Derivation of Exposure Values

[Nick Thornton]

Can anyone tell me how the numerical Exposure Values (EV) are calculated? Is the re a standard mathematical definition that relates a given speed and aperture to an EV number, or are EV's just an arbitrary sequence with each integer represen ting one stop?

[Bill C]

As per Norman Goldberg's "Camera Technology - The Dark Side of the Lens":

2^(EV) = N^2/T and EV = 3.222 log (N^2/T)

where: EV = exposure value N = f-stop T = shutter speed, seconds

[Bill Glickman]

Yes, each interger does represent one stop...