JPH1068887A - Prism optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a prism optical system having an image-forming function and bringing a clear image with less distortion even in an wide angle of view. SOLUTION: This optical system has an aperture 1 and is constituted so as to have a function of erecting an image formed by an objective. In this case, this optical system 5 is provided with reflection planes 31, 32, 33, 34, 41, 42, and 43, which are formed into curved surfaces with powers, and the forms of the curved surfaces are constituted of those of irrotational symmetry surface forms without rotational symmetry axes both in and out of the surfaces.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a prism optical system, and more particularly to a prism optical system having power constituted by eccentrically arranged reflecting surfaces.

[0002]

2. Description of the Related Art Conventionally, as a well-known compact decentering optical system, Japanese Patent Application Laid-Open No. Sho 59-84201 discloses a one-dimensional light receiving lens having a cylindrical reflecting surface.
Two-dimensional imaging is not possible. Also, Japanese Patent Application Laid-Open No. Sho 62-1441
No. 27 uses the same cylindrical surface for twice reflection in order to reduce the spherical aberration of the above invention.

Japanese Patent Application Laid-Open No. Sho 62-205547 discloses that an aspherical reflection is used as the shape of the reflecting surface, but does not mention the shape of the reflecting surface. Further, U.S. Pat. No. 3,810,221 and U.S. Pat.
No. 6,931 each show an example in which a finder optical system of a reflex camera uses a lens system having a rotationally symmetric aspherical mirror and a surface having only one plane of symmetry. However, a plane having only one plane of symmetry is used for correcting the inclination of the observed virtual image.

[0004] Japanese Patent Application Laid-Open No. 1-257834 (US Pat. No. 5,274,406) discloses a rear projection television in which a plane having only one plane of symmetry is used to correct image distortion. Although an example in which the present invention is used for a reflecting mirror is shown, a projection lens system is used for projection onto a screen, and a plane having only one plane of symmetry is used for correcting image distortion.

Japanese Patent Application Laid-Open No. 7-333551 discloses an example of a back-mirror type decentered optical system using an anamorphic surface and a toric surface as an observation optical system.
However, the correction of aberrations including image distortion is insufficient and cannot be used for an imaging optical system.

[0006] None of the above-mentioned prior arts uses a surface having only one symmetrical surface, and does not use a backside mirror in the folded optical path.

[0007]

However, in these prior arts, the refracting lens constituting the optical system is a rotationally symmetric optical system constituted by a rotationally symmetric surface about the optical axis.

If the aberration of the formed real image is corrected well and the distortion is not corrected properly, the formed figure or the like will be distorted, and the correct shape may be recorded. I can no longer do it. Further, since the optical path is straight, the entire optical system becomes longer in the optical axis direction, and there is a problem that the imaging device becomes large.

The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to provide a prism optical system which has an image forming function and provides a clear and less distorted image even at a wide angle of view. It is to provide.

[0010]

According to a first aspect of the present invention, there is provided a prism optical system which has an opening and has an effect of erecting an image formed by an objective lens. Has a reflecting surface for image erecting, and the reflecting surface is formed by a curved surface having power, and the shape of the curved surface corrects an eccentric aberration caused by reflection on the curved surface. It is characterized in that it has a non-rotationally symmetric surface shape having no rotation symmetry axis both inside and outside.

In this case, it is desirable that the non-rotationally symmetric surface shape has only one symmetry plane and has a free-form surface shape defined by the following equation. _{Z = C 2 + C 3 y} + C 4 x + C 5 y 2 + C 6 yx + C 7 x 2 + C 8 y 3 + C 9 y 2 x + C 10 yx 2 + C 11 x 3 + C 12 y 4 + C 13 y 3 x + C 14 y 2 x 2 + C ^{_{15 yx 3 + C 16 x 4}} + C 17 y 5 + C 18 y 4 x + C 19 y 3 x 2 + C 20 y 2 x 3 + C 21 yx 4 + C 22 x 5 + C 23 y 6 + C 24 y 5 x + C 25 y 4 x 2 + C ^{_{26 y 3 x 3 + C 27}} y 2 x 4 + C 28 yx 5 + C 29 x 6 + C 30 y 7 + C 31 y 6 x + C 32 y 5 x 2 + C 33 y 4 x 3 + C 34 y 3 x 4 + C 35 y 2 x ^{_{5 + C 36 yx 6 + C}} 37 x 7 ····· ···· (a) provided that, C _m (m is an integer of 2 or more) is a coefficient.

Another prism optical system according to the present invention is a prism optical system having a reflecting surface for inverting an image, wherein the reflecting surface has a different incident light path and an outgoing light path of a light beam, and is thereby non-rotationally symmetric. Is disposed in the prism optical system so that a large eccentric aberration occurs, and at least one of the reflecting surfaces or other reflecting surfaces or transmitting surfaces can correct the non-rotationally symmetric eccentric aberration. It has a non-rotationally symmetric shape.

In this case, it is desirable that the prism optical system be provided with four or more reflecting surfaces and two or more transmitting surfaces.

Still another prism optical system according to the present invention is a prism optical system having an roof and a roof prism formed of a curved surface, wherein the curved surface does not have a rotationally symmetric axis both in-plane and out-of-plane. It has at least one non-rotationally symmetric surface.

Still another prism optical system according to the present invention is a prism optical system having an aperture and a Porro prism formed of a curved surface, wherein the curved surface has no rotationally symmetric axis both in-plane and out-of-plane. It is characterized by having at least one symmetric surface.

In the following, the reason why the above configuration is adopted in the present invention and the operation thereof will be described. In general, roof prisms and porro prisms known as inverted prisms have no power because they are constituted by plane reflecting mirrors. For example, binoculars, ground telescopes, and the like arrange an inverted prism between an objective lens and an eyepiece lens to rectify an inverted image formed by the objective lens.

Therefore, the objective lens is omitted by imposing the image forming action of the objective lens on the inverted prism.
The configuration can be simplified. For example, the prism entrance surface and exit surface can be configured as spherical surfaces, so that the prism has power.

However, in this method, if the F-number is to be reduced, the positive power of the incident surface and the exit surface must be increased, and aberrations such as chromatic aberration, spherical aberration, and field curvature are deteriorated. And a good image with little aberration could not be obtained.

Therefore, according to the present invention, the power of the entire prism is increased by giving power to the reflecting surface arranged eccentrically as in the prism optical system, and the F-number is small and the aberration is well corrected. A prism optical system has been successfully constructed.

However, in order to give power to an eccentric surface, an aberration occurs due to eccentricity which cannot be corrected by a conventional rotationally symmetric aspherical surface. Aberrations caused by eccentricity include coma, astigmatism, image distortion, field curvature, and the like. In the prior art, there are examples of using a toric surface or an anamorphic surface to correct these aberrations, but emphasis is placed on astigmatism caused by eccentricity, and a wide angle of view, small size, In addition, there was no one in which sufficient aberration correction was performed up to image distortion.

Simultaneously and satisfactorily correcting these aberrations could not provide satisfactory results on toric surfaces, anamorphic surfaces, rotationally symmetric aspherical surfaces, and spherical surfaces.

According to the present invention, in order to simultaneously and satisfactorily correct the above-mentioned aberration, a plane-symmetric free-form surface having no axis of rotational symmetry both in-plane and out-of-plane and having only one plane of symmetry is used. It is characterized by.

Here, the free-form surface of the present invention is defined by the following equation. _{Z = C 2 + C 3 y} + C 4 x + C 5 y 2 + C 6 yx + C 7 x 2 + C 8 y 3 + C 9 y 2 x + C 10 yx 2 + C 11 x 3 + C 12 y 4 + C 13 y 3 x + C 14 y 2 x 2 + C ^{_{15 yx 3 + C 16 x 4}} + C 17 y 5 + C 18 y 4 x + C 19 y 3 x 2 + C 20 y 2 x 3 + C 21 yx 4 + C 22 x 5 + C 23 y 6 + C 24 y 5 x + C 25 y 4 x 2 + C ^{_{26 y 3 x 3 + C 27}} y 2 x 4 + C 28 yx 5 + C 29 x 6 + C 30 y 7 + C 31 y 6 x + C 32 y 5 x 2 + C 33 y 4 x 3 + C 34 y 3 x 4 + C 35 y 2 x ^{_{5 + C 36 yx 6 + C}} 37 x 7 ····· ···· (a) provided that, C _m (m is an integer of 2 or more) is a coefficient.

