Low tolerance, high sensitivity, large field, prime focus astronomical optical system

Abstract

The application discloses a low-tolerance and high-sensitivity large-view-field main-focus astronomical optical system, which comprises a main mirror, a correcting mirror A, a correcting mirror B, a correcting mirror C, a correcting mirror D, a correcting mirror E, a correcting mirror F and a focal plane; wherein light is reflected by the main mirror, and then sequentially passes through the correcting mirror A, the correcting mirror B, the correcting correcting mirror C, the correcting mirror D, the correcting mirror E and the correcting mirror F to reach the focal plane; the main mirror is a concave aspheric mirror, and the surface shape is a quadratic hyperboloid or a high-order aspheric surface. The application realizes low machining and assembling tolerance sensitivity while ensuring excellent large-view-field imaging of the main-focus optical system; through analyzing the distribution of aberration on each optical surface, the position and structure parameters of special glass materials and the optical power of optical elements are optimized, the average of the contribution of each optical surface aberration is realized, and thus the machining and assembling tolerance sensitivity is reduced.

Description

Technical Field

[0001] This invention belongs to the field of astronomical instruments, specifically relating to a low-tolerance, high-sensitivity, large-field-of-view astronomical optical system with a prime focus. Background Technology

[0002] Since the 20th century, the international astronomical community has intensified its exploration of outer space, leading to the development of numerous large optical telescopes. Technologies related to large-aperture ground-based optical telescopes and space telescopes have seen significant advancements. Currently, the mainstream large-aperture catadioptric telescopes internationally are mainly divided into three categories: Cassegraingard corrector type, Schmidt type, and prime focus type. Regarding the Cassegraingard corrector type, the SLOAN Sky Survey Telescope, Pan-STARRS, and the Spanish JST telescope all belong to this type, forming a double-reflection Cassegraingard system consisting of a primary mirror, secondary mirror, and corrector, with a system focal ratio between F3 and F5. Mass-produced examples include the RiFast 600 telescope from the Italian company Officina Stellare, which uses an optical system consisting of a primary mirror, secondary mirror, and corrector, achieving a maximum field of view of approximately 2.1°. Regarding the Schmidt type, the US 0.95-meter Kepler Mission telescope, the 1.2-meter UK Schmidt telescope, the 1.22-meter Zwicky Transient Facility telescope, the 1.2-meter China Xuyi Near-Earth Object Search Telescope, and the 0.5-meter China Antarctic Survey Telescope all belong to this type. As for the prime focus type, the US Dark Energy Spectroradiometer (DESI) consists of a 4-meter prime focus with four correctors and two atmospheric dispersion correctors, achieving a 5° ultra-wide field of view. The 0.7-meter MASTA wide field of view telescope and the 2.5-meter WFT telescope, both currently under development in China, are prime focus type telescopes.

[0003] Among the new generation of wide-field optical telescopes currently under development, prime focus telescopes occupy an important position. This not only reflects the future development trend of wide-field optical telescopes but also demonstrates the crucial role of prime focus telescopes in this field. Image quality is a key performance indicator for optical telescopes. For prime focus imaging systems, the design of the optical system, the manufacturing precision of optical components, and the system assembly and adjustment precision all directly affect the image quality, thus limiting the accuracy of astronomical observations. In traditional prime focus systems, the primary mirror is parabolic, and off-axis aberrations in a wide field of view are mainly corrected by subsequent mirror groups. If the selection of materials, the matching of optical structures, and the homogenization of optical power in subsequent mirror groups are not optimized properly, it can lead to some components of the prime focus optical system being extremely sensitive to tolerances, while others have very loose tolerances. This results in excessively high tolerance sensitivity for the entire system, adversely affecting subsequent manufacturing and assembly work.

[0004] Therefore, controlling the tolerance sensitivity of a large field-of-view prime focal system and rationally allocating the processing and assembly precision of optical components from the optical design stage are key steps in telescope design. A prime focal optical system with low tolerance sensitivity allows the actual assembled system to more closely approximate the theoretically designed imaging performance, improving the system's tolerance capability. With a large field of view and a large number of optical components, a low-tolerance-sensitivity prime focal optical system simplifies the assembly and adjustment process, reducing system complexity. Furthermore, a low-tolerance-sensitivity telescope system is better suited to harsh environments at field sites, such as strong winds and ground vibrations from construction. Even if the telescope's optical components experience minor misalignments due to various accidental or unforeseen circumstances, the system can still maintain excellent imaging, thereby improving detection accuracy. In summary, a low-tolerance-sensitivity optical system, with its relaxed tolerance requirements, can better resist image quality degradation caused by errors, reduce manufacturing costs, and improve the feasibility of the optical system. Summary of the Invention

[0005] This invention designs a low-tolerance sensitivity, large-field-of-view astronomical optical system with a prime focus. While ensuring excellent imaging across the large field of view, the prime focus optical system simultaneously achieves low processing and assembly tolerance sensitivity. By analyzing the distribution of aberrations on various optical surfaces, optimizing the position and structural parameters of special glass materials and the optical power of optical elements, the aberration contribution of each optical surface is averaged, thereby reducing processing and assembly tolerance sensitivity.

