Compact automatic design method for off-axis three-reflector system

Abstract

The invention discloses a compact automatic design method for an off-axis three-reflector system, belongs to the field of optical design, and aims to solve the problem that the compact design process of a traditional off-axis reflection system is tedious, time-consuming and labor-consuming. The method comprises the following steps: carrying out volume constraint on an off-axis three-reflector system to obtain a small-volume off-axis three-reflector system with a compact structure; image quality optimization is carried out on the obtained small-size off-axis three-mirror system, and the system imaging quality influenced by size constraint is optimized; and the volume constraint process and the image quality optimization process are subjected to cross iteration to output a compact off-axis three-mirror system with good image quality. According to the method, on one hand, the input off-axis three-reflector initial type can be automatically subjected to compact optimization design, and on the other hand, the method can also be used for rapidly and roughly estimating the minimum volume which can be reached by off-axis three-reflector systems of different specifications.

Description

Technical Field

[0001] The invention belongs to the technical field of optical system design, and in particular to a compact automatic design method for an off-axis three-mirror system. Background Art

[0002] With the continuous development and progress of optical technology, off-axis reflective systems have begun to attract more and more attention from optical design researchers. Off-axis three-mirror optical systems not only have many advantages of coaxial three-mirror optical systems, such as no chromatic aberration, no secondary spectrum, relatively few parts, large optical system aperture, relatively low material requirements, and very flexible design types. At the same time, with the development and use of off-axis reflective systems, there is an increasing demand for compact off-axis systems. Traditional methods of reducing system volume are difficult and cumbersome, and require designers to spend a lot of time and energy.

[0003] Generally speaking, it is not easy for optical designers to reduce the volume of off-axis reflective systems. Designers usually need to find an initial model and then use optical design software to assist in optimization to make the volume smaller. The traditional method is to impose a volume constraint on the initial model to reduce the volume. However, as a trial-and-error process, this process is very demanding on the designer's experience. Usually, reducing the volume of the off-axis three-mirror system takes a lot of time for designers. The main reasons are as follows: 1) When using the optimization algorithm to reduce the volume, since the volume reduction process of the off-axis three-mirror system is not a linear process, but the optimization algorithm usually uses a linear approximation method, which requires that the optimization step size cannot be too long. At the same time, it is very easy to fall into the trap of local optimal solutions during the optimization process. How to discover the situation where the system falls into the local optimal solution and how to solve the problem of the system falling into the local optimal solution not only require high professional ability and design experience of the designer, but also consume a lot of time for the designer to solve the problem. Especially when the target volume is relatively small compared to the initial model, the problem of falling into the local optimal solution many times may cause the optimization to fail and fail to obtain results that meet the requirements. 2) Due to the high degree of freedom of the off-axis three-mirror system, it is difficult for designers to obtain an initial model that meets the design requirements from existing patents or materials. This makes it difficult for designers to estimate the minimum volume that can be achieved through optimization of the initial model used during the design process. Therefore, designers are relatively blind when selecting the initial model for the off-axis three-mirror system design, and there is a high possibility that a series of problems will arise, such as the selected initial model cannot be optimized to meet the design requirements. Summary of the invention

[0004] The purpose of the present invention is to provide a compact automatic design method for an off-axis three-mirror system, so as to solve the problem that the traditional method of reducing the volume of the system is difficult and cumbersome.

[0005] The technical solution to achieve the purpose of the present invention is: a compact automatic design method for an off-axis three-mirror system, the method comprising:

[0006] Step 1, set the off-axis three-mirror design parameters and the corresponding initial model C0, set the threshold of the distance between the reflector end of the off-axis three-mirror system and its adjacent edge light, the threshold of the distance between the ideal image point and its adjacent edge light, and the maximum value σ of the root mean square of the distance between the ideal intersection point and the actual intersection point of the sampling light and the image plane MAX ;

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

[0008] Step 3, reconstructing the surface shape of the three mirrors of the off-axis three-mirror system obtained in step 2 by a construction iteration method, and determining the position of the ideal image point according to the distance threshold between the ideal image point and its adjacent edge light during the construction process, so that the focal length of the off-axis three-mirror system that has shifted in step 2 conforms to the off-axis three-mirror design parameters again, and constraining the distance between the ideal image point and its adjacent edge light to the corresponding threshold;

