A televisual curiosity

[Panrock]

This will be old news to NBTV enthusiasts but I thought it might interest some others here.

Here is a video of a large Mirror Screw mechanical televisor I made some years ago - in action. I haven't uploaded this particular extract before.  The picture is 120-lines and the 1939 colour film being screened is in the public domain.

The red, green and blue video originates from three brilliant lines of LEDs. The Mirror Screw then reflects this so it's 'pulled out' across a raster.

Another instance where Darryl's World Converter has proved so useful! Karen Orton also made an electronic 'slat angle corrector' for this display which improved the results appreciably.

One day, I'll do a proper presentation, explaining it and showing it being run up. It's a characteristic of a "high" definition mirror screw that to fill the "screen" you have to shoot the picture from some distance away - in this case across the room. The frame bars are, of course, an artefact from my phone, which was used to shoot the video and has also degraded the quality of the picture.  Sorry about the barometer - it's rather visually intrusive.

https://www.youtube.com/watch?v=Vf5Po5n1--k

Steve

[Amie]

Fascinating!

[ppppenguin]

This is an incredible piece of engineering. All credit to Steve for achiveing these results.

[`FRANK.C]

Hi Steve
That is really amazing. Its hard to believe that such good results could be achieved with mechanical TV.
I can imaging that the amount of time that went into building it must be huge.

Frank

[peter scott]

Imagining it as you were able to see it Steve without the aliasing frame bars it really is quite fabulous.

Peter

[Panrock]

The kind words are really much appreciated. I know several posters here are no strangers to big projects of various types.  Frank, the fact that it's 120-lines helps, and an equivalent Nipkow disc display would be tiny and dim, unless built on a gigantic scale.  And rather than just occupying a wedge at the rim of a disc like a Nipkow disc, the display from a Mirror Screw is as large as the screw itself. Here, we have a 12-inch (diagonal) picture.

There are corresponding disadvantages though... If you walk toward the screw when in action, apart from having your fingers chopped off (if you're really too close!) the picture width progressively shrinks and more pictures join it at the sides, each being one line further out of frame phase.

Seriously, when I made this, safety was a major concern. The screw itself weighs about 44 lbs and it rotates at 25 Hz. Moreover, after the slats' edges were re-polished it became out of balance and I've had to fit a correction weight. 

Steve

[Jac Janssen]

An incredible display of your craftsmanship Steve!

Jac

[peter scott]

Seriously, when I made this, safety was a major concern. The screw itself weighs about 44 lbs and it rotates at 25 Hz. Moreover, after the slats' edges were re-polished it became out of balance and I've had to fit a correction weight. 

Steve

Aha! You need a safety glass in front of the screw just like with a CRT. So there really is no advantage to this technology over the CRT?

Peter

[Panrock]

Ha ha! Was safety glass bullet proof? I worked out the g force once. I forget the answer now but it was terrific. If my balance weight came adrift it would be like a bullet. So as you can imagine it's pretty well fixed - bolted on in fact.

Looking back to the '30s, it really is incredible what TeKaDe achieved in constructing a (presumably) accurate 180-line mirror screw with the methods available at the time. The optical tolerances are very tight when you have a large number of lines. But then we also marvel at what Scophony achieved. The engineers of the 1930s were no dummies. And after all, precision engineering has long been needed for the likes of motor car and aircraft engines.

[peter scott]

Ah! Scophony, a beautifully wacky use of mechanical techology to provide television. Motors running at 30,375 rpm redefine the meaning of longevity.

Peter