CN114815200A - Large-relative-aperture off-axis five-mirror non-axial zooming imaging optical system - Google Patents
Large-relative-aperture off-axis five-mirror non-axial zooming imaging optical system Download PDFInfo
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- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B17/00—Systems with reflecting surfaces, with or without refracting elements
- G02B17/02—Catoptric systems, e.g. image erecting and reversing system
- G02B17/06—Catoptric systems, e.g. image erecting and reversing system using mirrors only, i.e. having only one curved mirror
- G02B17/0647—Catoptric systems, e.g. image erecting and reversing system using mirrors only, i.e. having only one curved mirror using more than three curved mirrors
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- G—PHYSICS
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- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B15/00—Optical objectives with means for varying the magnification
- G02B15/14—Optical objectives with means for varying the magnification by axial movement of one or more lenses or groups of lenses relative to the image plane for continuously varying the equivalent focal length of the objective
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B17/00—Systems with reflecting surfaces, with or without refracting elements
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B17/00—Systems with reflecting surfaces, with or without refracting elements
- G02B17/02—Catoptric systems, e.g. image erecting and reversing system
- G02B17/06—Catoptric systems, e.g. image erecting and reversing system using mirrors only, i.e. having only one curved mirror
Abstract
The invention discloses a large-relative-aperture off-axis five-mirror non-axial zooming imaging optical system, and belongs to the field of optical zooming imaging. The invention adopts a secondary imaging structure, and a non-axial synchronous zooming primary imaging subsystem adds vertical axis zooming adjustment on the basis of off-axis three-reflection full-motion zooming, so that the optimized degree of freedom of a zooming imaging optical system is increased; the synchronous adjustment of the axial movement and the vertical axis movement is realized through the non-axial movement vector, and the non-axial synchronous zooming of the zooming imaging optical system is realized. The subsequent imaging subsystem realizes the turnover, transmission and zoom imaging of the intermediate image plane at one time through two fixed reflectors. The primary image surface is imaged again through the relay imaging subsystem, and the field diaphragm is arranged at the primary image surface, so that stray light caused by the fact that a light blocking device is difficult to arrange due to movement of the reflector is remarkably reduced, and the stray light reaching the image surface of the detector is effectively eliminated. The invention does not need to use a free-form surface reflector, thereby reducing the processing and detection cost.
Description
Technical Field
The invention belongs to the field of optical zoom imaging, and particularly relates to an off-axis reflection zoom imaging optical system with a large relative aperture and a large zoom ratio.
Background
In the field of airborne earth observation, the design of a zoom optical system with wide spectrum band, large zoom ratio and high resolution has important significance. The off-axis total reflection type zoom optical system has the characteristics of no chromatic aberration, wide imaging spectrum, consideration of large field search and small field aiming, and no-blocking imaging, and meets the application requirements of a new generation of high-performance light and small airborne earth observation loads.
The off-axis total reflection type zoom optical system is divided into an active zoom type and a mechanical zoom type according to the principle. The off-axis total reflection type active zooming imaging system realizes the change of the system focal power by controlling the change of the curvature and the like of active optical elements (a deformable mirror, a spatial light modulator, a liquid lens and the like). The off-axis total reflection type active zoom imaging system has high response speed and relatively small volume, but still has the limitations of high regulation and control difficulty of an active optical element, high fitting difficulty of an off-axis surface type, relatively low data transmission speed and high cost. The off-axis total reflection type mechanical zoom imaging system realizes the change of the integral focal power by controlling the axial movement of the internal reflector of the system, and compared with the off-axis total reflection type active zoom imaging system, the off-axis total reflection type mechanical zoom imaging system has the advantages of slow response speed, large volume, relatively simple mechanical control and low cost. The traditional off-axis total reflection type mechanical zooming imaging system generally adopts a three-reflector and four-reflector structure, can realize zooming imaging with a large zoom ratio, but has an entrance pupil diameter with a fixed size and a small relative aperture, and particularly in a long-focus state, the relative aperture of the system is extremely small, so that the requirement of high-resolution imaging is difficult to meet. In addition, in order to realize high-resolution imaging in a large zoom ratio range, a free-form surface type mirror is used for correcting high-order asymmetric aberration of the system, but the processing difficulty and the detection difficulty of the free-form surface mirror are large, and the development difficulty and the cost of the system are greatly increased.
