I'm sure everybody knows that CRT monitors have superior picture quality. I just found out that CRT technology is over 100 years old, hence why can't they make slim CRT monitors?
Why can't they make slim CRT monitors?
- Thread starter malG
- Start date
Becuase there is an electron tube at the back of the cathode tube, in order to be able to "paint" the whole picture it must be located some distance from the screen.
The electron beam comes from the back of the tube, with the beam pointing at the center of the screen.
A electro-magnetic deflection system then bends the beam, sweeping the beam over the entire surface of the screen, line by line.
The deflection system can only bend the beam so sharply, meaning that the source has to be a fair distance from the screen.
Additionally, while at the centre of the screen, the beam hits the screen square, at the edge the beam hits the screen obliquely causing distortion and uneven brightness (this is why older CRTs were round "goldfish bowl" shaped - to try and keep the angle between the beam and the screen square). Modern technology has allowed distortion compensation, so flat CRTs are possible, but it is difficult to compensate for very large bending angles (I think 90 degrees is about the limit that is done in mainstream screens).
A electro-magnetic deflection system then bends the beam, sweeping the beam over the entire surface of the screen, line by line.
The deflection system can only bend the beam so sharply, meaning that the source has to be a fair distance from the screen.
Additionally, while at the centre of the screen, the beam hits the screen square, at the edge the beam hits the screen obliquely causing distortion and uneven brightness (this is why older CRTs were round "goldfish bowl" shaped - to try and keep the angle between the beam and the screen square). Modern technology has allowed distortion compensation, so flat CRTs are possible, but it is difficult to compensate for very large bending angles (I think 90 degrees is about the limit that is done in mainstream screens).
Born2bwire
Diamond Member
- Oct 28, 2005
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Canon and Toshiba are trying to market a TV that you would be interested in, SED, or Surface-conduction Electron-emitter Display. Instead of using a Cathode ray tube as the electron gun, they have an electron emitter for each pixel. So you no longer have any of the geometry, depth, weight, or resolution problems that you had with a CRT that involves a single electron source. They are still going to use the phosphor coating like they do for CRT so you should be able to retain the same image characteristics while at the same time having full 1080P resolution and a slim cabinet. The downside is that the idea has been around for a long time but nobody has succeeded on bringing it to mass market. Toshiba keeps pushing back the date when they will sell them but in the past year they have been able to show off 720P displays using the technology. They want to launch with full 1080P displays around the 50" size but I would not hold off waiting for one.
Simple: Deflection angle. You may have noticed that TV tubes are much flatter than computer monitor tubes. This is because if you want a focused and round (not elliptic) dot, you must make the beam hit the phosphor perpendicularly.
There have been a few attempts at "short tube" CRTs, e.g. from Samsung, but they weren't too popular. It drives cost up, makes good picture quality much more difficult particularly around the edges, and doesn't gain /that/ much depth.
There have been a few attempts at "short tube" CRTs, e.g. from Samsung, but they weren't too popular. It drives cost up, makes good picture quality much more difficult particularly around the edges, and doesn't gain /that/ much depth.
Yeah Born2bwire but SEDs have one major flaw that all the new display techs have. A native resolution. Gone are the days of being able to run any resolution you wanted. I love StarCraft but it looks like crap on my laptop with 1600x 1050. MY only hope will be a display that will try and keep the screen ratio while upscaling the picture so it stays pretty(er then lcds atleast).
One attempt at a slim CRT took the opposite approach and used an oblique neck so the electron beam hit the entire screen at an angle. Obviously it didn't work well because it never made the big time.
CRTs can change the beam brightness at will, no fixed horizontal pixels. Also, the number of lines and their spacing is also completely arbitrary.
There is an upper limit to what resolution can be displayed legibly, exactly from the dot pitch you mention. Above that, anything looks equally good. This is totally unlike LCD panels.
There is an upper limit to what resolution can be displayed legibly, exactly from the dot pitch you mention. Above that, anything looks equally good. This is totally unlike LCD panels.
sdifox
No Lifer
- Sep 30, 2005
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Technically speaking, a set of RGB phosphors constitute a pixel. So there is a fixed number of it on the tube. Mind you, I am not saying every tv of the same size has the same number of phosphor count, or even line count. It all depends on the dot pitch (distance between pixels) and dot size. I guess it is really a diction problem. Both CRT and LCD have fixed resolution, but CRT lets you play with what resolution you want to use, while LCD does not. Analogue scaling is a wonderful thing, if done right.
CRT is superior in transcient, since phosphors decay a lot faster than LCD. Some LCD claim to be faster than CRT on black to black, but I have yet to believe that claim. Too bad SED missed the window of opportunity, even if it comes out tomorrow, it's too late.
How is SED too late? Is there another tech about to launch that is better? Because nothing available now is better.
The point you keep missing is that CRT monitors aren't going to hit one of those RGB triplets /exactly/, ever - simply because beam control doesn't even know where they are. The pixel count is entirely theoretical, and as a consequence, all resolutions come out equally blurred.
