JP2004020972A - Photo-optical system and endoscope using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photo-optical system tolerant to an autoclave sterilization and inconspicuous in ghost light. <P>SOLUTION: The photo-optical system is composed of at least a cover glass which is exposed outside and an objective lens from object side to order, the cover glass is composed of a material which has ruggedness against the autoclave sterilization, the objective lens is composed by a pre-group which has a negative refraction, a brightness diaphragm and a back group which has a positive refraction from the object side to order, and the concave face of the pre-group which is closest to the object is directed to the object. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a photographic optical system and an endoscope using the photographic optical system.
[0002]
[Prior art]
2. Description of the Related Art In the medical field, endoscopes are widely used today to observe a deep portion of a body cavity by inserting an elongated insertion portion into the body cavity or the like, or to perform treatment, processing, and the like using a processing tool as necessary. ing.
[0003]
It is essential for these endoscopes to surely sterilize and sterilize them after use in order to prevent infectious diseases and the like.
[0004]
Recently, sterilization using high-temperature and high-pressure steam called autoclave sterilization, which can be used immediately after sterilization without complicated operations and has low running costs, is becoming the mainstream in sterilization of endoscope equipment.
[0005]
Further, in medical endoscopes, it is desired to reduce the diameter of the endoscope insertion portion and shorten the rigid distal end portion of the endoscope insertion portion in order to improve operability. For this reason, it is essential that the objective lenses used in these medical endoscopes have practically sufficient aberration correction, and that the lens has a small outer diameter and a short overall length. It is.
[0006]
As a conventional example of an imaging optical system having resistance to autoclave sterilization as described above, there is one described in Japanese Patent Application No. 2001-173908. As another conventional photographing optical system, for example, one described in JP-A-2001-260347 is known.
[0007]
[Problems to be solved by the invention]
An imaging optical system that is resistant to autoclave sterilization has a disadvantage that ghosts are likely to occur.
[0008]
The photographing optical system of the fifth embodiment of Japanese Patent Application No. 2001-173908 has a configuration that is resistant to autoclave sterilization by using a cover glass. The imaging optical system includes, in order from the object side, a first lens group including a cover glass made of a parallel flat plate made of sapphire, a plano-concave lens having a concave surface facing the image surface, and a plano-convex lens having a convex surface facing the image side. The second lens group includes a third lens group including a cemented lens of a biconvex positive lens and a negative lens.
[0009]
In the optical system of this conventional example, when an image of a high-luminance subject is taken, ghost light caused by the cover glass is generated.
[0010]
FIG. 19 shows an imaging optical path of ordinary light which is emitted from an object point and enters the imaging optical system at an incident angle (angle between an optical axis and a light ray) of 10 ° in the imaging optical system of the conventional example.
[0011]
FIG. 20 is a diagram showing an image forming optical path of ghost light emitted from an object point and incident on a photographing optical system at an incident angle of 10 ° in the same conventional optical system. The ghost light is reflected by the object-side surface of the objective lens, then reflected again by the object surface of the cover glass, and is imaged by the objective lens.
[0012]
The ghost light image formation position shown in FIG. 20 is close to the normal light image formation position shown in FIG. 19, both on the screen and on the optical axis.
[0013]
As described above, when the imaging position of the ghost light on the optical axis is close to the imaging position of the normal light on the optical axis, the ghost image is focused and the ghost image is clearly observed.
[0014]
The conventional optical system shown in FIG. 19 uses sapphire as a cover glass. This sapphire has a refractive index of 1.7682 and a high refractive index, so that light reflectance is high and ghosts are conspicuous.
[0015]
In the embodiments other than the fifth embodiment of Japanese Patent Application No. 2001-173908, no cover glass is used, and the first lens of the objective lens is formed of sapphire. Therefore, this optical system does not cause ghost, but since sapphire is extremely hard, it is difficult to process it into a lens, which increases the cost.
[0016]
Further, the endoscope photographing optical system is small, and it is generally difficult to process a lens even when sapphire is not used. For example, the first lens of the sixth embodiment of Japanese Patent Application No. 2001-173908 has a small radius of curvature of the image-side surface, and is difficult to process.
[0017]
The present invention has been made in view of the above-described problems of the conventional example, and is an imaging optical system having resistance to autoclave sterilization, an imaging optical system in which ghost light is inconspicuous, and an endoscope including the imaging optical system. Offers a mirror.
[0018]
Another object of the present invention is to provide an imaging optical system which is small and has good imaging performance, has good workability, and an endoscope provided with the imaging optical system.
[0019]
[Means for Solving the Problems]
The first configuration of the imaging optical system according to the present invention includes, in order from the object side, a cover glass exposed to the outside and an objective lens, and the cover glass is made of a material having autoclave resistance. In order from the object side, it consists of a front group with negative refractive power, a stop, and a rear group with positive refractive power, with the most object side surface of the front group facing the object side concave. It is a thing.
[0020]
The photographic optical system of the present invention having such a configuration can suppress the occurrence of ghost, despite the fact that a cover glass made of an autoclave-resistant material is disposed on the object side.
[0021]
Next, this point will be described based on a case where the object point is at infinity in an optical system similar to the thin optical system shown in FIG.
[0022]
FIG. 11 shows an optical system including a cover glass CG and an objective lens OBL, and an image forming position of normal light and ghost light by the optical system. Of these, the objective lens OBL is replaced by a thin lens and is indicated by an arrow in the figure. The focal length of the objective lens OBL is f.
[0023]
Normally, the light beam forms an image at P 'on the rear focal position FB' by the objective lens OBL as shown in FIG. 11A (normal light R).
[0024]
Also, the ghost light GR is reflected by the most object side surface (S1) of the front group of the objective lens OBL as shown in FIG. ₁ An image is formed once at the position of | / 2.
