Multi-band stray light testing device and method

Abstract

The invention discloses a multiband stray light testing device and method, and the device comprises a light source assembly, an optical filter assembly, a testing assembly, a rotary table assembly, and a main control computer. Wherein the light source assembly comprises a light source, a stabilized voltage supply, an adjustable collimator and an optical fiber coupler; the stabilized power supply is connected with a light source circuit; the light source is in coupling connection with the adjustable collimator through the optical fiber coupler; the optical filter assembly is arranged opposite to the light emitting end of the adjustable collimator; the test assembly is arranged opposite to the light emitting end of the optical filter assembly; the rotary table assembly is fixedly connected with the adjustable collimator; and the main control computer is in circuit connection with the voltage-stabilized power supply and the adjustable collimator respectively. According to the device, stray light testing can be carried out aiming at a small spectrum analysis instrument in a laboratory, the analysis technology vacancy of the instrument of the type is filled, meanwhile, the structural complexity of the testing device is simplified, and the universality of a light source is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of multi-band stray light testing, and more particularly to a multi-band stray light testing device and method. Background Art

[0002] At present, it is very important to establish a stray light noise test and analysis system to measure the complete instrument after design and assembly to obtain the actual stray light level of the system, which is the key to finally determine and verify the real stray noise suppression ability of the instrument. It is stipulated internationally that the indicators used to evaluate the size of stray noise are the veiling glare index (VGI) and the point source transmittance (PST). These two indicators use different forms to describe the level of stray light on the image plane of the optical system, and they differ in definition, measurement method, test capability and application scope. The stray light index measures the level of stray light in the field of view of the system through the traditional surface source method (black spot method), and is often used to evaluate the stray noise level of infrared band spectral systems. The point source transmittance measures the system's ability to suppress stray light in the off-axis field of view through the point source method, which is suitable for evaluating the stray noise level of ultraviolet-visible-infrared band spectral systems. Therefore, PST is more suitable for stray light detection of small wide-band spectrometers in laboratories.

[0003] The invention patent application with publication number CN118758563A provides a stray light detection device and method. The traditional outer shelter structure cannot meet the stray light suppression requirements of large-field-of-view corona observations, and as the demand for the outer shelter to suppress the stray light performance it generates continues to increase, after the stray light generated by it is successfully weakened to a level below the ambient light level, the ambient light that can usually suppress the stray light of the outer shelter can no longer be effectively suppressed, and the original detection method can no longer measure the stray light intensity of the outer shelter. This invention patent application mainly improves this problem, mainly optimizing the stray light detection of large optical systems and solar light systems.

[0004] The invention patent application with publication number CN109238656A provides an ultra-large aperture stray light test light source and its control method. When performing stray light testing, the control system can control each universal adjustment device to achieve light beam adjustment for different emission angles; the control system can also control the switch and strength of each light source to achieve adjustment of the beam size and strength. It can be applied to stray light testing of optical systems, especially ultra-large aperture stray light testing. This invention patent application provides a test light source optimization method for large-volume and large-aperture optical systems. However, it is only applicable to large-aperture and large-volume optical systems, such as star sensors, hyperspectral systems, etc.

[0005] A stray light test system is disclosed in the utility model with announcement number CN214539272U. An integrating sphere structure is used to achieve uniform illumination, and the illumination brightness is adjusted through a current controller to meet the lens test needs for different spectra and brightness requirements. In combination with a large-size light trap, a high brightness contrast ratio of more than 1000:1 is achieved to ensure the accuracy of the test results. This utility model optimizes the illumination light source based on an integrating sphere and a large-size light trap structure. The test structure is bulky. Although it makes up for the brightness accuracy, it is not suitable for testing small laboratory spectrometers and other optical systems.

[0006] In the invention patent application with publication number CN112697397A, a DMD stray light detection device and detection method are provided. By designing an illumination system with continuously adjustable converged light spot size and an imaging system that can clearly image the DMD micromirror unit, combined with the flexible configuration of the DMD micromirror unit, the flexible configuration of the micromirror unit is utilized, and the distribution of stray light at different positions is calculated by testing the light intensity distribution under different micromirror unit combination modes. This invention patent application proposes flexible configuration accessories for stray light detection in the DMD field, and is not suitable for laboratory testing of other optical systems.

