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themselves in a more or less typical fashion. The fluctuations of all emulsions were found to obey the probability law sufficiently well so that the G-value is descriptive of the occurrence of small as well as large fluctuations.
The records in Fig. 1 demonstrate moreover that the graininess increases with increasing sensitivity, for the emulsions are arranged in the order of their sensitivity properties. Experience in other emulsions shows, however, that this is not necessarily true as in recent years a number of fairly high sensitivity emulsions have been produced the graininess of which is very small (e. g. Agfa Finopan).
From previous discussions of the graininess problem it is obvious that the graininess must depend upon the density of the emulsion because the probability for the occurrence of a fluctuation depends naturally upon the number of grains present so that one should expect a larger graininess for a larger photographic density of the same emulsion. This dependence of the graininess upon the density is demonstrated in Figs. 2a 2e, where samples of the same emulsion (Agfa Superpan) have been analyzed for 5
different
densities.
The data result
ing are the following ones:
a.)
Density:
.10, G = 58
h.)
99 99
.25. G 75
c. )
99 99
.41, G = 93
d.)
99 99
.67. G = 92
e.)
99 99
1.09, G = 57
Fig. 3
represents
these results in a
diagrammatic form
where the graini
ness is plotted versus the density and it is shown that the graininess has a maximum in the density range of .4 — .8 which is in very good agreement
Fig. 3 — Graininess versus density for a panchromatic emulsion ( same as Fig. 2). The curve demonstrates the maximum of graininess for medium densities and the decline towards larger densities. The dashed part of the curve is an abitrary extrapolation and does take into account the graininess due to base, gelatin, and fog.
with the visual impression of imohomogeneitv. It is a well known experience to every one familiar with photography that the regions of low and high density in a photographic negative are of a much more homogeneous character when projected, than the medium densities.
Close inspection of the records ( Figs. 2a 2d l reveals, however, another very interesting fact: It has been mentioned above that the width of the smallest detail of the recorded pattern is indicative of the size of the individual grain (granularity). The records show, in fact, that the width is practically unaffected by the density, demonstrating that it does not affect greatly the size of the individual grain. The variation of the graininess with different densities is due to the fact that the size of the fluctuations increases considerably, in other words, the occurrence of large fluctuations increases with the number of grains present. This behavior is somewhat reversed for very high densities (Fig. 2d) where the grains begin to “overlap" which fact is indicated by
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