High-precision focal length detection device and method for long-focal-length optical system

Abstract

The invention discloses a focal length high-precision detection device and method for a long-focal-length optical system. The problems that an existing focal length detection method is low in detection repetition precision, poor in precision and not suitable for the long-focal-length optical system are solved. According to the invention, a light spot of light returned by an optical system is focused on a detector with clear imaging by using a beam splitter prism to replace a conventional detection method for observing and aiming a Perot plate image, adjusting the deflection angle of a plane mirror, and respectively recording the movement position of the light spot and the deflection angle of the plane mirror; 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.

Description

Technical Field

[0001] The 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 and long-focal-length optical systems are widely used in fields such as earth observation and astronomical technology research. The detection and assembly of large-aperture optical systems is one of the cutting-edge projects of current hard technology, and has important commercial value for a series of applications such as long-distance imaging in space and focusing of laser weapons. As the aperture of optical systems continues to increase, more requirements are put forward for optical detection and assembly.

[0003] The focal length of an optical system is a very critical physical quantity of the system, and its high-precision measurement is a key link in the system development stage. Common methods for measuring the focal length of long-focal-length optical systems include the detection method combining theodolite and Pero plate and the precision angle measurement method. When testing the detection method combining theodolite and Pero plate, the Pero plate is installed at the focal plane of the optical system, illuminated by a light source, and the angle between the Pero plate lines is measured using the theodolite to obtain the focal length of the optical system. During the Pero plate detection method, a high-precision theodolite is required to observe the image points 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. Affected by airflow and human eye resolution, the error in each observation and reading is large, which brings a large error to the final focal length calculation of the optical system. The actual detection process is a semi-quantitative detection method because it requires judgment by the naked eye and experience, and cannot meet the image quality detection and adjustment requirements of modern optical systems; therefore, the focal length detection repeatability of this method is low and the accuracy is poor. The precision angle measurement method requires the optical system to be placed on a turntable for angle rotation, and a large-caliber collimator is required to provide an infinitely distant target image, which places high demands on the hardware in the actual process. Therefore, a high-precision and easy-to-use detection method and device are urgently needed to achieve high-precision detection of the focal length of a long-focal-length optical system. Summary of the invention

[0004] In order to solve the technical problems that the existing focal length detection method has low detection repetition accuracy, poor precision 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 beam splitter to split the light, the light spot of the optical system's return light is focused on a detector with clear imaging, instead of observing the Porro plate image using conventional detection methods. 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 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 purpose 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 relatively to each other;

[0009] The special features thereof are: comprising a high-precision angle measuring 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 then reflect the light out through the secondary mirror of the optical system and the primary mirror of the optical system in sequence to form parallel light;

[0013] The second plane reflector is arranged on the optical path where the parallel light is located, and is used to return the parallel light to the primary mirror of the optical system, and 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 returned transmitted light and returned reflected light by the beam splitter prism; the returned 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 less than the F-number of the optical system;

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

[0021] Further, 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 special in that it comprises the following steps:

[0024] Step 1: construct the high-precision focal length detection device of the long focal length optical system mentioned above, so that the second plane reflector can reflect the 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 its target surface based on the initial light spot position image A;

[0027] Step 4, adjust the deflection 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 the light spot position image B1 through the detector, and obtain the deflection angle θ1 of the second plane reflector through monitoring by a high-precision angle measurement system;

[0028] Step 5, adjust the deflection 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 the light spot position image C1 through the detector, and obtain the deflection angle θ2 of the second plane reflector through monitoring by the 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 image B2 and spot position image C2 when the spot approaches the edges of both sides of the detector target surface, as well as the deflection angles θ3 and θ4 monitored by the high-precision angle measurement system;

[0030] Step 7, obtain the light spot centroid position movement linear quantity t1 through the light spot position picture B1 and the light spot position picture C1; obtain the light spot centroid position movement linear quantity t2 through the light spot position picture B2 and the light spot position picture C2;

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

[0032] Furthermore, step 2 specifically includes:

[0033] 2.1. Adjust the yaw angle and pitch angle 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 posture of the interferometer body based on the movement of the light spot on the detector, and adjust the position of the detector in the direction of approaching or moving away from the beam splitter prism until the wavefront power measured by the interferometer body and the light spot on the detector target surface are minimized;

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

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

[0037] M first images are obtained through the detector, and the centroid positions of the light spots in each first image are 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 is adjusted to the center of its target surface, M≥50.

