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Some good points here. I recall John Watkinson wrote a paper in 1998 on Video Oversampling. He stated that because of the optical filtering ahead of the sensor, it is not necessary to use so many lines to deliver HD. If on the otherhand, the number of pixels on the sensor is substantially higher followed by the optical low pass filter, rescaling to fewer lines will not result in loss of spatial resolution. The only caveat is that oversampling only really works with non-interlaced video.
I believe we now underestimate the resolution of Image Orthicon video since resolution was limited by the structure of the target element and not by a digital imager's pixel array. Hence higher number of pixel imagers, rescaling and progressive scan is the future.
Nevertheless, I would have liked to have seen what a 4" IO tube could yield in terms of spatial resolution.
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