Electrostatic vidicons? - Page 1
Forum section: electronics / projects

author: Unknown
author_rank: Unknown
timestamp: April 06, 2019, 05:26:35 pm
content: I want to play around with an analog TV system using non-raster scanning - I want to try spiral scanning, etc., to see what that looks like.My idea is to have a microcontroller drive the X/Y deflection of a vidicon and also of a (black-and-white) CRT for display. (Or, use an oscilloscope for display).Would an electrostatically-deflected vidicon be better for this than a magnetically-deflected one? The only electrostatic vidicons I can find on eBay are Soviet LI-441 and LI-475 types.One vendor (https://www.ebay.com/itm/Russia-USSR-Vidicon-Vacuum-Tube-LI441-with-deflection-system-OS-5-MilitaryCamera/162951316269) is selling one "with deflection system", which confuses me because I thought electrostatic vidicons did all the deflection with voltages at the tube pins (no yoke or anything external to the tube). Am I confused?I don't know much about this stuff; am trying to learn. Any thoughts from people who know more would be helpful!

author: jopapeca
author_rank: Newbie
timestamp: April 06, 2019, 09:40:51 pm
content: HiIf you look closer you could see the cable that connects to the deflection could, the outer metallic case are the deflection coils.I had use those in the past in rx imaging.PauloEnviado do meu SM-G935F através do Tapatalk

author: chris_leyson
author_rank: Super Contributor
timestamp: April 06, 2019, 10:24:03 pm
content: THOMSON-CSF manufactured a few electrostatic deflection vidiconshttps://frank.pocnet.net/other/ThomsonCSF/ThomsonCSF_Special-Vidicons_1971.pdf

author: james_s
author_rank: Super Contributor
timestamp: April 08, 2019, 03:12:06 am
content: You'll probably have to go with electrostatic if you want to do something like a spiral scan, conventional vidicons use a deflection yoke designed for TV scan frequencies, the horizontal is wound for a much higher frequency than the vertical.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 08, 2019, 03:20:37 am
content: This is really spoilsporting, but if you are interested in the image artifacts from various scan mechanisms you could just simulate it. Do it all on your PC. Might not be able to generate video frame rates, but you could generate however many frames you want and then play back at full rate. I've seen this done with a number of systems. Some back when it was a real technical challenge, but computer hardware and software has really come a long way.If you are interested in the artifacts from the processing train you can still do it in simulation, but it is much harder to do, and nearly impossible to know if it is "right". But that isn't totally different from building an analog setup. You can't really know how much of the artifacts are intrinsic to the scan method and processing and how much is due to your specific implementation. I have run into a couple of cases of folks building something to establish feasibility, deciding it isn't feasible, and then finding later they had botched something in the build (or to be more fair, in many cases missed the simple and clever technique that eliminated a huge part of the problems.).

author: Unknown
author_rank: Unknown
timestamp: April 08, 2019, 05:02:00 pm
content: Thanks, all.Quote from: jopapeca on April 06, 2019, 09:40:51 pmI discovered (perhttps://www.ebay.com/itm/LI-441-LI-441-vidicon-cathode-ray-tube-USSR-1987-1-LOT-1-PCS-/264260419173?oid=264216720419) that the LI-441 is electrostatically focused, butmagneticallydeflected.So that explains the external "deflection system"; the LI-441 seems to be not a good choice for this.Does anybody know if the Russian LI-475 is electrostatically deflected? Or where to get a genuine electrostatic vidicon? (Can't seem to find any on eBay.)Quote from: CatalinaWOW on April 08, 2019, 03:20:37 amI've considered that - I think I'll try it before doing a build.Here's my real interest in this:A conventional TV system has a fixed frame rate (typically 25 or 30 Hz, ignoring interlace) and fixed resolution (# scan lines, or #X and Y pixels).What if instead of scanning the image in a repeating pattern (as with a raster), you moved the scanning beam around the image in acompletely randompattern?The time between re-visiting each spot in the image would be random, instead of 1/25s or 1/30s. So in some places you'd get more temporal resolution (more than 30 Hz) and in other places less. There would be no "frame flicker" effect. And no visible raster pattern.If you did it fast enough (bandwidth limited), persistence of vision (and maybe phosphor persistence) would make it look smooth.Of course it's also a less efficient scanning pattern because you re-visit some places more often than necessary.But what would it look like? Would it have advantages re seeing quick movements that would otherwise be lost between frames?I want to try it and see.

