Filters

If the response of a filter has been tabulated, then the table of values may be used to generate a `spiketrum', which may then be turned into a calibration spectrum. See the section on `spiketra' for details about these things, which are essentially ways of turning sets of tabulated values into spectra by interpolation.

Say the spectrum to be corrected for a filter response is called `spect'. A table for the filter response might look like

   *
   *     Filter transmission table
   *
       3000    .05
       4000    .10
       4200    .55
       4400    .90
       4600    .95
       5000    .95
       5500    .95
       6000    .95         and so on..

This is not a particularly realistic table. A proper table should have enough points to ensure that there are a reasonable number of values tabulated over the region of the spectrum to be corrected. With this table in `filter.tab', a filter calibration spectrum can be produced and applied as follows:

   ICL> gspike  spectrum=spect table=filter.tab spiketrum=filter
   ICL> interp  spiketrum=filter spectrum=calib
   ICL> idiv    image=spect image1=calib output=spect

Note that `idiv' is used to apply the corrections, which is simply a case of dividing the spectrum to be corrected by the interpolated filter response. The same calibration spectrum may be used for any other spectra that cover the same wavelength range.