Optical glass, precision press-molding preform, optical element and process for producing the same

1. An optical glass comprising, by cationic %,

20 to 50% of B 3+ ,

0 to 10% of Si 4+ ,

5 to 35% of La 3+ ,

0 to 10% of Gd 3+ ,

0 to 10% of Y 3+ ,

0 to 10% of Yb 3+ ,

0 to 4% of Ti 4+ ,

1 to 30% of Nb 5+ ,

0.5 to 15% of Ta 5+ ,

0 to 5% of W 6+ ,

0 to 10% of Zr 4+ ,

11 to 40% of Zn 2+ ,

0 to 10% of Mg 2+ ,

0 to 10% of Ca 2+ ,

0 to 10% of Sr 2+ ,

0 to 10% of Ba 2+ ,

0 to 10% of Li + ,

0 to 10% of Na + ,

0 to 10% of K + ,

0 to 10% of Te 4+ ,

0 to 10% of Ge 4+ ,

0 to 10% of Bi 3+ , and

0 to 10% of Al 3+ ,

the total content of B 3+ and Si 4+ (B 3+ +Si 4+ ) being 20 to 50%,

the total content of La 3+ , Gd 3+ and Y 3+ (La 3+ +Gd 3+ +Y 3+ ) being 5 to 35%,

the cationic ratio of ((B 3+ +Si 4+ )/(La 3+ +Gd 3+ +Y 3+ )) being from 1 to 5,

the total content of Ti 4+ , Nb 5+ , Ta 5+ and W 6+ (Ti 4+ +Nb 5+ +Ta 5+ +W 6+ ) being 10 to 35%,

the cationic ratio of ((Nb 5+ +Ta 5+ )/(Ti 4+ +Nb 5+ +Ta 5+ +W 6+ )) being from 0.7 to 1,

the cationic ratio of ((B 3+ +Si 4+ )/(Ti 4+ +Nb 5+ +Ta 5+ +W 6+ )) being from 0.5 to 4,

the cationic ratio of ((La 3+ +Gd 3+ +Y 3+ )/(Ti 4+ +Nb 5+ +Ta 5+ +W 6+ )) being from 0.2 to 3,

the cationic ratio of the content of Zn 2+ to the total content of Zn 2+ , Mg 2+ , Ca 2+ , Sr 2+ and Ba 2+ (Zn 2+ /(Zn 2+ +Mg 2+ +Ca 2+ +Sr 2+ +Ba 2+ ) being from 0.8 to 1,

the optical glass having a refractive index nd of 1.89 or more and an Abbe's number νd of 27 to 37.

2. The optical glass of claim 1 , wherein the total content of Nb 5+ and Ta 5+ (Nb 5+ +Ta 5+ ) is 5 to 35 cationic %, and the total content of Ti 4+ and W 6+ (Ti 4+ +W 6+ ) is 0 to 6 cationic %.

3. The optical glass of claim 1 , which has a glass transition temperature of 630° C. or lower.

4. The optical glass of claim 1 , which has a liquidus temperature of 1,200° C. or lower.

5. The optical glass of claim 1 , which has a partial dispersion ratio Pg,F having a deviation ΔPg,F of 0.006 or less.

6. A precision press-molding preform formed of the optical glass recited in claim 5 .

7. An optical element formed of the optical glass recited in claim 1 .

8. A process for producing an optical element, which comprises heating the precision press-molding preform recited in claim 6 and precision press-molding the precision press-molding preform with a press mold.

9. The optical glass of claim 1 , which is a glass that is not fused to a testing board in a test in which it is placed on the testing board composed of a material having a carbon content of 50 atomic % or more, heated and held together with the testing board up to a temperature at which the glass comes to have a viscosity of 10 5 to 10 9 dPa·s and then cooled to room temperature.

10. The optical glass of claim 9 , which has a refractive index nd of 1.89 or more, an Abbe's number νd of 27 or more but less than 31 and an Nb 5+ content of 5 to 30%.

11. The optical glass of claim 9 , which has a refractive index nd of 1.89 or more, an Abbe's number νd of 27 or more but less than 31 and a W 6+ content of 0 to 3.5%.

12. The optical glass of claim 1 , which has a refractive index nd of 1.89 or more, an Abbe's number νd of 27 or more but less than 31, an Nb 5+ content of 5 to 30% and a W 6+ content of 0 to 3.5%.

13. The optical glass of claim 1 , which has a refractive index nd of 1.89 or more, an Abbe's number νd of 31 to 33 and an Nb 5+ content of 5 to 20%.

14. The optical glass of claim 1 , which has a refractive index nd of 1.89 or more, an Abbe's number νd of 31 to 33 and a W 6+ content of 0 to 3.5%.

15. The optical glass of claim 1 , which has a refractive index nd of 1.89 or more, an Abbe's number νd of 31 to 33, an Nb 5+ content of 5 to 20% and a W 6+ content of 0 to 3.5%.

16. The optical glass of claim 1 , which has a refractive index nd of 1.89 or more, an Abbe's number νd of over 33 but 37 or less and a Ta 5+ content of 3 to 13%.

17. The optical glass of claim 1 , which has a refractive index nd of 1.89 or more, an Abbe's number νd of over 33 but 37 or less and a W 6+ content of 0 to 3.5%.

18. The optical glass of claim 1 , which has a refractive index nd of 1.89 or more, an Abbe's number νd of over 33 but 37 or less, a Ta 5+ content of 3 to 13% and a W content of 0 to 3.5%.

19. The optical glass of claim 9 , which has a refractive index nd of 1.89 or more, an Abbe's number νd of 27 or more but less than 31, an Nb 5+ content of 5 to 30% and a W 6+ content of 0 to 3.5%.

20. The optical glass of claim 9 , which has a refractive index nd of 1.89 or more, an Abbe's number νd of 31 to 33 and an Nb 5+ content of 5 to 20%.

21. The optical glass of claim 9 , which has a refractive index nd of 1.89 or more, an Abbe's number νd of 31 to 33 and a W 6+ content of 0 to 3.5%.

22. The optical glass of claim 9 , which has a refractive index nd of 1.89 or more, an Abbe's number νd of 31 to 33, an Nb 5+ content of 5 to 20% and a W 6+ content of 0 to 3.5%.

23. The optical glass of claim 9 , which has a refractive index nd of 1.89 or more, an Abbe's number νd of over 33 but 37 or less and a Ta 5+ content of 3 to 13%.

24. The optical glass of claim 9 , which has a refractive index nd of 1.89 or more, an Abbe's number νd of over 33 but 37 or less and a W 6+ content of 0 to 3.5%.

25. The optical glass of claim 9 , which has a refractive index nd of 1.89 or more, an Abbe's number νd of over 33 but 37 or less, a Ta 5+ content of 3 to 13% and a W 6+ content of 0 to 3.5%.