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You have finished now preparing the ``initial'' frames (bias, preflash and flat field) for the reduction of one night's objects. You might have different flat fields for each telescope configuration.

Object by object you can proceed as follows:

  1. Check for -- and eliminate -- hot spots.

  2. Trim the edges to the same size of the bias frame.

  3. Obtain the mean value of the dark current from the underscan columns (now 1-4, for example) and add that number to the bias frame.

  4. Subtract the resulting frame from the one obtained after step 3.

  5. Subtract the ``scaled'' preflash (if used).

  6. Divide by the normalized flat field.
Calibration frames are treated as objects.

Wed Apr 6 22:56:39 BST 1994