Starting at the beginning with Mirror Screws

Forum for discussion of narrow-bandwidth mechanical television

Moderators: Dave Moll, Andrew Davie, Steve Anderson

Re: Starting at the beginning with Mirror Screws

Postby Steve Anderson » Mon Jan 02, 2017 5:24 pm

Panrock wrote:....until I get the WC-01 back, which this time I expect to send back to the USA. Steve O


If it does have to go to the US let's hope you get it back before the convention. Also let's hope it doesn't go 'phut' again prior either.

I'm going to be in the UK later this month, initially for two weeks only. But if I can pick up some 'real work' over there and it goes on through April I may actually make it to the convention for the first time!

Steve A.
User avatar
Steve Anderson
"Fester! Don't do that to 'Thing'"
 
Posts: 5361
Joined: Fri Mar 30, 2007 10:54 pm
Location: Bangkok, Thailand

Re: Starting at the beginning with Mirror Screws

Postby Panrock » Mon Jan 02, 2017 10:35 pm

If you're in the UK - and it's convenient - you must drop in here Steve A... but not until the Mirror Screw is back up and running! The conditions for demonstrating something like this, requiring a lot of space and a best viewing position, are far better in a private home than at a Convention. I'd see if I could persuade Karen O to visit at the same time and we could all go off and have lunch somewhere in the country.

Anyway, I missed you when I was in Penang. Maybe this time...

Steve O
Panrock
Green padded cells are quite homely.
 
Posts: 870
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Re: Starting at the beginning with Mirror Screws

Postby Steve Anderson » Tue Jan 03, 2017 1:04 pm

Panrock wrote:...you must drop in here Steve A... Steve O

Thanks for the invite Steve. I have a number of things to do whilst in the UK beyond seeing my parents, but I'll try to squeeze in a visit to Sedgeberrow. Perhaps you could PM me your phone number if it's different to the one(s) on the Radiocraft website.

Steve A.
User avatar
Steve Anderson
"Fester! Don't do that to 'Thing'"
 
Posts: 5361
Joined: Fri Mar 30, 2007 10:54 pm
Location: Bangkok, Thailand

Re: Starting at the beginning with Mirror Screws

Postby Panrock » Tue Jan 31, 2017 2:17 am

Now the WC-01 has returned from the USA (with Darryl finding nothing wrong - my frame pulse could have been 'corrupted'), things are coming together with this Mirror Screw. I hope to be meeting Steve A within the next week or less, and he'll be given a private demonstration.

I had a neighbour banging frantically on the door this afternoon. Apparently there was a brilliant flickering light coming from my house, visible across the road, and they thought my house was on fire! :mrgreen: When I invited him in to see the apparatus he just didn't know what to make of it. This was nothing like he had ever seen before.

Well, the new line-of-light is pretty bright - too bright to safely look at - but this means I get a nice bright picture with it 4 metres away from the screw, as Karen recommended.

More news soon.

Steve O
Panrock
Green padded cells are quite homely.
 
Posts: 870
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Re: Starting at the beginning with Mirror Screws

Postby Panrock » Thu Feb 02, 2017 6:50 am

You can now have a peep at it working on YouTube at


youtu.be/ELk4DmqwNms

This is the first time I've ever uploaded anything to the Tube so please bear with me. Due to the characteristic of a mirror screw display, I had to shoot this on my phone from right across the room, on 4x (max) zoom. Maybe Steve A when he visits will have a better movie camera? The travelling black bar is a camera artifact.

Shame I didn't think to take down the barometer from the wall before shooting! It makes the view look rather odd.

If you want a proper look you'll have to come to the Convention! :lol:

Steve O
Last edited by Panrock on Thu Mar 16, 2017 6:12 am, edited 3 times in total.
Panrock
Green padded cells are quite homely.
 
Posts: 870
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Re: Starting at the beginning with Mirror Screws

Postby Harry Dalek » Thu Feb 02, 2017 5:32 pm

Panrock wrote:You can now have a peep at it working on YouTube at https://www.youtube.com/watch?v=ELk4DmqwNms

This is the first time I've ever uploaded anything to the Tube so please bear with me. Due to the characteristic of a mirror screw display, I had to shoot this on my phone from right across the room, on 4x (max) zoom. Maybe Steve A when he visits will have a better movie camera?

