A focal length high-precision detection device and method for a long focal length optical system

Abstract

The application discloses a kind of focal length high-precision detection device and method for long focal length optical system, solve the problem that the existing focal length detection method detects low, poor accuracy and is not applicable to long focal length optical system.The application focuses the light spot of optical system return light on the detector of clear imaging by using the method of light splitting prism, instead of the observation of bolognese plate image in conventional detection method, adjusts the deflection angle of plane mirror, records the moving position of light spot and the deflection angle of plane mirror respectively, and then accurately calculates the moving amount of light spot through image processing, and further calculates the focal length of optical system.

Description

Technical Field

[0001] The present invention relates to a focal length detection device and method, and in particular to a focal length high-precision detection device and method for a long focal length optical system. Background Art

[0002] Large-aperture, long-focal-length optical systems are widely used in fields such as Earth observation and astronomical research. The inspection and assembly of large-aperture optical systems is currently at the forefront of hard technology, with significant commercial value for applications such as long-range space imaging and laser weapon focusing. As the aperture of optical systems continues to increase, more requirements are placed on optical inspection and assembly.

[0003] The focal length of an optical system is a critical physical quantity, and its high-precision measurement is a key step in the system development phase. Common methods for measuring the focal length of long-focal-length optical systems include the theodolite-Porro plate method and the precision angle measurement method. In the theodolite-Porro plate method, a Pero plate is mounted at the focal plane of the optical system, illuminated by a light source, and the angle between the Pero plate's lines is measured using a theodolite to determine the focal length of the optical system. The Pero plate method requires a high-precision theodolite to observe the image point of the Pero plate passing through the optical system. Due to the large ratio between the focal length of the optical system and the focal length of the theodolite, the image point size is very small. This is affected by airflow and the resolution of the human eye, resulting in significant errors in each observation reading, which in turn leads to significant errors in the final focal length calculation of the optical system. The actual measurement process, which relies on visual judgment and experience, is a semi-quantitative method that cannot meet the image quality inspection and alignment requirements of modern optical systems. Consequently, this method suffers from low repeatability and poor accuracy in focal length measurement. Precision angle measurement requires the optical system to be placed on a turntable for angular rotation, and a large-aperture collimator is required to provide an infinitely distant target image. This places high demands on the hardware in practice. Therefore, a high-precision, convenient detection method and device are urgently needed to achieve high-precision focal length detection of long-focal-length optical systems. Summary of the Invention

[0004] In order to solve the technical problems that the existing focal length detection method has low detection repeatability and poor accuracy and is not suitable for long focal length optical systems, the present invention provides a high-precision focal length detection device and method for long focal length optical systems.

[0005] The inventive concept of the present invention is:

[0006] By using a spectroscopic prism to split the light, the light spot returned by the optical system is focused on a detector with clear imaging, replacing the conventional detection method of observing the Porro plate image. The deflection angle of the plane mirror is adjusted, and the moving position of the light spot and the deflection angle of the plane mirror are recorded respectively. Subsequently, the movement amount of the light spot is accurately calculated through image processing, and then the focal length of the optical system is calculated.

[0007] In order to achieve the above objectives and complete the above invention concept, the present invention adopts the following technical solutions:

[0008] A high-precision focal length detection device for a long-focal-length optical system, wherein the optical system comprises an optical system primary mirror and an optical system secondary mirror arranged opposite to each other;

[0009] The special features of the device are: it includes a high-precision angle measurement system, a second plane reflector, a first plane reflector, a first interferometer lens, a beam splitter prism, a detector, a second interferometer lens and an interferometer body;

[0010] The interferometer body emits measurement light;

[0011] The beam splitter prism is used to transmit the measuring light;

[0012] The first plane reflector is used to reflect the transmitted measuring light to the secondary mirror of the optical system, and reflect the light out in sequence through the secondary mirror of the optical system and the primary mirror of the optical system to form parallel light;

[0013] The second plane reflector is arranged on the optical path of the parallel light and is used to return the parallel light to the primary mirror of the optical system. The returned light is reflected by the primary mirror of the optical system, the secondary mirror of the optical system, and the first plane reflector in sequence to the beam splitter prism, and then is divided into return transmitted light and return reflected light by the beam splitter prism. The return transmitted light enters the interferometer body.

