Here are some practical tips for observing with the Cross-disperser.
Focusing is best done with a R1200Y grating and the Copper Neon lamp.
There is no software to extract the orders on-line, however,
FOS software can be used afterwards to extract about three
orders. This is easily done because they are straight
lines (see figure 4.10).
Wavelength calibration is rather difficult due to the lack of a
lamp with wide wavelength coverage. A planetary nebula (such as
NGC 7027) can be used. Figure 4.10 shows maps of the CCD images for
grating angles of 60.75 , 60 and 59.25 with enough
lines even in the ultraviolet. See also Table 3.3.
Do not use a grating angle outside the range 60 1 ,
otherwise the efficiency falls off rapidly.
The FOS-dekker is best used, in order to ensure that there is no
overlap of orders in the spatial direction. It has a 24.5 arcsec
long slit which is ideal for use with the cross-disperser.