By using such a free-form surface as at least one reflecting surface having a reflecting action, the eccentric direction is the Y axis, the optical axis direction which exits the center of the object point and faces the center of the opening is the Z axis, and the Y axis is the Y axis. Assuming that an axis orthogonal to the Z-axis is the X-axis, an inclination in the Y-direction at an arbitrary position on the X-axis can be arbitrarily given. This can correct image distortion generated by an eccentrically arranged concave mirror, particularly, image distortion that changes depending on the image height in the X-axis direction and occurs in the Y-axis direction. In other words, as a result, it is possible to satisfactorily correct the image distortion observed when the horizontal line is bowed.

Next, a trapezoidal distortion generated by the concave mirror arranged eccentrically will be described. If this image distortion is explained by the reverse tracking from the observer's eyeball, the light beam having a spread in the X-axis direction emitted from the eyeball is reflected by a concave mirror arranged eccentrically, but is reflected in the positive Y-axis direction of the concave mirror. Due to the difference in the optical path length between the light ray on the negative side of the Y axis and the light ray on the negative side, the spread in the X axis direction is greatly different, and then reflected by the concave mirror. For this reason, the size of the image in the positive Y-axis direction and the size of the image in the negative Y-axis direction are formed differently, and as a result, the observed image has a trapezoidal distortion, or the eccentricity also occurs on the axis. A large coma aberration occurs.

The distortion and coma can be corrected by using a free-form surface. this is,
This is because the free-form surface has an odd-order term of Y and an even-order term of X whose curvature can be arbitrarily changed in the X-axis direction depending on the sign of the Y-axis, as is clear from the definition equation (a).

Next, the rotationally asymmetric curvature of field caused by the concave mirror arranged eccentrically will be described. In this curvature of field, for example, a ray of light incident on a concave mirror from an object point at infinity is reflected by the concave mirror, but the distance to the image plane after the ray hits is half the curvature of the part hit by the ray. . That is, an image plane is formed that is inclined with respect to the traveling direction of the light beam after reflection by the concave mirror that is arranged eccentrically. By using a free-form surface, it is possible to arbitrarily give the X-axis and Y-axis directions of curvature at any point in the positive and negative directions on the Y-axis. This is, as is clear from the definition of the free-form surface, Y
This is because it has an odd-order term of Y whose curvature can be arbitrarily changed depending on the sign of the axis. This effectively works for correcting rotationally asymmetric curvature of field generated by the concave mirror arranged eccentrically, particularly for correcting the inclination of the image plane.

Next, the rotationally symmetric field curvature will be described. The reflecting mirror generally causes a curvature of field along the reflecting surface. In the case of the prism optical system of the present invention, generally,
As described above, the curvature of field is configured to be corrected by the convex mirror paired with the concave mirror, but is not completely corrected because the number of surfaces is small. In order to correct the field curvature that cannot be completely corrected, a free-form surface capable of giving an arbitrary curvature at an arbitrary position is preferable in terms of aberration correction.

Further, astigmatism can be achieved by appropriately changing the difference between the curvature in the X-axis direction and the curvature in the Y-axis direction.

More preferably, in consideration of the manufacturability of optical parts, it is desirable that the free-form surface be minimized.
Therefore, manufacturability can be improved by making one of the at least three reflecting surfaces a free-form surface and the other surface a flat surface, a spherical surface, or an eccentric rotationally symmetric surface.

In the present invention, the above-mentioned free-form surface is used as at least one reflecting surface having a reflecting action. In this case, the surface shape of the reflecting surface is set to be a rotationally symmetric axis both inside and outside the surface. And a plane-symmetric free-form surface having only one plane of symmetry. This is, for example, FIG.
When a coordinate system is taken as described above, by forming a free-form surface such that the YZ plane, which is a surface including the eccentric direction of the eccentrically arranged surface, is a symmetric surface, the image forming surface in the ray tracing is This is because the image can also be made symmetric on both sides with its YZ plane as the plane of symmetry, and the labor for aberration correction can be greatly reduced.

In the present invention, the reflection surface having a reflection effect includes all reflection surfaces having a reflection effect, such as a total reflection surface, a mirror coat surface, and a semi-transmission reflection surface.

As described above, when a plane-symmetric free-form surface having only one symmetric surface is used as at least one reflection surface of the prism optical system, a wide image can be obtained by further satisfying the following conditions. It is possible to provide a prism optical system which is angular and has been subjected to aberration correction.

First, the X axis, Y axis, Z
When the axis is determined, the ray that exits the center of the object, passes through the center of the aperture, and enters the imaging plane is defined as the axial principal ray, and the maximum and minimum in the Y direction and the X direction in the effective area of each reflecting surface. The maximum part is determined as shown in Table 1 below.

[0035]

That is, as described in Table 1 above, the portion where the axial chief ray hits is defined as the upper effective region maximum portion, the lateral maximum region is defined as the lower effective region maximum region. And the part. Then, an expression defining the shape of each surface in this effective area (an expression in which the Z axis is expressed as an axis of the surface,
Alternatively, assuming that the surface has no eccentricity, Z = f (X,
The inclination in the Y-axis direction, which corresponds to the eccentric direction of the surface, in these parts of the expression (1) to (5) in the form of Y) is represented by DY1.
DY3, DY5, and the curvature are CY1 to CY3, C, respectively.
Let it be Y5. Also, the inclination in the X-axis direction orthogonal to the above is DX1-DX3, DX5, respectively, and the curvature is CX1, respectively.
To CX3 and CX5.

As an actual example of an inverted prism to which the present invention is applied, first, a Schmidt prism, which is a kind of roof prism whose schematic shape is shown in FIG. This prism optical system 5
The first prism 3 and the second prism 4 are arranged close to each other, and the center of the entrance aperture 1 is set as the origin (in the first embodiment described later, the aperture is formed on the first surface 31 of the first prism 3). In the second embodiment, since the opening is located on a virtual plane between the first prism 3 and the second prism 4, the center is set as the origin.
The origin is the top position of the surface 31. When the axis passing through the center is the optical axis 2, the direction from the aperture 1 to the optical axis 2 is the Z-axis direction, and the light beam is bent by the prism optical system 5 through the center of the aperture 1 orthogonal to the Z axis. The direction in the plane is orthogonal to the Y-axis direction, the Z-axis, and the Y-axis, and the direction passing through the center of the opening 1 is defined as the X-axis direction. The direction from the opening 1 toward the prism optical system 5 is defined as the positive direction of the Z-axis. The direction of the second prism 4 is defined as the positive direction of the Y axis, and the direction forming the right-handed system with the Z axis and the Y axis is defined as the positive direction of the X axis.

The first prism 3 of the prism optical system 5
Is a first surface 31 of a transmission surface, and a second surface 31 which also serves as a reflection surface and a transmission surface.
The second prism 4 includes a first surface 41 serving also as a transmission surface and a reflection surface, a second surface 42 serving also as a reflection surface and a transmission surface, and a roof surface. Third surface 4
The light exiting from the object, passing through the aperture 1 and entering from the first surface 31 of the first prism 3 is the second surface of the second prism 3 (three surfaces when the roof surface is counted as two surfaces). 32, then reflected at the third surface 33, this time passing through the second surface 32, exiting from the first prism 3, and its second surface 32
The light enters the second prism 4 from the first surface 41 of the second prism 4 facing the second prism 4, is reflected by the second surface 42, and
The light is reflected by the surface 43, then reflected by the first surface 41, finally transmitted through the second surface 42, and exits along the optical axis 2.

By the way, with the Y-axis direction as the up-down direction, the direction perpendicular to the eccentric direction of the surface in the equation that defines the shape of the surface at the portion where the axial chief ray in the Z-axis direction at the center of the object intersects the target surface. The curvature in the plane including the X axis corresponding to and the normal of the plane is expressed as CX
Assuming that the curvature in a plane including the Y axis corresponding to the eccentric direction and the normal to the plane is CY2, the ratio of CX2 to CY2 on at least one plane in the prism optical system is CX2 / CY2.
Then, it is desirable to satisfy the following conditional expression: CX2 / CY2 <0 (1-1)

This is a condition necessary to reduce the occurrence of astigmatism on the decentered reflecting surface. In the case of a spherical surface, CX2 / CY2 = 1, but a spherical surface arranged eccentrically generates large image distortion, astigmatism, coma, and the like. Therefore, when the eccentric surface is formed only by the spherical surface, it becomes difficult to correct the astigmatism on the axis, and it becomes difficult to observe a clear observation image even at the center of the visual field. In order to correct these, the reflecting surface having the largest reflecting and refracting power in the prism optical system is constituted by a surface having only one symmetric surface, and also satisfies the conditional expression (1-1). By arranging at least one reflecting surface, it is possible to observe an observation image without astigmatism even on an axis for the first time.

