JP6879723B2 - Catadioptric optics, imaging devices and artificial satellites - Google Patents

Description

The present invention corrects the imaging performance of a primary mirror unit composed of a concave reflector, a secondary mirror unit composed of a convex flat or positive meniscus lens and a plano-concave or negative meniscus lens and a convex reflector, and a primary mirror and a secondary mirror. The present invention relates to a catadioptric optical system, which is composed of a refracting part and the reflecting surface is entirely composed of a spherical surface, an imaging device using the same, or an artificial satellite on which the lens is mounted.

In the catadioptric system used for astronomical observation and photography, the Cassegrain type, which can reduce the overall length, is often used. In the classical Cassegrain optical system, the primary mirror consists of a paraboloid, the secondary mirror consists of a hyperboloid and two aspherical surfaces. In the Ritchie-Krechan optical system, which is an improved version of this Cassegrain optical system, both the primary mirror and the secondary mirror are hyperboloids in order to further correct aberrations and widen the field of view, and more accurately, a higher-order aspherical surface is used. However, these aspherical surfaces are more difficult to manufacture than spherical surfaces, and their shapes are also difficult to measure. Therefore, processing takes time, and processing and measurement costs are high.

Further, there is also known a technique of correcting residual aberrations caused by the primary mirror and the secondary mirror by an optical system arranged between the secondary mirror and the image plane.

Patent Document 2 discloses a loss correction lens to be combined with a Ritchie-Crechan optical system or a Cassegrain optical system. The loss lens consists of two lenses, a positive lens and a negative lens, and corrects coma and astigmatism, but does not correct spherical aberration. Therefore, since at least spherical aberration must be corrected in the primary / secondary mirror system, an aspherical surface must be used for either the primary / secondary mirror.

Patent Document 3 discloses an example in which a correction system composed of three lenses is combined with a classical Cassegrain optical system in which the primary mirror is a paraboloid and the secondary mirror is a hyperboloid. However, the mirror surface is an aspherical surface, and although three lens systems for correcting aberrations are disclosed, only the number of lenses and the unevenness of the surface are shown, there is no specific data, and which aberration is corrected to what extent. I don't know if it is.

JP-A-59-222809 JP-A-2015-45887 Japanese Unexamined Patent Publication No. 2016-35499

All-Spherical Catadioptric System for 0.8 m F / 4.5 Astronomical Telescope: Can We Compete With the Ritchey-Chretien Design? (Mehdi Bahrami, Alexander V. Goncharov, and Christopher Dainty, International Optical Design Conference 2010)

As described above, using an aspherical surface makes it difficult to manufacture , so it is sufficient if only a spherical surface can be used.

In a paper such as Bahrami of Non-Patent Document 1, a telescope having only a spherical surface is examined in order to avoid this problem. In this paper, since the telescope used on the ground blurs the image due to the fluctuation of the atmosphere, it is sufficient that the aberration is corrected to the extent of the blur of the image determined by the fluctuation of the atmosphere, and the performance of the diffraction limit normally required is obtained. Not.

Another problem is that the secondary mirror is a plane mirror and the total length is not sufficiently small.

Patent Document 1 mentions the difficulty of manufacturing an aspherical surface of a secondary mirror which is a convex mirror and makes it spherical, but the primary mirror is an aspherical surface. The larger the aperture of a telescope, the higher the resolution, so the primary mirror tends to become larger year by year. Since the difficulty of processing an aspherical surface increases as the size increases, it cannot be said that the difficulty of processing has been avoided if the primary mirror remains an aspherical surface.

Non-Patent Document 1, Patent Documents 1, 2 and 3 also indicate an adaptive optics system arranged between the secondary mirror and the image plane. However, all of them are used in combination with an aspherical reflector, and cannot be said to be sufficient for making the reflector spherical.

The present invention has been made in view of the above problems, and provides a high-performance catadioptric optical system in which the reflector is composed of only a spherical surface, a Cassegrain type is adopted, the size is small, and the diffraction limit is satisfied. With the goal.

The catadioptric optical system of the present invention is a primary mirror portion composed of a spherical concave mirror whose concave surface is directed toward the object side in the order in which light passes from the object side, and is arranged on the object side with respect to the primary mirror portion and is convex on the image side. It consists of a secondary mirror unit having a spherical convex mirror facing the lens, a refracting unit arranged between the secondary mirror unit and the image plane and having a magnification, and the secondary mirror unit is arranged on the image side of the convex mirror and is an object. a plano-convex or meniscus positive lens having a convex surface directed toward the side, the is disposed at a positive lens and spacing of the plano-convex or meniscus, is concave or flat with a concave surface facing the image side Ri Do and a negative lens of meniscus, The positive lens and the negative lens are characterized in that after the light rays from the primary mirror portion pass through, the light rays reflected by the convex mirror pass through again.

According to the present invention, the reflector is spherical on both sides, so that it is easier to manufacture and measure than an aspherical surface, and as a result, the manufacturing cost is kept low. A catadioptric optical system with is obtained.