[0007] In summary, through the investigation of existing stray light technology, it can be known that the current stray light detection is mostly aimed at star sensors or other space optical systems in the aerospace field, mainly solving the problems of calibration and PST index correction before launch. However, the stray light PST index of small laboratory spectrometers is easily overlooked, and there is no complete, mature, and miniaturized laboratory detection system. In addition, the application of existing technologies is limited, the operation is complicated, and the versatility of the light source is poor (that is, only single-band measurement can be achieved), which cannot meet the laboratory's fast, small-volume, full-band PST measurement.

[0008] Therefore, how to implement stray light testing on a small laboratory spectrometer while simplifying the structural complexity of the test device and improving the versatility of the light source is an urgent problem that technicians in this field need to solve. Summary of the invention

[0009] In view of the above problems, the present invention provides a multi-band stray light testing device and method to at least solve some of the technical problems mentioned in the above background technology.

[0010] In order to achieve the above object, the present invention adopts the following technical solution:

[0011] In one aspect, the present invention provides a multi-band stray light testing device, comprising: a light source assembly, a filter assembly, a testing assembly, a turntable assembly and a main control machine;

[0012] The light source assembly includes a light source, a voltage-stabilized power supply, an adjustable collimator and a fiber coupler;

[0013] The voltage-stabilized power supply is connected to the light source circuit;

[0014] The light source is coupled to the adjustable collimator via the optical fiber coupler;

[0015] The filter assembly is installed facing the light emitting end of the adjustable collimator;

[0016] The test component is installed facing the light emitting end of the filter component;

[0017] The turntable assembly is fixedly connected to the adjustable collimator;

[0018] The main control machine is connected to the voltage-stabilized power supply and the adjustable collimator circuit respectively.

[0019] Furthermore, the filter assembly includes a filter wheel and a plurality of narrow-band filters of different wavelength bands;

[0020] The filter wheel is installed facing the light emitting end of the adjustable collimator;

[0021] The plurality of narrowband filters of different wavelength bands are fixed to a plurality of different hole positions of the filter wheel via threads and locking rings; and the main optical axis of each narrowband filter (10) is coupled to the main optical axis of the adjustable collimator (8).

[0022] Furthermore, the narrowband filter is a shortwave pass filter.

[0023] Further, the test assembly includes: an instrument to be tested and an imaging device;

[0024] The light entrance window of the instrument to be tested is in contact and coupled with the narrow-band filter;

[0025] The imaging device is installed at the imaging focal plane of the instrument under test.

[0026] Furthermore, the imaging device is a CCD camera that can capture images in the 180nm-900nm band;

[0027] Furthermore, the optical axes of the adjustable collimator, the narrow-band filter and the instrument to be tested are on the same straight line and at the same horizontal height.

[0028] Further, the turntable assembly includes a servo motor turntable and an ARM control device;

[0029] The adjustable collimator is fixed on the servo motor turntable through a threaded hole, and the main optical axis is adjusted based on a rotation angle of 0°;

[0030] The ARM control device is connected to the servo motor turntable circuit.

[0031] Furthermore, the ARM control device adopts an STM32 main control chip.

[0032] Furthermore, the main control machine adopts an FPGA chip.

[0033] On the other hand, the present invention further provides a multi-band stray light testing method, which is applied to the multi-band stray light testing device mentioned above, and comprises the following steps:

[0034] S1. According to the working band and imaging mode of the instrument to be tested, as well as the number of stray light test bands required, select multiple narrow-band filters of different bands, and fix them to multiple different holes of the filter wheel through threads and locking rings;

[0035] S2. After adjusting the output aperture of the adjustable collimator through the main control computer according to the entrance pupil area of ​​the instrument to be tested, the adjustable collimator is fixed on the servo motor turntable, and the 0° rotation angle is used as the main optical axis adjustment reference;

