Can anyone tell me how the numerical Exposure Values (EV) are calculated? Is there 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 representing one stop?

-- Nick Thornton (Nick.Thornton@liffe.com), October 19, 1999

Answers

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 C (bcarriel@cpicorp.com), October 19, 1999.

Yes, each interger does represent one stop...

-- Bill Glickman (Bglick@pclv.com), November 01, 1999.