Optical system vacuum environment best focal plane preset method and optical system

Abstract

The application relates to a method for presetting the best focal plane of an optical system in a vacuum environment, belonging to the field of optics. The method uses optical design software to simulate the imaging quality of the optical system in a vacuum environment, and compares the changes of the focal length and the best image plane position. According to the magnification and other parameters of the focal length of the optical system in vacuum and non-vacuum states, a vacuum defocus compensation lens is designed, so that after the vacuum defocus compensation lens is integrated with the optical system in a normal temperature and pressure state, the best image plane position, the focal length and the imaging quality of the optical system are consistent with those in the vacuum environment. The focal plane presetting method provided by the application can realize accurate presetting of the vacuum focal plane position of the optical system in a normal temperature and pressure state, and the presetting precision and the correctness of the focal plane presetting can be verified through software simulation and laboratory measured data. The application can test and calibrate the best focal plane position in a normal temperature and pressure condition without relying on vacuum equipment, and the process is simple and the efficiency is higher.

Description

Technical Field

[0001] This invention belongs to the field of optical technology, specifically relating to a method for presetting the optimal focal plane of an optical system in a vacuum environment. Background Technology

[0002] An optical system consists of multiple sets of optical elements, and the spacing between these elements is one of the key design parameters. Once launched into orbit, the optical system operates in a vacuum environment. The spacing between the optical elements changes from air to vacuum, causing a significant change in the refractive index of the spacing. This alters the optimal imaging position of the optical system, severely impacting its imaging quality. Furthermore, the assembly and testing environments differ from the space environment. Therefore, aerospace optical systems often experience a focal plane deviation from the ground-calibrated position after launch, a phenomenon known as vacuum defocusing.

[0003] There are two common solutions to the problem of vacuum defocusing in aerospace optical systems. One is to calculate the optical system parameters to maximize the depth of focus. When the vacuum defocusing amount is less than the depth of focus, the optical system can maintain clear imaging in a vacuum. The other is to design a focusing mechanism to perform on-orbit focusing based on actual images, controlling the image plane position in real time to ensure image clarity after focusing. Both methods have limitations. The first method is only suitable for long focal length, small relative aperture optical systems and cannot meet the needs of short focal length, relatively aperture optical systems. The second method has two problems: the focusing mechanism increases system complexity and reduces system reliability; if the mechanism jams, the aerospace system will permanently lose its ability to achieve clear imaging. Furthermore, it significantly increases the system weight, increasing the cost and burden of space launches.

[0004] The vacuum focal plane preset method for aerospace cameras proposed in patent CN102679963A requires testing the MTF (Mean Transmission Factor) in both vacuum and non-vacuum conditions, and then assigning the non-vacuum MTF value to the MTF of the optical system in vacuum to complete the vacuum focal plane preset of the camera. The correctness of the focal plane preset is then verified in a vacuum environment. This method has three problems: First, the accuracy of the focal plane preset depends entirely on the MTF test results. Typically, the repeatability and dispersion of MTF test results are relatively large, making it difficult to guarantee the accuracy of the focal plane preset. Second, when the MTF measurement results have large dispersion, it is difficult to assign MTF values ​​in both vacuum and non-vacuum conditions. Third, testing the MTF in a vacuum environment requires a vacuum chamber and a high-precision light-transmitting window, resulting in poor practicality and versatility. Patent CN108072361A proposes a device and method for presetting the focal plane of a probe camera. This method first tests the overfocus curve of a star simulator at room temperature and pressure, then uses the star simulator to calibrate the optimal image plane position of the probe camera under room pressure. Next, the probe camera is placed in a vacuum environment, and the star simulator is placed at room temperature and pressure to calibrate the optimal image plane position of the probe camera under vacuum. Finally, based on the conjugate relationship between the star simulator and the probe camera, the defocus amount of the probe camera is calculated using the defocus amount of the star simulator. This method avoids movement of the probe camera's focal plane assembly and eliminates the need for repeated fixing and adjustment of the probe camera's focal plane assembly attitude. The key to this method lies in the calibration of the star simulator's overfocus curve, a complex process that requires extremely high calibration accuracy from the star simulator. Summary of the Invention

