JPH075364A - Non-axial and confocal zoom reflection optical system - Google Patents

Abstract

PURPOSE:To continuously vary the focal distance of an entire optical system by attaining the combination of a large number of reflection surfaces, introducing a large number of variable parameters, using the combination of secondary curved surfaces with point focuses, and changing an angle made by the symmetric axes of the front and rear surfaces with confocal relation. CONSTITUTION:A first surface S1 as an incident plane is constituted of a rotational parabolic surface, second surface S2 is constituted of the outside reflection surface of a rotational elliptic surface, and third surface S3 is constituted of the inside reflection surface of the rotational elliptic surface. The positions of a light exit focus F1' of the first surface S1 and an incident focus F2 of the second surface S2, and the positions of a light exit focus F2' of the second surface S2 and an incident focus F3 of the third surface S3 are in the confocal relation in the same positions. Moreover, rotational symmetric axes F1-F1', F2-F2', and F3-F3' of each surface S1, S2, and S3 are arranged so as not be co-axial but be non-axial. Angles beta21 and beta32 made by each rotational symmetric axes F1-F1', F2-F2', and F3-F3', and an angle Bi made by the F3-F3' and an image surface are changed, so that the focal distance of the optical system can be continuously changed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-coaxial confocal zoom catoptric system capable of zooming with a wide field of view and high resolution.

[0002]

2. Description of the Related Art An image forming optical system has a function of collecting sunlight reflected from an object or infrared light emitted from the object itself to form an image of the light. Also, the afocal optical system is used in combination with some kind of imaging optical system,
Like an imaging optical system, it has the function of forming an image of the light of an object.

An optical system of this type has a wide field of view, high resolution, a wide wavelength range, a large aperture, bright brightness, easy processing, and a plane straight line image, and a continuous focal length. There has been a long-felt need for a zoomed lens that can be changed to.

By the way, the optical system is roughly classified into a refracting optical system using a refracting material such as a lens and a reflecting optical system using a reflecting surface such as a metal.

Table 1 shows a comparison of advantages and disadvantages of the refractive optical system and the reflective optical system.

[0006]

[Table 1]

As can be seen from this table, even though the reflection optical system has many advantages, like the astronomical telescope,
It is used only for special applications with a narrow field of view (for example, 1 degree or less), and many cameras and the like are refractive optical systems. It is considered that this is simply due to the narrow field of view of the reflective optical system and difficulty in zooming.

Then, why is the field of refraction optical system wide and can be designed to be zoomed, but the reflection optical system cannot be designed to have a wide field of view and zoomed?
This can be considered as follows.

In the refracting optical system, light travels in one direction along the optical axis, and a combination of many lenses can be easily constructed.
Therefore, it is possible to combine a large number of various parameters such as a combination of many spherical surfaces with different curvatures (or an aspherical surface based on a spherical surface), a combination of various surface intervals, and a combination of materials with different refractive indexes. There are many parameters that can be changed, and if the combination is designed properly, a wide image format surface with no blurring can be created even in the periphery, and a zoom optical system with high resolution over a wide field of view can be realized.

On the other hand, since the reflection optical system is a reflection phenomenon, the light ray does not travel in one direction along the optical axis, but travels in the opposite direction with each reflection, and is reflected in Newton, Cassegrain, Gregory type reflection optical system, etc. As is typical, in the conventional zoom reflection optical system having the coaxial arrangement shown in FIG. 3, four reflection surfaces S10, S11, S12, S13 are arranged on the coaxial L10-L10 ', and each surface S10, S11, Although the focal length can be changed by changing the distance between S12 and S13, many surfaces cannot be combined, and at most four combinations are possible. Therefore, the number of parameters that can be changed is small, and it is not possible to correct aberrations over a wide range of the image format surface. Naturally, it is impossible to design a zoomed wide-field reflective optical system that requires more parameters. Is.

[0011]

In summary, although the reflective optical system has many advantages, many parameters cannot be changed in the conventional coaxial arrangement having the optical axis, and therefore the number of parameters that can be changed is small. Not only is it impossible to correct aberrations, but it is almost impossible to design a zoom with a wide field of view that is even more difficult, and it can be said that the catoptric system can only be used for special applications such as astronomical telescopes where zooming is not possible with a narrow field of view. .

Therefore, the conventional reflective optical system shown in FIG.
Since the reflecting surfaces are coaxially arranged and used, it is possible to combine only a few of them at most, and it has been impossible to design a wide-field, high-resolution zoom reflecting optical system that corrects aberrations and is easy to process.

