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BROWDER
August
upward to the light-valve objective lens. This lens forms a spatial image of the lamp filament at the plane of the light-valve ribbons. The reflecting surfaces of the ribbons in turn form virtual images of sections of the filament image, which virtual images are limited in extent by the width of the ribbons and are located also at the ribbon plane. The light-valve objective lens then picks up these reflected images and reprojects them, this time through the clear slit in the inclined mirror and to the film. The cylindrical lens located near the
POSITION OF LAMP FOR RECORDING 'VARIABLE AREA NEGATIVE SOUND TRACK
RECORDING LAMP IN ' POSITION FOR DIRECT POSITIVE RECORDING
LIGHT TUNNEL 1 CONDENSER LENS USED FOR NEGATIVE RECORDING
REFLECTING SURFACE OF LIGHT VALVE RIBBON
CONDENSER LENS FOR DIRECT POSITIVE RECORDING
^RECORDING IMAGE
PARTIALLY REFLECTING GLASS HERE REFLECTS FRACTION OF RECORDING BEAM BACK TO PHOTOCELL FOR PEC MONITORING OR FORWARD TO EYEPIECE FOR VISUAL MONITORING
Fig. 2 — Optical system schematic of variable-area modulator.
film gathers the beam of light from the slit and converges it to the narrow line required for the recording image.
OPTICAL SYSTEM
The complete optical system of this modulator is depicted schematically in Fig. 2. The recording lamp is of the pref ocused type rated at 5 amperes and 10 volts having a single-helix, curved, horizontal filament. The axis of the filament is rotated at 45 degrees to the optical axis which has the effect of reducing the pitch of the filament helix to the point where there are no dark spaces between the coils and the whole length of the filament appears uniformly bright. Some gain in optical efficiency and a considerable saving in space is achieved by locating the lamp fairly close to the light valve employing an auxiliary lens to throw a virtual image of the lamp filament back to the