If you want a proper look you'll have to come to the Convention! :lol:

Steve O


Funny story about the neighbour :D reminds me of my father inlaw walking in on me working on a my past NBTV 2 drum slit monitor had no idea what early television was i explained but i think he thought i was having him on :roll:

So the light slit is out of sight screw reflecting the light in sync ..it looks really good i would say best colour mirror screw i have seen ...Steve as some one who has not made one and what to expect at different distances and angles i would be interested to see this effect ...i know this is best view distance different not so good position will give an idea of what a mirrow screw is like .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
User avatar
Harry Dalek
"Fester! Don't do that to 'Thing'"
 
Posts: 5364
Joined: Fri Sep 26, 2008 4:58 pm
Location: Australia

Re: Starting at the beginning with Mirror Screws

Postby Panrock » Thu Feb 02, 2017 9:51 pm

Thanks for the nice comments Harry, both here and on YouTube.

You can see in the video how the mean DC content of the RGB pictures alters the general illumination of the stand bearing the mirror screw!

The following explanation assumes horizontal scanning.

Basically, as you walk toward the screw, the picture gets thinner and thinner (the width decreases), with more equally thin pictures appearing either side - the frame phase of each displaced downwards or upwards by one line compared to its neighbour.

When you are right up next to the screw, there will be masses of these stick-thin pictures!

If you view from one side, then your central picture is going to be the 'wrong' one, not the one set up for the correct frame phase.

Now in this particular case, the neighbouring pictures are of poorer quality too, since the Timing Corrector can only be set up to cancel the slat angle errors of the 'correct' picture.

In the vertical sense too, the reflection angles must be right. But here, if they are not, you simply won't see anything. In other words, if you want to view the picture from above the screw, the line-of-light must be below the screw - and vice versa. This effect can be mitigated somewhat by having a very long line-of-light.

The long and short of it is that there is just one good viewing position. It won't be easy with the hubbub at the Convention!

Steve O
Panrock
Green padded cells are quite homely.
 
Posts: 870
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Re: Starting at the beginning with Mirror Screws

Postby Harry Dalek » Fri Feb 03, 2017 5:54 pm

Thanks Steve
Thats interesting just not seen the effect of a mirror screw every one shows it at its best not its worst so it is good that you explained it here Steve .
It must be similar to a mirror drum in some ways but i recall the mirror drum is like a Nipkow viewing it ..multiple images each mirror till the light levels fade away ..i don't know if its been looked at what is the best mechanical television way thats better for viewing angles .
I think there are a few Colour mirrors about at 60 line but 120 line you must one of the few or have the only one .
I recall seeing the German mirror screw somewhere on the net with the slit light in the same case ,if the screw is small like that is the viewing angle greater or the same it seems much harder with yours ? is it more the problem of dropping the size of the light slit for the mirror screw when you are running more lines ....i suppose as every thing when it has to do with mechanical television it gets harder more lines you go for .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
User avatar
Harry Dalek
"Fester! Don't do that to 'Thing'"
 
Posts: 5364
Joined: Fri Sep 26, 2008 4:58 pm
Location: Australia

Re: Starting at the beginning with Mirror Screws

Postby Panrock » Fri Feb 03, 2017 7:36 pm

Harry Dalek wrote:I recall seeing the German mirror screw somewhere on the net with the slit light in the same case ,if the screw is small like that is the viewing angle greater or the same it seems much harder with yours ? is it more the problem of dropping the size of the light slit for the mirror screw when you are running more lines ....i suppose as every thing when it has to do with mechanical television it gets harder more lines you go for .

Assuming the same picture shape, everything is 16x harder at 120-lines than at 30-lines... 16x more exacting angle tolerances, 16x smaller picture area, 16x smaller scanning spot, 16x more light needed at the 'screen' from a source 4x times farther away. It's been difficult!

