Return flat-free telescope alignment using sine condition test and deflectometry

Hyemin Yoo; Matthew B. Dubin

doi:10.1117/12.2571484

20 August 2020 Return flat-free telescope alignment using sine condition test and deflectometry

Hyemin Yoo, Matthew B. Dubin

Proceedings Volume 11488, Optical System Alignment, Tolerancing, and Verification XIII; 114880M (2020) https://doi.org/10.1117/12.2571484
Event: SPIE Optical Engineering + Applications, 2020, Online Only

Abstract

A common method for aligning a telescope in a laboratory setting is to place an interferometer at the focal plane and a return flat in collimated space. For some long wavelength systems that need to be aligned, or checked in the field, transporting an interferometer and a large flat are not practical. One example is a balloon borne terahertz telescope. In this paper, we present an alignment approach that does not require an interferometer or return flat. Instead of using a traditional approach, we are proposing the use of deflectometry and the sine condition test to determine the state of alignment. Both of these tests can be done with the same equipment which primarily consists of a camera and an LCD larger than the clear aperture of the telescope. Deflectometry is used to measure defocus, spherical, and on axis coma while the sine condition test measures linearly field dependent astigmatism. These are the low order aberrations that will be affected by misalignments, and their magnitudes and orientations can be used to align the system. We explain how this approach is used, show the results of simulations, and predict the expected performance of a telescope aligned with this approach.

Conference Presentation

Citation Download Citation

Hyemin Yoo and Matthew B. Dubin "Return flat-free telescope alignment using sine condition test and deflectometry", Proc. SPIE 11488, Optical System Alignment, Tolerancing, and Verification XIII, 114880M (20 August 2020); https://doi.org/10.1117/12.2571484

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