Optical glass and optical element

Abstract

To provide an optical glass having high dispersibility, and low partial dispersion ratio PC, t in an infrared wavelength area, and an optical element.SOLUTION: An optical glass having a Nb2O5 content of 20.00 mass% or less, a total content of P2O5, SiO2,and B2O3 [P2O5+SiO2+B2O3] of 20.00 mass% or less, a total content of BaO and ZnO [BaO+ZnO] of 4.80 mass% or more, a total content of Nb2O5, TiO2, and WO3 [Nb2O5+TiO2+WO3] of 2.70 mass% or more, and a mass ratio of the BaO content to the total content of P2O5, SiO2, and B2O3 [BaO / (P2O5+SiO2+B2O3)] of 0.250 or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an optical glass and an optical element. [Background technology]

[0002] Many surveillance cameras and security cameras are equipped with a night vision function, and their imaging optical systems are required to have imaging performance in the infrared wavelength range in addition to imaging performance in the visible short wavelength range.

[0003] In order to correct high-order chromatic aberrations from the visible short wavelength region to the infrared wavelength region, two types of lenses may be combined. Examples of the two types of lenses include a combination of a convex lens and a concave lens, or a combination of a low dispersion lens and a high dispersion lens. It is desirable that the difference between the Abbe numbers of these two types of lenses is large, the difference between the partial dispersion ratios Pg,F in the visible short wavelength region is small, and the difference between the partial dispersion ratios PC,t in the infrared wavelength region is small.

[0004] In order to correct high-order chromatic aberrations from the visible short wavelength region to the infrared wavelength region, one of the two types of lenses may be made of glass that has high dispersion and a low partial dispersion ratio P C,t in the infrared wavelength region.

[0005] In Patent Documents 1 and 2, focusing on anomalous partial dispersion, optical glass having a dispersion within a predetermined range is proposed. However, Patent Documents 1 and 2 propose only optical glass having a relatively high partial dispersion ratio P C,t in the infrared wavelength region, and do not pay any attention to optical glass having a low partial dispersion ratio P C,t.

[0006] Therefore, in order to correct high-order chromatic aberrations from the visible short wavelength region to the infrared wavelength region, there is a demand for lenses made of glass with a small Abbe number vd and a low partial dispersion ratio PC,t in the infrared wavelength region. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2019-119633 A [Patent Document 2] JP 2019-119634 A Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made in view of the above circumstances, and has an object to provide an optical glass and an optical element that have high dispersion and a low partial dispersion ratio PC,t in the infrared wavelength region. [Means for solving the problem]

[0009] The gist of the present invention is as follows. (1) The content of Nb2O5 is 20.00 mass% or less, The total content of P2O5, SiO2, and B2O3 [P2O5+SiO2+B2O3] is 20.00 mass% or less, The total content of BaO and ZnO [BaO + ZnO] is 4.80 mass% or more, The total content of Nb2O5, TiO2, and WO3 [Nb2O5+TiO2+WO3] is 2.70 mass% or more; An optical glass having a mass ratio of BaO content to the total content of P2O5, SiO2, and B2O3 [BaO / (P2O5+SiO2+B2O3)] of 0.250 or more.

[0010] (2) The optical glass according to (1), in which the total content of Li2O, Na2O, and K2O [Li2O + Na2O + K2O] is greater than 0 mass% and equal to or less than 5.00 mass%.

[0011] (3) The optical glass according to (1), in which the mass ratio of the total content of SiO2 and B2O3 to the total content of P2O5, SiO2, and B2O3 [(SiO2+B2O3) / (P2O5+SiO2+B2O3)] is 0.050 or less.

[0012] (4) The optical glass according to (1), in which the mass ratio of the BaO content to the Nb2O5 content [BaO / Nb2O5] is 0.370 or more.

[0013] (5) The optical glass according to (1), wherein a partial dispersion ratio P C,t satisfies the following formula: 0.0047×νd+0.500≦P C,t≦0.0047×νd+0.546

[0014] (6) An optical element made of the optical glass described in (1) above. Effect of the Invention

[0015] According to the present invention, it is possible to provide an optical glass and an optical element that have high dispersion and a low partial dispersion ratio PC,t in the infrared wavelength region. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] In the present invention, the content of the glass component can be quantified by a known method, for example, inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), or the like.

[0017] In this specification, the thermal stability and reheating stability of glass both refer to the difficulty of crystal precipitation in the glass. In particular, the thermal stability refers to the difficulty of crystal precipitation when molten glass solidifies, and the reheating stability refers to the difficulty of crystal precipitation when solidified glass is reheated, such as during reheat pressing.

[0018] In this specification, unless otherwise specified, the refractive index refers to the refractive index nd at the d line of helium (wavelength 587.56 nm).

[0019] The glass composition of optical glass is expressed on an oxide basis unless otherwise specified. Here, "glass composition on an oxide basis" refers to a glass composition obtained by converting the glass raw materials into oxides present in the optical glass after all of them are decomposed during melting, and the notation of each glass component is conventionally written as SiO2, TiO2, etc. The content and total content of glass components are on a mass basis unless otherwise specified, and "%" means "mass %". The mass ratio refers to the ratio (ratio) of the content of glass components (including the total content of multiple glass components) in mass %. In addition, in this specification and the present invention, the content of a glass component is 0% means that the glass component is substantially not contained, and it is acceptable for the component to be contained at an unavoidable impurity level.

[0020] An embodiment of the present invention will be described below.

[0021] In the optical glass according to this embodiment, the content of Nb2O5 is 20.00% or less. The upper limit of the content of Nb2O5 is preferably 19.50%, and more preferably 19.00%, 18.50%, 18.00%, and 17.50% in that order. The lower limit of the content of Nb2O5 is preferably 0%. The content of Nb2O5 may exceed 0%.

[0022] By setting the content of Nb2O5 within the above range, it is possible to obtain glass that has a high refractive index, high dispersion, and improved thermal stability.

[0023] In the optical glass according to this embodiment, the total content of P2O5, SiO2, and B2O3 [P2O5+SiO2+B2O3] is 20.00% or less. The upper limit of the total content is preferably 20.00%, and more preferably 19.00%, 18.00%, 17.00%, 16.00%, 15.00%, 14.00%, and 13.54% in that order. The lower limit of the total content is preferably 5.00%, and more preferably 6.00%, 7.00%, 8.00%, 9.00%, 10.00%, 11.00%, and 12.00% in that order.

[0024] P2O5, SiO2, and B2O3 are glass network formers, and are glass components that act to lower the liquidus temperature LT and increase thermal stability. On the other hand, if these components are introduced in excess, the refractive index nd may decrease and the partial dispersion ratio PC,t may increase. By setting the total content [P2O5+SiO2+B2O3] within the above range, an optical glass with high dispersion and low partial dispersion ratio PC,t can be obtained.

