Scanning pentaprism test for the GMT 8.4-m off-axis segments

Richard Allen; Peng Su; James H. Burge; Brian Cuerden; Hubert M. Martin

doi:10.1117/12.857901

19 July 2010 Scanning pentaprism test for the GMT 8.4-m off-axis segments

Richard Allen, Peng Su, James H. Burge, Brian Cuerden, Hubert M. Martin

Proceedings Volume 7739, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation; 773911 (2010) https://doi.org/10.1117/12.857901
Event: SPIE Astronomical Telescopes + Instrumentation, 2010, San Diego, California, United States

Abstract

The scanning pentaprism system for testing the 8.4 m off-axis segments for the Giant Magellan Telescope has recently been completed. The system uses a fiber source and a carriage mounted pentaprism to scan a 40 mm collimated beam across the surface of the segment under test. Since the scanning beam is parallel to the optical axis of the parent mirror, it comes to focus on a detector at the telescope's prime focus, where displacement of the spot is proportional to the slope error. A second collimated beam from a stationary reference pentaprism is used to compensate for any changes in the relative positions of the optical components during testing. The optical components are suspended over the mirror on a rail system that can be rotated so that scans can be made across any diameter of the segment. The test is capable of measuring wavefront slope errors to 1 μrad rms, adequate to verify that power, astigmatism, coma, and other low-order aberrations are small enough to be corrected easily at the telescope with the segment's active support system.

Citation Download Citation

Richard Allen, Peng Su, James H. Burge, Brian Cuerden, and Hubert M. Martin "Scanning pentaprism test for the GMT 8.4-m off-axis segments", Proc. SPIE 7739, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation, 773911 (19 July 2010); https://doi.org/10.1117/12.857901

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