Cassegrain f/13.7 focus
Sandiford Cassegrain Echelle Spectrometer (SES)
Brian Roman is the McDonald Operations staff member responsible for SES. The Sandiford Cassegrain Echelle spectrograph is capable of R = 60,000 (5 km/s) resolution for two 27 micron pixels using a slit of one arcsecond. The spectrograph operates over the wavelength range from 3,700 Å to 11,000 Å with high efficiency. Wavelength coverage is continuous (no gaps between orders) for wavelengths less than 8,500 Å. Cross dispersion is provided by an LF5 prism in double pass; total spectral coverage in a single exposure is 1,000 Å to 1,500 Å, depending on central wavelength, greatest in the red and near infrared, and slit lengths up to 6 arcseconds are permitted. The spectrograph operates very close to true Littrow, and matches the free spectral range of a 23.2 gr/mm, R2 echelle grating to the long dimension of a Reticon 1200 x 400 CCD (RA2). Autoguiding is available using software optimized for guiding on a slit. A new set of slit apertures was just installed with significant improvement to the stability and reflectivity of the slit assembly.