JP3244306B2 - Endoscope with switching optics - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an endoscope with a switching optical system, that is, an endoscope provided with an objective lens having a different focal length or an objective lens having a variable power function.

[0002]

2. Description of the Related Art In endoscopes, particularly endoscopes for examining the large intestine, etc., there is an increasing demand for observation with an objective lens having a variable power function.

FIG. 20 is a view showing a state of examining the large intestine with an endoscope. FIG. 20A is an overall view of the large intestine, and FIG. 20B is an enlarged sectional view of a part of the large intestine. The large intestine 21 is shown in FIG.
As shown in (B), it is difficult to observe while inserting the endoscope 22 because of many bending. Therefore, observation of the large intestine
First, as shown in FIG. 20 (C), the end of the large intestine, that is, the cecum 23 shown in FIG. 20 (A) is inserted, and then the bending of the large intestine is corrected. And treat the disease.

In the case of the above inspection method, the angle of view of the objective lens when the endoscope is inserted is desirably 120 ° to 140 °. The level of distortion of the objective lens is defined as follows: when the image height is h, the half angle of view of the objective lens is ω, and the focal length is f,
The level indicated by the following equation (a) is desirable. h = fsin ω (a) When the endoscope is inserted, as shown in FIG. 20B, the large intestine has many bends. The above is desirable. In addition, when the distortion is generated as in the above equation (a), the magnification near the center of the image increases even with the same angle of view.
The hole to be advanced next may be seen close, and it is better to generate it to some extent during insertion. However, even if the angle is too wide to generate distortion, the visible range remains substantially unchanged. At the time of insertion, it is not necessary to pay much attention to the periphery of the image, so the angle of view is suitably within 140 °.

Now, the objective lens having the distortion represented by the above equation (a) will be called an fsin ω type objective lens.

On the other hand, the most difficult thing in observation with an endoscope at the time of removal is to find a diseased piece such as a polyp 25 formed inside the valve part (house tiger) 24 of the large intestine shown in FIG. Is the case. It is the conventional
As shown in (E), the endoscope was bent to find a diseased piece, so that the examination time was prolonged and the patient suffered.

As a means for solving this drawback, it is conceivable to increase the angle of view. However, when the fsin ω type objective lens is used, even if the angle of view is increased, the substantial inspection ability is not improved. .

FIG. 21 shows a square grid 14 on a cylindrical object.
FIG. 7 is a diagram showing a state in which an endoscope having an objective lens is inserted into a section obtained by cutting and the observation is performed. In the case of a field mask of an endoscope in which a CCD is arranged at the tip like a recent videoscope, an octagonal shape as shown in FIG. 22 is generally used. FIG. 23 shows the observable visual field range of this endoscope when observing the inside of the cylinder with an endoscope having an fsin ω-type objective lens as shown in FIG. FIG.
16 is a range that can be observed at a diagonal angle of view of 133 °,
Reference numeral 17 denotes a range that can be observed at a diagonal angle of view of 163 °. As can be seen from FIG. 23, the observable range in the diagonal direction is widened by widening the angle of view, but is not wide in the diagonal direction. FIG. 24 is a diagram when this observation range is actually observed in the visual field mask. The outer range 17 is a 163 ° appearance, and the range 16 is a 133 ° appearance.

As can be seen from FIGS. 23 and 24,
The fsin ω type objective lens has a large distortion, so that the peripheral image shrinks and the actual inspection ability does not change.

For the above reasons, it is effective to remove the distortion of the objective lens to be used and to use an objective lens satisfying the following relationship when performing the inspection at the time of removal. h = f · ω (b) Hereinafter, an objective lens satisfying the above relationship is referred to as an f · ω type objective lens.

FIG. 25 shows an image on a field mask when a cylinder is observed with an objective lens having a distortion angle near f · ω type at an angle of view of 170 °. When observing with this objective lens, the square lattice in the cylinder looks almost square due to the correction of distortion. Also, 17 and 16 in FIG.
The observation range is 170 ° and 140 ° for the nω type objective lens, respectively. As described above, the observability of the periphery is improved, and it is effective when performing an inspection when removing. However, the center magnification is reduced, and the next hole to be advanced at the time of insertion appears to be far away, so that it is effective at the time of removal but becomes a disadvantage at the time of insertion.

