JP7430966B2 - Imaging optical system and imaging device equipped with the same - Google Patents

Description

The present invention relates to an imaging optical system and an imaging device equipped with the same.

Medical endoscopes are used to perform detailed diagnosis of diseased areas. Therefore, the objective optical system of a medical endoscope is required to be capable of magnifying observation of a lesion.

An objective optical system capable of magnified observation can perform magnified observation by focusing on a nearby object point. In addition, normal observation can be performed by focusing on a distant object point.

The magnification for normal observation is smaller than the magnification for magnified observation. Therefore, in normal observation, for example, a wide range including the lesion and its surrounding area can be observed. Magnified observation allows the lesion to be observed in detail.

Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4 disclose objective optical systems that can perform magnified observation.

These objective optical systems include a first lens group with positive refractive power, a second lens group with negative refractive power, and a third lens group with positive refractive power. When focusing, the second lens group moves.

Patent No. 5148403 (3rd example) Patent No. 5985133 (1st example) Patent No. 5580956 (1st example) Patent No. 4653823 (4th example)

In a medical endoscope, an insertion section is inserted into the body. Therefore, it is preferable that the insertion portion has a small diameter. Furthermore, in order to improve the diagnostic accuracy of a lesion, it is preferable to be able to observe a narrow range with high resolution. Therefore, the objective optical system is required to have high resolution while being small.

In order to make the optical system compact, it is sufficient to increase the negative refractive power in the first lens group. If the negative refractive power in the first lens group cannot be increased, the entrance pupil will be located on the image side. When the entrance pupil is located on the image side, the first lens group becomes larger. Therefore, it is not possible to downsize the optical system.

In the objective optical system disclosed in Patent Document 1, the objective optical system disclosed in Patent Document 2, and the objective optical system disclosed in Patent Document 3, the first lens group includes a single lens and a cemented lens. has.

In the first lens group of these objective optical systems, a single lens having negative refractive power (hereinafter referred to as a "negative single lens") is arranged closest to the object side. A single lens with positive refractive power (hereinafter referred to as "positive single lens") and a cemented lens with positive refractive power (hereinafter referred to as "positive cemented lens") on the image side of the negative single lens. is located.

In this case, the negative refractive power in the first lens group is determined only by the refractive power of the single negative lens. With only a negative single lens, it is not possible to increase the negative refractive power in the first lens group while suppressing the occurrence of aberrations. Therefore, these objective optical systems cannot be called compact optical systems.

Furthermore, in order to make the optical system compact, the aperture stop may be placed on the object side. If the aperture stop cannot be placed on the object side, the height of the light beam in the first lens group will increase. As the height of the light beam in the first lens group increases, the first lens group becomes larger. Therefore, it is not possible to downsize the optical system.

In the objective optical system disclosed in Patent Document 2 and the objective optical system disclosed in Patent Document 4, the aperture stop is arranged in the second lens group. If the aperture stop is placed in the second lens group, the height of the light ray in the first lens group will not be reduced. Therefore, these objective optical systems cannot be called compact optical systems.

The present invention has been made in view of these problems, and an object of the present invention is to provide an imaging optical system that is compact but has high resolution. Another object of the present invention is to provide an imaging device that can acquire high-definition images.

In order to solve the above-mentioned problems and achieve the objectives, an imaging optical system according to at least some embodiments of the present invention includes the following:
Has multiple lens groups,
Each of the plurality of lens groups has a lens component,
The lens component has a plurality of optical surfaces,
In the lens component, two optical surfaces are in contact with air, and at least one optical surface is a curved surface,
The multiple lens groups are arranged in order from the object side.
a first lens group having positive refractive power;
a second lens group having negative refractive power;
consisting of a third lens group having positive refractive power,
When focusing from far point to near point, only the second lens group moves toward the image side,
The first lens group includes, in order from the object side, a first negative lens component, a second negative lens component, and a plurality of positive lens components,
The second lens group has a negative lens component,
The aperture stop is arranged in the first lens group ,
The second negative lens component is characterized by having, in order from the object side, a negative single lens and a positive single lens .
Further, the imaging optical system according to at least some embodiments of the present invention includes:
Has multiple lens groups,
Each of the plurality of lens groups has a lens component,
The lens component has a plurality of optical surfaces,
In the lens component, two optical surfaces are in contact with air, and at least one optical surface is a curved surface,
The multiple lens groups are arranged in order from the object side.
a first lens group having positive refractive power;
a second lens group having negative refractive power;
consisting of a third lens group having positive refractive power,
When focusing from far point to near point, only the second lens group moves toward the image side,
The first lens group includes, in order from the object side, a first negative lens component, a second negative lens component, and a plurality of positive lens components,
The second lens group has a negative lens component,
The aperture stop is arranged in the first lens group,
It is characterized by satisfying the following conditional expression (5).
-0.80<f1Gn1/f1G<-0.55 (5)
here,
f1Gn1 is the focal length of the first negative lens component,
f1G is the focal length of the first lens group,
It is.
Further, the imaging optical system according to at least some embodiments of the present invention includes:
Has multiple lens groups,
Each of the plurality of lens groups has a lens component,
The lens component has a plurality of optical surfaces,
In the lens component, two optical surfaces are in contact with air, and at least one optical surface is a curved surface,
The multiple lens groups are arranged in order from the object side.
a first lens group having positive refractive power;
a second lens group having negative refractive power;
consisting of a third lens group having positive refractive power,
When focusing from far point to near point, only the second lens group moves toward the image side,
The first lens group includes, in order from the object side, a first negative lens component, a second negative lens component, and a plurality of positive lens components,
The second lens group has a negative lens component,
The aperture stop is arranged in the first lens group,
It is characterized by satisfying the following conditional expressions (7) and (8).
-0.12<β1Gfar<-0.050 (7)
-0.80<β1Gnear<-0.400 (8)
here,
β1Gfar is the lateral magnification of the first lens group when focusing on the far point,
β1Gnear is the lateral magnification of the first lens group at near point focusing,
It is.
Further, the imaging optical system according to at least some embodiments of the present invention includes:
Has multiple lens groups,
Each of the plurality of lens groups has a lens component,
The lens component has a plurality of optical surfaces,
In the lens component, two optical surfaces are in contact with air, and at least one optical surface is a curved surface,
The multiple lens groups are arranged in order from the object side.
a first lens group having positive refractive power;
a second lens group having negative refractive power;
consisting of a third lens group having positive refractive power,
When focusing from far point to near point, only the second lens group moves toward the image side,
The first lens group includes, in order from the object side, a first negative lens component, a second negative lens component, and a plurality of positive lens components,
The second lens group has a negative lens component,
The aperture stop is arranged in the first lens group,
It is characterized by satisfying the following conditional expression (10).
1.5<f1G/ffar<2.4 (10)
here,
f1G is the focal length of the first lens group,
ffar is the focal length of the imaging optical system when focusing on the far point,
It is.
Further, the imaging optical system according to at least some embodiments of the present invention includes:
Has multiple lens groups,
Each of the plurality of lens groups has a lens component,
The lens component has a plurality of optical surfaces,
In the lens component, two optical surfaces are in contact with air, and at least one optical surface is a curved surface,
The multiple lens groups are arranged in order from the object side.
a first lens group having positive refractive power;
a second lens group having negative refractive power;
consisting of a third lens group having positive refractive power,
When focusing from far point to near point, only the second lens group moves toward the image side,
The first lens group includes, in order from the object side, a first negative lens component, a second negative lens component, and a plurality of positive lens components,
The second lens group has a negative lens component,
The aperture stop is arranged in the first lens group,
It is characterized by satisfying the following conditional expressions (13) and (14).
-0.30<(1-β2Gfar×β2Gfar)×β3Gfar×β3Gfar<-0.11 (13)
-0.40<(1-β2Gnear×β2Gnear)×β3Gnear×β3Gnear<-0.18 (14)
here,
β2Gfar is the lateral magnification of the second lens group when focusing on the far point,
β2Gnear is the lateral magnification of the second lens group at near point focusing,
β3Gfar is the lateral magnification of the third lens group when focusing on far point,
β3Gnear is the lateral magnification of the third lens group at near point focusing,
It is.

