Iconoscope

Jai Ganesh · 2025-07-01 18:09:12

Iconoscope

Gist

The iconoscope was an early electronic camera tube used to scan an image for the transmission of television. No other practical television scanning device prior to it was completely electronic, although some, such as the Nipkow disc, combined electronic elements with mechanical ones.

The iconoscope is an early electronic camera tube that was crucial for the development of television broadcasting. Invented by Vladimir Zworykin, it converted optical images into electrical signals, enabling the transmission and reception of moving pictures. Though superseded by later technologies, the iconoscope was the first practical video camera tube and a key step in the evolution of television.

Summary

In 1923 Vladimir ZworykinOffsite Link, a Russian immigrant to the United States, working at WestinghouseOffsite Link Laboratories in Pittsburgh, patented the iconoscopeOffsite Link, the first electronic television camera. His design, however, was incomplete:

"Vladimir Zworykin is also sometimes cited as the father of electronic television because of his invention of the iconoscope in 1923 and his invention of the kinescopeOffsite Link in 1929. His design was one of the first to demonstrate a television system with all the features of modern picture tubes. His previous work with Rosing on electromechanical television gave him key insights into how to produce such a system, but his (and RCA's) claim to being its original inventor was largely invalidated by three facts: a) Zworykin's 1923 patent presented an incomplete design, incapable of working in its given form (it was not until 1933 that Zworykin achieved a working implementation), b) the 1923 patent application was not granted until 1938, and not until it had been seriously revised, and c) courts eventually found that RCA was in violation of the television design patented by Philo Taylor FarnsworthOffsite Link, whose lab Zworykin had visited while working on his designs for RCA.

"The controversy over whether it was first Farnsworth or Zworykin who invented modern television is still hotly debated today. Some of this debate stems from the fact that while Farnsworth appears to have gotten there first, it was RCA that first marketed working television sets, and it was RCA employees who first wrote the history of television. Even though Farnsworth eventually won the legal battle over this issue, he was never able to fully capitalize financially on his invention".

Details

The iconoscope (from the Greek: εἰκών "image" and σκοπεῖν "to look, to see") was the first practical video camera tube to be used in early television cameras. The iconoscope produced a much stronger signal than earlier mechanical designs, and could be used under any well-lit conditions. This was the first fully electronic system to replace earlier cameras, which used special spotlights or spinning disks to capture light from a single very brightly lit spot.

Some of the principles of this apparatus were described when Vladimir Zworykin filed two patents for a television system in 1923 and 1925. A research group at Westinghouse Electric Company headed by Zworykin presented the iconoscope to the general public in a press conference in June 1933, and two detailed technical papers were published in September and October of the same year. The German company Telefunken bought the rights from RCA and built the superikonoskop camera[6] used for the historical TV transmission at the 1936 Summer Olympics in Berlin.

The iconoscope was replaced in Europe around 1936 by the much more sensitive Super-Emitron and Superikonoskop, while in the United States the iconoscope was the leading camera tube used for broadcasting from 1936 until 1946, when it was replaced by the image orthicon tube.

Zworykin's patent diagram of a UV-microscope 1931. The apparatus is similar to the iconoscope. The image entered through the series of lenses at upper right, and hit the photoelectric cells on the image plate at left. The cathode ray at the right swept the image plate, charging it, and the photoelectric cells emitted an electric charge in variance with the amount of light hitting them. The resulting image signal was carried out the left side of the tube and amplified.

Operation

The main image forming element in the iconoscope was a mica plate with a pattern of photosensitive granules deposited on the front using an electrically insulating glue. The granules were typically made of silver grains covered with caesium or caesium oxide. The back of the mica plate, opposite the granules, was covered with a thin film of silver. The separation between the silver on the back of the plate and the silver in the granules caused them to form individual capacitors, able to store electrical charge. These were typically deposited as small spots, creating pixels. The system as a whole was referred to as a "mosaic".

The system is first charged up by scanning the plate with an electron gun similar to one in a conventional television cathode ray display tube. This process deposits charges into the granules, which in a dark room would slowly decay away at a known rate. When exposed to light, the photosensitive coating releases electrons which are supplied by the charge stored in the silver. The emission rate increases in proportion to the intensity of the light. Through this process, the plate forms an electrical analog of the visual image, with the stored charge representing the inverse of the average brightness of the image at that location.

