JP2018025591A - Objective optical system for endoscope and endoscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which it is difficult to design an objective optical system that is small and has a wide angle of view while keeping optical performance excellent.SOLUTION: An objective optical system for an endoscope is composed of, in order from an object side, a first lens group having negative power and a second lens group having positive power. The first lens group is composed of, in order from the object side, a negative lens training a concave surface on an image side and a positive lens training a convex surface on the image side. The second lens group at least includes, in order from the object side, a positive lens training a convex surface on the image side and a doublet composed of a negative lens and a positive lens joined together. The objective optical system satisfies prescribed conditions.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an endoscope objective optical system and an endoscope incorporating the endoscope objective optical system.

  As a device for diagnosing the inside of a body cavity of a patient, an endoscope (a fiber scope or an electronic scope) is generally known and used practically. It is desired that the distal end portion of this type of endoscope is designed to be small (small diameter and short overall length) so that it can be smoothly inserted into a minute gap.

  The minimum design possible outer shape of the endoscope tip is substantially defined by a mounting component having a large size. For example, an endoscope objective optical system is an example of a large-sized mounting component. Selecting a small endoscope objective optical system as a mounted component is one of effective means for reducing the size of the endoscope tip.

  In addition, in order to reduce oversight of a lesioned part or the like by an operator, it is desired that the endoscope objective optical system is designed to have a wide observation field of view, that is, a wide angle of view.

  For example, in an endoscope objective optical system for a digestive organ, the angle of view is generally about 140 °. With such an angle of view, it is necessary to change the direction of the distal end portion of the endoscope by bending the curved portion of the endoscope when observing the tube wall in the large intestine or the back side of the fold. However, for example, when the lumen diameter is small, the movement of the endoscope distal end is restricted, and therefore the endoscope distal end may not be changed to a desired orientation.

  For example, Patent Literature 1 and Patent Literature 2 disclose an endoscope objective optical system designed to have a wider angle of view than 140 °. By further widening the angle of view of the endoscope objective optical system, it becomes easier to observe the tube wall in the large intestine, the back side of the folds, etc. without changing the direction of the distal end of the endoscope. .

Japanese Patent No. 4819203 Japanese Patent No. 5750618

  The endoscope objective optical system described in Patent Document 1 has a wide angle of view exceeding 180 °. However, in the endoscope objective optical system described in Patent Document 1, since the Petzval sum is large, for example, when observing a lumen such as the digestive tract, the peripheral resolution differs depending on the observation direction. Further, since the incident angle to the lens surface arranged closest to the object side in the endoscope objective optical system is large, the amount of incident light is reduced. Further, in the endoscope objective optical system described in Patent Document 2, it is necessary to increase the angle of view by increasing the negative power of the lens arranged closest to the object side in the endoscope objective optical system. The curvature radius of each lens surface in the endoscope objective optical system becomes small, and correction of coma and astigmatism becomes insufficient. That is, in the endoscope objective optical system described in Patent Document 1 or Patent Document 2, at least optical performance is sacrificed in order to realize a wide angle of view.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an endoscope objective optical system and an endoscope that have a good optical performance but are designed to have a small size and a wide angle of view. Is to provide a mirror.

An endoscope objective optical system according to an embodiment of the present invention includes, in order from the object side, a first lens group having a negative power and a second lens group having a positive power. The first lens group includes, in order from the object side, a negative lens having a concave surface facing the image side and a positive lens having a convex surface facing the image side. The second lens group includes at least a positive lens having a convex surface facing the image side and a cemented lens in which a negative lens and a positive lens are cemented in order from the object side. In the endoscope objective optical system according to one embodiment of the present invention, the focal length of the negative lens located closest to the object side in the first lens group is defined as f ₁ (unit: mm). Is defined as f _F (unit: mm), and an effective diameter at the maximum image height of the surface closest to the object in the first lens group is defined as ED (unit: mm). When the combined focal length of the first lens group and the second lens group is defined as f (unit: mm), the following two conditions 0.2 <f ₁ / f _F <0.5
4.0 <ED / f <5.0
Meet.

