British Kinematography (1953)

138 BRITISH KINEMATOGRAPHY Vol. 23, No. 5 of which, be it lens or screen, can be used alone without grave detriment to the new form. In photographing the picture an optical attachment, known as an " Anamorphic,"' is fitted to the camera lens. The anamorphic attachment records a wider picture than the conventional camera lens but does not affect the height, the result being as though the picture were photographed with a wide angle lens in a horizontal direction and with an ordinary lens in the vertical direction. Observation of the film shows the image to be compressed horizontally. By fitting an anamorphic attachment to the existing projector lens, the image is restored optically to the proportions of the original scene. If a short focus lens has been fitted to the projector for use with the so-called wide screen, this must be replaced by the original lens used for the conventional 4 : 3 picture ratio. The great width of the CinemaScope picture has caused uninformed people to fear the appearance of a ribbon of picture or a letter box. This fear is quite unfounded since the height of picture is determined by the sidelines of the theatre and every effort should be made to preserve the picture height as in the theatre at the present time. Once the height of the picture is established, the width for CinemaScope is determined by the aspect ratio at 2-55 times that height. This gives a picture roughly twice as wide as the conventional 4 by 3 picture for the same height. If a situation exists in a particular theatre which positively limits the picture width, then the height is determined by dividing the maximum width by 2*55. In a number of small theatres it has been found that, with thought and engineering ingenuity, it is possible to install a screen of considerable width and the resulting picture height for CinemaScope remained the same as the former height in the theatre. If the existing projector lens is used in CinemaScope the image on the screen will have a greater height by approximately 19 per cent. Since a larger picture results from the CinemaScope system, screen luminance would suffer unless the efficiency of the screen could be improved or the projector illumination increased. It was for this reason that the Miracle Mirror Screen was developed. The screen recommended for use with CinemaScope is the controlled reflectance type, with a metallic surface, and the Miracle Mirror Screen was developed specifically for presentation of films by the CinemaScope system. The screen is designed so that, within the normal theatre seating region, the distribution is quite uniform. The uniform area of distribution includes 30 above and below and 50° to each side of a line perpendicular to the screen. It will, therefore, be recognized that the typical theatre is adequately covered. There are two types of Miracle Mirror Screen ; one pattern for " head-on " projection and a tilted pattern for ** high-angle ** projection. The choice of pattern depends on the theatre conditions determined at the time of survey. CinemaScope employs four magnetic tracks for stereophonic sound. Three tracks are for the main loud speaker system centre, left and right behind the screen, and the fourth track on a 12 kc carrier, is for the operation of auditorium speakers. Preceding the power amplifier is a simple amplifier-rectifier combination and a separation circuit. The separation circuit routes the audio signal through a low-pass filter and a low-gain (approximately 10 db) amplifier which is normally biased to depress the gain of the channel at least 30 db. The 12 kc control signal is derived from the complex signal by a sharply tuned circuit, is rectified and supplies a bias to the amplifier which restores the gain to normal when the signal is present. The bias circuit is so arranged that when •05 volts or more of 12 kc component is presented to the input terminals of the control device, the amplifier bias reaches a predetermined value ; thus the gain is not variably controlled and the system operates as a simple on-off scheme. The gain of this channel is adjusted to produce a surround level compatible with the screen loud speaker levels. Audience participation is greatly enhanced by this fourth track. 20th Century Fox Ltd., Soho Square, London, W.l. PERSONAL NEWS OF MEMBERS Members are urged to keep fellow members conversant with their activities through the medium of British Kinematography. N. Leevers (Fellow) designed the magnetic tape recording equipment now being used by the B.B.C. mobile recording engineers and by British Movietonews to cover the Royal Australasian tour. The recent operation of separating the threemonths old West African " Siamese " twins was filmed by Stanley Schofield. Obviously a film record of such an event is invaluable for teaching purposes and a very careful study of the requirements from a scientific standpoint was made by Mr. Schofield. No funds were available for the production of the film and so Mr. Schofield decided to produce it at his own cost and present it as a contribution towards the advancement of science.