A new cinedensitometer has been developed specifically for the purpose of extracting densitometric data from 16 mm motion picture films. By means of a tracking mirror arrangement, the film density of a moving image can be measured dynamically as the film is being projected in a cine mode. Two photo-electric detectors along with various remote controlled aperture wheels are mounted behind the projection screen to measure image and back-ground densities simultaneously. Overall readout is precise to about ± .03 density units.
Raymond H. Lambert,
"A New Cinedensitometer for Rapid Analysis of Re-entry Observables," Optical Engineering 6(2), 060254 (1 January 1968). https://doi.org/10.1117/12.7971393