JP3270591B2 - Optical adapter for endoscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical adapter which is attached to an eyepiece of an endoscope so that a photographing operation and a television camera observation can be performed.

[0002]

2. Description of the Related Art Generally, a detachable optical adapter is used behind an eyepiece to guide an image of a body cavity or the like obtained by an endoscope to an imaging device. An endoscope television camera using this optical adapter is provided with an imaging lens 6 behind an eyepiece 4 such as a rigid endoscope as shown in FIG.
Attaching an adapter 5 equipped with
And the like, so that an image can be formed on an image sensor and observed on the monitor television 8. The rigid mirror 1 is provided with an objective lens 2, a relay lens 3, and the like. Reference numeral 9 denotes a CCU, and reference numeral 10 denotes a low-pass filter.

When observing an image by a rigid endoscope on a television,
There is a problem that the depth of field is shallow. In recent years, CCDs, which are imaging devices for television cameras, have been trending toward higher pixels.
This has enabled high resolution of the subject. However, this reduces the size of one pixel (pixel pitch), and therefore the diameter of the permissible circle of confusion of the imaging lens must be reduced, further reducing the depth of field. If the blur is within the range of the allowable circle of confusion diameter φ as shown in FIG. 16, it can be said that the object is in focus and within the depth of field ΔS. In FIG. 16, (A) shows a case where focus is achieved, (B) shows a case of near point, and (C) shows a case of far point.
However, as shown in FIG. 17, if the permissible circle of confusion diameter is reduced as phi what had been a _{a φ b (φ b <φ} a) , the depth of field becomes shallow. In FIG. 17, the horizontal axis indicates the depth of field, the side F indicates the far point side, the side N indicates the near point side, the vertical direction indicates the diameter of the circle of confusion, and the upward direction indicates the direction in which the diameter increases. As described above, when the pixel pitch is reduced, the diameter of the permissible circle of confusion must be reduced, so that the depth of field is reduced.

As described above, an endoscope optical system such as a rigid endoscope has a shallow depth of field, so that when performing an operation by operating an endoscope, a focusing lens is moved to focus. It is necessary and not preferable.

[0005] In order to solve the above-mentioned drawbacks, that is, to provide a rigid aperture television camera system with a fixed aperture stop in order to improve the depth of field, when a fixed aperture stop is used for a remote point observation requiring brightness, Depending on the characteristics of the rigid endoscope combined with the system, there is a disadvantage of insufficient brightness. Further, depending on the position where the stop is installed, the on-axis light beam and the off-axis light beam cannot be uniformly stopped down, and the off-axis light beam may be largely stopped down, resulting in insufficient peripheral light quantity.

An eyepiece used in a rigid endoscope is shown in FIG.
Since the positive cemented lens has a relatively simple configuration as shown in FIG. 5, the curvature of field is not corrected, and therefore, it is necessary to make the image plane flat when the adapter lens is combined with the eyepiece. There is. A conventional example of an adapter lens taking this point into consideration is known from Japanese Patent Publication No. 4-11005, but this conventional example has a stop. Is not described at all. Furthermore, there is no description that the aperture of the diaphragm is variable.

[0007]

SUMMARY OF THE INVENTION The present invention is used in combination with an endoscope, and can improve the depth of field and control the brightness according to the characteristics of the endoscope. An object of the present invention is to provide a compact optical adapter which has no influence on the amount of light and whose aberration is sufficiently corrected.

[0008]

An optical adapter for an endoscope according to the present invention is used in combination with an endoscope such as a rigid endoscope, and includes an exit pupil of an eyepiece of a rigid endoscope and a photographing lens of an optical adapter. to attach to match the entrance pupil, which bore to the pupil position is provided an aperture stop is variable
In this order, the taking lens is, in order from the object side, a positive first lens and a negative first lens.
The second lens and the third positive lens satisfy the following conditions:
Optical adapter for endoscopes,
You. (1) 1.0 <f {( n 2 -1) / r 4} <3.5 (2) 0.3 <f 1 /f<1.0 (3) 0.15 <| f 2 | / f <0.4 (4) 2 <| r ₆ / r ₇ | <6 (5) 0.15 <d ₃ /f<0.6 , where f ₁ is the focal length of the first lens and f ₂ is the second 2 len
F, f is the focal length of the entire lens system, and n ₂ is
Refractive index of the first lens, d ₃ is first Renzuma from variable throttle
, R ₄ is the radius of curvature of the first surface of the first lens, r ₆
Is the radius of curvature of the first surface of the second lens , and r ₇ is the radius of curvature of the second lens.
This is the radius of curvature of the second surface.

