Patent ID: 7930901

Claim:
A process for producing an optical element, which comprises precision press-molding a preform formed of an optical glass comprising 17 to 35 mol % of P 2 O 5 , 0.5 to 4 mol % of SiO 2 , Li 2 O, 1 to 12 mol % of Bi 2 O 3 , 12 to 23 mol % of Nb 2 O 5 and 2 to 10 mol % of TiO 2 as essential components, comprising Na 2 O and K 2 O as optional components, having a total content of Li 2 O, Na 2 O and K 2 O of over 28 mol % but less than 42 mol % having an Li 2 O/(Li 2 O+Na 2 O+K 2 O) molar ratio of from ½ to ⅘, having a total content of Nb 2 O 5 , WO 3 , TiO 2 and Bi 2 O 3 of 25 to 45 mol % and having an Abbe's number (νd) of 30 or less, a refractive index (nd) of 1.84 or more, a sag temperature (Ts) of 514° C. or lower, a liquidus temperature (LT) of 890° C. or lower, a viscosity, measured at its liquidus temperature, of 2 dPa·s or more and transmittance properties that when light is caused to vertically enter one of two plane and mutually parallel optically polished surfaces of a sample of the glass having a thickness of 10.0±0.1 mm and caused to exit from the other surface, the wavelength at which the transmittance represented by the ratio of transmitted light intensity to incidence light intensity (transmitted light intensity/incidence light intensity) comes to be 70% is 510 nm or shorter.