In addition, the endoscope objective optical system according to an embodiment of the present invention has a stop between the first lens group and the second lens group, and is the most stop in the first lens group. When the focal length of the positive lens located on the side is defined as f ₂ (unit: mm), the following condition 0.5 <| f ₂ / f _F | <2.0
It is good also as composition which satisfies.

  In one embodiment of the present invention, the positive lens in the first lens group has a flat surface on the object side, for example.

In the endoscope objective optical system according to an embodiment of the present invention, when the maximum image height on the imaging plane is defined as y (unit: mm), the following condition 3.0 <ED / y < 4.0
It is good also as composition which satisfies.

  Further, the endoscope objective optical system according to an embodiment of the present invention may have a configuration in which the angle of view exceeds 180 °.

  In the endoscope objective optical system according to an embodiment of the present invention, the lens surfaces of all the lenses included in the first lens group and the second lens group may be spherical.

  An endoscope according to an embodiment of the present invention is a device in which the above-described endoscope objective optical system is incorporated at the tip.

  According to an embodiment of the present invention, there are provided an endoscope objective optical system and an endoscope that are designed to have a small size and a wide angle of view while having good optical performance.

It is an external view which shows the external appearance of the electronic scope which concerns on one Embodiment of this invention. It is sectional drawing which shows arrangement | positioning of the objective optical system for endoscopes which concerns on one Embodiment (Example 1) of this invention, and the optical component arrange | positioned in the back | latter stage. FIG. 6 is a diagram showing various aberrations of the endoscope objective optical system according to one embodiment (Example 1) of the present invention. It is sectional drawing which shows arrangement | positioning of the objective optical system for endoscopes which concerns on Example 2 of this invention, and the optical component arrange | positioned in the back | latter stage. FIG. 6 is a diagram illustrating various aberrations of the endoscope objective optical system according to Example 2 of the present invention. It is sectional drawing which shows arrangement | positioning of the objective optical system for endoscopes based on Example 3 of this invention, and the optical component arrange | positioned in the back | latter stage. FIG. 10 is a diagram showing various aberrations of the endoscope objective optical system according to Example 3 of the present invention. It is sectional drawing which shows arrangement | positioning of the objective optical system for endoscopes based on Example 4 of this invention, and the optical component arrange | positioned in the back | latter stage. FIG. 10 is a diagram illustrating various aberrations of the endoscope objective optical system according to Example 4 of the present invention. It is sectional drawing which shows arrangement | positioning of the objective optical system for endoscopes concerning Example 5 of this invention, and the optical component arrange | positioned in the back | latter stage. FIG. 10 is a diagram showing various aberrations of the endoscope objective optical system according to Example 5 of the present invention. It is sectional drawing which shows arrangement | positioning of the objective optical system for endoscopes based on Example 6 of this invention, and the optical component arrange | positioned in the back | latter stage. It is various aberrational figures of the objective optical system for endoscopes which concerns on Example 6 of this invention.

  Hereinafter, an endoscope objective optical system according to an embodiment of the present invention and an electronic scope incorporating the endoscope objective optical system will be described with reference to the drawings.

  FIG. 1 is an external view showing the external appearance of an electronic scope 1 according to an embodiment of the present invention. As shown in FIG. 1, the electronic scope 1 includes an insertion portion flexible tube 11 that is sheathed by a flexible sheath 11 a. The distal end portion (bending portion 14) of the insertion portion flexible tube 11 is remotely operated from the hand operating portion 13 connected to the proximal end of the insertion portion flexible tube 11 (specifically, the bending operation knob 13a is rotated). ) To curve. The bending mechanism is a well-known mechanism incorporated in a general endoscope, and bends the bending portion 14 by pulling the operation wire in conjunction with the rotation operation of the bending operation knob 13a. The proximal end of the distal end portion 12 covered with a hard resin housing is connected to the distal end of the bending portion 14. When the direction of the distal end portion 12 changes according to the bending operation by the rotation operation of the bending operation knob 13a, the imaging region by the electronic scope 1 moves.

