Objective lens for endoscope and endoscope

Abstract

Provided are: an objective lens for an endoscope, which has a focusing function and maintains good optical performance in observation of the entire object distance from the farthest point to the closest point; and an endoscope provided with the objective lens for an endoscope. An objective lens for an endoscope includes, in order from an object side to an image side, a first lens group having a positive refractive power and a second lens group having a positive refractive power. During focusing, only the second lens group moves. The first lens group includes a single lens having a negative refractive power at a position closest to the object side. The objective lens for an endoscope satisfies a predetermined conditional expression pertaining to the maximum image height, the focal length of the entire system, the maximum half viewing angle, the focal length of the first lens group, the focal length of the second lens group, and the focal length of the single lens of the first lens group.

Description

Technical Field

[0001] The present invention relates to an objective lens for an endoscope and an endoscope. Background Art

[0002] Conventionally, as objective lenses for endoscopes, objective lenses described in Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, and Patent Document 5 below are known.

[0003] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2022-033521

[0004] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2011-075915

[0005] Patent Document 3: Japanese Unexamined Patent Application Publication No. 2002-028126

[0006] Patent Document 4: International Publication No. 2019 / 163744

[0007] Patent Document 5: Japanese Unexamined Patent Application Publication No. 2001-091832

[0008] There has been a need for an objective lens for an endoscope that has a focusing function and maintains good optical performance in observation over the entire object distance range from the farthest point to the nearest point. This required level has been increasing year by year. Summary of the Invention

[0009] The present invention has been made in view of the above circumstances, and an object thereof is to provide an objective lens for an endoscope that has a focusing function and maintains good optical performance in observation over the entire object distance range from the farthest point to the nearest point, and an endoscope equipped with the objective lens for an endoscope.

[0010] The objective lens for an endoscope according to one aspect of the present invention includes, in order from the object side to the image side, a first lens group having a positive refractive power and a second lens group having a positive refractive power. When focusing from the farthest point object to the nearest point object, the first lens group is fixed relative to the image plane, and only the second lens group moves along the optical axis. The first lens group includes a single lens having a negative refractive power on the side closest to the object. The objective lens for an endoscope satisfies conditional expressions (1), (2), and (3) represented by 0 < Y / (fF × tan ωf) < 0.6 (1), 0 < f1 / f2 < 0.25 (2), and -1.2 < fL1 / fF < 0 (3).

[0011] The symbols of each conditional expression are defined as follows. The maximum image height is set as Y. The focal length of the entire system in the state of focusing on the farthest point object is set as fF. The maximum half field angle in the state of focusing on the farthest point object is set as ωf. The focal length of the first lens group is set as f1. The focal length of the second lens group is set as f2. The focal length of the above single lens of the first lens group is set as fL1.

[0012] When the F value in the state of focusing on the object at the farthest point is set to FNof, the objective lens for an endoscope of the above-described method preferably satisfies the conditional expression (4) represented by 0 < FNof / tanωf < 2 (4).

[0013] The objective lens for an endoscope of the above-described method preferably satisfies the conditional expression (5) represented by 0 < fF / f1 < 2 (5).

[0014] The objective lens for an endoscope of the above-described method preferably satisfies the conditional expression (6) represented by 0 < fF / f2 < 0.5 (6).

[0015] The objective lens for an endoscope of the above-described method preferably satisfies the conditional expression (7) represented by -1.5 < fL1 / f1 < 0 (7).

[0016] The lens surface on the object side of the single lens of the first lens group is preferably a plane.

[0017] In a structure in which the first lens group includes a first a lens group having a positive refractive power, an aperture stop, and a first b lens group having a positive refractive power in order from the object side to the image side, when the focal length of the first a lens group is set to f1a, the objective lens for an endoscope of the above-described method preferably satisfies the conditional expression (8) represented by 0 < fF / f1a < 1 (8).

[0018] In a structure in which the first lens group includes a first a lens group having a positive refractive power, an aperture stop, and a first b lens group having a positive refractive power in order from the object side to the image side, when the focal length of the first a lens group is set to f1a, the objective lens for an endoscope of the above-described method preferably satisfies the conditional expression (9) represented by 0 < f1 / f1a < 1 (9).

[0019] In a structure in which the first lens group includes a first a lens group having a positive refractive power, an aperture stop, and a first b lens group having a positive refractive power in order from the object side to the image side, when the focal length of the first b lens group is set to f1b, the objective lens for an endoscope of the above-described method preferably satisfies the conditional expression (10) represented by 0 < fF / flb < 1 (10).

[0020] In a structure in which the first lens group includes a first a lens group having a positive refractive power, an aperture stop, and a first b lens group having a positive refractive power in order from the object side to the image side, when the focal length of the first b lens group is set to f1b, the objective lens for an endoscope of the above-described method preferably satisfies the conditional expression (11) represented by 0 < f1 / f1b < 1 (11).

[0021] When the distance moved by the second lens group when focusing from the farthest object to the nearest object is set to M, the paraxial imaging magnification of the entire system when focusing on the farthest object is set to βf, and the paraxial imaging magnification of the entire system when focusing on the nearest object is set to βn, the above-mentioned endoscope objective lens preferably satisfies the conditional formula (12) expressed by 0.01<(fF / |M|)×(βf / βn)<1(12).

[0022] In the structure in which the first lens group includes, from the object side to the image side, a lens group 1a with positive refractive power, an aperture stop, and a lens group 1b with positive refractive power, the lens group 1a preferably includes a cemented lens formed by cementing at least one negative lens and at least one positive lens.

[0023] When the average value of the Abbe numbers of all the positive lenses included in the above-mentioned combined lenses of the 1a-th lens group on the d-ray basis is set to v lp, and the average value of the Abbe numbers of all the negative lenses included in the combined lenses of the 1a-th lens group on the d-ray basis is set to v ln, the above-mentioned endoscope objective lens preferably satisfies the conditional formula (13) expressed by 0<|v 1p-v ln|<40(13).

[0024] 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.

[0025] The second lens group may be configured as a single cemented lens including at least one negative lens and at least one positive lens cemented together.

[0026] When the average value of the Abbe numbers of all the positive lenses included in the above-mentioned combined lens of the second lens group on the d-ray basis is set to v 2p, and the average value of the Abbe numbers of all the negative lenses included in the above-mentioned combined lens of the second lens group on the d-ray basis is set to v 2n, the objective lens for the endoscope of the above-mentioned method preferably satisfies the conditional formula (14) expressed by 25<|v 2p-v 2n|<85(14).

[0027] The endoscope of the present invention includes the endoscope objective lens of the present invention.

[0028] In addition, the term "comprising to" in this specification means that in addition to the listed components, optical components other than lenses such as lenses having substantially no refractive power, apertures, filters, and cover glasses, as well as lens flanges, lens barrels, and imaging elements may also be included.

[0029] The "group of lenses having positive power" in this specification means that the group as a whole has positive power. "Lens having positive refractive power" and "positive lens" have the same meaning. "Lens having negative refractive power" and "negative lens" have the same meaning. "Group of lenses" is not limited to a structure including multiple lenses, and can also be set to a structure including only one lens.

[0030] "Single lens" refers to a single lens that is not cemented. However, a composite aspheric lens (a lens (e.g., a spherical lens) and a film having an aspheric shape formed on the spherical lens are integrated and function as a single aspheric lens as a whole) is considered to be a single lens and not a cemented lens. Unless otherwise specified, the sign of the refractive power and the surface shape of the lens including an aspheric surface use the sign of the refractive power and the surface shape of the paraxial region.