[0025] In the optical glass according to this embodiment, the total content of BaO and ZnO [BaO+ZnO] is 4.80% or more. The lower limit of the total content is preferably 5.00%, and more preferably 5.25%, 5.50%, 5.75%, 6.00%, 6.25%, 6.50%, and 6.71%, in that order. The upper limit of the total content is preferably 50.00%, 49.00%, 48.00%, 47.00%, 46.00%, 45.00%, 44.00%, 43.00%, 42.00%, 41.00%, 40.00%, 39.50%, 39.00%, 38.50%, 38.00%, 37.50%, 37.00%, 36.50%, 36.00%, 35.50%, 35.00%, 34.5 ... The following are more preferred in order: .00%, 33.50%, 33.00%, 32.50%, 32.00%, 31.50%, 31.00%, 30.50%, 30.00%, 29.50%, 29.00%, 28.50%, 28.00%, 27.50%, 27.00%, 26.50%, 26.00%, 25.50%, 25.00%, 24.50%, 24.00%, 23.50%, 23.00%, and 22.50%.

[0026] By setting the lower limit of the total content of BaO and ZnO [BaO+ZnO] as above, the partial dispersion ratio P C,t can be reduced. In addition, from the viewpoint of maintaining thermal stability, it is preferable to set the upper limit of the total content as above.

[0027] In the optical glass according to this embodiment, the total content of Nb2O5, TiO2, and WO3 [Nb2O5+TiO2+WO3] is 2.70% or more. The lower limit of the total content is preferably 5.00%, and more preferably 7.50%, 10.00%, 15.00%, 16.00%, 17.00%, 18.00%, 19.00%, 20.00%, 21.00%, 22.00%, 23.00%, 24.00%, 25.00%, 26.00%, and 26.10% in that order. The upper limit of the total content is preferably 45.00%, and more preferably 44.50%, 44.00%, 43.50%, 43.00%, 42.50%, 42.00%, and 41.50% in that order.

[0028] By setting the total content of Nb2O5, TiO2, and WO3 [Nb2O5+TiO2+WO3] within the above range, it is possible to obtain an optical glass having high dispersion without impairing thermal stability.

[0029] In the optical glass according to this embodiment, the mass ratio of the BaO content to the total content of P2O5, SiO2, and B2O3 [BaO / (P2O5+SiO2+B2O3)] is 0.250 or more. The lower limit of this mass ratio is preferably 0.275, and more preferably 0.300, 0.325, 0.350, 0.375, 0.400, 0.425, 0.450, 0.460, 0.470, 0.480, 0.490, 0.500, and 0.513, in that order. Furthermore, the upper limit of the mass ratio is preferably 2.500, 2.400, 2.300, 2.200, 2.100, 2.000, 1.975, 1.950, 1.925, 1.900, 1.875, 1.850, 1.840, 1.830, 1.820, 1.810, 1.800, and 1.792, in that order.

[0030] By setting the mass ratio of the BaO content to the total content of P2O5, SiO2, and B2O3 [BaO / (P2O5+SiO2+B2O3)] within the above range, it is possible to obtain an optical glass having a low partial dispersion ratio Pc,t without compromising thermal stability.

[0031] Non-limiting examples of the contents and ratios of glass components other than those described above in the optical glass according to this embodiment are given below.

[0032] In the optical glass according to this embodiment, the lower limit of the mass ratio of the total content of SiO2 and B2O3 to the total content of P2O5, SiO2, and B2O3 [(SiO2+B2O3) / (P2O5+SiO2+B2O3)] is preferably 0. This mass ratio may exceed 0. The upper limit of this mass ratio is preferably 0.050, and more preferably 0.040, 0.030, 0.020, 0.015, 0.010, and 0.005, in that order.

[0033] From the viewpoint of maintaining the thermal stability of the glass, it is preferable that the lower and upper limits of the mass ratio of the total content of SiO2 and B2O3 to the total content of P2O5, SiO2, and B2O3 [(SiO2+B2O3) / (P2O5+SiO2+B2O3)] be set as described above.

[0034] In the optical glass according to this embodiment, the lower limit of the total content of Li2O, Na2O, and K2O [Li2O+Na2O+K2O] is preferably 0%. The total content may exceed 0%. The lower limit of the total content is more preferably 0.10%, and more preferably 0.20%, 0.30%, 0.40%, 0.50%, 0.60%, 0.70%, and 0.79% in this order. The upper limit of the total content is preferably 5.00%, and more preferably 4.50%, 4.00%, 3.50%, 3.00%, 2.50%, 2.00%, 1.75%, 1.50%, 1.25%, 1.00%, and 0.87% in this order.

[0035] The alkali metal components Li2O, Na2O, and K2O are components that improve the melting property of glass, lower the melting temperature, and lower the glass transition temperature Tg. On the other hand, if these components are introduced in excess, the refractive index nd may decrease, the thermal stability may decrease, and the viscosity at the liquidus temperature LT may also decrease. Therefore, it is preferable that the total content of Li2O, Na2O, and K2O [Li2O+Na2O+K2O] is within the above range.

[0036] In the optical glass according to this embodiment, the lower limit of the total content of Nb2O5, TiO2, WO3, and Bi2O3 [Nb2O5+TiO2+WO3+Bi2O3] is preferably 30.00%, and further preferably 35.00%, 40.00%, 41.00%, 42.00%, 43.00%, 44.00%, 45.00%, 46. The following are more preferable in order: 00%, 47.00%, 48.00%, 49.00%, 50.00%, 51.00%, 52.00%, 53.00%, 54.00%, 55.00%, 56.00%, 57.00%, 58.00%, 59.00%, 60.00%, 61.00%, 62.00%, 63.00%, 64.00%, and 64.53%. Furthermore, the upper limit of the total content is preferably 90.00%, 89.00%, 88.00%, 87.00%, 86.00%, 85.00%, 84.50%, 84.00%, 83.50%, 83.00%, 82.50%, 82.00%, 81.50%, 81.00%, 80.50%, 80.00%, and 79.50%, in that order.

[0037] From the viewpoint of obtaining a glass having a high refractive index and high dispersion, it is preferable to set the lower limit of the total content of Nb2O5, TiO2, WO3, and Bi2O3 [Nb2O5+TiO2+WO3+Bi2O3] as described above. Also, from the viewpoint of maintaining the thermal stability of the glass, it is preferable to set the upper limit of the total content as described above.