[0025]
Next, the light beam is reflected by the cover glass CG on the object side of the objective lens OBL as shown in FIG. ₁ An image is formed at a position Q of | / 2.
[0026]
Further, an image is formed again by the objective lens OBL, and finally an image is formed at a position Q ′ at a distance b from the objective lens OBL. Here, as shown in FIG. 11D, the point Q ′ is a position shifted toward the object side from the point P ′.
[0027]
The difference Δ between the image positions of the ghost light GR and the normal light R in the optical axis direction is as follows by paraxial calculation.
[0028]
Δ = Q'-P '
−1 / a + 1 / b = 1 / f
Here, a is the object point distance, and b is the image point distance. By substituting a = 1/2 × | r1 | into the above equation, the value of b is obtained as follows.
b = (f × | r1 |) / (| r1 | + 2 × f)
[0029]
Therefore, Δ is expressed as follows.
Δ = f × (2 × f / (| r1 | + 2 × f))
[0030]
The ratio Δ / f to the focal length is as follows.
Δ / f = 2 × f / (| r1 | + 2 × f)
[0031]
As described above, the object point of the ghost light GR for the objective lens OBL moves to a point farther than the object point of the normal light R due to the reflection of the first surface S1 and the cover glass CG, thereby forming an image. This means that the position has shifted to the object point side.
[0032]
As a result, the image position of the ghost light can be shifted from the image plane, and the ghost image is blurred and not clear.
[0033]
Further, the imaging optical system of the present invention, with respect to the image formation position on the screen (image formation position in the direction perpendicular to the optical axis), is located outside the screen (in the direction away from the optical axis) from the image formation position of normal light. Shift. As a result, the occurrence of ghost light is reduced.
[0034]
The objective lens of the photographing optical system of the present invention is a retrofocus type including a front group having a negative refractive power, a brightness stop, and a rear group having a positive refractive power. In such a retrofocus type lens system, the distance from the first surface to the principal point position of the entire objective lens system is large. Therefore, the image forming position due to the reflection of the concave surface of the first surface of the objective lens and the cover glass and the principal point position of the objective lens tend to be close to each other. As a result, the imaging magnification of the objective lens becomes larger than the estimation with the thin lens. The direction in which the imaging magnification of the ghost image by the objective lens increases is a direction away from the optical axis. If a high-luminance subject is located around the screen, the ghost will be out of the screen and will not be observed.
[0035]
For the above reasons, the imaging optical system having the above-described configuration of the present invention can obtain a good observation image in which a ghost image is not conspicuous even for a subject having a high luminance portion on a screen.
[0036]
The photographic optical system according to the present invention described above includes, in addition to the ghost light shown in FIG. 11C, the objective lens which is reflected on the most object side surface S1 of the objective lens and further reflected on the image side surface of the cover glass. It is also possible to improve the ghost light imaged at.
[0037]
Further, in the imaging optical system of the present invention, since the most object side surface of the objective lens (the most object side surface of the front group) has a negative refractive power, the surface of the negative refractive power of the front group has the negative refractive power. It is possible to share the refractive power. Therefore, it is possible to increase the radius of curvature of the other surface of the front group, and the processing of the lens becomes easy.
[0038]
Further, in the imaging optical system of the present invention, generation of ghost is suppressed even when an optical member having high resistance to high-temperature and high-pressure steam such as synthetic quartz, permeable YAG, and spinel is used instead of sapphire as a material having autoclave resistance. And a good observation image can be obtained.
[0039]
In the imaging optical system having the first configuration according to the present invention, it is preferable that the following condition (1) is satisfied.
(1) -2 <f / r _a <-0.02, r _a <0
Where f is the focal length of the entire objective lens system, r _a Is the radius of curvature of the object-side surface of the negative lens in the front group.
[0040]
Condition (1) defines the refractive power of the surface closest to the object in the front group.
[0041]
Under this condition (1), f / r _a Exceeds the upper limit of -0.02, the defocus amount of the ghost image is too small, and the effect of improving the ghost light is small. F / r _a Is larger than the lower limit of −2 to condition (1), it is advantageous for improving ghost light, but | r _a Becomes smaller, and it becomes difficult to obtain a wide angle of view.
[0042]
Note that f / r _a Is -0.02, which is the upper limit value defined in the condition (1), Δ / f ≒ 0.04 in the thin optical system, and the image position of the ghost light can be shifted by about 4% of the focal length.
[0043]
The estimated value in the thin optical system is different from the value in the actual optical system which is a thick lens, but in the defocus direction of the ghost image, Q 'is always closer to the object side than P'.
[0044]
In the optical system having the above configuration, it is more preferable that the following condition (1-1) is satisfied instead of the condition (1).
(1-1) −1.5 <f / r _a <-0.02, r _a <0
[0045]
When the lower limit is -1.5 as in the condition (1-1), ghost light is further improved, and a wide angle of view (2ω) of 70 ° or more can be easily secured. It is preferable as a photographing lens for an endoscope.
[0046]
Next, a second configuration of the present invention is characterized in that the objective lens is as follows.
[0047]
In the objective lens according to the present invention, the front group includes a negative lens whose concave surface faces the object side, and the rear group includes a positive lens and a cemented lens in order from the object side. , (4), and (5) are preferably satisfied.
(3) −0.95 <(r _b + R _a ) / (R _b -R _a ) <1.05
(4) 1.5 <fB / IH <2.7
(5) ν _d (C) <19
Where r _a Is the radius of curvature of the object-side surface of the negative lens in the front group, r _b Is the radius of curvature of the image-side surface of the negative lens in the front group, fB is the distance from the most image-side surface of the objective lens to the rear focal position, IH is the maximum image height, ν _d (C) is the Abbe number of the negative lens of the cemented lens.