When the electron beam scans the plate again, any residual charge in the granules resists refilling by the beam. The beam energy is set so that any charge resisted by the granules is reflected back into the tube, where it is collected by the collector ring, a ring of metal placed around the screen. The charge collected by the collector ring varies in relation to the charge stored in that location. This signal is then amplified and inverted, and then represents a positive video signal.

The collector ring is also used to collect electrons being released from the granules in the photoemission process. If the gun is scanning a dark area few electrons would be released directly from the scanned granules, but the rest of the mosaic will also be releasing electrons that will be collected during that time. As a result, the black level of the image will float depending on the average brightness of the image, which caused the iconoscope to have a distinctive patchy visual style. This was normally combatted by keeping the image continually and very brightly lit. This also led to clear visual differences between scenes shot indoors and those shot outdoors in good lighting conditions.

As the electron gun and the image itself both have to be focused on the same side of the tube, some attention has to be paid to the mechanical arrangement of the components. Iconocopes were typically built with the mosaic inside a cylindrical tube with flat ends, with the plate positioned in front of one of the ends. A conventional movie camera lens was placed in front of the other end, focused on the plate. The electron gun was then placed below the lens, tilted so that it was also aimed at the plate, although at an angle. This arrangement has the advantage that both the lens and electron gun lie in front of the imaging plate, which allows the system to be compartmentalized in a box-shaped enclosure with the lens completely within the case.

As the electron gun is tilted compared to the screen, its image of the screen is not as a rectangular plate, but a keystone shape. Additionally, the time needed for the electrons to reach the upper portions of the screen was longer than the lower areas, which were closer to the gun. Electronics in the camera adjusted for this effect by slightly changing the scanning rates.

The accumulation and storage of photoelectric charges during each scanning cycle greatly increased the electrical output of the iconoscope relative to non-storage type image scanning devices. In the 1931 version, the electron beam scanned the granules; while in the 1925 version, the electron beam scanned the back of the image plate.

Additional Information

The iconoscope was an early electronic camera tube used to scan an image for the transmission of television. No other practical television scanning device prior to it was completely electronic, although some, such as the Nipkow disc, combined electronic elements with mechanical ones. Within glass housing, the iconoscope contained a photosensitive plate or “mosaic,” which divided the image to be televised into tiny sections called pixels. An electron gun, also placed in the housing, projected a scanning beam of electrons toward the plate. Deflecting coils directed the electron beam, which charged the plate’s pixels. The charge of individual pixels was proportional to the brightness of light initially focused on them, so that the electrical signal produced derived from the original image. From the output of the camera tube, the signal traveled to an amplifier before being transmitted to a receiver.

A Russian-born American, Vladimir Zworykin, invented the iconoscope in 1923. Now commonly referred to as the “father of television,” Zworykin worked at the Westinghouse Electronic Company at the time he filed a patent for the iconoscope. According to the patent, he planned for the device to be part of a completely electronic television system. It would take Zworykin six more years, however, before he could actually construct an effective electronic receiver, which he dubbed the kinescope. The Radio Corporation of America (RCA), the parent company of Westinghouse, funded Zworykin’s television research. In 1939, RCA finally reaped the benefits from their investment when they used Zworykin’s system to broadcast TV to the public for the first time.

In the decades following the iconoscope’s invention, improved camera tubes appeared and gradually replaced Zworykin’s version. Many of them, however, were based on the same basic principles as the iconoscope and featured somewhat similar designs. As TV broadcasting was refined and the technology involved became more affordable, more and more people became familiar with television.

Television eventually became fully integrated into the daily lives of Americans. Today in the United States, people watch more than four hours of TV each day on average, and a typical American household contains at least two television sets. Despite his role in its development, Zworykin, who lived into the early 1980s, became concerned with the direction television had taken and its affect on society. He had hoped TV would serve to educate the public and to broadcast cultural events. Dismayed at the trivial and counterproductive materials often featured on television, Zworykin lamented in his later years, "I hate what they've done to my child ... I would never let my own children watch it."

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#1 2025-07-01 18:09:12

Iconoscope

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