JP2009080410A - Optical system and endoscope using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact and inexpensive optical system that has both an optical path of an angle of view having a wide observation and an enlarging optical path and that can simultaneously pick up images through both optical paths on one imaging device with simple constitution without using a complicated mechanism such as a zoom mechanism, and to provide an endoscope using the same. <P>SOLUTION: A double focus optical system has a front group Gf, a rear group Gb having positive refractive power and an aperture S arranged between the front group Gf and the rear group Gb, is rotationally symmetric around a center axis 2, and forms an intermediate image on an image surface without forming it in the optical path. In the double optical system, the front group Gf has at least one double focus optical element Lf or Lb constituted in surface shape comprising two or more surfaces. The double focus optical device Lf or Lb images the images of different object points in the same direction on different areas on the same plane by action of the different rotationally symmetric surface shapes divided concentrically respectively to the optical paths A and B from at least two different object point distances. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical system and an endoscope using the same, and in particular, has two optical paths: an optical path for observing a distant object point with a wide angle of view and an optical path for magnifying and observing a nearby object point. The present invention relates to an imaging optical system or a projection optical system having a function of forming an image as an annular or circular image on one image sensor.

Conventionally, there have been Patent Document 1 and Patent Document 2 as double focus optical systems. Moreover, there exist patent document 3 and patent document 4 as an optical system which has two optical paths.
JP-A-8-320401 Japanese Patent Laid-Open No. 11-23809 US Patent Publication No. 2004-0254424 International Patent Publication No. 2003/042743

  However, none of the optical systems described in any of the patent documents has a small configuration and a wide-field optical path and an enlarged optical path.

  The present invention has been made in view of such a situation in the prior art, and its purpose is to provide both a wide observation field angle optical path and an enlarged optical path with a simple configuration without a complicated mechanism such as a zoom mechanism. It is an object to provide a small and inexpensive optical system capable of capturing both images of an optical system having the same image on a single image sensor and an endoscope using the same.

  An optical system of the present invention that achieves the above object has a front group, a rear group having a positive refractive power, and an aperture disposed between the front group and the rear group, and is arranged around a central axis. In the bifocal optical system that is rotationally symmetric and forms an image on the image plane without forming an intermediate image in the optical path, the front group includes at least a bifocal optical element configured with two or more surface shapes. And the bifocal optical element has different object points in the same direction by the action of different rotationally symmetric surface shapes that are concentrically divided with respect to optical paths from at least two different object point distances. Are formed in different regions on the same plane.

  The bifocal optical element has a peripheral optical path in a peripheral portion and a central optical path in a central portion.

  The field angle of the peripheral optical path is larger than the field angle of the central optical path.

  The peripheral optical path and the central optical path have a common opening.

  The peripheral optical path and the central optical path share at least one transmissive optical element in the rear group.

  Further, at least one surface of the bifocal optical element is a toric surface.

  Further, at least one surface of the bifocal optical element is formed of an extended rotation free-form surface formed by rotating an arbitrary-shaped line segment having no symmetry plane around the central axis. .

  Further, at least one surface of the bifocal optical element is constituted by an extended rotation free-form surface formed by rotating an arbitrary-shaped line segment including an odd-order term around the central axis.

  The peripheral optical path of the bifocal optical element includes a first transmission surface disposed around the central axis, and a first transmission surface disposed on the image plane side with respect to the first transmission surface and having a concave surface facing the image plane side. A reflective surface, a second reflective surface disposed on the opposite side of the image surface from the first reflective surface, with a concave surface facing the image surface side, and a second transmission surface disposed on the image surface side of the second reflective surface It is formed by these.

  Further, the peripheral optical path enters the bifocal optical element through the first transmission surface in the order of forward ray tracing, and is reflected by the first reflection surface to the side opposite to the image surface, and the second reflection surface. A substantially Z-shaped optical path which is reflected to the image plane side and goes out from the bifocal optical element to the image plane side through the second transmission surface.

  Further, at least a portion between the first reflecting surface and the second reflecting surface in the peripheral optical path is configured only on one side with respect to the central axis.

  The peripheral optical path is characterized in that an intermediate image is not formed in the optical path, but is formed in an annular shape on the image plane.

  In addition, the central optical path is constituted only by a transmission surface.

  The bifocal optical element has a third transmission surface in the vicinity of the central axis of the first transmission surface, and a light beam incident on the bifocal optical element is transmitted in the order of the third transmission in the order of forward ray tracing. A central optical path is formed which enters the bifocal optical element through a surface and exits from the bifocal optical element to the image plane side through the second transmission surface.

  Further, the bifocal optical element has a third transmission surface in the vicinity of the central axis of the second transmission surface, and a light beam incident on the bifocal optical element is the first transmission in the order of forward ray tracing. A central optical path is formed which enters the bifocal optical element through a surface and exits from the bifocal optical element to the image plane side through the third transmission surface.

  Further, a plurality of the bifocal optical elements are arranged in the front group and the rear group.

When the maximum image height is I, and the distance from the bifocal plane to the aperture when the bifocal plane of the bifocal element is on the object side is d1,
0.5 <d1 / I <3 (1)
It satisfies the following condition.

When the maximum image height is I, and the distance from the bifocal plane to the aperture when the bifocal plane of the bifocal element is on the image plane side is d2,
0.5 <d2 / I <5 (1)
It satisfies the following condition.

When the maximum image height is I and the outer diameter of the bifocal optical element is D,
1 <D / I <10 (3)
It satisfies the following condition.

  Furthermore, the present invention for achieving the above object is an endoscope using the optical system.

  In the optical system of the present invention described above, it is possible to obtain a small optical system with good resolving power with a well-corrected aberration capable of observing a wide angle of view or projecting an image at a wide angle of view with a simple configuration. it can.

  The optical system of the present invention will be described below based on examples.

  FIG. 3 is a cross-sectional view taken along the central axis (rotation symmetry axis) 2 of the optical system 1 of Example 1 described later. In the following description, the imaging optical system will be described. However, it can be used as a projection optical system with the optical path reversed.

  The optical system 1 according to the present invention is rotationally symmetric with respect to the central axis 2 and has a front group Gf, a rear group Gb having a positive refractive power, and an aperture S disposed between the front group Gf and the rear group Gb. And an optical system 1 that forms or projects an image without forming an intermediate image in the optical path. A parallel flat plate near the image plane 5 is a cover glass C of the image sensor.