author: james_s
author_rank: Super Contributor
timestamp: April 08, 2019, 05:33:54 pm
content: If it was random I think you'd end up with large variations in brightness across different portions of the screen. It would likely end up looking like an image projected on a pile of yarn.

author: Unknown
author_rank: Unknown
timestamp: April 08, 2019, 05:48:04 pm
content: Quote from: james_s on April 08, 2019, 05:33:54 pmIf the bandwidth were too low, yes. If you do it fast enough, the Law of Large Numbers should kick in and average things out. I think.

author: chris_leyson
author_rank: Super Contributor
timestamp: April 08, 2019, 06:39:09 pm
content: A long time ago the BBC had a GB patent on using fractal scanning using space filling curves, either Hilbert or Peano curves. The idea behind it was that you could take a high resolution Hilbert scanned image and still display it lower resolution Hilbert scanned monitor, and vice versa probably. BBC R&D report herehttp://downloads.bbc.co.uk/rd/pubs/reports/1991-04.pdf

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 08, 2019, 08:52:44 pm
content: Quote from: Dave92F1 on April 08, 2019, 05:02:00 pmInteresting concept, and a simulation might work if played back on a high frame rate monitor. Many TVs now actually scan at several multiples of the base frame rate and use some internal interpolation to achieve the same effect. I think your idea would be more productive if instead of random scan you used motion detection to prioritize scan areas, much as is done in several video compression schemes. The advantage your idea would have is that at relatively low bandwidth cost you would have real data at a higher sample rate instead of the interpolated data that current TVs use.All of this interacts with the human vision system in ways I can't even guess about, but you might be on to something.

author: Unknown
author_rank: Unknown
timestamp: April 09, 2019, 02:11:11 am
content: Quote from: chris_leyson on April 08, 2019, 06:39:09 pmA fascinating idea!! In principle that ought to work, tho I'm not sure it's at all practical. I downloaded the report. I can't immediately think of a way to combine that with an efficient coding scheme (to make it practical). Modern video codecs have a practical (well, it works) way of doing that - for examplehttps://en.wikipedia.org/wiki/Scalable_Video_Coding(I know most of the inventors of that - very bright people.)Quote from: CatalinaWOW on April 08, 2019, 08:52:44 pmYes, also many "gaming" monitors are on the market that do up to 240 Hz frame rate. I don't have one, but I could do a simulation with a 30 Hz source video of something very slow (airplanes moving around on an airport, clouds moving across the sky), then speed it up and try coding it with the random scanning.QuoteFor sure that would be something to try if I were interested in something practical. But I'm not - I just want to see what it looks like. It's a hobby project.I got interested in this 20 years ago when I was involved in video coding standardization (I was on the H.264 standards committee). There's this tradeoff between spatial and temporal video resolution, and this seems like an interesting (but probably impractical) way of making that tradeoff. Anyway, I always wanted to see what it would look like, then saw old electrostatic CRTs on eBay (bought a few), then decided I could try it if I had an electrostatically deflected vidicon...QuoteYes, indeed. That's what I want to see.

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 09, 2019, 02:23:56 am
content: Quote from: chris_leyson on April 08, 2019, 06:39:09 pmI see that as a very crude "cave-man era" broad-concept scheme precursor of what modern video codecs do these days in software.

author: james_s
author_rank: Super Contributor
timestamp: April 10, 2019, 05:42:45 pm
content: Quote from: Dave92F1 on April 08, 2019, 05:48:04 pmI think you'd have to go really, *really* fast before that worked.

author: chris_leyson
author_rank: Super Contributor
timestamp: April 10, 2019, 09:18:35 pm
content: The BBC space filling curve scanning idea was maybe GB2193411A or US4843468 or a closely related patent. The idea that the patent was putting across was that you could display the fractal image use a lower bandwith magnetic scanning system because the beam path doesn't change but you just loose a bit of spatial resolution. I think the patent also implied that you could use existing raster scan coils. Hmmm.. I've just given a Vectrex console a funny look