[0038] In the optical glass according to this embodiment, the lower limit of the mass ratio [Bi2O3 / (Nb2O5+TiO2+WO3+Bi2O3)] of the content of Bi2O3 to the total content of Nb2O5, TiO2, WO3, and Bi2O3 is preferably 0.300, and more preferably 0.310, 0.320, 0.330, 0.340, 0.350, 0.360, 0.370, 0.380, 0.390, 0.400, 0.410, 0.415, 0.420, 0.425, 0.430, 0.435, 0.440, 0.445, 0.450, and 0.455, in that order. Furthermore, the upper limit of the mass ratio is preferably 0.840, and more preferably 0.800, 0.750, 0.740, 0.730, 0.720, 0.710, 0.700, 0.690, 0.680, 0.670, 0.660, 0.650, 0.645, 0.640, 0.635, 0.630, 0.625, 0.620, 0.615, 0.610, 0.605, 0.600, and 0.590, in that order.

[0039] From the viewpoint of suppressing an increase in the partial dispersion ratio P C,t, it is preferable to set the lower limit of the mass ratio of the content of Bi2O3 to the total content of Nb2O5, TiO2, WO3, and Bi2O3 [Bi2O3 / (Nb2O5+TiO2+WO3+Bi2O3)] as described above. Also, from the viewpoint of maintaining the thermal stability of the glass, it is preferable to set the upper limit of the mass ratio as described above.

[0040] In the optical glass according to this embodiment, the lower limit of the mass ratio of the BaO content to the Nb2O5 content [BaO / Nb2O5] is preferably 0.370, more preferably 0.375, 0.380, 0.385, 0.390, 0.395, and 0.397 in that order. The upper limit of the mass ratio is preferably 3.000, more preferably 2.900, 2.800, 2.700, 2.650, 2.600, 2.575, 2.550, 2.525, 2.500, 2.475, 2.450, and 2.425 in that order.

[0041] From the viewpoint of suppressing an increase in the partial dispersion ratio P C,t, it is preferable to set the lower limit of the mass ratio of the BaO content to the Nb2O5 content [BaO / Nb2O5] as described above. Also, from the viewpoint of maintaining the thermal stability of the glass, it is preferable to set the upper limit of the mass ratio as described above.

[0042] In the optical glass according to this embodiment, the lower limit of the mass ratio of the total content of BaO and Bi2O3 to the content of P2O5 [(BaO+Bi2O3) / P2O5] is preferably 3.100, and more preferably 3.110, 3.120, 3.130, 3.140, 3.150, 3.160, 3.170, 3.180, 3.190, 3.200, 3.210, 3.220, 3.230, 3.240, 3.245, 3.250, 3.255, 3.260, 3.265, 3.270, 3.275, and 3.280, in that order. Furthermore, the upper limit of the mass ratio is preferably 5.990, and more preferably 5.900, 5.800, 5.700, 5.600, 5.500, 5.400, 5.300, 5.200, 5.100, 5.000, 4.900, 4.890, and 4.880 in that order.

[0043] From the viewpoint of obtaining an optical glass having a high refractive index and a reduced partial dispersion ratio P C,t, it is preferable to set the lower limit of the mass ratio of the total content of BaO and Bi2O3 to the content of P2O5 [(BaO+Bi2O3) / P2O5] as described above. Also, from the viewpoint of maintaining the thermal stability of the glass, it is preferable to set the upper limit of the mass ratio as described above.

[0044] In the optical glass according to this embodiment, the lower limit of the mass ratio of the total content of Bi2O3 and BaO to the total content of P2O5, SiO2, and B2O3 [(Bi2O3+BaO) / (P2O5+SiO2+B2O3)] is preferably 2.500, and more preferably 2.600, 2.700, 2.800, 2.900, 3.000, 3.100, 3.200, 3.210, 3.220, 3.230, 3.240, 3.250, 3.260, 3.270, 3.280, and 3.500, in that order. Furthermore, the upper limit of the mass ratio is preferably 5.500, and more preferably 5.400, 5.300, 5.200, 5.100, 5.000, 4.990, 4.980, 4.970, 4.960, 4.950, 4.940, 4.930, 4.920, 4.910, 4.900, 4.890, and 4.880, in that order.

[0045] From the viewpoint of obtaining an optical glass having high dispersion and a low partial dispersion ratio P C,t, it is preferable that the mass ratio of the total content of Bi2O3 and BaO to the total content of P2O5, SiO2, and B2O3 [(Bi2O3+BaO) / (P2O5+SiO2+B2O3)] is within the above range.

[0046] In the optical glass according to this embodiment, the lower limit of the P2O5 content is preferably 4.00%, and more preferably 4.50%, 5.00%, 5.50%, 6.00%, 6.50%, 7.00%, 7.50%, 8.00%, 8.25%, 8.50%, 8.75%, 9.00%, 9.25%, 9.50%, 9.75%, 10.00%, 10.25%, 10.50%, 10.75%, 11.00%, 11.25%, 11.50%, 11.75%, 12.00%, and 12.25%, in that order. The upper limit of the P2O5 content is preferably 25.00%, and more preferably 24.00%, 23.00%, 22.50%, 22.00%, 21.50%, 21.00%, 20.50%, 20.00%, 19.50%, 19.00%, 18.50%, 18.00%, 17.50%, 17.25%, 17.00%, 16.75%, 16.50%, 16.25%, 16.00%, 15.75%, 15.50%, 15.25%, 15.00%, 14.75%, 14.50%, 14.25%, 14.00%, 13.75%, and 13.54% in that order.

[0047] P2O5 is a glass network former and a glass component that acts to lower the liquidus temperature LT and increase thermal stability. In order to lower the liquidus temperature LT of the glass and increase the thermal stability, it is preferable to set the lower limit of the P2O5 content as described above. On the other hand, if P2O5 is introduced in excess, the refractive index nd may decrease and the partial dispersion ratio PC,t may increase. Therefore, it is preferable to set the upper limit of the P2O5 content as described above.

[0048] In the optical glass according to this embodiment, the upper limit of the SiO2 content is preferably 5.00%, and more preferably 4.00%, 3.00%, and 2.00% in that order. The lower limit of the SiO2 content is 0%. The SiO2 content may be 0%.

[0049] SiO2 is a component that reduces the refractive index nd. If an excessive amount of SiO2 is introduced, the partial dispersion ratio PC,t may increase, and the liquidus temperature LT of the glass may increase. Therefore, it is preferable that the content of SiO2 is within the above range.

[0050] In the optical glass according to this embodiment, the upper limit of the B2O3 content is preferably 10.00%, and more preferably 8.00%, 6.00%, 4.00%, and 2.00% in that order. The lower limit of the B2O3 content is 0%. The B2O3 content may be 0%.

[0051] B2O3 improves the thermal stability and meltability of glass, increases viscosity, and decreases the liquidus temperature LT. On the other hand, the viscosity-increasing effect of B2O3 increases the temperature at which glass can be refined, which tends to result in a worsening of the coloring of the glass produced. If the B2O3 content is excessive, the partial dispersion ratio PC,t may increase, the refractive index nd may decrease, the thermal stability of the glass may decrease, the liquidus temperature LT may increase, and coloring of the glass due to reduction of the high refractive index component may be promoted. For this reason, it is preferable to set the B2O3 content within the above range.

