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

PostPosted: Tue Mar 20, 2018 4:18 am
by gebseng
Klaas Robers wrote: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.

Thanks Klaas! I already tried a 5 by 5 cm slide projector, but made the mistake of treating the Nipkow disk as the screen, and focussed on that. I will try that again according to your recommendation,