The 2.5 m Telescope of the Sloan Digital Sky Survey

TLDR

The paper describes the design, construction, and performance of the Sloan Digital Sky Survey 2.5‑m telescope at Apache Point Observatory. The telescope is a modified two‑corrector Ritchey‑Chrétien with a 2.5‑m primary, 1.08‑m secondary, interchangeable aspheric correctors, f/5 focal ratio, a 3° wide‑field CCD camera, fiber‑fed spectrographs, and design features such as low distortion for TDI imaging, high‑precision motion, and a wind‑baffle enclosure to maximize image quality. First light was achieved in May 1998, and the telescope entered regular survey operations in 2000.

Abstract

We describe the design, construction, and performance of the Sloan Digital Sky Survey Telescope located at Apache Point Observatory. The telescope is a modified two-corrector Ritchey-Chretien design which has a 2.5-m, f/2.25 primary, a 1.08-m secondary, a Gascoigne astigmatism corrector, and one of a pair of interchangeable highly aspheric correctors near the focal focal plane, one for imaging and the other for spectroscopy. The final focal ratio is f/5. The telescope is instrumented by a wide-area, multiband CCD camera and a pair of fiber-fed double spectrographs. Novel features of the telescope include: (1) A 3 degree diameter (0.65 m) focal plane that has excellent image quality and small geometrical distortions over a wide wavelength range (3000 to 10,600 Angstroms) in the imaging mode, and good image quality combined with very small lateral and longitudinal color errors in the spectroscopic mode. The unusual requirement of very low distortion is set by the demands of time-delay-and-integrate (TDI) imaging; (2) Very high precision motion to support open loop TDI observations; and (3) A unique wind baffle/enclosure construction to maximize image quality and minimize construction costs. The telescope had first light in May 1998 and began regular survey operations in 2000.