In general, when the optical system is focused on a near point, the depth of field becomes shallower than when the optical system is focused on a far point. However, the depth of field can be improved by narrowing the aperture stop. In the case of a rigid endoscope or the like, the distance between the tip of the endoscope and the subject is short, and the captured image is bright. However, the brightness can be controlled simultaneously by narrowing the aperture stop. For example, at the far point, the distance between the tip of the rigid endoscope and the subject is long, so the captured image at the far point becomes relatively dark, but the lack of brightness is improved by increasing the aperture of the aperture. You can do it.

[0010] Next, as shown in FIG. 13, the variable throttle S ₁
, Ie , the exit pupil position Ep of the eyepiece, the on-axis rays and the off-axis rays passing through the eyepiece are evenly converged when the aperture diameter is changed and reduced. However, a position (for example, S
When installed the aperture to position ₂ or S _3), when gradually reducing the diameter of the aperture, will be focused more off-axis rays than axial rays, insufficient peripheral light aperture efficiency is deteriorated I do. Therefore, by arranging the stop at the exit pupil position of the eyepiece, the stop diameter can be changed while maintaining the aperture efficiency.

For the reasons described above, the optical adapter of the present invention has a variable aperture in the optical system.
Depending on the characteristics of the endoscope used in combination or the purpose of use, it is possible to freely select shooting by changing the aperture diameter and improving the depth of field or shooting with priority on brightness,
Furthermore, since the optical adapter is configured so that the entrance pupil position coincides with the exit pupil of the eyepiece of the endoscope, the aperture efficiency does not deteriorate due to a change in the aperture diameter, and the peripheral light amount does not run short.

The aperture of the aperture stop may be controlled manually or automatically based on a signal such as a luminance signal from a television camera.

Next, as the taking lens used in the optical adapter of the present invention, the following configuration is desirable. For example, as shown in FIG. 1, a triplet type of a positive first lens, a negative second lens, and a positive third lens in order from the object side, and is located at the exit pupil position of the eyepiece of the endoscope. The following conditions (1) to (4) are used in order to secure a space for installing a variable-diameter aperture stop and to make the entire image plane flat when combined with an eyepiece. It is preferable that the configuration satisfy the condition (5).

(1) 1.0 <f ｛(n ₂ −1) / r ₄ ｝ <3.5 (2) 0.3 <f ₁ /f<1.0 (3) 0.15 <| f ₂ | / f <0.4 (4) 2 <| r ₆ / r ₇ | <6 (5) 0.15 <d ₃ /f<0.6 where f ₁ is the focal length of the first lens and f ₂ is the focal length of the second lens, f is the focal length of the entire photographing lens system, n ₂ is the refractive index of the first lens, d ₃ is the distance from the variable aperture to the first lens, and r ₄ is the first lens of the first lens. Radius of curvature of one surface, r ₆
Is the radius of curvature of the first surface of the second lens, and r ₇ is the radius of curvature of the second surface of the second lens.

The condition (1) defines the power of the first surface of the first lens. In the adapter of the present invention, since the aperture mechanism having a variable aperture is provided at the exit pupil position of the eyepiece, the distance between the entrance pupil of the adapter lens and the first surface of the first lens is large. Therefore, when the upper ray of the peripheral light beam is incident on the first surface, the ray height becomes higher, and it becomes difficult to correct coma. Therefore, in condition (1), if the lower limit of 1.0 is exceeded, the coma due to the upper ray will be overcorrected negatively, and if it exceeds the upper limit of 3.5, spherical aberration will be overcorrected.

The condition (2) defines the power of the first lens. To get a long back focus,
It is necessary to move the principal point position of the adapter lens backward, so that the power of the first lens needs to be reduced. In the condition (2), if the lower limit of 0.3 is exceeded, a long back focus cannot be obtained. Further, the focal length f of the whole system and the focal length f ₁ of the first lens, the magnification β _{2 of} the second lens, and the magnification β _{3 of} the third lens are obtained by paraxial theory.
From the relational expression f = f ₁ × β ₂ × β ₃ , when the focal length f ₁ of the first lens is reduced, the magnifications β ₂ and β _{3 of} the second lens and the third lens become too large, and this occurs on the front side. Since the aberration is enlarged by the second lens and the third lens, it becomes difficult to correct various aberrations. Therefore, when the value exceeds the upper limit of 1.0 in the condition (2), it becomes difficult to correct various aberrations. In addition, the back focus becomes too long and lacks compactness.

