Image orthicon, << AWR thuh kon, >> is a vacuum tube that was used in some television cameras to take the television picture. It changes light from the scene being televised into electronic signals. RCA Corporation developed the image orthicon in the early 1940’s. Most television cameras used the image orthicon until the mid-1960’s. Today, nearly all television cameras capture the picture using light-sensitive electronic components called charge-coupled devices. See Charge-coupled device ; Television (Creating television signals) .
The front of the image orthicon contains a screen called a photocathode that releases electrons when struck by light focused through the camera lens. Bright parts of the scene release more electrons than dim parts do. Another screen behind the photocathode, called the target, attracts the released electrons, and a positively charged electronic image of the scene forms on the target. This image consists of strongly and weakly charged spots that correspond to the bright and dim areas of the scene. A beam of electrons then scans the target, which absorbs electrons from the beam in proportion to those released by the image. The remaining electrons in the beam bounce from the target.
At the rear of the image orthicon, a device called an electron multiplier strengthens the returning beam several thousand times. This beam becomes the television picture signal.