[0012]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an endoscope with a switching optical system that enables good observation both during insertion and observation.

[0013]

An endoscope according to the present invention includes an objective lens having a switchable focal length, and a field mask having a variable shape. The shape of the field mask is changed simultaneously with the switching.

In another endoscope of the present invention, the objective lens is an objective lens close to fsin ω type on the narrow angle side of the observation field and an objective lens close to f · ω type on the wide angle side. is there.

FIG. 1 is an enlarged view of the distal end portion of the endoscope of the present invention, which has a window L for supplying illumination light at the time of observation and two objective lenses O for observation. ₁ , O ₂
Is provided. Each of the objective lenses has the configuration shown in FIG. 2 and the field masks M ₁ and M ₂ are arranged in front of the CCD. Of these objective lenses, for example, (A)
The objective lens O ₁ shown in FIG. ₂ has a diagonal angle of view 2ω of 133 °, and the objective lens O ₂ shown in FIG. The distortion of the objective lens is of the fsin ω type, and the field mask used for the objective lens O ₁ shown in FIG. 2A is shown in FIG. 3A and FIG. those used in the objective lens O ₂ shown in is in the form of as shown in FIG. 3 (B). Among these field masks, the field mask 1 shown in (A) has the same shape as that shown in FIG. 22, but the field mask 2 shown in FIG. It is longer than that.

When the endoscope is inserted, the objective lens shown in FIG. 2A is used, and the shape of the visual field mask is as shown in FIG.

[0017] Also when pulled out, the objective lens is used in FIG. 2 (B), the field mask has a shape shown in FIG. 3 (B).

The objective lens of the present invention has a fsi
Since the objective lens is close to the nω type, there is no problem during insertion. Also, there is no problem at the time of removal, for the following reasons.

As described above, FIGS. 23 and 24 show the difference in the angle of view and the visible range when the fsin .omega. Type is used and the shape of the field mask is the same as that shown in FIG. 3A. FIG. Here, if the visual field mask shown in FIG. 3B is used instead of the visual field mask, the result is as shown in FIG. 4 and the range of appearance is greatly improved. In this figure, 12 is the 16 shown in FIG.
23, the viewing angle at the diagonal of 163 ° is significantly improved in the angle of view in the opposite side direction as compared with 17 in FIG. Therefore, even if the peripheral image shrinks due to the influence of distortion as compared to the case shown in FIG. 24, it can contribute to an improvement in the observability at the periphery at the time of extraction. If the wide-angle side objective lens has been corrected for distortion, the peripheral observability is further improved.

FIG. 6 is a view showing a means for switching the field mask. When the endoscope is inserted by the signal output of the two CCDs,
Switch according to when you pull out. That is, in FIG. 6, 5 is a changeover switch, 6 is a signal processing circuit, 7 is a television monitor, and 8 is an image by an endoscope.

As described above, considering the distortion of the objective lens on the narrow angle side at the time of insertion, the fsin ω type is good, and when the objective lens is pulled out, the wide angle is obtained, and the distortion is f · ω type.

In the objective lens shown in FIG. 2, if the objective lens shown on the wide-angle side (B) is an f.omega.-type objective lens, the observability is improved as shown in FIG. 25 without changing the field mask . I can do it.

Here, the half angle of view of the objective lens on the narrow angle side is θ.
_T , its focal length is f _T , the half angle of view of the wide-angle side objective lens is θ _W , its focal length is f _W , and the maximum image height is h, so that the following relationship is established. h = f _T sin θ _T (c) h = f _W θ _W (d) From the expressions (c) and (d), the relationship represented by the following expression (e) is established. f _T / f _W = θ _W / sin θ _T (e) This equation (e) represents the difference in the amount of distortion generated between the wide-angle side and the narrow-angle side, and the distortion of the objective lens on the narrow-angle side. Is substantially of the fsin ω type and the following condition (1) is satisfied, the amount of distortion of the objective lens on the wide-angle side can be suppressed. (1) sin θ _W / sin θ _T <f _T / f _{W The} configuration shown in FIG. 1, that is, two CCDs as shown in FIG.
When an (objective lens) is used, the outer diameter of the endoscope becomes large,
Pain for the patient. Therefore, it is desirable to use one objective lens and use a variable power lens that changes the focal length by moving at least one lens group (lens component) in the objective lens.

