JP2007010916A - Eyepiece for endoscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an eyepiece for endoscope in which the entire length of an optical system is short despite a relatively small number of lenses composing the eyepiece (i.e., three), and satisfactory optical performance and high magnification are ensured. <P>SOLUTION: The eyepiece includes in order from the object side: a first lens L<SB>1</SB>composed of a positive meniscus lens whose concave face is disposed on the object side; a second lens L<SB>2</SB>composed of a negative lens whose concave face is disposed on the eye side; and a third lens L<SB>3</SB>composed of convex lenses on both sides. The second lens L<SB>2</SB>and third lens L<SB>3</SB>form a positive cemented lens. The eyepiece satisfies the following expressions: (1) 0.5<(d-aBP+bFP)/f<0.8, (2) 1.4<¾R1F¾/f<1.9, and (3) 25.0<υ<SB>3</SB>- υ<SB>2</SB>, wherein f denotes the focal distance of the entire system, d denotes a spacial interval between the first and second lenses, aBP denotes a distance from the eye-side face of the first lens to the eye-side principal point of the first lens, bFP is a distance from the object-side face of the second lens to the object-side principal point of the cemented lens, R1F denotes the curvature radius of the object-side face of the first lens, and υ2 and υ3 denote the Abbe's numbers of the second lens and third lens respectively. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a high-magnification eyepiece mainly used for an endoscope.

  The eyepiece of the endoscope is incorporated in the operation unit main body at hand, so that the image on the exit end face of the fiber bundle sent from the objective lens at the tip through the optical fiber bundle can be enlarged and observed. It is an optical system. Therefore, when the eyepiece magnification of the eyepiece is low, the observation image is small and difficult to see, which may hinder the examination and diagnosis by the endoscope. In order to make the image easy to observe, the focal length is short and the magnification is high, the distance from the eyepiece to the position of the observer's pupil (eyepoint distance) is long, and the number of eyepieces is small. It was necessary. As eyepieces in consideration of such circumstances, there are those described in Patent Document 1 and Patent Document 2 below. However, these eyepieces are used for a finder optical system of an electronic still camera, and the magnification is not sufficient for use as an endoscope eyepiece. Therefore, in the following Patent Document 3, the applicant of the present invention has a simple configuration of three lenses, but the eyepiece magnification is 34 times, and the distance from the end face of the optical fiber bundle is a distance sufficient for diopter adjustment. An eyepiece that can secure a sufficient eye point distance is proposed.

JP-A-61-48809 JP-A-1-108516 Japanese Patent No. 2791496

  However, in recent years, there has been a demand for smaller and thinner endoscope objective lenses from the medical field, and the corresponding reduction in the diameter of the optical fiber bundle has led to a significant increase in the exit end face of the optical fiber bundle. Accordingly, an eyepiece for an endoscope having a higher magnification has been desired.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an endoscope eyepiece having a relatively small three-lens configuration with a short overall lens system, good optical performance, and high magnification. Is.

An endoscope eyepiece according to the present invention includes, in order from the object side, a first lens composed of a positive meniscus lens having a concave surface facing the object side, a second lens composed of a negative lens facing the concave surface toward the eye side, and both A third lens made of a convex lens is arranged, and the second lens and the third lens are cemented together to form a positive cemented lens, which satisfies the following conditional expressions (1) to (3): It is characterized by this.
(1) 0.5 <(d−aBP + bFP) / f <0.8
(2) 1.4 <| R1F | / f <1.9
(3) 25.0 <ν ₃ −ν ₂
However,
f: Focal length of the entire system
d: Air distance between the first lens and the second lens
aBP: Distance from the eye-side surface of the first lens to the eye-side principal point of the first lens
bFP: Distance from the object side surface of the second lens to the object side principal point of the cemented lens
R1F: radius of curvature of the object side surface of the first lens ν ₂ : Abbe number of the second lens ν ₃ : Abbe number of the third lens

  The endoscope eyepiece according to the present invention satisfies the conditional expressions (1) to (3) with a simple lens configuration of positive, negative, and positive three elements in order from the object side, thereby synthesizing the lens system. Although the focal length is short and the eyepiece magnification is as extremely large as 50 times, for example, it is possible to realize a small eyepiece that can maintain a sufficient distance from the end face of the optical fiber bundle. That is, it is possible to obtain an eyepiece for an endoscope having a short overall lens system and good optical performance in spite of a relatively small lens configuration of three lenses.

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The endoscope eyepiece of the embodiment shown in FIG. 1 (representing the lens of Example 1 as a representative) is a first lens composed of a positive meniscus lens having a concave surface facing the object side in order from the object side. L ₁ , a second lens L _{2 made of} a negative meniscus lens having a concave surface facing the eye side, and a third lens L ₃ made of a biconvex lens are arranged, and the second lens L ₂ and the third lens L ₃ are mutually connected. It is an ocular lens for an endoscope which is cemented to form a positive cemented lens. Note that the vertical line 1 on the object side of the first lens L ₁ represents the position of the surface to be observed (for example, the position of the optical fiber exit end face), and the vertical line 3 between the third lens L ₃ and the image plane 2 is the exit pupil position. Represents.

