Journal of the Society of Motion Picture Engineers (1930-1949)

Oct., 1932] MEASUREMENT OF FILTER FACTORS 373 the standard surface, S, and the other half of which contains an image of the test or unknown surface, X, is now imaged by means of the two-component objective, L4 and L5, on the exposure plane, E. A field lens, L3, forms an image of the lenses L2X and L2S in the lens system L4 and L5. In the exposure plane, E, the line in the figure represents a cross-section of standard 35 mm. motion picture film which travels downward through the plane of the drawing at a uniform linear velocity. The motion picture film is carried by a sprocket of the usual type mounted in a film box on the top of which may be placed a standard Bell & Howell magazine carrying SUPPLY -v -TAKE-UP FIG. 5. Schematic cross-sectional elevation through the line no!0 of Fig. 3 ; (a) photometric cube as seen from L4L5 of Fig. 3; (6) disposition of the images of the photometric field and scale on the photographic film. an adequate film supply and providing take-up of the exposed film. In Fig. 5 the arrangement of the photographic film relative to the photometer cube is shown in greater detail, this being a schematic cross-sectional elevation through the line noI0, as shown in Fig 3. It will be noted that the unexposed film enters the film box, B (in Fig. 5), from above, is pulled down by the film sprocket S, and is taken out through the top of the box to the take-up reel. An adjustable slit consisting of two jaws, Jl and J2, is placed immediately in front of the exposure plane which is occupied by the film. Since the film moves at a constant linear velocity past this slit, the varia