Best amount of images for stacking

Started Aug 10, 2022 | Questions thread
Ferguson Senior Member • Posts: 1,993
Re: Best amount of images for stacking

There's no straightforward answer to your question as it depends on your skies, your equipment, your target.

Generally speaking for light frames the more data the less noise, the noise goes down with the square root of the number of images roughly, so 4 times the images is half the noise, 100 times is 1/10th the noise.

As to darks the same sort of impact occurs with many images, to average out the noise. Two is a tiny, tiny number.  Also, flats are quite important in astrophotography, some people think of them as only helping with dust motes, but that is not true, it adjusts the field for both small scale and large scale (e.g. vignette) effects.

What most people look for is a point of diminishing returns, and experience helps if you try to predict it rather than wait for it.  I do a trial stack after each night's runs, and when my image stops getting substantially better I know it is time to move on.

For more casual work where you may be doing it all in one night, and anxious to call it an evening, it is more difficult.  Though there are programs that will do live stacking as you shoot, so you can see it "developing" as you go and judge.

But as a general statement -- more is always better.  Just a LOT more is only a little better.


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