Disclosure of Invention
In order to overcome the defects of small relative aperture and complex surface type of the traditional off-axis total reflection type mechanical zoom imaging system, the invention mainly aims to provide an off-axis five-mirror non-axial zoom imaging optical system with a large relative aperture. The structure of secondary imaging is adopted, namely five reflectors are divided into a non-axial synchronous zooming primary imaging subsystem and a post-relay imaging subsystem according to the imaging structure and functions. The non-axial synchronous zooming primary imaging subsystem adds vertical axis zooming adjustment on the basis of off-axis three-reflection full-motion zooming, and increases the optimized degree of freedom of the zooming imaging optical system; in addition, the synchronous adjustment of axial movement and vertical axis movement is realized through the non-axial movement vector, and the non-axial synchronous zooming of the zooming imaging optical system is realized, so that the imaging quality is good under different focal length states. The subsequent imaging subsystem realizes the turnover, transmission and zoom imaging of the intermediate image plane at one time through two fixed reflectors. The relay imaging subsystem is used for imaging the primary image surface of the non-axial synchronous zooming primary imaging subsystem again, a field stop can be arranged at the primary image surface, stray light caused by the fact that a light blocking device is difficult to arrange due to movement of a reflector is remarkably reduced, and therefore the stray light reaching the detector image surface is effectively eliminated. The invention also has the following advantages: and a free-form surface reflector is not needed, so that the processing and detection cost is reduced.
The purpose of the invention is realized by the following technical scheme:
the invention discloses a large-relative-aperture off-axis five-mirror non-axial zooming imaging optical system which comprises an iris diaphragm, a main reflector, a secondary reflector, a third reflector, a fourth reflector, a fifth reflector and a detector image surface, and further comprises a translation table used for moving the main reflector, the secondary reflector and the third reflector.
The iris diaphragm is an aperture diaphragm, and the aperture of the aperture diaphragm changes along with the change of the focal length. The relative aperture of the zooming imaging optical system is ensured to be fixed by adjusting the aperture of the aperture diaphragm.
The main reflector, the secondary reflector and the third reflector are zooming group and compensation group elements, and zooming imaging is realized by non-axially moving the three reflectors. The non-axial movement is realized based on a non-axial movement vector, and the non-axial movement vector is a non-axial movement vector formed by combining an axial movement amount and a vertical axis movement amount. The change of the focal length of the non-axial zooming imaging optical system is realized through axial movement; the degree of freedom of the zoom imaging optical system is increased through the movement in the vertical axis direction, the wave aberration among multiple structures of the zoom imaging optical system is actively balanced by the action of the eccentric amounts of the three reflectors, namely the main reflector, the secondary reflector and the third reflector, on an aberration field, and the correction of high-order astigmatism and coma aberration of the non-axial zoom imaging optical system under different focal length structures is realized. The non-axial movement vector is used for realizing the synchronous adjustment of the axial movement and the vertical movement, and the non-axial synchronous zooming of the zooming imaging optical system is realized, so that the imaging quality is good under different focal length states, and a free-form surface is not required.
Preferably, the wave aberration among multiple structures of the zoom imaging optical system is actively balanced by using the effect of the eccentricity of the three reflectors on the aberration field, and the implementation method is as follows:
step one, determining the axial movement amount of the three reflectors according to an axial movement formula (1).
Where r is the radius of curvature of the mirrors, t is the distance between the mirrors, α ji Is a barrier ratio, beta ji To increase the magnification, f j The focal length under different structures.
Determining a primary wave aberration coefficient of the zoom imaging optical system according to the formula (2), wherein the primary wave aberration coefficient is related to alpha ji ,β ji ,f j As a function of (c).
Wherein:
wherein: k is the same as i Is the coefficient of the quadratic surface of the mirror i, and
n i 1(i is an odd number), n i 1(i is an even number), n i ' -1(i is an odd number), n i ' 1(i is even number) (5)
u j1 ＝0,u j1 '＝2h j1 /r 1 ,u j2 ＝u j1 ',u j2 '＝u j2 /β j1 ,u j3 ＝u j2 ',u j3 '＝u j3 /β j2 (6)
Step three, based on the primary wave aberration coefficient of the zoom imaging optical system determined in the step two, determining the eccentricity sigma of the reflecting mirror under different structures through a formula (7) ji And according to said eccentricity σ ji The wave aberration among multiple structures of the zoom imaging optical system is actively balanced, and the correction of high-order astigmatism and coma aberration of the non-axial zoom imaging optical system under different focal length structures is realized. The eccentricity amount sigma ji Difference of (a) delta sigma j1 ,△σ j2 ,△σ j3 I.e. the amount of vertical movement of the three mirrors.