[0014] The high-precision angle measurement system is used to measure the angle of the second plane reflector;

[0015] The detector is arranged on the optical path of the returned reflected light and is used to detect the light spot;

[0016] The first interferometer lens is arranged between the beam splitter prism and the first plane reflector to converge the transmitted measuring light; the second interferometer lens is arranged between the beam splitter prism and the detector to converge the return reflected light;

[0017] Alternatively, the second interferometer lens is arranged between the beam splitter prism and the first plane reflector to converge the transmitted measuring light; and the first interferometer lens is arranged between the beam splitter prism and the detector to converge the return reflected light.

[0018] Furthermore, the aperture of the second plane reflector is larger than the aperture of the primary mirror of the optical system, and the root mean square error of its surface shape is less than 1 / 40 wavelength;

[0019] The F-number of the first interferometer lens and the second interferometer lens is smaller than the F-number of the optical system;

[0020] The light-transmitting aperture of the beam splitter prism is larger than the light-emitting aperture of the interferometer body, and the beam splitting ratio is 1:1.

[0021] Furthermore, the detector is a CCD camera;

[0022] The interferometer body is a dynamic interferometer.

[0023] A method for high-precision detection of focal length of a long-focal-length optical system, using the above-mentioned high-precision detection device for focal length of a long-focal-length optical system, is characterized in that it comprises the following steps:

[0024] Step 1: Build the high-precision focal length detection device of the long-focal-length optical system described above, so that the second plane reflector can reflect parallel light back to the main mirror of the optical system until it is incident on the target surface of the interferometer body and the detector;

[0025] Step 2: Adjust the focal length high-precision detection device so that the target surface of the detector is perpendicular to the optical axis of the second interferometer lens, the wavefront power measured by the interferometer body and the light spot on the target surface of the detector are minimized, and the high-precision angle measurement system and the second plane reflector are self-aligned;

[0026] Step 3: Obtain an initial light spot position image A through the detector, and adjust the light spot received by the detector to the center of the target surface based on the initial light spot position image A;

[0027] Step 4: Adjust the yaw posture of the second plane reflector so that the light spot on the detector is close to the edge of one side of its target surface. The light spot position image B1 is obtained through the detector, and the yaw angle θ1 of the second plane reflector is monitored and obtained by the high-precision angle measurement system.

[0028] Step 5: Adjust the yaw posture of the second plane reflector so that the light spot on the detector is close to the edge of the other side of the target surface. The light spot position image C1 is obtained by the detector, and the yaw angle θ2 of the second plane reflector is monitored by a high-precision angle measurement system.

[0029] Step 6: Swap the positions of the first interferometer lens and the second interferometer lens, and use the methods of steps 2 to 5 to obtain the corresponding spot position images B2 and C2 when the light spot approaches the edges of the detector target surface, as well as the yaw angles θ3 and θ4 monitored by the high-precision angle measurement system;

[0030] Step 7: Obtain the linear displacement t1 of the center of mass of the light spot through the light spot position images B1 and C1; obtain the linear displacement t2 of the center of mass of the light spot through the light spot position images B2 and C2;

[0031] Step 8: Calculate the focal length of the optical system

[0032] Furthermore, step 2 specifically includes:

[0033] 2.1. Adjust the yaw and pitch angles of the detector so that the target surface of the detector is perpendicular to the optical axis of the second interferometer lens;

[0034] 2.2. Adjust the interferometer's posture based on the amount of light spot movement on the detector, and adjust the detector's position toward or away from the beam splitter until the wavefront power measured by the interferometer and the light spot on the detector's target surface are minimized.

[0035] 2.3. Adjust the position and angle of the high-precision angle measurement system so that it can achieve self-alignment with the second plane reflector.

[0036] Furthermore, step 3 is specifically as follows:

[0037] Obtain M first images through the detector, average the centroid position of the light spot in each first image to obtain an initial light spot position image A, and adjust the light spot received by the detector to the center of its target surface based on the initial light spot position image A, M ≥ 50.

