JP2017049531A - Image capturing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image capturing device capable of providing good optical performance with a small number of lens components.SOLUTION: A lens component is defined as a lens having just two surfaces, an object-side surface and image-side surface, exposed to air in a path of light contributing to image formation, or an effective light path. An image capturing device comprises; an imaging optical system comprising two lens components, an object-side lens component L1 and image-side lens component L2, in order from the object side to the image side; and an image capturing unit disposed on the image side of the imaging optical system and provided with a concavely curved image capturing surface I on the object side. A most object-side surface of the object-side lens component has a concave portion that is concave in a meridional direction at least in an off-axis effective area on the object side, and a most image-side surface of the image-side lens component is a curved surface.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an imaging apparatus.

  As an optical system having a wide field angle and forming a curved image, there is a wide-angle lens described in Patent Document 1. The wide-angle lens described in Patent Document 1 includes a first lens, a second lens, and a third lens in order from the object side. The first lens has a meniscus lens having a convex surface facing the object side, the second lens has a positive refractive power, and the third lens has a concave surface facing the image side.

International Publication No. 2012/090729

  The wide-angle lens described in Patent Document 1 has a wide angle of view. However, the wide-angle lens described in Patent Document 1 has a large lens component and a large size.

  The present invention has been made in view of the above, and an object of the present invention is to provide an imaging apparatus including an imaging optical system that can ensure good optical performance with a small number of lens components.

  In order to solve the above-described problems and achieve the object, the imaging apparatus according to the present invention is configured such that the surface contacting the air is an image of the object side surface in the effective optical path that is the optical path through which the light beam contributing to the imaging through the lens component passes. When the lens has only two side surfaces, in order from the object side to the image side, an imaging optical system composed of two lens components, an object side lens component and an image side lens component, and an image side of the imaging optical system An imaging unit having an imaging surface that is arranged and has a concavely curved imaging surface on the object side, wherein the most object-side surface of the object-side lens component is at least an off-axis effective surface in the meridional direction on the object side The image side lens component is a surface having a concave portion, and the most image side surface of the image side lens component is a curved surface.

  The present invention has an effect that it is possible to provide an imaging apparatus that can easily ensure optical performance with a small number of lens components.

It is a figure explaining the parameter used by the conditional expression. It is another figure explaining the parameter used by the conditional expression. It is another figure explaining the parameter used by the conditional expression. FIG. 4 is a cross-sectional view and aberration diagrams of the image forming optical system according to Example 1, where (a) is a lens cross-sectional view, and (b), (c), (d), and (e) are aberration diagrams. FIG. 4 is a cross-sectional view and aberration diagrams of the imaging optical system according to Example 2, wherein (a) is a lens cross-sectional view, and (b), (c), (d), and (e) are aberration diagrams. FIG. 4 is a cross-sectional view and aberration diagrams of an image forming optical system according to Example 3, wherein (a) is a lens cross-sectional view, and (b), (c), (d), and (e) are aberration diagrams. FIG. 7A is a cross-sectional view of an imaging optical system according to Example 4 and aberration diagrams. FIG. 5A is a lens cross-sectional view, and FIG. 5B is an aberration diagram. FIG. 7A is a cross-sectional view of an imaging optical system according to Example 5 and aberration diagrams. FIG. 5A is a lens cross-sectional view, and FIG. 5B is an aberration diagram. FIG. 7A is a cross-sectional view of an imaging optical system according to Example 6 and aberration diagrams. FIG. 9A is a lens cross-sectional view, and FIG. 9B is an aberration diagram. FIG. 7A is a cross-sectional view of an imaging optical system according to Example 7 and aberration diagrams. FIG. 5A is a lens cross-sectional view, and FIG. 5B is an aberration diagram. FIG. 9A is a cross-sectional view of an imaging optical system according to Example 8 and aberration diagrams. FIG. 10A is a lens cross-sectional view, and FIG. 9B is an aberration diagram. 9A and 9B are cross-sectional views and aberration diagrams of the image forming optical system according to Example 9, in which (a) is a lens cross-sectional view, and (b), (c), (d), and (e) are aberration diagrams. FIG. 10 is a cross-sectional view and aberration diagrams of the imaging optical system according to Example 10, where (a) is a lens cross-sectional view, and (b), (c), (d), and (e) are aberration diagrams. FIG. 10 is a cross-sectional view and aberration diagrams of the imaging optical system according to Example 11, wherein (a) is a lens cross-sectional view, and (b), (c), (d), and (e) are aberration diagrams. FIG. 14 is a cross-sectional view and aberration diagrams of the imaging optical system according to Example 12, where (a) is a lens cross-sectional view, and (b), (c), (d), and (e) are aberration diagrams. 14 is a cross-sectional view of an imaging optical system according to Example 13. FIG. It is a figure which shows schematic structure of a capsule endoscope. It is a figure which shows a vehicle-mounted camera, Comprising: (a) is a figure which shows the example which mounted the vehicle-mounted camera outside the vehicle, (b) is a figure which shows the example which mounted the vehicle-mounted camera in the vehicle.

  Hereinafter, embodiments and examples of an imaging apparatus according to the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited by this embodiment and an Example.

  In the imaging apparatus according to the present embodiment, when an effective optical path that is an optical path through which a light beam that contributes to imaging passes is used as a lens component, a lens that has only two surfaces, the object side surface and the image side surface, is used. An imaging optical system composed of two lens components, an object side lens component and an image side lens component, in order from the image side to the image side, and an imaging surface that is arranged on the image side of the imaging optical system and is curved concavely on the object side An imaging device comprising: an imaging device comprising: an object-side lens component having a concave-shaped portion that is concave on the object side in a meridional direction in an effective plane off the axis. The most image side surface of the image side lens component is a curved surface.

  In an optical system that forms an image (hereinafter referred to as a “curved image”) curved in a concave shape on the object side, in whole or in part, correction of field curvature can be allowed. Therefore, in an optical system that forms a curved image, the burden of aberration correction is reduced compared to an optical system that forms a flat image.

  For example, in an optical system that forms a curved image, the number of lenses for correcting Petzval sum can be reduced. Therefore, the number of lens components can be reduced and the optical system can be downsized.

  Further, in an optical system that forms a flat image, it is necessary to arrange a correction lens at a position away from the aperture stop (brightness stop) in order to satisfactorily correct field curvature. However, when a correction lens is arranged, the outer diameter of the optical system increases, and the number of lens components further increases. Thus, the correction lens is one of the factors that increase the outer diameter of the optical system and increase the number of lens components.

  On the other hand, in an optical system that forms a curved image, there is no need to arrange a correction lens. Therefore, in an optical system that forms a curved image, the outer diameter of the optical system can be reduced and the number of lenses can be reduced.

  In addition, distortion can be easily corrected by receiving an image of the optical system with an imaging element having a curved imaging surface. In addition, a telecentric optical system may not be used in order to make light incident on the imaging surface substantially vertical. Therefore, in an optical system that forms a curved image, the degree of freedom in designing for both miniaturization and optical performance is widened.

  The imaging optical system in this embodiment is also an optical system that forms a curved image. Therefore, the number of lens components can be reduced and the optical system can be downsized. Furthermore, since the degree of freedom of design is widened, an optical system having high imaging performance can be realized with a small number of lens components.

  In the imaging apparatus according to the present embodiment, when an effective optical path that is an optical path through which a light beam that contributes to imaging passes is used as a lens component, a lens that has only two surfaces, the object side surface and the image side surface, is used. An imaging optical system including two lens components, that is, an object side lens component and an image side lens component, is sequentially provided from the image side to the image side.

  Aberration correction is performed because the object side surface of the object side lens component and the image side surface of the image side lens component are curved to reduce aberrations, and the object side surface is concave at least off-axis in the meridional direction. Or it is advantageous for securing a wide angle of view.

  As described above, according to the present embodiment, on the imaging surface curved in a concave shape on the object side while keeping the angle of view and the amount of occurrence of field curvature optimally, despite the small number of lens components of two lens components. Along with this, it is possible to achieve good imaging performance.

  In the imaging apparatus of the present embodiment, it is preferable that the most image-side surface of the image-side lens component is a convex surface on the image side.

