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# Less-Deep CRTs

Use multiple groups of electron guns
 (+9) [vote for, against]

I did some Googling to see if this Idea was already out there somewhere, and I found a vague hint or two that it might be, but no details. So, here are the details I have in mind:

Let's imagine we have an old-fashioned television or computer monitor with a Cathode Ray Tube (CRT). As you know, these things are pretty bulky, which is one reason why thin-screen displays are all the rage these days (that prices have come down is another, of course!). There actually is a rule-of-thumb for the overall size of a CRT: Its depth is about the same as its diagonal screen measurement. So, a 19-inch CRT is usually also about 19 inches deep (about 48cm), and so on.

OK, let's pretend we have a nice-sized CRT in terms of mathematical computation, say 20 inches (50cm), and let's divide it into quarters. On the FRONT of this new CRT we see the plain ordinary 20-inch-diagonal screen, but on the BACK of this new CRT we see four glass necks, each containing the standard electron guns for painting images, and each handling 1/4 of the overall screen. Since each of those quarter-screen sections is the equivalent of a 10-inch diagonal CRT, the overall conglomeration is that we have a 20-inch-diagonal CRT which is only 10 inches (25cm) deep!

Sure, I know that this means lots of extra control electronics to run 12 electron guns (3 per neck, one each for red/green/blue) instead of the usual 3 total. But these days they put most of that electronics into just a few integrated-circuit chips, and so these days it can't really be all that tough to control 12 guns instead of 3. A few extra adjustments and calibrations are obviously going to be needed, but once set, the settings tend to be recorded in those integrated-circuit chips, and so this should be a workable Idea.

Naturally, the Idea lends itself to expansion. You say you want a big High Definition monitor? There's nothing stopping the manufacturer from making the BACK of the overall unit from a 16x9 array of 4-inch necks (they DO make CRTs that small!), for a total of 432 electron guns (3 in each of 144 necks), and an overall size of something like 48x27 inches (122x69cm) (I'm assuming each 4-inch neck controls a 1:1 square area (just less than 3 inches on a side) on the monitor's front face, instead of the usual 4:3 rectangle) -- and thus it has an overall diagonal of 55 inches (140cm). And it's only 4 inches deep!

Finally, I do know that the ultimate version of this is something called a Field Emission Display, where one electron gun shoots at just one pixel, and the monitor depth is maybe an inch at most, but those things have been under development for more than a decade, and still haven't arrived. This Idea could be implemented almost immediately.

 — Vernon, Jun 02 2005

overlap problem fix http://www.patentst...atents/6437500.html
Seamless electron transfer for multiple-gun direct view CRTS [csea, Jun 03 2005]

Digital convergence system for a multi-gun CRT http://www.freepate...ne.com/4095137.html
another interesting patent with 5 convergence areas [csea, Jun 03 2005]

Soft-edging http://www.barco.co...duct.asp?GenNr=1451
Barco's implementation of soft-edging for projector image overlap. [wagster, Jun 03 2005]

Field emission display https://en.wikipedi...ld_emission_display
This idea taken ALL THE WAY [notexactly, Nov 09 2015]

 So the screen visible to the user would be made up of 4 sub-screens in a square pattern, right? I think you'd have a bit of a problem with interference between adjacent guns at the edges of their sub-screens. Tolerances in this region are hard to control, and tend to get worse with heat and time (and age).

You'd wind up with a set of distorted artifacts (or blank spots) in a central vertical stripe and a central horizontal stripe, all meeting in the very centre where the eye is naturally drawn. Users would not like this, methinks.
 — phlogiston, Jun 02 2005

Sans Phlog's problem and this is good. Though the added CRT's will accumulate costs. [+]
 — daseva, Jun 02 2005

[phlogiston], considering that in recent months they have managed to start producing CRTs that break the rule-of-thumb, by being notice-ably less-deep than their diagonal measure, I'd say they have managed to lick some of those issues you raised. Still, this Idea doesn't REQUIRE the rule-of-thumb to be followed. For that initial 4-neck tube, where I gave a depth-measure of 10 inches, it could instead be 11, allowing greater control of the beams without harming the overall Idea much.
 — Vernon, Jun 02 2005

 Though the tolerances and precision assembly requirements would likely introduce new issues, could you more definitely delimit each gun's contribution to the picture by physically masking each of the 4 sections?

 [later]: Maybe some temperature sensors in the right places could provide additional input to the control circuitry.

The general process of controlling the electron beam is open loop. Could you close that loop by using some method of detecting when the beam reaches the outer perimeter of its assigned operational envelope?
 — half, Jun 02 2005

[half], I think most of those issues can be solved by the molds they use to cast those glass necks. That is, all the alignment and relative-locations-of-necks is done BEFORE the glass is poured. I think. :)
 — Vernon, Jun 03 2005

 + I think the overlap problem can be addressed fairly easily see [link] "overlap problem fix."