In addition, the endoscope objective lens of the present embodiment satisfies the following conditional expressions (1) to (3).
(1) 0.5 <(d−aBP + bFP) / f <0.8
(2) 1.4 <| R1F | / f <1.9
(3) 25.0 <ν ₃ −ν ₂
However,
f: Focal length of the entire system
d: Air distance between the first lens and the second lens
aBP: Distance from the eye-side surface of the first lens to the eye-side principal point of the first lens
bFP: Distance from the object side surface of the second lens to the object side principal point of the cemented lens
R1F: radius of curvature of the object side surface of the first lens ν ₂ : Abbe number of the second lens ν ₃ : Abbe number of the third lens

  Hereinafter, the technical significance of the conditional expressions (1) to (3) described above will be described.

Condition (1) is intended to delimit the distance between the object side principal point of the first lens L ₁ of the eye-side principal point and a cemented lens, high magnification and exceeds the upper limit of the conditional expression (1) It becomes difficult. If the lower limit of the one condition (1), it becomes difficult to ensure the air gap between the first lens L ₁ and second lens L _2, we can not maintain the lens system. Where the combined power of the two lenses is
φ = φ ₁ + φ ₂ −Δφ ₁ φ ₂
It is represented by Δ is the air spacing. That is, from this equation, the air distance between the first lens L ₁ and second lens L ₂ becomes large, it is apparent that the synthesized power is reduced.

Condition (2) is intended to define a radius of curvature in the range of the surface of the first lens L ₁ on the object side, beyond the upper limit of the conditional expression (2), sufficient eye point distance can not be obtained. If the lower limit of the one condition (2), the distance of the first lens L ₁ and the optical fiber emitting end face can not be sufficiently secured.

Condition (3) is a cemented lens, intended to define a second lens L ₂ to the range of Abbe number of the difference between the third lens L ₃ both lateral chromatic aberration increases below this lower limit, around The resolution of the part will be reduced.

  The endoscope eyepiece of the present invention will be further described below using specific examples and comparative examples according to the prior art.

<Example 1>
FIG. 1 shows a schematic configuration of the endoscope eyepiece according to the first embodiment. This endoscope eyepiece is, in order from the object side, a first lens L ₁ composed of a positive meniscus lens having a concave surface facing the object side, and a second lens L composed of a negative meniscus lens having a concave surface facing the eye side. _2, are arranged a third lens L ₃ which is a biconvex lens having a surface with a stronger curvature on the object side. However, the second lens L ₂ and third lens L ₃ is bonded to each other to constitute a positive cemented lens.

  The radius of curvature R (mm) of each lens surface of the endoscope eyepiece, the center thickness of each lens, and the air spacing between the lenses (hereinafter collectively referred to as the axial top surface spacing) D (mm), Table 1 shows values of the refractive index N and the Abbe number ν at the d-line of the lens. The numbers in the table represent the order from the object side (the same applies to Examples 2, 3 and Comparative Examples).

  Further, according to the endoscope eyepiece of Example 1, as shown in Table 1, all the conditional expressions (1) to (3) are satisfied. The total length of the lens system is about 9.90 mm, and the eyepiece magnification is about 49.78 times.

Figure 2 shows spherical aberration of the endoscope eyepiece lens of Example 1, astigmatism, coma, and aberration figure illustrating lateral and distortion, the distance 15mm from the surface of the eye side of the third lens L _3, This is when an aberration lens having a focal length of 20 mm is arranged instead of the eye. The scale of 0.4 mm in the spherical aberration diagram and astigmatism diagram corresponds to 1 diopter, and the scale of 0.058 mm in the chromatic aberration diagram and coma aberration diagram corresponds to an angle of 10 minutes (in FIGS. 4, 6 and 8 described later). The same). In the astigmatism diagram, aberrations with respect to the sagittal image surface and the tangential image surface are shown. In these aberration diagrams, ω represents a half angle of view. As is clear from these aberration diagrams, according to the endoscope eyepiece of Example 1, it is possible to correct each aberration satisfactorily while maintaining a high magnification.

<Example 2>
FIG. 3 shows a schematic configuration of the endoscope eyepiece according to the second embodiment. The configuration of the endoscope eyepiece is substantially the same as that of the first embodiment, and in the description of the corresponding drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted.
The radius of curvature R (mm) of each lens surface of the endoscope eyepiece, the center thickness of each lens and the air space D (mm) between the lenses, the refractive index N and the Abbe number ν at the d-line of each lens The values are shown in Table 2.

  Further, according to the endoscope eyepiece of Example 2, as shown in Table 2, all the conditional expressions (1) to (3) are satisfied. The total length of the lens system is about 9.92 mm, and the eyepiece magnification is about 49.76 times.

