British Kinematography (1948)

56 DISCUSSION Mr. N. Leevers : Recently there has been a tendency to use penumbra recording, which produces the same type of density track as the light valve. Has Mr. Sewell any information of the relative results so far as fidelity and general efficiency are concerned ? The Author : As I understand it, the penumbra characteristic can be made nonlinear in any desired manner, in order to compensate for non-linearity of the photographic characteristic. Mr. T. S. Lyndon-Haynes : Mr. Sewell said that he would like to use perspective to get a certain off-stage quality when a line was spoken off-screen. Most editors when they are cutting generally use the track that was recorded when the person speaking was actually photographed. Does Mr. Sewell think it worth getting an offstage quality ? The Author : Yes, I do think it worth while, and we usually get tracks of that nature to cover such scenes. If the editor uses the wrong track we get it altered. Mr. Cole : I understand that in the Western Electric system compression is used purely as a limiter, whereas in the RCA system it depends to a considerable extent upon individual preference. Could Mr. Sewell tell us whether it is advisable to set up a particular ratio and held it throughout the production, irrespective of background and set, or is it advisable to change the ratio to suit the particular set ? Also, is it advisable to use compression again in re-recording ? The Author : I think it probably is desirable in some cases to alter the ratio. With a noisy set, you get an excessive backgiound, with the use of compression on the other hand, if you want to get compression you get that effect anyway. If you can be sure that you have got the right amount of compression, it is. better in the original channel ; on the other hand, it might not be enough, and you can add a bit in the re-recording channel. Some types of dialogue may require less compression than others — particularly dialogue which is not declamatory, and low speech. Mr. Gibson : Are there any serious difficulties caused by film base halation at high frequencies ? The Author : There used to be such difficulties, but with the excellent stocks now provided, such difficulties have become almost unobservable. PROJECTION PROBLEMS Discussion between members of the B.K.S. Theatre Division on April 20th, 1947. Why does a condenser arc appear to give a better definition than a reflector arc ? Mr. R. Pulman : It seems that the questioner really means quality of screen illumination rather than sharpness of focus. Dealing first with the spectral composition of the light, the collection angle of the reflector arc is in the neighbourhood of 140°, which suggests that the reflector must receive some light emission from the incandescent shell of the positive carbon, therefore inclining towards the red end of the spectrum. The collection angle of the condenser arc is only about 75°, the light therefore inclining towards the blue end of the spectrum. . Consideration of the polar curves of the carbons and of the geometric forms of overlapping and enlarged images of the crater, suggests that the reflector type of arc can be expected to give a much flatter distribution across the screen. A fall-off at the sides might be preferable. It should not be forgotten that the quality and type of all materials which transmit or reflect light of the various wavelengths leaving the carbon crater can appreciably alter the spectral composition of the resultant emission incident upon the observer's eye. Dr. F. S. Hawkins : Another factor in the matter might be the greater gate heat of the mirror arc, due to which the film would presumably buckle more in the gate, so reducing definition. I recall a paper by Kodak in