JP2866729B2 - Endoscope eyepiece - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an endoscope eyepiece, such as a fiberscope or a rigid endoscope, for observing and photographing while arbitrarily enlarging an image size.

[Conventional technology]

In a conventional endoscope eyepiece, various aberrations are satisfactorily corrected by combining a plurality of lenses having a positive power and a lens having a negative power. For example, in the case of a fiberscope that transmits an image of an objective optical system to an eyepiece using an image guide, one fiber is used.
Various aberrations are suppressed below the book diameter. One example of such an endoscope eyepiece is shown in FIG. This means that, in order from the object side, a parallel plane plate (cover glass) 1, a positive lens 2, a positive lens 3, a negative lens 4, a negative lens 5, a positive lens 6, a positive lens 7, a brightness stop 8, a parallel plane plate ( Cover glass) 9
Is a Gaussian type lens system composed of As shown in the aberration diagram of FIG. 16, this lens system has good performance for an exit-side numerical aperture of 0.25 and an image height of about 0.11, but on the other hand, the number of lenses is large and the configuration is complicated. , High cost.

On the other hand, as another eyepiece, as shown in FIG.
A doublet-type lens system including a positive lens 10, a negative lens 11, and a plane-parallel plate (cover glass) 12 in order from the object side is known. This is a simple configuration in which the positive lens 10 and the negative lens 11 are joined, but the performance is inferior to that of the Gauss type. Figures 18 to 21 show that the image height is gradually increased to 10%, 20%, 50%, and 80% compared to the Gaussian type. This figure shows a doublet (designed separately according to the image height) designed to obtain an infinite degree of contrast (MTF) and the relationship between Gaussian type contrast and frequency (good resolution). When the doublet is designed in this way, the numerical aperture is 70%, 60%, 40%, and 20%, respectively, as compared to the Gaussian type. As the image height is increased, the entrance side numerical aperture of the doublet gradually decreases. That is, it can be seen that it is impossible to perform sufficient aberration correction for the numerical aperture and image height of the doublet similar to that of the Gauss type, and one of the numerical aperture and image height must be sacrificed. As described above, the conventional eyepiece cannot achieve both image height, numerical aperture, aberration correction, and simplification of the lens system.

[Problems to be solved by the invention]

As described above, the conventional six-piece Gaussian-type endoscope eyepiece has good optical performance, but has a high optical performance depending on the number of lenses and the peripheral members (frames, spacing rings, etc.) corresponding thereto. There is a disadvantage that costs. Further, in the case of a doublet type for cost reduction, it is difficult to obtain good optical performance by increasing both the image height and the numerical aperture.

By the way, in endoscope eyepieces such as fiberscopes and rigid endoscopes, the numerical aperture of the light emitted from the optical fiber is large, and the rigid endoscope also has a large numerical aperture since an equal-magnification image is relayed. For these reasons, it is required that various aberrations be corrected to a larger numerical aperture than an eyepiece for a camera, a microscope, or the like.

The present invention has been made in view of the above circumstances, and its purpose is to reduce the cost, the numerical aperture,
An object of the present invention is to provide an endoscope eyepiece having good optical performance despite high image heights.

[Means for solving the problem]

In the present invention, the above object has been achieved by introducing an aspheric surface based on a doublet or a simple structure similar thereto.

Specifically, the endoscope eyepiece of the present invention is an eyepiece used for a fiberscope or a rigid scope, and is a single lens having a positive refractive power, and a positive lens as a whole in which a positive lens and a negative lens are joined. A lens system having a refractive power, or a lens system having a positive refractive power as a whole comprising a negative lens arranged in proximity to a positive lens, and any one of the lens surfaces is made aspherical, the fiber scope or The rigid mirror and the single lens or the lens system satisfy the following conditional expression.

