Off-axis three-mirror system compact automatic design method

Abstract

This invention discloses an automated method for compact design of off-axis three-mirror systems, belonging to the field of optical design, to solve the problem of cumbersome, time-consuming, and labor-intensive processes in the compact design of traditional off-axis reflection systems. The method includes: imposing volume constraints on the off-axis three-mirror system to obtain a compact, small-volume off-axis three-mirror system; optimizing the image quality of the obtained small-volume off-axis three-mirror system to improve the system's imaging quality affected by the volume constraints; and iteratively combining the volume constraint process and the image quality optimization process to output a compact off-axis three-mirror system with good image quality. This invention can automatically perform compact optimization design on the input initial model of an off-axis three-mirror system, and it can also be used to quickly and roughly estimate the minimum achievable volume of off-axis three-mirror systems of different specifications.

Description

Technical Field

[0001] This invention belongs to the field of optical system design technology, and in particular to a compact automatic design method for off-axis three-mirror systems. Background Technology

[0002] With the continuous development and advancement of optical technology, off-axis reflection systems have begun to attract increasing attention from optical design researchers. Off-axis three-mirror optical systems not only possess many advantages of coaxial three-mirror optical systems, such as no chromatic aberration, no second-order spectrum, relatively fewer parts, a large aperture that can be made, relatively low material requirements, and highly flexible design, but also, along with the development and use of off-axis reflection systems, there is an increasing demand for compactness. Traditional methods for reducing system size are difficult and cumbersome, requiring a significant investment of time and effort from designers.

[0003] Generally speaking, reducing the size of an off-axis reflective system is not a simple task for optical designers. Designers usually need to find an initial model and then use optical design software to optimize it to reduce the size. The traditional method is to apply a volume constraint to the initial model to reduce the size. However, as a trial-and-error process, this process is very demanding on the designer's experience. The operation of reducing the size of an off-axis three-mirror system usually consumes a lot of the designer's time. The main reasons are as follows: 1) When using optimization algorithms to reduce the size, the process of reducing the size of an off-axis three-mirror system is not a linear process, but the optimization algorithm usually uses a linear approximation method. This requires that the optimization step size cannot be too long. At the same time, it is very easy to get trapped in local optima during the optimization process. How to find the system trapped in local optima and how to solve the problem of the system trapped in local optima not only requires high professional ability and design experience of the designer, but also requires a lot of time to solve the problem. Especially when the target size is relatively small compared with the initial model, the problem of repeatedly getting trapped in local optima may lead to optimization failure and failure to obtain the desired result. 2) Due to the high degree of freedom of off-axis three-reflector systems, it is difficult for designers to obtain a suitable initial model from existing patents or materials. This makes it difficult for designers to estimate the minimum volume that can be achieved by optimizing the initial model used during the design process. Therefore, designers are relatively blind when selecting an initial model for off-axis three-reflector system design, and there may be a series of problems such as the selected initial model not being able to be optimized to meet the design requirements. Summary of the Invention

[0004] The purpose of this invention is to provide a compact automatic design method for off-axis three-reflector systems, solving the problem that traditional methods for reducing system size are difficult and cumbersome.

[0005] The technical solution for achieving the objective of this invention is: a compact automatic design method for an off-axis three-reflector system, the method comprising:

[0006] Step 1: Set the off-axis three-mirror design parameters and the corresponding initial model C0. Set the threshold values ​​for the distance between the mirror end of the off-axis three-mirror system and its adjacent edge rays, the threshold values ​​for the distance between the ideal image point and its adjacent edge rays, and the maximum root mean square value σ of the distance between the ideal intersection point and the actual intersection point of the sampled ray and the image plane. MAX ;

[0007] Step 2: Adjust the structural parameters of the off-axis three-mirror system so that the distance between the mirror end of the off-axis three-mirror system and its adjacent edge light reaches the corresponding threshold, thereby obtaining a compact off-axis three-mirror system with strictly limited constraint distance.

