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638
J. A. MAURER
[J. S. M. P. E.
must be cut down if the clear side has a deposit of the density shown in the lower row of figures.
The most interesting point which is brought out by these curves is the large reduction in output which is caused by what, to the eye, is a very slight fogging of the clear side of the sound track. All the values plotted in the lower curve are very low in the scale. A density of 0.2 appears to the eye as a light gray. A density of 0.05 is almost invisible unless we have a clear strip of film with which to compare it. Yet this density, as we see, reduces the sound output by 1 1 per cent. Thus from the standpoint of efficiency it is much more important to keep the clear side of the track free from fog than to strive for very high densities on the dark side.
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0 .f .6 .8 1.0 '-2 '• + 1-6 1-9 2.0 DENSITY OF Df\KK SIDE OF SOUND TKf\CH (UPPER CURVE). 0 .02. .01 .06 ,08 .tO .12. ,/f ,16 .19 ,ZO FOG DENSITY ON LIGHT SIDE. OF TRACK (LOWER CU*V£).
FIG. 2. Increase in sound output with increasing track density and loss of sound output with fogging of clear side.
If we have an accurate "H and D" curve for the film we use in printing, developed to the proper degree of contrast, we can determine from it and the curves of Fig. 2 just how a given sound negative will behave in printing. Such a curve is given in Fig. 3. This curve is for Eastman positive stock developed to a "gamma" (contrast factor) of 2.0 in a typical developer such as would be used for prints. From such data as are available to the writer this seems to be an average gamma for the prints being made at the present time. The curves obtained in experimental work on other film stocks resemble this one so closely in shape that the results obtained from it should be generally applicable.