A calibration device and calibration method for the relationship between camera focal plane position and temperature

Abstract

The present invention provides a calibration device and a calibration method for the relationship between the focal plane position and temperature of a camera, which mainly solves the problem of poor imaging quality of existing cameras when they are running on track. The calibration device includes a collimator, a vacuum tank, a streak plate, a translation stage, an integrating sphere, a temperature measurement control unit and an air-floating seismic isolation platform; the camera to be tested is located at the light outlet of the collimator, and the collimator is used to provide an infinitely distant target for the camera to be tested; the vacuum tank is located on the air-floating seismic isolation platform, and the collimator and the camera to be tested are located in the vacuum tank; the streak plate is located at the focal plane position of the collimator, and is used to provide a streak image for the camera to be tested, and the integrating sphere is located behind the streak plate, and the streak plate and the integrating sphere are arranged on the translation stage, and the translation stage drives the streak plate and the integrating sphere to move; the temperature measurement control unit is arranged on the collimator and each lens and plane mirror of the camera to be tested, and is used to measure and control the temperature of the collimator and the camera to be tested.

Description

Technical Field

[0001] The invention belongs to the field of optical detection, and in particular relates to a device and a method for calibrating the relationship between the focal plane position and temperature of a camera in a vacuum or low-pressure environment. Background Art

[0002] With the rapid development of space optical technology, satellite-borne cameras are widely used in important fields such as military reconnaissance, earth mapping, and environmental disaster reduction. At the same time, there are increasingly higher requirements for the imaging quality of satellite-borne cameras on orbit. Whether the focal plane position of the camera coincides with the target surface of the detector is an important factor in determining clear imaging, and the relationship between the focal plane position of the camera and the temperature can play a role in ensuring the temperature focusing of the camera on orbit.

[0003] Currently, the camera undergoes a focal plane preset test on the ground. During the focal plane preset test, factors such as insufficient camera deflation and test errors may result in suboptimal imaging quality when the camera is running in orbit, causing the camera to fail to meet initial expectations. Summary of the invention

[0004] The purpose of the present invention is to solve the problem of poor imaging quality of existing cameras when they are running on orbit, and to provide a calibration device and a calibration method for the relationship between the focal plane position and temperature of a camera in a vacuum or low pressure environment.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The device for calibrating the relationship between the focal plane position and temperature of a camera of the present invention comprises a collimator, a vacuum tank, a streak plate, a translation stage, an integrating sphere, a temperature measurement control unit and an air-floating seismic isolation platform; the camera to be tested is located at the light outlet of the collimator, and the collimator is used to provide an infinitely distant target for the camera to be tested; the vacuum tank is located on the air-floating seismic isolation platform, the collimator and the camera to be tested are located in the vacuum tank, and the vacuum tank is used to provide a vacuum or low-pressure environment; the streak plate is located at the focal plane position of the collimator, and is used to provide a streak image for the camera to be tested, the integrating sphere is located behind the streak plate, and is used to evenly illuminate the streak plate, the streak plate and the integrating sphere are arranged on the translation stage, and the translation stage drives the streak plate and the integrating sphere to move, so as to realize the defocusing of the collimator; the temperature measurement control unit is arranged on the lenses and plane mirrors of the collimator and the camera to be tested, and is used to measure and control the temperature of the collimator and the camera to be tested.

[0007] Furthermore, the minimum stroke D of the translation stage is calculated according to the following formula:

[0008]

[0009] Where: D is the minimum travel of the translation stage, λ is the center wavelength of the camera under test, and f 光管 is the focal length of the collimator, f 相机is the focal length of the camera under test, and F is the F number of the camera under test.

[0010] Furthermore, the focal length of the collimator is 2 to 5 times the focal length of the camera being tested.

[0011] Furthermore, the stripe plate is a black and white stripe plate with equal width, and the contrast ratio of the black and white stripes is greater than 0.98.