[0009] Step 4, reconstructing the primary mirror, the secondary mirror and the third mirror in the off-axis three-mirror system reconstructed in step 3 by a construction iteration method, and optimizing the imaging quality of the off-axis three-mirror system after steps 2 and 3;

[0010] Step 5: Determine whether the off-axis three-mirror system obtained in step 4 meets the requirements of σ according to the system design requirements. RMS <σ MAX If it meets the requirements, go to step 6, otherwise go to step 7 and save the current off-axis three-mirror system as C i ; σ RMS is the root mean square of the distance between the ideal intersection point and the actual intersection point of the sampling light and the image plane;

[0011] Step 6, applying angle deflection to the primary mirror, the secondary mirror, and the third mirror of the off-axis three-mirror system, and then returning to step 2;

[0012] Step 7: Output the off-axis three-mirror system C entered in step 6 last time i-1 .

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

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

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

[0016] M fields of view are selected, the aperture of each field of view is divided into N equal parts, and P characteristic rays at different aperture positions are selected in each equal 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, the circular aperture of each field of view is equally divided into N angles, and characteristic light rays at P different aperture positions are taken along the radial direction of each angle.

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

[0020] First, keep the primary mirror, secondary mirror, and three mirrors of the off-axis three-mirror system unchanged, and change the primary mirror tilt angle θ1 The change of the tilt angle θ2 of the three mirrors The change amount l1 of the distance D1 between the primary mirror and the secondary mirror and the change amount l2 of the distance D2 between the secondary mirror and the third mirror are used as variables. According to the 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 from small to large in order of influence, so as to obtain a preliminarily reduced off-axis three-mirror system. At this time, the first constraint distance L1 and the fourth constraint distance L4 have tended to infinitesimal.

[0021] After that, the primary mirror, secondary mirror, and three mirrors of the off-axis three-mirror system are kept unchanged, and the preset small range of l1, l2, The influence on the first constraint distance L1, the second constraint distance L2, the third constraint distance L3 and the fourth constraint distance L4 is in a linear relationship, and the first constraint distance L1, the second constraint distance L2, the third constraint distance L3 and the fourth constraint distance L4 are limited to corresponding thresholds according to the linear relationship.

[0022] Furthermore, the four variables are adjusted in order from small to large in terms of impact, specifically including:

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

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

[0025] (3) Determine whether any of 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) is a negative value. If so, adjust the adjustment step size according to the current downward adjustment 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 according to the method (2) to (4) until all four variables are adjusted;

[0028] (6) Determine whether there is a constraint distance value that is less than p times its corresponding threshold value. If so, 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 is further performed: reducing the current downward adjustment value.

[0030] Furthermore, the root mean square σ of the distance between the ideal intersection point of the sampling light and the image plane in step 5 and the actual intersection point RMS , expressed as:

[0031]

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

[0033] Compared with the prior art, the present invention has the following significant advantages:

[0034] (1) The present invention only needs to input a compact off-axis three-mirror system and a small number of constraint condition parameters to automatically output a compact system, and no designer needs to be involved in the optimization process.

[0035] (2) The use of the present invention to compact the off-axis three-mirror system will not cause the designer to fall into a local minimum when performing the off-axis three-mirror compactification operation, thereby increasing the possibility of successful optimization.

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

[0037] The present invention is further described in detail below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a flow chart of the automatic design method for off-axis three-reactor compactness of the present invention.

[0039] Figure 2 It 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 The figure is an initial schematic diagram of a compact automatic design method for an off-axis three-mirror system provided in one embodiment.

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

[0042] Figure 5 It is the RMS value of the point diagram of an off-axis three-mirror optical system that is compacted to good quality, 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 an off-axis three-mirror optical system compacted to good quality output by an automatic design method for compacting an off-axis three-mirror system provided in an embodiment.

