vidicon

Vidicon is a type of vacuum tube image sensor used in television cameras. It was developed in the mid-20th century and became a common imaging device in broadcast and field cameras before being largely superseded by solid-state sensors.

The tube contains a photoconductive target—typically cadmium sulfide (CdS)—deposited on a transparent glass substrate, and an electron gun. A high voltage is applied to the target assembly. When light from the scene hits the photoconductive layer, its resistance changes in proportion to brightness, creating a charge distribution on the target.

The image is read out by scanning the target with a focused electron beam. As the beam sweeps the surface, the local resistance modulates the current collected by the tube, producing a video signal that corresponds to the brightness at each point. The target is periodically refreshed, which can introduce some lag or smear in fast-moving scenes.

Development and use: Vidicon tubes were introduced in the 1950s and became widely used in professional broadcast cameras through the 1960s to the 1980s. In color television, three vidicon tubes were commonly used for the RGB channels in early color cameras, or they formed part of color processing in later designs.

Advantages and limitations: Vidicons are relatively inexpensive, rugged, and compact, with moderate sensitivity. Limitations include noise, limited dynamic range, lag due to charge storage in the photoconductive layer, and color performance that did not match later solid-state sensors.

Decline and legacy: With the rise of CCD and CMOS image sensors, vidicons fell from favor in new equipment by the late 1980s and 1990s, though some archival gear and specialized applications continued to use them for some time.