Aspherical lens and process for the production thereof

Abstract

An aspherical lens formed of a high-refractivity low-dispersion glass, which is useful for constituting a compact and high-function image-sensing optical unit and which is formed by precision press-molding, the optical glass having a refractive index (nd) of over 1.83 and an Abbe's number (νd) of 40 or more and comprising, by mol %, 20 to 45% of B2O3, 5 to 24% of La2O3 and 22 to 42% of ZnO but containing no Li2O, the aspherical lens having an optical thin film formed on a surface thereof.

Description

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a schematic cross-sectional view of one example of the precision press-molding apparatus used in Example 1.

Claims

1. An aspherical lens formed by precision press-molding an optical glass, the aspherical lens being formed of an optical glass having a refractive index (nd) of over 1.83 and an Abbe's number (νd) of 40 or more and comprising, by mol %, 20 to 45% of B2O3, 5 to 24% of La2O3 and 22 to 42% of ZnO but containing no Li2O, the aspherical lens having an optical thin film formed on a surface thereof.

2. The aspherical lens of claim 1, wherein said optical glass contains, as optional components, 0 to 20% of Gd2O3, 0 to 20% of SiO2, 0 to 10% of ZrO2, 0 to 10% of Ta2O5, 0 to 10% of WO3, 0 to 10% of Nb2O5, 0 to 10% of TiO2, 0 to 10% of Bi2O3, 0 to 10% of GeO2, 0 to 10% of Ga2O3, 0 to 10% of Al2O3, 0 to 10% of BaO, 0 to 10% of Y2O3 and 0 to 10% of Yb2O3.

3. The aspherical lens of claim 1, wherein said optical glass has a glass transition temperature of less than 640° C.

4. The aspherical lens of claim 1, which is a lens to be positioned closest to an object in an image-sensing optical system having a plurality of lenses that are arranged from an object side to an image side.

5. A process for the production of an aspherical lens through the steps of heating a glass material formed of an optical glass and precision press-molding the glass material, the process comprising heating a glass material formed of an optical glass that has a refractive index (nd) of over 1.83 and an Abbe's number (νd) of 40 or more, that comprises, by mol %, 20 to 45% of B2O3, 5 to 24% of La2O3 and 22 to 42% of ZnO but that contains no Li2O, precision press-molding the glass material and forming an optical thin film on a surface thereof.

6. The process for the production of an aspherical lens as recited in claim 5, wherein an aspherical lens obtained by the precision press-molding is annealed and then ground or polished to form a non-optical function surface, the aspherical lens is washed and then the optical thin film is formed on the optical function surface.

7. A lens unit having either the aspherical lens recited in claim 1 and a lens with positive refractive power which is formed of an optical glass having a refractive index (nd) of 1.82 or more and an Abbe's number (νd) of 25 or less and which has an anti-reflection film, said aspherical lens having negative refractive power and having an anti-reflection film,said aspherical lens and said lens with positive refractive power being combined to correct chromatic aberration.

8. An image-sensing optical unit comprising the lens unit recited in claim 7.

9. An aspherical lens produced by the process recited in claim 5 and a lens with positive refractive power which is formed of an optical glass having a refractive index (nd) of 1.82 or more and an Abbe's number (νd) of 25 or less and which has an anti-reflection film, said aspherical lens having negative refractive power and having an anti-reflection film,said aspherical lens and said lens with positive refractive power being combined to correct chromatic aberration.