  The optical system 1 according to the first embodiment includes a front group Gf, a rear group Gb having a positive refractive power, and an opening S disposed between the front group Gf and the rear group Gb. In the bifocal optical system which is rotationally symmetric and forms an image on the image plane 5 without forming an intermediate image in the optical path, the front group Gf is a bifocal optical element configured with two or more surface shapes The double-focus optical element Lf has at least one Lf, and the optical elements Lf are arranged in the same direction by the action of different rotationally symmetric surface shapes that are concentrically divided with respect to the optical path from at least two different object point distances. It is important to image different object points in different areas on the same plane. With such a configuration, it is possible to obtain a small optical system with a good resolving power in which aberrations are well corrected and which can observe a wide angle of view or project an image with a wide angle of view with a simple configuration.

  Further, it is desirable that the bifocal optical element Lf has a peripheral optical path A in the peripheral portion and a central optical path B in the central portion. Accordingly, it is possible to simultaneously observe the peripheral and central observation images with one image sensor. More preferably, the number of reflections of the central optical path and the peripheral optical path is preferably a combination of an even number of 0, 2, and 4. As a result, the relationship between the upper and lower sides and the left and right coincides with the rotation center axis in the two images. This facilitates the operation of the optical system.

  Further, it is important that the angle of view of the peripheral optical path A is larger than the angle of view of the central optical path B. By looking for a place you want to see in the surrounding wide-angle observation optical path and magnifying the necessary part with the central magnifying optical system, you will naturally bring the observation object to the center of the screen when you try to see it well. It becomes the operation.

  Further, it is desirable that the peripheral optical path A and the central optical path B have a common opening S. By sharing the aperture S, both optical paths can be made variable by making one aperture variable. In addition, it is possible to reduce the parallax between the two optical paths as compared with the case where the two optical paths are arranged in parallel.

  In addition, it is desirable that the peripheral optical path A and the central optical path B share at least one transmissive optical element in the rear group Gb. By sharing at least one transmission optical element, it is possible to configure with an optical element sharing the imaging action of both optical paths, and it is possible to configure the optical system in a small size.

  Moreover, it is desirable that at least one surface of the bifocal optical element Lf is a toric surface. By configuring with a toric surface, it is possible to arbitrarily set the curvature of the sagittal section and the meridional section because it is not subject to the restrictions imposed by a general spherical surface or aspherical surface where the intersection of the central axis 2 and the surface is orthogonal. At the same time, like the first reflecting surface 22 of the first embodiment, a surface shape that rotates around the Z axis can be defined as a line shape that opens in the positive direction of the Z axis, and the degree of freedom in design is dramatically increased.

  In addition, it is desirable that at least one surface of the bifocal optical element Lf is composed of an extended rotation free-form surface formed by rotating an arbitrarily shaped line segment having no symmetry plane around the central axis 2. By not having a symmetry plane, it is possible to correct distortion in the peripheral portion of the field angle of the peripheral optical path having a wide observation field angle.

  In addition, it is desirable that at least one surface of the bifocal optical element Lf is composed of an extended rotation free-form surface formed by rotating an arbitrary-shaped line segment including an odd-order term around the central axis 2. By this odd order term, it becomes possible to further correct the distortion of the peripheral portion of the screen of the peripheral optical path.

  The peripheral optical path A of the bifocal optical element Lf includes a first transmission surface 21 disposed around the central axis 2, and is disposed closer to the image surface 5 than the first transmission surface 21, and has a concave surface on the image surface 5 side. The first reflecting surface 22 facing the second reflecting surface 23, which is disposed on the opposite side of the image surface 5 from the first reflecting surface 22, and has a concave surface facing the image surface 5, and the image surface 5 from the second reflecting surface 23. And the second transmission surface 24 arranged on the side.

  Further, the peripheral optical path A enters the bifocal optical element Lf through the first transmission surface 21 in the order of forward ray tracing, and is reflected by the first reflection surface 22 on the side opposite to the image surface 5, and the second reflection surface. It is desirable to form a substantially Z-shaped optical path that is reflected to the image plane 5 side by 23 and exits to the image plane 5 side from the bifocal optical element Lf through the second transmission surface 24. By disposing the transmission surface closer to the object side than the first reflection surface 22, the first reflection surface 22 and the second reflection surface 23 can be configured as back mirrors, and the occurrence of decentration aberration can be reduced. . In addition, by forming a Z-shape, the two reflecting surfaces face each other, and the incident angle of the central ray at the center of the angle of view incident on each reflecting surface can be reduced, thereby reducing the occurrence of decentration aberrations. Is possible.

  Further, it is desirable that at least the optical path between the first reflecting surface 22 and the second reflecting surface 23 in the peripheral optical path A is configured on one side with respect to the central axis 2. This makes it difficult for surface interference with the central optical path B to occur, so that the viewing angle of view of the peripheral optical path A can be increased.

  In addition, it is desirable that the peripheral optical path A is formed in an annular shape on the image plane without forming an intermediate image in the optical path. When the intermediate image is formed, the degree of freedom such as the focal length of the optical system 1 increases, but the optical path length becomes long, which is not preferable when the very small optical system 1 is configured as in the present invention.

  Further, it is desirable that the central optical path B is composed only of a transmission surface. By configuring the central optical path only with the transmission surface, the bifocal optical element Lf can be made thin, and in particular, the small optical system 1 can be configured in the rotationally symmetric axis direction.

  The bifocal optical element Lf has a third transmission surface 26 in the vicinity of the central axis 2 of the first transmission surface 21, and the light beam incident on the bifocal optical element Lf is the third in the order of forward ray tracing. It is desirable to form a central optical path B that enters the bifocal optical element Lf through the transmission surface 26 and exits from the bifocal optical element Lf to the image plane 5 side through the second transmission surface 22. The peripheral light path A and the central optical path B can use the second transmission surface 22 in common.

  Further, the bifocal optical element Lf has a fourth transmission surface 27 in the vicinity of the central axis of the second transmission surface 24, and the light beam incident on the bifocal optical element Lf is the first light beam in the order of forward ray tracing. It is desirable to form a central optical path B that enters the bifocal optical element Lf through the transmission surface 21 and exits from the bifocal optical element Lf to the image plane 5 side through the fourth transmission surface 27. The first transmission surface 21 can be used in common for the peripheral optical path A and the central optical path B.

