This is a term that caught my attention recently, and I think the possible ramifications are quite interesting.
Effectively, the theory is that with some modern sensors, the noise added as a result of increasing the ISO when taking the photo is similar to the result of lifting exposure in post-processing afterwards.
I recently read an article where the writer claimed that, for star photography, it is better to shoot under-exposed at a lower ISO, because at lower ISO's the camera captures more dynamic range and the resulting noise will be the same as the shutter speed and aperture are basically set in stone anyway.
I recently experimented with this a little bit. The following images were taken at the same shutter speed and aperture, under similar if not exactly the same lighting conditions (some of the foreground lighting was a campfire), one at ISO 8000 and the other at ISO800, and had the exposure lifted by 3 1/3 stops. The results look as follows:
A crop of the highlight area:
And the shadow area:
In short, I can't really see much difference, although maybe the ISO800 image has a little bit more detail in the shadow areas.
Edited by Peter Connan, 21 August 2016 - 05:36 PM.