  An endoscope objective optical system 100 (a block indicated by a broken line in FIG. 1) is incorporated in the resin casing of the distal end portion 12. The endoscope objective optical system 100 forms an image of light from a subject on a light receiving surface of a solid-state imaging device (not shown) in order to collect image data of the subject in the imaging region. Examples of the solid-state imaging device include a CCD (Charge Coupled Device) image sensor and a CMOS (Complementary Metal Oxide Semiconductor) image sensor.

  FIG. 2 is a cross-sectional view showing the arrangement of an endoscope objective optical system 100 according to Embodiment 1 (details will be described later) of the present invention and optical components arranged at the subsequent stage. In the following, with reference to FIG. 2, the endoscope objective optical system 100 according to an embodiment of the present invention will be described in detail.

  As shown in FIG. 2, the endoscope objective optical system 100 includes at least a first lens group G1, a diaphragm S, and a second lens group G2 in order from the object (subject) side. Each optical lens constituting the first lens group G1 and the second lens group G2 has a rotationally symmetric shape about the optical axis AX of the endoscope objective optical system 100. A color correction filter F for a solid-state image sensor is disposed at the subsequent stage of the second lens group G2. The color correction filter F is bonded to a cover glass (not shown) that protects the solid-state imaging device.

  The reason for having “at least” in the above is that there may be a configuration example in which another optical element is added within the scope of the technical idea of the present invention. For example, the configuration example in which a parallel plate that does not substantially contribute to the optical performance is added to the endoscope objective optical system according to the present invention, and the configuration and effect of the endoscope objective optical system according to the present invention are maintained. However, a configuration example in which another optical element is added is assumed. In the description of the first lens group G1 and the second lens group G2, it is expressed as “at least” for the same reason.

  The first lens group G1 is a lens group disposed on the object side of the stop S. The first lens group G1 includes, in order from the object side, at least a negative lens L1 having a concave surface facing the image side and a positive lens L2 having a convex surface facing the image side. The first lens group G1 has a negative power as a whole in order to widen the angle of view of the endoscope objective optical system 100, that is, to capture a subject over a wide range.

  When the power of the negative lens L1 is increased to widen the angle of view, the asymmetry between the first lens group G1 and the second lens group G2 increases, so that it becomes difficult to correct distortion and negative refraction. Since the curvature of the surface increases, various aberrations such as coma and chromatic aberration increase. Therefore, in the present embodiment, a configuration is adopted in which the positive lens L2 is disposed in front of the aperture stop S and the strong negative power from the negative lens L1 is canceled in the first lens group G1.

  In addition, the positive lens L2 effectively suppresses a decrease in resolution around the observation visual field due to image plane tilting, which tends to occur when the negative lens L1 is widened, and a decrease in resolution around the observation visual field due to distortion. Therefore, it is desirable that the object side surface be a flat surface.

  The second lens group G2 is a lens group disposed on the image side of the stop S. The second lens group G2 includes at least a cemented lens CL in which a positive lens L3, a negative lens L4, and a positive lens L5 are cemented in order from the object side. The second lens group G2 has a positive power as a whole in order to form an image of a wide range of subjects captured by the first lens group G1 on the light receiving surface of the solid-state imaging device.

  In the second lens group G2 having positive power, when a lens having a concave surface on the image side is adopted as the positive lens L3, the emission angle becomes large. Therefore, it is difficult to ensure a sufficient exit pupil distance. In order to avoid this problem, in the present embodiment, the positive lens L3 is disposed with the convex surface facing the image side.

  Further, the chromatic aberration of magnification generated in the first lens group G1 increases as the negative power of the first lens group G1 is increased for widening the angle of view. In order to efficiently correct the lateral chromatic aberration generated in the first lens group G1, the present embodiment employs a configuration in which the cemented lens CL is disposed in the second lens group G2 passing through the position where the off-axis ray is the highest. doing.