Therefore, the present invention makes it possible to combine a large number of reflecting surfaces by eliminating the conventional coaxial (optical axis), thereby introducing many variable parameters and guiding principles. As a reflection curved surface to be used, not as an arbitrary curved surface, a combination of a rotation paraboloid, a rotation ellipsoid, a rotation bilobular hyperboloid, a spherical surface, and a plane (hereinafter referred to as a focused quadric surface) as the reflection surface It is an object of the present invention to provide a wide-field, high-resolution reflective optical system in which the focal length of the entire optical system can be continuously changed by using.

[0014]

In order to achieve the above object, the non-coaxial confocal zoom catoptric system according to claim 1 uses a plurality of curved surfaces having a focal point, and a part of the curved surfaces is a reflecting surface. And each reflecting surface has a rotational symmetry axis, and at least one of the individual rotational symmetry axes is arranged not to lie on one fixed straight line, and the focal point of any curved surface and its It is characterized in that the focal points of the front and rear curved surfaces are placed at the same position, and the focal length is continuously changed by changing the angle formed by the two symmetry axes of the front and rear curved surfaces.
Further, in claim 2, the first incident surface of the curved surface is a paraboloid of revolution. Further, in the afocal reflection optical system according to the third aspect, the first incident surface and the last exit surface of the curved surface are rotation paraboloids. Further, in claim 4, the curved surface is slightly deformed from the surface based on the surface shape having the focus.

[0015]

It is well known that one of the spheroidal surfaces and the rotating bilobed hyperboloids used as the curved surface of the present invention has two different focal points. If it is considered that the paraboloid of revolution also has another focus at infinity in addition to the normal focus, it can be considered as a plane having two different focuses. Further, the spherical surface has one focal point, and the flat surface is considered to be a focal point everywhere. Here, the focus is a geometrical optical meaning of a real or imaginary point light source due to a reflecting surface,
It is a point peculiar to the reflecting surface that is exactly a real or imaginary point image.

If there is an object near the focal point of a certain quadric surface with a focal point, its optical image, including the real image and the virtual image, should also be near the other focal point of the curved surface. This is because, in a quite strict sense, a light beam emitted from or directed to a focus is focused on or diverged from another focus, that is, an exact point image of real or imaginary is formed, and , Since this action is performed continuously, if there is a strict point image correspondence between the object-side focus and the image-side focus, even in the vicinity of the focus, the image can still be in the vicinity of the focus without considering the degree of blurring. Because. If the unblurred neighborhood of this image is fairly wide,
Since the aberration has been corrected, a wide field of view can be achieved. It should be noted that the correction of aberration means that an allowable range is indicated depending on the application in which the optical system is used, and is not a general and strict determination, and always includes a certain allowable range.

As described above, a single plane is considered, but a large number of focal points 2
By constructing the quadric surface while focusing on the front and back surfaces,
The above discussion holds true. That is, by making the confocal point, the configuration of the reflective optical system in which spherical aberration in the narrow sense is completely removed can be guaranteed, and the image generating action is continuously performed. A light image is formed in the vicinity of the exit focal point, and it is possible to design by expanding many parameters in the vicinity without blurring by changing many parameters. Also, it is possible to change many parameters easily by making the reflecting surface non-coaxial. In the present invention, a large number of reflective surfaces having a wide field of view and high resolution are configured by arranging a large number of reflective surfaces having a focal point confocally in the front and rear, and arranging them non-coaxially. Here, the non-coaxial arrangement means an arrangement in which each surface has a rotational symmetry axis, but does not coincide with one straight line which is also one of the rotational symmetry axes. Further, a certain confocal position is a point where the symmetry axes of the reflection surfaces before and after the confocal position intersect, but in the present invention, the angle formed by the two symmetry axes is changed as the confocal point so that the entire optical system is changed. The focal length can be changed continuously.

When the object is sufficiently far away, the parabolic surface, which is considered to have the focal point at infinity, should be the incident surface, and in the afocal system, the incident surface and the exit surface are rotational paraboloids. It is composed of faces.

Like the curved surface used for the incident surface of the reflective Schmidt optical system, aspherical surface processing without a rotational symmetry axis is still difficult to process in modern times, but a parabolic surface used in the present invention as a curved surface with a focus, Elliptical surfaces and hyperboloids are aspherical surfaces, but they have an axis of rotational symmetry, and even the machining of surfaces far away from that axis is easy to machine in modern times when ultra-precision machining technologies such as diamond turning have matured. is there.

In order to reduce the number of surfaces in a refracting optical system, an aspherical surface based on a spherical surface is often introduced into a small number of surfaces. In the present invention, this idea is applied to construct a reflecting optical system. The number of curved surfaces can be reduced.

[0021]

FIG. 1 shows an embodiment of an image forming type non-coaxial confocal zoom catoptric optical system having a three-sided structure according to the present invention.