[0052] In the optical glass according to this embodiment, the upper limit of the Al2O3 content is preferably 5.00%, and more preferably 4.00%, 3.00%, and 2.00% in that order. The lower limit of the Al2O3 content is 0%. The Al2O3 content may be 0%.

[0053] Al2O3 is a glass component that acts to lower the refractive index nd and to raise the liquidus temperature LT of the glass, so it is preferable that the content of Al2O3 is within the above range.

[0054] In the optical glass according to this embodiment, the lower limit of the Li2O content is preferably 0%. The Li2O content may exceed 0%. The upper limit of the Li2O content is preferably 5.00%, and more preferably 4.50%, 4.00%, 3.50%, 3.00%, 2.50%, 2.00%, 1.75%, 1.50%, 1.25%, 1.00%, 0.75%, and 0.50%, in that order.

[0055] Li2O is a component that improves the melting property of glass, lowers the melting temperature, and lowers the glass transition temperature Tg. If Li2O is introduced in excess, the partial dispersion ratio PC,t may increase, the refractive index nd may decrease, the thermal stability may decrease, and the viscosity at the liquidus temperature LT may also decrease. Therefore, it is preferable that the content of Li2O is within the above range.

[0056] In the optical glass according to this embodiment, the lower limit of the Na2O content is preferably 0%. The Na2O content may exceed 0%. The upper limit of the Na2O content is preferably 5.00%, and more preferably 4.50%, 4.00%, 3.50%, 3.00%, 2.50%, 2.00%, 1.75%, 1.50%, 1.25%, 1.00%, 0.75%, 0.54%, and 0.50%, in that order.

[0057] Na2O is a component that improves the melting property of glass, lowers the melting temperature, and lowers the glass transition temperature Tg. If Na2O is introduced in excess, the refractive index nd may decrease, the thermal stability may decrease, and the viscosity at the liquidus temperature LT may also decrease. Therefore, it is preferable to set the content of Na2O within the above range.

[0058] In the optical glass according to this embodiment, the lower limit of the K2O content is preferably 0%. The K2O content may exceed 0%. The upper limit of the K2O content is preferably 5.00%, and more preferably 4.50%, 4.00%, 3.50%, 3.00%, 2.50%, 2.00%, 1.75%, 1.50%, 1.25%, 1.00%, 0.75%, 0.50%, and 0.33%, in that order.

[0059] K2O is a component that improves the melting property of glass, lowers the melting temperature, and lowers the glass transition temperature Tg. If K2O is introduced in excess, the refractive index nd may decrease, the thermal stability may decrease, and the viscosity at the liquidus temperature LT may also decrease. Therefore, it is preferable to set the content of K2O within the above range.

[0060] In the optical glass according to this embodiment, the lower limit of the Cs2O content is preferably 0%. The Cs2O content may exceed 0%. The upper limit of the Cs2O content is preferably 5.00%, and more preferably 4.50%, 4.00%, 3.50%, 3.00%, 2.50%, 2.00%, 1.75%, 1.50%, 1.25%, 1.00%, 0.75%, and 0.50%, in that order.

[0061] Cs2O is a component that improves the melting property of glass, lowers the melting temperature, and lowers the glass transition temperature Tg. If Cs2O is introduced in excess, the refractive index nd may decrease, the thermal stability may decrease, and the viscosity at the liquidus temperature LT may also decrease. Therefore, it is preferable to set the content of Cs2O within the above range.

[0062] In the optical glass according to this embodiment, the lower limit of the RbO content is preferably 0%. The RbO content may exceed 0%. The upper limit of the RbO content is preferably 5.00%, and more preferably 4.50%, 4.00%, 3.50%, 3.00%, 2.50%, 2.00%, 1.75%, 1.50%, 1.25%, 1.00%, 0.75%, and 0.50%, in that order.

[0063] Rb2O is a component that has the function of improving the melting property. On the other hand, Rb2O is expensive compared to other alkali metal components. Therefore, it is preferable that the content of Rb2O is within the above range.

[0064] In the optical glass according to this embodiment, the lower limit of the MgO content is preferably 0%. The MgO content may exceed 0%. The upper limit of the MgO content is preferably 10.00%, and more preferably 5.00%, 4.50%, 4.00%, 3.50%, 3.00%, 2.50%, 2.00%, 1.75%, 1.50%, 1.25%, 1.00%, 0.75%, 0.54%, and 0.50%, in that order.

[0065] In the optical glass according to this embodiment, the lower limit of the CaO content is preferably 0%. The CaO content may exceed 0%. The upper limit of the CaO content is preferably 10.00%, and more preferably 5.00%, 4.50%, 4.00%, 3.50%, 3.00%, 2.50%, 2.00%, 1.75%, 1.50%, 1.25%, 1.00%, 0.75%, and 0.50%, in that order.

[0066] In the optical glass according to this embodiment, the lower limit of the SrO content is preferably 0%. The SrO content may exceed 0%. The upper limit of the SrO content is preferably 10.00%, and more preferably 5.00%, 4.50%, 4.00%, 3.50%, 3.00%, 2.50%, 2.00%, 1.75%, 1.50%, 1.25%, 1.00%, 0.75%, and 0.50%, in that order.

[0067] MgO, CaO, and SrO are glass components that improve the thermal stability of the glass, increase the viscosity at the liquidus temperature LT, and improve the melting property. On the other hand, if these are introduced in excess, the refractive index nd may decrease. Therefore, it is preferable to set the content of these glass components within the above range.

[0068] In the optical glass according to this embodiment, the lower limit of the BaO content is preferably 2.00%, and more preferably 2.25%, 2.50%, 2.75%, 3.00%, 3.25%, 3.50%, 3.75%, 4.00%, 4.25%, 4.50%, 4.60%, 4.75%, 5.00%, 5.75%, 6.00%, 6.25%, 6.50%, and 6.71%, in that order. The upper limit of the BaO content is preferably 50.00%, and further preferably 49.00%, 48.00%, 47.00%, 46.00%, 45.00%, 44.00%, 43.00%, 42.00%, 41.00%, 40.00%, 39.50%, 39.00%, 38.50%, 38.00%, 37.50%, 37.00%, 36.50%, 36.00%, 35.50%, 35.00%, 34.50%, %, 34.00%, 33.50%, 33.00%, 32.50%, 32.00%, 31.50%, 31.00%, 30.50%, 30.00%, 29.50%, 29.00%, 28.50%, 28.00%, 27.50%, 27.00%, 26.50%, 26.00%, 25.50%, 25.00%, 24.50%, 24.00%, 23.50%, 23.00%, and 22.26% are more preferable in this order.

