Objective lens for endoscope and endoscope

Abstract

The present application provides an objective lens for endoscope and an endoscope with the objective lens, which can switch focus between far point object and near point object, has wide depth of field in near point object observation state, and has good optical performance. The objective lens for endoscope comprises an aperture, a lens arranged closer to the object side than the aperture, at least one image side lens surface being concave, and at least one set of joint lenses arranged closer to the image side than the aperture, a part of the whole system lenses being focused from the farthest point object to the nearest point object by moving along the optical axis, having a total angle of view of 120 degrees or more in the state of focusing on the farthest point object and the state of focusing on the nearest point object, and satisfying a predetermined conditional expression.

Description

TECHNICAL FIELD

[0001] The present application relates to an objective lens for an endoscope and an endoscope. BACKGROUND

[0002] In the past, as an objective lens for an endoscope that focuses from a far point object to a near point object, an objective lens for an endoscope described in Patent Literature 1 is known.

[0003] Patent Literature 1: Japanese Patent Publication No. 2016-114870

[0004] In recent years, an objective lens for an endoscope that can switch focus from a far point object to a near point object and has a wide depth of field in a near point object observation state is required. SUMMARY

[0005] The present application was completed in view of the above circumstances, and aims to provide an objective lens for an endoscope that can switch focus from a far point object to a near point object, has a wide depth of field in a near point object observation state, and has good optical performance, and an endoscope provided with the objective lens.

[0006] The first objective lens for an endoscope of the present application is provided with: an aperture; a lens disposed closer to an object side than the aperture, a less one piece of an image side lens face being a concave face; and at least one set of a cemented lens disposed closer to an image side than the aperture, a part of the entire system focusing from a far point object to a near point object by moving along an optical axis, having a total angle of view of 120 degrees or more in a state of focusing on the far point object and a state of focusing on the near point object, in a case where a focal length of the entire system in the state of focusing on the near point object is set as fn, a half angle of view in the state of focusing on the near point object is set as θn, and a maximum image height in the state of focusing on the near point object is set as Hn, the following conditional expression (1) is satisfied.

[0007] 1.4 < fn x (tan θn) / Hn < 2 (1)

[0008] The second objective lens for an endoscope of the present application is provided with: an aperture; a lens disposed closer to an object side than the aperture, at least one piece of an image side lens face being a concave face; and at least one set of a cemented lens disposed closer to an image side than the aperture, a part of the entire system focusing from a far point object to a near point object by moving along an optical axis, having a total angle of view of 120 degrees or more in a state of focusing on the far point object and a state of focusing on the near point object, in a case where an F number in the state of focusing on the near point object is set as Fn, and an F number in the state of focusing on the far point object is set as Ff, the following conditional expression (2) is satisfied.

[0009] 1.1 < Fn / Ff < 3 (2)

[0010] In the following, the first endoscope objective lens of the present application and the second endoscope objective lens of the present application are collectively referred to as the endoscope objective lens of the present application.

[0011] In a case where a focal length of the entire system in a state where the closest point object is in focus is set as fn, a half viewing angle in a state where the closest point object is in focus is set as θn, and a maximum image height in a state where the closest point object is in focus is set as Hn, the endoscope objective lens of the present application preferably satisfies the following conditional expression (1-1), and more preferably satisfies the following conditional expression (1-2).

[0012] 1.5 < fn x (tan θn) / Hn < 1.9 (1-1)

[0013] 1.6 < fn x (tan θn) / Hn < 1.9 (1-2)

[0014] In a case where an F number in a state where the closest point object is in focus is set as Fn, and an F number in a state where the farthest point object is in focus is set as Ff, the endoscope objective lens of the present application preferably satisfies the following conditional expression (2-1), and more preferably satisfies the following conditional expression (2-2).

[0015] 1.2 < Fn / Ff < 2.5 (2-1)

[0016] 1.2 < Fn / Ff < 2 (2-2)

[0017] In a case where a focal length of the entire system in a state where the closest point object is in focus is set as fn, and a focal length of the entire system in a state where the farthest point object is in focus is set as ff, the endoscope objective lens of the present application preferably satisfies the following conditional expression (3), and more preferably satisfies the following conditional expression (3-1).

[0018] 0.7 < fn / ff < 1.2 (3)

[0019] 0.8 < fn / ff < 1.1 (3-1)

[0020] The endoscope objective lens of the present application can be configured as follows: including an aperture member having an opening portion, and an F number is changed by moving the aperture member when focusing is performed. In this configuration, in a case where a distance on the optical axis between a lens disposed continuously with the aperture on the object side of the aperture and a lens disposed continuously with the aperture on the image side of the aperture in a state where the farthest point object is in focus is set as Df, and a focal length of the entire system in a state where the farthest point object is in focus is set as ff, the following conditional expression (4) is preferably satisfied, and the following conditional expression (4-1) is more preferably satisfied.

[0021] 0.3 < ff / Df < 15 (4)

[0022] 0.5 < ff / Df < 12 (4-1)

[0023] The objective lens for an endoscope according to the present application can be configured as follows: including, on the object side closer than the stop, a lens having a meniscus shape in which the object side lens surface is convex near the optical axis and the positive refractive power becomes stronger as it approaches the periphery.

[0024] In a case where the focal length of the entire system in a state where the closest point object is in focus is set as fn, and the interval on the optical axis of the lens disposed on the object side of the stop and the stop in a state where the closest point object is in focus is set as Dsn, it is preferable to satisfy the following conditional expression (5), and more preferably to satisfy the following conditional expression (5-1).

[0025] 0.3 < fn / Dsn < 2.5 (5)

[0026] 0.5 < fn / Dsn < 2 (5-1)

[0027] The object side lens surface of the lens disposed on the object side of the stop is preferably convex.

[0028] The objective lens for an endoscope according to the present application can be configured as follows: the lens group including the lens closest to the image side of the entire system is focused from the farthest point object to the closest point object by moving integrally along the optical axis.

[0029] The objective lens for an endoscope according to the present application can be configured as follows: the lens group including at least one lens disposed continuously with the stop is focused from the farthest point object to the closest point object by moving integrally along the optical axis.

[0030] The endoscope according to the present application is provided with the objective lens for an endoscope according to the present application.