[0006] This invention is achieved through the following technical solution:

[0007] A low-tolerance, high-sensitivity, large-field-of-view astronomical optical system includes: a primary mirror, corrector A, corrector B, corrector C, corrector D, corrector E, corrector F, and a focal plane; wherein light is reflected by the primary mirror and sequentially passes through corrector A, corrector B, corrector C, corrector D, corrector E, and corrector F to reach the focal plane;

[0008] The primary mirror is a concave aspherical mirror made of SiC or glass, with a surface shape of a hyperboloid or a higher-order aspherical surface, determined by the following formula.

[0009]

[0010] In the formula, c is the vertex curvature, K is the quadratic curve constant, d, e... are coefficients, and x is the height loss of the aspherical surface.

[0011] Compared to a parabolic surface, the primary mirror is a hyperboloid or a higher-order aspherical surface, which can retain some spherical aberration in the off-axis field of view (e.g., ±3°), thus canceling out aberrations with those of the subsequent correction lens group to balance the aberrations across the entire field of view. The vertex radius of curvature R of the primary mirror and its aperture D conform to the relationship: 1.5 < R / 2D < 1.7. At this point, the machining allowance of the primary mirror is moderate, around 0.03mm (primary mirror aperture 700mm), and the machining ring size matches the dimensions of conventional machining tools, which helps improve the machining efficiency of the primary mirror. The vertex radius of curvature of the primary mirror should not be too large, as this will lead to an increase in the aperture of the correction lens group, resulting in large central occlusion and reduced system efficiency.

[0012] The corrector A is a positive meniscus lens, in which the radius of curvature of the concave surface is greater than that of the convex surface, Rconcave / Rconvex≈3. At this time, the positive meniscus lens is thin at the edge and thick at the center, and the convex surface faces the primary mirror, which can cause light to converge, reduce off-axis high-order spherical aberration, and increase the relative aperture of the system without introducing spherical aberration.

[0013] The corrector lens B is a negative meniscus lens with a convex surface radius of curvature greater than that of the concave surface, Rconvex / Rconcave≈3, thin at the center and thick at the edges, and with the convex surface facing the main mirror, which can maximize the divergence of incident light.

[0014] The corrector mirrors A and B work together, one positive and one negative, to initially balance off-axis spherical aberration, coma, astigmatism, etc. The materials used are H-K9L (or N-BK7, quartz, etc. crown glass), which have stable refractive index, low stress, good uniformity, and large size. These materials have good performance, moderate price, and good processing performance, making them the preferred materials for low tolerance sensitive designs.

[0015] The corrector lens C is a high-dispersion glass lens with a relatively low optical power and an F-number (f#) between 10.5 and 12.5. Its optical power can be positive or negative. The corrector lens C introduced here does not participate in much monochromatic aberration correction; it is mainly used to generate large chromatic aberration values ​​in different wavelength bands. Combined with positive and negative meniscus lenses, it prepares for subsequent achromatic correction. High-dispersion flint glass materials generally suffer from severe short-wavelength transmittance attenuation; therefore, materials with higher transmittance must be selected during the design process.

[0016] The materials of the corrector mirror A and the corrector mirror B are basically located on the glass line.

[0017] The material of the corrector mirror C is located to the left of the glass line, which is positively offset from the glass.

[0018] The corrector lens D is a negative lens, located in the middle of the corrector lens group. Its refractive index and dispersion coefficient are both located in the middle of the entire glass line, and the material is mostly lanthanide flint glass.

[0019] The material of the corrector mirror D is all located to the right of the glass line, and is negative offset glass.

[0020] The corrector lens C and corrector lens D are made of opposite materials, one positive and one negative, which complement each other to improve the ability to achromatic.

[0021] The corrector lens E is a biconvex thick lens made of special glass with low refractive index and low dispersion, forming an apochromatic combination with the aforementioned lens.

[0022] The corrector lens F is a biconvex thick lens made of special glass with low refractive index and low dispersion. Located near the focal plane, it not only apochromatic with the aforementioned material but also flattens the field and corrects field curvature.

