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On the subject of intersting and unusual television systems.

 
Katie Bush
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Evening all,

Quite some years ago, I seem to recall an edition of "Tomorrow's World" which featured an interesting television system that used coloured lasers and angled mirrors on revolving drums to scan and produce a raster/image on a screen.

I have a vague recollection of the presenters saying that the hardest obstacle to overcome was the "blue" laser.. This, I think, was acheived by using a green laser and filtering the light that it emitted.

If memory serves me, there were two revolving drums, one to produce the "Field" and another to produce the "Line" scans.

This ponderous beast was demonstrated on air, and was claimed to be able to produce a sharp focus image on anything from a postcard, to the side of a barn, without the need to refocus, or to converge the three coloured lasers.

Working at either 625, or 1250, lines, it's major drawback was the clearly visible scan lines at larger screen sizes.

From what I remember, it looked like an impressive piece of kit that was set revolutionise cinemas and other venues where large screen images were required.

Can anyone else remember this system, and what it was called? And ultimately, what happened to it? In the latter case, I would asume it was waylaid by the advent LCD technology that didn't suffer from the obvious scan lines.

Marion

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Topic starter Posted : 14/01/2014 12:54 am
Lloyd
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That sounds interesting, I wish I'd seen that.

I was thinking along similar lines the other day, using a laser (or 3!), shine it through a prism or something, with a magnet attached to it, but using existing scan coils of a normal TV set to deflect it. Probably wouldn't work for some reason or other, but I might try it out at some pint to see what happens! I thought it would be quite handy for seeing if a TV chassis is actually doing something without a tube fitted.

Lloyd.

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Posted : 14/01/2014 1:02 am
Anonymous
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Three lasers Plus spinning drums are used for very bright outdoor projectors. Always in focus no matter the distance. No lenses. I saw one in 1989!

A laser printer uses "video". The polygon motor is lines (illuminated by laser) and the photo drum is "field". Frame rate is pages per minute / 60 :)

Full 3 chip DLP use a moving mirror for each pixel on the chip and LED, Laser or Xenon depending on application. Cheap domestic DLP use a single chip and a spinning wheel with clear and 3 coloured segments. Xenon or LED light sources depending on size/brightness and application.

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Posted : 14/01/2014 1:24 am
Terry
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I remember seeing a demonstration of 3D holography on two dimensional TV! The object was a model of a Victorian steam loco on a section of girder bridge and the TV camera went round the image to demonstrate that it was truly three dimensional ...

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Posted : 14/01/2014 1:38 am
Refugee
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It can't be that different to one of those portable cinema things that they carry around in third world countries that consist of an inflatable tent with a back projection screen stitched into the side.
I am pretty sure they remain converged during wind rock and so on and in any case they have to operate without engineers that can cope with no more than pitching the tent and starting the fan and little more than that.

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Posted : 14/01/2014 2:02 am
Terry
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It can't be that different to one of those portable cinema things that they carry around in third world countries ...

Not quite the same thing but I remember the first Indian satellite TV experiments. They were at the top end of Band V and were quite a catch for the DX-TV enthusiasts in this country!

The idea was that a TV, dish, tent and generator could be set up in remote villages with the intention of showing the villagers how they could improve their crops, amongst other things ...

After the first series they found there was a problem that they'd completely overlooked! The villagers had never seen TV before so, when they were shown close ups of the pests that were damaging their crops they breathed a sigh of relief and thanked God that they only had microscopically small versions of these insects to deal with. These, they reasoned, couldn't possibly cause the havoc that the monsters on the TV did, so the measures they were being incited to take couldn't possibly apply to them, could they ...?

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Posted : 14/01/2014 1:19 pm
Refugee
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What was missing from the road show was a microscope demonstration so that the pests could be shown magnified in stages before the eyes of the viewer.
This would have helped greatly in developing an understanding of what is going on in the real world.
A composite video microscope would have been a worth while thing to add to such a road show.

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Posted : 14/01/2014 1:40 pm
Anonymous
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The Indian village "dishes" made by excavating a suitable hole and putting chicken wire down. Presumably a small UHF dipole at the focus hung on a stick across the pit.

I've seen a photo.

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Posted : 14/01/2014 2:24 pm
Refugee
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Yes there are quite a few home made designs for receiving aerials and dishes out there and the choice of satellite band also supports this.
I think the content confusion is caused be producers showing off there special effects on output that is for viewing by those who have never owned a TV or watched very much if any at all.
They will not understand lenses or magnified images because they have never seen them before.

