JP6074246B2 - Endoscope - Google Patents

Description

  The present invention relates to a condensing optical system that condenses light emitted from a point light source moving on a predetermined surface, and an observation instrument including the condensing optical system.

  2. Description of the Related Art As an observation instrument for observing a subject such as a living tissue, one that can scan a subject (surface to be examined) with predetermined scanning light and obtain an image thereof is known. A specific configuration of this type of observation instrument is described in Patent Document 1, for example.

  The observation instrument described in Patent Document 1 is a confocal probe designed by applying the principle of a confocal microscope, and is incorporated in the distal end portion of an endoscope. The confocal probe is emitted from the point light source while periodically moving the emission end (point light source) of the optical fiber on a predetermined plane substantially orthogonal to the optical axis by shaking the optical fiber disposed in the probe. The point image of the reflected light (excitation light) is scanned on the surface to be examined via the condensing optical system. Hereinafter, a condensing optical system that scans the surface to be inspected with light emitted from a point light source moving on a predetermined surface is referred to as a “scanning condensing optical system”. The confocal probe captures fluorescence emitted from the test surface excited by the excitation light and transmits the fluorescence to a predetermined image generation apparatus.

JP 2005-80769 A

  This type of condensing optical system for scanning exemplified in Patent Document 1 is required to be further miniaturized in order to reduce the burden on the patient while the observation instrument is inserted into the body cavity. . Further, in order to observe a subject in a body cavity with a wide field of view, a wider angle of view is also required. However, in the condensing optical system for scanning, when trying to achieve both a further reduction in size and a wide angle of view, it is difficult to suppress the occurrence of various aberrations including field curvature. Therefore, the present inventor has made extensive studies and has found a condensing optical system suitable for suppressing the occurrence of various aberrations including field curvature while achieving both a reduction in size and a wide angle of view. The invention has been completed.

A condensing optical system according to an aspect of the present invention is a condensing optical system for scanning that condenses light emitted from a point light source moving on a predetermined surface, and has positive power sequentially from the point light source side. A first group having a second group having a positive power. The axial light between the first group and the second group is substantially parallel light. In the first group, in order from the point light source side, a _first meniscus lens having a concave surface facing the point light source side, a _first positive lens having a convex surface facing the test surface side, and a convex surface facing the point light source side second _first positive lens, a concave surface on the object surface side, and a first ₁ of the cemented lens consisting of a negative lens and a positive lens. The second group, in order from the point light source side, a concave surface facing the point light source side, the first _{and second} cemented lens consisting of a negative lens and a positive lens, the first _{and second} positive lens, a concave surface on the object surface side having _{first and second} meniscus lens. The condensing optical system, the curvature radius of the light source side surface points of the first ₁ of the meniscus lens is defined as r _11, defines a radius of curvature of the surface of the test surface side of the first _one meniscus lens with r ₂₁ and, if the radius of curvature of the light source side surface points of the first _{and second} meniscus lens is defined as r _12, where the radius of curvature of the surface of the test surface side of the first _{and second} meniscus lens is defined as r _22, the following Conditional expression of −0.4 <SF ₁ <0.0
−0.6 <SF ₂ <−0.1
However,
SF ₁ : (r ₁₁ −r ₂₁ ) / (r ₁₁ + r ₂₁ )
_{SF 2: (r 12 -r 22} ) / (r 12 + r 22)
Meet.

A condensing optical system according to an aspect of the present invention is a condensing optical system for scanning that condenses light emitted from a point light source moving on a predetermined surface, and has positive power sequentially from the point light source side. A first group having a second group having a positive power. The axial light between the first group and the second group is substantially parallel light. The first group includes, in order from the point light source side, a _first meniscus lens having a concave surface facing the point light source side, a _first positive lens having a convex surface facing the test surface side, a negative lens, and a positive lens. 1 ₁ of the cemented lens, having a second _one meniscus lens having a concave surface on the object surface side. The second group, in order from the point light source side, a concave surface facing the point light source side, the first _{and second} cemented lens consisting of a negative lens and a positive lens, the first _{and second} positive lens, a concave surface on the object surface side having _{first and second} meniscus lens. The condensing optical system has the following conditional expression −0.4 <SF ₁ <0.0.
−0.6 <SF ₂ <−0.1
However,
SF ₁ : (r ₁₁ −r ₂₁ ) / (r ₁₁ + r ₂₁ )
_{SF 2: (r 12 -r 22} ) / (r 12 + r 22)
Meet.

  According to one aspect and another aspect of the present invention, the field curvature (and coma aberration, astigmatism, spherical aberration, chromatic aberration, etc.) can be achieved even when the condensing optical system is downsized and widened. Aberration) can be suppressed, the emitted light emitted from the point light source can be taken in efficiently, and the excitation light can be efficiently irradiated onto the test surface. Fluorescence can be taken up efficiently.

Further, the condensing optical system defines a focal length of a lens having the strongest negative power among lenses constituting the first group as f _1n and defines a focal length of the first group as f ₁ . The following conditional expression −4.5 ≦ f _1n / f ₁ ≦ −0.5
It is good also as composition which satisfies.

Further, the condensing optical system, the focal length of the strong lens the most negative power among the lenses constituting the second group is defined as f _2n, the focal length of the second lens group when defined as f _2, The following conditional expression −0.9 ≦ f _2n / f ₂ ≦ −0.5
It is good also as composition which satisfies.

Further, the condensing optical system, the focal length of the strong lens the most positive power of the lenses constituting the first group when defined as f _1p, the following conditional expression 1.0 ≦ f _{1p /} f ₁ ≦ 4.0
It is good also as composition which satisfies.

Further, the condensing optical system, the focal length of the strong lens the most positive power of the lenses constituting the second group when defined as f _2p, the following conditional expression 0.5 ≦ f _{2p /} f ₂ ≦ 3.0
It is good also as composition which satisfies.

Further, the condensing optical system, when the focal length of the _{first 1} of the meniscus lens is defined as f _{1 m,} the following conditional expression _{5.0 ≦ | f 1m / f 1} | ≦ 20.0
It is good also as composition which satisfies.

Further, the condensing optical system, when the focal length of the _{first and second} meniscus lens is defined as _{f 2m,} the following conditional expression _{1.5 ≦ | f 2m / f 2} | ≦ 4.5
It is good also as composition which satisfies.

