An integrating sphere type of physical densitometer has been developed with a view to standardizing density measurements in the motion picture industry. The instrument accommodates films or plates up to 5″ wide. Scanning beam dimensions of 0.025″×0.100″ are used but may readily be changed. Density values corresponding to (1) the equivalent of standard visual diffuse or (2) photographic printing density may be obtained by insertion of suitable optical filters. Densities up to 3.0 are read directly on a special three‐scale logarithmic meter which provides a uniform density scale. A chopper in the light path makes possible a.c. amplification using a highly stabilized amplifier with a highly selective gain‐frequency characteristic. This latter feature permits operation in daylight or in a room illuminated with ordinary a.c. lamps. Calibration is based on the inverse square law.