[0031] In addition, "composed of," "consisting of" in the present specification means that, in addition to the recited components, it can include: a lens having substantially no refractive power; a stop, a filter, a cover glass, and the like, optical components other than the lens; and a lens flange, a lens barrel, an imaging element, and the like.

[0032] In the present specification, the meaning of "a lens having positive refractive power" and "a positive lens" is the same. The meaning of "a lens having negative refractive power" and "a negative lens" is the same. A "single lens" means a lens that is not cemented. However, a compound aspherical lens (a lens in which a spherical lens and an aspherical shape film formed on the spherical lens are integrated, and the entire lens functions as one aspherical lens) is not regarded as a cemented lens, but is handled as a single lens. Unless otherwise specified, the sign of the refractive power and the surface shape related to the lens including an aspherical surface are considered in the paraxial region.

[0033] In the present specification, "the entire system" means an objective lens for an endoscope. The "focal length" used in the conditional expression is the paraxial focal length. The values used in the conditional expression are values when the d line is used as a reference. The "d line", "C line", "F line", and "e line" described in the present specification are bright lines, the wavelength of the d line is 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 e line is 546.07 nm (nanometers).

[0034] Effects of the Invention

[0035] According to the present application, it is possible to provide an objective lens for an endoscope and an endoscope provided with the objective lens for an endoscope, which can switch focus between a far point object and a near point object, has a wide depth of field in a near point object observation state, and has good optical performance. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is a cross-sectional view showing the structure of the objective lens for an endoscope of Example 1.

[0037] Figure 2 is a cross-sectional view showing the structure and light beams of the objective lens for an endoscope of Figure 1

[0038] Figure 3 are graphs showing each aberration of the objective lens for an endoscope of Example 1.

[0039] Figure 4 is a cross-sectional view showing the structure of the objective lens for an endoscope of Example 2.

[0040] Figure 5 are graphs showing each aberration of the objective lens for an endoscope of Example 2.

[0041] Figure 6 is a cross-sectional view showing the structure of the objective lens for an endoscope of Example 3.

[0042] Figure 7 are graphs showing each aberration of the objective lens for an endoscope of Example 3.

[0043] Figure 8 is a cross-sectional view showing the structure of the objective lens for an endoscope of Example 4.

[0044] Figure 9 are graphs showing each aberration of the objective lens for an endoscope of Example 4.

[0045] Figure 10 is a cross-sectional view showing the structure of the objective lens for an endoscope of Example 5.

[0046] Figure 11 ​is each aberration diagram of the objective lens for an endoscope of Example 5.

[0047] Figure 12 is a diagram showing a first structure example of an aperture member.

[0048] Figure 13 is a diagram showing a second structure example of an aperture member.

[0049] Figure 14 is a diagram showing a third structure example of an aperture member.

[0050] Figure 15 is a schematic configuration diagram of an endoscope according to an embodiment.

[0051] Explanation of symbols

[0052] 1 - objective lens for an endoscope, 2 - imaging element, 10, 30, 40, 50 - aperture member, 12 - first opening portion, 14 - second opening portion, 16, 36 - center, 20 - surface, 32, 42, 52 - opening portion, 100 - endoscope, 102 - operation portion, 104 - insertion portion, 106 - general-purpose plug cord, 107 - soft portion, 108 - bending portion, 109 - bending operation knob, 110 - distal end portion, A, B, C - arrow, Hf, Hn - maximum image height, LI ~ L9 - lens, PI, PP - optical member, Sim - image surface, St - aperture stop, Z - optical axis, θf, θn - half view angle. DETAILED DESCRIPTION

[0053] Hereinafter, an embodiment of the present application will be described in detail with reference to the drawings.

[0054] In an endoscope, it is desired to observe a wide range as a whole, and it is desired to observe a lesion or the like found in the overall observation in detail locally. In order to meet this demand, the objective lens for an endoscope according to the embodiment is configured to be able to focus on a far point object and a near point object. Thereby, it is possible to switch and use a far point side observation state suitable for overall observation and a near point side observation state suitable for local observation. Hereinafter, a state of focusing on a farthest point object will be referred to as a farthest point focus state, and a state of focusing on a nearest point object will be referred to as a nearest point focus state. The farthest point focus state corresponds to a farthest point object observation state, and the nearest point focus state corresponds to a nearest point object observation state.

[0055] Figure 1 is a diagram showing a structure in a cross section including the optical axis Z of the objective lens for an endoscope according to an embodiment of the present application. Figure 2 is a diagram showing a structure in a cross section including the optical axis Z of the objective lens for an endoscope according to an embodiment of the present application. Figure 1 is a diagram showing a structure in a cross section including the optical axis Z of the objective lens for an endoscope according to an embodiment of the present application and a light flux. Figure 2 In the diagram, an on-axis light flux and a light flux of a maximum image height are shown as the light flux. Figure 1and Figure 2 The example shown corresponds to the embodiment 1 described later. In Figure 1 and Figure 2 In the drawings, the left side is the object side, and the right side is the image side. The upper section marked "far point" shows the farthest point focusing state, and the lower section marked "near point" shows the nearest point focusing state. Hereinafter, the description will be mainly made with reference to Figure 1

[0056] As an example, Figure 1 The endoscope objective lens is composed of, in order from the object side toward the image side along the optical axis Z, a lens L1, a lens L2, an opening stop St, a lens L3, a lens L4, and a lens L5. The lens L4 and the lens L5 are joined to each other.

[0057] Figure 1 An example in which an optical member PP having parallel incident and emergent surfaces is disposed between the lens L5 and the image plane Sim is shown in

[0058] The endoscope objective lens is configured as follows: in both the farthest point focusing state and the nearest point focusing state, the total angle of view is 120 degrees or more. According to this configuration, a wide field of view can be ensured. Figure 2 The half angle of view θf in the farthest point focusing state and the half angle of view θn in the nearest point focusing state are shown in

[0059] The endoscope objective lens has: an opening stop St; a lens disposed closer to the object side than the opening stop St, at least one image side lens surface of which is concave; and at least one set of joined lenses disposed closer to the image side than the opening stop St. By adopting this configuration, it is possible to widen the angle of the optical system while suppressing astigmatism. In Figure 1 In the example of

[0060] In the endoscope objective lens, a part of the entire system is moved along the optical axis Z to focus from the farthest point object to the nearest point object. That is, only a part of the endoscope objective lens is moved along the optical axis Z when focusing from the farthest point object to the nearest point object. Hereinafter, the lens group that is moved at the time of focusing will be referred to as a focusing lens group. When focusing, the configuration in which only a part of the endoscope objective lens is moved can miniaturize the lens moving mechanism compared to the configuration in which the entire lens system is moved.