The condition (1) indicates the amount of change in distortion between the wide-angle side and the narrow-angle side. As described above, the type of distortion on the wide angle side is desirably h = fsin ω. Here, the amount of generation of distortion is represented as follows. h = fksin (θ / k) (f) When the value of k is changed from 1 to ∞ in this equation (f), h
Changes from f sin θ to f θ. Here, the value of k is as follows when the third order is approximated by Taylor expansion.

As long as the amount of distortion represented by the above equation (f) is within the range satisfying the following condition (2) on the narrow angle side, there is no problem. (2) k <1.55 Therefore, when the endoscope of the present invention is configured by using one variable-power objective lens, it is desirable to use an objective lens that satisfies the above conditions (1) and (2). .

[0026]

Next, embodiments of the objective lens used in the endoscope of the present invention will be described. Example 1 f = 1.000 (wide angle end) to 1.269 (narrow angle end), image height = 1.0620 to 1.0620 ω = 79.991 ° to 53.082 °, object distance = -10.6667 to -8.00000 r ₁ = 6.6784 d ₁ = 0.4000 n ₁ = 1.88300 v ₁ = 40.78 r ₂ = 0.8325 d ₂ = 1.3593 r ₃ = ∞ d ₃ = 1.3373 n ₂ = 1.69680 v ₂ = 55.52 r ₄ = -10.9644 d ₄ = 0.2257 r ₅ = ∞ (aperture) d ₅ = D _{1 r 6 = 105.0297 d 6 =} 0.8667 n 3 = 1.56873 ν 3 = 63.16 r 7 = -3.1264 d 7 = 0.0667 r 8 = 3.9505 d 8 = 0.6000 n 4 = 1.56873 ν 4 = 63.16 r 9 = -52.1035 d 9 = D ₂ r ₁₀ = 12.7877 d ₁₀ = 1.2000 n ₅ = 1.51633 v ₅ = 64.15 r ₁₁ = −2.2604 d ₁₁ = 0.4667 n ₆ = 1.84666 v ₆ = 23.78 r ₁₂ = −5.2190 (aspherical surface) d ₁₂ = 0.1000 r _{13 = ∞ d 13 = 0.3333 n 7} = 1.51633 ν 7 = 64.15 r 14 = ∞ d 14 = 1.8400 r 15 = ∞ d 15 = 0.6667 n 8 = 1.51633 ν 8 = 64.15 r 16 = ∞ aspherical coefficients P = 1.0071, A ₄ = -0.30913 × 10 ^-2 f 1.000 1.269 D ₁ 1.535 0.814 D ₂ 0.774 1.523

