Scanning pentaprism measurements of off-axis aspherics

Peng Su, James H. Burge, Brian Cuerden, Jose Sasian, Hubert M. Martin

Research output: Chapter in Book/Report/Conference proceedingConference contribution

25 Scopus citations


The pentaprism test is based on the property of a paraboloidal surface where all rays parallel to the optical axis will go through its focal point. We have developed a scanning pentaprism system that exploits this geometry to measure off-axis paraboloidal mirrors such as those for the Giant Magellan Telescope primary mirror. Extension of the pentaprism test to off-axis mirrors requires special attention to field effects that can be ignored in the measurement of an axisymmetric mirror. The test was demonstrated on a 1. -m diameter off-axis mirror and proved to have about 50nm rms surface accuracy. This paper gives detailed performance results for the measurement of the 1.7 m mirror, and designs and analysis for the test of the GMT segments.

Original languageEnglish (US)
Title of host publicationAdvanced Optical and Mechanical Technologies in Telescopes and Instrumentation
StatePublished - 2008
EventAdvanced Optical and Mechanical Technologies in Telescopes and Instrumentation - Marseille, France
Duration: Jun 23 2008Jun 28 2008

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X


OtherAdvanced Optical and Mechanical Technologies in Telescopes and Instrumentation


  • Aspherics
  • Optical testing
  • Telescope

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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