# Patent

## Title
Optical glass, press-molding glass material, and optical element and method of the same

## Abstract

An aspect of the present invention relates to optical glass, which is oxide glass comprising various cationic components in prescribed amounts without Pb, with a refractive index nd of 1.750 to 1.850, an Abbé number νd of 29.0 to 40.0, and a glass transition temperature of less than 630° C.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of priority under 35 USC 119 to Japanese Patent Application No. 2011-93273 filed on Apr. 19, 2011 and Japanese Patent Application No. 2012-55305 filed on Mar. 13, 2012, which are expressly incorporated herein by reference in their entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optical glass, a press-molding glass material and an optical element which are comprised of the optical glass, and a method of manufacturing an optical element employing the press-molding glass material.
2. Discussion of the Background
In recent years, as image pickup devices have achieved ever greater functionality and become ever more compact, the demand for lenses made of high refractive index glass has increased. For example, the optical glasses disclosed in Document 1 (Japanese Unexamined Patent Publication (KOKAI) No. 2009-120485) and Document 2 (Japanese Unexamined Patent Publication (KOKAI) No. 2006-219365) or English language family members US2008/254965A1 and U.S. Pat. No. 7,897,531, which are expressly incorporated herein by reference in their entirety, are known as such lens materials.
However, based on investigation by the present inventor, conventional high refractive index glasses, including the optical glasses described in Documents 1 and 2, present various manufacturing problems. These include having a high glass transition temperature, which renders the glass unsuited to precision press molding; the necessity for a high annealing temperature, subjecting the annealing furnace to wear and tear; and having a high liquidus temperature, compromising manufacturing stability.
SUMMARY OF THE INVENTION
An aspect of the present invention provides for optical glass that is of high refractive index and is highly suitable to manufacturing, a press-molding glass material and an optical element which are comprised of the optical glass, and a method of manufacturing an optical element employing the press-molding glass material.
An aspect of the present invention relates to optical glass, which is oxide glass comprising, denoted as cation percentages:

    Si4+ 0 to 30%;
    B3+ 15 to 60%;
    Li+ 0 to 10%;
    Na+ 0 to 10%;
    K+ 0 to 15%;
    Mg2+ 0 to 20%;
    Ca2+ 0 to 15%;
    Sr2+ 0 to 20%;
    Ba2+ 0 to 20%;
    Zn2+ 13 to 40%;
    La3+ 0 to 11%;
    Gd3+ 0 to 10%;
    Y3+ 0 to 6%;
    Yb3+ 0 to 6%;
    Zr4+ 0 to 5%;
    Ti4+ 0 to 7%;
    Nb5+ 2 to 20%;
    Ta5+ 0 to 5%;
    W6+ 0 to 10%;
    Te4+ 0 to 5%;
    Ge4+ 0 to 5%;
    Bi3+ 0 to 5%; and
    Al3+ 0 to 5%;
    wherein a combined content of Si4+ and B3+ ranges from 35 to 65%;
    a cation ratio of a content of B3+ to the combined content of Si4+ and B3+, B3+/(Si4++B3+), ranges from 0.3 to 1;
    a combined content of Li+, Na+, and K+ ranges from 0 to 20%;
    a cation ratio of a content of Zn2+ to a combined content of Mg2+, Ca2+, Sr2+, Ba2+, and Zn2+, Zn2+/(Mg2++Ca2++Sr2++Ba2++Zn2+), ranges from 0.30 to 1;
    a combined content of La3+, Gd3+, and Y3+ ranges from 0 to 20%;
    a combined content of Ti4+, Nb5+, Ta5+, and W6+ ranges from 10 to 20%;
    a cation ratio of a content of Ti4+ to a combined content of Ti4+ and Nb5+, Ti4+/(Ti4++Nb5+, ranges from 0 to 0.60;
    a cation ratio of a combined content of Ti4+ and W6+ to a combined content of Ti4+, Nb5+, Ta5+, and W6+,(Ti4++W6+)/(Ti4++Nb5++Ta5++W6+), ranges from 0 to 0.70;
    and comprising no Pb, with a refractive index nd ranging from 1.750 to 1.850, an Abbé number νd ranging from 29.0 to 40.0, and a glass transition temperature of less than 630° C.


The optical glass may have a partial dispersion ratio, Pg,F, of equal to or lower than 0.600, the partial dispersion ratio being denoted as (ng−nF)/(nF−nc) with a refractive index ng at a g line, nF at an F line, and nc at a c line.
The optical glass may have a deviation, ΔPg,F, of a partial dispersion ratio, Pg,F, of equal to or lower than 0.02, wherein the ΔPg,F is calculated by the following equation:

ΔPg,F=Pg,F+(0.0018×νd)−0.6483

and in the equation, Pg,F is a partial dispersion ratio denoted as (ng−nF)/(nF−nc) with a refractive index ng at a g line, nF at an F line, and nc at a c line, and νd is an Abbé number.

The optical glass may have a specific gravity of equal to or lower than 4.5.
The optical glass may have a liquidus temperature of lower than 1,100° C.
The wavelength λ70 of the optical glass may be equal to or lower than 450 nm. In this context, the λ70 is a wavelength at which light transmittance over a wavelength range of 280 to 700 nm is 70%.
The wavelength λ5 of the optical glass may be equal to or lower than 370 nm. In this context, the λ5 is a wavelength at which light transmittance over a wavelength range of 280 to 700 nm is 5%.
A further aspect of the present invention relates to a press-molding glass material, which is comprised of the above optical glass.
A still further aspect of the present invention relates to an optical element, which is comprised of the above optical glass.
A still further aspect of the present invention relates to a method of manufacturing an optical element, which comprises heating and precision press molding with a pressing mold the above press-molding glass material.
The present invention can provide optical glass with a high refractive index, a low glass transition temperature, and good manufacturing stability; a press-molding glass material and an optical element which are comprised of the optical glass; and a method of manufacturing an optical element employing the above press-molding glass material.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure.


DETAILED DESCRIPTION OF THE EMBODIMENTS
Unless otherwise stated, a reference to a compound or component includes the compound or component by itself, as well as in combination with other compounds or components, such as mixtures of compounds.
As used herein, the singular forms “a,” “an,” and “the” include the plural reference unless the context clearly dictates otherwise.
Except where otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not to be considered as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should be construed in light of the number of significant digits and ordinary rounding conventions.
Additionally, the recitation of numerical ranges within this specification is considered to be a disclosure of all numerical values and ranges within that range. For example, if a range is from about 1 to about 50, it is deemed to include, for example, 1, 7, 34, 46.1, 23.7, or any other value or range within the range.
The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and non-limiting to the remainder of the disclosure in any way whatsoever. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for fundamental understanding of the present invention; the description making apparent to those skilled in the art how several forms of the present invention may be embodied in practice.
Optical Glass
The optical glass of the present invention is oxide glass comprising, denoted as cation percentages:

    Si4+ 0 to 30%;
    B3+ 15 to 60%;
    Li+ 0 to 10%;
    Na+ 0 to 10%;
    K+ 0 to 15%;
    Mg2+ 0 to 20%;
    Ca2+ 0 to 15%;
    Sr2+ 0 to 20%;
    Ba2+ 0 to 20%;
    Zn2+ 13 to 40%;
    La3+ 0 to 11%;
    Gd3+ 0 to 10%;
    Y3+ 0 to 6%;
    Yb3+ 0 to 6%;
    Zr4+ 0 to 5%;
    Ti4+ 0 to 7%;
    Nb5+ 2 to 20%;
    Ta5+ 0 to 5%;
    W6+ 0 to 10%;
    Te4+ 0 to 5%;
    Ge4+ 0 to 5%;
    Bi3+ 0 to 5%; and
    Al3+ 0 to 5%;
    wherein a combined content of Si4+ and B3+ ranges from 35 to 65%;
    a cation ratio of a content of B3+ to the combined content of Si4+ and B3+, B3+/(Si4++B3+), ranges from 0.3 to 1;
    a combined content of Li+, Na+, and K+ ranges from 0 to 20%;
    a cation ratio of a content of Zn2+ to a combined content of Mg2+, Ca2+, Sr2+, Ba2+, and Zn2+, Zn2+/(Mg2++Ca2++Sr2++Ba2++Zn2+), ranges from 0.30 to 1;
    a combined content of La3+, Gd3+, and Y3+ ranges from 0 to 20%;
    a combined content of Ti4+, Nb5+, Ta5+, and W6+ ranges from 10 to 20%;
    a cation ratio of a content of Ti4+ to a combined content of Ti4+ and Nb5+, Ti4+/(Ti4++Nb5+, ranges from 0 to 0.60;
    a cation ratio of a combined content of Ti4+ and W6+ to a combined content of Ti4+, Nb5+, Ta5+, and W6+,(Ti4++W6+)/(Ti4++Nb5++Ta5++W6+), ranges from 0 to 0.70;
    and comprising no Pb, with a refractive index nd ranging from 1.750 to 1.850, an Abbé number νd ranging from 29.0 to 40.0, and a glass transition temperature of less than 630° C.