The condensing optical system includes a surface arranged closest to the test surface among lens surfaces of the lenses constituting the first group and a point light source side closest to the lens surfaces of the lenses constituting the second group. A pair of concave surfaces facing each other is a pair of concave surfaces, and at least one of the concave surfaces is a negative lens. Of the pair of concave surfaces, the radius of curvature of the concave surface facing the test surface side is defined as r ₃₁ , When the curvature radius of the concave surface facing the concave surface having the radius r ₃₁ is defined as r ₃₂ , the following conditional expression −0.2 <SF ₃ <0.0
However,
_{SF 3: (r 31 + r} 32) / (r 31 -r 32)
It is good also as composition which satisfies.

A lens having a concave surface with a radius of curvature r ₃₁ and a lens having a concave surface with a radius of curvature r ₃₂ are combined with lenses having different powers to form a pair of positive and negative cemented lenses. Also good.

  An observation instrument according to one embodiment of the present invention is characterized in that the light collecting optical system is incorporated in a distal end portion.

  According to one aspect and another aspect of the present invention, a condensing optical system suitable for suppressing the occurrence of various aberrations including field curvature while achieving both a reduction in size and a wide angle of view, and the condensing optical system An observation instrument is provided.

It is a sectional side view which shows the internal structure of the front-end | tip part of the integrated endoscope of embodiment of this invention. It is an enlarged view near the condensing optical system for scanning in the confocal optical system with which the integrated endoscope of the embodiment of the present invention is provided. It is sectional drawing which shows arrangement | positioning of the condensing optical system for a scanning of embodiment (Example 1) of this invention, and a subsequent stage optical component. FIG. 4 is various aberration diagrams of the scanning condensing optical system according to Example 1 of the present invention. It is sectional drawing which shows arrangement | positioning of the condensing optical system for a scanning of Example 2 of this invention, and the optical component of the back | latter stage. It is various aberrational figures of the condensing optical system for scanning of Example 2 of this invention. It is sectional drawing which shows arrangement | positioning of the condensing optical system for a scanning of Example 3 of this invention, and the optical component of the back | latter stage. It is various aberrational figures of the condensing optical system for scanning of Example 3 of this invention. It is sectional drawing which shows arrangement | positioning of the condensing optical system for a scanning of Example 4 of this invention, and the optical component of the back | latter stage. It is various aberrational figures of the condensing optical system for scanning of Example 4 of this invention. It is sectional drawing which shows arrangement | positioning of the condensing optical system for a scanning of Example 5 of this invention, and the optical component of the back | latter stage. It is various aberrational figures of the condensing optical system for scanning of Example 5 of this invention. It is sectional drawing which shows arrangement | positioning of the condensing optical system for a scanning of Example 6 of this invention, and the optical component of the back | latter stage. It is various aberrational figures of the condensing optical system for scanning of Example 6 of this invention. It is sectional drawing which shows arrangement | positioning of the condensing optical system for a scanning of Example 7 of this invention, and the optical component of the back | latter stage. It is various aberrational figures of the condensing optical system for scanning of Example 7 of this invention. It is sectional drawing which shows arrangement | positioning of the condensing optical system for a scanning of Example 8 of this invention, and its subsequent stage optical components. It is various aberrational figures of the condensing optical system for scanning of Example 8 of this invention. It is sectional drawing which shows arrangement | positioning of the condensing optical system for a scan of the comparative example 1, and the optical component of the latter stage. FIG. 6 is various aberration diagrams of the scanning condensing optical system of Comparative Example 1.

  Hereinafter, an integrated endoscope including a condensing optical system for scanning according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a side sectional view showing the internal configuration of the distal end portion of the integrated endoscope 300 of the present embodiment. As shown in FIG. 1, a confocal optical system 100 for observing a subject (biological tissue 400 in a body cavity) at a high magnification (confocal observation) and a living body are provided in the distal end portion of the integrated endoscope 300. A normal observation optical system 200 for normal observation of the tissue 400 is incorporated. The integrated endoscope 300 is connected to a processor (not shown). The processor includes a light source unit corresponding to each optical system and an image processing unit that processes an imaging signal of the living tissue 400 imaged by each optical system. Since these units are well-known, description of the concrete structure is abbreviate | omitted. Moreover, in each figure, the optical axis direction of the condensing optical system 10 for scanning of the confocal optical system 100 is defined as the Z direction, and the directions perpendicular to the Z direction and perpendicular to each other are defined as the X direction and the Y direction, respectively. Define. That is, the X direction and the Y direction define a plane (XY plane) orthogonal to the Z direction.

  The normal observation optical system 200 includes an illumination optical system that irradiates the living tissue 400 with light from a light source (for example, a xenon lamp) included in the light source unit, a solid-state imaging device that images the irradiated living tissue 400, and the like. .

  The confocal optical system 100 includes a scanning condensing optical system 10, a single mode optical fiber (hereinafter simply referred to as "optical fiber") 20, piezoelectric elements 30A and 30B (biaxial actuator), a shape memory alloy 40, a cover. Glass 80 is provided. The scanning condensing optical system 10 and the optical fiber 20 are held in a cylindrical frame 50. The frame 50 is slidably held in a cylindrical metal pipe 60 having a diameter slightly larger than the diameter of the frame 50.

  The optical fiber 20 transmits laser light (excitation light) incident from the light source unit, and the transmitted excitation light is disposed in the distal end portion of the integrated endoscope 300 (in the confocal optical system 100). Eject more. The exit end 21 of the optical fiber 20 functions as a secondary point light source of the confocal optical system 100. The position in the two-dimensional direction (XY directions) of the emission end 21 that is a point light source periodically changes according to the operation of the piezoelectric elements 30A and 30B. Specifically, the processor generates a drive signal to drive and control the piezoelectric elements 30A and 30B that are bonded and fixed to the outer peripheral surface of the optical fiber 20 near the emission end 21. The piezoelectric elements 30A and 30B are deformed in the XY directions by the inverse piezoelectric effect according to the drive signal, and the vicinity of the emission end 21 is referred to as a surface approximating the XY plane (hereinafter referred to as “XY approximate surface”). (It will be described later.) The exit end 21 moves periodically according to the frame rate so as to draw a predetermined scanning locus on the XY approximate plane. For this type of two-dimensional scanning, there are various types such as spiral scanning around the central axis AX, raster scanning method for reciprocating scanning in the horizontal direction of the scanning range, and Lissajous scanning method for scanning the scanning range sinusoidally. A scheme can be applied.

  A shape memory alloy 40 and a compression coil spring 70 are attached between the outer wall surface 51 of the frame 50 and the inner wall surface 61 of the metal pipe 60. Both the outer wall surface 51 and the inner wall surface 61 are substantially orthogonal to the Z direction (that is, on the XY plane). The shape memory alloy 40 can be deformed when an external force is applied at room temperature, and when it is heated to a certain temperature or more in a deformed state, the shape memory alloy 40 is restored to a memorized state. More specifically, the shape memory alloy 40 contracts in the Z direction when heated. On the other hand, the compression coil spring 70 is attached between the outer wall surface 51 and the inner wall surface 61 in a compressed state from the natural length. That is, the compression coil spring 70 urges the frame 50 toward the cover glass 80 in the metal pipe 60.

