Mechanical camera - need advice

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Re: Mechanical camera - need advice

Postby smeezekitty » Sun Jul 07, 2019 10:13 am

Harry Dalek wrote:
smeezekitty wrote:
Harry Dalek wrote:

I was thinking; since we use an LED array behind a defuser for mechanical displays, why can't one do the opposite for a mechanical camera. That is, have an array of phototransistors in parallel behind a defuser?


That had crossed my mind as well and i can't say i have heard of any one trying it out ,i would think it would work apart from any problems hooking them up in parallel or series,only thing its easier to just use a small solar cell sensitive enough have the bandwidth ..they have the surface area size spot on for a nipkow disk scan ...found in toys ,solar lights or buy new .
i haven't tried a single photo transistor in a nipkow just sstv tv camera scanning i just know you need to focus the scan down to its surface ...try to avoid optics part as much as a can .
viewtopic.php?f=23&t=1890&start=120

viewtopic.php?f=23&t=1890&start=150

I tried a solar cell but I actually got worse results because the signal/noise ratio was poorer. Maybe once I build a better headamp it will work.

I would think that I could just put them straight in parallel? I'm not sure. Only way to know is to try.
I unfortunately don't have access to as large of repertoire of photo sensitive components as you do.

In case anyone is interested, I am uploading some of the programs I am using to process my NBTV. They're command line and kind of taylor made for what I'm working with but maybe someone will find them useful regardless.
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Re: Mechanical camera - need advice

Postby Harry Dalek » Sun Jul 07, 2019 7:03 pm

smeezekitty wrote:I tried a solar cell but I actually got worse results because the signal/noise ratio was poorer. Maybe once I build a better headamp it will work.

I would think that I could just put them straight in parallel? I'm not sure. Only way to know is to try.
I unfortunately don't have access to as large of repertoire of photo sensitive components as you do.

In case anyone is interested, I am uploading some of the programs I am using to process my NBTV. They're command line and kind of taylor made for what I'm working with but maybe someone will find them useful regardless.


The circuits are all different for different devices cameras have been made via about all light sensitive devices ...
I feel it might not be as simple hooking them all up in parallel they may need say hooking up to a amplifier say a transistor and all these signals out feeding to the rest of the head amp circuit ..its very experimental i can only say or try hooking 2 or 3 up and seeing if its worth it do they effect each out is series better ..trial and error is one way of doing it .
The program is 64 bit ? it crashed trying to load it oh well . i will PM you some circuits to try .
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Re: Mechanical camera - need advice

Postby Steve Anderson » Mon Jul 08, 2019 2:50 pm

Using multiple sensors to gain sensitivity is one way of doing it, it also should improve the signal-to-noise ratio. The biggest headache is the mechanical/optical arrangement.

Generally if you add two coherent signals together the amplitude should go up by double (6db). Non-coherent signals (random noise) will increase by 3db. In improvement of 3db in the signal-to-noise ratio. Note, this won't apply to hum which would be a coherent signal.

Adding even more sensors, if you can, improves things, but you are getting into the realms of diminishing returns.

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Re: Mechanical camera - need advice

Postby smeezekitty » Mon Jul 08, 2019 4:24 pm

Harry Dalek wrote:The program is 64 bit ? it crashed trying to load it oh well . i will PM you some circuits to try .

Yeah, it probably is. I built it was a native compiler since I wans't really planning on releasing it at first.
But it is likely you will need to mess with parameters in the source code to use it for a specific application so I included to source code so that someone can compile it themselves if they want.


Using multiple sensors to gain sensitivity is one way of doing it, it also should improve the signal-to-noise ratio. The biggest headache is the mechanical/optical arrangement.

Generally if you add two coherent signals together the amplitude should go up by double (6db). Non-coherent signals (random noise) will increase by 3db. In improvement of 3db in the signal-to-noise ratio. Note, this won't apply to hum which would be a coherent signal.

Adding even more sensors, if you can, improves things, but you are getting into the realms of diminishing returns.

Really? That's interesting. I didn't know that. But unfortunately, hum is currently my single biggest source of noise.
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Re: Mechanical camera - need advice

Postby Steve Anderson » Mon Jul 08, 2019 6:38 pm

smeezekitty wrote:Really? That's interesting. I didn't know that. But unfortunately, hum is currently my single biggest source of noise.

Ah! that's usually quite easy to fix.

1) Are the power supplies clean, i.e. no hum/ripple on them?
2) Are the low-level signals run in screened cables?
3) Is the whole device properly earthed/grounded?
4) Are there screens on the pre-amps/low-level circuits? i.e. placed in a tin box which itself should be earthed?
5) Have you created an earth-loop somewhere?
6) Keep low-level signal cables as short as possible.
7) Are externally connected equipment also properly earthed? e.g. an oscilloscope, PC, etc...
8) The sensor itself may need screening, but still allow light to impinge on it.
9) Is the light source clean also, no tungsten or flouro tubes...daylight is best. You can check this by operating it in the dark and using a battery torch/flashlight to provide a 'signal'.