[0061] ​The focusing lens group can be a lens group including the lens closest to the image side of the entire system, and can also be configured to focus from the farthest point object to the closest point object by moving integrally along the optical axis Z. In this case, it is advantageous to suppress the variation in the focal length of the entire system at the time of focusing to be small.

[0062] In Figure 1 In the example of the above paragraph and the following paragraph, the focusing lens group is composed of the cemented lens composed of the lens L4 and the lens L5, and the focusing lens group moves toward the object side when focusing from the farthest point object to the closest point object. Figure 1

[0063] Alternatively, the focusing lens group can be a lens group including at least one lens disposed continuously with the opening stop St, and can also be configured to focus from the farthest point object to the closest point object by moving integrally along the optical axis Z. In this case, since the focusing lens group can be miniaturized, it is advantageous to miniaturize the diameter of the entire lens system.

[0064] In addition, in the present specification, "integrally moving" means moving the same amount in the same direction at the same time. Also, in the present specification, "a lens group" is not limited to a structure composed of a plurality of lenses, and can also be configured to be composed of only one lens.

[0065] In a case where the focal length of the entire system in the closest point focusing state is set to fn, the half viewing angle in the closest point focusing state is set to θn, and the maximum image height in the closest point focusing state is set to Hn, the endoscope objective lens preferably satisfies the following conditional expression (1). The tan of conditional expression (1) is the tangent. By being set to not become lower than the lower limit of conditional expression (1), it is advantageous to maintain the magnification in the vicinity of the center of the imaging region to be significantly large, and thus it is easier to perform observation and diagnosis in an appropriate state. By being set to not become higher than the upper limit of conditional expression (1), the focal length in the closest point focusing state does not become excessively long, and thus it is advantageous to widen the depth of field in the closest point focusing state. In order to obtain better characteristics, the endoscope objective lens more preferably satisfies the following conditional expression (1-1), and further more preferably satisfies the following conditional expression (1-2).

[0066] 1.4 < fn x (tan θn) / Hn < 2 (1)

[0067] 1.5 < fn x (tan θn) / Hn < 1.9 (1-1)

[0068] ​1.6 < fn x (tan θn) / Hn < 1.9 (1-2)

[0069] In a case where an F value in a closest point focusing state is set as Fn, and an F value in a farthest point focusing state is set as Ff, the endoscope objective lens preferably satisfies the following conditional expression (2). By being set to be not lower than the lower limit of the conditional expression (2), it is advantageous to widen the depth of field in the closest point focusing state. By being set to be not higher than the upper limit of the conditional expression (2), it is possible to suppress deterioration of the contrast of an image in the closest point focusing state. In order to obtain better characteristics, the endoscope objective lens more preferably satisfies the following conditional expression (2-1), and further more preferably satisfies the following conditional expression (2-2).

[0070] 1.1 < Fn / Ff < 3 (2)

[0071] 1.2 < Fn / Ff < 2.5 (2-1)

[0072] 1.2 < Fn / Ff < 2 (2-2)

[0073] In the near point side observation state of the endoscope, the observation object and the endoscope objective lens are in a state of being very close, and therefore the depth of field is narrowed in the conventional endoscope objective lens, and when diagnosis and / or examination and the like are performed, it can impose a burden on the user. Therefore, if it is configured in a manner satisfying at least one of the above conditional expressions (1) and (2), it is advantageous to widen the depth of field in the closest point focusing state, and therefore the burden on the user is alleviated, and it is easy to shorten the time of diagnosis and / or examination and the like.

[0074] In a case where the focal length of the entire system in the closest point focusing state is set as fn, and the focal length of the entire system in the farthest point focusing state is set as ff, the endoscope objective lens preferably satisfies the following conditional expression (3). By being set to be not lower than the lower limit of the conditional expression (3), the angle of view in the closest point focusing state does not become too wide, and therefore it is easier to perform observation and diagnosis in an appropriate state. By being set to be not higher than the upper limit of the conditional expression (3), it is advantageous to widen the depth of field in the closest point focusing state. In order to obtain better characteristics, the endoscope objective lens more preferably satisfies the following conditional expression (3-1).

[0075] 0.7 < fn / ff < 1.2 (3)

[0076] 0.8 < fn / ff < 1.1 (3-1)

[0077] An endoscope objective lens can be configured to include an aperture component with an opening, the F-number of which changes when focusing. In this configuration, the opening size can be varied over a very small area, and the depth of field can be increased during close-point focusing. Furthermore, the opening of the aperture component can be a hole or a window composed of a transmissive component that allows light to pass through.

[0078] Figure 12 The first structural example of the aperture component is shown. Figure 12 The image above shows the structure under the condition of focusing at the farthest point. Figure 12 The image below shows the structure under the closest point focusing state.

[0079] Figure 12 The aperture component 10 is made of metal or resin, composed of flat plate components, and is fan-shaped. A first opening 12 and a second opening 14 are formed on the aperture component 10. Both the first opening 12 and the second opening 14 are transmissive and are circular in shape. The second opening 14 is a smaller circle than the first opening 12. The portion of the aperture component 10 other than the first opening 12 and the second opening 14 is a light-blocking portion that does not transmit light. Figure 12 The light-shielding portion is given a diagonal line. The aperture component 10 is configured such that the plane of the plate is parallel to the plane perpendicular to the optical axis Z. The aperture component 10 can be rotated in the plane perpendicular to the optical axis Z around the center of a fan-shaped arc 16 by a moving mechanism (not shown). Figure 12 Surface 20 is the surface perpendicular to the optical axis Z at the position of the aperture of the endoscope objective lens, and the center of surface 20 is located on the optical axis.

