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RECORDER
The negative gamma shown is 0.6, and it is seen that differences on the exposure axis are in this case reduced when plotted on to the density axis. In this way, the negative gains latitude, by reducing exposure variations, and the high positive gamma is necessary in order to restore the original tone range to unity.
It will be noticed, however, that the combined gamma of negative and print in the example WBSSMSM^ shown equals 1.5, that ; is, greater than unity. F!gm 2
This is deliberate, and
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Methods of producing the Sound on 16mm. Film.
is done in order to overcome the loss of contrast that will inevitably occur through light scatter in lenses and in the projection theatre.
It is immediately obvious that the extent of the range of negative densities, i.e., the contrast of the negative, is very important. The contrast of any emulsion is increased by lengthening the developing time, and a series of curves for a range of developing times can be plotted. It is then usual to prepare a time-gamma curve, in which the increasing gammas so obtained are plotted against the increased developing times, for all emulsions handled. Reference to this time-gamma curve will immediately determine correct developing times for a desired contrast for a particular emulsion. (Figs. 5 and 6.)
Three Differences in Contrast between Highlight and Shadow
The first of three differences is under-exposure when much of the shadow detail in the curve is lost on the toe of the curve. When more exposure is given, the potential latitude of the negative curve is fully exploited, and the differences in density of the developed negative will be the same, though double the exposure has been given. Adequate exposure will ensure that all the tones are rendered, and it is in fact possible to blow up a scene, originally taken on 16mm., to 35mm., with excellent results. Had the exposure ibeen cut, as frequently happens, this would be quite impossible.
In order to obtain a positive image capable of projection, the question of the correct exposure in printing of that emulsion makes grading arrangements very necessary. The ideal printing light would place the tones on the positive emulsion well into the over-exposed range, although the differences in negative contrast are quite normal. It is therefore necessary to reduce the printing light by the requisite number of printer points (a printer point I is .05 of negative density) to bring the positive within the projection range.
Duping
The fullest possible application of control of contrast is found in the process
i of producing a print by means of a duplicate negative. It may be that in
a particular case, the original negative is too hard, i.e., the rang? of contrast
is too great to compress within the positive emulsion range unless the positive
gamma is considerably reduced. This can be done by varying the positive