[0048]
Condition (3) defines the radii of curvature of the object-side and image-side surfaces of the negative lens in the front group, and is provided to improve the workability of the negative lens and ensure the imaging performance.
[0049]
In order to satisfy the condition (3), the negative refractive power of the negative lens of the front group is shared on both surfaces, whereby the radius of curvature is increased and the workability of the lens is improved. Further, astigmatism can be satisfactorily corrected by forming the negative lens into a shape satisfying the condition (3).
[0050]
If the lower limit of the condition (3) is exceeded by -0.95, the effect of sharing the negative refractive power of the negative lens on both surfaces is lost, and the workability of the lens cannot be improved. In addition, astigmatism is insufficiently corrected, and the mesa diagonal image plane is likely to be negative. When the value exceeds the upper limit of 1.05 of the condition (3), the effect of sharing the negative refractive power of the negative lens on both surfaces is lost, and the workability of the lens is not improved. Further, the radius of curvature of the object-side surface of the negative lens becomes small, which is disadvantageous for widening the angle of view. In addition, astigmatism tends to be overcorrected, and the meridional image plane tends to be positive.
[0051]
In order to reduce the size of the endoscope, it is desirable to satisfy the condition (4). That is, by securing the back focus so as to satisfy the condition (4), it is possible to achieve both miniaturization of the endoscope and securing of a space for disposing the filter.
[0052]
If the value of fB / IH exceeds the upper limit of 2.7 of the condition (4), the back focus becomes unnecessarily large, which is disadvantageous for miniaturization. When the value of fB / IH exceeds the lower limit of 1.5 of the condition (4), it is advantageous for miniaturization, but the back focus becomes small. Therefore, there is no space for disposing a filter or the like, which is not preferable.
[0053]
It is more preferable that the following condition (4-1) is satisfied instead of the condition (4).
(4-1) 2 <fB / IH <2.4
[0054]
If the upper limit and the lower limit of the value of fB / IH are set to 2.4 and 2, respectively, as in the condition (4-1), it is more preferable to achieve both miniaturization and securing a space for disposing filters and the like. .
[0055]
Next, the condition (5) defines the Abbe number of the negative lens of the cemented lens in the rear group, and relates to correction of chromatic aberration and workability of the cemented lens.
[0056]
When the front group having a negative refractive power, such as the objective lens of the endoscope of the present invention, is composed of only a negative lens, chromatic aberration of magnification is likely to be insufficiently corrected. Therefore, it is important to arrange an effective glass material at an effective position.
[0057]
In the objective lens of the present invention, the effective arrangement position of the negative lens is on the image side of the aperture stop, and is a position away from the stop.
[0058]
Therefore, the present invention provides a cemented lens in which a negative lens made of a glass material that satisfies the condition (5), which is an effective glass material for correcting chromatic aberration of magnification, is disposed on the image side of the aperture stop and closest to the image side. , It is possible to effectively correct chromatic aberration of magnification that is likely to be insufficiently corrected.
[0059]
Further, it is preferable that the cemented lens is composed of a positive lens and a negative lens in order from the object side.
[0060]
Further, considering the workability of the cemented lens, it is not necessary to reduce the radius of curvature of the cemented surface by using a glass material having a small Abbe number and increasing the Abbe number difference between the positive lens and the negative lens. That is, the Abbe number ν of the negative lens _d If (C) exceeds the upper limit of 19 in the condition (5), chromatic aberration of magnification is effectively corrected, and a cemented lens with good workability cannot be obtained.
[0061]
As described above, according to the second configuration of the present invention, it is possible to obtain an imaging optical system of an endoscope that is small and has good imaging performance, in which various aberrations including chromatic aberration of magnification in particular are corrected well. .
[0062]
In the objective lens having the second configuration of the present invention, when a cover glass is arranged on the object side to form a photographing optical system, the cover glass is provided by the distance between the objective lens and the cover glass and the thickness of the cover glass. , The off-axis ray height on the object side surface increases, and the diameter of the cover glass tends to increase.
[0063]
In order to solve this problem, it is preferable to satisfy the following condition (2).
(2) 0.13 <d _F / F <1
Where d _F Is the distance from the image-side surface of the lens closest to the object side in the front group to the aperture stop, and is the actual size including the case where there is a medium other than air.
[0064]
The condition (2) is a condition for downsizing the photographing optical system using the cover glass.
[0065]
d _F If the value of / f exceeds the upper limit of 1 in condition (2), the height of off-axis rays increases, and the diameter of the cover glass increases, which is not preferable. An optical system having a wide angle of view such as an endoscope is not particularly preferable. Also, d _F If / f exceeds the lower limit of 0.13 of the condition (2), it is preferable in that the diameter of the cover glass can be reduced. However, it is difficult to secure the back focus. Becomes difficult.
[0066]
Furthermore, the third configuration of the present invention includes, in order from the object side, at least a cover glass exposed to the outside and an objective lens, wherein the cover glass is made of a material having autoclave resistance, and the objective lens is sequentially arranged from the object side. , A front group having a negative refractive power, a brightness stop, and a rear group having a positive refractive power. The front group includes a negative lens having a concave surface facing the object side, and the rear group includes an object side. , The objective lens satisfies the following conditions (1) to (5).
(1) -2 <f / r _a <-0.02, r _a <0
(2) 0.13 <d _F / F <1
(3) −0.95 <(r _b + R _a ) / (R _b -R _a ) <1.05
(4) 1.5 <fB / IH <2.7
(5) ν _d (C) <19
Where f is the focal length of the entire objective lens system, r _a Is the radius of curvature of the object-side surface of the negative lens in the front group, r _b Is the radius of curvature of the image-side surface of the negative lens in the front group, d _F Is the distance from the image side surface of the lens closest to the object side of the front group to the aperture stop, and the actual size including the case where a filter is placed between them. FB is the distance from the most image side surface of the objective lens to the rear. Distance to side focus position, IH is maximum image height, ν _d (C) is the Abbe number of the negative lens of the cemented lens.
