Originally posted by ScooterMaxi Jim Let me put it another way -- the buckets (pixels) can only collect so many photons. This is a hardware property. The size of a full bucket corresponds to the native ISO of the sensor system. If the native ISO were "only theoretical", well then we'd be able to change the native ISO with a dial on our cameras, and noise at 800 would be just as low more-or-less than at 100 because we'd have changed the "real ISO" of the whole system somehow. But hardware is hardware -- there are very real physical limits.
So yes, we can argue that today's sensors (and the processing of the signal they create) are much better than they were 5-10 years ago, and so the practical effect of native ISO isn't as great as it used to be GIVEN THAT WE DON'T ALSO WANT TO PUSH THE NEW BOUNDARIES CREATED but are merely happy that it is easier to stay within the old ones, i.e. at some point there will be so many megapixels and so much sensitivity for low light at low noise, etc etc that any improvements we make we won't be able to detect in any practical way with our human vision when looking at our images. But we are not there yet, so the limits still matter. (Of course, that's only if we restrict the discussion to "normal" types of photography -- once we get into the realm of imaging for scientific uses, well then they will always be looking to push the boundaries as far as they can.)