[old_tv_nut]

Focus in a standard definition CRT can be too good. When the EFL tubes came out, the focus was so sharp that the beam would saturate the green phosphor (and the blue to some extent, I think) and turn the whites pinkish. When the focus was best overall, this would occur in a blurry circular area halfway between the center and the edges. The effect would move in or out as the best focus was adjusted to be center or edge. This got nicknamed "the toilet seat problem," because the affected area looked about the same shape. I was not part of the group looking at the problem, and don't know what was done to fix it either temporarily or permanently.