  In this paper a preliminary design for a prime focus corrector to be mounted
at the Telescopio Nazionale Galileo (TNG) is presented. The telescope is
located on La Palma (Canary Islands) and has a primary mirror of 3.5 m with a
hyperbolic sag. Two optical designs have been considered in order to exploit
detectors with 1k x 1k and 2k x 2k pixels. Each design makes use of four
lenses, two of which are aspherical. The first lens diameters are,
respectively, of 140 mm and 320 mm for the two kind of detectors. For both
designs the telescope pupil is deliberately not re-imaged, and therefore it
will not be possible to insert a cold stop. For such a reason particular care
has been dedicated to the telescope thermal background study, in order to
optimise the baffling system. The optics is able to correct fields of 11' x 11'
and of 60'x60', depending on the design. It should be considered that the
particular geometry of the focal plane array mosaic does not permit a full
exploitation of the entire field, being based on a combination of four
detectors. The selected chips are HgCdTe manufactured by Rockwell, i.e. Hawaii
I in the 1k x 1k case and Hawaii II in the 2k x 2k case.

Astrophysics