0.05 ≦ | I | + | NA · f | ≦ 0.3 Here, I is an image guide image of the fiberscope when the focal length f of the entire system is normalized to 1, or
The image height, NA, of the relay image of the rigid endoscope is si when the angle between the optical axis and the marginal incident light beam on the first lens surface is θ.
The value of nθ, f, is the focal length of the entire system normalized to 1.

Another endoscope eyepiece of the present invention is an eyepiece used for a fiberscope or a rigid endoscope,
The lens system comprises a lens system having a positive refractive power as a whole in which a positive lens and a negative lens are joined, and any one of the lens surfaces is made aspherical, and the following conditional expression is satisfied.

−5 <φ _A / φ _B <0 Here, φ _A and φ _B are the refracting power of the third surface from the object side of the lens system and the refracting power of the second surface which is the cemented surface, respectively.

[Action]

The endoscope eyepiece of the present invention may be any one of a single lens having a positive refractive power, or a lens system having a positive refractive power as a whole including a positive lens and a negative lens disposed in close proximity thereto. Is an endoscope eyepiece in which various aberrations are satisfactorily corrected over a large image height and a numerical aperture while having a simple configuration in which the lens surface is aspheric.

 The details will be described below.

In the endoscope eyepiece of the present invention, the angle between the optical axis and the marginal incident light beam on the first lens surface is θ, and si
If nθ is NA, the image height when the focal length f of the entire system is normalized to 1 is I, and the focal length of the entire system normalized to 1 is f, the following conditional expression should be satisfied. Is desirable.

0.05 ≦ | I | + | NA · f | ≦ 0.3 ... Explaining the reason, when | I | + | NA · f | becomes smaller than 0.05 below the lower limit of the condition, NA or I is very small. It means that it is within the range, and as described in the conventional example, it is not practical and not effective. If, for example,
If an aspherical surface is used for an eyepiece within the range of 0.05> | I | + | NA · f |, the optical performance is certainly improved, but eventually N
Since A and I are very small, use of an aspherical surface is meaningless and is not preferable.

On the other hand, when | I | + | NA · f |> 0.3 exceeds the upper limit of the condition, it means that the NA and the image height I are larger than the aspherical effective range. If it is assumed that the optical performance of an eyepiece lens in the range of | I | + | NA · f |> 0.3 is to be improved, the required aspherical shape may cause a range in which the lens can be manufactured. In addition, since the outer shape of the eyepiece becomes large and the endoscope becomes large, it is not preferable for the endoscope which needs to be carried. Therefore, it is desirable that the eyepiece of the present invention satisfies the conditions.

Further, it is desirable that the aspherical surface used in the present invention has such a shape that the curvature gradually decreases as the distance from the optical axis increases. If the aspherical shape is the opposite, that is, if the curvature gradually increases from the optical axis toward the periphery of the lens, the angle of incidence of the light beam on the lens surface increases, and on-axis spherical aberration, coma, astigmatism, etc. In addition, the off-axis aberration deteriorates, which is not preferable.

Further, the aspherical surface used in the present invention will be described. In the endoscope eyepiece according to the present invention, it is desirable that the displacement amount X (As) of the aspherical shape with respect to the approximate spherical shape near the optical axis be within a range satisfying the following condition.

−0.1 ≦ X (As) ≦ 0.1 Because, if −0.1> X (As), the aspherical amount with respect to the spherical surface becomes insufficient, and not only axial aberration such as spherical aberration but also coma aberration, astigmatism, etc. Is insufficiently corrected, which is not preferable. On the other hand, when X (As)> 0.1, the amount of aspherical surface with respect to the spherical surface rapidly increases, and although various aberrations other than astigmatism are corrected, the shape becomes difficult to manufacture, which is also not preferable.

In the endoscope eyepiece according to the present invention, when the aspheric shape is represented by the following equation, it is preferable that the following conditions (1) to (4) are satisfied.

