Phil Hobbes: State of the art electro-optical design in 1938

I thought you might get a laugh out of this concept.

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Reply to
Michael A. Terrell
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Fun, thanks.

IIRC there was a construction article in Electronics Illustrated in the early '60s about a B&W->colour TV conversion, using a gigantic colour wheel synchronized with the frame rate. All tubes, probably 12 of them. (I was always interested in old electronics mags--I read it in probably

1972ish.)

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Phil Hobbs

Actually that scanning system is very clever, and allows a pretty bright picture even with a spatially incoherent source (which is all they had at the time, of course). They used an acousto-optic modulator whose acoustic velocity was synchronized with the line scan, so they could use nearly a whole line time for each pixel.

That gave them about 200 times more light than a flying spot system.

This anticipates the idea of time delay integration used in line-scanning photoreconnaissance satellites, where a long skinny CCD array (e.g. 4096 x 64) is scanned at the same rate the image moves, so ideally you get 64 times as many photoelectrons per pixel.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Phil Hobbs

Did you read the part about the expected 2,000 hour life for the scanning motor? :)

Don't some of the light engines for laser light shows use a similar system? One of those NASA Science road shows visited my high school in the late '60s. They had a couple motorized mirrors and a LASER that they used to project crude images on the screen in our auditorium. After the show I asked one of the NASA engineers why they couldn't use a pair of synchronized motors, and modulate the LASER to project video. Their answer was, "Why would anyone want to do that?"

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Reply to
Michael A. Terrell

The color wheel was a proposal by CBS when the FCC was looking at adding color to existing B&W service. Sequential color frames. The problems were many. The size of the wheel for a 25" CRT would almost touch the ceiling. It increased the flicker rate, and the mechanical parts weren't silent. So, the existing NTSC standards were modified to add the chroma channel, and to tweak the vertical and horizontal scan rates to eliminate problems caused by the added chroma signals. All in all, quick an accomplishment in the days of tubes and 20% resistors. :)

Scans of Popular Electronics, from 1954 to 1982:

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Reply to
Michael A. Terrell

Sure. You can't direct-modulate gas lasers at megahertz rates, so most syst ems use AO or EO modulators. (Steve Roberts knows more about the entertainm ent laser field than I do--to me they're like Crescent wrenches.)

It's super easy with a laser because you can focus its whole output into a small spot. In that case the acoustic delay is a nuisance, because with a l inear scan it produces astigmatism proportional to the beam diameter and sc an rate. Each pixel is illuminated for 1/M line times per frame.

The Scophony turned that into a feature, by storing basically an entire sca n line in the acoustic wave (think mercury delay line memory), and synchron izing the line scan rate with the acoustic wave. That way, every pixel gets illuminated for almost a whole line time, so you get about 200x the photon efficiency.

Scophony also used compound cylindrical optics, very much like a modern las er printer, so the residual astigmatism was easily adjusted to zero.

Clever.

Cheers

Phil Hobbs

Reply to
Phil Hobbs

Vaguely related, advanced IC lithography things used to be called "steppers" but now are "scanners", because the exposure is done with the optics and the wafer in motion.

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John Larkin         Highland Technology, Inc 
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John Larkin

Yep. The politics is almost as interesting as the technology: The FCC couldn't decide between the CBS monstrosity and the RCA all electronic version, which didn't work. The FCC adopted the CBS system, but the set manufacturers refused to build it. It took about

3 years for RCA to finally produce something that worked, which allowed the FCC to change its bureaucratic mind and change the color TV standard to the RCA system. In the last 66 year, the ability of the FCC to select the superior technology has not improved (AM stereo, IBOC HD Radio, ATSC, P25, interleaved allocations, etc).

Note that there was a third standard presented for FCC approval in

1950: Although the CTI system was functional, it looked bad due to flicker:

Incidentally, scanning disks were how we initially generated color video from the moon: The irony is that most of these cameras were made by RCA (and a few by Westinghouse).

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Reply to
Jeff Liebermann

I am familiar with the various systems, from the early Nipkov disk adapters for radios, onward. At one time I had access to the Crosley Corporate Library in what had later become AVCO, then Cincinnati Electronics. It included several books about the creation of the original NTSC standard, and the battles that followed. It was next door to the museum of Crosley's early products.

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Reply to
Michael A. Terrell

Speaking of color wheels reminds me that the early Apollo mission TV cameras got color with a spinning color filter wheel in the lens system of a conventional b/w vidicon camera. It was then standards converted by optical means* on the ground. Read about it in a 1968 or 69 TV magazine

- pre moon landing so I think it may have been Apollo 7 or 8.

*As I read it at the time that was a NTSC camera pointing at the reproduced color wheel system. No fancy electronics!

piglet

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piglet

I would love to find the old 16mm newsreels that NASA gave to TV stations back in the '60s & '70s. We had a pile of them at the AFRTS TV station I was assigned to in the early '70s. They covered a lot of the current science used by NASA, including the manufacturing of state of the art semiconductors.

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Reply to
Michael A. Terrell

Sorry - I now see that Jeff Lieberman has already covered this much better than me.

piglet

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piglet

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:)

-Lasse

Reply to
Lasse Langwadt Christensen

there is quite few old documentaries on youtube

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-Lasse

Reply to
Lasse Langwadt Christensen

These were short fillers for stations to follow a movie or sporting event. They ran form 30 seconds, to just shy of a half hour, depending on the subject. We had a whole rack of full sized reels full of film, with the running times of each item marked on the reel's labels. I would load and run one when working on the equipment, after sign off. A month after I left, it all went into the landfill. :(

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Reply to
Michael A. Terrell

To answer your question, Begin rant on the state of mechanical scanning:

The only reason you use a laser source for TV is for color gamut or to repl ace arc lamps. Arc lamp based video has far surpassed laser projection vide o except for color gamut.

