Iconoscope facts for kids
The iconoscope was the very first practical video camera tube used in early television cameras. It got its name from the Greek words "eikon" (meaning "image") and "skopein" (meaning "to look" or "to see").
This invention was a big step forward for television. Before the iconoscope, TV cameras used mechanical parts like spinning disks or special bright lights to capture images. The iconoscope was different because it was a fully electronic system. This meant it could produce a much stronger signal and work well in normal, well-lit places.
Vladimir Zworykin first described some of the ideas behind this device in patent applications in 1923 and 1925. His research team at Westinghouse Electronic Company showed the iconoscope to the public in June 1933. Later that year, detailed technical papers about it were published.
In Europe, the German company Telefunken bought the rights from RCA. They built a camera called the "superikonoskop." This camera was used for the famous TV broadcast at the 1936 Summer Olympics in Berlin.
The iconoscope was replaced in Europe around 1936 by more sensitive cameras like the Super-Emitron and Superikonoskop. In the United States, the iconoscope was the main camera tube for TV broadcasting from 1936 until 1946. It was then replaced by the image orthicon tube.
Contents
How the Iconoscope Works
The main part of the iconoscope that captured images was a special plate. This plate was made of mica, a type of mineral. On the front of the mica plate, there were tiny dots of material that were sensitive to light. These dots were usually made of silver covered with caesium. They were stuck to the plate with a special glue that didn't conduct electricity.
The back of the mica plate was covered with a thin layer of silver. This setup created many tiny "capacitors." A capacitor is like a tiny battery that can store an electrical charge. Each tiny dot on the plate acted like a pixel, storing a small amount of electrical charge. This whole system was called a "mosaic."
Capturing the Image
First, an electron gun inside the tube would "scan" the plate. This gun is similar to the one in old TV screens. When it scanned, it put electrical charges onto the tiny dots. If the room was dark, these charges would slowly fade away.
But when light hit the photosensitive dots, they would release electrons. The brighter the light, the more electrons were released. This process used up the stored charge in the silver dots. So, the plate would create an electrical "picture" of the image. Areas with more light would have less stored charge, and darker areas would have more.
Reading the Signal
When the electron beam scanned the plate again, it would "read" the remaining charge. Any charge that was still stored in the dots would push back against the beam. This "resisted" charge would then be reflected back into the tube.
A special metal ring, called a collector ring, would gather these reflected electrons. The amount of charge collected by this ring would change depending on how much charge was stored at each spot on the plate. This changing signal was then amplified and turned into the video signal that made up the TV picture.
The collector ring also picked up electrons released by the light-sensitive dots themselves. This could sometimes make dark parts of the image look a bit uneven, depending on the overall brightness of the scene. To fix this, the image was usually kept very brightly lit.
Tube Design
The iconoscope was designed so that both the camera lens and the electron gun pointed at the same side of the plate. The plate was usually placed inside a cylindrical tube with flat ends. A regular camera lens was put in front of one end, focused on the plate. The electron gun was placed below the lens, angled to also aim at the plate.
Because the electron gun was tilted, the image it "saw" on the plate wasn't a perfect rectangle. It was more like a keystone shape. Also, electrons took longer to reach the top of the screen than the bottom. The camera had special electronics to adjust for these effects and make the picture look right.
The ability of the iconoscope to collect and store electrical charges during each scan made its electrical output much stronger than earlier camera devices.
History of the Iconoscope
Early electronic camera tubes, like the image dissector, had a big problem: they were not very sensitive to light. They only captured the tiny bit of light at the exact moment the scanning system passed over it. This meant they needed extremely bright lights to work.
A better solution was needed, and it came from a new idea called "charge-storage." This idea was discovered and patented by Hungarian physicist Kálmán Tihanyi in 1926. However, it took until about 1930 for this new idea to be fully understood and recognized.
Tihanyi's solution was a camera tube that could collect and store electrical charges (from light) throughout each scanning cycle. He first described this device in a patent application in Hungary in March 1926. He called his television system "Radioskop." After making more improvements in 1928, Tihanyi applied for patents in the United States.
Tihanyi's Radioskop patent is so important that UNESCO recognized it as a "Document of Universal Significance" in 2001. It is now part of the Memory of the World Programme.
Zworykin presented his idea for a completely electronic television system in 1923. In July 1925, he applied for a patent for a "Television System." This system included a charge storage plate made of tiny, light-sensitive dots. The first image from this device was sent in late summer of 1925. However, the quality of the image wasn't very good, and Zworykin was told to work on "something useful."
The first truly practical iconoscope was built in 1931 by Sanford Essig. He accidentally left a silvered mica sheet in an oven for too long. When he looked at it under a microscope, he saw that the silver layer had broken into many tiny, separate silver dots. He realized that these tiny dots could greatly improve the image quality of the iconoscope.
As the head of television development at RCA, Zworykin filed a patent application for this improved design in November 1931, which was granted in 1935.
However, Zworykin's team wasn't the only one working on charge-storage devices. In 1932, Tedham and McGee, working under Isaac Shoenberg in Britain, applied for a patent for a new device they called "the emitron." A 405-line broadcasting service using a more advanced version, the "super-emitron," began at Alexandra Palace in 1936.
Meanwhile, in 1933, Philo Farnsworth also applied for a patent for a device that used a charge storage plate. His patent was granted in 1937.
The iconoscope was shown to the public in June 1933. It was much more sensitive than Farnsworth's image dissector. It could work well with normal lighting conditions. It was also easier to make and produced a very clear image. The iconoscope was the main camera tube used in American broadcasting from 1936 until 1946.
In Britain, engineers Lubszynski, Rodda, and MacGee developed the "super-emitron" (also known as "superikonoscop" in Germany) in 1934. This new device was ten to fifteen times more sensitive than the original emitron and iconoscope. The BBC used it for public broadcasting for the first time on Armistice Day in 1937.
See also
- Image dissector
- Video camera tube