Wherein: the vertical axis movement is expressed as the eccentricity sigma of the reflector under different structures ji In contrast, j denotes the jth reconstruction and i denotes the ith mirror. As shown in equation (7), the coma center and astigmatism center of the off-axis zoom imaging system are always related to α ji ,β ji ,f j ,
The function of (3) is added with the movement in the vertical axis direction on the basis of the axial movement, the degree of freedom of the system is increased, and the multijunction of the zoom system is actively balanced by utilizing the action characteristic of the offset of the off-axis system on an aberration fieldThe wave aberration between the structures.
The fourth reflector and the fifth reflector form a relay imaging subsystem with the magnification of b, and the spatial position of the relay imaging subsystem is unchanged, so that the curvature radius and the thickness parameter of the relay imaging subsystem can be independently calculated. Defining the fourth mirror to have a magnification of beta 4 The fifth mirror has a magnification of beta 5 And satisfy beta 4 β 5 ＝b。
The relay imaging subsystem formed by the fourth reflector and the fifth reflector performs secondary imaging on the primary image surface of the non-axial synchronous zooming primary imaging subsystem, and in order to ensure that imaging is clear and free of stray light, a view field diaphragm is arranged at the primary image surface position as an optimal choice, so that stray light caused by the fact that a light blocking device is difficult to arrange due to movement of the reflectors is remarkably reduced, and the stray light capable of reaching the image surface of the detector is effectively eliminated.
Preferably, the primary mirror, the third mirror, the fourth mirror and the fifth mirror are concave mirrors, the secondary mirror is a convex mirror, and all five mirrors are 8-order aspheric surfaces. The reflecting surfaces of the main reflector and the secondary reflector are oppositely arranged, the reflecting surfaces of the secondary reflector and the third reflector are oppositely arranged, the reflecting surfaces of the third reflector and the fourth reflector are oppositely arranged, the reflecting surfaces of the fourth reflector and the fifth reflector are oppositely arranged, and the fifth reflector and the detector image surface are oppositely arranged. The variable diaphragm and the center of the mirror surface of the main reflector are eccentrically arranged along the Y-axis direction, the eccentricity is the same, the secondary reflector, the third reflector, the fourth reflector and the fifth reflector are all eccentrically and obliquely arranged on the optical axis, and the eccentricity and the inclination of each reflector are different.
The invention discloses a working method of a large relative aperture off-axis five-mirror non-axial zooming imaging optical system, which comprises the following steps:
the light passing through the iris diaphragm is incident on the reflecting surface of the main reflecting mirror, forms first reflected light after being reflected by the reflecting surface of the main reflecting mirror, the first reflected light is incident on the reflecting surface of the secondary reflecting mirror, forms second reflected light after being reflected by the reflecting surface of the secondary reflecting mirror, the second reflected light is incident on the reflecting surface of the third reflecting mirror, forms third reflected light after being reflected by the reflecting surface of the third reflecting mirror, the third reflected light is incident on the reflecting surface of the fourth reflecting mirror, forms fourth reflected light after being reflected by the reflecting surface of the fourth reflecting mirror, the fourth reflected light is incident on the reflecting surface of the fifth reflecting mirror, forms fifth reflected light after being reflected by the reflecting surface of the fifth reflecting mirror, and the fifth reflected light is received by the detector and forms an image. When the main reflector, the secondary reflector and the third reflector respectively move to corresponding positions in a non-axial direction, the system is switched to a long-focus state with amplified resolution, and the object in the range of the field of view is subjected to clear imaging with higher object space resolution.
The synchronous adjustment of the axial movement and the vertical axis movement is realized through the non-axial movement vector, and the non-axial synchronous zooming of the zooming imaging optical system is realized. And the secondary imaging subsystem is used for imaging the primary intermediate image again, and the field diaphragm is added at the stable primary intermediate image surface position, so that the stray light entering the secondary imaging subsystem and the detector image surface is effectively eliminated. Through the arrangement, the imaging quality under different focal length states is ensured to be good, a free-form surface is not required, and the processing and detection cost is reduced.
