The Precise Measurement of Filter Factors and Photographic Reflecting Powers--

A n instrument is described in which the theoretically correct conditions for precise photographic photometry are realized. It permits the measurement of filter factors, photographic reflection and transmission of coefficients of colored materials, and the photographic intensity of light sources with higher precision and greater repeatability than it has been possible to realize with the majority of other methods commonly used for these purposes. The method of procedure and the results obtained are illustrated by the projection of motion pictures showing the changes that occur in the photometric field during the process of making the determinations.