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Proceedings Paper

4-m off-axis telescope
Author(s): Gilberto Moretto; Jeff R. Kuhn
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Paper Abstract

We describe here a possible off-axis configuration for a 4.0 m class telescope. The improvements in the scattered light performance of such a telescope in comparison to a conventional concentric design are described. We consider a modified Ritchey-Chretien (RC) design for the off-axis configuration which allows three possible instrument focal planes: a wide field (15') f/10, a `bare' polarimetric and coronagraphic narrow field f/10, and a moderate field (7') f/16 focal plane. The design uses a primary mirror that is an off-axis section of a conic quasi-paraboloid parent mirror that produces a 4.0 m off-axis section optimized for the f/16 configurations. Using this same primary we proceed with the f/10 optimization using a second dedicated secondary and a three element powered Fused-Silica lens corrector for the visible (U-J) that yields a near- diffraction limited 15 arcmin FOV. The bare, two reflection, f/10 focus provides comparable encircled energy performance over a 10' field if the secondary is not tilted and translated, or if it is translated (and tilted) by approximately 4 cm it achieves comparable core energy concentration over a 3' field. Mirror polish, optical mount and enclosure cost data suggest that the off-axis telescope would cost approximately 10% more to build than a conventional RC concentric 4 m telescope. The construction cost normalized by the effective aperture of an on- and off- axis telescope are approximately equal.

Paper Details

Date Published: 25 August 1998
PDF: 10 pages
Proc. SPIE 3352, Advanced Technology Optical/IR Telescopes VI, (25 August 1998); doi: 10.1117/12.319311
Show Author Affiliations
Gilberto Moretto, National Optical Astronomy Observatories (United Kingdom)
Jeff R. Kuhn, Michigan State Univ. and National Optical Astronomy Observatories (United States)

Published in SPIE Proceedings Vol. 3352:
Advanced Technology Optical/IR Telescopes VI
Larry M. Stepp, Editor(s)

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