British Kinematography (1953)

August, 1953 HAWKINS I SCREEN LUMINANCE 45 installation, and not necessarily one of the most powerful and expensive type. Two of the four cinemas that complied strictly with the conditions of the new standard were burning 7mm. H.I. positives at 50 amps, in their projectors. The Diversity of Luminance The facility, available at the laboratories of the Morgan Crucible Company, for projecting simultaneously side by side, two pictures of regulated luminance brought out a number of interesting points on the effect of diversity on the viewing of the picture. The projection of black-and-white films rather than coloured was perhaps more interesting, because it posed a less complicated problem in which only contrasts in luminance were involved, with the exclusion of contrasts in colour. In these tests one projector was set up to give a particular central screen luminance and diversity, the other was set to give the same central luminance ; the diversity was altered. The central luminance was set within the limits given in the standard. Matched prints were then run through the two projectors. Contrary to expectation small diversities, numerically greater than 0.8, did not produce the most sparkling picture. Simultaneous viewing of two pictures, both having the same central luminance, one having a diversity in excess of 0.8, the other being set at 0.7 showed the latter to be the more acceptable picture. It had more life and sparkle and appeared to have the higher central luminance. This was an optical illusion arising from the greater contrast between the centre and edges of the screen when the diversity was 0.7. Further increase in diversity to values below 0.55 caused a hot spot to appear in the centre of the screen ; the luminance in the corners became too low for comfortable viewing. The Future. The revised standard, which was completed at the end of May, 1953, was based on measurements made on screens of normal aspect ratio, between 10 ft. and 26 ft. wide, and intended to be used for showing two dimensional films. During the time the standard was prepared the three dimensional and the wide screen film had not arrived nor indeed had the news of their coming. Both of these types of film may involve processes of vision which are either not used or of minor importance in the viewing of the normal two dimensional film. It therefore appears that revision of the present standard of screen luminance will be required before it is applicable to the newer methods of projection, but it would be fair comment at the present time to say that the standardization of other features, particularly those involving dimensions of screens and projectors and the marking and identification of the prints appears to have the greater urgency. REFERENCES 1. B.S. 1404: 1953 — Screen Luminance (Brightness) the accuracy of measurements of the luminance for the Projection of 35mm. Film. and illumination of kinema screens." Brit. Kine., 2. Losty, H. H. W., and Hawkins, F. S. "Notes on 19, 77, 1951. NEW BRITISH STANDARDS B.S. 1985 : 1953 — Test Films for In 1948 the British Standards Institution issued B.S. 1488 covering a series of test films for 16mm. cinematograph projectors. Since that time consideration has been given to the preparation of standards for a corresponding series of test films for 35mm. projectors. Five standards have recently been published : — B.S. 1985 Part 1. Multi-frequency test films. B.S. 1985 Part 2. Buzz track test films. 35mm. Cinematograph Projectors. B.S. 1985 Part 3. 1000 cycle balancing and sound level test films. B.S. 1985 Part 4. Sound focusing test films. B.S. 1985 Part 5. Scanning beam uniformity test films (laboratory and service types). Consideration was also given to flutter test films. It is not at present considered practicable to prepare any form of comprehensive standard for a test film,