The Cine Technician (1953-1956)

Jan. -Feb., 1953 THE CINE-TECHNICIAN as cartoon drawings or puppets in which the movement can he controlled. 2. By the use of three separate films which each record only one spectral band in a special camera known as a beam splitter or three-strip camera. 3. By using in a normal black and white camera a special film stock which records each spectral band in a separate emulsion layer, the three layers being physically separable in the laboratory either before or after development to negative silver images. The first method can be sub-divided into two very similar methods, successive strip and successive frame photography. A normal black and white camera which has the necessary register pins such as a Mitchell or a Bell-Howell is used and is firmly set up so that it cannot move in relation to the subject, for example on a cartoon bench. The work is shot three times, each time to full screen footage, once through a blue filter, once through a red filter and finally through a green filter. This method can only be used when the subject is absolutely static and can be held in a fixed position for considerable periods. Such work as simple title cards or drawings for slide-on-film can be handled in this way. Successive frame work consists of photographing three frames, one each through the blue, green and red filters, for every screen frame. It will be seen that this method produces a single strip of film three times the length of the final screen footage. There must, of course, be absolutely no movement of the subject between the exposure of the blue, red and green frames which go together. For this type of work the filters are usually mounted in a disc which rotates before the camera lens either continuously or in steps in synchronism with the film pull-down. The latter method is preferable and Ernest F. Moy Ltd. make a suitable filter disc and Maltese cross mechanism which will drive it. Gelatin filters are more satisfactory than glass and either the Wratten or the Ilford tricolour set are usually used. In tungsten lighting a normal tricolour set does not give equally exposed negatives at the same stop and the filters should be ordered with combined neutral density to equalise their transmissions, specifying the type of lighting and the film stock with which they are to be used. Control Methods In photographing successive strip and successive frame film, a grey scale of some six or seven steps, with a black step made of flock paper should be used. This scale is shot at the head end of every scene as an exposure check and for grading in the laboratory. A length of three feet for successive frames and one foot for each record on successive strips is generally adequate. Successive frame negatives are generally processed to a IIB gamma which is normal for the stock they are photographed on, say within the range 0.65 to 0.70. With successive strip negative however, since they are in separate strips, a slight increase in the development time to give a higher white light gamma can be given to the blue record negative. If the red and green negatives are developed to a IIB gamma of 0.68 the blue negative will usually be of about the correct contrast to balance the other two, if it is developed to a gamma of 0.71 or 0.72. The lower contrast to blue light which most panchromatic emulsions exhibit is, of course, not always so easily corrected and nothing can be done about it in the case of successive frame negative, for example, at this stage. The printing procedure for successive frame negatives will depend very much on the print process which is to be used, but since it is not very likely that it will be possible or desirable to use an optical printer to make the release copies, the single strip successive frame negative must usually be converted into three separate strips. For this a normal master positive will be made on a suitable stock such as Eastman 5365 and three duplicate negatives made from this on an optical printer. The contact printer which is used for printing the master positive must have register pins in the same positions as the camera which was used to photograph the negative and it should preferably have a gate aperture which has been opened out to slightly larger than the old silent dimensions. This will give a black frame line on the master. If the gate does not have an aperture of this size and a silent dimension aperture is used on the optical printer there will be a considerable area of clear film passing light which will give a considerable amount of flare in the optical printer lens and hence some degradation. The optical printer need only be of the simplest type but it must have a suitable mechanism which will skip two frames in three so that all the blue record frames can be printed on to the negative in one run, all the red in a second and all the green in a third run of the master positive. Both heads must have correct register pins. The gamma to which the master positive is developed should be normal for the stock used, generally about 1.40 or 1.50 and the duplicate negative gammas can be varied, since the three records are now in separate strips, to equalise the contrasts of the three records. The actual gammas for the three negatives will depend on the print process which is to be used, and the compensation which must be made for the contrast increase given by the optical printer. Grading The most satisfactory grading method, in our opinion, is based on the fact that if a neutral grey object in the original scene is reproduced as grey in the print, all the other colours will be correct, at least to a first approximation. If the three separations are correctly exposed, a neutral grey object will have the same density on the three re PRISM BLOCK The prism and film layout which has now become almost standard for running three films in a colour camera has a red, and a blue sensitive film running as a bipack in the reflected beam and a single green sensitive film in the gate which is on the principal axis of the lens