[0005] To address the technical problems of existing focal plane presetting methods for aerospace optical systems, such as cumbersome processes, low efficiency, and reliance on testing in a vacuum environment, this invention provides a method for presetting the optimal focal plane position of aerospace optical systems under vacuum conditions at room temperature and pressure. This method allows for testing and calibration of the optimal focal plane position under normal temperature and pressure conditions without relying on vacuum equipment, and is simpler and more efficient.

[0006] The technical solution adopted by this invention to solve the technical problem is as follows:

[0007] The present invention provides a method for presetting the optimal focal plane of an optical system under vacuum conditions, comprising the following steps:

[0008] Step 1: Use optical design software to simulate the imaging quality of the optical system under vacuum to obtain the vacuum defocusing amount and vacuum focal length;

[0009] Step 2: Calculate the vacuum magnification of the optical system under vacuum and non-vacuum conditions;

[0010] Step 3: Design a vacuum defocus compensation lens based on the vacuum magnification and optical system parameters;

[0011] Step 4: At room temperature and pressure, use optical design software and vacuum defocusing to simulate the imaging quality of the optical system at the optimal focal plane in a vacuum.

[0012] Step 5: Under normal temperature and pressure, use optical design software to simulate the compensation effect of the vacuum defocus compensation lens on vacuum defocus, and evaluate the compensation effect using the image quality and focal length of the optical system.

[0013] Step 6: Under normal temperature and pressure, calibrate the optimal focal plane position of the optical system without a vacuum defocus compensation lens installed;

[0014] Step 7: Under normal temperature and pressure, calibrate the optimal focal plane position of the optical system after installing the vacuum defocus compensation lens;

[0015] Step 8: Verify the relationship between the change in the optimal focal plane position and the amount of vacuum defocusing before and after the vacuum defocus compensation lens is installed, and verify the accuracy of the focal plane calibration and the correctness of the focal plane preset.

[0016] Step 9: Without installing the vacuum defocus compensation lens, test the imaging quality of the optical system in a vacuum to further verify the focal plane preset method and focal plane preset accuracy.

[0017] Furthermore, in step one, the vacuum defocus amount is Δd. A positive vacuum defocus amount indicates that the image plane is far away from the optical system, i.e., Δd>0; a negative vacuum defocus amount indicates that the image plane is close to the optical system, i.e., Δd<0.

[0018] Furthermore, in step two, the vacuum magnification is the ratio of the focal length of the optical system under vacuum to that under non-vacuum conditions, that is: β is the vacuum magnification, f' s f' is the vacuum focal length obtained in step one, and f' is the focal length of the optical system under normal temperature and pressure.

[0019] Furthermore, in step three, the magnification of the vacuum defocus compensation lens is 1 / β, where β is the vacuum magnification.

[0020] Furthermore, in steps six and seven, the calibration method is as follows: using a collimator to generate an infinitely distant target, and calibrating the focal plane position of the optical system based on the object-image conjugate relationship.

[0021] Furthermore, in step eight, the change in the optimal focal plane position is |d1-d2|, where d1 is the optimal focal plane position of the optical system without the vacuum defocus compensation lens obtained in step six, and d2 is the optimal focal plane position of the optical system after the vacuum defocus compensation lens is installed obtained in step seven.

[0022] Furthermore, in step eight, the correctness of the focal plane preset means that when the vacuum defocusing amount Δd>0, d2-d1>0; when the vacuum defocusing amount Δd<0, d2-d1<0; when the focal plane preset is correct, the actual focal plane preset direction is the same as the vacuum defocusing simulation direction.

