A long-tube catadioptric zoom system assembly and adjustment method and system

Abstract

The present invention belongs to the technical field related to optical alignment and discloses a method and system for aligning a long-tube catadioptric zoom system. The method includes the following steps: aligning the optical axis of an autocollimator with the optical axis of a plane interferometer; measuring the optical axis error of a plano-concave lens using the autocollimator, and aligning the optical axes of a primary mirror assembly and a plano-concave lens assembly with the optical axis of the autocollimator; constructing an interference simulation model of a system consisting of a primary mirror, a secondary mirror, and a plano-concave lens; calculating the misalignment using the Zernike expansion coefficient of the system's wavefront aberration; and adjusting the optical axes of the secondary mirror assembly and the plano-concave lens assembly to be coaxial with the optical axis of the primary mirror assembly. Furthermore, the spacing between the primary mirror assembly and the secondary mirror assembly, and between the secondary mirror assembly and the plano-concave lens assembly, is adjusted to meet preset requirements, thereby ensuring that the system's wavefront aberration meets preset threshold requirements; and removing and replacing the plano-concave lens assembly with a correction mirror assembly to complete the alignment of the long-tube catadioptric zoom system. The present invention enables efficient and high-precision alignment of a long-tube catadioptric zoom system.

Description

Technical Field

[0001] The present invention belongs to the technical field related to optical alignment, and more specifically, relates to an alignment method and system for a long-tube catadioptric zoom system. Background Art

[0002] There are two basic types of optical systems composed of dual mirrors (primary mirror and secondary mirror): Gregorian optical system and Cassegrain optical system. The focal length of Cassegrain optical system is usually larger. In the dual mirror optical system, the primary mirror is used to increase the aperture of the optical system and increase the ability of the optical system to collect light energy. The secondary mirror is used to converge the compressed light beam and correct the aberration of the primary mirror. When designing a Cassegrain optical system, refractive elements are usually used near the focal plane to increase the field of view and correct off-axis aberrations and field curvature. How to efficiently and accurately control the eccentricity error, tilt error, and optical spacing error of the dual mirrors and refractive elements is a difficult point in the assembly and adjustment of the system. Another difficulty is that the standard spherical interferometer cannot perform full-aperture testing of the wavefront aberration of the long-tube catadioptric zoom system.

[0003] CN201910881551.6 discloses a centering and adjustment method for a catadioptric common-aperture system containing a relay mirror group. The invention uses a center deviation measuring instrument to first align the optical axes of the primary mirror and the relay mirror group, and then uses a spherical interferometer and a standard plane mirror to adjust the secondary mirror in the optical system. This invention has the advantage of high precision, but it uses a standard spherical interferometer to perform full-aperture wavefront aberration testing; CN201910881002.9 discloses a method for adjusting a common-aperture optical system containing a secondary mirror focusing mechanism. The optical system targeted by this invention is secondary mirror focusing; CN202211363678.7 discloses a precision assembly method for an off-axis two-mirror and lens combination optical system. The optical system targeted by this invention is an off-axis reflection system. Therefore, there is an urgent need for an adjustment method suitable for a long-tube catadioptric zoom system. Summary of the Invention

[0004] In view of the above defects or improvement needs of the prior art, the present invention provides a method and system for assembling and adjusting a long-tube catadioptric zoom system to solve the assembly and adjustment problems of the long-tube catadioptric zoom system.

[0005] To achieve the above object, according to one aspect of the present invention, a method for assembling and adjusting a long-tube catadioptric zoom system is provided, the method comprising the following steps:

[0006] A plane interferometer and an autocollimator are respectively arranged on both sides of the adjustment platform, and the optical axis of the autocollimator is parallel to the optical axis of the plane interferometer;

[0007] Mounting a plano-concave lens assembly on the primary mirror assembly, and then mounting the primary mirror assembly with the plano-concave lens assembly mounted thereon on an adjustment stage, such that the optical axis of the plano-concave lens assembly is coaxial with the optical axis of the primary mirror assembly and is parallel to the optical axis of the autocollimator;

[0008] The secondary mirror assembly is connected to the primary mirror assembly, and light emitted by the plane interferometer passes through the primary mirror assembly, the secondary mirror assembly, and the plano-concave lens assembly in sequence and then returns along the original path, thereby forming interference fringes in the plane interferometer; the interference fringes are used to calculate the total misalignment of the secondary mirror assembly and the plano-concave lens assembly in all directions; and the plano-concave lens assembly and the secondary mirror assembly are respectively adjusted according to the calculated total misalignment, so that the optical axis of the secondary mirror assembly is coaxial with that of the primary mirror assembly, and the spacing between the primary mirror assembly and the secondary mirror assembly, and between the secondary mirror assembly and the plano-concave lens assembly, meet preset requirements, thereby ensuring that the wavefront aberration of the optical system composed of the primary mirror assembly, the secondary mirror assembly, and the plano-concave lens assembly meets a preset threshold requirement;

[0009] The plano-concave lens assembly is disassembled and replaced with a correction lens assembly to complete the assembly and adjustment of the long-tube catadioptric zoom system.

[0010] Further preferably, the total misalignment includes the misalignment of the secondary mirror assembly and the misalignment of the plano-concave lens assembly, the misalignment of the secondary mirror assembly includes the translation of the secondary mirror assembly along the X, Y and Z directions respectively, and the rotation of the secondary mirror assembly around the X and Y directions, and the misalignment of the plano-concave lens assembly is the translation of the plano-concave lens assembly along the Z direction.

