You may also have to change the arc lamp. Currently there is only provision for one arc lamp at a time, which is mounted (manually) in a `car headlamp' affair which is shone onto the Naysmyth flat. To change the arc lamps, disconnect the power cord, pull back the brass clip and remove the wooden block holding the arc lamp. Unscrew the white plaster screw holding the lamp in the block and carefully put the arc lamp back in its box-the lamps are expensive and easily broken. Reverse the operation to replace with a new arc lamp. Make sure the calibration lamp is on the optical axis of the Nasmyth focus (is marked faintly in black marker on the optical table), and close to the end of the table nearest the Nasmyth opening. Also make sure the power cord for the calibration lamp is passed through the diaphragm into the next room and plugged into the outlet marked `1' (there are 4 altogether in the VME room); then the lamps can be operated remotely via the ICL (wcal 1 on).
There are three arc lamps: Hg, Ne and Ar. Arc maps are in the WYFFOS folder in the control room, and can also be found **here**. The arc lamps and slit filters (BG39, GG495, OG530 and RG630) are kept in the WYFFOS cupboard on the side of the dome. Because of the Baranne optics in WYFFOS there is some scattering (3-4% level) in WYFFOS. This scattering is quite obvious, particularly if there are strong lines off the edge of the chip (e.g. the strong lines at ;SPMgt;7000Å in the Ar arc). In that case, you may wish to use the BG39 filter to block them out. Transmission curves of the slit filters are available **here**.
Everything you need should be in the WYFFOS cupboard. The slit filters are in a cardboard box-file, and you'll find the calibration lamp and sources (Hg, He, Ne) there as well.