- DARK
Dark frames are made at the same exposure time and ISO as the subject light frames but in the dark: use your lens/telescope cap for example. They should also be made at approximately the same temperature as the light frames, this is the reason why we make dark frames at the end, or in the middle of the imaging session. The dark frames are used to remove the dark signal from the light frames and like the BIAS frames, the more dark exposures are used for the calculation of the master dark, the less noise will be introduced into the corrected images. Also, you can stack dark frames with the median algorithm (or Winsorized by checking the rejection levels at the end of the process (< 0.500)), but be sure to use No Normalisation !