As an exercise to see how many frames I needed to collect. I made an animated gif of increasing numbers of stacked cropped frames. These stacked frames have been upsized by a factor of 6.4.
1, 4, 9, 16, 25, 36, 49, 64 and 81.
In theory the signal to noise is improved by a factor of the square root of the number of frames. This only applies to the Poisson or statistical noise not 'noisy' or 'hot' pixels.
Here is a small version 900kB
http://d1355990.i49.quadrahosting.co...amestestsm.gif
For a better effect here is a large one 23MB
http://d1355990.i49.quadrahosting.co...amestest02.gif
The exposures were for 60s at an ISO of 1600 and dithered. All were corrected with darks and flats.
It is a very clear demonstration of how useful stacking is to reduce noise and thus enhance signal.
The very dim stars appear out of the noise as if by magic. The major factor here is the dithering as inherent residual sensor noise is not enhanced.
Bert