[0038] Furthermore, step 4 is specifically as follows:

[0039] Adjust the yaw posture of the second plane reflector so that the light spot on the detector is close to the edge of one side of its target surface. Obtain M second images through the detector, average the centroid position of the light spot in each second image to obtain the light spot position image B1, and obtain the yaw angle θ1 of the second plane reflector through monitoring by a high-precision angle measurement system.

[0040] Furthermore, step 5 is specifically as follows:

[0041] Adjust the yaw posture of the second plane reflector so that the light spot on the detector is close to the edge of the other side of its target surface. Obtain M third images through the detector. Average the centroid position of the light spot in each third image to obtain the light spot position image C1. Use the high-precision angle measurement system to monitor and obtain the yaw angle θ2 of the second plane reflector.

[0042] Furthermore, before step 6 and after step 5, the following steps are also included:

[0043] Repeat steps 4 and 5 to obtain multiple deflection angles θ1 and θ2 of the second plane reflector, and calculate the average value of the multiple deflection angles θ1 respectively. Calculate the average value of multiple deflection angles θ2

[0044] Then in step 6, get the corresponding average value and

[0045] Then step 8 is specifically: calculate the focal length of the optical system

[0046] Furthermore, step 1 specifically includes:

[0047] 1.1. A first plane reflector is provided at the output end of the interferometer body. The interferometer body emits the measuring light, and the first plane reflector reflects the measuring light to the secondary mirror of the optical system.

[0048] 1.2. A beam splitter prism is arranged on the optical path between the interferometer body and the first plane reflector. The beam splitter prism transmits the measuring light to the first plane reflector. The first plane reflector reflects the transmitted measuring light to the secondary mirror of the optical system. The light is then reflected by the secondary mirror of the optical system and the primary mirror of the optical system in sequence to form parallel light.

[0049] 1.3. A second plane reflector is provided on the optical path of the parallel light. The second plane reflector returns the parallel light to the primary mirror of the optical system. The returned light is reflected by the primary mirror of the optical system, the secondary mirror of the optical system, and the first plane reflector to the beam splitter prism. The beam splitter prism then separates the returned transmitted light into the returned reflected light. The returned transmitted light enters the interferometer body.

[0050] 1.4. A detector is provided on the optical path of the return reflected light, a first interferometer lens is installed between the beam splitter prism and the first plane reflector, and a second interferometer lens is installed between the beam splitter prism and the detector;

[0051] 1.5. Adjust the various components so that the second plane mirror can reflect the parallel light back to the main mirror of the optical system and finally enter the target surface of the interferometer body and the detector.

[0052] Beneficial effects of the present invention:

[0053] 1. The high-precision focal length detection device and method provided by the present invention combines interferometry technology with a two-step spectroscopic test method to measure focal length. It can achieve quantitative measurement of optical systems with a focal length of 20 meters or even more than 30 meters. It can quantify the focal length offset of the optical system and accurately guide system installation and detection.

[0054] 2. Compared with the Boro plate detection method, the high-precision focal length detection device and method provided by the present invention use a high-resolution detector to record the light spot position of the optical system multiple times, calculate the light spot position movement distance, and calculate the average of multiple detection results, which greatly reduces the detection error caused by human eye observation and the light spot position drift caused by airflow disturbance, and improves the detection efficiency and detection accuracy.

[0055] 3. The high-precision focal length detection device provided by the present invention has a simple structure, low cost, easy installation and adjustment process, and a short detection process. It can well solve the problem of high-precision quantitative measurement of the focal length of a long-focal-length optical system in its operating posture.

[0056] 4. When performing high-precision focal length detection, the present invention uses two interferometer lenses (a first interferometer lens and a second interferometer lens) to converge the corresponding light beams, and also exchanges the positions of the two interferometer lenses during the detection process. This can achieve online calibration of the focal length magnification between the two interferometer lenses. The calibrated magnification can be directly used for the subsequent focal length calculation of the optical system. This online calibration method helps to improve test accuracy and test efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 The diagram is a structural diagram of an embodiment of a high-precision focal length detection device for a long-focal-length optical system according to the present invention.