  In the following, for convenience of explanation, the object-side surface and the image-side surface of each optical component are referred to as a first surface and a second surface, respectively. The diaphragm S is a plate-like member having a predetermined circular opening centered on the optical axis AX, or a lens surface closest to the diaphragm S of the first lens group G1 (in the configuration example of FIG. 2, a positive lens L2). The light-shielding film is coated on the second surface r4) other than a predetermined circular region centered on the optical axis AX. The thickness of the diaphragm S is very thin compared to the thickness of each optical lens such as the negative lens L1 and the positive lens L2, and can be ignored in calculating the optical performance of the endoscope objective optical system 100. Therefore, in the present specification, the description will be made assuming that the thickness of the diaphragm S is zero.

The endoscope objective optical system 100 defines the focal length of the negative lens L1 located closest to the object side in the first lens group G1 as f ₁ (unit: mm), and the focal point of the first lens group G1. The distance is defined as f _F (unit: mm), and the effective diameter at the maximum image height of the surface closest to the object side (first surface r1 of the negative lens L1) in the first lens group G1 is ED (unit: mm). ) And the focal length of the entire system (combination of the first lens group G1 and the second lens group G2) is defined as f (unit: mm), the following two conditions (1) and ( 2)
0.2 <f ₁ / f _F <0.5 (1)
4.0 <ED / f <5.0 (2)
It is the composition which satisfies.

Condition (1) is provided with a focal length f ₁ of the negative lens L1 is located closest to the object side in the first lens group G1, defining the ratio between the focal length f _F of the first lens group G1. When the condition (1) is satisfied, the object angle is set to an appropriate size (for example, an angle of view exceeding 180 °) when the first lens group G1 and the second lens group G2 are combined. The effective diameter of the negative lens L1 located on the side can be suppressed.

In the condition (1), when “f ₁ / f _F ” is equal to or greater than the value on the right side (= 0.5), various aberrations such as coma can be corrected well, but the effective diameter ED of the negative lens L1 can be corrected. Therefore, the endoscope objective optical system 100 does not have a small diameter. Since it is necessary to incorporate the endoscope objective optical system 100 into the distal end portion 12 of the electronic scope 1, the distal end portion 12 cannot be designed to have a small diameter, and the design freedom for the distal end portion 12 is greatly restricted. I'll be relaxed. In addition, since the magnification of the positive lens L2 becomes too large, it is difficult to suppress the image plane collapse when the positive lens L2 is assembled eccentrically (shifted in the direction perpendicular to the optical axis AX).

In the condition (1), when “f ₁ / f _F ” is equal to or less than the value on the left side (= 0.2), the effective diameter ED of the negative lens L1 is decreased to reduce the small diameter of the endoscope objective optical system 100. However, since the power of the negative lens L1 becomes too strong, it is difficult to achieve both a wide angle of view and correction of aberrations (mainly coma and chromatic aberration). In addition, since the magnification of the second lens group G2 must be set high, it is possible to suppress variations in the angle of view due to an error in the group spacing between the first lens group G1 and the second lens group G2 during assembly. It is difficult.

  Condition (2) is a ratio of the effective diameter ED at the maximum image height of the surface closest to the object side (first surface r1 of the negative lens L1) in the first lens group G1 to the focal length f of the entire system. Stipulate. By satisfying the condition (2), the endoscope objective optical system 100 is not increased in size (increased in diameter and length is increased) (in other words, the endoscope objective optical system 100 is reduced in size). The negative lens L1 can be shaped to be easy to handle.

  Here, the first surface r <b> 1 of the negative lens L <b> 1 is exposed as an appearance on the distal end surface of the distal end portion 12 of the electronic scope 1. When the condition (2) is satisfied, since the negative lens L1 has a small diameter of the first surface r1, the cleaning range is small and the protrusion amount of the first surface r1 on the tip surface is small. For this reason, the negative lens L1 is suppressed from being deteriorated in the cleaning performance of the distal end portion 12, and the risk of the first surface r1 colliding with other structures or the like during the management of the electronic scope 1 is also suppressed. The shape is easy to handle.

