A NOVEL ZOOM-LENS SPECTROGRAPH FOR A SMALL ASTRONOMICAL TELESCOPE

A novel astronomical spectrogpaph has been constructed using a zoom le ns as the focusing element. The linear dispersion is continuously vari able from 33 to 1272 Angstrom mm(-1) by the use of a grating turret wi th three gratings and a zoom lens with a focal length range of 50-250 mm. The absorption losses and chromatic aberration are shown to be acc eptable. The instrument has been used successfully on a 0.4-m Cassegra in telescope with a cooled CCD detector for a number of student projec ts, including the determination of the redshift of the brightest quasa r, 3C 273.