  Astigmatism can be reduced by making the most image side surface of the image side lens component close to the image surface convex toward the image side.

  In the imaging apparatus of the present embodiment, it is preferable that the most object-side surface of the object-side lens component is an aspherical surface.

  As described above, a curved image is formed in the imaging apparatus of the present embodiment. The curved image is captured by an image sensor, for example. When the amount of bending in the curved image is large, the amount of bending of the imaging surface of the image sensor also increases. Since there is a limit to the amount of curvature of the imaging surface in manufacturing, it is preferable to set the amount of curvature in the curved image to an appropriate amount.

  In the curved image, it is preferable that the aberration is corrected satisfactorily.

  Therefore, the imaging optical system is required to form a curved image having a wide field angle, an appropriate amount of field curvature, and a well-corrected aberration other than field curvature. . Therefore, by making the object-side optical surface an aspherical surface, it becomes advantageous to form a wide-angle curved image in which the amount of occurrence of field curvature is appropriate and aberrations other than field curvature are well corrected. .

  In the imaging device of the present embodiment, the aspherical surface of the object-side lens component closest to the object-side lens component is preferably a surface having an inflection point in an effective surface outside the optical axis on a cross section including the optical axis. .

  This is preferable because a wider angle of view can be realized while making the amount of curvature of field appropriate.

The imaging apparatus according to the present embodiment preferably satisfies the following conditional expression (1).
SAG ₁₁ / f <0 (1)
here,
In the SAG ₁₁ , the most peripheral effective ray incident from the surface vertex (the vertex of the surface) to the maximum image height in the imaging optical system is the most object side of the object side lens component on the most object side surface of the object side lens component. The distance in the direction along the optical axis to the point passing through the surface of
f is the focal length of the imaging optical system,
It is.

FIG. 1 is a diagram for explaining the parameter SAG ₁₁ . The parameter SAG ₁₁ indicates that, on the most object-side surface S 1 of the object-side lens component L 1, the most peripheral effective ray incident on the maximum image height in the imaging optical system from the surface apex of the surface is This is the distance in the direction along the optical axis AX to the point passing through the side surface S1. Here, the direction in which the light travels is a positive sign.

  By satisfying conditional expression (1), it is possible to achieve a wide angle of view while maintaining an optimum amount of field curvature.

  Since the uppermost value of conditional expression (1) is not exceeded and the most object-side surface of the object-side lens component has a negative refractive power in whole or in part, it is advantageous for securing a wide angle of view.

It is more preferable to satisfy the following conditional expression (1-1) instead of conditional expression (1).
−0.03 <SAG ₁₁ / f <0 (1-1)

  By making it not fall below the lower limit value of the conditional expression (1-1), it is advantageous for reducing off-axis aberrations and reducing the influence of the assembly error on the aberrations.

  It is preferable that the lower limit value of conditional expression (1-1) be −0.02, more preferably −0.015. More preferably, the upper limit values of conditional expressions (1) and (1-1) are set to -0.0005, and more preferably -0.001.

The imaging apparatus according to the present embodiment preferably satisfies the following conditional expression (2).
0 <| R _2e / R _img | ≦ 2.0 (2)
here,
R _2e is a radius of curvature of the most image side surface of the image side lens component,
R _img is a virtual spherical surface including a point where the optical axis and the imaging surface intersect with each other as a surface vertex, and a point where the surface vertex and a point where the light beam incident at a half angle of view of 60 degrees on the imaging optical system intersects the imaging surface. The minimum radius of curvature,
It is.

FIG. 2 is a diagram for explaining the parameter R _img . When the imaging surface has a curved shape that is axially symmetric, the value of the radius of curvature of the phantom spherical surface is the same regardless of the direction of the angle of view (for example, the vertical ray B and the horizontal ray A on the paper surface). Also, if the imaging surface is a cylindrical surface, a toric surface, or a shape that connects multiple planes, the value of the radius of curvature of the virtual sphere differs depending on the direction of the angle of view. In that case, the minimum value that can be taken And

Conditional expression (2) defines the radius of curvature of the image-side surface of the image-side lens component and the above-mentioned R _img .

  By satisfying conditional expression (2), astigmatism on the imaging surface can be kept small and good imaging performance can be obtained.

  It is preferable to correct astigmatism by reducing the radius of curvature of the image-side lens component closest to the imaging surface so as not to exceed the upper limit of conditional expression (2).

  If the lower limit of conditional expression (2) is not reached, the imaging surface becomes flat, and it becomes difficult to correct curvature of field with a small number of lens components.

  For conditional expression (2), it is more preferable to set the lower limit value to 0.1, further 0.2. For conditional expression (2), the upper limit value is more preferably set to 1.5, and more preferably 1.0.

The imaging apparatus according to the present embodiment preferably satisfies the following conditional expression (3).
L _1e /TL≦0.65 (3)
here,
L _1e is the distance on the optical axis from the most object side surface of the object side lens component to the most image side surface of the image side lens component;
TL is the distance on the optical axis from the most object-side surface of the object-side lens component to the imaging surface,
It is.

  By satisfying conditional expression (3), a sufficient back focus can be secured.

  By ensuring the back focus so as not to exceed the upper limit value of conditional expression (3), the imaging optical system can be made smaller and lighter with respect to the size of the image plane.

It is more preferable to satisfy the following conditional expression (3-1) instead of conditional expression (3).
0.2 <L _1e /TL≦0.5 (3-1)

  The technical significance of the upper limit value of conditional expression (3-1) is the same as the technical significance of conditional expression (3).

  A sufficient distance on the optical axis from the most object-side surface of the object-side lens component to the most image-side surface of the image-side lens component is ensured so as not to fall below the lower limit value of conditional expression (3-1). This is advantageous for aberration correction and is advantageous for ensuring good imaging performance.

  For conditional expression (3), the upper limit value is more preferably 0.61, and even more preferably 0.5. For conditional expression (3) and conditional expression (3-1), it is more preferable to set the lower limit value to 0.25, more preferably 0.3.

ここで、
ｉは、結像光学系中の各レンズの物体側からの順番、
ｋは、結像光学系中のレンズの総数、
ｎ_ｉは、ｉ番目のレンズのｄ線での屈折率、
ｆ_ｉは、ｉ番目のレンズの焦点距離、
である。 When the imaging device of the present embodiment is a lens having only two surfaces, which are an object side surface and an image side surface, in contact with air in an effective optical path that is an optical path through which a light beam contributing to imaging passes as a lens component,
An imaging optical system that includes two lens components, an object side lens component and an image side lens component, in order from the object side to the image side, and connects an image to an imaging surface that is concavely curved toward the object side. It is preferable to satisfy (4).
PS × SAG ₁₁ <0 (4)
here,
The SAG ₁₁ is configured such that, on the most object-side surface of the object-side lens component, the outermost effective ray incident on the maximum image height in the imaging optical system from the surface vertex of the surface is the most object-side surface of the object-side lens component. It is the distance in the direction along the optical axis to the passing point, and the direction in which the light beam travels is a positive sign,
PS is the Petzval sum of the imaging optical system,
Petzval sum PS is expressed by the following equation.

here,
i is the order from the object side of each lens in the imaging optical system,
k is the total number of lenses in the imaging optical system,
n _i is the refractive index of the i-th lens at the d-line,
f _i is the focal length of the i th lens,
It is.

  The object side lens component has a concave portion on the object side in the effective surface off the axis of the surface closest to the object side, and satisfies the conditional expression (4), while ensuring the angle of view. It is possible to achieve good imaging performance along the imaging surface that is concavely curved toward the object side while keeping the amount of curvature of field optimally.

It is preferable to satisfy the following conditional expression (4-1) instead of conditional expression (4).
−0.02 <PS × SAG ₁₁ <0 (4-1)

  Conditional expressions (4) and (4-1) are made so as not to exceed the upper limit value, and it becomes easy to secure negative refractive power in the whole or part of the effective area of the most object side surface of the object side lens component, This is advantageous for widening the angle of view.

