Originally Posted by tkerr
I'm well aware of that. I don't really want to argue either and I mean absolutely no disrespect, but a lot of great astrophotographers (whose results make mine look laughable) say just what you are saying. I believe they are confused or misinformed.
(For example, flats correct uneven illumination, but unless I'm sorely mistaken, they don't do a thing to SNR)
The article you posted seems ro me to be exactly right- but unless I misunderstood, it is comparing a single image with several images of the same exposure time (eg, 1 one minute exposure vs 4 one minute exposures). Of course in this case, the stacked image will have a higher SNR. But if you made a single image with the combined exposure time of all the stacked image and compared it to a stacked image (eg, 1 four minute exposure vs 4 one minute exposures), the signal to photon noise ratio would be the same. The stacked image would have more range, but it would not have less noise. The formulas in the article you linked to (together with the fact that photon SNR in a single image goes like 1 / sqrt (exposure time) ) agree with what I'm saying.
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