[0044] Figure 7 A line graph showing the reduction in system volume during the iterative process of an off-axis three-mirror optical system towards a compact off-axis three-mirror system of good quality, output by an automatic off-axis three-mirror system compactification design method provided in one embodiment. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

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

[0047] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0048] In order to solve the problem that the compact design process of the traditional off-axis reflection system is cumbersome, time-consuming and labor-intensive, the present invention proposes a design method that can automatically obtain a compact off-axis three-mirror system without the participation of designers, including: performing volume constraints on the off-axis three-mirror system to obtain a small-volume off-axis three-mirror system with a compact structure; performing image quality optimization on the obtained small-volume off-axis three-mirror system to optimize the system imaging quality affected by the volume constraints; and cross-iterating 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, in combination Figure 1 , provides a compact automatic design method for an off-axis three-mirror system, the method comprising:

[0050] Step 1, set the off-axis three-mirror design parameters and the corresponding initial model C0, set the threshold of the distance between the reflector end of the off-axis three-mirror system and its adjacent edge light, the threshold of the distance between the ideal image point and its adjacent edge light, and the maximum value σ of the root mean square of the distance between the ideal intersection point and the actual intersection point of the sampling light and the image plane MAX ;

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

[0052] Step 3, reconstructing the surface shape of the three mirrors 8 of the off-axis three-mirror system obtained in step 2 by a construction iteration method, and determining the position of the ideal image point according to the distance threshold between the ideal image point and its adjacent edge light during the construction process, so that the focal length of the off-axis three-mirror system that has shifted in step 2 conforms to the off-axis three-mirror design parameters again, and constraining the distance between the ideal image point and its adjacent edge light to the corresponding threshold;

[0053] Step 4, performing secondary surface reconstruction of the primary mirror 6, the secondary mirror 7 and the third mirror 8 in the off-axis three-mirror system reconstructed in step 3 by a construction iteration method, so as to optimize the imaging quality of the off-axis three-mirror system after steps 2 and 3;

[0054] Step 5: Determine whether the off-axis three-mirror system obtained in step 4 meets the requirements of σ according to the system design requirements. RMS <σ MAX If it meets the requirements, go to step 6, otherwise go to step 7 and save the current off-axis three-mirror system as C i ; σ RMS is the root mean square of the distance between the ideal intersection point and the actual intersection point of the sampling light and the image plane;

[0055] Step 6, applying angle deflection to the primary mirror 6, the secondary mirror 7, and the tertiary mirror 8 of the off-axis three-mirror system, and then returning to step 2;

[0056] Step 7: Output the off-axis three-mirror system C entered in step 6 last time i-1 .

[0057] Further, in one embodiment, in combination Figure 2 , the thresholds of the distances between the reflector end of the off-axis three-mirror system and its adjacent edge light in step 1 include: a threshold of a first constraint distance L11, a threshold of a second constraint distance L22, a threshold of a third constraint distance L33, and a threshold of a fourth constraint distance L44; the first constraint distance 1 is the distance between the lower end point of the primary mirror and the outgoing light from the upper edge of the secondary mirror, the second constraint distance 2 is the distance between the upper end point of the secondary mirror and the incident light from the lower edge of the primary mirror, the third constraint distance 3 is the distance between the upper end point of the three mirrors and the incident light from the lower edge of the secondary mirror, and the fourth constraint distance 4 is the distance between the lower end point of the secondary mirror and the outgoing light from the upper edge of the three mirrors;

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

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

[0060] M fields of view are selected, the aperture of each field of view is divided into N equal parts, and P characteristic rays at different aperture positions are selected in each equal 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 equally divided into N angles, and characteristic light rays at P different aperture positions are taken along the radial direction of each angle.

[0063] Further, in one embodiment, the structural parameters of the off-axis three-mirror system are adjusted in step 2 so that the distance between the reflector end of the off-axis three-mirror system and its adjacent edge light reaches a corresponding threshold, specifically including:

[0064] First, keep the primary mirror 6, secondary mirror 7, and third mirror 8 of the off-axis three-mirror system unchanged, and change the primary mirror inclination angle θ1 The change of the tilt angle θ2 of the three mirrors The change l1 of the distance D1 between the primary mirror and the secondary mirror and the change l2 of the distance D2 between the secondary mirror and the third mirror are used as variables. According to the 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 from small to large in order of influence, so as to obtain a preliminarily reduced off-axis three-mirror system. At this time, the first constraint distance L11 and the fourth constraint distance L44 have tended to infinitesimal.

