Fresnel lens manufacturing apparatus

A Fresnel plate producing apparatus including stationary and removable molds, in which a Fresnel forming face is formed on one of the said stationary and movable molds, said Fresnel forming face including plural annular slope sections and plural annular rise sections, said annular slope sections and annular rise sections being arranged alternately and concentrically, said Fresnel forming face being adapted to form from resin a Fresnel plate having circular ridges whose summits lie in a reference plane, said Fresnel plate producing apparatus comprising:

• a first slit, formed in said Fresnel forming face, for applying compressed air to a formed said Fresnel plate when said Fresnel plate is to be released from said apparatus;
• there being a first ridge line disposed between a first of said plural slope sections and a first of said plural rise sections adjacent to said first slope section, said Fresnel forming face projecting at said first ridge line;
• said first rise section being formed between said first ridge line and a first bottom line adjacent to said first ridge line, and inclined in reverse to said first slope section;
• wherein said first slope section and said first rise section satisfy the relationship:
• 0.1.ltoreq.b/L1.ltoreq.0.9
• wherein L1 satisfies the relationship:
• L1=P.cndot.sin .theta..cndot.tan .theta.
• wherein .theta. is the angle defined between said first slope section and said reference plane;
• p is the width of said first slope section in a direction along said reference plane;
• and
• b is the distance between a first intersection point and said first ridge line, wherein said first intersection point is by the intersection of an extension of said first slope section and a perpendicular surface passing through said first bottom line and perpendicular to said reference plane.