[0069] BaO is a component that acts to reduce the partial dispersion ratio PC,t. BaO also acts to improve the thermal stability of the glass, increase the viscosity at the liquidus temperature LT, and improve the melting property. Therefore, it is preferable to set the lower limit of the BaO content as described above. On the other hand, if the BaO content is too high, the thermal stability of the glass may decrease. Therefore, it is preferable to set the upper limit of the BaO content as described above.

[0070] In the optical glass according to this embodiment, the lower limit of the ZnO content is preferably 0%. The ZnO content may be 0% or may exceed 0%. The upper limit of the ZnO content is preferably 30.00%, and may be 25.00%, 20.00%, 15.00%, 14.00%, 13.00%, 12.00%, 11.00%, 10.00%, 9.00%, 8.00%, 7.00%, 6.00%, 5.00%, or 4.61%.

[0071] ZnO is a component that acts to reduce the glass transition temperature Tg and improve meltability while suppressing the decrease in the refractive index nd. ZnO also acts to reduce the partial dispersion ratio PC,t. On the other hand, if the ZnO content is too high, the liquidus temperature LT may increase and the thermal stability of the glass may decrease. Therefore, it is preferable to set the ZnO content within the above range.

[0072] In the optical glass according to this embodiment, the lower limit of the TiO2 content is preferably 0%. The TiO2 content may be 0% or may exceed 0%. The upper limit of the TiO2 content is preferably 13.00%, and more preferably 12.50%, 12.00%, 11.50%, 11.00%, 10.50%, 10.00%, 9.50%, 9.00%, 8.50%, 8.00%, 7.50%, 7.00%, 6.50%, 6.00%, and 5.61% in that order.

[0073] TiO2 is a component that contributes to increasing the refractive index and dispersion of glass, and improves thermal stability and chemical durability. On the other hand, if TiO2 is introduced in excess, the transmittance of the glass may decrease. Therefore, it is preferable to set the content of TiO2 within the above range.

[0074] In the optical glass according to this embodiment, the lower limit of the WO3 content is preferably 0%. The WO3 content may exceed 0%. The lower limit of the WO3 content is more preferably 2.00%, and further more preferably 4.00%, 5.00%, 6.00%, 7.00%, 8.00%, 8.50%, 9.00%, 9.50%, 10.00%, 10.50%, 11.00%, 11.50%, and 11.80% in that order. Furthermore, the upper limit of the WO3 content is preferably 27.00%, and more preferably 26.50%, 26.00%, 25.50%, 25.00%, 24.50%, 24.00%, 23.50%, 23.00%, 22.50%, 22.00%, 21.50%, 21.00%, 20.50%, 20.00%, 19.50%, 19.00%, and 18.50%, in that order.

[0075] WO3 is a component that contributes to increasing the refractive index and dispersion of glass, and lowers the liquidus temperature LT and glass transition temperature Tg of glass. On the other hand, if WO3 is incorporated in excess, the transmittance of glass may decrease. Therefore, it is preferable to set the content of WO3 within the above range.

[0076] In the optical glass according to this embodiment, the lower limit of the Bi2O3 content is preferably 10.00%, and more preferably 15.00%, 17.00%, 19.00%, 20.00%, 21.00%, 22.00%, 23.00%, 24.00%, 25.00%, 26.00%, 27.00%, 28.00%, 29.00%, 30.00%, 30.50%, 31.00%, 31.50%, 32.00%, 32.50%, 33.00%, 33.50%, 34.00%, 34.50%, and 35.00%, in that order. Furthermore, the upper limit of the Bi2O3 content is preferably 70.00%, and more preferably 65.00%, 60.00%, 59.00%, 58.00%, 57.00%, 56.00%, 55.00%, 54.00%, 53.00%, 52.00%, 51.00%, 50.00%, 49.50%, 49.00%, 48.50%, 48.00%, 47.50%, 47.00%, 46.50%, 46.00%, 45.50%, 45.00%, 44.50%, 44.00%, 43.50%, 43.00%, 42.50%, and 42.00% in that order.

[0077] Bi2O3 is a glass component that contributes to increasing the refractive index and dispersion of glass, and has the functions of decreasing the partial dispersion ratio PC,t, decreasing the liquidus temperature LT, and decreasing the glass transition temperature Tg. From the viewpoint of decreasing the partial dispersion ratio PC,t, it is preferable to set the lower limit of the Bi2O3 content as described above. Also, from the viewpoint of maintaining thermal stability, it is preferable to set the upper limit of the Bi2O3 content as described above.

[0078] In the optical glass according to this embodiment, the TeO2 content is preferably 0 to 0.1%, more preferably 0 to 0.05%, even more preferably 0 to 0.01%, still more preferably 0 to 0.005%, even more preferably 0 to 0.001%, and it is particularly preferable that no TeO2 is contained.

[0079] TeO2 is a component that contributes to increasing the refractive index and dispersion of glass and improves the thermal stability of glass. However, in consideration of the impact on the environment, it is preferable that the content of TeO2 is small. Therefore, it is preferable that the content of TeO2 is within the above range.

[0080] In the optical glass according to this embodiment, the lower limit of the ZrO2 content is preferably 0%. The ZrO2 content may exceed 0%. The upper limit of the ZrO2 content is preferably 10.00%, and more preferably 5.00%, 3.00%, and 2.00% in that order.

[0081] From the viewpoint of suppressing an increase in the partial dispersion ratio PC,t and also suppressing an increase in the liquidus temperature LT and a decrease in stability during reheating, it is preferable that the content of ZrO2 is within the above range.

[0082] In the optical glass according to this embodiment, the lower limit of the La2O3 content is preferably 0%. The La2O3 content may exceed 0%. The upper limit of the La2O3 content is preferably 20.00%, and more preferably 15.00%, 10.00%, 5.00%, 4.00%, 3.50%, 3.00%, 2.50%, 2.00%, 1.75%, 1.50%, 1.25%, 1.00%, 0.75%, and 0.50%, in that order.

[0083] In the optical glass according to this embodiment, the lower limit of the Gd2O3 content is preferably 0%. The Gd2O3 content may exceed 0%. The upper limit of the Gd2O3 content is preferably 20.00%, and more preferably 15.00%, 10.00%, 5.00%, 4.00%, 3.50%, 3.00%, 2.50%, 2.00%, 1.75%, 1.50%, 1.25%, 1.00%, 0.75%, and 0.50%, in that order.

[0084] In the optical glass according to this embodiment, the lower limit of the Y2O3 content is preferably 0%. The Y2O3 content may exceed 0%. The upper limit of the Y2O3 content is preferably 20.00%, 15.00%, 10.00%, 5.00%, 4.00%, 3.50%, 3.00%, 2.50%, 2.00%, 1.75%, 1.50%, 1.25%, 1.00%, 0.75%, and 0.50%, in that order.

[0085] La2O3, Gd2O3, and Y2O3 are components that increase the refractive index nd and maintain or improve the thermal stability of the glass. On the other hand, if the content of these components is high, the liquidus temperature LT may increase and the thermal stability of the glass may decrease. Therefore, it is preferable to set the content of these components within the above range.

