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Part of the problem is that cameras (digital or film) that produce pleasing pictures of natural scenes have a contrast boost in the mid tones, with a gradual S-curve compression of highlights and lowlights,compared to the original scene. TV systems have this contrast boost as well. The result when photographing the screen is a double contrast boost. The raw capture of a digital camera actually has enough dynamic range, so if you can capture in raw mode and reduce the contrast in Photoshop, you may get decent results.
There is one other problem that can occur (less so on color CRTs than monochrome) - if the CRT is resolving scanning lines with dark spaces in between, this means that the average level in an area (which the eye can see quite well) is made up of bright lines and dark spaces. Both film and digital cameras have a hard time accomodating that dynamic range. The actual video variation of the bright lines ends up compressed into the highlight region of the digital sensor or film when the average is correct. For best gray scale, the focus (either CRT or camera) needs to be just not so sharp that lines with spaces are visible. Some film recording systems used a vertical spot wobble at a high frequency to just make the bright lines touch each other. Your use of reduced resolution may help by averaging nearby pixels, but it may not be a cure if some of those pixels are overexposed and some are seeing black. An alternative is to underexpose the average, then blur the lines together precisely in Photoshop (by reducing resolution), and then boost the average back to normal. This problem is similar to taking pictures of stars at night. The system really can't handle the dynamic range, but a tiny bit of defocussing changes the brightness modulation somewhat into an area modulation (brighter stars light up bigger blobs of pixels) and gives the right final impression.
So, something to try:
Shoot at highest resolution, with exposure compensated down by at least one stop;
Then reduce the resolution to average the bright and dark adjacent pixels;
Finally, increase the levels to the correct average.
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