Mechanical Television primer

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Offline albert

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Mechanical Television primer
« on: Tue November 21, 2017, 02:35:33 AM »
Hi!- My name is Albert and I have been invited over to this forum by my friend Wolfgang Mayer.

While watching his incredible home cinema with all the latest technology some days ago, we thought it would be interesting to think back to how it all started in the 1920s.

So many things we take for granted today were the result of much headache, suffering and heartburn by the intrepid inventors who dedicated their lives to the idea of “seeing by wireless” or “radiovision” as the early experiments were called.
I am by no means a historian of television, but I love  to build things. So I started to research the early days with the idea to follow in the footsteps of the pioneers. I will try to let you follow this adventure.

Early television was a mechanical system. Before you laugh: Today’s sophisticated high end video projectors are full of mechanical parts. The creation of color images  with a black and white DMD device makes use of the idea of the color wheel, projecting the base colors in sequence. The ultra miniaturized DMD device is itself a mechanical system for switching single pixels.

It all started in 1883 when a young German student named PAUL NIPKOW sat in his little flat in Berlin around Christmas time and longed to see his family and parents back in Pomerania, where he came from. A train ticket was too expensive for him, and so he sat down and conceived a method to transmit images on a telegraph line.


He came up with the idea of  a fast-rotating disc with a series of holes punched into it. These holes were arranged in a spiral shape. A small window of the disc would be the scanning area. One hole in the disc traverses this window. As it exits the other side, the next hole moves across, but one hole diameter further to the inside of the disc. This way a scanning motion is imparted. the idea was so good it shaped the research and development of TV up until the 1930s when the first purely electronic tv systems started to emerge.



Young Nipkow patented his system as “electrical telescope” in 1883. But his invention came too early: Crucial parts of the system did not yet exist.  There had to be a way to capture the light across the Nipkow disc, and to amplify the very small currents created by the incoming beam of light . The photoelectric cell using selenium as the light sensitive element was still a very new invention, and in 1883 there was no way to amplify its signal. The patent proposes a clever controllable light source but at the time thiscould not be realized. So  Nipkow never made a dime from his invention.





Linkback: http://dci-forum.com/back-roots-tv-history-beginning/24/mechanical-television-primer/2463/
« Last Edit: Wed November 22, 2017, 10:06:20 PM by albert »

Offline MrPixels

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Re: Mechanical Television primer
« Reply #1 on: Tue November 21, 2017, 09:46:58 AM »
Welcome to the forum Albert, very informative first post. Until now I was not aware of this rotating disc and the technology behind it as well as its place in history. Thank you for explaining everything I am smarter for reading your post. I hope other others read and appreciate your knowledge.
Keep up the good work.
« Last Edit: Tue November 21, 2017, 06:08:43 PM by MrPixels »

Online w.mayer

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« Reply #2 on: Tue November 21, 2017, 06:00:40 PM »
Nice to see you here Albert.

As we spoke this is all very interesting things and I am sure many people will love to read all this.
In many Forums there was something inside from it from time to time but not a whole  section so very good to have it now here.
May some day I can share something from the 1980 years where CRT Projection was the King.

Sad I still can not see the pictures but lets wait a bit may the forum need some time to make it visible.
Cant wait to hear more from it and may some day I can see this first steps in TV with my own eyes.

Online donaldk

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« Reply #3 on: Wed November 22, 2017, 12:04:09 AM »
Thank you Albert. May I point out Mark Schubin's work, he traces the history back to the Werner von Siemens Electronic Eye of 1876, the first publicly discussed/presented selenium opto-electrical visual sensor. William von Siemens his brother in London discussed it the next year 1877. Nipkow seems to be building on this, as were many others. The word/term Television was launched at the Paris World fair in 1900, according one of his presentations. If one want's to paint with a really wide brush, there was a 'camera' in the 5th century bc;-).
 
http://dci-forum.com/news/2/mark-schubin-tracing-concept-television-1877-1876-siemens-electric-eye/1660/msg2750#msg2750
« Last Edit: Wed November 22, 2017, 12:09:54 AM by donaldk »

Online donaldk

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Re: Mechanical Television primer
« Reply #4 on: Wed November 22, 2017, 12:13:00 AM »
Just as an aside, about Wolfgang's lacking images remark. Albert I see you attached the images, can you upload images to the media gallery? I still can't. In the past i could, but since september I get the wrong filetype error (jpg), in August it started with having other errors. The attachments show fine here. The big disadvantage to using attachments is that they all get hung at the bottom of the article. They can not be  coupled to a particular part of the article, to illustrate the text. Using the media gallery one can, by using the img tags.
« Last Edit: Wed November 22, 2017, 12:17:56 AM by donaldk »

Online w.mayer

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« Reply #5 on: Wed November 22, 2017, 04:57:08 AM »
Now I can see this images.