^{x = (y 2 / r)} / [1+ {1-P (y 2 / r 2)} 1/2] + Ey 4 + Fy 6 + Gy 8 + ... However, the direction of taking images of the optical axis on the x-axis positive, The y-axis is a coordinate value taken in a direction orthogonal to the x-axis with the intersection of the lens surface and the optical axis as the origin, r is the radius of curvature of a circle in contact with this aspheric surface near the optical axis, P is the cone count, E, F, G... Are fourth-order, sixth-order, eighth-order... Aspherical coefficients, respectively. Also, P =
When 1, E, F, G,... Are all 0, the above equation represents a spherical surface.

−0.8 ≦ E ≦ 0.5 -1 ≦ F ≦ 0.1 −1 × 10 ⁻³ ≦ G ≦ 1 × 10 ^-4 … | ( ^EF ) / E | ≦ 10… 0.8 ≦ | (G−F) / F | ≦ 1.2 The meaning of each condition is explained. Under the conditions, -0.8>
If E, aberrations, particularly spherical aberration, are insufficiently corrected near the optical axis, which is not preferable. If E> 0.5, the aspherical surface becomes extremely curved with respect to the approximate spherical surface, for example, becomes a curved surface having an inflection point, and it becomes difficult to manufacture.

For the same reason, it is preferable that the respective aspherical coefficients F and G are within the range of the condition. The feature of the condition is that it is more related to the aspherical displacement amount around the lens than the condition. This is apparent from the above equation relating to the aspherical shape because F and G are coefficients of higher-order terms.

Furthermore, it is preferable that the above conditions are satisfied. In other words, the relationship between the conditions
Range. The equation shows the relationship between E and F, and determines the most effective range of the aspherical shape near the optical axis. On the other hand, the formula relatively determines the aspherical shape around the lens. That is, in the formula, the values of the aspheric coefficients E and F do not show a large difference,
In the equation, it is indicated that the value of G must be a very small numerical value.

Next, the shape of the lens will be described. In the present invention, when an aspherical surface is used, in the most frequently used doublet type represented by the type shown in FIG. 1, the refractive power φ _A of the third surface from the object side and the refractive power of the second surface which is the bonding surface the ratio of the force phi _{B is, -5 <(φ a / φ} B) <0 ... it is desirable that. Here, φ _A = (n ₀ −
n ₂ ) / r ₃ , φ _B = (n ₂ −n ₃ ) / r ₄ , where n ₀ is the refractive index of the medium outside the lens (air), n _{2 is} the refractive index of the negative lens 23, and r _{3 is} the refractive index of the negative lens 23. 3
The radius of curvature of the surface, n ₃ : the refractive index of the positive lens 22, and r ₄ : the radius of curvature of the second surface (joining surface). In the case of a negative lens 23 and positive lens 22 is arranged close to separate without being bonded type, phi _B is assumed to refer to the refractive power of the surface of the positive lens 22 side of the negative lens 23 .

The condition indicates the amount of generation of spherical aberration, coma, and astigmatism according to the relationship between the aspherical shape of the third surface and the joining surface of the second surface. If the equation is (φ _A / φ _B )> 0, the aspherical shape becomes strong, and it is possible to correct spherical aberration and coma, but it is difficult to correct aspherical aberration and to obtain good performance. You can't get it. Further, the aspherical shape also shows extreme deformation, making it difficult to manufacture. Also, φ _A / φ _B <
If the value is −5, the curvature of the second surface, which is the bonding surface, becomes small, which also hinders manufacturing.

In the endoscope eyepiece of this type in the present invention, the radius of curvature r _A of the object-side air surface and the radius of curvature r _B of the observation-side air surface viewed from the object side are ranges satisfying the following conditions. I hope that.

0.07 <r _A ... -0.07> r _B. However, the focal length f of the entire system is set to 1.

Here, if when expression was 0.07> r _A, the radius of curvature manufacture becomes difficult very small, which is not preferable. Similarly, even when the expression satisfies −0.07 <r _B , the radius of curvature is too small, making it difficult to manufacture.

