Determination of the best focus position of Formosat-8

Shih-Fang Liao; Tse Li; Shenq-Tsong Chang; Po-Ming Lin; Chun-Chieh Lien; Po-Hsuan Huang

doi:10.1117/12.3046841

10 January 2025 Determination of the best focus position of Formosat-8

Shih-Fang Liao, Tse Li, Shenq-Tsong Chang, Po-Ming Lin, Chun-Chieh Lien, Po-Hsuan Huang

Author Affiliations +

Proceedings Volume 13267, Earth Observing Missions and Sensors: Development, Implementation, and Characterization VI; 1326710 (2025) https://doi.org/10.1117/12.3046841
Event: Asia-Pacific Remote Sensing, 2024, Kaohsiung, Taiwan

Conference Poster

Abstract

The method for aligning the focal plane assembly (FPA) with the optical structure assembly (OSA) involves finding a position with optimal focus. The experimental setup includes a collimator with an effective focal length of 10,500 mm and a free aperture of 700 mm. An electronic ground support equipment (EGSE) is responsible for capturing the sensor signals. Processing these data allows the derivation of the contrast transfer function (CTF) value using a line-pair pattern. At the beginning of the FPA alignment process, the attitude and position of the FPA are controlled with the assistance of a hexapod positioning system (a six-axis robot). After determining the attitude and the best focus position of the FPA, shimming is performed to adjust the gap between the FPA and the OSA. Based on the shim thickness required at three orientations, shim rings with the relevant thickness are installed. Due to the uncertainties from shimming, shim ring thickness manufacturing tolerance, and the residual of the tip/tilt angle between the FPA and the OSA during alignment, it is crucial to confirm and fine-tune the shim ring thickness. Once the FPA is fixed on the OSA, moving the FPA for the through-focus measurement is not feasible. However, the distance between the primary mirror and the secondary mirror of the collimator is tunable. By adjusting this distance, the collimation beam can be modified to a converging or diverging beam, thereby changing the focal plane position. Consequently, through-focus measurements can still be conducted by moving the secondary mirror of the collimator.

(2025) Published by SPIE. Downloading of the abstract is permitted for personal use only.

Citation Download Citation

Shih-Fang Liao, Tse Li, Shenq-Tsong Chang, Po-Ming Lin, Chun-Chieh Lien, and Po-Hsuan Huang "Determination of the best focus position of Formosat-8", Proc. SPIE 13267, Earth Observing Missions and Sensors: Development, Implementation, and Characterization VI, 1326710 (10 January 2025); https://doi.org/10.1117/12.3046841

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