In the early days I tried concave (magnifying) mirror slats and these did indeed give a larger picture closer up. I used a cylindrical figure of (I think) radius 2 metres. However I was unable to obtain the degree of polish needed on curved surfaces of stainless steel. I only later managed this with the present flat surfaces, using professional grinding and polishing services. But then doing this knocked out the mechanical balance. Another headache!

The whole thing is very large and heavy and rotates very fast compared to all other mirror screws, past and present. I live in fear of the bottom thrust bearing giving up... it has a hard job to do and is now completely inaccessible.

Steve O
Panrock
Green padded cells are quite homely.
 
Posts: 870
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Re: Starting at the beginning with Mirror Screws

Postby Panrock » Sun Jul 30, 2017 4:15 am

You can't keep an old thread down! :D

Karen is now writing up her Timing Corrector for a forthcoming bulletin and in due course I too will contribute an article about the 120-line mirror screw.

The information in this long thread has proved a useful record of fact about this five-year-long saga - far more reliable than my own rickety memory banks.

Now we've got this working, what next? Well it is decidedly impractical having to view the display from one favoured viewing position. Could the image be viewed on a ground glass screen instead and enjoyed by many? I don't think so, unless the red, green and blue lines of light were line-pattern lasers. However, maybe the existing system could be made to work by using a giant (water filled?) cylindrical condensing lens between the LED lines-of-light and the remote projection screen.

Views on this are welcome.

Cheers,

Steve O
Panrock
Green padded cells are quite homely.
 
Posts: 870
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Re: Starting at the beginning with Mirror Screws

Postby albertMunich » Thu Aug 03, 2017 12:37 am

Hi everyone,
my name is albert and I live next to Munich, Germany. One of my favorite childhood places was the "Deutsches Museum" -one of the largest technical museums in the world. And one of the most interesting collections there was the television department, where they had all the mechanical devices from the first crude Nipkow disk to the sophisticated scanner that had the disc running in a vacuum chamber to get rid of the wind and friction problems.
I also remember the mirror drums and mirror screws on exhibit there. Unfortunately none of these things was in working order let alone running.
Recently I came across the incredible sites dealing with NBTV and the various attempts to resurrect these techniques. Its just amazing to see how many people are doing experimental work - never thought it possible to DIY a mirror screw. Kudos to your perseverance and stamina to bring this off. And then Color! My jaw dropped!
Thinking of that, television has in some ways come full circle. A modern day beamer is nothing but a mechanical tv system. Including the color wheel that was forgotten in a corner of tv history until it came back...and the DMD or DLP devices are mechanical, although in a way that would have given the pioneers of the 1930s a massive coronary had they seen it...
This is fascinating and I hope to be able to do some work myself when I have more time after retirement.
The reason why I write in this thread: I have more than 30 years of experience in 3D stereoscopic photography, projection and adjacent fields like 3d video.
You ask in your last post- where to go from now?
Reading your story and the varius experiments you did- I wonder if the mirror screw can be used to free view 3d stereoscopic pictures or video. No glasses! You describe the various effects when approaching the screw or changing the viewing angle. This makes me wonder what would happen if one used two light lines at a slight distance from each other to illuminate the screw? Would you see two different images at different angles? could these be made to be 2 cones of light with just the right interocular distance so that each would be seen by just one eye? Would there be crosstalk?
This might be a complete failure, or it might be a workable idea.
The other idea I had when reading about all the synchronization problems inherent in these mechanical devices- has anybody used model aircraft brushless motors? These are basically steppers without the noise and when run by a dedicated controller from the same timing pulse, they would be automatically in synch. ??
Please continue to publish your work, its a great inspiration.
My last thought is that a nipkow disk is hard to 3d print, but I believe the slats for a mirror screw could be 3d printed if there could be a way to make them reflective...? Some kind of electro plating process?
This would make for a screw thats a lot lighter and it would be less of a butchers nightmare!