[0031] In this specification, "entire system" refers to the objective lens for endoscopes. The "focal length" used in the conditional expression is the paraxial focal length. The value used in the conditional expression is the value when the d-ray is used as the reference. The "d-ray", "C-ray", "F-ray" and "h-ray" recorded in this specification are bright lines, and the wavelength of the d-ray is set to 587.56nm (nanometers), the wavelength of the C-ray is set to 656.27nm (nanometers), the wavelength of the F-ray is set to 486.13nm (nanometers), and the wavelength of the h-ray is set to 404.66nm (nanometers).

[0032] Effects of the Invention

[0033] According to the present invention, it is possible to provide an endoscope objective lens having a focusing function and maintaining good optical performance in observation over the entire range of object distances from the farthest point to the closest point, and an endoscope including the endoscope objective lens. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a cross-sectional view showing the structure of an endoscope objective lens and a light beam according to an embodiment, corresponding to the endoscope objective lens of Example 1.

[0035] Figure 2 It is a cross-sectional view showing the structure of the endoscope objective lens of Example 1.

[0036] Figure 3 1 and 2 are diagrams showing various aberrations of the endoscope objective lens of Example 1.

[0037] Figure 4 It is a cross-sectional view showing the structure of the endoscope objective lens of Example 2.

[0038] Figure 5 1 and 10 are diagrams showing various aberrations of the endoscope objective lens of Example 2.

[0039] Figure 6It is a cross-sectional view showing the structure of the endoscope objective lens of Example 3.

[0040] Figure 7 1 and 10 are diagrams showing various aberrations of the endoscope objective lens of Example 3.

[0041] Figure 8 It is a cross-sectional view showing the structure of an endoscope objective lens according to Example 4.

[0042] Fig. 9 1 and 10 are diagrams showing various aberrations of the endoscope objective lens of Example 4.

[0043] Fig.10 It is a cross-sectional view showing the structure of the endoscope objective lens of Example 5.

[0044] Fig.11 1 and 10 are diagrams showing various aberrations of the endoscope objective lens of Example 5.

[0045] Fig.12 This is a schematic structural diagram of an endoscope according to one embodiment.

[0046] Explanation of symbols

[0047] 1-objective lens for endoscope, 2-camera element, 100-endoscope, 102-operating part, 104-insertion part, 106-universal cord, 107-flexible part, 108-bending part, 109-bending operation knob, 110-front end part, G1-1st lens group, G1a-1a lens group, G1b-1b lens group, G2-2nd lens group, L11~L22-lens, M-distance, P1-optical component, PP-optical component, Sim-image plane, St-aperture stop, Y-maximum image height, Z-optical axis, ωf-maximum half viewing angle, ωn-maximum half viewing angle. DETAILED DESCRIPTION

[0048] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0049] In an endoscope, there is a need for overall observation of a wide range and a need for local detailed observation of an affected part found during the overall observation. In order to observe a wide range as a whole, a wide-angle optical system is used for observation in a state away from the object to be observed, and this state corresponds to the far-point side observation state. On the other hand, in order to observe the affected part in a local detail, it is necessary to observe in a state where the endoscope is closer to the object to be observed, and this state corresponds to the near-point side observation state. In order to meet the above two needs, the objective lens for the endoscope is required to have a focusing function so as to be able to observe the entire object distance from the farthest point to the closest point well. Hereinafter, the state in which the objective lens of the endoscope focuses on the farthest point object is referred to as the farthest point observation state, and the state in which the objective lens of the endoscope focuses on the closest point object is referred to as the closest point observation state.

[0050] Figure 1 The structure and light beams in a cross section including the optical axis Z of an endoscope objective lens according to one embodiment of the present invention are shown. Figure 1 The example shown corresponds to Embodiment 1 described later. Figure 1 In the figure, the left side is the object side and the right side is the image side. Figure 1 In the figure, the farthest point observation state is shown in the upper part, and the closest point observation state is shown in the lower part. Figure 1 In FIG. 1 , as light beams, the on-axis light beam and the light beam with the maximum half viewing angle ωf in the farthest point observation state and the on-axis light beam and the light beam with the maximum half viewing angle ωn in the closest point observation state are shown.

[0051] The objective lens for endoscope of the present invention includes a first lens group G1 having positive refractive power and a second lens group G2 having positive refractive power in order from the object side to the image side along the optical axis Z. By setting such a structure, it is beneficial to ensure good optical performance in the observation of the entire area of ​​object distance from the farthest point to the closest point.

[0052] As an example, Figure 1 The configuration of each group of the example is as follows. The first lens group G1 includes lens L11, optical component P1, lens L12, lens L13, aperture stop St, lens L14 and lens L15 in order from the object side to the image side. The second lens group G2 includes lens L21 and lens L22 in order from the object side to the image side. The optical component P1 is a component assumed to be a filter, etc., and is a component with an incident surface and an exit surface parallel to each other and having no refractive power. Figure 1 The aperture stop St indicates the position on the optical axis rather than the size or shape.

[0053] exist Figure 1 In the example of , an optical component PP having an incident surface and an exit surface parallel to each other is arranged between the lens L22 and the image plane Sim. The optical component PP is assumed to be a component such as a prism, a filter, and a cover glass. The optical component PP is a component without a refractive power, and a structure in which the optical component PP is omitted is also possible.

[0054] The objective lens for endoscope of the present invention has a focusing function. When focusing from the farthest point object to the closest point object, the first lens group G1 is fixed relative to the image plane Sim, and only the second lens group G2 moves along the optical axis Z. That is, in the present invention, a rear focus type structure is adopted in which only one lens group is set to move during focusing. According to the structure of the present invention, compared with the type and the internal focus type in which multiple lens groups move during focusing, the structure required for focusing can be simplified. And, as shown in the present invention, it is beneficial to ensure airtightness by fixing the lens group closest to the object side, that is, the first lens group G1, during focusing. In an endoscope, in most cases, the objective lens for endoscope is mounted on the endoscope without a protective component, so that the lens closest to the object side in the objective lens for endoscope also has the function of an optical window. And, at this time, it is required to maintain airtightness, so it is advantageous for the first lens group G1 to be a fixed structure.

[0055] As an example, in Figure 1 In the example of FIG. 1 , when focusing from the farthest point object to the closest point object, the second lens group G2 moves toward the object side. Figure 2 Show Figure 1 A cross-sectional view of the structure of an endoscope objective lens. Figure 2 The basic diagramming method and Figure 1 However, in Figure 2 In FIG. 1 , the light beam is omitted from illustration, and an arrow indicating the approximate moving direction of the second lens group G2 when focusing from the farthest point object to the closest point object is written between the upper and lower sections.

[0056] The first lens group G1 includes a single lens having negative refractive power on the most object side. This configuration is advantageous in achieving both wide angle and compactness of the lens system.

[0057] The lens surface on the object side of the single lens with negative refractive power closest to the object side of the first lens group G1 is preferably a flat surface. When set in this way, it is beneficial to suppress the outer diameter of the single lens with negative refractive power closest to the object side from increasing. In addition, the manufacturability of the single lens can be improved, and the adhesion of liquid, etc. to the surface on the object side of the single lens can be reduced.

[0058] The first lens group G1 preferably includes, 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. When configured in this way, it is advantageous to ensure good optical performance in observation of the entire range of object distances from the farthest point to the closest point.

[0059] As an example, in Figure 1 In the example, the 1a-th lens group G1a includes lens L11, optical component P1, lens L12 and lens L13 in order from the object side to the image side, and the 1b-th lens group G1b includes lens L14 and lens L15 in order from the object side to the image side.

[0060] The first lens group G1a preferably includes a cemented lens formed by cementing at least one negative lens and at least one positive lens. When set in this way, it is beneficial to suppress axial chromatic aberration and lateral chromatic aberration in the short wavelength region from the visible region to around 400 nm in wavelength.