  In addition, it is desirable to place a plurality of the bifocal optical elements Lf and Lb in the front group Gf and the rear group Gb. By disposing the bifocal optical element Lf on the object side and the image side with the aperture S interposed therebetween, the degree of freedom of both the focal position and the principal point position of the peripheral optical path A can be obtained, which is preferable in terms of aberration correction.

When the maximum image height is I, and the distance from the bifocal plane to the aperture when the bifocal plane of the bifocal element is on the object side is d1,
0.5 <d1 / I <3 (1)
It is desirable to satisfy the following conditions.

  If the lower limit of the conditional expression (1) is exceeded, the distance from the aperture S to the bifocal optical element Lf becomes too short, and the central optical path B and the peripheral optical path A are not sufficiently separated. As a result, the viewing angle of view is not wide. If the upper limit is exceeded, the length of the entire optical system 1 in the direction of the central axis 2 becomes long. A small optical system 1 cannot be realized.

When the maximum image height is I, and the distance from the bifocal plane to the aperture when the bifocal plane of the bifocal element is on the image plane side is d2,
0.5 <d2 / I <5 (1)
It is desirable to satisfy the following conditions.

  If the lower limit of the conditional expression (2) is exceeded, the distance from the aperture S to the bifocal optical element Lf becomes too short, and the central optical path B and the peripheral optical path A are not sufficiently separated. As a result, the viewing angle of view is not wide. If the upper limit is exceeded, the length of the entire optical system 1 in the direction of the central axis 2 becomes long. A small optical system 1 cannot be realized.

When the maximum image height is I and the outer diameter of the bifocal optical element is D,
1 <D / I <10 (3)
It satisfies the following condition.

  If the lower limit of the conditional expression (3) is exceeded, the central optical path B and the peripheral optical path A are not sufficiently separated, and both light beams interfere with each other, resulting in a wide observation angle of view. If the upper limit is exceeded, the outer diameter of the optical system 1 becomes large, and the thin optical system 1 cannot be realized.

  Furthermore, the present invention for achieving the above object is an endoscope using the optical system.

  In addition, although all the examples are configured by spherical surfaces other than the ERFS surface, they may be configured by normal aspherical surfaces. The parallel plane on the object side is for protecting the optical system. There is no need. The parallel plane on the image side is for protecting the image sensor and may be omitted.

  Examples 1 to 4 of the optical system of the present invention will be described below. The configuration parameters of these optical systems will be described later.

  In forward ray tracing, for example, as shown in FIG. 1, the coordinate system uses the point where the stop and the central axis 2 intersect as the origin O of the decentered optical surface, and the direction orthogonal to the central axis 2 as the Y-axis direction. The YZ plane is the inside of the sheet. The direction on the image plane 5 side in FIG. 1 is the Z axis positive direction, and the Y axis, the Z axis, and the axis constituting the right-handed orthogonal coordinate system are the X axis positive direction.

  For the decentered surface, the decentering amount from the origin O of the optical system 1 of the coordinate system in which the surface is defined (X-axis direction, Y-axis direction, and Z-axis direction are X, Y, and Z, respectively), and the optical system 1 The inclination angles (α, β, γ (°), respectively) of the coordinate system defining the respective planes centered on the X axis, the Y axis, and the Z axis of the coordinate system defined by the origin O are given. . In this case, positive α and β mean counterclockwise rotation with respect to the positive direction of each axis, and positive γ means clockwise rotation with respect to the positive direction of the Z axis. Note that the α, β, and γ rotations of the central axis of the surface are performed by rotating the coordinate system defining each surface counterclockwise around the X axis of the coordinate system defined at the origin of the optical system. Then rotate it around the Y axis of the new rotated coordinate system by β and then rotate it around the Z axis of another rotated new coordinate system by γ. It is.

  Further, among the optical action surfaces constituting the optical system of each embodiment, when a specific surface and a subsequent surface constitute a coaxial optical system, a surface interval is given, in addition, the curvature radius of the surface, The refractive index and Abbe number of the medium are given according to conventional methods.

  In addition, a term relating to an aspheric surface for which no data is described in the constituent parameters described later is zero. The refractive index and the Abbe number are shown for the d-line (wavelength 587.56 nm). The unit of length is mm. As described above, the eccentricity of each surface is expressed by the amount of eccentricity from the reference surface.

The aspheric surface is a rotationally symmetric aspheric surface given by the following definition.
^{Z = (Y 2 / R)} / [1+ {1- (1 + k) Y 2 / R 2} 1/2]
+ AY ⁴ + bY ⁶ + cY ⁸ + dY ¹⁰ +...
... (a)
However, Z is taken as an axis, and Y is taken in a direction perpendicular to the axis. Here, R is a paraxial radius of curvature, k is a conic constant, a, b, c, d,... Are fourth-order, sixth-order, eighth-order, and tenth-order aspherical coefficients, respectively. The Z axis of this defining formula is the axis of a rotationally symmetric aspherical surface.

  The extended rotation free-form surface is a rotationally symmetric surface given by the following definition.

  First, as shown in FIG. 2, the following curve (b) passing through the origin on the YZ coordinate plane is determined.

^{Z = (Y 2 / RY)} / [1+ {1- (C 1 +1) Y 2 / RY 2} 1/2]
+ C ₂ Y + C ₃ Y ² + C ₄ Y ³ + C ₅ Y ⁴ + C ₆ Y ⁵ + C ₇ Y ⁶
+ ··· + C ₂₁ Y ²⁰ + ··· + C _{n + 1} Y ⁿ + ····
... (b)
Next, a curve F (Y) obtained by rotating the curve (b) in the positive direction of the X-axis and turning it counterclockwise to be positive is determined. This curve F (Y) also passes through the origin on the YZ coordinate plane.

  The curve F (Y) is translated in the Y positive direction by a distance R (Y negative direction if negative), and then the rotationally symmetric surface is rotated by rotating the translated curve around the Z axis. Let it be a free-form surface.

  As a result, the extended rotation free-form surface becomes a free-form surface (free-form curve) in the YZ plane and a circle with a radius | R | in the XY plane.

  From this definition, the Z-axis becomes the axis of the extended rotation free-form surface (rotation symmetry axis).

Where RY is the radius of curvature of the spherical term in the YZ section, C ₁ is the conic constant, C ₂ , C ₃ , C ₄ , C ₅ . Aspheric coefficient.

A conical surface having the Z axis as the central axis is given as one of the extended rotation free-form surfaces, and RY = ∞, C ₁ , C ₂ , C ₃ , C ₄ , C ₅ ,... = 0, and θ = ( The inclination angle of the conical surface), R = (the radius of the bottom surface in the XZ plane).

