Below the slit is a six-position filter wheel containing several 2--in. blocking filters. These generally remain in place, and can be accessed only when the spectrograph is off the telescope. They are positioned by turning a knob on the mounting plate [S]; the corresponding position number becomes centered in the window when the filter is seated. The present filter complement (also listed [T] on Side 3 of the spectrograph) is:
Do not attempt to turn the filter wheel past 6 to 1 --- it will break. Figure 7.1 displays the transmissions of the blocking filters.
Figure 7.1: Available filters.