  It is preferable not to fall below the lower limit value of conditional expression (4-1) so as to suppress the Petzval sum and to suppress an excessive amount of field curvature. Alternatively, if the value is below the lower limit value, the sag of the most object side surface of the object side lens component is increased. Therefore, it is preferable to suppress the sag so as to facilitate the molding of the lens so as not to fall below the lower limit value.

  It is preferable that the lower limit value of conditional expression (4-1) be −0.015, more preferably −0.01. It is more preferable to set the upper limit values of conditional expressions (4) and (4-1) to -0.0003, more preferably -0.001.

ここで、
ｉは、結像光学系中の各レンズの物体側からの順番、
ｋは、結像光学系中のレンズの総数、
ｎ_ｉは、ｉ番目のレンズのｄ線での屈折率、
ｆ_ｉは、ｉ番目のレンズの焦点距離、
ＥＸＰは、像から結像光学系の近軸射出瞳位置までの光軸に沿った距離であり、近軸射出瞳位置が像よりも物体側にある場合の符号を負とする、
である。 The imaging apparatus according to the present embodiment preferably includes an aperture stop that limits the axial light beam, and satisfies the following conditional expression (5).
PS × EXP <−0.7 (5)
here,
PS is the Petzval sum of the imaging optical system,
Petzval sum PS is expressed by the following equation.

here,
i is the order from the object side of each lens in the imaging optical system,
k is the total number of lenses in the imaging optical system,
n _i is the refractive index of the i-th lens at the d-line,
f _i is the focal length of the i th lens,
EXP is the distance along the optical axis from the image to the paraxial exit pupil position of the imaging optical system, and the sign when the paraxial exit pupil position is on the object side of the image is negative.
It is.

  Satisfying the conditional expression (5) is advantageous in appropriately performing the generated curvature of field and the light incident angle on the imaging surface with respect to the curved imaging surface.

It is preferable to satisfy the following conditional expression (5-1) instead of conditional expression (5).
−1.7 <PS × EXP <−0.7 (5-1)

  It is advantageous to increase the Petzval sum so as not to exceed the upper limit values of the conditional expressions (5) and (5-1), and to ensure the amount of curvature of the image plane of the imaging optical system. Alternatively, it is advantageous to obtain a good image by suppressing the exit pupil position from being too close to the imaging surface and suppressing the light incident angle on the curved imaging surface. For example, it becomes easy to suppress the occurrence of color shading due to the effect of oblique incidence of light rays on the image sensor.

  By avoiding falling below the lower limit of conditional expression (5-1), suppressing excessive Petzval sum and preventing large field curvature from occurring in the imaging optical system, the image plane of the imaging optical system This is advantageous in reducing the production cost of an image sensor approximated to the shape of the image sensor. Alternatively, it is advantageous to prevent the exit pupil position from being far from the imaging surface and to suppress the increase in the light incident angle on the curved imaging surface.

  For conditional expression (5-1), it is preferable to let the lower limit value to be −1.5, more preferably −1.4. For conditional expressions (5) and (5-1), it is more preferable to set the upper limit to −0.8, and further to −0.87.

  In the imaging apparatus according to the present embodiment, it is preferable that the aperture stop be disposed between the object side lens component and the image side lens component.

  In the present embodiment, for example, an aperture stop is disposed between the object-side lens component and the image-side lens component, which is more advantageous for downsizing each lens component. In addition, this configuration makes it easy to maintain optical performance.

The image pickup apparatus according to the present embodiment preferably includes an aperture stop that limits the axial light beam, and satisfies the following conditional expression (6).
(EXP / f) / (φ _e / φ ₁ ) <− 1.3 (6)
here,
EXP is the distance along the optical axis from the image to the paraxial exit pupil position of the imaging optical system, and the sign when the paraxial exit pupil position is on the object side of the image is negative,
f is the focal length of the imaging optical system,
φ _e is the maximum diameter when measured perpendicular to the optical axis of the region through which the effective light beam contributing to image formation at the maximum image height position on the most object-side surface of the object-side lens component passes,
φ ₁ is the maximum diameter measured perpendicular to the optical axis of the region through which the axial light beam of the imaging optical system passes on the most object-side surface of the object-side lens component,
It is.

FIG. 3 is a diagram for explaining the parameters φ _e and φ ₁ . φ _e is the maximum diameter when measured perpendicular to the optical axis AX of the region through which the effective light beam contributing to image formation at the maximum image height position on the most object-side surface S1 of the object-side lens component L1 passes. , Φ ₁ is the maximum diameter measured perpendicularly to the optical axis AX of the region through which the axial light beam of the imaging optical system passes on the most object-side surface S1 of the object-side lens component L1.

  By satisfying conditional expression (6), in order to suppress the occurrence of shading, the change in the amount of light on and off the optical axis is reduced, and the light incident angle on the imaging surface is set to a curved imaging surface. It is advantageous to make it appropriate.

It is preferable to satisfy the following conditional expression (6-1) instead of conditional expression (6).
−2.5 <(EXP / f) / (φ _e / φ ₁ ) <− 1.3 (6-1)

  By making the difference between the light beam diameters on and off the optical axis small so as not to exceed the upper limit values of conditional expressions (6) and (6-1), it is advantageous for securing the peripheral light amount. Alternatively, by preventing the exit pupil position from being too close to the imaging surface, the light incident angle on the curved imaging surface can be reduced and color shading can be easily suppressed.

  By keeping the lower limit value of conditional expression (6-1) below and not making the exit pupil position too far from the imaging surface, the light incident angle on the curved imaging surface is suppressed, and color shading is suppressed. It becomes easy.

The imaging apparatus according to the present embodiment preferably includes an illumination unit and a transparent cover that simultaneously covers the front surfaces of both the imaging optical system and the illumination unit. Thereby, it is possible to pick up an image with good optical performance while irradiating an image.
Moreover, it is preferable to configure the imaging apparatus of the present embodiment as a capsule endoscope. Thereby, a capsule endoscope having a small size and good optical performance can be obtained.

  Hereinafter, embodiments of an imaging apparatus according to an aspect of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

  Aberration diagrams will be described. (B) shows spherical aberration (SA), (c) shows astigmatism (AS), (d) shows distortion (DT), and (e) shows lateral chromatic aberration (CC). The upper end of the vertical axis of the astigmatism (AS), distortion (DT), and lateral chromatic aberration diagrams (CC) corresponds to the maximum angle of view. The aberration diagram of astigmatism (AS) shows the amount of aberration from the curved imaging surface.

  The imaging optical system according to the first exemplary embodiment includes, in order from the object side, a biconcave negative lens L1 and a planoconvex positive lens L2. The imaging surface is spherical and is curved concavely on the object side.

  An aperture stop S is disposed between the biconcave negative lens L1 and the planoconvex positive lens L2. The aspheric surfaces are provided on both surfaces of the biconcave negative lens L1.

  The imaging optical system of Example 2 is composed of, in order from the object side, a negative meniscus lens L1 having a convex surface facing the image side, and a planoconvex positive lens L2. The imaging surface is spherical and is curved concavely on the object side.

  An aperture stop S is disposed between the negative meniscus lens L1 and the planoconvex positive lens L2. The aspheric surfaces are provided on both surfaces of the negative meniscus lens L1.

  The imaging optical system of Example 3 includes, in order from the object side, a negative meniscus lens L1 having a convex surface directed toward the image side, and a planoconvex positive lens L2. The imaging surface is spherical and is curved concavely on the object side.

  An aperture stop S is disposed between the negative meniscus lens L1 and the planoconvex positive lens L2. The aspheric surfaces are provided on both surfaces of the negative meniscus lens L1.

  The imaging optical system of Example 4 is composed of, in order from the object side, a biconvex positive lens L1 and a planoconvex positive lens L2. The imaging surface is spherical and is curved concavely on the object side.

  An aperture stop S is disposed between the biconvex positive lens L1 and the planoconvex positive lens L2. The aspheric surfaces are provided on both surfaces of the biconvex positive lens L1.

  The imaging optical system of Example 5 includes, in order from the object side, a biconvex positive lens L1 and a planoconvex positive lens L2. The imaging surface is spherical and is curved concavely on the object side.

  An aperture stop S is disposed between the biconvex positive lens L1 and the planoconvex positive lens L2. The aspheric surfaces are provided on both surfaces of the biconvex positive lens L1.

