A catadioptric telescope optical system with quasi-aluminum characteristics and its installation and adjustment method

Abstract

The present invention discloses a catadioptric telescope optical system with quasi-brightness characteristics and an adjustment method. The system includes a primary mirror, a secondary mirror, a correction lens group, a system focal plane, and a conjugate image point. Light passes through the primary mirror, the secondary mirror, and the correction lens group in sequence to reach the system focal plane. The correction lens group includes at least one correction lens, which is a correction lens D with a brightness characteristic. When the correction lens group includes two or more correction lenses, the concave surface of the correction lens D serves as the conjugate image point reflection surface, and a distance d is provided between the system focal plane and the conjugate image point. While maintaining the original structural advantages of the catadioptric optical system, the system of the present invention has a clear adjustment reference point, simplifying the adjustment steps. The use of quasi-brightness lenses does not introduce additional aberrations. When the interferometer is axially moved a distance d, the focus is exactly the center of the concave surface of the lens, and the interferometer can measure straight fringes. The system imaging of the self-collimated reflection of the plane mirror is in a defocused state, with clear characteristics and convenient comparison.

Description

Technical Field

[0001] The present invention belongs to the field of astronomical instruments, and in particular relates to a catadioptric telescope optical system with quasi-aperture characteristics and an assembly and adjustment method thereof. Background Art

[0002] Most astronomical imaging optical systems that combine large aperture, large field of view, and high image quality are of the catadioptric type. Transmissive optical systems can achieve a larger field of view, but due to material size limitations, the aperture is difficult to expand. Reflecting telescopes can typically be made very large, but due to the limitations of the reflecting telescope's ability to correct for aberrations, the usable field of view of these telescopes is generally very small. The classic Cassegrain system's prime and Cassegrain focal points only eliminate spherical aberration. While the commonly used RC system eliminates spherical aberration and coma, the field of view with good image quality is still limited due to astigmatism and field curvature. To improve image quality and obtain a larger working field of view, a transmissive element is added before the focal point to correct for aberrations, resulting in a catadioptric optical system.

[0003] Most of the current mainstream large-aperture, wide-field telescopes are catadioptric. The 4-meter VISTA telescope uses an RC plus corrector catadioptric design, with four corrector lenses in the infrared end, giving a 1.65° field of view, and three corrector lenses and two atmospheric dispersion filters in the visible end, giving a 2.1° field of view. The 2.6-meter JST telescope uses a corrector lens assembly consisting of three aspheric lenses, with a 3° field of view. The Sloan Survey Telescope uses a two-lens corrector assembly, with a 3° field of view. In terms of prime focus catadioptric telescopes, the 4-meter Dark Energy Spectrometer DESI has four corrective mirrors and two atmospheric dispersion corrector mirrors in front of the prime focus, which can achieve a 5° ultra-large field of view; the 0.7-meter MASTA large field of view telescope and the 2.5-meter WFST telescope under development in China are both prime focus telescopes; in terms of Schmidt catadioptric telescopes, the United States' 0.95-meter Kepler Mission telescope, the 1.2-meter China Xuyi Near-Earth Object Search Telescope, and the 0.5-meter China Antarctic Survey Telescope are all of this type.

[0004] For catadioptric telescope optical systems, optical system design, optical component processing, and system alignment all directly impact the imaging quality, with alignment being particularly critical. Traditional catadioptric systems require repeated adjustments to correct the three-dimensional orientation of the mirror assembly during alignment, leading to numerous uncertainties, difficulty identifying the source of errors, and difficulty quantifying the magnitude of errors. Considering the alignment datum during optical design is particularly crucial. Existing satellite payload off-axis three-mirror mirror systems employ a common datum design approach for the main and three mirrors, placing the main mirror and the parent mirror of the three mirrors on the same axis. This reduces subsequent alignment work and improves alignment efficiency. Alternatively, a double-sided co-body reflector is employed, where different optical surfaces are machined onto the same mirror body to reduce alignment freedom. These approaches can increase system stability and improve alignment efficiency. However, this approach is not applicable to coaxial catadioptric telescope optical systems. The symmetric characteristic of an optical system refers to the presence of a pair of conjugate image points on-axis that simultaneously eliminate spherical aberration and coma. This characteristic is widely used in small-aperture microscopes, illumination systems, and optical measurement systems. Summary of the Invention

