OPTICAL GLASS

Abstract

An optical glass has optical constants of a refractive index (nd) within a range from 1.73 to less than 1.80 and an Abbe number (νd) within a range from 43 to 55, comprises SiO2, B2O3, Y2O3, La2O3, ZnO and Li2O as essential components, is substantially free of lead component, arsenic component and fluorine component, has a ratio of SiO2/B2O3 of 0.30 to 1.55 and a ratio of Y2O3/La2O3 of 0.15 to 1.00, and has a glass transition temperature (Tg) of 620° C. or below.

Description

Claims

1. An optical glass having optical constants of a refractive index (nd) within a range from 1.73 to less than 1.80 and an Abbe number (νd) within a range from 43 to 55, comprising SiO2, B2O3, Y2O3, La2O3, ZnO and Li2O as essential components, being substantially free of lead component, arsenic component and fluorine component, having a ratio of SiO2/B2O3 of 0.30 to 1.55 and a ratio of Y2O3/La2O3 of 0.15 to 1.00, and having a glass transition temperature (Tg) of 620° C. or below.

2. An optical glass as defined in claim 1 which comprises, in mass % on oxide basis, more than 1% Li2O and has a glass transition temperature (Tg) of 570° C. or below.

3. An optical glass as defined in claim 1 which comprises, in mass % on oxide basis, more than 5% of Y2O3 and 10% or over of La2O3, and has specific gravity of 4.5 or below.

4. An optical glass comprising in mass % on oxide basis:

5. An optical glass as defined in claim 1 comprising in mass % on oxide basis:

6. An optical glass as defined in claim 4 further comprising in mass % on oxide basis:

7. An optical glass as defined in claim 1 having liquidus temperature of 1160° C. or below and log η which is logarithm of viscosity (dPa·s) at liquidus temperature is within a range from 0.3 to 2.0.

8. A lens preform made of an optical glass as defined in any of claims 1-7.

9. An optical element made by precision press molding a lens preform as defined in claim 8.

10. An optical element made by precision press molding an optical glass as defined in any of claims 1-7.