The condition (3) defines the power of the second lens. In order to obtain a flat image when the adapter of the present invention is combined with an eyepiece, it is necessary to sufficiently correct the field curvature. That it is necessary to reduce the Petzval sum, in order from the Petzval sum PS = Σ {1 / (n i -f i)}, to be the appropriate power of the negative lens to the Petzval sum small is is important. In the condition (3), if the lower limit of 0.15 is exceeded, the correction of the curvature of field becomes excessive. If the upper limit of 0.4 is exceeded, the field curvature will be insufficiently corrected,
Spherical aberration is insufficiently corrected in the positive direction and is excessively corrected in the entire adapter lens.

Condition (4) defines the ratio of the curvature of both surfaces of the second lens. To correct the negative coma of the upper ray generated on the first surface of the first lens to a positive
It is necessary to increase the curvature of the surface. At this time, it is necessary to set the bending of the negative lens to an appropriate value in order to reduce the astigmatic difference generated on each surface. In condition (4), if the lower limit of 2 is exceeded, the positive correction of the coma of the upper ray will be insufficient. If the upper limit of 6 is exceeded, the astigmatic difference will be overcorrected.

Condition (5) defines the distance from the aperture stop to the first surface of the first lens. Condition (5)
If the lower limit of 0.15 is exceeded, it becomes impossible to secure a space for providing a diaphragm mechanism having a variable aperture at the exit pupil position of the eyepiece. In condition (5), the upper limit of 0.6
When the distance exceeds the distance, the distance between the position of the entrance pupil of the adapter lens and the first surface of the first lens becomes large, so that the height of the upper ray of the peripheral luminous flux to the first surface increases, making it difficult to correct coma aberration. Become. Also, since the height of the light beam is high, the outer diameter of the lens must be increased, and the adapter becomes large.

[0020]

EXAMPLES Next, examples of the adapter lens according to the present invention will be described. Example 1 R ₁ = 6.2364 D ₁ = 0.2645 N ₁ = 1.78472 V ₁ = 25.71 R ₂ = 2.4028 D ₂ = 0.7642 N ₂ = 1.66672 V ₂ = 48.32 R ₃ = -5.5245 D ₃ = 0.5878 R ₄ = ∞D ₄ = 0.8818 N ₃ = 1.76820 V ₃ = 71.79 R ₅ = ∞ D ₅ = 0.9406 r ₁ = ∞ d ₁ = 0.2939 n ₁ = 1.51633 ν ₁ = 64.15 r ₂ = ∞ d ₂ = 2.0104 r ₃ = ∞ d ₃ = 4.5440 r ₄ = 3.2934 d ₄ = 1.2727 n ₂ = 1.777250 v ₂ = 49.66 r ₅ = 8.7911 d ₅ = 1.0258 r ₆ = -10.3089 d ₆ = 0.7172 n ₃ = 1.76182 v ₃ = 26.55 r ₇ = 2.3422 d ₇ = 1.4226 r _{8 = 7.6057 d 8 = 1.6254 n} 4 = 1.72916 ν 4 = 54.68 r 9 = -4.7306 d 9 = 2.2015 r 10 = ∞ d 10 = 0.2939 n 5 = 1.51633 ν 5 = 64.15 r 11 = ∞ f = 10, the image height = 1.25, f ₁ = 6.192, f ₂ = −2.445 f {(n ₂ −1) / r ₄ } = 2.35, f ₁ /f=0.62, | f ₂ | /f=0.25 | r ₆ / r ₇ | = 4.40, d ₃ /f=0.45

Example 2 R ₁ = 7.4774 D ₁ = 0.3172 N ₁ = 1.78472 V ₁ = 25.71 R ₂ = 2.8810 D ₂ = 0.9163 N ₂ = 1.66672 V ₂ = 48.32 R ₃ = -6.6239 D ₃ = 0.7048 R ₄ = _{∞ D 4 = 1.0572 n 3 =} 1.76820 V 3 = 71.79 R 5 = ∞ D 5 = 1.1277 r 1 = ∞ d 1 = 0.3524 n 1 = 1.51633 ν 1 = 64.15 r 2 = ∞ d 2 = 2.4105 r 3 = ∞ d _{3 = 2.5504 r 4 = 5.6977 d} 4 = 1.5056 n 2 = 1.78800 ν 2 = 47.38 r 5 = 34.8195 d 5 = 1.7316 r 6 = -12.7401 d 6 = 0.9512 n 3 = 1.75520 ν 3 = 27.51 r 7 = 2.9152 d 7 _{= 1.3568 r 8 = 7.6089 d 8} = 1.0572 n 4 = 1.72916 ν 4 = 54.68 r 9 = -4.8582 d 9 = 0.9867 r 10 = ∞ d 10 = 0.3524 n 5 = 1.51633 ν 5 = 64.15 r 11 = ∞ f = 10 , Image height = 1.256, f ₁ = 8.453, f ₂ = −3.061 f {(n ₂ −1) / r ₄ } = 1.38, f ₁ /f=0.85, | f ₂ | /f=0.31 | r ₆ / r ₇ | = 4.37, d ₃ /f=0.26