Further, the imaging device of the present invention includes:
optical system and
an imaging element having an imaging surface and converting an image formed on the imaging surface by an optical system into an electrical signal;
It is characterized in that the optical system is the above-mentioned imaging optical system.

According to the present invention, it is possible to provide an imaging optical system that is small but has high resolution. Furthermore, it is possible to provide an imaging device that can acquire high-definition images.

3 is a cross-sectional view of a lens of the imaging optical system of Example 1. FIG. FIG. 3 is a cross-sectional view of the lens of the imaging optical system of Example 2. FIG. 7 is a cross-sectional view of a lens of the imaging optical system of Example 3. FIG. 4 is a cross-sectional view of the lens of the imaging optical system of Example 4. FIG. 7 is a cross-sectional view of the lens of the imaging optical system of Example 5. 3 is an aberration diagram of the imaging optical system of Example 1. FIG. FIG. 7 is an aberration diagram of the imaging optical system of Example 2. FIG. 7 is an aberration diagram of the imaging optical system of Example 3. FIG. 4 is an aberration diagram of the imaging optical system of Example 4. FIG. 7 is an aberration diagram of the imaging optical system of Example 5. FIG. 1 is a diagram showing a schematic configuration of an endoscope system.

Prior to describing Examples, the effects of embodiments according to certain aspects of the present invention will be described. In addition, when explaining specifically the effect of this embodiment, a specific example will be shown and demonstrated. However, as in the case of the embodiments described later, the illustrated aspects are only some of the aspects included in the present invention, and there are many variations in the aspects. Therefore, the present invention is not limited to the illustrated embodiments.

In the imaging optical system of this embodiment, an object point located near the optical system (hereinafter referred to as "near point") and an object point located further away than the near point (hereinafter referred to as "far point") are aligned. You can focus on it. By focusing on the near point, magnified observation can be performed. In addition, normal observation can be performed by focusing on a far point.

The imaging optical system of this embodiment has a plurality of lens groups, each of the plurality of lens groups has a lens component, the lens component has a plurality of optical surfaces, and the lens component has two optical surfaces. The surface is in contact with air, and at least one optical surface is a curved surface, and the plurality of lens groups include, in order from the object side, a first lens group having a positive refractive power and a second lens group having a negative refractive power. When focusing from a far point to a near point, only the second lens group moves toward the image side, and the first lens group moves toward the image side. In order from the side, the second lens group includes a first negative lens component, a second negative lens component, and a plurality of positive lens components, and the aperture diaphragm includes a first negative lens component. It is characterized by being located in.

The imaging optical system of this embodiment has a plurality of lens groups. The plurality of lens groups include, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power.

When focusing, only the second lens group moves. Therefore, during focusing, the first lens group and the third lens group are fixed.

In the imaging optical system of this embodiment, lens groups having positive refractive power are located on both sides of a second lens group having negative refractive power. During focusing, the lens group having positive refractive power is fixed. Therefore, by moving the second lens group, it is possible to focus on the far point and focus on the near point.

When focusing from the far point to the near point, the lateral magnification of the second lens group can be increased by moving the second lens group toward the image side. Therefore, by moving the second lens group toward the image side, the amount of movement of the second lens group during focusing can be reduced.

As described above, the imaging optical system of this embodiment has a plurality of lens groups. Each of the plurality of lens groups has a lens component. The lens component has multiple optical surfaces. In the lens component, two optical surfaces are in contact with air, and at least one optical surface is a curved surface. The lens component is, for example, a single lens or a cemented lens.

The first lens group includes, in order from the object side, a first negative lens component, a second negative lens component, and a plurality of positive lens components. The first negative lens component and the second negative lens component are lens components having negative refractive power. A positive lens component is a lens component that has positive refractive power.

By arranging the negative lens component closest to the object side of the optical system, the entrance pupil can be located on the object side. By locating the entrance pupil on the object side, the negative lens component can be made smaller.

In the imaging optical system of this embodiment, the first lens group is located closest to the object side. Furthermore, in the first lens group, the first negative lens component is located closest to the object side. Therefore, the diameter of the first negative lens component can be reduced. Furthermore, the diameter of the first lens group can be reduced.

A single negative lens can be used for the first negative lens component. By using a negative single lens, the thickness of the first lens group can be reduced.

A second negative lens component is arranged on the image side of the first negative lens component. The second negative lens component is adjacent to the first negative lens component. Therefore, the entrance pupil can be positioned further toward the object side. Therefore, the diameter of the second negative lens component can be reduced. As a result, the diameter of the first lens group can be further reduced.

Moreover, the negative refractive power in the first lens group can be shared between the first negative lens component and the second negative lens component. Therefore, the negative refractive power of the first lens group can be increased while suppressing the occurrence of various aberrations. As a result, the diameter of the first lens group can be reduced. Furthermore, the angle of view of the optical system can be increased.

A plurality of positive lens components are arranged on the image side of the second negative lens component. By using a plurality of positive lens components, the positive refractive power in the first lens group can be shared among the plurality of positive lens components. Therefore, the positive refractive power of the first lens group can be increased while suppressing the occurrence of spherical aberration.

By suppressing the occurrence of spherical aberration, the resolution of the optical system can be improved. Furthermore, since the positive refractive power in the first lens group can be increased, the height of the light rays emitted from the first lens group can be reduced. As a result, the diameter of the lens located closer to the image side than the first lens group can be made smaller.

The second lens group has a negative lens component. A negative lens component is a lens component that has negative refractive power.

The second lens group can be formed by only a negative lens component or by a negative lens component and another lens component. Moreover, a negative single lens or a cemented lens having negative refractive power (hereinafter referred to as a "negative cemented lens") can be used as the negative lens component of the second lens group.

When the second lens group is formed only of negative lens components and the negative lens component is a single negative lens, it is preferable that the second lens group is formed of only one negative single lens.

When the second lens group is formed of only a negative lens component and the negative lens component is a negative cemented lens, the second lens group is formed of only one negative cemented lens. In this case, the negative cemented lens is preferably a cemented negative single lens and a positive single lens.

When the second lens group is formed of a negative lens component and another lens component, and the negative lens component is a negative single lens, the second lens group includes one negative single lens and one positive single lens. Preferably, it is formed of only a single lens. In this case, it is preferable that the negative single lens and the positive single lens are not cemented.

By forming the second lens group with one single lens or two single lenses, the second lens group can be made smaller and lighter. As described above, the second lens group moves during focusing. By making the second lens group small and lightweight, focusing can be performed at high speed and with high precision.

The aperture stop is arranged in the first lens group. During focusing, the first lens group is fixed. Therefore, when focusing, the aperture stop is also fixed.

By arranging the aperture stop in the first lens group, the height of off-axis rays passing through the first lens group can be lowered. Therefore, the diameter of the first lens group can be reduced.

The aperture stop can be placed on the image side of the first lens group. In this case, the aperture stop is preferably placed near the lens surface located closest to the image side of the first lens group.

The imaging optical system of this embodiment preferably satisfies the following conditional expression (1).
17<νd1Gobp<46 (1)
here,
νd1Gobp is the Abbe number of the positive lens on the object side,
The object side positive lens is a positive single lens located closest to the object side among the positive single lenses in the first lens group.
It is.

Conditional expression (1) below is a conditional expression regarding the Abbe number of the object-side positive lens. The object side positive lens is a positive single lens located closest to the object side among the positive single lenses in the first lens group.