Just watch the Videolink.
Very good.
« Last Edit: Wed November 22, 2017, 05:32:14 AM by w.mayer »

Online donaldk

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Re: Mechanical Television primer
« Reply #6 on: Wed November 22, 2017, 05:40:03 AM »
Wolfgang I don't see a video link, just images. Or do you mean Mark's presentation?

Offline albert

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Re: Mechanical Television primer
« Reply #7 on: Wed November 22, 2017, 05:47:30 AM »
Thank you all for the comments. I hope we can get a lively discussion here!

Of course there were other people - not just Paul Nipkow. We must also mention the fact that very early attempts to transmit still images had been made at the end of the 19th century. From this the whole line of "FAX" technology branched off- my "Brockhaus" dictionary from 1908 shows this image as  a result of "Bild-Telegrafie"- still image transmission. Not bad huh? The machines resembled an old Edison phonograph or a small lathe. But remember this could take 20 to 30 minutes for a still image, a far cry from transmitting moving images.

Offline albert

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« Reply #8 on: Wed November 22, 2017, 05:51:21 AM »
Now, let’s jump forward to the 1920’s. By this time the  first radio stations had taken up regular broadcasting services on the shortwave band.
The first television pioneers succeeded in transmitting silhouette images of a cross or a pair of scissors, but no one had been able to transmit a greyscale image so far. Many countries had their TV pioneers, in France it was René Barthélemy, in the U.S. an inventor named Jenkins, and in Germany we had Manfred von Ardenne and the Hungarian Denes von Mihály.

Online w.mayer

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« Reply #9 on: Wed November 22, 2017, 06:13:28 AM »
I saw the Videolink you had post.

Online donaldk

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« Reply #10 on: Wed November 22, 2017, 08:12:03 AM »
Mark is a fine historian, and a true gentleman. His presentations have recuring themes, but they culminated in the linked article in IEEE Xplore. He also has done talks about how the opera was the first to use all modern communications technologies. Aswell as the inspiration for TV: http://www.sportsvideo.org/blogs/?blog=schubin-cafe&news=the-polish-polymath-who-came-up-with-television-for-opera-in-1878. Dating back 'cable' and Pay-Per-view/Hear to the 1800s. On more direct engineering there are issues of contrast/MTF and resolution. Check out http://www.schubincafe.com/category/schubin-cafe/.

Is he always that nice;-)...

Quote
From: Mark Schubin <tvmark@xxxxxxxxxxxxx>
Date: Mon, 12 Dec 2011 13:09:45 -0500
Well, as long as we're throwing in arcana, I am the person responsible for killing what I believe to have been the only actual ongoing 625/50 NTSC broadcasts (in Barbados). I got them to switch to 525/59.94 NTSC. The power on the island remains 50 Hz, so many older TVs needed power-supply filtering.


More goodies, like RCA's PAL pre-decessor CPA, Color Phase Alternation http://www.earlytelevision.org/rca_cpa_restoration.html. And a colourwheel based NTSC monitor: http://www.earlytelevision.org/dumont_monitor_restoration.html#feb2813.

There also has been a mechanical light valve projector back in 1936 that had a big wheel with mirrors, as well as a lightvalve showing lightvalve projectors are nothing new and pre-date or co-date CRT projectors;-).  Now where is that early technology site with chronoloical ordering of technologies when you need it.
« Last Edit: Wed November 22, 2017, 08:44:52 AM by donaldk »

Offline albert

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« Reply #11 on: Wed November 22, 2017, 10:03:53 PM »
Thanks for the link to the Schubin video-if you have the time to watch it, by all means do so. He shows that television was a long standing dream like heavier-than-air flight. And like that it became a reality as soon as certain principal inventions had been made.