[0058] Figure Number:

[0059] 1- High-precision angle measurement system, 2- Second plane reflector, 3- Optical system primary mirror, 4- Optical system secondary mirror, 5- First plane reflector, 6- Optical system focal plane, 7- First interferometer lens, 8- Beam splitter prism, 9- CCD detector, 10- Second interferometer lens, 11- Interferometer body. DETAILED DESCRIPTION

[0060] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the accompanying drawings and embodiments. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0061] like Figure 1 As shown, the optical system includes an optical system primary mirror 3 and an optical system secondary mirror 4 that are arranged opposite to each other; the optical system is the optical system to be measured.

[0062] Example 1:

[0063] This embodiment provides a high-precision focal length detection device for a long-focal-length optical system, including a high-precision angle measurement system 1, a second plane reflector 2, a first plane reflector 5, a first interferometer lens 7, a beam splitter prism 8, a detector 9, a second interferometer lens 10, and an interferometer body 11.

[0064] The interferometer body 11 emits measuring light; the interferometer body 11 is a dynamic interferometer.

[0065] The beam splitter prism 8 is used to transmit the measurement light. The aperture of the beam splitter prism 8 is larger than the exit light aperture of the interferometer body 11, and its splitting ratio is 1:1. The beam splitter prism 8 is installed at the exit end of the interferometer body 11 through an adapter ring.

[0066] The first plane reflector 5 is used to reflect the transmitted measuring light to the optical system secondary mirror 4 , and the light is reflected out in sequence by the optical system secondary mirror 4 and the optical system primary mirror 3 to form parallel light.

[0067] The second plane reflector 2 is arranged on the optical path of the parallel light, and is used to return the parallel light to the optical system main mirror 3. The returned light is reflected by the optical system main mirror 3, the optical system secondary mirror 4, and the first plane reflector 5 to the dichroic prism 8 in sequence, and then divided into returned transmitted light and returned reflected light by the dichroic prism 8; the returned transmitted light enters the interferometer body 11; the aperture of the second plane reflector 2 is larger than the aperture of the optical system main mirror 3; the second plane reflector 2 uses a plane reflector with a surface root mean square error of less than 1 / 40 wavelength; the posture of the second plane reflector 2 is controlled by a reflector control mechanism; the reflector control mechanism includes a vertical rotating electric control rail, a horizontal rotating electric control rail and a controller, the second plane reflector 2 is arranged on the horizontal rotating electric control rail and the vertical rotating electric control rail, and under the control of the controller, performs horizontal rotation movement on the horizontal rotating electric control rail and vertical rotation movement on the vertical rotating electric control rail to adjust the azimuth posture.

[0068] The high-precision angle measurement system 1 is used to measure the angle of the second plane reflector 2 .

[0069] The detector 9 is arranged on the optical path of the returned reflected light and is used to detect the light spot; in this embodiment, the detector 9 is a CCD camera.

[0070] The first interferometer lens 7 is disposed between the beam splitter prism 8 and the first plane reflector 5 to converge the transmitted measuring light; the second interferometer lens 10 is disposed between the beam splitter prism 8 and the detector 9 to converge the return reflected light.

[0071] Alternatively, the second interferometer lens 10 is disposed between the beam splitter prism 8 and the first plane reflector 5 to converge the transmitted measuring light; the first interferometer lens 7 is disposed between the beam splitter prism 8 and the detector 9 to converge the return reflected light.

[0072] The F number of the first interferometer lens 7 and the second interferometer lens 10 is smaller than the F number of the optical system; the first interferometer lens 7 and the second interferometer lens 10 are respectively mounted on the beam splitter prism 8 to ensure that the return light of the optical system enters the interferometer body 11 and the CCD camera target surface.

[0073] The optical path of the high-precision focal length detection device when in use is as follows:

[0074] The measuring light emitted from the interferometer body 11 is sequentially transmitted through the beam splitter prism 8, converged by the first interferometer lens 7, reflected by the first plane mirror 5, reflected by the secondary optical mirror 4, and reflected by the primary optical mirror 3, forming parallel light that enters the second plane mirror 2. It is then sequentially reflected by the second plane mirror 2, the primary optical mirror 3, the secondary optical mirror 4, the first plane mirror 5, and transmitted by the first interferometer lens 7. It is then split by the beam splitter prism 8, partially transmitted into the interferometer body 11, and partially reflected by the second interferometer lens 10, where it converges to the detector 9. The optical system focal plane 6 is located between the first plane mirror 5 and the first interferometer lens 7. The first and second interferometer lenses 7 and 10 are interchangeable.