[0080] exist Figure 12 In the structure shown in the figure above, the center of surface 20 is aligned with the center of the first opening 12. This is achieved by aligning the aperture component 10 with center 16 towards... Figure 12 Rotating in the direction indicated by arrow A, it can be used to... Figure 12 The structure shown in the above figure is switched to Figure 12 The structure is shown in the diagram below. Figure 12 In the figure below, the center of surface 20 coincides with the center of the second opening 14. Figure 12 Compared to the image above, in Figure 13 In the image below, the diameter of the aperture that allows light to pass through is small at the position of the aperture opening. Thus, by rotating the aperture component 10 to change the size of the aperture that allows light to pass through, the F-number can be changed.

[0081] Figure 13 The second structural example of the aperture component is shown. Figure 13 The image above shows the structure under the condition of focusing at the farthest point. Figure 13 The image below shows the structure under the closest point focusing state.

[0082] In the second structural example, two aperture components, aperture component 30 and aperture component 40, are used. Aperture component 30 is made of metal or resin, composed of flat plate components, and is fan-shaped. A circular opening 32 that allows light to pass through is formed on aperture component 30. The portion of aperture component 30 other than the opening 32 is a light-blocking portion that does not transmit light. Figure 13 The light-shielding portion is given a diagonal line. The aperture component 30 is configured such that the plane of the plate is parallel to the plane perpendicular to the optical axis Z. The aperture component 30 can be rotated in the plane perpendicular to the optical axis Z around the center of a fan-shaped arc 36 by a moving mechanism (not shown).

[0083] The aperture component 40 is made of metal or resin, composed of flat plate parts, and is circular in shape. A circular opening 42, which allows light to pass through, is formed at the center of the aperture component 40. The opening 42 is larger than the opening 32. The portion of the aperture component 40 other than the opening 42 is a light-blocking portion that does not transmit light. Figure 13 The light-shielding portion is given a diagonal line. The aperture component 40 is configured such that the plane of the plate is parallel to the plane perpendicular to the optical axis Z. The aperture component 40 is fixed to the position of the aperture of the endoscope objective lens such that the center of the opening 42 is located on the optical axis.

[0084] exist Figure 13 In the structure shown in the figure above, the aperture component 30 and the aperture component 40 do not overlap in the plane perpendicular to the optical axis Z. This is achieved by aligning the aperture component 30 with center 36... Figure 13 Rotating in the direction indicated by arrow B, it can be used to... Figure 13 The structure shown in the above figure is switched to Figure 13 The structure is shown in the diagram below. Figure 13 In the image below, the center of opening 32 coincides with the center of opening 42, and the portion of opening 42 that does not overlap with opening 32 is covered by the light-shielding portion of aperture component 30. Figure 14 Compared to the image above, in Figure 14 In the image below, the diameter of the aperture that allows light to pass through is small at the position of the aperture opening. Thus, by rotating the aperture component 30 to change the size of the aperture that allows light to pass through, the F-number can be changed.

[0085] Figure 14 The third structural example of the aperture component is shown in the figure. Figure 14 The image above shows the structure under the condition of focusing at the farthest point. Figure 14 The image below shows the structure under the closest point focusing state.

[0086] The third structural example replaces the diaphragm member 30 of the second structural example with a diaphragm member 50. The diaphragm member 50 is made of metal or resin, is composed of a flat plate member, and has an outer shape in which a circular shape is aligned with the center of an elongated rectangle. The circular shape of the diaphragm member 50 is a larger circular shape than the opening portion 42 of the diaphragm member 40. A circular opening portion 52 that can transmit light is formed in the center of the circular shape of the diaphragm member 50. The opening portion 52 is a smaller circle than the opening portion 42. The portion of the diaphragm member 50 other than the opening portion 52 is a light-shielding portion that does not transmit light, and Figure 14 a diagonal line is imparted to the light-shielding portion. The diaphragm member 50 is arranged so that the plane of the flat plate is parallel to the plane perpendicular to the optical axis Z. The diaphragm member 50 can be moved in parallel in the plane perpendicular to the optical axis Z by a movement mechanism not shown.

[0087] In the structure shown in the upper view of Figure 14 , the diaphragm member 30 and the diaphragm member 40 do not overlap in the plane perpendicular to the optical axis Z. By moving the diaphragm member 50 in the direction indicated by the arrow C of Figure 14 , it is possible to switch from the structure shown in the upper view of Figure 14 to the structure shown in the lower view of Figure 14 . In the lower view of Figure 1 , the center of the opening portion 52 coincides with the center of the opening portion 42, and the portion of the opening portion 42 that does not overlap with the opening portion 52 is covered by the light-shielding portion of the diaphragm member 50. In the lower view of Sn , the diameter of the opening portion through which light can be transmitted at the position of the opening diaphragm is smaller than in the upper view of Nd . Thus, by moving the diaphragm member 50 to change the size of the opening portion through which light can be transmitted, it is possible to change the F number.

[0088] In an objective lens for an endoscope including a diaphragm member having an opening portion and in which the F number is changed by movement of the diaphragm member, the objective lens for an endoscope preferably satisfies the following conditional expression (4). In the conditional expression (4), the interval on the optical axis of the lens arranged continuously with the opening diaphragm St on the object side of the opening diaphragm St and the lens arranged continuously with the opening diaphragm St on the image side of the opening diaphragm St in the farthest point focus state is set as Df, and the focal length of the entire system in the farthest point focus state is set as ff. By being set so as not to become lower than the lower limit of the conditional expression (4), it is advantageous to shorten the total optical length of the entire lens system. By being set so as not to become higher than the upper limit of the conditional expression (4), movement of the diaphragm member for changing the F number becomes easy. In order to obtain better characteristics, the objective lens for an endoscope more preferably satisfies the following conditional expression (4-1).

[0089] 0.3 < ff / Df < 15 (4)

[0090] 0.5 < ff / Df < 12 (4-1)

[0091] The endoscope objective lens preferably satisfies the following conditional expression (5) in a state where the focal length of the entire system in the closest point focusing state is set as fn, and the interval on the optical axis between the lens disposed on the object side of the opening stop St and the opening stop St, in the closest point focusing state, is set as Dsn. By being set to be not lower than the lower limit of conditional expression (5), it is advantageous to shorten the total optical length of the entire lens system. By being set to be not higher than the upper limit of conditional expression (5), it is advantageous to widen the depth of field in the closest point focusing state, or it is easier to change the F number. In order to obtain better characteristics, the endoscope objective lens more preferably satisfies the following conditional expression (5-1).

