L13 are cemented together. The lens L14 and the lens L15 are cemented together. The lens L21 and the lens L22 are cemented together. The lens L11 is a single lens.

[0110] Regarding the objective lens for an endoscope of Example 3, basic lens data is shown in Table 5, specifications and variable surface spacing are shown in Table 6, and each aberration diagram is shown in FIG.

[0111] [Table 5]

[0112] [Table 6]

[0113] [Example 4] 8 shows a cross-sectional view of the configuration of the endoscope objective lens of Example 4. The endoscope objective lens of Example 4 has a similar configuration to that of the endoscope objective lens of Example 1.

[0114] Each group of the objective lens for an endoscope of Example 4 is configured as follows. The 1a lens group G1a is composed of, in order from the object side to the image side, a lens L11, a lens L12, a lens L13, and a lens L14. The 1b lens group G1b is composed of a lens L15. The second lens group G2 is composed of, in order from the object side to the image side, a lens L21 and a lens L22. The lens L13 and the lens L14 are cemented together. The lens L21 and the lens L22 are cemented together. The lens L11, the lens L12, and the lens L15 are single lenses.

[0115] Regarding the objective lens for an endoscope of Example 4, basic lens data is shown in Table 7, specifications and variable surface spacing are shown in Table 8, and each aberration diagram is shown in FIG.

[0116] [Table 7]

[0117] [Table 8]

[0118] [Example 5] 10 is a cross-sectional view showing the configuration of the endoscope objective lens of Example 5. The endoscope objective lens of Example 5 has a configuration similar to that of the endoscope objective lens of Example 1.

[0119] Each group of the objective lenses for endoscopes in Example 5 is configured as follows. The first a lens group G1a consists of a lens L11, a lens L12, and a lens L13 in order from the object side to the image side. The first b lens group G1b consists of a lens L14. The second lens group G2 consists of a lens L21 and a lens L22 in order from the object side to the image side. The lens L12 and the lens L13 are joined to each other. The lens L21 and the lens L22 are joined to each other. The lens L11 and the lens L14 are single lenses.

[0120] Regarding the objective lens for an endoscope of Example 5, the basic lens data is shown in Table 9, the specifications and the variable surface intervals are shown in Table 10, and each aberration diagram is shown in FIG. 11.

[0121] [Table 9]

[0122] [Table 10]

[0123] Table 11 shows the corresponding values of the conditional expressions (1) to (14) of the objective lenses for endoscopes of Examples 1 to 5. The values based on the d line are shown in Table 11. The preferable ranges of the conditional expressions may be set using the corresponding values of the examples shown in Table 11 as the upper limit values or the lower limit values of the conditional expressions.

[0124] [Table 11]

[0125] The objective lenses for endoscopes of Examples 1 to 5 are configured to be small, but the total field angle in the farthest point observation state is 135° or more, ensuring a wide field angle. Further, the objective lenses for endoscopes of Examples 1 to 5 do not have a large change in performance between the farthest point observation state and the nearest point observation state, and various aberrations are well corrected in both states, maintaining high optical performance.

[0126] Next, an endoscope according to an embodiment of the present disclosure will be described. FIG. 12 shows a schematic overall configuration diagram of an endoscope according to an embodiment of the present disclosure. The endoscope 100 shown in FIG. 12 mainly includes an operation section 102, an insertion section 104, and a universal cord 106 connected to a connector section (not shown). Most of the insertion section 104 is a flexible section 107 that bends in any direction along the insertion path, and a bending section 108 is connected to the tip of the flexible section 107, and a tip section 110 is connected to the tip of the bending section 108. The bending section 108 is provided to direct the tip section 110 in a desired direction, and bending operation is possible by rotating a bending operation knob 109 provided on the operation section 102. An objective lens 1 for endoscopes according to an embodiment of the present disclosure and an image sensor 2 are disposed at the inner tip of the tip section 110. The image sensor 2 is, for example, a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor). The imaging element 2 is disposed so that its imaging plane coincides with the image plane of the endoscope objective lens 1. Note that the endoscope objective lens 1 and the imaging element 2 shown in Fig. 12 are conceptual diagrams.

[0127] Although the technology of the present disclosure has been described above by way of embodiments and examples, the technology of the present disclosure is not limited to the above embodiments and examples, and various modifications are possible. For example, the radius of curvature, surface spacing, refractive index, Abbe number, etc. of each lens are not limited to the values ​​shown in the above numerical examples, and may take other values.

