The Simplest Case

This paragraph shows the very simplest possible example of how to do the relative calibration of a CCD-frame. It is assumed that frames are only taken in a single filter (R in this case). The frames available are the following:

• Darks

  
  

  DARK01 is a 20 minute frame taken before/after observing

  
  

  DARK02 dito

  
  

  DARK03 dito

  
  

  DARK04 dito

• Flats

  
  

  FLATR1 20 sec dome flat in R-filter

  
  

  FLATR2 dito

  
  

  FLATR3 dito

• Data

  
  

  N5126R 20 minute exposure of NGC 5126

  
  

  N7794R 20 minute exposure of NGC 7794

In order to process these frames, the following commands would be executed.

AVERage/IMAge DARKAV = DARK01,DARK02,DARK03,DARK04
AVERage/IMAge FLATAV = FLATR1,FLATR2,FLATR3
COMPute/IMAge DENOM = FLATAV-DARKAV
COMPute/IMAge N5126RF = (N5126R-DARKAV)/DENOM
COMPute/IMAge N7794RF = (N7794R-DARKAV)/DENOM

The first two commands compute the simple averages of the dark and flat field images. The third command computes the dark subtracted average flat field. The final two commands perform the flat fielding of the data frames. Note that there has been no correction for bad columns in either the flat field, the dark frames or the data frames. The next example shows how to do this.