[0086] In the optical glass according to this embodiment, the lower limit of the Ta2O5 content is preferably 0%. The Ta2O5 content may exceed 0%. The upper limit of the Ta2O5 content is preferably 5.00%, and more preferably 4.00%, 3.00%, and 2.00% in that order.

[0087] Ta2O5 is a glass component that contributes to increasing the refractive index and dispersion of glass. On the other hand, if the content of Ta2O5 increases, the partial dispersion ratio PC,t may increase. In addition, the raw material cost may increase, and the specific gravity may increase. Therefore, it is preferable to set the content of Ta2O5 within the above range.

[0088] In the optical glass according to this embodiment, the Sc2O3 content is preferably 2% or less. The lower limit of the Sc2O3 content is preferably 0%.

[0089] In the optical glass according to this embodiment, the content of HfO2 is preferably 2% or less. The lower limit of the content of HfO2 is preferably 0%.

[0090] Sc2O3 and HfO2 are glass components that contribute to high dispersibility of the glass, but are expensive components, so it is preferable that the contents of Sc2O3 and HfO2 are each within the above range.

[0091] In the optical glass according to this embodiment, the content of Lu2O3 is preferably 2% or less. The lower limit of the content of Lu2O3 is preferably 0%.

[0092] Lu2O3 is a glass component that contributes to high dispersibility of the glass, but also increases the specific gravity of the glass due to its large molecular weight, so it is preferable that the content of Lu2O3 is within the above range.

[0093] In the optical glass according to this embodiment, the GeO2 content is preferably 2% or less. The lower limit of the GeO2 content is preferably 0%.

[0094] GeO2 is a glass component that contributes to high dispersibility of glass, but is an extremely expensive component among commonly used glass components. Therefore, from the viewpoint of reducing the manufacturing cost of glass, it is preferable to set the content of GeO2 in the above range.

[0095] In the optical glass according to this embodiment, the content of Yb2O3 is preferably 2% or less. The lower limit of the content of Yb2O3 is preferably 0%.

[0096] Yb2O3 has a larger molecular weight than La2O3, Gd2O3, and Y2O3, and therefore increases the specific gravity of the glass. In addition, if the content of Yb2O3 is too high, the thermal stability of the glass may decrease. From the viewpoint of preventing the decrease in the thermal stability of the glass and suppressing the increase in the specific gravity, it is preferable that the content of Yb2O3 is within the above range.

[0097] The optical glass according to this embodiment is preferably mainly composed of the above-mentioned glass components, that is, Nb2O5 as an essential component, and P2O5, SiO2, B2O3, Al2O3, Li2O, Na2O, K2O, Cs2O, Rb2O, MgO, CaO, SrO, BaO, ZnO, TiO2, WO3, Bi2O3, TeO2, ZrO2, La2O3, Gd2O3, Y2O3, Ta2O5, Sc2O3, HfO2, Lu2O3, GeO2, and Yb2O3 as optional components. The total content of the above-mentioned glass components is preferably 95% or more, more preferably 98% or more, even more preferably 99% or more, and particularly preferably 99.5% or more.

[0098] It is preferable that the optical glass according to this embodiment is basically composed of the above glass components, but it may contain other components as long as they do not impair the action and effect of the present invention. Furthermore, the present invention does not exclude the inclusion of unavoidable impurities.

[0099] In addition to the above components, the optical glass may contain a small amount of a fining agent such as Sb2O3. The total amount of the fining agent (exclusive amount added) is preferably 0% or more and less than 1%, and more preferably 0% or more and 0.5% or less.

[0100] The total content of the fining agent is expressed as a mass percentage when the total content of all glass components excluding the fining agent is taken as 100%.

[0101] Moreover, the optical glass can obtain high transmittance over a wide range of the visible region. To make the most of these characteristics, it is preferable that the glass does not contain any coloring elements. Examples of coloring elements include Cu, Co, Ni, Fe, Cr, Eu, Nd, Er, V, and Ag. Each element is preferably contained in an amount of less than 100 ppm by mass, more preferably 0 to 80 ppm by mass, and even more preferably 0 to 50 ppm by mass, and particularly preferably not contained substantially.

[0102] Ga, Tb, etc. are components that do not need to be incorporated and are expensive components, so the content range of Ga2O3 and TbO2 expressed in mass% is preferably 0 to 0.1%, more preferably 0 to 0.05%, further preferably 0 to 0.01%, even more preferably 0 to 0.005%, still more preferably 0 to 0.001%, and particularly preferably not substantially contained.

[0103] (Glass properties) <Abbe number νd> In the optical glass according to this embodiment, the lower limit of the Abbe number vd is preferably 16.00, and can also be 16.10, 16.20, 16.30, 16.40, 16.50, 16.60, 16.70, 16.80, 16.90, 17.00, 17.10, 17.20, or 17.30. The upper limit of the Abbe number vd is preferably 35.00, and can also be 34.00, 33.00, 32.00, 31.00, 30.00, 29.00, 28.00, 27.00, 26.00, 25.00, 24.50, 24.00, 23.50, 23.00, 22.50, 22.00, 21.50, or 21.00.

[0104] The Abbe number νd can be adjusted to a desired value by appropriately adjusting the content of each glass component. Components that relatively lower the Abbe number νd, i.e., high dispersion components, are Nb2O5, TiO2, ZrO2, WO3, Bi2O3, Ta2O5, etc. On the other hand, components that relatively increase the Abbe number νd, i.e., low dispersion components, are SiO2, B2O3, Li2O, Na2O, K2O, La2O3, BaO, CaO, SrO, etc.

[0105] In the present invention, the Abbe number νd and the partial dispersion ratio P C,t described later are calculated as follows. That is, the refractive index at 12 wavelengths shown in Table A is measured according to the Japanese Industrial Standards (JIS) JIS B 7071-1 Method for measuring the refractive index of optical glass - Part 1: Minimum deviation method. Next, the refractive index of each line obtained by measurement is applied to the shot dispersion formula defined in Annex B of the Japanese Industrial Standards (JIS) JIS B 7071-1 Method for measuring the refractive index of optical glass - Part 1: Minimum deviation method, and the constant of the shot dispersion formula is obtained by the least square method. Then, the Abbe number νd and the partial dispersion ratio P C,t described later are calculated from the value of each linear refractive index obtained using the shot dispersion formula with the constant determined.