[0092] 0.3 < fn / Dsn < 2.5 (5)

[0093] 0.5 < fn / Dsn < 2 (5-1)

[0094] The object side lens surface of the lens disposed on the object side of the opening stop St is preferably a convex surface. In this case, it is advantageous to suppress the generation of astigmatism.

[0095] The endoscope objective lens can be configured as follows: including, on the object side closer than the opening stop St, an aspherical lens whose object side lens surface is in a convex shape near the optical axis and has an aspherical shape in which the absolute value of the local radius of curvature becomes smaller as it approaches the periphery. In this case, it is advantageous to widen the depth of field while reducing the diameter of the lens on the object side closer than the opening stop St.

[0096] The number of lenses included by the endoscope objective lens on the object side closer than the opening stop St can be, for example, 2 or more and 4 or less. In this case, it is advantageous to achieve both miniaturization and ensure good performance. The number of lenses included by the endoscope objective lens on the image side closer than the opening stop St can be, for example, 3 or more and 5 or less. In this case, it is advantageous to achieve both miniaturization and ensure good performance.

[0097] The structures related to the conditional expressions can be combined in any manner, and the above-described preferred structures and achievable structures can be combined in any manner, and are preferably appropriately selected and adopted as needed.

[0098] The following describes two preferred modes of the endoscope objective lens of the present application. The first mode is an endoscope objective lens including: an opening stop St; a lens disposed closer to the object side than the opening stop St, at least one image-side lens surface of which is concave; and at least one set of cemented lenses disposed closer to the image side than the opening stop St, a part of the entire system moving along the optical axis Z to focus from the farthest point object to the closest point object, having a total angle of view of 120 degrees or more in a state of focusing on the farthest point object and a state of focusing on the closest point object, and satisfying the above conditional expression (1).

[0099] The second mode is an endoscope objective lens including: an opening stop St; a lens disposed closer to the object side than the opening stop St, at least one image-side lens surface of which is concave; and at least one set of cemented lenses disposed closer to the image side than the opening stop St, a part of the entire system moving along the optical axis Z to focus from the farthest point object to the closest point object, having a total angle of view of 120 degrees or more in a state of focusing on the farthest point object and a state of focusing on the closest point object, and satisfying the above conditional expression (2).

[0100] Next, embodiments of the endoscope objective lens of the present application are described. Note that the reference symbols assigned to the lenses in the sectional view of each embodiment are used independently in each embodiment to avoid complication of the description due to an increase in the number of digits of the reference symbols. Thus, even if the same reference symbols are assigned in the drawings of different embodiments, they do not necessarily indicate the same structure.

[0101] [Embodiment 1]

[0102] A structural sectional view of the endoscope objective lens of Embodiment 1 is shown in νd Since the method of illustration is as described above, a part of the repeated description is omitted here. The endoscope objective lens of Embodiment 1 is composed of, in order from the object side to the image side, a negative lens L1, a positive lens L2, the opening stop St, a positive lens L3, a positive lens L4, and a negative lens L5. The lenses L4 and L5 are cemented to each other, and the other lenses are single lenses. The focusing lens group is composed of the lenses L4 and L5. When focusing from the farthest point object to the closest point object, the focusing lens group moves to the object side.

[0103] Regarding the endoscope objective lens of Embodiment 1, the basic lens data is shown in Table 1, the specifications and variable surface intervals are shown in Table 2, and the aspheric coefficients are shown in Table 3. In Table 1, the surface number is shown in the Sn column when the object surface is set as the 0th surface and the numbering is sequentially increased toward the image side, the radius of curvature of each surface is shown in the R column, and the surface interval on the optical axis between each surface and the surface adjacent to the image side thereof is shown in the D column. The refractive index with respect to the d line of each component is shown in the Nd column, and the Abbe number of the d line reference of each component is shown in the vd column.

[0104] In Table 1, the sign of the radius of curvature of the face of the shape on the object side is made positive, and the sign of the radius of curvature of the face of the shape on the image side is made negative. The optical member PP is also shown in Table 1. In Table 1, in the column of the face number of the object face, the opening stop St, and the face corresponding to the image face Sim, the terms (Obj), (St), and (Sim) are recorded together with the face number. In Table 1, with respect to the interval that changes between the far point focus state and the near point focus state, the symbol of DD[ ] is used, and the face number on the object side of the interval is given in [ ] and recorded in the column of D. DD[0] of Table 1 is the distance from the object to the distal end of the endoscope objective lens on the optical axis, and is the so-called object distance.

[0105] In the upper table of Table 2, the focal length ff of the entire system, the F value Ff, the total angle of view 2θf, and the maximum image height Hf in the far point focus state are shown. In the lower table of Table 2, the focal length fn of the entire system, the F value Fn, the total angle of view 2θn, and the maximum image height Hn in the near point focus state are shown. The (°) of the column of the total angle of view means degree. The values shown in Table 2 are values when the d line is the reference.

[0106] In the basic lens data, the * mark is noted on the face number of the aspheric surface, and the numerical value of the curvature radius of the paraxial region is recorded in the column of the curvature radius of the aspheric surface. In Table 3, the face number of the aspheric surface is shown in the column of Sn, and the numerical value of the aspheric coefficient with respect to each aspheric surface is shown in the columns of KA and Am (m = 4, 6, 8, 10). The "E±n" (n: integer) of the numerical value of the aspheric coefficient of Table 3 means "x 10 ±n ". KA and Am are the aspheric coefficients in the aspheric surface represented by the following formula.

[0107] Zd = C x h 2 / {1 + (1 - KA x C 2 x h 2 ) 1 / 2} + ∑Am x h m

[0108] where,

[0109] Zd: aspheric depth (length of the perpendicular line from the point on the aspheric surface at height h to the plane perpendicular to the optical axis at the vertex of the aspheric surface)

[0110] h: height (distance from the optical axis to the lens face)

[0111] C: reciprocal of the paraxial curvature radius

[0112] KA, Am: aspheric coefficients

[0113] The ∑ of aspherical surface means the sum with respect to m.

