Patent ID: 6726859
Filing Date: 2004-04-27
Classification: G02B,G03B,Y10S

Abstract:
A method of manufacturing a lens forming mold, in which a lens forming mold is cut in a reversed shape of both a refractive prism portion and a total reflection type prism portion formed for each pitch area of a Fresnel lens by using a cutting tool, comprising:a main unit-prism portion cutting step of cutting the lens forming mold in a reversed shape of the refractive prism portion of a cutting pitch area by using the cutting tool; and a subordinate unit-prism portion cutting step of cutting the lens forming mold in a reversed shape of the total reflection prism portion of the cutting pitch area by using the cutting tool when a plane, obtained by extending an incident plane from the cutting pitch area in the reversed shape of the total reflection prism portion, intersects a trough line placed between the cutting pitch area and another cutting area adjacent to the cutting pitch area on a Fresnel center side or when the plane passes through an area shifted from the trough line toward a light outgoing side, wherein the-combination of the main unit-prism portion cutting step and the subordinate unit-prism portion cutting step is repeatedly performed by a prescribed number equal to the number of cutting pitch areas.