JP7544191B2 - Optical glass, optical element using the same, optical system, interchangeable lens for camera, and optical device - Google Patents

Description

The present invention relates to optical glass, and optical elements, optical systems, interchangeable camera lenses, and optical devices using the same. The present invention claims priority to Japanese Patent Application No. 2018-082588, filed on April 23, 2018, and the contents of that application are incorporated by reference into this application in designated states where incorporation by reference of documents is permitted.

For example, Patent Document 1 discloses optical glass made of fluorophosphate glass.

JP 2009-286670 A

A first aspect of the present invention is an optical glass having, in mass percentages, a _SiO2 content of 10 % or more and 28% or less , _{a B2O3} content of 6 % or more and 20% or less , _{a Nb2O5} content of 25 % or more and 44.08% or less , a _K2O content of 15 % or more and 30% or less , and _{a P2O5} content of 0% or more and 8% or less _.
A second aspect of the present invention is an optical glass having, in mass percentages, the following: SiO2 content : _{10 %} or more and 28% or less; B2O3 _{content :} 6% or more and 20% or less; Nb2O5 _content : 25% or more and 44.08% or less; K2O content _: 15% or more and 30% or less; and the ratio of the TiO2 content to the Nb2O5 content (TiO2 _{/ Nb2O5 )} being ₀ or more _{and 0.3} or less.

A third aspect of the present invention is an optical element using the above-mentioned optical glass.

A fourth aspect of the present invention is an optical system including the optical element described above.

A fifth aspect of the present invention is an interchangeable lens for a camera including the optical system described above.

A sixth aspect of the present invention is an objective lens for a microscope comprising the optical system described above.
A seventh aspect of the present invention is an optical device comprising the optical system described above.

FIG. 1 is a perspective view of an imaging device equipped with an optical element using the optical glass according to this embodiment. 2(a) and (b) are schematic diagrams of another example of an imaging device equipped with an optical element using the optical glass according to this embodiment, where FIG. 2(a) is a front view of the imaging device and FIG. 2(b) is a rear view of the imaging device. FIG. 3 is a block diagram showing an example of the configuration of a multiphoton microscope equipped with an optical element using the optical glass according to this embodiment. FIG. 4 is a graph plotting _λ5 vs. _vd for each of the examples and comparative examples. FIG. 5 is a graph plotting ΔP _g,F and ν _d for each of the examples and comparative examples. FIG. 6 is a graph plotting P _g,F and v _d for each of the examples and comparative examples.

The following describes an embodiment of the present invention (hereinafter, "the present embodiment"). The following embodiment is an example for explaining the present invention, and is not intended to limit the present invention to the following content.

The optical glass according to this embodiment is a SiO ₂ -B ₂ O ₃ -Nb ₂ O ₅ -K ₂ O type optical glass having the mass percentages of SiO ₂ : 10-30%, B ₂ O ₃ : 6-20%, Nb ₂ O ₅ : 25-50%, K ₂ O: 15-30%, TiO ₂ : 0-8%, P ₂ O ₅ : 0-8%, RO (wherein R represents at least one selected from the group consisting of Ca, Sr, Ba and Zn): 0-4%, Li ₂ O: 0-10%, and the ratio of the TiO ₂ content to the Nb ₂ O ₅ content (TiO ₂ /Nb ₂ O ₅ ) is 0-0.3.

In this specification, unless otherwise specified, the content of each component is expressed as mass % of the total weight of the glass in terms of oxide. The oxide-equivalent composition here is a composition in which each component contained in the glass is expressed, assuming that the oxides, complex salts, etc. used as raw materials for the glass components are all decomposed and converted to oxides when melted, and the total mass of the oxides is 100%.

Conventionally, microscope observations using ultraviolet light, such as fluorescent microscopes, have been widely conducted. Glass materials with high transmittance in the ultraviolet light region are desirable as optical glass materials for use in such optical devices. In addition, in the optical systems of such optical devices, chromatic aberration is corrected (achromatization) by combining glass materials with different refractive indices and dispersions. From the viewpoint of achromatization, glass materials with high dispersion (small Abbe number) and small partial dispersion ratios are desirable.

However, as a characteristic of typical optical glass, the partial dispersion ratio (P _g,F ) relative to the Abbe number (ν _d ) tends to increase as the dispersion increases, and therefore high-dispersion optical glass has a problem in that the relationship between the Abbe number and the partial dispersion ratio deviates significantly in the positive direction from the linear relationship (base line), resulting in large positive anomalous dispersion.

In this respect, the optical glass according to this embodiment has high dispersion and a low partial dispersion ratio (P _g,F ) relative to the Abbe number (ν _d ). The optical glass according to this embodiment also has high transmittance in a wide range including the ultraviolet light range. Furthermore, as a preferred aspect of this embodiment, for example, in a medium refractive index high dispersion range where 1.60≦n _d ≦1.80, 25≦ν _d ≦35, and n _d ≦−0.04×ν _d +3.00, it is possible to realize an optical glass that satisfies the relationships: the wavelength at which the internal transmittance is 5% is λ ₅ ≦355 nm, the anomalous dispersion value is ΔP _g,F ≦0.0080, and P _g,F ≦−0.0030×ν _d +0.6900.