Example 2 f = 1.000 (wide angle end) to 1.469 (narrow angle end), image height = 1.436 to 1.2436 ω = 81.399 ° to 53.131 °, object distance = −12.4902 to −9.3677 r ₁ = 7.6091 (aspherical surface) ) D ₁ = 0.4684 n ₁ = 1.88300 ν ₁ = 40.78 r ₂ = 1.0962 d ₂ = 1.5051 r ₃ = ∞ d ₃ = 1.4840 n ₂ = 1.69680 v ₂ = 55.52 r ₄ = -77.8015 d ₄ = 0.1665 r ₅ = ∞ (Aperture) d ₅ = D ₁ r ₆ = 227.6256 d ₆ = 1.2604 n ₃ = 1.56873 ν ₃ = 63.16 r ₇ = −2.4698 d ₇ = 0.0781 r ₈ = 7.0039 (aspherical surface) d ₈ = 0.4163 n ₄ = 1.56873 ν _{4 = 63.16 r 9 = -24.7415 d} 9 = D 2 r 10 = 16.6285 d 10 = 1.4052 n 5 = 1.51633 ν 5 = 64.15 r 11 = -2.1681 d 11 = 0.5464 n 6 = 1.84666 ν 6 = 23.78 r 12 = - 4.7673 (aspheric surface) d ₁₂ = 0.1171 r ₁₃ = ∞ d ₁₃ = 0.3903 n ₇ = 1.51633 v ₇ = 64.15 r ₁₄ = ∞ d ₁₄ = 1.7861 r ₁₅ = ∞ d ₁₅ = 0.7806 n ₈ = 1.51633 v ₈ = 64.15 r ₁₆ = ∞ aspherical coefficients (first _{) P = 0.9746, A 4 =} 0.20761 × 10 -2 ( surface No. _{8) P = 0.9903, A 4} = -0.93750 × 10 -2 ( twelfth _{surface) P = 0.9699, A 4 =} -0.79337 × 10 -2 f _{1.000 1.469 D 1 1.970 0.739 D 2} 0.645 1.878 f T / f W = 1.469, sin θ W / sin θ T = 1.236, k W
= 1.64, k _T = 1.28

Embodiment 3 f = 1.000 (wide-angle end) to 1.531 (narrow-angle end), image height = 1.3133 to 1.3133 ω = 81.474 ° to 52.999 °, object distance = −13.1904 to −9.88928 r ₁ = 8.6437 (aspherical surface) ) D ₁ = 0.4946 n ₁ = 1.88300 v ₁ = 40.78 r ₂ = 1.1662 d ₂ = 1.5837 r ₃ = ∞ d ₃ = 1.5644 n ₂ = 1.69680 v ₂ = 55.52 r ₄ = 44.6324 d ₄ = 0.1706 r ₅ = ∞ ( Aperture) d ₅ = D ₁ r ₆ = 73.9890 d ₆ = 1.3757 n ₃ = 1.56873 ν ₃ = 63.16 r ₇ = -2.3411 d ₇ = 0.0824 r ₈ = 8.5568 (aspherical surface) d ₈ = 0.4397 n ₄ = 1.56873 ν _{4 = 63.16 r 9 = -28.9048 d 9} = D 2 r 10 = 23.4230 d 10 = 1.4839 n 5 = 1.51633 ν 5 = 64.15 r 11 = -2.2420 d 11 = 0.5771 n 6 = 1.84666 ν 6 = 23.78 r 12 = -5.0689 (Aspherical surface) d ₁₂ = 0.1237 r ₁₃ = ∞ d ₁₃ = 0.4122 n ₇ = 1.51633 v ₇ = 64.15 r ₁₄ = ∞ d ₁₄ = 1.9125 r ₁₅ = ∞ d ₁₅ = 0.8244 n ₈ = 1.51633 v ₈ = 64.15 r ₁₆ = ∞ Aspherical surface coefficient (First surface _{P = 0.9711, A 4 = 0.28221} × 10 -2 ( eighth _{surface) P = 0.9899, A 4 =} -0.11663 × 10 -1 ( twelfth _{surface) P = 0.9688, A 4 =} -0.73647 × 10 -2 f 1.000 _{1.531 D 1 2.112 0.756 D 2 0.600} 1.961 f T / f W = 1.531, sin θ W / sin θ T = 1.238, k W
= 2.1, k _T = 1.4 where r ₁ , r ₂ ,... Are the radius of curvature of each lens surface, d
_.. , D ₂ ,...
₁ , n ₂ ,... Are the refractive indices of each lens, ν ₁ , ν ₂ ,.
Is the Abbe number of each lens.

The embodiment of the present invention comprises, for example, a negative lens component, a brightness stop, and three positive lens components as shown in FIG. 7, and the positive lens component closest to the image side is a cemented lens. . In these embodiments, zooming is performed by moving some of the lens components so that only one image sensor may be used.

The optical system according to the first embodiment moves the two positive lens components behind the stop along the optical axis, that is, the distance d _5.
By changing the distance d ₉ it is performed zooming and. In the first embodiment, the third-order astigmatism is overcorrected because the angle of view on the wide-angle side is an ultra-wide angle, and an aspherical surface is used to correct this.

