SIZEABLE TELEVISION IMAGES

Greymouth Evening Star, 23 June 1937, Page 13

SIZEABLE TELEVISION IMAGES

BASED ON ‘DISCARDED’ METHOD. NEW YORK, May 12. An idea, that almost went into the waste basket was introduced to the American Institute of Radio Engineers to-day as pointing the way to eventual success in the projection of sizable television images.

V. K. Zworykin, W. H. Painter and R. R. Law, ail of the Radio Corporation of America, disclosed that present achievements wit ha new high current electron gun or 18-inch television receiving tube, produces an image on its fluorescent screen about 11 by 21 inches so brilliant that a sfinpi© optical system will project it on a comparatively. largescreen. A projected picture, shown by Dr Law as a highlight of to-day’s symposium of technical reports, compared favourably in brightness with home motion pictures and was about 36 by 48 inches in size. Dr. Law explained that the gun is the structure in a television receiving tube which focuses flying electrons into an extremely slender beam. In projection, it is necessary to start with a much smaller and brighter picture than in the case of a. “kinescope” ■which is viewed directly. And since the brightness is dependent on the current in the beam, the smaller picture requires a much largfer beam •current in a smaller “spot.” Despite the enlargement which allowed several hundred engineers to witness the demonstration at once, it was difficult for the eye to detect line-scanning or other details by which the illusion of direct vision was accomplished. Possibly this was to some extent due to the 44-line standard adopted by RCA for practical field tests some months ago. The construction of the new tube which makes this advance possible calls foi* specification so rigid that the idea was at first almost discarded as impracticable. Essentially it is necessary that' the flood of electrons be regimented into the. solid column or narrow beam used to “paint” the received picture ' more vividly on the fluorescent screen of the “kinescope.” The electrons are conditioned for this job by being passed through three metal discs each with an aperture in its centre about the diameter of a lead pencil.

INTENSE BOMBARDMENT. Then they are passed through a fourth and final disc, similar to the others, but with an opening too small to admit a human hair. Electrons pour through’ this tiny opening to the fluorescent screen at the tube’s end. Bombardment is so intense that the light, produced on the screen of the projection kinescope may be spread over an area 100 to 400 times greater in a projected picture.

It. is the terrific electronic bombardment through this final, hole w’ith resultant shojt “life” for the fluorescent material which engineers agree to be one of the “kinks” in the new tube. R.A.C. frankly ' admits this to be true, and is inclined to further agree with engineers that Dr Law’s contribution cannot at this stage of development be incorporated into home television receivers.

The next step appears to be for laboratories to find a luminescent material which will withstand the necessary heavy bombardment, and make it possible for persons other than technical operators with special laboratory equipment to obtain satisfactory images. Another speaker in the symposium was C. E. Bufiiett, who described methods developed by which television receiving tubes may be, tested for faithful reproduction of television pictures. In this work the electrical impulses from the image of .the television camera are not u'sed, but a specially generated set of impulses are made to produce a uniform pattern im which any distortion is readily observed. Since television receiving tubes are most susceptible to distortion when recording impulses at high frequency, the test current is set to provide a pattern at the tube’s upper limit of frequency reproduction. The resulting, very fine, polka-dot pattern is the same as might lie obtained if a halftone engraving were made of a blank sheet of grey papdr. Such a pattern represents the very minimum of reproduction on the 441 line standard. It was pointed out that if the tube performs with uniform sight response at this frequency, it con be trusted to record larger areas of light from a televised subject with at least equal fidelity. The regulation of outdoor illumination to television pickup; the lightdulling effects of city smoke in the atmosphere; technical considerations of pick-up tubes employing cathoderay beam scanning; together with a discussion of the theory and performance of the “Inconoscope,” were themes for other papers read before Congress.