It is an optical path diagram of Example 1. It is a cross-sectional view of the lens of Example 1. FIG. It is a spherical aberration diagram of Example 1. FIG. It is a non-point aberration diagram of Example 1. FIG. 5 is a distortion diagram of the first embodiment. It is a cross-sectional view of the lens of Example 2. FIG. It is a spherical aberration diagram of Example 2. It is a non-point aberration diagram of Example 2. It is a distortion diagram of Example 2. It is a cross-sectional view of the lens of Example 3. FIG. It is a spherical aberration diagram of Example 3. It is a non-point aberration diagram of Example 3. It is a distortion diagram of Example 3. It is a cross-sectional view of the lens of Example 4. FIG. It is a spherical aberration diagram of Example 4. It is a non-point aberration diagram of Example 4. It is a distortion diagram of Example 4. It is the schematic of the image pickup apparatus of this invention. It is the schematic of the artificial satellite which carries the optical system of this invention.

Hereinafter, examples of the catadioptric optical system of the present invention will be described with reference to the drawings.

The catadioptric optical system of the present invention has a primary mirror portion composed of a concave spherical mirror with a concave surface facing the object side, and a secondary mirror arranged on the object side of the primary mirror and returning the light reflected from the primary mirror to the image plane side. It has a portion Ms and a refracting portion D1 which is arranged between the secondary mirror portion and the image plane and corrects residual aberration in the primary mirror and the secondary mirror portion.

The secondary mirror unit Ms is a secondary mirror which is a convex spherical mirror whose convex surface is directed to the image plane side in order from the object side, L1 of a convex flat or regular meniscus lens whose convex surface is directed to the object side, and a flat concave surface whose concave surface is directed to the image surface side. Or it consists of L2 of a negative meniscus lens.

Further, in the secondary mirror unit Ms, the light reflected from the primary mirror M1 passes from the image side toward the object side, is reflected by the secondary mirror Ms, and the light passes through the two lenses again from the object side toward the image side. Therefore, light passes through the two lenses of the secondary mirror unit Ms in a reciprocating manner.

The refracting portion D1 has a magnifying magnification and is divided into a front group Df and a rear group Dr at the maximum interval in the refracting portion D1, the front group Df is composed of at least one positive lens, and the rear group Dr is a negative lens and a positive lens. It consists of a lens. The negative lens and the positive lens of the rear group Dr are made of different optical materials.

FIG. 1 is an optical path diagram of the catadioptric optical system according to the first embodiment of the present invention.
Since the present invention adopts the so-called Cassegrain type, the light is turned back twice. This is for explaining the passage path of light at this time.

The light from the object is reflected by the primary mirror M1 and turned back toward the object. The light that is turned back by the primary mirror M1 and heads toward the object first enters the plano-concave or negative meniscus lens L2 of the secondary mirror portion Ms, then passes through the convex flat or positive meniscus lens L1 and is the secondary mirror M2 that is a convex mirror. It is reflected again and folded back to the image side.

The light returned to the image side by the secondary mirror M2 passes again in the order of the convex flat or positive meniscus lens L1 and the flat concave or negative meniscus lens L2. Therefore, the positive lens L1 and the negative lens L2 of the secondary mirror unit Ms pass through the light twice in a reciprocating manner. The light emitted from the secondary mirror portion Ms passes through the refracting portion D1 arranged between the secondary mirror portion Ms and the image plane and reaches the image plane.

Hereinafter, in other embodiments, light follows a similar path.
FIG. 2 is an explanatory diagram of the optical arrangement of the optical system according to the first embodiment of the present invention. In the figure, M1 is the primary mirror, M2 is the secondary mirror, L1 and L2 are the lenses of the secondary mirror portion, L3 to L8 are the refracting portions, L3 to L6 are the front group, and L7 and L8 are the rear group.

The primary mirror M1 is a concave mirror made of a spherical surface. The secondary mirror M2 is a convex mirror made of a spherical surface. In the first embodiment, the refracting portion is composed of six lenses from L3 to L8. Further, the front group consists of a positive lens L3, a positive lens L4, a negative lens L5, and a negative lens L6. The rear group consists of a negative lens L7 and a positive lens L8.

FIG. 3 is a spherical aberration diagram in Example 1 and shows the spherical aberration of each spectrum of d-Line, C-Line, and g-Line. FIG. 4 is an astigmatism diagram of d-Line in Example 1. The dotted line shows the tangier and the solid line shows the image plane of the sagittal. FIG. 5 shows the distortion in d-Line in Example 1.

FIG. 6 is an explanatory diagram of the optical arrangement of the optical system according to the second embodiment of the present invention. In the figure, M1 is the primary mirror, M2 is the secondary mirror, L1 and L2 are the lenses of the secondary mirror portion, L3 to L7 are the refracting portions, L3 to L5 are the front group, and L6 and L7 are the rear group. The primary mirror M1 is a concave mirror made of a spherical surface.