  The imaging optical system of Example 6 includes, in order from the object side, a negative meniscus lens L1 having a convex surface facing the image side and a biconvex positive lens L2. The imaging surface is spherical and is curved concavely on the object side.

  An aperture stop S is disposed at the same position as the top of the negative meniscus lens L1. The aspheric surfaces are provided on both surfaces of the negative meniscus lens L1. The aperture stop S may be disposed on the object side of the negative meniscus lens L1.

  The imaging optical system of Example 7 is composed of, in order from the object side, a negative meniscus lens L1 having a convex surface facing the image side and a positive meniscus lens L2 having a convex surface facing the image side. The image surface is a spherical surface and is concavely curved toward the object side.

  An aperture stop S is disposed at the same position as the top of the negative meniscus lens L1. The aspheric surfaces are provided on both surfaces of the negative meniscus lens L1. The aperture stop S may be disposed on the object side of the negative meniscus lens L1.

  The imaging optical system according to the eighth exemplary embodiment includes, in order from the object side, a positive meniscus lens L1 having a convex surface directed toward the image side, and a biconvex positive lens L2. The imaging surface is spherical and is curved concavely on the object side.

  An aperture stop S is disposed at the same position as the top of the positive meniscus lens L1. The aspheric surfaces are provided on both surfaces of the positive meniscus lens L1. The aperture stop S may be disposed on the object side of the positive meniscus lens L1.

  The image forming optical system according to the ninth exemplary embodiment includes, in order from the object side, a positive meniscus lens L1 having a convex surface directed toward the image side, and a planoconvex positive lens L2. The imaging surface is spherical and is curved concavely on the object side.

  An aperture stop S is disposed at the same position as the top of the positive meniscus lens L1. The aspheric surfaces are provided on both surfaces of the positive meniscus lens L1. The aperture stop S may be disposed on the object side of the positive meniscus lens L1.

  The imaging optical system of Example 10 includes a biconcave negative lens L1 and a planoconvex positive lens L2 in order from the object side. The imaging surface is aspheric and is curved concavely toward the object side.

  An aperture stop S is disposed between the biconcave negative lens L1 and the planoconvex positive lens L2. The aspheric surfaces are provided on both surfaces of the biconcave negative lens L1.

  The imaging optical system of Example 11 includes, in order from the object side, a biconcave negative lens L1, a negative meniscus lens L2 having a convex surface facing the object side, and a biconvex positive lens L3. Here, the negative meniscus lens L2 and the biconvex positive lens L3 are cemented. The imaging surface is spherical and is curved concavely on the object side.

  An aperture stop S is disposed between the biconcave negative lens L1 and the negative meniscus lens L2. The aspheric surfaces are provided on both surfaces of the biconcave negative lens L1.

  The imaging optical system of Example 12 includes, in order from the object side, a biconcave negative lens L1, a positive meniscus lens L2 with a convex surface facing the object side, a negative meniscus lens L3 with a convex surface facing the object side, and a biconvex lens. And a positive lens L4. Here, the biconcave negative lens L1 and the positive meniscus lens L2 are cemented. The negative meniscus lens L3 and the biconvex positive lens L4 are cemented. The imaging surface is spherical and is curved concavely on the object side.

  An aperture stop S is disposed between the positive meniscus lens L2 and the negative meniscus lens L3. The aspheric surfaces are provided on the object side surface of the negative meniscus lens L1 and the image side surface of the positive meniscus lens L2.

  As shown in FIG. 16, the imaging optical system of Example 13 is composed of an optical member CG, a biconcave negative lens L1, and a planoconvex positive lens L2 in this order from the object side. The imaging surface is spherical and is curved concavely on the object side. The optical system including the biconcave negative lens L1, the aperture stop S, and the planoconvex positive lens L2 is the same as the imaging optical system of the first embodiment.

  FIG. 16 is a schematic view illustrating that the optical member CG can be arranged. Therefore, the size and position of the optical member CG are not accurately drawn with respect to the size and position of the lens.

  The optical member CG is a bowl-shaped member, and both the object side surface and the image side surface are curved. In FIG. 16, since the object side surface and the image side surface are both spherical surfaces having the same center of curvature, the overall shape of the optical member CG is a hemisphere. In this embodiment, the thickness of the optical member CG, that is, the distance between the object side surface and the image side surface is constant in the direction toward the center of curvature.

  A material that transmits light is used for the optical member CG. Therefore, the light from the subject passes through the optical member CG and enters the negative lens L1. The optical member CG is disposed so that the center of curvature of the image side surface substantially coincides with the position of the entrance pupil. Therefore, almost no new aberration due to the optical member CG occurs. That is, the imaging performance of the imaging optical system of Example 13 is not different from the imaging performance of the imaging optical system of Example 1.

  The optical member CG functions as a cover glass. In this case, the optical member CG corresponds to, for example, an observation window provided in the exterior part of the capsule endoscope. Therefore, the imaging optical system of Example 13 can be used for an optical system of a capsule endoscope. The imaging optical systems of Examples 2 to 12 can also be used for the optical system of the capsule endoscope.

  Below, the numerical data of each said Example are shown. In the surface data, r is the radius of curvature of each lens surface, d is the distance between the lens surfaces, nd is the refractive index of the d-line of each lens, νd is the Abbe number of each lens, and * is an aspherical surface.

  In various data, f is the focal length of the entire system, FNO. Is the F number, ω is the half field angle, IH is the image height, LTL is the total length of the optical system, BF is the back focus, and the back focus is the distance from the lens surface closest to the image side to the paraxial image plane in terms of air It is a representation. The total length is obtained by adding BF (back focus) to the distance from the lens surface closest to the object side to the lens surface closest to the image side of the imaging optical system. Further, f1, f2, f3, and f4 are focal lengths of the respective lenses. The unit of half angle of view is degrees.

The aspherical shape is expressed by the following equation when the optical axis direction is z, the direction orthogonal to the optical axis is y, the cone coefficient is k, and the aspherical coefficients are A4, A6, A8, A10, A12. expressed.
z = (y ² / r) / [1+ {1− (1 + k) (y / r) ² } ^1/2 ]
+ A4y ⁴ + A6y ⁶ + A8y ⁸ + A10y ¹⁰ + A12y ¹² +
In the aspheric coefficient, “e−n” (n is an integer) indicates “10 ⁻ⁿ ”. The symbols of these specification values are common to the numerical data of the examples described later.

Numerical example 1
Unit mm

Surface data Surface number rd nd νd
Object plane ∞ 10.10
1 * -3.185 0.30 1.53110 56.00
2 * 1.738 0.05
3 (Aperture) ∞ 0.00
4 ∞ 0.34 1.53110 56.00
5 -0.375 1.07
Image plane -9.568

Aspheric data first surface
k = 0.000
A4 = 2.53231e-02, A6 = 2.07188e + 00, A8 = -5.74113e + 00
Second side
k = 0.000
A4 = 7.56464e + 00

Various data f 0.855
FNO. 3.047
2ω 164
IH 0.975
LTL 1.760
BF 1.07
f1 -2.065
f2 0.704

Numerical example 2
Unit mm

Surface data Surface number rd nd νd
Object plane ∞ 10.10
1 * -4.280 0.47 1.53110 56.00
2 * -6.524 0.06
3 (Aperture) ∞ 0.00
4 ∞ 0.37 1.53110 56.00
5 -0.512 1.09
Image plane -2.437

Aspheric data first surface
k = 0.000
A4 = -3.36755e-01, A6 = 1.43642e + 00, A8 = -1.68203e + 00
Second side
k = 0.000
A4 = 2.37328e + 00

Various data f 0.949
FNO. 3.330
2ω 164
IH 0.975
LTL 1.982
BF 1.09
f1 -25.152
f2 0.960

Numerical Example 3
Unit mm

Surface data Surface number rd nd νd
Object plane ∞ 10.10
1 * -3.773 0.30 1.53110 56.00
2 * -5.549 0.03
3 (Aperture) ∞ 0.00
4 ∞ 0.46 1.53110 56.00
5 -0.527 1.13
Image plane -1.507