For example, if the positive single lens cemented to the negative single lens is located closest to the object among the positive lenses in the first lens group, the positive single lens cemented to the negative single lens Corresponds to a lateral positive lens.

By satisfying conditional expression (1), longitudinal chromatic aberration and lateral chromatic aberration can be reduced. The smaller the longitudinal chromatic aberration and the lateral chromatic aberration, the higher the resolution of the optical system. By satisfying conditional expression (1), the resolution of the optical system can be increased.

When the lower limit of conditional expression (1) is exceeded, longitudinal chromatic aberration occurring in the object-side positive lens can be reduced.

When the upper limit of conditional expression (1) is exceeded, the lateral chromatic aberration generated in the first negative lens component can be corrected by the object-side positive lens.

The imaging optical system of this embodiment preferably satisfies the following conditional expression (2).
0.07<d1Gn12/d1G<0.34 (2)
here,
d1Gn12 is the air distance between the first negative lens component and the second negative lens component;
d1G is the thickness of the first lens group,
It is.

The thickness of the first lens group is expressed as the distance from the lens surface located closest to the object side to the lens surface located closest to the image side.

When the lower limit of conditional expression (2) is exceeded, the distance between the first negative lens component and the second negative lens component can be sufficiently widened. Therefore, a structure for holding the first negative lens component and a structure for holding the second negative lens component can be easily provided.

When it is less than the upper limit of conditional expression (2), the first negative lens component and the second negative lens component can be brought closer to each other. In this case, the entrance pupil can be located on the object side. Therefore, the diameter of the first negative lens component can be reduced.

In the imaging optical system of this embodiment, it is preferable that the second negative lens component includes, in order from the object side, a negative single lens and a positive single lens.

For example, a negative single lens is used for the first negative lens component, and a negative cemented lens is used for the second lens group. In the case of a negative cemented lens, a negative single lens is placed on the object side, and a positive single lens is placed on the image side. In this way, the single negative lens of the first negative lens component and the single negative lens of the second negative lens component are arranged near the object.

By arranging two negative single lenses near the object, it is possible to position the entrance pupil on the object side while suppressing the occurrence of astigmatism. Therefore, the diameter of the first negative lens component and the diameter of the second negative lens component can be reduced.

In the second negative lens component, a positive single lens is arranged on the image side of the negative single lens. In this case, the height of the marginal ray can be made lower on the image side than the positive single lens. Therefore, the diameter of the lens component located closer to the image side than the second negative lens component can be made smaller.

The imaging optical system of this embodiment preferably satisfies the following conditional expression (3).
64<νd1Gimp<99 (3)
here,
νd1Gimp is the Abbe number of the positive lens on the image side,
The image side positive lens is a positive single lens located closest to the image side among the positive single lenses in the first lens group.
It is.

Conditional expression (3) below is a conditional expression regarding the Abbe number of the image-side positive lens. The image-side positive lens is a positive single lens located closest to the image side among the positive single lenses in the first lens group.

For example, if the positive single lens cemented to the negative single lens is located closest to the image side among the positive lenses in the first lens group, the positive single lens cemented to the negative single lens Corresponds to a lateral positive lens.

When the lower limit of conditional expression (3) is exceeded, longitudinal chromatic aberration occurring in the image-side positive lens can be reduced.

If the upper limit of conditional expression (3) is not reached, a material that can satisfactorily perform color correction can be used for the image-side positive lens. In this case, since chromatic aberration can be corrected well, the resolution of the optical system can be increased.

In the imaging optical system of this embodiment, it is preferable that one positive lens component among the plurality of positive lens components has one or more negative single lenses.

The positive lens component has a positive single lens. A positive single lens produces spherical aberration and axial chromatic aberration. By arranging a negative single lens in the positive lens component, the spherical aberration and axial chromatic aberration generated by the positive single lens can be corrected by the negative single lens. As a result, it is possible to suppress the occurrence of spherical aberration and longitudinal chromatic aberration in the positive lens component.

The imaging optical system of this embodiment preferably satisfies the following conditional expression (4).
0.15<f1Gn1/f1Gn2<0.6 (4)
here,
f1Gn1 is the focal length of the first negative lens component,
f1Gn2 is the focal length of the second negative lens component,
It is.

Conditional expression (4) is a conditional expression concerning the ratio of the focal length of the first negative lens component and the focal length of the second negative lens component.

When the lower limit of conditional expression (4) is exceeded, the focal length of the second negative lens component can be shortened. In this case, since the refractive power of the second negative lens component can be increased, an increase in the refractive power of the first negative lens component can be suppressed. Therefore, the occurrence of astigmatism in the first negative lens component can be suppressed.

When the upper limit of conditional expression (4) is exceeded, the focal length of the first negative lens component can be shortened. In this case, the refractive power of the first negative lens component can be increased. Therefore, the diameter of the first negative lens component can be reduced.

The imaging optical system of this embodiment preferably satisfies the following conditional expression (5).
-0.80<f1Gn1/f1G<-0.55 (5)
here,
f1Gn1 is the focal length of the first negative lens component,
f1G is the focal length of the first lens group,
It is.

Conditional expression (5) is a conditional expression concerning the ratio between the focal length of the first negative lens component and the focal length of the first lens group.

When the lower limit of conditional expression (5) is exceeded, the focal length of the first negative lens component can be shortened. In this case, the refractive power of the first negative lens component can be increased. Therefore, the diameter of the first negative lens component can be reduced.

When the upper limit of conditional expression (5) is exceeded, the focal length of the first negative lens component can be increased. In this case, the refractive power of the first negative lens component can be reduced. Therefore, the occurrence of astigmatism and lateral chromatic aberration in the first negative lens component can be suppressed.

The imaging optical system of this embodiment preferably satisfies the following conditional expression (6).
0.50<f1Gp1/f1Gp2<2.50 (6)
here,
f1Gp1 is the focal length of the positive lens component on the object side,
f1Gp2 is the focal length of the image side positive lens component,
Object side positive lens component, the positive lens component located closest to the object side among the multiple positive lens components,
The image side positive lens component is the positive lens component located closest to the image side among the plurality of positive lens components.
It is.

Conditional expression (6) is a conditional expression regarding the ratio of the focal length of the object-side positive lens component to the focal length of the image-side positive lens component. The object-side positive lens component is a positive lens component located closest to the object side among the plurality of positive lens components. The image-side positive lens component is a positive lens component located closest to the image side among the plurality of positive lens components.

When the lower limit of conditional expression (6) is exceeded, the focal length of the image-side positive lens component can be shortened. In this case, since the refractive power of the image-side positive lens component can be increased, an increase in the refractive power of the object-side positive lens component can be suppressed. Therefore, the occurrence of spherical aberration in the object-side positive lens component can be suppressed.

When the upper limit of conditional expression (6) is exceeded, the focal length of the object-side positive lens component can be shortened. In this case, since the refractive power of the object-side positive lens component can be increased, it is possible to suppress an increase in the height of the light rays incident on the image-side positive lens component. Therefore, the diameter of the image-side positive lens component can be reduced.

The imaging optical system of this embodiment preferably satisfies the following conditional expressions (7) and (8).
-0.12<β1Gfar<-0.050 (7)
-0.80<β1Gnear<-0.400 (8)
here,
β1Gfar is the lateral magnification of the first lens group when focusing on the far point,
β1Gnear is the lateral magnification of the first lens group at near point focusing,
It is.

Conditional expression (7) and conditional expression (8) are conditional expressions regarding the lateral magnification of the first lens group.

When the lower limit of conditional expression (7) and the lower limit of conditional expression (8) are exceeded, the occurrence of aberrations in the first lens group can be suppressed.