On the other hand, the most frequently used lens types having a shape as shown in FIG. 4, that is, a positive lens 31 and a negative lens
When the third surface has a curved surface just opposite to the third surface in FIG. 1, it is preferable that the following condition be satisfied. In other words, it is preferably in the range of the radius of curvature r _D on the viewing side air surface when viewed from the radius of curvature r _C the object side of the object-side air surface satisfies the following equation.

0.07 <r _C , r _D … Because, taking the case of FIG. 4 as an example, if the equation is
0.07> If a r _C or r _D, the conditional expression, similar,
The radii of curvature of r ₃ (r _D ) and r ₅ (r _C ) are extremely small, which also makes fabrication difficult, which is not preferable.

In the present invention, as represented in FIG. 1, the chromatic aberration is satisfactorily corrected by using a glass having a large Avec number ν _d for the positive lens 22 and using a glass having a small ν _{d for the} negative lens 23. The number of lenses is effectively reduced. As a result, the manufacturing cost is reduced.

〔Example〕

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

FIG. 1 is a sectional view of an endoscope eyepiece according to a first embodiment of the present invention. The lens data of the eyepiece is shown below, and the display of the lens surface is shown in the order reverse to the traveling direction of the light beam. Symbols are as above, NA is numerical aperture, IH is image height,
r _1, r ₂ ... is the radius of curvature, d _1, d ₂ ... the spacing between the lens surfaces, n _d1, n _d2 ... d-line refractive index of each lens of the lens surface, [nu
_d1 , _νd2 ... are Abbe numbers of the respective lenses. Hereinafter, the same applies.

Example 1 f = 1.000 NA = 0.2375 IH = 0.0114 r ₁ = ∽ d ₁ = 0.1659 n _d1 = 1.51633 ν _d1 = 64.15 r ₂ = ∽ (aperture) d ₂ = 0.2489 r ₃ = 0.5518 (aspherical surface) d ₃ = 0.0909 n _d2 = 1.84666 v _d2 = 23.88 r ₄ = 0.3845 d ₄ = 0.3362 n _d3 = 1.60311 v _d3 = 60.70 r ₅ = -8.5392 Aspheric coefficient third surface P = 1 E = -0.21672 × 10 ⁰ F = -0.30331 in ^{× 10 0 G = -0.75949 × 10} -4 in this embodiment, as shown in FIG. 1, in order from the object side, a positive lens 22, negative lens 23, is composed of a plane-parallel plate (cover glass) 24, Surface 3 (3 above data)
Surface) is an aspheric surface. In order to explain the function of the aspherical surface, the aberration coefficients of the first embodiment are divided into a spherical component (aberration component generated in the reference spherical surface) and an aspherical component (difference between the actual value and the spherical component) in Table 1 below. Shown. Note that the total in Table 1 shows the value of the actual coefficient in that plane.

As described above, the aspherical shape according to the present invention is characterized in that the curvature gradually decreases with respect to the spherical shape near the optical axis from the optical axis to the periphery of the lens.
In the embodiment shown in FIG. 1, the third surface (surface number 3) from the object side greatly contributes to spherical aberration and coma aberration, as is clear from Table 1. The function of the aspherical surface on the third surface is to correct the aberration in the direction just opposite to the state of aberration by the spherical surface on the same lens surface. That is, the aspherical surface is formed in a direction that cancels out the aberration caused by the spherical surface.

The NA of Example 1 is as high as 95% of that of the Gaussian type NA of FIG. 15, and the optical performance is good as shown in the aberration diagram of FIG. That is, as described above, by using the aspherical surface, various aberrations in the off-axis principal ray and the off-axis dependent ray are favorably corrected. As described above, the first embodiment
Is suitable for fiberscopes because it can be used in a large NA range.

Next, FIG. 2 shows a lens cross section of the second embodiment. The lens data is as follows.

