NOAO Abstracts for SPIE Meeting in March
4-M Off-Axis Telescope
Authors:
G. Moretto and J. R. Kuhn
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 lense 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 4cm 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
4m telescope. The construction cost normalized by the effective
aperture of an on- and off-axis telescope are approximately equal.
[NOAO at the SPIE Meeting in
March]
National Optical Astronomy Observatories, 950 North Cherry Avenue,
P.O. Box 26732, Tucson, Arizona 85726 Phone: (520) 318-8000
Posted: 02Mar1998