  In addition, a term relating to an aspheric surface for which no data is described in the constituent parameters described later is zero. The refractive index and the Abbe number are shown for the d-line (wavelength 587.56 nm). The unit of length is mm. As described above, the eccentricity of each surface is expressed by the amount of eccentricity from the reference surface.

  A cross-sectional view taken along the central axis 2 of the optical system 1 of Example 1 is shown in FIG. Further, FIG. 4 shows a lateral aberration diagram of the peripheral optical path of the entire optical system of this example, and FIG. 5 shows a lateral aberration diagram of the central optical path.

  In this embodiment, the transmission surface and the reflection surface of a transparent medium having a refractive index larger than 1 concentrically symmetric with respect to the central axis 2 of the optical system 1 are all configured as different surfaces without being used in common.

  The optical system 1 is arranged coaxially on the central axis 2 between the front group Gf and the rear group Gb, the front group Gf rotationally symmetric about the central axis 2, the rear group Gb rotationally symmetric about the central axis 2 The front group Gf is composed of the front first group Gf1 and the front second group Gf2.

  The front first group Gf1 is made of a front group cover glass Cf having a refractive index that is rotationally symmetric about the central axis 2 and greater than 1. The front group cover glass Cf is made of a parallel plate and has a front first group first transmission surface 11 and a front first group second transmission surface 12 formed on the image side with respect to the front first group first transmission surface 11. .

  The front second group Gf2 is composed of a front second group transparent medium Lf2 having a refractive index rotationally symmetric around the central axis 2 greater than 1. The front second group transparent medium Lf2 is formed on the image side with respect to the front second group peripheral first transmission surface 21 formed of a toric surface in the peripheral part away from the central axis, and the front second group peripheral first transmission surface 21 is reflected. The front 4 group peripheral first reflective surface 22 made of a toric surface and a front surface of the second group peripheral first reflective surface 22 disposed on the side opposite to the image surface 5, and the reflective coating 4 b is made of a toric surface. It has a front second group peripheral second reflecting surface 23 and a front second group peripheral second transmitting surface 24 that is disposed on the image plane 5 side of the front second group peripheral second reflecting surface 23 and is formed of a spherical surface. Further, it is disposed on the central axis so as to face the front group cover glass Cf, and is formed on the image side with respect to the front second group center first transmission surface 26 and the front second group center first transmission surface 26 which are spherical surfaces. And a front second group center second transmission surface 27 having a spherical surface and having a spherical surface.

  The rear group Gb includes a positive meniscus lens Lb1 having a convex surface directed to the image plane side whose rotational refractive index is larger than 1 around the central axis 2 and a rotationally symmetrical refractive index larger than 1 around the central axis 2. It consists of a convex positive lens Lb2 and a rear group cover glass Cb whose refractive index rotationally symmetric around the central axis 2 is greater than 1.

  The positive meniscus lens Lb1 includes a rear group first transmission surface 31 and a rear group second transmission surface 32 formed on the image side with respect to the rear group first transmission surface 31. The biconvex positive lens Lb2 includes a rear group third transmission surface 41 and a rear group fourth transmission surface 42 formed on the image side with respect to the rear group third transmission surface 41. The rear group cover glass Cb is made of a parallel plate and includes a rear group fifth transmission surface 51 and a rear group sixth transmission surface 52 formed on the image side with respect to the rear group fifth transmission surface 51.

  The optical system 1 forms a peripheral optical path A and a central optical path B.

  In the peripheral optical path A, the light beam incident from the object surface 3 of the optical system 1 passes through the front first group first transmission surface 11 and the front first group second transmission surface 12 of the front group cover glass Cf, and the front second group transparent medium Lf2. Get inside. In the front second group transparent medium Lf2, the light enters through the front second group peripheral first transmission surface 21, partly by the reflective coating 4a and part by total reflection, opposite the image surface 5 by the front second group peripheral first reflection surface 22 Approximately Z which is reflected to the side, reflected from the front second group peripheral second reflecting surface 23 to the image surface 5 side by the reflective coating 4b, and exits from the front second group transparent medium Lf2 through the front second group peripheral second transmitting surface 24. It has a letter-shaped optical path. Then, it enters the rear group Gb through the opening S arranged coaxially with the central axis 2 between the front group Gf and the rear group Gb. In the rear group Gb, the light enters the positive meniscus lens Lb1 through the rear group first transmission surface 31, exits from the rear group second transmission surface 32, and enters the biconvex positive lens Lb2 through the rear group third transmission surface 41. Then, it exits from the rear group fourth transmission surface 42, enters the rear group cover glass Cb through the rear group fifth transmission surface 51, exits from the rear group sixth transmission surface 52, and is the central axis of the image plane 5 An image is formed in an annular shape at a predetermined position in the radial direction deviating from 2.

  In the central optical path B, the light enters the front second group transparent medium Lf2 through the front first group first transmission surface 11 and the front first group second transmission surface 12 of the front group cover glass Cf. The front second group transparent medium Lf2 enters through the front second group central first transmission surface 26 and exits from the front second group transparent medium Lf2 through the front second group central second transmission surface 27. Then, it enters the rear group Gb through the opening S arranged coaxially with the central axis 2 between the front group Gf and the rear group Gb. In the rear group Gb, the light enters the positive meniscus lens Lb1 through the rear group first transmission surface 31, exits from the rear group second transmission surface 32, and enters the biconvex positive lens Lb2 through the rear group third transmission surface 41. Then, it exits from the rear group fourth transmission surface 42, enters the rear group cover glass Cb through the rear group fifth transmission surface 51, exits from the rear group sixth transmission surface 52, and is the central axis of the image plane 5 2 is imaged.

The specification of this Example 1 is
Angle of view Ambient light path A 0.00 ° to 50.0 °
Central optical path B 0.00 ° ～ 5.00 °
Diaphragm diameter φ0.20mm
Image size Ambient light path A φ1.12 to φ1.90
Central optical path B φ0.94
It is.

  A sectional view taken along the central axis 2 of the optical system 1 of Example 2 is shown in FIG. Further, FIG. 7 shows a lateral aberration diagram of the peripheral optical path of the entire optical system of this example, and FIG. 8 shows a lateral aberration diagram of the central optical path.