[0075] The focal length detection is performed using the above-mentioned high-precision focal length detection device of the long focal length optical system, which specifically includes the following steps:

[0076] Step 1: Build a high-precision focal length detection device.

[0077] 1.1. A first plane reflector 5 is provided at the output end of the interferometer body 11. The interferometer body 11 emits the measuring light, and the first plane reflector 5 reflects the measuring light to the secondary mirror 4 of the optical system.

[0078] 1.2. A beam splitter prism 8 is provided on the optical path between the interferometer body 11 and the first plane reflector 5. The beam splitter prism 8 transmits the measuring light to the first plane reflector 5. The first plane reflector 5 reflects the transmitted measuring light to the secondary mirror 4 of the optical system. The light is then reflected by the secondary mirror 4 and the primary mirror 3 of the optical system in sequence to form parallel light.

[0079] 1.3. A second plane reflector 2 is provided on the optical path of the parallel light. The second plane reflector 2 returns the parallel light to the optical system primary mirror 3. The returned light is reflected by the optical system primary mirror 3, the optical system secondary mirror 4, and the first plane reflector 5 to the beam splitter prism 8. The beam splitter prism 8 then separates the returned transmitted light into the returned reflected light. The returned transmitted light enters the interferometer body 11.

[0080] 1.4. A detector 9 is provided on the optical path of the return reflected light, a first interferometer lens 7 is installed between the beam splitter prism 8 and the first plane reflector 5, and a second interferometer lens 10 is installed between the beam splitter prism 8 and the detector 9;

[0081] 1.5. Adjust the various components so that the second plane reflector 2 can reflect the parallel light back to the optical system primary mirror 3 and finally incident on the interferometer body 11 and the target surface of the detector 9.

[0082] Step 2: Adjust the focal length high-precision detection device so that the target surface of the detector 9 is perpendicular to the optical axis of the second interferometer lens 10, the wavefront power measured by the interferometer body 11 and the light spot on the target surface of the detector 9 are minimized, and the high-precision angle measurement system 1 and the second plane reflector 2 are self-aligned.

[0083] Step 3: Obtain an initial light spot position image A through the detector 9, and adjust the light spot received by the detector 9 to the center of its target surface based on the initial light spot position image A.

[0084] Step 4: Adjust the yaw posture of the second plane reflector 2 so that the light spot on the detector 9 is close to the edge of one side of its target surface, obtain the light spot position image B1 through the detector 9, and monitor the yaw angle θ1 of the second plane reflector 2 through the high-precision angle measurement system 1.

[0085] Step 5: Adjust the yaw posture of the second plane reflector 2 so that the light spot on the detector 9 is close to the edge of the other side of its target surface, obtain the light spot position image C1 through the detector 9, and monitor the yaw angle θ2 of the second plane reflector 2 through the high-precision angle measurement system 1.

[0086] Step 6: Interchange the positions of the first interferometer lens 7 and the second interferometer lens 10, and use the methods of steps 2 to 5 to obtain the corresponding spot position images B2 and C2 when the light spot approaches the edges of the target surface of the detector 9, as well as the deflection angles θ3 and θ4 monitored by the high-precision angle measurement system 1.

[0087] Step 7: Obtain the light spot centroid position movement linear quantity t1 through the light spot position images B1 and C1; obtain the light spot centroid position movement linear quantity t2 through the light spot position images B2 and C2.

[0088] This step is specifically as follows: obtain the difference 1 between the centroid positions of the two light spots in the light spot position image B1 and the light spot position image C1, and multiply the difference 1 between the two light spot positions by the pixel size of the detector 9 to obtain t 1。

[0089] Obtain the difference 2 between the centroid positions of the two light spots in the light spot position image B2 and the light spot position image C2, and multiply the difference 2 between the two light spot positions by the pixel size of the detector 9 to obtain t 2。

[0090] Step 8. Calculate the focal length of the optical system

[0091] Example 2:

[0092] The second embodiment is substantially the same as the first embodiment, except that, when performing focal length detection, in order to improve detection accuracy, step 2 includes:

[0093] 2.1. Adjust the yaw angle and pitch angle of the detector 9 so that the target surface of the detector 9 is perpendicular to the optical axis of the second interferometer lens 10.

