A method for producing a prismatic lens from the fresnel - type.

摘要

The method for forming Fresnel lens according to the present invention is such that a Fresnel lens comprising a body with a frontal surface having a plurality of annular Fresnel-type prism elements concentrically disposed thereon and a back surface formed substantially flat is formed from a molten sheet glass. The method comprises a step of preparing cavities of which the shapes are derived from inversion of the shapes of the plurality of annular Fresnel-type prism ele­ments, a step of disposing the molten sheet glass on a stationary mold having a substantially flat surface, a step of pressing the molten sheet glass with a moving mold having the cavities to make a portion of the molten glass flow into said cavities, and a step of solidifying the molten glass and removing the moving mold thereafter. The shapes of said cavities are previously designed so that portions of the molten glass corresponding to the Fresnel-type prism elements flow substantially only within small area corresponding to the corresponding Fresnel-type prism elements while the sheet glass is being pressed. This method permits to minimize surface defects such as wrinkle caused during forming, reduce the time required for forming, and to form a Fresnel lens having excellent optical properties.