[0012] Furthermore, the temperature measurement control unit includes a temperature sensor and a heating plate.

[0013] At the same time, the present invention also provides a calibration method based on the above calibration device, comprising the following steps:

[0014] Step 1: Install the camera under test at the light outlet of the collimator, turn on the integrating sphere, and let the camera under test image the stripe plate;

[0015] Step 2: Adjust the brightness of the integrating sphere so that the grayscale value of the streak plate image in the camera image is 50% to 90% of the camera saturation grayscale value;

[0016] Step 3: Rotate the streak plate around the optical axis of the collimator until the image of the streak plate is aligned with the arrangement direction of the detector pixels of the camera under test;

[0017] Step 4, record the temperature t1 of the camera under test;

[0018] Step 5: Record the focal position l1 of the collimator at this time, collect the stripe plate image, and record the grayscale response value DN of the dark stripe min , the grayscale response value DN of adjacent bright stripes max , calculate the transfer function MTF1 of the camera under test according to the following formula:

[0019]

[0020] Where: k is the waveform correction coefficient of the stripe plate, M i (γ) is the contrast between the bright and dark stripes of the target, DN max is the average output DN value corresponding to the bright stripes, DN min is the average output DN value corresponding to the dark fringes, and γ is the spatial frequency;

[0021] Step 6: Move the translation stage several times, record the focal position l2, l3, etc. of the collimator at each movement and the transfer function MTF2, MTF3, etc. of each focal position, and use the focal position as the X-axis and the transfer function as the Y-axis to calculate the matrix Use polynomial fitting to obtain the optimal focal plane position L1 of the camera under test at temperature t1;

[0022] Step 7: Change the temperature of the camera under test, and repeat steps 4 to 6 to obtain the best focal plane L2 of the camera under test at temperature t2, the best focal plane L3 of the camera under test at temperature t3, and so on. n The best focal plane L of the camera under test n ;

[0023] Step 8: Matrix Perform linear fitting to obtain the relationship between the focal plane position and temperature of the camera under test;

[0024] Step nine: according to the relationship between the focal plane position and the temperature of the camera under test obtained in step eight, the temperature of the camera under test during imaging is controlled.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. High calibration accuracy. During the calibration process of the relationship between the focal plane position and temperature of the camera, the main sources of error are the test error of the camera transfer function, the calculation error of the camera transfer function, and the fitting error of the curve. The factors affecting the test error of the camera transfer function include airflow and vibration, etc. The calibration device of the present invention provides a vacuum or low-pressure environment for the calibration process, which effectively reduces the influence of airflow on the camera MTF test. At the same time, the calibration device of the present invention provides an air-floating seismic isolation platform for the calibration process, which effectively reduces the influence of vibration on the camera MTF test, and the test repeatability is good, the results are reliable, and the fitting accuracy is high. At the same time, the camera is less affected by airflow in a low-pressure or vacuum environment, which improves the stability and repeatability of image acquisition, and thus has a significant improvement in the calculation accuracy of the camera transfer function and the fitting accuracy of the overfocus curve.

[0027] 2. High calibration efficiency. The calibration device of the present invention provides a temperature measurement control unit, which can quickly and effectively change the temperature of the camera to a preset temperature, and has very good temperature stability. In addition, the calibration device of the present invention provides a vacuum or low-pressure environment and an air-floating seismic isolation platform for the calibration process, which reduces the influencing factors of the test and greatly improves the test efficiency.

[0028] 3. The calibration accuracy of the method of the present invention is high. In terms of data processing, the method of the present invention uses two data fittings. First, the least squares method is used to perform quadratic curve fitting on the focal plane position and the camera transfer function at a single temperature, and then the optimal focal plane of the camera at a single temperature is obtained. Secondly, the least squares method is used to perform curve fitting on the temperature and the optimal focal plane of the camera, so that the calibration accuracy is high.