Has the advantages that:
1. the invention discloses a large-relative-aperture off-axis five-mirror non-axial zooming imaging optical system, wherein a fourth reflector and a fifth reflector are fixed reflectors, a main reflector, a secondary reflector and a third reflector are movable reflectors, the main reflector, the secondary reflector and the third reflector form a full-motion non-axial synchronous zooming primary imaging subsystem, and the fourth reflector and the fifth reflector form a post-relay imaging subsystem. The focal power of the reflector group is changed by non-axially moving the main reflector, the secondary reflector and the third reflector, so that zooming is realized. The subsequent imaging subsystem realizes the turnover, transmission and zoom imaging of the intermediate image plane at one time through two fixed reflectors. By adding the field diaphragm at the primary intermediate image surface position, stray light entering the subsequent relay imaging subsystem can be effectively eliminated. The non-axial movement vector is used for realizing the synchronous adjustment of the axial movement and the vertical movement, and the non-axial synchronous zooming of the zooming imaging optical system is realized, so that the imaging quality is good under different focal length states, and a free-form surface is not required.
2. The invention discloses a large-relative-aperture off-axis five-mirror non-axial zooming imaging optical system. The change of the focal length of the non-axial zooming imaging optical system is realized through axial movement; the degree of freedom of the zoom imaging optical system is increased through the movement in the vertical axis direction, the wave aberration among multiple structures of the zoom imaging optical system is actively balanced by the action of the eccentricity of the three reflectors on an aberration field, and the correction of high-order astigmatism and coma aberration of the non-axial zoom imaging optical system under different focal length structures is realized.
3. The invention discloses a large-relative-aperture off-axis five-mirror non-axial zooming imaging optical system, which establishes a correction method of high-order astigmatism and coma of the zooming imaging optical system according to a Seidel aberration theory and a vector aberration theory, actively balances the wave aberration among multiple structures of the zooming imaging optical system by utilizing the action of the eccentricity of three reflectors on an aberration field, and realizes the correction of the high-order astigmatism and the coma of the non-axial zooming imaging optical system under different focal length structures.
4. According to the large-relative-aperture off-axis five-mirror non-axial zooming imaging optical system disclosed by the invention, the field diaphragm is arranged at the stable primary image surface, so that the stray light which cannot be eliminated due to the movement of the reflector in the non-axial synchronous zooming primary imaging subsystem can be greatly reduced, and the stray light which can reach the image surface of a detector can be effectively eliminated.
5. The off-axis five-mirror non-axial zooming imaging optical system with the large relative aperture disclosed by the invention only needs to use a high-order aspheric reflector and does not need to use a free-form surface reflector, so that the processing and detection cost is reduced.
Drawings
FIG. 1 is a schematic view of the structure of the apparatus of the present invention.
Fig. 2 is a schematic diagram of a spatial coordinate system.
FIG. 3 is a short focus state optical path diagram of the apparatus of the present invention.
FIG. 4 is a diagram of the optical path of the device of the present invention in the tele state.
The optical system comprises an iris diaphragm 01, a main reflector 02, a secondary reflector 03, a third reflector 04, a fourth reflector 05, a fifth reflector 06 and a detector image plane 07.
Detailed Description
To better illustrate the objects and advantages of the present invention, the following detailed description of the invention is given by way of example with reference to the accompanying drawings.
As shown in fig. 1, the main object of the present invention is to provide an off-axis five-mirror non-axial zoom imaging optical system with large relative aperture, which includes an iris 01, a primary mirror 02, a secondary mirror 03, a third mirror 04, a fourth mirror 05, a fifth mirror 06, and a detector image plane 07.
The system is located in a spatial coordinate system (XYZ), with the directions of the coordinate axes as shown in fig. 2.
The iris diaphragm 01 is an aperture diaphragm of the system, the aperture of the iris diaphragm changes along with the change of the focal length, and the relative aperture of the system is ensured to be 1:4 all the time.
The main reflecting mirror 02 is a concave reflecting mirror, and the surface type is an 8-order aspheric surface, and is used for focusing and reflecting light from a target to form first reflected light.
The secondary reflector 03 is a convex reflector, and the surface type of the secondary reflector is an 8-order aspheric surface, and is used for reflecting the light from the primary reflector 02 again to form second reflected light.
The third reflector 04 is a concave reflector, and the surface type of the third reflector is an 8-order aspheric surface, and is used for focusing the light from the secondary reflector 03 on the primary image surface to form third reflected light.
