takesome1 said:
To sum up what I think of the conversation in regard to this subject. Eric Fossum is correct, Neuro is correct and your inability to look beyond a single point has left you with an incorrect assumption.
Speaking of assumptions, here is one, and it goes to my question above.
I assume that most people who deliberately set exposure on a camera typically choose exposure time and aperture based on the subject and their creative intent, and set sensitivity according to the availability of light and their desired brightness. That may be a poor assumption, but I'm self-centered and that's how I shoot.
So say I'm shooting a hummingbird in flight and want to stop motion. I want 1/4000 or faster exposure time. Say I'm using a lens combination which allows me f/5.6 aperture at the maximum, but I want f/8 for a little wider DOF given my distance to subject and a desire to have the entire bird in focus. That right there is the subject/creative intent side of the equation. Next comes light. I can't change or augment ambient - it is what it is. I'm at ISO1000, but a "chimped" glance at the histogram shows that I'm about 2 stops under where I want it to be in the first shot. Accordingly, I change to ISO4000 and shoot again. Can I expect more noise, less noise, or the same noise in the second shot?