Flaws in Television
A Recent Report ee | ey a recent paper ‘ written for the LR.E., ©. Francis Jenkins’ declares | that popular opinion grossly exaggerates the stage at which television has arrived. In his own words: . ® -"All television, radiovision and radio movie systems employ the method of scanning the picture at the receiver by observing a single light point moving . in successive adjacent lines. "The generally practised method consists in sighting and fluctuating light source through miniature holes spirally located in whirling disc. In such a mechanism the light source must be as large as the picture is, preferably somewhat larger. The resultant current requirement is therefore some 2500 times greater than would be required if the light could be limited to the visible spot alone. "In the new scanner, a drum turned four times per picture. The size of the mechanism is therefore reduced proportionately, that is, a seven-inch drum gives as large a picture asa 36 inch dise. "This type of scanner permits the employment of but a relatively small light cathode with a correspondingly small current required to light it, in a ratio of perhaps 1 to 20 of that required for a dise scanner. "Another advantageous feature incorporated in the drum scanner is the employment of quartz rods to overcome the inverse square light loss law. That it is very effective is conclusively shown by removing the rods, in which event not enough light reaches the drum surface to make a picture. "Again, as. persistence of vision is dependent on the assembly of the elementary .areas which make up the picture, the light strength on the eye is but one twenty-five-hundredth of the spot of intensity, so that the bright scanning aperture appears very dim in motion. ,
"While the drum type scanner 1s a great advance over the dise scanner, . both are believed to be inherently wrong in principle. In current-to-eye efficiency the dise is very faulty, being less than one fifty-thousandth of 1 per cent. The substitution of persistence of elementary area for persistence of vision is believed to promise far greater possibilities in development. . "A projector built on this principle for theatre screens is in work in the laboratory at this time, and with gratifyingly promising results."
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Radio Record, Volume III, Issue 7, 30 August 1929, Page 5
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371Flaws in Television Radio Record, Volume III, Issue 7, 30 August 1929, Page 5
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