The secondary mirror M2 is a convex mirror made of a spherical surface. In the second embodiment, the refracting portion is composed of five lenses from L3 to L7. Further, the front group consists of a positive lens L3, a negative lens L4, and a negative lens L5. The rear group consists of a negative lens L6 and a positive lens L7.

FIG. 7 is a spherical aberration diagram in Example 2 showing the spherical aberration of each spectrum of d-Line, C-Line, and g-Line. FIG. 8 is an astigmatism diagram of d-Line in Example 2. The dotted line shows the tangier and the solid line shows the image plane of the sagittal. FIG. 9 shows the distortion in d-Line in Example 2.

FIG. 10 is an explanatory diagram of the optical arrangement of the optical system according to the third embodiment of the present invention. In the figure, M1 is the primary mirror, M2 is the secondary mirror, L1 and L2 are the lenses of the secondary mirror portion, L3 to L6 are the refracting portions, L3 and L4 are the front group, and L5 and L6 are the rear group. The primary mirror M1 is a concave mirror made of a spherical surface. The secondary mirror M2 is a convex mirror made of a spherical surface.

In the third embodiment, the refracting portion is composed of four lenses L3 to L6. Furthermore, the front group consists of a positive lens L3 and a negative lens L4. The rear group consists of a negative lens L5 and a positive lens L6.

FIG. 11 is a spherical aberration diagram in Example 3 showing the spherical aberration of each spectrum of d-Line, C-Line, and g-Line. FIG. 12 is an astigmatism diagram of d-Line in Example 3. The dotted line shows the tangier and the solid line shows the image plane of the sagittal. FIG. 13 shows the distortion in d-Line in Example 3.

FIG. 14 is an explanatory diagram of the optical arrangement of the optical system according to the fourth embodiment of the present invention. In the figure, M1 is the primary mirror, M2 is the secondary mirror, L1 and L2 are the lenses of the secondary mirror portion, L3 to L5 are the refracting portions, L3 is the front group, and L4 and L5 are the rear groups. The primary mirror M1 is a concave mirror made of a spherical surface. The secondary mirror M2 is a convex mirror made of a spherical surface.

In the fourth embodiment, the refracting portion is composed of three lenses from L3 to L5. Furthermore, the front group consists of a positive lens L3. The rear group consists of a negative lens L4 and a positive lens L5.

FIG. 15 is a spherical aberration diagram in Example 4 showing the spherical aberration of each spectrum of d-Line, C-Line, and g-Line. FIG. 16 is an astigmatism diagram of d-Line in Example 4. The dotted line shows the tangier and the solid line shows the image plane of the sagittal. FIG. 17 shows the distortion at d-Line in Example 4.

The catadioptric optical system of the present invention can be applied to an optical device such as an imaging device or a device mounted on an artificial satellite to image the earth or other celestial bodies.

In the present invention, a casegren type optical system is adopted, and both the primary mirror and the secondary mirror are spherical, so that the manufacturing is easy and the cost is reduced, and the secondary mirror lens group constituting the secondary mirror unit is formed. With respect to, the secondary mirror arranged most on the object side is a spherical surface with a convex surface facing the image side, and a convex flat or positive meniscus lens with a convex surface facing the object side is used as the first lens on the image side of this secondary mirror. By arranging it, and further arranging a plano-concave lens with a concave surface facing the image side or a negative meniscus lens as the second lens on the image side of the first lens, spherical aberration and coma generated in the spherical mirror can be corrected. By arranging a refracting portion having a magnifying magnification between the optical path between the secondary mirror portion and the image plane of such a lens configuration, non-point aberration and the like mainly generated with the angle of view are corrected, and at the same time A high-performance catadioptric optical system that satisfies the desired refraction limit is realized while reducing the size of the optical system formed by the primary and secondary mirrors to further reduce the overall size of the optical system. is there.

As described above, in the present invention, both the primary mirror and the secondary mirror are formed by a spherical surface. Therefore, spherical aberration is greatly generated in the primary mirror and the secondary mirror. In order to correct this spherical aberration, two lenses L1 and L2, positive and negative, are arranged in the secondary mirror unit Ms. The shapes of these two lenses are as follows: L1 is a convex flat or positive meniscus lens with a convex surface facing the object side, and L2 is a flat concave or negative meniscus lens with a concave surface facing the image side.

This is an arrangement and shape for correcting spherical aberration, and is relatively Fno. The negative spherical aberration of the primary mirror M1 which is small and bright is corrected by the positive spherical aberration of the concave surface on the image side of L2. Furthermore, the coma is also corrected by combining with L1.

The lens of the secondary mirror Ms passes light twice in a reciprocating manner, but after correcting the spherical aberration and coma of the light beam from the primary mirror M1, the light reflected and folded back by the secondary mirror M2 passes through L1 and L2 again. In order not to generate extra aberrations, the shape is close to concentric with respect to the focal point of the light reflected and focused by the secondary mirror M2.

