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Otto Schade did research in which the raster was reduced in size. With a fine beam, it showed that the target was capable of finer resolution.
In pickup tubes, it is necessary to have the beam wide enough to produce complete discharge of the target in one field (not one frame). Otherwise, there is an inverse raster of unread charge remaining on the target. The next scan will then produce a coarse moire' or flicker as it scans slightly out of register with the original scan. This can occur for either interlace or progressive. Of course, for interlace, the beam must be twice as wide as for progressive with the same number of total lines per frame. In old recordings, you can sometimes see this flicker in areas where the beam focus was too good. A similar effect could occur on kinescope recordings when they were rebroadcast, but there the moire' was more often a higher frequency swirly line pattern because the rescan had a much worse match to the original scan than the two fields in a camera.
In CCD pickups, it was found that using every other line of elements for interlaced scanning resulted in far too much vertical resolution, producing excessive interline flicker in interlaced CRT displays. Therefore, rows were combined (with a coefficient that was adjustable to set the vertical peaking in high-end gear). This was the equivalent of the wide scanning beam in tube pickups.
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