Can anyone tell me what the difference would be of taking 50 exposures of a star group and stacking them and making 50 copies of an exposure and stacking them. It is probably a stupid question but I tend to learn from asking them.
I think the key is signal to noise ratio.
If you stacked the same frames the noise duplicates (and is reinforced)
along with the data.
In a set of different subs, the noise tends to be random and is therefore
rejected as noise in a stack while the data is reinforced as true data.
The more frames you stack in theory, the more the noise 'drops away'
down to a mathematical noise floor.
You reach a point though, eventually where you gain nothing more by
adding frames....
Someone better versed in the maths can help out here.