[0008] Step 3: The surface shape of the three mirrors of the off-axis three-lens system obtained in Step 2 is reconstructed by constructing an iterative method. During the construction process, the position of the ideal image point is determined according to the distance threshold between the ideal image point and its adjacent edge rays, so that the focal length of the off-axis three-lens system that was offset in Step 2 can be made to conform to the off-axis three-lens design parameters again, and the distance between the ideal image point and its adjacent edge rays is constrained to the corresponding threshold.

[0009] Step 4: The primary mirror, secondary mirror, and third mirror in the off-axis three-mirror system reconstructed in Step 3 are reconstructed a second time using the construction iteration method to optimize the imaging quality of the off-axis three-mirror system after Steps 2 and 3.

[0010] Step 5: Determine whether the off-axis three-reflector system obtained in Step 4 meets the σ requirement based on the system design requirements. RMS <σ MAX If the condition is met, proceed to step 6; otherwise, proceed to step 7, and simultaneously save the current off-axis three-way reversing system as C. i ;σ RMS The root mean square of the distance between the ideal intersection point and the actual intersection point of the sampling ray and the image plane;

[0011] Step 6: Apply angular deflection to the primary mirror, secondary mirror, and third mirror of the off-axis three-mirror system, and then return to step 2;

[0012] Step 7, output the off-axis three-way reversing system C that last entered step 6. i-1 .

[0013] Further, the threshold values ​​for the distance between the reflector end of the off-axis three-mirror system and its adjacent edge rays in step 1 include: a threshold value for a first constraint distance L1, a threshold value for a second constraint distance L2, a threshold value for a third constraint distance L3, and a threshold value for a fourth constraint distance L4; the first constraint distance is the distance between the lower end of the primary mirror and the light rays emitted from the upper edge of the secondary mirror, the second constraint distance is the distance between the upper end of the secondary mirror and the light rays incident on the lower edge of the primary mirror, the third constraint distance is the distance between the upper end of the three mirrors and the light rays incident on the lower edge of the secondary mirror, and the fourth constraint distance is the distance between the lower end of the secondary mirror and the light rays emitted from the upper edge of the three mirrors;

[0014] The threshold for the distance between the ideal image point and its adjacent edge rays includes the threshold for the fifth constraint distance, which is the distance between the ideal image point and the incident light rays at the lower edge of the three mirrors.

[0015] Furthermore, the process of selecting the sampling light in step 1 includes:

[0016] Select M fields of view, divide the aperture of each field of view into N equal parts, and select P characteristic rays at different aperture positions in each part as sampling rays.

[0017] Furthermore, the field of view is a circular field of view, a rectangular field of view, a square field of view, or an elliptical field of view.

[0018] Furthermore, the aperture of each field of view is circular, and the circular aperture of each field of view is divided into N angles, and P characteristic rays at different aperture positions are taken along the radial direction of each angle.

[0019] Furthermore, the adjustment of the structural parameters of the off-axis three-mirror system in step 2, so that the distance between the mirror end of the off-axis three-mirror system and its adjacent edge rays reaches a corresponding threshold, specifically includes:

[0020] First, keep the primary, secondary, and tertiary mirror planes of the off-axis three-mirror system unchanged, and measure the change in the primary mirror tilt angle θ1. Change in the tilt angle θ2 of the three mirrors The change in distance D1 between the primary mirror and the secondary mirror, l1, and the change in distance D2 between the secondary mirror and the third mirror, l2, are used as variables. Based on the degree of influence of each variable on the first constraint distance L1, the second constraint distance L2, the third constraint distance L3, and the fourth constraint distance L4, the four variables are adjusted in order of increasing influence to obtain a preliminary reduced off-axis three-mirror system. At this time, the first constraint distance L1 and the fourth constraint distance L4 have approached infinitesimal.

