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

Page scan 000261 from Principles of cinematography : a handbook of motion picture technology

Record Details:

Title:
Principles of cinematography : a handbook of motion picture technology
Date:
1953
Publisher:
London : Fountain Press
Volume:
Principles of cinematography : a handbook of motion picture technology
Leaf #:
000261
Language:
English
Subjects:
Motion Pictures, Motion Picture Technology
Collection:
Books
Format:
Books
Contributor:
Niles Essanay Silent Film Museum
Sponsor:
Media History Digital Library
Coordinator:
Media History Digital Library
Date Added:
May 15, 2025
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SOUND REPRODUCTION 257 beam is modulated in proportion to the nature of the recording on the track. The track is caused to move past the beam from the exciter lamp at a constant speed and by one of a number of systems employing rollers, fluid flywheels and other devices whereby the film may be isolated from any variations in speed which may be set up by other parts of the projector mechanism and, particularly, from the intermittent forward movement created by the picture moving device. After passing through the film at this point the now varying light beam is focused by an optical unit onto the 'Photo-Cell'. The 'Sound Optics' is so designed that it is capable of isolating one cycle of the highest frequency which will be recorded on the film and will, therefore, be able to present to the photo-cell a light varying in intensity and frequency in exact relationship to the variations in the photographic sound record. The photo-cell is an instrument which is capable of causing an electrical response in true proportion to the amount of light which strikes its surface and, by this instrument, the variations in the light beam, caused by variations in the film track, are converted into electrical energy. Since these electrical variations are initially very small they must be fed to a 'PreAmplifier'. This unit is usually situated within the projector sound head and is used to strengthen the small signals to such a degree that they may be fed by cables to the 'Main Amplifier' (this unit may be some distance from the projector) without any dangerous loss in signal strength. Before passing to the main amplifiers the signal strength may be adjusted by a 'Volume Control' to ensure that the output from both projectors \tia2 PROJECTORS Fig. 116. — Block schematic of sound reproduction.