Aspheric data first surface
k = 0.000
A4 = -8.23828e-02, A6 = 1.38064e + 00, A8 = -2.37738e + 00
Second side
k = 0.000
A4 = 1.78525e + 00

Various data f 0.988
FNO. 3.405
2ω 162
IH 0.975
LTL 1.929
BF 1.13
f1 -23.496
f2 0.988

Numerical Example 4
Unit mm

Surface data Surface number rd nd νd
Object plane ∞ 10.10
1 * 83.990 0.50 1.53110 56.00
2 * -3.320 0.06
3 (Aperture) ∞ 0.00
4 ∞ 0.36 1.53110 56.00
5 -0.570 0.99
Image plane -1.952

Aspheric data first surface
k = 0.000
A4 = -5.60219e-01, A6 = 1.37170e + 00, A8 = -1.12862e + 00
Second side
k = 0.000
A4 = 1.58678e + 00

Various data f 0.948
FNO. 3.167
2ω 163
IH 0.975
LTL 1.902
BF 0.99
f1 6.000
f2 1.069

Numerical Example 5
Unit mm

Surface data Surface number rd nd νd
Object plane ∞ 10.10
1 * 8.422 0.49 1.53110 56.00
2 * -1.934 0.05
3 (Aperture) ∞ 0.00
4 ∞ 0.42 1.53110 56.00
5 -0.690 0.97
Image plane -1.506

Aspheric data first surface
k = 0.000
A4 = -6.27531e-01, A6 = 1.03387e + 00, A8 = -5.88990e-01
Second side
k = 0.000
A4 = 5.30326e-01

Various data f 0.993
FNO. 3.224
2ω 162
IH 0.975
LTL 1.931
BF 0.97
f1 2.998
f2 1.294

Numerical Example 6
Unit mm

Surface data Surface number rd nd νd
Object plane ∞ 10.10
1 (Aperture) ∞ 0.00
2 * -1.471 0.30 1.63493 23.89
3 * -1.685 0.05
4 30.637 0.30 1.77250 49.60
5 -0.819 1.15
Image plane -2.410

Aspheric data 2nd surface
k = 0.000
A4 = -1.52940e + 00, A6 = 4.61522e + 01, A8 = -2.70647e + 03, A10 = 5.28160e + 04
Third side
k = 0.000
A4 = 2.92858e-01, A6 = -1.48191e + 01, A8 = 1.78831e + 02, A10 = -5.81275e + 02

Various data f 0.974
FNO. 3.282
2ω 160
IH 0.975
LTL 1.802
BF 1.15
f1 -39.920
f2 1.032

Numerical Example 7
Unit mm

Surface data Surface number rd nd νd
Object plane ∞ 10.10
1 (Aperture) ∞ 0.00
2 * -3.775 0.30 1.63493 23.89
3 * -4.623 0.05
4 -37.325 0.30 1.77250 49.60
5 -0.764 1.13
Image plane --1.491

Aspheric data 2nd surface
k = 0.000
A4 = -1.00244e + 00, A6 = 3.67646e + 01, A8 = -2.55931e + 03, A10 = 4.05208e + 04
Third side
k = 0.000
A4 = 3.76741e-01, A6 = -1.46146e + 01, A8 = 1.55644e + 02, A10 = -4.99373e + 02

Various data f 0.991
FNO. 3.340
2ω 173
IH 0.975
LTL 1.784
BF 1.13
f1 -37.207
f2 1.001

Numerical Example 8
Unit mm

Surface data Surface number rd nd νd
Object plane ∞ 10.10
1 (Aperture) ∞ 0.00
2 * -2.258 0.37 1.53110 56.00
3 * -0.864 0.05
4 4.873 0.44 1.53110 56.00
5 -0.981 0.98
Image plane -1.946

Aspheric data 2nd surface
k = 0.000
A4 = -7.49745e-01, A6 = 8.48354e + 01, A8 = -6.16466e + 03, A10 = 1.26740e + 05
Third side
k = 0.000
A4 = 6.12011e-01, A6 = -1.00316e + 01, A8 = 5.20328e + 01, A10 = -1.02293e + 02

Various data f 0.989
FNO. 3.334
2ω 162
IH 0.975
LTL 1.831
BF 0.98
f1 2.403
f2 1.571

Numerical Example 9
Unit mm

Surface data Surface number rd nd νd
Object plane ∞ 10.10
1 (Aperture) ∞ 0.00
2 * -19.712 0.46 1.53110 56.00
3 * -0.657 0.05
4 ∞ 0.30 1.53110 56.00
5 -1.951 0.90
Image plane -1.503

Aspheric data 2nd surface
k = 0.000
A4 = -1.69752e + 00, A6 = 8.48174e + 01, A8 = -4.79152e + 03, A10 = 8.61262e + 04
Third side
k = 0.000
A4 = 1.57455e-01, A6 = -5.33428e + 00, A8 = 2.21803e + 01, A10 = -8.34925e + 01

Various data f 0.986
FNO. 3.325
2ω 162
IH 0.975
LTL 1.714
BF 0.90
f1 1.263
f2 3.658

Numerical Example 10
Unit mm

Surface data Surface number rd nd νd
Object plane ∞ 10.10
1 * -6.802 0.30 1.53110 56.00
2 * 7.707 0.05
3 (Aperture) ∞ 0.00
4 ∞ 0.33 1.53110 56.00
5 -0.427 0.98
Image plane * -9.807

Aspheric data first surface
k = 0.000
A4 = -2.55684e-01, A6 = 2.55471e + 00, A8 = -5.39397e + 00
Second side
k = 0.000
A4 = 4.91252e + 00
Image plane
k = 0.000
A4 = -1.09530e + 00, A6 = 1.89310e + 00, A8 = -6.95550e-01, A10 = -2.08580e-01

Various data f 0.856
FNO. 2.953
2ω 163
IH 0.975
LTL 1.653
BF 0.98
f1 -6.726
f2 0.800

Numerical Example 11
Unit mm

Surface data Surface number rd nd νd
Object plane ∞ 10.10
1 * -10.000 0.30 1.53110 56.00
2 * 4.442 0.02
3 (Aperture) ∞ 0.00
4 8.146 0.30 1.84666 23.78
5 0.806 0.35 1.80610 40.92
6 -0.658 0.97
Image plane -9.785

Aspheric data first surface
k = 0.000
A4 = -5.46945e-01, A6 = 3.59115e + 00, A8 = -7.35098e + 00
Second side
k = 0.000
A4 = 3.11619e + 00

Various data f 0.857
FNO. 2.913
2ω 163
IH 0.975
LTL 1.940
BF 0.97
f1 -5.725
f2 -1.067
f3 0.501

Numerical example 12
Unit mm

Surface data Surface number rd nd νd
Object plane ∞ 10.10
1 * -20.000 0.30 1.58913 61.15
2 0.800 0.30 1.80610 40.88
3 * 4.197 0.01
4 (Aperture) ∞ 0.00
5 22.625 0.30 1.84666 23.78
6 0.806 0.40 1.80610 40.92
7 -0.675 0.88
Image plane -9.636

Aspheric data first surface
k = 0.000
A4 = -2.81491e-01, A6 = 8.35553e-01, A8 = -7.60061e-01
Third side
k = 0.000
A4 = 1.86377e + 00

Various data f 0.853
FNO. 3.182
2ω 164
IH 0.975
LTL 2.188
BF 0.88
f1 -1.294
f2 1.173
f3 -0.984
f4 0.515

Next, the value of the conditional expression in each example is shown below.

(1) SAG11 / f
(2) | R2e / Rimg |
(3) L1e / TL
(4) PS × SAG11
(5) PS x EXP
(6) (EXP / f) / (φe / φ1)

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6
(1) -0.008 -0.013 -0.004 -0.007 -0.001 -0.008
(2) 0.039 0.210 0.350 0.292 0.458 0.340
(3) 0.392 0.451 0.414 0.478 0.499 0.361
(4) -0.004 -0.008 -0.003 -0.004 -0.001 -0.004
(5) -0.860 -0.918 -0.987 -0.926 -0.952 -0.947
(6) -1.992 -1.588 -1.579 -1.506 -1.250 -1.890

Example 7 Example 8 Example 9 Example 10 Example 11 Example 12
(1) -0.001 -0.005 -0.001 -0.005 -0.002 -0.009
(2) 0.512 0.504 1.298 0.044 0.067 0.070
(3) 0.364 0.466 0.472 0.409 0.498 0.601
(4) -0.001 -0.003 -0.001 -0.003 -0.001 -0.005
(5) -0.987 -1.303 -1.161 -0.913 -0.972 -1.005
(6) -2.210 -1.952 -1.706 -1.861 -2.295 -2.296

Next, parameter values in each example are shown below.