[0005] In response to the aforementioned problems existing in the prior art, the present invention provides a catadioptric astronomical telescope optical system and an adjustment method thereof with quasi-chiming characteristics. The present invention applies the object-image conjugate relationship of the chiming characteristic to the correction lens assembly of the catadioptric optical system, and designs a catadioptric astronomical telescope optical system with quasi-chiming characteristics by controlling operands. During adjustment of the system, the coaxial and aberration-free characteristics of the two conjugate image points can be utilized to quickly locate the position of the correction lens assembly, shortening adjustment time. Furthermore, the use of conjugate image points does not introduce additional aberrations. Furthermore, by optimizing the conjugate distance, the reflected image of the optical element near the focal plane can be controlled to be exactly at the center aperture obstruction position of the catadioptric system, thereby avoiding ghost interference caused by the two conjugate image points during measurement.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A catadioptric telescope optical system with a quasi-clear-light characteristic comprises a primary mirror, a secondary mirror, a correcting lens group, a system focal plane, and a conjugate image point. Light rays sequentially pass through the primary mirror, the secondary mirror, and the correcting lens group to reach the system focal plane. The correcting lens group comprises at least one correcting lens, which is a correcting lens D with a clear-light characteristic. When the correcting lens group comprises two or more correcting lenses, the correcting lens D is closest to the system focal plane. The surface of the correcting lens D close to the system focal plane is a spherical concave surface with a vertex curvature radius of R1. The surface of the correcting lens D away from the system focal plane is a spherical convex surface with a vertex curvature radius of R2. The center thickness of the correcting lens D is , the corrector D satisfies the condition ,in, is the refractive index of the correcting mirror D, n is the refractive index of the medium, in the catadioptric telescope optical system, the concave surface of the correcting mirror D is the conjugate image point reflection surface, the center of the concave surface is the location of the conjugate image point, and there is a distance d between the focal plane of the system and the conjugate image point.

[0008] Furthermore, the primary mirror and the secondary mirror are both aspherical reflectors, and the surface shape is a quadratic hyperbola or a high-order aspheric surface.

[0009] Furthermore, the correcting lens D can be combined with other optical surfaces to correct off-axis aberrations without introducing additional aberrations.

[0010] Furthermore, the distance d ranges from 5 to 10 mm.

[0011] A method for assembling and adjusting a catadioptric telescope optical system with quasi-zimming characteristics is disclosed. An interferometer point light source is placed at the focal plane of the system. A portion of the spherical light beam emitted by the point light source passes through a correction lens group, is reflected in sequence by a secondary mirror and a primary mirror, and finally is reflected by a self-collimating plane mirror before returning along the original path to form system interference fringes. A portion of the light beam is directly reflected back to the interferometer by the concave surface of the correction lens D to form reference interference fringes. Due to the distance d between the system focal plane and the conjugate image point, the presence of defocus causes the reference interference fringes to be concentric ring-shaped. By adjusting the tilt and pitch posture of the correction lens group, the reference interference fringes are positioned at the center of the interferometer field of view, i.e., the center of the secondary mirror obstruction. At this time, the optical axis of the correction lens group is coaxial with the optical axes of the primary and secondary mirrors.

[0012] Furthermore, when the correcting lens group includes two or more correcting lenses, the correcting lens group is individually adjusted using a centering device and then integrated with the primary and secondary mirror systems.

[0013] Furthermore, the installation and adjustment method includes the following steps:

[0014] Step 1: The primary and secondary mirror reflection systems are tested and adjusted using an interferometer;

[0015] Step 2: After the installation and adjustment is completed, the interferometer remains in place, the interferometer point light source is placed at the focal plane of the system, and the correction lens group is preliminarily installed;

[0016] The spherical wave beam emitted by the interferometer point light source is directly reflected back to the interferometer by the concave surface of the correction mirror D to form reference interference fringes. If the optical axis of the correction mirror group coincides with the optical axis of the interferometer, the returned reference interference fringes are in the center of the interferometer field of view and are concentric rings. Otherwise, adjust the tilt and pitch attitude of the correction mirror group until the returned reference fringes are in the center of the interferometer field of view and are concentric rings.