All the best

Albert
albertMunich
Laboratory Assistant
 
Posts: 23
Joined: Thu Aug 03, 2017 12:08 am

Re: Starting at the beginning with Mirror Screws

Postby Harry Dalek » Thu Aug 03, 2017 8:02 pm

Hi Steve
I wonder if it would work viewing off a curved screen ? i see your thinking of using a same sort of idea water lens .
You seem to need a fair distance for it to work can you adjust it for a closer focus ? adjusting the mirror slats or lenses ?
Screen perhaps plastic that would curve .
I wonder if also you could out of interest if you had 2 or more light strips pointed at the mirror screw would it project the 2 rasters as is or mix them ? i think due to the angles you would get 2 rasters
Its a hard one as not many of us have a mirror screw and i am in the not camp can only speculate.
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
User avatar
Harry Dalek
"Fester! Don't do that to 'Thing'"
 
Posts: 5364
Joined: Fri Sep 26, 2008 4:58 pm
Location: Australia

Re: Starting at the beginning with Mirror Screws

Postby albertMunich » Thu Aug 03, 2017 9:47 pm

I made this on Fusion 360 yesterday. 60 lines / 2. 5 mm slats / 150 mm wide. 6 degrees spacing. Would this be correct? Just to see if it can be 3d printed in ONE piece-with an FDM printer it does not work without supports. Getting the sides to be reflective would be the next problem. but doing it in a fused piece and not in separate pieces should lessen or kill the adjustment torture described in this thread...

Bild 03.08.17 um 08.34.jpg


Doing a vertical cut it could be made in two pieces with a minimum of overhang lying on its side. Just to have something in hand.
I also tried to get a raytraced simulation of the thing in rotation but I cannot create the light line to illuminate it at the moment. I still believe to get a 3d printed screw is easier than to make a Nipkow disk with a 3d printer....
The question of the two rasters being scanned is also of great interest to me. Elsewhere I found something on 3D with a mirror screw but so far it's a bit fuzzy in my imagination how this could work.

Bild 03.08.17 um 08.35.jpg
albertMunich
Laboratory Assistant
 
Posts: 23
Joined: Thu Aug 03, 2017 12:08 am

Re: Starting at the beginning with Mirror Screws

Postby Panrock » Fri Aug 04, 2017 2:12 pm

Welcome, Albert of Munich! Good to have you on board. You have a most interesting background. Thanks too goes to Harry in Australia for his ever-present interest and enthusiasm.

albertMunich wrote:And one of the most interesting collections there was the television department, where they had all the mechanical devices from the first crude Nipkow disk to the sophisticated scanner that had the disc running in a vacuum chamber to get rid of the wind and friction problems.

I wonder if there also you saw the early 1930s TeKaDe 180-line mirror screw! If this indeed originally gave good results, the mind boggles at the engineering precision required!

albertMunich wrote: I have more than 30 years of experience in 3D stereoscopic photography, projection and adjacent fields like 3d video.

Fascinating! In my humble way, some years ago I did demonstrate 3D NBTV at a Convention. It used beam splitters and left-right shutters (at both camera and monitor), switching 30-line views at half frame speed... 6¼ Hz!... involved no glasses, and televised a vertical pencil in front of a more remote background. You had to lie on the floor with your head exactly in the right position to see the effect. It wasn't very convincing.

albertMunich wrote:You describe the various effects when approaching the screw or changing the viewing angle. This makes me wonder what would happen if one used two light lines at a slight distance from each other to illuminate the screw? Would you see two different images at different angles? could these be made to be 2 cones of light with just the right interocular distance so that each would be seen by just one eye? Would there be crosstalk?

I have also been wondering about this. The last time I had the mirror screw running (it's a pain: it takes half an hour to set up and means a mess of trailing leads all over the living room) I considered this question briefly and it seemed that the effect of switching between eyes was the opposite of that required for stereo.

I'm due to set it all up again though for the photographs that will accompany my article in a future club magazine. I'll then consider the question more carefully. As you say, crosstalk is likely to be a problem. Because the mirror screw demands viewing at the correct distance to get the aspect ratio right and fill the 'screen' with only one picture, we don't have the luxury of adjusting the viewing distance to get the reflected parallax right for stereoscopic television (even assuming the parallax has the correct polarity, which as I have said, I don't think it has).

albertMunich wrote:The other idea I had when reading about all the synchronization problems inherent in these mechanical devices- has anybody used model aircraft brushless motors? These are basically steppers without the noise and when run by a dedicated controller from the same timing pulse, they would be automatically in synch. ??