As a result, the lenses L1 and L2 of the secondary mirror unit Ms correct the aberration of the primary mirror M1 with a large positive spherical aberration when the light from the primary mirror M1 passes through, and when the light from the secondary mirror M2 passes through, the lens L1 and L2 correct the aberration of the primary mirror M1. Only relatively small aberrations are generated, and the aberrations of the primary mirror M1 and the secondary mirror M2 are corrected in total. More specifically, it is preferable that each of the L1 and L2 lenses has a shape that satisfies the following conditions.

1.0 <SFp <5.0 ... (3)
-5.0 <SFn <-1.0 ... (4)
-0.5 <SFp + SFn <0.5 ... (5)

However, the above SF is a shape factor, and is expressed by the following equation when the radius of curvature on the object side of the lens is r1 and the radius of curvature on the image side is r2.
SF = (r2 + r1) / (r2-r1)

The SFp in the conditional expression (3) indicates the shape factor of L1 which is a positive lens. SFn in the conditional expression (4) indicates the shape factor of L2, which is a negative lens. Conditional expression (5) is the sum of the shape factors of L1 and L2.

If the lower limit of the conditional expression (3) is exceeded, the shape of L1 becomes a biconvex lens, and the light beam on the return path after reflecting the secondary mirror M2 causes positive spherical aberration on the image side surface of L1. Aberration cannot be properly suppressed.

Further, if the upper limit of the conditional equation (3) is exceeded, the curvature becomes too strong, and the system is too far from the concentric with respect to the focal point of the system consisting of the primary mirror M1 and the secondary mirror portion Ms, causing negative spherical aberration. It becomes impossible to properly suppress the spherical aberration of.

If the upper limit of the conditional expression (4) is exceeded, the shape of L2 becomes a biconcave lens, and the light beam on the return path after reflecting the secondary mirror M2 causes positive spherical aberration on the side surface of the object of L2, resulting in a spherical surface of the entire system. Aberration cannot be properly suppressed.

If the lower limit of the conditional equation (4) is exceeded, the curvature becomes too strong, and the system is too far from the focal point of the system consisting of the primary mirror M1 and the secondary mirror part Ms, causing negative spherical aberration. Aberration cannot be properly suppressed.

The conditional expression (5) defines the shapes of both L1 and L2, and represents that the sum of the shape factors of both lenses is near 0. This means that the object side surface of L1 and the image side surface of L2, that is, the outer surface of L1 and L2 and the inner surface between L1 and L2 have similar curvatures, respectively.

That is, when L1 and L2 are combined, they form a shape like a meniscus lens with weak power. A weak-powered meniscus lens with a concave surface facing the object side on the object side of the spherical primary mirror, as is generally known in the so-called Maksutov optical system, has spherical aberration and coma opposite to the concave spherical mirror. have.

In the present invention, the spherical aberration of the spherical mirror is corrected by the same principle. However, a meniscus lens with weak power has a small Z value and is difficult to keep in mind. Also, the correction of spherical aberration and coma is not sufficient. Therefore, in the present invention, the weak meniscus lens is divided into a positive meniscus lens and a negative meniscus lens.

As a result, it is possible to avoid the difficulty of manufacturing a meniscus lens having a weak power, and to highly correct spherical aberration and coma by the curvature of the inner surface of the two lenses and the degree of freedom of the material.

Regardless of which of the upper and lower limits of the conditional expression (5) is deviated, the condition of the concentric meniscus is deviated, and spherical aberration and coma are generated from the outer surface or inner surface of L1 and L2, or all surfaces, and the whole system is affected. Aberration cannot be properly suppressed.

Further, each embodiment has a refracting portion D1 arranged between the secondary mirror portion Ms and the image plane. The refracting portion D1 serves as a field correction system for correcting spherical aberration and coma with the primary mirror M1 and the secondary mirror portion Ms, and then correcting the remaining astigmatism and curvature of field that mainly occur with respect to the angle of view. is working.

The refracting portion D1 is composed of a different number of lenses in each embodiment, but at least three lenses are required to correct the aberration of the image plane of the whole system and to correct the chromatic aberration.

Further, since the refracting portion D1 has a magnifying magnification, the system including the primary mirror M1 and the secondary mirror portion Ms can be reduced with respect to the required focal length, which also contributes to the reduction of the overall length. Therefore, the refracting portion D1 satisfies the following conditional expression (1).
1.0 <Md <1.5 ... (1)

The Md of the conditional expression (1) represents the magnification of the refracting portion D1, and if the lower limit of the conditional expression is less than this in the sense of the enlargement magnification, the effect of reducing the total length is lost, but rather it becomes large. When the magnification increases beyond the upper limit of the conditional expression, the focal length of the system consisting of the primary mirror M1 and the secondary mirror portion Ms becomes short, and Fno. Becomes smaller and the occurrence of spherical aberration and the like becomes too large, and it becomes impossible to properly suppress the aberration of the entire system. In addition, the power of the refracting portion D1 becomes stronger and chromatic aberration or the like is generated, so that the aberration of the entire system cannot be maintained.

