Let’s be careful not to confuse exposure with film speed. Metering or the scene luminance range has nothing to do with the speed of film, although the meter can play an important part with certain methodologies toward determining “film speed.”

This brings me to another thought about film speed and that concerns expressing a film speed result without referencing the testing methodology used. We all know that different approaches yield different results. This is the strongest argument for standardization. When the ISO prefix is placed in front of a film speed, it is stating the procedures of the standard have been adhered to.

Comparing the WBM method and the ISO method clearly illustrates my point. Without getting into the merits of either method, there is around a 0.15 to 0.23 log-H difference between the two speed points. The same test wedge with the same data will yield speeds differing between ˝ to 2/3 stops. So, if communicating speeds results is to have any validity, I thing the testing methodology needs to be included.