I'm building a DIY OHP based on a 15" 1600x1200 laptop screen. I'm looking at the Lumen Labs Pro kits, however, I dont want to be confined by the lock throw distance. My wall that I will be projecting onto is about 130" horizontal and I would like to use most of it. But to achieve a small or larger projected image, the projector must be pulled closer or further from the wall. In basic terms (describing how to use the lenses) how would i be able to create a adjustable image size without moving the PJ?