[0023] Furthermore, in step nine, the focal plane preset accuracy refers to the absolute value of the difference between the absolute value of the change in the optimal focal plane position and the vacuum defocusing amount. The focal plane preset accuracy should be less than the half-depth of focus of the optical system, that is:

[0024] ||d1-d2|-Δd|≤2λ×(f' / D) 2

[0025] In the formula, d1 is the optimal focal plane position of the optical system without the vacuum defocus compensation lens obtained in step six, d2 is the optimal focal plane position of the optical system after the vacuum defocus compensation lens is installed obtained in step seven, Δd is the vacuum defocus amount, f' is the focal length of the optical system at normal temperature and pressure, D is the aperture of the optical system, and λ is the center wavelength of the optical system.

[0026] This invention discloses an aerospace application optical system. The focal plane of this aerospace application optical system is set using a preset method for the optimal focal plane of an optical system under vacuum conditions. The aerospace application optical system includes: a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a vacuum defocus compensation lens; the vacuum defocus compensation lens includes a seventh lens and an eighth lens; the half-apertures of the first to eighth lenses are 25.778mm, 22.030mm, 22.030mm, 18.420mm, 18.420mm, 23.218mm, 29.126mm, and 27.742mm, respectively; the materials of the first to eighth lenses are NSSK2_SCHOTT, NSK2_SCHOTT, F5_SCHOTT, F5_SCHOTT, NSK16_SCHOTT, NSK16_SCHOTT, SILICA_SPECIAL, and HK9L_CDGM, respectively.

[0027] The beneficial effects of this invention are:

[0028] This invention provides a method for presetting the optimal focal plane of an optical system under vacuum conditions. Using optical design software, it simulates the imaging quality of the optical system in a vacuum environment, comparing changes in focal length and optimal image plane position. Based on parameters such as the magnification of the optical system's focal length under vacuum and non-vacuum conditions, a vacuum defocus compensation lens is designed. This ensures that, after integration with the optical system at room temperature and pressure, the optimal image plane position, focal length, and imaging quality of the optical system remain consistent with those under vacuum conditions. Thus, after assembling the optical system, the focal plane presetting method provided by this invention allows for accurate presetting of the vacuum focal plane position of the optical system at room temperature and pressure. The accuracy and correctness of the presetting can be verified through software simulation and laboratory measurement data.

[0029] This invention enables the preset and calibration of the optimal image plane of an optical system under vacuum conditions during ground-based atmospheric pressure commissioning, ensuring clear imaging in a vacuum environment. Compared with existing technologies, this invention has the following advantages:

[0030] 1. This invention uses a vacuum defocus compensation lens to preset the optimal focal plane of the optical system in a vacuum environment, and can accurately determine whether the preset direction is correct and whether the focal plane preset accuracy is within half a focal depth.

[0031] 2. The focal plane presetting method proposed in this invention completes the entire focal plane presetting process at room temperature and pressure. At the same time, combined with computer modeling and simulation, it simplifies the complexity of the focal plane presetting process of the optical system. While improving efficiency, it also significantly reduces the requirements for the experimental environment, experimental equipment and personnel for the focal plane presetting work, and reduces calibration errors caused by environmental, equipment and human factors.

[0032] 3. The focal plane preset method proposed in this invention, with vacuum focal plane position, can also perform other image quality tests and simulations without relying on a vacuum environment. Attached Figure Description

[0033] Figure 1 This is a flowchart of a method for presetting the optimal focal plane of an optical system under vacuum conditions according to the present invention.

[0034] Figure 2 Optical path diagram for aerospace application optical systems.

[0035] Figure 3 This is the optical path diagram of the optical system after installing a vacuum defocus compensation lens. (Except for...) Figure 2 In addition to the six lenses, it also includes a set of vacuum defocus compensation lenses, which contain two optical lenses.

[0036] Figure 4MTF curves for aerospace optical systems under normal temperature and pressure.