The optical glass of the present invention will be described in greater detail below. Hereinafter, unless specifically stated otherwise, the symbol “%” is to be interpreted as meaning “cation %”.
Glass Composition
The optical glass of the present invention is oxide glass. The chief anion component is O2−. The O2− content is desirably equal to or greater than 95 anion %, preferably equal to or greater than 98 anion %, more preferably equal to or greater than 99 anion %, and still more preferably, 100 anion %.
The cationic components will be described next.
Si4+ functions to increase the viscosity of the glass, enhance the stability of the glass, and increase the moldability of the glass. However, when more than 30% is incorporated, the refractive index drops, the glass transition temperature rises, and the precision press moldability and melt property deteriorate. Accordingly, the Si4+ content is specified as 0 to 30%.
The upper limit of the Si4+ content is desirably 20%, preferably 15%, more preferably 10%, still more preferably 9%, and yet still more preferably, 8%. The lower limit of the Si4+ content is desirably 1%, preferably 2.0%, more preferably 3%, still more preferably 4%, and yet still more preferably, 5%.
B3+ is a component that functions to enhance the stability of the glass, lower the liquidus temperature, and enhance glass moldability. However, when the content of B3+ is less than 15%, the refractive index rises, the stability of the glass decreases, and the liquidus temperature rises, compromising manufacturing stability. When more than 60% is incorporated, the refractive index drops. Accordingly, the B3+ content is specified as 15 to 60%.
The upper limit of the B3+ content is desirably 55%, preferably 50%, more preferably 48%, still more preferably 47%, and yet still more preferably, 45%. The lower limit of the B3+ content is desirably 20%, preferably 25%, more preferably 30%, still more preferably 35%, and yet still more preferably, 38%.
Both Si4+ and B3+ are glass network-forming components. When the combined content of Si4+ and B3+ is less than 35%, the refractive index rises but the Abbé number decreases, the stability of the glass diminishes, and the liquidus temperature rises. When the combined content of Si4+ and B3+ exceeds 65%, the refractive index drops and the Abbé number increases. Thus, the combined content of Si4+ and B3+ is specified as 35 to 65%.
The upper limit of the combined content of Si4+ and B3+ is desirably 60%, preferably 58%, more preferably 56%, still more preferably 54%, and yet still more preferably, 53%. The lower limit of the combined content of Si4+ and B3+ is desirably 38%, preferably 40%, more preferably 42%, still more preferably 44%, and yet still more preferably, 46%.
The combined content of Si4+ and B3+ is as stated above. However, when the cation ratio of the content of B3+ to the above combined content (B3+/(Si4++B3+)) is less than 0.3, the refractive index drops and the liquidus temperature rises. Thus, the cation ratio (B3+/(Si4++B3+)) is specified as 0.3 to 1.
To enhance the stability of the glass, the upper limit of the cation ratio (B3+/(Si4++B3+)) is desirably 0.99, preferably 0.97, more preferably 0.95, still more preferably 0.93, and yet still more preferably, 0.90. The lower limit of the cation ratio (B3+/(Si4++B3+)) is desirably 0.40, preferably 0.50, more preferably 0.60, still more preferably 0.70, and yet still more preferably, 0.80.
Li+ is a component that has the effects of greatly lowering the glass transition temperature and enhancing the melt property. However, when the content of Li+ exceeds 10%, the refractive index and glass stability decrease. Accordingly, the content of Li+ is specified as 0 to 10%. The Li+ content desirably falls within a range of 0 to 8%, preferably within a range of 0 to 6%, more preferably within a range of 0 to 4%, and still more preferably, within a range of 0 to 2%.
Na+ is also a component that has the effects of greatly lowering the glass transition temperature and enhancing the melt property. However, when the content of Na+ exceeds 10%, the refractive index and the glass stability decrease. Accordingly, the content of Na+ is specified as 0 to 10%. The content of Na+ desirably falls within a range of 0 to 8%, preferably within a range of 0 to 6%, more preferably within a range of 0 to 4%, and still more preferably, within a range of 0 to 2%.
K+ is also a component that has the effects of greatly lowering the glass transition temperature and enhancing the melt property. However, when the content of K+ exceeds 15%, the refractive index and the glass stability decrease. Accordingly, the content of K+ is specified as 0 to 15%. The content of K+ desirably falls within a range of 0 to 10%, preferably within a range of 0 to 8%, more preferably within a range of 0 to 6%, still more preferably with a range of 0 to 4%, and yet still more preferably, within a range of 0 to 2%.
The contents of Li+, Na+, and K+ are as stated above. However, when the combined content of Li+, Na+, and K+ exceeds 20%, the refractive index and glass stability drop. Accordingly, the combined content of Li+, Na+, and K+ is specified as 0 to 20%. The upper limit of the combined content of Li+, Na+, and K+ is desirably 15%, preferably 10%, more preferably 6%, still more preferably 4%, and yet still more preferably, 2%. The lower limit of the combined content of Li+, Na+, and K+ is desirably 0.1%, preferably 0.5%, and more preferably, 1.0%.
Mg2+ is a component serving to enhance the melt property and lower the specific gravity. However, when the content of Mg2+ exceeds 20%, the Abbé number increases, the glass stability decreases, and the liquidus temperature rises. Accordingly, the content of Mg2+ is specified as 0 to 20%. The Mg2+ content desirably falls within a range of 0 to 15%, preferably within a range of 0 to 15%, more preferably within a range of 0 to 10%, still more preferably within a range of 0 to 8%, yet still more preferably within a range of 0 to 6%, and further preferably, no Mg2+ is incorporated.
Ca+ is a component that functions to enhance the melt property and lower the specific gravity of the glass. However, when the quantity of Ca exceeds 15%, the Abbé number increases, the stability of the glass decreases, and the liquidus temperature rises. Accordingly, the Ca2+ content is specified as 0 to 15%. The upper limit of the Ca2+ content is desirably 12%, preferably 10%, more preferably 8%, still more preferably 6%, and yet still more preferably, 4%. The lower limit of the Ca2+ content is desirably 0.5%, preferably 1%, and more preferably, 2%.
Sr2+ is a component that functions to enhance the melt property and increase the stability of the glass. However, when the content of Sr2 exceeds 20%, the Abbé number increases and the stability of the glass decreases. Accordingly, the content of Sr2+ is specified as 0 to 20%. The content of Sr2+ desirably falls within a range of 0 to 15%, preferably within a range of 0 to 10%, more preferably within a range of 0 to 8%, still more preferably within a range of 0 to 6%, and further preferably, no Sr2+ is incorporated.
Ba2+ is a component that functions to enhance the melt property and increase the stability of the glass. However, when the content of Ba2+ exceeds 20%, the Abbé number increases, the stability of the glass decreases, and the specific gravity increases. Accordingly, the content of Ba2+ is specified as 0 to 20%. The upper limit of the Ba2+ content is desirably 15%, preferably 10%, more preferably 8%, still more preferably 6%, and yet still more preferably, 5%. The lower limit of the Ba2+ content is desirably 0.5%, preferably 1%, more preferably 2%, and still more preferably, 3%.
Zn2+ is a component that functions to enhance the melt property and lower the glass transition temperature while maintaining a high refractive index. However, when the Zn2+ content is less than 13%, the glass transition temperature rises. Further, since the refractive index drops and the Abbé number increases, it becomes necessary to incorporate large quantities of Ti4+, Nb5+, Ta5+, and W6+, which function to raise the refractive index and lower the Abbé number. Although Ti4+, Nb5+, Ta5+, and W6+ are components that raise the refractive in index, they also increase the ΔPg, F value, which is an index of the partial dispersion characteristic, described further below, and compromise precision press moldability. Accordingly, when the Zn content is less than 13%, the ΔPg, F value indirectly rises and precision press moldability deteriorates. Additionally, when the content of Zn2+ exceeds 40%, the stability of the glass deteriorates. Accordingly, the content of Zn2+ is specified as 13 to 40%. The upper limit of the Zn2+ content is desirably 35%, preferably 30%, more preferably 28%, still more preferably 25%, and yet still more preferably, 23%. The lower limit of the Zn2+ content is desirably 14%, preferably 15%, more preferably 16%, and still more preferably, 18%.
The quantities of Mg2+, Ca2+, Sr2+, Ba2+, and Zn2+ are as set forth above. However, when the cation ratio of the quantity of Zn2+ to the combined content of Mg2+, Ca2+, Sr2+, Ba2+, and Zn2+ (Zn2+/(Mg2++Ca2++Sr2++Ba2++Zn2+)) is less than 0.30, the Abbé number increases, the glass stability decreases, and the liquidus temperature rises. Accordingly, the cation ratio of (Zn2+/(Mg2+Ca2+Sr2+Ba2+Zn2+)) is specified as 0.30 to 1. The upper limit of the cation ratio of (Zn2+/(Mg2++Ca2++Sr2++Ba2++Zn2+)) is desirably 0.98, preferably 0.95, more preferably 0.90, still more preferably 0.85, and yet still more preferably, 0.80. To enhance the stability of the glass and lower the liquidus temperature, the lower limit of the cation ratio of (Zn2+/(Mg2++Ca2++Sr2++Ba2++Zn2+)) is desirably 0.40, preferably 0.50, more preferably 0.60, still more preferably, 0.65, and yet still more preferably, 0.70.
