Patent ID: 7638450

Claim:
A lead-free, fluorine-free and arsenic-free optical glass having a refractive index n d of 1.75≦n d ≦1.83 and an Abbe number v d of 34≦v d ≦44, said glass comprising, in percent by weight based on oxide content: SiO 2 0.5-8 B 2 O 3 10-25 ZnO 16.2-22 La 2 O 3 23-34 Ta 2 O 5 >15-25 Nb 2 O 5 0.5-15 Al 2 O 3 0-2 Li 2 O 0-5 Na 2 O 0-6 K 2 O 0-8 Cs 2 O 0-9 MgO 0-5 CaO 0-5 SrO 0-5 BaO 0-5 Y 2 O 3 0-10 TiO 2 0-6 ZrO 2 0-11 HfO 2 0-6 Σ B 2 O 3 , ZnO 33-41 Σ Alkali metal oxides 1.65-10 Σ Alkaline-earth metal oxides 0-8 Σ Al 2 O 3 , Y 2 O 3 , TiO 2 , ZrO 2 , 0-15 HfO 2 , Alkaline-earth metal oxides at least one refining agents 0-2; wherein said glass is free of WO 3 , said glass is free of TeO 2 , said glass is free of lead, said glass is free of fluorine, and said glass is free of arsenic; and having a transformation temperature Tg that is at most 560° C. and a viscosity that decreases from 10 7.6 to 10 13 dPas when a temperature decrease of at most 100° K. occurs.