  The optical system 1 is arranged coaxially on the central axis 2 between the front group Gf and the rear group Gb, the front group Gf rotationally symmetric about the central axis 2, the rear group Gb rotationally symmetric about the central axis 2 The front group Gf is composed of the front first group Gf1 and the front second group Gf2.

  The front first group Gf1 is made of a front group cover glass Cf having a refractive index that is rotationally symmetric about the central axis 2 and greater than 1. The front group cover glass Cf is made of a parallel plate and has a front first group first transmission surface 11 and a front first group second transmission surface 12 formed on the image side with respect to the front first group first transmission surface 11. .

  The front second group Gf2 is composed of a front second group transparent medium Lf2 having a refractive index rotationally symmetric around the central axis 2 greater than 1. The front second group transparent medium Lf2 is formed on the image side with respect to the front second group peripheral first transmission surface 21 formed of an extended rotation free surface at the peripheral part away from the central axis, and the front second group peripheral first transmission surface 21. The front second group peripheral second transmission surface 24 is a flat surface.

  Further, it is disposed on the central axis so as to face the front group cover glass Cf, and is formed on the image side with respect to the front second group center first transmission surface 26 and the front second group center first transmission surface 26 which are flat surfaces. The front second group center second transmitting surface 27 is further provided.

  The rear group Gb includes a plano-convex positive lens Lb1 having a convex surface directed toward the image plane whose rotational refractive index is greater than 1 around the central axis 2, and a rotationally symmetrical refractive index greater than 1 around the central axis 2. The rear group transparent medium Lb2 and the rear group cover glass Cb whose refractive index rotationally symmetric around the central axis 2 is larger than 1.

  The plano-convex positive lens Lb1 includes a rear group first transmission surface 31 and a rear group second transmission surface 32 formed on the image side with respect to the rear group first transmission surface 31.

  The rear group transparent medium Lb2 includes a rear group peripheral third transmission surface 41 formed of an extended rotation free-form surface, and a rear group peripheral fourth transmission surface 42 formed on the image side with respect to the rear group peripheral third transmission surface 41 and formed of a plane. And have. Further, the rear group center fourth transmission surface 47 formed on the image side with respect to the rear group center third transmission surface 46 and the rear group center third transmission surface 46 formed of a spherical surface on the central axis, and formed of a plane on the central axis. It has further.

  The rear group cover glass Cb is made of a parallel plate and includes a rear group fifth transmission surface 51 and a rear group sixth transmission surface 52 formed on the image side with respect to the rear group fifth transmission surface 51.

  The optical system 1 forms a peripheral optical path A and a central optical path B.

  In the peripheral optical path A, the light beam incident from the object surface 3 of the optical system 1 passes through the front first group first transmission surface 11 and the front first group second transmission surface 12 of the front group cover glass Cf, and the front second group transparent medium Lf2. Get inside. The front second group transparent medium Lf2 enters through the front second group peripheral first transmission surface 21 and exits from the front second group transparent medium Lf2 through the front second group peripheral second transmission surface 24. Then, it enters the rear group Gb through the opening S arranged coaxially with the central axis 2 between the front group Gf and the rear group Gb. In the rear group Gb, the planoconvex positive lens Lb1 enters through the rear group first transmission surface 31, exits from the rear group second transmission surface 32, and the rear group peripheral third transmission surface 41 is formed on the rear group transparent medium Lb2. After entering, exiting from the rear group peripheral fourth transmission surface 42, entering the rear group cover glass Cb through the rear group fifth transmission surface 51, exiting from the rear group sixth transmission surface 52, and image surface 5 An image is formed in an annular shape at a predetermined position in the radial direction deviating from the central axis 2.

  In the central optical path B, the light enters the front second group transparent medium Lf2 through the front first group first transmission surface 11 and the front first group second transmission surface 12 of the front group cover glass Cf. The front second group transparent medium Lf2 enters through the front second group central first transmission surface 26 and exits from the front second group transparent medium Lf2 through the front second group central second transmission surface 27. Then, it enters the rear group Gb through the opening S arranged coaxially with the central axis 2 between the front group Gf and the rear group Gb. In the rear group Gb, the planoconvex positive lens Lb1 enters through the rear group first transmission surface 31, exits from the rear group second transmission surface 32, and the rear group center third transmission surface 46 is formed on the rear group transparent medium Lb2. After entering, exits from the rear group center fourth transmission surface 47, enters the rear group cover glass Cb through the rear group fifth transmission surface 51, exits from the rear group sixth transmission surface 52, and enters the image plane 5. The image is formed on the central axis 2 of.

The specification of Example 2 is
Angle of view Ambient light path A 3.44 ° ～ 50.23 °
Central optical path B 0.00 ° ～ 10.91 °
Diaphragm diameter φ0.20mm
Image size Ambient light path A φ0.98 to φ1.96
Center optical path B φ0.77
It is.

  A sectional view taken along the central axis 2 of the optical system 1 of Example 3 is shown in FIG. Further, FIG. 10 shows a lateral aberration diagram of the peripheral optical path of the entire optical system of this example, and FIG. 11 shows a lateral aberration diagram of the central optical path.

  The optical system 1 is arranged coaxially on the central axis 2 between the front group Gf and the rear group Gb, and the front group Gf rotationally symmetric about the central axis 2, the rear group Gb rotationally symmetric about the central axis 2. The front group Gf is composed of the front first group Gf1 and the front second group Gf2.

  The front first group Gf1 is made of a front group cover glass Cf having a refractive index that is rotationally symmetric about the central axis 2 and greater than 1. The front group cover glass Cf is made of a parallel plate and has a front first group first transmission surface 11 and a front first group second transmission surface 12 formed on the image side with respect to the front first group first transmission surface 11. .

  The front second group Gf2 is composed of a front second group transparent medium Lf2 having a refractive index rotationally symmetric around the central axis 2 greater than 1. The front second group transparent medium Lf2 is formed on the image side with respect to the front second group peripheral first transmission surface 21 formed of an extended rotation free-form surface at the peripheral part away from the central axis, and the front second group peripheral first transmission surface 21. The front second group peripheral second transmission surface 24 is a flat surface.

  Further, it is disposed on the central axis so as to face the front group cover glass Cf, and is formed on the image side with respect to the front second group center first transmission surface 26 and the front second group center first transmission surface 26 which are spherical surfaces. The front second group center second transmitting surface 27 is further provided.

