Comparing optical test methods for a lightweight primary mirror of a space-borne Cassegrain telescope

Wei Cheng Lin, Shenq Tsong Chang, Zong Ru Yu, Yu Chuan Lin, Cheng Fong Ho, Ting Ming Huang, Cheng-Huan Chen

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


A Cassegrain telescope with a 450 mm clear aperture was developed for use in a spaceborne optical remote-sensing instrument. Self-weight deformation and thermal distortion were considered: to this end, Zerodur was used to manufacture the primary mirror. The lightweight scheme adopted a hexagonal cell structure yielding a lightweight ratio of 50%. In general, optical testing on a lightweight mirror is a critical technique during both the manufacturing and assembly processes. To prevent unexpected measurement errors that cause erroneous judgment, this paper proposes a novel and reliable analytical method for optical testing, called the bench test. The proposed algorithm was used to distinguish the manufacturing form error from surface deformation caused by the mounting, supporter and gravity effects for the optical testing. The performance of the proposed bench test was compared with a conventional vertical setup for optical testing during the manufacturing process of the lightweight mirror.

Original languageEnglish
Article number094014
JournalMeasurement Science and Technology
Issue number9
StatePublished - 1 Sep 2014


  • Cassegrain telescope
  • bench test
  • form error
  • gravity effect
  • lightweight mirror


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