[0036] S3, adjusting the optical axes of the adjustable collimator and the filter wheel so that the optical axes of the adjustable collimator and the narrow-band filter are in the same straight line and at the same horizontal height as the optical axis of the instrument to be tested;

[0037] S4, turning on the voltage-stabilized power supply to provide the working voltage for the light source; after the light source is emitted, it passes through the optical fiber coupler and the adjustable collimator to generate a collimated parallel light source; filtering the wavelength band of the incident collimated parallel light source through multiple narrow-band filters, so that the filtered collimated parallel light source is incident on the instrument to be tested, so that the instrument to be tested is imaged at the imaging device;

[0038] S5, converting the imaging result into an irradiance value through the main control computer, recorded as E1;

[0039] S6. Divide the light intensity at the entrance pupil by the entrance pupil area of ​​the instrument under test to obtain the irradiance value at the entrance pupil, which is recorded as E2;

[0040] S7. Divide E1 by E2 to obtain the PST index value of the instrument under test when the incident angle is 0°;

[0041] S8, adjusting the servo motor turntable to rotate to a preset angle through the ARM control device, repeating steps S4 to S6, and obtaining the PST index value of the instrument under test at different angles;

[0042] S9, replacing multiple narrow-band filters of different wavelength bands, repeating steps S3 to S8, and obtaining the PST index value of the instrument under test at different wavelength bands and different angles.

[0043] It can be seen from the above technical solutions that, compared with the prior art, the present invention discloses a multi-band stray light testing device and method, which has the following beneficial effects:

[0044] The present invention can be used to carry out stray light testing on small-sized spectral analysis instruments in laboratories, thus filling the gap in analysis technology for such instruments.

[0045] The present invention adopts the form of a light source plus a filter wheel to realize stray light testing of multiple different bands without replacing different light sources, thereby realizing convenient operation of light source integration.

[0046] The present invention adopts a collimating lens with adjustable output aperture, which can be adapted to instruments to be tested with different apertures without replacing parts.

[0047] The traditional method uses the method of placing the instrument to be tested on a turntable, which increases the volume of the test system and the complexity of other matching components. However, the present invention sets a high-precision servo motor turntable in the light source part and adopts ARM+PID regulation to realize a test solution that combines miniaturization and high precision.

[0048] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0050] Figure 1 A schematic diagram of the structure of a multi-band stray light testing device provided in an embodiment of the present invention.

[0051] Among them: 1-light source assembly; 2-filter assembly; 3-test assembly; 4-turntable assembly; 5-main control machine; 6-light source; 7-voltage-stabilized power supply; 8-adjustable collimator; 9-filter wheel; 10-narrow-band filter; 11-instrument to be tested; 12-imaging device; 13-servo motor turntable; 14-ARM control device; 15-fiber coupler. DETAILED DESCRIPTION

[0052] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0053] The embodiment of the present invention discloses a multi-band stray light testing device, see Figure 1 As shown, it includes: a light source component 1, a filter component 2, a test component 3, a turntable component 4 and a main control machine 5; wherein:

[0054] The light source assembly 1 includes a light source 6, a voltage-stabilized power supply 7, an adjustable collimator 8 and a fiber coupler 15;

[0055] The voltage-stabilized power supply 7 is connected to the light source 6 circuit;

[0056] The light source 6 is coupled to the adjustable collimator 8 via a fiber coupler 15;

[0057] The filter assembly 2 is installed facing the light emitting end of the adjustable collimator 8;

[0058] The test component 3 is installed facing the light emitting end of the filter component 2;

[0059] The turntable assembly 4 is fixedly connected to the adjustable collimator 8;

[0060] The main control machine 5 is connected to the voltage-stabilized power supply 7 and the adjustable collimator 8 respectively.

[0061] Next, each of the above components is described in detail.