[0061] The second lens group G2 preferably includes a cemented lens formed by cementing at least one negative lens and at least one positive lens. When set in this way, it is beneficial to suppress axial chromatic aberration and lateral chromatic aberration in the short wavelength region from the visible region to around 400 nm in wavelength.

[0062] The second lens group G2 can be configured to include one cemented lens formed by cementing at least one negative lens and at least one positive lens. When set in this way, it is beneficial to suppress the enlargement of the lens system and is also beneficial to suppressing axial chromatic aberration and lateral chromatic aberration in the short wavelength region from the visible region to around 400 nm in wavelength. The second lens group G2 can be configured to include one cemented lens formed by cementing one negative lens and one positive lens. When set in this way, in addition to the above effects, it is also beneficial to the miniaturization of the lens system.

[0063] Next, the preferred structures and feasible structures related to the conditional expressions of the objective lens for an endoscope of the present invention will be described. In addition, in the descriptions related to the following conditional expressions, in order to avoid lengthy explanations, the same symbols are used for the parts with the same definitions, and the repeated explanations of the symbols are omitted. And hereinafter, in order to avoid lengthy explanations, the "objective lens for an endoscope of the present invention" is also simply referred to as the "objective lens for an endoscope".

[0064] The objective lens for an endoscope preferably satisfies the following conditional expression (1). Here, the maximum image height is set as Y. The focal length of the entire system in the state of focusing on the object at the farthest point is set as fF. The maximum half field angle in the state of focusing on the object at the farthest point is set as ωf. Tan is the tangent. As an example, in Figure 1 the maximum image height Y and the above-mentioned maximum half field angle ωf are shown. Regarding the lower limit of the conditional expression (1), since Y>0, fF>0, and tanωf>0, so 0 < Y / (fF×tanωf). By making the corresponding value of the conditional expression (1) not exceed the upper limit value, it is beneficial to perform wide field of view observation while increasing the magnification near the center of the imaging region.

[0065] 0 < Y / (fF×tanωf) < 0.6 (1)

[0066] And the objective lens for an endoscope preferably satisfies the following conditional expression (1-1). By making the corresponding value of the conditional expression (1-1) not fall below the lower limit value, the increase in the outer diameter of the lens can be suppressed.

[0067] 0.2 < Y / (fF×tanωf) < 0.6 (1-1)

[0068] For obtaining better characteristics, it is more preferable to set the upper limit values of conditional expression (1) and conditional expression (1-1) to 0.4. For example, the objective lens for an endoscope more preferably satisfies the following conditional expression (1-2).

[0069] 0.2 < Y / (fF×tanωf) < 0.4 (1-2)

[0070] When setting the focal length of the first lens group G1 to f1 and the focal length of the second lens group G2 to f2, the objective lens for an endoscope preferably satisfies the following conditional expression (2). Regarding the lower limit of conditional expression (2), since both the first lens group G1 and the second lens group G2 are groups having positive refractive power, f1 > 0 and f2 > 0, and thus 0 < f1 / f2. By satisfying conditional expression (2), it is easy to maintain the balance of various aberrations well, and thus it is beneficial to ensure good optical performance in the observation of the entire object distance range from the farthest point to the nearest point.

[0071] 0 < f1 / f2 < 0.25 (2)

[0072] For obtaining better characteristics, the objective lens for an endoscope preferably satisfies the following conditional expression (2-1).

[0073] 0 < f1 / f2 < 0.22 (2-1)

[0074] When setting the focal length of the single lens having negative refractive power closest to the object side of the first lens group G1 to fL1, it is preferable that the objective lens for an endoscope satisfies the following conditional expression (3). By preventing the corresponding value of conditional expression (3) from becoming below the lower limit value, it is beneficial to take into account both the wide-angleization and miniaturization of the lens system. Regarding the upper limit of conditional expression (3), since fL1 < 0 and fF > 0, fL1 / fF < 0.

[0075] -1.2 < fL1 / fF < 0 (3)

[0076] Moreover, the objective lens for an endoscope preferably satisfies the following conditional expression (3-1). By preventing the corresponding value of conditional expression (3-1) from becoming above the upper limit value, it is beneficial to ensure good optical performance in the observation of the entire object distance range from the farthest point to the nearest point.

[0077] -1.2 < fL1 / fF < -0.8 (3-1)

[0078] For obtaining better characteristics, it is more preferable to set the lower limit values of conditional expression (3) and conditional expression (3-1) to -1.1. For example, the objective lens for an endoscope more preferably satisfies the following conditional expression (3-2).

[0079] -1.1 < fL1 / fF < -0.8 (3-2)

[0080] When the F value in the state of focusing on the farthest object is set to 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, thus 0 < FNof / tanωf. By preventing the corresponding value of the conditional expression (4) from exceeding the upper limit value, it is beneficial to ensure a small F value and widen the angle of view of the lens system.

[0081] 0 < FNof / tanωof < 2 (4)

[0082] Moreover, the objective lens for an endoscope preferably satisfies the following conditional expression (4-1). By preventing the corresponding value of the conditional expression (4-1) from falling below the lower limit value, it is beneficial to ensure good optical performance in the entire object distance range from the farthest point to the nearest point.

[0083] 0.6 < FNof / tanωf < 2 (4-1)

[0084] To obtain better characteristics, it is more preferable to set the upper limit value of the conditional expression (4) and the conditional expression (4-1) to 1.6. For example, the objective lens for an endoscope more preferably satisfies the following conditional expression (4-2).

[0085] 0.6 < FNof / tanωf < 1.6 (4-2)

[0086] 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, thus 0 < fF / f1. By preventing the corresponding value of the conditional expression (5) from exceeding the upper limit value, it is beneficial to ensure good optical performance in the entire object distance range from the farthest point to the nearest point.

[0087] 0 < fF / f1 < 2 (5)

[0088] Moreover, the objective lens for an endoscope preferably satisfies the following conditional expression (5-1). By preventing the corresponding value of the conditional expression (5-1) from falling below the lower limit value, it is beneficial to suppress the enlargement of the lens system.

[0089] 0.5 < fF / f1 < 2 (5-1)

[0090] To obtain better characteristics, it is more preferable to set the upper limit value of the conditional expression (5) and the conditional expression (5-1) to 1. For example, the objective lens for an endoscope more preferably satisfies the following conditional expression (5-2).

[0091] 0.5 < fF / f1 < 1 (5-2)

[0092] The objective lens for an endoscope preferably satisfies the following conditional expression (6). Regarding the lower limit of conditional expression (6), since fF > 0 and f2 > 0, thus 0 < fF / f2. By ensuring that the corresponding value of conditional expression (6) does not exceed the upper limit value, it is beneficial to ensure good optical performance in the observation of the entire object distance range from the farthest point to the nearest point.

[0093] 0 < fF / f2 < 0.5 (6)

[0094] Moreover, the objective lens for an endoscope preferably satisfies the following conditional expression (6-1). By ensuring that the corresponding value of conditional expression (6-1) does not fall below the lower limit value, it is beneficial to suppress the enlargement of the lens system.

[0095] 0.1 < fF / f2 < 0.5 (6-1)

[0096] To obtain better characteristics, it is more preferable to set the upper limit value of conditional expression (6) and conditional expression (6-1) to 0.2. For example, the objective lens for an endoscope more preferably satisfies the following conditional expression (6-2).

[0097] 0.1 < fF / f2 < 0.2 (6-2)

[0098] The objective lens for an endoscope preferably satisfies the following conditional expression (7). Regarding the upper limit of conditional expression (7), since fL1 < 0 and f1 > 0, thus fL1 / f1 < 0. By ensuring that the corresponding value of conditional expression (7) does not fall below the lower limit value, it is beneficial to suppress the enlargement of the lens system.