[0067]
The photographing optical system having the third configuration is characterized in that the rear group of the objective lens includes a positive lens and a cemented lens in which the positive lens and the negative lens are cemented.
[0068]
Further, the conditions (1) to (5) are satisfied.
[0069]
These conditions are as described above, and the condition (1) is the first surface r of the front group. ₃ Is specified to increase the ghost light removing effect.
[0070]
The condition (2) is for realizing miniaturization and the like of a photographing optical system using a cover glass.
[0071]
The condition (3) defines the shape of the negative lens in the front group, and is provided for improving the workability of the lens.
[0072]
The condition (4) is to ensure the back focus and to secure the space for disposing the filters and downsize the optical system.
[0073]
Further, the condition (5) is for correcting chromatic aberration of magnification.
[0074]
The setting of the upper limit value and the lower limit value in each condition is based on the same reason as described above.
[0075]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described based on the illustrated embodiments.
[0076]
FIG. 1 to FIG. 5 are diagrams showing the configurations of Embodiments 1 to 5 of the endoscope photographing optical system according to the present invention, respectively. These examples have the following data.
[0077]
Example 1
f = 1, 2ω = 86.5 °, F / 4.008
r ₀ = ∞d ₀ = 22.1625
r ₁ = ∞d ₁ = 0.3694 n ₁ = 1.76820 ν ₁ = 71.79
r ₂ = ∞d ₂ = 0.2586
r ₃ = -3.7344 d ₃ = 0.2216 n ₂ = 1.88300 ν ₂ = 40.76
r ₄ = 1.0202 d ₄ = 0.2955
r ₅ = ∞ (aperture) d ₅ = 0.0222
r ₆ = ∞d ₆ = 1.0195 n ₃ = 1.88300 ν ₃ = 40.76
r ₇ = -0.9766 d ₇ = -0.0813
r ₈ = ∞d ₈ = 0.1182
r ₉ = 7.0100 d ₉ = 0.8643 n ₄ = 1.72916 ν ₄ = 54.68
r ₁₀ = -0.9183 d ₁₀ = 0.2216 n ₅ = 1.92286 ν ₅ = 18.90
r ₁₁ = -3.0732 d ₁₁ = 0.0369
r ₁₂ = ∞d ₁₂ = 0.295 n ₆ = 1.52287 ν ₆ = 59.89
r ₁₃ = ∞d ₁₃ = 0.0222
r ₁₄ = ∞d ₁₄ = 0.7387 n ₇ = 1.49400 ν ₇ = 75.00
r _Fifteen = ∞d _Fifteen = 0.2290
r ₁₆ = ∞d ₁₆ = 0.0222
r ₁₇ = ∞d ₁₇ = 0.3694 n ₈ = 1.76820 ν ₈ = 71.79
r ₁₈ = ∞d ₁₈ = 0.3694 n ₉ = 1.51633 ν ₉ = 64.14
r ₁₉ = ∞d ₁₉ = 0.0570
r ₂₀ = ∞
r _a = -3.7344, f / r _a = -0.268
d _F = 0.2955, d _F /F=0.296
r _b = 1.0202, (r _b + R _a ) / (R _b -R _a ) =-0.571 fB = 1.4633, IH = 0.673, fB / IH = 2.176
ν _d (C) = 18.9
[0078]
Example 2
f = 1, 2ω = 70.2 °, F / 4.018
r ₀ = ∞d ₀ = 18.0066
r ₁ = ∞d ₁ = 0.3001 n ₁ = 1.76820 ν ₁ = 71.79
r ₂ = ∞d ₂ = 0.2101
r ₃ = -0.9602 d ₃ = 0.1918 n ₂ = 1.88300 ν ₂ = 40.76
r ₄ = ∞d ₄ = 0.1426
r ₅ = ∞ (aperture) d ₅ = 0.0216
r ₆ = ∞d ₆ = 0.7965 n ₃ = 1.88300 ν ₃ = 40.76
r ₇ = -1.3593 d ₇ = 0
r ₈ = ∞d ₈ = 0.0300
r ₉ = 1.5644 d ₉ = 0.7702 n ₄ = 1.72916 ν ₄ = 54.68
r ₁₀ = -0.9141 d ₁₀ = 0.1801 n ₅ = 1.92286 ν ₅ = 18.90
r ₁₁ = -3.0006 d ₁₁ = 0.0300
r ₁₂ = ∞d ₁₂ = 0.2401 n ₆ = 1.52287 ν ₆ = 59.89
r ₁₃ = ∞d ₁₃ = 0.0300
r ₁₄ = ∞d ₁₄ = 0.6002 n ₇ = 1.49400 ν ₇ = 75.00
r _Fifteen = ∞d _Fifteen = 0.1889
r ₁₆ = ∞d ₁₆ = 0.0180
r ₁₇ = ∞d ₁₇ = 0.3001 n ₈ = 1.76820 ν ₈ = 71.79
r ₁₈ = ∞d ₁₈ = 0.3001 n ₉ = 1.51633 ν ₉ = 64.14
r ₁₉ = ∞d ₁₉ = 0.0288
r ₂₀ = ∞
r _a = -0.9602, f / r _a = -1.041
d _F = 0.1426, d _F /F=0.143
r _b = ∞, (r _b + R _a ) / (R _b -R _a ) = 1.000
fB = 1.1680, IH = 0.547, fB / IH = 2.135