[0062] 1. Light source component 1:

[0063] The light source assembly 1 is used to emit a collimated parallel light source with an adjustable output aperture through a voltage-stabilized power supply 7, a light source 6, a fiber coupler 15 and an adjustable collimator 8; wherein:

[0064] The light source assembly 1 uses a continuous light source covering 180nm-900nm, which can realize the band test of the instrument to be tested 11 in this embodiment;

[0065] The voltage-stabilized power supply 7 is connected to the light source 6 circuit and is used to provide the light source 6 with a working voltage;

[0066] The light source 6 is coupled to the adjustable collimator 8 through the optical fiber coupler 15 to realize the collimation and beam expansion operation of the optical fiber emitted by the light source 6, so as to realize the emission of collimated parallel light source;

[0067] The light source 6 is a point light source. In a specific application, its wavelength requirement can be selected according to the detection requirements and the working wavelength of the instrument 11 to be tested.

[0068] 2. Filter assembly 2:

[0069] The filter assembly 2 is installed opposite to the light emitting end of the adjustable collimator 8; it helps to transmit the collimated parallel light source to the filter assembly 2, so that the wavelength band of the collimated parallel light source can be selected through the filter assembly 2; the filter assembly 2 includes a filter wheel 9 and a plurality of narrow-band filters 10 of different wavelength bands;

[0070] The filter wheel 9 is installed opposite to the light emitting end of the adjustable collimator 8, which helps the collimated parallel light source emitted by the adjustable collimator 8 to pass through the filter wheel 9;

[0071] Multiple narrowband filters 10 of different wavelength bands are fixed to multiple different holes of the filter wheel 9 through threads and lock rings; and the main optical axis of each narrowband filter 10 is coupled with the main optical axis of the adjustable collimator 8; based on this, the collimated parallel light source emitted by the adjustable collimator 8 can be selected in different wavelength bands through the narrowband filters 10 under different wavelength bands, and the integration of light sources under multiple wavelength bands is realized through the form of a wheel;

[0072] The hole diameter of the filter wheel 9 is 50 mm; the narrowband filter 10 is a short-wave pass filter covering the far ultraviolet band (180 nm-400 nm), the visible light band (400 nm-750 nm) and the near infrared band (750 nm-900 nm); since the embodiment of the present invention covers the far ultraviolet band (180 nm-400 nm), the stray light test in the ultraviolet band can be realized, filling the gap in the stray light test technology in the ultraviolet band. In specific applications, the specific filter band of the narrowband filter 10 can be selected according to the detection requirements and the working band of the instrument 11 to be tested.

[0073] 3. Test component 3:

[0074] The test component 3 is installed facing the light emitting end of the filter component 2, which helps to make the filtered collimated parallel light source incident on the test component 3 to achieve light source imaging; the test component 3 includes a test instrument 11 and an imaging device 12;

[0075] The instrument to be tested 11 is a small laboratory spectrometer. The light entrance window of the instrument to be tested 11 is directly contacted and coupled with the narrow-band filter 10. Since the light emitted by the adjustable collimator 8 is completely collimated light, the collimated light can fill the entire entrance pupil window of the instrument to be tested 11 through direct contact and tight coupling, and the incidence of ambient stray light can be avoided.

[0076] The imaging device 12 is installed at the imaging focal plane of the instrument under test 11; the imaging device 12 is a CCD camera that covers the 180nm-900nm band, and uses a CCD detection chip to collect the radiation brightness generated by the light source at the focal plane and transmit it to the main control machine 5 through a communication line.

[0077] The optical axes of the adjustable collimator 8, the narrowband filter 10 and the instrument to be measured 11 are on the same straight line and at the same horizontal height.

[0078] 4. Turntable assembly 4:

[0079] The turntable assembly 4 is fixedly connected to the adjustable collimator 8 and is used to adjust the angle of the adjustable collimator 8; the turntable assembly 4 includes a servo motor turntable 13 and an ARM control device 14; wherein:

[0080] The adjustable collimator 8 is fixed on the servo motor turntable 13 through a threaded hole, and the 0° rotation angle is used as the main optical axis adjustment reference;

[0081] The ARM control device 14 adopts the STM32 main control chip, which is connected to the servo motor turntable 13 line, and uses the STM32+PID method to control the rotation of the servo motor turntable 13, thereby driving the adjustable collimator 8 to rotate, thereby realizing high-precision, micro-angle rotation of the adjustable collimator 8, for example, the angle of each rotation can be controlled within ±10°.