More preferably, it is important that at least two reflecting surfaces satisfy the above-mentioned conditional expression.
More preferably, at least 3 that satisfies the conditional expression is satisfied.
It is important to configure the surface with a reflective surface.

The first prism, which also serves as the exit surface of the second prism,
It is important that the reflecting surface satisfies the above conditional expression. This is important for correcting the field curvature aberration generated on the second reflection surface of the first prism with the field curvature aberration generated on the first reflection surface of the second prism, and canceling each other.

More preferably, it is important that the above-mentioned conditional expression is arranged in each of the first prism that makes two reflections and the second prism that makes three or more reflections.
This is a conditional expression required for the first prism and the second prism to properly correct astigmatism and image distortion.

[0044] More preferably, said two surfaces are of the first type.
More desirably, they are arranged on the prism second surface and the second prism first surface. This is because the two surfaces are arranged close to each other, and the incidence angles of the light beams are substantially the same, so that the occurrence of aberration is equal.

Next, the power of the second reflecting surface of the first prism will be described. The focal length of this surface in the Y-axis direction is
Assuming that the focal length of the entire optical system is f, it is preferable from the viewpoint of aberration correction that the following conditional expression is satisfied: | FY1-2 / f | <1 (2-1)

If the upper limit of 1 to condition (2-1) is exceeded, the power of the second reflecting surface of the first prism is weakened and the focal length is extended, so that the effect of correcting the surface for correcting field curvature is reduced. In the case of the present invention, the curvature of field convex at the center cannot be corrected.

More preferably, it is important that the power of the second reflection surface of the first prism is a regular reflection surface having a converging function in the Y-axis direction. By making the power of this surface in the Y-axis direction positive, the interval between the principal points of the prism optical system can be shortened, which is important when a compact imaging optical system is configured.

More preferably, it is important that the power of the second reflection surface of the first prism is a negative reflection surface having a diverging effect in the X-axis direction. By making the power of this surface in the X-axis direction negative, a good result in aberration correction can be obtained.

Next, the power of the first reflecting surface of the second prism will be described. The focal length in the Y-axis direction of this surface is
When the focal length of the entire optical system is f, it is preferable from the viewpoint of aberration correction that the following conditional expression is satisfied: | FY2-1 / f | <1 (3-1)

If the upper limit of 1 to condition (3-1) is exceeded, the power of the surface is weakened and the focal length is extended, so that the effect of correcting the surface for correcting the curvature of field is reduced. In this case, it is impossible to correct the curvature of field convex at the center.

More preferably, it is important that the power of the first reflection surface of the second prism is a negative reflection surface having a diverging effect in the Y-axis direction. By making the power of this surface in the Y-axis direction negative, the interval between the principal points of the prism optical system can be shortened, which is important when a compact imaging optical system is configured.

More preferably, it is important that the power of the first reflecting surface of the second prism is a regular reflecting surface having a converging function in the X-axis direction. By making the power of this surface in the X-axis direction positive, a good result in aberration correction can be obtained.

Next, the power of the third reflecting surface of the second prism will be described. The focal length in the Y-axis direction of this surface is
When the focal length of the entire optical system is f, it is preferable from the viewpoint of aberration correction that the following conditional expression is satisfied: | FY2−3 / f | <1 (4-1)

If the upper limit of 1 to condition (4-1) is exceeded, the power of the third reflecting surface of the second prism is weakened and the focal length is extended, so that the effect of correcting the surface for correcting the field curvature is reduced. In the case of the present invention, the curvature of field convex at the center cannot be corrected.

More preferably, it is important that the power of the third reflecting surface of the second prism be a regular reflecting surface having a converging function in the Y-axis direction. By making the power of this surface in the Y-axis direction positive, the interval between the principal points of the prism optical system can be shortened, which is important when a compact imaging optical system is configured.

More preferably, it is important that the power of the third reflecting surface of the second prism is a negative reflecting surface having a diverging effect in the X-axis direction. By making the power of this surface in the X-axis direction negative, a good result in aberration correction can be obtained.

Next, conditions for the power arrangement of each surface will be described. First prism first reflecting surface, first prism second
The powers in the X and Y directions of the reflection surface, the second prism first reflection surface, and the second prism third reflection surface are denoted by CX1-1 and CX, respectively.
1-2, CX2-1, CX2-3 and CY1-1, CY1-2, C
When Y2-1 and CY2-3 are used, among the above four reflecting surfaces,
It is important that the power of any three reflecting surfaces has a positive-negative-positive power arrangement. This condition is effective in correcting field curvature and coma aberration, and can perform excellent aberration correction, as in the case of a general rotation-symmetric optical system triplet type.

More preferably, the curvature in the X direction is
CX1-1, CX1-2, CX2-1, the curvature in the Y direction is CY
1-2, CY2-1, and CY2-3 are preferably disposed on the reflecting surfaces.

Next, conditions for reducing the occurrence of asymmetric image distortion caused by eccentricity will be described. By satisfying the following conditional expression, it is possible to reduce the occurrence of image distortion in which a straight line in the horizontal direction is formed in an arc shape and the coma aberration generated even on the axis. The condition is that the inclination of the surface in the Y-axis direction, which corresponds to the eccentric direction of the surface of the expression defining the shape of the surface at the right end portion of the effective area, is defined as DY2, DY5. age,
Also, when the Z-axis is defined such that light rays enter the surface from the negative direction of the Z-axis in the definition formula of the surface and are reflected in the negative direction of the Z-axis, (according to the Z-axis direction of the embodiment, ) When the difference between DY5 and DY2 of the first prism first reflection surface is DY1-1 and the difference between DY5 and DY2 of the first prism second reflection surface is DY1-2, 0 <DY1-1 (5) -1) DY1-2> 0 (5-2) It is preferable from the viewpoint of aberration correction to satisfy any one of the conditional expressions.

The lower limit of condition (5-1), 0, (5-
If the lower limit of 0 in 2) is exceeded, Y at the right center in the effective area
The inclination of the direction is not appropriate, and it is impossible to correct the occurrence of bow-like field curvature and the on-axis coma.

More preferably, one of the following conditional expressions is satisfied: 0.001 <DY1-1 (5-3) DY1-2> 0.001 (5-4) This is preferable for aberration correction.

More preferably, it is more preferable to satisfy all of the above conditional expressions.

Next, the focal lengths of the first prism second reflecting surface and the second prism first reflecting surface are represented by FY1-2,
When FY2-1 is satisfied, it is preferable from the viewpoint of aberration correction to satisfy the following condition: 0.5 <| FY1-2 / FY2-1 | <10 (6-1)

If the upper limit of 10 and the lower limit of 0.5 of the above conditional expression are exceeded, the power arrangement of two closely arranged reflecting surfaces having a relatively strong reflecting and refracting power in the imaging optical system is appropriate. However, it becomes impossible to form a wide and flat image over the entire image plane.

More preferably, it is important to satisfy the following conditional expression: 0.8 <| FY1-2 / FY2-1 | <5 (6-2), and more preferably, 1 <| FY1 -2 / FY2-1 | <2 (6-3) It is important to satisfy the following conditional expression.

Both of the conditional expressions (6-2) and (6-3) are necessary for obtaining a good image when a bright optical system having an F-number of 10 or less and 5 or less is formed. .

Next, on the surface of the prism optical system having particularly strong reflection and refracting power, it is important to further satisfy the following conditional expression. This is an important condition for correcting all aberrations generated on a surface having only one symmetrical surface eccentrically arranged in a well-balanced manner and for arranging the image plane with a small inclination. This conditional expression is particularly important in an optical system using two decentered concave mirrors as in the present invention.

The difference between the curvatures CX1 and CX3 in the X direction of the upper and lower portions where the axial principal ray is reflected by at least one reflection surface in the optical system is CX3-CX1, and the first prism first CX3-CX1 on the reflective surface is replaced with CX3-
1 (1-1), CX3-CX1 of the first prism second reflection surface is C
X3-1 (1-2), CX3-CX1 of the second prism first reflection surface
Where CX3-1 (2-1), 0 <CX3-1 (1-1) <0.01 (1 / mm) (7-1) -0.01 <CX3-1 (1 -2) <0 (1 / mm) (7-2) 0 <CX3-1 (2-1) <0.01 (1 / mm) (7-3) It is preferable to satisfy at least one of them for aberration correction.