[0114] The values of each table shown below and the data of aberration diagrams described later are values when the focal length of the entire system in the state of focusing at the far point is made 1.000. Also, in each table shown below, the numerical values rounded off by a predetermined number of digits are described.

[0115] [Table 1]

[0116] Example 1

[0117] 0 (Obj) R D DD[0] 5 (St) DD[7] ∞ DD

[10] *1 7.142 0.357 1.85135 40.1 *2 0.845 0.630 3 -22.588 2.542 1.89286 20.4 4 -4.064 0.000 14 (Sim) ∞ 0.138 6 -3.946 0.954 1.618 63.3 7 -1.558 Sn 8 -26.081 0.990 1.59522 67.7 9 -1.135 0.408 1.89286 20.4 10 -1.957 KA 11 ∞ 3.265 1.55920 53.9 12 ∞ 0.306 1.51633 64.1 13 ∞ 0.050 Figure 3

[0118] [Table 2]

[0119] Example 1

[0120]

[0121]

[0122] [Table 3]

[0123] Example 1

[0124] Figure 3 1 2 Figure 3 1.0000000E+00 1.0000000E+00 A4 1.0155127E-01 -1.7185666E-01 A6 -3.7152932E-02 7.8355761E-01 A8 2.6922216E-03 -3.6399038E-01 A10 8.8580013E-04 -5.1535956E-01

[0125] Figure 3 In the middle, each aberration diagram of the objective lens for an endoscope of Example 1 is shown. In Figure 4 In the middle, from the left, a spherical aberration diagram, a coma diagram, a distortion aberration diagram, and a magnification chromatic aberration diagram are shown. In Figure 5 In the middle, in the upper section, each aberration diagram in the state of focusing at the far point is shown, and in the lower section, each aberration diagram in the state of focusing at the near point is shown. Each aberration diagram in the state of focusing at the far point and the state of focusing at the near point is an aberration diagram when the object distance is the DD[0] value of the above table. In the spherical aberration diagram, the aberration in the e line, the F line, and the c line is represented by a solid line, a broken line, and a double-dot chain line, respectively. In the coma diagram, the aberration in the e line in the sagittal direction is represented by a solid line, and the aberration in the e line in the meridional direction is represented by a short broken line. In the distortion aberration diagram, the aberration in the e line is represented by a solid line. In the magnification chromatic aberration diagram, the aberration in the F line and the c line is represented by a broken line and a double-dot chain line, respectively. In Sn In the middle, the F value and the value of the half viewing angle corresponding to the upper end of the vertical axis of each diagram are written on each diagram.

[0126] The symbols, meanings, and description methods of each data related to the above-described Example 1 are the same in the following examples unless otherwise specified, and thus a part of the repeated description is omitted below.

[0127] [Example 2]

[0128] A structure sectional view of the objective lens for an endoscope of Example 2 is shown inNd The structure sectional view of the objective lens for an endoscope of Example 2 is shown in FIG. 2. The objective lens for an endoscope of Example 2 is composed of, in order from the object side to the image side, a negative lens Ll, a negative lens L2, a positive lens L3, an opening stop St, a positive lens L4, a positive lens L5, and a negative lens L6. The lens L2 and the lens L3 are cemented to each other, the lens L5 and the lens L6 are cemented to each other, and the other lenses are single lenses. The focusing lens group is composed of the lens L5 and the lens L6. When focusing from the farthest point object to the closest point object, the focusing lens group moves to the object side.

[0129] The basic lens data of the objective lens for an endoscope of Example 2 is shown in Table 4, the specifications and variable face intervals are shown in Table 5, the aspherical coefficients are shown in Table 6, and the aberration diagrams of each are shown in FIGS. 3A to 3F. νd The structure sectional view of the objective lens for an endoscope of Example 3 is shown in FIG. 4. The objective lens for an endoscope of Example 3 is composed of, in order from the object side to the image side, a negative lens Ll, a negative lens L2, a negative lens L3, a positive lens L4, an opening stop St, a positive lens L5, a positive lens L6, and a negative lens L7. The lens L3 and the lens L4 are cemented to each other, the lens L6 and the lens L7 are cemented to each other, and the other lenses are single lenses. The focusing lens group is composed of the lens L6 and the lens L7. When focusing from the farthest point object to the closest point object, the focusing lens group moves to the object side.

[0130] [Table 4]

[0131] Example 2

[0132] 0 (Obj) R D DD[0] 6 (St) DD[8] ∞ DD

[11] *1 2.691 0.355 1.88202 37.2 *2 0.673 0.565 3 -5.814 0.532 1.88300 40.8 4 0.962 1.137 1.74 28.3 5 -2.8713 0.146 15 (Sim) ∞ 0.086 7 -5.299 0.763 1.49700 81.5 8 -1.067 Sn 9 -18.047 0.924 1.61800 63.3 10 -1.084 0.406 1.85896 22.7 11 -2.0798 KA 12 ∞ 3.248 1.5592 53.9 13 ∞ 0.304 1.51633 64.1 14 ∞ 0.051 Figure 6 ∞

[0133] [Table 5]

[0134] Example 2

[0135]

[0136]

[0137] [Table 6]

[0138] Example 2

[0139] Figure 7 1 2 Sn 1.0000000E+00 1.0000000E+00 A4 1.4745937E-01 -1.9571303E-01 A6 -2.0620125E-01 9.7477283E-01 A8 1.2199511E-01 -3.0360557E+00 A10 -2.2199092E-02 5.9481829E-01

[0140] [Example 3]

[0141] The structure sectional view of the objective lens for an endoscope of Example 3 is shown in FIG. 4. The objective lens for an endoscope of Example 3 is composed of, in order from the object side to the image side, a negative lens Ll, a negative lens L2, a negative lens L3, a positive lens L4, an opening stop St, a positive lens L5, a positive lens L6, and a negative lens L7. The lens L3 and the lens L4 are cemented to each other, the lens L6 and the lens L7 are cemented to each other, and the other lenses are single lenses. The focusing lens group is composed of the lens L6 and the lens L7. When focusing from the farthest point object to the closest point object, the focusing lens group moves to the object side. Nd The basic lens data of the objective lens for an endoscope of Example 3 is shown in Table 7, the specifications and variable face intervals are shown in Table 8, the aspherical coefficients are shown in Table 9, and the aberration diagrams of each are shown in FIGS. 5A to 5F.

