Thanks for the reply.
I have bought cheap mirrorcard ready to make a prototype.
My memory of the one from childhood (during the early years of WW2) is of a triangular tube with the far end cut at an angle and a short length of one of the three sides cut back for light to fall in onto the front, viewed, side of the pretty bits. The ones I have seen so far are simpler, letting all the light in from the rear, opposite end to the eye, so the picture is not as bright as it could be. I wonder about the angle of the back end panel and whether it should also be transparent, or block the light off to enhance the light from the cut-away side piece. The angle will affect the picture, no doubt.
Could a better picture be produced by a four- or five-sided tube?
I will experiment and find the best design. I also would like to have not just one set of colourful bits, but a rotating 'magazine' of three or four, each giving a different type of picture eg tone, stars and planets etc.
I wonder whether I should have started this!