If the upper and lower limits of the conditional expressions (7-1) to (7-3) are exceeded, the curvature in the X direction of the surface in the effective area will be too different, and the correction of the high-order coma aberration will be difficult in the entire optical system. Would be excessive. On the other hand, if these differences are 0, the occurrence of high-order coma cannot be corrected.

More preferably, it is important that both of the at least two reflecting surfaces satisfy the above conditional expression.

More preferably, it is important that all of the three reflecting surfaces satisfy the above conditional expression.

Next, on the surface of the prism optical system having particularly strong reflection and refracting power, it is important to further satisfy the following conditional expression. This corresponds to the above (7-1)-
Similarly to the conditional expression (7-3), it is important to correct all aberrations occurring on a surface having only one symmetrical surface eccentrically arranged in a well-balanced manner and to reduce the inclination of the image plane. Conditions. In particular, this conditional expression is particularly important in an optical system using two concave mirrors arranged eccentrically as in the present invention.

The difference between the curvatures CY1 and CY3 in the X direction of the upper and lower portions where the axial principal ray is reflected by at least one reflection surface in the optical system is CX3-CX1, and the first prism second CY3-CY1 on the reflective surface is replaced by CY3-
1 (1-2), CY3-CY1 of the second prism first reflection surface is C
Y3-1 (2-1), CY3-CY1 of the second prism second reflection surface
Where CY3-1 (2-2), 0 <CY3-1 (1-2) <0.01 (1 / mm) (8-1) -0.01 <CY3-1 (1 -1) <0 (1 / mm) (8-2) 0 <CY3-1 (2-2) <0.01 (1 / mm) (8-3) It is preferable to satisfy at least one of them for aberration correction.

If the upper and lower limits of the conditional expressions (8-1) to (8-3) are exceeded, the curvature of the surface in the effective area in the Y direction is too different, and the correction of the high-order coma aberration is performed in the entire optical system. Would be excessive. On the other hand, if these differences are 0, the occurrence of high-order coma cannot be corrected.

More preferably, it is important that both of the at least two reflecting surfaces satisfy the above conditional expression.

More preferably, it is important that all of the three reflecting surfaces satisfy the above conditional expression.

The conditions (1-1) to (8-
Regarding 3), the surface shape of any of the reflecting surfaces constituting the image forming optical system is a plane-symmetric free-form surface having no rotationally symmetric axis both in-plane and out-of-plane, and having only one plane of symmetry. Not only that, when formed on an anamorphic surface that does not have a rotationally symmetric axis both inside and outside the plane, that is, a non-rotationally symmetric surface shape that does not have a rotationally symmetric axis both inside and outside the plane. It can be applied to both cases.

In the above-mentioned Schmidt prism, which is a kind of roof prism, by making the second prism second reflection surface a roof surface, an inverted image can be obtained without using an imaging lens in the optical system. , An inverted image can be obtained by the prism optical system of the present invention.

Next, as another example of the inverted prism to which the present invention is applied, a porro prism whose shape is schematically shown in FIG. The prism optical system 5 includes a first prism 3 and a second prism 4 arranged close to each other, and a coordinate system is separately defined by the first prism 3 and the second prism 4.
The coordinate system of the prism 3 has the origin at the center of the entrance aperture 1 (in the third and fourth embodiments described later, the first surface 4 of the second prism 4).
Since there is an opening on the top 1, the origin is set at the top of the first surface 31 of the first prism 3. If the axis passing through the center is the optical axis 2, the direction from the aperture 1 to the optical axis 2 is the Z-axis direction, and the light beam is bent by the first prism 3 through the center of the aperture 1 orthogonal to the Z axis. The direction in the plane is the Y-axis direction, the Z-axis, the direction orthogonal to the Y-axis and passing through the center of the opening 1 is the X-axis direction, the direction from the opening 1 to the first prism 3 is the positive direction of the Z-axis, and the direction from the optical axis 2 is The direction of the second prism 4 is defined as the positive direction of the Y axis, and the direction forming the right-handed system with the Z axis and the Y axis is defined as the positive direction of the X axis. The coordinate system of the second prism 4 is obtained by rotating the coordinate system of the first prism 3 by 90 ° counterclockwise around the Z axis (the origin of the coordinate system of the second prism 4 will be described later). In the case of Examples 3 and 4,
The coordinate system is the same as that of the first prism 3. ).

The first prism 3 of the prism optical system 5
Is composed of a first surface 31 of a transmission surface, a second surface 32 of a reflection surface, a third surface 33 of a reflection surface, and a fourth surface 34 of a transmission surface. The second prism 4 also has a first surface of the transmission surface. A surface 41, a second surface 42 of the reflection surface, a third surface 43 of the reflection surface, and a fourth surface 44 of the transmission surface.
The light incident from the first surface 31 of the prism 3
2. The first light is reflected by the third surface 33 and transmitted through the fourth surface 34,
The light exits from the prism 3, enters the second prism 4 from the first surface 41 of the second prism 4 opposed to the fourth surface 44, is reflected by the second surface 42 and the third surface 43, and finally passes through the fourth surface 44. The light is emitted through the four surfaces 44.

In this case, when the aperture is arranged on the object side of the prism optical system, it is necessary to reduce the power of the transmission surface in order to reduce the occurrence of chromatic aberration of magnification. When the minimum focal length of the transmitting surface of the prism optical system is Ftmin and the minimum focal length of the reflecting surface is Frmin, | 2 × Ftmin |> | Frmin | (9-1) It is important to satisfy

More preferably, it is important to satisfy the following condition: | 1.5 × Ftmin |> | Frmin | (9-2)

More preferably, it is important to satisfy the following condition: | 1.2 × Ftmin |> | Frmin | (9-3)

If none of the above conditional expressions is satisfied, the power of the transmitting surface becomes too strong, the chromatic aberration of magnification becomes too large, the resolution around the image deteriorates, and the generation of axial chromatic aberration can be neglected. Disappears.

Next, the eccentric direction of the prism is defined as the eccentric direction of the prism at the portion where the axial principal ray in the Z-axis direction at the center of the object intersects with the target surface. When the curvature in the plane including the normal to the X axis and the plane corresponding to the perpendicular direction is CX2 and the curvature in the plane including the normal to the Y axis and the plane corresponding to the eccentric direction is CY2, at least in the optical system, With one reflecting surface, the ratio of CX2 to CY2 is CX2 / CY
When it is set to 2, it is desirable to satisfy the following conditional expression: 1 <CX2 / CY2 (10-1)

This is a condition necessary for reducing the occurrence of astigmatism on the decentered reflecting surface. In the case of a spherical surface, CX2 / CY2 = 1, but a spherical surface arranged eccentrically generates large image distortion, astigmatism, coma, and the like. Therefore, when the eccentric surface is formed only by the spherical surface, it becomes difficult to correct the astigmatism on the axis, and it becomes difficult to observe a clear observation image even at the center of the visual field. In order to correct these, the reflecting surface having the largest reflecting and refracting power in the optical system is changed to one symmetrical surface.
Surface, and the conditional expression (10-
By arranging at least one reflecting surface that satisfies 1), it is possible to observe an observation image without astigmatism even on an axis for the first time.

It is more preferable to satisfy the following condition: 1.2 <CX2 / CY2 (10-2) for further aberration correction.

More preferably, it is important that at least two reflecting surfaces satisfy the above conditional expression.

More preferably, when the prism on the object side is the first prism and the prism on the image side is the second prism, the two reflecting surfaces satisfying the conditional expression are the first reflecting surface of the second prism and the second reflecting surface. It is preferable to dispose it on the second reflecting surface of the two prisms for aberration correction.

Next, the eccentric direction of the prism is defined as the eccentric direction of the prism at the portion where the axial principal ray in the Z-axis direction at the center of the object intersects with the target surface. When the curvature in the plane including the normal to the X axis and the plane corresponding to the perpendicular direction is CX2 and the curvature in the plane including the normal to the Y axis and the plane corresponding to the eccentric direction is CY2, at least in the optical system, When the ratio of CX2 to CY2 is CX2 / CY2 on one surface, it is desirable to satisfy the following conditional expression: CX2 / CY2 <1 (11-1).