Further, the refracting portion D1 is divided into a front group Df and a rear group Dr at the maximum interval in the refracting portion. The front group Df consists of at least one positive lens, and the rear group Dr consists of at least a negative lens and a positive lens. After this, the rear group Dr also has a magnifying magnification, which contributes to reducing the overall length like the telephoto type and reducing the overall length of the entire system.

Actually, it is placed in the convergent luminous flux from the secondary mirror unit Ms, so it is slightly different from the general telephoto type for parallel luminous flux, but it is a telephoto type because the convergent light from the front group Df is magnified by the rear group Dr. The total length becomes smaller as well.

Since the front group Df converges the luminous flux from the secondary mirror unit Ms, it must have at least one positive lens. The rear group has a magnifying magnification and is a negative lens system, but the magnification may be slightly higher, and at least one negative lens and one positive lens are required in consideration of chromatic aberration correction and the like. Here, the rear group Dr satisfies the following conditional expression (2).
1.05 <Mr <4.0 ... (2)

Mr of the conditional expression (2) represents the magnification of the rear group Dr, and when the magnification becomes smaller than the lower limit of the conditional expression (2), the effect of reducing the total length disappears. If the magnification increases beyond the upper limit of the conditional expression (2), the power of the rear group Dr becomes too strong, and it becomes impossible to properly maintain the aberration of the entire system such as chromatic aberration.

Here, in order to correct the chromatic aberration, it is preferable to select the material of the rear group Dr so as to satisfy the following conditions.
1.0 <Vdp --Vdn <20 ... (6)

Here, Vdp represents the Abbe number of the positive lens of the rear group Dr, and Vdn represents the Abbe number of the negative lens. For example, in Japanese Patent Application Laid-Open No. 2016-35499, an adaptive optics system composed of three lenses is used as the same glass material. However, although the reflector is responsible for the main power, in order to be able to use it in the visible light region, it is not possible to sufficiently correct chromatic aberration unless materials with even slightly different Abbe numbers are combined. Can not.

If the difference in Abbe number becomes smaller than the lower limit of the conditional expression (6), the color is not erased, the width from C-Line to g-Line becomes too large, and the performance of the diffraction limit cannot be satisfied. If the difference in Abbe number becomes large beyond the upper limit of the conditional expression (6), the chromatic aberration will be overcorrected.

As described above, if the refraction section D1 is configured, an optical system satisfying the diffraction limit performance can be obtained, but in each embodiment, the number of lenses of the refraction section D1 is different, and the degree of aberration correction is actually different. As the number of lenses decreases, the aberration correction ability also decreases, and it is desired to reduce the aberration generated in the system including the primary mirror M1 and the secondary mirror unit Ms by that amount.

Specifically, as the number of lenses in the refracting portion D1 decreases, the focal length of the primary mirror M1 is gradually increased to obtain Fno. Is increased to reduce the spherical aberration generated in the primary mirror M1. However, if it is left as it is, the total length will be long due to the lengthening of the focal length of the primary mirror M1, so the distance between the negative lenses L2 and L1 of the secondary mirror part Ms is increased to form a telephoto system with the primary mirrors M1 and L2 to increase the total length. I'm holding it down. At the same time, the height of incidence on L2 is increased to increase the positive spherical aberration generated in L2, and the spherical aberration of the entire system is suppressed.

The following conditional expression (7) expresses this condition.
-0.016N + 0.112 <d / L <-0.016N + 0.128 ... (7)

The distance d between the lenses L1 and L2 of the secondary mirror unit Ms is divided by the distance L from the concave surface of the negative lens L2 of the secondary mirror unit Ms to the apex of the surface of the refracting unit D1 on the most object side. N is the number of lenses in the refracting portion D1.

When the lower limit of the conditional expression (7) is exceeded, the distance between L1 and L2 becomes small, the magnification of L2 of the telephoto system combined with the primary mirror M1 becomes small, the effect of suppressing the total length becomes small, and the total length becomes large. Further, the height of incidence of L2 on the concave surface on the image side becomes low, the effect of correcting spherical aberration becomes small, and it becomes impossible to properly suppress the aberration of the entire system.

If the upper limit of the conditional expression (7) is exceeded, the incident height of L2 on the concave surface on the image side becomes too large, positive spherical aberration occurs, and it becomes impossible to properly suppress the spherical aberration of the entire system.

Hereinafter, the configuration of the optical system in each embodiment will be described.
In the first embodiment, a secondary mirror M1 having a concave surface facing the object side in the order in which light passes from the object side, a spherical convex mirror M2 arranged on the object side of the primary mirror and facing the convex surface toward the image side, and two lenses are provided. It consists of a mirror part Ms, a refracting part D1 which is arranged between the secondary mirror part Ms and the image plane and has a magnification, and the secondary mirror part Ms is a convex flat or a positive meniscus with the convex surface facing the image side of the convex mirror and the object side. It is composed of a lens L1 and a flat concave or meniscus negative lens L2 which is arranged at a distance and has a concave surface facing the image side.

