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Proceedings Paper

Passive compensation of gravity flexure in optical instruments
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Paper Abstract

We present case studies on the application of passive compensation in two large astronomical instruments: the Gemini Near Infrared Spectrograph (GNIRS), including actual performance, and the NOAO Extremely Wide Field Infrared Mosaic (NEWFIRM) camera. Image motion due to gravity flexure is a problem in large astronomical instruments. We present solutions for two different cases using passive mechanical compensation of the optical train. For the Gemini Near Infrared Spectrograph (GNIRS), articulation of a single sensitive optic is used. Adjustable cantilevered weights, designed to respond to specific gravity components, are employed to drive tilt flexures connected to the collimator mirror. An additional requirement is that cryocooler vibration must not dynamically excite this mirror. Performance testing of the complete instrument shows that image motion has been satisfactorily compensated. Some image blur due to dynamic excitation by the cryocoolers was noted. A successful damping scheme has been developed experimentally. For the NOAO Extremely Wide Field Infrared Mosaic camera (NEWFIRM), the entire optical support structure is mechanically tuned to deflect and rotate precisely as a rigid body relative to the telescope focal plane. This causes the optical train to remain pointed at a fixed position in the focal plane, minimizing image motion on the science detector. This instrument is still in fabrication.

Paper Details

Date Published: 29 September 2004
PDF: 14 pages
Proc. SPIE 5495, Astronomical Structures and Mechanisms Technology, (29 September 2004); doi: 10.1117/12.550466
Show Author Affiliations
Edward A. Hileman, National Optical Astronomy Observatory (United States)
Jay Elias, National Optical Astronomy Observatory (United States)
Richard Joyce, National Optical Astronomy Observatory (United States)
Ronald Probst, National Optical Astronomy Observatory (United States)
Ming Liang, National Optical Astronomy Observatory (United States)
Earl Pearson, National Optical Astronomy Observatory (United States)


Published in SPIE Proceedings Vol. 5495:
Astronomical Structures and Mechanisms Technology
Joseph Antebi; Dietrich Lemke, Editor(s)

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