Another patent (which I initially thought used multiple guns) in fact uses a standard 3 gun CRT, but has 5 separate convergence zones (top, bottom, Left, center, right.) [link2]
 — csea, Jun 03 2005

?, Vernon. I was referring to [phlogistons]'s concerns about the interference between adjacent guns. I assumed the reference was to one beam slopping over in to the next sub-screen region or falling short of the edge of its own due to the inability to precisely control the beam at the extremes.
 — half, Jun 03 2005

Dinosaurs mating.
 — bristolz, Jun 03 2005

 [half], THAT can be solved not by "passing the beam" relay fashion, but by having all the guns going simultaneously, sweeping in sync. (They already have electronics for collecting all the data for one frame and distributing it however-they-want.) Then "crossing the streams" is NEVER going to happen. :)

[bristolz], that was funny. And this IS the HalfBakery....
 — Vernon, Jun 03 2005

Can't do that, Vern, unless you wanna delay your programming a bit.
 — daseva, Jun 03 2005

This is pure steampunk, bun.
 — zeno, Jun 03 2005

 [daseva], I'm pretty sure that the delay you are talking about (1/30th second or less) is already being done in some types of (mostly experimental) monitor technologies. This delay is also unnotice-able, considering that for TV it already comes on top of various data-transmission delays (possibly including satellite).

[DrCurry], see the last paragraph of the main text.
 — Vernon, Jun 03 2005

 Somebody's disconnected here. I didn't say anything about any sort of handoff scheme. That sounds counterproductive to me.

 You're saying that each of the necks controls a small area of the screen. Focusing on the horizontal sweep for the sake of discussion: can the horizontal sweep can be controlled accurately enough that the vertical edges of adjacent screen areas will be perfectly seamless and never overlap? I think that's the issue that [phlogiston] is referring to and is the issue that I feebly attempted to address.

I must not be writing clearly today. You seem to be responding to something that I didn't think I was saying, so I'll retire from the discussion having contributed at least a croissant.
 — half, Jun 03 2005

Vernon: ah, didn't get that far...
 — DrCurry, Jun 03 2005

 Nice. [phlogiston]'s point is going to hold true regardless I'm afraid, which is why this hasn't been done before. Converging any point source projection system well is a little tricky (I do this a lot) and converging CRT tubes is the hardest of all, in fact it's a nightmare. Barco have attempted to overcome the [phlogiston] problem in large scale LCD projection systems using a system called "soft-edging" where one image gently crossfades into the next. It didn't work very well, and that was using LCD technology which can align and hold it's geometrics in the way that CRT just can't.

I'd love to see someone try this though. [+]
 — wagster, Jun 03 2005

[IT} Yes, I remember the Sinclar tube (I think Sony had a similar system too) - I think he got away with electrostatic deflection too to reduce weight, but I never worked out how he controlled spot distortion at the extremely shallow angles furthest from the gun.
I don't get the "steam punk" and "dinosaur" jibes - can someone explain please?
 — coprocephalous, Jun 03 2005

Would there be less distortion if there was a combination of electron guns being fired at different times and each electron beam being deflected like the Sinclair tube but at different angles, so that the focussing coils would be fairly distant from each other? So for instance there might be an array of nine electron guns in a square with the central one sticking out backwards, the corner ones at forty-five degrees and the edge ones at ninety degrees to the edges?
Also, if the field emission display were used, would that not mean that the distortion problem is confined to individual pixels, i.e. eliminated? So, if instead of using guns firing at individual pixels, i would suggest an array of guns each firing at nine pixels, nine of them in the square arrangement i just described, then staggered firing allowing a further array of nine. That way, there would be a little distortion around the edge pixels but it would affect less than a single pixel and could perhaps be compensated for by boosting the signal at those points.
 — nineteenthly, Jun 03 2005

 [half], well, once you have all the data for a full-screen image, and can divide it any which-way, you could deliberately provide each gun with overlapping data. That would actually make the overall alignment issue easier to do (if the overlaps are off, that section of the image will be fuzzy). I can even imagine a nice finely-checkered test-pattern that the electronics is programmed to be able to display, to aid aligning the overlapping subsections of the screen. AND I can imagine the incorporation of a camera circuit (or several), inside this multi-neck CRT, allowing the electronics to diagnose and automatically adjust and lock-in its own test-pattern (it IS known that if the electron beams can get through the shadow mask, then light from the phosphors can also get back to the rear of the tube, where the image can be viewed/analyzed)....

 Then there was the thing I wrote about using a slightly narrower/longer (11 vs 10 inchs) neck, so that max deflection is lessened and more control is obtained.

 Also, nobody here seems to be noticing that if the overall gun-to-screen length is shorter (in first example, 10 vs 20 inches), you DO have somewhat better control over the beam than when the distance is longer. So, I think the issues you raise are solvable.

[coprocephalous], I dunno about the steampunk reference, but the single-neck CRT IS a dinosaur technology (a vacuum tube!) in the electronics world.
 — Vernon, Jun 03 2005

The Sony Jumbotron system uses three CRTs per pixel. Each CRT is about 1cm across (diagonal) and coated in the appropriate phosphor, red green or blue. The screen is effectively flat with each section being about 3' by 3' with a depth of about 1'. A screen made of 108 modules arranged as a 12x9 matrix is still only 1' thick even though it is 36' across. I don't even want to think how many CRTs were involved, you can work it out for yourselves if you like.
 — wagster, Jun 03 2005

[wagster], if they are using individual CRTs in the Jumbotron (and actually I thought they were using LEDs), then that just means that the Jumbotron is an extreme version of the old wall-of-monitors idea. Whole separate CRTs, that is, and obviously the Jumbotron works because it is so big that the viewer can be so far away that the gaps between CRTs are invisible. This Idea avoids the gaps because the continuous screen is shared by the guns. And I already mentioned that distributing deliberately-overlapping data to the guns can help ENSURE there are no gaps in the overall image.
 — Vernon, Jun 03 2005

Did they not try this with plasma television?
 — travbm, Oct 29 2015

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