CN112229603A - Two-dimensional optical transfer function measuring device and method - Google Patents
Two-dimensional optical transfer function measuring device and method Download PDFInfo
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- CN112229603A CN112229603A CN202010927713.8A CN202010927713A CN112229603A CN 112229603 A CN112229603 A CN 112229603A CN 202010927713 A CN202010927713 A CN 202010927713A CN 112229603 A CN112229603 A CN 112229603A
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- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
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Abstract
A two-dimensional optical transfer function measuring device and method comprises a light source, a random coding plate, a microscope, a two-dimensional photoelectric detector, a computer and data acquisition and processing software; the light source illuminates the random coding plate as the target, mount the auxiliary lens in the light path according to the lens type to be measured and cooperate with the lens to be measured to image the target, the image is magnified by the microscope, record the image formed by the two-dimentional photodetector finally; and changing different random coded images for many times in one measurement, recording a plurality of images, performing Fourier transform on the recorded images and the known coded images, and finally calculating a two-dimensional optical transfer function containing all aperture directions in Fourier frequency domain scanning iteration. Based on a frequency domain scanning technology, the two-dimensional PTF is accurately measured while the two-dimensional MTF of high-precision and large-range frequency is measured; the instrument is used for lens detection, and plays a great promoting role in improving image quality.
Description
Technical Field
The invention relates to the field of imaging measurement of an Optical system, in particular to a device and a method based on a two-dimensional Optical Transfer Function (OTF), including a Modulation Transfer Function (MTF) and a Phase Transfer Function (PTF).
Background
The evaluation of the imaging quality of an optical system is always a matter of great concern in the optical field. Among many image quality evaluation methods, Modulation Transfer Function (MTF) can accurately, objectively and quantitatively evaluate the imaging quality of an optical system, and is generally recognized as the most effective and comprehensive method at present. As the demand for high quality, high resolution optical systems becomes more prevalent, optical designers and scientists are increasingly using MTF to characterize optical system related characteristics. No matter a large astronomical telescope, a satellite remote sensing imaging system, an unmanned aerial vehicle panoramic lens and a mobile phone camera are required to be detected before leaving a factory, and the MTF detection method is a necessary step for evaluating the optical performance of the large astronomical telescope, the satellite remote sensing imaging system, the unmanned aerial vehicle panoramic lens and the mobile phone camera. Moreover, the MTF has wide application range, and is not only used for evaluating the image quality of a diffraction limit system, a large aberration system and the like, detecting the image quality of an infrared imaging system, a panoramic imaging instrument and the like, but also used for evaluating other links of object information transmission. The emerging frequency domain scanning Fourier Ptychographic technology can realize the measurement of two-dimensional MTF with large field angle and high spatial frequency, and simultaneously can accurately measure the two-dimensional PTF, and also plays a great promoting role in the aspect of image quality improvement. Most of the existing MTF measuring instruments are digital image Fourier analysis methods based on knife edges, and have the defects of single measuring result direction and only one-dimensional result; the dispersion function deviation is susceptible to various errors; the high frequency band signal intensity is so small that the signal-to-noise ratio is too small; the PTF cannot be measured, and the cost is too high.
Disclosure of Invention
The technical problem to be solved by the present invention is to overcome the above-mentioned deficiencies of the prior art, and to provide a device and a method for directly measuring a two-dimensional optical transfer function in a frequency domain with high precision.
The technical solution of the invention is as follows:
a two-dimensional optical transfer function measuring device is characterized by comprising a light source, a random coding plate, a microscope, a two-dimensional photoelectric detector and a computer. For the infinite working distance lens, the light source, the random coding plate, the collimating lens, the lens to be detected, the microscope and the two-dimensional photoelectric detector are all fixed on the base, and are adjusted to be aligned with the optical axis and focused to form clear images. The light source evenly shine random coding board on, random coding board be located the preceding focal plane department of collimating mirror, by the collimating mirror image in infinity, microscope's multiplying power select in order to satisfy two-dimensional photoelectric detector's sampling theorem, two-dimensional photoelectric detector is located microscope back focal plane, the camera lens that awaits measuring become random coding board's image process the microscope enlarge the back by two-dimensional photoelectric detector receive, transmit to the computer that has corresponding software on. For the infinite-infinite conjugate lens to be measured, a relay lens is added behind the lens to be measured. For the lens to be measured with limited working distance, the random coding plate is directly placed at the position required by measurement without the collimating lens.
The random coding plate (2) is provided with N two-dimensional patterns which are designed or randomly generated according to the measurement requirements, the two-dimensional patterns comprise a plurality of randomly distributed star point patterns, radial star target patterns, randomly generated binary patterns, gray patterns and the like, the patterns are randomly arranged or designed according to the measurement requirements, the reciprocal of the size of a minimum unit or pixel in the patterns, namely the spatial frequency of the minimum unit or pixel in the patterns is higher than the optical transfer function cut-off frequency of the lens to be measured, and all the spatial frequencies required by the lens to be measured are covered.
