Image Stacking

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Image stacking is used to bring out the details in an object. By stacking more images, you are basically creating a longer exposure. For example, if you stack five 60 second exposures, that will give you the equivalence of a single 5 minute exposure. Why not just take a single 5 minute exposure? Getting long exposures (5 minutes and longer) requires a very good mount, excellent tracking, great drift aligment, etc. Plus, in some cases local light pollution may limit the exposures to 1-2 minutes at best. Finally, if something ruins an image (e.g. airplane) you haven't lost a 5 or 10 minute exposure but a much shorter one.

Here's a general recipe for stacking images that very in exposure (e.g. 60 sec, 90 sec, 120 sec)

  1. Subtrack dark frame using a dark frame with the same exposure
  2. Stack images with the same exposures
  3. Edit levels/curves for each stacked exposure
  4. Stack edited images of varying exposures together
  5. Edit levels/curves of the new stacked image

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