La3+ is a component that increases the stability of the glass and raises the refractive index without increasing the ΔP,F value. However, then the content of La3+ exceeds 11%, the refractive index and Abbé number rise, the stability of the glass drops, and the liquidus temperature, specific gravity, and glass transition temperature rise. Accordingly, the content of La3+ is specified as 0 to 11%. The upper limit of La3+ is desirably 10%, preferably 9%, more preferably 8%, still more preferably 7%, and yet still more preferably, 6%. The lower limit of the La3+ content is desirably 0.5%, preferably 1%, more preferably 2%, and still more preferably, 3%.
Gd3+ is a component that raises the refractive index without increasing the ΔPg,F value. However, when the content of Gd3+ exceeds 10%, the refractive index and the Abbé number increase, the stability of the glass decreases, and the liquidus temperature, specific gravity, and glass transition temperature rise. Accordingly, the Gd3+ content is specified as 0 to 10%. The Gd3+ content desirably falls within a range of 0 to 8%, preferably within a range of 0 to 6%, more preferably within a range of 0 to 4%, still more preferably within a range of 0 to 2%, and yet still more preferably, no Gd3+ is incorporated.
Y3+ is a component that raises the refractive index without increasing the ΔPg,F value. However, when the content of Y3+ exceeds 6%, the refractive index and the Abbé number increase, the stability of the glass decreases, and the liquidus temperature, specific gravity, and glass transition temperature rise. Accordingly, the Y3+ content is specified as 0 to 6%. The Y3+ content desirably falls within a range of 0 to 4%, preferably within a range of 0 to 3%, and more preferably, no Y3+ is incorporated.
The La3+, Gd3+, and Y3+ content are as set forth above. However, to achieve a desired refractive index and Abbé number, maintain the stability of the glass, suppress the increase of the liquidus temperature, the specific gravity, and the glass transition temperature, the combined content of La3+, Gd3+, and Y3+ is specified as 0 to 20%. The upper limit of the combined content of La3+, Gd3+, and Y3+ is desirably 12%, preferably 10%, more preferably 9%, still more preferably 8%, yet still more preferably 7%, and even more preferably, 6%. The lower limit of the combined content of La3+, Gd3+, and Y3+ is desirably 0.5%, preferably 1%, more preferably 2%, and still more preferably, 3%.
Yb3+ is a component that raises the refractive index without increasing the ΔPg,F value. However, when the content of Yb3+ exceeds 6%, the refractive index and the Abbé number increase, the stability of the glass decreases, and the liquidus temperature, specific gravity, and glass transition temperature rise. Accordingly, the Yb3+ content is specified as 0 to 6%. The content of Yb3+ desirably falls within a range of 0 to 4%, preferably within a range of 0 to 3%, and more preferably, no Yb3+ is incorporated.
Zr4+ is a component that functions to raise the refractive index. However, when the Zr4+ content exceeds 5%, the stability of the glass drops and the liquidus temperature rises. Accordingly, the Zr4+ content is specified as 0 to 5%. The upper limit of Zr4+ is desirably 4%, preferably 3%, more preferably 2%, and still more preferably, 1%. The lower limit of the Zr4+ content is desirably 0.5%.
Ti4+ is a component that raises the refractive index and lowers the Abbé number. However, when the content of Ti4+ exceeds 7%, the refractive index rises, the Abbé number decreases, the ΔPg,F value increase, the stability of the glass decreases, and precision press moldability deteriorates. The glass also develops coloration. Accordingly, the Ti4+ content is specified as 0 to 7%. The upper limit of Ti4+ is desirably 6%, preferably 5%, and more preferably, 4%. The lower limit of the Ti4+ content is desirably 0.5%, preferably 1%, and more preferably, 2%.
Nb5+ is a component that functions to raise the refractive index and lower the Abbé number. Its effect on lowering the ΔP,F value is more than that of Ti4+ and W6+. However, when the content of Nb5+ is less than 2%, it becomes difficult to achieve desired optical characteristics, the ΔP,F value increases, the stability of the glass decreases, and the liquidus temperature rises. Additionally, when the content of Nb5+ exceeds 20%, the refractive index rises, the Abbé number decreases, the stability of the glass diminishes, and the liquidus temperature rises. Accordingly, the Nb5+ content is specified as 2 to 20%. The upper limit of Nb5+ is desirably 18%, preferably 16%, more preferably 14%, still more preferably 13%, and yet still more preferably, 12%. The lower limit of the Nb5+ content is desirably 4%, preferably 5%, more preferably 6%, still more preferably 8%, yet still more preferably 9%, and even more preferably, 10%.
Ta5+ is a component that raises the refractive index, exhibiting lower dispersibility than other components that similarly raise the refractive index in the form of Ti4+, Nb5+, and W6+. It has a greater reducing effect on the ΔP,F value than Ti4+ and W6+. However, when the content of Ta5+ exceeds 5%, the refractive index rises, the stability of the glass decreases, and the liquidus temperature and the specific gravity increase. Accordingly, the Ta5+ content is specified as 0 to 5%. The Ta5+ content desirably falls within a range of 0 to 4%, preferably within a range of 0 to 3%, and more preferably, no Ta5+ is incorporated.
W6+ is a component that raises the refractive index and lowers the Abbé number. However, when the W6+ content exceeds 10%, the refractive index, the ΔP,F value, and the specific gravity increase, the Abbé number decreases, the stability of the glass decreases, and precision press moldability deteriorates. The glass also develops coloration. Accordingly, the W6+ content is specified as 0 to 10%. The W6+ content desirably falls within a range of 0 to 8%, preferably within a range of 0 to 6%, more preferably within a range of 0 to 4%, still more preferably within a range of 0 to 3%, and yet still more preferably, no W6+ is incorporated.
As set forth above, Ti4+, Nb5+, Ta5+, and W6+ are components that raise the refractive index and lower the Abbé number. However, when the combined content of Ti4+, Nb5+, Ta5+, and W6+ is less than 10%, it becomes difficult to produce a glass satisfying the desired optical characteristics. When the combined content exceeds 20%, the refractive index increases, the Abbé number decreases, the ΔP,F value increases, the stability of the glass decreases, and the liquidus temperature rises. The glass also develops coloration. Accordingly, the combined content of Ti4+, Nb5+, Ta5+, and W6+ is specified as 10 to 20%. The upper limit of the combined content of Ti4+, Nb5+, Ta5+, and W6+ is desirably 19%, preferably 18%, more preferably 17%, still more preferably 16%, and yet still more preferably, 15%. The lower limit of the combined content of Ti4+, Nb5+, Ta5+, and W6+ is desirably 11%, preferably 12%.
When the cation ratio of the content of Ti4+ to the combined content of Ti4+ and Nb5+(Ti4+/(Ti4++Nb5+)) exceeds 0.60, the stability of the glass decreases, the liquidus temperature rises, the ΔP,F value increases, and precision press moldability decreases. Accordingly, the cation ratio (Ti4+/(Ti4++Nb5+)) is specified as 0 to 0.60. The upper limit of the cation ratio (Ti4+/(Ti4++Nb5+)) is desirably 0.55, preferably 0.51, more preferably 0.45, still more preferably 0.40, yet still more preferably 0.30, and even more preferably, equal to or lower than 0.20. To maintain the stability of the glass and inhibit a rise in the liquidus temperature, the lower limit of the cation ratio (Ti4+/(Ti4++Nb5+)) is desirably 0.02, preferably 0.05, still more preferably 0.08, yet still more preferably 0.10, and even more preferably, 0.12.
When the cation ratio of the combined content of Ti4+ and W6+ to the combined content of Ti4+, Nb5+, Ta5+, and W6+ ((Ti4++W6+)/(Ti4++Nb5++Ta5++W6+)) exceeds 0.70, the ΔP,F value increases, the stability of the glass diminishes, the liquidus temperature rises, the glass develops coloration, and precision press moldability decreases. Accordingly, the cation ratio (Ti4+W6+)/(Ti++Nb5++Ta5++W6+) is specified as 0 to 0.70. The upper limit of the cation ratio of ((Ti4++W6+)/(Ti4++Nb5++Ta5++W6+)) is desirably 0.60, preferably 0.50, more preferably 0.40, still more preferably 0.30, and yet still more preferably, 0.20. To maintain the stability of the glass and inhibit a rise in the liquidus temperature, the lower limit of the cation ratio of ((Ti4++W6+)/(Ti4++Nb5++Ta5++W6+)) is desirably 0.02, preferably 0.05, more preferably 0.08, still more preferably 0.10, and yet still more preferably, 0.12.
Te4+ is a component that functions to raise the refractive index and increase the stability of the glass. However, when the content of Te4+ exceeds 5%, the stability of the glass diminishes. Accordingly, the Te4+ content is specified as 0 to 5%. The content of Te4+ desirably falls within a range of 0 to 4%, preferably within a range of 0 to 3%. From the perspective of concern for the environment, it is desirable to reduce the quantity of Te4+ employed, and preferable to employ no Te4+.