[0037] Figure 5 The MTF curve of the aerospace application optical system at the vacuum defocusing position under normal temperature and pressure without the installation of a vacuum defocusing compensation lens.

[0038] Figure 6 The MTF curve of the aerospace application optical system at the vacuum defocusing position after installing a vacuum defocusing compensation lens at room temperature and pressure. Detailed Implementation

[0039] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0040] This invention provides a method for presetting the optimal focal plane of an optical system under vacuum conditions. This method can preset the optimal focal plane position of the optical system under normal temperature and pressure, and can also test the vacuum performance of the optical system under normal temperature and pressure.

[0041] See Figure 1 The present invention provides a method for presetting the optimal focal plane of an optical system under vacuum conditions, which specifically includes the following steps:

[0042] Step 1: Based on the optical system parameter data, simulate the imaging quality of the optical system under vacuum in optical design software to obtain the vacuum defocusing amount Δd and the vacuum focal length f'. s ;

[0043] The optical design software used in this invention can be software such as CODEV and ZEMAX, or other optical system design software.

[0044] The vacuum defocusing amount Δd can be positive or negative. Positive defocusing means that the image plane is far away from the optical system, i.e., Δd>0; negative defocusing means that the image plane is close to the optical system, i.e., Δd<0.

[0045] Step 2: Based on the vacuum focal length f' obtained in Step 1 s , and the focal length f' of the optical system under normal temperature and pressure, calculate the vacuum magnification β of the optical system under vacuum and non-vacuum conditions;

[0046] Wherein, the vacuum magnification β is the ratio of the focal length of the optical system under vacuum conditions to that under non-vacuum conditions, that is:

[0047]

[0048] For conventional optical systems, the vacuum magnification β is close to 1, which can be greater than or less than 1.

[0049] Step 3: Based on the vacuum magnification β from Step 2 and the field of view and aperture of the optical system, design a vacuum defocus compensation lens with a magnification of 1 / β.

[0050] Step 4: Input the vacuum defocusing amount Δd obtained in Step 1 into the optical design software to simulate the imaging quality of the optical system at the optimal focal plane in a vacuum under normal temperature and pressure.

[0051] Step 5: Under normal temperature and pressure, simulate the compensation effect of the vacuum defocus compensation lens on vacuum defocus using optical design software. Evaluate the compensation effect using the image quality and focal length of the optical system. Use the system MTF to evaluate the compensation effect. If the system MTF after configuring the defocus compensation lens differs significantly from the MTF of the optical system under vacuum and without compensation, the compensation effect is considered poor. In this case, the parameter data of the vacuum defocus compensation lens should be optimized until the compensation effect is satisfactory.

[0052] Step 6: At room temperature and pressure, use a collimator to generate an infinity target. Based on the object-image conjugate relationship, calibrate the optimal focal plane position d1 of the optical system without a vacuum defocus compensation lens.

[0053] Step 7: At room temperature and pressure, install the vacuum defocus compensation lens at the front of the optical system. Using the focal plane calibration method in Step 6, calibrate the focal plane position d2 of the optical system after installing the vacuum defocus compensation lens. This focal plane position d2 is the optimal focal plane position of the optical system under vacuum.

[0054] Step 8: Compare and verify the relationship between the absolute value of the change in the optimal focal plane position |d1-d2| and the magnitude and direction of the vacuum defocusing amount Δd, and verify the accuracy of the focal plane calibration and the correctness of the focal plane preset.

[0055] The correctness of the focal plane preset means that when the vacuum defocusing amount Δd>0, d2-d1>0; when the vacuum defocusing amount Δd<0, d2-d1<0; when the focal plane preset is correct, the actual focal plane preset direction is the same as the vacuum defocusing simulation direction.

[0056] Step 9: Without installing the vacuum defocus compensation lens, test the imaging quality of the optical system in a vacuum chamber to verify the focal plane preset method and focal plane preset accuracy in steps 1 to 8.