[0099] -1.5 < fL1 / f1 < 0 (7)

[0100] Moreover, the objective lens for an endoscope preferably satisfies the following conditional expression (7-1). By ensuring that the corresponding value of conditional expression (7-1) does not exceed the upper limit value, it is beneficial to ensure good optical performance in the observation of the entire object distance range from the farthest point to the nearest point.

[0101] -1.5 < fL1 / f1 < -0.6 (7-1)

[0102] To obtain better characteristics, it is more preferable to set the lower limit value of conditional expression (7) and conditional expression (7-1) to -0.9. For example, the objective lens for an endoscope more preferably satisfies the following conditional expression (7-2).

[0103] -0.9 < fL1 / f1 < -0.6 (7-2)

[0104] In a structure where the first lens group G1 includes, in order from the object side to the image side, a first lens group G1a having a positive refractive power, an aperture stop St, and a first lens group G1b having a positive refractive power, the objective lens for an endoscope preferably satisfies at least one of the following conditional expressions (8), (9), (10), and (11). Here, the focal length of the first lens group G1a is set as f1a, and the focal length of the first lens group G1b is set as f1b.

[0105] 0 < fF / f1a < 1 (8)

[0106] 0 < f1 / f1a < 1 (9)

[0107] 0 < fF / f1b < 1 (10)

[0108] 0 < f1 / f1b < 1 (11)

[0109] Regarding the lower limit of the conditional expression (8), since fF > 0 and f1a > 0, 0 < fF / f1a. By preventing the corresponding value of the conditional expression (8) from exceeding the upper limit value, it is beneficial to ensure good optical performance in the entire object distance range from the farthest point to the nearest point.

[0110] Moreover, the objective lens for an endoscope preferably satisfies the following conditional expression (8-1). By preventing the corresponding value of the conditional expression (8-1) from falling below the lower limit value, it is beneficial to suppress the enlargement of the lens system.

[0111] 0.005 < fF / fla < 1 (8-1)

[0112] To obtain better characteristics, it is more preferable to set the upper limit value of the conditional expressions (8) and (8-1) to 0.6. For example, the objective lens for an endoscope more preferably satisfies the following conditional expression (8-2).

[0113] 0 < fF / fla < 0.6 (8-2)

[0114] Regarding the lower limit of the conditional expression (9), since f1 > 0 and f1a > 0, 0 < f1 / f1a. By preventing the corresponding value of the conditional expression (9) from exceeding the upper limit value, it is beneficial to ensure good optical performance in the entire object distance range from the farthest point to the nearest point.

[0115] Moreover, the objective lens for an endoscope preferably satisfies the following conditional expression (9-1). By preventing the corresponding value of the conditional expression (9-1) from falling below the lower limit value, it is beneficial to suppress the enlargement of the lens system.

[0116] 0.005 < f1 / fla < 1 (9-1)

[0117] In order to obtain better characteristics, it is more preferable to set the upper limit values of conditional expression (9) and conditional expression (9-1) to 0.7. For example, the objective lens for an endoscope more preferably satisfies the following conditional expression (9-2).

[0118] 0 < f1 / fla < 0.7 (9-2)

[0119] Regarding the lower limit of conditional expression (10), since fF > 0 and f1b > 0, then 0 < fF / f1b. By ensuring that the corresponding value of conditional expression (10) does not exceed the upper limit value, it is beneficial to ensure good optical performance in the entire object distance range from the farthest point to the nearest point during observation.

[0120] Moreover, 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 beneficial to suppress the enlargement of the lens system.

[0121] 0.1 < fF / flb < 1 (10-1)

[0122] In order to obtain better characteristics, it is more preferable to set the upper limit values of conditional expression (10) and conditional expression (10-1) to 0.3. For example, the objective lens for an endoscope more preferably satisfies the following conditional expression (10-2).

[0123] 0.1 < fF / flb < 0.3 (10-2)

[0124] Regarding the lower limit of conditional expression (11), since f1 > 0 and f1b > 0, then 0 < f1 / flb. By ensuring that the corresponding value of conditional expression (11) does not exceed the upper limit value, it is beneficial to ensure good optical performance in the entire object distance range from the farthest point to the nearest point during observation.

[0125] Moreover, 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 beneficial to suppress the enlargement of the lens system.

[0126] 0.1 < f1 / f1b < 1 (11-1)

[0127] In order to obtain better characteristics, it is more preferable to set the upper limit values of conditional expression (11) and conditional expression (11-1) to 0.4. For example, the objective lens for an endoscope more preferably satisfies the following conditional expression (11-2).

[0128] 0.1 < f1 / flb < 0.4 (11-2)

[0129] In a structure in which the first lens group G1 includes, from the object side to the image side, a lens group G1a having positive refractive power, an aperture stop St, and a lens group G1b having positive refractive power, and the lens group G1a having positive refractive power includes at least one negative lens and at least one positive lens joined together, the objective lens for an endoscope preferably satisfies the following conditional expression (13). Here, the average value of the Abbe numbers of all the positive lenses included in the above-mentioned joint lens of the lens group G1a having positive refractive power on the d-ray basis is set to v1p. The average value of the Abbe numbers of all the negative lenses included in the above-mentioned joint lens of the lens group G1a having positive refractive power on the d-ray basis is set to v1n. Regarding the lower limit of the conditional expression (13), since |v1p-v1n| is an absolute value, 0<|v1p-v1n|. By making the corresponding value of conditional expression (13) not exceed the upper limit value, it is possible to suppress the correction amount of axial chromatic aberration and lateral chromatic aberration from being excessive, which is advantageous in optimally controlling axial chromatic aberration and lateral chromatic aberration.

[0130] 0<|v 1p-v 1n|<40 (13)

[0131] Furthermore, the objective lens for endoscope preferably satisfies the following conditional expression (13-1). By making the corresponding value of conditional expression (13-1) not be less than the lower limit value, it is beneficial to suppress axial chromatic aberration and magnification chromatic aberration in the short wavelength region from the visible region to the wavelength of about 400nm.

[0132] 5.5<|v 1p-v 1n|<40 (13-1)

[0133] In order to obtain better characteristics, it is more preferable to set the upper limit values ​​of conditional expressions (13) and (13-1) to 37. For example, the endoscope objective lens more preferably satisfies the following conditional expression (13-2).

[0134] 5.5<|v 1p-v 1n|<37 (13-2)

[0135] In the structure of the second lens group G2 including a cemented lens formed by cementing at least one negative lens and at least one positive lens, it is preferred that the objective lens for endoscope satisfies the following conditional expression (14). Here, the average value of the Abbe numbers of all the positive lenses included in the cemented lens of the second lens group G2 on the d-ray basis is set to v 2p. The average value of the Abbe numbers of all the negative lenses included in the cemented lens of the second lens group G2 on the d-ray basis is set to v 2n. By making the corresponding value of the conditional expression (14) not be less than the lower limit value, it is beneficial to suppress the axial chromatic aberration and the chromatic aberration of magnification in the short wavelength region from the visible region to the wavelength of about 400nm. By making the corresponding value of the conditional expression (14) not be more than the upper limit value, it is possible to suppress the excessive correction amount of the axial chromatic aberration and the chromatic aberration of magnification, so it is beneficial to control the axial chromatic aberration and the chromatic aberration of magnification to the best.

[0136] 25<|v 2p-v 2n|<85 (14)

[0137] In order to obtain better characteristics, it is more preferable to set the lower limit value of conditional expression (14) to 26. Furthermore, it is more preferable to set the upper limit value of conditional expression (14) to 70. For example, the objective lens for an endoscope more preferably satisfies the following conditional expression (14-1).