Scottish inventor JOHN LOGIE BAIRD was one of the dominating figures in 1920s television history. He came from nowhere and succeeded where others in well equipped labs had problems. He had enormous effects on the beginning of the tv industry. But he fell to the wayside when electronic television became available.
He was the typical “lone wolf” inventor, who, after being largely unsuccessful with his “Baird Undersocks” that were supposed to keep your feet warm in the rainy English winters, decided to throw himself at the burgeoning field of television. He was plagued with health problems  all his life, and the determination he showed was all the more remarkable. He tackled the problems without a budget and was forced to haunt the London surplus shops where army material from WW I was sold at low prices. Some of his Nipkow discs were made from old hatboxes and his motor came from a garage sale. But his contraptions worked.
Baird overcame the basic problem of the Nipkow disc when this system was used as a camera: Only 0.1 % of the light passes though the holes in the disc to the photo-electric cell. He made a “lens disc” from plywood where he inserted glass lenses (from bicycle headlights) into the disc to form an image. These discs could not rotate at very high speed - he had an accident where one of these discs shattered and threw shards of glass across the room- so he made a secondary disc that rotated at high speed to interrupt the light beams from the lens disc and create more “resolution”.
He needed so much light for his first experiments that he would set people’s hair on fire when they were “televised”. So he did his first experiments with the head of a ventriloquist’s doll affectionately named “Stooky Bill.” This subject never complained and his features could be delineated with black paint.
With this whirling noisy contraption that barely held together he could transmit a grey scale image of “Stooky Bill” in his  Soho flat from one room to the next. He agreed to show his machine at the London department store “Selfridge’s” because he would have starved otherwise.

« Last Edit: Wed November 22, 2017, 10:12:52 PM by albert »

Offline albert

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« Reply #12 on: Sun November 26, 2017, 10:06:19 AM »
Let's stay a bit longer with John Logie Baird:

On January 26. 1926 about 50 scientists from the prestigious ROYAL INSTITUTION climbed to Baird's attic laboratory in London to witness the first transmission of a live tv image of a person's face. With this feat J.L. Baird made history- he is recognized now as being the first inventor whose system was able to transmit greyscale images - albeit in very low resolution. - 30 lines- and 12.5 images per second.

Feb. 08. 1928: Baird made history again by transmitting the first live tv images across the Atlantic Ocean.

Still in the year 1928, Baird showed a first primitive color TV system with a rotating color filter. This might be called the birth of color-sequential tv, a technique used today in most consumer video projectors.

From 1929 to 1935, the BBC showed  experimental television via shortwave radio. Baird developed a machine called the TELEVISOR - for wealthy customers- since at the time it was quite expensive.
But it could also be built from a kit by  tech-savvy radio amateurs. These were the first to be able to see regular television anyway, since the running of these machines was far from "you push the button, we do the rest".
Thanks to Baird and other pioneers,  TV had quickly become a commercial reality, and made it from wooden contraptions in labs to something that would not look out of place in a consumer household.
The image quality was still very poor, but at least recognizable faces and other detailed objects could be clearly seen on the tiny  area of the Nipkow disc.

 

Online w.mayer

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« Reply #13 on: Sun November 26, 2017, 10:11:20 AM »
I think the last picture show the 32 line TV right?
WOW what happen less than 100 years ago and think what we will have in 100 years from now!

Offline albert

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« Reply #14 on: Sun November 26, 2017, 10:21:04 AM »
Hi Wolfgang!

The picture was photographed off the rotating disc and according to the caption it shows a business partner of J.L. Baird, Oliver Hutchinson.  So then this would be a 30 line image, the later NBTV "club" standard is 32 lines.
Apparently this picture accompanied the article in the "TIMES" about Baird's successful demonstration for the Royal Society in 1926. Source: The English Wikipedia article on JL Baird.
It is really staggering to think about the development of TV in the past 100 years. We should put one of the rotating disc machines next to your projector one day!
« Last Edit: Sun November 26, 2017, 10:24:13 AM by albert »

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« Reply #15 on: Sun November 26, 2017, 11:05:14 AM »
I love to do a separate room with some antic stuff inside like the a good CRT Projector an old early Tube TV and if possible some of the stuff you talk about.

