Journal of the Society of Motion Picture and Television Engineers (1950-1954)

Fig. 2. Essential equipment of experimental setup shown opposite: (A) radiant energy source; (B) sight box and associated impediments to air flow; (C) film trap; (D) black film, coated with temperature-sensitive phosphor; (E) film-trap door; (F) ultraviolet-absorbing camera lens filter; (G) camera; and (H) ultraviolet light source. example, a series of pictures at constant radiant flux but varying air flow from a given jet will show the change in film temperature resulting from the change in cooling, but any wide change will shift the fluorescent light so far toward high Brightness or low brightness that the 'tonal range" the indication of temperature distribution — will be less extensive. If, on the other hand, the radiant flux heating the phosphor:oated film is changed with each change in air flow, it is possible to maintain at all low rates a clear rendition of the detailed pattern of air flow at the expense a ready comparison of film temperatures between flow rates. This simpliied technique, therefore, allows either temperature level or distribution to be :ompared at will. First interest in the design of air jets is usually in the detail of air flow and distribution. When all jets have been compared in this way, the better ones can then be compared at constant radiant lux to determine relative efficiencies of the jets. Specific apparatus for the evaluation of air ets is shown in Fig. 1, and the components are identified in Fig. 2. While it is perfectly possible to use a complete proection mechanism, we found it more con venient to mount the film trap, baffles, fire shutter, etc, on a base plate duplicating the main frame casting, and to construct on this plate a nonoperating mock-up of the projector. The radiant flux was supplied by an incandescent lamp (a Photospot RSP-2 on variable voltage) located to give the proper energy distribution across the gate, and baffled so as not to contribute significantly to the general room illumination. The strip of black phosphor-coated 35mm film was held stationary in the gate. Ultraviolet excitation at 3650A was provided by a G. E. 100-w CH-4 projector spot lamp covered with a Corning No. 5874 filter and set about 15 in. from the phosphor-coated film, with the incident ultraviolet nearly normal to the film. A camera was set along the optic axis of the mock projector, to photograph the fluorescence pattern of the phosphor-coated film. Uniform absorption was obtained over the entire frame by using a black strip of film — representative of very low-key photography and of the dense scenes that generally cause trouble first when film is overheated. The black, opaque frame together with the baffling of the incandescent lamp heating the film kept the incident light out of the room, and permitted convenient examination of the fluorescent image of the phosphor without the degradation of spill-light. While the fluorescent pattern is visible with adequate contrast, a photograph taken without further precautions has its contrast greatly reduced by the actinic ultraviolet which floods the scene. Adequate photographs can be made only by equipping the camera with an ultraviolet-absorbing filter such as the Wratten No. 2B. The mock projector as a first approximation has given useful results, even though there are obvious differences between film temperatures in the mock projector and film temperatures in an actual projector. This simplified apparatus used for convenience, however, comes closer Kolb and Urbach: Evaluation of Air Jets 367