ν _d (C) = 18.9
[0079]
Example 3
f = 1, 2ω = 110.2 °, F / 4.018
r ₀ = ∞d ₀ = 24.4417
r ₁ = ∞d ₁ = 0.4074 n ₁ = 1.76820 ν ₁ = 71.79
r ₂ = ∞d ₂ = 0.2444
r ₃ = -2.0480 d ₃ = 0.2603 n ₂ = 1.88300 ν ₂ = 40.76
r ₄ = 1.3030 d ₄ = 0.4649
r ₅ = ∞ (aperture) d ₅ = 0.0147
r ₆ = 10.2683 d ₆ = 1.3455 n ₃ = 1.88300 ν ₃ = 40.76
r ₇ = -1.3686 d ₇ = 0
r ₈ = ∞d ₈ = 0.0407
r ₉ = 2.7762 d ₉ = 0.9584 n ₄ = 1.72916 ν ₄ = 54.68
r ₁₀ = -1.2409 d ₁₀ = 0.2444 n ₅ = 1.92286 ν ₅ = 18.90
r ₁₁ = -8.8720 d ₁₁ = 0.0407
r ₁₂ = ∞d ₁₂ = 0.3259 n ₆ = 1.52287 ν ₆ = 59.89
r ₁₃ = ∞d ₁₃ = 0.0407
r ₁₄ = ∞d ₁₄ = 0.8147 n ₇ = 1.49400 ν ₇ = 75.00
r _Fifteen = ∞d _Fifteen = 0.2331
r ₁₆ = ∞d ₁₆ = 0.0244
r ₁₇ = ∞d ₁₇ = 0.4074 n ₈ = 1.76820 ν ₈ = 71.79
r ₁₈ = ∞d ₁₈ = 0.4074 n ₉ = 1.51633 ν ₉ = 64.14
r ₁₉ = ∞d ₁₉ = 0.0400
r ₂₀ = ∞
r _a = -2.0480, f / r _a = −0.488
d _F = 0.4649, d _F /F=0.465
r _b = 1.3226, (r _b + R _a ) / (R _b -R _a ) = − 0.222 fB = 1.9755, IH = 0.742, fB / IH = 2.153
ν _d (C) = 18.9
[0080]
Example 4
f = 1, 2ω = 130.2 °, F / 4.018
r ₀ = ∞d ₀ = 28.4127
r ₁ = ∞d ₁ = 0.4735 n ₁ = 1.76820 ν ₁ = 71.79
r ₂ = ∞d ₂ = 0.1894
r ₃ = -5.9985 d ₃ = 0.3026 n ₂ = 1.88300 ν ₂ = 40.76
r ₄ = 1.0984 d ₄ = 0.7574
r ₅ = ∞ (aperture) d ₅ = 0.0467
r ₆ = -12.0492 d ₆ = 1.5722 n ₃ = 1.88300 ν ₃ = 40.76
r ₇ = -1.4815 d ₇ = 0
r ₈ = ∞d ₈ = 0.0474
r ₉ = 4.066 d ₉ = 1.2406 n ₄ = 1.72916 ν ₄ = 54.68
r ₁₀ = -1.3080 d ₁₀ = 0.2841 n ₅ = 1.92286 ν ₅ = 18.90
r ₁₁ = -6.1617 d ₁₁ = 0.0474
r ₁₂ = ∞d ₁₂ = 0.3788 n ₆ = 1.52287 ν ₆ = 59.89
r ₁₃ = ∞d ₁₃ = 0.0474
r ₁₄ = ∞d ₁₄ = 0.9471 n ₇ = 1.49400 ν ₇ = 75.00
r _Fifteen = ∞d _Fifteen = 0.2679
r ₁₆ = ∞d ₁₆ = 0.0284
r ₁₇ = ∞d ₁₇ = 0.4735 n ₈ = 1.76820 ν ₈ = 71.79
r ₁₈ = ∞d ₁₈ = 0.4735 n ₉ = 1.51633 ν ₉ = 64.14
r ₁₉ = ∞d ₁₉ = 0.0468
r ₂₀ = ∞
r _a = −− 5.99985, f / r _a = -0.167
d _F = 0.7574, d _F / F = 0.757
r _b = 1.0984, (r _b + R _a ) / (R _b -R _a ) = − 0.690 fB = 1.665, IH = 0.633, fB / IH = 2.163
ν _d (C) = 18.9
[0081]
Example 5
f = 1, 2ω = 152.3 °, F / 4.018
r ₀ = ∞d ₀ = 32.0198
r ₁ = ∞d ₁ = 0.5337 n ₁ = 1.76820 ν ₁ = 71.79
r ₂ = ∞d ₂ = 0.1067
r ₃ = -3.55.5776 d ₃ = 0.3410 n ₂ = 1.88300 ν ₂ = 40.76
r ₄ = 1.109 d ₄ = 0.9060
r ₅ = ∞ (aperture) d ₅ = 0.0759
r ₆ = -3.9484 d ₆ = 2.0721 n ₃ = 1.88300 ν ₃ = 40.76
r ₇ = -1.6220 d ₇ = 0
r ₈ = ∞d ₈ = 0.0534
r ₉ = 3.5587 d ₉ = 1.3536 n ₄ = 1.72916 ν ₄ = 54.68
r ₁₀ = -1.5334d ₁₀ = 0.3202 n ₅ = 1.92286 ν ₅ = 18.90
r ₁₁ = -13.4984 d ₁₁ = 0.0534
r ₁₂ = ∞d ₁₂ = 0.4269 n ₆ = 1.52287 ν ₆ = 59.89
r ₁₃ = ∞d ₁₃ = 0.0534
r ₁₄ = ∞d ₁₄ = 1.067 n ₇ = 1.49400 ν ₇ = 75.00
r _Fifteen = ∞d _Fifteen = 0.2793
r ₁₆ = ∞d ₁₆ = 0.0320
r ₁₇ = ∞d ₁₇ = 0.5337 n ₈ = 1.76820 ν ₈ = 71.79
r ₁₈ = ∞d ₁₈ = 0.5337 n ₉ = 1.51633 ν ₉ = 64.14
r ₁₉ = ∞d ₁₉ = 0.0820
r ₂₀ = ∞
r _a = −35.5776, f / r _a = -0.028
d _F = 0.9060, d _F /F=0.906
r _b = 1.109, (r _b + R _a ) / (R _b -R _a ) = − 0.940 fB = 2.1183, IH = 0.772, fB / IH = 2.179
ν _d (C) = 18.9
Where r ₁ , R ₂ , ... are the radii of curvature of the respective surfaces of the lens, d ₁ , D ₂ ,... Indicate the thickness and air space of each lens, n ₁ , N ₂ ,... Are the refractive indices of each lens for the d-line, ν ₁ , Ν ₂ ,... Are Abbe numbers of each lens with respect to the d-line. Note that r ₀ Is the object plane, d ₀ Is the distance from the object plane to the cover glass.
