CN113253416B - Telescope efficient and accurate focusing method based on star image ellipticity model - Google Patents

Telescope efficient and accurate focusing method based on star image ellipticity model Download PDF

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CN113253416B
CN113253416B CN202110521795.0A CN202110521795A CN113253416B CN 113253416 B CN113253416 B CN 113253416B CN 202110521795 A CN202110521795 A CN 202110521795A CN 113253416 B CN113253416 B CN 113253416B
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ellipticity
telescope
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袁祥岩
李博
李正阳
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Nanjing Institute of Astronomical Optics and Technology NIAOT of CAS
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B7/00—Mountings, adjusting means, or light-tight connections, for optical elements
    • G02B7/28—Systems for automatic generation of focusing signals
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B23/00—Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices

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Abstract

The invention discloses a telescope efficient and accurate focusing method based on an star image ellipticity model. The method relates to the field of focusing of optical systems, and solves the problems of low focusing precision, low adjusting speed and the like. The method comprises the following steps: (1) based on scientific CCD real shot star maps; (2) deducting image background noise; (2) restoring the gray distribution of the star image by using a principal component analysis method; (3) describing the point spread function form of the star image of the view field by using an star image ellipticity model; (4) randomly generating image plane position parameter seeds of a telescope system, substituting the image plane position parameter seeds into an optical system model, calculating a system evaluation function, and iteratively solving a difference value and a direction between a telescope focus position and a current scientific CCD position through an intelligent optimization algorithm; (5) instruct motor adjustment science CCD camera.

