Method of manufacturing optical element having annular zones and method of manufacturing mold for forming the same

A method of manufacturing a mold for forming an optical element having a circular portion and at least a first and a second annular zone formed thereon,

• the circular portion having a circular profile and centered about an optical axis as viewed from a direction of an optical axis,
• each annular zone comprising an annular zonal face and a boundary wall face formed concentrically around a periphery of the circular portion, and
• each boundary wall face linking between the circular portion and the annular zonal face of the first annular zone or linking between the annular zonal faces of the first and the second annular zones,
• the method being performed by:
• rotating a workpiece about a rotation axis corresponding to the optical axis;
• and
• allowing a sharply pointed front end of a tip to prick the workpiece to a portion corresponding to an angle defined by each annular zonal face of the mold and each boundary wall face of the mold so that at least each annular zonal face of the mold is formed by side edges of a rake face of the tip,
• wherein:
• a direction parallel to the rotation axis is set to be a Z direction,
• a direction orthogonal to the Z direction and extending through a rotation center of the circular portion and a first position at which the front end of the tip pricks the workpiece when forming the first annular zone is set to be an X direction, and
• a direction orthogonal to the Z direction and to the X direction is set to be a Y direction,
• the method further comprises setting a second position at which the front end of the tip pricks the workpiece when forming the second annular zone at a position shifted from the first position in the X direction and the Y direction, so as to incline the rake face of the tip at a predetermined angle relative to a line extending through the rotation center and the second position, thereby to change an angle of the angled portion defined by each annular zonal face and boundary wall face between the first and the second annular zones.