[0011] Further preferably, the calculation of the offset is performed according to the following steps:

[0012] Construct an optical interference simulation model based on the optical parameters of the primary mirror assembly, the secondary mirror assembly and the plano-concave lens assembly;

[0013] Misalignment D of the plano-concave lens assembly H Assign values ​​and input them into the optical interference simulation model to obtain different D H The defocus Z4 of the optical system composed of the corresponding primary mirror assembly, secondary mirror assembly and plano-concave lens assembly is thus fitted with Z4 and D H The curvilinear relationship between the two;

[0014] Constructing a relationship between the wavefront aberration Zernike expansion coefficient Z of the interference fringes and the total misalignment X, assigning a value to the total misalignment X and inputting the value into the optical interference simulation model to obtain a corresponding Zernike expansion coefficient, thereby determining the relationship between the total misalignment X and the Zernike expansion coefficient Z;

[0015] Get the measured defocus Z4 and Zernike expansion coefficient Z, and use the Z4 and D HThe curve relationship between the two and the relationship between the total offset X and the Zernike expansion coefficient Z are used to calculate the actual offset D H and the total offset X.

[0016] Further preferably, the total imbalance X is calculated according to the following formula:

[0017] Z=AX

[0018] Z=[Z5 Z6 Z7 Z8 Z9] T

[0019]

[0020] X=[T x T y T z R x R y D H ] T

[0021] Among them, Z5, Z6, Z7, Z8 and Z9 are respectively the X-axis first-order astigmatism, Y-axis first-order astigmatism, X-axis first-order coma aberration, Y-axis first-order coma aberration and first-order spherical aberration of the optical system composed of the primary mirror assembly, secondary mirror assembly and plano-concave lens assembly. Tx, Ty, Tz, Rx and Ry are respectively the translation of the secondary mirror along the X, Y and Z directions and the rotation around the X and Y directions. D H is the misalignment of the plano-concave lens assembly.

[0022] Further preferably, the misalignment D of the plano-concave lens assembly is H Calculate using the following formula:

[0023] D H =-1.438·Z4 2 +27.56·Z4

[0024] Among them, Z4 is the defocus of the optical system consisting of the primary mirror assembly, the secondary mirror assembly and the plano-concave lens assembly.

[0025] Further preferably, before disassembling the plano-concave lens assembly and replacing it with the correction lens assembly, the actual required thickness of the trimming pad of the correction lens assembly is calculated. The calculation formula for the thickness is as follows:

[0026] JZJZXQD_L=JZJZXQD_L(theoretical)-△JZJZ_H+△R-△H_PATJZ-△PATJXQD_L

[0027] Among them, JZJZXQD_L is the actual required thickness of the trimming pad in the correction lens assembly, JZJZXQD_L(theoretical) is the theoretical thickness of the trimming pad in the correction lens assembly, △JZJZ_H is the distance error from the concave vertex of the lens in the correction lens assembly to the mounting end face of the correction lens group, △R is the curvature radius error of the plano-concave lens, △H_PATJZ is the distance error from the concave vertex of the plano-concave lens to the end face of the plano-concave lens barrel, and △PATJXQD_L is the thickness error of the trimming pad in the plano-concave lens assembly.

[0028] Further preferably, before installing the plano-concave lens assembly on the primary mirror assembly, the following steps are performed:

[0029] Adjusting the optical axis of the primary mirror in the primary mirror assembly to be coaxial with the central axis of the primary lens barrel and perpendicular to the end face of the primary lens barrel;

[0030] The optical axis of the plano-concave lens in the plano-concave lens assembly is adjusted to be coaxial with the central axis of the plano-concave lens barrel and perpendicular to the end surface of the plano-concave lens barrel.

[0031] Further preferably, the method of adjusting the optical axis of the main mirror in the main mirror assembly to be coaxial with the central axis of the main lens barrel and perpendicular to the end face of the main lens barrel is: aligning and connecting the center hole and back side of the main mirror with the main lens barrel.

[0032] Further preferably, the method for adjusting the optical axis of the plano-concave lens in the plano-concave lens assembly to be coaxial with the central axis of the plano-concave lens barrel and perpendicular to the end face of the plano-concave lens barrel is: taking the optical axis of the plano-concave lens as a reference, centering and edge-turning the outer cylindrical surface and the end face of the plano-concave lens barrel so that the central axis of the outer cylindrical surface is coaxial with the optical axis of the plano-concave lens, and the end face of the plano-concave lens barrel is perpendicular to the optical axis of the plano-concave lens.

[0033] According to another aspect of the present invention, a system for adjusting the long-tube catadioptric zoom lens using the above-mentioned adjustment method is provided, the system comprising: a planar interferometer, an autocollimator, an adjustment stage, a primary mirror assembly, a secondary mirror assembly, a plano-concave lens assembly, and a correction mirror assembly, wherein:

[0034] The plane interferometer and the autocollimator are arranged on both sides of the adjustment platform, and the primary mirror assembly, the secondary mirror assembly, the plano-concave lens assembly and the correction mirror assembly are all arranged on the adjustment platform;

[0035] The plano-concave lens assembly is arranged on the primary mirror assembly and is used to adjust the optical axes of the primary mirror assembly, the secondary mirror assembly and the correction mirror assembly and the optical spacing between them;

[0036] The secondary mirror assembly is arranged between the plano-concave lens assembly and the plane interferometer and is connected to the primary mirror assembly;

[0037] The correction lens assembly is used to replace the plano-concave lens assembly after the primary mirror assembly, the secondary mirror assembly and the plano-concave lens assembly are assembled and adjusted.