[0142] νd [Table 7]

[0143] [Table 8]

[0144] ​Example 3

[0145] 0 (Obj) R D DD[0] 7 (St) 8 (St) ∞ DD

[10] 1 3.727 0.347 1.88300 40.8 2 1.531 0.702 3 6.020 0.347 1.90366 31.3 4 1.511 0.451 5 -27.8141 0.472 1.83481 42.7 6 2.6494 1.382 1.69895 30.1 DD

[13] -2.227 1.317 17 (Sim) ∞ 0.27 9 -2.433 0.750 1.49700 81.5 10 -1.236 Figure 8 11 24.4857 0.91 1.53775 74.7 12 -1.265 0.396 1.89286 20.4 13 -2.1036 Figure 9 14 ∞ 3.171 1.55920 53.9 15 ∞ 0.297 1.51633 64.1 16 ∞ 0.050 Sn ∞

[0146] [Table 8]

[0147] Example 3

[0148]

[0149]

[0150] [Example 4]

[0151] A sectional view of the structure of the endoscope objective lens of Example 4 is shown in Nd Example 4 is composed of, in order from the object side to the image side, a negative lens Ll, an optical member Pl, a positive lens L2, a positive lens L3, a negative lens L4, an opening stop St, a positive lens L5, a negative lens L6, a positive lens L7, a positive lens L8, and a negative lens L9. The optical member Pl is a flat plate-shaped member that assumes a filter or a cover glass, and is a member that does not have a refractive power. The optical member Pl can be omitted to constitute the endoscope objective lens. The lens L2 and the lens L3 are bonded to each other, the lens L5 and the lens L6 are bonded to each other, the lens L8 and the lens L9 are bonded to each other, and the other lenses are single lenses. The focusing lens group is composed of the lens L4. When focusing from the most distant point object to the nearest point object, the focusing lens group moves to the object side.

[0152] With respect to the endoscope objective lens of Example 4, the basic lens data is shown in Table 9, the specifications and variable face intervals are shown in Table 10, and the various aberrations are shown in νd

[0153] [Table 9]

[0154] Example 4

[0155] 0 (Obj) R D DD[0] DD[7] DD[9] ∞ 10 (St) 1 ∞ 0.354 1.88299 40.78 2 1.101 0.579 3 ∞ 0.304 2.00100 29.13 4 ∞ 0.364 5 -4.092 0.486 1.79887 47.85 6 -1.372 0.822 1.43875 94.66 7 -1.580 22 (Sim) 8 -1.857 0.415 1.75500 52.32 9 1.967 Figure 10 Figure 11 ∞ 0.068 11 1.006 0.618 1.57968 40.06 12 -0.674 0.253 1.90094 37.91 13 -3.002 0.810 14 3.268 0.921 1.43875 94.66 15 -7.612 0.101 16 2.003 0.780 1.43875 94.66 17 -1.037 0.354 1.95227 32.77 18 -2.703 1.255 19 ∞ 1.619 1.88299 40.78 20 ∞ 1.619 1.88299 40.78 21 ∞ 0.405 1.47144 65.41 Sn ∞

[0156] [Table 10]

[0157] Example 4

[0158]

[0159]

[0160] [Example 5]

[0161] A sectional view of the structure of the endoscope objective lens of Example 5 is shown in Nd ​The objective lens for an endoscope of Example 5 is composed of, in order from the object side to the image side, a negative lens Ll, an optical member Pl, a positive lens L2, a negative lens L3, a positive lens L4, an opening stop St, a positive lens L5, a negative lens L6, a positive lens L7, a positive lens L8, and a negative lens L9. The optical member Pl of Example 5 is the same member as the optical member Pl of Example 4. The lens L2 and the lens L3 are bonded to each other, the lens L5 and the lens L6 are bonded to each other, the lens L8 and the lens L9 are bonded to each other, and the other lenses are single lenses. The focusing lens group is composed of the lens L5 and the lens L6. When focusing from the farthest point object to the closest point object, the focusing lens group is moved toward the image side.

[0162] With respect to the objective lens for an endoscope of Example 5, the basic lens data is shown in Table 11, the specifications and variable face intervals are shown in Table 12, and the graphs of each aberration are shown in νd

[0163] [Table 11]

[0164] Example 5

[0165] 0 (Obj) R D DD[0] 10 (St) DD

[10] ∞ DD

[13] 1 ∞ 0.379 1.88299 40.78 2 1.314 0.644 3 ∞ 0.325 2.00100 29.13 4 ∞ 0.206 5 -25.340 0.650 1.80264 47.74 6 -1.509 0.336 1.43875 94.66 7 1.041 1.461 8 2.486 0.698 1.49700 81.54 9 -1.764 0.539 22 (Sim) ∞ Formula No. 11 -1.753 0.357 1.89286 20.36 12 -0.613 0.271 2.00069 25.46 13 -2.119 Formula 14 -3.502 0.433 1.49700 81.54 15 -1.502 0.108 16 -17.919 0.606 1.43875 94.66 17 -1.164 0.325 1.94595 17.98 18 -1.895 1.126 19 ∞ 1.732 1.88299 40.78 20 ∞ 1.732 1.88299 40.78 21 ∞ 0.433 1.47144 65.41 Example 1 ∞

[0166] [Table 12]

[0167] Example 5

[0168]

[0169]

[0170] The corresponding values of the conditional expressions (1) to (5) of the objective lenses for endoscopes of Examples 1 to 5 are shown in Table 13. The values under the d-line reference are shown in Table 13.

