A reflection screen includes a light transmittable base portion and a reflecting portion. The reflecting portion is arranged on two rear side of the base portion and has a reflecting surface. Either the base portion or the reflecting portion has the shape of a Fresnel lens, which has an optical center...http://www.google.es/patents/US6023369?utm_source=gb-gplus-sharePatente US6023369 - Reflection screen and front projection system