When the upper limit of conditional expression (7) and the upper limit of conditional expression (8) are satisfied, the first lens group can be brought closer to the second lens. Therefore, the lateral magnification of the second lens group can be easily increased.

The imaging optical system of this embodiment preferably satisfies the following conditional expression (9).
1<fnear/ffar<1.5 (9)
here,
fnear is the focal length of the imaging optical system at near point focusing,
ffar is the focal length of the imaging optical system when focusing on the far point,
It is.

In the imaging optical system of this embodiment, the focal length of the imaging optical system during near point focusing is different from the focal length of the imaging optical system during far point focusing. Therefore, by focusing on the near point, magnified observation can be performed. In addition, normal observation can be performed by focusing on a far point.

The magnification when focusing on the near point and the magnification when focusing on the far point are different. Therefore, when the focus position is changed between the near point and the far point, the magnification changes. As the magnification changes, the axial chromatic aberration changes.

Conditional expression (9) is a conditional expression regarding the ratio of the focal length of the imaging optical system during near-point focusing and the focal length of the imaging optical system during far-point focusing.

When the lower limit of conditional expression (9) is exceeded, the focal length of the imaging optical system during near-point focusing can be increased. In this case, the magnification ratio for magnified observation can be increased.

When the upper limit of conditional expression (9) is exceeded, fluctuations in magnification when changing the focus position can be made small. Therefore, fluctuations in longitudinal chromatic aberration when changing the focal position can be suppressed.

The imaging optical system of this embodiment preferably satisfies the following conditional expression (10).
1.5<f1G/ffar<2.4 (10)
here,
f1G is the focal length of the first lens group,
ffar is the focal length of the imaging optical system when focusing on the far point,
It is.

Conditional expression (10) is a conditional expression concerning the ratio between the focal length of the first lens group and the focal length of the imaging optical system when focusing on a far point.

When the lower limit of conditional expression (10) is exceeded, the focal length of the first lens group can be increased. In this case, the refractive power of the first lens group can be reduced. Therefore, the occurrence of astigmatism and chromatic aberration of magnification in the first lens group can be suppressed.

When the upper limit of conditional expression (10) is exceeded, the focal length of the first lens group can be shortened. In this case, it is possible to suppress an increase in the height of the marginal rays incident on the second lens group. Therefore, the occurrence of spherical aberration in the second lens group can be suppressed.

The imaging optical system of this embodiment preferably satisfies the following conditional expression (11).
-6.0<f2G/ffar<-3 (11)
here,
f2G is the focal length of the second lens group,
ffar is the focal length of the imaging optical system when focusing on the far point,
It is.

Conditional expression (11) is a conditional expression concerning the ratio between the focal length of the second lens group and the focal length of the imaging optical system when focusing on a far point.

When the lower limit of conditional expression (11) is exceeded, the focal length of the second lens group can be made shorter than the focal length of the imaging optical system during far point focusing. In this case, the refractive power of the second lens group can be increased. Therefore, comatic aberration and spherical aberration generated in the first lens group can be corrected by the second lens group.

When less than the upper limit of conditional expression (11), the focal length of the second lens group can be made longer than the focal length of the imaging optical system when focusing on a far point. In this case, the refractive power of the second lens group can be reduced. Therefore, during far point focusing, it is possible to suppress the occurrence of astigmatism and lateral chromatic aberration in the second lens group.

The imaging optical system of this embodiment preferably satisfies the following conditional expression (12).
2.5<f3G/ffar<4 (12)
here,
f3G is the focal length of the third lens group,
ffar is the focal length of the imaging optical system when focusing on the far point,
It is.

Conditional expression (12) is a conditional expression regarding the ratio between the focal length of the third lens group and the focal length of the imaging optical system when focusing on a far point.

When the lower limit of conditional expression (12) is exceeded, the focal length of the third lens group can be made longer than the focal length of the imaging optical system during far point focusing. In this case, the refractive power of the third lens group can be reduced. Therefore, the occurrence of astigmatism in the third lens group can be suppressed.

When the upper limit of conditional expression (12) is exceeded, the focal length of the third lens group can be made shorter than the focal length of the imaging optical system when focusing on a far point. In this case, the refractive power of the third lens group can be increased. Therefore, the distance from the third lens group to the image plane can be shortened.

The imaging optical system of this embodiment preferably satisfies the following conditional expressions (13) and (14).
-0.30<(1-β2Gfar×β2Gfar)×β3Gfar×β3Gfar<-0.11 (13)
-0.40<(1-β2Gnear×β2Gnear)×β3Gnear×β3Gnear<-0.18 (14)
here,
β2Gfar is the lateral magnification of the second lens group when focusing on the far point,
β2Gnear is the lateral magnification of the second lens group at near point focusing,
β3Gfar is the lateral magnification of the third lens group when focusing on far point,
β3Gnear is the lateral magnification of the third lens group at near point focusing,
It is.

Conditional expression (13) and conditional expression (14) are conditional expressions regarding focus sensitivity. Focus sensitivity represents the amount of movement of the image plane relative to the amount of movement of the focus lens group. The amount of movement is expressed as a distance along the optical axis.

When the lower limit of conditional expression (13) and the lower limit of conditional expression (14) are exceeded, the focus sensitivity does not become too large. Therefore, the occurrence of astigmatism during movement of the second lens group can be suppressed.

When the upper limit value of conditional expression (13) and the upper limit value of conditional expression (14) are below, the focus sensitivity does not become too small. In this case, since appropriate focus sensitivity can be obtained, an increase in the amount of movement of the second lens group can be suppressed. Therefore, fluctuations in astigmatism when the second lens group moves can be suppressed.

Further, an increase in the amount of movement of the second lens group can be suppressed. Therefore, the space required for moving the second lens group can be reduced. As a result, the total length of the optical system can be shortened.

The imaging device of this embodiment has an optical system and an imaging element disposed on an image plane, and the imaging element has an imaging plane and converts the image formed on the imaging plane by the optical system into an electrical signal. , and the optical system is the imaging optical system of this embodiment.

An imaging device that can obtain high-definition images can be provided.

It is more preferable that a plurality of the above-mentioned configurations are mutually satisfied at the same time. Further, some of the configurations may be satisfied at the same time. For example, any of the other imaging optical systems described above may be used in place of any of the imaging optical systems described above.

Regarding the conditional expressions, each conditional expression may be satisfied individually. This is preferable because it makes it easier to obtain the respective effects.

For each conditional expression, the lower limit value or upper limit value may be changed as shown below. This is preferable because the effect of each conditional expression can be further ensured.

Conditional expression (1) is as follows.
It is preferable to set the lower limit to 20 or 23.
It is preferable to set the upper limit to 41 or 37.
Conditional expression (2) is as follows.
It is preferable to set the lower limit to 0.10 or 0.12.
It is preferable to set the upper limit to 0.31 or 0.25.
Conditional expression (3) is as follows.
It is preferable to set the lower limit to 70 or 80.
It is preferable to set the upper limit to 97 or 95.
Conditional expression (4) is as follows.
It is preferable to set the lower limit to 0.2 or 0.23.
It is preferable to set the upper limit to 0.5 or 0.45.
Conditional expression (5) is as follows.
It is preferable to set the lower limit to -0.75 or -0.71.
It is preferable to set the upper limit to -0.58 or -0.61.
Conditional expression (6) is as follows.
It is preferable to set the lower limit to 0.55 or 0.6.
It is preferable to set the upper limit to 2.20 or 1.95.
Conditional expression (7) is as follows.
It is preferable to set the lower limit to -0.11 or -0.10.
It is preferable to set the upper limit to -0.055 or -0.060.
Conditional expression (8) is as follows.
It is preferable to set the lower limit to -0.76 or -0.73.
It is preferable to set the upper limit to -0.45 or -0.53.
Conditional expression (9) is as follows.
It is preferable to set the lower limit to 1.1 or 1.18.
It is preferable to set the upper limit to 1.4 or 1.35.
Conditional expression (10) is as follows.
It is preferable to set the lower limit to 1.6 or 1.7.
It is preferable to set the upper limit to 2.2 or 1.9.
Conditional expression (11) is as follows.
It is preferable to set the lower limit to -5.5 or -4.6.
It is preferable to set the upper limit to -3.5 or -3.7.
Conditional expression (12) is as follows.
It is preferable to set the lower limit to 2.7 or 2.9.
It is preferable to set the upper limit to 3.6 or 3.4.
Conditional expression (13) is as follows.
It is preferable to set the lower limit to -0.27 or -0.25.
It is preferable to set the upper limit to -0.13 or -0.15.
Conditional expression (14) is as follows.
It is preferable to set the lower limit to -0.38 or -0.36.
It is preferable to set the upper limit to -0.21 or -0.28.