[0094] In this step, when the position of the detector 9 is adjusted in the direction of approaching or moving away from the dichroic prism 8, the movement position of the bright spot is observed on its screen. If the light spot moves up and down when the detector 9 is moved, it indicates that the detector 9 is not perpendicular to the second interferometer lens 10. At this time, the movement line quantity obtained is an invalid value. Therefore, by observing the movement position of the light spot, the pitch angle of the detector 9 is continuously adjusted until the light spot position does not shift during movement. At this time, the target surface of the detector 9 is perpendicular to the optical axis of the second interferometer lens 10.

[0095] 2.2. Adjust the posture of the interferometer body 11 based on the movement of the light spot on the detector 9, and adjust the position of the detector 9 in the direction of approaching or moving away from the beam splitter prism 8 until the wavefront power measured by the interferometer body 11 and the light spot on the target surface of the detector 9 are minimized.

[0096] 2.3. Adjust the position and angle of the high-precision angle measurement system 1 so that it can achieve self-alignment with the second plane reflector 2.

[0097] Step 3 is: obtaining multiple first images (more than 50) through the detector 9, averaging the centroid position of the light spot in each first image to obtain an initial light spot position image A, and adjusting the light spot received by the detector 9 to the center of its target surface based on the initial light spot position image A.

[0098] Step 4 is: adjust the yaw posture of the second plane reflector 2 so that the light spot on the detector 9 is close to the edge of one side of its target surface, obtain multiple second images (more than 50 images) through the detector 9, average the center of mass position of the light spot in each second image, and obtain the light spot position image B1, and monitor the yaw angle θ1 of the second plane reflector 2 through the high-precision angle measurement system 1.

[0099] Step 5 is: adjust the yaw posture of the second plane reflector 2 so that the light spot on the detector 9 is close to the edge of the other side of its target surface, obtain multiple third images (more than 50 images) through the detector 9, average the center of mass position of the light spot in each third image, and obtain the light spot position image C1, and monitor the yaw angle θ2 of the second plane reflector 2 through the high-precision angle measurement system 1.

[0100] Acquiring multiple first images, second images, and third images can reduce the light spot position drift caused by environmental vibration and airflow during the detection process, as well as the random error caused by the calculation of the center of mass position during data processing, thereby improving the detection accuracy.

[0101] Example 3:

[0102] The third embodiment is substantially the same as the second embodiment, except that, when performing focal length detection, in order to improve detection accuracy, the following steps are further included before step 6 and after step 5:

[0103] Repeat steps 4 and 5 to obtain multiple deflection angles θ1 and θ2 of the second plane reflector 2, and calculate the average value of the multiple deflection angles θ1 respectively. Calculate the average value of multiple deflection angles θ2

[0104] Then in step 6, get the corresponding average value and

[0105] Step 8: Calculate the focal length of the optical system

[0106] This invention uses a beam splitter prism to focus the spot of light returned from the optical system onto a CCD camera, replacing conventional detection methods that rely on observing the glass plate image. The high-resolution CCD camera provides clear images and a fast response. By adjusting the deflection angle of the second plane reflector, the movement position of the light spot and the deflection angle of the plane mirror are recorded. Subsequent image processing accurately calculates the movement of the light spot, and thus the focal length of the optical system. This method can achieve high-precision and rapid detection of optical system focal lengths of 20 meters or even more than 30 meters.

