Optical glass, preform, and optical element

Abstract

An optical glass having a small partial dispersion ratio (θg,F), while having a refractive index (n d ) and Abbe number (ν d ) within desired ranges, is obtained. The optical glass, in mass %, comprises 10.0 to 70.0% of an SiO 2 component, 1.0 to 50.0% of an Nb 2 O 5 component, and 1.0 to 30.0% of an Na 2 O component, and has a refractive index (n d ) of 1.62 to 1.75, an Abbe number (ν d ) of 30 to 42, and a partial dispersion ratio (θg,F) of no greater than 0.594.

What is claimed is: 
     
         1 . An optical glass comprising, in mass %,
 10.0 to 70.0% of an SiO 2  component,   1.0 to 50.0% of an Nb 2 O 5  component, and   1.0 to 30.0% of an Na 2 O component,   and having   a refractive index (n d ) of 1.62 to 1.75,   an Abbe number (ν d ) of 30 to 42, and   a partial dispersion ratio (θg,F) of no greater than 0.594.   
     
     
         2 . An optical glass according to  claim 1 , wherein, in mass %, a content of a B 2 O 3  component is no greater than 25.0%. 
     
     
         3 . An optical glass according to  claim 1 , wherein a mass ratio (LiO 2 +Na 2 O)/(ZrO 2 ) is no less than 0.50. 
     
     
         4 . An optical glass according to  claim 1 , wherein, in mass %, a content of an Li 2 O component is no greater than 20.0%. 
     
     
         5 . An optical glass according to  claim 1 , wherein a mass ratio (SiO 2 )/(SiO 2 +B 2 O 3 ) is no less than 0.50. 
     
     
         6 . An optical glass according to  claim 1 , wherein a mass ratio (SiO 2 )/(SiO 2 +B 2 O 3 ) is no greater than 0.95. 
     
     
         7 . An optical glass according to  claim 1 , wherein, in mass %, a content of a ZrO 2  component is no greater than 25.0%. 
     
     
         8 . An optical glass according to  claim 1 , wherein, in mass %,
 an K 2 O component is 0 to 20.0%,   a TiO 2  component is 0 to 20.0%,   an MgO component is 0 to 10.0%,   a CaO component is 0 to 10.0%,   an SrO component is 0 to 10.0%,   a BaO component is 0 to 20.0%,   a Ta 2 O 3  component is 0 to 10.0%,   an La 2 O 3  component is 0 to 10.0%,   a Gd 2 O 3  component is 0 to 10.0%,   a Y 2 O 3  component is 0 to 20.0%,   a Yb 2 O 3  component is 0 to 10.0%,   a P 2 O 5  component is 0 to 10.0%,   a GeO 2  component is 0 to 10.0%,   an Al 2 O 3  component is 0 to 15.0%,   a Ga 2 O 3  component is 0 to 10.0%,   a WO 3  component is 0 to 10.0%,   a Bi 2 O 3  component is 0 to 10.0%,   a ZnO component is 0 to 30.0%,   a TeO 2  component is 0 to 15.0%,   an SnO 2  component is 0 to 5.0%, and   an Sb 2 O 3  component is 0 to 1.0%.   
     
     
         9 . An optical glass according to  claim 1 , wherein a mass sum of an Rn 2 O component (in the formula, Rn is at least one selected from the group consisting of Li, Na, and K) is 1.0% to 30.0%. 
     
     
         10 . An optical glass according to  claim 1 , wherein a mass ratio of Li 2 O/Rn 2 O is no less than 0.01. 
     
     
         11 . An optical glass according to  claim 1 , wherein a mass sum of an RO component (in the formula, R is at least one selected from the group consisting of Mg, Ca, Sr, and Ba) is no greater than 25.0%. 
     
     
         12 . An optical glass according to  claim 1 , wherein a mass sum of an Ln 2 O 3  component (in the formula, Ln is at least one selected from the group consisting of Y, La, Gd, and Yb) is no more than 20.0%. 
     
     
         13 . A preform for use in a polishing process or precision press molding, consisting of the optical glass of  claim 1 . 
     
     
         14 . An optical element consisting of the optical glass according to  claim 1 .