We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
TYPES OF FILM RECORDING
25
VOLTAGE ON LAMP
V0 = BIAS VOLTAGE
V, = MINIMUM VOLTAGE
V2 = MAX I MUM VOLTAGE
Figure 8 — Curve showing the relation between light intensity and impressed voltage of an Aeo-lamp.
Figure 8 shows the relation between the light intensity and the voltage. The bias value should be such that the no-signal intensity falls in the center of the straight line portion of the curve, while the maximum alternating -current variation, either plus or minus, must also be within the straight line portion, or distortion will result.
This method of producing variable density records has been superseded in the studios by the variable slit-width method.
(b) Variable Density Recording
Recording by the variable density method is also accomplished by means of a lamp of constant intensity, the light from which is focused by means of a lens on a slit. This slit varies in width according to the electrical intensity of the signal to be recorded, and so varies the amount of transmitted light in proportion to the electrical
impulses. Such a light modulator is called a "Light Valve." The transmitted light is in turn focused upon the film by means of a second lens system.
A current carrying conductor, when placed in a magnetic field, is subjected to a force proportional to changes in the current passing through the conductor. If free to move, the conductor will move a distance proportional to the change in, and the direction governed by, the flow of current. Light valves operate on this principle.
A conductor, placed in a magnetic field and carrying a current, would tend to bow if the ends of this conductor were fixed. The center section of this conductor, if the conductor's length is great compared to its cross-section, would for all practical purposes, move parallel to itself as shown in Figure 9. In commercial application of this principle to the recording light valve, two ribbons are used, as shown in Figure 10.
The light valve ribbon is formed of two strips of duraluminum, 0.0005" by 0.006", spaced 0.001" apart. The ribbon has a natural frequency of its own, depending upon its tension and length, and is consequently tuned for a frequency above the highest frequency to be recorded, which in commercial practice is always above 8,500 cycles. Tuning is accomplished in exactly the same way a violin string is tuned, by changing the tension on the ribbon. The current flows in opposite directions in each of the ribbons of the valve, resulting in an opening