Response to What's the point with ISO 125?

The point is simply showing a bigger number! In the old days manufacturers thought they could gain a competitive advantage with "faster" films. Like General Motors, big companies make changes in attitude slowly, if at all. This is especially puzzling because the published ISO's (EI's) are never accurate! They are usually off by as much as one stop. True film speed is determined by measuring the point on the curve where density is 0.1 above film base + fog. By this method, the published ISO's are irrelevent. You should measure your own personal film speed, but if you don't have access to a transmission densitomiter, a safe bet is just to divide the published ISO by 2. See Ansel Adams' book "The Negative" or Fred Picker's VHS "Photograhic Technique" (avalilable from Calumet) on the proceedure for film speed and development time tests.

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