Well, that's a start...

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Re: Mechanical camera - need advice

Postby smeezekitty » Sun Jul 14, 2019 1:57 pm

Steve Anderson wrote:
smeezekitty wrote:Really? That's interesting. I didn't know that. But unfortunately, hum is currently my single biggest source of noise.

Ah! that's usually quite easy to fix.

1) Are the power supplies clean, i.e. no hum/ripple on them?
2) Are the low-level signals run in screened cables?
3) Is the whole device properly earthed/grounded?
4) Are there screens on the pre-amps/low-level circuits? i.e. placed in a tin box which itself should be earthed?
5) Have you created an earth-loop somewhere?
6) Keep low-level signal cables as short as possible.
7) Are externally connected equipment also properly earthed? e.g. an oscilloscope, PC, etc...
8) The sensor itself may need screening, but still allow light to impinge on it.
9) Is the light source clean also, no tungsten or flouro tubes...daylight is best. You can check this by operating it in the dark and using a battery torch/flashlight to provide a 'signal'.

Well, that's a start...

Steve A.

Indeed the problem was that my cables were not shielded/screened. I replaced the wire to the sensor, the output of the pre-amp and the pre-amp power cable with shielded wire and nearly all the hum is eliminated.
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Re: Mechanical camera - need advice

Postby smeezekitty » Sun Jul 14, 2019 2:48 pm

I installed a new disc which was drilled using my new Nipkow disc drilling apparatus. It isn't perfect but it is a big improvement from the last one.
I also shielded all the power and signal cables. And strangely enough, I added an LED light *behind* the light sensor to bias it.


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Re: Mechanical camera - need advice

Postby Harry Dalek » Sun Jul 14, 2019 9:01 pm

smeezekitty wrote:I installed a new disc which was drilled using my new Nipkow disc drilling apparatus. It isn't perfect but it is a big improvement from the last one.
I also shielded all the power and signal cables. And strangely enough, I added an LED light *behind* the light sensor to bias it.






Pretty good I forgot to mention a camera Nipkow is very forgiving unlike a monitor where the camera will line up the raster lines always remove the gaps ..i always liked that ..but yes the results are better again .
Focus is a little off still wondering if an adjustment can be made here as i am not sure of your lens system ...i always picked a scrapped video camera or 35mm never tried a single lens ...the noise seems a bit better odd bit of static pixels /
Have you tried it a night in a darken room and day light in case of light is getting in doe's not take much a pin prick to also case trouble .
Little the test cards saw your hand and the cat checker board thats a camera alright
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Re: Mechanical camera - need advice

Postby Klaas Robers » Sun Jul 14, 2019 9:18 pm

You should be aware that the picture of the taking lens is focussed at the Nipkow disc. So place a piece of opaque paper at the place of the disc, Place an object before the taking lens at the distance that you like an see if the imace on the frosted paper is sharp. Position the lens such that it becomes sharp. Then replace the disc in position and do it again. I got the impression that your optical picture was very unsharp.

Then secondly as much of the light that exits the taking lens shoud be focussed on the opto sensor. That is why there is a lens behind the disc and before the sensor. In a slide projector this is called the condensor lens. You can check this also with the help of the frosted paper. Remove again the Nipkow disc, Place a bright illuminated white sheet as an object before the taking lens and place the frosted paper at the position of the sensor. Then make the light spot on the frosted paper as small as possible. That should also be the size of your opto sensor.
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Re: Mechanical camera - need advice

Postby smeezekitty » Mon Jul 15, 2019 4:56 am

Harry Dalek wrote:
smeezekitty wrote:I installed a new disc which was drilled using my new Nipkow disc drilling apparatus. It isn't perfect but it is a big improvement from the last one.
I also shielded all the power and signal cables. And strangely enough, I added an LED light *behind* the light sensor to bias it.






Pretty good I forgot to mention a camera Nipkow is very forgiving unlike a monitor where the camera will line up the raster lines always remove the gaps ..i always liked that ..but yes the results are better again .

The last disc had a very obvious defect down the center so I had to change it.
Focus is a little off still wondering if an adjustment can be made here as i am not sure of your lens system ...i always picked a scrapped video camera or 35mm never tried a single lens ...the noise seems a bit better odd bit of static pixels /

I am using a projector lens on a tripod in front of it. I also have the lens from the camcorder I can try but I need to disassemble it some more.
It looks in focus on the disc to me...
The static is still brush noise from the motor.
20190714_100646.jpg

20190714_100708.jpg


Have you tried it a night in a darken room and day light in case of light is getting in doe's not take much a pin prick to also case trouble .