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

[0039] The yaw posture of the second plane reflector is adjusted so that the light spot on the detector is close to the edge of one side of its target surface. M second images are obtained through the detector. The centroid positions of the light spots in each second image are averaged to obtain the light spot position image B1. The yaw angle θ1 of the second plane reflector is monitored and obtained by the high-precision angle measurement system.

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

[0041] The yaw posture of the second plane reflector is adjusted so that the light spot on the detector is close to the edge of the other side of its target surface. M third images are obtained through the detector. The centroid positions of the light spots in each third image are averaged to obtain the light spot position image C1. The yaw angle θ2 of the second plane reflector is monitored and obtained by the high-precision angle measurement system.

[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 multiple deflection angles 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: calculating the focal length of the optical system

[0046] Furthermore, step 1 specifically includes:

[0047] 1.1. A first plane reflector is arranged 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 out 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 arranged on the optical path of the parallel light, and 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 in sequence, and then is divided into returned transmitted light and returned reflected light by the beam splitter prism; the returned transmitted light enters the interferometer body;

[0050] 1.4. A detector is arranged 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 each component so that the second plane reflector 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 the interference measurement technology with the two-step spectroscopic test method to measure the focal length, which can realize the quantitative measurement of the optical system with a focal length of 20 meters or even more than 30 meters, and can quantify the focal length offset of the optical system, accurately guiding the system installation and detection.

[0054] 2. Compared with the Pero 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 moving distance of the light spot position, 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 focal length high-precision 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 a use 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 ratio between the two interferometer lenses. The calibrated ratio can be directly used for subsequent focal length calculations 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 present invention is a schematic structural diagram of a high-precision focal length detection device for a long focal length optical system according to an embodiment of the present invention.

[0058] Figure Number:

[0059] 1-high-precision angle measurement system, 2-second plane reflector, 3-primary mirror of optical system, 4-secondary mirror of optical system, 5-first plane reflector, 6-focal plane of optical system, 7-first interferometer lens, 8-beam splitter prism, 9-CCD detector, 10-second interferometer lens, 11-interferometer body. DETAILED DESCRIPTION

[0060] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work 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 which are arranged opposite to each other; the optical system is the optical system to be tested.

[0062] Embodiment 1:

[0063] The present embodiment provides a high-precision focal length detection device for a long focal length optical system, comprising 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 measuring light; the aperture of the beam splitter prism 8 is larger than the aperture of the output light of the interferometer body 11, and the splitting ratio is 1:1. The beam splitter prism 8 is installed at the output 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 by the optical system secondary mirror 4 and the optical system primary mirror 3 in sequence to form parallel light.

[0067] The second plane reflector 2 is arranged on the optical path where the parallel light is located, 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 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, the second plane reflector 2 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 arranged between the beam splitter prism 8 and the first plane reflector 5 to converge the transmitted measuring light; the second interferometer lens 10 is arranged 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 focal length high-precision detection device when in use is as follows:

[0074] The measuring light emitted by the interferometer body 11 is sequentially transmitted through the beam splitter prism 8, transmitted and converged by the first interferometer lens 7, reflected by the first plane reflector 5, reflected by the secondary mirror 4 of the optical system, and reflected by the primary mirror 3 of the optical system, forming parallel light and entering the second plane reflector 2; then sequentially reflected by the second plane reflector 2, reflected by the primary mirror 3 of the optical system, reflected by the secondary mirror 4 of the optical system, reflected by the first plane reflector 5, and transmitted by the first interferometer lens 7, and then split by the beam splitter prism 8, partially transmitted into the interferometer body 11, partially reflected to the second interferometer lens 10, and converged to the detector 9 through the second interferometer lens 10. The optical system focal plane 6 of the optical system is located between the first plane reflector 5 and the first interferometer lens 7. The first interferometer lens 7 and the second interferometer lens 10 can be interchanged.

[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 arranged 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 arranged 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 optical system secondary mirror 4, and the measuring light is reflected by the optical system secondary mirror 4 and the optical system primary mirror 3 in sequence to form parallel light.