[0029] 4. High calibration accuracy. When calibrating the present invention, the focal length of the collimator used is 2 to 5 times that of the camera being tested. Therefore, the camera focal plane deviation caused by the position deviation of the collimator is 1 / 4 to 1 / 25 times that of the collimator focal plane position deviation, which has little influence. Furthermore, the smaller the contrast of the black and white stripe plate as the transfer function measurement standard, the greater the influence on the transfer function test. The method of the present invention proposes a black and white stripe plate with a contrast greater than 0.98, which further improves the calibration accuracy of the method of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The figure is a schematic structural diagram of a device for calibrating the relationship between the focal plane position and temperature of a camera according to the present invention.

[0031] Among them: 1-collimator, 2-vacuum tank, 3-tested camera, 4-stripe plate, 5-translation stage, 6-integrating sphere, 7-temperature measurement control unit, 8-air-floating seismic isolation platform. DETAILED DESCRIPTION

[0032] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0033] The present invention provides a calibration device and a calibration method for the relationship between the focal plane position and temperature of a camera in a vacuum or low-pressure environment. In the ground calibration stage of the camera, the relationship between the focal plane and the temperature of the camera is calibrated. By changing the temperature of the camera, the focal plane of the camera optical system is made to coincide with the target surface of the detector to achieve optimal imaging.

[0034] like Figure 1 As shown, the calibration device for the relationship between the focal plane position and temperature of a camera of the present invention comprises a collimator 1, a vacuum tank 2, a streak plate 4, a translation stage 5, an integrating sphere 6, a temperature measurement control unit 7 and an air-floating seismic isolation platform 8; the camera 3 to be tested is located at the light outlet of the collimator 1, and the collimator 1 provides an infinitely distant target for the camera 3 to be tested. At this time, the focal length of the collimator 1 can be set to 2 to 5 times the focal length of the camera 3 to be tested; the volume of the vacuum tank 2 needs to be able to accommodate the collimator 1 and the camera 3 to be tested at the same time, the collimator 1 and the camera 3 to be tested are located in the vacuum tank 2, and the vacuum tank 2 is used to provide a vacuum environment or low air pressure (air pressure is less than or equal to 100Pa); the vacuum tank 2 is located on the air-floating seismic isolation platform 8, and the air-floating seismic isolation platform 8 can provide a seismic isolation environment for the calibration system to reduce the impact of vibration on the test.

[0035] The temperature measurement control unit 7 is arranged on the collimator 1 and the lenses and plane mirrors of the camera 3 under test; the temperature measurement control unit 7 can measure the temperature of the camera 3 under test and the collimator 1 in real time, and can also change the temperature of the camera 3 under test and the collimator 1 to control the absence of temperature difference between the components of the camera 3 under test and the collimator 1. During the calibration process of the present invention, the collimator 1 needs to maintain a constant temperature; in the embodiment of the present invention, the temperature measurement control unit 7 may specifically include a temperature sensor and a heating plate.

[0036] The stripe plate 4 is located at the focal plane of the collimator 1, and the integrating sphere 6 is located behind the stripe plate 4, and is used to evenly illuminate the stripe plate 4. The stripe plate 4 and the integrating sphere 6 are located on the translation stage 5, and together form a focal plane system of the collimator 1. In the embodiment of the present invention, the stripe plate 4 is specifically a black and white stripe plate with equal width, and the contrast ratio of the black and white stripes is greater than 0.98. The stripe plate 4 is located at the focal plane of the collimator 1, and is used to provide a stripe image for the camera, and the camera transfer function test can be performed. The width b of the stripes of the stripe plate 4 can be calculated according to the following formula:

[0037] b=d×f 光管 / f 相机

[0038] Where: b is the width of the stripe plate 4, d is the detector pixel size, f is 光管 is the focal length of collimator 1, f 相机 is the focal length of the camera 3 under test;

[0039] The middle stroke of the translation stage 5 is located at the focal plane position of the collimator 1, carrying the above-mentioned stripe plate 4, which is used to defocus the collimator 1 and fit the optimal focal plane position of the camera. The minimum stroke D of the translation stage 5 is calculated according to the following formula. The minimum stroke D of the translation stage 5 makes the curve fitting more complete and avoids the generation of errors.

