Mechanical Television primer

[donaldk]

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:




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


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

[albert]

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....

https://vimeo.com/224027916

[albert]

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.

[donaldk]

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.

[albert]

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.

[donaldk]

According to wikipedia the Jeffree cell used by Scophony let 200 times more light through compared to the Kerr cell.

[albert]

I have found this website - it has the most stringent info on the Jeffree Cell so far...

http://www.bluehaze.com.au/modlight/UltrasoundMod.htm

I think this type of cell could be used in holographic imaging today.

[albert]

More on Scophony. This seems to be the most overlooked TV system ever.
Think about it- they had in 1938 a motor driving a small mirror scanner at more than 30 000 rpm in sync with the video signal. And they had the ultrasonic modulator light valve.
Hard to believe. When I think how the Ampex people struggled later on with their head wheel for their first 2 inch quad video recorder....this had to run @ 10. 000 rpm - in Europe @ 15. 000- and the entire head wheel/motor assembly had a lifetime of only 300 hours at first.

[w.mayer]

Still very nice to read here!

Is it not strange what kind of big development we only got in less than 80 years!
So think what we will have in 80 years from now.....
Hope I can at least see the next 20 to 25 years........

[dirk goetze]

Thank you putting this together here Albert,

I really enjoy reading and the pictures as well.

I remember the the hateful first Russian Color TV "Raduga" in former Eastgermany, hateful because he had only the French/russian SESAM Modul in it...that means our  window to the West, the Westgerman TV Station can be only been recieved in black and white

[donaldk]

And we had the same issue with DX-ing AFN. Pioneers ahead of me always had issues with not just French, but also Eastern terrestrial and satellite channels. On Gorizont the USSR also added a large FM sweep to its TV signals to enhance video recovery, but early Western satellite receivers did not have this, so unstable on top of black and white. Raduga, or Rainbow(?) was later re-used for a series of Russian satellites http://www.russianspaceweb.com/raduga1m.html.

I see the Raduga pre-dates SECAM with a Field Sequential Color system: http://www.earlytelevision.org/raduga.html.

Anyway all very much Post-War and Electronic, not mechanical.