[0171] [Table 13]

[0172] Example 2 Example 3 Example 4 Example 5 fn x (tan θn) / Hn Fn / Ff fn / ff (1) ff / Df 1.62 1.63 1.68 1.86 1.76 (2) fn / Dsn 1.46 1.67 1.28 1.36 1.36 (3) Figure 15 0.98 0.97 0.99 0.93 1.07 (4) Figure 15 7.26 4.30 0.63 1.41 1.13 (5) Figure 15 - 6.62 0.75 1.31 1.99

[0173] Next, an endoscope according to an embodiment of the present application will be described. ​ A schematic overall configuration diagram of an endoscope according to an embodiment of the present application is shown in FIG. 1. ​ ​The endoscope 100 shown in FIG. 1 mainly has an operation section 102, an insertion section 104, and a general-purpose plug cord 106 connected to a connector section (not shown). The insertion section 104 has a soft section 107 that is bent in any direction along an insertion path, a bending section 108 connected to a front end of the soft section 107, and a front end section 110 connected to a front end of the bending section 108. The bending section 108 is provided to direct the front end section 110 in a desired direction, and bending operation can be performed by rotating a bending operation knob 109 provided on the operation section 102. Inside a front end of the front end section 110, an endoscope objective lens 1 and an imaging element 2 according to the embodiment of the present application are provided. The imaging element 2 is, for example, a CCD (Charge Coupled Device) or a CMOS (complementary metal-oxide-semiconductor), or the like. The imaging element 2 is disposed so that an imaging surface thereof coincides with an image surface of the endoscope objective lens 1. In addition, in the embodiment, the endoscope objective lens 1 and the imaging element 2 are conceptually shown in FIG. 2. ​

[0174] The above describes the technology of the present application with reference to the embodiment and examples, but the technology of the present application is not limited to the above-described embodiment and examples, and various modifications can be made. For example, the radius of curvature, the interval between surfaces, the refractive index, the dispersion coefficient, and the asphericity coefficient of each lens are not limited to the values shown in the above-described numerical examples, and other values can be used.​

Claims

1. An objective lens for an endoscope, characterized by, Possessing: an aperture; a lens disposed closer to an object side than the aperture, at least one image-side lens face being concave; and at least one group of cemented lenses disposed closer to an image side than the aperture, a part of the entire system focusing from a farthest point object to a closest point object by moving along an optical axis, having a total view angle of 120 degrees or more in a state of focusing on the farthest point object and a state of focusing on the closest point object, in a case where a focal length of the entire system in the state of focusing on the closest point object is set as fn, a half view angle in the state of focusing on the closest point object is set as θn, a maximum image height in the state of focusing on the closest point object is set as Hn, condition formulae (1) and (5) represented by are satisfied in a case where a separation on the optical axis of a lens disposed on the object side of the aperture and the aperture in the state of focusing on the closest point object is set as Dsn.

2. An objective lens for an endoscope, characterized by, Possessing: an aperture; a lens disposed closer to an object side than the aperture, at least one image-side lens face being concave; and at least one group of cemented lenses disposed closer to an image side than the aperture, a part of the entire system focusing from a farthest point object to a closest point object by moving along an optical axis, having a total view angle of 120 degrees or more in a state of focusing on the farthest point object and a state of focusing on the closest point object, in a case where an F number in the state of focusing on the closest point object is set as Fn, an F number in the state of focusing on the farthest point object is set as Ff, a focal length of the entire system in the state of focusing on the closest point object is set as fn, condition formulae (2) and (5) represented by are satisfied in a case where a separation on the optical axis of a lens disposed on the object side of the aperture and the aperture in the state of focusing on the closest point object is set as Dsn.

3. The endoscope objective lens according to claim 1 or 2, wherein, in a case where a focal length of the entire system in the state of focusing on the closest point object is set as fn, a half view angle in the state of focusing on the closest point object is set as θn, a maximum image height in the state of focusing on the closest point object is set as Hn, condition formula (1-1) represented by is satisfied.

4. The endoscope objective lens according to claim 1 or 2, wherein, in a case where an F number in the state of focusing on the closest point object is set as Fn, an F number in the state of focusing on the farthest point object is set as Ff, condition formula (2-1) represented by is satisfied.

5. The endoscope objective lens according to claim 1 or 2, wherein, in a case where a focal length of the entire system in the state of focusing on the closest point object is set as fn, a focal length of the entire system in the state of focusing on the farthest point object is set as ff, condition formula (3) represented by is satisfied.

6. The endoscope objective lens according to claim 1 or 2, wherein, an aperture member having an opening portion is included, when the focusing is performed, an F number is changed by moving the aperture member.

7. The endoscope objective lens according to claim 6, wherein, a distance between the lens disposed on the object side of the stop and the lens disposed on the image side of the stop in a state where the focus is on the most distant object is set to Df, a focal length of the entire system in a state where the focus is on the most distant object is set to ff, and a condition (4) represented by is satisfied.

8. The endoscope objective lens according to claim 1 or 2, wherein the lens disposed on the object side of the stop includes an object side lens surface that is in a shape of an aspheric surface in which a convex surface shape is provided around the optical axis and a positive refractive power is made stronger as it approaches the periphery.

9. The endoscope objective lens according to claim 1 or 2, wherein the object side lens surface of the lens disposed on the object side of the stop is a convex surface.

10. The endoscope objective lens according to claim 1 or 2, wherein a lens group including the lens closest to the image side of the entire system is focused from the most distant object to the nearest object by moving integrally along the optical axis.

11. The endoscope objective lens according to claim 1 or 2, wherein a lens group including at least one lens disposed continuously with the stop is focused from the most distant object to the nearest object by moving integrally along the optical axis.

12. The endoscope objective lens according to claim 3, wherein a condition (1-2) represented by 1.6 < fn x (tan θn) / Hn < 1.9 (1-2) is satisfied.

13. The endoscope objective lens according to claim 4, wherein a condition (2-2) represented by 1.2 < Fn / Ff < 2 (2-2) is satisfied.

14. The endoscope objective lens according to claim 5, wherein a condition (3-1) represented by 0.8 < fn / ff < 1.1 (3-1) is satisfied.

15. The endoscope objective lens according to claim 7, wherein a condition (4-1) represented by 0.5 < ff / Df < 12 (4-1) is satisfied.

16. The endoscope objective lens according to claim 1 or 2, wherein a condition (5-1) represented by 0.5 < fn / Dsn < 2 (5-1) is satisfied. The endoscope objective lens according to any one of claims 1 to 16. ​ ​ ​ ​ 17. An endoscope, characterized by ​

Images