[0106] [Table A] Shot distribution: n 2 =a0+a1λ 2 +a2λ -2 +a3λ -4 +a4λ -6 +a5λ -8 Here, n is the refractive index, λ is the wavelength (μm), and a0, a1, a2, a3, a4, and a5 are constants. The Abbe number νd is expressed as follows using the refractive indices nd, nF, and nC for the d-line, F-line, and C-line. νd=(nd-1) / (nF-nC) The partial dispersion ratio P C,t is expressed as follows using the refractive indices nt, nF, and nC for the t-line, F-line, and C-line, respectively: PC,t=(nC-nt) / (nF-nC)

[0107] <Refractive index nd> In the optical glass according to this embodiment, the lower limit of the refractive index nd is preferably 1.6000, and can also be 1.7000, 1.7500, 1.8000, 1.8250, 1.8500, 1.8750, or 1.9000. The upper limit of the refractive index nd is preferably 2.2000, and can also be 2.1900, 2.1800, 2.1700, 2.1600, 2.1500, 2.1400, 2.1300, 2.1200, or 2.1100.

[0108] The refractive index nd can be adjusted to a desired value by appropriately adjusting the content of each glass component. Components that act to relatively increase the refractive index nd (high refractive index components) include Nb2O5, TiO2, ZrO2, Ta2O5, La2O3, etc. On the other hand, components that act to relatively decrease the refractive index nd (low refractive index components) include SiO2, B2O3, Li2O, Na2O, K2O, etc.

[0109] <Partial dispersion ratio PC,t> In the optical glass according to this embodiment, the upper limit of the partial dispersion ratio PC,t in the infrared wavelength region is preferably 0.6350, and more preferably 0.6300, 0.6250, and 0.6238 in that order. By setting the partial dispersion ratio PC,t within the above range, an optical glass suitable for correcting high-order chromatic aberration can be obtained. On the other hand, the lower limit of the partial dispersion ratio PC,t is preferably 0.6000, and more preferably 0.6050, 0.6100, and 0.6139 in that order.

[0110] The optical glass according to this embodiment has a low partial dispersion ratio P C,t relative to the Abbe number v and has a negative anomalous dispersion ΔP C,t. That is, in the optical glass according to this embodiment, it is preferable that the partial dispersion ratio P C,t satisfies the following formula [1]. 0.0047×νd+0.500≦P C,t≦0.0047×νd+0.546 〔1〕 The partial dispersion ratio PC,t more preferably satisfies the following formula [3], even more preferably satisfies the following formula [4], and even more preferably satisfies the following formula [5]. 0.0047×νd+0.510≦PC,t...[3] 0.0047×νd+0.520≦PC,t···[4] 0.0047×νd+0.530≦PC,t...[5] Moreover, the partial dispersion ratio PC,t more preferably satisfies the following formula [7], and further preferably satisfies the following formula [8]. PC,t≦0.0047×νd+0.540...[7] PC,t≦0.0047×νd+0.534 ··· [8]

[0111] When the partial dispersion ratio PC,t satisfies the above formula, the optical element made of the optical glass according to this embodiment can satisfactorily correct chromatic aberration over a wide wavelength range.

[0112] The partial dispersion ratio P C,t is calculated using the above shot dispersion formula. The partial dispersion ratio P C,t is expressed as follows using the refractive indices nt, nF, and nC for the t-line, F-line, and C-line, respectively: PC,t=(nC-nt) / (nF-nC) Moreover, in a plane in which the horizontal axis represents the Abbe number vd and the vertical axis represents the partial dispersion ratio P C,t, the normal line is expressed by the following equation. PC,t(0)=0.5461+(0.004667×νd)

[0113] The partial dispersion ratio P C,t can be adjusted to a desired value by appropriately adjusting the content of each glass component. Components that act to relatively lower the partial dispersion ratio P C,t include SrO, BaO, ZnO, La2O3, TiO2, Nb2O5, WO3, etc. On the other hand, components that act to relatively increase the partial dispersion ratio P C,t include SiO2, B2O3, Al2O3, Li2O, etc.

[0114] <Glass transition temperature Tg> The lower limit of the glass transition temperature Tg of the optical glass according to this embodiment is preferably 450° C., and more preferably 500° C., 510° C., and 527° C. in that order. The upper limit of the glass transition temperature Tg is preferably 600° C., and more preferably 590° C., 580° C., and 570° C. in that order.

[0115] Components that relatively lower the glass transition temperature Tg are Li2O, Na2O, K2O, etc. Components that relatively raise the glass transition temperature Tg are La2O3, ZrO2, Nb2O5, etc. The glass transition temperature Tg can be controlled by appropriately adjusting the contents of these components.

[0116] (Optical glass manufacturing) The optical glass according to this embodiment may be produced by blending glass raw materials to obtain the above-mentioned predetermined composition, and using the blended glass raw materials according to a known glass manufacturing method. For example, a plurality of compounds are blended and thoroughly mixed to obtain a blended raw material, and the blended raw material is placed in a quartz crucible or platinum crucible to be roughly melted (rough melt). The molten material obtained by rough melting is quenched and crushed to produce cullet. The cullet is placed in a platinum or gold crucible, heated, and remelted (remelt) to obtain a molten glass, which is then clarified and homogenized, molded, and slowly cooled to obtain an optical glass. A known method may be applied to the molding and slow cooling of the molten glass.

[0117] In addition, as long as the desired glass components can be introduced into the glass in the desired content, the compound used in the mixed raw material is not particularly limited. Examples of such compounds include oxides, carbonates, nitrates, hydroxides, and fluorides.

[0118] It is also possible to prepare optical glass by preparing a plurality of types of cullets having different optical properties by the above-mentioned method, mixing these cullets so as to obtain the required optical properties, and then melting, refining and molding the mixture.

[0119] (Manufacture of glass materials for press molding) The glass material for press molding according to this embodiment (hereinafter referred to as glass material) is made of the optical glass according to this embodiment. To obtain the glass material according to this embodiment, for example, the mixed raw materials are heated, melted, and molded so as to obtain the optical glass according to this embodiment. The glass molded body thus produced is processed to produce a glass material equivalent to the amount of one press-molded product. In addition to this method, any known method for producing a glass material for press molding from molten glass can be applied.

[0120] (Manufacturing of optical elements, etc.) The optical element according to this embodiment is made of the optical glass according to this embodiment described above. The optical element according to the present embodiment can be obtained by processing the optical glass according to the present embodiment described above, or by producing optical glass by the method for producing optical glass according to the present embodiment described above and processing the produced optical glass.

[0121] Processing to obtain an optical element can be carried out by known methods such as precision press molding, grinding, polishing, etc. For example, an optical element can be produced by known methods such as a method of polishing the surface of a molded body obtained by molding the optical glass according to this embodiment, a method of heating and press molding the glass material for press molding according to this embodiment to produce an optical element blank, and grinding and polishing this optical element blank, and a method of heating and precision press molding the glass material for press molding according to this embodiment to produce an optical element.