Description

Telescope efficient and accurate focusing method based on star image ellipticity model
Technical Field
The invention relates to the technical field of high-efficiency focusing of a telescope system, in particular to a high-efficiency and accurate focusing method of a telescope based on an image ellipticity model.
Background
In the observation process of a large telescope, optical image quality can be degraded due to factors such as optical element maladjustment, gravity change, environmental impact and the like, and the problem to be solved is to accurately position an optical focus before the optical image quality is compared. At present, optical focusing is widely applied to the fields of aerospace, military and the like.
Aiming at the problem of high-efficiency focusing of a telescope, the current common method comprises the following steps: firstly, defining star point image characteristics, such as: image sharpness function or star point size; and then adjusting the CCD camera to gradually and iteratively approach the highest point of the star point energy or the point with the minimum size. The method needs to continuously track and shoot the star map by using a CCD camera, calculates the star point characteristic value, is difficult to control the step length, has higher time cost and is difficult to ensure the precision.
Disclosure of Invention
The purpose of the invention is as follows: in view of the above problems, the invention provides a telescope high-efficiency and accurate focusing method based on an ellipsoid ellipticity model. The method measures field star point PSF of a scientific observation star map by using an ellipticity model, combines a telescope optical system defocusing adjustment simulation process, and carries out iterative solution by using a particle swarm optimization algorithm to finally realize high-precision focus adjustment of the optical system.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention relates to a telescope high-efficiency and accurate focusing method based on an ellipsoid ellipticity model, which comprises the following steps:
shooting an astronomical image;
denoising by a threshold method;
extracting high signal-to-noise ratio unsaturated star point signals, and recording star point gray level images and mass center coordinates as target sampling data;
step (4) carrying out gray distribution reduction on the extracted star point signals by using a principal component analysis method;
step 5, describing the star point signals by utilizing ellipticity models e1, e2 and R components to serve as a target function;
randomly generating defocus parameter seeds of optical system elements, inputting the current defocus parameter seeds into a model of a current detuning telescope optical system, acquiring a point spread function of a field of view where a sampling star point is located in the step (3) in a current defocus state through simulation, and obtaining ellipticity e1, e2 and R components under a simulation condition as a test function by using the method in the step (5);
step (7) calculating a current optimization evaluation function value according to the actually obtained target function and the current test function;
and (8): judging whether the current optimization evaluation function value is greater than or equal to a preset optimization evaluation threshold value;
and (9): and if the current optimization evaluation function value is smaller than the preset optimization evaluation threshold, setting the current test out-of-focus parameter seed as a target parameter, and adjusting the focus of the optical system according to the target parameter.
Further, the step (1) is taken by a scientific CCD camera during the observation of a telescope;
further, denoising is carried out in the step (2) by adopting a double-peak threshold method, the threshold value can be properly adjusted to be low, most of background noise is filtered, and all information of the star image is kept;
furthermore, the edge star image in the astronomical image is extracted as much as possible in the step (3), the adjustment direction of the CCD is easy to judge by an algorithm, three star points can be extracted in different fields of view, and the method can be used for detecting the parallel degree of the plane and the focal plane of the CCD camera;
further, the ellipticity model of step (5) adopts a KSB + (Kaiser Squires Broadhurst) model, which is proposed for studying the weak gravity lens effect. The model can be applied, and the ellipticity of a single star point is described by three parameters of e1, e2 and R.
Figure BDA0003064264430000021
Figure BDA0003064264430000022
Figure BDA0003064264430000023
Wherein I is 1,2, j is 1,2, I (x, y) is the single field star point spread function gray distribution,
Figure BDA0003064264430000024
Figure BDA0003064264430000025
further, the current optimization evaluation function in the step (7) is the difference between the objective function and the test function, and the formula is as follows:
var 1 ＝e 1 ；var 2 ＝e 2 ；var 3 ＝R
Figure BDA0003064264430000026
further, if the current optimization evaluation function value in the step (8) is greater than or equal to the preset optimization evaluation threshold, iteratively updating the current defocus parameter seeds of the optical system elements according to a group intelligent optimization algorithm to obtain updated current defocus parameter seeds, and returning to the step (6).
The invention has the following beneficial effects:
by denoising and sampling the star points and performing numerical description on ellipticity models e1, e2 and R components, the characteristics of defocused star points can be fully described, reverse optimization is performed in an optical model by using an intelligent optimization algorithm, and the characteristics are compared with actual star point characteristics, so that the displacement and the direction of the CCD camera which need to move can be accurately solved at one time, the time for shooting, calculating and adjusting the CCD camera is saved, and the model solving precision is high.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the related art, the drawings required to be used in the description of the embodiments or the related art will be briefly described below, and 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 these drawings without creative efforts.
FIG. 1 is a flow chart of the method of the present invention.
Fig. 2 is a schematic diagram of a scientific CCD camera star map.
Fig. 3 is a schematic diagram of star point acquisition (acquisition of star point PSF).
FIG. 4 is a comparison of before and after reduction of the star point by principal component analysis.
Fig. 5 is a schematic diagram of before and after the focus is adjusted by the star point.
Fig. 6 is a particle swarm optimization algorithm iteration completion curve.
Detailed Description
The present invention will be described in detail below. Aiming at the defects of the existing high-efficiency focusing method of the telescope, a novel automatic focusing method of the telescope is provided. Namely: and modeling the field-of-view star point PSF by using an ellipticity model, and performing iterative calculation on the optical system model by using an intelligent optimization algorithm until a high-precision imbalance numerical solution meeting the requirement is solved. The process flow of the present invention is shown in FIG. 1 and described in detail below.
Shooting an astronomical image; as shown in fig. 2, in this embodiment, step (1) is captured by a scientific CCD camera at the time of observation by a telescope.
Denoising by a threshold method; in this embodiment, a bimodal threshold method is specifically used for denoising, and the threshold value can be properly adjusted down, so that most of background noise is filtered, and all information of the star image is retained.
Step (3) extracting high signal-to-noise ratio unsaturated star point signals, and recording star point gray level images and centroid coordinates as target sampling data, as shown in fig. 3; in the step, edge star images in the astronomical image are extracted as much as possible, the adjustment direction of the CCD is easy to judge by an algorithm, and three star points can be extracted in different fields of view and can be used for detecting the parallel degree of the plane and the focal plane of the CCD camera.
And (4) carrying out gray distribution reduction on the extracted star point signals by using a principal component analysis method, as shown in fig. 4.
Step 5, describing the star point signals by utilizing ellipticity models e1, e2 and R components to serve as a target function; in this embodiment, the ellipticity model in this step is a KSB + (Kaiser Squires Broadhurst) model, which is proposed for studying the weak gravity lens effect. The model can be applied, and the ellipticity of a single star point is described by three parameters of e1, e2 and R.
Figure BDA0003064264430000041
Figure BDA0003064264430000042
Figure BDA0003064264430000043
Wherein I is 1,2, j is 1,2, I (x, y) is the single field star point spread function gray distribution,
Figure BDA0003064264430000044
Figure BDA0003064264430000045
and (6) randomly generating defocus parameter seeds of optical system elements, inputting the current defocus parameter seeds into a model of the current detuning telescope optical system, acquiring a point spread function of a field of view where the sampling star points are located in the step (3) in the current defocus state through simulation, and obtaining ellipticity e1, e2 and R components under the simulation condition as a test function by using the method in the step (5).
Step (7) calculating a current optimization evaluation function value according to the actually obtained target function and the current test function; in this embodiment, the current optimization evaluation function in this step is the difference between the objective function and the test function, and the formula is as follows:
var 1 ＝e 1 ；var 2 ＝e 2 ；var 3 ＝R
Figure BDA0003064264430000046
and (8): judging whether the current optimization evaluation function value is greater than or equal to a preset optimization evaluation threshold value; in this embodiment, if the current optimization evaluation function value is greater than or equal to the preset optimization evaluation threshold, iteratively updating the current defocus parameter seed of the optical system element according to the group intelligent optimization algorithm to obtain an updated current defocus parameter seed, and returning to the step (6).
And (9): and if the current optimization evaluation function value is smaller than the preset optimization evaluation threshold, setting the current test out-of-focus parameter seed as a target parameter, and adjusting the focus of the optical system according to the target parameter. The front and back cases of the star point adjusting focal length are shown in figure 5.
It should be noted that the group intelligent optimization algorithm in the present invention is not unique, and includes particle swarm optimization algorithm, simulated annealing algorithm, genetic algorithm, and other algorithms and their extension algorithms. The particle swarm optimization algorithm iteration completion curve is shown in fig. 6.
The principle of the invention is as follows:
(1) the change of the star image shape and size can represent the defocusing condition of the telescope optical system;
(2) the morphological change of the star image is accurately and sufficiently described by utilizing the component quantification of the ellipticity model.
In conclusion, the invention provides the telescope efficient and accurate focusing method based on the star image ellipticity model. The method measures field star point PSF of a scientific observation star map by using an ellipticity model, combines a telescope optical system defocusing adjustment simulation process, and carries out iterative solution by using a particle swarm optimization algorithm to finally realize high-precision focus adjustment of the optical system. The flatness research of the focal plane of the CCD camera and the optical system can be further carried out by utilizing the model.
The above description is only an example of the present invention, and is not intended to limit the present invention. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (6)

