FRESNEL LENS, PROJECTION SCREEN, CORRESPONDING PROJECTION DEVICE AND SYSTEM.

摘要

The invention relates to a Fresnel lens. Each refractive structure of the lens is defined by two surfaces, the second surface creates a second angle (ß) with the normal on the plane of incidence (P). At least two refractive structure area are provided, wherein the second angle (ß) is equal to the entrance angle (thetaint) of a beam. Each first surface refracts the light according to a direction which is parallel to or which is not parallel to the axis of the lens according to the area in question. The invention also relates to a system comprising a folding mirror and a Fresnel lens wherein the second angle is equal to the entrance angle of a parasitic ray obtained by reflection on the Fresnel lens and subsequently on the mirror. The invention further relates to a screen and to a corresponding overhead projection device.