  In the condition (2), when “ED / f” is equal to or greater than the value on the right side (= 5.0), the protrusion amount of the first surface r1 on the tip surface becomes large. For this reason, the cleaning performance of the distal end portion 12 is deteriorated (for example, it becomes difficult to remove dirt when cleaning the distal end surface), and the first surface r1 collides with another structure or the like when the electronic scope 1 is managed and is damaged. The risk of The protrusion amount of the first surface r1 is defined as the distance in the optical axis AX direction between the tangential plane of the first surface r1 on the optical axis AX and the outermost periphery of the effective diameter of the first surface r1.

  In the condition (2), when “ED / f” is equal to or less than the value on the left side (= 4.0), the protrusion of the first surface r1 on the distal end surface is caused as the effective diameter ED of the negative lens L1 decreases. The amount is also reduced. However, the amount of light reflected on the surface of the first surface r1 increases, and the light amount loss increases. Further, the overall length of the endoscope objective optical system 100 is increased. Since it is necessary to incorporate the endoscope objective optical system 100 having a long overall length into the distal end portion 12 of the electronic scope 1, it is difficult to keep the entire length of the distal end portion 12 short. When the total length of the distal end portion 12 having rigidity is increased, for example, the insertion property (ease of insertion) of the electronic scope 1 into the body cavity is reduced, and the burden on the patient when the electronic scope 1 is inserted is increased. I will.

  In this way, the endoscope objective optical system 100 is satisfactory by satisfying the conditions (1) and (2) at the same time in the lens arrangement (the first lens group G1 and the second lens group G2). Although it has optical performance, a small size and a wide angle of view (for example, a wide angle of view exceeding 180 ° suitable for lumen observation) have been achieved. For example, in combination with a high-definition solid-state image sensor It is suitable.

  In addition, since the objective optical system 100 for an endoscope does not require an aspheric lens for correcting various aberrations, the burden of design development is reduced and processing is easy. In each embodiment of the present invention, the lens surfaces of all the lenses included in the first lens group G1 and the second lens group G2 are spherical.

Further, the endoscope objective optical system 100 has the following condition (when the focal length of the positive lens L2 located closest to the diaphragm side in the first lens group G1 is defined as f ₂ (unit: mm)) 3)
0.5 <| f ₂ / f _F | <2.0 (3)
It is the composition which satisfies.

Condition (3), the focal length f ₂ of the positive lens L2 positioned closest stop side in the first lens group G1, defining the ratio between the focal length f _F of the first lens group G1. By satisfying the condition (3), the deterioration of the optical performance around the observation visual field, which is a concern when the angle of view is widened, can be more suitably suppressed.

In the condition (3), when “| f ₂ / f _F |” is equal to or greater than the value on the right side (= 2.0), for example, an image with little distortion is obtained from the center of the observation field to the periphery of the observation field during lumen observation. However, since the magnification in the vicinity of the observation visual field becomes low, for example, when a lesion is found and brought to the center of the observation visual field, the lesion cannot be imaged with high resolution.

In the condition (3), when “| f ₂ / f _F |” is equal to or less than the value on the left side (= 0.5), for example, the closer to the periphery of the observation field at the time of luminal observation, the greater the distortion of the image. The object-side resolution at will be low.

The endoscope objective optical system 100 has the following condition (4) when the maximum image height on the image plane is defined as y (unit: mm).
3.0 <ED / y <4.0 (4)
It is the composition which satisfies.

  Condition (4) is that the effective diameter ED at the maximum image height of the surface closest to the object side (the first surface r1 of the negative lens L1) in the first lens group G1 and the maximum image height y at the imaging surface Specify the ratio. By satisfying the condition (4), the endoscope objective optical system 100 is not increased in size (in other words, the endoscope objective optical system 100 can be reduced in size), and the negative lens L1 can be handled. Easy shape.

