British Kinematography (1950)

204 BRITISH KINEMATOGRAPHY Vol. 17, No . 6 MINIATURE CONDENSER MICROPHONE J. Soc. Mot. Pic. and Telex. Eng., Mar. 1950, p. 303. The microphone comprises a transducer of 0.6 in. diameter, coupled to a miniature valve working as a cathode follower. This unit is connected by cable to a supply unit containing amplifier components and power pack. Radial response curves and constructional details are given. N. L. SUPPLEMENTARY MAGNETIC FACILITIES FOR PHOTOGRAPHIC SOUND SYSTEMS J. Soc. Mot. Pic. and Te/ev. Eng., Mar. 1950, p. 315. Facilities designed for converting to magnetic operation several types of Western Electric equipment are described, including both photographic recording and re-recording machines. Photographic operation may be retained with the magnetic adaption in position if desired. N. L. SPROCKETLESS SYNCHRONOUS MAGNETIC TAPE J. Soc. Mot. Pic. and Te/ev. Eng., Mar. 1950, p. 328 The tape recorder uses standard i-inch unperforated tape on which, in addition to the longitudinal recording of the signal, a transverse recording of a 60 c/s synchronising tone is recorded. In reproduction or re-recording, the synchronising tone may be used to control motor speed. N. L. ADJUSTMENTS FOR OBTAINING OPTIMUM PERFORMANCE IN MAGNETIC RECORDING Albert W. Friend, RCA Review, Mar. 1950. Response curves obtained with " Scotch " magnetic tape demonstrate how the second harmonic can be avoided by carefully adjusting a direct current in the recording head by means of a so-called harmonic-null potentiometer. The choice of suitable bias in order to obtain the minimum of third harmonic and the maximum of sensitivity is also described. Finally, the author concludes that the simplest method of obtaining the harmonic null adjustment referred to is aurally, especially as most amplifiers produce a certain amount of residual hum ; the adjustment is then made to the minimum of noise, which is equivalent to the minimum of second harmonic distortion. O. K. K. A PRESERVATION RECTIFIER WITH ELECTRONICALLY STABILIZED CHARGING VOLTAGE E. Cassee, Philips Tech. Rev., Mar. 1950, p. 253. In a battery charging lectifier, the battery voltage is amplified to provide control current to a transductor. Consistency of charging voltage to within ±0.5°o is attained. R. H. C. THE LABORATORY TECHNICIAN The Editor, grounding in the English language, but a " British Kinematography." laboratory technician who has not a Dear Sir fundamental knowledge of the tools with Dr. Levenson's review of Lobel and which his technique is operated is nothing Dubois in the October number of British but a labourer and such he should remain Kinematography raises a question on which unless he studies the rudiments of mathe there may well be differences of opinion. matics and physics as such, and not as mere In my view "intermediate grounding in tncks b* whlch sensitometry can be made physics and algebra " is not only an ad ea^ifr' r . , . , tt *, vantage but a necessity for those who work Therefore I say, when Jones Photo in sensitometry, or indeed in any techno 8raPhulc Sensitometry is reprinted, leave logical branch of kinematography. °ut the, introductory section and send A case may be made out for photo tne readers t0 schooK graphers who know nothing or care less i arr,5 sir, Yours faithfully, about photography, or for script writers who have not even an intermediate J. L. French.