NBTV Camera Question

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Postby gary » Fri Apr 20, 2012 12:19 am

Hi Harry - not sure if I follow you there, but if you are building a flying spot camera the dome sensor can be anywhere it can "see" the object being televised - it needn't be on the camera at all, but in this case the light source that is producing the flying spot needs to be in alignment with the modulation source to avoid frame misalignment. But if you are building a moving spot camera, that is where the dome sensor is behind the disk, then it is the dome sensor that needs to be in alignment with the modulation source.
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Postby Harry Dalek » Fri Apr 20, 2012 1:00 am

gary wrote:Hi Harry - not sure if I follow you there, but if you are building a flying spot camera the dome sensor can be anywhere it can "see" the object being televised - it needn't be on the camera at all, but in this case the light source that is producing the flying spot needs to be in alignment with the modulation source to avoid frame misalignment. But if you are building a moving spot camera, that is where the dome sensor is behind the disk, then it is the dome sensor that needs to be in alignment with the modulation source.


I was thinking the the dome sensor could be anywhere ,i couldn't really tell in your photo if it was behind the disk at the side or side above ....

It sounds like it could do either of your examples ,i am thinking the first sounds easier and what i was thinking of when starting this ,what is the advantage of it behind the disk Gary ? as i never heard of this type.
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Postby gary » Fri Apr 20, 2012 11:40 am

hmmmm, Sorry, I'm obviously confusing you Harry, I think that's because I am still not sure what type of camera it is that you are building so I have been referring to both basic (Nipkow disk) types, Flying Spot, and NON-Flying Spot.

For the NON-Flying Spot there are basically two types:

1) Moving Point (spiral apertures)

2) Moving Image (spiral lenses)

It is for the NON-Flying Spot cameras that the sensor is BEHIND the disk. For the Flying Spot camera the sensor is positioned wherever it can pick up the most light reflected off the subject, usually in front of and above the projection lens.

You can look at it this way, Harry, a camera needs a light source and a sensor to pick up the (scanned) light.

For a Flying Spot Camera the light source is behind the disk and the sensor in front of the disk, for a NON-Flying Spot Camera the positions are reversed, i.e. the sensor is behind the disk, and the light source is in front of the disk.

The point I was trying to make is, whichever the type of camera, whatever is behind the disk needs to be on the same (usually horizontal) axis as the motor and the modulating light source of the monitor to achieve correct framing.

BTW, MY first example was of the Moving Point (Non-FSS) type, whereas the second example was of the FSS type.
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Postby Harry Dalek » Fri Apr 20, 2012 1:29 pm

gary wrote:hmmmm, Sorry, I'm obviously confusing you Harry, I think that's because I am still not sure what type of camera it is that you are building so I have been referring to both basic (Nipkow disk) types, Flying Spot, and NON-Flying Spot.

For the NON-Flying Spot there are basically two types:

1) Moving Point (spiral apertures)

2) Moving Image (spiral lenses)

It is for the NON-Flying Spot cameras that the sensor is BEHIND the disk. For the Flying Spot camera the sensor is positioned wherever it can pick up the most light reflected off the subject, usually in front of and above the projection lens.

You can look at it this way, Harry, a camera needs a light source and a sensor to pick up the (scanned) light.

For a Flying Spot Camera the light source is behind the disk and the sensor in front of the disk, for a NON-Flying Spot Camera the positions are reversed, i.e. the sensor is behind the disk, and the light source is in front of the disk.

The point I was trying to make is, whichever the type of camera, whatever is behind the disk needs to be on the same (usually horizontal) axis as the motor and the modulating light source of the monitor to achieve correct framing.

BTW, MY first example was of the Moving Point (Non-FSS) type, whereas the second example was of the FSS type.


Yes i had it at first in my mind to do a sensor behind the cameras nipkow but from your advice i have switched that to a light behind the nipkow flying spot i suppose and the dome sensor sitting somewhere on the front of the camera to pick up to moving light spots from the projected moving light.....i am sort of keen to see this and try and focus this.
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Postby gary » Fri Apr 20, 2012 1:47 pm

Ok Harry, I'm with you now - I just wasn't sure that the lens you have there was suitable for that or not, presumably you have tested it with a light source and are getting a nice focused spot of light where your subject will be?

Anyway yes the sensor (or sensors!) should be in front of the disk pointed at the subject - note you don't need a lens for the sensor at all, although you are meant to get better results if you use a large fresnel lens in front of it. I tried that as shown in the attached picture but didn't noticed any appreciable increase in performance and so just went with the just the sensor itself.
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Postby Harry Dalek » Fri Apr 20, 2012 3:41 pm

gary wrote:Ok Harry, I'm with you now - I just wasn't sure that the lens you have there was suitable for that or not, presumably you have tested it with a light source and are getting a nice focused spot of light where your subject will be?

Anyway yes the sensor (or sensors!) should be in front of the disk pointed at the subject - note you don't need a lens for the sensor at all, although you are meant to get better results if you use a large fresnel lens in front of it. I tried that as shown in the attached picture but didn't noticed any appreciable increase in performance and so just went with the just the sensor itself.