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6
Rimg -9.568 -2.437 -1.507 -1.952 -1.506 -2.410
L1e 0.690 0.893 0.799 0.910 0.963 0.650
PS 0.617 0.651 0.631 0.719 0.725 0.514
EXP -1.393 -1.409 -1.565 -1.289 -1.313 -1.841
R11 -3.185 -4.280 -3.773 83.990 8.422 -1.471
R2e -0.375 -0.512 -0.527 -0.570 -0.690 -0.819
SAG11 -0.007 -0.013 -0.004 -0.006 -0.001 -0.008
φ1 0.274 0.275 0.284 0.288 0.297 0.297
φe 0.224 0.258 0.285 0.260 0.314 0.296

Example 7 Example 8 Example 9 Example 10 Example 11 Example 12
Rimg -1.491 -1.946 -1.503 -9.807 -9.785 -9.636
L1e 0.650 0.853 0.809 0.676 0.967 1.314
PS 0.542 0.675 0.690 0.718 0.608 0.637
EXP -1.823 -1.931 -1.682 -1.271 -1.599 -1.577
R11 -3.775 -2.258 -19.712 -6.802 -10.000 -20.000
R2e -0.764 -0.981 -1.951 -0.427 -0.658 -0.675
SAG11 -0.001 -0.005 -0.001 -0.004 -0.002 -0.008
φ1 0.297 0.296 0.296 0.283 0.288 0.259
φe 0.247 0.296 0.296 0.226 0.234 0.208

  FIG. 17 is an example of an optical device. In this example, the optical device is a capsule endoscope. The capsule endoscope 100 includes a capsule cover 101 and a transparent cover 102. The capsule cover 101 and the transparent cover 102 constitute an exterior part of the capsule endoscope 100.

  The capsule cover 101 includes a substantially cylindrical center portion and a substantially bowl-shaped bottom portion. The transparent cover 102 is disposed at a position facing the bottom with the center portion interposed therebetween. The transparent cover 102 is configured by a substantially bowl-shaped transparent member. The capsule cover 101 and the transparent cover 102 are connected to each other in a watertight manner.

  The capsule endoscope 100 includes an imaging optical system 103, an illumination unit 104, an image sensor 105, a drive control unit 106, and a signal processing unit 107. The transparent cover 102 is disposed at a position that simultaneously covers the front surfaces of both the imaging optical system 103 and the illumination unit 104. Although not shown, a power receiving unit and a transmission unit are provided inside the capsule endoscope 100.

  Illumination light is emitted from the illumination unit 104. The illumination light passes through the transparent cover 102 and is irradiated onto the subject. Light from the subject enters the imaging optical system 103. The imaging optical system 103 forms an optical image of the subject at the imaging surface position.

  The optical image is captured by the image sensor 105. The drive control unit 106 drives and controls the image sensor 105. Further, the output signal from the image sensor 105 is processed by the signal processing unit 107 as necessary.

  Here, as the imaging optical system 103, for example, the imaging optical system of the above-described first embodiment is used. Therefore, an optical image in a very wide range (an angle of view of about 160 °) is formed. The optical image is an image curved concavely toward the object side.

  The imaging surface of the imaging element 105 is curved concavely toward the object side. Further, the radius of curvature of the imaging surface is the same as the radius of curvature of the optical image. Therefore, it is possible to acquire a clear image from the center to the periphery while capturing an image of a very wide range.

  FIG. 18 shows another example of the optical device. In this example, the optical device is an in-vehicle camera. FIG. 18A is a diagram illustrating an example in which an in-vehicle camera is mounted outside the vehicle. FIG. 18B is a diagram illustrating an example in which a vehicle-mounted camera is mounted in the vehicle.

  As shown in FIG. 18 (a), the in-vehicle camera 201 is provided on the front grill of the automobile 200. The in-vehicle camera 201 includes an imaging optical system and an image sensor.

  For example, the imaging optical system of Example 1 described above is used for the imaging optical system of the in-vehicle camera 201. Therefore, an optical image in a very wide range (an angle of view of about 160 °) is formed. Further, the imaging surface of the imaging device is curved concavely toward the object side. The curvature radius of the imaging surface is the same as the curvature radius of the optical image. Therefore, it is possible to acquire a clear image from the center to the periphery while capturing an image of a very wide range.

  As shown in FIG. 18B, the in-vehicle camera 201 is provided near the ceiling of the automobile 200. The operational effects of the in-vehicle camera 201 are as already described.

  The vehicle-mounted camera 201 may be arranged at the corners or the tops of the poles of the head if it is outdoor. Moreover, if it is indoors, you may arrange | position in the vicinity of a rear-view mirror.

ここで、
ｉは、前記結像光学系中の各レンズの物体側からの順番、
ｋは、前記結像光学系中のレンズの総数、
ｎ_ｉは、ｉ番目のレンズのｄ線での屈折率、
ｆ_ｉは、ｉ番目のレンズの焦点距離、
である。
（付記項１−９）
前記物体側レンズ成分の最も物体側の面が少なくとも軸外の有効面内においてメリディオナル方向で物体側に凹形状となる凹形状部分を有する面であることを特徴とする付記項（１−８）に記載の結像光学系。
（付記項１−１０）
前記像側レンズ成分の最も像側の面が像側に凸形状の面であることを特徴とする付記項（１−８）又は（１−９）に記載の結像光学系。
（付記項１−１１）
前記物体側レンズ成分の最も物体側の面が非球面であることを特徴とする付記項（１−８）から（１−１０）のいずれか一項に記載の結像光学系。
（付記項１−１２）
前記物体側レンズ成分の最も物体側の面の非球面は、光軸を含む断面上にて光軸外の有効面内に変曲点を持つ面であることを特徴とする付記項（１−１１）に記載の結像光学系。
（付記項２−１）
軸上光束を制限する明るさ絞りを有し、
レンズ成分を結像に寄与する光束が通過する光路である有効光路にて空気に接触する面が物体側面と像側面の２面のみのレンズとしたときに、
物体側から像側に順に、物体側レンズ成分、像側レンズ成分の２つのレンズ成分からなり、物体側に凹状に湾曲した撮像面に像を結ぶ結像光学系であって、
以下の条件式（２−１）を満足することを特徴とする結像光学系。
ＰＳ×ＥＸＰ＜−０．７ …（２−１）
ここで、
ＰＳは、前記結像光学系のペッツバール和であり、
ペッツバール和ＰＳは以下の式で表される。