[0038] In general, the above technical solutions conceived by the present invention have the following beneficial effects compared with the prior art:

[0039] 1. The present invention adopts a plane interferometer to obtain interference fringes, calculates the misalignment of the secondary mirror assembly and the plano-concave lens assembly and uses the misalignment to adjust the position of the secondary mirror assembly and the plano-concave lens assembly, thereby making the optical axis of the secondary mirror assembly and the plano-concave lens assembly coaxial with the optical axis of the primary mirror assembly, and the intervals between the primary mirror assembly and the secondary mirror assembly, and between the secondary mirror assembly and the plano-concave lens assembly meet preset requirements, thereby making the wavefront aberration of the optical system meet the preset threshold requirements, and realizing full-aperture testing of the wavefront aberration of the long-tube optical system, and the method has high assembly and adjustment accuracy and efficiency.

[0040] 2. In the process of assembly and adjustment, the present invention uses a plano-concave lens assembly to adjust the optical axes of the primary mirror, secondary mirror, and correction mirror group, as well as the intervals between the primary mirror and the secondary mirror, and between the secondary mirror and the correction mirror group. A plane interferometer, primary mirror, secondary mirror, and plano-concave lens are used to form an interference measurement system, an optical interference simulation model is established, and the misalignment value D is constructed in the simulation model. H The misalignment is calculated based on the relationship between X and the Zernike first-order aberration coefficients Z4 and Z. This method guides the secondary mirror adjustment with high efficiency and high precision.

[0041] 3. The present invention combines the distance error between the adopted plano-concave lens assembly and the end face of the main lens barrel to construct a calculation formula for the actual thickness required for the trimming pad of the correction lens group. The thickness of the trimming pad obtained by using this calculation formula is accurate, the error after installation is small, and the optical spacing error between the double reflector and the refractive assembly is effectively controlled. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a cross-sectional schematic diagram of a catadioptric zoom system constructed according to a preferred embodiment of the present invention;

[0043] Figure 2 1 is a schematic structural diagram of a catadioptric zoom system assembly and adjustment system constructed according to a preferred embodiment of the present invention;

[0044] Figure 3 It is a schematic diagram of the position tolerances of the primary mirror reference surface, the reflective surface, and the outer cylindrical surface constructed according to the preferred embodiment of the present invention;

[0045] Figure 4 Schematic diagram of the position tolerance of the main lens barrel reference surface and the mounting surface constructed according to the preferred embodiment of the present invention, wherein (a) is a left view and (b) is a front view;

[0046] Figure 5is a schematic diagram of a correction lens assembly constructed according to a preferred embodiment of the present invention and its dimensions to be measured;

[0047] Figure 6 It is a structural diagram of the primary mirror installation and gluing method constructed according to the preferred embodiment of the present invention;

[0048] Figure 7 is a schematic structural diagram of a plano-concave lens constructed according to a preferred embodiment of the present invention;

[0049] Figure 8 1 is a schematic structural diagram of a plano-concave lens assembly centering and edge turning process constructed according to a preferred embodiment of the present invention;

[0050] Figure 9 Schematic diagram of the structure of the trimming pad of the correction lens assembly constructed according to the preferred embodiment of the present invention, wherein (a) is a front view and (b) is a right side view;

[0051] Figure 10 Schematic diagram of the structure of a plano-concave lens assembly trimming pad constructed according to a preferred embodiment of the present invention, wherein (a) is a front view and (b) is a right side view;

[0052] Figure 11 : is the relationship between the misalignment of the secondary mirror along the X-axis and the change in the Zernike expansion coefficients constructed according to the preferred embodiment of the present invention, wherein (a) is the relationship between the translation of the secondary mirror along the X-axis and the change in the seven Zernike coefficients, (b) is the relationship between the translation of the secondary mirror along the X-axis and the change in the two Zernike coefficients, (c) is the relationship between the rotation of the secondary mirror about the X-axis and the change in the seven Zernike coefficients, and (d) is the relationship between the rotation of the secondary mirror about the X-axis and the change in the two Zernike coefficients;

[0053] Figure 12 : The relationship between the misalignment of the secondary mirror along the Y direction and the change in the Zernike expansion coefficients constructed according to the preferred embodiment of the present invention is shown in FIG. (a) is the relationship between the translation of the secondary mirror along the Y axis and the change in the seven Zernike coefficients, (b) is the relationship between the translation of the secondary mirror along the Y axis and the change in the two Zernike coefficients, (c) is the relationship between the rotation of the secondary mirror about the Y axis and the change in the seven Zernike coefficients, and (d) is the relationship between the rotation of the secondary mirror about the Y axis and the change in the two Zernike coefficients.

[0054] Figure 13 : is the relationship between the misalignment of the secondary mirror along the Z direction and the change in the Zernike expansion coefficient constructed according to the preferred embodiment of the present invention, wherein (a) is the relationship between the translation of the secondary mirror along the Z axis and the change in the seven Zernike coefficients, (b) is the relationship between the translation of the secondary mirror along the Z axis and the change in the two Zernike coefficients, (c) is the relationship between the rotation of the secondary mirror about the Z axis and the change in the seven Zernike coefficients, and (d) is the relationship between the rotation of the secondary mirror about the Z axis and the change in the two Zernike coefficients;

[0055] Figure 14 : This is the relationship between the misalignment of the plano-concave lens constructed according to the preferred embodiment of the present invention and the change in the Zernike expansion coefficients, wherein (a) is the relationship between the translation of the plano-concave lens along the Z axis and the change in the seven Zernike coefficients, and (b) is the relationship between the translation of the plano-concave lens along the Z axis and the change in the two Zernike coefficients.