[0128] Regarding the above-mentioned embodiments and examples, the following supplementary notes are further disclosed. [Appendix 1] The optical system comprises, in order from the object side to the image side, a first lens group having positive refractive power and a second lens group having positive refractive power; During focusing from the farthest object to the nearest object, the first lens group is fixed with respect to an image plane, and only the second lens group moves along the optical axis; the first lens group includes a single lens having negative refractive power and located closest to the object, The maximum image height is Y. The focal length of the entire system when focused on the farthest object is fF. The maximum half angle of view when the farthest object is in focus is ωf. The focal length of the first lens group is f1, The focal length of the second lens group is f2. If the focal length of the single lens is fL1, 0 <Y / (fF×tanωf)<0.6 (1) 0 <f1 / f2<0.25 (2) -1.2 <fL1 / fF<0 (3) An objective lens for an endoscope that satisfies conditional expressions (1), (2), and (3) expressed by: [Appendix 2] If the F-number when the lens is focused on the farthest object is FNof, 0 <FNof / tanωf<2 (4) 2. The objective lens for an endoscope according to claim 1, which satisfies conditional expression (4) represented by: [Appendix 3] 0 <fF / f1<2 (5) The objective lens for an endoscope according to claim 1 or 2, which satisfies conditional expression (5) represented by: [Appendix 4] 0 <fF / f2<0.5 (6) 4. The objective lens for an endoscope according to claim 1, which satisfies conditional expression (6) represented by: [Appendix 5] -1.5 <fL1 / f1<0 (7) 5. The objective lens for an endoscope according to claim 1, which satisfies conditional expression (7) represented by: [Appendix 6] 6. An objective lens for endoscopes according to claim 1, wherein the object-side lens surface of the single lens is flat. [Appendix 7] the first lens group includes, in order from the object side to the image side, a 1a lens group having positive refractive power, an aperture stop, and a 1b lens group having positive refractive power; If the focal length of the 1a lens group is f1a, 0 <fF / f1a<1 (8) 7. The objective lens for an endoscope according to claim 1, which satisfies conditional expression (8) represented by: [Appendix 8] the first lens group includes, in order from the object side to the image side, a 1a lens group having positive refractive power, an aperture stop, and a 1b lens group having positive refractive power; If the focal length of the 1a lens group is f1a, 0 <f1 / f1a<1 (9) 8. The objective lens for an endoscope according to claim 1, which satisfies conditional expression (9) represented by: [Appendix 9] the first lens group includes, in order from the object side to the image side, a 1a lens group having positive refractive power, an aperture stop, and a 1b lens group having positive refractive power; If the focal length of the 1b lens group is f1b, 0 <fF / f1b<1 (10) 9. The objective lens for an endoscope according to claim 1, which satisfies conditional expression (10) represented by: [Appendix 10] the first lens group includes, in order from the object side to the image side, a 1a lens group having positive refractive power, an aperture stop, and a 1b lens group having positive refractive power; If the focal length of the 1b lens group is f1b, 0 <f1 / f1b<1 (11) 10. The objective lens for an endoscope according to claim 1, which satisfies conditional expression (11) represented by: [Appendix 11] The distance that the second lens group moves when focusing from the farthest object to the nearest object is M. The paraxial imaging magnification of the entire system when focused on the farthest object is βf. If the paraxial imaging magnification of the entire system when focused on the nearest object is βn, 0.01<(fF / |M|)×(βf / βn)<1 (12) 11. The objective lens for an endoscope according to claim 1, which satisfies conditional expression (12) represented by: [Appendix 12] the first lens group includes, in order from the object side to the image side, a 1a lens group having positive refractive power, an aperture stop, and a 1b lens group having positive refractive power; The objective lens for an endoscope according to any one of claims 1 to 11, wherein the 1a lens group includes a cemented lens in which at least one negative lens and at least one positive lens are cemented together. [Appendix 13] The average Abbe number based on the d-line of all the positive lenses included in the cemented lens of the 1a lens group is ν1p, When the average value of the Abbe numbers based on the d-line of all the negative lenses included in the cemented lens of the 1a lens group is ν1n, 0<|ν1p-ν1n|<40 (13) 13. The objective lens for an endoscope according to claim 12, which satisfies conditional expression (13) represented by: [Appendix 14] The objective lens for an endoscope according to any one of claims 1 to 13, wherein the second lens group includes a cemented lens in which at least one negative lens and at least one positive lens are cemented together. [Appendix 15] The objective lens for endoscopes according to any one of claims 1 to 14, wherein the second lens group is composed of one cemented lens in which at least one negative lens and at least one positive lens are cemented together. [Appendix 16] The average Abbe number based on the d-line of all the positive lenses included in the cemented lens of the second lens group is ν2p, When the average value of the Abbe numbers based on the d-line of all the negative lenses included in the cemented lens of the second lens group is ν, 25<|ν2p-ν2n|<85 (14) 15. The objective lens for an endoscope according to claim 14, which satisfies conditional expression (14) represented by: [Appendix 17] An endoscope comprising an objective lens for an endoscope according to any one of claims 1 to 16. [Explanation of symbols]

[0129] 1. Endoscope Objective Lenses 2. Image sensor 100 Endoscope 102 Operation section 104 Insertion part 106 Universal Code 107 Soft part 108 Curved section 109 Curvature control knob 110 Tip G1 First lens group G1a 1a lens group G1b 1bth lens group G2 2nd lens group L11~L22 Lens M distance P1 Optical components PP Optical Components Sim image plane St Aperture Y Maximum image height Z optical axis ωf Maximum half angle of view ωn Maximum half angle of view