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Posted : 14/01/2014 2:51 pm
Valvebloke
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... I have a vague recollection of the presenters saying that the hardest obstacle to overcome was the "blue" laser.. This, I think, was acheived by using a green laser and filtering the light that it emitted ...

Not quite. I didn't see this programme but since it wasn't recent it's likely that they would have been using an argon ion laser for the blue and green light. Unlike most lasers the argon ion system can lase on several atomic (strictly 'ionic') transitions simultaneously. So unless measures are taken to stop it it will emit light at a number of very specific wavelengths at the same time. These can then be separated using, for example, a prism. The strongest lines in Ar+ are at 488.0nm and 514.5nm. The latter is a rather pleasing green. The former is distinctly blue, but not really deep enough blue to make full colour rendition easy. Furthermore the laser generally delivers less power at 488.0nm than at 514.5nm but our eyes' sensitivity varies the other way. We're less sensitive to blue light so we need more power there. It should also be said that full-size Ar+ lasers are beasts to operate. They are inefficient (typical conversion efficiency from wall-plug power to light is 0.1%), they need substantial cooling (tends to be noisy and can be unreliable), they run at lethally high voltage and, of course, the full power beams present a catastrophic eye hazard in the event of inadvertent access.

When I was doing my PhD (in laser science) the guy upstairs was trying to make the strontium vapour laser work more effectively. They'd already got copper vapour (511nm green and 578nm yellow) and gold vapour (628nm red) working and the strontium transition (430nm blue) would have been a good complement. In the end it was just too technically tricky though and the metal vapour technology was overtaken by solid-state devices.

VB

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Posted : 14/01/2014 3:49 pm
ntscuser
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I've seen a demonstration on the Open University of a full colour system using a monochrome camera and single colour filter at one end, and monochrome monitor plus single colour filter at the other. It worked on the principle of colour subtraction as opposed to the colour addition used in conventional colour TV systems.

The only drawback that I could see was that the system was totally incompatible with existing TV systems whether colour or monochrome. I suspect that is the reason it was never considered for broadcast use.

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Posted : 14/01/2014 6:49 pm
Anonymous
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Mechanical scan TV systems go all the way back to Baird.

Eh?

Mirror based projection systems start in the Baird era (though only with success more than 10 years after Baird started and not actually really using any of Baird's work), but Baird was the last gasp of Domestic Mechanical TV (started nearly 30 years before Baird). The Scophony system scanners are not that different to concept of a Laser printer or laser projector (in both no device like Jeffrey or Kerr cell is needed as the laser can be directly modulated.

The dominant projection system (other than CRT) till DLP & LCD & laser was the mad spinning disk with oil in vacuum.
http://en.wikipedia.org/wiki/Eidophor
http://www.earlytelevision.org/eidophor.html

It made the insane Scophony mechanics look sane. But was much better & brighter. Which is no doubt why no Scophony survives.

Hilarious that the colour wheel is back (used in all cheap DLP projectors)!

With Digital processing now cheap any kind of display can work from any kind of signal. The only limit now is making a Projection or display cost effective.

FM SECAM though pretty daft compared to PAL, NTSC and AM subcarrier SECAM.

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Posted : 14/01/2014 7:42 pm
Anonymous
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There was at least one AM subcarrier SECAM or was that only in a lab? Was there 4 or 6 versions?
Séquentiel couleur à mémoire
Transmits B-Y and R-Y on alternate lines rather than both the same time.

I have a memory (!) that the SECAM delay line mysteriously isn't same as PAL time delay. Why should ANY Chroma delay line be other than one line duration?

I used to receive Analogue Satellite SECAM and had a 6" TV that worked in PAL/NTSC/SECAM, from 5W Telecom.
My more recently died Mitsubishi / Vestel 28" TV did SECAM and NTSC and I did watch some 12.5W CNBC "NTSC" Digital feeds on it, but don't remember ever watching the Analogue SECAM (one of the last Analogue Satellite to go as it also feed some remote Analogue TV sites) on it.

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Posted : 14/01/2014 10:10 pm
Anonymous
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OK that makes sense. So actually a PAL Delay line will work in an SECAM decoder, but not vice versa.

I forget the explanation of how the Japanese sets got round the patent, it must be 35+ years ago I heard it. I becoming vintage myself.

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Posted : 14/01/2014 11:49 pm