Knife-edge device and method for measuring focal length in assembly and adjustment of reflecting telephoto telescope

Abstract

The present invention discloses a knife-edge device and a measuring method for measuring the focal length in the assembly and adjustment of a reflective telephoto telescope. In the assembly and adjustment process of a large-aperture telescope, a knife-edge device with a high-precision five-dimensional adjustment frame with readable data is used, and a laser interferometer and a photoelectric autocollimator used in the assembly and adjustment process are attached, so that the focal length of the telescope system can be tested with high precision in the assembly and adjustment process of a large-aperture reflective telephoto telescope, and the problem that the focal length of the primary and secondary mirrors cannot be accurately controlled in the assembly and adjustment process of a traditional large-aperture reflective telephoto telescope is solved, and the assembly and adjustment precision and optical calibration efficiency are greatly improved.

Description

Technical Field

[0001] The invention belongs to the field of optical testing and optical adjustment, and relates to a knife-edge device and method for measuring focal length in the adjustment of a reflective telephoto telescope. The invention also relates to a method for measuring the focal length of a large-aperture reflective telephoto telescope system during the adjustment process by using the knife-edge device. Background Art

[0002] In order to achieve higher resolution, the telescope system has a larger and larger aperture and a longer focal length, which requires more and more precise control of the focal length of the large-aperture reflective telescope optical system. This requires precise testing and control of the focal length of the large-aperture reflective telescope system during the optical processing and optical assembly process.

[0003] Traditionally, there are two main methods for measuring the focal length of a large-aperture reflective telescope system during the optical adjustment process: the first method is to place a Pero plate (a parallel plate with a fixed-width line pair) on the focal plane of the telescope system, and then use a theodolite to test the angle corresponding to the fixed-width line pair in front of the primary mirror of the telescope system, and then the focal length of the system can be calculated. In this method, since the Pero plate has a certain thickness, the surface where the fixed-width line pair is actually tested is not on the focal plane. In addition, in the process of using the theodolite to test the angle corresponding to the fixed line width, the error in the focal length test of the telescope is large due to the human error in the line pressure judgment. The second method requires placing a detector on the focal plane of the telescope, and then the telescope system and the detector are used as a whole to align the telephoto collimator. The point light source on the focal plane of the collimator forms an image point on the detector. The telescope system is rotated a fixed angle, and the distance between the two image points on the detector is tested, and then the focal length of the system can be calculated. This method requires the installation of a detector on the focal plane of the telescope system. The installation accuracy of this process affects the test accuracy. In addition, testing the telescope system requires a special test optical path change, and the detector needs to be reinstalled for each test. The optical assembly efficiency for large-aperture telescope systems is very low.

[0004] Therefore, in the process of optical assembly, how to test the focal length of a large-aperture reflecting telescope system in real time, with high precision and high efficiency to guide the assembly is a problem that needs to be solved in the field of optical assembly. Summary of the invention

[0005] The purpose of the present invention is to provide a knife-edge device for testing the focal length of a large-aperture reflective telephoto telescope during the optical adjustment process. The lower part of the device is a high-precision five-dimensional adjustment frame 3 that can read the data. The upper part of the device is a cubic prism 2 with a crosshair and a knife-edge 1 placed on the high-precision five-dimensional adjustment frame 3. The laser interferometer 4 emits an ideal spherical wave from point A, which becomes parallel light after passing through a telescope system composed of a primary mirror (8) and a secondary mirror 9, and is incident on a large-aperture standard plane mirror 10, reflected back to the telescope system, and converged at point B. When the optical axis of the telescope system coincides with the normal of the large-aperture standard plane mirror 10, points A and B coincide. When the optical axis of the telescope system and the normal of the large-aperture standard plane mirror 10 are at a certain angle, points A and B do not coincide. According to the distance and angle between points A and B, the focal length of the telescope system can be calculated.

