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The optimal distance between fresnel and projection lens is slighty vary depending on distance on the wall.Try thiswww.tronixbee.com/projcalc/
I was planing on building diy projector with almost same config as yours. Im planning using in my small bedroom. So the distance is not too far.Here's my plan :- 7" 1280x800 lcd- 100w led- f120 f170 fresnel-f180 lensBut i dont know is the focal length are match or not. Is these combination of focal lenses works?Im already done my diy pj with 11.6" lcd, 100w led, f220 f300 fresnel and 318mm lens. And the result is enjoyable but not really impressive. Plus, the case/box is too big.My goal is to build small projector with nice picture and project at least 75".Please give some advice :)Sorry for bad english :p