Replacement tide? Is there some sort of periodical mass TV buys? The majority of TV owners still don't have HDTVs. It seems that we are still in the adoption phase of HDTV, so I really don't see why there would be an issue with a new tech coming out in the near future. Still plenty of people to which to sell SED. And wouldn't the debug time be right now? Working SED TVs have already been shown.
They can be faster in some conditions: http://www.lesnumeriques.com/duels.php?...1=76&p1=806&ma2=120&mo2=61&p2=689&ph=2
With a slower white on black transition it was very obvious my TN LCD was faster than my CRT as well.
However I don't think they'll be able to get overdrive good enough to surpass the CRT in colorful transitions (the fall time isn't low enough). That is territory best left to SED and OLED. The color-filter-less LCDs did look intriguing though (they have another way of displaying colors).
LCDs can be made with high pixel density (see 15.4" WUXGA notebook screens @ 0.173mm), and with the lower dot pitch scaling has potential to improve greatly. SEDs with CNT (carbon nanotube) pixels will be able to reach even lower dot pitches, and likely OLED as well.
sdifox
No Lifer
- Sep 30, 2005
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Advertising is heavy on LCD and Plasmas. by the time people are ready to buy, those are the ones they remember. How many people do you know that have heard about SED? then you throw in the negative association with TUBE. Joe sixpack ain't buying it and guess what, that is where the money is.
But those techs are currently available so many people do know about them. All new techs go through the same period of penetrating the general consumer conscience so I really don't see how that makes SED "too late".
What negative association is there with "tubes"? CRTs are at the top of heap in image quality when properly calibrated and there are still plenty being sold. Yeah, they tend to be bulky, but that won't be a problem with SED.
Also, why would they even associate SED with tubes in the first place? The average consumers doesn't really know anything about the actual technology. They won't have any idea they are somewhat related to tubes. All they will see is a flat panel display that spanks the LCDs, DLPs, and plasmas sitting next to it.
Also your arguments could be used against any new technology. If what you are saying is true then "joe sixpack" would never buy anything but tubes.
Here's a picture of those slim CRTs. You can really see the high deflection angle. It does save a lot of space over a regular CRT though.
http://news.com.com/2009-1041-5473476.html
What if they had a series of magnets in there to curve the path of the electrons so that they hit the screen at a less shallow angle? A set of magnets with the - side facing in would repel the electrons, bending them back twoards the screen. (One would likely use electromagnets, as this would likely be a tricky operation indeed.)
That said, the method of having a single electron gun for each pixel sounds sweet to me. However, to make it work, I might suggest that the whole electron gun assembly be made by making a layer of copper, a layer of insulator with tiny holes in it, and a layer of copper with tiny holes in it.
By placing the conductors in stripes (the bottom layer horizontal, the top layer vertical stripes), an individual pixel could be lit by choosing the appropriate two stripes (X and Y value) for the voltage; the others would only have the + or - side working, but not both. It would scan a lot like a traditional CRT, but it would be able to do so very, very fast. (Alternately, they could use an "active matrix" design like an LCD, but this seems more expensive).
As an added bonus, it would be very cheap to make. Just put it against a flourescent-coated sheet of glass, suck out the air, and seal it tight. Plus, the edges of the TV would be very, very small.
That said, the method of having a single electron gun for each pixel sounds sweet to me. However, to make it work, I might suggest that the whole electron gun assembly be made by making a layer of copper, a layer of insulator with tiny holes in it, and a layer of copper with tiny holes in it.
By placing the conductors in stripes (the bottom layer horizontal, the top layer vertical stripes), an individual pixel could be lit by choosing the appropriate two stripes (X and Y value) for the voltage; the others would only have the + or - side working, but not both. It would scan a lot like a traditional CRT, but it would be able to do so very, very fast. (Alternately, they could use an "active matrix" design like an LCD, but this seems more expensive).
As an added bonus, it would be very cheap to make. Just put it against a flourescent-coated sheet of glass, suck out the air, and seal it tight. Plus, the edges of the TV would be very, very small.
So you are saying that Joe Sixpack has already replaced all of his TV's with flat-panels? I don't see that the tide has at all turned with regards to TV conversion. If anything, I don't really see that it has even started yet. In my mind, Joe Sixpack and his wife go to Sam's club and admire the LCD/PDP TV's but they are still too pricey.
With a couple of Google searches, I found that the majority of TV's being sold right now are still of the CRT variety. From a DisplaySearch report in Q4 of last year: "The flat panel TV unit share, covering LCD and plasma TVs, rose from 6% in Q3'04 and 13% in Q2'05 to 16% in Q3'05." I couldn't find more recent data but estimates put flat-panel penetration at 22% for this year - so only 22% of total TV sales worldwide are flat-panel (PDP or LCD). There's a lot of room for SED. I don't consider the digital TV / HDTV migration to have even begun in earnest yet. If SED isn't out by 2009, then they have started to miss the boat, in my opinion.
So what if the TV is thick? I don't care. Computer Displays, maybe depending on desk size, but TVs are no problem.
It's hard to get magnets to deflect the signal correctly for such an extreme angle. However, SED displays, which have three electron guns per pixel are very thin.
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