The random coding plate is realized by etching and coating a film on a substrate material such as glass to form a pattern; patterning using a spatial light modulation device such as a DMD chip, liquid crystal, or the like; and methods of displaying, printing pictures, etc. using a display screen or LED array. The images on the N random coding plates can be replaced in one measurement, the images are directly controlled and converted by a computer by using a display screen or a spatial light modulation device, and the solid patterns are moved or the solid is replaced by a mechanical positioning device.
The method for measuring the lens to be measured by using the device is characterized by comprising the following steps:
1) preparation work: according to the F number of the lens to be measured and the wavelength required by measurement, determining the cut-off frequency of the lens to be measured, selecting the random coding plate which meets the condition that the spatial frequency is higher than the spatial cut-off frequency of the lens to be measured, selecting the microscope and the two-dimensional photoelectric detector according to the sampling theorem, and adjusting all the modules on the base to the central position to be on the optical axis and meet the imaging relation;
2) recording images, replacing the random coding plate after recording one image, and recording at most j images, wherein j is less than or equal to N;
3) performing iterative operation on the j images, wherein the iterative operation comprises the following steps:
a) initialization work: scaling the object and the image to the same pixel number, and then carrying out Fourier transform on each object and image to obtain frequency spectrums OF OF j corresponding objectsjSum image spectrum IFj；
b) In the first iteration, the OTF (x, y) is initially guessed to be a two-dimensional 0 matrix;
let n be 1, n is defined as,
let j equal 1, update OTF, formula as follows:
wherein, represents a complex conjugate operation, | OFj|maxIs the maximum of the intensity of the object spectrum;
j equals j +1, and the next picture is calculated until the j pairs of images are calculated;
c) calculating the similarity between the n +1 th time and the nth time, and entering the step 4 after the iteration is completed when the similarity reaches 1), or entering the next iteration;
4) and obtaining the Modulation Transfer Function (MTF) of the lens to be measured by taking the intensity of the OTF, and simultaneously taking the phase of the OTF as the Phase Transfer Function (PTF).
The invention has the following technical effects:
1. the invention adopts a brand-new frequency domain scanning measurement principle, removes the convolution of a known target by utilizing iterative computation based on computational optics, and directly measures the imaging quality of the system in the frequency domain, because OTF measurement starting from spatial frequency has no principle error, the principle has more advantages, and PTF measurement which is difficult to realize by a traditional instrument is also realized;
2. the OTF two-dimensional data measurement is realized, and compared with the traditional instrument, only one-dimensional data such as meridian or sagittal direction and the like can be obtained;
3. has the advantages of simple structure, convenient operation and quick measurement.
Drawings
FIG. 1 is a schematic diagram of a two-dimensional optical transfer function measuring device according to the present invention;
in the figure: 1-a light source, 2-a random coding plate, 3-a collimating mirror, 4-a lens to be tested, 5-a microscope, 6-a two-dimensional photoelectric detector, 7-a base and 8-a computer with corresponding software;
FIG. 2 is four examples of patterns (A) (B) (C) (D) on a random encoder board;
fig. 3 is a flow chart of the present invention for calculating an optical transfer function using an iterative algorithm based on the frequency domain iterative principle.
Detailed Description
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Referring to fig. 1, it can be seen from the figure that the two-dimensional optical transfer function measuring device of the present invention includes a light source 1, a random encoding plate 2, a collimating lens 3, a lens 4 to be measured, a microscope 5, a two-dimensional photoelectric detector 6, and a computer 8. For the lens with infinite working distance, the light source 1, the random coding plate 2, the collimating lens 3, the lens 4 to be measured, the microscope 5 and the two-dimensional photoelectric detector 6 are all fixed on the base 7 and adjusted to be aligned with each other until the optical axis is aligned and the focusing is performed until the imaging is clear. Light source 1 evenly shine random coding board 2 on, random coding board 2 be located collimating mirror 3's preceding focal plane department, by collimating mirror 3 image in infinity, microscope 5's multiplying power select with the sampling theorem that satisfies two-dimensional photoelectric detector 6, two-dimensional photoelectric detector 6 is located microscope 5's back focal plane, the camera lens 4 that awaits measuring become random coding board 2's image warp microscope 5 enlarge after by two-dimensional photoelectric detector 6 receive, transmit to the computer 8 that has corresponding software on. For the lens 4 to be measured with limited working distance, the collimating lens 3 is not needed, and the random coding plate 2 is directly placed at the position required by measurement.
