What are the advantages of a flat-screen CRT television/monitor/whatever versus a standard round-screen CRT?
Meta-question: how do flat CRTs work, anyway? I’d imagine mostly the same process as a round CRT, but what makes flat CRTs different, other than the flatness?
originaly all CRTs were curved as it was the only way to focus the beam but gradually the focusing was improved and the curvature radius improved to the point where the screen could be made flat. Still, the curvature of most monitors today is close to being flat.
CRT monitors that claim to be flat screen, are actually slightly concave. The purpose of having a flat is to get an almost completely distortion-free image.
Flat screens tend to have less reflection too. A convex surface will reflect pretty much everything in the room, including all light sources and windows.
The ones I’ve seen actually are flat. The reason for the curvature of standard CRTs is so the distance to the screen from the electron gun is the same no matter where on the screen the bean is pointing, thus the focus is maintained. With modern electronic technology, the focus of the beam can be adjusted on the fly to compensate accurately for where on the screen the beam is pointing, so that a flat screen can be used while maintaining sharp focus across the entire field. Incidentally, in the inustry, this is referred to as flat tube, as opposed to flat screen, which is reserved for LCD and plasma flat-panel monitors and TVs.
Actually, this is the other way around. A screen which is part of a sphere with the center at the cathode electron gun would have no distortion. A flat screen without correction would make central pixels smaller and edge pixels larger, just as happens in a flat photograph or flat movie screen.
Making a flat, or close to flat, CRT is pretty complex as the differing geometry at the center and edges needs to be taken into account and compensated for. Also the shadow mask for the different colors has to be designed for it. http://entertainment.howstuffworks.com/tv2.htm
>Actually, this is the other way around. A screen which is part of a sphere with the center at the cathode electron gun would have no distortion.
No, it’s more complicated than that. It depends on how you define distortion.
From the point of view of an ideal computing environment, the programmer’s model of a display is that it’s planar and has pixels mapped in a Cartesian lattice. Similarly if you print a display on paper you can do so without distortion and the paper will lay flat on a planar surface.
From the point of view of the human eye, there’s a lens (the curved cornea at the very front, not the “crystalline lens” inside which is really more for fine tuning), and it projects onto a concave retina, more like a spherical screen. To first order this is mapping solid angle onto a spherical surface and doesn’t need to introduce any distortion.
From the point of view of geometry one adopts one of the infinite variety of transforms from spherical coordinates (like solid angle in the real world) and Cartesian coordinates (like Windows). For any such transform there is some sense in which there is no distortion, and in every other sense there must be distortion. Remember the different forms of map projection, like Mercator?
From the point of view of CRT technology, it would be somewhat easier to design a CRT if the screen were a constant distance from the electon guns, which would make it spherical but convex from the point of view of the user.
Practically, all display designers acknowledge that the ultimate goal is to provide a flat Cartesian mapping, and recent advances in CRTs have concerned the focus mechanism and suchlike things like Q.E.D. and sailor say.
Hauky, if you look at some at Circuit city you can see if they look better to you. They usually have an edge to edge sharpness, but then alot of the time I don’t look at my tv edges because they don’t put much info in the corners.
howstuffworks.com howthingswork.com should have some tech info.