We previously described a method utilizing the flow of developer solution over an exposed photographic film for imaging mass uptake patterns at solid surfaces. We have now formulated a calibration equation that converts optical density of the developed black-and-white him to the local mass transfer coefficient. This equation was evaluated with measurements of mass transfer at the surface of a spinning disk and in the entry region of a straight tube. The product of developer dilution and development time dictated the broadest range of measurable mass transfer coefficient values and had an optimum value of approximately 1.0 min.