I think about it since many years.
But the room I had plan for this is blocked by my daughter for the next years :)

Online donaldk

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« Reply #16 on: Sun November 26, 2017, 02:33:46 PM »
That trans Atlantic transmission was actually captured on a record, yup phonogram/-graph became a videograph. Low information content made that it could be captured onto a shellac disc. A number of years ago this disc was decoded using modern computer technology.

http://www.telegraph.co.uk/culture/tvandradio/11898165/John-Logie-Baird-recording-saved-by-anonymous-donor.html
http://www.tvdawn.com/earliest-tv/phonovision-experiments-1927-28/the-recovered-images/


Online donaldk

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« Reply #17 on: Sun November 26, 2017, 02:34:50 PM »
Wolfgang, so you already collected a Saba Schauinsland, and a Volksbox?

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« Reply #18 on: Sun November 26, 2017, 04:10:07 PM »
No I not have it but I may will buy some if I can get a good deal.

Offline albert

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« Reply #19 on: Mon November 27, 2017, 06:13:50 AM »
Wolfgang- it would be great to have a little museum next to your projection room- but I guess your daughter would not like it!
Donaldk- I'm glad you mentioned the Baird "Phonovision" system, it was the first video recording process, long before AMPEX & co. in the 1950s. A British engineer managed to retrieve the images on these first discs - something Baird himself had never been able to do.
Today, the shellac disc of old has been replaced by the compact disc, and the low band video signals of the Baird process can be recorded on a CD-ROM as an uncompressed wave file. The sound for the video can be recorded on the other audio channel.

Mechanical television is by no means dead today. We will get to it!

The years from 1925 to 1939 were a time of feverish development. What had begun with a 30 line system and wooden discs ended here in Germany (just before the World War interrupted everything) with a fully electronic 441 line system including interlace.
The 2 MHz bandwidth of 441 line tv could not be transmitted on shortwave anymore, so TV helped bring in a new era of what we call FM ukw radio today.
But the Nipkow disc was used way into the fully electronic era, mainly for film scanning purposes. Here the inherent light loss of the Nipkow system could be compensated by using arc lights for the scanning process.
This led to one of the craziest inventions: "Zwischenfilmverfahren" in German.
If you wanted to "televise" an outdoor daylight scene, the Nipkow disc was not useable because of its light loss. So the rather incredible idea was

To film a scene on 35 mm movie film,
run this out of the camera into a super fast developing machine ...
then scan the still wet film with a Nipkow disc scanner.

This whole contraption was built into a big truck with a platform on top where the film camera stood on a hollow pedestal. The exposed film would run thru the pedestal into the truck to be developed and scanned ...and bingo! Here was your "Zwischenfilm " - in-between-film- process.
Below is a design for a 441 line Nipkow disk with several spirals and synchronization holes.
The second image shows the last Fernseh AG scanner built before the war - combined film scanner and a system like a videophone for transmitting images of the "talking head" type- 441 lines with a rotating disc in a vacuum housing. 10.000 rpms! If something goes wrong with such a monster, it's "duck and cover!"
« Last Edit: Mon November 27, 2017, 08:23:52 AM by albert »

Online donaldk

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« Reply #20 on: Mon November 27, 2017, 12:40:46 PM »
Indeed (again) Mark Schubin has presentation(s) that include descriptions of this system used at the 1936 Olympics.

Mechanical Television primer

Another little history in English on Fersehen AG http://people.ischool.berkeley.edu/~buckland/television.html

Quote
John Logie Baird began developing the process in 1932, borrowing the idea of Georg Oskar Schubert from his licensees in Germany, where it was demonstrated by Fernseh AG in 1932 and used for broadcasting in 1934.[2] The BBC used Baird's version of the process during the first three months of its then-"high-definition" television service from November 1936 through January 1937,[3] and German television used it during broadcasts of the 1936 Summer Olympics.[4] In both cases, intermediate film cameras alternated with newly introduced direct television cameras.

https://ipfs.io/ipfs/QmXoypizjW3WknFiJnKLwHCnL72vedxjQkDDP1mXWo6uco/wiki/Intermediate_film_system.html (oops originally from wikipedia)

Fernsehkanone for the intermediate film system:

Mechanical Television primer

And for the Telefunke Electronic system (cameraman is Walter Bruch inventor of the PAL-system):

Mechanical Television primer

BTW, this site shows that Fersehen AG has also released at least two CRT TVs.
http://www.tvhistory.tv/1935-1941.htm

A glimpse is available of both the (front) lens to the and an 30 centimeter CRT set by FernSehen AG.