[0138] 26<|v 2p-v 2n|<70 (14-1)

[0139] The objective lens for endoscope preferably satisfies the following conditional formula (12). Here, the distance that the second lens group G2 moves when focusing from the farthest point object to the closest point object is set to M. The paraxial imaging magnification of the whole system in the state of focusing on the farthest point object is set to βf. The paraxial imaging magnification of the whole system in the state of focusing on the closest point object is set to βn. βf and βn use lateral magnification instead of longitudinal magnification. As an example, in Figure 1 The distance M is shown in FIG. By making the corresponding value of conditional expression (12) not less than the lower limit value, it is beneficial to suppress the enlargement of the lens system. By making the corresponding value of conditional expression (12) not more than the upper limit value, it is possible to suppress the sharpening of the focus sensitivity when the second lens group G2 moves, which is beneficial to improve the ease of focusing.

[0140] 0.01<(fF / |M|)×(βf / βn)<1(12)

[0141] In order to obtain better characteristics, it is more preferable to set the lower limit value of conditional expression (12) to 0.15. Furthermore, it is more preferable to set the upper limit value of conditional expression (12) to 0.5. For example, the objective lens for endoscope preferably satisfies the following conditional expression (12-1).

[0142] 0.15<(fF / |M|)×(βf / βn)<0.5(12-1)

[0143] in addition, Figure 1 The example shown is only an example, and various modifications can be made within the scope of the technical purpose of the present invention. For example, the number of lenses included in each lens group can be the same as Figure 1 Furthermore, the structure of the lenses included in each lens group can also be set to be different from Figure 1 Examples of different structures.

[0144] For example, the 1a-th lens group G1a may be configured to include, in order from the object side to the image side, a single lens with negative refractive power whose plane faces the object side, a negative lens, and a positive lens. Alternatively, the 1a-th lens group G1a may also be configured to include, in order from the object side to the image side, a single lens with negative refractive power whose plane faces the object side, a single lens with positive refractive power, a negative lens, and a positive lens. When the 1a-th lens group G1a includes a cemented lens formed by cementing at least one negative lens and at least one positive lens, the cemented lens may be disposed adjacent to the object side of the aperture stop St.

[0145] The 1b-th lens group G1b may be configured to include a positive lens and a negative lens in order from the object side to the image side. In this case, the positive lens and the negative lens of the 1b-th lens group G1b may be bonded to each other. The 1b-th lens group G1b may also be configured to include one bonded lens. Alternatively, the 1b-th lens group G1b may also be configured to include one positive lens.

[0146] The second lens group G2 may be configured as a cemented lens including a negative lens and a positive lens cemented in sequence from the object side. Alternatively, the second lens group G2 may be configured as a cemented lens including a positive lens and a negative lens cemented in sequence from the object side.

[0147] The above-mentioned preferred structures and feasible structures, including structures related to conditional expressions, can be arbitrarily combined within a range that does not conflict with each other, and are preferably appropriately and selectively adopted according to the required specifications.

[0148] As an example, a preferred embodiment of the objective lens for an endoscope of the present invention includes, in sequence 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 point object to the nearest point object, the first lens group G1 is fixed relative to the image plane Sim, and only the second lens group G2 moves along the optical axis Z. The first lens group G1 includes a single lens having negative refractive power on the side closest to the object. The objective lens for an endoscope satisfies the above-mentioned conditional expressions (1), (2) and (3).

[0149] Next, with reference to the accompanying drawings, the embodiments of the endoscope objective lens of the present invention are described. In addition, the reference symbols on each lens and each group in the cross-sectional view of each embodiment are used independently in each embodiment to avoid the complication of the description and the accompanying drawings caused by the increase in the number of digits of the reference symbols. Therefore, even if the same reference symbols are marked in the accompanying drawings of different embodiments, they are not necessarily the same structure.

[0150] [Example 1]

[0151] A cross-sectional view showing the structure of the endoscope objective lens of Example 1 is shown in FIG. Figure 1 and Figure 2As shown, the diagramming method is as described above, so some repeated descriptions are omitted here. The endoscope objective lens of Example 1 includes, from the object side to the image side, a first lens group G1 with positive refractive power and a second lens group G2 with positive refractive power. When focusing from the farthest point object to the closest point object, the first lens group G1 is fixed relative to the image plane Sim, and the second lens group G2 moves toward the object side. The first lens group G1 includes, from the object side to the image side, a 1a lens group G1a with positive refractive power, an aperture stop St, and a 1b lens group G1b with positive refractive power. The above is an overview of the endoscope objective lens of Example 1.

[0152] Each group of the endoscope objective lens of Example 1 is constructed as follows. The 1a lens group G1a includes lens L11, optical component P1, lens L12 and lens L13 in order from the object side to the image side. The 1b lens group G1b includes lens L14 and lens L15 in order from the object side to the image side. The second lens group G2 includes lens L21 and lens L22 in order from the object side to the image side. Lens L12 and lens L13 are bonded to each other. Lens L14 and lens L15 are bonded to each other. Lens L21 and lens L22 are bonded to each other. Lens L11 is a single lens.

[0153] Regarding the endoscope objective lens of Example 1, basic lens data is shown in Table 1, and specifications and variable surface intervals are shown in Table 2.

[0154] The table of basic lens data is as follows. The "Sn" column shows the surface number when the surface closest to the object side is the first surface and the number increases one by one 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 the surface adjacent to its image side. The "Nd" column shows the refractive index of each lens with respect to the d-ray. The "vd" column shows the Abbe number of each lens based on the d-ray.

[0155] In the table of basic lens data, the sign of the radius of curvature of the surface that makes the convex shape face the object side is set to positive, and the sign of the radius of curvature of the surface that makes the convex shape face the image side is set to negative. In Table 1, the surface number and the term (St) are marked in the surface number column corresponding to the aperture stop St. Table 1 also records the optical component PP. The value at the bottom of the D column in the table is the interval between the surface closest to the image side in the table and the image surface Sim. For the variable surface interval during focusing, the symbol DD[] is used, and the surface number on the object side of the interval is marked in [] and recorded in the surface interval column.

[0156] Table 2 shows the focal length, back focal length at air conversion distance, F value, 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 closest point observation state. In addition, the object distance refers to 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 full angle of view column indicates that the unit is degree. The values ​​shown in Table 2 are values ​​when the d-ray is used as the reference.

[0157] In the data of each table, degrees are used as the unit of angle and mm (millimeter) is used as the unit of length. Since the optical system can be used at a magnified or reduced ratio, other appropriate units may be used. In addition, the values ​​rounded to a preset number of digits are recorded in each table shown below.

[0158] [Table 1]

[0159] Example 1

[0160] Sn R D Nd vd 1 0.2500 2.00100 29.13 2 0.6100 0.3200 3 0.3000 1.51633 64.14 4 0.3700 5 0.2600 1.59522 67.73 6 0.7062 0.7400 1.68893 31.07 7 1.4691 0.1550 8(St) 0.1050 9 0.5700 1.69680 55.53 10 0.5775 0.2500 2.00069 25.46 11 1.3023 DD

[11] 12 9.9601 0.2500 2.00069 25.46 13 1.9932 0.7200 1.43875 94.66 14 1.3023 DD

[14] 15 1.8400 1.88299 40.78 16 0.1500 1.51633 64.06 17 0.0100

[0161] [Table 2]

[0162] Example 1

[0163] Farthest point observation state Closest point observation status focal length 0.695 0.661 Back focus 1.491 1.705 F-number 4.01 3.91 Maximum full viewing angle [°] 137.7 143.4 Maximum image height 0.675 0.675 Object distance 20.00 2.25 Paraxial imaging magnification 0.0340 0.2428 DD