[0057] Here, focal plane preset accuracy refers to the difference between the preset focal plane position and the actual measured focal plane position under vacuum. In this invention, focal plane preset accuracy refers to the absolute value of the difference between the absolute value of the change in the optimal focal plane position |d1-d2| and the vacuum defocusing amount Δd. The focal plane preset accuracy should be less than the half-depth of focal length of the optical system. That is:

[0058] ||d1-d2|-Δd|≤2λ×(f' / D) 2

[0059] In the formula, f' is the focal length of the optical system under normal temperature and pressure, D is the aperture of the optical system, and λ is the center wavelength of the optical system.

[0060] Experimental Example 1

[0061] Under normal temperature and pressure, the main parameters of the aerospace application optical system are: focal length f' = 100mm, aperture D = 30mm, and center wavelength 650nm. The optical path of the aerospace application optical system is as follows: Figure 2 As shown, image quality is characterized by the optical system modulation transfer function (MTF), such as... Figure 4 As shown in Table 1, the aerospace application optical system consists of six lenses (lens 1, 2, 3, 4, 5, and 6).

[0062] Table 1

[0063]

[0064]

[0065] According to step one of the present invention, under vacuum, the focal length f' = 100 mm of the aerospace application optical system is changed to f' s =99.94mm, vacuum defocusing amount Δd=-0.131mm.

[0066] According to step two of the present invention, the vacuum magnification β of the aerospace application optical system under vacuum and non-vacuum conditions is:

[0067]

[0068] Because the depth of field in aerospace optical systems is:

[0069] l = 2λ × (f' / D) 2 = 2 × 650nm × (100 / 30) 2 =0.014mm

[0070] Therefore, the vacuum defocusing amount Δd = -0.131 mm is much greater than the system half-focus depth l = 0.014 mm.

[0071] When an aerospace optical system transitions from a non-vacuum state to a vacuum state, the system's imaging quality is severely degraded, and the system's MTF curve is as follows: Figure 5 As shown.

[0072] According to step three of the present invention, and simultaneously based on β = 0.9994 × The design magnification is 1.0006. × The vacuum defocus compensation lens consists of two lenses, and the specific parameters of the vacuum defocus compensation lens are shown in Table 2.

[0073] Table 2

[0074]

[0075] The vacuum defocus compensation lens is installed at the front end of the aerospace application optical system. The optical path of the aerospace application optical system after the vacuum defocus compensation lens is installed is as follows: Figure 3 As shown, after correction by the vacuum defocus compensation lens, the MTF curve of the aerospace application optical system at the vacuum defocus position of the image plane under normal temperature and pressure is as follows. Figure 6 As shown.

[0076] The above experiments show that the method for presetting the optimal focal plane of an optical system under vacuum conditions, as proposed in this invention, has good accuracy in focal plane presetting and good system imaging quality.

