English: Two iconoscope tubes. The iconoscope, invented by Vladimir Zworykin in 1933, was the first practical video camera tube, used in the first historic television broadcasts such as the 1936 Berlin Olympics, and used until about 1946. The RCA type 1849 (top) was the typical tube used in studio television cameras. In the round section (right) looking through the optical "window" in the tube, the dark photosensitive "mosaic" surface can be seen, made of a metal plate covered with a mica sheet with a coating of microscopic silver grains. An electron gun in the "neck" of the tube (left) first scans this surface, depositing a negative charge on it. The camera's lens focuses the image on this surface, and in areas where light falls electrons are ejected from the surface, discharging it. When the electron beam scans the surface again, charged areas reflect the beam, and the reflected electrons strike the "collector ring" electrode around the periphery of the tube and produce the video signal at the contacts on the side, which were connected to the video amplifier. The type 1847 (bottom) was smaller but worked similarly.