  The rear group Gb includes a plano-convex positive lens Lb1 having a convex surface directed toward the image plane whose rotational refractive index is greater than 1 around the central axis 2, and a rotationally symmetrical refractive index greater than 1 around the central axis 2. The rear group transparent medium Lb2 and the rear group cover glass Cb whose refractive index rotationally symmetric around the central axis 2 is larger than 1.

  The plano-convex positive lens Lb1 includes a rear group first transmission surface 31 and a rear group second transmission surface 32 formed on the image side with respect to the rear group first transmission surface 31.

  The rear group transparent medium Lb2 includes a rear group peripheral third transmission surface 41 that is a flat surface, and a rear group peripheral fourth transmission surface 42 that is formed on the image side with respect to the rear group peripheral third transmission surface 41 and includes an extended rotation free-form surface. And have. Further, a rear group center fourth transmission surface 47 formed on the image side with respect to the rear group center third transmission surface 46 and the rear group center third transmission surface 46 formed of a plane on the central axis, and formed of a spherical surface on the central axis. It has further.

  The rear group cover glass Cb is made of a parallel plate and includes a rear group fifth transmission surface 51 and a rear group sixth transmission surface 52 formed on the image side with respect to the rear group fifth transmission surface 51.

  The optical system 1 forms a peripheral optical path A and a central optical path B.

  In the peripheral optical path A, the light beam incident from the object plane 3 of the optical system 1 passes through the front first group first transmission surface 11 and the front first group second transmission surface 12 of the front group cover glass Cf, and the front second group transparent medium Lf2. Get inside. The front second group transparent medium Lf2 enters through the front second group peripheral first transmission surface 21 and exits from the front second group transparent medium Lf2 through the front second group peripheral second transmission surface 24. Then, it enters the rear group Gb through the opening S arranged coaxially with the central axis 2 between the front group Gf and the rear group Gb. In the rear group Gb, the planoconvex positive lens Lb1 enters through the rear group first transmission surface 31, exits from the rear group second transmission surface 32, and the rear group peripheral third transmission surface 41 is formed on the rear group transparent medium Lb2. After entering, exiting from the rear group peripheral fourth transmission surface 42, entering the rear group cover glass Cb through the rear group fifth transmission surface 51, exiting from the rear group sixth transmission surface 52, and image surface 5 An image is formed in an annular shape at a predetermined position in the radial direction deviating from the central axis 2.

  In the central optical path B, the light enters the front second group transparent medium Lf2 through the front first group first transmission surface 11 and the front first group second transmission surface 12 of the front group cover glass Cf. The front second group transparent medium Lf2 enters through the front second group central first transmission surface 26 and exits from the front second group transparent medium Lf2 through the front second group central second transmission surface 27. Then, it enters the rear group Gb through the opening S arranged coaxially with the central axis 2 between the front group Gf and the rear group Gb. In the rear group Gb, the planoconvex positive lens Lb1 enters through the rear group first transmission surface 31, exits from the rear group second transmission surface 32, and the rear group center third transmission surface 46 is formed on the rear group transparent medium Lb2. After entering, exits from the rear group center fourth transmission surface 47, enters the rear group cover glass Cb through the rear group fifth transmission surface 51, exits from the rear group sixth transmission surface 52, and enters the image plane 5. The image is formed on the central axis 2 of.

The specification of this Example 3 is
Angle of view Ambient light path A 7.06 ° to 52.3 °
Central optical path B 0.00 ° ～ 9.35 °
Diaphragm diameter φ0.20mm
Image size Ambient light path A φ0.99 to φ1.89
Center optical path B φ0.79
It is.

Also, the maximum image height is I (mm), the distance d1 (mm) from the bifocal plane to the aperture when the bifocal plane of the bifocal element is on the object side, the bifocal plane of the bifocal element Is the distance d2 (mm) from the bifocal plane to the aperture when D is on the image side, and the outer diameter of the bifocal element is D (mm),
Example 1 Example 2 Example 3
I 0.95 0.98 0.95
d1 3.95 3.20 4.60
d2 3.20 4.40
D (φ) 6.30 3.40 3.50
d1 / I 0.95 0.98 0.95
d2 / I 3.27 4.86
D / I 6.64 3.47 3.70
It is.

  The configuration parameters of Examples 1 to 3 are shown below. In the table below, “RE” indicates a reflecting surface.

Example 1
Ambient optical path number Curvature radius Surface spacing Eccentricity Refractive index Abbe number Object surface ∞ 6.70
1 ∞ 0.50 1.5163 64.1
2 ∞ 0.05
3 ERFS [1] 0.00 Eccentricity (1) 1.8348 42.7
4 (RE) ERFS [2] 0.00 Eccentricity (2) 1.8348 42.7
5 (RE) ERFS [3] 0.00 Eccentricity (3) 1.8348 42.7
6 63.69 3.97 Eccentricity (4)
7 ∞ (Aperture) 0.82
8 -5.75 0.60 1.7292 54.7
9 -1.58 0.10
10 3.86 1.00 1.8830 40.7
11 -13.93 0.87
12 ∞ 0.40 1.5163 64.1
13 ∞ 0.10
Image plane ∞
ERFS [1]
RY 1.46
θ -70.69
R 3.04
ERFS [2]
RY 0.98
θ -7.87
R 2.55
ERFS [3]
RY 4.05
θ 7.00
R 1.91
Eccentric [1]
X 0.00 Y 0.00 Z -3.33
α 0.00 β 0.00 γ 0.00
Eccentric [2]
X 0.00 Y 0.00 Z -2.86
α 0.00 β 0.00 γ 0.00
Eccentric [3]
X 0.00 Y 0.00 Z -3.97
α 0.00 β 0.00 γ 0.00
Eccentric [4]
X 0.00 Y 0.00 Z -2.87
α 0.00 β 0.00 γ 0.00
Central optical path number of curvature radius Surface spacing Eccentricity Refractive index Abbe number Object surface ∞ 6.70
1 ∞ 0.50 1.5163 64.1
2 ∞ 0.05
3 4.05 1.09 1.8348 42.7
4 63.69 2.88
5 ∞ (Aperture) 0.82
6 -5.75 0.60 1.7292 54.7
7 -1.58 0.10
8 3.86 1.00 1.8830 40.7
9 -13.93 0.87
10 ∞ 0.40 1.5163 64.1
11 ∞ 0.10
Image plane ∞