[0021] Then, keeping the primary, secondary, and tertiary mirror surfaces of the off-axis three-mirror system unchanged, within a preset small range, l1, l2, The effects of the first constraint distance L1, the second constraint distance L2, the third constraint distance L3, and the fourth constraint distance L4 are linearly related. Based on this linear relationship, the first constraint distance L1, the second constraint distance L2, the third constraint distance L3, and the fourth constraint distance L4 are limited to their corresponding thresholds.

[0022] Furthermore, the adjustment of the four variables in order of increasing influence specifically includes:

[0023] (1) For each variable, initialize the corresponding adjustment step size and downward adjustment value, and set the adjustment lower limit value;

[0024] (2) For the first variable arranged in ascending order of influence, adjust it according to its corresponding adjustment step size;

[0025] (3) Determine whether there is a negative value among the first constraint distance L1(1), the second constraint distance L2(2), the third constraint distance L3(3) and the fourth constraint distance L4(4). If so, adjust the adjustment step size according to the current downward value based on the current adjustment step size, and then execute (4); otherwise execute (5).

[0026] (4) Determine whether the current adjustment step size is lower than the adjustment lower limit. If so, jump to (5); otherwise, adjust the variable with the current adjustment step size and then return to execute (3).

[0027] (5) For the next variable, adjust it in the manner of (2) to (4) until all four variables have been adjusted;

[0028] (6) Determine whether there exists a constraint distance value that is less than p times its corresponding threshold. If it exists, end the adjustment process; otherwise, return to (2); where p < 1.

[0029] Furthermore, after adjusting the adjustment step size according to the current downward adjustment value, the following action is taken: reduce the current downward adjustment value.

[0030] Furthermore, the root mean square σ of the distance between the ideal intersection point and the actual intersection point of the sampling ray and the image plane described in step 5... RMS , is represented as:

[0031]

[0032] Where, δ m It is the distance between the ideal intersection point and the actual intersection point of the m-th sampling ray and the object-image plane, where M is the total number of sampling rays.

[0033] Compared with the prior art, the significant advantages of this invention are:

[0034] (1) This invention only requires input of a compact off-axis three-reflector system and a few limiting parameters to automatically output a compact system, and no designer is required to participate in the optimization process.

[0035] (2) Using the present invention to compact off-axis three-mirror systems will not result in the situation where designers are prone to getting stuck in local minima when performing off-axis three-mirror compaction operations, thus increasing the likelihood of successful optimization.

[0036] (3) This invention can also be used to estimate the minimum volume of off-axis three-reflector systems of different specifications, and guide the determination and optimization of volume parameters.

[0037] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0038] Figure 1 This is a flowchart of the off-axis three-reflector compact automatic design method of the present invention.

[0039] Figure 2 This is a schematic diagram of the first constraint distance L1, the second constraint distance L2, the third constraint distance L3, the fourth constraint distance L4, and the fifth constraint distance L5 of the present invention.

[0040] Figure 3 This is an initial schematic diagram of an automatic design method for compact off-axis three-reflector systems provided in one embodiment.

[0041] Figure 4 This is a schematic diagram of a compact off-axis three-mirror optical system with good image quality, output by the automatic design method for compact off-axis three-mirror systems provided in one embodiment.

[0042] Figure 5 The point plot RMS values ​​of a compacted off-axis three-mirror optical system are output by the automatic design method for compacting an off-axis three-mirror system provided in one embodiment.

[0043] Figure 6 The MTF diagram of a high-quality compacted off-axis three-mirror optical system is output by the automatic design method for compacting off-axis three-mirror systems provided in one embodiment.

[0044] Figure 7 The graph shows the system volume reduction during the iterative process of building a high-quality compact off-axis three-mirror optical system, output by the automatic design method for compacting an off-axis three-mirror system provided in one embodiment. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0046] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0047] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0048] To address the cumbersome, time-consuming, and labor-intensive process of designing compact off-axis reflective systems, this invention proposes a design method that can automatically obtain a compact off-axis three-mirror system without the need for designer intervention. The method includes: imposing volume constraints on the off-axis three-mirror system to obtain a compact, small-volume off-axis three-mirror system; optimizing the image quality of the obtained small-volume off-axis three-mirror system to improve the system's imaging quality affected by the volume constraints; and iteratively combining the volume constraint process and the image quality optimization process to output a compact off-axis three-mirror system with good image quality.