ここで、
ｉは、結像光学系中の各レンズの物体側からの順番、
ｋは、結像光学系中のレンズの総数、
ｎ_ｉは、ｉ番目のレンズのｄ線での屈折率、
ｆ_ｉは、ｉ番目のレンズの焦点距離、
ＥＸＰは、前記像から前記結像光学系の近軸射出瞳位置までの光軸に沿った距離であり、前記近軸射出瞳位置が前記像よりも物体側にある場合の符号を負とする、
である。
（付記項２−２）
前記明るさ絞りが、前記物体側レンズ成分と前記像側レンズ成分との間に配置され、以下の条件式（２−２）を満足することを特徴とする付記項（２−１）に記載の結像光学系。
Ｌ_１ｅ／ＴＬ≦０．６５ …（２−２）
ここで、
Ｌ_１ｅは、前記物体側レンズ成分の最も物体側の面から前記像側レンズ成分の最も像側の面までの光軸上での距離、
ＴＬは、前記物体側レンズ成分の最も物体側の面から前記撮像面までの光軸上での距離、
である。
（付記項２−３）
前記物体側レンズ成分の最も物体側の面が物体側に凹形状の面であることを特徴とする付記項（２−１）又は（２−２）に記載の結像光学系。
（付記項２−４）
前記物体側レンズ成分の最も物体側の面が少なくとも軸外の有効面内においてメリディオナル方向で物体側に凹形状となる凹形状部分を有する面であることを特徴とする付記項（２−１）又は（２−２）に記載の結像光学系。
（付記項２−５）
前記像側レンズ成分の最も像側の面が像側に凸形状の面であることを特徴とする付記項（２−１）から（２−４）のいずれか一項に記載の結像光学系。
（付記項２−６）
前記物体側レンズ成分の最も物体側の面が非球面であることを特徴とする付記項（２−１）から（２−５）のいずれか一項に記載の結像光学系。
（付記項２−７）
付記項（２−１）から（２−６）のいずれか一項に記載の結像光学系と、
前記結像光学系の像側に配置され、物体側に凹状に湾曲した撮像面を持つ撮像部と、
を備えた撮像装置。
（付記項３−１）
軸上光束を制限する明るさ絞りを有し、
レンズ成分を結像に寄与する光束が通過する光路である有効光路にて空気に接触する面が物体側面と像側面の２面のみのレンズとしたときに、
物体側から像側に順に、物体側レンズ成分、像側レンズ成分の２つのレンズ成分からなり、物体側に凹状に湾曲した撮像面に像を結ぶ結像光学系であって、以下の条件式（３−１）を満足することを特徴とする結像光学系。
（ＥＸＰ／ｆ）／（φ_ｅ／φ_１）＜−１．３ …（３−１）
ここで、
ＥＸＰは、前記像から前記結像光学系の近軸射出瞳位置までの光軸に沿った距離であり、前記近軸射出瞳位置が前記像よりも物体側にある場合の符号を負とし、
ｆは、前記結像光学系の焦点距離、
φ_ｅは、前記物体側レンズ成分の最も物体側の面における、最大像高位置への結像に寄与する有効光束が通過する領域の光軸に対して垂直に測ったときの最大直径、
φ_１は、前記物体側レンズ成分の最も物体側の面における、前記結像光学系の軸上光束が通過する領域の光軸に対して垂直に測った最大直径、即ち入射瞳径、
である。
（付記項３−２）
以下の条件式（３−２）を満足することを特徴とする付記項（３−１）に記載の結像光学系。
Ｌ_１ｅ／ＴＬ≦０．６５ …（３−２）
ここで、
Ｌ_１ｅは、前記物体側レンズ成分の最も物体側の面から前記像側レンズ成分の最も像側の面までの光軸上での距離、
ＴＬは、前記物体側レンズ成分の最も物体側の面から前記撮像面までの光軸上での距離、
である。
（付記項３−３）
前記物体側レンズ成分の最も物体側の面が物体側に凹形状の面であることを特徴とする付記項（３−１）又は（３−２）に記載の結像光学系。
（付記項３−４）
前記物体側レンズ成分の最も物体側の面が少なくとも軸外の有効面内においてメリディオナル方向で物体側に凹形状となる凹形状部分を有する面であることを特徴とする付記項（３−１）又は（３−２）に記載の結像光学系。
（付記項３−５）
前記像側レンズ成分の最も像側の面が像側に凸形状の面であることを特徴とする付記項（３−１）から（３−４）のいずれか一項に記載の結像光学系。
（付記項３−６）
前記物体側レンズ成分の最も物体側の面が非球面であることを特徴とする付記項（３−１）から（３−５）のいずれか一項に記載の結像光学系。
（付記項３−７）
付記項（３−１）から（３−６）のいずれか一項に記載の結像光学系と、
前記結像光学系の像側に配置され、物体側に凹状に湾曲した撮像面を持つ撮像部と、
を備えた撮像装置。 (Appendix)
In addition, the invention of the following structures is guide | induced from these Examples.
(Appendix 1-8)
When the lens component has only two surfaces, the object side surface and the image side surface, in contact with air in the effective optical path, which is the optical path through which the light flux contributing to image formation passes,
An imaging optical system that consists of two lens components, an object side lens component and an image side lens component, in order from the object side to the image side, and connects an image to an imaging surface that is concavely curved toward the object side,
An imaging optical system characterized by satisfying the following conditional expression (1-4):
PS × SAG ₁₁ <0 (1-4)
here,
The SAG ₁₁ is the most object effective surface of the object side lens component with the most effective light ray incident on the maximum image height in the imaging optical system from the surface apex of the surface on the most object side surface of the object side lens component. It is the distance in the direction along the optical axis to the point passing through the side surface, and the direction in which the light beam travels is a positive sign,
PS is the Petzval sum of the imaging optical system,
Petzval sum PS is expressed by the following equation.

here,
i is the order from the object side of each lens in the imaging optical system,
k is the total number of lenses in the imaging optical system,
n _i is the refractive index of the i-th lens at the d-line,
f _i is the focal length of the i th lens,
It is.
(Appendix 1-9)
Additional remark (1-8), wherein the most object side surface of the object side lens component is a surface having a concave portion that is concave on the object side in the meridional direction within at least an off-axis effective surface. The imaging optical system described in 1.
(Appendix 1-10)
The imaging optical system according to (1-8) or (1-9), wherein a surface closest to the image side of the image side lens component is a convex surface on the image side.
(Appendix 1-11)
The imaging optical system according to any one of appendices (1-8) to (1-10), wherein the most object-side surface of the object-side lens component is an aspherical surface.
(Appendix 1-12)
The aspherical surface of the most object side surface of the object side lens component is a surface having an inflection point in an effective surface outside the optical axis on a cross section including the optical axis (1- The imaging optical system according to 11).
(Appendix 2-1)
Has an aperture stop that limits the axial luminous flux,
When the lens component has only two surfaces, the object side surface and the image side surface, in contact with air in the effective optical path, which is the optical path through which the light flux contributing to image formation passes,
An imaging optical system that consists of two lens components, an object side lens component and an image side lens component, in order from the object side to the image side, and connects an image to an imaging surface that is concavely curved toward the object side,
An imaging optical system satisfying the following conditional expression (2-1):
PS × EXP <−0.7 (2-1)
here,
PS is the Petzval sum of the imaging optical system,
Petzval sum PS is expressed by the following equation.

