There are a lot of armchair experts on this topic but many of them rely on folklore or limited empirical experience rather than physics. If you're really interested I'd recommend reading something authored by a person with a clue (i.e. a basic understanding of the science and mathematics behind imaging.) The articles by Craig Stark on signal to noise are a good start:
http://www.stark-labs.com/craig/articles/articles.html
Cheers,
Rick.