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104
CINEMATOGRAPHIC ANNUAL
Another important consideration in studying the need of the Super Sensitive film necessitates a study of the quality of the light sources to which this film is exposed. For that purpose sensitometric tests have been made to daylight and to tungsten. Inasmuch as the mode of testing an emulsion to any light source is practically identical we shall for the sake of brevity and clarity consider only the curves obtained by exposure to tungsten.
1.6 l.«f It
10 0* 0.6 0*
o.t
Exposure : Tungsten
e Mim. inBoxax
i. Present Films
2. Super Sensitive Film
"Relative Loo E
0.0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 Vk 2.7
Fig. 1
Figure 1 shows the sensitivity curve of the present and Super Sensitive type of film for tungsten exposures developed for a fixed time, nine minutes in a standard borax developer. It will be observed that the Super Sensitive curve lies above the curve for the present type of film and the separation of these curves gives an indication of the speed difference existing between the two films. In making a numerical estimate of the speed we do not consider the actual density values produced for a given exposure. The customary method is to deduce speed from the exposure value obtained at the point where the straight line portions of these sensitivity curves, extended, intersect the exposure axis. Speed, is actually defined by the following formula:
1 — x C = Speed,
where i, the inertia, is the exposure value of the intersection point and C is an arbitrarily chosen constant. For the curves shown in Figure I we find that the speed of the Super Sensitive film, as represented by curve No. 2, is three times that for the present type films. Identical tests made to day-light show that the Super Sensitive film is twice the speed of the present type. With reference to Figure 1 attention should be called to the marked difference in the low exposure region, that is in the toe of the H and D curve. In this region the Super Sensitive film definitely differentiates between exposures of very low intensities. Particular reference is made to the exposure region to the left of the relative log exposure value of 0.3.
The cause for the difference in relative speeds between the two types of films to tungsten and to daylight, or to any other source, is entirely dependent upon the color distribution of light from the