  In the condition (4), when “ED / y” is equal to or greater than the value on the right side (= 4.0), the protrusion amount of the first surface r1 on the distal end surface of the distal end portion 12 of the electronic scope 1 is reduced. However, the amount of light reflected on the surface of the first surface r1 increases, and the light amount loss increases. Further, the overall length of the endoscope objective optical system 100 is increased. Since it is necessary to incorporate the endoscope objective optical system 100 having a long overall length into the distal end portion 12 of the electronic scope 1, it is difficult to keep the entire length of the distal end portion 12 short. When the total length of the distal end portion 12 having rigidity is increased, for example, the insertion property of the electronic scope 1 into the body cavity is reduced, or the burden on the patient when the electronic scope 1 is inserted is increased.

  In the condition (4), when “ED / y” is equal to or less than the value on the left side (= 3.0), the protrusion amount of the first surface r1 on the tip surface becomes large. Therefore, the cleaning performance of the distal end portion 12 is deteriorated, and the risk of the first surface r1 colliding with other structures or the like during the management of the electronic scope 1 is increased.

  Next, six specific numerical examples of the endoscope objective optical system 100 described so far will be described. The endoscope objective optical system 100 according to Numerical Examples 1 to 6 is incorporated in the distal end portion 12 of the electronic scope 1 shown in FIG.

  As described above, the configuration of the endoscope objective optical system 100 according to the first embodiment of the present invention is as shown in FIG.

  Table 1 shows specific numerical configurations (design values) of the endoscope objective optical system 100 (and optical components arranged in the subsequent stage) according to the first embodiment. The surface number NO shown in the upper column (surface data) of Table 1 corresponds to the surface code rn (n is a natural number) in FIG. 2 except for the surface number 5 corresponding to the aperture S. In the upper column of Table 1, R (unit: mm) is the radius of curvature of each surface of the optical member, D (unit: mm) is the optical member thickness or optical member interval on the optical axis AX, and N (d) is The refractive index of d-line (wavelength 588 nm) is indicated, and νd is the Abbe number of d-line. In the lower column of Table 1 (various data), the specifications (effective F number, focal length (unit: mm) of the entire system, optical magnification, half angle of view of the objective optical system 100 for an endoscope according to the first embodiment are shown. (Unit: degree), image height (unit: mm)).

  A list of values calculated when conditions (1) to (4) are applied to the endoscope objective optical system 100 according to the first embodiment is shown.

Condition _{(1): f 1 / f} F = 0.35
Condition (2): ED / f = 4.17
Condition (3): | f ₂ / f _F | = 1.10
Condition (4): ED / y = 3.11

  Graphs A to D in FIG. 3 are various aberration diagrams of the endoscope objective optical system 100 according to the first example. Graph A shows spherical aberration and axial chromatic aberration at d-line, g-line (wavelength 436 nm), and C-line (wavelength 656 nm). Graph B shows chromatic aberration of magnification at d-line, g-line, and C-line. In the graphs A and B, the solid line indicates the aberration at the d line, the dotted line indicates the aberration at the g line, and the alternate long and short dash line indicates the aberration at the C line. Graph C shows astigmatism. In the graph C, a solid line indicates a sagittal component, and a dotted line indicates a meridional component. Graph D shows distortion. In the graphs A to C, the vertical axis represents the image height, and the horizontal axis represents the aberration amount. The vertical axis of the graph D represents the image height, and the horizontal axis represents the distortion. In addition, the description about the chart of this Example 1 is applied also to the chart presented in each subsequent Example.

  FIG. 4 is a cross-sectional view showing the arrangement of optical components including the endoscope objective optical system 100 according to Embodiment 2 of the present invention. Graphs A to D in FIG. 5 are graphs showing various aberrations (spherical aberration, longitudinal chromatic aberration, lateral chromatic aberration, astigmatism, distortion) of the endoscope objective optical system 100 according to the second embodiment. Table 2 shows specific numerical configurations and specifications of the endoscope objective optical system 100 according to the second embodiment.

