Vidicon

A video camera tube design in which the target material is a photoconductor.

A vidicon tube is a video camera tube design in which the target material is a photoconductor. The vidicon was developed in the 1950s at RCA by P. K. Weimer, S. V. Forgue, and R. R. Goodrich as a simple alternative to the structurally and electrically complex image orthicon. While the initial photoconductor used was selenium, other targets—including silicon diode arrays—have been used.

The vidicon is a storage-type camera tube in which a charge-density pattern is formed by the imaged scene radiation on a photoconductive surface which is then scanned by a beam of low-velocity electrons. The fluctuating voltage coupled out to a video amplifier can be used to reproduce the scene being imaged. The electrical charge produced by an image will remain in the faceplate until it is scanned or until the charge dissipates. By using a pyroelectric material such as triglycene sulfate (TGS) as the target, a vidicon sensitive over a broad portion of the infrared spectrum is possible. This technology was a precursor to modern microbolometer technology.

Prior to the design and construction of the Galileo probe to Jupiter in the late 1970s to early 1980s, NASA used vidicon cameras on nearly all the unmanned deep-space probes equipped with remote sensing ability. Vidicon tubes were also used aboard the first three Landsat earth imaging satellites launched in 1972, as part of each spacecraft's Return Beam Vidicon (RBV) imaging system. The Uvicon, a UV-variant Vidicon was also used by NASA for UV duties.

Vidicon tubes were popular in the 1970s and 1980s, after which they were rendered obsolete by solid-state image sensors, with the charge-coupled device (CCD) and then the CMOS sensor.

All vidicon and similar tubes are prone to image lag, better known as ghosting, smearing, burn-in, comet tails, luma trails, and luminance blooming. Image lag consists of noticeable (usually white) trails that appear after a bright object (such as a light or reflection) has moved, leaving a trail that eventually fades into the image. The trail itself does not move, rather it progressively fades as time passes, so areas that were exposed the first fade before areas that were later exposed fade. It cannot be avoided or eliminated, as it is inherent to the technology. To what degree the image generated by the vidicon is affected will depend on the properties of the target material used on the vidicon, and the capacitance of the target material (known as the storage effect) as well as the resistance of the electron beam used to scan the target. The higher the capacitance of the target, the higher the charge it can hold, and the longer it will take for the trail to disappear. The remnant charges on the target eventually dissipate making the trail disappear.

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Vidicon
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Adapted from content published on wikipedia.org
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Last modified on August 16, 2020, 12:04 am
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