> Image noise does NOT come from high ISO, it comes from low exposure [...] changing the ISO on a digital camera will NOT introduce any more noise (except for at the extremes of the range, where, for example, analog readout noise may play a role).
Sounds like you're saying that setting higher ISO does cause noise, but as long as you don't go too high you won't really notice the difference?
No. What they're saying is ISO multiplies brightness, essentially exasperating differences. Roughly, ISO 200 is 2x gain and so on. So if you have one pixel with a brightness value of 1, and the pixel to the left has a brightness of 5, and an ISO of 500, then it becomes brightness 5 and 25 respectively. Oversimplification.
Sounds like you're saying that setting higher ISO does cause noise, but as long as you don't go too high you won't really notice the difference?