317 mm fresnel lens help

[makaveli956]

i am a newbie i am trying to make my own projection tv i just ordered the 317mm focal length Fresnel Lens and dimensions are : 12 9/16" (319mm) x 9 15/16" (252.4mm) x 2mm Groove Pitch: 0.5mm was wondering is 1 enough to get the job done or do i need 2

 

[zzonbi]

It's enough, but you can use more as well. Usually 2 are used. Now make sure you get a projection lens with a longer focal, let's say twice 317mm.