[0049] In one embodiment, combined Figure 1 A compact automatic design method for off-axis three-reflector systems is provided, the method comprising:

[0050] Step 1: Set the off-axis three-mirror design parameters and the corresponding initial model C0. Set the threshold values ​​for the distance between the mirror end of the off-axis three-mirror system and its adjacent edge rays, the threshold values ​​for the distance between the ideal image point and its adjacent edge rays, and the maximum root mean square value σ of the distance between the ideal intersection point and the actual intersection point of the sampled ray and the image plane. MAX ;

[0051] Step 2: Adjust the structural parameters of the off-axis three-mirror system so that the distance between the mirror end of the off-axis three-mirror system and its adjacent edge light reaches the corresponding threshold, thereby obtaining a compact off-axis three-mirror system with strictly limited constraint distance.

[0052] Step 3: The surface shape of the three mirrors 8 of the off-axis three-lens system obtained in Step 2 is reconstructed by constructing an iterative method. During the construction process, the position of the ideal image point is determined according to the distance threshold between the ideal image point and its adjacent edge rays, so that the focal length of the off-axis three-lens system that was offset in Step 2 can be made to conform to the off-axis three-lens design parameters again, and the distance between the ideal image point and its adjacent edge rays is constrained to the corresponding threshold.

[0053] Step 4: The primary mirror 6, secondary mirror 7 and third mirror 8 of the off-axis three-mirror system reconstructed in Step 3 are reconstructed a second time using the construction iteration method to optimize the imaging quality of the off-axis three-mirror system after Step 2 and Step 3.

[0054] Step 5: Determine whether the off-axis three-reflector system obtained in Step 4 meets the σ requirement based on the system design requirements. RMS <σ MAX If the condition is met, proceed to step 6; otherwise, proceed to step 7, and simultaneously save the current off-axis three-way reversing system as C. i ;σ RMS The root mean square of the distance between the ideal intersection point and the actual intersection point of the sampling ray and the image plane;

[0055] Step 6: Apply angular deflection to the primary mirror 6, secondary mirror 7, and third mirror 8 of the off-axis three-mirror system, and then return to step 2;

[0056] Step 7, output the off-axis three-way reversing system C that last entered step 6. i-1 .

[0057] Furthermore, in one embodiment, combined with Figure 2 The threshold values ​​for the distance between the reflector end of the off-axis three-mirror system and its adjacent edge rays in step 1 include: the threshold value of the first constraint distance L11, the threshold value of the second constraint distance L22, the threshold value of the third constraint distance L33, and the threshold value of the fourth constraint distance L44; the first constraint distance 1 is the distance between the lower end of the primary mirror and the light rays emitted from the upper edge of the secondary mirror, the second constraint distance 2 is the distance between the upper end of the secondary mirror and the light rays incident on the lower edge of the primary mirror, the third constraint distance 3 is the distance between the upper end of the three mirrors and the light rays incident on the lower edge of the secondary mirror, and the fourth constraint distance 4 is the distance between the lower end of the secondary mirror and the light rays emitted from the upper edge of the three mirrors;

[0058] The threshold for the distance between the ideal image point and its adjacent edge rays includes the threshold for the fifth constraint distance 5, which is the distance between the ideal image point and the incident light rays at the lower edge of the three mirrors.

[0059] Furthermore, in one embodiment, the process of selecting the sampling light in step 1 includes:

[0060] Select M fields of view, divide the aperture of each field of view into N equal parts, and select P characteristic rays at different aperture positions in each part as sampling rays.

[0061] Preferably, in some embodiments, the field of view is one of a circular field of view, a rectangular field of view, a square field of view, or an elliptical field of view.