[0023] The corrector lenses C, D, E, and F form a combination of high and low refractive indices and high and low dispersion parameters. Combined with different lens structures, they maximize the chromatic aberration correction capability. The optical element parameters are reasonable, ensuring good processability.

[0024] The distance between the two lenses, from correction lens A to correction lens E, is between 20 and 50 mm. There is no excessively small distance of less than 10 mm, which would cause sensitivity to small distance tolerances; nor would the distance be too large, affecting centering and adjustment.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] 1. This invention provides a low-tolerance sensitivity, large field of view, and main focal point telescope optical system. This system is a catadioptric optical system with small central obstruction and good imaging quality.

[0027] 2. The primary mirror in this invention is a hyperboloid or a high-order aspherical surface. The amount of material removed during the primary mirror processing is precisely controlled during the design process. The maximum asphericity is only about 0.03mm. The processing cycle is short and high-precision detection can be easily achieved.

[0028] 3. The main focal point optical system of the present invention can achieve high imaging quality with 80% of the energy concentrated within a diameter of 8 μm in a 6° wide field of view and a 0.4 μm to 0.9 μm wavelength range;

[0029] 4. The corrector lens group of the present invention has low tolerance sensitivity. For the same field of view, the light rays at the surface of each element converge gradually between 10° and 15°, with a small range of variation. The light ray path is smooth, the aberration correction amount is evenly distributed, and there are no prominent tolerance sensitive points.

[0030] 5. The corrective lens assembly of the present invention has moderate spacing between each lens and no small gap error, which can not only balance aberrations well, but also take into account the grinding of the gaskets during assembly and the range during centering and assembly.

[0031] 6. The corrector lens assembly of the present invention has a maximum lens diameter of 340mm, and the two largest lenses are made of K9 glass (or quartz glass), which has good material properties, good processability, and is easy to obtain, thus reducing the cost of the corrector lens assembly.

[0032] 7. Compared with existing prime focus telescopes, the prime focus optical system of this invention improves imaging quality, reduces tolerance sensitivity, and can better adapt to the harsh environment of field sites, such as strong winds and ground construction vibrations.

[0033] 8. The low-tolerance sensitivity optical system of the present invention has relaxed tolerance requirements, which can better resist image quality degradation caused by errors, reduce manufacturing costs, and improve the feasibility of the optical system. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the optical structure of the present invention;

[0035] Figure 2 This is an optical path diagram of Embodiment 1 of the present invention;

[0036] Figure 3 This is a diagram illustrating an embodiment of the present invention;

[0037] Figure 4 This is an energy concentration diagram of Embodiment 1 of the present invention;

[0038] Figure 5 This is a perturbation diagram of energy concentration after tolerance analysis in Embodiment 1 of the present invention.

[0039] The markings in the diagram are: 1-primary lens; 2-correction lens A; 3-correction lens B; 4-correction lens C; 5-correction lens D; 6-correction lens E; 7-correction lens F; 8-focal plane. Detailed Implementation

[0040] The present invention will now be described in further detail with reference to the accompanying drawings.

[0041] This invention discloses a low-tolerance, high-sensitivity, large-field-of-view astronomical optical system with a prime focal point, comprising: a primary mirror 1, a corrector mirror A2, a corrector mirror B3, a corrector mirror C4, a corrector mirror D5, a corrector mirror E6, a corrector mirror F7, and a focal plane 8; wherein light is reflected by the primary mirror and sequentially passes through corrector mirrors A, B, C, D, E, and F to reach the focal plane.

[0042] The primary mirror is a concave aspherical mirror made of SiC or glass, with a surface shape of a hyperboloid or a higher-order aspherical surface, determined by the following formula.

[0043]

[0044] In the formula, c is the vertex curvature, K is the quadratic curve constant, d, e... are coefficients, and x is the height loss of the aspherical surface.

[0045] Compared to a parabolic surface, the primary mirror is a hyperboloid or a higher-order aspherical surface, which can retain some spherical aberration in the off-axis field of view (e.g., ±3°), thus canceling out aberrations with those of the subsequent correction lens group to balance the aberrations across the entire field of view. The vertex radius of curvature R of the primary mirror and its aperture D conform to the relationship: 1.5 < R / 2D < 1.7. At this point, the machining allowance of the primary mirror is moderate, around 0.03mm (primary mirror aperture 700mm), and the machining ring size matches the dimensions of conventional machining tools, which helps improve the machining efficiency of the primary mirror. The vertex radius of curvature of the primary mirror should not be too large, as this will lead to an increase in the aperture of the correction lens group, resulting in large central occlusion and reduced system efficiency.