Ge4+ is a component that functions to raise the refractive index and enhance the stability of the glass. However, when the content thereof exceeds 5%, the stability of the glass diminishes. Accordingly, the content of Ge4+ is specified as 0 to 5%. Among substances employed as glass components, Ge4+ is one of the more expensive. Thus, from the perspective of preventing a rise in manufacturing costs, the quantity employed is desirably kept low. Accordingly, the range of the Ge4+ content is desirably 0 to 4%, preferably 0 to 3%, and more preferably, no Ge4+ is incorporated.
Bi3+ is a component the functions to raise the refractive index and enhance the stability of the glass. However, when the content thereof exceeds 5%, the stability of the glass decreases and the glass exhibits a tendency to develop coloration. Precision press moldability also deteriorates. Accordingly, the Bi3+ content is specified as 0 to 5%. The range of the Bi3+ content desirably falls within a range of 0 to 4%, preferably within a range of 0 to 3%, and more preferably, no Bi3+ is incorporated.
Al3+ is a component that functions to enhance glass stability and chemical durability. However, when more than 5% is incorporated, the refractive index drops and the stability of the glass tends to diminish. Accordingly, the Al3+ content is specified as 0 to 5%. The content of Al3+ desirably falls within a range of 0 to 4%, preferably within a range of 0 to 3%, and more preferably, no Al3+ is incorporated.
Clarifying agents in the form of Sb, Sn, and the like can be added to the optical glass of the present invention in addition to the components set forth above. In that case, the quantity of Sb added, as converted to Sb2O3 as a ratio relative to the total of the other components excluding the clarifying agents, is desirably 0 to 1 weight %, preferably 0 to 0.5 weight %, and the quantity of Sn added, as converted to SnO2 as a ratio relative to the total of the other components excluding the clarifying agents, is desirably 0 to 1 weight %, preferably 0 to 0.5 weight %.
The glass of the present invention is optical glass and thus little coloration is desirable. Accordingly, it is desirable not to incorporate V, Cr, Mn, Cu, Ni, Fe, Pr, Nd, Eu, Tb, Ho, and Er, which impart coloration. To reduce the influence on the environment, the optical glass of the present invention contains no Pb. To further reduce the influence on the environment, it is desirable not to incorporate Cd, Th, U, Tl, Se, and As.
Ga3+, Lu3+, In3+, and He+ can be incorporated in small quantities. However, these components do not produce significant effects and are all expensive. Thus, the content of each is desirably kept to within a range of 0 to 2%, preferably within a range of 0 to 1%, more preferably within a range of 0 to less than 0.5%, still more preferably to within a range of 0 to less than 0.1%, and yet still more preferably, none is incorporated to keep down the cost of producing the glass.
In the present invention, the phrase “none is incorporated” or “not contained” means that none is added as a glass component, but does not exclude levels of impurities and the like that are unavoidably mixed into the glass.
Refractive Index and Abbé Number
The refractive index nd of the optical glass of the present invention is 1.750 to 1.850. By having a refractive index of equal to or higher than 1.750, it becomes possible to use the optical glass of the present invention to provide the optical elements that constitute highly functional and compact optical systems. However, as the refractive index of a high refractive index glass rises, the liquidus temperature and glass transition temperature tend to rise and manufacturing suitability decreases. Thus, the upper limit of the refractive index nd in the present invention is specified as 1.850 to maintain the moldability and manufacturing stability of the glass. Having a refractive index nd of equal to or lower than 1.850 is also effective in terms of inhibiting an increase in the specific gravity.
The upper limit of the refractive index nd is desirably 1.840, preferably 1.830, more preferably 1.825, still more preferably 1.820, yet still more preferably 1.815, and even more preferably, 1.810.
The lower limit of the refractive index nd is desirably 1.760, preferably 1.770, more preferably 1.780, still more preferably 1.790, yet still more preferably 1.795, and even more preferably, 1.800.
The optical glass of the present invention has an Abbé number νd falling within a range of 29.0 to 40.0 in addition to a refractive index falling within the range set forth above. Keeping the Abbé number νd within the above range makes it possible to achieve a good chromatic aberration correction function by combination with optical elements comprised of various optical glasses.
The upper limit of the Abbé number νd is desirably 38.0, preferably 37.0, more preferably 36.0, still more preferably 35.0, yet still more preferably 34.5, and even more preferably, 34.0.
The lower limit of the Abbé number νd is 30.0, preferably 31.0, more preferably 31.5, still more preferably 32.0, yet still more preferably 32.5, and even more preferably, 33.0.
Glass Transition Temperature
The glass transition temperature of the optical glass of the present invention is less than 630° C. The optical glass of the present invention, with a glass transition temperature of less than 630° C., makes it possible to inhibit a rise in the temperature of the glass and the temperature of pressing mold during press molding, yielding good press moldability.
The optical glass of the present invention comprises an essential component in the form of Nb5+ and optional components in the form of Ti4+, Ta5+, and W6+. During press molding, these components react with the molding surface of the pressing mold, compromise the quality of the surface of the press molded product, and aggravate deterioration of the molding surface. Such phenomena should be avoided, particularly in precision press molding. This reaction is greatly affected by the temperature of the glass and the pressing mold during press molding, and can thus be inhibited by lowering the press molding temperature. Accordingly, the optical glass of the present invention, in which a rise in the press molding temperature can be inhibited by a glass transition temperature of less than 630° C., is suited to precision press molding. The optical glass of the present invention, in which the glass transition temperature is less than 630° C., can also lend itself to the use of a lower annealing temperature, thereby inhibiting deterioration and wear and tear on the annealing furnace.
The upper limit of the glass transition temperature of the optical glass of the present invention is desirably 610° C., preferably 600° C., more preferably 590° C., still more preferably 580° C., and yet still more preferably, 570° C. When the glass transition temperature is made excessively low, the refractive index drops and there is a tendency for the glass to undergo deterioration in stability. Thus, the glass transition temperature is desirably equal to or higher than 500° C., preferably equal to or higher than 520° C., more preferably equal to or higher than 530° C., still more preferably equal to or higher than 540° C., and yet still more preferably, equal to or higher than 550° C.
Partial Dispersion
In image pickup optical systems, projection optical systems, and the like, combining a lens comprised of the optical glass of the present invention with a lens comprised of a glass of low dispersion is an effective way to achieve high-order chromatic aberration correction. However, many glasses on the low dispersion side have high partial dispersion ratios. Thus, when conducting higher-order chromatic aberration correction, the optical glass of the present invention that is combined with lenses made of low dispersion glasses is desirable to have a low partial dispersion ratio.
The partial dispersion ratio Pg,F is denoted using the various refractive indexes ng, nF, nc at the g line, F line, and c line as (ng−nF)/(nF−nc).
To provide a glass that is suited to high-order chromatic aberration correction, the partial dispersion ratio Pg,F in the optical glass of the present invention is desirably equal to or lower than 0.600, preferably equal to or lower than 0.598, more preferably equal to or lower than 0.596, still more preferably equal to or lower than 0.594, yet still more preferably equal to or lower than 0.592, and even more preferably, equal to or lower than 0.590.
However, an excessively low partial dispersion ratio Pg,F tends to cause other characteristics to deviate from their desired ranges. Thus, the partial dispersion ratio Pg,F is desirably equal to or higher than 0.570. The lower limit of the partial dispersion ratio Pg,F is preferably 0.575, more preferably 0.580, still more preferably 0.582, yet still more preferably 0.584, and even more preferably, 0.586.
In a plot of the partial dispersion ratio Pg,F against the Abbé number νd, when the partial dispersion ratio on the normal line that is the reference for a normal partial dispersion glass is denoted as Pg,F(0), Pg,F(0) can be denoted by the following equation using the Abbé number νd:

Pg,F(0)=0.6483−(0.0018×νd)

ΔPg,F is the deviation of the partial dispersion ratio Pg,F from the above normal line and is given by the following equation:




  
    
      
        
          Δ
          ⁢
          
            
          
          ⁢
          Pg
        
        ,
        
          F
          =
          Pg
        
        ,
        
          F
          -
          Pg
        
        ,
        
          F
          ⁡
          
            (
            0
            )
          
        
      
    
  
  
    
      
        
          =
          Pg
        
        ,
        
          F
          +
          
            (
            
              0.0018
              ×
              vd
            
            )
          
          -
          0.6483
        
      
    
  




In a desirable form of the optical glass of the present invention, the deviation ΔPg,F is equal to or lower than 0.02, making it suitable as an optical element material for use in high-order correction of chromatic aberration. In the present invention, ΔPg,F desirably falls within a range of equal to or lower than 0.015, preferably within a range of equal to or lower than 0.01, more preferably within a range of equal to or lower than 0.008, still more preferably within a range of equal to or lower than 0.006, and yet still more preferably, within a range of equal to or lower than 0.005.
Specific Gravity
The optical glass of the present invention is a high refractive index glass with a refractive index nd falling within a range of 1.750 to 1.850. In general, the specific gravity of a glass tends to increase with the increase of the refractive index. However, an increase in specific gravity is undesirable because it invites an increase in the weight of optical elements. In this regard, by having the, glass composition set forth above, the optical glass of the present invention can achieve a specific gravity of equal to or lower than 4.5 in a high refractive index glass. In the optical glass of the present invention, the upper limit of the specific gravity is desirably 4.4, preferably 4.3, more preferably 4.2, and still more preferably, 4.1. Conversely, when the specific gravity is made excessively low, the stability of the glass decreases and there is a tendency for the liquidus temperature to rise. Thus, the specific gravity is desirably equal to or higher than 3.5, preferably equal to or higher than 3.6, more preferably equal to or higher than 3.7, still more preferably equal to or higher than 3.8, and yet still more preferably, equal to or higher than 3.9.
Liquidus Temperature
By having the glass composition set forth above, the optical glass of the present invention can exhibit a liquidus temperature of less than 1,100° C. Since rises in the melting temperature and the temperature at which the glass melt flows out can be inhibited, it becomes possible to achieve a high refractive index as well as both high homogeneity and the suppression of coloration.
In the present invention, the liquidus temperature is desirably equal to or lower than 1,090° C., preferably equal to or lower than 1,070° C., more preferably equal to or lower than 1,050° C., still more preferably equal to or lower than 1,040° C., and yet still more preferably, equal to or lower than 1,030° C.
In addition, an excessively low liquidus temperature makes it difficult to achieve the desired refractive index and Abbé number. Further, the value of the partial dispersion ratio Pg,F rises. Accordingly, the liquidus temperature is desirably equal to or higher than 950° C., preferably equal to or higher than 970° C., more preferably equal to or higher than 980° C., still more preferably equal to or higher than 990° C., and yet still more preferably, equal to or higher than 1,000° C.
Coloration (λ70, λ5)
By having the glass composition set forth above, the optical glass of the present invention makes it possible to reduce or inhibit coloration, thereby achieving high optical transparency over a broad range of the visible light region. The wavelength λ70 at which light transmittance over the wavelength range of 280 to 700 nm is 70% and the wavelength λ5 at which this same light transmittance is 5% can be employed as the indexes of coloration of an optical glass. In this context, the light transmittance is the spectral transmittance obtained by directing light in a direction perpendicular to the polished surfaces of a glass sample having mutually parallel surfaces that have been polished to a thickness of 10.0±0.1 mm. That is, denoting the intensity of the light entering the sample as Iin and the intensity of the light passing through the sample as Tout, it is given by Iout/Iin. The spectral transmittance includes losses due to reflection of light off the sample surface. The above polishing means smoothing to a state of adequately low surface roughness relative to the wavelength of the measurement wavelength region. For λ70, the optical glass of the present invention can exhibit a λ70 of equal to or lower than 450 nm. The λ70 of the optical glass of the present invention is desirably equal to or lower than 440 nm, preferably equal to or lower than 430 nm, more preferably equal to or lower than 420 nm, still more preferably equal to or lower than 410 nm, and yet still more preferably, equal to or lower than 400 nm. However, an excessively low λ70 makes it difficult to satisfy the desired optical characteristics, the stability of the glass decreases, and the liquidus temperature sometimes tends to rise. The λ70 is desirably equal to or higher than 350 nm, preferably equal to or higher than 360 nm, more preferably equal to or higher than 370 nm, still more preferably equal to or higher than 380 nm, and yet still more preferably, equal to or higher than 390 nm.
The λ5 of the optical glass of the present invention desirably falls within a range of equal to or lower than 370 nm, preferably within a range of equal to or lower than 365 nm, more preferably within a range of equal to or lower than 360 nm, still more preferably within a range of equal to or lower than 355 nm, and yet still more preferably within a range of equal to or lower than 350 nm.
As set forth above, the optical glass of the present invention can exhibit good optical transparency in a high refractive index glass, and is suitable as a material for optical elements constituting image pickup optical systems and projection optical systems.
Method of Manufacturing Optical Glass
The optical glass of the present invention can be manufactured by the melt method. In the melt method, stating materials in the form of oxides and various salts are weighed out so as to yield glass of desired composition and optical characteristics, and mixed to obtain a mixed starting material. The mixed starting material is heated and melted. The melt obtained is clarified, homogenized, and made to flow out to obtain formed articles comprised of homogeneous glass. Alternatively, the mixed starting material can be charged to a crucible and roughly melted to vitrify the glass, from which cullets are prepared. The cullet starting materials are then blended so as to obtain an optical glass of desired optical characteristics, heated, and melted. The melt obtained can then be clarified, homogenized, and made to flow out to obtain formed articles comprised of homogenous glass.
Press-Molding Glass Material
The press-molding glass material, that is a glass material for press molding, of the present invention (referred to as the “glass material” hereinafter) is comprised of the above optical glass of the present invention.
The glass material can be prepared by first preparing formed glass articles by heating, melting, and forming glass starting materials that have been blended to yield the optical glass of the present invention. The formed glass articles are then processed to prepare a glass material corresponding to the quantity of one press molded article.
As an example, the glass melt is cast into a mold, molded into plate or block form, and annealed. It can then be mechanically processed—that is, cut, ground, and polished—to obtain a glass material.
Alternatively, the glass melt can be made to flow out of pipe, a gob of glass melt corresponding to the quantity of one press molded article can be separated from the tip of the glass melt flow, and the glass melt gob can be molded into a glass material on a forming mold. In that case, it is possible to mold the glass gob into a glass material while being floated with blown air on the mold, or to press mold the glass melt gob on the mold and then cooled while being floated with blown air to prepare a glass material.
Optical Element and Method of Manufacturing the Same
The optical element of the present invention is comprised of the optical glass of the present invention.
Specific examples of the optical element of the present invention are lenses such as aspherical lenses, spherical lenses, lenses one surface of which is a flat surface and the other surface of which is a concave, lenses one surface of which is a flat surface and the other surface of which is a convex, lenses both surface of which are a concave, lenses both surface of which are a convex, convex meniscus lenses, and concave meniscus lenses; various lenses such as microlenses, lens arrays, and lenses with diffraction gratings; prisms; and prisms with lens functions. Antireflective films, wavelength-selective partially reflective films, and the like can be provided as needed on lens surfaces.
The optical element of the present invention can achieve both a high refractive index and a low partial dispersion ratio. Thus, by combination with optical elements comprised of other glasses, good chromatic aberration correction can be achieved. Further, since the optical glass of the present invention can achieve both a high refractive index and a low specific gravity, the weight reduction of optical elements can be achieved with the optical glass of the present invention. The optical element of the present invention is suited to the image pickup optical systems of various cameras, such as digital still cameras, digital video cameras, monitor cameras, and vehicle-mounted cameras; and optical elements directing light for the reading and writing of data on optical recording media such as DVDs and CDs. For example, it is suited to optical pickup lenses and collimator lenses. It is also suitable as an optical element for optical communication.
The method of manufacturing an optical element of the present invention comprises heating the press-molding glass material of the present invention and precision press molding it to obtain an optical element. In this context, the term “precision press molding”, also widely known as mold optics molding, refers to a method of forming the optically functional surface of an optical element by transferring the molding surface of a pressing mold. The term “optically functional surface” refers to a surface on an optical element that bends, reflects, diffracts, admits, or emits light that is being controlled. An optically functional surface corresponds to a lens surface in the case of a lens. The use of a glass material comprised of the optical glass of the present invention having good precision press moldability permits the manufacturing with high productivity of high-quality optical elements by the application of known precision press molding methods.
The optical element of the present invention can also be fabricated by methods other than precision press molding. For example, the glass material can be melted by heating and press molded to obtain an optical element blank having the shape of an optical element with grinding and polishing allowances. The optical element blank can then be ground and polished to fabricate an optical element. Alternatively, a molded glass article comprised of the optical glass of the present invention can be ground and polished to obtain an optical element.
EXAMPLES
The present invention will be described in greater detail below through Examples.
1. Preparation of Optical Glass
Starting materials for incorporating various components, in the form of corresponding oxides, carbonates, sulfates, nitrates, hydroxides, and the like, were weighed out to yield the glass composition shown in Table 1 and thoroughly mixed to obtain a mixed starting material. This was charged to a platinum crucible, heated for 1 to 3 hours at 1,200 to 1,350° C., melted, clarified, and homogenized. The glass melt obtained was made to flow into a carbon mold, cooled to the glass transition temperature, and then immediately placed in an annealing furnace. After annealing for about 1 hour to within the glass transition temperature range, the glass was cooled to room temperature within the furnace to obtain optical glass. Observation by a microscope revealed that no crystals had precipitated in the optical glass obtained. Table 1 gives the characteristics of the optical glasses thus obtained.
































TABLE 1







No.

Si4+
B3+
Li+
Na+
K+
Mg2+
Ca2+
Sr2+
Ba2+
Zn2+
La3+
Gd3+
Y3+
Yb3+
Zr4+
Ti4+
Nb5+
Ta5+
W6+
Ta4+
Ga4+
Bi3+
Al3+
Total





1
cationic %
20.33
25.59
1.48
0.00
0.00
0.00
9.09
0.00
3.81
21.76
4.10
0.00
0.00
0.00
0.93
4.56
8.35
0.00
0.00
0.00
0.00
0.00
0.00
100.00


2
cationic %
12.22
33.70
1.48
0.00
0.00
0.00
9.09
0.00
3.81
21.76
4.10
0.00
0.00
0.00
0.93
4.56
8.35
0.00
0.00
0.00
0.00
0.00
0.00
100.00


3
cationic %
6.22
39.70
1.48
0.00
0.00
0.00
9.09
0.00
3.81
21.76
4.10
0.00
0.00
0.00
0.93
4.56
8.35
0.00
0.00
0.00
0.00
0.00
0.00
100.00


4
cationic %
6.42
40.94
1.52
0.00
0.00
0.00
9.37
0.00
3.92
22.43
4.23
0.00
0.00
0.00
0.96
1.61
8.60
0.00
0.00
0.00
0.00
0.00
0.00
100.00


5
cationic %
6.22
39.71
1.48
0.00
0.00
0.00
9.09
0.00
0.00
25.56
4.10
0.00
0.00
0.00
0.93
4.58
8.35
0.00
0.00
0.00
0.00
0.00
0.00
100.00


6
cationic %
6.49
41.41
1.54
0.00
0.00
0.00
9.48
0.00
1.88
24.77
0.00
0.00
0.00
0.00
0.97
4.76
8.70
0.00
0.00
0.00
0.00
0.00
0.00
100.00


7
cationic %
6.22
43.51
1.48
0.00
0.00
0.00
9.09
0.00
0.00
21.76
4.10
0.00
0.00
0.00
0.93
4.56
8.35
0.00
0.00
0.00
0.00
0.00
0.00
100.00


8
cationic %
6.22
43.70
1.48
0.00
0.00
0.00
5.09
0.00
3.81
21.76
4.10
0.00
0.00
0.00
0.93
1.56
11.35
0.00
0.00
0.00
0.00
0.00
0.00
100.00


9
cationic %
6.22
43.70
1.48
0.00
0.00
0.00
5.09
0.00
3.81
21.76
4.10
0.00
0.00
0.00
0.93
6.56
6.35
0.00
0.00
0.00
0.00
0.00
0.00
100.00


10
cationic %
7.72
43.70
1.48
0.00
0.00
0.00
2.59
0.00
3.81
21.76
4.10
0.00
0.00
0.00
0.93
2.56
11.35
0.00
0.00
0.00
0.00
0.00
0.00
100.00


11
cationic %
7.72
43.70
0.00
0.00
1.48
0.00
2.59
0.00
3.81
21.76
4.10
0.00
0.00
0.00
0.93
2.56
11.35
0.00
0.00
0.00
0.00
0.00
0.00
100.00


12
cationic %
7.72
43.70
0.00
1.48
0.00
0.00
2.59
0.00
3.81
21.76
4.10
0.00
0.00
0.00
0.93
2.56
11.35
0.00
0.00
0.00
0.00
0.00
0.00
100.00