[0062] Preferably, in some embodiments, the aperture of each field of view is circular, the circular aperture of each field of view is divided into N angles, and characteristic rays at P different aperture positions are taken along the radial direction of each angle.

[0063] Furthermore, in one embodiment, adjusting the structural parameters of the off-axis three-mirror system in step 2, so that the distance between the mirror end of the off-axis three-mirror system and its adjacent edge rays reaches a corresponding threshold, specifically includes:

[0064] First, keep the surface shapes of the primary mirror 6, secondary mirror 7, and third mirror 8 of the off-axis three-mirror system unchanged, and measure the change in the tilt angle θ1 of the primary mirror. Change in the tilt angle θ2 of the three mirrors The change in distance D1 between the primary mirror and the secondary mirror, l1, and the change in distance D2 between the secondary mirror and the third mirror, l2, are used as variables. Based on the degree of influence of each variable on the first constraint distance L11, the second constraint distance L22, the third constraint distance L33, and the fourth constraint distance L44, the four variables are adjusted in order of increasing influence to obtain a preliminary reduced off-axis three-mirror system. At this time, the first constraint distance L11 and the fourth constraint distance L44 have approached infinitesimal.

[0065] Then, keeping the surface shapes of the primary mirror 6, secondary mirror 7, and third mirror 8 of the off-axis three-mirror system unchanged, within a preset small range, l1, l2, The effects of the first constraint distance L11, the second constraint distance L22, the third constraint distance L33, and the fourth constraint distance L44 are linearly related. Based on this linear relationship, the first constraint distance L11, the second constraint distance L22, the third constraint distance L33, and the fourth constraint distance L44 are limited to their corresponding thresholds.

[0066] Preferably, in some embodiments, adjusting the four variables sequentially in order of increasing influence specifically includes:

[0067] (1) For each variable, initialize the corresponding adjustment step size and downward adjustment value, and set the adjustment lower limit value;

[0068] (2) For the first variable arranged in ascending order of influence, adjust it according to its corresponding adjustment step size;

[0069] (3) Determine whether there is a negative value among the first constraint distance L1(1), the second constraint distance L2(2), the third constraint distance L3(3) and the fourth constraint distance L4(4). If so, adjust the adjustment step size according to the current downward value based on the current adjustment step size, and then execute (4); otherwise execute (5).

[0070] (4) Determine whether the current adjustment step size is lower than the adjustment lower limit. If so, jump to (5); otherwise, adjust the variable with the current adjustment step size and then return to execute (3).

[0071] (5) For the next variable, adjust it in the manner of (2) to (4) until all four variables have been adjusted;

[0072] (6) Determine whether there exists a constraint distance value that is less than p times its corresponding threshold. If it exists, end the adjustment process; otherwise, return to (2); where p < 1.

[0073] Furthermore, in some embodiments, after adjusting the adjustment step size according to the current downward adjustment value, the following is also performed: reducing the current downward adjustment value.

[0074] Preferably, the initial adjustment step size is 1%, the initial downward adjustment value is 0.5%, and the adjustment lower limit value is 0.001%. Reducing the current downward adjustment value specifically means reducing it to half of its original value.

[0075] Preferably, p is 0.1.

[0076] Furthermore, in one embodiment, the root mean square σ of the distance between the ideal intersection point and the actual intersection point of the sampling ray and the image plane in step 5 is... RMS , is represented as:

[0077]

[0078] Where, δ m It is the distance between the ideal intersection point and the actual intersection point of the m-th sampling ray and the object-image plane, where M is the total number of sampling rays.

[0079] As a specific example, the invention will be further described and verified in detail in one embodiment.

[0080] The parameters of the freeform off-axis three-mirror optical system to be designed in this embodiment are as follows:

[0081] Table 1 Parameters of the System to be Designed

[0082]

[0083] Based on the parameter requirements of the desired freeform off-axis three-mirror optical system, a simple, unobstructed initial system structure is established, such as... Figure 3 As shown. The method of this invention is then used for design.