  The shape memory alloy 40 contracts against the tension of the compression coil spring 70 when heated by energization. As the shape memory alloy 40 contracts, the frame 50 slides in the metal pipe 60 to the rear of the distal end of the endoscope (in a direction away from the cover glass 80). Thereby, the condensing position of the light beam emitted from the exit end 21 which is a point light source and passing through the condensing optical system for scanning 10 is shifted in the Z direction. That is, scanning is performed in the Z direction. By combining the periodic movement of the point light source on the XY approximate plane by the biaxial actuator (piezoelectric elements 30A and 30B) and the advance and retreat of the point light source in the Z direction by the action of the shape memory alloy 40 and the compression coil spring 70, Can be three-dimensionally scanned.

  The exit end 21 of the optical fiber 20 is disposed at the object side focal position of the scanning condensing optical system 10 (in other words, a position optically conjugate with the image side focal position of the scanning condensing optical system 10). Therefore, it functions as a confocal pinhole. Of the scattered component (fluorescence) of the subject excited by the excitation light, only the fluorescence from the condensing point optically conjugate with the emission end 21 is incident on the emission end 21. The fluorescence is transmitted through the optical fiber 20 and enters an image unit (not shown) for generating a confocal image provided in the processor. By the processing by the unit, a three-dimensional image of the living tissue 400 is obtained.

  FIG. 2 is an enlarged view of the vicinity of the condensing optical system 10 for scanning in the confocal optical system 100. As shown in FIG. 2, the XY approximate plane on which the exit end 21, which is a point light source, moves is an extension line (dashed line) of the principal ray of the light beam emitted from the exit end 21 and the optical axis (dashed line) AX. It becomes a curved surface (arrow dotted line) with the intersection point P as the center of curvature. The approximate XY plane is curved toward the base end side of the optical fiber 20 with respect to the XY plane. The amount of curvature of the XY approximate plane with respect to the XY plane increases as the distance from the optical axis AX increases. As shown in FIG. 2, the intersection point P is located closer to the scanning condensing optical system 10 than the bending center C of the optical fiber 20. The scanning condensing optical system 10 is disposed so that the entrance pupil is located at the intersection P.

  In order to achieve a wide angle of view in the condensing optical system for scanning, in order to capture the emission light from the point light source that moves in a wide range while setting the movement range of the emission end of the optical fiber that is a point light source large It is necessary to design a large effective beam diameter. However, since the amount of curvature of the XY approximate plane (object plane) with respect to the XY plane increases as the movement range of the point light source increases, the under-direction image plane may be reduced due to the potential under-surface curvature of the condensing optical system. Further curvature is added. Further, the scanning condensing optical system is preferably an equal-magnification optical system (or an optical system with a higher magnification) in which, for example, the image-side NA and the object-side NA are equal in order to observe the subject at a high magnification. However, in the case of an equal magnification optical system, the amount of curvature of the XY approximate surface with respect to the XY plane appears as it is on the image side. As described above, in the scanning condensing optical system, there is a possibility that a large curvature of field occurs due to the amount of curvature of the XY approximate surface with respect to the XY plane, and it is difficult to avoid a decrease in peripheral resolution. Accordingly, the present inventor has conducted extensive studies and has achieved a scan suitable for suppressing the field curvature (and other various aberrations) that can occur as described above, while achieving both a reduction in size and a wide angle of view. The condensing optical system 10 was found.

  FIG. 3 is a cross-sectional view showing the arrangement of the condensing optical system 10 for scanning and the optical component (cover glass 80) in the subsequent stage according to Embodiment 1 (details will be described later) of the present invention. Here, the scanning condensing optical system 10 according to the embodiment of the present invention will be described in detail with reference to FIG. Note that in each configuration diagram of the condensing optical system 10 for scanning including FIG. 3, the left side in the drawing is the object side (the exit end 21 side which is a point light source), and the right side in the drawing is the image side (surface to be tested). Side).

  As shown in FIG. 3, the scanning condensing optical system 10 includes at least a first group G1 and a second group G2 in order from the point light source side. Each optical lens constituting each group G1 and G2 has a rotationally symmetric shape with the optical axis AX of the condensing optical system 10 for scanning as the center. A cover glass 80 is disposed on the test surface side from the second group G2. The cover glass 80 is designed to have an appropriate thickness in order to correct spherical aberration. In the above description, “has at least” is because 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, a configuration example in which a parallel plate that does not substantially contribute to optical performance is added to the condensing optical system for scanning according to the present invention, and the configuration and effect of the condensing optical system for scanning according to the present invention are maintained. A configuration example in which another optical element is added is assumed. In the description of the first group G1 and the second group G2, it is expressed as “at least” for the same reason.

  The axial light between the first group G1 and the second group G2 is light substantially parallel to the optical axis AX (substantially parallel light). By making substantially parallel light between the first group G1 and the second group G2, the optical performance of each group can be measured by, for example, interference fringe observation using an interferometer before the first group G1 and the second group G2 are assembled. Can be evaluated independently. Further, after combining appropriate groups based on the evaluation result of each group, as described in, for example, Japanese Patent No. 4320184 by the present applicant, one lens is used as an alignment lens, and this is adjusted. By aligning with the core jig, errors in the assembled state of both groups can be efficiently reduced.

  In addition, by making the light between the first group G1 and the second group G2 substantially parallel light, there is substantially no change in magnification due to a change in group spacing (the NA on the surface to be examined does not change substantially). Therefore, for example, by moving only the second group G2 in the optical axis direction, the observation depth (observation position in the depth direction of the living tissue 400) by the scanning condensing optical system 10 can be changed.

  As shown in FIG. 3, the first group G1 is a lens group having positive power, and in order from the point light source side, the meniscus lens L1 having a concave surface directed to the point light source side and the convex surface directed to the test surface side. A positive lens L2, a positive lens L3 having a convex surface facing the point light source side, a negative lens L4 having a concave surface facing the test surface side, and a cemented lens CL1 including at least a positive lens L5.

  The first group G1 is a lens group having positive power, and in order from the point light source side, a meniscus lens having a concave surface facing the point light source side, a positive lens having a convex surface facing the test surface side, and a negative lens, It is good also as a structure which has at least the cemented lens which consists of a positive lens, and the meniscus lens which orient | assigned the concave surface to the to-be-tested surface side (refer Example 2 mentioned later).