The fourth reflector 05 is a concave reflector, has an 8-order aspheric surface, and has a constant spatial position, and is configured to reflect the light from the third reflector 04 to form four reflected lights.
The fifth reflector 06 is a concave reflector, the surface type of which is an 8-order aspheric surface, and the spatial position of which is unchanged, and is used for focusing and imaging the light from the fourth reflector 05 on the target surface of the detector 07.
The main mirror 02, the sub-mirror 03 and the third mirror 04 are moved to the predetermined positions by the translation stage.
The main reflector 02, the secondary reflector 03 and the third reflector 04 form a full-motion non-axial synchronous zooming primary imaging subsystem, and the fourth reflector 05 and the fifth reflector 06 form a relay imaging subsystem with the magnification of 1.
The relay imaging subsystem performs secondary imaging on a primary image surface of the non-axial synchronous zooming primary imaging subsystem, and as an optimal choice, a field stop can be arranged at the position of the primary image surface, so that stray light caused by the fact that a light blocking device is difficult to arrange due to movement of a reflector is greatly reduced, and the stray light reaching the image surface of the detector is effectively eliminated.
The main reflector 02, the secondary reflector 03 and the third reflector 04 are elements of a zoom group and a compensation group, the change of the focal length of the system is realized by non-axially moving the three reflectors, and the zoom ratio is 5 times.
The position of the primary intermediate image surface of the non-axial synchronous zooming primary imaging subsystem is unchanged, so that the position of the detector image surface 07 is unchanged.
The non-axial movement is realized based on a non-axial movement vector, and the non-axial movement vector is a non-axial movement vector formed by combining an axial movement amount and a vertical axis movement amount. The change of the focal length of the non-axial zooming imaging optical system is realized through axial movement; the degree of freedom of the zoom imaging optical system is increased through the movement in the vertical axis direction, the wave aberration among multiple structures of the zoom imaging optical system is actively balanced by the action of the eccentricity of the three reflectors on an aberration field, and the correction of high-order astigmatism and coma aberration of the non-axial zoom imaging optical system under different focal length structures is realized. The non-axial movement vector is used for realizing the synchronous adjustment of the axial movement and the vertical movement, and the non-axial synchronous zooming of the zooming imaging optical system is realized, so that the imaging quality is good under different focal length states, and a free-form surface is not required.
The non-axial movement of the main reflector 02, the secondary reflector 03 and the third reflector 04 is movement in a one-dimensional direction in a YZ plane, and can be decomposed into an axial (Z direction) movement component and a vertical axis (Y direction) movement component, and specifically, in different focal length states, the distances from the main reflector 02, the secondary reflector 03 and the third reflector 04 to the previous surface are different, and the Y-axis eccentricity amounts of the main reflector 02, the secondary reflector 03 and the third reflector 04 are different. The zoom imaging optical system comprises a zoom imaging optical system, a vertical axis (Y direction) and a non-axial moving vector, wherein the axial (Z direction) movement is used for realizing the change of the focal length of the system, the vertical axis (Y direction) movement is used for realizing the correction of high-order astigmatism and coma aberration of the system under different focal length structures, the non-axial moving vector is used for realizing the synchronous adjustment of the axial movement and the vertical axis movement, and the non-axial synchronous zooming of the zoom imaging optical system is realized, so that the imaging quality under different focal length states is ensured to be good, and a free curved surface is not required.
The general expression for an 8 th order aspheric surface is:
wherein z is the curved surface vector height, c is the curved surface curvature, k is the conic coefficient, alpha i Is the coefficient of the i-th term in the polynomial.
According to the implementation method for actively balancing the wave aberration among the multiple structures of the zoom imaging optical system by utilizing the effect of the eccentric amounts of the three reflectors on the aberration field disclosed by the embodiment and the subsequent optimization determination of the surface type parameters and the non-axial movement amount of the reflectors, the method comprises the following steps:
in this embodiment, the radius r of the reflecting surfaces of the main mirror 02, the sub-mirror 03, the third mirror 04, the fourth mirror 05, and the fifth mirror 06 is the inverse of the curvature c, the conic coefficient k, and the coefficient α i See table 1 for values of (a). It will be appreciated that the radius r, the conic coefficient k, and the coefficients a i The values of (A) are also not limited to those described in Table 1, and can be adjusted by those skilled in the art according to actual needs.