This aspheric surface is represented by the following equation. Where x. As shown in FIG. 11, y is a direction in which the light axis travels positively with the optical axis as the x-axis and the y-axis is taken in a direction perpendicular to the optical axis. The intersection of the lens surface and the optical axis is the origin of the coordinates. is there. The first term indicates a spherical surface, and r is the radius of curvature of the lens surface at the coordinate origin. The second term is a term giving an aspherical portion, and A _2i is a 2i-th order aspherical coefficient. In the following description, these aspherical coefficients are used as they are, but other aspherical surfaces represented by axisymmetric functions can be converted to the form of the above expression by tailoring the function and formulating the expression. The description holds for all axisymmetric aspheric surfaces.

As is well known, the aspherical coefficient of each order affects the aberration coefficient of one order, the aspherical coefficient A _{4 in} the above equation affects the third order aberration coefficient, and A ₆ represents the fifth order aberration coefficient. Affects the aberration coefficient.

In the present invention, the Petzval sum is overcorrected because the power of the negative lens component is very strong. Although the image planes of meridional and sagittal are determined by the Petzval sum and the astigmatism coefficient, only the astigmatism coefficient can be corrected by the aspherical surface. Therefore, it is necessary to reduce the astigmatism coefficient by using an aspheric surface.

In order to correct the third-order region of astigmatism,
It is necessary to select a surface having a high principal ray height and a low marginal ray height that does not significantly affect other aberrations. The aspheric surface must satisfy the following condition (3). _{(3) A · (n a} -n a ') <0 where A is the fourth-order aspheric coefficient of the aspherical, n _a is the refractive index of the object-side medium of the aspherical, n _a' this aspherical Is the refractive index of the medium on the image side.

If the above conditions are not satisfied, the effect of insufficient correction of astigmatism due to this aspheric surface is lost.

The shape of the field mask of this embodiment is as shown in FIG. 3, where (A) is on the narrow-angle side and (B) is on the wide-angle side. FIG. 10 is a diagram showing a switching circuit for the field mask. The video signal from the CCD at the tip of the video endoscope is converted into a video signal by the video signal processing circuit system 6. Circuits 9 and 10 for creating two types of field masks having the shapes of are inserted into the camera control unit 11, and the field switch is switched by the changeover switch 5. In FIG. 10, 7 is a television monitor, and 8 is an image of an electric field mask on the television monitor.

Although the video endoscope has been described in this embodiment, an endoscope using an image guide may be used instead of the image pickup device.

Embodiment 2 is an example in which the ratio of occurrence of distortion is changed together with the switching of the observation field angle in the configuration shown in FIG. 12, and a part of the lens group of the objective lens (two The magnification is changed by moving the positive lens component. The distortion at the wide-angle side and the narrow-angle side of the objective lens of this embodiment is as shown in FIG. In this figure, (A) is on the wide angle side and (B) is on the narrow angle side. In these figures, the horizontal axis is a half angle of view, and the vertical axis is h / f. In the figure, curve a is for Example 2, curve b is for an objective lens of h = ftan θ, curve c is for h = fθ type, and curve d is for h = fsin θ type. As can be seen from this figure, the objective lens of Example 2 has h = fθ on the wide-angle side.
And on the narrow angle side it is close to the type of h = fsin θ.

In order for the objective lens to have such a characteristic, it is necessary to provide an aspherical surface at a place where the ray height of the off-axis principal ray greatly changes between the wide-angle side and the narrow-angle side and at least does not significantly affect the spherical aberration. Need to be placed.

The objective lens of this embodiment is a retro-focus type, in which an aspheric surface for correcting astigmatism is provided on the lens surface behind the aperture stop. In this case, the objective lens can be formed as in this embodiment. As far as possible, it is preferably provided on the image side surface. That is, in the second embodiment, the two aspheric surfaces are provided in the positive lens component behind the aperture stop.