The random coding plate 2 is provided with N two-dimensional patterns designed or randomly generated according to the measurement requirements, the two-dimensional patterns comprise a plurality of randomly distributed star point patterns, radial star target patterns, randomly generated binary patterns, gray patterns and the like, the patterns are randomly arranged or designed according to the measurement requirements, the reciprocal of the size of the minimum unit or pixel in the pattern, namely the spatial frequency of the minimum unit or pixel in the pattern is higher than the optical transfer function cut-off frequency of the lens 4 to be measured, and all the spatial frequencies required by the lens 4 to be measured are covered. The random access code plate 2 is shown in fig. 2.
The random coding plate 2 is realized by etching and coating a film on a substrate material such as glass to form a pattern; patterning using a spatial light modulation device such as a DMD chip, liquid crystal, or the like; and methods of displaying, printing pictures, etc. using a display screen or LED array. The images on the N random encoding plates 2 can be replaced in one measurement, the images are directly controlled and converted by a computer by using a display screen or a spatial light modulation device, and the solid patterns are moved or the solid is replaced by a mechanical positioning device.
In example 1:
aiming at common photographing, monitoring and industrial imaging lenses, namely infinite-finite conjugate lenses to be detected, the light source 1, the random coding plate 2, the collimating lens 3, the lens 4 to be detected, the microscope 5 and the two-dimensional photoelectric detector 6 are all fixed on the base 7 and adjusted to be aligned with each other until the optical axis is aligned and the focusing is carried out until the imaging is clear. The light source 1 with consistent wavelength is selected according to the measurement requirement wavelength, the light source 1 is uniformly irradiated on the random coding plate 2, the random coding plate 2 is positioned at the front focal plane of the collimating mirror 3, the collimating mirror 3 images at infinity, the cut-off frequency of the random coding plate is determined according to the F number of the lens 4 to be measured and the measurement requirement wavelength, the cut-off frequency is 1/(wavelength F number), so that the random coding plate 2 with the spatial frequency (the reciprocal of the size) higher than the cut-off frequency of the lens 4 to be measured is selected, the magnification times of the microscope 5 and the sampling frequency of the two-dimensional photoelectric detector 6 are required to be more than twice of the cut-off frequency of the lens 4 to be measured, and the sampling theorem is met. The two-dimensional photoelectric detector 6 is positioned on the back focal plane of the microscope 5, and the image of the random coding plate 2 formed by the lens 4 to be detected is received by the two-dimensional photoelectric detector 6 after being amplified by the microscope 5.
The measurement process after the installation and adjustment is as follows:
1) recording images, replacing the random coding plate 2 after recording one image, and recording at most j images, wherein j is less than or equal to N;
2) performing iterative operation on the j images, wherein the iterative operation comprises the following steps:
a) initialization work: scaling the object and the image to the same pixel number, and then carrying out Fourier transform on each object and image to obtain frequency spectrums OF OF j corresponding objectsjSum image spectrum IFj；
b) In the first iteration, the OTF (x, y) is initially guessed to be a two-dimensional 0 matrix;
let n be 1, n is defined as,
let j equal 1, update OTF, formula as follows:
wherein, represents a complex conjugate operation, | OFj|maxIs the maximum of the intensity of the object spectrum;
j equals j +1, and the next picture is calculated until the j pairs of images are calculated;
c) calculating the similarity between the n +1 th time and the nth time, and entering the step 4 after the iteration is completed when the similarity reaches 1), or entering the next iteration;
3) the Modulation Transfer Function (MTF) of the lens 4 to be measured can be obtained by taking the intensity of the OTF, and the phase of the OTF is taken as the Phase Transfer Function (PTF).
In example 2:
for the lens 4 to be measured with finite working distance, i.e. finite-finite conjugate, the random code plate 2 is directly placed at the position required by the measurement of the lens 4 to be measured without the collimator lens 3. The subsequent measurement steps correspond to example 1.
In example 3:
for the infinite-infinite conjugate lens 4 to be measured, such as a telescope, a relay lens is added behind the lens 4 to be measured, the whole of the two is equivalent to the lens 4 to be measured in the embodiment 1, and other measuring steps are consistent with those in the embodiment 1.
In example 4:
and measuring the off-axis OTF of the lens 4 to be measured, and rotating the whole consisting of the lens 4 to be measured, the microscope 5 and the two-dimensional photoelectric detector 6 by taking the pupil center of the lens 4 to be measured as an original point. The other measurement steps were in accordance with example 1.
