  Near-infrared Imager Spectrometer and Polarimeter (NISP) is a camera, an
intermediate resolution spectrograph and an imaging polarimeter being developed
for upcoming 2.5m telescope of Physical Research Laboratory at Mount Abu,
India. NISP is designed to work in the Near-IR (0.8-2.5 micron) using a H2RG
detector. Collimator and camera lenses would transfer the image from the focal
plane of the telescope to the detector plane. The entire optics, mechanical
support structures, detector-SIDECAR assembly will be cooled to
cryo-temperatures using an open cycle Liquid Nitrogen tank inside a vacuum
Dewar. GFRP support structures would be used to isolate cryogenic system from
the Dewar. Two layer thermal shielding would be used to reduce the radiative
heat transfer. Molecular sieve (getter) would be used to enhance the vacuum
level inside Dewar. Magnet-reedswitch combination are used for absolute
positioning of filterwheels. Here we describe the mechanical aspects in detail.
