A Preliminary Note on the Uniform Development of Motion Picture Film

F. F. Renwick

Being well aware of the difficulty of securing uniform development of photographic plates by any of the ordinary methods of dish or tank development, it occurred to the writer that it would be interesting to make a study of the degree of uniformity of development usual in the commercial development of motion picture film. For this purpose, it was proposed to employ motion picture film free from irregularities in the thickness of its sensitive coating, to expose a number of lengths of such film as uniformly as possible to a moderately wide range of light intensities, and to have them developed in several different commercial laboratories. In the attempt to produce uniform exposures over each picture area, one of the regular commercial printing machines was first employed. It was found, however, that the illumination was far too uneven for our purpose, and this leads me to suggest that users of motion picture printing machines will be well advised to examine carefully from time to time the uniformity of the illumination by which they are printing their pictures, since it is evident that it is very easy to spoil the beautiful gradation of a picture by printing it unevenly. In the experiments upon which the following short note is based, irregularities due to lack of uniformity of the exposure over the area of a single picture were reduced to a small amount by exposing the film in a kinema camera to a sheet of white blotting paper, uniformly illuminated by a bank of mercury vapor lamps, while lack of uniformity in coating is doubtless very small in amount owing to the use of commercial motion picture film of known excellence. I may say, however, that in prosecuting this work further, it will be desirable to adopt a different method of exposing the film, since the camera method employed in these experiments did not prove entirely satisfactory. The small irregularities arising from this cause have, however, been eliminated by the method of computation adopted. Lengths of film 200 ft. long were exposed in the manner mentioned at four different lens apertures and were then sent to a number of different laboratories engaged in the commercial development of motion picture film for development. On their return, ten picture areas at each exposure were carefully measured in a photometer at five different places on each picture area (three lying along the center line of the film, the other two being at the middle of the sides of each picture area). The results were grouped to determine the average density for each location and the average departures from these mean values were then calculated. The same procedure was, of course, adopted for each of the four differently exposed areas. Results obtained from seven separate rolls of film are dealt with in this note. In this way, it was found that although there was evidence of a small lack of uniformity in the lighting of the picture areas, this was insufficient to render doubtful the conclusions to be drawn later concerning development. By considering the average deviations in density at each spot separately, we have determined the liabilities to fluctuation in density over each portion of the picture apart from the above mentioned small irregularities due to exposure. Our results do not disclose any regular tendency towards larger fluctuations of density at one part than another of each picture area due to irregularities in development and drying conditions, and this is true whether the film had been developed in a machine or on racks by the ordinary tank system, but I should not like it to be inferred that irregularities of this kind cannot happen, since in certain circumstances, I think they are likely to arise.

Print ISSN
Published
1923-05
Content type
Original Research
DOI
10.5594/J11637