[0082] 5. Main control machine 5:

[0083] The main control machine 5 is connected to the voltage-stabilized power supply 7, the adjustable collimator 8 and the ARM control device 14 respectively, and is used to control the voltage-stabilized power supply 7 to start, to adjust the output aperture of the adjustable collimator 8, and to control the ARM control device 14 to adjust the servo motor turntable 13;

[0084] The main control machine 5 uses an FPGA chip and its configuration circuit to achieve high-precision coordinated control of several components.

[0085] The embodiment of the present invention further provides a multi-band stray light testing method, which is applied to the multi-band stray light testing device mentioned above. The testing method comprises the following steps:

[0086] S1. According to the working band and imaging mode of the instrument under test 11 and the number of stray light test bands required, select multiple narrow-band filters 10 of different bands, and fix them to multiple different holes of the filter wheel 9 through threads and locking rings;

[0087] S2. After adjusting the output aperture of the adjustable collimator 8 through the main control machine 5 according to the entrance pupil area of ​​the instrument to be tested 11, the adjustable collimator 8 is fixed on the servo motor turntable 13, and the 0° rotation angle is used as the main optical axis adjustment reference;

[0088] S3, adjusting the optical axes of the adjustable collimator 8 and the filter wheel 9, so that the optical axes of the adjustable collimator 8 and the narrow-band filter 10 are in the same straight line and at the same horizontal height as the optical axis of the instrument to be tested 11;

[0089] S4, turn on the voltage-stabilized power supply 7 to provide the working voltage for the light source 6; after the light source 6 is emitted, it passes through the optical fiber coupler 15 and the adjustable collimator 8 to generate a collimated parallel light source; the wavelength band of the incident collimated parallel light source is filtered by a plurality of narrow-band filters 10, so that the filtered collimated parallel light source is incident on the instrument under test 11, so that the instrument under test 11 is imaged at the imaging device 12;

[0090] S5, converting the imaging result into an irradiance value through the main control computer 5, recorded as E1;

[0091] S6, dividing the light intensity at the entrance pupil by the entrance pupil area of ​​the instrument under test 11, and obtaining the irradiance value at the entrance pupil, which is recorded as E2;

[0092] S7, dividing E1 by E2 to obtain the PST index value of the instrument under test 11 under the condition of an incident angle of 0°;

[0093] S8, adjusting the servo motor turntable 13 to rotate to a preset angle through the ARM control device 14, repeating steps S4 to S6, and obtaining the PST index value of the instrument under test 11 at different angles;

[0094] S9, replace multiple narrow-band filters 10 of different wavelength bands, repeat steps S3 to S8, and obtain the PST index value of the instrument under test 11 at different wavelength bands and different angles.

[0095] In particular, in the above step S1 , the different wavelength bands of the narrowband filter 10 need to cover the entire wavelength band of the device under test 11 .

[0096] In particular, in the above step S2, the output aperture of the adjustable collimator 8 is adjusted to adjust the output spot size of the adjustable collimator 8; in a specific application, the output spot size of the adjustable collimator 8 is made larger than the entrance pupil area of ​​the instrument under test 11 to ensure that the entire field of view of the entrance pupil can be filled.

[0097] Particularly, in the above step S8, the range of the preset angle is ±10°.

[0098] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0099] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A multi-band stray light testing device, characterized in that: include: A light source assembly (1), a filter assembly (2), a test assembly (3), a turntable assembly (4) and a main control machine (5); The light source assembly (1) comprises a light source (6), a voltage-stabilized power supply (7), an adjustable collimator (8) and an optical fiber coupler (15); The voltage-stabilized power supply (7) is connected to the light source (6) circuit; The light source (6) is coupled to the adjustable collimator (8) via the optical fiber coupler (15); The optical filter assembly (2) is installed facing the light emitting end of the adjustable collimator (8); The test component (3) is installed facing the light emitting end of the filter component (2); The turntable assembly (4) is fixedly connected to the adjustable collimator (8); The main control machine (5) is connected to the voltage-stabilized power supply (7) and the adjustable collimator (8) respectively.

