Principles of cinematography : a handbook of motion picture technology (1953)

GENERAL TRENDS AND RECENT INVENTIONS 429 cinema attendants are capable of illuminating the aisles intelligently and, in fact, usually succeed in temporarily blinding not only the new patrons but also those who are seated in the near vicinity. It is therefore most likely that this new medium will be quite as useful as it is pleasing in appearance. Since, with continual use, the carpet may become coated with dirt, and presumably the fluorescent design would then be obscured, it is necessary to restrict the use of such material to that part of the cinema which is within the auditorium and to provide sufficient carpeting of the normal type or, in wet weather, carpet covering between the auditorium and the main entrances in order to collect the bulk of the dirt which is normally carried in from the street. (d) Stereoscopic Pictures by Coloured Spectacles. Before leaving the presentation, or theatre aspects of cinematography, it is necessary to mention one other technique which, although it cannot be classified as recent or wholely successful, indicates one line of research which has engaged the attention of many people. As is well known, the impression of realism would be greatly increased if the screen picture could be given the third dimension. Efforts to produce this stereoscopic effect have, in general, been made in three main fields namely (1) by the use of coloured filters, (2) by the use of Pola Screens and, (3) by steel wire grids mounted in front of the screen. Present day two-dimensional pictures appear to be 'flat' because they are photographed from one position whereas, in real life, scenes are always viewed from two positions. These two positions, corresponding to the distance between the two eyes, enable us to estimate the relative separation between objects located at different distances from the viewing position. This fact may be easily proved by attempting to thread a needle with cotton when both are held at arms' length and one eye is closed. Stereoscopic pictures are accomplished when two films are taken through two camera lenses which are separated by a distance equal to the separation between the human eyes. Each film must afterwards be projected so that only that film which was taken by the left hand camera will be seen by the left eye whilst that film which was taken by the right hand camera will be seen by the right eye. One of the earliest methods employed to obtain this requirement was to mount two cameras at the required separation and, therefore, to produce the two required negatives. These negatives were printed onto separate positive reels which were then projected in such a manner that the film corresponding to that taken by the left hand camera was projected through a red filter, whilst that corresponding to the right hand camera was projected through a green filter. The audience was then required to wear spectacles, the left glass of which carried a red filter whilst the right carried a green filter. In some cases the actual projection arrangements have been modified so that two projectors are not necessary and both the original negatives are combined onto one positive film. This combined picture is then projected at double speed through one machine and a rotating disc, carrying alternate red and green filters, is then mounted in front of the projection lens so that the pictures corresponding to the view points are again separated and each is caused to appear only to the corresponding eye