[0079] 1.3. A second plane reflector 2 is arranged on the optical path of the parallel light, and 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 in sequence, and then is divided into the returned transmitted light and the returned reflected light by the beam splitter prism 8; the returned transmitted light enters the interferometer body 11;

[0080] 1.4. A detector 9 is arranged 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 each component 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 target surface of the interferometer body 11 and 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: Acquire 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 and obtain 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 and obtain 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 image B2 and spot position image C2 when the spot approaches the edges on both sides 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 picture B1 and the light spot position picture C1; obtain the light spot centroid position movement linear quantity t2 through the light spot position picture B2 and the light spot position picture C2.

[0088] The specific step is: 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] Embodiment 2:

[0092] The second embodiment is basically 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 moving 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 moving line quantity obtained is an invalid value. Therefore, by observing the moving position of the light spot, the pitch angle of the detector 9 is continuously adjusted until the light spot position does not shift when moving. 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 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.

[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 images) through the detector 9, averaging the centroid positions of the light spots 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 pictures (more than 50 pictures) through the detector 9, average the centroid positions of the light spots in each second picture, and obtain the light spot position picture B1, and monitor and obtain the yaw angle θ1 of the second plane reflector 2 through the high-precision angle measurement system 1.

[0099] Step 5 is: adjust the swing 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 centroid positions of the light spots in each third image, and obtain the light spot position image C1, and monitor and obtain the swing 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] Embodiment three:

[0102] The third embodiment is basically 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 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

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

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

[0106] The present invention uses a method of splitting light by a beam splitter prism to focus the light spot of the optical system return light on a CCD camera, replacing the conventional detection method for observing the imaging of the glass plate. The high-resolution CCD camera has clear imaging and fast response speed. By adjusting the deflection angle of the second plane reflector, the moving position of the light spot and the deflection angle of the plane mirror are recorded respectively. The subsequent image processing is performed to accurately calculate the movement amount of the light spot, and then the focal length of the optical system is calculated. The method can complete the high-precision and rapid detection of the focal length of the optical system of 20 meters or even more than 30 meters.

[0107] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A high-precision focal length detection device for a long focal length optical system, the optical system comprising an optical system primary mirror (3) and an optical system secondary mirror (4) arranged opposite to each other; Features: 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 through the optical system secondary mirror (4) and the optical system primary mirror (3) in sequence to form 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) to the beam splitter prism (8), and then is divided into return transmission light and return reflection light by the beam splitter prism (8); the return transmission 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 measuring 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 main mirror (3) of the optical system, 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) are self-aligned; 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: adjusting the deflection 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, obtaining the light spot position image B1 through the detector (9), and monitoring and obtaining the deflection angle θ1 of the second plane reflector (2) through the high-precision angle measurement system (1); Step 5, adjusting the deflection 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, obtaining the light spot position image C1 through the detector (9), and monitoring and obtaining the deflection 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 both sides 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 light spot centroid position movement linear quantity t1 through the light spot position picture B1 and the light spot position picture C1; obtain the light spot centroid position movement linear quantity t2 through the light spot position picture B2 and the light spot position picture 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, characterized in that: 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. Adjust the posture of the interferometer body (11) based on the movement amount of the light spot on the detector (9), and adjust 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 for a long focal length optical system according to claim 5, characterized in that: Step 3 is as follows: M first images are acquired through the detector (9), the centroid position of the light spot in each first image is averaged to obtain an initial light spot position image A, and the light spot received by the detector (9) is adjusted to the center of its target surface based on the initial light spot position image A, M≥50.

7. The method for high-precision focal length detection of a long focal length optical system according to claim 6, characterized in that: Step 4 is as follows: The deflection 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 deflection 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, characterized in that: Step 5 is as follows: The deflection 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 centroid position of the light spot in each third image is averaged to obtain a light spot position image C1, and the deflection 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, characterized in that: Before step 6 and after step 5, the following steps are also included: Repeat steps 4 and 5 to obtain a plurality of deflection angles θ1 and a plurality of deflection angles θ2 of the second plane reflector (2), and calculate the average value of the plurality of 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: calculating the focal length of the optical system 10. The method for high-precision focal length detection for a long focal length optical system according to any one of claims 4 to 8, characterized in that: Step 1 specifically includes: 1.

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

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

4. A detector (9) is arranged 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 optical system main mirror (3), and finally incident on the interferometer body (11) and the target surface of the detector (9).

Images