[0017] The spherical wave beam emitted by the interferometer point light source passes through the correction mirror group, is reflected by the secondary mirror and the primary mirror in sequence, and finally reflected by the self-collimating plane mirror and returns to the original path to form the system interference fringes. The axial distance of the correction mirror group is adjusted to make the system interference fringes straight fringes, while keeping the reference interference fringes in the center of the interferometer field of view;

[0018] Step 3: Move the interferometer axially until the central reference fringe changes from concentric rings to straight stripes. At this point, the interferometer focus should be exactly at the center of the concave sphere of the correcting mirror D. Measure the distance the interferometer moves axially. If the deviation between this distance and the theoretical distance d between the system focal plane and the conjugate image point is less than the preset value, it means that the correcting mirror assembly is adjusted in place.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The present invention provides a catadioptric telescope optical system with quasi-sunlight characteristics. The system is a catadioptric optical system with a large field of view and good imaging quality.

[0021] 2. The traditional catadioptric telescope optical system is improved and designed by combining the characteristics of the Qiming lens. The Qiming lens is applied to the correction lens group of the catadioptric optical system. This makes the optical system have a clear adjustment reference point while maintaining the original structural advantages of the catadioptric optical system, simplifies the adjustment steps of the catadioptric optical system, and improves the adjustment accuracy.

[0022] 3. The application of the ZM-like lens of the present invention does not introduce additional aberrations and can cooperate with other optical elements to correct off-axis aberrations.

[0023] 4. The quasi-Qiming lens of the present invention can make the interference reference fringes fall exactly into the central aperture blocking area of ​​the refraction and reflection system by controlling d, without affecting the high-precision assembly and adjustment of the system.

[0024] 5. When the interferometer moves axially a distance d, the focus is exactly at the center of the sphere on the lens R1 surface. The interferometer can measure straight fringes, while the imaging of the plane mirror self-collimation reflection system is in a defocused state. The characteristics are clear and easy to compare. By comparing the measured distance d with the theoretically calculated distance d, the correctness of the system can be roughly judged. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the optical structure of the system of the present invention;

[0026] Figure 2 This is the principle diagram of the Qiming lens;

[0027] Figure 3 This is a schematic diagram of the principle of the Qiming-like lens of the present invention;

[0028] Figure 4 is a light path diagram of an embodiment of the present invention;

[0029] Figure 5 is a spot diagram of an embodiment of the present invention;

[0030] Figure 6 This is a schematic diagram of the installation principle of an embodiment of the present invention;

[0031] Figure 7 The interferometer is located at Figure 3 Interference fringe images at position S3 are shown. (a) The concentric rings in the image are not in the center, indicating that the correction lens group is misaligned. (b) The concentric rings in the image are in the center, indicating that the correction lens group is aligned.

[0032] Markings in the figure: 1-primary mirror; 2-secondary mirror; 3-correction mirror A; 4-correction mirror B; 5-correction mirror C; 6-correction mirror D; 7-system focal plane; 8-conjugate image point; 9-plane reflecting mirror; 10-correction mirror group; 11-conjugate plane return light; 12-interferometer. DETAILED DESCRIPTION

[0033] The present invention will be described in further detail below with reference to the accompanying drawings.

[0034] The present invention provides a catadioptric telescope optical system with a quasi-sunlight characteristic, comprising: a primary mirror 1, a secondary mirror 2, a correcting mirror A3, a correcting mirror B4, a correcting mirror C5, a correcting mirror D6, a system focal plane 7, and a conjugate image point 8. Light rays sequentially pass through the primary mirror 1, the secondary mirror 2, the correcting mirror A3, the correcting mirror B4, the correcting mirror C5, and the correcting mirror D6 to reach the system focal plane 7. Figure 1 shown.

[0035] The concave surface of the correcting mirror D is a conjugate image point reflection surface, and the vertex curvature radius thereof is designed to be a specific value according to system parameters.

[0036] The center of the concave surface of the correcting mirror D is the location of the conjugate image point 8.

[0037] The distance d between the system focal plane 7 and the conjugate image point 8 is determined by the relative aperture of the system.

[0038] The primary mirror and the secondary mirror are both aspheric reflectors, made of glass or SIC, with a surface shape of a quadratic hyperboloid or a high-order aspheric surface, and the surface shape is determined by the following formula:

[0039]

[0040] Where, is the vertex curvature, K is the quadratic constant, d, e... are coefficients, It is the height loss of the aspheric surface.