Example 3 R ₁ = 7.4680 D ₁ = 0.3168 N ₁ = 1.78472 V ₁ = 25.71 R ₂ = 2.8773 D ₂ = 0.9151 N ₂ = 1.66672 V ₂ = 48.32 R ₃ = -6.6155 D ₃ = 0.7039 R ₄ = _{∞ D 4 = 1.0559 n 3 =} 1.76820 V 3 = 71.79 R 5 = ∞ D 5 = 1.1263 r 1 = ∞ d 1 = 0.3520 n 1 = 1.51633 ν 1 = 64.15 r 2 = ∞ d 2 = 2.4074 r 3 = ∞ d _{3 = 3.9570 r 4 = 4.0545 d} 4 = 1.3238 n 2 = 1.83481 ν 2 = 42.72 r 5 = -63.3980 d 5 = 0.4305 r 6 = -9.7482 d 6 = 0.7225 n 3 = 1.80518 ν 3 = 25.43 r 7 = 3.0125 d _{7 = 2.0647 r 8 = 25.3661 d} 8 = 1.6234 n 4 = 1.77250 ν 4 = 49.66 r 9 = -5.4811 d 9 = 1.0559 r 10 = ∞ d 10 = 0.3520 n 5 = 1.51633 ν 5 = 64.15 r 11 = ∞ f = 10, the image height _{= 1.263, f 1 = 4.606,} f 2 = -2.788 f {(n 2 -1) / r 4} = 2.06, f 1 /f=0.46,|f 2 | /f=0.28 | r 6 / R ₇ | = 3.24, d ₃ /f=3.96

Example 4 R ₁ = 6.3373 D ₁ = 0.2688 N ₁ = 1.78472 V ₁ = 25.71 R ₂ = 2.4417 D ₂ = 0.7766 N ₂ = 1.66672 V ₂ = 48.32 R ₃ = -5.6139 D ₃ = 1.0125 R ₄ = _{∞ D 4 = 0.8960 n 3 =} 1.76820 V 3 = 71.79 R 5 = ∞ D 5 = 0.9558 r 1 = ∞ d 1 = 2.5059 n 1 = 1.76820 ν 1 = 71.79 r 2 = ∞ d 2 = 0.8960 r 3 = ∞ d ₃ = 2.8374 r ₄ = 2.9868 d ₄ = 1.2455 n ₂ = 1.81600 v ₂ = 46.62 r ₅ = 12.981 1 d ₅ = 0.8005 r ₆ = -8.1987 d ₆ = 0.8662 n ₃ = 1.74077 v ₃ = 27.79 r ₇ = 1.9913 d ₇ = 0.9976 r ₈ = 4.3440 d ₈ = 1.0215 n ₄ = 1.67003 v ₄ = 47.25 r ₉ = -7.6419 d ₉ = 1.4934 r ₁₀ = ∞ d ₁₀ = 0.2987 n ₅ = 1.51633 v ₅ = 64.15 r ₁₁ = ∞ f = 10 , Image height = 1.275, f ₁ = 4.502, f ₂ = −2.087 f {(n ₂ −1) / r ₄ } = 2.73, f ₁ /f=0.45, | f ₂ | /f=0.21 | r ₆ / _{r 7 | = 4.12, d 3} /f=0.28 where R _1, R _{2, ··, R 5, r 1,} r 2, ···,
r ₁₁ is the radius of curvature of each lens surface, D ₁ , D ₂ ,.
_{5, d 1, d 2,} ···, d 10 is the thickness and lens distance of each _{lens, N 1, N 2, N} 3, n 1, n 2, ···, n 5
Is the refractive index of each lens, V ₁ , V ₂ , V ₃ , ν ₁ , ν ₂ ,
.., Ν ₅ is the Abbe number of each lens.

The above-described embodiments show the state shown in FIGS. 1 to 4, respectively, attached to an eyepiece of an endoscope. R ₁ to R ₅ in the data in each example both are eyepiece, r ₁ ~r ₂ is the entrance pupil position of the cover glass, the exit pupil, i.e. the adapter lens r ₃ eyepiece, r ₆ ~
r ₁₁ is the adapter lens (photographic lens). The data also shows the focal length of the adapter lens (photography lens) as 1
This is the value when 0 is set.