13
cationic %
7.50
42.45
0.46
0.00
0.97
0.00
2.52
0.00
3.69
21.12
3.98
0.00
0.00
0.00
0.90
2.49
11.01
0.00
2.91
0.00
0.00
0.00
0.00
100.00


14
cationic %
7.50
42.44
0.46
0.00
0.97
0.00
2.52
0.00
3.69
21.12
3.98
0.00
0.00
0.00
0.90
2.49
13.93
0.00
0.00
0.00
0.00
0.00
0.00
100.00


15
cationic %
7.50
42.45
0.46
0.00
0.97
0.00
2.52
0.00
3.69
21.12
3.98
0.00
0.00
0.00
0.90
2.49
11.01
2.91
0.00
0.00
0.00
0.00
0.00
100.00


16
cationic %
7.80
44.11
0.48
0.00
1.01
0.00
2.52
0.00
3.84
21.96
4.14
0.00
0.00
0.00
0.00
2.59
11.45
0.00
0.00
0.00
0.00
0.00
0.00
100.00


17
cationic %
7.57
42.86
0.47
0.00
0.98
0.00
2.54
0.00
3.73
21.33
4.02
0.00
0.00
0.00
2.87
2.51
11.12
0.00
0.00
0.00
0.00
0.00
0.00
100.00


18
cationic %
7.50
42.45
0.46
0.00
0.97
0.00
2.52
0.00
3.69
21.12
3.98
2.91
0.00
0.00
0.90
2.49
11.01
0.00
0.00
0.00
0.00
0.00
0.00
100.00


19
cationic %
7.29
41.22
0.45
0.00
0.94
0.00
2.45
0.00
3.59
20.53
3.87
5.66
0.00
0.00
0.88
2.42
10.70
0.00
0.00
0.00
0.00
0.00
0.00
100.00


20
cationic %
7.50
42.45
0.46
0.00
0.97
0.00
2.52
0.00
3.69
21.12
3.98
0.00
2.91
0.00
0.90
2.49
11.01
0.00
0.00
0.00
0.00
0.00
0.00
100.00


21
cationic %
7.50
42.44
0.46
0.00
0.97
0.00
2.52
0.00
3.69
21.12
6.90
0.00
0.00
0.00
0.90
2.49
11.01
0.00
0.00
0.00
0.00
0.00
0.00
100.00


22
cationic %
7.29
41.22
0.45
0.00
0.94
0.00
2.45
0.00
3.59
20.53
9.53
0.00
0.00
0.00
0.88
2.42
10.70
0.00
0.00
0.00
0.00
0.00
0.00
100.00


23
cationic %
7.72
43.70
0.48
0.00
1.00
0.00
2.58
0.00
3.81
21.76
2.10
2.00
0.00
0.00
0.93
2.56
11.35
0.00
0.00
0.00
0.00
0.00
0.00
100.00


24
cationic %
7.72
43.70
0.48
0.00
1.00
0.00
2.59
0.00
3.81
21.76
2.10
0.00
2.00
0.00
0.93
2.56
11.35
0.00
0.00
0.00
0.00
0.00
0.00
100.00


25
cationic %
7.96
45.06
0.49
0.00
1.03
0.00
2.67
0.00
3.92
19.34
4.23
0.00
0.00
0.00
0.96
2.64
11.70
0.00
0.00
0.00
0.00
0.00
0.00
100.00


26
cationic %
8.22
46.49
0.51
0.00
1.06
0.00
2.76
0.00
4.05
16.76
4.36
0.00
0.00
0.00
0.99
2.73
12.07
0.00
0.00
0.00
0.00
0.00
0.00
100.00


27
cationic %
7.29
41.22
0.45
0.00
0.94
0.00
2.45
0.00
3.59
26.19
3.87
0.00
0.00
0.00
0.88
2.42
10.70
0.00
0.00
0.00
0.00
0.00
0.00
100.00


28
cationic %
7.09
40.09
0.44
0.00
0.92
0.00
2.38
0.00
3.49
28.22
3.76
0.00
0.00
0.00
0.85
2.35
10.41
0.00
0.00
0.00
0.00
0.00
0.00
100.00


29
cationic %
7.50
42.44
0.46
0.00
0.97
0.00
2.52
0.00
6.61
21.12
3.98
0.00
0.00
0.00
0.90
2.49
11.01
0.00
0.00
0.00
0.00
0.00
0.00
100.00


30
cationic %
7.29
41.22
0.45
0.00
0.94
0.00
2.45
0.00
9.25
20.53
3.87
0.00
0.00
0.00
0.88
2.42
10.70
0.00
0.00
0.00
0.00
0.00
0.00
100.00


31
cationic %
7.09
40.09
0.44
0.00
0.92
0.00
2.38
0.00
11.75
19.96
3.76
0.00
0.00
0.00
0.85
2.35
10.41
0.00
0.00
0.00
0.00
0.00
0.00
100.00


32
cationic %
7.72
43.20
0.48
0.00
1.00
0.00
2.59
0.00
3.81
21.76
4.60
0.00
0.00
0.00
0.93
3.31
10.60
0.00
0.00
0.00
0.00
0.00
0.00
100.00


33
cationic %
7.50
42.45
0.46
0.00
0.97
2.91
2.52
0.00
3.69
21.12
3.98
0.00
0.00
0.00
0.90
2.49
11.01
0.00
0.00
0.00
0.00
0.00
0.00
100.00


34
cationic %
7.29
41.22
0.45
0.00
0.94
5.66
2.45
0.00
3.59
20.53
3.87
0.00
0.00
0.00
0.88
2.42
10.70
0.00
0.00
0.00
0.00
0.00
0.00
100.00


35
cationic %
7.60
42.45
0.46
0.00
0.97
0.00
2.52
2.91
3.69
21.12
3.98
0.00
0.00
0.00
0.90
2.49
11.01
0.00
0.00
0.00
0.00
0.00
0.00
100.00


36
cationic %
7.29
41.22
0.45
0.00
0.94
0.00
2.45
5.66
3.59
20.53
3.87
0.00
0.00
0.00
0.88
2.42
10.70
0.00
0.00
0.00
0.00
0.00
0.00
100.00


37
cationic %
7.72
43.20
0.48
0.00
1.00
0.00
0.00
0.00
6.40
21.76
4.60
0.00
0.00
0.00
0.93
2.56
11.35
0.00
0.00
0.00
0.00
0.00
0.00
100.00


38
cationic %
7.72
41.20
1.48
0.00
2.00
0.00
0.00
0.00
6.40
21.76
4.60
0.00
0.00
0.00
0.93
2.56
11.35
0.00
0.00
0.00
0.00
0.00
0.00
100.00


39
cationic %
7.50
40.01
4.35
0.00
1.94
0.00
0.00
0.00
6.21
21.12
4.47
0.00
0.00
0.00
0.90
2.49
11.01
0.00
0.00
0.00
0.00
0.00
0.00
100.00


40
cationic %
7.84
43.87
0.00
0.00
0.00
0.00
0.00
0.00
6.49
22.08
4.67
0.00
0.00
0.00
0.94
2.60
11.51
0.00
0.00
0.00
0.00
0.00
0.00
100.00


41
cationic %
7.50
40.02
1.43
2.91
1.94
0.00
0.00
0.00
6.21
21.12
4.47
0.00
0.00
0.00
0.90
2.49
11.01
0.00
0.00
0.00
0.00
0.00
0.00
100.00


42
cationic %
7.50
40.02
1.43
0.00
4.85
0.00
0.00
0.00
6.21
21.12
4.47
0.00
0.00
0.00
0.90
2.49
11.01
0.00
0.00
0.00
0.00
0.00
0.00
100.00


43
cationic %
7.50
41.96
0.46
0.00
0.97
0.00
0.00
0.00
6.21
21.12
4.47
0.00
0.00
0.00
0.90
2.49
11.01
0.00
0.00
0.00
0.00
0.00
2.91
100.00


44
cationic %
1.72
49.20
0.48
0.00
1.00
0.00
0.00
0.00
6.40
21.76
4.60
0.00
0.00
0.00
0.93
2.56
11.35
0.00
0.00
0.00
0.00
0.00
0.00
100.00


45
cationic %
0.00
50.92
0.48
0.00
1.00
0.00
0.00
0.00
6.40
21.76
4.60
0.00
0.00
0.00
0.93
2.56
11.35
0.00
0.00
0.00
0.00
0.00
0.00
100.00


46
cationic %
7.72
43.20
0.48
0.00
1.00
0.00
0.00
0.00
6.40
21.76
2.60
0.00
0.00
2.00
0.93
2.56
11.35
0.00
0.00
0.00
0.00
0.00
0.00
100.00


47
cationic %
7.72
43.20
0.48
0.00
1.00
0.00
0.00
0.00
6.40
21.76
4.60
0.00
0.00
0.00
0.93
0.58
13.35
0.00
0.00
0.00
0.00
0.00
0.00
100.00


48
cationic %
7.72
43.20
0.48
0.00
1.00
0.00
0.00
0.00
6.40
21.76
3.60
0.00
0.00
0.00
1.93
1.56
12.35
0.00
0.00
0.00
0.00
0.00
0.00
100.00


49
cationic %
7.72
43.20
0.48
0.00
1.00
0.00
0.00
0.00
6.40
21.28
4.60
0.00
0.00
0.00
0.93
0.58
12.35
0.00
1.50
0.00
0.00
0.00
0.00
100.00


50
cationic %
7.72
41.20
1.48
0.00
2.00
0.00
0.00
0.00
5.40
21.51
4.60
0.00
0.00
0.00
0.93
1.56
12.60
0.00
0.00
0.00
0.00
0.00
1.00
100.00


51
cationic %
7.72
44.68
0.00
0.00
0.00
0.00
0.00
0.00
5.40
21.51
4.60
0.00
0.00
0.00
0.93
1.56
12.60
0.00
0.00
0.00
0.00
0.00
1.00
100.00


























Zn2+/
Ti4+/
(Ti4+ + W6+)/


No.

