| 摘要 |
An optical glass taking account of meltability and the moldability of a preform, having optical constants including a refractive index (nd) of at least 1.57 but less than 1.67 and an Abbe's number (nud) of over 55 but not more than 65, having the property of softening at a low temperature and being suitable as a glass for precision press-molding, the optical glass including an optical glass containing B<SUB>2</SUB>O<SUB>3</SUB>, SiO<SUB>2</SUB>, La<SUB>2</SUB>O<SUB>3</SUB>, Gd<SUB>2</SUB>O<SUB>3</SUB>, an alkali metal oxide and an alkaline earth metal oxide as essential components, having a B<SUB>2</SUB>O<SUB>3 </SUB>and SiO<SUB>2 </SUB>total content of 52% by weight or more and having an SiO<SUB>2</SUB>/B<SUB>2</SUB>O<SUB>3 </SUB>content ratio of from 0.38 to 1.2, and an optical glass wherein the relationship of the refractive index (nd) and the Abbe's number (nud) satisfies the equation (1), <?in-line-formulae description="In-line Formulae" end="lead"?>nud>260-126xnd (1).<?in-line-formulae description="In-line Formulae" end="tail"?>
|
