Patent ID: 7087542

Claim:
An optical glass having optical constants of a refractive index (n d ) within a range from 1.60 to 1.69 and Abbe number (u d ) within a range from 35 to 45, having a glass transition point (Tg) within a range from 300° to 500°, being free from devitrification when the optical glass is held at a temperature which is higher by 100° C. than the glass transition point (Tg) for 30 minutes, comprising in mass % on oxide basis: SiO 2 20–less than 40% B 2 O 3 5–20% Al 2 O 3 0–5% ZrO 2 more than 3%–15% Nb 2 O 5 10–30% MgO + CaO 0–less than 5% in which MgO 0–less than 5% CaO 0–less than 5% SrO 0–10% BaO 0–10% ZnO 0–18% Li 2 O more than 5%–15% Na 2 O 1–10% K 2 O 1–10% Sb 2 O 3 0–1%.