Optical Filters

3.4 Redshifted [OII] Quad Filters

The redshifted [OII] quad filter was designed to map onto a four-faceted WFC configuration. A partial SOFA wheel rotation of -33 degrees is required to move filter quadrant 1 (3763Å) into WF2 and WF3, with some vignetting of both camera fields. The projections of the redshifted [OII] filter settings FQUVN and FQUVN33 onto the field-of-view are essentially identical to those of the POLQ and POLQN33 filters, respectively (Figure 3.6
). The vignetted regions are similar, and the location of aperture FQUVN33 is identical to that of POLQN33.

The nominal and rotated filter wheel positions for the redshifted [OII] quad filter are each associated with different filter names. This allows pipeline calibration and database retrievals to proceed smoothly. The filter names are summarized in Table 3.9.

The required central wavelength is selected by filter name and aperture location. Filter element FQUVN (Filter Quad UltraViolet Narrow) has three possible apertures, each of which is nominally centered in one of the three WF channels and associated with a unique central wavelength. The filter element FQUVN33 corresponds to a single central wavelength. In addition to the filter name and aperture, a central wavelength is also requested in the proposal instructions in order to provide a consistency check. Aperture names are discussed further in section 3.9, "Apertures", on page 56.

Table 3.9: Redshifted [OII] Quad Filter Elements.