[0056] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0057] Primary mirror assembly: 1-primary mirror, 2-primary mirror barrel, 3-primary mirror barrel bracket, 5-primary mirror pressure ring, 4-system adjustment fixture;

[0058] Secondary mirror assembly: 6-secondary mirror bracket, 7-secondary mirror bracket pressure ring, 8-secondary mirror mount, 9-secondary mirror trimming pad, 10-secondary mirror;

[0059] Correction lens assembly: 11-correction lens group, 12-correction lens group pressure ring, 13-correction lens group cutting pad;

[0060] Plano-concave lens assembly: 16-plano-concave lens, 17-plano-concave lens barrel, 18-plano-concave lens pressure ring, 19-plano-concave lens group trimming pad;

[0061] 14- zoom group, 15- focusing group, 20- adjustment stage, 21- plane interferometer, 22- autocollimator, 23- correction lens group lens 1, 24- ultra-precision air-floating turntable. DETAILED DESCRIPTION

[0062] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0063] like Figure 1As shown, a long-tube catadioptric zoom system is composed of a primary mirror assembly, a secondary mirror assembly, a correction mirror assembly, a zoom group 14, a focusing group 15, etc., wherein the primary mirror assembly includes a primary mirror 1, a primary mirror pressure ring 5, a primary lens barrel 2, a primary lens barrel bracket 3, and a system assembly fixture 4; the secondary mirror assembly includes a secondary mirror 10, a secondary mirror bracket 6, a secondary mirror bracket pressure ring 7, a secondary mirror mount 8, and a secondary mirror trimming pad 9; and the correction mirror assembly includes a correction lens group 11, a correction lens group pressure ring 12, and a correction lens group trimming pad 13. In one embodiment of the present invention, the Cassegrain optical system composed of the primary mirror 1 and the secondary mirror 10 has an aperture of 200 mm and an F number of 2.5. The distance from the focus of the Cassegrain optical system to the rear end surface of the primary lens barrel 2 is 204 mm, and the maximum diameter of the inner hole of the primary lens barrel 2 is Φ45 mm.

[0064] The plano-concave lens assembly includes a plano-concave lens 16 , a plano-concave lens barrel 17 , a plano-concave lens pressing ring 18 and a plano-concave lens group trimming pad 19 .

[0065] The primary mirror 1 and secondary mirror 10 are reflective mirrors, while the correction lens group 11, zoom group 14, and focusing group 15 are refractive elements. The zoom group 14 and focusing group 15 are used for zooming and focusing of the optical system, respectively. The primary mirror 1 is fixed to the outer circumference and end face of the main lens barrel 2 via a center hole and back-side gluing. The primary mirror pressure ring 5 is installed to the main lens barrel 2 via a threaded connection to protect the primary mirror 1. The main lens barrel 2 is installed to the main lens barrel bracket 3 via screws and cylindrical pins, and the main lens barrel bracket 3 is installed to the system adjustment fixture 4 via screws. The secondary mirror 10 is fixed to the secondary mirror base 8 via back-side gluing. A secondary mirror trimming pad 9 is installed between the secondary mirror base 8 and the secondary mirror bracket 6 and connected via screws. The secondary mirror bracket 6 and the main lens barrel 2 have a small clearance between the axial hole and are end-face mounted. The secondary mirror bracket pressure ring 7 is threaded to the main lens barrel 2 to press the secondary mirror bracket 6 to the main lens barrel 2. The correction lens assembly 11 and the main lens barrel 2 are fitted with a small clearance between the shaft and hole, and are end-mounted. A correction lens assembly trimming pad 13 is installed between the correction lens assembly 11 and the main lens barrel 2. The correction lens assembly pressure ring 12 is threadedly connected to the main lens barrel 2, pressing the correction lens assembly 11 and the correction lens assembly trimming pad 13 to the main lens barrel 2. The main lens barrel bracket 3 is mounted on the system assembly fixture 4 via screws. The zoom group 14 and focus group 15 are also fitted with a small clearance between the shaft and hole of the main lens barrel 2.

[0066] The following describes the installation and adjustment method of the long-tube catadioptric zoom system. The specific steps are as follows:

[0067] S1: Place a plane interferometer and an autocollimator on both sides of the adjustment table, adjust the pitch and yaw angles of the autocollimator 22 so that the optical axes of the autocollimator and the plane interferometer are parallel, and keep the plane interferometer 21 and the autocollimator 22 unchanged.

[0068] S2 adjusts the optical axes of the primary mirror assembly and the plano-concave lens assembly to be coaxial, and adjusts the optical axes of the primary mirror assembly and the plano-concave lens assembly to be parallel to the optical axis of the autocollimator. Specifically, it includes the following steps:

[0069] (1) Adjust the optical axis of the main mirror in the main mirror assembly to be coaxial with the central axis of the main lens barrel and perpendicular to the end face of the main lens barrel.

