photograph of the 40-inch
telescope taken during the daytime with the dome open

MLO 40-inch Telescope


The principal research telescope at Mount Laguna Observatory (MLO) is a 40-inch (1.0-meter) reflector built by Astro Mechanics, Inc. The current primary mirror is actually 42-inches in diameter, and is the second primary installed in the telescope since its manufacture in 1966. However, since the telescope was originally named the "40-inch" reflector, the name stuck in spite of a slightly larger mirror size. The telescope has an off-axis equatorial mount. It was formerly located at the Prairie Observatory of the University of Illinois at Urbana-Champaign (UIUC), but was moved to MLO in 1981, and is now operated jointly by SDSU and UIUC. The telescope has f/7.6 and f/13.5 Cassegrain and f/33 coude foci.

Direct imaging at the f/7.6 Cassegrain focus with a 2048x2048 CCD accounts for about 50% of the scheduled observing time. This CCD was manufactured by Fairchild Imaging Systems (CCD447), and has an anti-reflection (AR) coating that boosts the Quantum Efficiency (QE) up to 98% at 5500 Angstroms. The CCD has 15 micron square pixels to provide a plate scale of 0.41 arcseconds per pixel for a field of view of 14 arcminutes on a side. Available filter sets include UBVRI, Stromgren 4-color, and DDO, as well as filters for selected spectral features.

Spectroscopy with the Illinois "white" spectrograph attached to the f/7.6 Cassegrain focus accounts for about 20% of the observing time. This instrument currently uses a Lick3 2660X448 CCD as its imaging detector. Three camera configurations (38 and 31 cm Nikon, and 15 cm Bowen Schmidt) and four gratings (300, 400, 831, and 1200 line per mm) are available. The most frequently used (relatively high) dispersions are 0.4 and 0.2 Angstroms per pixel in first-order red and second-order blue, respectively, with a resolution of 2.5 pixels FWHM.

An automated single-channel photoelectric photometer is scheduled for about 20% of the observing time. However, this instrument is usually mounted at the Cassegrain focus (on a side port) along with the "white" spectrograph for nearly simultaneous photometric and spectroscopic observations of relatively bright (10th magnitude) variable stars. The photometer employs a specially selected RCA 31034A GaAs photomultiplier tube. The most frequently used filters are the Stromgren uvby and customized near-infrared.

A Near-InfraRed IMager, NIRIM, built jointly with UIUC, is scheduled about 10% of the time. This camera employs a Rockwell 256x256 NICMOS3 array detector, along with cooled reimaging optics and filters. Plates scales range from 0.5 to 2.0 arcseconds per pixel to provide fields of view up to 8.5 arcminutes on a side. The useful spectral sensitivity range is from 0.8 to 2.5 microns. Commonly used filters are IJHK.

Currently under development is a High-Speed camera based upon an E2V 1024x1024 frame-transfer CCD. Sequences of exposures spaced at fractions of a second have been obtained to observe high-time frequency phenomena.


40-inch Manual On-Line
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