The Optical Magic Lantern Journal (December 1900)

The Optical Magic Lantern Journal and Photographic Enlarger. 165 In short, it is absolutely necassary, in order to obtain a true colour record, to photograph through ‘ colourcurve screens, and correct synthesis is possible only with “ pure colour ’’ screcns. It is true it may happen that, in dealing with compound colours, the cflects of departure from theoretically correct conditions will not always result so disastrously as in dealing with the spectrum itself; but no reliance | | | can be placed upon any but fundamentally correct methods. It is also true that the habit of the eye and mind, due to familiarity with monochromatic photographic reproductions, makes some dilution of colour acceptable to most people, but a recognition of the principle I have stated is necessary in order to introduce this dilution without change of hue. The dilution must be equivalent to adiixture of white light only, and this is roost per° fectly effected by broadening the spectrum bands which are taken as synthesis colours without materially displacing them In positive synthesis we build up our composite colour photographic image by adding lignt to light, red, grecn, and biuc, as already described ; but we may also employ a method of negative synthesis, producing fixed colour prints upon paper or glass, in which case we commence with our white surface, and build up the picture by superposing coloured shadows (transparent colour prints) upon it. This method is essentially complementary to the other, and the colours of the transparent prints are like tke shadows of the corresponding positions in the white field of the triple lantern. Red, green, and blue, being the colours in positive oY ban & Fase PRESTWICH PROJECTOR, In the new cinematograph projector lately introduced by the Prestwich Manufacturing Co., of 744, High-road, Tottenham, there is a very ingenious method of ensuring that the pic ' tures shall appear in the correct relation to the synthesis, minus red, minus grecn, and minus blue, or : cyan blue, bright crimson, and yellow, are the printing colours. If our white surface, against which these colour prints are superposed, were a white made by mixing red, blue, and green spectrum rays, no further definition of the printing colours would be necessary. Inasmuch, however, as our white is ordinarily madc up of all the spectrum rays. it becomes necessary to consider the absorption of the colours in the intermediate spectrum regions. The function of the printing colours is to most efficiently subtract irom ordinary white light the visual impression belonging to the respective simplc colour elements. In other words, the printing colours as seen in ordinary white light should appear to match as nearly as possible the minus (shadow) colours which may be produced in the physiologically white field of a device for positive synthesis. This would not be accomplished by absorptions complementary to the correct photographic action, for the reason, for instance, that a minus red (c line) is considerably more antichromatic to the red clement than a minus yellow (D line), although the yellow is morc active than the red in the production of tke respective negative, in accordance with Maxwell's curves. I will give one practical illustration. The absorption of the dye cyanine is in approximate concordance with the Maxwell red curve, and, when it is used as a colour sensitiser on a suitable photographic plate, it yields a density curve also pretty close to the Maxwell red curve; but this colour, in ordinary daylight, is no more like our minus red than cobalt-blue glass is like signal-green. The relative efficiency of the absorption falls as we go towards the next “primary” in the spectrum, because it involves simultaneous damping of the visual impression of that other “primary.” (Lo be continued.) : is shifted. Ty ENS oe en en ee, é / mask. Some instruments are so arranged that the mask is made to move upwards or downwards, but this occasions a dodging about on the screen, whereas with the method adopted in the instrument in question, the mask or aperture remains stationary and the film itself At the lower part of the illustration a small crank handle will be seen, this controls