  In the first group G1, the positive lens contributes to correction of spherical aberration, and the cemented lens contributes to correction of chromatic aberration.

  As shown in FIG. 3, the second group G2 is a lens group having a positive power, and in order from the point light source side, a cemented lens CL2 including a negative lens L6 and a positive lens L7 with a concave surface facing the point light source side. And a positive lens L8 and at least a meniscus lens L9 having a concave surface facing the test surface.

  Also in the second group G2, the positive lens contributes to correction of spherical aberration, and the cemented lens contributes to correction of chromatic aberration.

  The condensing optical system for scanning 10 has a surface disposed closest to the point light source (a surface on the point light source side of the meniscus lens L1) and a surface disposed closest to the test surface (the surface on the test surface side of the meniscus lens L9). By making both surfaces concave, the occurrence of coma and astigmatism at the time of entering and exiting the condensing optical system 10 for scanning is suppressed.

Here, the curvature radius of the light source side surface points of the meniscus lens L1 is defined as r _11, the radius of curvature of the surface of the test surface side of the meniscus lens L1 is defined as r _21, the point light sources side of the meniscus lens L9 When the curvature radius of the surface is defined as r ₁₂ and the curvature radius of the surface of the meniscus lens L9 on the test surface side is defined as r ₂₂ , the condensing optical system for scanning 10 has the following conditional expressions (1) and ( 2)
−0.4 <SF ₁ <0.0 (1)
−0.6 <SF ₂ <−0.1 (2)
However,
SF ₁ : (r ₁₁ −r ₂₁ ) / (r ₁₁ + r ₂₁ )
_{SF 2: (r 12 -r 22} ) / (r 12 + r 22)
Meet.

If the upper limit of SF ₁ defined in the conditional expression (1) is exceeded, the power of the meniscus lens L1 becomes too strong, so that coma and astigmatism are greatly generated and correction becomes difficult. In addition, since the positive power of the first lens group G1 becomes too strong, it is difficult to secure the negative power necessary for correcting the curvature of field (prone to insufficient correction). On the other hand, even when the value falls below the lower limit of SF ₁ defined in the conditional expression (1), the power of the meniscus lens L1 becomes too strong, resulting in large coma and astigmatism, which makes correction difficult. Further, since the negative power of the first lens group G1 becomes too strong, a large off-axis chromatic aberration occurs and correction becomes difficult. Furthermore, the incident height of off-axis light becomes large, which is disadvantageous for the design for reducing the diameter of the condensing optical system 10 for scanning. In other words, it becomes difficult to incorporate the condensing optical system 10 for scanning into the distal end portion of the integrated endoscope 300 having a small diameter.

If the upper limit of SF ₂ defined in the conditional expression (2) is exceeded, the power of the meniscus lens L9 becomes too weak, and therefore the incident angle of the excitation light with respect to the test surface and the return light to the meniscus lens L9 (test The incident angle of the autofluorescence generated on the surface increases, and the irradiation efficiency of the test surface by the excitation light and the fluorescence capture efficiency can be reduced. On the other hand, if the lower limit of SF ₂ defined by the conditional expression (2) is not reached, the power of the positive lens in the second group G2 becomes too strong, resulting in large coma and astigmatism, making correction difficult. It becomes. In addition, the height of off-axis light emission is increased, which is disadvantageous for the design for reducing the diameter of the condensing optical system 10 for scanning. In other words, it becomes difficult to incorporate the condensing optical system 10 for scanning into the distal end portion of the integrated endoscope 300 having a small diameter.

  When the conditional expressions (1) and (2) are satisfied at the same time, the field curvature (and coma, astigmatism, spherical surface) can be achieved even when both the downsizing and the wide angle of view of the condensing optical system 10 for scanning are achieved. Occurrence of various aberrations such as aberration and chromatic aberration), can efficiently capture the light emitted from the point light source, and can efficiently irradiate and irradiate the test surface with the excitation light. It is possible to efficiently capture fluorescence from the test surface. In addition, when the conditional expressions (1) and (2) are simultaneously satisfied, even when the object plane (XY approximate plane) is curved as in the confocal optical system 100, the curvature of field is suppressed. be able to. Further, the scanning condensing optical system 10 can be designed with a size suitable for incorporation into the distal end portion of the integrated endoscope 300 having a small diameter.

The scanning condensing optical system 10 defines, for example, the focal length of the lens having the strongest negative power among the lenses constituting the first group G1 as f _1n, and the focal length of the first group G1 as f _1. The following conditional expression (3)
−4.5 ≦ f _1n / f ₁ ≦ −0.5 (3)
Is further satisfied.

When falls below conditional expression lower limit of f _{1n /} f ₁ as defined in (3), it is difficult to secure a negative power required for correction of the field curvature (likely under-corrected). On the other hand, if exceed the upper limit of f _{1n /} f ₁ as defined in conditional expression (3), with an increase in negative power, it becomes possible to increase the curvature of the lens surface, processing becomes difficult. Further, since the negative power is too strong, the sensitivity (change in aberration according to the assembly error) is increased, which causes a problem such as a decrease in yield.

  By satisfying conditional expression (3), field curvature can be suppressed even when the object plane (XY approximate plane) is curved as in the confocal optical system 100. In addition, since it is not necessary to set the curvature of the lens surface to be excessively large, the lens surface can be designed in consideration of processing. Moreover, since sensitivity can be suppressed and tolerance for assembly errors and the like can be increased, for example, a decrease in yield can be suppressed.

Further, the scanning light focusing optical system 10, e.g., a strong lens focal length of the most the negative power among the lenses constituting the second lens group G2 is defined as f _2n, the focal length of the second lens group G2 f ₂ The following conditional expression (4)
−0.9 ≦ f _2n / f ₂ ≦ −0.5 (4)
Is further satisfied.

When falls below conditional expression lower limit of f _{2n /} f ₂ as defined in (4), (likely under-corrected) it is difficult to ensure the negative power required for correction of the field curvature. On the other hand, if exceed the upper limit of f _{2n /} f ₂ as defined in conditional expression (4), with an increase in negative power, it becomes possible to increase the curvature of the lens surface, processing becomes difficult. Further, since the negative power is too strong, the sensitivity is increased, and thus a problem such as a decrease in yield occurs.

  By satisfying conditional expression (4), field curvature can be suppressed even when the object plane (XY approximate plane) is curved as in the confocal optical system 100. In addition, since it is not necessary to set the curvature of the lens surface to be excessively large, the lens surface can be designed in consideration of processing. Moreover, since sensitivity can be suppressed and tolerance for assembly errors and the like can be increased, for example, a decrease in yield can be suppressed.