[0006] Another object of the present invention is to provide a method for measuring the focal length of a large-aperture reflective telescope optical system using the knife-edge device. The specific steps of the measuring method are as follows:

[0007] Step 1: Place the knife edge 1, the cubic prism 2 with cross marks, the high-precision five-dimensional adjustment frame 3 with readings, the laser interferometer 4, the large five-dimensional adjustment frame 5, the plane reflector 6, and the large-aperture reflective telescope system to be tested consisting of a primary mirror 8 and a secondary mirror 9 on the same large turntable, and adjust the large-aperture standard plane mirror 10 and the laser interferometer 4 so that the normal of the large-aperture standard plane mirror 10, the optical axis of the laser interferometer 4 and the optical axis of the large-aperture reflective telescope system consisting of the primary mirror 8 and the secondary mirror 9 are collinear, and use the laser interferometer 4 to test the zero field wave aberration of the large-aperture telescope system consisting of the primary mirror 8 and the secondary mirror 9, and make the defocus value zero, as shown in the attached figure. Figure 3 (1) as shown;

[0008] Step 2: Replace the spherical lens of the laser interferometer 4 with a flat lens, and adjust the rotation and pitch dimensions of the readable high-precision five-dimensional adjustment frame 3 so that the normal of the cubic prism 2 with cross marks is collinear with the optical axis of the laser interferometer 4, as shown in the attached figure. Figure 3 (2) as shown;

[0009] Step 3: Replace the plane lens of the laser interferometer 4 with a spherical lens, adjust the translation dimension of the high-precision five-dimensional adjustment frame 3 that can be read perpendicular to the optical axis, so that the blade is exactly cut at the focus A of the interferometer lens, and make a judgment by checking the interference fringes on the interferometer. Record the reading H1 of the translation dimension of the high-precision five-dimensional adjustment frame 3 perpendicular to the optical axis at this time, as shown in the attached figure. Figure 3 (3) as shown;

[0010] Step 4: Align the photoelectric autocollimator 7 with the plane reflector 6 on the large turntable, record the angle θ1 at this time, rotate the large turntable, and record the angle θ2 of the photoelectric autocollimator 7 at this time, as shown in the attached figure. Figure 3 (4) as shown;

[0011] Step 5: Adjust the translation dimension of the readable high-precision five-dimensional adjustment frame 3 perpendicular to the optical axis so that the knife edge coincides with the laser emitted by the laser interferometer 4, which passes through the large-aperture telescope system composed of the primary mirror 8 and the secondary mirror 9, and then is reflected by the large-aperture standard plane mirror 10, and then re-passes through the large-aperture telescope system. The reading H2 of the translation dimension of the high-precision five-dimensional adjustment frame 3 perpendicular to the optical axis is recorded at this time, as shown in the attached figure. Figure 3 (5) and (6);

[0012] Step 6: The focal length of the large-aperture telescope system can be calculated as:

[0013]

[0014] The characteristics and beneficial effects of the present invention are mainly reflected in the following aspects: (1) The knife-edge device for measuring the focal length is simple and compact, and easy to build; (2) High-precision testing equipment can be used to test the two parameters of the focal length, and the focal length of the large-aperture reflecting telephoto telescope system can be tested with high accuracy; (3) The knife-edge device and the measuring method can be tested during the optical assembly process of the large-aperture reflecting telephoto telescope system, without the need to dismantle the optical assembly light path or to transfer the scene, and the test can be carried out at any time, thereby improving the test efficiency; (4) During the test process, the equipment test data is used to eliminate the human reading error, thereby greatly improving the test repetition accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A schematic diagram of the composition of the knife-edge device and the test optical path of the present invention;

[0016] Figure 2 The present invention is a schematic diagram of the self-optical calibration steps of the knife-edge device for testing the focal length of a large-aperture reflective telescope: Figure (1) is a schematic diagram of the first step of the self-optical calibration of the knife-edge device, Figure (2) is a schematic diagram of the second step of the self-optical calibration of the knife-edge device, and Figure (3) is a schematic diagram of the third step of the self-optical calibration of the knife-edge device;

[0017] Figure 3 The present invention is a schematic diagram of a method for testing the focal length of a large-aperture reflecting telescope. FIG. (1) is a schematic diagram of step one for measuring the focal length, FIG. (2) is a schematic diagram of step two for measuring the focal length, FIG. (3) is a schematic diagram of step three for measuring the focal length, FIG. (4) is a schematic diagram of step four for measuring the focal length, FIG. (5) is a schematic diagram of step five for measuring the focal length, and FIG. (6) is a schematic diagram of step six for measuring the focal length. DETAILED DESCRIPTION

[0018] The following is a detailed description of an implementation example of the method of the present invention with reference to the accompanying drawings.

