Optical glass, preform for precision press molding and method of manufacturing thereof, optical element and method of manufacturing thereof

An optical glass comprising:

• a glass wherein
• (i) SiO2, B2O3, La2O3 and Gd2O3 are contained as essential components;
• (ii) the content of SiO2 ranges from 11 to 18 mole percent;
• (iii) the content of La2O3 ranges from 5 to 15 mole percent;
• (iv) the content of Gd2O3 ranges from 1 to 12 mole percent;
• (v) the combined quantity of SiO2 and B2O3 ranges from 50 to 72 mole percent;
• (vi) the mole ratio (SiO2/B2O3) of the SiO2 content to the B2O3 content ranges from 0.1 to 0.90, and
• wherein said glass has a refractive index (nd) that exceeds 1.70 and an Abbé number (ν (nu)d) of greater than or equal to 50 for use in precision press molding, exhibiting that a ratio α (alpha)1/α (alpha)2 is less than 17 when temperature denoting maximum value of differential in amount of elongation of glass relative to temperature differential DELTAT (where DELTAT denotes a constant value of 1° C. or less) over a temperature range from glass transition temperature (Tg) to sag temperature (Ts) is denoted as T1, average coefficient of linear expansion over a range from T1−5° C. to T1+5° C. is denoted as alpha1, and average coefficient of linear expansion over a range from the glass transition temperature (Tg)−160° C. to the glass transition temperature (Tg)−140° C. is denoted as alpha2.