[0082]
As shown in FIG. 1, the photographing optical system according to the first embodiment includes an objective lens including a cover glass C1, a front group GF having a negative refractive power, a brightness stop S, and a rear group GR having a positive refractive power. , Filters F1 and F2, an image sensor cover glass C2 and an image sensor sealing glass C3, and the front group GF is a biconcave lens (r ₃ ~ R ₄ ), And the rear group GR is a positive lens (r ₆ ~ R ₇ ) And a positive cemented lens (r ₉ ~ R ₁₁ ). FS is a flare stop.
[0083]
Examples 2 to 5 have the same configurations as those shown in FIGS. 2 to 5, respectively, and have substantially the same lens configuration as Example 1.
[0084]
6 to 10 are aberration curve diagrams of Examples 1 to 5, respectively.
[0085]
Image light and ghost light in the optical systems of Examples 1 to 5 will be described.
[0086]
FIGS. 12 and 13 show an imaging optical path of normal light and an imaging optical path of ghost light in the imaging optical system of the first embodiment.
[0087]
In these figures, FIG. 12 shows a normal image forming optical path when a light beam emitted from an object point enters the imaging optical system of the present invention (Example 1) at an incident angle of 10 °.
[0088]
The paraxial imaging position in this case is the plane r ₁₉ The distance is 0.057 closer to the image side.
[0089]
FIG. 13 shows an image forming optical path of ghost light emitted from an object point and incident on the imaging optical system of Example 1 at an incident angle of 10 °.
[0090]
The paraxial image position of this ghost light is on the nineteenth surface (r ₁₉ ) On the object side of 0.965. That is, r in FIG. ₁₄ And r _Fifteen And in the filter F.
[0091]
As described above, the ghost light imaging position Q ′ is shifted 1.022 toward the object side from the regular light imaging position P ′. Further, the image forming position on the screen (image forming position in the direction perpendicular to the optical axis) is shifted to the outside of the screen (in the direction away from the optical axis) from the layering position of normal light.
[0092]
As a result, the ghost is blurred and not clear. In addition, if a high-luminance subject is located at the periphery of the screen, it will not be observed outside the ghost screen.
[0093]
FIG. 18 shows the positional relationship between normal light and ghost light on the screen.
[0094]
In FIG. 18, R1 is an image of the normal light (imaging light) near the center of the screen, RG1 is a ghost by the normal light R1, R2 is an image of the peripheral portion of the normal light on the screen, and RG2 is a ghost by the normal light R2.
[0095]
As shown in this figure, the ghost light RG1 is blurred because the image formation position is shifted from the screen in the optical axis direction. Also, the ghost light RG2 is blurred and out of the screen.
[0096]
The above is the optical system in the apparatus using the autoclave in the first embodiment.
[0097]
In the case of an apparatus that does not use an autoclave, the photographing optical system may have the configuration shown in the figure.
[0098]
FIG. 14 shows a photographing optical system that does not use a cover glass, in which S-BSL7 (manufactured by OHARA CORPORATION) is used as the glass material of the cover glass C2 of the image sensor.
[0099]
FIG. 15 shows a case where S-BSL7 is used as the material of the cover glass C1 on the object side.
[0100]
As described above, the photographing optical system used in the apparatus that does not use the autoclave does not need to use sapphire as the material of the cover glass. Therefore, the cost can be reduced by using B-BSL7 as the material of the cover glass.
[0101]
Further, in all the optical systems of the embodiments, the optical system can be made of a glass material that does not contain lead or arsenic.
[0102]
For example, in Example 1, the cover glass C1 is sapphire and the first lens (r ₃ ~ R ₄ ) And the second lens (r ₆ ~ R ₇ ) Is S-LAH58 (manufactured by OHARA CORPORATION) and the third lens (r ₉ ~ R ₁₀ ) Is S-NPH2 (manufactured by OHARA Co., Ltd.), filter F1 is white plate or S-BSL7 (manufactured by OHARA Co., Ltd.), filter F2 is CM5000 (manufactured by HOYA CORPORATION), cover glass C2 is sapphire, and image sensor sealing glass C3. Is S-BSL7 (produced by Ohara Corporation).
[0103]
Therefore, the photographic optical system has a configuration that is resistant to autoclave sterilization and ghosts are inconspicuous, small in size, has good workability of individual lenses, and does not contain harmful lead and arsenic and is also preferable for the environment. is there. Further, the photographing optical system according to the present embodiment can reduce the disposal cost even when the photographing optical system is collected after the end of its useful life and disassembled and disposed.
[0104]
Although the first embodiment has been described above, the imaging optical systems of the second to fourth embodiments also have a lens configuration similar to that of the first embodiment, and the same glass material is used.