Examples of the imaging optical system will be described in detail below based on the drawings. Note that the present invention is not limited to this example.

Lens cross-sectional views of each embodiment shown in FIGS. 1 to 5 will be explained. (a) shows a cross-sectional view of the lens when focusing on a far point. (b) shows a cross-sectional view of the lens during near-point focusing.

The aberration diagrams of each embodiment shown in FIGS. 6 to 10 will be explained. (a), (b), (c), and (d) show aberration diagrams when focusing on a far point. (e), (f), (g), and (h) show aberration diagrams at near point focusing.

(a) and (e) show spherical aberration (SA). (b) and (f) show astigmatism (AS). (c) and (g) show distortion aberration (DT). (d) and (h) show lateral chromatic aberration (CC).

The first lens group is indicated by G1, the second lens group by G2, the third lens group by G3, the aperture stop by S, and the image plane (imaging plane) by I. Further, a cover glass C is arranged between the third lens group G3 and the image plane I.

The imaging optical system of Example 1 shown in FIG. 1 includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a second lens group G2 having a positive refractive power. It has a third lens group G3. A cover glass C is arranged on the image side of the third lens group G3.

The first lens group G1 includes a plano-concave negative lens L1, a biconcave negative lens L2, a biconvex positive lens L3, a biconvex positive lens L4, a negative meniscus lens L5 with a convex surface facing the image side, and a biconvex It has a positive lens L6 and a negative meniscus lens L7 with a convex surface facing the image side.

A biconcave negative lens L2 and a biconvex positive lens L3 are cemented together. A biconvex positive lens L4 and a negative meniscus lens L5 are cemented together. A biconvex positive lens L6 and a negative meniscus lens L7 are cemented together.

The second lens group G2 includes a biconcave negative lens L8 and a positive meniscus lens L9 with a convex surface facing the object side. A biconcave negative lens L8 and a positive meniscus lens L9 are cemented together.

The third lens group G3 includes a biconvex positive lens L10, a biconvex positive lens L11, and a negative meniscus lens L12 with a convex surface facing the image side. A biconvex positive lens L11 and a negative meniscus lens L12 are cemented together.

When focusing from the far point to the near point, the second lens group G2 moves toward the image side. The first lens group G1 and the third lens group G3 are fixed.

The aperture stop S is arranged in the first lens group G1. More specifically, the aperture stop S is arranged on the image side of the negative meniscus lens L7. During focusing, the aperture stop S is fixed.

Aspherical surfaces are provided on a total of two surfaces: the image side surface of the plano-concave negative lens L1 and the object side surface of the biconvex positive lens L6.

The imaging optical system of Example 2 shown in FIG. 2 includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a second lens group having a positive refractive power. It has a third lens group G3. A cover glass C is arranged on the image side of the third lens group G3.

The first lens group G1 includes a plano-concave negative lens L1, a biconcave negative lens L2, a biconvex positive lens L3, a biconvex positive lens L4, a negative meniscus lens L5 with a convex surface facing the image side, and a biconvex It has a positive lens L6.

A biconcave negative lens L2 and a biconvex positive lens L3 are cemented together. A biconvex positive lens L4 and a negative meniscus lens L5 are cemented together.

The second lens group G2 includes a biconcave negative lens L7 and a positive meniscus lens L8 with a convex surface facing the object side. A biconcave negative lens L7 and a positive meniscus lens L8 are cemented together.

The third lens group G3 includes a biconvex positive lens L9, a biconvex positive lens L10, and a plano-concave negative lens L11. A biconvex positive lens L10 and a plano-concave negative lens L11 are cemented together.

When focusing from the far point to the near point, the second lens group G2 moves toward the image side. The first lens group G1 and the third lens group G3 are fixed.

The aperture stop S is arranged in the first lens group G1. More specifically, the aperture stop S is arranged on the image side of the biconvex positive lens L6. During focusing, the aperture stop S is fixed.

Aspherical surfaces are provided on a total of two surfaces: the image side surface of the plano-concave negative lens L1 and the object side surface of the biconvex positive lens L6.

The imaging optical system of Example 3 shown in FIG. 3 includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a second lens group G2 having a positive refractive power. It has a third lens group G3. A cover glass C is arranged on the image side of the third lens group G3.

The first lens group G1 includes a plano-concave negative lens L1, a biconcave negative lens L2, a biconvex positive lens L3, a biconvex positive lens L4, a negative meniscus lens L5 with a convex surface facing the image side, and a biconvex It has a positive lens L6.

A biconcave negative lens L2 and a biconvex positive lens L3 are cemented together. A biconvex positive lens L4 and a negative meniscus lens L5 are cemented together.

The second lens group G2 includes a negative meniscus lens L7 with a convex surface facing the object side, and a positive meniscus lens L8 with a convex surface facing the object side. A negative meniscus lens L7 and a positive meniscus lens L8 are cemented together.

The third lens group G3 includes a biconvex positive lens L9, a biconvex positive lens L10, and a biconcave negative lens L11. A biconvex positive lens L10 and a biconcave negative lens L11 are cemented together.

When focusing from the far point to the near point, the second lens group G2 moves toward the image side. The first lens group G1 and the third lens group G3 are fixed.

The aperture stop S is arranged in the first lens group G1. More specifically, the aperture stop S is arranged on the image side of the biconvex positive lens L6. During focusing, the aperture stop S is fixed.

Aspherical surfaces are provided on a total of two surfaces: the image side surface of the plano-concave negative lens L1 and the object side surface of the biconvex positive lens L6.

The imaging optical system of Example 4 shown in FIG. 4 includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a second lens group G2 having a positive refractive power. It has a third lens group G3. A cover glass C is arranged on the image side of the third lens group G3.

The first lens group G1 includes a plano-concave negative lens L1, a biconcave negative lens L2, a biconvex positive lens L3, a biconvex positive lens L4, a biconcave negative lens L5, and a biconvex positive lens L6. have

A biconcave negative lens L2 and a biconvex positive lens L3 are cemented together. A biconvex positive lens L4 and a biconcave negative lens L5 are cemented together.

The second lens group G2 includes a negative meniscus lens L7 with a convex surface facing the object side, and a positive meniscus lens L8 with a convex surface facing the object side. A negative meniscus lens L7 and a positive meniscus lens L8 are cemented together.

The third lens group G3 includes a biconvex positive lens L9, a biconvex positive lens L10, a biconcave negative lens L11, and a planoconvex positive lens L12. A biconvex positive lens L10 and a biconcave negative lens L11 are cemented together. A plano-convex positive lens L12 and a cover glass C are bonded together.

When focusing from the far point to the near point, the second lens group G2 moves toward the image side. The first lens group G1 and the third lens group G3 are fixed.