The shapes of the positive lens L1 and the negative lens L2 satisfy the conditional equations (3), (4) and (5), whereby the spherical aberration and coma generated by the primary mirror M1 and the secondary mirror M2, which are spherical mirrors, are good. It is corrected to. Further, the distance d between the positive lens L1 and the negative lens L2 satisfies the conditional expression (7), whereby the overall length is reduced and the diffraction limit performance is achieved regardless of the configuration of the refracting portion D1.

The refracting portion D1 is composed of a front group Df and a rear group Dr divided by the maximum lens spacing in the refracting portion D1. The front group Df consists of the positive lens L3, the positive lens L4, the negative lens L5, and the negative lens L6 in order from the object side, and the rear group Dr consists of the negative lens L7 and the positive lens L8 in order from the object side. It is configured.

With these configurations, astigmatism and curvature of field that occur mainly with the angle of view are corrected, and the performance of the diffraction limit is satisfied. The refracting portion D1 has a magnifying magnification and satisfies the conditional expression (1), thereby obtaining the effect of shortening the total length of the optical system. Further, the magnification of the rear group Dr satisfies the conditional expression (2), whereby the total length of the optical system is kept small.

The negative lens L7 and the positive lens L8 constituting the rear group Dr are made of different materials, and the Abbe number satisfies the conditional equation (6), and the chromatic aberration and the like of the whole system are kept good.

In the second embodiment, a secondary mirror M1 having a concave surface facing the object side in the order in which light passes from the object side, a spherical convex mirror M2 arranged on the object side of the primary mirror and facing the convex surface toward the image side, and two lenses are provided. It consists of a mirror part Ms, a refracting part D1 which is arranged between the secondary mirror part Ms and the image plane and has a magnification, and the secondary mirror part Ms is a convex flat or a positive meniscus with the convex surface facing the image side of the convex mirror and the object side. It is composed of a lens L1 and a flat concave or meniscus negative lens L2 which is arranged at a distance and has a concave surface facing the image side.

The shapes of the positive lens L1 and the negative lens L2 satisfy the conditional equations (3), (4) and (5), whereby the spherical aberration and coma generated by the primary mirror M1 and the secondary mirror M2, which are spherical mirrors, are good. It is corrected to. Further, the distance d between the positive lens L1 and the negative lens L2 satisfies the conditional expression (7), whereby the overall length is reduced and the diffraction limit performance is achieved regardless of the configuration of the refracting portion D1.

The refracting portion D1 is composed of a front group Df and a rear group Dr divided by the maximum lens spacing in the refracting portion D1. The front group Df is composed of a positive lens L3, a negative lens L4, and a negative lens L5 in order from the object side, and the rear group Dr is composed of a negative lens L6 and a positive lens L7 in order from the object side.

With these configurations, astigmatism and curvature of field that occur mainly with the angle of view are corrected, and the performance of the diffraction limit is satisfied. The refracting portion D1 has a magnifying magnification and satisfies the conditional expression (1), thereby obtaining the effect of shortening the total length of the optical system.

Further, the magnification of the rear group Dr satisfies the conditional expression (2), whereby the total length of the optical system is kept small. The negative lens L6 and the positive lens L7 constituting the rear group Dr are made of different materials, and the Abbe number satisfies the conditional equation (6), and the chromatic aberration and the like of the whole system are kept good.

Example 3 has a spherical mirror M1 having a concave surface facing the object side in the order in which light passes from the object side, a spherical convex mirror M2 arranged on the object side of the primary mirror and having a convex surface facing the image side, and a secondary lens having two lenses. It consists of a mirror part Ms, a refracting part D1 which is arranged between the secondary mirror part Ms and the image plane and has a magnification, and the secondary mirror part Ms is a convex flat or a positive meniscus with the convex surface facing the image side of the convex mirror and the object side. It is composed of a lens L1 and a flat concave or meniscus negative lens L2 which is arranged at a distance and has a concave surface facing the image side.

The shapes of the positive lens L1 and the negative lens L2 satisfy the conditional equations (3), (4) and (5), whereby the spherical aberration and coma generated by the primary mirror M1 and the secondary mirror M2, which are spherical mirrors, are good. It is corrected to. Further, the distance d between the positive lens L1 and the negative lens L2 satisfies the conditional expression (7), whereby the overall length is reduced and the diffraction limit performance is achieved regardless of the configuration of the refracting portion D1.

The refracting portion D1 is composed of a front group Df and a rear group Dr divided by the maximum lens spacing in the refracting portion D1. The front group Df is composed of a positive lens L3 and a negative lens L4 in order from the object side, and the rear group Dr is composed of a negative lens L5 and a positive lens L6 in order from the object side.

With these configurations, astigmatism and curvature of field that occur mainly with the angle of view are corrected, and the performance of the diffraction limit is satisfied. The refracting portion D1 has a magnifying magnification and satisfies the conditional expression (1), thereby obtaining the effect of shortening the total length of the optical system.