The only people who use push-broom scanners with NNNxXX line arrays for la ser shows, or past laser TV systems, are a rare few hobbyists who think th ey re-invented laser TV.. They have videos on Youtube of multibeam laser c locks or text displays, for none of them can code a scan converter into a F PGA... All of their stuff flickers, and none of it syncs to outside video. Just a toy ran by a microprocessor.

That and maybe a few recon sats, and high end medical scanning systems.

There is one successful company that runs 1 x 8 UV array into a phosphor d isplay using a very slow resonant scanner. For video walls that need more r esolution then LEDs can provide.

There is another company that uses all AO scanning with the Scophony set up in Russia that is quite successful. I've seen it run, and its beautiful . Ex Soviet military command and control display system, now on the civil market. Recently converted to color. It does a reasonably wide angle. Howe ver, every other commercial AO or EO scanner has perhaps 1 to 3 degrees of deflection, and that is not enough without expensive scan angle magnifying lenses.

The reason for using a single beam gets tied into syncing video with a moving mass. Most moving masses that are not spinning polygons have a sinus oidal motion. So your pixel clock has to speed up and slow down constantly. This scan converter gets expensive and difficult for one bidirectional sca n line at a time, let alone 2,4,8, etc..

So your scanner clocks your video source, not the other way around. No t too many video sources these days allow external clocking. That drove com panies to DLP light valves, and mechanical TV is now a lab and hobbyist thi ng.

It also gets difficult to make a fast mirror that holds multiple beams, esp ecially with Galvanometer Scanning, where a fast mirror is limited to about 3 x 5 mm in size and no more then 0.8 mm in thickness for video speeds. S ame for resonant scanners.

Galvos live on because of laser marking, and biological applications. Nothi ng else moves a 2 Kilowatt laser beam like a Galvo.

Paying for a 20,000 or 30,000 RPM air bearing polygon with eight sides, has driven laser video to resonant scanners. Resonant Scanners suffer from a small mirror and a small angle, but they are cheap and work. They come in 3892,7785, and 15,570 Hz But only one or two laser beams fit on the mirr or. But now they are used as cameras, and only very rarely for video proj ection.

More recently, laser light sources are now used with some very high end MEMS and light valve systems, Your normal DLP MEMs chip burns up under e ven moderate levels of laser light. Because the mirrors are not dielectric coated, but merely aluminized.

One solid state RGB laser array will be, and is, driving four MEMs arrays in some high end theatres via a huge fiber bundle. This eliminates the arc lamp. In some theatres, the one laser array will drive four or more theat res, in the near future... So that has caused the death of mechanical syste ms with large moving masses.

Those of us who do laser shows are quite happy with analog, moving mirro r, X-Y vector scanning at a maximum small angle jump of ~ 3.5 KHz at 2 degr ees, which is the about the physical speed limit for discrete jumps of a mo ving mass. One thing that people have problems understanding is while our m oving magnet Galvo scanners can do typically a peak 2500 Hz, is that for la rge angles they slow down in a non-linear way to cover their whole range of +/- 30 degrees..

Most people who use them cannot even wrap their head around the optical and capacitive position sensing systems that drive the analog PID loops, w hich allow them to do this. They are now a common item and the price is do wn, cloned by the Chinese. No longer do you have to be a skilled "Laserist" , now your run of the mill "DJ" can buy a cheap system. And they get cheap results, because making an audience happy requires skill, and/or very high power lasers.

Whereas when I started you needed to be a skilled specialist to run and tu ne the system. It would cost 30,000$ or more. Now the cost is down to trivi al, and so is demand for our services. Until you get to the few clients wit h very deep pockets, who are quite willing to pay for a good looking show. New users with stars in their eyes think they are going to do all this ama zing stuff, until they learn about the angle and bandwidth limitations.

Our international standard Galvo test pattern is for JUST 8 degrees, an d all it does is allow you to tune the PID loops to match between users. It does not allow you to characterize the scanner's system bandwidth. That is difficult... :-)

Mechanical scanning for video lives on in laser based microscopes for B iology and Semiconductor Manufacturing, and is getting even better.. There has been attempts to make laser pico-projectors for cell phones, but even t hese are going MEMS.

Many microscope engineers have skipped past raster laser scanning and we nt straight to complex Lissajous patterns using a combination of resonant s canners and ordinary galvos. They just let them free run with sine waves. The reason being its easier to simultaneously digitize the position of the mirrors, the recovered signals, and the position of the source laser beam, then to try to force the scanners to go where you want them at high speed. Especially for confocal microscopy, which now uses lasers with femtosecond pulse durations, and wavelengths into the mid IR. :-)

I still have one minor advantage with show lasers, nothing else can put a large logo on a mountain or building with such style, and high contrast rat io..

I can also do some artistic things that the theatrical intelligent light ing guys will never understand, when projecting into haze or fog for beam e ffects. because I can make drastic artistic changes with a 60th of a secon d time resolution in the software, while synced to music, while changing th e RGB color mix at up to 10,000 times per second..

end rant

Steve

Reply to
sroberts6328

The major producer of mechanically scanned video is Prysm..

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Prysm uses a UV diode laser to excite phosphors. They get around the mechanical limitations by using stacked arrays of projectors in plastic cubes.. Basically parallel computing applied to video.

Steve

Reply to
sroberts6328

Cool, but what's a "Jefferies cell"?

Mark L. Fergerson

Reply to
Alien8752

This sounds like the spinning wheel TV systems of John Logie Baird.

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Les Cargill
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Les Cargill

I wonder if any of that was incorporated into the series "Moon Machines"? If you ain't seen "Moon Machines", do.

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Les Cargill

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