The aperture stop S is arranged in the first lens group G1. More specifically, the aperture stop S is arranged on the image side of the biconvex positive lens L6. During focusing, the aperture stop S is fixed.

Aspheric surfaces are provided on a total of three surfaces: the image side surface of the plano-concave negative lens L1, the object side surface of the biconvex positive lens L6, and the object side surface of the biconvex positive lens L9.

The imaging optical system of Example 5 shown in FIG. 5 includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a second lens group G2 having a positive refractive power. It has a third lens group G3. A cover glass C is arranged on the image side of the third lens group G3.

The first lens group G1 includes a plano-concave negative lens L1, a biconcave negative lens L2, a biconvex positive lens L3, a biconvex positive lens L4, a negative meniscus lens L5 with a convex surface facing the image side, and a biconvex It has a positive lens L6.

A biconcave negative lens L2 and a biconvex positive lens L3 are cemented together. A biconvex positive lens L4 and a negative meniscus lens L5 are cemented together.

The second lens group G2 includes a negative meniscus lens L7 with a convex surface facing the object side, and a positive meniscus lens L8 with a convex surface facing the object side. A negative meniscus lens L7 and a positive meniscus lens L8 are cemented together.

The third lens group G3 includes a biconvex positive lens L9, a biconvex positive lens L10, and a biconcave negative lens L11. A biconvex positive lens L10 and a biconcave negative lens L11 are cemented together.

When focusing from the far point to the near point, the second lens group G2 moves toward the image side. The first lens group G1 and the third lens group G3 are fixed.

The aperture stop S is arranged in the first lens group G1. More specifically, the aperture stop S is arranged on the image side of the biconvex positive lens L6. During focusing, the aperture stop S is fixed.

Aspheric surfaces are provided on a total of three surfaces: the image side surface of the plano-concave negative lens L1, the object side surface of the biconvex positive lens L6, and the object side surface of the biconvex positive lens L9.

Numerical data for each of the above examples is shown below. In the surface data, r is the radius of curvature of each lens surface, d is the distance between each lens surface, nd is the d-line refractive index of each lens, νd is the Abbe number of each lens, and the * mark is an aspheric surface. The diaphragm is an aperture diaphragm.

In various data, OBJ is the object distance, f is the focal length of the entire system, FNO. is the F number, ω is the half angle of view, IH is the image height, and LTL is the total length of the optical system. The back focus is the distance from the lens surface closest to the image side to the paraxial image plane expressed in air terms. The total length is the distance from the lens surface closest to the object side to the lens surface closest to the image side plus the back focus.

In each group focal length, f1, f2, . . . are the focal lengths of each lens group.

The aspherical shape is expressed by the following formula, where the optical axis direction is z, the direction perpendicular to the optical axis is y, the conic coefficient is k, and the aspherical coefficients are A4, A6, A8, A10, A12... Ru.
z=( ^y2 /r)/[1+{1-(1+k)(y/r) ² } ^1/2 ]
+A4y ⁴ +A6y ⁶ +A8y ⁸ +A10y ¹⁰ +A12y ¹² +…
Furthermore, in the aspheric coefficient, "en" (n is an integer) indicates "10 ^-n ". Note that the symbols of these specification values are also common to the numerical data of the examples described later.

Numerical example 1
Unit: mm

Surface data Surface number rd nd νd
1 ∞ 0.2353 1.88300 40.76
2* 0.8522 0.6299
3 -2.354 0.2451 1.88300 40.76
4 1.235 0.9314 1.72825 28.46
5 -3.828 0.1471
6 2.284 1.0474 1.48749 70.23
7 -1.701 0.2842 1.83400 37.16
8 -2.416 0.0980
9* 6.3927 0.7665 1.43875 94.66
10 -0.959 0.2549 1.88300 40.76
11 -1.527 0.0098
12 (aperture) ∞ variable
13 -38.435 0.2451 1.88300 40.76
14 1.783 0.4020 1.92286 18.90
15 2.810 Variable
16 5.539 0.8529 1.49700 81.54
17 -2.895 0.0980
18 2.216 1.5196 1.49700 81.54
19 -2.535 0.4412 1.84666 23.78
20 -42.372 0.8180
21 ∞ 1.4700 1.51633 64.14
22 ∞ 0.0000
Image plane ∞

Aspheric data second surface
k=-4.8465
A4=8.16140e-01,A6=-1.22255e+00,A8=1.73222e+00,
A10=-1.05987e+00,A12=-5.40354e-08
9th page
k=0.0000
A4=-4.73440e-03,A6=5.54469e-02

Various data
Far point Peria point OBJ 18.400 1.995
f 0.7892 1.0542
FNO. 3.602 4.812
2ω 143.76 86.57
IH 0.800 0.800
LTL 12.307 12.307

d12 0.3039 1.4136
d15 1.5063 0.3966

Focal length of each group
f1=1.4181 f2=-3.0299 f3=2.4747

Numerical example 2
Unit: mm

Surface data Surface number rd nd νd
1 ∞ 0.2451 1.88300 40.76
2* 0.8440 0.6160
3 -3.353 0.2647 1.88300 40.76
4 1.347 0.7196 1.62004 36.26
5 -5.635 0.0980
6 1.816 0.8529 1.51742 52.43
7 -1.500 0.5757 1.88300 40.76
8 -5.587 0.0980
9* 4.7293 0.8151 1.43875 94.66
10 -1.369 0.0098
11 (Aperture) ∞ Variable
12 -10.235 0.3922 1.72916 54.68
13 1.577 0.4020 1.76182 26.52
14 2.733 Variable
15 6.706 0.8333 1.49700 81.54
16 -2.857 0.0980
17 2.134 1.4706 1.49700 81.54
18 -3.147 0.2941 1.92286 18.90
19 ∞ 1.1176
20 ∞ 1.4700 1.51633 64.14
21 ∞ 0.0000
Image plane ∞

Aspheric data second surface
k=-3.6364
A4=5.87345e-01,A6=-5.94734e-01,A8=6.58226e-01,
A10=-3.21280e-01,A12=7.69676e-14
9th page
k=35.0000
A4=-1.47266e-01,A6=-8.89928e-02

Various data
Far point Peria point OBJ 20.000 2.020
f 0.7893 1.0548
FNO. 3.692 4.932
2ω 143.78 86.54
IH 0.800 0.800
LTL 12.198 12.198

d11 0.3333 1.4134
d14 1.4918 0.4118

Focal length of each group
f1=1.3659 f2=-2.9705 f3=2.5437

Numerical example 3
Unit: mm

Surface data Surface number rd nd νd
1 ∞ 0.2451 1.88300 40.76
2* 0.9248 0.5543
3 -3.184 0.2451 1.88300 40.76
4 1.197 0.8095 1.58144 40.75
5 -5.764 0.0980
6 1.783 0.8166 1.53172 48.84
7 -1.370 0.4889 1.88300 40.76
8 -5.361 0.0980
9* 3.7016 0.5947 1.43875 94.66
10 -1.462 0.0098
11 (Aperture) ∞ Variable
12 13.227 0.2451 1.72916 54.68
13 1.496 0.3922 1.76182 26.52
14 2.154 Variable
15 7.492 0.8275 1.49700 81.54
16 -2.659 0.0980
17 1.805 1.0974 1.49700 81.54
18 -4.462 0.2451 1.92286 18.90
19 8.365 0.8627
20 ∞ 1.4700 1.51633 64.14
21 ∞ 0.0000
Image plane ∞

Aspheric data second surface
k=-0.8704
A4=5.29507e-02,A6=1.39204e-01,A8=-1.67054e-01,
A10=1.73956e-01,A12=1.12187e-17
9th page
k=-2.8749
A4=-8.99972e-02,A6=-2.15320e-02