TABLE 1 surface type parameters of the primary mirror 02, secondary mirror 03, third mirror 04, fourth mirror 05 and fifth mirror 06
Spatial positions of the main mirror 02, the sub-mirror 03, and the third mirror 04 in the short focus and long focus states are shown in table 2. It is understood that the values of the distance between the lenses and the eccentricity of the lenses are not limited to those shown in table 2, and can be adjusted by those skilled in the art according to the actual needs.
TABLE 2 spatial position parameters of the main mirror 02, the sub-mirror 03, and the third mirror 04
The main reflector 02, the secondary reflector 03, the third reflector 04, the fourth reflector 05 and the fifth reflector 06 can be made of aluminum alloy, beryllium aluminum alloy, silicon carbide and the like as processing substrates. In order to increase the reflectance of the main mirror 02, the sub-mirror 03, the third mirror 04, the fourth mirror 05, and the fifth mirror 06, the respective reflecting surfaces may be coated with a silver film or a gold film for increasing the reflectance.
The working optical path of the large-relative-aperture off-axis five-mirror non-axial zooming imaging optical system is as follows: the light passing through the iris 01 is incident on the reflection surface of the main mirror 02, and is reflected by the reflection surface of the main mirror 02 to form a first reflected light, the first reflected light is incident on the reflection surface of the sub-mirror 03, and is reflected by the reflection surface of the sub-mirror 03 to form a second reflected light, the second reflected light is incident on the reflection surface of the third mirror 04, and is reflected by the reflection surface of the third mirror 04 to form a third reflected light, the third reflected light is incident on the reflection surface of the fourth mirror 05, and is reflected by the reflection surface of the fourth mirror 05 to form a fourth reflected light, the fourth reflected light is incident on the reflection surface of the fifth mirror 06, and is reflected by the reflection surface of the fifth mirror 06 to form a fifth reflected light, and the fifth reflected light is received by the detector image plane 07 and is imaged. As shown in fig. 3, which is a schematic diagram of a short focus state of the system, when the main mirror 02, the secondary mirror 03, and the third mirror 04 are located at designated positions, the system can perform clear imaging on a large field of view, and when the main mirror 02, the secondary mirror 03, and the third mirror 04 respectively move to corresponding positions shown in fig. 4 in a non-axial direction, the system is switched to a long focus state enlarged by 4.5 times, so as to perform clear imaging with a higher object space resolution on an object within the field of view.
The off-axis five-mirror non-axial zooming imaging optical system with large relative aperture provided by the embodiment of the invention has the following advantages:
1. the invention discloses a large-relative-aperture off-axis five-mirror non-axial zooming imaging optical system, wherein a fourth reflector and a fifth reflector are fixed reflectors, a main reflector, a secondary reflector and a third reflector are movable reflectors, the main reflector, the secondary reflector and the third reflector form a non-axial synchronous zooming primary imaging subsystem, and the fourth reflector and the fifth reflector form a post-relay imaging subsystem. The focal power of the reflector group is changed by non-axially moving the main reflector, the secondary reflector and the third reflector, so that zooming is realized. The subsequent imaging subsystem realizes the turnover, transmission and zoom imaging of the intermediate image plane at one time through two fixed reflectors. By adding the field diaphragm at the primary intermediate image surface position, stray light entering the subsequent relay imaging subsystem can be effectively eliminated. The non-axial movement vector is used for realizing the synchronous adjustment of the axial movement and the vertical movement, and the non-axial synchronous zooming of the zooming imaging optical system is realized, so that the imaging quality is good under different focal length states, and a free-form surface is not required.
2. The invention discloses a large-relative-aperture off-axis five-reflection type non-axial zooming imaging optical system. The change of the focal length of the non-axial zooming imaging optical system is realized through axial movement; the degree of freedom of the zoom imaging optical system is increased through the movement in the vertical axis direction, the wave aberration among multiple structures of the zoom imaging optical system is actively balanced by utilizing the effect of the eccentricity of the three reflectors on an aberration field, and the correction of high-order astigmatism and coma aberration of the non-axial zoom imaging optical system under different focal length structures is realized.
3. The invention discloses a large-relative-aperture off-axis five-reflection type non-axial zooming imaging optical system, which establishes a correction method of high-order astigmatism and coma of the zooming imaging optical system according to a Seidel aberration theory and a vector aberration theory, actively balances the wave aberration among multiple structures of the zooming imaging optical system by utilizing the action of the eccentricity of three reflectors on an aberration field, and realizes the correction of the high-order astigmatism and the coma of the non-axial zooming imaging optical system under different focal length structures.
