Quote Originally Posted by spacer View Post
If I'm understanding the question right, once the ISO value is determined, the camera computes exposure with no other consideration for the film.
This is a good generalization of it. I have some reservations about the "no other consideration part", but will discuss that later. What I'm asking about is the specifics of the relationship. How does the film speed value interact with the exposure meter and why? So far everyone is being very general or just offering an overview. How about nailing it down?

No one has given the film speed equations for either B&W negative film or color reversal film. I believe this is a good place to start, because we need to know where on the characteristic curve the film speed point is and where the metered exposure point is in order to determine what their relationship is. Most of this can be found on pages 187 and 188 of the Connelly paper. One small note: There has been a change in the equation for color reversal film speed since this paper was published which I believe offers further insight into way in which film speed and exposure placement work.