Between the offset guider box and the spectrograph body is a half-inch spacer plate and a thick black anodized plate which contains two filter wheels [O], each containing up to six 2--in. filters, such as those used for broad and narrow-band imaging. The access slots are located on Sides 2 and 4 of the spectrograph, and are customarily sealed with strips of duct tape in case of light leaks. Each filter position accepts an individual filter holder, which slides out of the filter wheel assembly through a notch. The wheels turn manually with the aid of the individual filter holder handles, and will stop at a detent for each filter position. You must therefore count three stops for the filter you just inserted to be positioned in the beam. The colored-glass filters just sit on the lip within the trays, and do not require restraining clips. Quartz-substrate neutral density filters are also available, mounted in their own holders. Both sets of filters may be found in wooden boxes in the filter storage room. You must remove your filters from the wheel at the end of your run and return them to the box; it is also good practice to check that your predecessor has not forgotten to do the same. Note that these above-the-slit filters affect all the light from the telescope, but do not intercept the comparison lamps.