  FIG. 4 is an aberration diagram showing spherical aberration, astigmatism, coma aberration, lateral chromatic aberration, and distortion of the endoscope eyepiece of Example 2. In the astigmatism diagram, aberrations with respect to the sagittal image surface and the tangential image surface are shown. In these aberration diagrams, ω represents a half angle of view. As is apparent from these aberration diagrams, according to the endoscope eyepiece of Example 2, it is possible to correct each aberration satisfactorily while maintaining a high magnification.

<Example 3>
FIG. 5 shows a schematic configuration of the endoscope eyepiece according to the third embodiment. The configuration of the endoscope eyepiece is substantially the same as that of the first embodiment, and in the description of the corresponding drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted.
The radius of curvature R (mm) of each lens surface of the endoscope eyepiece, the center thickness of each lens and the air space D (mm) between the lenses, the refractive index N and the Abbe number ν at the d-line of each lens Table 3 shows the values.

  Further, according to the endoscope eyepiece of Example 3, as shown in Table 3, all the conditional expressions (1) to (3) are satisfied. The total length of the lens system is about 9.14 mm, and the eyepiece magnification is about 50.18 times.

  FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, coma aberration, lateral chromatic aberration, and distortion of the endoscope eyepiece of Example 3. In the astigmatism diagram, aberrations with respect to the sagittal image surface and the tangential image surface are shown. In these aberration diagrams, ω represents a half angle of view. As is clear from these aberration diagrams, according to the endoscope eyepiece of Example 3, each aberration can be corrected extremely well even though the magnification is high.

<Comparative example>
FIG. 7 shows a schematic configuration of an endoscope eyepiece according to a comparative example. Since the endoscope eyepiece according to the comparative example has a lens configuration substantially the same as that of the first embodiment, the same elements are denoted by the same reference numerals in the description of the corresponding drawings, and overlapping descriptions are given. Is omitted.
The radius of curvature R (mm) of each lens surface of the endoscope eyepiece, the center thickness of each lens and the air gap D (mm) between the lenses, the refractive index N and the Abbe number ν at the d-line of each lens Table 4 shows the values.

  Further, in the endoscope eyepiece of the comparative example, the values corresponding to the conditional expressions (1) to (3) are as shown in Table 4, and the conditional expression (3) is satisfied. Conditional expressions (1) and (2) are not satisfied. The total length of the lens system is about 14.26 mm, and the eyepiece magnification is about 34.00 times.

  FIG. 8 is an aberration diagram showing spherical aberration, astigmatism, coma aberration, lateral chromatic aberration, and distortion of the endoscope eyepiece of the comparative example. In the astigmatism diagram, aberrations with respect to the sagittal image surface and the tangential image surface are shown. In these aberration diagrams, ω represents a half angle of view.

Schematic which shows the structure of the eyepiece for endoscopes which concerns on Example 1 of this invention. Aberration diagram showing various aberrations (spherical aberration, astigmatism, coma aberration, lateral chromatic aberration and distortion) of the endoscope eyepiece of Example 1 Schematic which shows the structure of the eyepiece for endoscopes which concerns on Example 2 of this invention. Aberration diagram showing various aberrations (spherical aberration, astigmatism, coma aberration, lateral chromatic aberration and distortion) of the endoscope eyepiece of Example 2 Schematic which shows the structure of the eyepiece for endoscopes which concerns on Example 3 of this invention. Aberration diagram showing various aberrations (spherical aberration, astigmatism, coma aberration, chromatic aberration of magnification and distortion) of the endoscope eyepiece of Example 3 Schematic which shows the structure of the eyepiece for endoscopes which concerns on a comparative example Aberration diagram showing various aberrations (spherical aberration, astigmatism, coma aberration, lateral chromatic aberration and distortion) of the endoscope eyepiece of the comparative example

Explanation of symbols

L _{1 to} L ₃ lens X optical axis 1 observation surface position 2 image surface 3 exit pupil position

Claims (1)

In order from the object side, a first lens composed of a positive meniscus lens with a concave surface facing the object side, a second lens composed of a negative lens with a concave surface facing the eye side, and a third lens composed of a biconvex lens are arranged. The second lens and the third lens are joined together to form a positive cemented lens, and satisfy the following conditional expressions (1) to (3): .
(1) 0.5 <(d−aBP + bFP) / f <0.8
(2) 1.4 <| R1F | / f <1.9
(3) 25.0 <ν ₃ −ν ₂
However,
f: Focal length of the entire system
d: Air distance between the first lens and the second lens
aBP: Distance from the eye-side surface of the first lens to the eye-side principal point of the first lens
bFP: Distance from the object side surface of the second lens to the object side principal point of the cemented lens
R1F: radius of curvature of the object side surface of the first lens ν ₂ : Abbe number of the second lens ν ₃ : Abbe number of the third lens

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