Example 2 f = 1.000 NA = 0.275 IH = 0.0114 r ₁ = ∽ d ₁ = 0.1659 n _d1 = 1.51633 ν _d1 = 64.15 r ₂ = ∽ (aperture) d ₂ = 0.2489 r ₃ = 0.6533 (aspherical surface) d ₃ = 0.0909 n _d2 = 1.80518 ν _d2 = 25.43 r ₄ = 0.3754 d ₄ = 0.3362 n _d3 = 1.67790 ν _d3 = 55.33 r ₅ = −5.9869 (aspheric surface) Aspherical coefficient Third surface P = 1 E = −0.30588 × 10 ⁰ F = −0.63020 × 10 ⁰ G = −0.58247 × 10 ^-3 Fifth surface P = 1 E = −0.56401 × 10 ⁰ F = 0.37288 × 10 ⁻¹ G = 0.32648 × 10 ^{-4 In} the eyepiece of Example 1, Even if you try to get a large NA, there is naturally a limit. That is, a large load is applied to the aspherical surface used for the third surface, which makes it difficult to manufacture. Therefore, in the second embodiment, an aspherical surface is similarly used for the first surface to reduce the aspherical surface dependence of the third surface and to enable use in a larger NA range. That is, the eyepiece of FIG. 2 is the most frequently used type, and uses an aspherical surface for the first surface (surface number 5) and the third surface (surface number 3) from the object side. The configuration includes, in order from the object side, a positive lens 25, a negative lens 26, and a plane-parallel plate (cover glass) 27. The NA of this example exceeds the NA of the conventional Gaussian type shown in FIG. 15, and when compared, as much as 110% can be obtained. The optical performance is also good as shown in the aberration diagram of FIG. As a feature of the second embodiment, the dependence of the aspheric surface on the third surface is reduced by using the aspheric surface for the first surface in addition to the third surface. In other words, it can be said that it is possible to further increase the NA by deforming the aspherical shape of the third surface so as not to hinder the production (compared with the first embodiment).

FIG. 3 shows a lens cross section of the third embodiment. The lens data is as follows.

Example 3 f = 1.000 NA = 0.2 IH = 0.0568 r ₁ = ∽ d ₁ = 0.1659 n _d1 = 1.51633 ν _d1 = 64.15 r ₂ = ∽ (aperture) d ₂ = 0.2489 r ₃ = 0.5298 (aspherical surface) d ₃ = 0.0909 n _d2 = 1.78472 v _d2 = 25.71 r ₄ = 0.3088 d ₄ = 0.3362 n _d3 = 1.63854 v _d3 = 55.38 r ₅ = 10.4278 Aspheric coefficient third surface P = 1 E = −0.19422 × 10 ⁻¹ F = −0.55261 × 10 ⁺¹ G = 0.57347 × 10 ^{+2 As} shown in FIG. 3, the configuration of the third embodiment includes, in order from the object side, a positive lens 28, a negative lens 29, and a plane-parallel plate (cover glass) 30, An aspheric surface is used for the third surface (surface number 3). The optical performance is shown in the aberration diagram of FIG. As a feature of this embodiment, first, the first surface (surface number 5) is concave. This makes it difficult for off-axis aberrations (such as coma and astigmatism) to occur.
The NA and image height of this embodiment are 80% NA and 50% image height compared to the Gaussian type shown in FIG. Even if it is simply compared with the conventional doublet type (see FIG. 17), the type of the third embodiment using the aspherical surface has an NA of 40 even at the same image height.
% Improvement has been achieved.

Next, FIG. 4 shows a lens cross section of the fourth embodiment. The lens data is as follows.