[0040]

[0041] Where: D is the minimum travel of the translation stage 5, λ is the central wavelength of the camera 3 under test, f 光管 is the focal length of collimator 1, f 相机 is the focal length of the camera 3 under test, and F is the F number of the camera 3 under test.

[0042] Based on the above system, the present invention provides a method for calibrating the relationship between the focal plane position and temperature of a camera, which specifically includes the following steps:

[0043] Step 1: Install the camera 3 under test at the light outlet of the collimator 1, turn on the integrating sphere 6, and open the camera ground inspection software to make the camera 3 under test image the stripe plate 4;

[0044] Step 2: Adjust the brightness of the integrating sphere 6 so that the grayscale value of the streak plate image in the camera image is 50% to 90% of the camera saturation grayscale value;

[0045] Step 3, rotating the streak plate 4 around the optical axis of the collimator 1 until the image of the streak plate 4 is aligned with the arrangement direction of the detector pixels of the camera 3 under test;

[0046] Step 4, record the temperature t1 of the camera 3 under test at this time;

[0047] Step 5: Record the focal position l1 of the collimator 1 at this moment, collect the image of the stripe plate 4, and record the grayscale response value DN of the dark stripe. min , the grayscale response value DN of adjacent bright stripes max , calculate the transfer function MTF1 of the camera at this moment according to the following formula:

[0048]

[0049] Where: k is the waveform correction coefficient of the square wave stripe plate 4, generally л / 4, M(γ)(M i (γ) is the contrast of the target bright and dark stripes, which can be approximately taken as 1 when it is above 0.98. max is the average output DN value corresponding to the bright stripes, DN min is the average output DN value corresponding to the dark fringes, and γ is the spatial frequency;

[0050] Step 6: Move the translation stage 5 multiple times, record the focal plane position l2, l3... of the collimator 1 and the transfer function MTF2, MTF3... of each position during each movement, and use the focal plane position as the X-axis and the transfer function as the Y-axis to calculate the matrix Using polynomial fitting, the best focal plane position L1 of the camera 3 under test at temperature t1 is obtained;

[0051] In this step, the movement amount of the translation stage 5 is greater than Preferably, the amount of movement of the translation stage 5 each time is

[0052] Step 7: The temperature measurement control unit 7 changes the temperature of the camera 3 under test, and repeats steps 4 to 6 to test the best focal plane L2 of the camera at temperature t2, the best focal plane L3 of the camera at temperature t3, etc., in the same way. n The best focal plane L of the camera 3 under test n ;

[0053] Step 8: Matrix By performing linear fitting, the relationship between the focal plane position of the camera and the temperature can be obtained, where L is the focal plane position of the collimator 1;

[0054] Step nine: when the camera 3 under test is imaging, according to the relationship between the camera focal plane position and the temperature obtained in step eight, the temperature of the camera 3 under test is changed, so that the focal plane of the camera optical system coincides with the detector target surface to achieve optimal imaging.