I did not know there were mechnical Television broadcasts here in Holland as well in pre-war. I just knew about the electronic TV experiments, like radio the decade before backed by Philips. http://www.tvhistory.tv/1935-TV-Netherlands.htm
« Last Edit: Mon November 27, 2017, 02:18:56 PM by donaldk »

Online donaldk

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« Reply #21 on: Mon November 27, 2017, 02:57:02 PM »
Phonovision:



Offline albert

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« Reply #22 on: Mon November 27, 2017, 11:42:11 PM »
donaldk, you're faster than a speeding bullet! Thanks for showing these pictures- I was kinda baffled as to how to translate the German "tapeworm" of a word "Zwischenfilmverfahren". Intermediate film...easy.


This documentary shows some of the retrieved footage done with the intermediate film process. Thanks to these images- from about 11 minutes into the film- we can imagine today what the "programs" must have looked like. The documentary can be found under several names - the link I posted had the best image quality but it is in German. If you want to find the English versions google for "Television Under the Swastika".
BTW- the images above show the "TV Cannon " iconoscope camera used during the '36 Olympic Games - the intermediate film camera was much smaller and mounted on a truck - it, too, can be seen in the documentary film.
Fernseh AG became one of the "motors" of television technology- one of it's founding fathers was none other than John Logie Baird. He was disappointed with the BBC and so turned elsewhere to find business partners.
In Pre war times, Fernseh AG was in touch with the American tv developers at RCA . The US lab had trouble finding suitable phosphors for their CRT tube development. The German side  gave them this stuff and in turn received an Iconoscope from Dr. Zworykin. This was quickly duplicated and found its way into the Fernseh-Cannon camera. The other system, Farnsworths Image Dissector tube was also duplicated in Germany. But I digress...we are still "mechanical" at the moment......
« Last Edit: Mon November 27, 2017, 11:43:30 PM by albert »

Online donaldk

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« Reply #23 on: Tue November 28, 2017, 04:50:58 AM »
Actually the biggest of the two TV Cannons was the intermediate film one, that one like the electronic iconoscope one it came in a long distance version. At least the sources for those images declare that the long one with the large white box at the end is for the intermediate film process. Those cannons use huge lenses. I showed the intermediate film processing version first, followed by the iconoscope one manned by the PAL inventor. You are refering to the one directly on top of the truck, more or less a regular 35mm (or split 35mm =17.5mm) film camera (Zeiss Ikon?), that was used for capturing from coser distances (wider shots with the long lens ones for close ups, I gather).

Speaking of RCA and CRT (kinescope): Promotional film for the introduction at the 1939 New York World Fair.
« Last Edit: Tue November 28, 2017, 05:03:47 AM by donaldk »

Offline albert

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« Reply #24 on: Tue November 28, 2017, 06:58:22 AM »
Sorry, donaldk, both of the images you posted show the iconoscope camera. The intermediate camera was much smaller and it came on top of a truck, much like in your drawing. To my knowledge the stationary camera in the stadium did not use the intermediate process. They also had smaller tv cams with the Farnsworth dissector tube - referred to as "Sondenröhre" in the old FERNSEH  AG litterature.
The very large lens diameter of the Olympic Cannon clearly indicates  the iconoscope camera. The target of  the iconoscope was much larger than a 35 mm frame. This accounts for the lens diameter, which would not make sense for an outdoor daylight film camera. The extremely long focal length was needed in the stadium.
I have attached  an image of the "Zwischenfilm" truck.

I refer you to these pages:
http://www.fernsehmuseum.info/walter-bruch.html
Gert Redlich's virtual tv museum is a great source of information. It takes a long time to read thru all of this, though. And its in German...

I'd just love to know how to get images directly into the text .....so far I have not been able to find the trick.
« Last Edit: Tue November 28, 2017, 07:06:17 AM by albert »

Online donaldk

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« Reply #25 on: Tue November 28, 2017, 07:28:48 AM »
If they are hosted somewhere online (the dci-forum mediagaller no longer works for me, you might try that to upload images). Type
Code: [Select]
[img]url[/img] and it is shows there.

Iike:

Mechanical Television primer

Or linking a version hosted elsewhere, I found through google:

Mechanical Television primer

« Last Edit: Tue November 28, 2017, 07:40:12 AM by donaldk »

Offline albert

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« Reply #26 on: Wed November 29, 2017, 04:33:17 AM »
Thank you, I'll try this!