For example, when the focal length of the lens having the strongest positive power among the lenses constituting the first group G1 is defined as _f1p , the scanning condensing optical system 10 satisfies the following conditional expression (5).
1.0 ≦ f _1p / f ₁ ≦ 4.0 (5)
Is further satisfied.

When the upper limit of f _1p / f ₁ defined in the conditional expression (5) is exceeded, the positive power becomes weak and the change in aberration on each surface of the first group G1 becomes gradual (that is, the sensitivity becomes low). However, as a compensation, the total length of the scanning condensing optical system 10 becomes long and the curvature of field is also insufficiently corrected. On the other hand, if it falls below the lower limit of f _1p / f ₁ defined in the conditional expression (5), the total length of the condensing optical system 10 for scanning can be shortened, but at the expense of large spherical aberration and coma aberration. This makes correction difficult. In addition, since the change in aberration on each surface of the first group G1 becomes large (that is, the sensitivity becomes high), aberration is likely to occur due to an assembly error or the like.

  By satisfying conditional expression (5), spherical aberration and coma aberration in the first group G1 can be suppressed while correcting curvature of field in the entire scanning condensing optical system 10. In addition, the overall length of the scanning condensing optical system 10 can be suppressed, and the sensitivity can also be suppressed.

For example, when the focal length of the lens having the strongest positive power among the lenses constituting the second group G2 is defined as _f2p , the scanning condensing optical system 10 satisfies the following conditional expression (6).
0.5 ≦ f _2p / f ₂ ≦ 3.0 (6)
Is further satisfied.

If the upper limit of f _2p / f ₂ defined in the conditional expression (6) is exceeded, the positive power becomes weak and the change in aberration on each surface of the second group G2 becomes gradual (that is, the sensitivity becomes low). However, as a compensation, the total length of the scanning condensing optical system 10 becomes long and the curvature of field is also insufficiently corrected. On the other hand, if the lower limit of f _2p / f ₂ stipulated in the conditional expression (6) is not reached, the total length of the condensing optical system 10 for scanning can be shortened, but at the cost of large spherical aberration and coma aberration. This makes correction difficult. Further, since the change in aberration on each surface of the second group G2 becomes large (that is, the sensitivity becomes high), aberrations are likely to occur due to assembly errors and the like.

  By satisfying conditional expression (6), spherical aberration and coma aberration in the second lens group G2 can be suppressed while correcting curvature of field in the entire scanning condensing optical system 10. In addition, the overall length of the scanning condensing optical system 10 can be suppressed, and the sensitivity can also be suppressed.

For example, when the focal length of the meniscus lens L1 is defined as f _1m , the scanning condensing optical system 10 has the following conditional expression (7):
5.0 ≦ | f _1m / f ₁ | ≦ 20.0 (7)
Is further satisfied.

If the upper limit of | f _1m / f ₁ | defined in the conditional expression (7) is exceeded, the power of the meniscus lens L1 becomes weak, and the change in aberration on each surface of the first group G1 becomes gentle (that is, sensitivity). However, the total length of the condensing optical system for scanning 10 is increased as a price. On the other hand, when the value falls below the lower limit of | f _1m / f ₁ | defined in the conditional expression (7), the power of the meniscus lens L1 becomes strong, so that the total length of the condensing optical system 10 for scanning can be shortened. As a compensation, spherical aberration and astigmatism become large and correction becomes difficult. In addition, since the change in aberration on each surface of the first group G1 becomes large (that is, the sensitivity becomes high), aberration is likely to occur due to an assembly error or the like.

  By satisfying conditional expression (7), spherical aberration and astigmatism in the first lens group G1 can be suppressed while correcting curvature of field in the entire scanning condensing optical system 10. In addition, the overall length of the scanning condensing optical system 10 can be suppressed, and the sensitivity can also be suppressed.

For example, when the focal length of the meniscus lens L9 is defined as f _{2 m} , the condensing optical system 10 for scanning has the following conditional expression (8)
1.5 ≦ | f _2m / f ₂ | ≦ 4.5 (8)
Is further satisfied.

If the upper limit of | f _2m / f ₂ | defined in the conditional expression (8) is exceeded, the power of the meniscus lens L9 becomes weak, so that the incident angle of the excitation light with respect to the test surface becomes gentle, and the cover glass A distance between the surface 80 and the test surface (the working distance WD shown in FIG. 2) can be ensured, but the total length of the scanning condensing optical system 10 is increased as a price. On the other hand, if the value falls below the lower limit of | f _2m / f ₂ | defined in the conditional expression (8), the power of the meniscus lens L9 becomes too strong, making it difficult to secure the working distance or in the radial direction. growing.

  By satisfying conditional expression (8), the total length of the scanning condensing optical system 10 can be suppressed while ensuring a working distance.

In addition, the scanning condensing optical system 10 does not divide and arrange strong negative power in the entire system, but instead arranges the object power to be curved by temporarily strengthening the negative power and narrowing the light beam once. This is advantageous for correction of curvature of field caused by moving the point light source on (XY approximate surface). As an example, by arranging lenses having strong negative power side by side near the boundary between the first group G1 and the second group G2, the negative power is locally increased near the eyelid and the luminous flux is once narrowed. The curvature of field is corrected. The lens having a strong negative power here is, for example, the following conditional expression (9) when the refractive index with respect to the e-line is defined as _nne.
n _ne ≧ 1.85 (9)
It is a lens that satisfies When a high refractive index material is used, since strong negative power can be obtained while suppressing the curvature of the negative lens, various aberrations that occur depending on the curvature can be suppressed.

The scanning condensing optical system 10 includes a surface arranged closest to the test surface in the first group G1 (a surface on the test surface side of the positive lens L5 in FIG. 3), and a second group G2. Among them, a pair of concave surfaces facing each other (a surface on the side of the point light source of the negative lens L6 in FIG. 3) that is arranged closest to the point light source side are concave surfaces facing the test surface side among the pair of concave surfaces. Is defined as r _31, and the curvature radius of the concave surface facing the concave surface having the curvature radius r ₃₁ (facing the point light source side) is defined as r ₃₂ , the following conditional expression (10)
−0.2 <SF ₃ <0.0 (10)
However,
_{SF 3: (r 31 + r} 32) / (r 31 -r 32)
Is further satisfied. When the conditional expression (10) is satisfied in such a lens arrangement, the Petzval sum can be kept small or negative in addition to the coma aberration correcting action by arranging the concave surfaces facing each other. Even when the (XY approximate surface) is curved, the curvature of field can be suppressed.