Example 4 f = 1.000 NA = 0.2 IH = 0.0909 r ₁ = ∽ d ₁ = 0.1659 n _d1 = 1.51633 ν _d1 = 64.15 r ₂ = ∽ (aperture) d ₂ = 0.2489 r ₃ = 1.9900 (aspherical surface) d ₃ = 0.0909 n _d2 = 1.62004 v _d2 = 36.25 r ₄ = 0.3550 d ₄ = 0.3362 n _d3 = 1.71300 v _d3 = 53.48 r ₅ = 0.7002 (aspherical surface) Aspheric coefficient Third surface P = 1 E = −0.12294 × 10 ⁺¹ F = −0.32492 × 10 ^{+ 2} G = 0.28172 × 10 ^{+ 3} Fifth Surface P = 1 E = 0.213378 × 10 ⁰ F = −0.91958 × 10 ^{+ 1} G = 0.11510 × 10 ^{+ 3} The configuration of the fourth embodiment is as follows. As shown in FIG. 4, in order from the object side, a positive lens 31, a negative lens 32, and a parallel flat plate (cover glass) 33 are provided, and are arranged on a first surface (surface number 5) and a third surface (surface number 3). An aspheric surface is used. The optical performance is shown in the aberration diagram of FIG. The feature of the fourth embodiment is that, as in the second embodiment, by using two aspheric surfaces,
By reducing the dependence on the two aspheric surfaces, the aspheric shape is maintained in a manufacturable state, and the NA and the image height can be used in a larger area. In the fourth embodiment, the third surface (surface number 3) is a concave surface.
The generation of aberrations due to off-axis chief rays and off-axis dependent rays is minimized. The NA and the image height of this embodiment are 80% of those of the Gaussian type shown in FIG. 15, respectively, and it can be said that the object of the present invention is sufficiently achieved. From this,
The fourth embodiment can be used in a range where the NA is relatively small, and can be said to be suitable for a rigid endoscope.

However, the evaluation of the resolution in Examples 3 and 4 described above is performed in a region where the spatial frequency is low (about 1 /
4).

Further, FIG. 5 shows a lens cross section of Example 5. The lens data is as follows.

Example 5 f = 1.000 NA = 0.275 IH = 0.0114 r ₁ = ∽ d ₁ = 0.1659 n _d1 = 1.51633 ν _d1 = 64.15 r ₂ = ∽ (aperture) d ₂ = 0.2489 r ₃ = 0.9291 (aspherical surface) d ₃ = 0.3362 n _d2 = 1.80518 ν _d2 = 25.43 r ₄ = 5.0616 (aspherical surface) Aspherical surface coefficient Third surface P = 1 E = −0.57733 × 10 ⁰ F = 0.10769 × 10 ^{+ 1} G = 0.29429 × 10 ⁻² Fourth surface P = 1 E = −0.81557 × 10 ⁰ F = 0.70819 × 10 ⁰ G = 0.14920 × 10 ⁻² The fifth embodiment is an example in which a single lens is used and has a larger NA. As shown in the aberration diagram of FIG. 12, since it is a single lens, it is somewhat difficult to correct chromatic aberration, but other aberrations are corrected relatively well.

FIG. 6 shows a lens cross section of Example 6. The lens data is as follows.

Example 6 f = 1.000 NA = 0.216 IH = 0.114 r ₁ = ∽ d ₁ = 0.1659 n _d1 = 1.51633 ν _d1 = 64.15 r ₂ = ∽ (aperture) d ₂ = 0.2489 r ₃ = 0.6173 (aspherical surface) d ₃ = 0.3362 n _d2 = 1.58313 ν _d2 = 59.36 r ₄ = −0.4262 d ₄ = 0.0909 n _d3 = 1.74000 ν _d3 = 28.29 r ₅ = 1.6202 Aspheric coefficient third surface P = 1 E = 0.85346 × 10 ⁻¹ F = 0.13910 × 10 ⁻² G = 0.24849 × 10 ^{−5 In} the sixth embodiment, as shown in FIG. 6, the joining surface is reversed, and a negative lens, a positive lens, and a plane parallel plate (cover glass) are arranged in this order from the object side. In this example, even if the joining surface is reversed, the same performance can be obtained as shown in the aberration diagram of FIG. 13 (the level is similar to that of the third embodiment).

FIG. 7 shows a lens cross section of the seventh embodiment. The lens data is as follows.