[0019] The main components used in the present invention are described as follows:

[0020] Cubic prism 2: custom-made, side length 35mm, 90-degree angle difference and pyramidal difference are better than 3 seconds, each face RMS is better than 1 / 15 wavelength @ 633nm, six sides are aluminum-coated reflective film, one side is engraved with crosshairs, material K9.

[0021] Photoelectric autocollimator 8: TriAngle company model is TA500-57 photoelectric autocollimator, with a light aperture of 50mm, a field of view of 1300X950 seconds, a resolution of 0.02 seconds, and a repeatability of ±0.05 seconds.

[0022] High-precision five-dimensional adjustment stand 3 with readable data: used to adjust the orientation of the blade, including horizontal dimension adjustment, front-back dimension adjustment, height dimension adjustment, pitch dimension adjustment, and rotation dimension adjustment. The horizontal dimension adjustment accuracy is better than 5um and can be read.

[0023] The specific steps of the knife-edge device for testing the focal length of a large-aperture reflective telescope of the present invention are as follows:

[0024] Step 1: Install the cubic prism 2 on the horizontal dimension perpendicular to the optical axis of the interferometer on the readable high-precision five-dimensional adjustment frame 3, with the side of the cubic prism 2 engraved with the crosshairs facing the direction of the horizontal dimension adjustment. Use the photoelectric internal focus 11 to align the cubic prism 2, and adjust the photoelectric internal focus 11 so that the light emitted by the photoelectric internal focus 11, the crosshairs of the return path through the surface of the cubic prism 2 are located at the center of the detector of the photoelectric internal focus 11, as shown in the attached figure. Figure 2 (1) as shown.

[0025] Step 2: Adjust the focal length of the photoelectric internal focus 11 so that the internal focus image is aligned with the surface of the cubic prism 2, and adjust the translation of the photoelectric internal focus 11 so that the crosshairs on the surface of the cubic prism 2 are located at the center of the detector of the photoelectric internal focus 11, as shown in the attached figure. Figure 2 (2) as shown.

[0026] Step 3: Adjust the horizontal dimension of the readable high-precision five-dimensional adjustment frame 3 perpendicular to the optical axis of the interferometer to the other end, and adjust the focal length of the photoelectric internal focus 11 so that the cross-marked lines on the surface of the cubic prism 2 are clearly imaged on the detector of the photoelectric internal focus 11. At this time, check whether there is a deviation between the image of the cross-marked lines on the surface of the cubic prism 2 and the center of the detector. If there is a deviation, adjust the angle of the cubic prism 2, then return to step 1), and then proceed to step 2), step 3), until the image of the cross-marked lines on the surface of the cubic prism 2 in step 3) is not deviated from the center of the detector, as shown in the attached figure. Figure 2 As shown in (3), the knife-edge device for testing the focal length of the large-aperture reflecting telephoto telescope system is assembled and adjusted.

Claims

1. A knife-edge device for measuring focal length in the adjustment of a reflective telescope, comprising a knife-edge (1), a cubic prism with cross marks (2), a readable high-precision five-dimensional adjustment frame (3), a laser interferometer (4), a large five-dimensional adjustment frame (5), a plane reflector (6), and a photoelectric autocollimator (7), characterized in that: The lower part of the knife-edge device is a readable high-precision five-dimensional adjustment frame (3), and the upper part of the knife-edge device is a cubic prism (2) with a crosshair and a knife-edge (1) placed on the high-precision five-dimensional adjustment frame (3). The laser interferometer (4) emits an ideal spherical wave from point A, which passes through a telescope system composed of a primary mirror (8) and a secondary mirror (9) to become parallel light, is incident on a large-aperture standard plane mirror (10), is reflected back to the telescope system, and converges at point B. When the optical axis of the telescope system coincides with the normal of the large-aperture standard plane mirror (10), points A and B coincide. When the optical axis of the telescope system and the normal of the large-aperture standard plane mirror (10) are at a certain angle, points A and B do not coincide. According to the distance and angle between points A and B, the focal length of the telescope system can be calculated.