[0107] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present invention shall be covered by the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A high-precision focal length detection device for a long-focal-length optical system, wherein the optical system comprises an optical system primary mirror (3) and an optical system secondary mirror (4) arranged opposite to each other; Its characteristics are: It comprises a high-precision angle measurement system (1), a second plane reflector (2), a first plane reflector (5), a first interferometer lens (7), a beam splitter prism (8), a detector (9), a second interferometer lens (10), and an interferometer body (11); The interferometer body (11) emits measuring light; The beam splitter prism (8) is used to transmit the measuring light; The first plane reflector (5) is used to reflect the transmitted measuring light to the optical system secondary mirror (4), and reflect the light out in sequence through the optical system secondary mirror (4) and the optical system primary mirror (3), thereby forming parallel light; The second plane reflector (2) is arranged on the optical path of the parallel light and is used to return the parallel light to the optical system primary mirror (3); the returned light is reflected by the optical system primary mirror (3), the optical system secondary mirror (4), and the first plane reflector (5) in sequence to the beam splitter prism (8); and then is divided into return transmitted light and return reflected light by the beam splitter prism (8); the return transmitted light enters the interferometer body (11); The high-precision angle measurement system (1) is used to measure the angle of the second plane reflector (2); The detector (9) is arranged on the optical path of the returned reflected light and is used to detect the light spot; The first interferometer lens (7) is arranged between the beam splitter prism (8) and the first plane reflector (5) to converge the transmitted measurement light; the second interferometer lens (10) is arranged between the beam splitter prism (8) and the detector (9) to converge the return reflected light; Alternatively, the second interferometer lens (10) is arranged between the beam splitter prism (8) and the first plane reflector (5) to converge the transmitted measuring light; and the first interferometer lens (7) is arranged between the beam splitter prism (8) and the detector (9) to converge the return reflected light.

2. The high-precision focal length detection device for a long-focal-length optical system according to claim 1, characterized in that: The aperture of the second plane reflector (2) is larger than the aperture of the optical system main mirror (3), and the root mean square error of its surface shape is less than 1 / 40 wavelength; The F number of the first interferometer lens (7) and the second interferometer lens (10) is smaller than the F number of the optical system; The light aperture of the beam splitter prism (8) is larger than the light exiting aperture of the interferometer body (11), and the beam splitting ratio is 1:

1.

3. The high-precision focal length detection device for a long-focal-length optical system according to claim 1 or 2, characterized in that: The detector (9) is a CCD camera; The interferometer body (11) is a dynamic interferometer.

4. A method for high-precision detection of focal length of a long focal length optical system, using the high-precision detection device for focal length of a long focal length optical system according to any one of claims 1 to 3, characterized in that: The following steps are involved: Step 1: constructing a high-precision focal length detection device for a long-focal-length optical system as described in any one of claims 1 to 3, so that the second plane reflector (2) can reflect parallel light back to the main mirror (3) of the optical system until it is incident on the target surface of the interferometer body (11) and the detector (9); Step 2, adjusting the focal length high-precision detection device so that the target surface of the detector (9) is perpendicular to the optical axis of the second interferometer lens (10), the wavefront power measured by the interferometer body (11) and the light spot on the target surface of the detector (9) are minimized, and the high-precision angle measurement system (1) and the second plane reflector (2) achieve self-alignment; Step 3: obtaining an initial light spot position image A through the detector (9), and adjusting the light spot received by the detector (9) to the center of its target surface based on the initial light spot position image A; Step 4: Adjust the yaw posture of the second plane reflector (2) so that the light spot on the detector (9) is close to the edge of one side of the target surface, obtain the light spot position image B1 through the detector (9), and monitor and obtain the yaw angle θ1 of the second plane reflector (2) through the high-precision angle measurement system (1); Step 5: Adjust the yaw posture of the second plane reflector (2) so that the light spot on the detector (9) is close to the edge of the other side of the target surface, obtain the light spot position image C1 through the detector (9), and monitor and obtain the yaw angle θ2 of the second plane reflector (2) through the high-precision angle measurement system (1); Step 6: Interchange the positions of the first interferometer lens (7) and the second interferometer lens (10), and use the methods of steps 2 to 5 to obtain the corresponding light spot position image B2 and light spot position image C2 when the light spot approaches the edges of the target surface of the detector (9), as well as the deflection angles θ3 and θ4 monitored by the high-precision angle measurement system (1); Step 7: Obtain the linear displacement t1 of the center of mass of the light spot through the light spot position images B1 and C1; obtain the linear displacement t2 of the center of mass of the light spot through the light spot position images B2 and C2; Step 8: Calculate the focal length of the optical system 5. The method for high-precision focal length detection of a long focal length optical system according to claim 4, wherein: Step 2 specifically includes: 2.