[0065] After that, the primary mirror 6, secondary mirror 7, and third mirror 8 of the off-axis three-mirror system are kept unchanged, and the surfaces of l1, l2, The influence on the first constraint distance L11, the second constraint distance L22, the third constraint distance L33 and the fourth constraint distance L44 is in a linear relationship, and the first constraint distance L11, the second constraint distance L22, the third constraint distance L33 and the fourth constraint distance L44 are limited to corresponding thresholds according to the linear relationship.

[0066] Preferably, in some embodiments, the adjusting of the four variables in order of influence from small to large specifically includes:

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

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

[0069] (3) Determine whether any of 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) is a negative value. If so, adjust the adjustment step size according to the current downward adjustment 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 according to the method (2) to (4) until all four variables are adjusted;

[0072] (6) Determine whether there is a constraint distance value that is less than p times its corresponding threshold value. If so, 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 further performed: reducing the current downward adjustment value.

[0074] Here preferably, the initial adjustment step is 1%, the initial down-adjustment value is 0.5%, and the adjustment lower limit is 0.001%. Reducing the current down-adjustment value specifically means reducing it to half of the original value.

[0075] Here, 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 light and the image plane in step 5 is RMS , expressed as:

[0077]

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

[0079] As a specific example, in one of the embodiments, the present invention is further verified and explained in detail.

[0080] The parameters of the free-form surface 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] According to the parameter requirements of the free-form surface off-axis three-mirror optical system to be obtained, a simple unobstructed system initial structure is established, such as Figure 3 Then the method of the present invention is used for design.

[0084] The structure of the compact off-axis three-mirror system is as follows: Figure 4 As shown in the figure, it can be seen that the structure of the system is more compact and the system volume is significantly reduced. Figure 5 and Figure 6 The RMS value of the spot diagram and the FFTMTF diagram of the off-axis three-mirror system after being compacted by the present invention are given. It can be seen from the diagram that the image quality of the compacted system is good.

[0085] Combination Figure 7 , lists the process of system volume reduction with the number of iterations during the iterative process of the off-axis three-mirror system compactification automatic design method of this embodiment, the horizontal axis is the number of system iterations, and the vertical axis is the percentage of the system volume at the current iteration number relative to the initial system volume.

[0086] In summary, the present invention can automatically optimize the compact design of the input off-axis three-mirror initial model on the one hand, and can also be used to quickly and roughly estimate the minimum volume that can be achieved by off-axis three-mirror systems of different specifications on the other hand.

[0087] The above shows and describes 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 by the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A compact automatic design method for an off-axis three-mirror system, characterized in that: The method comprises: Step 1, set the off-axis three-mirror design parameters and the corresponding initial model C0, set the threshold of the distance between the reflector end of the off-axis three-mirror system and its adjacent edge light, the threshold of the distance between the ideal image point and its adjacent edge light, and the maximum value σ of the root mean square of the distance between the ideal intersection point and the actual intersection point of the sampling light and the image plane MAX ; Step 2, adjusting the structural parameters of the off-axis three-mirror system so that the distance between the reflector end of the off-axis three-mirror system and its adjacent edge light reaches a corresponding threshold, thereby obtaining a compact off-axis three-mirror system with a strictly limited constraint distance; Step 3, reconstructing the surface shape of the three mirrors of the off-axis three-mirror system obtained in step 2 by a construction iteration method, and determining the position of the ideal image point according to the distance threshold between the ideal image point and its adjacent edge light during the construction process, so that the focal length of the off-axis three-mirror system that has shifted in step 2 conforms to the off-axis three-mirror design parameters again, and constraining the distance between the ideal image point and its adjacent edge light to the corresponding threshold; Step 4, reconstructing the primary mirror, the secondary mirror and the third mirror in the off-axis three-mirror system reconstructed in step 3 by a construction iteration method, so as 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-mirror system obtained in step 4 meets the requirements of σ according to the system design requirements. RMS <σ MAX If it meets the requirements, go to step 6, otherwise go to step 7 and save the current off-axis three-mirror system as C i ; σ RMS is the root mean square of the distance between the ideal intersection point and the actual intersection point of the sampling light and the image plane; Step 6, applying angle deflection to the primary mirror, the secondary mirror, and the third mirror of the off-axis three-mirror system, and then returning to step 2; Step 7: Output the off-axis three-mirror system C entered in step 6 last time i-1 .