4. According to the large-relative-aperture off-axis five-reflection type non-axial zooming imaging optical system disclosed by the invention, the field diaphragm is arranged at the stable primary image surface, so that the stray light which cannot be eliminated due to the movement of the reflector in the non-axial synchronous zooming primary imaging subsystem can be greatly reduced, and the stray light which can reach the image surface of a detector can be effectively eliminated.
5. The off-axis five-reflection type non-axial zooming imaging optical system with the large relative aperture disclosed by the invention only needs to use a high-order aspheric reflector and does not need to use a free-form surface reflector, so that the processing and detection cost is reduced.
In summary, the above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (6)
1. A large relative aperture off-axis five-mirror non-axial zoom imaging optical system is characterized in that: the device comprises an iris diaphragm, a main reflector, a secondary reflector, a third reflector, a fourth reflector, a fifth reflector and a detector image surface, and further comprises a translation table for moving the main reflector, the secondary reflector and the third reflector;
the iris diaphragm is an aperture diaphragm, and the aperture of the aperture diaphragm changes along with the change of the focal length; the relative aperture of the zooming imaging optical system is ensured to be fixed by adjusting the aperture of the aperture diaphragm;
the main reflector, the secondary reflector and the third reflector are zooming group and compensation group elements, and zooming imaging is realized by non-axially moving the three reflectors; the non-axial movement is realized based on a non-axial movement vector, and the non-axial movement vector is a non-axial movement vector synthesized by an axial movement amount and a vertical movement amount; the change of the focal length of the non-axial zooming imaging optical system is realized through axial movement; the degree of freedom of the zoom imaging optical system is increased through the movement in the vertical axis direction, the wave aberration among multiple structures of the zoom imaging optical system is actively balanced by the action of the eccentric amounts of the three reflectors, namely the main reflector, the secondary reflector and the third reflector, on an aberration field, and the correction of high-order astigmatism and coma aberration of the non-axial zoom imaging optical system under different focal length structures is realized; the non-axial movement vector is used for realizing the synchronous adjustment of the axial movement and the vertical movement, and the non-axial synchronous zooming of the zooming imaging optical system is realized, so that the imaging quality is good under different focal length states, and a free-form surface is not required.
2. The large relative-aperture off-axis five-mirror non-axial zoom imaging optical system of claim 1, wherein: the wave aberration between multiple structures of the zoom imaging optical system is actively balanced by utilizing the action of the eccentricity of the three reflectors on the aberration field, the realization method is as follows,
step one, determining the axial movement amount of three reflectors according to an axial movement formula (1);
where r is the radius of curvature of the mirrors, t is the distance between the mirrors, α ji Is a barrier ratio, beta ji To increase the magnification, f j Focal lengths under different configurations;
determining a primary wave aberration coefficient of the zoom imaging optical system according to the formula (2), wherein the primary wave aberration coefficient is related to alpha ji ,β ji ,f j A function of (a);
wherein:
wherein: k is i Is the coefficient of the quadratic surface of the mirror i, and
n i 1(i is an odd number), n i 1(i is an even number), n i ' -1(i is an odd number), n i ' 1(i is even number) (5)
u j1 ＝0,u j1 '＝2h j1 /r 1 ,u j2 ＝u j1 ',u j2 '＝u j2 /β j1 ,u j3 ＝u j2 ',u j3 '＝u j3 /β j2 (6)
Step three, based on the primary wave aberration coefficient of the zoom imaging optical system determined in the step two, determining the eccentricity sigma of the reflecting mirror under different structures through a formula (7) ji And according to said eccentricity σ ji Actively balancing wave aberration among multiple structures of the zoom imaging optical system, and realizing correction of high-order astigmatism and coma aberration of the non-axial zoom imaging optical system under different focal length structures; the eccentricity amount sigma ji Difference of (a) delta sigma j1 ,△σ j2 ,△σ j3 Namely the vertical axis movement amount of the three reflectors;
wherein: the vertical axis movement is expressed as the eccentricity sigma of the reflector under different structures ji In a difference thatJ denotes the jth reconstruction, i denotes the ith mirror; as shown in equation (7), the coma center and astigmatism center of the off-axis zoom imaging system are always related to α ji ,β ji ,f j ,
The function of (3) is added with the movement in the vertical axis direction on the basis of the axial movement, the degree of freedom of the system is increased, and the wave aberration among multiple structures of the zoom system is actively balanced by utilizing the action characteristic of the offset of the off-axis system on an aberration field;
the fourth reflector and the fifth reflector form a relay imaging subsystem with the magnification of b, and the spatial position is unchanged, so that the curvature radius and the thickness parameter of the relay imaging subsystem can be independently calculated; defining the fourth mirror to have a magnification of beta 4 The fifth mirror has a magnification of beta 5 And satisfy beta 4 β 5 ＝b。
3. The large relative-aperture off-axis five-mirror non-axial zoom imaging optical system of claim 1, wherein: the relay imaging subsystem formed by the fourth reflector and the fifth reflector performs secondary imaging on the primary image surface of the non-axial synchronous zooming primary imaging subsystem, and in order to ensure that imaging is clear and free of stray light, the field stop is arranged at the primary image surface position, so that stray light caused by the fact that a light blocking device is difficult to arrange due to movement of the reflectors is remarkably reduced, and the stray light capable of reaching the image surface of the detector is effectively eliminated.