Yes the lens part does still need testing the end part comes off i have taken out the shutter for light amount control maximum light need i should think ..
i can play around with this part of it ...good thing about the lens is its got a good range of focus distances i think i might just have to move the end small lens in or out a bit but as you are thinking really need to test this part and i will find out !.

I think i do have a fresnel lens handy in the googles its very large but i wonder if those half egg shaped lenes in 35mm slide projectors would be any good for a test i have a few of those ....see how it gos any way as is .

I just finished the monitor electronics part of it i might just work on the light part of it now as you say i need to see a focused spot of light ....i hope at arms length at least .
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Picture 2322.jpg
this is where i will mount the sensors
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Postby Harry Dalek » Sat Apr 21, 2012 12:05 am

Today i have been working on the projection side of it ...it Projects alright its a fair distance and the dot is focused but large ..so need to see if i can do this closer .

If you are out there Gary how small does the dot have to be i am thinking tiny much smaller than what i am getting ? i can remove a lens and check again as i think this last one is the trouble maker next to the nipkow.

Heres some pictures and a video of what i am getting so far its not to bad in room light as well oh well getting there.
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Picture 2327.jpg
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Postby gary » Sat Apr 21, 2012 12:16 am

Hi Harry, well the size of the spot will depend on how far it is away from the projecting lens. As long as it makes a raster with no or little overlap between each line, and providing it is a nice sharp spot, it should be fine.

Note, of course, you will have to mask off the additional 16 holes so that there is only one spot present at any one time.

But I would say that looks pretty good.
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Postby Harry Dalek » Sat Apr 21, 2012 8:52 am

gary wrote:Hi Harry, well the size of the spot will depend on how far it is away from the projecting lens. As long as it makes a raster with no or little overlap between each line, and providing it is a nice sharp spot, it should be fine.

Note, of course, you will have to mask off the additional 16 holes so that there is only one spot present at any one time.

But I would say that looks pretty good.


Thanks for the reply there Gary needed your advice here ,i should think then it would work like that at that distance ,didn't really have time to try a distance closer apart from my hand and looks like it would do half that again but smaller scan.

I will play around more with it and see if i can get focus at closer distance and yes i need a mask.

I was expecting a larger scan area but at a distance like that but get what you get with the lenses you use ..

let you know how i go/
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Postby gary » Sat Apr 21, 2012 11:59 am

harry dalek wrote:I was expecting a larger scan area but at a distance like that but get what you get with the lenses you use ../


Yes - I suppose that's why most of us use slide projectors or similar.

It'll be interesting to see what kind of picture you get. You'll notice that, whilst you have a nice strong spot there, that once the disk gets up to speed the projected light will be very dim - that's why coming up with a good pre-amp for the sensor (i.e. high amplification) is so difficult. Certainly the brighter you can make you light source the better.

Good luck!
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Postby Harry Dalek » Sat Apr 21, 2012 3:46 pm

gary wrote:
harry dalek wrote:I was expecting a larger scan area but at a distance like that but get what you get with the lenses you use ../


Yes - I suppose that's why most of us use slide projectors or similar.

It'll be interesting to see what kind of picture you get. You'll notice that, whilst you have a nice strong spot there, that once the disk gets up to speed the projected light will be very dim - that's why coming up with a good pre-amp for the sensor (i.e. high amplification) is so difficult. Certainly the brighter you can make you light source the better.

Good luck!


Yes True i will see how i go with the adjustments to the lens when i look at it to night.
I have made the circuit for a start that was at the top of my post for the dome sensors since i have never played around with them i was thinking this was the best start instead of me trying to come up with something similar .
I just have to mount the sensors and i will test the circuit the old fingers crossed it works ...did the fault finding as i was making it which was good as there was a short in the first transistor now that would of been a no goer !
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Postby gary » Sat Apr 21, 2012 3:53 pm

BTW, I found that the motor brushes are the biggest source of noise for that amp - so try to keep it shielded and isolated (power) from that as much as possible, also snubbing caps across the motor terminals also helps.
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Postby Harry Dalek » Sat Apr 21, 2012 10:54 pm

gary wrote:BTW, I found that the motor brushes are the biggest source of noise for that amp - so try to keep it shielded and isolated (power) from that as much as possible, also snubbing caps across the motor terminals also helps.



Hi Gary i have been doing something i was hoping not to tonight and thats fault finding similar lawnboys problem a few years ago !

Ive had to pull that circuit out ,i have found that one of the dome sensors is faulty so i have done some thing to it ,it worked fine this afternoon testing them both with my meter ,the circuit with the transistor replacements doesn't work correctly ...never liked transistor replacements.....i'll have another go time willing tomorrow.
Last edited by Harry Dalek on Sun Apr 22, 2012 1:44 am, edited 1 time in total.
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.
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Postby Harry Dalek » Sun Apr 22, 2012 1:42 am

Had a bit of time to night to think the problem over while reading old newsletters and i switched to another circuit the camera head amp circuit in vol 19 4 this seems to work so far in the amplifying side of it,i had those transistors so just a matter of copying so lets see how mark 2 gos .
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Postby gary » Mon Apr 23, 2012 10:35 am

Well at least you seem to be able to produce these boards quickly - good luck with that one.
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