Hi Suavi,
I did this simple S/N calculator, it's far from perfect but still get ideas how exposure length, readoutnoise, background light and vignetting sum up in the S/N relation at the end.
http://astrofriend.eu/astronomy/tuto...ng.html#part06
With a very low noise camera it doesn't influence so much on the noise if divided on lot of short sub images, but you get better dynamics. But heavy to process all those sub images.
I try to correct it when I found something wrong in the calulations.
At my place my exposure length limit are from 30 to 60 seconds. F/5.3, ISO800, Canond 6D. When our summer house observatory is ready for use I hope I can extend it to 120 to 300 seconds.
/Lars