Further, the magnification of the rear group Dr satisfies the conditional expression (2), whereby the total length of the optical system is kept small. The negative lens L5 and the positive lens L6 constituting the rear group Dr are made of different materials, and the Abbe number satisfies the conditional expression (6), and the chromatic aberration and the like of the whole system are kept good.

In the fourth embodiment, a secondary mirror M1 having a concave surface facing the object side in the order in which light passes from the object side, a spherical convex mirror M2 arranged on the object side of the primary mirror and facing the convex surface toward the image side, and two lenses are provided. It consists of a mirror part Ms, a refracting part D1 which is arranged between the secondary mirror part Ms and the image plane and has a magnification, and the secondary mirror part Ms is a convex flat or a positive meniscus with the convex surface facing the image side of the convex mirror and the object side. It is composed of a lens L1 and a flat concave or meniscus negative lens L2 which is arranged at a distance and has a concave surface facing the image side.

The shapes of the positive lens L1 and the negative lens L2 satisfy the conditional equations (3), (4) and (5), whereby the spherical aberration and coma generated by the primary mirror M1 and the secondary mirror M2, which are spherical mirrors, are good. It is corrected to. Further, the distance d between the positive lens L1 and the negative lens L2 satisfies the conditional expression (7), whereby the overall length is reduced and the diffraction limit performance is achieved regardless of the configuration of the refracting portion D1.

The refracting portion D1 is composed of a front group Df and a rear group Dr divided by the maximum lens spacing in the refracting portion D1. The front group Df is composed of a positive lens L3 in order from the object side, and the rear group Dr is composed of a negative lens L4 and a positive lens L5 in order from the object side.

With these configurations, astigmatism and curvature of field that occur mainly with the angle of view are corrected, and the performance of the diffraction limit is satisfied. The refracting portion D1 has a magnifying magnification and satisfies the conditional expression (1), thereby obtaining the effect of shortening the total length of the optical system.

Further, the magnification of the rear group Dr satisfies the conditional expression (2), whereby the total length of the optical system is kept small. The negative lens L4 and the positive lens L5 constituting the rear group Dr are made of different materials, and the Abbe number satisfies the conditional equation (6), and the chromatic aberration and the like of the whole system are kept good.

FIG. 18 shows a case where the optical system of the present invention is used as an image pickup apparatus. On the image plane, a solid-state image sensor (photoelectric conversion element) or a silver salt film that receives an image formed by an optical system, such as a CCD sensor or a CMOS sensor, is arranged. The benefits described in Examples 1 to 4 are effectively enjoyed in the imaging apparatus as disclosed in this Example.

Further, FIG. 19 shows a case where the optical system of the present invention is mounted on an artificial satellite as an imaging device. An artificial satellite in which the optical system of the present invention is applied to an imaging device may be mounted on an artificial satellite that observes and images the earth and other celestial bodies from outer space. The benefits described in Examples 1 to 4 are effectively enjoyed even when mounted on an artificial satellite.

When the optical system of the present invention is mounted on an artificial satellite, it is preferable to select a low thermal expansion material as the material of the primary mirror M1 and the secondary mirror M2. Since there is no air in space, there is a large temperature difference between when the sun is shining and when the sun is not shining, so if the mirror is deformed due to temperature changes, the focus shift and aberrations may change and the desired performance may not be obtained. It will occur. Specifically, it is desirable that the coefficient of linear expansion is 10 × 10 ^ -6 or less.

Further, when the optical system of the present invention is mounted on an artificial satellite, it is preferable to select a material having a relatively low refractive index for the lenses L1 and L2 in the secondary mirror unit Ms and the refraction unit D1. In space, the intensity of radiation is stronger than on the earth, and it is known that ordinary glass will be colored if it is continuously exposed to radiation such as gamma rays. This shortens the useful life of the artificial satellite.

To avoid this, radiation-resistant glass may be used, but since it is a special purpose, there are fewer types than ordinary optical glass. Moreover, there are many glass materials with a low refractive index on the so-called Sea of Japan side of the refractive index-Abe number map of glass. Therefore, more specifically, it is desirable to select and design a material having a refractive index of 1.7 or less. In particular, it is necessary to make the lens in the secondary mirror unit Ms directly exposed to outer space and the lens on the most object side of the refracting unit D1 have a low refractive index.

Although the preferred examples of the zoom lens of the present invention have been described above, it goes without saying that the present invention is not limited to these examples, and various modifications and changes can be made within the scope of the gist thereof.

Numerical examples corresponding to Examples 1 to 4 are shown below. In each numerical embodiment, i indicates the order of the planes from the object plane. In the numerical embodiment, R is the radius of curvature of the lens surface, D is the lens thickness and lens spacing, and Nd and Vd are the refractive index and Abbe number in d-Line of the lens material, respectively.

Table 5 shows the calculation results of each conditional expression based on the lens data of the numerical examples 1 to 4 described below.