Various data
Far point Peria point OBJ 19.300 1.962
f 0.8278 0.9994
FNO. 3.731 4.502
2ω 144.07 94.32
IH 0.800 0.800
LTL 10.968 10.968

d11 0.3333 1.3489
d14 1.4371 0.4216

Focal length of each group
f1=1.5275 f2=-3.7298 f3=2.5362

Numerical example 4
Unit: mm

Surface data Surface number rd nd νd
1 ∞ 0.2454 1.88300 40.76
2* 0.9395 1.0000
3 -4.524 0.2400 1.88300 40.76
4 1.707 1.1045 1.54814 45.79
5 -6.574 0.0900
6 1.404 0.8411 1.51633 64.14
7 -1.558 0.2500 1.72916 54.68
8 13.965 0.1000
9* 4.1650 0.4040 1.49700 81.54
10 -1.927 0.0100
11 (Aperture) ∞ Variable
12 10.543 0.2400 1.72916 54.68
13 1.493 0.3400 1.76182 26.52
14 2.359 Variable
15* 5.6691 0.8440 1.49700 81.54
16 -3.094 0.1600
17 1.807 1.0442 1.49700 81.54
18 -4.347 0.2400 1.92286 18.90
19 5.431 0.8496
20 4.509 0.5000 1.51633 64.14
21 ∞ 1.0000 1.51633 64.14
22 ∞ 0.0000
Image plane ∞

Aspheric data second surface
k=-0.8440
A4=7.83987e-02,A6=3.35426e-02,A8=1.46736e-02,
A10=8.99301e-03,A12=-6.27290e-16
9th page
k=-3.6883
A4=-9.56270e-02,A6=-6.64041e-03
Page 15
k=17.1911
A4=-9.30440e-03,A6=-7.06860e-03

Various data
Far point Peria point OBJ 17.178 1.914
f 0.8200 1.0047
FNO. 3.773 4.617
2ω 144.00 96.87
IH 0.800 0.800
LTL 11.441 11.441

d11 0.3428 1.5184
d14 1.5956 0.4200

Focal length of each group
f1=1.6962 f2=-4.4770 f3=2.6802

Numerical example 5
Unit: mm

Surface data Surface number rd nd νd
1 ∞ 0.2454 1.88300 40.76
2* 1.1071 1.4000
3 -4.204 0.2418 1.88300 40.76
4 1.661 0.7988 1.54814 45.79
5 -9.263 0.0900
6 1.486 0.8954 1.51633 64.14
7 -1.375 0.3048 1.72916 54.68
8 -9.950 0.1000
9* 6.0276 0.5182 1.51633 64.14
10 -2.254 0.0100
11 (Aperture) ∞ Variable
12 13.232 0.2400 1.72916 54.68
13 1.716 0.3217 1.76182 26.52
14 2.520 Variable
15* 6.0509 0.8609 1.49700 81.54
16 -2.864 0.1087
17 1.751 1.0430 1.49700 81.54
18 -4.537 0.2407 1.92286 18.90
19 5.794 0.8720
20 ∞ 1.5000 1.51633 64.14
21 ∞ 0.0000
Image plane ∞

Aspheric data second surface
k=-0.4157
A4=1.26815e-03,A6=1.81637e-02,A8=-1.11325e-02,
A10=7.33606e-03,A12=-6.41676e-16
9th page
k=-4.0249
A4=-6.86368e-02,A6=-2.94860e-03
Page 15
k=15.7528
A4=-1.05324e-02,A6=-2.86066e-03

Various data
Far point Peria point OBJ 19.000 2.000
f 0.8306 1.0257
FNO. 3.650 4.503
2ω 144.00 92.36
IH 0.800 0.800
LTL 11.812 11.812

d11 0.3000 1.6113
d14 1.7205 0.4092

Focal length of each group
f1=1.7990 f2=-4.5056 f3=2.6663

Next, the values of the conditional expressions in each example are listed below. The lateral magnification is calculated based on the object distance value described in various data.
Example 1 Example 2 Example 3
(1)νd1Gobp 28.46 36.26 40.75
(2)d1Gn12/d1G 0.1358 0.1438 0.1403
(3)νd1Gimp 94.66 94.66 94.66
(4)f1Gn1/f1Gn2 0.24616 0.31441 0.42526
(5)f1Gn1/f1G -0.6806 -0.6998 -0.6857
(6)f1Gp1/f1Gp2 0.6298 1.8953 1.8571
(7)β1Gfar -0.07530 -0.06678 -0.07756
(8)β1Gnear -0.58417 -0.55220 -0.64828
(9)fnear/ffar 1.33579 1.33646 1.20728
(10)f1G/ffar 1.79696 1.73058 1.84527
(11)f2G/ffar -3.83939 -3.76375 -4.50557
(12)f3G/ffar 3.13581 3.22288 3.06367
(13)(1-β2Gfar×β2Gfar)
×β3Gfar×β3Gfar -0.16929 -0.16724 -0.23907
(14)(1-β2Gnear×β2Gnear)
×β3Gnear×β3Gnear -0.33089 -0.35190 -0.30352

Example 4 Example 5
(1)νd1Gobp 45.79 45.79
(2)d1Gn12/d1G 0.2339 0.3047
(3)νd1Gimp 81.54 64.14
(4)f1Gn1/f1Gn2 0.30557 0.43075
(5)f1Gn1/f1G -0.6272 -0.6970
(6)f1Gp1/f1Gp2 1.6818 1.1010
(7)β1Gfar -0.09634 -0.09213
(8)β1Gnear -0.72409 -0.71187
(9)fnear/ffar 1.22527 1.23498
(10)f1G/ffar 2.06868 2.16596
(11)f2G/ffar -5.46002 -5.42463
(12)f3G/ffar 3.26866 3.21019
(13)(1-β2Gfar×β2Gfar)
×β3Gfar×β3Gfar -0.20000 -0.17000
(14)(1-β2Gnear×β2Gnear)
×β3Gnear×β3Gnear -0.23875 -0.22155

An example of the imaging device of this embodiment will be explained using an endoscope system. FIG. 11 is a diagram showing a schematic configuration of an endoscope system. The endoscope system has an electronic endoscope. The electronic endoscope is the imaging device of this embodiment.

The endoscope system 300 is an observation system using an electronic endoscope. The endoscope system 300 includes an electronic endoscope 310 and an image processing device 320. The electronic endoscope 310 includes a scope section 310a and a connection cord section 310b. Further, a display unit 330 is connected to the image processing device 320.

The scope section 310a is roughly divided into an operation section 340 and an insertion section 341. The insertion portion 341 is elongated and can be inserted into a patient's body cavity. Further, the insertion portion 341 is made of a flexible member. The observer can perform various operations using the angle knob and the like provided on the operation section 340.

Furthermore, a connection cord section 310b extends from the operation section 340. The connection cord section 310b includes a universal cord 350. Universal cord 350 is connected to image processing device 320 via connector 360.

The universal code 350 is used for transmitting and receiving various signals. Various signals include power supply voltage signals, CCD drive signals, and the like. These signals are transmitted from the power supply device and video processor to the scope section 310a. Further, various types of signals include video signals. This signal is sent from the scope section 310a to the video processor.

Note that peripheral devices such as a storage device and a video printer (not shown) can be connected to the video processor in the image processing device 320. The video processor performs signal processing on the video signal from the scope section 310a. An endoscopic image is displayed on the display screen of display unit 330 based on the video signal.

An optical system is arranged at the distal end portion 342 of the insertion section 341. The imaging optical system of this embodiment is used as an optical system.

As described above, the present invention is suitable for an imaging optical system that is small but has high resolution. Further, it is suitable for an imaging device that can obtain high-definition images.