Example 7 f = 1.000 NA = 0.276 IH = 0.114 r ₁ = ∽ d ₁ = 0.1659 n _d1 = 1.51633 ν _d1 = 64.15 r ₂ = ∽ (aperture) d ₂ = 0.2489 r ₃ = 0.6504 (aspherical surface) d ₃ = 0.0909 n _d2 = 1.80518 ν _d2 = 25.43 r ₄ = 0.3754 d ₄ = 0.0045 r ₅ = 0.3828 d ₅ = 0.3362 n _d3 = 1.67790 ν _d3 = 55.33 r ₆ = −4.8599 (aspheric surface) Aspheric surface third surface P = 1 E = -0.19888 × 10 ⁰ F = −0.62985 × 10 ⁰ G = −0.58184 × 10 ^-3 Fifth surface P = 1 E = −0.51060 × 10 ⁰ F = 0.37296 × 10 ⁻¹ G = 0.32626 × 10 ^-4 In the seventh embodiment, a positive lens and a negative lens are not joined, and an air lens is interposed between them. As shown in the aberration diagram of FIG. 14, similar performance can be obtained. It is a type with a large NA.

As described above, the values corresponding to the conditions in Examples 1 to 7 are summarized in Table 2 below.

According to Table 2, it can be said that Examples 1 to 7 satisfy the conditions and formulas, and that the optical performance is good by using the aspherical surface. [Effect of the Invention] According to the present invention as described above. By using a doublet or a single lens having a positive refractive power and making any one of the lens surfaces an aspheric surface, both the numerical aperture and the image height are as large as those of the conventional six-element Gaussian type lens. In addition, it is possible to provide an endoscope eyepiece in which various aberrations are satisfactorily corrected, the number of lenses is small, and manufacturing and assembly costs are reduced.

[Brief description of the drawings]

1 to 7 are cross-sectional views of Examples 1 to 7 of the endoscope eyepiece of the present invention, FIGS. 8 to 14 are aberration diagrams of Examples 1 to 7, respectively, and FIG. FIG. 16 is a cross-sectional view of a known Gaussian eyepiece, FIG. 16 is an aberration diagram of the eyepiece of FIG. 15, FIG. 17 is a cross-sectional view of a conventionally known doublet-type eyepiece, and FIGS. 18 to 21 are doublets. FIG. 4 is a diagram showing the relationship between the contrast and the spatial frequency of both types of eyepieces when separately designed according to the image height so as to obtain a contrast comparable to that of a Gaussian eyepiece. 22, 25, 28, 31 Positive lens, 23, 26, 29 Negative lens, 24, 27, 30, 33 Parallel flat plate (cover glass)

Claims (2)

(57) [Claims] 1. An eyepiece used for a fiberscope or a rigid scope, wherein the eyepiece is a single lens having a positive refractive power.
A lens system having a positive refractive power as a whole in which a positive lens and a negative lens are joined, or a lens system including a negative lens disposed close to the positive lens and having a positive refractive power as a whole, An endoscope eyepiece, wherein the fiber surface or the rigid endoscope and the single lens or the lens system satisfy the following conditional expression. 0.05 ≦ | I | + | NA · f | ≦ 0.3 where I is the image guide image of the fiberscope when the focal length f of the entire system is normalized to 1, or the image of the relay image of the rigid mirror. High, NA is sin when the angle between the optical axis and the marginal incident ray on the first lens surface is θ.
The value of θ and f is the focal length of the entire system normalized to 1. 2. An eyepiece used for a fiberscope or a rigid endoscope, comprising a lens system having a positive refractive power as a whole in which a positive lens and a negative lens are joined,
An endoscope eyepiece characterized in that any one of the lens surfaces is aspherical and the following conditional expression is satisfied. −5 <φ _A / φ _B <0 Here, φ _A and φ _B are the refracting power of the third surface from the object side of the lens system and the refracting power of the second surface which is the cemented surface, respectively.