Synphot Data User's Guide  

3.1 WFPC2 Quad filters
Filter wheel 11 contains 3 specialized quadrant (quad) filters in which each quadrant corresponds to a facet of the pyramid, and therefore to a distinct camera relay. One quad filter, fquvn, contains four narrowband, redshifted [OII] filters. The second, fqch4n, contains four methane (CH4) band filters, and the third, polq, contains four polarizing elements. The instrument graph table is constructed so that distinct throughput values are automatically selected for a given quadrant of the fquvn and fqch4n filters based on the selected detector.
Note that all three of the quad filters were designed to map onto a fourfaceted WFC configuration. However, in the final design of the instrument, with WF quadrant 1 replaced by the PC, it is necessary to rotate the quad filters by 33° in order to bring filter quadrant 1 into the WF 2 and 3 relays. In addition, partial rotations of 15° and +15° have been implemented for the methane (CH4) filter in order to bring two of its quadrants into the PC relay, and partial rotations of 18° and +15° have been implemented for the polarizer (pol) filter in order to allow observations with different polarization angles (see the WFPC2 Instrument Handbook for more details). Unique component keywords have been implemented in the instrument graph for the nominal and rotated positions of each of these filters. The nominal positions are designated as fquvn, fqch4n, and polq. The rotated positions are designated as fquvn33 (33°), fqch4n33 (33°), fqch4n15 (15°), fqch4p15 (+15°), polqn33 (33°), polqn18 (18°), and polqp15 (+15°).
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