Claims

1. The optical system comprises, in order from the object side to the image side, a first lens group having positive refractive power and a second lens group having positive refractive power, During focusing from the farthest object to the nearest object, the first lens group is fixed with respect to an image plane, and only the second lens group moves along the optical axis; the first lens group includes a single lens having negative refractive power and located closest to the object, The maximum image height is Y. The focal length of the entire system when focused on the farthest object is fF. The maximum half angle of view when the farthest object is in focus is ωf. The focal length of the first lens group is f1, The focal length of the second lens group is f2. If the focal length of the single lens is fL1, 0<Y / (fF×tanωf)<0.6 (1) 0<f1 / f2<0.25 (2) -1.2<fL1 / fF<0 (3) The objective lens for an endoscope satisfies the conditional expressions (1), (2), and (3) represented by the following formula:

2. If the F-number when the lens is focused on the farthest object is FNof, 0<FNof / tanωf<2 (4) 2. The objective lens for an endoscope according to claim 1, which satisfies conditional expression (4) expressed as follows:

3. 0<fF / f1<2 (5) 2. The objective lens for an endoscope according to claim 1, which satisfies conditional expression (5) expressed as follows:

4. 0<fF / f2<0.5 (6) 2. The objective lens for an endoscope according to claim 1, which satisfies conditional expression (6) expressed as follows:

5. -1.5<fL1 / f1<0 (7) 2. The objective lens for endoscopes according to claim 1, which satisfies conditional expression (7) expressed as follows:

6. 2. The objective lens for an endoscope according to claim 1, wherein the lens surface on the object side of said single lens is flat.

7. the first lens group includes, in order from the object side to the image side, a 1a lens group having positive refractive power, an aperture stop, and a 1b lens group having positive refractive power; When the focal length of the 1a lens group is f1a, 0<fF / f1a<1 (8) 2. The objective lens for an endoscope according to claim 1, which satisfies conditional expression (8) expressed as follows:

8. the first lens group includes, in order from the object side to the image side, a 1a lens group having positive refractive power, an aperture stop, and a 1b lens group having positive refractive power; When the focal length of the 1a lens group is f1a, 0<f1 / f1a<1 (9) 2. The objective lens for endoscopes according to claim 1, which satisfies conditional expression (9) expressed as:

9. the first lens group includes, in order from the object side to the image side, a 1a lens group having positive refractive power, an aperture stop, and a 1b lens group having positive refractive power; When the focal length of the 1b lens group is f1b, 0<fF / f1b<1 (10) 2. The objective lens for an endoscope according to claim 1, which satisfies conditional expression (10) expressed as:

10. the first lens group includes, in order from the object side to the image side, a 1a lens group having positive refractive power, an aperture stop, and a 1b lens group having positive refractive power; When the focal length of the 1b lens group is f1b, 0<f1 / f1b<1 (11) 2. The objective lens for an endoscope according to claim 1, which satisfies conditional expression (11) represented by:

11. The distance that the second lens group moves when focusing from the farthest object to the nearest object is M. The paraxial imaging magnification of the entire system when focused on the farthest object is βf. When the paraxial imaging magnification of the entire system in a state where the lens is focused on the nearest object is βn, 0.01<(fF / |M|)×(βf / βn)<1 (12) 2. The objective lens for an endoscope according to claim 1, which satisfies conditional expression (12) expressed as follows:

12. the first lens group includes, in order from the object side to the image side, a 1a lens group having positive refractive power, an aperture stop, and a 1b lens group having positive refractive power; 2. The objective lens for an endoscope according to claim 1, wherein the 1a lens group includes a cemented lens in which at least one negative lens and at least one positive lens are cemented together.

13. The average Abbe number based on the d-line of all the positive lenses included in the cemented lens of the 1a lens group is ν1p, When the average value of the Abbe numbers based on the d-line of all the negative lenses included in the cemented lens of the 1a lens group is ν1n, 0<|ν1p−ν1n|<40 (13) 13. The objective lens for an endoscope according to claim 12, which satisfies conditional expression (13) expressed as follows:

14. 2. The objective lens for an endoscope according to claim 1, wherein the second lens group includes a cemented lens in which at least one negative lens and at least one positive lens are cemented together.

15. 2. The objective lens for an endoscope according to claim 1, wherein the second lens group is composed of one cemented lens in which at least one negative lens and at least one positive lens are cemented together.

16. The average Abbe number based on the d-line of all the positive lenses included in the cemented lens of the second lens group is ν2p, When the average value of the Abbe numbers based on the d-line of all the negative lenses included in the cemented lens of the second lens group is ν2n, 25<|ν2p−ν2n|<85 (14) 15. The objective lens for an endoscope according to claim 14, which satisfies conditional expression (14) represented by:

17. An endoscope comprising the objective lens for an endoscope according to any one of claims 1 to 16.

Images