large scale Baird/Nipkow Televisor project "Big Paul"

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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby gebseng » Mon Mar 12, 2018 8:23 am

Klaas Robers wrote:For the flying spot source there is no need for a fine point light source. The light source should illuminate the picture area of the Nipkow disc evenly. Look what happens in a slide projector In fact the flying spot source is a slide projector, where the Nipkow disc is the slide. It projects a focussed moving spot on the scene.

The light sensors around the scene have the same behaviour as the lamps on a film or TV scene. You can have spot-lights, more or less focussed, or flood lights. It is only the running direction of the light that is reversed. You need also more light sensors to eliminate sharp "shaddows". The faders in the output signals of the sensors are comparable in function to the dimmers of the studio lighting in a TV studio.


Thanks Klaas, that makes things easier.
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby gebseng » Sat Mar 17, 2018 1:17 am

Klaas Robers wrote:For the flying spot source there is no need for a fine point light source. The light source should illuminate the picture area of the Nipkow disc evenly. Look what happens in a slide projector In fact the flying spot source is a slide projector, where the Nipkow disc is the slide. It projects a focussed moving spot on the scene.

The light sensors around the scene have the same behaviour as the lamps on a film or TV scene. You can have spot-lights, more or less focussed, or flood lights. It is only the running direction of the light that is reversed. You need also more light sensors to eliminate sharp "shaddows". The faders in the output signals of the sensors are comparable in function to the dimmers of the studio lighting in a TV studio.


Hi again, I made a quick test, and my results were different, I'm not sure why.

First, I put a very soft ligh source (LED in a softbox with a piece of opaque acrylic in front) very close to the disk (with 0.5 mm holes in it), I did not get a light spot on the other side, just a very soft shine:

IMG_4211.jpg

IMG_4209.jpg

IMG_4210.jpg


Then I removed the opaque acrylic in front of the LED and moved the LED farther away, to get a hard light source with parallel rays. the result was a pretty sharp and defined spot (plus some extra reflections, because I did not remove the reflective box around the LED):

IMG_4212.jpg

IMG_4217.jpg

IMG_4218.jpg


What do you think?

thanks,

geb

(sorry again about the orientation of the photos. Once you click on them, you see them upright)
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby Robonz » Sat Mar 17, 2018 11:17 am

The light source needs to be focused. Adding the diffuser is a good thing for the viewing side but not the camera side. Having a reflector is bad too, you want a black matte shroud. Having a reflector gives multi-path which is not good.

A single led is "almost" focused as you get something close to a point source. If you add just one lens in front of the led you can get a decent focus but this may not be needed. I found even those cheap $5 Fresnel lenses focus leds okay. e.g. credit card sized Fresnel lens.

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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby gebseng » Sat Mar 17, 2018 2:12 pm

Robonz wrote:The light source needs to be focused. Adding the diffuser is a good thing for the viewing side but not the camera side. Having a reflector is bad too, you want a black matte shroud. Having a reflector gives multi-path which is not good.

A single led is "almost" focused as you get something close to a point source. If you add just one lens in front of the led you can get a decent focus but this may not be needed. I found even those cheap $5 Fresnel lenses focus leds okay. e.g. credit card sized Fresnel lens.

Cheers
Keith


Thanks Keith! What about the aperture size? Should it be the same as in the viewer (0.5mm in my case)?

Best

Gebhard
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby Robonz » Sat Mar 17, 2018 2:36 pm

Here is how I would experimentally set things up.

1) Set up a "target" e.g. white card where you would like the camera to be focused. e.g. set up the card to match the height and width of what you want to shoot at the distance you desire. e.g. If you are take pictures of peoples faces then you would make your card a bit bigger than a persons head and move the card to where you would like them to place their head for the image to be taken.

2) Adjust the distance of your light source from the disc until you get the scan to fill the width and height of the card

3) Adjust the focus of the light source by moving a lens in front of the led until you get some clean circular spots. Re do step 2

4) Scan the image slowly and use a pen to mark in the coverage of the light spot/lines. I would expect the light spots to overlap by around 15 to 20 percent. If they do not overlap you need bigger apertures.

The thickness of your apertures is very important, if the apertures are too thick your light dots will get smaller towards the sides of the image. This is called optical parallax. You can fix this by using thinner apertures or by making the holes bigger.

5) Take some video of your attempt so we can enjoy your experience haha.