The zoom reflection optical system of this embodiment is composed of three focal quadric surfaces having a focal point. In the figure, S1 is an incident surface and a first surface is a paraboloid of revolution, S2 is an outer reflecting surface of the spheroid of the second surface, and S3 is an inner reflecting surface of the spheroid of the third surface. F1 is the entrance focal point of the first surface S1 existing at infinity, and F1 'is the exit focal point of the first surface S1. Similarly, F2 is the incident focal point of the second surface S2, F2
2'is the exit focal point of the second surface S2, F3 is the entrance focal point of the third surface S3, and F3 'is the exit focal point of the third surface S3.

The exit focal point F1 'of the first surface S1 and the entrance focal point F2 of the second surface S2 are at the same position. Similarly, the second surface S
The exit focal point F2 'of the second surface S3 and the incident focal point F3 of the third surface S3 are in the same position and have a confocal relationship, and an optical image is formed in the vicinity of the exit focal point F3' of the third surface S3. ing.

The axis of rotational symmetry is the paraboloid S1 of the first surface and is F1-
F1 ', the second elliptical surface S2 is F2-F2', and the third elliptical surface S3 is F3-F3 '. These axes are not coaxial,
It is arranged non-coaxially. Further, βji is an angle formed by the rotational symmetry axis of the i-plane (i is an integer) and the j-plane following the i-plane.

It can be understood that the inner reflection of the ellipsoid and the outer reflection of the hyperboloid have the same action, and the faces that have the opposite action are the outer reflection of the ellipsoid and the inner reflection of the hyperboloid. Therefore, aberrations can be corrected by combining a large number of elliptical surfaces and inner and outer surfaces of hyperboloids as reflecting surfaces. As a combination thereof, in the case of a two-sheet configuration, the inside reflection of an ellipsoid and the outside reflection of an ellipsoid, the inside reflection of a hyperboloid and the outside reflection of a hyperboloid, the inside reflection of an ellipsoid and the inside reflection of a hyperboloid, the ellipsoid There are four possibilities: outer reflection and hyperbolic outer reflection.

In the zoom catoptric system constructed as described above, light (parallel light) from a sufficiently distant point is incident off-axis on the parabolic surface S1 of the first surface, and then the exit focal point of the first surface S1. Attempt to focus on F1 '. The F1 'and the incident focal point F2 of the elliptical surface S2 of the second surface are placed at the same position, and the light to be condensed is reflected by the outer surface of the elliptic surface S2 of the second surface and is not reflected by the other surface of the elliptic surface S2. The light is reflected as if it came out from one focal point, the exit focal point F2 '.

On the other hand, F3, which is the incident focal point of the ellipsoidal surface S3 of the third surface, is located at the same position as F2 ', and the light beam diverged by the second surface S2 is the inner reflection surface of the elliptical surface of the third surface S3. And is imaged at F3 ', which is the exit focal point of the elliptical surface S3.

Normally, if there is an optical axis, the image can be made perpendicular to the optical axis, but in the present embodiment, since it is not coaxial, it cannot be generally said that the image can be made perpendicular to the axis.

Generally, the curved surface shape of a quadric surface with focus is expressed by polar coordinates with the focus at the origin, and can be expressed as ρ (θ) = L / (1 + ε · cos (θ)). Here, L is a vertical length (a parameter that determines the inner reflection or the outer reflection and represents the size of the curved surface), and ε is an eccentricity (which determines the type of the curved surface and the inner reflection or the outer reflection).

The focal length fa of the non-coaxial confocal zoom catoptric system described above can be expressed by the following equation by theoretical analysis.

[0031]

[Equation 1]

Where yp is the incident height, θ 2 is the angle between the line connecting the focal point and the point where the ray hits the reflecting surface, and the axis of symmetry, β
i is the angle between the image plane and the symmetry axis, and Δθ is the angle between the reflected ray and the focal point with reference to the reflection point. The subscript υ represents an arbitrary surface, p represents an incident parabolic surface, and k represents a final surface. The angle βji formed by the two axes of symmetry does not appear explicitly in this equation, but the focal length of the optical system changes continuously by changing βji. If the parameters are selected properly, high resolution and wide field of view can be maintained over the entire zoom area.

In the arrangement of βji in FIG. 1, the focal length f
a is 1821.47 mm. Further, as shown in FIG. 2, when the angle βji formed by the axis of symmetry is changed while keeping the confocal point using the same reflecting surface as in FIG. 1, the focal length fa is 1094.77 mm in the arrangement of βji. .

In this embodiment, since three curved surfaces are arranged in a non-coaxial and confocal relationship in a multifaceted manner, the eccentricity and vertical length of each surface can be converted, and the angle formed by the axes ( Βji) in Fig. 1 can also be changed.

Further, like the curved surface used for the entrance surface of the reflective Schmidt optical system, aspherical surface processing without a rotational symmetry axis is still difficult in modern times, but it is used as a curved surface with a focus in this embodiment. Object surfaces, ellipsoids, and hyperboloids are aspherical surfaces, but they have an axis of rotational symmetry, and even surfaces far away from the axis can be easily processed by using ultra-precision processing technology such as diamond turning. be able to.

