The Cine Technician (1938-1939)

I THE CINE-TECHNICIAN May-June, 1938 THE DUPLICATE NEGATIVE I. D. WRATTEN (Technical Service Kodak Ltd.) Based on a lecture given to A. CI', members on T March ljtli, 1938 seems to be no doubt that the making ol 2 20 * 00 HEBE duplicate negatives is a process on which there are many and varied opinions as to the most suitable procedure. Theoretically, at least, the print from the duplicate negative should compare favourably with a print from the original negative, but in actual practice this state of affairs is rarely obtained, and it is usually fairly easy for the observer to determine whether a projected print has or has not been obtained from a duplicate negative. Prints from the duplicate negatives frequently show a loss in the reproduction of tonal values coupled with an increase in graininess, and it is on these two delects that we might well start our discussion on duplication procedure. In order to obtain correct tone reproduction it is necessary that the exposure for both the master positive and the duplicate negative should produce minimum densities within the straight line portion of the characteristic curves of the two materials, and that the overall gamma, i.e. the product of the positive and negative gamma values, should be equal to unity. The avoidance of graininess is the second difficulty, and while a small increase in graininess appears to be inevitable, it can be kept within satisfactory limits by developing the two duplicating materials in accordance with their graininess characteristics, i.e., to develop the duplicating positive film to a relatively high gamma value and to develop the duplicating negative film to a correspondingly low gamma value. This is a fairly simple matter to accomplish, but great care should be taken not to develop the master positive to too high a gamma value, because at high gamma values the latitude of the duplicating positive is diminished and if the original negative tends to be contrasty there will be a serious loss in tone reproduction. In Fig 1 is shown a series of characteristic curves of duplicating positive film developed in D.16 developer, and if. therefore, we select a gamma value of 1.90 as being satisfactory, we must ensure that the minimum density on our master positive print shall be on the straight lino portion of the curve if the highlights of the original nega Duplicating tIetatlTe .(Type 1505) developed In D.76. LOG Cj030SU«C Fig. 2 tive are to he satisfactorily rendered, and it will be seen that in this case the density should be about 0.5. In Fig. 2 will be seen a series of characteristic curves of duplicating negative film, and here a gamma value of between 0.5 and 0.05 will be satisfactory and the mini mum densitv on the negative should be between 0.35 and 0.4. The master positive will, thereiore, differ in appearance from an ordinary release print by reason of its increased density, and the duplicate negative will appear only slightly heavier than the original negative. There is little doubt but that this method is the most suitable for obtaining a really satisfactory duplicate negative with the normal duplicating films, and the only other point worthy of emphasis is that exceptional care should be taken in grading (or timing) when making the master positive. Test strips should be made and the minimum densities on these strips measured if uniformly good results are to be obtained from scene to scene on each reel of film. It is assumed that it is unnecessary to point out the necessity for carefully cleaning the original negative before making the master positive, for ensuring close and uniform contact of the films at the printing aperture, and for using the most careful developing technique, because these are all basic requirements in the duplication process and it must be obvious that when the exhibition print is made irom a duplicate negative three developing operations have intervened, and all defects are cumulative. While the normal duplicating films are capable of reproducing faithfully the tonal values of the original, the duplicating process is usually accompanied by an increase in graininess. Quite recently, however, the Kodakorganisation introduced on to the American and English markets two entirely new products designed for making satisfactory duplicates free from graininess. These two films are named Eastman Fine Grain Duplicating Positive and Eastman Fine Grain Duplicating Negative, and since their use entails certain departures from normal duplicating practice it will be worth while discussing these two new products fairly completely. The new fine grain Duplicating Positive film consists of a yellow dyed positive type emulsion coated on a clear support, the photographic speed being considerably less than that of the normal positive product. The most satisfactory development characteristics are obtained when this film is developed in a D.76 type of developer, within ,-i gamma range of 1.00 and 1.5. Fig. 3 shows a