G1 First lens group G2 Second lens group G3 Third lens group C Cover glass L1-L12 Lens S Aperture diaphragm 300 Endoscope system 310 Electronic endoscope 320 Image processing device 310a Scope section 310b Connection cord section 330 Display unit 340 Operation section 341 Insertion section 342 Tip section 350 Universal cord 360 Connector 320 Image processing device

Claims (15)

Has multiple lens groups,
Each of the plurality of lens groups has a lens component,
The lens component has a plurality of optical surfaces,
In the lens component, two of the optical surfaces are in contact with air, and at least one of the optical surfaces is a curved surface,
The plurality of lens groups are, in order from the object side,
a first lens group having positive refractive power;
a second lens group having negative refractive power;
consisting of a third lens group having positive refractive power,
When focusing from a far point to a near point, only the second lens group moves toward the image side,
The first lens group includes, in order from the object side, a first negative lens component, a second negative lens component, and a plurality of positive lens components,
The second lens group has a negative lens component,
an aperture stop arranged in the first lens group ,
The imaging optical system is characterized in that the second negative lens component includes, in order from the object side, a negative single lens and a positive single lens . The imaging optical system according to claim 1, characterized in that the following conditional expression (1) is satisfied.
17<νd1Gobp<46 (1)
here,
νd1Gobp is the Abbe number of the positive lens on the object side,
The object side positive lens is a positive single lens located closest to the object side among the positive single lenses in the first lens group;
It is. The imaging optical system according to claim 1, characterized in that the following conditional expression (2) is satisfied.
0.07<d1Gn12/d1G<0.34 (2)
here,
d1Gn12 is an air distance between the first negative lens component and the second negative lens component;
d1G is the thickness of the first lens group,
It is. The imaging optical system according to claim 1, characterized in that the following conditional expression (3) is satisfied.
64<νd1Gimp<99 (3)
here,
νd1Gimp is the Abbe number of the positive lens on the image side,
The image-side positive lens is a positive single lens located closest to the image side among the positive single lenses in the first lens group;
It is. The imaging optical system according to claim 1, wherein one positive lens component among the plurality of positive lens components includes one or more negative single lenses. The imaging optical system according to claim 1, characterized in that the following conditional expression (4) is satisfied.
0.15<f1Gn1/f1Gn2<0.6 (4)
here,
f1Gn1 is the focal length of the first negative lens component,
f1Gn2 is the focal length of the second negative lens component,
It is. Has multiple lens groups,
Each of the plurality of lens groups has a lens component,
The lens component has a plurality of optical surfaces,
In the lens component, two of the optical surfaces are in contact with air, and at least one of the optical surfaces is a curved surface,
The plurality of lens groups are, in order from the object side,
a first lens group having positive refractive power;
a second lens group having negative refractive power;
consisting of a third lens group having positive refractive power,
When focusing from a far point to a near point, only the second lens group moves toward the image side,
The first lens group includes, in order from the object side, a first negative lens component, a second negative lens component, and a plurality of positive lens components,
The second lens group has a negative lens component,
an aperture stop arranged in the first lens group,
An imaging optical system characterized by satisfying the following conditional expression (5).
-0.80<f1Gn1/f1G<-0.55 (5)
here,
f1Gn1 is the focal length of the first negative lens component,
f1G is the focal length of the first lens group,
It is. The imaging optical system according to any one of claims 1 to 7, characterized in that the following conditional expression (6) is satisfied.
0.50<f1Gp1/f1Gp2<2.50 (6)
here,
f1Gp1 is the focal length of the positive lens component on the object side,
f1Gp2 is the focal length of the image side positive lens component,
the object side positive lens component, the positive lens component located closest to the object side among the plurality of positive lens components;
The image-side positive lens component is a positive lens component located closest to the image side among the plurality of positive lens components;
It is. Has multiple lens groups,
Each of the plurality of lens groups has a lens component,
The lens component has a plurality of optical surfaces,
In the lens component, two of the optical surfaces are in contact with air, and at least one of the optical surfaces is a curved surface,
The plurality of lens groups are, in order from the object side,
a first lens group having positive refractive power;
a second lens group having negative refractive power;
consisting of a third lens group having positive refractive power,
When focusing from a far point to a near point, only the second lens group moves toward the image side,
The first lens group includes, in order from the object side, a first negative lens component, a second negative lens component, and a plurality of positive lens components,
The second lens group has a negative lens component,
an aperture stop arranged in the first lens group,
An imaging optical system characterized by satisfying the following conditional expressions (7) and (8).
-0.12<β1Gfar<-0.050 (7)
-0.80<β1Gnear<-0.400 (8)
here,
β1Gfar is the lateral magnification of the first lens group when focusing on a far point;
β1Gnear is the lateral magnification of the first lens group at near point focusing;
It is. The imaging optical system according to any one of claims 1 to 9, characterized in that the following conditional expression (9) is satisfied.
1<fnear/ffar<1.5 (9)
here,
fnear is the focal length of the imaging optical system at near point focusing;
ffar is the focal length of the imaging optical system when focusing on a far point;
It is. Has multiple lens groups,
Each of the plurality of lens groups has a lens component,
The lens component has a plurality of optical surfaces,
In the lens component, two of the optical surfaces are in contact with air, and at least one of the optical surfaces is a curved surface,
The plurality of lens groups are, in order from the object side,
a first lens group having positive refractive power;
a second lens group having negative refractive power;
consisting of a third lens group having positive refractive power,
When focusing from a far point to a near point, only the second lens group moves toward the image side,
The first lens group includes, in order from the object side, a first negative lens component, a second negative lens component, and a plurality of positive lens components,
The second lens group has a negative lens component,
an aperture stop arranged in the first lens group,
An imaging optical system characterized by satisfying the following conditional expression (10).
1.5<f1G/ffar<2.4 (10)
here,
f1G is the focal length of the first lens group,
ffar is the focal length of the imaging optical system when focusing on a far point;
It is. The imaging optical system according to any one of claims 1 to 11, characterized in that the following conditional expression (11) is satisfied.
-6.0<f2G/ffar<-3 (11)
here,
f2G is the focal length of the second lens group,
ffar is the focal length of the imaging optical system when focusing on a far point;
It is. The imaging optical system according to any one of claims 1 to 12, characterized in that the following conditional expression (12) is satisfied.
2.5<f3G/ffar<4 (12)
here,
f3G is the focal length of the third lens group,
ffar is the focal length of the imaging optical system when focusing on a far point;
It is. Has multiple lens groups,
Each of the plurality of lens groups has a lens component,
The lens component has a plurality of optical surfaces,
In the lens component, two of the optical surfaces are in contact with air, and at least one of the optical surfaces is a curved surface,
The plurality of lens groups are, in order from the object side,
a first lens group having positive refractive power;
a second lens group having negative refractive power;
consisting of a third lens group having positive refractive power,
When focusing from a far point to a near point, only the second lens group moves toward the image side,
The first lens group includes, in order from the object side, a first negative lens component, a second negative lens component, and a plurality of positive lens components,
The second lens group has a negative lens component,
an aperture stop arranged in the first lens group,
An imaging optical system characterized by satisfying the following conditional expressions (13) and (14).
-0.30<(1-β2Gfar×β2Gfar)×β3Gfar×β3Gfar<-0.11 (13)
-0.40<(1-β2Gnear×β2Gnear)×β3Gnear×β3Gnear<-0.18 (14)
here,
β2Gfar is the lateral magnification of the second lens group when focusing on a far point;
β2Gnear is the lateral magnification of the second lens group at near point focusing;
β3Gfar is the lateral magnification of the third lens group when focusing on a far point;
β3Gnear is the lateral magnification of the third lens group at near point focusing;
It is. optical system and
an imaging element having an imaging surface and converting an image formed on the imaging surface by an optical system into an electrical signal;
An imaging apparatus characterized in that the optical system is the imaging optical system according to claim 1 .

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