2. The off-axis three-mirror system compact automatic design method according to claim 1, characterized in that: It is characterized in that The thresholds of the distances between the reflector end of the off-axis three-mirror system and its adjacent edge light in step 1 include: a threshold of a first constraint distance L1, a threshold of a second constraint distance L2, a threshold of a third constraint distance L3, and a threshold of a fourth constraint distance L4; the first constraint distance is the distance between the lower end point of the primary mirror and the outgoing light from the upper edge of the secondary mirror, the second constraint distance is the distance between the upper end point of the secondary mirror and the incident light from the lower edge of the primary mirror, the third constraint distance is the distance between the upper end point of the three mirrors and the incident light from the lower edge of the secondary mirror, and the fourth constraint distance is the distance between the lower end point of the secondary mirror and the outgoing light from the upper edge of the three mirrors; The threshold of the distance between the ideal image point and its adjacent edge light includes the threshold of the fifth constraint distance, and the fifth constraint distance is the distance between the ideal image point and the incident light of the lower edge of the three mirrors.

3. The off-axis three-mirror system compact automatic design method according to claim 1, characterized in that: The sampling light selection process described in step 1 includes: M fields of view are selected, the aperture of each field of view is divided into N equal parts, and P characteristic rays at different aperture positions are selected in each equal part as sampling rays.

4. The off-axis three-mirror system compact automatic design method according to claim 3, characterized in that: 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.

5. The off-axis three-mirror system compact automatic design method according to claim 3, characterized in that: The aperture of each field of view is circular, and the circular aperture of each field of view is equally divided into N angles, and characteristic light rays at P different aperture positions are taken along the radial direction of each angle.

6. The off-axis three-mirror system compact automatic design method according to claim 2, characterized in that: The step 2 of adjusting the structural parameters of the off-axis three-mirror system so that the distance between the reflector end of the off-axis three-mirror system and its adjacent edge light reaches a corresponding threshold value specifically includes: First, keep the primary mirror, secondary mirror, and three mirrors of the off-axis three-mirror system unchanged, and change the primary mirror tilt angle θ1 The change of the tilt angle θ2 of the three mirrors The change amount l1 of the distance D1 between the primary mirror and the secondary mirror and the change amount l2 of the distance D2 between the secondary mirror and the third mirror are used as variables. According to the 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 from small to large in order of influence, so as to obtain a preliminarily reduced off-axis three-mirror system. At this time, the first constraint distance L1 and the fourth constraint distance L4 have tended to infinitesimal. After that, the primary mirror, secondary mirror, and three mirrors of the off-axis three-mirror system are kept unchanged, and the preset small range of l1, l2, The influence on the first constraint distance L1, the second constraint distance L2, the third constraint distance L3 and the fourth constraint distance L4 is in a linear relationship, and the first constraint distance L1, the second constraint distance L2, the third constraint distance L3 and the fourth constraint distance L4 are limited to corresponding thresholds according to the linear relationship.

7. The off-axis three-mirror system compact automatic design method according to claim 6, characterized in that: The four variables are adjusted in order from small to large in terms of impact, specifically including: (1) For each variable, initialize the corresponding adjustment step and downward adjustment value, and set the adjustment lower limit; (2) For the first variable arranged in ascending order of influence, adjust it according to its corresponding adjustment step; (3) Determine whether any of 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) is a negative value. If so, adjust the adjustment step size according to the current downward adjustment 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 according to (2) to (4) until all four variables have been adjusted; (6) Determine whether there is a constraint distance value that is less than p times its corresponding threshold value. If so, end the adjustment process; otherwise, return to (2); where p<1.

8. The off-axis three-mirror system compact automatic design method according to claim 7, characterized in that: After adjusting the adjustment step size according to the current downward adjustment value, further performing: reducing the current downward adjustment value.

9. The off-axis three-mirror system compact automatic design method according to claim 7, characterized in that: The p is set to 0.

1.

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

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