[0077] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only used to facilitate the description of this invention and to simplify the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the scope of protection of this invention.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. However, these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for presetting the optimal focal plane of an optical system under vacuum conditions, characterized in that, Includes the following steps: Step 1: Use optical design software to simulate the imaging quality of the optical system under vacuum to obtain the vacuum defocusing amount and vacuum focal length; Step 2: Calculate the vacuum magnification of the optical system under vacuum and non-vacuum conditions; The vacuum magnification is the ratio of the focal length of the optical system under vacuum to that under non-vacuum conditions, that is: β is the vacuum magnification, f' s f' is the vacuum focal length obtained in step one, and f' is the focal length of the optical system under normal temperature and pressure. Step 3: Design a vacuum defocus compensation lens based on the vacuum magnification and optical system parameters; Step 4: At room temperature and pressure, use optical design software and vacuum defocusing to simulate the imaging quality of the optical system at the optimal focal plane in a vacuum. Step 5: Under normal temperature and pressure, use optical design software to simulate the compensation effect of the vacuum defocus compensation lens on vacuum defocus, and evaluate the compensation effect using the image quality and focal length of the optical system. Step 6: Under normal temperature and pressure, calibrate the optimal focal plane position of the optical system without a vacuum defocus compensation lens installed; Step 7: Under normal temperature and pressure, calibrate the optimal focal plane position of the optical system after installing the vacuum defocus compensation lens; Step 8: Verify the relationship between the change in the optimal focal plane position and the amount of vacuum defocusing before and after the vacuum defocus compensation lens is installed, and verify the accuracy of the focal plane calibration and the correctness of the focal plane preset. Step 9: Without installing the vacuum defocus compensation lens, test the imaging quality of the optical system in a vacuum to further verify the focal plane preset method and focal plane preset accuracy. The focal plane preset accuracy refers to the absolute value of the difference between the absolute value of the change in the optimal focal plane position and the vacuum defocusing amount. The focal plane preset accuracy should be less than the half-depth of focus of the optical system, that is: ； In the formula, d1 is the optimal focal plane position of the optical system without the vacuum defocus compensation lens obtained in step six, d2 is the optimal focal plane position of the optical system after the vacuum defocus compensation lens is installed obtained in step seven, Δd is the vacuum defocus amount, f' is the focal length of the optical system at normal temperature and pressure, D is the aperture of the optical system, and λ is the center wavelength of the optical system.

2. The method for presetting the optimal focal plane of an optical system under vacuum conditions according to claim 1, characterized in that, In step one, the vacuum defocus amount is Δd. A positive vacuum defocus amount means that the image plane is far away from the optical system, i.e., Δd>0; a negative vacuum defocus amount means that the image plane is close to the optical system, i.e., Δd<0.

3. The method for presetting the optimal focal plane of an optical system under vacuum conditions according to claim 1, characterized in that, In step three, the magnification of the vacuum defocus compensation lens is 1 / β, where β is the vacuum magnification.

4. The method for presetting the optimal focal plane of an optical system under vacuum conditions according to claim 1, characterized in that, In steps six and seven, the calibration method is as follows: use a collimator to generate an infinitely distant target, and calibrate the focal plane position of the optical system based on the object-image conjugate relationship.

5. The method for presetting the optimal focal plane of an optical system under vacuum conditions according to claim 1, characterized in that, In step eight, the change in the optimal focal plane position is |d1-d2|, where d1 is the optimal focal plane position of the optical system without the vacuum defocus compensation lens obtained in step six, and d2 is the optimal focal plane position of the optical system after the vacuum defocus compensation lens is installed obtained in step seven.

6. The method for presetting the optimal focal plane of an optical system under vacuum conditions according to claim 1, characterized in that, In step eight, the correctness of the focal plane preset means that when the vacuum defocusing amount Δd>0, d2-d1>0; when the vacuum defocusing amount Δd<0, d2-d1<0; when the focal plane preset is correct, the actual focal plane preset direction is the same as the vacuum defocusing simulation direction.

7. An optical system for aerospace applications, characterized in that, The focal plane of this aerospace application optical system is set using a preset method for the optimal focal plane of an optical system in a vacuum environment, as described in any one of claims 1 to 6. The aerospace application optical system includes: a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a vacuum defocus compensation lens; the vacuum defocus compensation lens includes a seventh lens and an eighth lens; the half-apertures of the first to eighth lenses are respectively: The lens diameters are 25.778mm, 22.030mm, 22.030mm, 18.420mm, 18.420mm, 23.218mm, 29.126mm, and 27.742mm, respectively; the materials of the first to eighth lenses are NSSK2_SCHOTT, NSK2_SCHOTT, F5_SCHOTT, F5_SCHOTT, NSK16_SCHOTT, NSK16_SCHOTT, SILICA_SPECIAL, and HK9L_CDGM, respectively.

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