[0105]
Therefore, it has the same features as described in the first embodiment.
[0106]
Example 5 has a configuration as shown in FIG. The fifth embodiment is an optical system similar in lens configuration to the other embodiments. f / r ₃ Is close to the upper limit of the condition (1), but the ghost can be improved also in the present embodiment. That is, the image position Q 'of the ghost light is shifted toward the object side from the image position P' of the normal light.
[0107]
FIG. 16 shows a normal imaging optical path which is emitted from the object point and enters the imaging optical system at an incident angle of 20 ° in the optical system of the fifth embodiment. The paraxial imaging position of this optical system is at the nineteenth surface (r ₁₉ ) At a distance of 0.082 from the image side.
[0108]
FIG. 17 shows an imaging optical path of ghost light emitted from the object point and incident on the imaging optical system at an incident angle of 20 ° in the fifth embodiment.
[0109]
In the fifth embodiment, the paraxial imaging position of the ghost light is on the 19th surface (r ₁₉ ) Is closer to the image side by 0.025.
[0110]
In the fifth embodiment, the image position Q ′ of the ghost light is shifted by 0.057 toward the object side from the image position of the normal light.
[0111]
The present invention has been described in detail above. In addition to the inventions described in the claims, the inventions described in the following items can also achieve the objects.
[0112]
(1) An optical system according to claim 1, wherein the following condition (1) is satisfied.
(1) -2 <f / r _a <-0.02, r _a <0
Where f is the focal length of the entire objective lens system, r _a Is the radius of curvature of the object-side surface of the negative lens in the front group.
[0113]
(2) An imaging optical system according to claim 1, wherein the following condition (2) is satisfied.
(2) 0.13 <d _F / F <1
Where d _F Is the distance from the image-side surface of the lens closest to the object side in the front group to the aperture stop, and is the actual size including the case where there is a medium other than air.
[0114]
(3) The imaging optical system according to claim 2, wherein the positive lens in the rear group is a plano-convex lens having a flat object-side surface.
[0115]
(4) The optical system according to claim 2, wherein in the cemented lens in the rear group, the image-side lens is a negative lens.
[0116]
(5) An optical system according to claim 2, wherein the following condition (2) is satisfied.
(2) 0.13 <d _F / F <1
Where d _F Is the distance from the image-side surface of the lens closest to the object side in the front group to the aperture stop, and is the actual size including the case where there is a medium other than air.
[0117]
(6) In order from the object side, at least including a cover glass exposed to the outside and an objective lens, the cover glass is made of a material having autoclave resistance, and the objective lens has a negative refractive power in order from the object side. The front group, the aperture stop, and the rear group having a positive refractive power, the most object side surface of the front group having the concave surface facing the object side, and satisfying the following condition (1-1). Optical system.
(1-1) −1.5 <f / r _a <-0.02, r _a <0
Where f is the focal length of the entire objective lens system, r _a Is the radius of curvature of the object-side surface of the negative lens in the front group.
[0118]
(7) An imaging optical system according to the above (6), wherein the following condition (2) is satisfied.
(2) 0.13 <d _F / F <1
Where d _F Is the distance from the image-side surface of the lens closest to the object side in the front group to the aperture stop, and is the actual size including the case where there is a medium other than air.
[0119]
(8) In order from the object side, the front unit includes a front unit having a negative refractive power, a brightness stop, and a rear unit having a positive refractive power. The front unit includes a negative lens having a concave surface facing the object side. An objective lens in which the rear group includes, in order from the object side, a plano-convex lens having a flat surface on the object side and a cemented lens having a negative lens on the image side, and satisfying the following conditions (3), (4-1), and (5).
(3) −0.95 <(r _b + R _a ) / (R _b -R _a ) <1.05
(4-1) 2 <fB / IH <2.4
(5) ν _d (C) <19
Where r _a Is the radius of curvature of the object-side surface of the negative lens in the front group, r _b Is the radius of curvature of the image-side surface of the negative lens in the front group, fB is the distance from the most image-side surface of the objective lens to the rear focal position, IH is the maximum image height, ν _d (C) is the Abbe number of the negative lens of the cemented lens.
[0120]
(9) In order from the object side, the front unit includes a front unit having a negative refractive power, a brightness stop, and a rear unit having a positive refractive power. The front unit includes a negative lens having a concave surface facing the object side. The rear group includes, in order from the object side, a plano-convex lens having a flat surface on the object side and a cemented lens having a negative lens on the image side, and satisfying the following conditions (2), (3), (4-1), and (5). lens.
(2) 0.13 <d _F / F <1
(3) −0.95 <(r _b + R _a ) / (R _b -R _a ) <1.05
(4-1) 2 <fB / IH <2.4
(5) ν _d (C) <19
Where r _a Is the radius of curvature of the object-side surface of the negative lens in the front group, r _b Is the radius of curvature of the image-side surface of the negative lens in the front group, fB is the distance from the most image-side surface of the objective lens to the rear focal position, IH is the maximum image height, ν _d (C) is the Abbe number of the negative lens of the cemented lens.
[0121]
(10) In order from the object side, at least an externally exposed cover glass and an objective lens, and the cover glass is made of a material having autoclave resistance, and the objective lens has a negative refractive power in order from the object side. The front group consists of a front lens group, a brightness stop, and a rear lens group with positive refractive power.The front lens group consists of a negative lens with a concave surface facing the object side. The rear lens group consists of a positive lens and a cemented lens in order from the object side. The imaging optical system according to claim 1, wherein the objective lens satisfies the following conditions (1-1), (2), (3), (4-1), and (5).
