Patent ID: 8357624

Claim:
The process for the production of a lens by precision press-molding a glass material, which comprises the steps of introducing a glass material formed of an optical glass having a refractive index (n d ) of over 1.83, an Abbe's number (v d ) of 40 or more and a glass transition temperature (T g ) of 640° C. or lower and containing, by mol %, 20 to 43% of B 2 O 3 , 5 to 24% of La 2 O 3 and 22 to 42% of ZnO, as essential components, and optionally 0 to 18% SiO 2 , and a total content of La 2 O 3 , Gd 2 O 3 , Y 2 O 3 and Yb 2 O 3 is 10 to 24%, and no Li 2 O, no PbO and no cadmium into a press mold, softening the glass material by heating and pressing the glass material with a mold comprising a first mold member whose molding surface for forming an optical-function surface of a lens to be obtained is a concave surface or a flat surface and a second mold member whose molding surface is a convex surface, cooling said mold until said glass material in said mold comes to have a temperature of a glass transition temperature (T g ) or lower, and taking said glass material cooled out of said mold, the cooling being carried out in said step of cooling the mold in a manner that the temperature of the first mold member reaches the glass transition temperature (T g ) of said glass material before the temperature of the second mold member.