This is a condition necessary to reduce the occurrence of astigmatism on the decentered reflecting surface, as in the above conditional expression (10-1). By arranging the surfaces in the optical system as surfaces having only one symmetric surface and arranging at least one surface satisfying the conditional expression (11-1), the conditional expression (10-1) is satisfied. This is important for canceling out aberrations by canceling aberrations with a surface that satisfies (1).

More preferably, it is desirable to satisfy the following conditional expression: CX2 / CY2 <0.8 (11-2)

It is more preferable that the surface satisfying the conditional expression be constituted by a transmission surface, since the distance from the reflection surface can be reduced, and it is important to suppress the occurrence of higher-order aberrations.

More preferably, the prism on the image side is connected to the second prism.
When a prism is used, two reflecting surfaces satisfying the condition (10-1) are arranged on the first reflecting surface of the second prism and the second reflecting surface of the second prism, and the conditional expression (11-1) is satisfied. It is preferable from the viewpoint of aberration correction to dispose the transmitting surface to be formed on the first transmitting surface of the second prism.

Next, a case will be described in which the aperture is arranged near the middle of the two prisms. If an aperture is arranged in the middle of the prism, the occurrence of chromatic aberration of magnification is reduced in the configuration, so that the power of the transmission surface of each prism can be increased. Then, the positive-negative-positive plane, which is generally known as a triplet, can be arranged, and the rear focal length can be shortened. That is, it is important for aberration correction to take a positive-negative-positive arrangement in each direction regardless of the Y direction and the X direction.

More preferably, in the X direction, a first transmitting surface of the first prism, a first transmitting surface of the second prism,
It is preferable that the first prism has a positive-negative-positive arrangement on the first reflecting surface, the second reflecting surface, or the second transmitting surface of the second prism.

In the Y direction, it is preferable that the first reflecting surface of the second prism, the second reflecting surface of the second prism, and the second transmitting surface of the second prism have a positive-negative-positive arrangement.

Next, on the surface of the prism optical system having particularly strong reflection and refracting power, it is important to further satisfy the following conditional expression. This is an important condition for correcting all aberrations generated on a plane having only one symmetrical plane eccentrically arranged in a well-balanced manner, and arranging the imaging plane with a small inclination. In particular, this conditional expression is particularly important in an optical system using two decentered concave mirrors as in the present invention.

When the difference between the curvatures CX1 and CX3 in the X direction of the upper and lower portions where the axial principal ray is reflected by at least one reflecting surface in the optical system is CX3-1, 1 <CX3-1 <0 (12-1) It is preferable from the viewpoint of aberration correction to arrange at least one reflecting surface satisfying the following conditional expression.

If the upper and lower limits of the conditional expression (12-1) are exceeded, the curvature in the X direction of the surface within the effective area will differ too much, and the correction of high-order coma will be excessive in the entire optical system. . On the other hand, if this difference is 0, the occurrence of higher-order coma cannot be corrected.

More preferably, it is important that at least two reflecting surfaces satisfy the above conditional expression.

More preferably, at least two surfaces satisfying the above conditional expression are the first reflecting surface of the second prism and the second reflecting surface.
That is, it is arranged on the reflection surface.

More preferably, the above condition is satisfied, and CX3-1 on the first transmitting surface of the second prism is changed to CX3-1 (2-
Assuming that t1), it is important to satisfy the following condition: 0 <CX3-1 (2-t1) <0.1 (12-2) With this configuration, particularly, the occurrence of coma can be effectively corrected.

Next, on the surface of the prism optical system having particularly strong reflection and refracting power, it is important to further satisfy the following conditional expression. This is based on the above (12-1),
Similarly to the conditional expression (12-2), it is important to correct all the aberrations generated on the surface having only one symmetrical surface eccentrically arranged in a well-balanced manner and to arrange the image plane with a small inclination. Conditions. In particular, this conditional expression is particularly important in an optical system using two decentered concave mirrors as in the present invention.

The difference CX3-1 between the curvatures CY1 and CY3 in the X direction of the upper and lower effective areas where the axial principal ray is reflected by at least one reflecting surface in the optical system is given by: -0.1 <CY3-1 <0 (13-1) It is preferable from the viewpoint of aberration correction to arrange at least one reflecting surface satisfying the following conditional expression.

If the upper and lower limits of the conditional expression (13-1) are exceeded, the curvature of the surface in the effective area in the Y direction will be too different, and the correction of high-order coma will be excessive in the entire optical system. . On the other hand, if this difference is 0, the occurrence of higher-order coma cannot be corrected.

More preferably, it is important that at least two reflecting surfaces both satisfy the above conditional expression.

More preferably, at least two surfaces satisfying the above conditional expression are the first reflecting surface of the second prism and the second reflecting surface.
That is, it is arranged on the reflection surface.

More preferably, it is important that the above condition is satisfied, and that the first transmitting surface of the second prism also satisfies the above conditional expression. With this configuration, particularly, the occurrence of coma can be effectively corrected.

In the case of a Porro prism, by making the two prisms the same shape, parts can be shared and the number of parts can be reduced.

The above conditions (1-1) to (13-
Regarding 1), it is desirable to satisfy any one of them, and further, by combining any two or more conditions, a more desirable prism optical system can be obtained. As for the roof prism, (1-1), (5)
-1), (7-1), and (8-1) are important conditions in this order. Regarding the Porro prism, (9-1), (1)
Important conditions are in the order of (2-1) and (13-1).

[0112]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments 1 to 4 of the prism optical system according to the present invention will be described below. Examples 1 to be described later
1, the optical axis 2 is set to the center of the object (not shown in the figure) with the top of the first surface 31 of the first prism 3 of the prism optical system 5 as the origin of the optical system, as shown in FIG. , And define it as a ray passing through the origin.
To the Z-axis direction, orthogonal to this Z-axis and passing through the origin,
The direction in the plane where the light beam is bent by the first prism 3 is defined as the Y-axis direction, and the direction orthogonal to the Z-axis and the Y-axis and passing through the origin is defined as X.
The direction from the origin to the image plane is the positive direction of the Z axis, the direction from the optical axis 2 to the direction of the second prism 4 is the positive direction of the Y axis, and the direction that constitutes the Z axis, the Y axis and the right-handed system is the axial direction. The direction is the positive direction of the X axis. In Examples 3 and 4, the first
Fourth surface 34 of prism 3 and first surface 41 of second prism 4
(Opening 1), an imaginary plane exists, in which the coordinate system is rotated 90 ° counterclockwise around the Z axis (γ =
−90 °; γ represents the amount of rotation about the Z axis, with the clockwise direction being positive. ), And thereafter, based on the transformed coordinate system.

Regarding the eccentricity of each surface, α represents the amount of eccentricity in the X-axis, Y-axis, and Z-axis directions from the origin of the surface top, and the amount of rotation of the center axis of the surface around the X-axis. ing. In that case, positive means counterclockwise.

The shape of the free-form surface is as described in the above (a).
Defined by an expression. The Z axis of the definition is the axis of the free-form surface. Note that the term relating to the aspheric surface for which no data is described is zero. Regarding the refractive index, d-line (wavelength 587.
56 nm). The unit of the length is mm.

The prism optical system 5 of each of the following first and second embodiments is an embodiment of the Schmidt prism shown in FIG. 9, and the YZ sectional views of the first and second embodiments are shown in FIGS.
Shown in Each is composed of two prisms, a first prism 3 and a second prism 4.
The first surface 31 of the transmission surface, and the second surface 3 which also serves as the reflection surface and the transmission surface
The second prism 4 includes a first surface 41 that also functions as a transmission surface and a reflection surface, a second surface 42 that also functions as a reflection surface and a transmission surface, and a roof surface. It comprises three surfaces 43 (four when the roof surface is counted as two), and the space between the three surfaces of each prism is filled with a medium having a refractive index larger than 1. Then, light emitted from the object and incident from the first surface 31 of the first prism 3 is
Reflected at the second surface 32 and then at the third surface 33,
This time, the light passes through the second surface 32, exits from the first prism 3, enters the second prism 4 from the first surface 41 of the second prism 4 facing the second surface 32, and enters the second prism 4. 42, then the third surface 43, this time the first surface 4
1 and finally passes through the second surface 42 to form an object image on the image plane. The aperture 1 is the first prism 3 in the first embodiment.
The second embodiment is located between the first prism 3 and the second prism 4.