(1-1) −1.5 <f / r _a <-0.02, r _a <0
(2) 0.13 <d _F / F <1
(3) −0.95 <(r _b + R _a ) / (R _b -R _a ) <1.05
(4-1) 2 <fB / IH <2.4
(5) ν _d (C) <19
Where f is the focal length of the entire objective lens system, r _a Is the radius of curvature of the object-side surface of the negative lens in the front group, r _b Is the radius of curvature of the image-side surface of the negative lens in the front group, d _F Is the distance from the image side surface of the lens closest to the object side of the front group to the aperture stop, and the actual size including the case where a filter is placed between them. FB is the distance from the most image side surface of the objective lens to the rear. Distance to side focus position, IH is maximum image height, ν _d (C) is the Abbe number of the negative lens of the cemented lens.
[0122]
(11) The imaging optical system according to the above (9), wherein the cemented lens comprises a positive lens and a negative lens in order from the object side.
[0123]
(12) The imaging optical system according to the above (10), wherein the cemented lens comprises a positive lens and a negative lens in order from the object side.
[0124]
(13) The optical system according to the above (6), wherein the imaging optical system is made of a material that does not contain harmful substances such as arsenic and lead.
[0125]
(14) The optical system according to the above (8), wherein the imaging optical system is made of a material that does not contain harmful substances such as arsenic and lead.
[0126]
(15) An endoscope using the photographing optical system according to any one of the claims (1), (2) or (3) or the above (1) to (14). .
[0127]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, it has resistance to autoclave sterilization and can implement | achieve the imaging | photography optical system which ghost light is not outstanding, and the endoscope using the same. Further, a small-sized imaging optical system having good imaging performance and good workability and an endoscope using the same can be realized.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a photographing optical system according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view of Embodiment 2 of the photographing optical system of the present invention.
FIG. 3 is a sectional view of a third embodiment of a photographing optical system according to the present invention;
FIG. 4 is a cross-sectional view of a photographing optical system according to a fourth embodiment of the present invention.
FIG. 5 is a cross-sectional view of Embodiment 5 of the imaging optical system of the present invention.
FIG. 6 is an aberration curve diagram of the imaging optical system according to the first embodiment of the present invention.
FIG. 7 is an aberration curve diagram of Embodiment 2 of the imaging optical system of the present invention.
FIG. 8 is an aberration curve diagram of the photographing optical system according to the third embodiment of the present invention.
FIG. 9 is an aberration curve diagram of the photographing optical system according to the fourth embodiment of the present invention.
FIG. 10 is an aberration curve diagram of the fifth embodiment of the imaging optical system of the present invention.
FIG. 11 is a diagram illustrating an image formation and the like of normal light and ghost light of a photographing optical system including a cover glass and an objective lens.
FIG. 12 is an optical path diagram of normal light according to the first embodiment of the present invention.
FIG. 13 is an optical path diagram of ghost light according to the first embodiment of the present invention.
FIG. 14 is a diagram illustrating a configuration of an optical system that does not use a cover glass.
FIG. 15 is a diagram showing a configuration of an optical system using a cover glass of S-BSL7.
FIG. 16 is an optical path diagram of normal light according to a fifth embodiment of the present invention.
FIG. 17 is an optical path diagram of ghost light according to a fifth embodiment of the present invention.
FIG. 18 is a diagram showing image formation positions of normal light and ghost light on a screen.
FIG. 19 is an optical path diagram of normal light of a conventional photographing optical system.
20 is an optical path diagram of ghost light of the conventional photographing optical system shown in FIG.

Claims (3)

In order from the object side, a cover glass exposed to the outside and an objective lens, the cover glass is made of a material having autoclave resistance, and the objective lens is, in order from the object side, a front group having a negative refractive power. 1. An imaging optical system comprising a brightness stop and a rear group having a positive refractive power, wherein a surface closest to the object side of the front group has a concave surface facing the object side. An objective lens, wherein the objective lens includes, in order from the object side, a front group having a negative refractive power, a brightness stop, and a rear group having a positive refractive power, and the front group has a concave surface facing the object side. The rear unit includes a positive lens and a cemented lens in order from the object side, and the objective lens satisfies the following conditions (3), (4), and (5).
_{(3) -0.95 <(r b} + r a) / (r b -r a) <1.05
(4) 1.5 <fB / IH <2.7
(5) ν _d (C) <19
However, r _a is the radius of curvature of the object side surface of the negative lens of the front group, r _b is the radius of curvature of the image side surface of the negative lens of the front group, fB is back focal from the surface located nearest to the image side of the objective lens The distance to the position, IH is the maximum image height, and ν _d (C) is the Abbe number of the negative lens of the cemented lens. In order from the object side, at least a cover glass exposed to the outside, and an objective lens, wherein the cover glass is made of a material having autoclave resistance, and the objective lens is, in order from the object side, a front group having a negative refractive power. , A brightness stop, and a rear group having a positive refractive power, the front group includes a negative lens having a concave surface facing the object side, and the rear group includes a positive lens and a cemented lens in order from the object side. Wherein the objective lens satisfies the following conditions (1), (2), (3), (4), and (5).
_{(1) -2 <f / r} a <-0.02, r a <0
(2) 0.13 <d _F / f <1
_{(3) -0.95 <(r b} + r a) / (r b -r a) <1.05
(4) 1.5 <fB / IH <2.7
(5) ν _d (C) <19
However, f is the focal length of the objective lens system, r _a is the radius of curvature of the object side surface of the negative lens of the front group, r _b is the radius of curvature of the image side surface of the negative lens of the front group, d _F before The actual size including the distance between the image-side surface of the lens located closest to the object side of the group and the aperture stop and the filter in between, and fB is the focal point from the most image-side surface of the objective lens to the rear focal point. The distance to the position, IH is the maximum image height, and ν _d (C) is the Abbe number of the negative lens of the cemented lens.

Images