[0084] The structure of the compact off-axis three-reflector system is as follows: Figure 4 As shown in the figure, the system structure is more compact and the system volume is significantly reduced. Figure 5 and Figure 6 The RMS value and FFTMTF plot of the off-axis three-lens reflex camera after compaction using the present invention are given. It can be seen from the figure that the image quality of the compacted system is good.

[0085] Combination Figure 7 The diagram shows the process of system volume reduction with each iteration in the iterative process of the off-axis three-reflector system compact automatic design method of this embodiment. The horizontal axis represents the number of system iterations, and the vertical axis represents the percentage of the system volume at the current iteration number relative to the initial system volume.

[0086] In summary, this invention can automatically optimize the design of the input off-axis three-mirror initial model for compactness, and it can also be used to quickly and roughly estimate the minimum volume that off-axis three-mirror systems of different specifications can achieve.

[0087] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention without departing from its spirit and scope should be included within the protection scope of the present invention.

Claims

1. A compact automatic design method for an off-axis three-reflector system, characterized in that, The method includes: Step 1: Set the off-axis three-mirror design parameters and the corresponding initial model C0. Set the threshold values ​​for the distance between the mirror end of the off-axis three-mirror system and its adjacent edge rays, the threshold values ​​for the distance between the ideal image point and its adjacent edge rays, and the maximum root mean square value σ of the distance between the ideal intersection point and the actual intersection point of the sampled ray and the image plane. MAX ; Step 2: Adjust the structural parameters of the off-axis three-mirror system so that the distance between the mirror end of the off-axis three-mirror system and its adjacent edge light reaches the corresponding threshold, thereby obtaining a compact off-axis three-mirror system with strictly limited constraint distance. Step 3: The surface shape of the three mirrors of the off-axis three-lens system obtained in Step 2 is reconstructed by constructing an iterative method. During the construction process, the position of the ideal image point is determined according to the distance threshold between the ideal image point and its adjacent edge rays, so that the focal length of the off-axis three-lens system that was offset in Step 2 can be made to conform to the off-axis three-lens design parameters again, and the distance between the ideal image point and its adjacent edge rays is constrained to the corresponding threshold. Step 4: The primary mirror, secondary mirror, and third mirror in the off-axis three-mirror system reconstructed in Step 3 are reconstructed a second time using the construction iteration method to optimize the imaging quality of the off-axis three-mirror system after Steps 2 and 3. Step 5: Determine whether the off-axis three-reflector system obtained in Step 4 meets the σ requirement based on the system design requirements. RMS <σ MAX If the condition is met, proceed to step 6; otherwise, proceed to step 7, and simultaneously save the current off-axis three-way reversing system as C. i ;σ RMS The root mean square of the distance between the ideal intersection point and the actual intersection point of the sampling ray and the image plane; Step 6: Apply angular deflection to the primary mirror, secondary mirror, and third mirror of the off-axis three-mirror system, and then return to step 2; Step 7, output the off-axis three-way reversing system C that last entered step 6. i-1 .

2. The compact automatic design method for an off-axis three-reflector system according to claim 1, characterized in that, Its features are, The threshold values ​​for the distance between the reflector end of the off-axis three-mirror system and its adjacent edge rays in step 1 include: the threshold value of the first constraint distance L1, the threshold value of the second constraint distance L2, the threshold value of the third constraint distance L3, and the threshold value of the fourth constraint distance L4; the first constraint distance is the distance between the lower end of the primary mirror and the light rays emitted from the upper edge of the secondary mirror, the second constraint distance is the distance between the upper end of the secondary mirror and the light rays incident on the lower edge of the primary mirror, the third constraint distance is the distance between the upper end of the three mirrors and the light rays incident on the lower edge of the secondary mirror, and the fourth constraint distance is the distance between the lower end of the secondary mirror and the light rays emitted from the upper edge of the three mirrors; The threshold for the distance between the ideal image point and its adjacent edge rays includes the threshold for the fifth constraint distance, which is the distance between the ideal image point and the incident light rays at the lower edge of the three mirrors.