Good luck
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby Harry Dalek » Sat Mar 17, 2018 6:52 pm

Hi Gebseng
Pretty much as Keith mentioned ....yes the disk should be black the light should be close as you can get to the disk but i did test as you are doing now on a reflective one mine was even worse than yours but did go with a black disk on the scanning experiments .
The subject you can scan depends on your lens system and amount of light have ,you can do some distance with the disk not moving via one hole but when you rotate the thing making a raster on your subject this light soon fades to something much lower .
I started out on this first go with a green unfocused laser that is the lens removed so the size of the beam could be adjusted behind the disk to the size of the line scan .. and it gives large amount of light ..at the time green laser seemed a good idea since i was using 2 solar cells for the head amp natural sun light is mostly green reason most leaves on plants are green .
the solar cells also give you a large surface area to pick up the weak light from the scanner .
I tried photo diodes and transistors such but due to the small pick up surface area i would get weak pick up strong and then weak pick up again worse depending on the size of the scanning area ...so light pick up is very important thing to work out...
My set up i ended up using a luxeon torch as the light it was weaker than the laser ,the laser died due to a wiring mistake later on :roll: or i would of used it :wink:
Most people use a slide projector for the lens and light .i went small with a torch cd and old zoom video camera lens which was good for different distances and light dot size ...good luck on your mighty scanner .




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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby gebseng » Sun Mar 18, 2018 12:30 am

Thanks Keith and Harry for the very useful explanations and examples!!!

The setup with a photographic lens seems easy to do and straight forward, I will keep you updated on my results. I don't think I can use a laser duo to safety issues, since it would be shining into people's eyes directly when scanning a face.

About the solar cells: My understanding is that a solar cell is more or less the same as a photo diode. But opposed to a photo diode, which is engineered to have high sensitivity/low dark current and is used in reverse bias for quick response time, the solar cell is optimized to generate as much energy as possible. So, the question is if a solar cell still has a response time at least in the 500kHz range, which I would need for my resolution. Do you have any experiences or suggestions with that, before I start experimenting? E.g. should I start with amorphous, monocrystalline or polycrystalline cells?

best,

geb
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby gebseng » Sun Mar 18, 2018 12:51 am

This research paper, if I understand it right, suggests a response time for dye-sensitized solar cells in the 50-100ms range, which would be way too slow even for 32 line. I don't know how representative this is for other types of solar cells:

http://www.ecn.nl/docs/library/report/1997/rx97034.pdf
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby gebseng » Sun Mar 18, 2018 1:08 am

On a side note: this looks like the ideal sensor:
https://en.wikipedia.org/wiki/Photomultiplier

"Photomultipliers are typically used as the detectors in flying-spot scanners."
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby smeezekitty » Sun Mar 18, 2018 3:00 am

I can't imagine how solar cells could possibly be that slow since the light energy is being converted directly to electricity.
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby gebseng » Sun Mar 18, 2018 5:08 am

smeezekitty wrote:I can't imagine how solar cells could possibly be that slow since the light energy is being converted directly to electricity.


I'm not an expert either, but it's something about them acting as a capacitor becaus of their large surface.
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby Panrock » Sun Mar 18, 2018 8:04 am

Two quick comments:

For this application, I personally wouldn't use a photomultiplier or photomultipliers as the pick-up devices. They can easily be damaged by ambient light when powered up. Or is your flying spot raster going to be in a guaranteed blacked-out environment? Also you'll have the hassle of arranging a high voltage power supply and the potential divider chain(s).

As I think Harry has indicated, you'll need a lens - in practice as large as possible - that will gather as much light as possible and project a focussed image of the Nipkow disc raster. The projected raster size will be the ratio of the distance ahead of and behind the lens multiplied by the size of the native Nipkow raster. The light behind the Nipkow disc needs to be from a source evenly spread over the raster and very bright. But you probably know this already... :)

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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby Harry Dalek » Sun Mar 18, 2018 12:07 pm

HI Steve O
Yes the flying spot environment room does have to be dark depending on what your doing it depends but on the amount of flying spot light you have and how light in colour the flying spot light is reflecting back to the sensor doing the scanning it was even pushing it for me with my PMT ,i had to do the reflective off objects work at night lights off ,my scope is very weak after its projected at a distance .
So Gebseng you will have to experiment a lot what works i would go test cards first work your way up to televising people .
Here's one of my sons via scope flying spot and PMTpick up .......when you get yours working the quality will be many times better think these were on 64 line
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gebseng wrote:Thanks Keith and Harry for the very useful explanations and examples!!!

The setup with a photographic lens seems easy to do and straight forward, I will keep you updated on my results. I don't think I can use a laser duo to safety issues, since it would be shining into people's eyes directly when scanning a face.

