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336 PRINCIPLES OF CINEMATOGRAPHY
two film emulsions, the 35-mm original and the 16-mm positive copy. In sketch 'B' it is assumed that a 35-mm negative has been supplied to the Laboratory and, by use of the optical reduction printer, a 16-mm positive copy is produced. This 16-mm copy is then used to produce a 16-mm duplicate negative by printing the two in contact on a continuous or rotary machine. Finally, the duplicate negative is used to produce the many 16-mm positive copies which are made on the rotary contact printer. In sketch 'C the first copying operation is not to produce a 16-mm positive as was the case in sketch 'B' but to produce a 35-mm positive. This 35-mm positive is then used to produce a 16-mm duplicate negative via the reduction printer and in one operation. This duplicate negative is then used to make the many 16-mm positive copies on the rotary contact printer.
Assuming that the highest quality film stocks were used on every occasion and that printing machines of equal capabilities were available for use with each process, it would be found that the most consistent high quality results would be obtained when using process 'A' and that process 'C would be superior to process 'B\ In any reduction printing operations involving work both on 35-mm and 16-mm negative and positive films it is always advisable to carry out as many operations as possible with films of 35-mm width and to arrange the reduction to 16-mm width to take place in the final operation. In this manner the graininess of the resultant 16-mm copy will be reduced to a minimum.
A further consideration which does much to alter the photographic contrast of the final prints produced by any of the three systems shown in Figure 147 concerns the difference between specular and diffuse densities of a silver image. When an optical projection system, such as that found in reduction printing equipment is used, only that light which does not suffer a change in direction (as a result of passing through the emulsion) will form the final image. The density of a silver image measured in this manner is known as the 'specular density'. When films are printed by contact both the specular illumination and also those light rays which are diffused or scattered by the negative emulsion will reach the positive stock since no space or apparatus exist between the two emulsion surfaces. The density of a silver image measured by contact is known as the 'diffuse density' and is, therefore, always lower than the specular density of the same silver image.
Since the specular density is higher so also will be the contrast of the final positive print and, therefore, reduction prints made by the optical reduction process indicated at 'A', Figure 147, should