The prism optical system 5 of the third and fourth embodiments
Is an embodiment of the Porro prism shown in FIG. 10, and YZ plan views (a) and XZ plan views (b) of Examples 3 and 4 are shown in FIGS. 3 and 4, respectively. Both the first prism 3 and the second prism
The first prism 3 includes a first surface 31 of a transmission surface, a second surface 32 of a reflection surface, a third surface 33 of a reflection surface, and a fourth surface 34 of a transmission surface. The second prism 4 also includes a first surface 41 of a transmission surface, a second surface 42 of a reflection surface, a third surface 43 of a reflection surface, and a fourth surface of a transmission surface.
The surface 44 is composed of four surfaces.
The space between the two surfaces is filled with a medium having a refractive index greater than 1. Then, the light is emitted from the object and the first prism 3
The light incident from the surface 31 is reflected by the second surface 32 and the third surface 33, passes through the fourth surface 34, exits from the first prism 3, and faces the second prism 44 facing the fourth surface 44. 4 enters the second prism 4 from the first surface 41, is reflected by the second surface 42 and the third surface 43, and finally passes through the fourth surface 44 to form an object image on the image surface. The opening 1 is the second in Examples 3 and 4
It is located on the first surface 41 of the prism 4.

Further, the above Examples 1 to 4 are the same as those of Examples 1 and 2
Except for the third surface 43, which is the roof surface of the second prism 4 described above, all the surfaces are formed as free-form surfaces. The imaging angle of view in the first and second embodiments is 6.55 ° in the horizontal angle of view and 8.7 in the vertical angle of view.
3 °, the pupil diameter is 12 mm, and the imaging angle of view in Example 3 and Example 4 is 8.73 ° for the horizontal angle of view, 6.55 ° for the vertical angle of view,
The pupil diameter is 12 mm.

The following is a description of the structural parameters of the first to fourth embodiments. Example 1 Surface number Curvature radius Interval Refractive index Abbe number Object surface ∞ ∞ 1 Aperture (aperture surface) Free curved surface 1.52540 55.78 Transmitting surface 2 Reflecting surface Free curved surface Eccentricity (1) 1.52540 55.78 3 Reflecting surface Free curved surface Eccentricity (2) 1.52540 55.78 4 Transmission surface Free-form surface Eccentricity (1) 5 Transmission surface Free-form surface Eccentricity (3) 1.52540 55.78 6 Reflection surface Free-form surface Eccentricity (4) 1.52540 55.78 7 Reflection surface 偏 Eccentricity (5) 1.52540 55.78 8 Reflection surface Free-form surface Eccentricity (3) 1.52540 55.78 9 transmitting surface free curved eccentric (4) image surface ∞ eccentricity (6) free curved surface ^{_{C 5 -1.2672 × 10 -2 C 7}} -2.4694 × 10 -3 C 8 1.9822 × 10 -4 C 10 -1.5083 × 10 - ⁴ C ₁₂ 5.4976 × 10 ^-5 C ₁₄ 2.2634 × 10 ^-5 C ₁₆ -8.2 911 × 10 ^-7 C ₁₇ 5.6 469 × 10 ^-6 C ₁₉ 3.0942 × 10 ^-6 C ₂₁ 7.9423 × 10 ^-7 Free-form surface C ₅ -1.6754 × 10 ^-3 C ₇ -3.6548 × 10 ^-3 C ₈ 4.3133 × 10 ^-5 C ₁₀ 8.0769 × 10 ^-5 C ₁₂ 3.4304 × 10 ^-6 C ₁₄ 3.6553 × 10 ^-6 C ₁₆ 9.6636 × 10 ^-7 C ₁₇ 1.2202 _{^{× 10 -7 C 19 1.9265 × 10}} -7 C 21 2.0913 × 10 -7 free curved surface C ₅ 6.5630 × 10 ^{-3 _{7 -1.5128 × 10 -3 C 8 -1.4118}} × 10 -4 C 10 1.2660 × 10 -4 C 12 1.8982 × 10 -5 C 14 6.8144 × 10 -6 C 16 5.2233 × 10 -7 C 17 -7.8296 × 10 - ⁷ C ₁₉ -3.3872 × 10 ^-7 C ₂₁ 1.2250 × 10 ^-7 Free-form surface C ₅ 3.8047 × 10 ^-3 C ₇ -2.6090 × 10 ^-3 C ₈ -2.4041 × 10 ^-6 C ₁₀ 3.2978 × 10 ^-6 C _{12 ^{1.6621 × 10 -6 C 16 -5.1102 ×}} 10 -7 C 17 -9.6361 × 10 -8 C 19 -2.9727 × 10 -8 C 21 4.9809 × 10 -8 free curved surface ^{_{C 5 1.0138 × 10 -2 C 7}} - 4.0864 × 10 ^-3 C ₈ -3.1166 ×
10 ^-4 C ₁₀ 1.2642 × 10 ^-4 C ₁₂ 2.7031 × 10 ^-5 C ₁₆ 5.3789 × 10 ^-7 C ₁₇ -8.3 168 × 10 ^-7 C ₁₉ 1.5190 × 10 ^-7 C ₂₁ 4.9311 × 10 ^-9 XYZ (°) Eccentricity (1) 0.0000 0.0000 9.6081 53.5671 Eccentricity (2) 0.0000 -10.6887 12.9033 79.5124 Eccentricity (3) 0.0000 0.0000 11.0438 48.1028 Eccentricity (4) 0.0000 0.0000 20.9895 0.0000 Eccentricity (5) 0.0000 13.9044 9.5319 -67.5000 Eccentricity (6) 0.0000 0.0000 47.6929 0.0000.

Example 2 Surface number Curvature radius Interval Refractive index Abbe number Object surface ∞ ∞ 1 Transmission surface Free curved surface 1.52540 55.78 2 Reflecting surface Free curved surface Eccentricity (1) 1.52540 55.78 3 Reflecting surface Free curved surface Eccentricity (2) 1.52540 55.78 4 Transmission Surface Free-form surface Eccentricity (1) 5 Aperture (aperture surface) ∞ Eccentricity (3) 6 Transmission surface Free-form surface Eccentricity (4) 1.52540 55.78 7 Reflection surface Free-form surface Eccentricity (5) 1.52540 55.78 8 Reflection surface ∞ Eccentricity (6) 1.52540 55.78 9 reflecting surface free curved eccentric (4) 1.52540 55.78 10 transmitting surface free curved eccentric (5) image surface ∞ eccentricity (7) free curved surface ^{_{C 5 -8.4338 × 10 -3 C 7}} 7.2691 × 10 -3 C 8 4.9129 × 10 - ⁴ C ₁₀ -5.6806 × 10 ^-4 C ₁₂ 8.4037 × 10 ^-5 C ₁₄ -3.9580 × 10 ^-5 C ₁₆ -2.4513 × 10 ^-6 C ₁₇ 3.3639 × 10 ^-6 C ₁₉ -1.4356 × 10 ^-6 C ₂₁ 4.6090 × 10 ^-8 free curved surface ^{_{C 5 -1.6485 × 10 -3 C 7}} -5.7123 × 10 -3 C 8 2.0846 × 10 -5 C 10 5.7306 × 10 -5 C 12 3.8048 × 10 -6 C 14 -5.9229 × 10 - ⁶ C ₁₆ 8.3327 × 10 ^-7 C ₁₇ 4.3404 × 10 ^-8 C ₁₉ -8.7 139 × 10 ^-8 C ₂₁ 1.2811 × 1 0 ^-7 Free-form surface C ₅ 7.1321 × 10 ^-3 C ₇ -7.5 450 × 10 ^-3 C ₈ -2.4375 × 10 ^-4 C ₁₀ 1.4177 × 10 ^-4 C ₁₂ 6.7969 × 10 ^-6 C ₁₄ 7.9771 × 10 ^-6 C ₁₆ 2.3814 × 10 ^-7 C ₁₇ -6.7 217 × 10 ^-8 C ₁₉ -2.4099 × 10 ^-7 C ₂₁ 2.1750 × 10 ^-7 Free-form surface C ₅ 5.6909 × 10 ^-3 C ₇ -6.3367 × 10 ^-3 C ₈ -7.5474 × 10 ^-5 C ₁₀ -8.8192 × 10 ^-6 C ₁₂ -4.1440 × 10 ^-6 C ₁₆ -8.5026 × 10 ^-6 C ₁₇ 4.2168 × 10 ^-7 C ₁₉ 2.0 300 × 10 ^-7 C ₂₁ 3.0959 × 10 ^-7 Free curved ^{_{C 5 1.0838 × 10 -2 C 7}} -6.6868 × 10 -3 C 8 -3.3957 × 10 -4 C 10 2.3590 × 10 -4 C 12 -4.8016 × 10 -6 C 16 -1.7332 × 10 -7 C 17 - 6.5143 × 10 ^-8 C ₁₉ 5.3375 × 10 ^-7 C ₂₁ 1.2878 × 10 ^-7 XYZ α (°) Eccentricity (1) 0.0000 0.0000 3.7369 50.8281 Eccentricity (2) 0.0000 -16.5960 12.6304 78.3384 Eccentricity (3) 0.0000 -10.1084 16.9474 48.8210 Eccentricity (4) 0.0000 0.0000 14.6074 49.3989 Eccentricity (5) 0.0000 0.0000 22.2261
0.0000 Eccentricity (6) 0.0000 11.4491 12.8339
-67.5000 Eccentricity (7) 0.0000 0.0000 32.0261 0.0000.

