The Cine Technician (1953-1956)

THE CINE -TECHNICIAN Jan. -Feb., 1953 The register and resolution chart showing the register marks, resolution charts and small grey scale. This chart is normally photographed at a standard distance using <i standard focal It ngth U ns oj 50mm. is sometimes obstinate and needs a second treatment. This makes life intolerably complicated if a second run is needed on the regular negative processing machine. The printing of the separation negatives made in a three-strip camera must, of course, be done on a register pin printer; but the situation is complicated by the fact that the red record (cyan printer) is laterally inverted since it is photographed with the normal emulsion position but after reflection by the beam splitter. To maintain the correct image orientation and correct register pin position, the red record negative has to be printed through its base, that is, with the celluloid side to the emulsion of the raw stock. This naturally tends to make a print from this negative less sharp than the other two, and since the red record is already less sharp than the other two by virtue Of the fact that it is the rear element of the bipack this is quite a serious matter. This problem can be satisfactorily solved by the use of printers with a specially designed optical system which gave substantially parallel light. The alternative to a parallel light printer is optical printing. Three master positives must be made from the three negatives on a contact printer with all three negatives emulsion to emulsion with the raw stock. This means that two gates will be needed with the large register pin on opposite sides and with silent aperture. From these master positives duplicate negatives can be made in the optical printer with the cyan master printed through the base. This gives three right-way-round duplicate negatives. Making master positives and duplicate negatives from three-strip negatives corresponds to good black and white practice exactly. In addition care must be taken to maintain equality of contrast for all three records throughout the process, and it is good technique, just as it is in black and white, to splice in a short length of grey scale to the tail of all rolls which are to be duplicated. For threecolour the scale should consist of about twelve steps and should be photographed on three-strip negative material so that they will have the same base characteristics as the negative they are spliced up with. From these grey scales the print-through between 03 are may be gammas can be plotted for all stages of the process and each step thus checked for deviation from the normal. The effects of unequal contrast in colour photography are not perhaps as fully recognised as they ought to be, although they arc responsible for many of the out-of-balance effects which are commonly seen in processes which use monopack throughout. They are particularly troublesome here because it is generally not possible with monopack to do anything to correct such unequal contrasts. However, we shall have more to say on this subject later. If, for example, the blue record negative is flatter than the other two and the exposure used in printing this negative is correct for the middle of the tone scale, then both the highlights and the shadows will show colour casts, but in opposite directions — the highlights will be yellow and the shadows blue. That is the situation assuming that both the heavy densities and the light densities in the print at these points should be neutral; if they form part of any coloured areas they will effect this colour rendering in a similar way, the areas which should have a small proportion of yellow will have too much and those areas which should carry a heavy weight of yellow will not have enough. As can be imagined, this would have quite a serious effect on the colour rendition. The same reasoning can be followed through for unequal contrast of any of the other records, and if all three have different contrast then the results can be quite disastrous. At IIB control gammas about .70 a variation in gamma of .05 records is clearly visible and errors of noticeable. Grading The grading of three-strip negatives carried out working on the same basic assumptions as the grading of successive frame negatives. The basic grading for the green record negative can be arrived at by any of the methods in common use in black and white laboratory practice — Cinex strips, visually by experienced operators, or by a combination of visual and spot density measurements. We believe that the last two methods are more satisfactory in practice since the making of Cinex strips usually holds up the flow of work considerably. As soon as each scene has been given a green record grading, the density of a certain point on the lily, using the same frame for each record, is read and noted. The other two records are then graded directly from these density readings. Assuming that printer points of .05 log. E are used and lily readings of 1.20, 1.25 and 1.15 are obtained for the blue, red and green negatives of a certain scene, then the gradings would be | 1 and 2 points relative to the green, whatever it was. This method of grading does, of course, pre-suppose that all negatives have equal contrast and it equalises the highlight for balance. If it were used with a release print material which needed negatives of unequal contrast it would no longer hold good. This grading method when used for three-strip negatives has the disadvantage that if the negatives are fairly heavily exposed there is a risk that the lily will have densities which are over the shoulder of the blue record. The blue record gives a low maximum density because it is thinly coated, and a thin emulsion is essential if anything like good red record definition is to be obtained. So for lily densities on the green record greater than about i.45 there is a likelihood that the ha lance given by the three density readings will not be the best balance. Of course, this over-exposure of the lily can be avoided by care on the part of the camera