I often find myself taking still pictures of some gizmo using a tripod mounted DLSR. One decision that always vexes me is what ISO to set my camera to and so minimise sensor noise. The important aspect of tripod mounted photography is that there is no need to consider any form of camera shake (given a decent firmly erected tripod).
I expect to find an absolute quantitative scientific answer, such as set ISO = 755.2, either from a formula or a graph. I've reviewed this forum and specifically this, this and this question. Disappointingly I find words and pictures of books. All very qualitative. I don't find any formulae or graphs. I don't accept that noise level is an artistic or subjective choice. It's a Gaussian distribution around a mean per each sensor pixel.
For my make of model of camera at a fixed temperature, sensor noise is a function so:-
Noise amplitude = f(ISO setting, exposure duration, sensor incident light)
and you might develop sensor incident light as:-
f(aperture, ambient light)
I'm holding image exposure level as a constant as it's got to fit into about 4 - 5 stops, otherwise you can't see it. Noise is a stochastic predictable process. The distribution's size and shape is entirely deterministic via experimentation. So it's a function of maybe four variables. These variables can be related together in a formula or series of graphs that could be published by a camera manufacturer. Where's that noise formula as I can't find it? Or is it as simple as use lowest ISO irrespective of exposure duration?