Example 3 Surface number Curvature radius Interval Refractive index Abbe number Object surface ∞ ∞ 1 Transmission surface Free-form surface 1.52540 55.78 2 Reflection surface Free-form surface Eccentricity (1) 1.52540 55.78 3 Reflection surface Free-form surface Eccentricity (2) 1.52540 55.78 4 Transmission Surface Free-form surface Eccentricity (3) 5 Virtual surface (coordinate transformation) γ = -90 ° 6 Aperture (aperture surface) Free-form surface Eccentricity (4) 1.52540 55.78 Transmission surface 7 Reflection surface Free-form surface Eccentricity (5) 1.52540 55.78 8 Reflection surface Free Curved surface Eccentricity (6) 1.52540 55.78 9 Transmission surface Free-form surface Eccentricity (7) Image surface ∞ Eccentricity (8) Free-form surface C ₅ 6.3478 × 10 ^-3 C ₇ 6.1098 × 10 ^-3 C ₈ -5.2845 × 10 ^-5 C ₁₀ 4.3671 × 10 ^-5 C ₁₂ -1.0668 × 10 ^-6 C ₁₄ -6.5356 × 10 ^-6 C ₁₆ -8.0227 × 10 ^-8 Free-form surface C ₅ 3.3439 × 10 ^-4 C ₇ 1.1954 × 10 ^-4 C ₈ -7.6601 × 10 ^-7 C ₁₀ 2.3193 × 10 ^-5 C ₁₂ -6.4152 × 10 ^-8 C ₁₄ 3.9565 × 10 ^-8 C ₁₆ 2.1228 × 10 ^-7 Free-form surface C ₅ -1.9344 × 10 ^-4 C ₇ 1.3011 × 10 ^-4 C ₈ 1.4449 × 10 ^-6 C ₁₀ 3.7046 × 10 ^-5 C ₁₂ -3.2961 × 10 ^-8 C ₁₄ 1.7349 × 10 ^-7 C _{1 6} 2.2626 × 10 ^-7 Free-form surface C ₅ -6.9225 × 10 ^-3 C ₇ -1.6391 × 10 ^-3 C ₈ -2.7289 ×
10 ^-5 C ₁₀ 1.2587 × 10 ^-4 C ₁₂ 1.4172 × 10 ^-6 C ₁₄ 1.3824 × 10 ^-5 C ₁₆ 1.5349 × 10 ^-6 Free-form surface C ₅ 1.4944 × 10 ^-2 C ₇ 8.8404 × 10 ^-3 C ₈ 4.1480 × 10 ^-5 C ₁₀ -1.4278 × 10 ^-4 C ₁₂ 2.8749 × 10 ^-6 C ₁₄ 8.8455 × 10 ^-6 C ₁₆ 4.0113 × 10 ^-6 Free-form surface C ₅ 1.0955 × 10 ^-3 C ₇ 2.9999 × 10 ^-3 C ₈ -1.3343 × 10 ^-5 C ₁₀ -4.1797 × 10 ^-5 C ₁₂ 9.3618 × 10 ^-8 C ₁₄ 3.9 593 × 10 ^-7 C ₁₆ 7.8035 × 10 ^-8 Free-form surface C ₅ 2.0731 × 10 ^-3 C ₇ 3.1675 × 10 ^{_{-3 C 8 -5.4006 × 10 -6 C}} 10 -2.7537 × 10 -6 C 12 2.9107 × 10 -8 C 14 1.1778 × 10 -8 C 16 1.4379 × 10 -7 free curved surface _{C 5 1.6872 C 7 1.1294 × 10} - ¹ C ₈ 1.4224 × 10 ^-1 C ₁₀ 4.5371 × 10 ^-1 C ₁₂ 6.1650 × 10 ^-3 C ₁₄ 1.4675 × 10 ^-1 C ₁₆ 2.9785 × 10 ^-5 XYZ α (°) Eccentricity (1) 0.0000 0.0000 9.0000 -45.0000 Eccentricity (2) 0.0000 16.0000 9.0000 45.0000 Eccentricity (3) 0.0000 16.0000 0.0000 0.0000 Eccentricity (4) -16.0000 0.0000 -1.0000 0.0000 Eccentricity (5) -16.0000 0.0000 -9.0000 45.0000 Eccentricity (6) -16.0000 -16.0000 -9.0000 -45.0000 Eccentricity (7) -16.0000 -16.0000 -1.0000 0.0000 Eccentricity (8) -16.0000 -16.0000 53.5879 0.0000.

Example 4 Surface number Curvature radius Interval Refractive index Abbe number Object surface ∞ ∞ 1 Transmission surface Free-form surface 1.52540 55.78 2 Reflection surface Free-form surface Eccentricity (1) 1.52540 55.78 3 Reflection surface Free-form surface Eccentricity (2) 1.52540 55.78 4 Transmission Surface Free-form surface Eccentricity (3) 5 Virtual surface (coordinate transformation) γ = -90 ° 6 Aperture (aperture surface) Free-form surface Eccentricity (4) 1.52540 55.78 Transmission surface 7 Reflection surface Free-form surface Eccentricity (5) 1.52540 55.78 8 Reflection surface Free Curved surface Eccentricity (6) 1.52540 55.78 9 Transmission surface Free-form surface Eccentricity (7) Image surface ∞ Eccentricity (8) Free-form surface C ₅ 5.4177 × 10 ^-3 C ₇ 9.0765 × 10 ^-3 C ₈ -7.2301 × 10 ^-6 C ₁₀ 7.8054 × 10 ^-5 C ₁₂ 3.1203 × 10 ^-6 C ₁₄ 3.3945 × 10 ^-6 C ₁₆ -2.6158 × 10 ^-6 Free-form surface C ₅ -8.6724 × 10 ^-4 C ₇ -4.7126 × 10 ^-4 C ₈ -1.0676 × 10 ^-5 C ₁₀ 4.4208 × 10 ^-6 C ₁₂ -3.5592 × 10 ^-8 C ₁₄ 2.1417 × 10 ^-7 C ₁₆ -6.4613 × 10 ^-7 Free-form surface C ₅ -4.9621 × 10 ^-4 C ₇ -5.1478 × 10 ^-4 C ₈ -1.4168 × 10 ^-5 C ₁₀ -4.6223 × 10 ^-5 C ₁₂ -1.6551 × 10 ^-7 C ₁₄ -1.9654 × 10 ^-7 C ₁₆ -1.7943 × 10 ^-6 Free-form surface C ₅ 4.0099 × 10 ^-3 C ₇ -5.0153 × 10 ^-3 C ₈ -7.6126 × 10 ^-6 C ₁₀ -2.4184 × 10 ^-4 C ₁₂ 4.2354 × 10 ^-6 C ₁₄ 1.6559 × 10 ^-5 C ₁₆ -1.0877 × 10 ^-5 Free-form surface C ₅ 1.5616 × 10 ^-2 C ₇ 2.2239 × 10 ^-2 C ₈ -4.9487 × 10 ^-4 C ₁₀ 4.6623 × 10 ^-5 C ₁₂ -6.6355 × 10 ^-7 C ₁₄ -2.3443 × 10 ^-5 C ₁₆ -1.7264 × 10 ^-5 Free-form surface C ₅ 2.4847 × 10 ^-3 C ₇ 1.9982 × 10 ^-3 C ₈ -2.3559 × 10 ^-5 C ₁₀ 1.9553 × 10 ^-5 C ₁₂ 4.8948 × 10 ^-7 C ₁₄ -1.0977 × 10 ^-6 C ₁₆ -2.7790 × 10 ^-6 Free-form surface C ₅ 4.0231 × 10 ^-4 C ₇ 2.4728 × 10 ^-3 C ₈ 2.0277 × 10 ^-5 C ₁₀ 2.1493 × 10 ^-5 C ₁₂ -2.4306 × 10 ^-7 C ₁₄ -4.2267 × 10 ^-6 C ₁₆ -2.9463 × 10 ^-6 Free-form surface C ₅ 1.5588 C ₇ -8.9439 × 10 ^-1 C ₈ 5.8243 × 10 ^-1 C ₁₀ -7.3696 × 10 ^-1 C ₁₂ 1.4114 × 10 ^-2 C ₁₄ -2.3933 × 10 ^-1 C ₁₆ 1.9057 × 10 ^-2 XYZ α (°) Eccentricity (1) 0.0000 0.0000 9.0000 -45.0000 Eccentricity (2) 0.0000 16.0000 9.0000 45.0000 Eccentricity (3) 0.0000 16.0000 0.0000 0.0000 Eccentricity (4) -16.0000 0.0000 -1.0000 0.0000 Eccentricity (5) -16.0000 0.0000 -9.0000 45.0000 eccentric (6) -16.0000 -16.0000 -9.0000 -45.0000 eccentric (7) -16.0000 -16.0000 -1.0000 0.0000 eccentric (8) -16.0000 -16.0000 33.4746 0.0000.

