Previous: Flat field
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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
Object by object you can proceed as follows:
Calibration frames are treated as objects.
- Check for -- and eliminate -- hot spots.
- Trim the edges to the same size of the bias frame.
- 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.
- Subtract the resulting frame from the one obtained after step 3.
- Subtract the ``scaled'' preflash (if used).
- Divide by the normalized flat field.