This sounds a great idea if the motor has sufficient power for the application. I'll defer comment to the motor synch experts here. As you know, my mirror screw used a simpler (for me) arrangement, synching the source to the screw rather than the other way round.

albertMunich wrote:Please continue to publish your work, its a great inspiration.

Your comment is most kind and helps morale greatly, because often I wonder what is the point of it all... what a strange and eccentric waste of time this is in an age of otherwise advanced technology, etc...

albertMunich wrote:My last thought is that a nipkow disk is hard to 3d print, but I believe the slats for a mirror screw could be 3d printed if there could be a way to make them reflective...? Some kind of electro plating process?

This might be possible. It certainly was possible to plate fibreglass for example, as was done in the "Retrovisor Imperial" I made in 1993 (shown below). A conductive coating was plated first with copper, then nickle. Nickle has a slightly 'warmer' tone than chrome and the overall effect was a television set made of silver!

Harry Dalek wrote:I wonder if it would work viewing off a curved screen ? i see your thinking of using a same sort of idea water lens.

Probably a curved screen would give more even focus. Whether this (or the curve) would be noticeable at a practical viewing distance is a moot point though.

Harry Dalek wrote:You seem to need a fair distance for it to work can you adjust it for a closer focus ? adjusting the mirror slats or lenses ? Screen perhaps plastic that would curve.

We are talking close-in, off angle, lens positioning using standard LED-based lines-of-light, which of course produce diverging 'fans' of light. I no longer think line-pattern lasers would work because there would be no 'fan' pattern to fill the horizontal travel of the reflected spot. The cylindrical lens would have to be larger than the screw and close by, to capture all the light.

Harry Dalek wrote:I wonder if also you could out of interest if you had 2 or more light strips pointed at the mirror screw would it project the 2 rasters as is or mix them ? i think due to the angles you would get 2 rasters

Well Harry, I am using three displaced (red, green and blue) rasters at present and they are being successfully converged by having different delays applied by Karen's Timing Corrector. Once we interpose a screen though, this might change, or even remove this effect. I shall have to think carefully about this.

All the above comes with a health warning. I still don't really understand the optics of mirror screws!

Steve O
Attachments
Retrovisor_Imperial_.jpg
Retrovisor_Imperial_.jpg (53.61 KiB) Viewed 10672 times
Panrock
Green padded cells are quite homely.
 
Posts: 870
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Re: Starting at the beginning with Mirror Screws

Postby Andrew Davie » Fri Aug 04, 2017 8:31 pm

Just for anyone who wants to play/test, I did a very quick script in OpenSCAD for generating mirror screws...
Perhaps instead of printing as one huge 3D block, just generate the slats with some sort of inbuilt snap/guide that lets you assemble them together accurately.
Here's a video of the script being used, for those who don't/won't play with OpenSCAD...



Code: Select all
// Mirror screw
// Andrew Davie August 2017

LINES = 32;             // MODIFY AS REQUIRED # SCANLINES
RADIUS = 300;           // units: mm
HEIGHT = 400;           // units: mm



SLAT_WIDTH = (2*PI*RADIUS)/LINES;
SHAFT_RADIUS = SLAT_WIDTH/2;
SHAFT_HOLE_RADIUS = SHAFT_RADIUS/2;

difference() {

    union() {

        for (line=[0:LINES-1])
            translate([0,0,line*HEIGHT/LINES])
                rotate([0,0,360*line/LINES])
                    translate([-RADIUS,-SLAT_WIDTH/2,0])
                        cube([RADIUS*2,SLAT_WIDTH,HEIGHT/LINES]);

        cylinder(r=SHAFT_RADIUS,h=HEIGHT);
    }

    cylinder(r=SHAFT_HOLE_RADIUS,h=HEIGHT);
}

Attachments
screw2b.mp4
(4.28 MiB) Downloaded 930 times
User avatar
Andrew Davie
"Gomez!", "Oh Morticia."
 
Posts: 1590
Joined: Wed Jan 24, 2007 4:42 pm
Location: Queensland, Australia

PreviousNext

Return to Mechanical NBTV

Who is online

Users browsing this forum: No registered users and 36 guests