here,
i is the order from the object side of each lens in the imaging optical system,
k is the total number of lenses in the imaging optical system,
n _i is the refractive index of the i-th lens at the d-line,
f _i is the focal length of the i th lens,
EXP is the distance along the optical axis from the image to the paraxial exit pupil position of the imaging optical system, and the sign when the paraxial exit pupil position is on the object side of the image is negative. ,
It is.
(Appendix 2-2)
The brightness stop is disposed between the object-side lens component and the image-side lens component, and satisfies the following conditional expression (2-2): Additional remark (2-1) Imaging optical system.
L _1e /TL≦0.65 (2-2)
here,
L _1e is the distance on the optical axis from the most object side surface of the object side lens component to the most image side surface of the image side lens component;
TL is the distance on the optical axis from the most object-side surface of the object-side lens component to the imaging surface,
It is.
(Appendix 2-3)
The imaging optical system according to (2-1) or (2-2), wherein the most object side surface of the object side lens component is a concave surface on the object side.
(Appendix 2-4)
Additional remark (2-1), wherein the most object-side surface of the object-side lens component is a surface having a concave portion that is concave on the object side in the meridional direction at least in an off-axis effective surface. Or the imaging optical system as described in (2-2).
(Appendix 2-5)
The imaging optics according to any one of items (2-1) to (2-4), wherein the most image-side surface of the image-side lens component is a surface convex toward the image side. system.
(Appendix 2-6)
The imaging optical system according to any one of appendices (2-1) to (2-5), wherein the most object-side surface of the object-side lens component is an aspherical surface.
(Appendix 2-7)
Additional image (2-1) to (2-6) The imaging optical system according to any one of the above,
An imaging unit disposed on the image side of the imaging optical system and having an imaging surface curved concavely on the object side;
An imaging apparatus comprising:
(Appendix 3-1)
Has an aperture stop that limits the axial luminous flux,
When the lens component has only two surfaces, the object side surface and the image side surface, in contact with air in the effective optical path, which is the optical path through which the light flux contributing to image formation passes,
An imaging optical system that includes two lens components, an object side lens component and an image side lens component, in order from the object side to the image side, and connects an image to an imaging surface that is concavely curved toward the object side. An imaging optical system characterized by satisfying (3-1).
(EXP / f) / (φ _e / φ ₁ ) <− 1.3 (3-1)
here,
EXP is the distance along the optical axis from the image to the paraxial exit pupil position of the imaging optical system, and the sign when the paraxial exit pupil position is on the object side of the image is negative,
f is a focal length of the imaging optical system,
φ _e is the maximum diameter when measured perpendicular to the optical axis of the region through which the effective light beam contributing to image formation at the maximum image height position on the most object side surface of the object side lens component passes,
φ ₁ is the maximum diameter measured perpendicular to the optical axis of the region through which the on-axis light beam of the imaging optical system passes on the most object-side surface of the object-side lens component, that is, the entrance pupil diameter,
It is.
(Appendix 3-2)
The imaging optical system according to item (3-1), wherein the following conditional expression (3-2) is satisfied.
L _1e /TL≦0.65 (3-2)
here,
L _1e is the distance on the optical axis from the most object side surface of the object side lens component to the most image side surface of the image side lens component;
TL is the distance on the optical axis from the most object-side surface of the object-side lens component to the imaging surface,
It is.
(Additional Item 3-3)
The imaging optical system according to (3-1) or (3-2), wherein the most object side surface of the object side lens component is a concave surface on the object side.
(Appendix 3-4)
Additional remark (3-1), wherein the most object-side surface of the object-side lens component is a surface having a concave portion that is concave on the object side in the meridional direction within at least an off-axis effective surface. Or the imaging optical system as described in (3-2).
(Appendix 3-5)
The imaging optics according to any one of items (3-1) to (3-4), wherein the most image-side surface of the image-side lens component is a surface convex toward the image side. system.
(Appendix 3-6)
The imaging optical system according to any one of appendices (3-1) to (3-5), wherein the most object-side surface of the object-side lens component is an aspherical surface.
(Appendix 3-7)
The imaging optical system according to any one of additional items (3-1) to (3-6);
An imaging unit disposed on the image side of the imaging optical system and having an imaging surface curved concavely on the object side;
An imaging apparatus comprising:

  Further, it is preferable that the above-described inventions satisfy a plurality at the same time, so that the respective effects such as downsizing, high performance, and wide angle of view can be ensured.

  As described above, the present invention is useful for an imaging apparatus that can capture a wide range with a high resolution with a small number of lens components while being small.

L1, L2, L3, L4 Lens S Aperture stop (brightness stop)
I Image surface CG Optical member S ₁ Optical surface AX Optical axis 100 Capsule endoscope 101 Capsule cover 102 Transparent cover 103 Imaging optical system 104 Illumination unit 105 Imaging element 106 Drive control unit 107 Signal processing unit 200 Automotive 201 Car-mounted camera

Claims (13)

When the lens component has only two surfaces, the object side surface and the image side surface, in contact with air in the effective optical path, which is the optical path through which the light flux contributing to image formation passes,
In order from the object side to the image side, an imaging optical system composed of two lens components, an object side lens component and an image side lens component;
An imaging unit disposed on the image side of the imaging optical system and having an imaging surface curved concavely on the object side;
An imaging device comprising:
The most object-side surface of the object-side lens component is a surface having a concave portion that is concave on the object side in the meridional direction within at least an off-axis effective surface;
An image pickup apparatus, wherein the most image side surface of the image side lens component is a curved surface.   The imaging apparatus according to claim 1, wherein the most image-side surface of the image-side lens component is a surface convex toward the image side.   The imaging apparatus according to claim 1, wherein a most object side surface of the object side lens component is an aspherical surface.   The aspherical surface of the object side lens component closest to the object side is a surface having an inflection point in an effective surface outside the optical axis on a cross section including the optical axis. The imaging device according to any one of the above. The imaging apparatus according to claim 1, wherein the following conditional expression (1) is satisfied.
SAG ₁₁ / f <0 (1)
here,
The SAG ₁₁ is the most object effective surface of the object side lens component with the most effective light ray incident on the maximum image height in the imaging optical system from the surface apex of the surface on the most object side surface of the object side lens component. It is the distance in the direction along the optical axis to the point passing through the side surface, and the direction in which the light beam travels is a positive sign,
f is a focal length of the imaging optical system,
It is. The imaging apparatus according to claim 1, wherein the following conditional expression (2) is satisfied.
0 <| R _2e / R _img | ≦ 2.0 (2)
here,
R _2e is the radius of curvature of the most image-side surface of the image-side lens component,
R _img is a point where the optical axis and the imaging surface intersect with each other as a surface vertex, and the surface vertex, and a point where a light beam incident on the imaging optical system at a half angle of view of 60 degrees intersects the imaging surface. The minimum radius of curvature of the phantom sphere, including
It is. The imaging apparatus according to claim 1, wherein the following conditional expression (3) is satisfied.
L _1e /TL≦0.65 (3)
here,
L _1e is the distance on the optical axis from the most object side surface of the object side lens component to the most image side surface of the image side lens component;
TL is the distance on the optical axis from the most object-side surface of the object-side lens component to the imaging surface,
It is. When the imaging optical system is a lens having only two surfaces, an object side surface and an image side surface, in contact with air in an effective optical path through which a light beam contributing to imaging passes through a lens component,
An imaging optical system that consists of two lens components, an object side lens component and an image side lens component, in order from the object side to the image side, and connects an image to an imaging surface that is concavely curved toward the object side,
The imaging apparatus according to claim 1, wherein the following conditional expression (4) is satisfied.
PS × SAG ₁₁ <0 (4)
here,
The SAG ₁₁ is the most object effective surface of the object side lens component with the most effective light ray incident on the maximum image height in the imaging optical system from the surface apex of the surface on the most object side surface of the object side lens component. It is the distance in the direction along the optical axis to the point passing through the side surface, and the direction in which the light beam travels is a positive sign,
PS is the Petzval sum of the imaging optical system,
Petzval sum PS is expressed by the following equation.

here,
i is the order from the object side of each lens in the imaging optical system,
k is the total number of lenses in the imaging optical system,
n _i is the refractive index of the i-th lens at the d-line,
f _i is the focal length of the i th lens,
It is. Has an aperture stop that limits the axial luminous flux,
The imaging apparatus according to claim 1, wherein the following conditional expression (5) is satisfied.
PS × EXP <−0.7 (5)
here,
PS is the Petzval sum of the imaging optical system,
Petzval sum PS is expressed by the following equation.

here,
i is the order from the object side of each lens in the imaging optical system,
k is the total number of lenses in the imaging optical system,
n _i is the refractive index of the i-th lens at the d-line,
f _i is the focal length of the i th lens,
EXP is the distance along the optical axis from the image to the paraxial exit pupil position of the imaging optical system, and the sign when the paraxial exit pupil position is on the object side of the image is negative. ,
It is.   The imaging apparatus according to claim 9, wherein the brightness stop is disposed between the object side lens component and the image side lens component. Has an aperture stop that limits the axial luminous flux,
The imaging apparatus according to claim 1, wherein the following conditional expression (6) is satisfied.
(EXP / f) / (φ _e / φ ₁ ) <− 1.3 (6)
here,
EXP is the distance along the optical axis from the image to the paraxial exit pupil position of the imaging optical system, and the sign when the paraxial exit pupil position is on the object side of the image is negative,
f is a focal length of the imaging optical system,
φ _e is the maximum diameter when measured perpendicular to the optical axis of the region through which the effective light beam contributing to image formation at the maximum image height position on the most object side surface of the object side lens component passes,
φ ₁ is the maximum diameter measured perpendicularly to the optical axis of the region through which the axial light beam of the imaging optical system passes on the most object-side surface of the object-side lens component,
It is. An illumination unit;
The imaging apparatus according to claim 1, further comprising a transparent cover that simultaneously covers front surfaces of both the imaging optical system and the illumination unit.   The imaging apparatus according to claim 12, wherein the imaging apparatus is configured as a capsule endoscope.

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