25 August 1998 4-m off-axis telescope
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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.
© (1998) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Gilberto Moretto, Jeff R. Kuhn, "4-m off-axis telescope", Proc. SPIE 3352, Advanced Technology Optical/IR Telescopes VI, (25 August 1998); doi: 10.1117/12.319311; https://doi.org/10.1117/12.319311

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