The Cine Technician (1953-1956)

THE CINE-TECHNICIAN Jan. -Feb., 1953 cords and if these three negatives are printed at the same printer light settings, the print process should be so set up and maintained that the grey will reproduce as a grey. If now the printers are correctly calibrated to give known and equal increments of log exposure for each light then the relative gradings for each record can be assigned from density readings on a neutral object or the white step on the grey scale. In practice this system is operated in the following way. The green record negative is taken as a standard, since it most resembles a normal black and white negative, and is graded visually or by any other method preferred such as Cinex strip or spot density readings. The white step density of each record is then read on the densitometer and the densities noted. Let us suppose that the densities are blue 1.25, red 1.40 and green 1.35, then if for example the printer points are set at 0.05 log E, and the green record needs light 11, the blue will need light 9 and the red 12. For cartoon work, once a particular laboratory has set up its processing standards the basic green record gradings can also be made from the white step density reading. But, although exactly the same method as that described may be used for colour grading the three records for Wedge spectograms for the Eastman three-strip stocks used in the colour camera. Tin bottom print shows the basic sensitivity oj tin red record film (8227) and the top print the sunn Hint after filtering l'ii thi red tilti i layer. The seco>ul print from the bottom shows tin sensitivity of tin green record (822^1 exposed without a yellow filter. Tht third print from tin bottom shows the sensitivity of tht blm record film (8229) winch carries the red filter layt r puppet and live action photography, the basic green record grading must be assigned by more normal methods such as those suggested above. Three-Strip Camera Negatives Beam splitter cameras use three special Eastman raw stocks which each record only one-third of the spectrum. These three films are designed to be used in a camera layout which has become the only successful one of the many possible film arrangements in a beam splitting colour camera. This arrangement is generally known as bipack and one — and has a single, green recording film in the direct beam from the camera lens and a blue and red recording bipack in the reflected beam. The front film of the bipack is blue recording and is exposed through the base; the emulsion of this film carries on its upper surface a thin layer of red dye which effectively restricts the rear film to recording the red in spite of its additional blue sensitivity. The single film is in fact equally sensitive to blue as it is to green but is exposed through a light yellow filter, an Aero 2 which cuts off at about 460-470 m„. The latest type of this three-strip stock being made by Eastman at the present moment gives more or less equally exposed records in light of daylight quality, say 6,500° K. For high intensity arcs a Y-l filter gives correct balance whilst a Duarc is satisfactory without a filter. A key light level of 300 foot candles is needed under these conditions for this film at f/2 and a gold semi-reflector in the camera prism gives the most efficient transmittancereflectance ratio by virtue of its slightly dichroic effect. If a silver semi-reflector is used in the prism a higher blue reflectance can be obtained and the new emulsions exposed in tungsten lighting of about 3,350° K. and at key light levels of the order of 150 foot candles. The registration of the negatives obtained in a throe-strip camera is primarily a matter of engineering. It involves the precise fitting of the lenses, the prism and the two gates so that the three images are of exactly the same size and will be in register if printed on suitable gates with a fullyfitting pin in the correct position. Good register in a colour camera also demands engineering to exceedingly fine limits. A difference of image placing of 2/10 of 1 T,000in. is visible as a fringe 1/10 of l/l,000in. as a lack of critical definition. Even with the most careful maintenance such accuracy is difficult to hold under normal studio and location conditions and so there is always a possibility that negatives made in a colour camera may be out of register. Register may vary in one or more of three ways — horizontally, vertically or skew. The first two can be fairly simply corrected by optical printing but skew register is very difficult to correct. We feel that it is probable that an optical printer is, on occasion, an essential adjunct to a colour camera. The most scrupulous camera maintenance is also needed to ensure the best possible bipack contact at the moment of exposure. Consistent with good rear element definition the pressure on the bipack should be small enough to ensure that scratches are avoided. An average of 25 to 28 lines per millimetre resolution on the rear film of the bipack should be aimed at, and under good conditions 30 to 33 lines per millimetre should be possible. When photographing with a three-Strip camera. there are two types of chart which must be shot from time to time if adequate control is to be main