Chris,
Stacking ALWAYS reduces noise - it is the nature of noise, being a random signal, it averages out over the frame
The wanted signal, on the other hand, is not random - and the stacking process increases this signal.
The end result is increased Signal/Noise ratio, exactly what we want to achieve.
Now, the background illumination (LP) reduces contrast and shifts the colour balance. When you stretch the histogram, the consequence is reduced S/N ratio, plus increased readout and quantisation noise (this is because of limited dynamic range of the camera ADC ).
How to overcome all this?
Dark site, more light frames and adequate numbers of dark frames plus flats plus bias frames (the last two could be done once for the specific camera and lens).
There is no need to spend k$ for a decent result. Of course, if you have plenty of them, no worries.. But even the most expensive camera will have noise, vignetting, readout noise.. the only way to overcome all those limitations is patience and knowhow.
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