About the solar cells: My understanding is that a solar cell is more or less the same as a photo diode. But opposed to a photo diode, which is engineered to have high sensitivity/low dark current and is used in reverse bias for quick response time, the solar cell is optimized to generate as much energy as possible. So, the question is if a solar cell still has a response time at least in the 500kHz range, which I would need for my resolution. Do you have any experiences or suggestions with that, before I start experimenting? E.g. should I start with amorphous, monocrystalline or polycrystalline cells?

best,

geb


Hi Gebseng
That's ok i think you sort of get the idea of a set up on the flying spot scanner one of those things once you see it going its easier :wink:
I like you are pushing the Nipkow to this line rate and size of the thing !.
Its not that one is more sensitive than the other and you want a sensitive device for you head amp ...but the surface area pick up is very important i tried lens in in front of photo diodes and such but for that idea at the time it ended up being solar solar cells my limits of know how at the time ...
A Fresnel lens would be another idea in front of a photo diode or bank of photo diodes ...just need to get that surface area pickup evenly or it will go from once extreme to the other picking up your light signals .
As far as the bandwidth go's Steve 0 has done light transmitting on higher bandwidths had to ask him on he's pick up device.
Solar cells have a bandwidth where they are sensitive more or less to different light wave lengths so 500khz would be nothing to it but i understand the response time is something to take into account and i have only ever worked them in audio frequencies ..if you could modulate a led at this frequency ? and connect a scope to the cell ,suppose they have oscilloscopes in this range and have a look ...again i have only done this at audio frequencies .
As far as which cells are better than another i your guess is as good as mine due the sensitivity on the dome sensor which seems to be a tiny solar cell i tried it but again surface area still to small using just one donated via Gary as i did.
http://www.excelitas.com/Lists/Photodio ... aspx?ID=46
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As far as lasers i took the lens off mine so no beam the light dot seen via the last photos posted were pointing adjusting the distance of the defocused laser to the line scan size via the back of the nipkow disk and then a lens.....here photo below is it with the nipkow removed really just a very bright torch light circle grows larger with distance like this ..I can understand the worry with a laser but it is defused light more than likely safe enough now behind a nipkow scanning .
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby Harry Dalek » Sun Mar 18, 2018 3:01 pm

HI again you had a few questions up have experience experimenting with PMTS
First up i love them they have to be my favourite electronic device ever ...Now i have to disagree in a way with that they can be damaged in ambient light well at least room light is fine out side light i have not tried !.....if used correctly they seem to be fine in this situation powered up .
I agree the Photomultiplier would more than likely be killed at top operating voltage range to direct light but below this i have found no evidence in any of my experiments opertaing them in room light it seems to not do any thing to them in the low hundreds of volts range high 200's to 400's.
Here below is a B&K Television Analyzer PMT in operation lid open to the room light and no problems .......as i recall from the schematics its PMT is running at 300 or so volts picking up the UV raster light from the scanned image testcard .

youtu.be/LF9bckHvfhA
In all my experiments i would of failed both my cameras if i had used my PMT's at their top negative voltage range they would of been over loading amplifying the light ,by luck i made their power supplies either switchable or variable .
To really fine tune them an inverter type power supply is safer and you can adjust the best working conditions ,the inverter i made this one below in schematic .....link here see you tube video bottom of page ....remember it works off the negative side
The little transformer board comes from printer scanners....but works well .
http://www.hardhack.org.au/hv_reg_power
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So going with a PMT can work it you treat them right ...run them from low voltage to operational depending surrounding lighting in your room area .
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I always run them from a low voltage up to when they start working and that comes down to the amount of light at the time they are amplifying ...using my PMT camera for picking up at this time oscilloscope flying spot scanning light i found i had to adjust the voltage to the camera PMT tube due to more room light in the morning to less in the afternoon ..less light more voltage visa versa..
Even in the dark it seems 600 volts range seems enough for this weak light work direct reflection light off a subject ..
May be its my PMTs for this range but both times i have used different PMT tubes and acted the same way to light for me .
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Above night flying spot camera test PMT tube around the 600 volts ..old trio scope raster focused via a lens on me.
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby Klaas Robers » Tue Mar 20, 2018 2:10 am

Of course you need a lens in front of the disc. Look carefully at a slide projector. There the light source, the (small) filament of the lamp, has a hollow back mirror, to reflect light from the back side again to the front side. In fact this mirror makes an image of the filament next to the real filament. Sometimes the image filament wires are just in between the real filament wires. In this way you get a square / rectangle of evenly lit filaments.

Then there is the condensor lens. This lens makes an image of this light square into the projection lens. Suppose there is no slide in the projector, then all lamp light goes through the projector lens to the screen. As little light is spilled in this case.

The slide, in your case the Nipkow disc, is placed close to the condensor lens. So the slide is evenly lit by the still rather wide beam of light. But the light in front of the slide is still converging towards the projector lens.

The projector lens then makes an image of the slide on the screen.

In your case the slide is replaced by the Nipkow disc and the screen is replaced by the studio scene. If you find a slide projector for slides of the size of your Nipkow viewing window, you can use all optical components, including the powerfull lamp.

Do not go for a point shaped light source without any lenses. The light output is far less than from a 200W, or even more, projection lamp.
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