CTIO 5.75 x 5.75 -inch FILTERS

The Mosaic II imager, used at the Blanco 4-m prime focus, takes filters that are 146x146 mm and 12 mm (nominal) thick. A set of standardized filter names and IDs for both Mosaic I on the KPNO Mayall and Mosaic II on the CTIO Blanco have been developed to ensure proper application of astrometric solutions and real-time display processing (as well as future archive uniformity). These official names are listed in the Mosaic filter list web page.

Focus offsets are referred to the R filter, since this is the filter we use for taking focus frames each night when the Mosaic is installed in order to monitor telescope performance.

Note: The central wavelength of narrow band filters (actually all filters, but it is very significant for narrow band filters) is shifted
~15A to the BLUE in the f/2.87 beam of the Blanco 4m + PFADC corrector as compared to the transmission measured in parallel
light.  The central wavelengths quoated below are nominally for when the filters used at PF, with the ~15A shift included.  Furthermore,
the filter transmission curves presented below show the simulated filter tranmission curve for the Blanco 4m + PFADC f/2.87 beam.

Note: The Blanco prime focus corrector has poor response in the UV: 90% (4000A), 85% (3800A), 74% (3650A), 54% (3500A), 31% (3400A), 11% (3350A), 0% (3300A). These are calculations from the glass types and AR coating specifications, and the figures for 3300-3400A are rather uncertain. YOU STRONGLY ENCOURAGED TO USE THE u(SDSS) filter rather than the U filter. Neither of these filters, in combination with the CCDs and optical corrector, match the standard passbands perfectly. The U filter uses a (troublesome!) copper sulphate solution as red blocker, whereas the SDSS u filter is an interference filter.