What is a dark frame in astrophotography?
Steve says: “During the long exposures required for many deep-sky images, the sensor warms up, generating ‘thermal noise’ in the images. This noise tricks the sensor into believing that it has received some additional photons.
Among other unwanted artefacts, this can result in a peppering of white pixels across the image looking rather like tiny stars.
Dark frames are images taken with the telescope capped, using exposures of the same length and camera temperature as your main images.
They contain just the thermal noise as no actual light has reached the sensor. Subtracting these special images from your normal images using software like DeekSkyStacker or Photoshop removes the sensor noise.”
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