[11] 0.5400 0.1892 DD

[14] 0.4288 0.7796

[0164] exist Figure 3 , various aberration diagrams of the endoscope objective lens of Example 1 are shown. Figure 3 In FIG. 1 , the spherical aberration diagram, the astigmatism diagram, the distortion diagram, and the lateral chromatic aberration diagram are shown from the left. Figure 3 In FIG. 1 , the upper section shows various aberration diagrams of the farthest point observation state, and the lower section shows various aberration diagrams of the closest point observation state. Figure 3 In the figure, the value of the object distance is shown on the right side of "Distance:". In the spherical aberration diagram, the aberrations at the d-ray, C-ray, F-ray and h-ray are represented by solid lines, long dashed lines, short dashed lines and single-dash lines, respectively. In the astigmatism diagram, the aberrations at the d-ray in the sagittal direction are represented by solid lines, and the aberrations at the d-ray in the meridional direction are represented by short dashed lines. In the distortion aberration diagram, the aberrations at the d-ray are represented by solid lines. In the chromatic aberration of magnification diagram, the aberrations under the C-ray, F-ray and h-ray are represented by long dashed lines, short dashed lines and single-dash lines, respectively. In the spherical aberration diagram, the value of the F value in each state is shown after "FNo.=". In the other aberration diagrams, the value of the maximum half viewing angle in each state is shown after "ω=".

[0165] Unless otherwise specified, the symbols, meanings, recording methods, and graphical representation methods of various data related to the above-mentioned embodiment 1 are the same in the following embodiments, and therefore, repeated descriptions are omitted below.

[0166] [Example 2]

[0167] A cross-sectional view of the structure of the endoscope objective lens of Example 2 is shown in FIG. Figure 4 The endoscope objective lens of Example 2 has the same structure as the endoscope objective lens of Example 1.

[0168] Each group of the endoscope objective lens of Example 2 is constructed as follows. The 1a lens group G1a includes lens L11, optical component P1, lens L12 and lens L13 in order from the object side to the image side. The 1b lens group G1b includes lens L14 and lens L15 in order from the object side to the image side. The second lens group G2 includes lens L21 and lens L22 in order from the object side to the image side. Lens L12 and lens L13 are bonded to each other. Lens L14 and lens L15 are bonded to each other. Lens L21 and lens L22 are bonded to each other. Lens L11 is a single lens.

[0169] Regarding the endoscope objective lens of Example 2, basic lens data is shown in Table 3, specifications and variable surface spacing are shown in Table 4, and various aberration diagrams are shown in Table 5. Figure 5 .

[0170] [Table 3]

[0171] Example 2

[0172] Sn R D Nd vd 1 ∞ 0.2500 2.00100 29.13 2 0.6442 0.3000 3 ∞ 0.3000 1.51633 64.14 4 ∞ 0.1400 5 -4.6681 0.2600 1.69680 55.53 6 0.8922 0.9900 1.80518 25.42 7 -1.5928 0.1350 8(St) ∞ 0.0750 9 ∞ 0.6300 1.69680 55.53 10 -0.5775 0.2500 2.00069 25.46 11 -1.1757 DD

[11] 12 8.3054 0.2500 2.00069 25.46 13 1.3800 0.7700 1.51742 52.43 14 -1.3800 DD

[14] 15 ∞ 1.8500 1.88299 40.78 16 ∞ 0.1500 1.51633 64.06 17 ∞ 0.0100

[0173] [Table 4]

[0174] Example 2

[0175] Farthest point Closest point focal length 0.678 0.643 Back focus 1.511 1.732 F-number 3.90 3.80 Maximum full viewing angle [°] 153.0 172.4 Maximum image height 0.710 0.710 Object distance 20.00 2.25 Paraxial imaging magnification -0.0331 -0.2358 DD

[11] 0.4900 0.1398 DD

[14] 0.4422 0.7924

[0176] [Example 3]

[0177] A cross-sectional view of the structure of the endoscope objective lens of Example 3 is shown in FIG. Figure 6 The endoscope objective lens of Example 3 has the same structure as that of the endoscope objective lens of Example 1.

[0178] Each group of the endoscope objective lens of Example 3 is constructed as follows. The 1a lens group Gla includes lens L11, optical component P1, lens L12 and lens L13 in order from the object side to the image side. The 1b lens group G1b includes lens L14 and lens L15 in order from the object side to the image side. The 2nd lens group G2 includes lens L21 and lens L22 in order from the object side to the image side. Lens L12 and lens L13 are bonded to each other. Lens L14 and lens L15 are bonded to each other. Lens L21 and lens L22 are bonded to each other. Lens L11 is a single lens.

[0179] Regarding the endoscope objective lens of Example 3, basic lens data is shown in Table 5, specifications and variable surface spacing are shown in Table 6, and various aberration diagrams are shown in Table 7. Figure 7 .

[0180] [Table 5]

[0181] Example 3

[0182] Sn R D Nd vd 1 ∞ 0.2500 2.00100 29.13 2 0.5775 0.3300 3 ∞ 0.2500 2.00100 29.13 4 ∞ 0.3600 5 3.5051 0.3000 1.59522 67.73 6 0.7768 0.9200 1.68893 31.07 7 -1.2496 0.1250 8(St) ∞ 0.0350 9 ∞ 0.5800 1.69680 55.53 10 -0.5775 0.2500 2.00069 25.46 11 -1.5391 DD

[11] 12 -3.5051 0.2500 2.00069 25.46 13 3.8959 0.6400 1.69680 55.53 14 -1.3800 DD

[14] 15 ∞ 1.8500 1.88299 40.78 16 ∞ 0.1500 1.51633 64.06 17 ∞ 0.0100

[0183] [Table 6]

[0184] Example 3

[0185] Farthest point Closest point focal length 0.711 0.662 Back focus 1.499 1.751 F-number 2.99 2.83 Maximum full viewing angle [°] 137.0 148.3 Maximum image height 0.675 0.675 Object distance 20.00 2.25 Paraxial imaging magnification -0.0347 -0.2441 DD

[11] 0.5200 0.1304 DD

[14] 0.4319 0.8215

[0186] [Example 4]

[0187] A cross-sectional view of the structure of the endoscope objective lens of Example 4 is shown in Figure 8 The endoscope objective lens of the fourth embodiment has the same structure as the endoscope objective lens of the first embodiment.

[0188] Each group of the endoscope objective lens of Example 4 is constructed as follows. The 1a lens group G1a includes lens L11, lens L12, lens L13 and lens L14 in order from the object side to the image side. The 1b lens group G1b includes lens L15. The 2nd lens group G2 includes lens L21 and lens L22 in order from the object side to the image side. Lens L13 and lens L14 are cemented to each other. Lens L21 and lens L22 are cemented to each other. Lens L11, lens L12 and lens L15 are single lenses.

[0189] Regarding the endoscope objective lens of Example 4, basic lens data is shown in Table 7, specifications and variable surface spacing are shown in Table 8, and various aberration diagrams are shown in Table 9. Fig. 9 .

[0190] [Table 7]

[0191] Example 4

[0192] Sn R D Nd vd 1 ∞ 0.2500 2.00100 29.13 2 0.6007 0.2986 3 4.6684 0.9452 1.94595 17.98 4 -2.1032 0.1514 5 -1.6042 0.2500 1.95375 32.32 6 0.7224 0.5800 1.72342 37.95 7 -0.9017 0.0650 8(St) ∞ 0.0350 9 ∞ 0.3370 1.43875 94.66 10 -1.4693 DD

[10] 11 -2.2858 0.5585 1.53775 74.70 12 -0.6823 0.2500 1.94595 17.98 13 -1.0154 DD

[13] 14 ∞ 1.8000 1.55919 53.90 15 ∞ 0.1500 1.51633 64.06 16 ∞ 0.0100

[0193] [Table 8]

[0194] Example 4

[0195] Farthest point Closest point focal length 0.713 0.680 Back focus 1.774 1.931 F-number 2.95 2.87 Maximum full viewing angle [°] 155.6 168.5 Maximum image height 0.715 0.715 Object distance 20.00 3.00 Paraxial imaging magnification -0.0348 -0.1962 DD

[10] 0.6113 0.3464 DD

[13] 0.5357 0.8006

[0196] [Example 5]

[0197] A cross-sectional view showing the structure of the endoscope objective lens of Example 5 is shown in FIG. Fig.10 The endoscope objective lens of Example 5 has the same structure as that of the endoscope objective lens of Example 1.

