In the reimaging/spectrograph mode, the observer can choose between a series of available longslits or can prepare his/her own multislit mask. There are six aperture positions; one is permanently clear, while the other five are available for various masks. There is no standard mask set-up. As it has aged, COSMIC has become mainly a multi-object spectrograph. The aperture wheel has no standard set-up. It is the observer's resposibility to bring the aperture masks needed to complete his/her science goals. See the section on aperture masks in this manual.
There exist two kinds of slitmask holders: the ``older'', flat-topped version, onto which the masks are attached using tape; and the ``newer'' version with a metal cover that locks on top of the mask itself. There are 5+ of each kind available in one of the COSMIC black pouches, although one or more of each kind appear not to work (and are labelled as BAD).
It is recommended that you do not use the metal longslit, as it has collected a great deal of garbage onto the slit opening which results in an uneven width along the slit. It is suggested that you use one of the film longslits instead.