Your question interested me enough to do a little googling. There is a Telejector company in New England that had its first patent in 1941 for a projector used in bowling alleys to project the scorepad on an overhead screen. That kind of system was used for about fifty years. They also had some projectors that would fit on a regular televisiona and project the picture on a screen and a slide projector used in early television studios to broadcast still pictures. More of a description or even better, a couple of pictures might help.