Further, in the conventional reflection optical system of the Newton type or the like arranged coaxially, the second reflecting surface and its support function as a light shielding plate, which is a problem as an imager in the infrared region. In the zoom reflection optical system, since the curved surfaces are arranged non-coaxially, there is no support for blocking the light in the entire luminous flux, which is also suitable for an infrared imager.

When the object is sufficiently far away, it is necessary to make the parabolic surface, which is considered to have the focus at infinity, the incident surface, and in the afocal reflection optical system, the incident surface The exit surface is a paraboloid of revolution.

Further, in order to reduce the number of surfaces in the refracting optical system, an aspherical surface based on a spherical surface is often introduced into a small number of surfaces, but in this embodiment, this idea is applied and a focal point is provided. Surface shape, that is, a paraboloid of revolution that is a quadric surface with focus,
The number of curved surfaces can be reduced by forming a reflective optical system by slightly deforming the surface based on a spheroidal surface, a hyperboloid of rotation, a spherical surface, and a flat surface.

By the way, in the present embodiment, the curved surface used has a three-sided structure, but if the curved surface has the above-mentioned asynchronous confocal arrangement, any number of surfaces can be formed, and parameters that can be changed accordingly. It is possible to design a zoom reflection optical system that does not have aberrations up to the periphery of the image format surface.

Further, in the present embodiment, all three rotational symmetry axes are included in the two-dimensional plane (the real paper surface),
The axes of rotational symmetry may be arranged three-dimensionally.

[0041]

According to the present invention, since it is non-coaxial without an optical axis, many reflecting surfaces can be introduced, and the reflecting surfaces having a focal point are confocal on the front and rear surfaces. The configuration of the optical system in which the spherical aberration is completely eliminated is always guaranteed, and the focal length of the entire optical system can be continuously changed by changing the angle formed by the axis of rotational symmetry while keeping the confocal point. Also, by introducing more surfaces, a large number of parameters can be taken, and by appropriately selecting those parameters, it is possible to realize a catoptric system with a zoomed wide field of view and high resolution.

Further, since all the surfaces used in the present invention have a rotational symmetry axis, even an aspherical surface can be easily processed by using modern ultra-precision processing technology.

Further, in the conventional zoom reflection optical system, since the respective reflecting surfaces are coaxially arranged, as can be seen from the example of FIG. 3, the second and third reflecting surfaces and their supports serve as a light shielding plate. Although it worked, it was a defect as an imager in the infrared region, but in the zoom reflection optical system of the present invention, since each curved surface is arranged non-coaxially, there is no support or the like that blocks light in the entire light flux, It is also perfect for

Further, it is possible to reduce the number of curved surfaces to be used by slightly deforming the surface having a focal point as a basic shape.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a three-sided image-forming non-coaxial confocal zoom catoptric optical system according to the present invention.

FIG. 2 is a diagram showing a reflection optical system when the angle βji formed by the rotational symmetry axis is changed using the same reflection surface as in FIG.

FIG. 3 is a diagram showing a configuration example of a conventional coaxial zoom catoptric optical system having a four-element configuration with an optical axis.

[Explanation of symbols]

S1 ... Rotating paraboloid (first surface), S2 ... Spherical ellipsoid (second surface)
Surface), S3 ... spheroidal surface (third surface), F1 ... first surface entrance focus, F1 '... first surface exit focus, F2 ... second surface entrance focus, F2' ... second surface exit Focus, F3 ... Elliptical entrance focus, F3 '... Third surface exit focus, F1-F1' ... First surface rotational symmetry axis, F2-F2 '... Second surface rotational symmetry axis, F3-F
3 '... The angle formed between the rotational symmetry axis of the third surface and β ... rotational symmetry axis.

Claims (4)

[Claims] 1. A plurality of curved surfaces having a focal point are used, and a part of the curved surfaces is used as a reflecting surface, each reflecting surface having a rotational symmetry axis, and at least one of the individual rotational symmetry axes is By arranging the focal point of a given curved surface and the focal points of the curved surfaces before and after it on the same position without arranging them on a fixed straight line, and by changing the angle formed by the two symmetry axes of the front and rear curved surfaces. A non-coaxial confocal zoom catoptric system characterized in that the focal length changes continuously. 2. The non-coaxial confocal zoom catoptric system according to claim 1, wherein the first entrance surface of the curved surface is a paraboloid of revolution. 3. The non-coaxial confocal zoom catoptric system according to claim 1, wherein the first entrance surface and the last exit surface of the curved surface are rotation paraboloids. 4. The non-coaxial confocal zoom catoptric system according to claim 1, wherein the curved surface is basically a surface having a focal point and is slightly deformed from the surface.