[0041] The correcting lens group is composed of spherical or aspherical surfaces, and the element close to the focal plane must be a spherical surface.

[0042] The principle of Qiming lens is as follows Figure 2 As shown, the vertex curvature radius of the first surface of the Qiming lens is R1, the vertex curvature radius of the second surface is R2, and point O2 is the center of the sphere of R1. The light emitted from O2 does not deflect when passing through the R1 surface, but is refracted at point P on the R2 surface. The reverse extension line of the refracted light intersects at point O1. O1 and O2 are aligned points and the following conditions must be met:

[0043]

[0044] Where R1 is the radius of curvature of the first vertex, R2 is the radius of curvature of the second vertex, a is the center thickness of the lens, is the refractive index of the lens, and n is the refractive index of the medium.

[0045] The principle of the Qiming lens in the present invention is as follows Figure 3 As shown, the light is emitted from point S3, and after being refracted by the lens, the reverse extension line intersects at point S1. However, S3 is not the center of the first sphere. The center of the first sphere is S2. When designing the catadioptric optical system, the focal plane position is reasonably optimized and controlled to be located at S3. At this time, the quasi-Ziming lens does not introduce additional aberrations, and can be combined with other optical surfaces to correct off-axis aberrations.

[0046] The quasi-color characteristic is determined by the distance d between S2 and S3 and the number of fringes produced by defocus. It should not be too large according to the aberration requirements, otherwise the interferometer fringes will be too dense. According to the experience of interferometer use, the fringes are clearer when d is controlled at 5~10mm.

[0047] In the catadioptric optical system with quasi-QM characteristics, when the correction lens assembly and the primary and secondary mirror systems are self-aligned, the interferometer point light source is placed at the system focal plane S3. A portion of the spherical light beam emitted by the point light source passes through the correction lens assembly, is reflected in sequence by the secondary mirror and the primary mirror, and finally is reflected by the self-collimating plane mirror before returning along the original path to form interference fringes. A very small portion of the light is directly reflected back to the interferometer by the lens surface R1 of the correction lens assembly to form reference interference fringes. Since S3 is a certain distance d from the sphere center S2, the presence of defocus causes the reference interference fringes to be concentric ring-shaped. The posture of the correction lens assembly is adjusted (the primary and secondary mirror systems and the interferometer have been aligned and adjusted) so that the concentric rings are located at the center of the interferometer field of view, i.e., the center position of the secondary mirror obstruction. At this time, it can be quickly determined that the optical axis of the correction lens assembly is coaxial with the optical axes of the primary and secondary mirrors, thereby simplifying the adjustment steps.

[0048] When the catadioptric optical system with quasi-QM characteristics is assembled and adjusted, the size of d can be controlled so that the area of ​​the reference interference fringes is smaller than the area formed by the central aperture obstruction, thereby not affecting the test of the system imaging quality.

[0049] The structural diagram of the 2.5-meter aperture catadioptric optical system of this embodiment is as follows: Figure 4 As shown, its point diagram is as follows Figure 5 As shown, the parameters of the system are as follows:

[0050] Effective caliber: 2.5 meters

[0051] Optical field of view: full field of view 2.8°

[0052] Working band: 0.45um~0.75um

[0053] System focal length: 10000mm

[0054] Image quality: 80% of the energy is concentrated within a diameter of 18um

[0055] The concave surface of the corrector D is the conjugate image point reflection surface, with a vertex radius of curvature R0 = 562.96 mm. The focal plane is 571.32 mm from the center of the concave surface of the corrector D, and d = 8.36 mm is calculated.

[0056] The parameters of the grid elements in this optical system are as follows:

[0057]

[0058] Image quality evaluation of the 2.5-meter catadioptric optical system: full field of view 2.8°, 80% of the energy in the 0.45um~0.75um band is concentrated within a diameter of 16um, there is little difference in on-axis and off-axis energy concentration, and the imaging is uniform.