The aberration situation of the adapter lens of the first embodiment is
As shown in FIG. 5, this adapter lens is
FIG. 6 shows the aberration situation when combined with. Real
The aberration situation of the adapter lens of Example 2 is as shown in FIG.
So when this adapter lens is combined with an eyepiece
Are as shown in FIG. Example 3 Adapter
The aberration of the lens is as shown in FIG.
Figure shows the aberration situation when the tar lens is combined with the eyepiece.
As shown in FIG. Of the adapter lens of Example 4
The aberration situation is as shown in FIG.
Fig. 12 shows the aberration when the lens is combined with the eyepiece.
It is on the street.

As can be seen from the comparison between FIGS. 5 and 6 showing the aberrations of the first embodiment, for example, astigmatism appears in the positive direction only with the taking lens of the optical adapter. In the state combined with the lens, the correction is sufficiently performed.

Also, as shown in the first embodiment, by appropriately setting r, d, and n of the taking lens , the aperture of the stop can be adjusted to the position of the exit pupil of the eyepiece without deteriorating the above-mentioned imaging performance. Space for a variable mechanism can be provided.

As described above, as shown in the embodiments, the taking lens of the optical adapter for an endoscope of the present invention requires a mechanical space for installing a variable-diameter aperture stop at the exit pupil position of the eyepiece. And an overall flat image plane when combined with an eyepiece.

[0029]

According to the endoscope optical adapter of the present invention, the exit pupil of the eyepiece of the endoscope and the entrance pupil of the photographing lens are made to coincide with each other, and a variable aperture aperture stop is arranged at this position. When priority is given to improving the depth of field,
When the aperture stop is stopped down and the brightness is prioritized, the aperture stop can be opened to cope with each case. In addition, there is no shortage of the peripheral light amount by arranging the stop at the above position.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is a sectional view of a second embodiment of the present invention.

FIG. 3 is a sectional view of a third embodiment of the present invention.

FIG. 4 is a sectional view of a fourth embodiment of the present invention.

FIG. 5 is an aberration curve diagram of the adapter lens according to the first embodiment of the present invention.

FIG. 6 shows an adapter lens and an eyepiece according to the first embodiment of the present invention.
Aberration curve diagram of when a combination of the lens

FIG. 7 is an aberration curve diagram of the adapter lens according to the second embodiment of the present invention.

FIG. 8 shows an adapter lens and an eyepiece according to a second embodiment of the present invention.
Aberration curve diagram of when a combination of the lens

FIG. 9 is an aberration curve diagram of the adapter lens according to the third embodiment of the present invention.

FIG. 10 shows an adapter lens and an eyepiece according to a third embodiment of the present invention.
Aberration curve diagram when combined with lens

FIG. 11 is an aberration curve diagram of the adapter lens according to the fourth embodiment of the present invention.

FIG. 12 shows an adapter lens and an eyepiece according to a fourth embodiment of the present invention.
Aberration curve diagram when combined with lens

FIG. 13 is a diagram showing the relationship between the exit pupil of the eyepiece and the aperture stop.

FIG. 14 is a diagram showing a configuration of a rigid endoscope television camera system.

FIG. 15 is a diagram showing a configuration of an optical system in which a conventional eyepiece lens and an adapter lens are combined.

FIG. 16 is a diagram showing the relationship between the permissible circle of confusion diameter of the lens system and the depth of field.

FIG. 17 is a diagram showing a change in the depth of field due to a change in the allowable circle of confusion diameter;

Claims (1)

(57) [Claims] An adapter provided with a taking lens used in combination with an endoscope, wherein an entrance pupil position of the taking lens is made coincident with an exit pupil position of an eyepiece of the endoscope, and an aperture is provided at the entrance pupil position. In a configuration in which a variable aperture is arranged, the photographing lens includes, in order from the object side, a first positive lens, a second negative lens, and a third positive lens, and satisfies the following condition. Endoscope optical adapter. (1) 1.0 <f {( n 2 -1) / r 4} <3.5 (2) 0.3 <f 1 /f<1.0 (3) 0.15 <| f 2 | / f <0.4 (4) 2 <| r ₆ / r ₇ | <6 (5) 0.15 <d ₃ /f<0.6 where f ₁ is the focal length of the first lens, and f ₂ is the _second lens. The focal length of the two lenses, f is the focal length of the entire photographing lens system, n ₂ is the refractive index of the first lens, d ₃ is the distance from the variable aperture to the first lens, and r ₄ is the first surface of the first lens. Radius of curvature, r ₆
Is the radius of curvature of the first surface of the second lens, and r ₇ is the radius of curvature of the second surface of the second lens.