[0046] Among them, the corrector A is a positive meniscus lens, where the radius of curvature of the concave surface is greater than the radius of curvature of the convex surface, R A凹 / R A凸 ≈3, at this time the positive meniscus lens is thin at the edge and thick at the center, and the convex surface faces the primary mirror, which can cause light to converge, reduce off-axis high-order spherical aberration, and increase the relative aperture of the system without introducing spherical aberration;

[0047] Among them, the corrector B is a negative meniscus lens, with the radius of curvature of its convex surface being greater than that of its concave surface, R. B凸 / R B凹 ≈3, thin at the center and thick at the edges, with the convex surface facing the primary mirror, which allows the incident light to diverge to the maximum extent.

[0048] The materials of the corrector mirror A and the corrector mirror B are basically located on the glass line.

[0049] The corrector mirrors A and B work together, one positive and one negative, to initially balance off-axis spherical aberration, coma, astigmatism, etc. The materials used are H-K9L (or N-BK7, quartz, etc. crown glass), which have stable refractive index, low stress, good uniformity, and large size. These materials have good performance, moderate price, and good processing performance, making them the preferred materials for low tolerance sensitive designs.

[0050] Among them, the corrector lens C is a high-dispersion glass lens with a relatively low optical power and an F-number (f#) between 10.5 and 12.5. Its optical power can be positive or negative. The corrector lens C introduced here does not participate in much monochromatic aberration correction; it is mainly used to generate large chromatic aberration values ​​in different wavelength bands. Combined with positive and negative meniscus lenses, it prepares for subsequent achromatic correction. High-dispersion flint glass materials generally have severely reduced short-wavelength transmittance; therefore, materials with higher transmittance must be selected during the design process.

[0051] The material of the corrector mirror C is located to the left of the glass line, which is positively offset from the glass.

[0052] Among them, the corrector lens D is a negative lens, located in the middle of the corrector lens group. Its refractive index and dispersion coefficient are both located in the middle of the entire glass line, and the material is mostly lanthanide flint glass.

[0053] The material of the corrector mirror D is all located to the right of the glass line, and is negative offset glass.

[0054] The corrector lens C and corrector lens D are made of opposite materials, one positive and one negative, which complement each other to improve the ability to achromatic.

[0055] Among them, the corrector E is a biconvex thick lens made of special glass with low refractive index and low dispersion, which forms an apochromatic combination with the aforementioned lens.

[0056] Among them, the corrector lens F is a biconvex thick lens made of special glass with low refractive index and low dispersion. It is located near the focal plane and not only works with the aforementioned material to apochromatic but also plays a role in flattening the field and correcting field curvature.

[0057] The corrector lenses C, D, E, and F form a combination of high and low refractive indices and high and low dispersion parameters. Combined with different lens structures, they maximize the chromatic aberration correction capability. The optical element parameters are reasonable, ensuring good processability.

[0058] The distance between the two lenses, from correction lens A to correction lens E, is between 20 and 50 mm. There is no excessively small distance of less than 10 mm, which would cause sensitivity to small distance tolerances; nor would the distance be too large, affecting centering and adjustment.

[0059] The optical system design specifications for this embodiment are as follows:

[0060] Effective caliber: 710mm

[0061] Optical field of view: 6° full field of view

[0062] Operating wavelength: 0.4µm~0.9µm

[0063] System focal length: 1230mm

[0064] Image quality: 80% of the energy is concentrated within a diameter of 18µm.

[0065] A schematic diagram of the 710mm aperture optical system is shown below. Figure 1 As shown, the optical system includes a primary mirror 1, corrector mirrors A2, B3, C4, D5, E6, and F7, and a focal plane 8. The optical path of this optical system is as follows: Figure 2As shown, light enters the primary mirror, is reflected by the primary mirror, and then passes sequentially through corrector mirrors A2, B3, C4, D5, E6, and F7 to reach the focal plane 8. Corrector mirrors A and B are K9 material positive and negative meniscus lenses, working together to primarily balance off-axis monochromatic aberrations; corrector mirror C is a positive deviation material negative lens, corrector mirror D is a negative deviation material negative lens, and corrector mirror E is an ultra-low dispersion special material positive lens. Corrector mirrors C, D, and E form an apochromatic combination, mainly used for achromatic correction across the entire field of view; corrector mirror E, located near the focal plane, is used not only to balance residual aberrations but also to correct field curvature.