1. A telescope high-efficiency and accurate focusing method based on an star ellipticity model is characterized by comprising the following steps: the method measures field star point PSF of a scientific observation star map by using an ellipticity model, combines a telescope optical system defocusing adjustment simulation process, and carries out iterative solution by using a particle swarm optimization algorithm to finally realize high-precision focus adjustment of the optical system; the method comprises the following steps:
step 1: shooting an astronomical image;
step 2: denoising by a threshold method;
and step 3: extracting high signal-to-noise ratio unsaturated star point signals, and recording star point gray level images and mass center coordinates as target sampling data;
and 4, step 4: carrying out gray distribution reduction on the extracted star point signals by using a principal component analysis method;
and 5: describing the star point signals by utilizing ellipticity models e1, e2 and R components to serve as a target function; the ellipticity model adopts a KSB + model, and by applying the model, the ellipticity of a single star point is described by using three parameters of e1, e2 and R;
Figure FDA0003717815920000011
Figure FDA0003717815920000012
Figure FDA0003717815920000013
wherein I is 1,2, j is 1,2, I (x, y) is the single field star point spread function gray distribution,
Figure FDA0003717815920000014
Figure FDA0003717815920000015
step 6: randomly generating defocus parameter seeds of optical system elements, inputting the current defocus parameter seeds into a model of a current detuning telescope optical system, acquiring a point spread function of a field of view where a sampling star point is located in step 3 in a current defocus state through simulation, and obtaining ellipticity e1, e2 and R components under simulation conditions as test functions by using the method in step 5;
and 7: calculating a current optimization evaluation function value according to the actually obtained target function and the current test function;
and 8: judging whether the current optimization evaluation function value is greater than or equal to a preset optimization evaluation threshold value;
and step 9: and if the current optimization evaluation function value is smaller than the preset optimization evaluation threshold, setting the current test out-of-focus parameter seed as a target parameter, and adjusting the focus of the optical system according to the target parameter.
2. The method for efficiently and accurately focusing a telescope based on the star ellipticity model according to claim 1, wherein the method comprises the following steps: and step 1, shooting by a scientific CCD camera during observation by a telescope.
3. The method for efficiently and accurately focusing a telescope based on the star ellipticity model according to claim 1, wherein the method comprises the following steps: and 2, denoising by adopting a double-peak threshold method, reducing the threshold, filtering most background noise and keeping all information of the star image.
4. The method for efficiently and accurately focusing a telescope based on the star ellipticity model according to claim 1, wherein the method comprises the following steps: and 3, extracting edge star images in the astronomical image, easily judging the adjustment direction of the CCD by an algorithm, extracting a plurality of star points in different view fields, and detecting the parallel degree of the plane and the focal plane of the CCD camera.
5. The method for efficiently and accurately focusing a telescope based on the star ellipticity model according to claim 1, wherein the method comprises the following steps: in step 7, the current optimization evaluation function is the difference between the objective function and the test function, and the formula is as follows:
var 1 ＝e 1 ；var 2 ＝e 2 ；var 3 ＝R
Figure FDA0003717815920000021
6. the method for efficiently and accurately focusing a telescope based on the star ellipticity model according to claim 1, wherein the method comprises the following steps: and 8, if the current optimization evaluation function value is greater than or equal to the preset optimization evaluation threshold, iteratively updating the current defocus parameter seed of the optical system element according to the group intelligent optimization algorithm to obtain the updated current defocus parameter seed, and returning to execute the step 6.
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CN111796414A (en) * 2020-08-17 2020-10-20 中国科学院上海天文台 Telescope automatic focusing method based on arc length change between fixed stars
CN111985143A (en) * 2020-09-09 2020-11-24 中国科学院国家天文台南京天文光学技术研究所 Zernike polynomial decomposition-based active collimation method for full-field telescope

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CN106027911A (en) * 2016-07-12 2016-10-12 北京空间机电研究所 In-orbit focusing method of earth observation satellite-borne visible light transmission camera
CN106768876A (en) * 2016-11-29 2017-05-31 中国科学院长春光学精密机械与物理研究所 Space solar telescope wavefront sensing methods based on asterism hot spot
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CN111796414A (en) * 2020-08-17 2020-10-20 中国科学院上海天文台 Telescope automatic focusing method based on arc length change between fixed stars
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