Example 2
Ambient optical path number Curvature radius Surface spacing Eccentricity Refractive index Abbe number Object surface ∞ 6.70
1 ∞ 0.50 1.5163 64.1
2 ∞ 0.05
3 ∞ 0.00 1.8348 42.7
4 ERFS [1] 2.09 Eccentricity (1)
5 ∞ (Aperture) 0.10
6 ∞ 0.50 1.8348 42.7
7 -1.43 1.06
8 ERFS [2] 0.50 Eccentricity (2) 1.8348 42.7
12 ∞ 0.10
13 ∞ 0.40 1.5163 64.1
14 ∞ 0.00
Image plane ∞
ERFS [1]
RY 1.77
θ 4.09
R 0.88
C4 -1.1914E-01
ERFS [2]
RY 1.60
θ 16.77
R -0.62
C4 1.4142E-01
Eccentric [1]
X 0.00 Y 0.00 Z -1.69
α 0.00 β 0.00 γ 0.00
Eccentric [2]
X 0.00 Y 0.00 Z 1.73
α 0.00 β 0.00 γ 0.00
Central optical path number of curvature radius Surface spacing Eccentricity Refractive index Abbe number Object surface ∞ 4.10
1 ∞ 0.50 1.5163 64.1
2 ∞ 0.05
3 ∞ 0.50 1.8348 42.7
4 -5.47 1.59
5 ∞ (Aperture) 0.10
6 ∞ 0.50 1.8348 42.7
7 -1.43 1.06
8 3.04 0.50 1.8348 42.7
9 ∞ 0.10
10 ∞ 0.40 1.5163 64.1
11 ∞ 0.00
Image plane ∞

Example 3
Ambient optical path number Curvature radius Surface spacing Eccentricity Refractive index Abbe number Object surface ∞ 6.70
1 ∞ 0.50 1.5163 64.1
2 ∞ 0.05
3 ERFS [1] 0.30 Eccentricity (1) 1.8348 42.7
4 ∞ 2.00
5 ∞ (Aperture) 0.10
6 ∞ 0.40 1.8348 42.7
7 -1.44 1.00
8 ∞ 0.70 1.8348 42.7
8 ERFS [2] 0.03 Eccentricity (2)
9 ∞ 0.40 1.5163 64.1
10 ∞ 0.00
Image plane ∞
ERFS [1]
RY -1.75
θ 2.71
R 1.08
C4 2.0639E-01
ERFS [2]
RY -3.60
θ -19.25
R -0.67
C4 -4.9770E-01
Eccentric [1]
X 0.00 Y 0.00 Z -2.20
α 0.00 β 0.00 γ 0.00
Eccentric [2]
X 0.00 Y 0.00 Z 2.10
α 0.00 β 0.00 γ 0.00
Central optical path number of curvature radius Surface spacing Eccentricity Refractive index Abbe number Object surface ∞ 4.10
1 ∞ 0.50 1.5163 64.1
2 ∞ 0.05
3 4.72 0.30 1.8348 42.7
4 ∞ 2.00
5 ∞ (Aperture) 0.10
6 ∞ 0.40 1.8348 42.7
7 -1.44 1.00
8 ∞ 0.70 1.8348 42.7
9 -1.65 0.03
10 ∞ 0.40 1.5163 64.1
11 ∞ 0.00
Image plane ∞

  FIG. 12 shows an arrangement example of the image and the image sensor of the present embodiment. FIG. 12A shows an example in which an image sensor with a screen ratio of 16: 9 is used. When an image in the vertical direction is not used, it is preferable to match the size of the image sensor 50 with the left and right positions of the image A1 in the peripheral light path A. FIG. 12B is an example in which the image sensor 50 having a screen ratio of 4: 3 is used, and the size of the image sensor 50 is matched with the image B1 in the central optical path B, which is the same as FIG. Shows the case where the image in the vertical direction is not used. FIG. 12C illustrates an example in which the image sensor 50 having a screen ratio of 4: 3 is used, and the size of the image sensor 50 is matched with the image A1 in the peripheral optical path A. Thus, when arranged, both the image A1 of the peripheral optical path A and the image B1 of the central optical path B can be captured.

  Hereinafter, as an application example of the optical system 1 of the present invention, a usage example of the photographing optical system 101 or the projection optical system 102 will be described. FIG. 13 is a diagram for illustrating an example in which the photographing optical system 101 according to the present invention is used as the photographing optical system at the distal end of the endoscope, and FIG. 13A illustrates the present invention at the distal end 101 of the rigid endoscope 110. This is an example in which an imaging optical system is attached and an image is taken and observed. FIG. 13B shows a schematic configuration of the tip. A flare stop 107 made of a casing or the like having an opening 106 extending in the circumferential direction is disposed around the entrance surface 11 of the panoramic imaging optical system 101 according to the present invention to prevent the flare light from entering. FIG. 13C shows a panoramic imaging optical system 101 according to the present invention attached to the tip of the flexible electronic endoscope 113 in the same manner, and the image captured on the display device 114 is subjected to image processing to correct distortion. This is an example of displaying.

  FIG. 14 shows an example in which the photographing optical system 101 according to the present invention is attached to the capsule endoscope 120 and images of 360 ° omnidirectional images are taken and observed. A flare stop 107 is formed in a casing having an opening 106 extending in the circumferential direction around the first transmission surface 11 of the front group Gf in the peripheral optical path A of the photographing optical system 101 according to the present invention, and flare light is incident thereon. Is preventing.

  FIG. 15 (a) shows an image obtained by attaching a photographic optical system 101 according to the present invention as a photographic optical system in front of an automobile 130, and performing image processing on an image photographed through each photographic optical system 101 on a display device in a vehicle. FIG. 15B is a diagram showing an example in which distortion is corrected and simultaneously displayed, and FIG. 15B shows a photographing optical system 101 according to the present invention as a photographing optical system at each corner of the automobile 130 and the top of the pole of the head portion. It is a figure which shows the example which attached the plurality and displayed the image image | photographed through each imaging | photography optical system 101 on the display apparatus in a vehicle, performing image processing and correct | amending distortion simultaneously. In this case, as shown in FIG. 15A, it is preferable to match the size of the image sensor 50 to the left and right positions of the image A1 in the peripheral light path A, because the left and right images can be captured widely.

  16 uses the projection optical system 102 according to the present invention as the projection optical system of the projection apparatus 140, displays a panoramic image on a display element arranged on the image plane 5, and 360 ° in all directions through the projection optical system 102. This is an example in which a 360 ° omnidirectional image is projected and displayed on the arranged screen 141.

