LDSS-2 is a wide-field, multiaperture spectrograph recently installed on the 4.2-m William Herschel Telescope (WHT) in La Palma. The spectrograph has high system throughput (including the telescope and atmosphere) of -20% at blaze. The field of view is 11.5 arcmin, allowing it to produce spectra of several tens of objects simultaneously at spectral resolutions up to AE = 1000. The multiaperture masks are of exceptional quality and can be designed and manufactured rapidly at the telescope to improve target-mask registration and observational flexibility. This paper describes the instrument, the mask manufacturing facility, and the observing procedures required to acquire the target fields. Finally it presents examples of data obtained during the first commissioning run.

The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source• a link is made to the metadata record in Durham E-Theses• the full-text is not changed in any wayThe full-text must not be sold in any format or medium without the formal permission of the copyright holders. AbstractUnderstanding of the factors which limit the image quahty of a ground based telescope is still an interesting challenge despite the effort devoted to the problem since the early days of optical astronomy. At the Roque de los Muchachos observatory, on the island of La Palma (Canary Islands) this problem has been studied as part of a programme aimed to improve the optical performance of the biggest instrument at the observatory, the anglo-dutch William Herschel Telescope. The programme comprises a range of studies to investigate the possible factors deteriorating the image quality at the telescope. This thesis forms part of the meteorological studies of this programme and it is based on the data collected by a meteorological station recently installed at the observatory. In particular, phenomena such as wind direction, wind speed, pointing direction of the telescope dome relative to the wind direction, air and soil temperatures, relative internal/external temperatures, barometric pressure and humidity have been investigated and the relationship between these and the image quality at the telescope has been analyzed. The image quality is found to be particularly sensitive to the wind direction and the internal differences in temperatures. The season of the year also seems to have an influence on the image quality. In the conclusions, suggested further avenues of investigation are given.