Best review of the basic science I have seen online: http://johnlind.tripod.com/science/

The the lens calculations are a whole 'nother ball of wax, but here's the quick skinny on the exposure value system:

Av + Tv = Ev = Sv + Bv

Exposure value: Ev

Aperture value: Av = log2 (f^2)

Time value: Tv = log2 (1/t)

Speed value: Sv = log2 (0.32 * ISO)

Brightness value: Bv = subject luminance in foot-Lamberts