Si4+ + B2+
Li+ + Na+ + K+
La3+ + Gd3+ + Y3+
Ti4+ + Nb5+ + Ta5+ + W6+
B3+/(Si4+ + B3+)
(Mg2+ + Ca2+ + Sr2+ + Ba2+ + Zn2+)
(Ti4+ + Nb5+)
(Ti4+ + Nb5+ + Ta5+ + W6+)





1
cationic %
45.92
1.4800
4.10
12.91
0.66
0.63
0.35
0.35


2
cationic %
45.92
1.4800
4.10
12.91
0.73
0.63
0.35
0.35


3
cationic %
45.92
1.4800
4.10
12.91
0.86
0.63
0.35
0.35


4
cationic %
47.36
1.5200
4.23
10.21
0.86
0.63
0.16
0.16


5
cationic %
45.93
1.4800
4.10
12.91
0.86
0.74
0.35
0.35


6
cationic %
47.90
1.5400
0.00
13.46
0.86
0.69
0.35
0.35


7
cationic %
49.73
1.4800
4.10
12.91
0.87
0.71
0.35
0.35


8
cationic %
49.92
1.4800
4.10
12.91
0.88
0.71
0.12
0.12


9
cationic %
49.92
1.4800
4.10
12.91
0.88
0.71
0.51
0.51


10
cationic %
51.42
1.4800
4.10
13.91
0.85
0.77
0.18
0.18


11
cationic %
51.42
1.4800
4.10
13.91
0.85
0.77
0.18
0.18


12
cationic %
51.42
1.4800
4.10
13.91
0.85
0.77
0.18
0.18


13
cationic %
49.95
1.4300
3.98
16.41
0.85
0.77
0.18
0.33


14
cationic %
49.94
1.4300
3.98
16.42
0.85
0.77
0.15
0.15


15
cationic %
49.95
1.4300
3.98
16.41
0.85
0.77
0.18
0.15


16
cationic %
51.91
1.4900
4.14
14.04
0.85
0.77
0.18
0.18


17
cationic %
50.43
1.4500
4.02
13.63
0.85
0.77
0.18
0.18


18
cationic %
49.95
1.4300
6.89
13.50
0.85
0.77
0.18
0.18


19
cationic %
48.51
1.3900
9.53
13.12
0.85
0.77
0.18
0.18


20
cationic %
49.95
1.4300
6.89
13.50
0.85
0.77
0.18
0.18


21
cationic %
49.94
1.4300
6.90
13.50
0.85
0.77
0.18
0.18


22
cationic %
48.51
1.3900
9.53
13.12
0.85
0.77
0.18
0.18


23
cationic %
51.42
1.4800
4.10
13.91
0.85
0.77
0.18
0.18


24
cationic %
51.42
1.4800
4.10
13.91
0.85
0.77
0.18
0.18


25
cationic %
53.02
1.5200
4.23
14.34
0.86
0.75
0.18
0.18


26
cationic %
54.71
1.5700
4.36
14.80
0.85
0.71
0.18
0.18


27
cationic %
48.51
1.3900
3.87
13.12
0.85
0.81
0.18
0.18


28
cationic %
47.18
1.3600
3.76
12.76
0.85
0.83
0.18
0.18


29
cationic %
49.94
1.4300
3.98
13.50
0.85
0.70
0.18
0.18


30
cationic %
48.51
1.3900
3.87
13.12
0.85
0.64
0.18
0.18


31
cationic %
47.18
1.3600
3.76
12.76
0.85
0.59
0.18
0.18


32
cationic %
50.92
1.4800
4.60
13.91
0.85
0.77
0.24
0.24


33
cationic %
49.95
1.4300
3.98
13.50
0.85
0.70
0.18
0.18


34
cationic %
48.51
1.3900
3.87
13.12
0.85
0.64
0.18
0.18


35
cationic %
49.95
1.4300
3.98
13.50
0.85
0.70
0.18
0.18


36
cationic %
48.51
1.3900
3.87
13.12
0.85
0.64
0.18
0.18


37
cationic %
50.92
1.4800
4.60
13.91
0.85
0.77
0.18
0.18


38
cationic %
48.92
3.4800
4.60
13.91
0.84
0.77
0.18
0.18


39
cationic %
47.51
6.2900
4.47
13.50
0.84
0.77
0.18
0.18


40
cationic %
51.71
0.0000
4.67
14.11
0.85
0.77
0.18
0.18


41
cationic %
47.52
6.2800
4.47
13.50
0.84
0.77
0.18
0.18


42
cationic %
47.52
6.2800
4.47
13.50
0.84
0.77
0.18
0.18


43
cationic %
49.46
1.4300
4.47
13.50
0.85
0.77
0.18
0.18


44
cationic %
50.92
1.4800
4.60
13.91
0.97
0.77
0.18
0.18


45
cationic %
50.92
1.4800
4.60
13.91
1.00
0.77
0.18
0.18


46
cationic %
50.92
1.4800
2.60
13.91
0.85
0.77
0.18
0.18


47
cationic %
50.92
1.4800
4.60
13.91
0.85
0.77
0.04
0.04


48
cationic %
50.92
1.4800
3.60
13.91
0.85
0.77
0.11
0.11


49
cationic %
50.92
1.4800
4.60
14.41
0.85
0.77
0.04
0.14


50
cationic %
48.92
3.4800
4.60
14.16
0.84
0.80
0.11
0.11


51
cationic %
52.40
0.0000
4.60
14.16
0.85
0.80
0.11
0.11






















No.
nd
νd
Pg,F
  Pg,f
Specific gravity
Tg (° C.)
Ts (° C.)
LT (° C.)
λ70 (nm)
λ5 (nm)