<Example 1>

<Example 2>

<Example 3>

<Example 4>

Claims (9)

From the object side, in the order of light passing
A primary mirror unit consisting of a spherical concave mirror with a concave surface facing the object side,
A secondary mirror unit having a spherical convex mirror arranged on the object side with respect to the primary mirror unit and having a convex surface facing the image side.
It consists of a refracting part that is arranged between the secondary mirror part and the image plane and has a magnifying magnification.
The secondary mirror unit
A convex flat or meniscus positive lens arranged on the image side of the convex mirror and having a convex surface facing the object side,
The plano-convex or are arranged at a positive lens and spacing of the meniscus, is concave or flat with a concave surface facing the image side Ri Do and a negative lens of meniscus,
A catadioptric optical system characterized in that, after a light ray from the primary mirror portion passes through the positive lens and the negative lens, the light ray reflected by the convex mirror passes again. The refracting portion comprises a front group and a rear group separated by a maximum lens spacing in the refracting portion, the front group includes at least one positive lens, and the rear group consists of at least a negative lens and a positive lens. The catadioptric optical system according to claim 1. Assuming that the magnification of the refracted portion is Md,
1.0 <Md <1.5
The catadioptric optical system according to claim 1 or 2, wherein the catadioptric optical system is characterized in that. Assuming that the magnification of the rear group of the refracting portion is Mr.
1.05 <Mr <4.0
The catadioptric optical system according to claim 2, wherein the catadioptric optical system is characterized in that. From the object side, in the order of light passing
A primary mirror unit consisting of a spherical concave mirror with a concave surface facing the object side,
A secondary mirror unit having a spherical convex mirror arranged on the object side with respect to the primary mirror unit and having a convex surface facing the image side.
A refracting portion arranged between the secondary mirror portion and the image plane and having a magnifying magnification.
Consists of
The secondary mirror unit
A convex flat or meniscus positive lens arranged on the image side of the convex mirror and having a convex surface facing the object side,
With a flat concave or meniscus negative lens that is placed at a distance from the convex flat or meniscus positive lens and has a concave surface facing the image side.
Consists of
When the radius of curvature on the object side of the lens is r1 and the radius of curvature on the image side is r2,
SF = (r2 + r1) / (r2-r1)
For the shape factor SF represented by
Assuming that the shape factor of the positive lens of the secondary mirror is SFp and the shape factor of the negative lens is SFn,
1.0 <SFp <5.0
-5.0 <SFn <-1.0
-0.5 <SFp + SFn <0.5
Features and to Luke Tadi opto Rick optical system satisfies the. From the object side, in the order of light passing
A primary mirror unit consisting of a spherical concave mirror with a concave surface facing the object side,
A secondary mirror unit having a spherical convex mirror arranged on the object side with respect to the primary mirror unit and having a convex surface facing the image side.
A refracting portion arranged between the secondary mirror portion and the image plane and having a magnifying magnification.
Consists of
The secondary mirror unit
A convex flat or meniscus positive lens arranged on the image side of the convex mirror and having a convex surface facing the object side,
It is composed of a flat concave or meniscus negative lens that is arranged at a distance from the convex flat or meniscus positive lens and has a concave surface facing the image side .
The refracting portion comprises a front group and a rear group separated by a maximum lens spacing in the refracting portion, the front group including at least one positive lens, and the rear group consisting of at least a negative lens and a positive lens.
Assuming that the Abbe number of the negative lens in the rear group of the refracting portion is Vdn and the Abbe number of the positive lens is Vdp.
1.0 <Vdp − Vdn <20
Features and to Luke Tadi opto Rick optical system satisfies the. From the object side, in the order of light passing
A primary mirror unit consisting of a spherical concave mirror with a concave surface facing the object side,
A secondary mirror unit having a spherical convex mirror arranged on the object side with respect to the primary mirror unit and having a convex surface facing the image side.
A refracting portion arranged between the secondary mirror portion and the image plane and having a magnifying magnification.
Consists of
The secondary mirror unit
A convex flat or meniscus positive lens arranged on the image side of the convex mirror and having a convex surface facing the object side,
With a flat concave or meniscus negative lens that is placed at a distance from the convex flat or meniscus positive lens and has a concave surface facing the image side.
Consists of
The number of lenses of the refracting portion is N, the distance between the positive and negative lenses of the secondary mirror portion is d, and the distance from the concave surface of the negative lens of the secondary mirror portion to the apex of the surface closest to the object side of the refracting portion is L. Then,
d / L is
−0.016N + 0.112 <d / L <−0.016N + 0.128
Features and to Luke Tadi opto Rick optical system satisfies the. An image pickup apparatus comprising the catadioptric optical system according to any one of claims 1 to 7 and an image pickup element that receives an image formed by the catadioptric optical system. An artificial satellite equipped with the catadioptric optical system according to any one of claims 1 to 7.
An artificial satellite characterized in that the refractive index of the secondary mirror portion and the lens on the most object side of the refracting portion is 1.7 or less.

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