old Hughes video projector

Bob Rosenbloom bobalan at sbcglobal.net
Thu Jun 29 10:41:05 CDT 2006

>I've just got hold of an old (probably late-80s) Hughes 800 projector.
>It's a couple of feet long and very very heavy.  Inside is a big xenon
>lamp, a CRT of some kind, and some optics.  It appears to work by
>shining the lamp (through mirrors) onto the face of the CRT.  The big
>problem is, it doesn't appear to produce any video.  I can hear the CRT
>scan coils going.  The scan pitch changes when I remove the video
>source.  In fact, it does appear to do all the things I'd expect when I
>press buttons, but no picture comes out :-/

I think this might be an Image Light Amplifier (ILA). This used small CRT's coupled to a liquid crystal light valve.
The ILA was a sandwich of materials that included a photosensor and the liquid crystal material. The CRT wrote it's image onto the photosensor which converted the light into a varying voltage. This voltage was transferred to the liquid crystal material which could now reflect light from the Xenon source. This is not a pixel based system, the liquid crystal material was a continuos sheet so would be able to image the full resolution of the CRT. They can have an almost film like image because there is no pixel structure. I believe the CRT's were infrared and so you could not see an image on the CRT face directly.


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