British Kinematography (1950)

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December, 1950 ward : producing 16mm. colour films 191 it is even more desirable to do this with Kodachrome. It is unfortunately true that the speed rating of Kodachrome varies slightly from batch to batch and Kodachrome has very little latitude. Neither is the colour balance of every batch of film completely constant. For precision results, therefore, the need for tests before any new batch of film is used in production is obvious. Because of these factors, it is not desirable to change batches in mid-production, though this may sometimes be inevitable due to circumstances beyond control. Such tests can be carried out on a group of standard objects, such as a group of coloured bricks, well-known branded goods, a colour chart, and rounded objects, as well as black and white objects, but should also include one or more general scenes as nearly as possible in character to those intended in the film. The tests enable an estimate of the speed rating of the batch to be made in relation to the exposure-meter and high-light or other method used, and also a check to be made of the colour characteristics. They will naturally cover a range of exposures on the basis of which the general basic exposure to be used in the film will be decided. In processing the test film the laboratory will be informed that it is a test in order that it may be processed under optimum conditions, so that the effect of day-to-day variations may be avoided, or at least minimised. Nevertheless, day-to-day variations in processing do occur, so that even after establishing the basic exposure in actual shooting in production, bracket exposures should be made to minimise the effect of such variations. It may in exceptional cases even be necessary to change an opinion made of the basic exposure as a result of examination of a run of film from production, though this does not often happen. This leads to the question as to how the film from production should be processed. Certainly not in individual rolls. To wait until the entire picture is shot, however, is too extreme and the answer would seem to be to have it processed in sequences. Making bracketing exposures may seem to be an expensive method of working, but in my experience it is an insurance investment which pays dividends. One further word about exposure. Having established the basic and bracketing exposures — usually half or two-thirds of a stop on either side of the basic — these should as far as possible be fixed for the entire production, and each scene lit to a standard value. This is undoubtedly of assistance in producing a smoothly flowing picture. The exposure given should generally be as low as is reasonable having regard to the lighting available. Light Sources and Colour Temperatures. A test film was made with photoflood lamps and was designed to try to elucidate the effect of variable voltages on the colour of the image. The details are as follows : — Subject. — Miscellaneous well-known objects. Lighting. — 4 x 275 watt, 240-250 volt, photofloods in individual aluminium reflectors. Voltage. — Varied by means of a Variac transformer. Colour Temperature. — Measured by a Megatron meter directly at the lamps. Exposure. — Measured by S.E.I, meter and brought to standard by adjusting the distance of the lamps from the subject. The colour temperatures due to voltage variation and the lens apertures, are shown in Table I. The reason for the apparently high values for colour temperature is probably the use of newly-painted reflectors which have had a blueing effect. The values given, however, are comparable between themselves. The film was then projected, and showed only negligible variation in colour balance between 180v. and 260v. ; without direct side-by-side comparison it