[MarkusWandel]

It would make sense to adjust the "line width" (focus!) of the scanlines so they blur into each other. But on a multisync monitor, this would be matched to the highest resolution it can display. Without fancy defocusing circuitry, of course if you display only 200 scanlines on a monitor capable of 5x as many, you're going to get a lot of black space between them. This bothered me personally, in those days, in my case with a 20" CRT monitor and emulation of my old C64 environment. Modern "CRT emulation" is better than the real thing, in this case.