LCD : http://cgi.ebay.com/ws/eBayISAPI.dll?ViewI...em=300345646402

Hi there i'm going to make a projector with 4.8 inch lcd screen(800x480). And i would like to make it small(i mean the box). And 60"-80" screen size is enough for me.

So I'm looking for lenses with short focal lenghts. For example : Can i use 50mm or 100mm slide projector lens or another triplet lens?
And 4.8" lcd screen and 60" screen size what lumen output do i need?