[0059] like Figure 6 As shown, the mirror surface closest to the focal plane of the 2.5-meter catadioptric optical system has a quasi-clear characteristic. The correction mirror group is adjusted separately using a centering instrument and then integrated with the primary mirror and secondary mirror system for adjustment. When the system is adjusted, the correction mirror group and the optical axes of the primary and secondary mirrors need to be strictly aligned. When the system is adjusted, two interference fringes are generated. One is that a spherical wave beam is emitted from the focus of the interferometer, passes through the correction mirror group, is reflected by the secondary mirror and the primary mirror, and then reflected back to the interferometer by a standard plane reflector, forming a system interference fringe area; the other is that a spherical wave beam is emitted from the focus of the interferometer, and is directly reflected back by the conjugate surface to form a conjugate surface return image. The return image of the correction mirror group and the return image of the optical system are simultaneously collected on the interferometer CCD (the interference fringe image of the interferometer at the focal plane of the system is shown as Figure 7 As shown in the figure), adjust the tilt and pitch of the correction mirror group so that the conjugate plane return image is located at the center of the secondary mirror obstruction, that is, from Figure 7 The state shown in (a) is adjusted to Figure 7 The state shown in (b) indicates that the optical axis of the correction mirror group coincides with the optical axes of the primary and secondary mirrors, which simplifies the installation and adjustment steps and improves the installation and adjustment efficiency.

[0060] When the interferometer moves axially a distance d, the focus is exactly at the center of the concave surface of the correcting mirror D-6. The interferometer can measure straight fringes, while the system imaging of the plane mirror self-collimation reflection is in a defocused state. The characteristics are clear and convenient for comparison. By comparing the measured distance d with the theoretically calculated d=8.36mm, if there is a deviation in the distance, it means that the axial spacing of the correcting mirror group is incorrect. The correcting mirror can be adjusted axially according to the positive and negative deviation to accurately locate the correcting mirror position.

[0061] The specific installation and adjustment steps of the system are as follows:

[0062] (1) After the primary and secondary mirror reflection systems are tested and adjusted using an interferometer, the interferometer remains in place. Figure 6 As shown, the corrective lens group is preliminarily installed;

[0063] (2) The spherical wave beam emitted by the interferometer point light source is directly reflected back to the interferometer by the concave surface of the correction mirror group D-6 to form reference interference fringes. If the correction mirror and the interferometer optical axis coincide, the returned reference fringes are located in the center of the interferometer field of view and are concentric rings. Otherwise, adjust the tilt of the correction mirror group.

[0064] (3) The spherical light beam emitted by the interferometer point light source passes through the correction mirror group, is reflected by the secondary mirror and the primary mirror in turn, and finally is reflected by the self-collimating plane mirror and returns to the original path to form interference fringes. The axial distance of the correction mirror is adjusted to make the interferometer fringes straight fringes, while keeping the reference fringes in the center of the interferometer field of view.

[0065] (4) Adjust the interferometer axial distance d, and use the interferometer focus to be exactly at the center of the D-6 concave sphere. At this time, the central reference stripes change from concentric rings to straight stripes. Measure the adjusted distance d and compare it with the theoretical design value d = 8.36mm. The smaller the deviation, the better the correction mirror assembly is.