  A list of values calculated when conditions (1) to (4) are applied to the endoscope objective optical system 100 according to the second embodiment is shown.

Condition _{(1): f 1 / f} F = 0.37
Condition (2): ED / f = 4.07
Condition (3): | f ₂ / f _F | = 1.34
Condition (4): ED / y = 3.07

  FIG. 6 is a cross-sectional view showing the arrangement of optical components including the endoscope objective optical system 100 according to the third embodiment of the present invention. Graphs A to D in FIG. 7 are graphs showing various aberrations (spherical aberration, axial chromatic aberration, lateral chromatic aberration, astigmatism, distortion) of the endoscope objective optical system 100 according to the third embodiment. Table 3 shows specific numerical configurations and specifications of the endoscope objective optical system 100 according to the third embodiment.

  A list of values calculated when conditions (1) to (4) are applied to the endoscope objective optical system 100 according to the third embodiment is shown.

Condition _{(1): f 1 / f} F = 0.23
Condition (2): ED / f = 4.14
Condition (3): | f ₂ / f _F | = 0.67
Condition (4): ED / y = 3.07

  FIG. 8 is a cross-sectional view showing the arrangement of optical components including the endoscope objective optical system 100 according to Embodiment 4 of the present invention. Graphs A to D in FIG. 9 are graphs showing various aberrations (spherical aberration, axial chromatic aberration, lateral chromatic aberration, astigmatism, distortion) of the endoscope objective optical system 100 according to the fourth embodiment. Table 4 shows specific numerical configurations and specifications of the endoscope objective optical system 100 according to the fourth embodiment.

  A list of values calculated when conditions (1) to (4) are applied to the endoscope objective optical system 100 according to the fourth embodiment is shown.

Condition _{(1): f 1 / f} F = 0.37
Condition (2): ED / f = 4.46
Condition (3): | f ₂ / f _F | = 1.22
Condition (4): ED / y = 3.33

  FIG. 10 is a cross-sectional view showing the arrangement of optical components including the endoscope objective optical system 100 according to the fifth embodiment of the present invention. Graphs A to D in FIG. 11 are graphs showing various aberrations (spherical aberration, axial chromatic aberration, lateral chromatic aberration, astigmatism, distortion aberration) of the endoscope objective optical system 100 according to the fifth example. Table 5 shows specific numerical configurations and specifications of the endoscope objective optical system 100 according to the fifth embodiment.

  A list of values calculated when conditions (1) to (4) are applied to the endoscope objective optical system 100 according to the fifth embodiment is shown.

Condition _{(1): f 1 / f} F = 0.41
Condition (2): ED / f = 4.29
Condition (3): | f ₂ / f _F | = 1.45
Condition (4): ED / y = 3.25

  FIG. 12 is a cross-sectional view showing the arrangement of optical components including the endoscope objective optical system 100 according to Example 6 of the present invention. Graphs A to D in FIG. 13 are graphs showing various aberrations (spherical aberration, axial chromatic aberration, lateral chromatic aberration, astigmatism, distortion aberration) of the endoscope objective optical system 100 according to the sixth embodiment. Table 6 shows specific numerical configurations and specifications of the endoscope objective optical system 100 according to the sixth embodiment.

  A list of values calculated when conditions (1) to (4) are applied to the endoscope objective optical system 100 according to the sixth embodiment is shown.

