British Kinematography (1951)

Record Details:

Something wrong or inaccurate about this page? Let us Know!

Thanks for helping us continually improve the quality of the Lantern search engine for all of our users! We have millions of scanned pages, so user reports are incredibly helpful for us to identify places where we can improve and update the metadata.

Please describe the issue below, and click "Submit" to send your comments to our team! If you'd prefer, you can also send us an email to mhdl@commarts.wisc.edu with your comments.




We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.

Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.

56 Vol. 18. No. 2 BACK PROJECTION IN THE KINEMA J. L. Stableford (Member)* Read to the 8.K.S. Theatre Division on December 12% 1950 BACK projection was probably introduced into early theatres because of structural difficulties. For example, old type music halls, where it was not feasible to build a projection booth in the conventional position, were converted to back projection. The screens in such cases usually consisted of cotton. I. PRESENT SYSTEMS OF BACK PROJECTION A cotton sheet will produce a substantial real image by back projection, but direct rays of light will pass through the weave and completely mar the viewing. Therefore, the cotton was treated with a type of varnish or linseed oil medium, and was even kept continuously wet by dripping water down it. Judged by modern standards, the picture was unsatisfactory, even when the screen was new. The doping medium rapidly oxidised and collected surface dirt. The actual fibre of the fabric itself having a high refractive index therefore had considerable opacity. Whilst acting as an efficient diffuser, it also acted as an even more efficient absorber or stopping agent. Another unfortunate characteristic of this type of screen is that it acts as an efficient front projection screen; the doping of the fabric somewhat reduces this effect, but the net reflectivity* is still substantial, probably of the order of 50%. If a rear projection screen reflects back towards the incident ray something like half the total available light flux, there is only one-half of this light flux available for useful work. Of this remaining half, about 25% is absorbed by the textile material of the screen. The light that is available to form an image on the front surface of the screen is much attenuated. A number of theatres have survived in this country to the present day with back projection — somewhere between 30 and 40 out of a total of nearly 5,000 — but I do not recall any theatre which has been designed and built for use with back projection. Certainly, it has been used on modern oceangoing liners, but only because of thefr special requirements. Advantages of Back Projection There are advantages of changing to back projection. For example, the severity ot present day Home Office regulations produces an irksome technical and financial burden on theatre operators. If efficient and acceptable back projection were available, it is conceivable that the severity of these regulations could be relaxed. In a normal assembly hall used for varied types of entertainment, the moment a film is introduced into the building these regulations come into force. If the picture could be projected from a source remote from the hall, there is no obvious reason why these regulations should apply. With back projection, a theatre could be designed so that the projection booth, film storage and all ancillaries of a hazardous nature could be housed in a separate building to which the public had no access. It would be joined to the main building by a fireproof trunking and fireproof shutters to the portholes. Consideration of this advantage, however, has not been sufficient to induce even an occasional change-over to back projection. II. PHYSIOLOGICAL REQUIREMENTS OF KINEMA PROJECTION Our greatest sensation of stimuli is received by foveal or central vision, where the acuity .is of a very high order.1 This foveal vision functions over an extremely narrow arc, approximately 1°, and the fact that we appear to see things with great sharpness over a substantial area is due to the fact that * Stableford Screens Ltd.