What are the limitations of CRT display technology? resolution, nits, ....

[jman5000]

The beam current is also relevant (P = VI).
CRT design (particularly with three colour systems) is compromise all the way. You have to get good beam focus and colour convergence over a huge range of angles. There must also be a limit to the power density that the screen mechanism can handle.

I ask because I was looking into the fed/ sed display tech that was going to come out in the late 2000's, which had a electron emitter for every single subpixel. There is a 720p prototype you can see on YouTube. Wikipedia states it would allow for increased brightness due to not needing to steer the beam, but It just makes me wonder if that is actually true since I thought increased brightness meant higher acceleration voltage which is bad for xrays. I'm also not sure if these would be impulse displays or not.

 

[berkeman]

I ask because I was looking into the fed/ sed display tech that was going to come out in the late 2000's, which had a electron emitter for every single subpixel. There is a 720p prototype you can see on YouTube. Wikipedia states it would allow for increased brightness due to not needing to steer the beam, but It just makes me wonder if that is actually true since I thought increased brightness meant higher acceleration voltage which is bad for xrays. I'm also not sure if these would be impulse displays or not.

Can you provide a link to this please?

If there is no shadow mask, that eliminates a big e-beam power loss for color CRTs.

 

[jman5000]

Can you provide a link to this please?

If there is no shadow mask, that eliminates a big e-beam power loss for color CRTs.

Here is the prototype. It's just a video demo though.

The wiki for sed, which probably has inaccurate info because it's Wikipedia: https://en.wikipedia.org/wiki/Surface-conduction_electron-emitter_display

but that is probably too general for you. I found this more technical explanation as well: https://www.eetimes.com/a-technical-comparison-between-sed-and-fed/

I can't find the info stating they could be run at higher brightness. I might have imagined that. Apparently, this never made it to market due to legal patents. Although I don't know if it would even do anything better than current displays honestly.

I'm kind of curious if these would have issues with longevity as I understand it ion bombardment is a problem with crts that I think would be exacerbated by making the vacuums really small. Actually thinking about it, even if you could create brighter vacuum displays wouldn't that just result in heavier ion bombardment? Seems like a pretty fundamental part of vacuum tubes that limits what you can do.

 

[jman5000]

I've done a good amount of textbook reading on crt tubes since I last posted and acquired some better tubes. I still have a few questions though that I am not sure about.

First off, how does the color sampling aperture affect the maximum resolvable resolution? I read exceeding pitch is like super sampling which while good, isn't as good as natively showing all the pixels. My thinking is, if the electron gun addresses less phosphor holes at higher resolutions, then at some high enough resolution, it should be possible for two entire pixels to fit through one dotmask/ aperture hole? Is this true? I am curious as I can fit double my pitch into an interlaced signal and still be in spec. I'm wondering if I will get a dramatically sharper image if it can be done, meaning the higher the resolution sent to tube once over the aperture grille pitch, the closer it gets to a native rendering of that resolution? I'm guessing not since it would have been done already if possible?

Also, in regard to analog signal degradation, I think there are two points in which it happens in a tube? The first is according to this: https://people.csail.mit.edu/jaffer/Gamma/video-bw.html
I also found across multiple tubes that being above 70% bandwidth of the horizontal frequency will distort the signal, and I think I read this is due to saturating the transformer in the tube? Does that sound right and is that distinct from the degradation in the analog cord or are they the same chain of degradation? Why does 70% seem to be consistent across my tubes?

I'm trying to figure out why crts have poor sequential contrast, ie elevated black levels when lots of light is emitted from the screen. I read that when photons are emitted, they conserve momentum from what causes the emission. Does this mean the photon only travels in a straight line since the electron beam is traveling in a straight line? That can't be true, can it? I can see light of the same color at any angle from my tube. That would also mean there is actually a second image inside of the tube being reflected into the small area the electron beam traveled. Otherwise, I guess the image from the screen is just reflected into the tube regardless and thus raises black levels when more light is emitted? In any case, I think any display where pixels have a line of sight with other pixels means it would suffer poor ansi contrast, which must mean that modern pixels have walls around them preventing them from contaminating neighboring pixels?

 

[sophiecentaur]

Does this mean the photon only travels in a straight line

How could a photon do otherwise?
When an electron hits a phosphor dot is there any mechanism that could restrict the angular range of the light produced? Once an electron has landed, the photon it produces can go in any direction.

which must mean that modern pixels have walls around them

I think the phosphor dots are smaller than the electron beam width (which governs the pixel size). Where would a 'wall' be placed? If you look on a shadow mask tube face, the phosphor dots are tiny flat patches (underneath the glass front).

You obviouslu find this stuff interesting - which is good. But don't assume you could do experiments without the equipment that the tube manufacturers use. I remember having the production sequence for a shadow mask tube described to me. Each set of dots is produced in a separate operation, with the mask being removed and replaced in perfect registration and a new photo-resist coat is put on the tube face. Each time, a light is shone from where the relevant 'electron gun' will be. When the tube face is finally assembled, the electron paths are 'just right' for colour purity.

If you were particularly keen, you could do a scale model (optically) with three sources passing through a selective mask. There are much easier systems than shadow mask which are more efficient - but you will have come across them in your readings.

 

[jman5000]

Where would a 'wall' be placed?

Are there materials or mechanisms that allow electrons to pass through a gate unimpeded but block photons? That would make a solution really easy. I don't know much about photons and electrons, but I know they have different wavelengths. Can that fact be used to filter one but not the other even if they travel along the same path?

I've thought of some things, but it all depends on where the poor ansi contrast comes from. Does it come from light bleeding from behind the pixel and bouncing off the mask onto other pixels, or going through the slot the electron passed through and bouncing around in the rear of the tube, or from the sides of neighboring pixels?

 

[sophiecentaur]

Are there materials or mechanisms

That would be a good searching exercise for you. I have no idea what would do the job.

light bleeding from behind the pixel and bouncing off the mask onto other pixels,

I think you mean phosphor dots and not "pixels"
I would expect the first evidence for that problem would be colour purity.