If the upper limit of the SF ₃ as defined in the conditional expression (10), by the radius of curvature of the concave surface r ₃₂ facing the point light source side is reduced, a concave surface on the object surface side with the correction of the coma aberration becomes difficult The negative power of the directed lens becomes too large, making it difficult to correct field curvature. On the other hand, if the lower limit of SF ₃ defined in the conditional expression (10) is not reached, the curvature radius r _{31 of the} concave surface facing the test surface side is reduced, which is advantageous for correction of field curvature. As a price, it becomes difficult to correct coma.

  Further, for example, it is advantageous for correction of chromatic aberration by using each of the pair of lenses facing the concave surfaces as a cemented lens with a lens having a different power. As shown in FIG. 3, in this embodiment, in order to correct chromatic aberration, a pair of positive lens L5 and negative lens L6 with concave surfaces facing each other are cemented with a negative lens L4 and a positive lens L7, respectively, and cemented lenses CL1 and CL2 are used. It is said.

  Next, eight specific numerical examples of the condensing optical system 10 for scanning described so far will be described, and one comparative example to be compared with each numerical example 1 to 8 will be described. As shown in FIG. 1, the scanning condensing optical system 10 of each of Numerical Examples 1 to 8 and the scanning condensing optical system of Comparative Example 1 are arranged in the distal end portion of the integrated endoscope 300. .

  As described above, the configuration of the condensing optical system 10 for scanning according to the first embodiment of the present invention is as shown in FIG.

  Table 1 shows specific numerical configurations (design values) of the scanning condensing optical system 10 (and the cover glass 80 disposed in the subsequent stage) according to the first embodiment. The surface number NO shown in Table 1 corresponds to the surface code rn (n is a natural number) in FIG. 3 except for the surface number 1 corresponding to the stop. In Table 1, R (unit: mm) is a radius of curvature of each surface of the optical member, D (unit: mm) is an optical member thickness or optical member interval on the optical axis AX, and N (E) is an e-line ( ND represents the refractive index of the d-line (wavelength 588 nm), and νd represents the Abbe number of the d-line. Moreover, the condensing optical system 10 for scanning of Example 1 has NA (numerical aperture on the test surface side) of 0.30, an image height of 0.05 mm, and a back focus BF of 0.17 mm. In each example, since an equal-magnification optical system is assumed, the numerical aperture on the test surface side is equal to the numerical aperture on the object plane side.

  4A to 4D are graphs showing various aberrations of the condensing optical system 10 for scanning according to the first embodiment. Specifically, FIG. 4A shows spherical aberration and axial chromatic aberration at e-line (546 nm), d-line (588 nm), and F-line (486 nm). FIG. 4B shows lateral chromatic aberration at e-line, d-line, and F-line. 4A and 4B, the solid line indicates the aberration at the e-line, the dotted line indicates the aberration at the d-line, and the alternate long and short dash line indicates the aberration at the F-line. FIG. 4C shows astigmatism. In FIG.4 (c), a continuous line shows a sagittal component and a dotted line shows a meridional component, respectively. FIG. 4 (d) shows distortion. 4A to 4C, the vertical axis represents the image height, and the horizontal axis represents the aberration amount. In FIG. 4D, the vertical axis represents the image height, and the horizontal axis represents the distortion. In addition, the description about each table | surface or each drawing of the present Example 1 is applied also to each table | surface or each drawing shown by each subsequent numerical example or comparative example.

  FIG. 5 is a sectional view showing the arrangement of the condensing optical system 10 for scanning and the optical component (cover glass 80) at the subsequent stage according to the second embodiment of the present invention. As shown in FIG. 5, the condensing optical system 10 for scanning according to the second embodiment is different from the first embodiment in the configuration of the first group G1. Specifically, the first group G1 of Example 2 includes, in order from the point light source side, a meniscus lens L1 having a concave surface facing the point light source side, a positive lens L2 having a convex surface facing the test surface side, and a positive lens L11. A negative lens L12 and a meniscus lens L13 having a concave surface facing the test surface. 6A to 6D are diagrams showing various aberrations (spherical aberration, axial chromatic aberration, lateral chromatic aberration, astigmatism, distortion) of the condensing optical system 10 for scanning according to the second embodiment. Table 2 shows specific numerical configurations of optical components including the condensing optical system 10 for scanning according to the second embodiment. Moreover, the condensing optical system for scanning 10 of Example 2 has an NA (numerical aperture on the test surface side) of 0.30, an image height of 0.12 mm, and a back focus BF of 0.17 mm.

  FIG. 7 is a cross-sectional view showing the arrangement of the condensing optical system 10 for scanning and the optical component (cover glass 80) at the subsequent stage according to the third embodiment of the present invention. As shown in FIG. 7, the condensing optical system for scanning 10 of the third embodiment has the same lens arrangement as that of the first embodiment. 8A to 8D are graphs showing various aberrations (spherical aberration, longitudinal chromatic aberration, lateral chromatic aberration, astigmatism, distortion) of the condensing optical system 10 for scanning according to the third embodiment. Table 3 shows a specific numerical configuration of each optical component including the condensing optical system 10 for scanning according to the third embodiment. In the scanning condensing optical system 10 of the third embodiment, the NA (numerical aperture on the test surface side) is 0.30, the image height is 0.13 mm, and the back focus BF is 0.14 mm.

  FIG. 9 is a cross-sectional view showing the arrangement of the condensing optical system 10 for scanning and the optical component (cover glass 80) at the subsequent stage according to the fourth embodiment of the present invention. As shown in FIG. 9, the condensing optical system 10 for scanning of the fourth embodiment has the same lens arrangement as that of the first embodiment. 10A to 10D are graphs showing various aberrations (spherical aberration, longitudinal chromatic aberration, lateral chromatic aberration, astigmatism, distortion) of the condensing optical system 10 for scanning according to the fourth embodiment. Table 4 shows specific numerical configurations of optical components including the condensing optical system 10 for scanning according to the fourth embodiment. Further, the condensing optical system for scanning 10 of Example 4 has an NA (numerical aperture on the test surface side) of 0.40, an image height of 0.12 mm, and a back focus BF of 0.12 mm.

  FIG. 11 is a cross-sectional view showing the arrangement of the condensing optical system 10 for scanning and the optical component (cover glass 80) at the subsequent stage according to the fifth embodiment of the present invention. As shown in FIG. 11, the condensing optical system 10 for scanning of the fifth embodiment has the same lens arrangement as that of the first embodiment. However, in the fifth embodiment, the positive lenses L2 and L3 of the first embodiment are divided into three lenses L31 to L33. Further, the positive lens L8 of the first embodiment is divided into two lenses L41 and L42. 12A to 12D are diagrams showing various aberrations (spherical aberration, axial chromatic aberration, lateral chromatic aberration, astigmatism, distortion) of the condensing optical system 10 for scanning according to the fifth embodiment. Table 5 shows specific numerical configurations of optical components including the condensing optical system 10 for scanning according to the fifth embodiment. In the scanning condensing optical system 10 of the fifth embodiment, NA (numerical aperture on the test surface side) is 0.30, the image height is 0.14 mm, and the back focus BF is 0.14 mm.