[0070] In one embodiment of the present invention, Figure 3 、 Figure 4 、 Figure 6 As shown, the main mirror barrel 2 is mounted on the ultra-precision air-bearing turntable 24. Datum planes C and D are adjusted so that datum plane C of the main mirror barrel 2 coincides with the rotation axis of the ultra-precision air-bearing turntable 24, and datum plane D coincides and is perpendicular to the rotation axis of the ultra-precision air-bearing turntable 24. The primary mirror 1 is then mounted on the main mirror barrel 2. The eccentricity of the main mirror 1 is adjusted so that the radial runout of the outer cylindrical surface of the main mirror 1 meets the requirements. The center hole of the main mirror 1 is then glued to the outer cylindrical surface of the main mirror barrel 2, and the back of the main mirror 1 is glued to the end face of the main mirror barrel 2. The glue injection hole on the back of the main mirror barrel 2 is 3×Φ2, the glue reservoir is 3×Φ14 and 0.2mm deep, and the glue injection hole in the center hole is 6×Φ2.

[0071] (2) Adjusting the optical axis of the plano-concave lens in the plano-concave lens assembly to be coaxial with the central axis of the plano-concave lens barrel and perpendicular to the end face of the plano-concave lens barrel.

[0072] In one embodiment of the present invention, a plano-concave lens 16 is designed, and the center thickness and curvature radius of the plano-concave lens 16 are measured. The plano-concave lens 16 is installed in a plano-concave lens barrel 17, and a plano-concave lens pressure ring 18 is used to fix the plano-concave lens 16. An interferometer is used to detect the surface accuracy of the plano-concave lens 16 to ensure that the surface accuracy before and after the plano-concave lens 16 is unchanged. Silicone rubber is used to bond the plano-concave lens 16 to the plano-concave lens barrel 17. An ultra-precision centering lathe and a natural diamond turning tool are used to center and edge the outer cylindrical surface M and end surface N of the plano-concave lens barrel 17, control the eccentricity error between the outer cylindrical surface M of the plano-concave lens barrel 17 and the optical axis of the plano-concave lens 16, and control the perpendicularity error between the end surface N and the optical axis of the plano-concave lens 16. The distance H_PATJZ from the concave vertex of the plano-concave lens 16 to the end surface N of the plano-concave lens barrel 17 is measured.

[0073] (3) installing the plano-concave lens assembly on the primary mirror assembly so that the optical axis of the primary mirror assembly is coaxial with the optical axis of the plano-concave lens assembly;

[0074] (4) Figure 2 As shown, the assembled primary mirror assembly and plano-concave lens assembly are fixed on the adjustment table 20, and the Figure 2Place it between the plane interferometer 21 and the autocollimator 22. Use the autocollimator to measure the angular error between the optical axis of the plano-concave lens and the optical axis of the autocollimator, and use the adjustment stage to adjust the optical axes of the primary mirror assembly and the plano-concave lens assembly to be parallel to the optical axis of the autocollimator.

[0075] S3 connects the secondary mirror assembly to the primary mirror assembly. Light emitted by the plane interferometer passes through the primary mirror assembly, the secondary mirror assembly, and the plano-concave lens assembly in sequence before returning along the original path. Thus, the plane interferometer 21, the primary mirror 1, the secondary mirror 10, and the spherical surface of the plano-concave lens 16 form a normal-incidence interferometry system. This generates interference fringes and Zernike expansion coefficients of the system's wavefront aberration in the plane interferometer. These Zernike coefficients are used to calculate the misalignment of the secondary mirror assembly and the plano-concave lens assembly in various directions. Based on the calculated misalignment, the plano-concave lens assembly and the secondary mirror assembly are adjusted accordingly, ensuring that the optical axes of the secondary mirror assembly and the plano-concave lens assembly are coaxial with the reference, and that the spacing between the primary mirror assembly and the secondary mirror assembly, and between the secondary mirror assembly and the plano-concave lens assembly, meet preset requirements. This ensures that the system's wavefront aberration meets preset threshold requirements.

[0076] In one embodiment of the present invention, the misalignment includes 12 errors in total, namely, 6 rigid body displacements of the secondary mirror 10 and 6 rigid body displacements of the plano-concave lens 16. The Fringe Zernike expansion coefficients of the first-order aberration of the system are shown in Table 1. Since the outer cylindrical surface M and the end surface N of the plano-concave lens assembly have been centered and edged with the optical axis of the plano-concave lens 16 as the reference, after the plano-concave lens assembly is installed on the reference plane C and the reference plane D of the main lens barrel 2, the translation errors of the plano-concave lens 16 along the X-axis and the Y-axis and the rotation errors around the X-axis and the Y-axis have been eliminated. Since the spherical surface is a rotationally symmetrical surface, its rotation around the Z-axis will not change the wavefront aberration of the interference measurement system. Therefore, in the interference measurement system of the present invention, the misalignment can be simplified to the 7 errors shown in Table 2.

