Glossary - Calibration Frames

Flat Frames

updated: 2023-11-18

Flat Frames (or white frames) are used to capture flat calibration frames and belong to the group of calibration frames.

  • These frames should be taken during every imaging session because they depend on the alignment of the entire imaging train. 
  • Flat frames normally target a mean ADU of 22,000 to 25,000, but this will depend on camera and user preference. 
  • If your flats data is defined (per filter), selecting a flats event will automatically populate the saved exposure time (for the selected binning).


  • GAIN must be set to an identical value as the light frames you want to calibrate
  • Filters: If filters have been used you need a set of Flat Frames for every filter
  • Focal Length of the optical equipment must be the same as for the light frames
  • Focus must be identical as for the light frames
  • Exposure: set exposure time to AUTO or to any other value depending in the brightness
  • Temperature:  no temperature requirements
  • No. of Flat frames: typically the same amount of flats as light frames (but 20 photos are typically enough)
  • Use a evenly-lit light source, e.g. twilight sky, laptop screen, light panel, light box, TV screen, a white T-shirt to cover your telescope  or similar.

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