  FIG. 13 is a cross-sectional view showing the arrangement of the condensing optical system 10 for scanning and the optical component (cover glass 80) at the subsequent stage according to the sixth embodiment of the present invention. As shown in FIG. 13, the scanning condensing optical system 10 of the sixth embodiment has the same lens arrangement as that of the first embodiment. 14A to 14D are diagrams showing various aberrations (spherical aberration, axial chromatic aberration, lateral chromatic aberration, astigmatism, distortion aberration) of the condensing optical system 10 for scanning according to the sixth embodiment. Table 6 shows a specific numerical configuration of each optical component including the condensing optical system 10 for scanning according to the sixth embodiment. In the scanning condensing optical system 10 of Example 6, the NA (numerical aperture on the test surface side) is 0.30, the image height is 0.13 mm, and the back focus BF is 0.08 mm.

  FIG. 15 is a sectional view showing the arrangement of the condensing optical system 10 for scanning and the optical component (cover glass 80) at the subsequent stage according to the seventh embodiment of the present invention. As shown in FIG. 15, the scanning condensing optical system 10 of the seventh embodiment has the same lens arrangement as that of the first embodiment. FIGS. 16A to 16D are graphs showing various aberrations (spherical aberration, axial chromatic aberration, lateral chromatic aberration, astigmatism, distortion) of the condensing optical system 10 for scanning according to the seventh embodiment. Table 7 shows a specific numerical configuration of each optical component including the condensing optical system 10 for scanning according to the seventh embodiment. Further, the condensing optical system for scanning 10 of Example 7 has an NA (numerical aperture on the test surface side) of 0.30, an image height of 0.13 mm, and a back focus BF of 0.19 mm.

  FIG. 17 is a cross-sectional view showing the arrangement of the condensing optical system 10 for scanning and the optical component (cover glass 80) at the subsequent stage according to the eighth embodiment of the present invention. As shown in FIG. 17, the scanning condensing optical system 10 of the eighth embodiment has the same lens arrangement as that of the first embodiment. 18A to 18D are diagrams showing various aberrations (spherical aberration, axial chromatic aberration, lateral chromatic aberration, astigmatism, distortion aberration) of the condensing optical system 10 for scanning according to the eighth embodiment. Table 8 shows specific numerical configurations of optical components including the condensing optical system 10 for scanning according to the eighth embodiment. Further, the condensing optical system for scanning 10 of Example 8 has an NA (numerical aperture on the test surface side) of 0.30, an image height of 0.12 mm, and a back focus BF of 0.08 mm.

(Comparative Example 1)
FIG. 19 is a cross-sectional view showing the arrangement of the condensing optical system for scanning of Comparative Example 1 and the optical component (cover glass 80) at the subsequent stage. The scanning condensing optical system of Comparative Example 1 has the same lens arrangement as that of Example 1. 20A to 20D are diagrams showing various aberrations (spherical aberration, axial chromatic aberration, lateral chromatic aberration, astigmatism, distortion aberration) of the scanning condensing optical system of Comparative Example 1. FIG. Table 9 shows a specific numerical configuration of each optical component including the condensing optical system for scanning of Comparative Example 1. Further, the scanning condensing optical system of Comparative Example 1 has an NA (numerical aperture on the test surface side) of 0.30, an image height of 0.12 mm, and a back focus BF of 0.17 mm.

（比較検証）
表１０は、本実施例１〜８及び比較例１の各例において、条件式（１）〜（１０）のそれぞれを適用したときに算出される値の一覧表である。なお、表１０中、各条件式の各値の右隣に記載された符号は、当該条件式を主として規定するレンズを示す。条件式（１）及び（７）を主として規定するレンズは、全系のうち最も点光源側に配置されるレンズ（例えばメニスカスレンズＬ１）である。条件式（２）及び（８）を主として規定するレンズは、全系のうち最も被検面側に配置されるレンズ（例えばメニスカスレンズＬ１２）である。条件式（３）を主として規定するレンズは、第１群Ｇ１を構成するレンズのうち最も負のパワーの強いレンズ（例えば負レンズＬ４）である。条件式（４）を主として規定するレンズは、第２群Ｇ２を構成するレンズのうち最も負のパワーの強いレンズ（例えば負レンズＬ６）である。条件式（５）を主として規定するレンズは、第１群Ｇ１を構成するレンズのうち最も正のパワーの強いレンズ（例えば正レンズＬ５）である。条件式（６）を主として規定するレンズは、第２群Ｇ２を構成するレンズのうち最も正のパワーの強いレンズ（例えば正レンズＬ８）である。なお、条件式（９）については、当該条件式を満たす負レンズの符号が記載されている。

(Comparison verification)
Table 10 is a list of values calculated when each of the conditional expressions (1) to (10) is applied in each of Examples 1 to 8 and Comparative Example 1. Note that in Table 10, a symbol written to the right of each value in each conditional expression indicates a lens that mainly defines the conditional expression. The lens that mainly defines the conditional expressions (1) and (7) is a lens (for example, a meniscus lens L1) arranged closest to the point light source in the entire system. The lens that mainly defines the conditional expressions (2) and (8) is a lens (for example, a meniscus lens L12) arranged closest to the test surface in the entire system. The lens that mainly defines the conditional expression (3) is a lens having the strongest negative power (for example, the negative lens L4) among the lenses constituting the first group G1. The lens that mainly defines the conditional expression (4) is a lens having the strongest negative power (for example, the negative lens L6) among the lenses constituting the second group G2. The lens that mainly defines the conditional expression (5) is the lens having the strongest positive power (for example, the positive lens L5) among the lenses constituting the first group G1. The lens that mainly defines the conditional expression (6) is the lens having the strongest positive power (for example, the positive lens L8) among the lenses constituting the second group G2. Regarding conditional expression (9), the sign of a negative lens that satisfies the conditional expression is described.

  As shown in Table 10, the condensing optical system for scanning in Comparative Example 1 does not satisfy the conditional expression (2). Therefore, as shown in FIG. 20, the condensing optical system for scanning in Comparative Example 1 does not suppress spherical aberration, axial chromatic aberration, and lateral chromatic aberration. That is, as a result of trying to achieve both a reduction in size and a wide angle of view and correction of field curvature, at least a part of optical performance must be sacrificed.

