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192
BRITISH KINEMATOGRAPHY
Vol. 17, No. 6
TABLE I Colour Temperatures and Exposure Values on First Test
Voltage on
lamps
K. (colour temp.)
Expo.
sure at 24 f.p.s.
180
3150
-\
190
3300
200
3400
210
3420
220
3500
►
All at 7/2
230
3550
240
3650
250
3750
260
3850
250
m
250
f/2.5
250
...
//3.2
230
f/2
230
f/2.5
230
...
7/3.2
210
f/2
210
f/2.5
210
7/3.2
260 (gradually dr<
)pped to extinction)
7/2
would have been, difficult if not impossible to distinguish between the various takes. The difference in density between the various exposures in the second part of the film was such as might be expected. The last take in the film provided a complete fade-out to blackness, but very little degradation of colour was observed.
Small Influence of Colour Temperature.
The inference drawn as a result of these tests is that, as far as photoflood lighting is concerned, the influence of exposure variation is greater than that of variations of voltage and consequently of colour temperature. It is my opinion that unless gross differences in colour temperature are encountered, this factor is of considerably less importance than precision in exposure. Further, I have long held the view that of the factors contributing to colour balance in the final print, the effect of colour temperature of the light sources used is less than the combined effects of variations in the colour balance of stock, original and duplicating, and variations in processing, provided always that gross differences in colour temperatures are avoided, such as those due to change of type of light source, for example, arcs against incandescent lamps.
Nevertheless, there are occasions where, owing to large differences in colour temperatures of light sources, some control is important.
Choice of Filters.
Filters can be used for two purposes. It is important to keep these two uses quite distinct in the mind. First, they can be used to modify the characteristics of light sources, and second, they can be used to assist in correcting unwanted characteristics of the film itself.
Mention has already been made of slight variations in the colour characteristics of the stock. The extent of the variation will be revealed by tests on the lines outlined above, and if variation is detected which is considered undesirable, it becomes necessary to carry out further tests in order to decide what degree