2. A multi-band stray light testing device according to claim 1, characterized in that: The filter assembly (2) comprises a filter wheel (9) and a plurality of narrow-band filters (10) of different wavelength bands; The filter wheel (9) is installed facing the light emitting end of the adjustable collimator (8); The plurality of narrowband filters (10) of different wavelength bands are fixed to a plurality of different hole positions of the filter wheel (9) via threads and locking rings; and the main optical axis of each narrowband filter (10) is coupled to the main optical axis of the adjustable collimator (8).

3. A multi-band stray light testing device according to claim 2, characterized in that: The narrowband filter (10) is a short-wave pass filter.

4. The multi-band stray light testing device according to claim 2, characterized in that: The test assembly (3) comprises: an instrument to be tested (11) and an imaging device (12); The light entrance window of the instrument to be tested (11) is in contact and coupled with the narrow-band filter (10); The imaging device (12) is installed at the imaging focal plane of the instrument under test (11).

5. The multi-band stray light testing device according to claim 4, characterized in that: The imaging device (12) is a CCD camera capable of collecting wavelengths covering 180nm-900nm.

6. The multi-band stray light testing device according to claim 4, characterized in that: The optical axes of the adjustable collimator (8), the narrow-band filter (10) and the instrument to be measured (11) are on the same straight line and at the same horizontal height.

7. The multi-band stray light testing device according to claim 1, characterized in that: The turntable assembly (4) comprises a servo motor turntable (13) and an ARM control device (14); The adjustable collimator (8) is fixed on the servo motor turntable (13) through a threaded hole, and a rotation angle of 0° is used as a reference for adjusting the main optical axis; The ARM control device (14) is connected to the servo motor turntable (13) by a circuit.

8. The multi-band stray light testing device according to claim 7, characterized in that: The ARM control device (14) adopts an STM32 main control chip.

9. The multi-band stray light testing device according to claim 1, characterized in that: The main control machine (5) adopts an FPGA chip.

10. A multi-band stray light testing method, characterized in that: The multi-band stray light testing device according to any one of claims 1 to 9 comprises the following steps: S1. According to the working band and imaging mode of the instrument to be tested (11), as well as the number of stray light test bands required, multiple narrow-band filters (10) of different bands are selected, and the filters are fixed to multiple different hole positions of the filter wheel (9) via threads and locking rings; S2. After adjusting the output aperture of the adjustable collimator (8) by the main control machine (5) according to the entrance pupil area of ​​the instrument to be tested (11), the adjustable collimator (8) is fixed on the servo motor turntable (13), and the main optical axis is adjusted with a rotation angle of 0° as the reference; S3, adjusting the optical axes of the adjustable collimator (8) and the filter wheel (9) so that the optical axes of the adjustable collimator (8) and the narrow-band filter (10) are in the same straight line and at the same level as the optical axis of the instrument to be tested (11); S4, turning on the voltage-stabilized power supply (7) to provide a working voltage for the light source (6); after the light source (6) is emitted, it passes through the optical fiber coupler (15) and the adjustable collimator (8) to generate a collimated parallel light source; filtering the wavelength band of the incident collimated parallel light source through the narrow-band filter (10), so that the filtered collimated parallel light source is incident on the instrument to be tested (11), so that the instrument to be tested (11) is imaged at the imaging device (12); S5, converting the imaging result into an irradiance value through the main control computer (5), recorded as E1; S6, dividing the light intensity at the entrance pupil by the entrance pupil area of ​​the instrument to be tested (11), and obtaining the irradiance value at the entrance pupil, which is recorded as E2; S7, dividing E1 by E2 to obtain the PST index value of the instrument under test (11) under the condition of an incident angle of 0°; S8, adjusting the servo motor turntable (13) to rotate a preset angle through the ARM control device (14), repeating steps S4 to S6, and obtaining the PST index value of the instrument under test (11) at different angles; S9, replacing multiple narrow-band filters (10) of different wavelength bands, and repeating steps S3 to S8 to obtain the PST index value of the instrument under test (11) at different wavelength bands and different angles.

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