[0066] The present invention provides a catadioptric telescope optical system with a quasi-Qiming characteristic, which is a catadioptric optical system with a large field of view and good imaging quality. The present invention applies a Qiming lens to the correction lens group of the catadioptric optical system, so that the optical system has a clear adjustment reference point while maintaining the original structural advantages of the catadioptric optical system, simplifies the adjustment steps of the catadioptric optical system, and improves the adjustment accuracy. During the design, the reflection image point of the optical element near the focal plane is controlled to be close to the conjugate with the image point on the system axis. When the system is adjusted, the coaxial and aberration-free characteristics of the two conjugate image points are utilized to accurately position the correction lens group, shortening the adjustment time. The application of the Qiming-like lens of the present invention does not introduce additional aberrations, and can cooperate with other optical elements to correct off-axis aberrations. The Qiming-like lens of the present invention can make the interference reference fringes fall exactly into the center hole obstruction area of ​​the catadioptric system by controlling d, without affecting the high-precision adjustment of the system. When the interferometer is axially displaced a distance d, the focal point is precisely at the center of the sphere on lens surface R1. The interferometer can measure straight fringes, while the plane mirror's self-collimating reflection system image is out of focus, resulting in clear features and easy comparison. By comparing the measured distance d with the theoretically calculated d, the correctness of the system can be roughly determined. By optimizing the conjugate distance, the reflected image of the optical element near the focal plane can be controlled to be precisely located at the center aperture of the refraction-reflection system, thus avoiding ghost interference between the two conjugate image points during measurement.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A method for assembling an optical system of a catadioptric telescope having a quasi-sunrise characteristic, characterized in that: The system includes a primary mirror, a secondary mirror, a correcting mirror group, a system focal plane, and a conjugate image point. Light passes through the primary mirror, the secondary mirror, and the correcting mirror group in sequence to reach the system focal plane. The correcting mirror group includes at least one correcting mirror, which is a correcting mirror D with a bright spot characteristic. When the correcting mirror group includes two or more correcting mirrors, the correcting mirror D is closest to the system focal plane. The side of the correcting mirror D close to the system focal plane is a spherical concave surface with a vertex curvature radius of R1. The side of the correcting mirror D away from the system focal plane is a spherical convex surface with a vertex curvature radius of R2. The center thickness of the correcting mirror D is a, and the correcting mirror D meets the condition Wherein, n is the refractive index of the correcting mirror D, n is the refractive index of the medium, in the catadioptric telescope optical system, the concave surface of the correcting mirror D is the conjugate image point reflection surface, the center of the concave surface is the location of the conjugate image point, and there is a distance d between the focal plane of the system and the conjugate image point; the interferometer point light source is placed at the focal plane of the system, a portion of the spherical light beam emitted by the point light source passes through the correcting mirror group, is reflected by the secondary mirror and the primary mirror in sequence, and finally is reflected by the self-collimating plane mirror and returns to the original path to form system interference fringes, a portion of the light beam is directly reflected by the concave surface of the correcting mirror D back to the interferometer to form reference interference fringes, due to the distance d between the focal plane of the system and the conjugate image point, the existence of defocus makes the reference interference fringes appear in the shape of concentric rings, by adjusting the tilt and pitch posture of the correcting mirror group, the reference interference fringes are located at the center of the interferometer field of view, that is, the center position of the secondary mirror obstruction, at this time the optical axis of the correcting mirror group is coaxial with the optical axes of the primary mirror and the secondary mirror; the method specifically comprises the following steps: Step 1: The primary and secondary mirror reflection systems are tested and adjusted using an interferometer; Step 2: After the installation and adjustment is completed, the interferometer remains in place, the interferometer point light source is placed at the focal plane of the system, and the correction lens group is preliminarily installed; The spherical wave beam emitted by the interferometer point light source is directly reflected back to the interferometer by the concave surface of the correction mirror D to form reference interference fringes. If the optical axis of the correction mirror group coincides with the optical axis of the interferometer, the returned reference interference fringes are in the center of the interferometer field of view and are concentric rings. Otherwise, adjust the tilt and pitch attitude of the correction mirror group until the returned reference fringes are in the center of the interferometer field of view and are concentric rings. The spherical wave beam emitted by the interferometer point light source passes through the correction mirror group, is reflected by the secondary mirror and the primary mirror in sequence, and finally reflected by the self-collimating plane mirror and returns to the original path to form the system interference fringes. The axial distance of the correction mirror group is adjusted to make the system interference fringes straight fringes, while keeping the reference interference fringes in the center of the interferometer field of view; Step 3: Move the interferometer axially until the central reference fringe changes from concentric rings to straight stripes. At this point, the interferometer focus should be exactly at the center of the concave sphere of the correcting mirror D. Measure the distance the interferometer moves axially. If the deviation between this distance and the theoretical distance d between the system focal plane and the conjugate image point is less than the preset value, it means that the correcting mirror assembly is adjusted in place.

2. The adjustment method according to claim 1, characterized in that: When the correcting mirror group contains two or more correcting mirrors, the correcting mirror group is individually adjusted using a centering device and then integrated with the primary and secondary mirror systems.

3. The adjustment method according to claim 1, characterized in that: The primary mirror and the secondary mirror are both aspherical reflectors, and the surface shape is a quadratic hyperboloid or a high-order aspherical surface.

4. The adjustment method according to claim 1, characterized in that: The correcting lens D can be combined with other optical surfaces to correct off-axis aberrations without introducing additional aberrations.

5. The adjustment method according to claim 1, characterized in that: The range of the distance d is 5 to 10 mm.

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