Next, FIGS. 5 to 6 and FIGS. 7 to 8 show lateral aberration diagrams of the first and third embodiments, respectively. In these lateral aberration diagrams, the numbers in parentheses indicate (horizontal (X direction) angle of view, vertical (Y direction) angle of view), and indicate the lateral aberration at that angle of view.

The values of the parameters relating to the conditional expressions (1-1) to (13-1) in the respective embodiments of the present invention are shown below (for example, in the column indicating the plane, 1-1 means 1
3 shows a first reflecting surface of a prism. Further, “2-t1” indicates the first transmission surface of the second prism. ).

[0124]

In the above embodiment, each surface is formed by the free-form surface of the definition equation (a). However, it is needless to say that a surface of any definition can be used. However, no matter what definition formula was used, the aberration was corrected very well by satisfying any of the conditions shown in the present invention and by satisfying some of them. It goes without saying that a prism optical system can be obtained. In addition, the conditional expression used in the conventional non-eccentric system such as the curvature of the surface defined by the center of the definition coordinate system of the surface ignoring the eccentricity, the focal length of the surface is such that each surface is largely eccentric as in the present invention. If so, it has no meaning.

The aperture may be provided with a stop at that position, or may be structured so as to block a light beam by a prism frame or a light beam limiting means.

In the embodiment shown in FIGS. 1 and 2, the inverted image can be obtained by making the second prism second reflecting surface a roof surface, so that the image forming lens of the optical system can be obtained. It is possible to obtain an inverted image with the prism optical system of the present invention without arranging.

FIG. 11 is a diagram showing an optical system of binoculars.
FIG. 1 (a) shows a Porro prism type, and FIG. 2 (b) shows a roof prism type. By using a prism optical system having an image forming function according to the present invention as the Porro prism PP or the roof prism DP, the objective lens Ob or the eyepiece lens is used. Binoculars that do not require one or both of Ep can be configured. In this case, with the roof prism of the present invention, binoculars having a short overall length can be configured. Further, with the Porro prism of the present invention, binoculars having a small thickness can be configured.

FIG. 12 is a diagram showing an optical system of a binocular microscope. By using a prism optical system having an image forming function according to the present invention as a porro prism PP for adjusting the twist of an optical axis and an image, FIG. A binocular microscope that does not require one or both of the objective lens Ob and the eyepiece Ep can be configured.

Further, it goes without saying that the present invention can be applied not only to binoculars and binocular microscopes but also to monocular and monocular microscopes.
Furthermore, a small camera can be configured by using the camera as a viewfinder optical system such as a camera.

Further, it is also possible to use the prism optical system of the present invention in combination. Further, by disposing a lens before and after the optical system of the present invention or between the first prism and the second prism, it is possible to widen the range. It is also possible to increase the angle of view or to reduce the F number to make the image brighter. Further, by changing the relative position with respect to another lens system, zooming and the like can be performed.

[0132]

As is apparent from the above description, according to the present invention, it is possible to provide a prism optical system which has an image forming function and provides a clear image with little distortion even at a wide angle of view.

[Brief description of the drawings]

FIG. 1 is a sectional view of a prism optical system according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a prism optical system according to a second embodiment of the present invention.

FIG. 3 is a plan view of a prism optical system according to a third embodiment of the present invention.

FIG. 4 is a plan view of a prism optical system according to a fourth embodiment of the present invention.

FIG. 5 is a part of a lateral aberration diagram of the prism optical system according to the first embodiment of the present invention.

FIG. 6 is a remaining part of the lateral aberration diagram of the prism optical system according to the first embodiment of the present invention.

FIG. 7 is a part of a lateral aberration diagram of the prism optical system according to the third embodiment of the present invention.

FIG. 8 is a remaining part of the lateral aberration diagram of the prism optical system according to the third embodiment of the present invention.

FIG. 9 is an explanatory diagram of a Schmidt prism, which is a kind of an inverted prism targeted by the present invention.

FIG. 10 is a diagram illustrating a Porro prism, which is a kind of an inverted prism to which the present invention is applied.

FIG. 11 is a diagram showing an optical system of binoculars to which the present invention can be applied.

FIG. 12 is a diagram showing an optical system of a binocular microscope to which the present invention can be applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Opening 2 ... Optical axis 3 ... 1st prism 4 ... 2nd prism 5 ... Prism optical system 31 ... 1st surface 32 ... 2nd surface 33 ... 3rd surface 34 ... 4th surface 41 ... 1st surface 42 ... 1st 2nd surface 43 ... 3rd surface 44 ... 4th surface Ob ... Objective lens Ep ... Eyepiece PP ... Porro prism DP ... Dach prism

Claims (4)

[Claims] 1. A prism optical system having an opening and having the function of erecting an image formed by an objective lens, wherein the prism optical system has a reflecting surface for image erecting, and the reflecting surface has a power And a non-rotationally symmetric surface shape that does not have a rotationally symmetric axis both in-plane and out-of-plane so that the shape of the curved surface corrects eccentric aberration caused by reflection on the curved surface. A prism optical system characterized by comprising: 2. The non-rotationally symmetric surface shape has a symmetry plane of one.
2. The prism optical system according to claim 1, wherein the prism optical system has only one and has a free-form surface shape defined by the following equation. _{Z = C 2 + C 3 y} + C 4 x + C 5 y 2 + C 6 yx + C 7 x 2 + C 8 y 3 + C 9 y 2 x + C 10 yx 2 + C 11 x 3 + C 12 y 4 + C 13 y 3 x + C 14 y 2 x 2 + C ^{_{15 yx 3 + C 16 x 4}} + C 17 y 5 + C 18 y 4 x + C 19 y 3 x 2 + C 20 y 2 x 3 + C 21 yx 4 + C 22 x 5 + C 23 y 6 + C 24 y 5 x + C 25 y 4 x 2 + C ^{_{26 y 3 x 3 + C 27}} y 2 x 4 + C 28 yx 5 + C 29 x 6 + C 30 y 7 + C 31 y 6 x + C 32 y 5 x 2 + C 33 y 4 x 3 + C 34 y 3 x 4 + C 35 y 2 x ^{_{5 + C 36 yx 6 + C}} 37 x 7 ····· ···· (a) provided that, C _m (m is an integer of 2 or more) is a coefficient. 3. A prism optical system having a reflection surface for inverting an image, wherein the reflection surface has a light flux incident light path and a light flux emission light path different from each other.
The non-rotationally symmetric eccentric aberration is arranged in the prism optical system such that non-rotationally symmetric decentering aberration is generated. A prism optical system having a non-rotationally symmetrical shape capable of compensating for the angle. 4. The prism optical system according to claim 3, wherein said prism optical system has four or more reflection surfaces and two or more transmission surfaces.