Today I would like to look at early methods of synchronizing the Nipkow disc to the video signal. This was a difficult problem-perhaps THE problem-of early television.
Bairds first experiments simply had the transmitter and receiver discs running on the same shaft....until he had worked out the problems of capturing and amplifying the video signals.
But as soon as transmitter and receiver were in separate rooms, there had to be another way...
And when the first TV broadcasts started, the Nipkow receiver had to comprise a means of synchronization.
The easiest way would have been to use the 50 or 60 hz line frequency for this. But in the beginning of the "electric" era, the line frequency could differ during the day or even in different parts of the city or country. So that did not work in the early days.

The solution most often used was the "phonic wheel". Invented by LaCour in 1875, the phonic wheel was the first synchronous motor. Baird used a variation of this on his "televisor".
In its simplest form, the phonic wheel had a toothed gear on the motor shaft with the same number of teeth as there were lines in the video image. Two electromagnetic coils were set 180 degrees off this wheel with their pointed iron cores as close as possible to the teeth of the wheel.
The video signal was amplified, inverted (?) and run directly into the phonic wheel assembly on the motor shaft driving the disc. For this to work, it was necessary to regulate the "wild" motor speed as closely as possible to the desired speed of 750 rpm.
The video signal à la Baird contains a sync pulse indicating a new line and another one indicating a new frame every 30 lines.
This was simply a black "bar" around the image. 
When the motor ran too fast the impulses in the coil would "brake" the gear a little , pulling on the back side of the teeth.
When the motor was too slow the coils would give a small acceleration to the gear teeth, pulling on the advancing side of the wheel's teeth.
This worked in theory and the image would stop rolling vertically. ....but only if there was no black signal between different scenes and no scenes that were too dark. If this happened the sync would be lost.
The primitive system would take care of the general speed of the disc but not of the "line sync" or phase . If this was wrong you would see a picture split in half vertically.
To correct for this phase error, the entire assembly of the coils on the motor could be rotated  slightly with a knob on a gear.

Here are the original patent drawings and a page from an original Baird manual showing the motor and synchronizer. Note that the gear wheel on the motor shaft was made from many thin metal leaves like a modern transformer core.

"Watching TV" at the time was work and no job for "couch potatoes! "




« Last Edit: Wed November 29, 2017, 04:59:23 AM by albert »

Online donaldk

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« Reply #27 on: Wed November 29, 2017, 06:59:37 AM »
Issue with attaching and embedding images is that we get to see them twice.

Here are the original patent drawings and a page from an original Baird manual showing the motor and synchronizer. Note that the gear wheel on the motor shaft was made from many thin metal leaves like a modern transformer core.

Mechanical Television primer

"Watching TV" at the time was work and no job for "couch potatoes! "

Offline albert

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Re: Mechanical Television primer
« Reply #28 on: Sun December 03, 2017, 08:28:30 AM »
Since the Nipkow disc had many disadvantages, people looked for alternatives early on. To use the mechanical process for projection of the image onto a screen, the mirror drum invented by Lazare Weiller was used and improved for tv purposes by German professor Karolus in the 1930s.

This was a heavy piece of engineering and it required lengthy adjustment since the mirrors had to be perfectly aligned. Due to the weight mirror drums were difficult to synchronize.
Another idea was the mirror screw, the images could be viewed directly and they were a lot brighter than anything on the Nipkow disc. But again, a great deal of precision was necessary.


Offline albert

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Re: Mechanical Television primer
« Reply #29 on: Sun December 03, 2017, 08:35:50 AM »
A very nice pocket sized televisor was made in France in the 1930s, the Brami Visiola.  It used a 30 Line  mirror screw. To view either German/French TV or UK/Baird type tv, the whole device could be rotated to run either in a vertical or horizontal position.
As all mirror screw devices, this one had to be lit by a very long, small neon lamp that was longer than the screw itself.
This  was the "smartphone" size display of its day.


Online donaldk

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Re: Mechanical Television primer
« Reply #30 on: Mon December 04, 2017, 07:00:18 AM »
Albert, a mirror wheel like that was also used in a French public Television projector, using a lightvalve as lightsource. Must search for the name, and source as i saw the reference years ago. Machine was from 1936 it said.

Edit: Scophony https://en.wikipedia.org/wiki/Scophony, UK/Germany http://www.earlytelevision.org/scophony_projection_tv.html http://www.earlytelevision.org/pdf/pop_sci_7-49.pdf

Small projector:
Mechanical Television primer

Mechanical Television primerMechanical Television primer

The Schlierenstop made a return in the GLV laser projectors, most notably the ESLP.

