Active compensation of flexure on the High-Resolution Optical Spectrograph for Gemini

Paolo D'Arrigo, Francisco Diego, David D. Walker

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

4 Citations (Scopus)


Gravity-induced flexure has been a long-standing challenge in Cassegrain spectrographs at 4-meter class telescopes; it is the more so at the scale of 8-meter telescopes. This is of particular concern for the Gemini high resolution optical spectrograph, which will be Cassegrain-mounted for its routine mode of operation. In this paper we address the general flexure problem, and how to solve it with the use of active optics. We also present the results of an experimental active flexure compensation system for the ISIS (intermediate- dispersion spectroscopic and imaging system) spectrograph on the 4.2 m William Herschel Telescope (WHT). This instrument, called ISAAC (ISIS spectrograph automatic active collimator), is based on the concept of active correction, where spectrum drifts, due to the spectrograph flexing under the effect of gravity, are compensated by the movement of an active optical element (in this case a fine steering tip-tilt collimator mirror). The experiment showed that active compensation can reduce flexure down to less than 3 micrometer over four hours of telescope motions, dramatically improving the spectrograph performance. The results of the experiment are used to discuss a flexure compensation system for the high resolution optical spectrograph (HROS) for the 8 m Gemini telescope.

Original languageEnglish
Title of host publicationOptical Telescopes of Today and Tomorrow
EditorsArne L. Ardeberg
Number of pages12
ISBN (Print)0819422681, 9780819422682
Publication statusPublished - 21 Mar 1997
Externally publishedYes
EventOptical Telescopes of Today and Tomorrow - Landskrona/Hven, Sweden
Duration: 29 May 19962 Jun 1996

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


ConferenceOptical Telescopes of Today and Tomorrow
Internet address


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