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. One is accessed from the Side 2, the other from Side 4. Each wheel has six filter slots. Affects both lamps and sky.
Normal position is out.
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.