Mechanical Television primer
GE mechanical projection demo 1930, above, others doing the same that year: http://www.sportsvideo.org/blogs/?blog=schubin-cafe&news=getting-the-big-picture, others: http://www.earlytelevision.org/mechanical_theater_tv.html
« Last Edit: Mon December 04, 2017, 10:13:46 AM by donaldk »

Offline albert

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Re: Mechanical Television primer
« Reply #31 on: Thu December 07, 2017, 08:55:30 AM »
Donaldk, you're right- the first public demonstration of TV  in France made use of a mirror drum device and projected images. René Barthélémy was the inventor, not  a lone wolf like John Baird, but an accomplished mathematician/physicist - he was employed by "La Compagnie des Compteurs" in Montrouge, that was the company that did all the gas and electricity counters in France at the time. They had an incredibly skilled staff of mechanical engineers and so their equipment was very well made- a far cry from Baird's plywood and chewing gum approach. Everything was solidly engineered. Soon after these  humble beginnings, this staff switched to electronic cathode ray systems for recording and displaying tv images.
The scophony system you have mentioned was also using a mechanical scanner but with an interesting light valve that was years ahead of anything else. It used a liquid filled cell into which an ultrasonic crystal introduced vibrations at very high frequency, the Jeffree cell. I could not find much more detailed information on that.
The first French TV studio was not far from the Eiffel Tower, and it used a 60 line Nipkow disc camera system. Due to the tremendous light loss with the discs, the intensity of the light in the studio had to be above 20.000 lux. The air would be heated to 50  Celsius in no time. So they had to put in a tremendous amount of air conditioning. The outlets of this system made the studio floor look like the deck of an ocean liner.
The Eiffel Tower, by the way, owes its continued existence to the fact that it was an ideal place to put the first powerful radio and then TV transmitters. It was originally scheduled to be taken down after the 1900 world expo for which it was erected. Many people at the time were less than enamored with the Eiffel Tower and thought it was a disgrace to the beauty of Paris! That has changed a bit!

The images below come from these pages- a history of early television in France- in French.

http://819lignes.free.fr/Histoire_de_la_television_francaise.html

There is a great conference held at the cinemathèque in Paris in the summer of 2017- it features Don Mc Lean, the engineer who decoded the few remaining discs of Baird's phono vision- its slow because Don speaks English and is then translated to French. The second half of the conference is on early French TV by a French expert - Bernard Tichit- in French. For patient people only- 2 hours 33 minutes....





« Last Edit: Thu December 07, 2017, 09:06:49 AM by albert »

Offline albert

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Re: Mechanical Television primer
« Reply #32 on: Fri December 08, 2017, 11:34:40 AM »
Donaldk, could you please explain what you mean by Schlieren stop. I know about Schlieren optics and I believe this was used in the Scophony cell- as well as in the later Eidophor big screen projector.

Online donaldk

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Re: Mechanical Television primer
« Reply #33 on: Fri December 08, 2017, 12:27:18 PM »
It is indeed used to block part of the light. I presume it is the difference between English and German. In the small picture of the Scophony system it is labelled, the larger picture on the reight does identify other parts, so I posted both. I did not know it was in the Eidophor before this discussion, but I read about it for te first time in articles about the ESLP and the Sony/GLV Grating Light Valve projectors.

Offline albert

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Re: Mechanical Television primer
« Reply #34 on: Sat December 09, 2017, 07:06:28 AM »
Here is a link to an old movie describing a tv setup with a Nipkow disc "flying spot scanner" @ 48 lines from GE Company in Schenectady 1931.

https://www.youtube.com/watch?v=2WiV0FIFpHE&feature=youtu.be

The Nipkow disc on the transmitter side projects the bright spot from a high power incandescent lamp house onto the subject. The reflected light is taken up by massive photo cells and this is what drives the receiver side. The machine is shown in all its details which makes for interesting viewing. -
You can also see the results of the machine filmed directly off the receiver. This gives a good idea of what these images looked like at the time.

https://www.youtube.com/watch?v=2WiV0FIFpHE&feature=youtu.be

The receiver uses a lens disc to project the image onto a screen. The light from an arc lamp passes thru a "light valve"- again a Kerr cell or something similar to it.

This obviously was a well engineered system.


« Last Edit: Sat December 09, 2017, 07:15:49 AM by albert »