Claims (6)
1. A two-dimensional optical transfer function measuring apparatus, characterized by comprising: the device comprises a light source (1), a random coding plate (2), a microscope (5), a two-dimensional photoelectric detector (6) and a computer (8); the random coding plate (2), the lens (4) to be detected, the microscope (5) and the two-dimensional photoelectric detector (6) are sequentially arranged along the output direction of the light source (1) along the same optical axis; light source (1) shine random coding board (2) on, the multiplying power of microscope (5) satisfy two-dimensional photoelectric detector's (6) sampling theorem, two-dimensional photoelectric detector (6) be located microscope (5) back focal plane, the camera lens (4) that await measuring become random coding board (2) the image process microscope (5) enlarge the back by two-dimensional photoelectric detector (6) receive, transmit to computer (8) on.
2. A two-dimensional optical transfer function measuring device according to claim 1, wherein the random encoding plate (2) has N two-dimensional patterns, which are randomly arranged or designed according to the measurement requirements, and include randomly distributed star point patterns, radial star target patterns, randomly generated binary patterns, randomly generated gray patterns, and patterns generated by sine and cosine intensity variations; the reciprocal of the size of the minimum unit or pixel in the two-dimensional pattern is the spatial frequency of the minimum unit or pixel, the spatial frequency is higher than the optical transfer function cut-off frequency of the lens to be measured (4), and the spatial frequency required by all the measurements of the lens to be measured (4) is covered.
3. A two-dimensional optical transfer function measuring device according to claim 1, wherein the random code plate (2) is realized by etching, coating and patterning a substrate material such as glass; patterning using a spatial light modulation device such as a DMD chip, liquid crystal, or the like; and methods of displaying, printing pictures, etc. using a display screen or an LED array; the images on the N random coding plates (2) can be replaced in one measurement, the images are directly controlled and converted by a computer by using a display screen or a spatial light modulation device, and the solid patterns are moved or the solid is replaced by a mechanical positioning device.
4. A two-dimensional optical transfer function measuring device according to claim 1, wherein the light source (1), the random code plate (2), the lens (4) to be measured, the microscope (5) and the two-dimensional photodetector (6) are mounted on a base (7).
5. A two-dimensional optical transfer function measuring device according to any one of claims 1-4, characterized in that a collimating mirror (3) is further provided between the random code plate (2) and the lens (4) to be measured, and the random code plate is located at the front focal plane of the collimating mirror.
6. The method for measuring a lens (4) under test according to any one of claims 1-5, characterized in that the measuring method comprises the following steps:
1) preparation work: according to the F number of the lens (4) to be measured and the wavelength required by measurement, determining the cut-off frequency, and selecting a random coding plate (2) meeting the condition that the spatial frequency is higher than the spatial cut-off frequency of the lens to be measured;
2) recording images, replacing the random coding plate (2) after recording one image, and recording at most j images, wherein j is less than or equal to N;
3) performing iterative operation on the j images, wherein the iterative operation comprises the following steps:
a) initialization work: scaling the object and the image to the same pixel number, and then carrying out Fourier transform on each object and image to obtain frequency spectrums OF OF j corresponding objectsjSum image spectrum IFj；
b) In the first iteration, the OTF (x, y) is initially guessed to be a two-dimensional 0 matrix;
let n be 1, n is defined as,
let j equal 1, update OTF, formula as follows:
wherein, represents a complex conjugate operation, | OFj|maxIs the maximum of the intensity of the object spectrum;
j equals j +1, and the next picture is calculated until the j pairs of images are calculated;
c) calculating the similarity between the n +1 th time and the nth time, and entering the step 4 after the iteration is completed when the similarity reaches 1), or entering the next iteration;
4) and obtaining the modulation transfer function of the lens (4) to be measured by taking the intensity of the OTF, and simultaneously taking the phase of the OTF as the phase transfer function.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113804681A (en) * | 2021-09-13 | 2021-12-17 | 广州辰达精密光电科技有限公司 | Lens quality evaluation method and device based on intelligent optics |
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2020
- 2020-09-07 CN CN202010927713.8A patent/CN112229603A/en not_active Withdrawn
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| JPH04313042A (en) * | 1991-01-22 | 1992-11-05 | Nikon Corp | Otf measuring apparatus |
| CN1963430A (en) * | 2006-12-08 | 2007-05-16 | 中国科学院上海光学精密机械研究所 | Measuring apparatus and method for modulation transfer function |
| CN101813558A (en) * | 2010-04-29 | 2010-08-25 | 苏州大学 | Device for measuring modulation transfer function of optical system and method thereof |
| JP2018107541A (en) * | 2016-12-26 | 2018-07-05 | キヤノン株式会社 | Image processing apparatus, imaging device, image processing method, and image processing program |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113804681A (en) * | 2021-09-13 | 2021-12-17 | 广州辰达精密光电科技有限公司 | Lens quality evaluation method and device based on intelligent optics |
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Application publication date: 20210115 |