[0198] Each group of the endoscope objective lens of Example 5 is constructed as follows. The 1a lens group G1a includes lens L11, lens L12 and lens L13 in order from the object side to the image side. The 1b lens group G1b includes lens L14. The 2nd lens group G2 includes lens L21 and lens L22 in order from the object side to the image side. Lens L12 and lens L13 are cemented to each other. Lens L21 and lens L22 are cemented to each other. Lens L11 and lens L14 are single lenses.

[0199] Regarding the endoscope objective lens of Example 5, basic lens data is shown in Table 9, specifications and variable surface spacing are shown in Table 10, and various aberration diagrams are shown in Table 11. Fig.11 .

[0200] [Table 9]

[0201] Example 5

[0202] Sn R D Nd vd 1 ∞ 0.2500 1.88299 40.78 2 0.6649 0.8236 3 3.7510 0.3500 1.79472 48.53 4 0.5704 0.9967 1.57981 40.04 5 0.9501 0.1000 6(St) ∞ 0.0350 7 ∞ 0.4074 1.47510 83.83 8 -1.8556 DD[8] 9 -2.5640 0.6457 1.72425 55.29 10 -0.7402 0.2500 1.94595 17.98 11 -1.3417 DD

[11] 12 ∞ 1.9400 1.55919 53.90 13 ∞ 0.1500 1.51633 64.06 14 ∞ 0.0100

[0203] [Table 10]

[0204] Example 5

[0205] Farthest point Closest point focal length 0.696 0.646 Back focus 1.762 2.018 F-number 3.87 3.77 Maximum full viewing angle [°] 147.3 160.4 Maximum image height 0.700 0.700 Object distance 20.00 1.50 Paraxial imaging magnification -0.0338 0.3163 DD[8] 0.5221 0.0857 DD

[11] 0.4326 0.8690

[0206] Table 11 shows the corresponding values ​​of conditional expressions (1) to (14) of the endoscope objective lenses of Examples 1 to 5. Table 11 shows the values ​​of the d-ray reference. The corresponding values ​​of the examples shown in Table 11 may be used as the upper limit or lower limit of the conditional expression to set the preferred range of the conditional expression.

[0207] [Table 11]

[0208]

[0209]

[0210] Although the endoscope objective lenses of Examples 1 to 5 are small in size, the total viewing angle in the farthest point observation state is 135° or more, thereby ensuring a wide viewing angle. Furthermore, the performance of the endoscope objective lenses of Examples 1 to 5 does not change much between the farthest point observation state and the closest point observation state, and each aberration is well corrected in both states to maintain high optical performance.

[0211] Next, an endoscope according to an embodiment of the present invention will be described. Fig.12 Detailed description of the overall configuration of an endoscope according to an embodiment of the present invention is shown in FIG. Fig.12The endoscope 100 shown mainly includes an operating portion 102, an insertion portion 104, and a universal cord 106 connected to a connector portion (not shown). Most of the insertion portion 104 is a soft portion 107 that can be bent in any direction along the insertion path, and a bending portion 108 is connected to the front end of the soft portion 107, and a front end portion 110 is connected to the front end of the bending portion 108. The bending portion 108 is provided to direct the front end portion 110 in a desired direction, and a bending operation knob 109 provided on the operating portion 102 can be turned to perform a bending operation. An endoscope objective lens 1 and an imaging element 2 according to an embodiment of the present invention are provided at the inner front end of the front end portion 110. The imaging element 2 is, for example, a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductot). The imaging element 2 is configured so that its imaging surface coincides with the image surface of the endoscope objective lens 1. In addition, Fig.12 The endoscope objective lens 1 and the imaging element 2 shown are conceptual diagrams.

[0212] The above embodiments and examples are used to illustrate the technology of the present invention, but the technology of the present invention is not limited to the above embodiments and examples, and various modifications are possible. For example, the radius of curvature, surface spacing, refractive index and dispersion coefficient of each lens are not limited to the values ​​shown in the above numerical examples, and other values ​​can be used.

[0213] The following supplementary notes are further disclosed with respect to the above-mentioned embodiments and examples.

[0214] [Note 1]

[0215] An objective lens for an endoscope 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,

[0216] When focusing from the farthest object to the closest object, the first lens group is fixed relative to the image plane, and only the second lens group moves along the optical axis.

[0217] The first lens group includes a single lens having negative refractive power on the side closest to the object.

[0218] When the maximum image height is set to Y,

[0219] Set the focal length of the entire system when focusing on the farthest object to fF.

[0220] The maximum half angle of view when focusing on the farthest object is set to ωf.

[0221] The focal length of the first lens group is set to f1,

[0222] Set the focal length of the second lens group to f2,

[0223] when setting the focal length of the single lens to fL1,

[0224] the objective lens for an endoscope satisfies the conditional expressions (1), (2), and (3) represented by 0 < Y / (fF×tanωf) < 0.6 (1), 0 < f1 / f2 < 0.25 (2), and -1.2 < fL1 / fF < 0 (3).

[0225] [Supplementary Note 2]

[0226] The objective lens for an endoscope according to Supplementary Note 1 satisfies the conditional expression (4) represented by 0 < FNof / tanωf < 2 (4) when setting the F value in the state of focusing on an object at the farthest point to FNof.

[0227] [Supplementary Note 3]

[0228] The objective lens for an endoscope according to Supplementary Note 1 or Supplementary Note 2 satisfies the conditional expression (5) represented by 0 < fF / f1 < 2 (5).

[0229] [Supplementary Note 4]

[0230] The objective lens for an endoscope according to any one of Supplementary Notes 1 to 3 satisfies the conditional expression (6) represented by 0 < fF / f2 < 0.5 (6).

[0231] [Supplementary Note 5]

[0232] The objective lens for an endoscope according to any one of Supplementary Notes 1 to 4 satisfies the conditional expression (7) represented by -1.5 < fL1 / f1 < 0 (7).

[0233] [Supplementary Note 6]

[0234] The objective lens for an endoscope according to any one of Supplementary Notes 1 to 5, wherein,

[0235] the lens surface on the object side of the single lens is a plane.

[0236] [Supplementary Note 7]

[0237] The objective lens for an endoscope according to any one of Supplementary Notes 1 to 6, wherein,

[0238] the first lens group includes, in order from the object side to the image side, a first a-lens group having a positive refractive power, an aperture stop, and a first b-lens group having a positive refractive power,

[0239] when setting the focal length of the first a-lens group to f1a, the objective lens for an endoscope satisfies the conditional expression (8) represented by 0 < fF / fla < 1 (8).

[0240] [Supplementary Note 8]

[0241] The objective lens for an endoscope according to any one of Supplementary Notes 1 to 7, wherein,

[0242] the first lens group includes, in order from the object side to the image side, a first a lens group having a positive refractive power, an aperture stop, and a first b lens group having a positive refractive power,

[0243] when the focal length of the first a lens group is set to f1a, the objective lens for an endoscope satisfies the conditional expression (9) represented by 0 < f1 / fla < 1 (9).

