R-C Spectrograph Slit & Decker


The entrance slit has a length of 50 mm. Its width has a range from closure to 50 mm. One second of arc corresponds to approximately 150µ and, with the Blue Air Schmidt camera and Loral 3K×1K CCD now used with the R-C spectrograph, a 1" slit projects to 2 pixels on the CCD for small grating tilts. Because of anamorphic magnification, the 2-pixel projected slit width will be greater than 150µ at large grating tilts. Here is a plot showing the 2-pixel projected slit width as function of grating angle readout.


The decker plate for defining the length of the slit is normally left in the fully open position. With the decker fully open, the field of view is limited to 50 mm, 328 arcseconds, by the length of the slit. For reference the other available decker positions are:

  No. mm arcsec
       1 1.86 12
  2 3.71 24
  3 7.42 49
  4 14.85 97
  5 30.98 203


Michael Keane
Jack Baldwin 

Updated on June 9, 2021, 8:27 am