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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.
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.
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.
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.
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 ../
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!
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.
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