NEEDS TO BE UPDATED The two conventional gratings (600 and 1200 L/mm) are blazed for 4400, A. The gratings are mounted with the ``blaze to collimator'' i.e., angle of incidence greater than angle of diffraction. The 2400,L/mmm grating is used in a similar configuration but this type of grating is not specifically blazed.
The rotation angle given in the tables can be determined or set using the circular scale and control knob subdivisions. 0on the scale corresponds to the grating being normal to the collimated beam. Because the angle between the collimated beam and camera axis is 23, a setting of +11.5puts zero order centrally in the camera field.
There are mechanical limits to the maximum grating rotation. The limits correspond to scale readings of +60and -30. At high angles of incidence (larger than 30) the projected width of the 58,mm wide gratings is less than the collimated bean and so some light loss occurs.
The following three tables give for each grating the dispersions and wavelengths for the centre and edges of the camera field for a range of angle settings.
OBSOLETE February 1997: The tables are obsolete, and not reproduced in the Latex version.