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How does a screen work?

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572 points chkhd | 1 comments | 13 Jul 25 14:09 UTC | HN request time: 0.25s | source
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retrac ◴[13 Jul 25 16:39 UTC] No.44551618[source]▶
CRTs are still slightly magical to me. The image doesn't really exist. It's an illusion. If your eyes operated at electronic speeds, you would see a single incredibly bright dot-point drawing the raster pattern over and over. This YouTube video by "The Slow Mo Guys" shows this in action: https://youtu.be/3BJU2drrtCM?t=190
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grishka ◴[13 Jul 25 17:03 UTC] No.44551812[source]▶
To me the magical part about CRTs is color. I don't quite understand how the shadow mask works. Like, yeah, there are three guns, one for each color channel, and the openings in the mask match their layout, and somehow the beam coming out of each gun can only ever hit its corresponding phosphor dots. Even after being deflected. But... how? Also, wouldn't the deflection coils affect each of the three beams slightly differently?
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1. pulvinar ◴[13 Jul 25 17:35 UTC] No.44552016[source]▶
Each hole in the shadow mask acts as a pinhole camera, giving an inverted image (in electrons) of the three guns. All three beams get bent nearly the same amount, but yes there is some distortion which is traditionally corrected for by a set of convergence coils and corresponding circuit with knobs for static and dynamic convergence [0]. A pain to adjust, BTW.

[0] https://antiqueradio.org/art/RCACTC-11ConvergBoardNewRC.jpg