2. The knife-edge device for measuring focal length during the adjustment of a reflecting telephoto telescope according to claim 1, characterized in that: The cubic prism (2) with cross-marks is made of quartz material, with vertical angle difference and pyramidal difference better than 3 seconds, six facet RMS better than 1 / 15 wavelength @ 633nm, six faces are coated with aluminum reflective film, with reflectivity greater than 90%, and one face is engraved with cross-marks.

3. The knife-edge device for measuring focal length during the adjustment of a reflecting telephoto telescope according to claim 1, characterized in that: The readable high-precision five-dimensional adjustment frame (3) is used to adjust the orientation of the blade, including horizontal dimension adjustment, front-back dimension adjustment, height dimension adjustment, pitch dimension adjustment, and rotation dimension adjustment, wherein the horizontal dimension adjustment accuracy is better than 5um.

4. The knife-edge device for measuring focal length during the adjustment of a reflecting telephoto telescope according to claim 1, characterized in that: The large five-dimensional adjustment frame (5) is used to adjust the orientation of the interferometer, including horizontal dimension adjustment, front-back dimension adjustment, height dimension adjustment, pitch dimension adjustment, and rotation dimension adjustment.

5. The knife-edge device for measuring focal length during the adjustment of a reflecting telephoto telescope according to claim 1, characterized in that: The angular measurement resolution of the photoelectric autocollimator (7) is 0.02 seconds, and the repeatability is ±0.05 seconds.

6. A focal length measuring method based on the knife-edge device for measuring focal length in the assembly and adjustment of a reflective telescope according to claim 1, characterized in that The steps are as follows: Step 1: placing a knife edge (1), a cubic prism with cross marks (2), a high-precision five-dimensional adjustment frame (3) with a reading, a laser interferometer (4), a large five-dimensional adjustment frame (5), a plane reflector (6), and a large-aperture reflective telescope system to be tested consisting of a primary mirror (8) and a secondary mirror (9) on the same large turntable, and adjusting the large-aperture standard plane mirror (10) and the laser interferometer (4) so ​​that the normal of the large-aperture standard plane mirror (10), the optical axis of the laser interferometer (4) and the optical axis of the large-aperture reflective telescope system consisting of the primary mirror (8) and the secondary mirror (9) are collinear, and using the laser interferometer (4) to test the zero field wave aberration of the large-aperture telescope system consisting of the primary mirror (8) and the secondary mirror (9), and to make the defocus value zero; Step 2: Replace the spherical lens of the laser interferometer (4) with a flat lens, and adjust the rotation and pitch dimensions of the readable high-precision five-dimensional adjustment frame (3) so that the normal of the cubic prism (2) with cross marks is collinear with the optical axis of the laser interferometer (4); Step 3: Replace the plane lens of the laser interferometer (4) with a spherical lens, adjust the translation dimension of the high-precision five-dimensional adjustment frame (3) that can be read perpendicular to the optical axis, so that the blade is exactly cut at the focus A of the interferometer lens, and make a judgment by checking the interference fringes on the interferometer; record the reading H1 of the translation dimension of the high-precision five-dimensional adjustment frame (3) perpendicular to the optical axis at this time; Step 4: Align the photoelectric autocollimator (7) with the plane reflector (6) on the large turntable, record the angle θ1 at this time, rotate the large turntable, and record the angle θ2 of the photoelectric autocollimator (7) at this time; Step 5: Adjust the translation dimension of the high-precision five-dimensional adjustment frame (3) that can be read perpendicular to the optical axis so that the knife edge coincides with the laser emitted by the laser interferometer (4) passing through the large-aperture telescope system composed of the primary mirror (8) and the secondary mirror (9), and then reflected by the large-aperture standard plane mirror (10), and then re-passing through the large-aperture telescope system. The reading H2 of the translation dimension of the high-precision five-dimensional adjustment frame (3) perpendicular to the optical axis at this time is recorded; Step 6: The focal length of the large-aperture telescope system can be calculated as:

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