[0244] [Supplementary Note 9]

[0245] The objective lens for an endoscope according to any one of Supplementary Notes 1 to 8, wherein,

[0246] the first lens group includes, in order from the object side to the image side, a first a lens group having a positive refractive power, an aperture stop, and a first b lens group having a positive refractive power,

[0247] when the focal length of the first b lens group is set to f1b, the objective lens for an endoscope satisfies the conditional expression (10) represented by 0 < fF / flb < 1 (10).

[0248] [Supplementary Note 10]

[0249] The objective lens for an endoscope according to any one of Supplementary Notes 1 to 9, wherein,

[0250] the first lens group includes, in order from the object side to the image side, a first a lens group having a positive refractive power, an aperture stop, and a first b lens group having a positive refractive power,

[0251] when the focal length of the first b lens group is set to f1b,

[0252] the objective lens for an endoscope satisfies the conditional expression (11) represented by 0 < f1 / f1b < 1 (11).

[0253] [Supplementary Note 11]

[0254] The objective lens for an endoscope according to any one of Supplementary Notes 1 to 10, wherein,

[0255] when the distance that the second lens group moves when focusing from the farthest object point to the nearest object point is set to M, the paraxial imaging magnification of the entire system in the state of focusing on the farthest object point is set to βf, and the paraxial imaging magnification of the entire system in the state of focusing on the nearest object point is set to βn,

[0256] The endoscope objective lens satisfies conditional expression (12) represented by 0.01<(fF / |M|)×(βf / βn)<1(12).

[0257] [Note 12]

[0258] The objective lens for endoscope according to any one of Supplementary Notes 1 to 11, wherein

[0259] The first lens group includes, from the object side to the image side, a lens group 1a having positive refractive power, an aperture stop, and a lens group 1b having positive refractive power.

[0260] The 1a-th lens group includes a cemented lens formed by cementing at least one negative lens and at least one positive lens.

[0261] [Note 13]

[0262] The objective lens for endoscope according to Supplementary Note 12, wherein:

[0263] When the average value of the Abbe numbers of all the positive lenses included in the cemented lens of the 1a-th lens group on the d-ray basis is set to v 1p,

[0264] When the average value of the Abbe numbers of all negative lenses included in the cemented lens of the 1a-th lens group on the d-ray basis is set to v 1n,

[0265] The endoscope objective lens satisfies the conditional expression (13) represented by 0<|v 1p - V 1n|<40(13).

[0266] [Note 14]

[0267] The objective lens for endoscope according to any one of Supplementary Notes 1 to 13, wherein

[0268] The second lens group includes a cemented lens formed by cementing at least one negative lens and at least one positive lens.

[0269] [Note 15]

[0270] The objective lens for endoscope according to any one of Supplementary Notes 1 to 14, wherein

[0271] The second lens group includes a cemented lens in which at least one negative lens and at least one positive lens are cemented together.

[0272] [Note 16]

[0273] The objective lens for endoscope according to Supplementary Note 14, wherein:

[0274] When the average value of the Abbe numbers of all the positive lenses included in the cemented lens of the second lens group on a d-ray basis is set to v 2p,

[0275] When the average value of the Abbe numbers of all negative lenses included in the cemented lens of the second lens group on a d-ray basis is set to v 2n,

[0276] The endoscope objective lens satisfies conditional expression (14) represented by 25<|v 2p - v 2n|<85(14).

[0277] [Note 17]

[0278] An endoscope comprising the endoscope objective lens according to any one of Supplementary Notes 1 to 16.

Claims

1. An objective lens for an endoscope, comprising, 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, When focusing from the farthest object to the closest object, the first lens group is fixed relative to the 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 on the side closest to the object. When the maximum image height is set to Y, The focal length of the entire system when focusing on the farthest object is set to fF, and the maximum half angle of view when focusing on the farthest object is set to ωf. The focal length of the first lens group is set to f1, The focal length of the second lens group is set to f2, When the focal length of the single lens is set to fL1, The endoscope objective lens satisfies 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) are represented.

2. The objective lens for endoscope according to claim 1, wherein when the F value in the state of focusing on the farthest point object is set to FNof, 0 <FNof / tanωf<2 (4) The conditional expression (4) is represented.

3. The endoscope objective lens according to claim 1 or 2, which satisfies 0 <fF / f1<2 (5) The conditional expression (5) is represented.

4. The endoscope objective lens according to claim 1 or 2, which satisfies 0 <fF / f2<0.5 (6) The conditional expression (6) is represented.

5. The endoscope objective lens according to claim 1 or 2, which satisfies -1.5 <fL1 / f1<0 (7) The conditional expression (7) is represented.

6. The endoscope objective lens according to claim 1 or 2, wherein: The lens surface on the object side of the single lens is a flat surface.

7. The endoscope objective lens according to claim 1 or 2, wherein: The first lens group includes, from the object side to the image side, a lens group 1a having positive refractive power, an aperture stop, and a lens group 1b having positive refractive power. When the focal length of the lens group 1a is set to fla, the endoscope objective lens satisfies 0 <fF / f1a<1 (8) The conditional expression (8) is represented.

8. The endoscope objective lens according to claim 1 or 2, wherein: The first lens group includes, from the object side to the image side, a lens group 1a having positive refractive power, an aperture stop, and a lens group 1b having positive refractive power. When the focal length of the 1a-th lens group is set to f1a, the endoscope objective lens satisfies 0 <f1 / f1a<1 (9) The conditional expression (9) is represented.

9. The endoscope objective lens according to claim 1 or 2, wherein: The first lens group includes, from the object side to the image side, a lens group 1a having positive refractive power, an aperture stop, and a lens group 1b having positive refractive power. When the focal length of the 1b-th lens group is set to f1b, the endoscope objective lens satisfies 0 <fF / f1b<1 (10) The conditional expression (10) is represented.

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

11. The endoscope objective lens according to claim 1 or 2, wherein: When focusing from the farthest object to the closest object, the distance the second lens group moves is set to M. The paraxial imaging magnification of the entire system when focusing on the farthest object is set to βf. When the paraxial imaging magnification of the entire system is set to βn when the object is focused at the nearest point, The endoscope objective lens satisfies 0.01<(fF / |M|)×(βf / βn)<1 (12) The conditional expression (12) is represented.

12. The endoscope objective lens according to claim 1 or 2, wherein: The first lens group includes, from the object side to the image side, a lens group 1a having positive refractive power, an aperture stop, and a lens group 1b having positive refractive power. The 1a-th lens group includes a cemented lens formed by cementing at least one negative lens and at least one positive lens.

13. The endoscope objective lens according to claim 12, wherein: When the average value of the Abbe numbers of all the positive lenses included in the cemented lens of the 1a-th lens group on the d-ray basis is set to v1p, When the average value of the Abbe numbers of all negative lenses included in the cemented lens of the 1a-th lens group on the d-ray basis is set to v1n, The endoscope objective lens satisfies 0<|v1p-Vln|<40 (13) The conditional expression (13) is represented.

14. The endoscope objective lens according to claim 1 or 2, wherein: The second lens group includes a cemented lens formed by cementing at least one negative lens and at least one positive lens.

15. The endoscope objective lens according to claim 1 or 2, 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.

16. The endoscope objective lens according to claim 14, wherein: When the average value of the Abbe numbers of all the positive lenses included in the cemented lens of the second lens group on a d-ray basis is set to v 2p, When the average value of the Abbe numbers of all negative lenses included in the cemented lens of the second lens group on a d-ray basis is set to v 2n, The endoscope objective lens satisfies 25<|v 2p-v 2n|<85 (14) The conditional expression (14) is represented. 17 . An endoscope comprising the endoscope objective lens according to claim 1 .

Images