  Further, FIG. 17 shows that the photographing apparatus 151 using the photographing optical system 101 according to the present invention is attached to the outside of the building 150, and the projection apparatus 151 using the photographing optical system 101 according to the present invention is disposed indoors. It connects so that the imaged image may be sent to the projection device 140 via the electric wire 152. In such an arrangement, an outdoor 360 ° omnidirectional subject P is photographed by the photographing device 151 via the photographing optical system 101, and the video signal is sent to the projection device 140 via the electric wire 152 and disposed on the image plane. In this example, the image is displayed on the display element, and the image P ′ of the subject P is projected and displayed on an indoor wall surface or the like through the projection optical system 102.

It is a figure for demonstrating the coordinate system of the optical system of this invention. It is a figure which shows the principle of an extended rotation free-form surface. It is sectional drawing taken along the central axis of the optical system of Example 1 of this invention. 3 is a lateral aberration diagram of a peripheral optical path of the entire optical system of Example 1. FIG. FIG. 3 is a diagram illustrating a lateral aberration diagram of the central optical path of the entire optical system of Example 1. It is sectional drawing taken along the central axis of the optical system of Example 2 of this invention. 6 is a lateral aberration diagram of a peripheral optical path of the entire optical system of Example 2. FIG. 6 is a lateral aberration diagram of the central optical path of the entire optical system of Example 2. FIG. It is sectional drawing taken along the central axis of the optical system of Example 3 of this invention. 10 is a lateral aberration diagram of the peripheral optical path of the whole optical system of Example 3. FIG. 10 is a lateral aberration diagram of the central optical path of the entire optical system of Example 3. FIG. It is a figure which shows the example of arrangement | positioning of the image of the optical system of this invention, and an image pick-up element. It is a figure which shows the example which used the optical system of this invention as an imaging | photography optical system of the endoscope front-end | tip. It is a figure which shows the example which used the optical system of this invention as the imaging | photography optical system of a capsule endoscope. It is a figure which shows the example which used the optical system of this invention as the imaging | photography optical system of a motor vehicle. It is a figure which shows the example which used the optical system of this invention as a projection optical system of a projection apparatus. It is a figure which shows the example which used the optical system of this invention as an imaging | photography optical system which image | photographs the outdoor to-be-photographed object.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical system 2 ... Center axis 3 ... Object surface 5 ... Image surface

Claims (20)

  A front group, a rear group having a positive refractive power, and an aperture disposed between the front group and the rear group, and rotationally symmetric about a central axis, to form an intermediate image in the optical path; In the bifocal optical system that forms an image on the image plane, the front group includes at least one bifocal optical element configured with two or more surface shapes, and the bifocal optical element includes: , Imaging different object points in the same direction in different regions on the same plane by the action of different rotationally symmetric surface shapes that are concentrically divided with respect to the optical path from at least two different object point distances. An optical system characterized by   The optical system according to claim 1, wherein the bifocal optical element includes a peripheral optical path in a peripheral portion and a central optical path in a central portion.   The optical system according to claim 2, wherein an angle of view of the peripheral optical path is larger than an angle of view of the central optical path.   The optical system according to claim 2, wherein the peripheral optical path and the central optical path have a common aperture.   5. The optical system according to claim 2, wherein the peripheral optical path and the central optical path share at least one transmission optical element in the rear group.   6. The optical system according to claim 1, wherein at least one surface of the bifocal optical element is a toric surface.   The at least one surface of the bifocal optical element is formed of an extended rotation free-form surface formed by rotating an arbitrary-shaped line segment having no symmetry plane around a central axis. The optical system according to any one of claims 1 to 5.   The at least one surface of the bifocal optical element is formed of an extended rotation free-form surface formed by rotating an arbitrary-shaped line segment including an odd-order term around a central axis. The optical system according to claim 5.   The peripheral optical path of the bifocal optical element includes a first transmission surface disposed around the central axis, and a first reflection surface disposed on the image plane side with respect to the first transmission surface, with the concave surface facing the image plane side. A second reflecting surface that is disposed on the opposite side of the image surface from the first reflecting surface and has a concave surface facing the image surface, and a second transmitting surface that is disposed on the image surface side from the second reflecting surface; 9. The optical system according to claim 2, wherein the optical system is formed by:   The peripheral optical path enters the bifocal optical element through the first transmission surface in the order of forward ray tracing, is reflected to the opposite side of the image surface by the first reflection surface, and is imaged by the second reflection surface. 10. A substantially Z-shaped optical path which is reflected on the surface side and goes out from the bifocal optical element to the image surface side through the second transmission surface is formed. An optical system according to the above.   The optical path between at least the first reflecting surface and the second reflecting surface of the peripheral optical path is configured only on one side with respect to the central axis. The optical system described.   The optical system according to claim 2, wherein the peripheral optical path is formed in an annular shape on an image plane without forming an intermediate image in the optical path.   The optical system according to any one of claims 2 to 12, wherein the central optical path includes only a transmission surface.   The bifocal optical element has a third transmission surface in the vicinity of the central axis of the first transmission surface, and a light beam incident on the bifocal optical element passes through the third transmission surface in the order of forward ray tracing. 14. A central optical path that passes through the bifocal optical element through the second transmission surface and exits from the bifocal optical element to the image plane side is formed. Any one of the optical systems.   The bifocal optical element has a third transmission surface in the vicinity of the central axis of the second transmission surface, and a light beam incident on the bifocal optical element passes through the first transmission surface in the order of forward ray tracing. 14. A central optical path that passes through the bifocal optical element through the third transmission surface and exits from the bifocal optical element to the image plane side is formed. Any one of the optical systems.   The optical system according to any one of claims 1 to 15, wherein a plurality of the bifocal optical elements are arranged in the front group and the rear group. When the maximum image height is I, and the distance from the bifocal plane to the aperture when the bifocal plane of the bifocal element is on the object side is d1,
0.5 <d1 / I <3 (1)
The optical system according to claim 1, wherein the following condition is satisfied. When the maximum image height is I, and the distance from the bifocal plane to the aperture when the bifocal plane of the bifocal element is on the image plane side is d2,
0.5 <d2 / I <5 (1)
The optical system according to claim 1, wherein the following condition is satisfied. When the maximum image height is I and the outer diameter of the bifocal optical element is D,
1 <D / I <10 (3)
The optical system according to claim 1, wherein the following condition is satisfied.   An endoscope using the optical system according to any one of claims 1 to 19.

Images