1. Adjusting the yaw angle and pitch angle of the detector (9) so that the target surface of the detector (9) is perpendicular to the optical axis of the second interferometer lens (10); 2.

2. Adjusting the posture of the interferometer body (11) based on the amount of movement of the light spot on the detector (9), and adjusting the position of the detector (9) in a direction close to or away from the beam splitter prism (8) until the wavefront power measured by the interferometer body (11) and the light spot on the target surface of the detector (9) are minimized; 2.

3. Adjust the position and angle of the high-precision angle measuring system (1) so that it can achieve self-alignment with the second plane reflector (2).

6. The method for high-precision focal length detection of a long focal length optical system according to claim 5, wherein: Step 3 is as follows: M first images are acquired through a detector (9), and the centroid position of the light spot in each first image is averaged to obtain an initial light spot position image A. Based on the initial light spot position image A, the light spot received by the detector (9) is adjusted to the center of its target surface, M≥50.

7. The method for high-precision focal length detection of a long focal length optical system according to claim 6, wherein: Step 4 is as follows: The yaw posture of the second plane reflector (2) is adjusted so that the light spot on the detector (9) is close to the edge of one side of the target surface, M second images are obtained through the detector (9), the centroid position of the light spot in each second image is averaged to obtain a light spot position image B1, and the yaw angle θ1 of the second plane reflector (2) is monitored and obtained through the high-precision angle measurement system (1).

8. The method for high-precision focal length detection of a long focal length optical system according to claim 7, wherein: Step 5 is as follows: The yaw posture of the second plane reflector (2) is adjusted so that the light spot on the detector (9) is close to the edge of the other side of the target surface, M third images are obtained through the detector (9), the center of mass position of the light spot in each third image is averaged to obtain a light spot position image C1, and the yaw angle θ2 of the second plane reflector (2) is monitored and obtained through the high-precision angle measurement system (1).

9. The method for high-precision focal length detection of a long focal length optical system according to claim 8, wherein: Before step 6 and after step 5, the following steps are also included: Repeat steps 4 and 5 to obtain multiple deflection angles θ1 and multiple deflection angles θ2 of the second plane reflector (2), and calculate the average value of the multiple deflection angles θ1 respectively. Calculate the average value of multiple deflection angles θ2 Then in step 6, get the corresponding average value and Then step 8 is specifically: calculate the focal length of the optical system 10. The method for high-precision focal length detection of a long focal length optical system according to any one of claims 4 to 8, wherein: Step 1 specifically includes: 1.

1. A first plane reflector (5) is provided at the output end of the interferometer body (11), and the interferometer body (11) emits measurement light, so that the first plane reflector (5) reflects the measurement light to the secondary mirror (4) of the optical system; 1.

2. A beam splitter prism (8) is provided on the optical path between the interferometer body (11) and the first plane reflector (5). The beam splitter prism (8) transmits the measuring light to the first plane reflector (5). The first plane reflector (5) reflects the transmitted measuring light to the secondary mirror (4) of the optical system. The light is then reflected by the secondary mirror (4) and the primary mirror (3) of the optical system in sequence to form parallel light. 1.

3. A second plane reflector (2) is provided on the optical path of the parallel light. The second plane reflector (2) returns the parallel light to the optical system primary mirror (3). The returned light is reflected by the optical system primary mirror (3), the optical system secondary mirror (4), and the first plane reflector (5) to the beam splitter prism (8). The returned light is then divided into return transmitted light and return reflected light by the beam splitter prism (8). The return transmitted light enters the interferometer body (11). 1.

4. A detector (9) is provided on the optical path of the return reflected light, a first interferometer lens (7) is installed between the beam splitter prism (8) and the first plane reflector (5), and a second interferometer lens (10) is installed between the beam splitter prism (8) and the detector (9); 1.

5. Adjust the various components so that the second plane reflector (2) can reflect the parallel light back to the main mirror (3) of the optical system, and finally incident on the target surface of the interferometer body (11) and the detector (9).

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