Yeah that was at night. But I am actually adding light deliberately. There is a LED behind the CDS cell which sets the operating point. It gives much more output and has better frequency response with it on.

Little the test cards saw your hand and the cat checker board thats a camera alright

Cool. Thanks!!

You should be aware that the picture of the taking lens is focussed at the Nipkow disc. So place a piece of opaque paper at the place of the disc, Place an object before the taking lens at the distance that you like an see if the imace on the frosted paper is sharp. Position the lens such that it becomes sharp. Then replace the disc in position and do it again. I got the impression that your optical picture was very unsharp.

It looks pretty sharp to me. Could just be the frequency response of the sensor that is making it blurry.

Then secondly as much of the light that exits the taking lens shoud be focussed on the opto sensor. That is why there is a lens behind the disc and before the sensor. In a slide projector this is called the condensor lens. You can check this also with the help of the frosted paper. Remove again the Nipkow disc, Place a bright illuminated white sheet as an object before the taking lens and place the frosted paper at the position of the sensor. Then make the light spot on the frosted paper as small as possible. That should also be the size of your opto sensor.

Hmm. I don't have a lens behind the disc at all. I just put the sensor directly behind it...
Is that something I need to add then?
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Re: Mechanical camera - need advice

Postby Klaas Robers » Mon Jul 15, 2019 6:22 am

smeezekitty wrote:Hmm. I don't have a lens behind the disc at all. I just put the sensor directly behind it...
Is that something I need to add then?

That depends. If your sensor is as large as the projected image on the Nipkow disc, you might no need it. But if your sensor is smaller, it will only pick up light from the center of your picture. The result is a picture with only light in the center, which I have seen.

This is explained in the NBTV handbook. You can find that on http://www.nbtv.org, then goto [clubshop], then goto [handbook], then go into the handbook and choose 'Optics and Lenses'. You can go directly to this chapter at http://www.nbtv.org/optics.htm. There you can also find the solution of canibalizing an old slide projector. It contains the correct lenses for what you need, as a slide has almost the size of an NBTV picture. Oly the light goes the reverse direction.
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Re: Mechanical camera - need advice

Postby Steve Anderson » Mon Jul 15, 2019 2:32 pm

Another way to focus a camera is to have a sheet of paper, one half white, one half black, placed at the same distance as your subject. Such that every line traverses this black-white (or white-black) transition every line.

Then using a 'scope adjust the focus to get the sharpest transition between the black/white. Remove 'focusing card' and replace with subject.

Downside - you need a scope to do this....

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Re: Mechanical camera - need advice

Postby smeezekitty » Thu Jul 18, 2019 11:59 am

I guess I need to find another lens to scavange.

Using a scope really isn't a big deal. It's already set up right next to it.

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Re: Mechanical camera - need advice

Postby Steve Anderson » Thu Jul 18, 2019 1:54 pm

smeezekitty wrote:Using a scope really isn't a big deal. It's already set up right next to it.


Not everyone has access to a scope or can justify the cost of buying a dedicated instrument.

But I've had a look on e-bay and there's quite a selection of USB 'scopes at under 100 quid, those around the 60 quid mark would be adequate for 99% of NBTV usage as well as audio work. Fast logic work would require something more exotic.

60-80 quid gets you a dual-channel 10MHz 'scope, often with probes - don't forget those! On the assumption that it lasts 10 years, that's less than eight quid a year or 2.2 pence per day...

10MHz may sound a bit on the low side, but my scope is switchable between 20MHz and 100MHz, 99% of the time it's set to 20MHz, but I have to admit there are occasions where that 100MHz comes in real useful...but it's usually not when working on NBTV stuff.

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Re: Mechanical camera - need advice

Postby smeezekitty » Sat Jul 27, 2019 3:06 pm

I have a new lens setup. I took apart the lens from a broken camcorder and used only the front part. With a bit of cutting and sanding, it fits perfectly in the hole in the front of the case.
It is much more practical than having the lens on a tripod way out in front. I can turn the lens to focus it although it doesn't change it that much -- probably because how far it is from the disc. It only focuses on objects rather close in.
lens1.jpg

lens2.jpg

checkerboard3.PNG
checkerboard3.PNG (56.65 KiB) Viewed 1618 times

spiral3.PNG
spiral3.PNG (46.49 KiB) Viewed 1618 times


Not everyone has access to a scope or can justify the cost of buying a dedicated instrument.

I personally couldn't imagine not having one at this point. I have 3 in service.
They're honestly not that expensive if you buy used. $100 if you don't need digital storage will get you a decent 100Mhz scope at flea markets on on eBay.
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