In the second embodiment, an aspheric surface for correcting distortion is provided even before the aperture stop. Even with an aspheric surface provided before the stop, there is a large difference in the height of the principal ray between the narrow-angle end and the wide-angle end.

The shape of the aspherical surface is such that, in the case of a surface in a lens component that moves for zooming, the curvature is gradually reduced so that distortion is corrected, and a surface closer to the image side (positive cemented lens) is used. The aspherical surface on the image side) has a shape in which the curvature is gradually increased to correct astigmatism.

The aspherical surface provided for the moving lens component satisfies the following condition (4). _{(4) A (n a -n} a ')> 0 The aspherical surface provided on the surface of the more image-side, which satisfies the condition (3).

The third embodiment has the same configuration as that of the second embodiment, except that the level of occurrence of distortion on the narrow angle side is set at an intermediate level between the fsin θ type and the fθ type as shown in FIG. It was almost fθ type on the wide angle side.

[0045]

According to the endoscope of the present invention, by changing the focal length of the objective lens and the shape of the field mask at the same time, the insertion is easy and the field range and the distortion are easily inspected when the endoscope is removed. This allows the test to be performed in a shorter time, reducing the patient's pain.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of a distal end portion of an endoscope of the present invention.

FIG. 2 is a diagram showing a configuration of an objective lens used in the endoscope of the present invention.

FIG. 3 is a diagram showing the shape of a field mask used in the endoscope of the present invention.

FIG. 4 is a diagram showing a range of appearance when observing the inside of a cylindrical object cut into a lattice by the endoscope of the present invention.

FIG. 5 is a diagram showing the appearance when observing the object.

FIG. 6 is a diagram showing a switching circuit of a field mask in the endoscope of the present invention.

FIG. 7 is a cross-sectional view of Example 1 of the objective lens used in the present invention.

FIG. 8 is an aberration curve diagram at the wide end of the first embodiment.

FIG. 9 is an aberration curve diagram at the telephoto end according to the first embodiment.

FIG. 10 is a diagram showing a switching circuit of a field mask in the first embodiment.

FIG. 11 is a diagram showing a coordinate system of an expression representing an aspherical shape used in the first embodiment.

FIG. 12 is a sectional view of Embodiment 2 of the objective lens used in the present invention.

FIG. 13 is an aberration curve diagram at the wide-angle end in the second embodiment.

FIG. 14 is an aberration curve diagram at the telephoto end according to the second embodiment.

FIG. 15 is a diagram illustrating a state of occurrence of distortion according to the second embodiment.

FIG. 16 is a sectional view of Embodiment 3 of the objective lens used in the present invention.

FIG. 17 is an aberration curve diagram at the wide-angle end in the third embodiment.

FIG. 18 is an aberration curve diagram at the telephoto end according to the third embodiment.

FIG. 19 is a diagram showing a state of occurrence of distortion in the third embodiment.

FIG. 20 is a diagram showing a state of observing the large intestine using an endoscope.

FIG. 21 is a diagram showing a cylindrical object obtained by cutting a square grid;

FIG. 22 is a view showing the shape of a field mask used in a videoscope.

FIG. 23 is a diagram showing a range of appearance when the object shown in FIG. 21 is observed with a conventional endoscope.

FIG. 24 is a view showing the appearance when the object shown in FIG. 21 is observed with a conventional endoscope.

FIG. 25 shows an objective lens having a distortion close to that of the fω type, and FIG.
Figure showing the appearance when observing the object shown in

Claims (2)

(57) [Claims] 1. An objective lens capable of switching a focal length, at least two field masks having different shapes, and simultaneously switching the focal length of the objective lens ,
An endoscope with a switching optical system including a switching mechanism . 2. When the focal length and the half angle of view of the objective lens on the wide angle side are f _W and θ _W , respectively, and the focal length and the half angle of view of the objective lens on the narrow angle side are f _T and θ _T , respectively. (1) sin θ _W / sin θ _T <f _T / f _{W The} condition (2) is satisfied when the generation amount of distortion on the narrow angle side is given by the following equation. An endoscope designed to be used. h = f _T ksin (θ _T / k) (2) k <1.55