3. The compact automatic design method for an off-axis three-reflector system according to claim 1, characterized in that, The process of selecting the sampling light in step 1 includes: Select M fields of view, divide the aperture of each field of view into N equal parts, and select P characteristic rays at different aperture positions in each part as sampling rays.

4. The compact automatic design method for an off-axis three-reflector system according to claim 3, characterized in that, The field of view can be a circular field of view, a rectangular field of view, a square field of view, or an elliptical field of view.

5. The compact automatic design method for an off-axis three-reflector system according to claim 3, characterized in that, Each field of view has a circular aperture. The circular aperture of each field of view is divided into N angles, and P characteristic rays at different aperture positions are taken along the radius of each angle.

6. The compact automatic design method for an off-axis three-reflector system according to claim 2, characterized in that, Step 2 involves adjusting the structural parameters of the off-axis three-mirror system so that the distance between the mirror end of the off-axis three-mirror system and its adjacent edge rays reaches a corresponding threshold. Specifically, this includes: First, keep the primary, secondary, and tertiary mirror planes of the off-axis three-mirror system unchanged, and measure the change in the primary mirror tilt angle θ1. Change in the tilt angle θ2 of the three mirrors The change in distance D1 between the primary mirror and the secondary mirror, l1, and the change in distance D2 between the secondary mirror and the third mirror, l2, are used as variables. Based on the degree of influence of each variable on the first constraint distance L1, the second constraint distance L2, the third constraint distance L3, and the fourth constraint distance L4, the four variables are adjusted in order of increasing influence to obtain a preliminary reduced off-axis three-mirror system. At this time, the first constraint distance L1 and the fourth constraint distance L4 have approached infinitesimal. Then, keeping the primary, secondary, and tertiary mirror surfaces of the off-axis three-mirror system unchanged, within a preset small range, l1, l2, The effects of the first constraint distance L1, the second constraint distance L2, the third constraint distance L3, and the fourth constraint distance L4 are linearly related. Based on this linear relationship, the first constraint distance L1, the second constraint distance L2, the third constraint distance L3, and the fourth constraint distance L4 are limited to their corresponding thresholds.

7. The compact automatic design method for an off-axis three-reflector system according to claim 6, characterized in that, The adjustment of the four variables in ascending order of their impact includes: (1) For each variable, initialize the corresponding adjustment step size and downward adjustment value, and set the adjustment lower limit value; (2) For the first variable arranged in ascending order of influence, adjust it according to its corresponding adjustment step size; (3) Determine whether there is a negative value among the first constraint distance L1(1), the second constraint distance L2(2), the third constraint distance L3(3) and the fourth constraint distance L4(4). If so, adjust the adjustment step size according to the current downward value based on the current adjustment step size, and then execute (4); otherwise execute (5). (4) Determine whether the current adjustment step size is lower than the adjustment lower limit. If so, jump to (5); otherwise, adjust the variable with the current adjustment step size and then return to execute (3). (5) For the next variable, adjust it in the manner of (2) to (4) until all four variables have been adjusted; (6) Determine whether there exists a constraint distance value that is less than p times its corresponding threshold. If it exists, end the adjustment process; otherwise, return to (2); where p < 1.

8. The compact automatic design method for an off-axis three-reflector system according to claim 7, characterized in that, After adjusting the adjustment step size according to the current downward adjustment value, the following action is taken: reduce the current downward adjustment value.

9. The compact automatic design method for an off-axis three-reflector system according to claim 7, characterized in that, The value of p is 0.

1.

10. The compact automatic design method for an off-axis three-reflector system according to claim 1, characterized in that, The root mean square σ of the distance between the ideal intersection point and the actual intersection point of the sampling ray and the image plane described in step 5. RMS , is represented as: Where, δ m It is the distance between the ideal intersection point and the actual intersection point of the m-th sampling ray and the object-image plane, where M is the total number of sampling rays.

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