Claims

1. A calibration method for a calibration device for the relationship between the focal plane position and temperature of a camera, the calibration device for the relationship between the focal plane position and temperature of a camera comprising a collimator (1), a vacuum tank (2), a streak plate (4), a translation stage (5), an integrating sphere (6), a temperature measurement control unit (7) and an air-floating seismic isolation platform (8); the camera (3) to be tested is located at a light outlet of the collimator (1), and the collimator (1) is used to provide an infinitely distant target for the camera (3) to be tested; the vacuum tank (2) is located on the air-floating seismic isolation platform (8), the collimator (1) and the camera (3) to be tested are located in the vacuum tank (2), and the vacuum tank (2) is used to provide a vacuum or Low pressure environment; the stripe plate (4) is located at the focal plane of the collimator (1) and is used to provide a stripe image for the camera (3) under test; the integrating sphere (6) is located behind the stripe plate (4) and is used to evenly illuminate the stripe plate (4); the stripe plate (4) and the integrating sphere (6) are arranged on a translation stage (5); the translation stage (5) drives the stripe plate (4) and the integrating sphere (6) to move to achieve defocusing of the collimator (1); the temperature measurement control unit (7) is arranged on the lens and plane mirror of the collimator (1) and the camera (3) under test and is used to measure and control the temperature of the collimator (1) and the camera (3) under test; characterized in that: The following steps are involved: Step 1: Install the camera under test at the light outlet of the collimator, turn on the integrating sphere, and let the camera under test image the stripe plate; Step 2: Adjust the brightness of the integrating sphere so that the grayscale value of the streak plate image in the camera image is 50% to 90% of the camera saturation grayscale value; Step 3: Rotate the streak plate around the optical axis of the collimator until the image of the streak plate is aligned with the arrangement direction of the detector pixels of the camera under test; Step 4, record the temperature t1 of the camera under test; Step 5: Record the focal position l1 of the collimator at this time, collect the stripe plate image, and record the grayscale response value DN of the dark stripe min , the grayscale response value DN of adjacent bright stripes max , calculate the transfer function MTF1 of the camera under test according to the following formula: Where: k is the waveform correction coefficient of the stripe plate, M i (γ) is the contrast between the bright and dark stripes of the target, DN max is the average output DN value corresponding to the bright stripes, DN min is the average output DN value corresponding to the dark fringes, and γ is the spatial frequency; Step 6: Move the translation stage several times, record the focal position l2, l3, etc. of the collimator at each movement and the transfer function MTF2, MTF3, etc. of each focal position, and use the focal position as the X-axis and the transfer function as the Y-axis to calculate the matrix Use polynomial fitting to obtain the optimal focal plane position L1 of the camera under test at temperature t1; Step 7: Change the temperature of the camera under test, repeat steps 4 to 6, and obtain the best focal position L2 of the camera under test at temperature t2, the best focal position L3 of the camera under test at temperature t3, and so on. n The best focal position L of the camera under test n ; Step 8: Matrix Linear fitting is performed to obtain the relationship between the focal plane position and temperature of the camera under test, where L refers to the focal plane position of the collimator (1), and f 光管 is the focal length of the collimator (1), f 相机 is the focal length of the camera under test (3); Step nine: according to the relationship between the focal plane position and the temperature of the camera under test obtained in step eight, the temperature of the camera under test during imaging is controlled.

2. The calibration method of a camera focal plane position and temperature relationship calibration device according to claim 1, characterized in that: In step 6, the translation stage moves more than Where λ is the central wavelength of the camera under test (3), and F is the F number of the camera under test.

3. The calibration method of a camera focal plane position and temperature relationship calibration device according to claim 1 or 2, characterized in that: In step 6, the amount of movement of the translation stage each time is 4. The calibration method of the device for calibrating the relationship between the focal plane position and temperature of a camera according to claim 3, characterized in that: The minimum travel D of the translation stage (5) is calculated according to the following formula:

5. The calibration method of a camera focal plane position and temperature relationship calibration device according to claim 1, characterized in that: The focal length of the collimator (1) is 2 to 5 times the focal length of the camera (3) being tested.

6. The calibration method of a camera focal plane position and temperature relationship calibration device according to claim 1, characterized in that: The stripe plate (4) is a black and white stripe plate with equal width, and the contrast ratio of the black and white stripes is greater than 0.

98.

7. The calibration method of a camera focal plane position and temperature relationship calibration device according to claim 1, characterized in that: The temperature measurement control unit (7) comprises a temperature sensor and a heating plate.

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