Filters

There are 5 locations where filters may lurk, and it would be to one's advantage to check them each time a run is started. Details on the filter wheels themselves are outlined in the following sections of this chapter.

1. Above-the-slit filter wheels [O]: These are on top of the spectrograph and below the base of the telescope. One is accessed from the Side 2, the other from Side 4. Each wheel has six filter slots.
2. Below-the-slit filter wheel: This wheel is internal to the spectrograph and has 6 positions. The filters and positions are noted [T] over the adjusting knob [S], which is located on Side 3 of the spectrograph. Affects both lamps and sky.
3. Lamp filters: In front of each of the comparison lamps [X] is a place for two slides (neutral density). The Fe-Ne usually has a cardboard piece in one, which should be replaced before leaving the mountain, as this lamp is dangerous for another detector using this spectrograph (Reticon).
4. In front of the acquisition TV camera is a small lever [K] that either puts in or takes out a blue filter which only affects the TV. Normal position is out.
5. Directly in front of the continuum lamp bulb [in assembly X] is a small aluminum slide with an open aperture (when pulled half way out) and an aperture with a neutral density filter (pushed all the way in). This lamp is calibrated with the neutral density slide in, and should be left alone unless necessary, and certainly returned to its normal state if changed. We mention this slide primarily as a trouble-shooting area if counts are much higher or lower than normal.

• Above-the-Slit Filter Wheels
• Below-the-Slit Filter Wheel