[0066] Example 1: Optical System Parameters

[0067]

[0068] Image quality evaluation of the 710mm aperture prime focus optical system: Figure 3 Its point-to-point plot, Figure 4 Based on its energy concentration map, within a ±3° field of view, 80% of the energy in the 0.4µm to 0.9µm band is concentrated within a diameter of 8µm. The difference in on-axis and off-axis energy concentration is not significant, resulting in uniform imaging.

[0069] The tolerance sensitivity of the 710mm aperture master focal point optical system is specifically reflected as follows: The tolerance parameters of each optical element are set as shown in the table below. The component processing and assembly tolerances are relatively uniform and lenient. Substituting the data into the optical design software, using the RMS blur radius as the evaluation standard, and analyzing it using the sensitivity analysis model, the RMS blur radius obtained by error superposition is found to be 6.5µm, which meets the requirement that 80% of the capability is concentrated within 18µm. Figure 5 This is the energy concentration perturbation diagram after tolerance analysis.

[0070] The tolerance ranges for each optical element are set.

[0071]

[0072]

[0073] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A low-tolerance, high-sensitivity, large-field-of-view astronomical optical system with a principal focal point, characterized in that: include: The system comprises a primary mirror, corrector mirrors A, B, C, D, E, and F, and a focal plane. Light rays are reflected by the primary mirror and sequentially pass through corrector mirrors A, B, C, D, E, and F to reach the focal plane. The primary mirror is a concave aspherical mirror with a surface shape of a hyperboloid or a higher-order aspherical surface, determined by the following formula. In the formula, c is the vertex curvature, K is the quadratic curve constant, d, e... are coefficients, and x is the height loss of the aspherical surface; compared with the parabolic surface, the primary mirror is a quadratic hyperboloid or a higher-order aspherical surface, which can leave spherical aberration at the off-axis field of view, and form positive and negative cancellation with the aberration of the subsequent correction lens group to balance the aberration of the entire field of view. The corrector A is a positive meniscus lens, with its concave radius of curvature being greater than its convex radius of curvature, and its convex surface facing the main mirror, which can cause light to converge. The corrector B is a negative meniscus lens, with its convex surface having a larger radius of curvature than its concave surface. Its convex surface faces the main mirror, which allows the incident light to diverge to the maximum extent. The materials of the corrector mirror A and the corrector mirror B are located on the glass line; The corrector lens C is a high-dispersion glass lens with an optical power between 0.0003 and 0.0004 and an F number between 10.5 and 12.

5. It is made of a material with a transmittance higher than 99.5%, and its optical power can be positive or negative. Corrector lens C is used to generate large chromatic aberration values ​​in different wavelength bands. It is combined with corrector lens A and corrector lens B to prepare for subsequent achromatic correction. The material of corrector lens C is located to the left of the glass line, which is positively offset from the glass. The corrector lens D is a negative lens, located in the middle of the corrector lens group, with both its refractive index and dispersion coefficient located in the middle of the entire glass line; the material of the corrector lens D is located on the right side of the glass line, and is negative offset glass. The corrector lens E is a biconvex thick lens made of a special low-refractive-index, low-dispersion glass with a refractive index of less than 1.5 and a dispersion value of less than 70. It forms an apochromatic combination with corrector lenses A, B, C, and D. The corrector lens F is a biconvex thick lens made of a special low-refractive-index, low-dispersion glass with a refractive index of less than 1.5 and a dispersion value of less than 70. It is located near the focal plane and works with corrector lenses A, B, C, D, and E to apochromatic the image. It is also used for field flattening and field curvature correction. The corrector lenses A to E are spaced 20 to 50 mm apart.

2. The low-tolerance, high-sensitivity, large-field-of-view astronomical optical system according to claim 1, characterized in that, The vertex radius of curvature R of the primary mirror conforms to the following relationship with the aperture D: 1.5 < R / 2D < 1.

7.

3. The low-tolerance, high-sensitivity, large-field-of-view astronomical optical system according to claim 1, characterized in that, The primary mirror is made of SiC or glass.

4. The low-tolerance, high-sensitivity, large-field-of-view astronomical optical system according to claim 1, characterized in that, The ratio of the concave radius of curvature to the convex radius of curvature of the corrector mirror A is R. A凹 / R A凸 ≈3, the positive meniscus lens is thin at the edge and thick at the center, which is used to reduce off-axis advanced spherical aberration and increase the system's relative aperture without introducing spherical aberration.

5. The low-tolerance, high-sensitivity, large-field-of-view astronomical optical system according to claim 1, characterized in that, The ratio of the convex radius of curvature to the concave radius of curvature of the corrector mirror B is R. B凸 / R B凹 ≈3, the center of the negative meniscus lens is thin and the edge is thick.

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