What is stacking, and why does it work?

Adding many exposures of the same field together. The signal adds consistently and the noise does not, so the picture gets cleaner as frames accumulate — which is what allows the stretching that reveals faint detail.

It is the single technique that makes amateur deep-sky imaging possible, and the idea behind it is simple arithmetic.

Signal adds, noise does not

The object contributes the same amount to every frame, so adding frames adds it directly. Random noise contributes differently each time and partly cancels. The ratio between them improves as frames accumulate.

Why that matters

Because the processing that reveals faint detail — stretching the brightness scale hard — amplifies noise as much as signal. A clean stack survives that stretch; a single frame does not.

The frames that are not of the sky

Dark frames, taken with the lens or telescope capped at the same settings and temperature, record what the sensor produces on its own. Flat frames record dust and vignetting. Subtracting and dividing by them is what makes a stack clean rather than merely averaged.

What stacking cannot fix

Trailed stars, which average into longer trails. Focus, which averages into the same blur. And a gradient from light pollution, which is consistent and therefore adds exactly like signal.

If this page and the manufacturer’s own documentation disagree, follow the documentation. Every aperture, focal length, payload rating, field, eye relief, transmission figure and thread size on this page comes from the maker’s own published figures, with the unit as printed and the source named. None of it is measured here, and no figure is converted into another convention, because a converted number is a different number. And for any sensor: a pixel size means nothing without the focal length it sits behind. The same camera is well matched to one telescope and wasteful on another, and a frame rate quoted for the full sensor is not the rate achieved over the small region a planet occupies. This page reports the maker’s figures as published and computes no sampling from them.