[0077] Table 1 Fringe Zernike first-order aberration polynomial expansion coefficients

[0078]

[0079]

[0080] Table 2 Misalignment of the interferometric measurement system consisting of primary mirror 1, secondary mirror 10, and plano-concave lens 16

[0081]

[0082] Based on the optical parameters of the interferometric measurement system of the present invention shown in Table 3, an optical model of the interferometric measurement system was established in ZEMAX software. Using MATLAB and ZEMAX software for interaction, the seven misalignments of the secondary mirror 10 and the plano-concave lens 16 were assigned equally spaced errors. Multiple sets of Fringe Zernike coefficients were extracted and subtracted from the initial Fringe Zernike coefficients when the system was not misaligned to obtain the Fringe Zernike coefficient changes. The damped least squares method was then used to fit the Zernike coefficient changes to the corresponding misalignments, and the seven misalignments of the secondary mirror 10 and the plano-concave lens 16 and the changes in the Zernike expansion coefficients were obtained as shown in the attached figure. Figures 11-14 As shown by Figure 11 From (a) and (b), we can see that the translation of the secondary mirror along the X axis has the greatest impact on Z2, Z5, and Z7. Figure 11 From (c) and (d), we can see that the rotation of the secondary mirror around the X axis has the greatest impact on Z3 and Z8. Figure 12 From (a) and (b), we can see that the translation of the secondary mirror along the Y axis has the greatest impact on Z3 and Z8. Figure 12 From (c) and (d), we can see that the rotation of the secondary mirror around the Y axis has the greatest impact on Z2 and Z7. Figure 13 From (a) and (b), we can see that the translation of the secondary mirror along the Z axis has the greatest impact on Z1, Z4, and Z9. Figure 13 From (c) and (d) in the figure, we can see that the influence of the secondary mirror rotating around the Z axis on the Zernike coefficient is very small. Figure 14 From (a) and (b), it can be seen that the translation of the plano-concave lens along the Z axis has the greatest impact on Z1, Z4, and Z9.

[0083] Because the change in the wavefront aberration Zernike expansion coefficient of the interferometric measurement system of the present invention caused by the rotation of the secondary mirror 10 around the Z axis is negligible, the misalignment of the secondary mirror 10 and the plano-concave lens 16 can be further simplified to the six errors in Table 4.

[0084] Table 3 Optical parameters of the interferometric measurement system consisting of primary mirror 1, secondary mirror 10, and plano-concave lens 16 spherical surface

[0085]

[0086] The Z-direction translation misalignment of the plano-concave lens 16 is given an error with equal spacing, and the change in the Zernike coefficient Z4 is extracted. The change is plotted as discrete points with the corresponding misalignment error, and the discrete points are curve-fitted using the least squares method to obtain D H The relationship with Z4 is shown in formula (1).

[0087] D H =-1.438·Z4 2 +27.56·Z4 (1)

[0088] Where, Z4 unit is λ (λ=6.33×10-4mm), D H The unit is mm.

[0089] According to Taylor's theorem, if the function f(x) has an nth-order derivative at x0, then in a neighborhood around x0, for any x in the neighborhood, the value of the function in the neighborhood can be approximated by formula (2):

[0090]

[0091] The main purpose of system adjustment is to eliminate first-order aberrations. In the interferometer measurement system, Z1, Z2, and Z3 are system errors and can be eliminated by the interferometer software. In the interferometer measurement system of the present invention, the defocus Z4 can be compensated by the Z-direction translation of the spherical surface of the plano-concave lens 16. Assuming that there is a first-order linear relationship between the change in the Fringe Zernike first-order aberration coefficient and the misalignment, the change in the Fringe Zernike first-order aberration polynomial coefficient Zi can be expanded according to formula (2) as follows:

[0092]

[0093] Where, X=(Tx,Ty,Tz,Rx,Ry,D H ), Zi=(Z5, Z6, Z7, Z8, Z9), Zi unit is λ(λ=6.33×10 -4 mm), X is in mm.

[0094] By writing formula (3) in matrix form, we can get formula (4):

[0095] Z=AX (4)

[0096] Where,

[0097] According to the above method, the matrix A of formula (4) in the interferometric measurement system of the present invention is obtained as shown in Table 4. The unit of the Zernike expansion coefficient is λ (λ = 6.33 × 10 -4 The unit of misalignment is mm.

[0098] According to formula (4), using the damped least squares method, the relationship between the offset and the change in the Fringe Zernike first-order aberration polynomial coefficient Zi can be obtained as shown in formula (5):

[0099] X=(A T A+p 2 I) -1 A T Z (5)

[0100] Where p is the damping factor, whose absolute value is greater than or equal to 1; I is the unit matrix.

[0101] Table 4 Conversion matrix A of the Fringe Zernike expansion coefficient change and misalignment of the interferometric measurement system of the present invention

[0102]

[0103] After building the above-mentioned interferometry system and establishing a mathematical model for the above-mentioned misalignment and the change in the Fringe Zernike first-order aberration coefficient, all misalignments are calculated according to the above formula. The plano-concave lens assembly and secondary mirror assembly are adjusted according to the calculated misalignments, and the system can be assembled and adjusted efficiently and with high precision.

[0104] In one embodiment of the present invention, the steps of adjusting the plano-concave lens assembly and the secondary mirror assembly according to the calculated misalignment are as follows:

[0105] Keep the postures of the plane interferometer 21, the autocollimator 22, and the plano-concave lens 16 unchanged, and coarsely adjust the secondary mirror 10 so that the image point where the plane interferometer 21 light beam is reflected and converged by the primary mirror 1, the secondary mirror 10, and the plano-concave lens 16 coincides with the center of the plane interferometer 21 detector. Then check the corresponding values ​​of the defocus (Z4), the first-order astigmatism on the X axis (Z5), the first-order astigmatism on the Y axis (Z6), the first-order coma on the X axis (Z7), the first-order coma on the Y axis (Z8), and the first-order spherical aberration (Z9) in the Zernike aberration. According to formula (2), replace the plano-concave lens group trimming pad 19 with different thicknesses to make -0.02λ≤Z4≤0.02λ.