Condition _{(1): f 1 / f} F = 0.47
Condition (2): ED / f = 4.75
Condition (3): | f ₂ / f _F | = 1.83
Condition (4): ED / y = 3.45

(Comparison verification)
A first example of Patent Document 1 is given as a comparative example for Examples 1-6. The endoscope objective optical system according to the comparative example includes a front group having negative power (a negative meniscus lens having a convex surface facing the object side and a negative meniscus lens having a concave surface facing the object side in order from the object side). ) And a rear lens group having a positive power (in order from the object side, a plano-convex lens with a convex surface facing the image side (positive lens), a cemented lens of a biconvex lens that is a positive lens and a negative meniscus lens with a concave surface facing the object side) Group), and none of the conditions (1) to (4) is satisfied. Therefore, the endoscope objective optical system according to the comparative example has achieved a wide angle of view, but has not been sufficiently reduced in size. In addition, in order to achieve a wide angle of view, some optical characteristics related to peripheral resolution, incident light quantity, etc. are sacrificed.

  For reference, a list of values calculated when conditions (1) to (4) are applied to the endoscope objective optical system according to the comparative example is shown.

Condition _{(1): f 1 / f} F = 1.38
Condition (2): ED / f = 2.98
Condition (3): | f ₂ / f _F | = 4.75
Condition (4): ED / y = 2.31

  In contrast, the endoscope objective optical system 100 according to each of Examples 1 to 6 has a first lens group G1 having negative power (in order from the object side, a concave surface is directed to the image side). A lens group having at least a negative lens, a positive lens having a convex surface facing the image side) and a second lens group G2 having a positive power (a positive lens having a convex surface facing the image side in order from the object side), a negative lens And a lens group having at least a cemented lens in which a positive lens and a positive lens are cemented, and satisfies the conditions (1) and (2). Therefore, as shown in each table and various aberration diagrams, the endoscope objective optical system 100 according to each example has a configuration in which a small size and a wide angle of view are achieved while having good optical performance. It has become.

  In addition, the endoscope objective optical system 100 according to each of Examples 1 to 6 is configured to further satisfy the conditions (3) and (4). In each Example of the present Examples 1-6, the further effect by satisfy | filling condition (3) and condition (4) is show | played.

  The above is the description of the exemplary embodiments of the present invention. The embodiment of the present invention is not limited to the contents described above, and various modifications are possible within the scope of the technical idea of the present invention. For example, the embodiment of the present application also includes an embodiment that is exemplarily specified in the specification or a combination of obvious embodiments and the like as appropriate.

1 Electronic scope 100 Objective optical system for endoscope

Claims (7)

In order from the object side, it consists of a first lens group with negative power and a second lens group with positive power,
The first lens group includes:
In order from the object side, it consists of a negative lens with a concave surface on the image side and a positive lens with a convex surface on the image side.
The second lens group includes:
In order from the object side, at least a positive lens having a convex surface facing the image side, a cemented lens in which a negative lens and a positive lens are cemented,
The focal length of the negative lens located closest to the object in the first lens group is defined as f ₁ (unit: mm), and the focal length of the first lens group is defined as f _F (unit: mm). The effective diameter at the maximum image height of the surface closest to the object in the first lens group is defined as ED (unit: mm), and the first lens group and the second lens group are combined. When the focal length is defined as f (unit: mm), the following two conditions 0.2 <f ₁ / f _F <0.5
4.0 <ED / f <5.0
Meet,
Objective optical system for endoscope. Having a stop between the first lens group and the second lens group;
When the focal length of the positive lens located closest to the stop in the first lens group is defined as f ₂ (unit: mm), the following condition 0.5 <| f ₂ / f _F | <2 .0
Meet,
The endoscope objective optical system according to claim 1. The positive lens in the first lens group is
The object side surface is a plane,
Meet,
The objective optical system for endoscopes according to claim 1 or 2. When the maximum image height on the image plane is defined as y (unit: mm), the following condition 3.0 <ED / y <4.0
Meet,
The endoscope objective optical system according to any one of claims 1 to 3. The angle of view exceeds 180 °,
The objective optical system for endoscopes according to any one of claims 1 to 4. The lens surfaces of all the lenses included in the first lens group and the second lens group are spherical surfaces.
The endoscope objective optical system according to any one of claims 1 to 5. The endoscope objective optical system according to any one of claims 1 to 6 is incorporated at a tip.
Endoscope.

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