first timer question :)

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surplus shed triplet

I think maybe that is not the right kind of triplet. What you need is a Cooke Triplet. Besides, that lens would give you a 69" diagonal image from a 2.5" LCD with a throw distance of 8 feet. And that image would be VERY dim unless you used some lenses to condense all the light into the projection lens. It is only 18 mm in diameter, so this would be difficult!

For the specs you mentioned in earlier posts (42" image from 8'), you would need a lens with a focal length around 5.4" (137 mm). I think most CRT projection lenses (like the one I suggested from electronic goldmine) have focal lengths around 6". With exactly 6", you would get a 37.5" diagonal image, which is pretty close. And I think it probably IS a Cooke triplet design.

The other advantage of a CRT projection lens is that they are larger in diameter than your LCD, so you don't need to use a condensor system to get all the light into the projection lens. You can just send the light through the LCD in parallel, and it will get into the lens.
 
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