  On the other hand, as shown in Table 10, the condensing optical system for scanning 10 of Examples 1 to 8 satisfies the conditional expressions (1) and (2) at the same time, thereby reducing the size and wide angle of view. Even in the case where both are realized, curvature of field and occurrence of various aberrations are suppressed. Further, it is possible to efficiently capture the light emitted from the point light source, efficiently irradiate the test surface with the excitation light, and efficiently capture the autofluorescence from the irradiated test surface.

  Moreover, the condensing optical system 10 for a scanning of the present Examples 1-8 further satisfy | fills conditional expressions other than conditional expression (1) and (2). Therefore, in the scanning condensing optical systems 10 of the first to eighth embodiments, not only the effect of satisfying conditional expressions (1) and (2) but also the effect of satisfying other conditional expressions are exhibited.

  The above is the description of the exemplary embodiments of the present invention. Embodiments of the present invention are not limited to those 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 contents appropriately combined with examples and the like clearly shown in the specification or obvious examples.

10 Condensing optical system for scanning 100 Confocal optical system 300 Integrated endoscope

Claims (10)

An endoscope including a condensing optical system that condenses light emitted from a point light source moving on a predetermined surface,
The condensing optical system is
In order from the point light source side,
The first group with positive power,
The second group with positive power,
Consists of
The axial light between the first group and the second group is substantially parallel light,
The first group is:
In order from the point light source side,
A _first meniscus lens having a concave surface facing the point light source,
A _first positive lens having a convex surface directed toward the test surface on which the light is collected;
Second _first positive lens having a convex surface on the point light source side,
A _first cemented lens comprising a negative lens and a positive lens, the concave surface facing the test surface side;
Consists of
The second group is
In order from the point light source side,
A concave surface facing the point light source side, the first _{and second} cemented lens consisting of a negative lens and a positive lens,
_{First and second} positive lenses,
First _{and second} meniscus lens having a concave surface facing the predetermined surface side,
Consists of
The radius of curvature of the point light source side surface of the first ₁ of the meniscus lens is defined as r _11, the radius of curvature of the test surface side of the first _one meniscus lens is defined as r _21, wherein the radius of curvature of the point light source side surface of the first _{and second} meniscus lens is defined as r _12, the radius of curvature of the test surface side of the first _{and second} meniscus lens when defined as r _22, The following conditional expression −0.4 <SF ₁ <0.0
−0.6 <SF ₂ <−0.1
However,
SF ₁ : (r ₁₁ −r ₂₁ ) / (r ₁₁ + r ₂₁ )
_{SF 2: (r 12 -r 22} ) / (r 12 + r 22)
Meet ,
Endoscope . An endoscope including a condensing optical system that condenses light emitted from a point light source moving on a predetermined surface,
The condensing optical system is
In order from the point light source side,
The first group with positive power,
The second group with positive power,
Consists of
The axial light between the first group and the second group is substantially parallel light,
The first group is:
In order from the point light source side,
A _first meniscus lens having a concave surface facing the point light source,
A _first positive lens having a convex surface directed toward the test surface on which the light is collected;
A _first cemented lens comprising a negative lens and a positive lens;
Second _first meniscus lens having a concave surface facing the predetermined surface side,
Consists of
The second group is
In order from the point light source side,
A concave surface facing the point light source side, the first _{and second} cemented lens consisting of a negative lens and a positive lens,
_{First and second} positive lenses,
First _{and second} meniscus lens having a concave surface facing the predetermined surface side,
Consists of
The radius of curvature of the point light source side surface of the first ₁ of the meniscus lens is defined as r _11, the radius of curvature of the test surface side of the first _one meniscus lens is defined as r _21, wherein the radius of curvature of the point light source side surface of the first _{and second} meniscus lens is defined as r _12, the radius of curvature of the test surface side of the first _{and second} meniscus lens when defined as r _22, The following conditional expression −0.4 <SF ₁ <0.0
−0.6 <SF ₂ <−0.1
However,
SF ₁ : (r ₁₁ −r ₂₁ ) / (r ₁₁ + r ₂₁ )
_{SF 2: (r 12 -r 22} ) / (r 12 + r 22)
Meet ,
Endoscope . When the focal length of the lens having the strongest negative power among the lenses constituting the first group is defined as f _1n and the focal length of the first group is defined as f ₁ , the following conditional expression-4. 5 ≦ f _1n / f ₁ ≦ −0.5
Meet ,
The endoscope according to claim 1 or claim 2. When the focal length of the lens having the strongest negative power among the lenses constituting the second group is defined as f _2n and the focal length of the second group is defined as f ₂ , the following conditional expression −0. 9 ≦ f _2n / f ₂ ≦ −0.5
Meet ,
The endoscope according to any one of claims 1 to 3. When the focal length of the lens having the strongest positive power among the lenses constituting the first group is defined as f _1p and the focal length of the first group is defined as f ₁ , the following conditional expression 1.0 ≦ f _1p / f ₁ ≦ 4.0
Meet ,
The endoscope according to any one of the preceding claims 1. When the focal length of the lens having the strongest positive power among the lenses constituting the second group is defined as f _2p and the focal length of the second group is defined as f ₂ , the following conditional expression 0.5 ≦ f _2p / f ₂ ≦ 3.0
Meet ,
The endoscope according to any one of claims 1 to 5. When the focal length of the _first meniscus lens is defined as f _1m and the focal length of the first group is defined as f ₁ , the following conditional expression 5.0 ≦ | f _1m / f ₁ | ≦ 20 .0
Meet ,
The endoscope according to any one of claims 1 to 6. The focal length of the _{first and second} meniscus lens is defined as _{f 2m,} the focal length of said second group when defined as _{f 2,} the following conditional expression _{1.5 ≦ | f 2m / f 2} | ≦ 4 .5
Meet ,
The endoscope according to any one of claims 1 to 7. Of the lens surfaces of the lenses constituting the first group, the surface arranged closest to the test surface and the surface of the lenses constituting the second group arranged closest to the point light source are mutually connected. A pair of concave surfaces facing each other, at least one of the concave surfaces is a negative lens,
Of a pair of concave, the radius of curvature of the concave surface facing the object surface side is defined as r _31, the radius of curvature of the concave surface facing the concave surface with a curvature radius r ₃₁ when defined as r _32, the following Conditional expression-0.2 <SF ₃ <0.0
However,
_{SF 3: (r 31 + r} 32) / (r 31 -r 32)
Meet ,
The endoscope according to any one of claims 1 to 8. A lens having a concave surface with the radius of curvature r ₃₁ and a lens having a concave surface with the radius of curvature r ₃₂ are:
A pair of positive and negative cemented lenses are formed by being cemented with lenses having different powers, respectively .
The endoscope according to claim 9.

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