Initially the primary mirror of the 3.6m Devasthal Optical Telescope is uncoated polished zerodur glass supplied by Lytkarino Optical Glass Factory, Russia/Advanced Mechanical and Optical Systems, Belgium. In order to do the aluminium coating on the primary mirror the coating plant including washing unit is installed near the telescope (extension building of telescope) by Hind High Vacuum (HHV) Bangalore, India. Magnetron sputtering technique is used for the coating. Several coating trials are done before the primary mirror coating; samples are tested for reflectivity, uniformity, adhesivity and finally commissioned. The primary mirror is cleaned, coated by ARIES. We present here a brief description of the coating plant installation, Mirror cleaning and coating procedures and the testing results of the samples.
A Faint Object Spectrograph and Camera (FOSC) is designed for the upcoming 360-cm optical telescope at
Devasthal. The design is based on other available similar instruments, having a collimator and camera unit. The
instrument converts F/9 beam from the telescope to a nearly F/4.3 beam. The collimator and camera optics
have 7 and 5 elements respectively with one aspheric component. The low dispersion glasses such as CaF2 and
PBM/PBL/FSL are used in order to minimize the chromatic aberrations. These glasses also have very good
transmission near blue wavelengths. The imaging is possible both in narrow and broad band filters up to the
field of view of ~ 14' x 14' or 19' along the diagonal. The spectroscopy can be performed in the wavelength
range 350 - 900 nm with several choices of grisms and slits with resolution in the range of 250 - 2000. The
theoretical spot sizes in the imaging mode are expected in the range 0:04" - 0:11". The overall transmission of
the camera and collimator optics is expected as ~ 75% at 350 nm and > 95% at wavelengths above 400 nm.
The total weight of the instrument as designed is around 350 kg. The instrument is currently planned to be
assembled in the Institute laboratory and to be commissioned on the 360-cm telescope in October 2013. The
design methodology, techniques, and expected performance of the optics are presented here.