The Low Dispersion Survey Spectrograph LDSS-2 is a common-user wide-field multiaperture spectrograph mounted at the Cassegrain focus of the 4.2m William Herschel Telescope. LDSS-2 is similar to LDSS-1 (a non-common-user instrument at the AAT) but has a different optical design to cope with the WHT's f/11 Cassegrain focal ratio and to provide better images to exploit the superior seeing on La Palma.
LDSS-2 obtains spectra of many objects simultaneously using custom-made multiaperture masks held in the focal plane. Its high throughput and excellent sky subtraction provide good signal-to-noise spectra of faint objects while its large field of view and multiobject capability provide a large multiplex advantage for statistical projects.