[0106] Keeping the postures of the plane interferometer 21, the autocollimator 22, and the plano-concave lens 16 unchanged, the X-axis and Y-axis translation and tilt of the secondary mirror 10 are fine-tuned according to formula (4), Table 4, and formula (5) to make -0.05λ≤Z7≤0.05λ, -0.05λ≤Z8≤0.05λ, -0.05λ≤Z5≤0.05λ, and -0.05λ≤Z6≤0.05λ, so that the image point of the plane interferometer 21 light beam reflected by the primary mirror 1, the secondary mirror 10, and the plano-concave lens 16 coincides with the center of the detector; according to formula (4), Table 4, and formula (5), the Z-axis translation of the secondary mirror 10 is adjusted to make -0.03λ≤Z9≤0.03λ; according to formula (1), the plano-concave lens group trimming pads 19 of different thicknesses are replaced to make -0.02λ≤Z4≤0.02λ. Repeat this step to minimize Z4, Z5, Z6, Z7, Z8, and Z9, and ensure that the system wavefront aberration RMS is ≤ 0.05λ.

[0107] S4 disassembles the plano-concave lens assembly and replaces it with a correction lens group to complete the installation of the long-tube catadioptric zoom system.

[0108] In one embodiment of the present invention, Figure 5 、 Figure 7 、 Figure 8 、 Figure 9 、 Figure 10 As shown, based on the thickness error ΔPATJXQD_L (measured thickness - theoretical thickness) of the plano-concave lens group trimming pad 19, the curvature radius error ΔR (measured curvature radius - theoretical curvature radius) of the plano-concave lens 16, the distance error ΔH_PATJZ (measured distance - theoretical distance) from the concave vertex of the plano-concave lens 16 to the end surface N of the plano-concave lens barrel 17, and the distance error ΔJZJZ_H (measured distance - theoretical distance) from the concave vertex of the correction lens group lens 1 23 to the mounting end surface K of the correction lens group 11, the thickness JZJZXQD_L of the correction lens group trimming pad 13 is calculated according to formula (6). Then, the correction lens group trimming pad 13, the correction lens group 11, the correction lens group pressure ring 12, the zoom group 14, and the focusing group 15 are installed on the main lens barrel 2. At this point, the installation and adjustment of the primary mirror 1, secondary mirror 10, correction mirror group 11, zoom group 14, and focusing group 15 have been completed, and the wavefront aberration of the Cassegrain optical system has been controlled efficiently and accurately, as well as the eccentricity error, tilt error, and optical spacing error of the double reflecting mirrors and refractive elements.

[0109] JZJZXQD_L= JZJZXQD_L(theoretical)-△JZJZ_H+△R-△H_PATJZ-△PATJXQD_L (6)

[0110] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for assembling a long-tube catadioptric zoom system, characterized in that: The method comprises the following steps: A plane interferometer and an autocollimator are respectively arranged on both sides of the adjustment platform, and the optical axis of the autocollimator is parallel to the optical axis of the plane interferometer; Mounting the plano-concave lens assembly on the primary mirror assembly, and then mounting the primary mirror assembly with the plano-concave lens assembly mounted thereon on an adjustment stage, such that the optical axis of the plano-concave lens assembly is coaxial with the optical axis of the primary mirror assembly and is parallel to the optical axis of the autocollimator; Connecting a secondary mirror assembly to a primary mirror assembly, causing light emitted from the plane interferometer to sequentially pass through the primary mirror assembly, the secondary mirror assembly, and the plano-concave lens assembly and then return along the original path, thereby forming interference fringes in the plane interferometer; using the interference fringes to calculate a total misalignment of the secondary mirror assembly and the plano-concave lens assembly in all directions; and adjusting the plano-concave lens assembly and the secondary mirror assembly according to the calculated total misalignment, so that the optical axes of the secondary mirror assembly and the primary mirror assembly are coaxial, and the spacings between the primary mirror assembly and the secondary mirror assembly, and between the secondary mirror assembly and the plano-concave lens assembly, meet preset requirements, thereby ensuring that the wavefront aberration of the optical system composed of the primary mirror assembly, the secondary mirror assembly, and the plano-concave lens assembly meets a preset threshold requirement; The plano-concave lens assembly is disassembled and replaced with a correction lens assembly to complete the assembly and adjustment of the long-tube catadioptric zoom system.

2. The method for assembling and adjusting a long-tube catadioptric zoom system according to claim 1, wherein: The total misalignment includes the misalignment of the secondary mirror assembly and the misalignment of the plano-concave lens assembly. The misalignment of the secondary mirror assembly includes the translation of the secondary mirror assembly along the X, Y and Z directions, and the rotation of the secondary mirror assembly around the X and Y directions. The misalignment of the plano-concave lens assembly is the translation of the plano-concave lens assembly along the Z direction.

