How to calibrate DSLR data using
- flats with (matching ISO) bias frames
- lights with (matching ISO & exposure) dark frames
- and a Bad Pixel Map
by Mabula Haverkamp
Data is courtesy of Douglas Mason
- 5x light frames of M31
- 5x flat frames
- 5x dark frames that match the lights for ISO and exposure, so darks are used for dark subtraction from the light frames, this will then subtract the bias signal, bias pedestal and dark signal (The bias signal and pedestal are always included in any frame !)
- 5x bias frames that match the flats for ISO, so the bias frames are used to subtract the bias signal and bias pedestal from the flats
This workflow subtracts the bias pedestal once and only once from the lights and flats, which is needed for good flat-field calibration.
An explanation of the data calibration rules can be read here:
Astronomical data calibration principles/rules, must read !
Workflow:
- first create a Bad Pixel Map (BPM), using the flats and darks if you don’t have a BPM yet. You only need to create a BPM once per year give or take. See this tutorial: Creating a Bad Pixel Map
- create a master flat from flats which have the bias signal and pedestal subtracted and which are corrected with the BPM
- create a master dark
- calibrate the lights with the masterdark, masterflat and the BPM
- process up until integration