1
1.79126
34.86
0.586
0.000
3.94
576
627
Less than 1050° C.
386
350



2
1.80498
34.34
0.587
0.001
3.99
561
608
Less than 1030° C.
391
351



3
1.81444
33.96
0.588
0.001
4.02
549
594
Less than 1020° C.
394
351



4
1.79159
36.87
0.582
0.000
4.03
547
591
Less than 1020° C.
377
342



5
1.81757
33.37
0.590
0.002
3.96
546
590
Less than 1050° C.
399
355



6
1.79958
32.92
0.595
0.006
3.79
541
584
Less than 1050° C.
399
355



7
1.80713
33.67
0.591
0.003
3.85
555
599
Less than 1030° C.
402
357



8
1.80719
34.39
0.586
0.000
4.03
553
598
Less than 1020° C.
387
346



9
1.80741
33.38
0.593
0.005
3.96
554
598
Less than 1000° C.
407
359



10
1.80845
33.26
0.589
0.001
4.00
557
602
Less than 1020° C.
396
352



11
1.80048
33.49
0.589
0.001
3.97
567
609
Less than 1020° C.
396
352



12
1.80425
33.26
0.589
0.001
3.99
563
607
Less than 1020° C.
396
352



13
1.81491
32.03
0.595
0.004
4.13
560
602
Less than 1050° C.
409
359



14
1.82490
31.53
0.594
0.002
4.02
563
607
Less than 1050° C.
406
357



15
1.82149
32.23
0.592
0.002
4.16
568
611
Less than 1100° C.
397
355



16
1.79865
33.40
0.590
0.002
3.96
561
605
Less than 1050° C.
396
353



17
1.81262
33.22
0.590
0.001
4.02
567
611
Less than 1050° C.
397
352



18
1.81354
33.95
0.590
0.003
4.16
572
613
Less than 1100° C.
393
352



19
1.82295
34.36
0.585
−0.002
4.33
577
622
Less than 1100° C.
393
350



20
1.80993
33.97
0.588
0.001
4.05
570
614
Less than 1100° C.
392
352



21
1.81516
33.95
0.587
0.000
4.12
569
613
Lees than 1050° C.
395
350



22
1.82598
34.44
0.588
0.002
4.24
573
617
Less than 1050° C.
392
348



23
1.80177
33.38
0.590
0.001
4.01
565
608
Less than 1050° C.
397
353



24
1.79930
33.39
0.590
0.002
3.93
566
603
Less than 1100° C.
395
353



25
1.80405
33.32
0.592
0.004
3.93
566
611
Less than 1050° C.
397
355



26
1.79873
32.91
0.590
0.001
3.88
570
614
Less than 1050° C.
399
356



27
1.80628
33.62
0.588
0.001
4.06
557
597
Less than 1050° C.
391
352



28
1.80799
33.72
0.590
0.002
4.10
553
596
Less than 1050° C.
393
352



29
1.80435
33.97
0.590
0.003
4.08
563
606
Less than 1050° C.
391
351



30
1.80489
34.44
0.586
−0.001
4.17
561
604
Less than 1050° C.
388
348



31
1.80404
34.94
0.586
0.001
4.25
559
602
Less than 1050° C.
386
346



32
1.80612
33.26
0.589
0.001
4.00
565
608
Less than 1010° C.
398
353



33
1.79969
33.73
0.587
−0.001
3.96
566
610
Less than 1050° C.
401
353



34
1.79657
34.19
0.588
0.001
3.95
568
610
Less than 1050° C.
404
354



35
1.80274
34.00
0.590
0.002
4.03
564
607
Less than 1050° C.
390
349



36
1.80189
34.48
0.586
0.000
4.08
564
608
Less than 1050° C.
387
348



37
1.80709
33.52
0.590
0.002
4.10
562
604
Less than 990° C.
395
351



38
1.80685
33.38
0.590
0.001
4.10
551
595
Less than 1000° C.
392
351



39
1.80560
33.58
0.587
−0.001
4.09
532
576
Less than 1030° C.
392
350



40
1.81311
33.27
0.590
0.002
4.11
572
614
Less than 1030° C.
402
353



41
1.80025
33.48
0.585
−0.003
4.07
533
581
Less than 1050° C.
393
348



42
1.79484
33.68
0.590
0.002
4.04
541
587
Less than 1050° C.
394
348



43
1.79855
33.84
0.582
−0.006
4.05
563
608
Less than 1050° C.
399
351



44
1.81738
33.17
0.589
0.000
4.14
553
593
Less than 1000° C.
400
353



45
1.82023
33.02
0.589
0.000
4.15
550
590
Less than 1000° C.
401
354



46
1.80423
33.43
0.590
0.002
4.15
565
608
Less than 1080° C.
394
353



47
1.80775
33.83
0.589
0.001
4.13
562
605
Less than 1030° C.
386
345



48
1.80832
33.37
0.589
0.001
4.09
562
607
Less than 1030° C.
369
349



49
1.80681
33.66
0.589
0.001
4.19
561
604
Less than 1020° C.
391
350



50
1.80565
33.32
0.588
0.000
4.07
550
595
Less than 1000° C.
393
348



51
1.80746
33.41
0.589
0.001
4.07
572
613
Less than 1050° C.
396
351









The various characteristics of the optical glasses were measured by the following methods.
(1) Refractive Indexes nd, ng, nF, nc, and the Abbé Number νd
The refractive indexes nd, ng, nF, and nc, and the Abbé number νd of glasses obtained by lowering the temperature at a rate of 30° C./hour were measured by the refractive index measurement standards of the Japan Optical Glass Industry Association.
(2) Liquidus Temperature LT
The glass was maintained for 2 hours in a furnace heated to a prescribed temperature and cooled. The interior of the glass was then observed by an optical microscope at 100× magnification and the liquidus temperature was determined from the presence or absence of crystals.
(3) Glass Transition Temperature Tg and Yield Point Ts
Measurement was conducted at a rate of temperature increase of 4° C./minute using a thermomechanical analysis apparatus made by Rigaku Corporation.
(4) Partial Dispersion Ratio Pg,F
The Pg,F was calculated from the refractive indexes ng, nF, and nc.
(5) Difference from the Normal Line of the Partial Dispersion Ratio, ΔPg,F
The ΔPg,F was calculated from the partial dispersion ratio Pg,F(0) on the normal line calculated from the Abbé number νd and the partial dispersion ratio Pg,F.
(6) Specific Gravity
The specific gravity was measured by Archimedes' method.
(7) λ70, λ5
The λ70 and λ5 were obtained by measuring the spectral transmittance with a spectrophotometer.
2. Preparation of Press-Molding Glass Material (1)
The formed glass articles comprised of various glasses fabricated in 1. above were each cut into multiple pieces of glass. Each piece of glass was ground and polished to prepare a press-molding glass material.
3. Preparation of Press-Molding Glass Material (2)
Glass melts were prepared by the same manner as in 1. above and caused to flow out of pipes. The tip of the glass melt flow that flowed out was separated to obtain a glass melt gob. The glass melt gob was molded while being floated with blown air on a mold to prepare a press-molding glass material. The press-molding glass materials comprised of the various optical glasses indicated in Table 1 were thus prepared.
Alternatively, the glass melt gob can be press molded on a mold and then the press molded glass can be cooled while being floated on the mold to prepare a glass material.
4. Preparation of Optical Element
Each of the press-molding glass materials prepared in 2. and 3. above was separately introduced into a pressing mold, the glass material and the pressing mold were heated together, the glass material was softened, and precision press molding was conducted to prepare an aspherical lens.
Each of the press-molding glass materials prepared in 2. and 3. above was heated, softened, and introduced into a preheated pressing mold. Precision press molding was conducted to prepare an aspherical lens.
In all of the forms, high-quality optical elements were obtained by precision press molding.
5. Preparation of Image Pickup Device and Optical System
The various lenses prepared in 4. above were used to prepare interchangeable lenses for single lens reflex cameras with built-in lenses.
The various lenses prepared in 4. above were also used to prepare various optical systems for compact digital cameras and modularized. Image sensors such as CCDs and CMOSs were then mounted into these optical systems and modularized.
By employing the various lenses prepared in 4., it was possible to obtain highly functional, compact optical systems, interchangeable lenses, lens modules, and pickup devices. By combining the lenses prepared in 4. above with the high refractive index, high dispersion optical glass lenses, it was possible to obtain various optical systems conducting high-order chromatic aberration correction and image pickup devices equipped with these optical systems.
The optical glass of the present invention has high refractive index characteristics and good precision press moldability, a low glass transition temperature, and is suited to precision press molding. It is also suited to high-order chromatic aberration correction and use in preparing press-molding glass materials and optical elements.
Although the present invention has been described in considerable detail with regard to certain versions thereof, other versions are possible, and alterations, permutations and equivalents of the version shown will become apparent to those skilled in the art upon a reading of the specification and study of the drawings. Also, the various features of the versions herein can be combined in various ways to provide additional versions of the present invention. Furthermore, certain terminology has been used for the purposes of descriptive clarity, and not to limit the present invention. Therefore, any appended claims should not be limited to the description of the preferred versions contained herein and should include all such alterations, permutations, and equivalents as fall within the true spirit and scope of the present invention.
Having now fully described this invention, it will be understood to those of ordinary skill in the art that the methods of the present invention can be carried out with a wide and equivalent range of conditions, formulations, and other parameters without departing from the scope of the invention or any Examples thereof.
All patents and publications cited herein are hereby fully incorporated by reference in their entirety. The citation of any publication is for its disclosure prior to the filing date and should not be construed as an admission that such publication is prior art or that the present invention is not entitled to antedate such publication by virtue of prior invention.

## Claims

1. Optical glass, which is oxide glass comprising, denoted as cation percentages:
Si4+ 0 to 30%;
B3+ 15 to 60%;
Li+ 0 to 10%;
Na+ 0 to 10%;
K+ 0 to 15%;
Mg2+ 0 to 20%;
Ca2+ 0 to 15%;
Sr2+ 0 to 20%;
Ba2+ 0 to 20%;
Zn2+ 13 to 40%;
La3+ 0 to 11%;
Gd3+ 0 to 10%;
Y3+ 0 to 6%;
Yb3+ 0 to 6%;
Zr4+ 0 to 5%;
Ti4+ 0 to 7%;
Nb5+ 2 to 20%;
Ta5+ 0 to 5%;
W6+ 0 to 10%;
Te4+ 0 to 5%;
Ge4+ 0 to 5%;
Bi3+ 0 to 5%; and
Al3+ 0 to 5%;
wherein
a combined content of Si4+ and B3+ ranges from 35 to 65%;

a cation ratio of a content of B3+ to the combined content of Si4+ and B3+, B3+/(Si4++B3+), ranges from 0.3 to 1;
a combined content of Li+, Na+, and K+ ranges from 0 to 20%;
a cation ratio of a content of Zn2+ to a combined content of Mg2+, Ca2+, Sr2+, Ba2+, and Zn2+, Zn2+/(Mg2++Ca2+Sr2++Ba2++Zn2+), ranges from 0.30 to 1;
a combined content of La3+, Gd3+, and Y3+ ranges from 0 to 20%;
a combined content of Ti4+, Nb5+, Ta5+, and W6+ ranges from 10 to 20%;
a cation ratio of the content of Ti4+ to the combined content of Ti4+ and Nb5+ (Ti4+/(Ti4++Nb5+)) ranges from 0 to 0.20; and
a cation ratio of the combined content of Ti4+ and W6+ to the combined content of Ti4+, Nb5+, Ta5+, and W6+((Ti4++W6+)/(Ti4++Nb5++Ta5++W6+)) ranges from 0 to 0.20, and
comprising no Pb, with a refractive index nd ranging from 1.750 to 1.850, an Abbé number νd ranging from 29.0 to 40.0, and a glass transition temperature of less than 630° C.

2. The optical glass according to claim 1, which has a partial dispersion ratio, Pg,F, of equal to or lower than 0.600, the partial dispersion ratio being denoted as (ng−nF)/(nFnc) with a refractive index ng at a g line, nF at an F line, and nc at a c line.

3. The optical glass according to claim 1, which has a deviation, ΔPg,F, of a partial dispersion ratio, Pg,F, of equal to or lower than 0.02, wherein the ΔPg,F is calculated by the following equation:


ΔPg,F=Pg,F+(0.0018×νd)−0.6483


and in the equation, Pg,F is a partial dispersion ratio denoted as (ng−nF)/(nF−nc) with a refractive index ng at a g line, nF at an F line, and nc at a c line, and vd is an Abbú ́ number.

4. The optical glass according to claim 1, which has a specific gravity of equal to or lower than 4.5.

5. The optical glass according to claim 1, which has a liquidus temperature of lower than 1,100° C.

6. The optical glass according to claim 1, the wavelength λ70 of which is equal to or lower than 450 nm, the λ70 being a wavelength at which light transmittance over a wavelength range of 280 to 700 nm is 70%.

7. The optical glass according to claim 1, the wavelength λ5 of which is equal to or lower than 370 nm, the λ5 being a wavelength at which light transmittance over a wavelength range of 280 to 700 nm is 5%.

8. A press-molding glass material, which is comprised of the optical glass according to claim 1.

9. An optical element, which is comprised of the optical glass according to claim 1.

10. A method of manufacturing an optical element, which comprises:
heating and precision press molding with a pressing mold the press-molding glass material according to claim 8.