Kabushiki Kaisha Ohara

Michiko Morishita

Masahiro Onozawa

Muneo Nakahara

Ophthalmic and optical glasses have a composition in weight percent of 4.5-9.5% SiO,, 10-19.5% B,O,, 0-3% Al,O,, 0-5% GeO,, 18&mdash;less than 23% La,O,, 0.3&mdash;less than 2% Gd,O,, 5.5-13.5% TiO,, 0-7.5% ZrO,, 15-21% Nb,O,, 0-1.5% Ta,O,, 0.3-5% WO,, with the proviso that (Ta,O,&plus;WO,)/B,O,is 0.5 or below in the ration terms of weight, 2.1-10% ZnO, 0-5% MgO, 7-12.5% CaO, 0-5% SrO, 0-4% BaO, &gE;0.1% Li,O&plus;Na,O&plus;K,O in which 0-1% Li,O, 0-1% Na,O and 0-1% K,O, 0-0.5% As,O,and 0-0.5% Sb,O,and have a specific gravity of 4.1 or below, and optical constants of a refractive index (nd) exceeding 1.88 and up to 1.93 and an Abbe number j(&ngr; d) within a range from 28 to 31. A preferable range of Nb,O,is 15.5&mdash;less than 20.5% and a more preferable range of Nb,O,is less 15.5-20%.

Ophthalmic and optical glasses

An optical glass has a large negative anomalous dispersion value and optical constants of refractive index (nd) within a range of 1.65-1.80 and Abbe number (.nu.d) within a range of 28-42. The optical glass includes, as its essential ingredients, in weight percent, 20-50% SiO.sub.2, 6-20% B.sub.2 O.sub.3 where SiO.sub.2 /B.sub.2 O.sub.3 .ltoreq.6, 0.5-15% ZrO.sub.2 and 31-50% Nb.sub.2 O.sub.5.

Optical glass having a negative anomalous dispersion

An optical glass having optical constants of refractive index within the range of 1.55-1.75 and Abbe number (.nu. d) within the range of 25-51 and having large negative anomalous dispersion which is substantially free of lead and arsenic compounds includes as its essential ingredients in weigth percent 10-&gt;40% SiO.sub.2, 12.5-35% B.sub.2 O.sub.3, 3-20% ZrO.sub.2 and 6-30% Nb.sub.2 O.sub.5.

Growing community of inventors

Sagamihara, Japan

Michiko Morishita