[0122] Examples of optical elements include aspherical lenses, spherical lenses, or lenses such as plano-concave lenses, plano-convex lenses, biconcave lenses, biconvex lenses, convex meniscus lenses, and concave meniscus lenses, as well as various lenses such as microlenses, lens arrays, and lenses with diffraction gratings, prisms, and prisms with lens functions. If necessary, an anti-reflection film or a wavelength-selective partial reflection film may be provided on the surface of the optical element.

[0123] The optical element according to this embodiment is made of optical glass having high dispersion and low partial dispersion ratio PC,t in the infrared wavelength range, so that it can perform good chromatic aberration correction by combining it with optical elements made of other glasses. It is also effective in achieving a high zoom ratio, wide angle, and compact imaging optical system. Furthermore, while having high dispersion, it is possible to suppress an increase in specific gravity by adjusting the composition, so that it is possible to reduce the weight of the optical element, and it is also effective in preventing the focal position from shifting due to vibration.

[0124] The optical element of the present invention is also suitable for use in imaging optical systems of various cameras such as digital still cameras, digital video cameras, security cameras, and vehicle-mounted cameras, as well as optical elements for guiding light rays for writing and reading data to optical recording media such as DVDs and CDs, such as optical pickup lenses and collimator lenses, etc. It is also suitable as an optical element for optical communications. EXAMPLES

[0125] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to the embodiments shown in the examples.

[0126] Example 1 The compound raw materials were weighed and thoroughly mixed to obtain glass having the composition shown in Tables 1 to 3. The raw materials were then placed in a platinum crucible and heated to 1000°C to 1200°C for 1.5 to 2.0 hours while being appropriately stirred to obtain a molten glass. The molten glass was cast into a mold preheated to an appropriate temperature. The cast glass was heat-treated for 30 minutes at a temperature near the glass transition temperature Tg, and then allowed to cool to room temperature in a furnace to obtain a glass sample.

[0127] The refractive index nd, Abbe number vd, partial dispersion ratio PC,t, and glass transition temperature Tg of the obtained glass samples were measured as follows. The results are shown in Table 3.

[0128] (1) Refractive index nd, Abbe number νd, and partial dispersion ratio PC,t The refractive index of the above glass samples was measured at the 12 wavelengths shown in Table A above according to the Japanese Industrial Standards (JIS) JIS B 7071-1, Measurement method for refractive index of optical glass, Part 1: Minimum deviation angle method. Next, the refractive index of each line obtained by measurement was applied to the Schott dispersion formula defined in the Japanese Industrial Standards (JIS) JIS B 7071-1, Measurement of the refractive index of optical glass - Part 1: Minimum deviation angle method, Appendix B, and the constants of the Schott dispersion formula were obtained by the least squares method. Shot distribution: n 2 =a0+a1λ 2 +a2λ -2 +a3λ -4 +a4λ -6 +a5λ -8 Here, n is the refractive index, λ is the wavelength (μm), and a0, a1, a2, a3, a4, and a5 are constants. The refraction nd is the refractive index at a wavelength of 587.56 nm. The Abbe number vd was calculated as follows using the refractive indices nd, nF, and nC for the d line, F line, and C line. νd=(nd-1) / (nF-nC) The partial dispersion ratio P C,t was calculated as follows using the refractive indices nt, nF, and nC for the t-line, F-line, and C-line. PC,t=(nC-nt) / (nF-nC)

[0129] (2) Glass transition temperature Tg The glass transition temperature Tg was measured from the endothermic curve when the solid glass was heated using a differential scanning calorimeter DSC3300SA. The Tg measured by this method corresponds to the Tg measured based on the Japan Optical Glass Industry Association standard JOGIS-08.

[0130] [Table 1]

[0131] [Table 2]

[0132] [Table 3]

[0133] Example 2 In the same manner as in Example 1, the raw materials were heated, melted, clarified, and homogenized to obtain glass having the composition shown in Tables 1 to 3, and the resulting molten glass was poured into a mold and rapidly cooled to form glass black. This glass block was annealed, then cut and ground to produce a glass material for press molding.

[0134] Example 3 The press molding glass material prepared in Example 2 was heated and softened, and press molded by a known method using a press mold to prepare optical element blanks such as lens blanks and prism blanks. The obtained optical element blanks were precision annealed and precisely adjusted to the required refractive index, and then ground and polished by known methods to obtain lenses and prisms.

[0135] Example 4 The surface of the press molding glass material produced in Example 2 was polished to produce a press molding glass material for precision press molding. This glass material was heated and precision press molded to obtain an aspheric lens. Precision press molding was performed by a known method. In this manner, various lenses, prisms, and other optical elements were produced.

[0136] When an imaging optical system was constructed using the lenses obtained in Examples 3 and 4, an imaging device with good color reproducibility was obtained. In addition, when an imaging unit or an optical pickup unit mounted on a mobile phone was manufactured using the obtained lenses, a unit with extremely little focal position shift due to vibration was obtained. It was confirmed that the optical element obtained in this example can realize good chromatic aberration correction by combining it with an optical element made of low dispersion glass.

[0137] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0138] For example, by adjusting the composition described in the specification to the glass compositions exemplified above, an optical glass according to one aspect of the present invention can be produced. Furthermore, it is of course possible to arbitrarily combine two or more of the items described in the specification as examples or preferred ranges.

Claims

1. Nb 2 O 5 The content is 20.00 mass% or less, P 2 O 5 , SiO 2 , and B 2 O 3 The total content [P 2 O 5 +SiO 2 +B 2 O 3 ] is 20.00 mass% or less, The total content of BaO and ZnO [BaO + ZnO] is 4.80 mass% or more, Nb 2 O 5 , TiO 2 , and W.O. 3 The total content [Nb 2 O 5 + TiO 2 +W.O. 3 ] is 2.70 mass% or more, P 2 O 5 , SiO 2 , and B 2 O 3 The mass ratio of BaO content to the total content [BaO / (P 2 O 5 +SiO 2 +B 2 O 3 ) is 0.250 or more.

2. Li 2 O, Na 2 O, and K 2 The total content of O [Li 2 O+Na 2 O+K 2 2. The optical glass according to claim 1, wherein the content of O is greater than 0 mass % and is 5.00 mass % or less.

3. P 2 O 5 , SiO 2 , and B 2 O 3 SiO relative to the total content 2 and B 2 O 3 Mass ratio of the total content [(SiO 2 +B 2 O 3 ) / (P 2 O 5 +SiO 2 +B 2 O 3 2. The optical glass according to claim 1, wherein the refractive index is 0.050 or less.

4. Nb 2 O 5 The mass ratio of the BaO content to the Nb content [BaO / Nb 2 O 5 2. The optical glass according to claim 1, wherein the refractive index is 0.370 or greater.

5. 2. The optical glass according to claim 1, wherein the partial dispersion ratio PC,t satisfies the following formula: 0.0047×νd+0.500≦P C , t≦0.0047×νd+0.546

6. An optical element comprising the optical glass according to claim 1.

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