4. The large relative-aperture off-axis five-mirror non-axial zoom imaging optical system of claim 1, wherein: in order to ensure stable imaging of the zoom imaging optical system, preferably, the magnification ratios of the secondary reflector, the third reflector and the fourth reflector meet a zoom relationship with a constant conjugate distance, and the position of the primary intermediate image plane is ensured to be constant, so that the position of the detector image plane is ensured to be constant.
5. The large relative-aperture off-axis five-mirror non-axial zoom imaging optical system of claim 1, wherein: the main reflector, the third reflector, the fourth reflector and the fifth reflector are concave reflectors, the secondary reflector is a convex reflector, and the five reflector surfaces are 8-order aspheric surfaces; the reflecting surfaces of the main reflector and the secondary reflector are oppositely arranged, the reflecting surfaces of the secondary reflector and the third reflector are oppositely arranged, the reflecting surfaces of the third reflector and the fourth reflector are oppositely arranged, the reflecting surfaces of the fourth reflector and the fifth reflector are oppositely arranged, and the image surface of the fifth reflector and the detector are oppositely arranged; the variable diaphragm and the center of the mirror surface of the main reflector are eccentrically arranged along the Y-axis direction, the eccentricity is the same, the secondary reflector, the third reflector, the fourth reflector and the fifth reflector are all eccentrically and obliquely arranged on the optical axis, and the eccentricity and the inclination of each reflector are different.
6. The large relative-aperture off-axis five-mirror non-axial zoom imaging optical system of claim 1, 2, 3, 4, or 5, wherein: the working method is that,
the light passing through the iris diaphragm is incident on the reflecting surface of the main reflecting mirror, and forms a first reflected light after being reflected by the reflecting surface of the main reflecting mirror, the first reflected light is incident on the reflecting surface of the secondary reflecting mirror, and forms a second reflected light after being reflected by the reflecting surface of the secondary reflecting mirror, the second reflected light is incident on the reflecting surface of the third reflecting mirror, and forms a third reflected light after being reflected by the reflecting surface of the third reflecting mirror, the third reflected light is incident on the reflecting surface of the fourth reflecting mirror, and forms a fourth reflected light after being reflected by the reflecting surface of the fourth reflecting mirror, the fourth reflected light is incident on the reflecting surface of the fifth reflecting mirror, and forms a fifth reflected light after being reflected by the reflecting surface of the fifth reflecting mirror, and the fifth reflected light is received by the detector and forms an image; when the main reflector, the secondary reflector and the third reflector respectively move to corresponding positions in a non-axial direction, the system is switched to a long-focus state with enlarged resolution, and objects in a field range are clearly imaged with higher object space resolution;
synchronous adjustment of axial movement and vertical movement is realized through non-axial movement vectors, and non-axial synchronous zooming of the zooming imaging optical system is realized; the post-relay imaging subsystem is used for imaging the primary intermediate image again, and the field diaphragm is added at the stable primary intermediate image surface position, so that stray light entering the post-relay imaging subsystem and the detector image surface is effectively eliminated; through the arrangement, the imaging quality under different focal length states is ensured to be good, a free-form surface is not required, and the processing and detection cost is reduced.
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