3. The method for assembling and adjusting a long-tube catadioptric zoom system according to claim 2, wherein: The calculation of the offset is performed according to the following steps: Construct an optical interference simulation model based on the optical parameters of the primary mirror assembly, the secondary mirror assembly and the plano-concave lens assembly; Misalignment D of the plano-concave lens assembly H Assign values ​​and input them into the optical interference simulation model to obtain different D H The defocus Z4 of the optical system composed of the corresponding primary mirror assembly, secondary mirror assembly and plano-concave lens assembly is thus fitted with Z4 and D H The curvilinear relationship between the two; Constructing a relationship between the wavefront aberration Zernike expansion coefficient Z of the interference fringes and the total misalignment X, assigning a value to the total misalignment X and inputting the value into the optical interference simulation model to obtain a corresponding Zernike expansion coefficient, thereby determining the relationship between the total misalignment X and the Zernike expansion coefficient Z; Get the measured defocus Z4 and Zernike expansion coefficient Z, and use the Z4 and D H The curve relationship between the two and the relationship between the total offset X and the Zernike expansion coefficient Z are used to calculate the actual offset D H and the total offset X.

4. The method for assembling and adjusting a long-tube catadioptric zoom system according to claim 3, wherein: The total offset X is calculated according to the following formula: Z=AX Z=[Z5 Z6 Z7 Z8 Z9] T X=[T x T y T z R x R y D H ] T Among them, Z5, Z6, Z7, Z8 and Z9 are respectively the X-axis first-order astigmatism, Y-axis first-order astigmatism, X-axis first-order coma aberration, Y-axis first-order coma aberration and first-order spherical aberration of the optical system composed of the primary mirror assembly, secondary mirror assembly and plano-concave lens assembly. Tx, Ty, Tz, Rx and Ry are respectively the translation of the secondary mirror along the X, Y and Z directions and the rotation around the X and Y directions. D H is the misalignment of the plano-concave lens assembly.

5. A method for assembling and adjusting a long-tube catadioptric zoom system according to claim 3 or 4, characterized in that: The misalignment D of the plano-concave lens assembly H Calculate using the following formula: D H =-1.438 Z4 2 +27.56 Z4 Among them, Z4 is the defocus of the optical system consisting of the primary mirror assembly, the secondary mirror assembly and the plano-concave lens assembly.

6. A method for assembling and adjusting a long-tube catadioptric zoom system according to claim 1 or 2, characterized in that: Before disassembling the plano-concave lens assembly and replacing it with the correction lens assembly, the actual required thickness of the trimming pad of the correction lens assembly is calculated. The calculation formula for the thickness is as follows: JZJZXQD_L=JZJZXQD_L(theoretical)-△JZJZ_H+△R-△H_PATJZ-△PATJXQD_L Among them, JZJZXQD_L is the actual required thickness of the trimming pad in the correction lens assembly, JZJZXQD_L(theoretical) is the theoretical thickness of the trimming pad in the correction lens assembly, △JZJZ_H is the distance error from the concave vertex of the lens in the correction lens assembly to the mounting end face of the correction lens group, △R is the curvature radius error of the plano-concave lens, △H_PATJZ is the distance error from the concave vertex of the plano-concave lens to the end face of the plano-concave lens barrel, and △PATJXQD_L is the thickness error of the trimming pad in the plano-concave lens assembly.

7. The method for assembling and adjusting a long-tube catadioptric zoom system according to claim 1, wherein: Before installing the plano-concave lens assembly on the primary mirror assembly, perform the following steps: Adjusting the optical axis of the primary mirror in the primary mirror assembly to be coaxial with the central axis of the primary lens barrel and perpendicular to the end face of the primary lens barrel; The optical axis of the plano-concave lens in the plano-concave lens assembly is adjusted to be coaxial with the central axis of the plano-concave lens barrel and perpendicular to the end surface of the plano-concave lens barrel.

8. The method for assembling and adjusting a long-tube catadioptric zoom system according to claim 7, wherein: The method for adjusting the optical axis of the main mirror in the main mirror assembly to be coaxial with the central axis of the main lens barrel and perpendicular to the end face of the main lens barrel is: aligning the central hole and the back of the main mirror with the main lens barrel and connecting them.

9. A method for assembling and adjusting a long-tube catadioptric zoom system according to claim 7 or 8, characterized in that: The method for adjusting the optical axis of the plano-concave lens in the plano-concave lens assembly to be coaxial with the central axis of the plano-concave lens barrel and perpendicular to the end face of the plano-concave lens barrel is: taking the optical axis of the plano-concave lens as a reference, centering and edge-turning the outer cylindrical surface and the end face of the plano-concave lens barrel so that the central axis of the outer cylindrical surface is coaxial with the optical axis of the plano-concave lens, and the end face of the plano-concave lens barrel is perpendicular to the optical axis of the plano-concave lens.

10. A system for adjusting a long-tube catadioptric zoom lens using the method for adjusting a long-tube catadioptric zoom lens according to any one of claims 1 to 9, characterized in that: The system includes: a plane interferometer, an autocollimator, an adjustment stage, a primary mirror assembly, a secondary mirror assembly, a plano-concave lens assembly and a correction mirror assembly, wherein: The plane interferometer and the autocollimator are arranged on both sides of the adjustment platform, and the primary mirror assembly, the secondary mirror assembly, the plano-concave lens assembly and the correction mirror assembly are all arranged on the adjustment platform; The plano-concave lens assembly is arranged on the primary mirror assembly and is used to adjust the optical axes of the primary mirror assembly, the secondary mirror assembly and the correction mirror assembly and the optical spacing between them; The secondary mirror assembly is arranged between the plano-concave lens assembly and the plane interferometer and is connected to the primary mirror assembly; The correction lens assembly is used to replace the plano-concave lens assembly after the primary mirror assembly, the secondary mirror assembly and the plano-concave lens assembly are assembled and adjusted.

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