Study of off-axis telescope misalignment correction method using out-of-focus spot

Tian Siheng; Huang Yongmei; Xu Yangjie; Nan Xinyuan; Wu Qiongyan; Xiang Chunsheng; Tang Wei

doi:10.12086/oee.2023.230040

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Tian S H, Huang Y M, Xu Y J, et al. Study of off-axis telescope misalignment correction method using out-of-focus spot[J]. Opto-Electron Eng, 2023, 50(7): 230040. doi: 10.12086/oee.2023.230040

Citation:

Tian S H, Huang Y M, Xu Y J, et al. Study of off-axis telescope misalignment correction method using out-of-focus spot[J]. Opto-Electron Eng, 2023, 50(7): 230040. doi: 10.12086/oee.2023.230040

Study of off-axis telescope misalignment correction method using out-of-focus spot

1.
School of Electrical Engineering, Xinjiang University, Urumqi, Xinjiang 830046, China
2.
Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu, Sichuan 610209, China
3.
National Key Laboratory of Optical Field Manipulation Science and Technology, Chinese Academy of Sciences, Chengdu, Sichuan 610209, China
4.
Key Laboratory of Optical Engineering, Chinese Academy of Sciences, Chengdu, Sichuan 610209, China
5.
School of Electronic, Electrical and Communication Engineering, University of Chines Academy of Sciences, Beijing 100049, China

More Information

^*Corresponding author: huangym@ioe.ac.cn

Received Date 23 February 2023

Revised Date 10 April 2023

Accepted Date 11 April 2023

Published Date 20 August 2023

Abstract

Abstract

Off-axis reflector telescopes are mainly used in space astronomy observation and other related fields. The image quality of off-axis two-inversion telescopes is sensitive to lens misalignment and is more difficult to calibrate using a laser interferometer after misalignment in an operating environment. To address this challenge, this paper proposes a method that uses the out-of-focus spot map of the system for infinity point targets and uses the Swin-Transformer network to calculate the amount of lateral misalignment of the secondary mirror. Theoretical calculations were used to determine the camera defocus positions that could avoid the multi-solution problem, and simulations were used to investigate the effect of different defocus amounts on calibration accuracy. The trained network uses a frame of out-of-focus spot map of the out-of-tune system to perform the estimation of the amount of out-of-tune. Both simulation analysis and experimental results verify the effectiveness of the method, which can achieve high accuracy and fast correction of out-of-tune telescope systems in the working environment.
- optical imaging system /
- off-axis telescope /
- secondary mirror /
- defocused spot /
- neural Networks /
- quick adjustment

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References

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Overview

Overview

Off-axis reflector telescopes are mainly used in space astronomy observation and other fields. The imaging quality of off-axis two-reflection telescopes is sensitive to the lens misalignment. This makes the correction of out-of-tune telescope systems in the working environment hindered. To address this challenge, this paper proposes a method that uses the out-of-focus spot map of the system for infinity point targets and uses the Swin-Transformer network to calculate the amount of sub-mirror lateral misalignment. Through the derivation and analysis of the wavefront phase and point spread function formulas, it is pointed out that the use of a non-special location of the out-of-focus spot to avoid the focal spot can avoid the occurrence of multiple solutions so that the network can solve the system corresponding to the amount of misalignment from the spot morphology. In order to avoid the adverse effects of the special out-of-focus location, we observe the distribution range of the solution set and the pseudo-solution set through the Monte Carlo analysis method to determine whether the selected camera out-of-focus location is in a special position or not. We give the general implementation procedure of this method, according to which a reasonable amount of random transverse misalignment is applied to the simulation model secondary mirror in the simulation. The out-of-focus spot map is recorded to generate a dataset for network training. A test set is generated for validation, and the trained network can be used to estimate the amount of misalignment using one frame of the out-of-focus spot map of the misalignment system. The simulation shows that the out-of-focus amount is proportional to the correction accuracy within a certain out-of-focus range. Since this is an image-based method, we also tested the noise-resistance performance of the out-of-focus scheme with the highest accuracy. Finally, the predicted misalignment of the test sample set was verified by the experimental platform, and the mean prediction error of the eccentric misalignment was 0.0072 mm and the mean prediction error of the tilt misalignment was 0.0055° when compared with the real misalignment. The average computation time is less than 120 ms for a single computation when compared with the wavefront of the system before the misalignment. The simulation analysis and experimental results verify the effectiveness of the method, which can realize the misalignment telescope system in the working environment with high accuracy and fast correction.