Such optical glass has a high internal transmittance of ultraviolet light and a low partial dispersion ratio (P _g,F ) relative to the Abbe number (ν _d ), and the relationship between the Abbe number and the partial dispersion ratio is controlled to approximate a linear relationship (baseline). That is, the optical glass has a small deviation in the positive direction of the partial dispersion ratio from the base line, and has low positive anomalous dispersion. Furthermore, it is possible to obtain an optical glass with a unique internal transmittance in the ultraviolet light region, a refractive index (n _d ) relative to the Abbe number (ν _d ), and a unique partial dispersion ratio (P _g,F ) relative to the Abbe number (ν _d ). The optical glass according to this embodiment has such characteristics, and therefore can fully meet the above-mentioned requirements.

The component composition of the optical glass according to this embodiment is described below.

_SiO2 is an oxide that forms glass and can improve devitrification resistance. On the other hand, if it is contained in a large amount, it tends to deteriorate the melting property and increase the Abbe number. From this viewpoint, the content is 10 to 30%. The upper limit of the content may be 29% or 28%. The lower limit of the content may be 12% or 15%.

B ₂ O ₃ is an oxide that forms glass, and can improve meltability. It can also reduce the refractive index relative to the Abbe number. On the other hand, if it is contained in a large amount, the stability against devitrification decreases, and the Abbe number tends to increase. From this viewpoint, the content is 6 to 20%. The upper limit of the content may be 19% or 18%. The lower limit of the content may be 7% or 8%.

Nb ₂ O ₅ is an effective component for obtaining a desired Abbe number. It can also reduce the refractive index relative to the Abbe number. On the other hand, if it is contained in a large amount, the devitrification resistance and melting property tend to decrease, the partial dispersion ratio relative to the Abbe number tends to increase, and the transmittance tends to deteriorate. From this viewpoint, the content is 25 to 50%. The upper limit of the content is preferably 49%, more preferably 48%. The lower limit of the content is preferably 27%, more preferably 29%.

K ₂ O is an effective component for obtaining a desired partial dispersion ratio relative to the Abbe number. It can also improve the transmittance. On the other hand, if it is contained in a large amount, the stability against devitrification decreases and the Abbe number tends to increase. From this viewpoint, the content is 15 to 30%. The upper limit of the content may be 26% or 22%. The lower limit of the content may be more than 15% or 15.5%.

_TiO2 is an optional component that can reduce the refractive index relative to the Abbe number when it is contained in an amount exceeding 0%. On the other hand, when a large amount is contained, the transmittance tends to deteriorate. From this viewpoint, the content is 0 to 8%. The upper limit of the content may be 6% or 4%. The lower limit of the content may be greater than 0% or 1%.

If the content of _TiO2 relative to the content of _Nb2O5 is too high, _the transmittance tends to decrease. From this viewpoint, the ratio of the content of _TiO2 relative to _the content of _Nb2O5 ( _TiO2 / _Nb2O5 ) is 0 to _0.3 . The upper limit of this ratio may be 0.25 or 0.24. The lower limit of this ratio may be greater than 0 or 0.01.

P ₂ O ₅ is an optional component that, when contained in an amount exceeding 0%, reduces the refractive index relative to the Abbe number. On the other hand, when contained in a large amount, the partial dispersion ratio relative to the Abbe number becomes large, and the Abbe number tends to increase. From this viewpoint, the content is 0 to 8%. The upper limit of the content may be 7% or may be 6%. The lower limit of the content may be greater than 0% or may be 1%.

RO (R represents one or more selected from the group consisting of Ca, Sr, Ba, and Zn) is an optional component that, when contained in excess of 0%, reduces the partial dispersion ratio relative to the Abbe number. On the other hand, when contained in large amounts, the stability against devitrification decreases and the refractive index relative to the Abbe number tends to increase. From this perspective, the total content of the components corresponding to RO is 0 to 4%. The upper limit of the total content may be 3% or 2%. The lower limit of the total content may be greater than 0% or 0.3%.

Li ₂ O is an optional component that, when contained in an amount exceeding 0%, reduces the partial dispersion ratio relative to the Abbe number and improves the transmittance. On the other hand, when contained in a large amount, the stability against devitrification decreases, the Abbe number increases, and the refractive index relative to the Abbe number tends to increase. From this viewpoint, the content is 0 to 10%. The upper limit of the content may be 8% or 7%. The lower limit of the content may be greater than 0% or 1%.

Na ₂ O is an optional component that, when contained in an amount exceeding 0%, reduces the partial dispersion ratio relative to the Abbe number and improves the transmittance. On the other hand, when contained in a large amount, the stability against devitrification decreases, the Abbe number increases, and the refractive index relative to the Abbe number tends to increase. From this viewpoint, the content is 0 to 10%. The upper limit of the content may be 8% or 7%. The lower limit of the content may be greater than 0% or 1%.

_ZrO2 is an optional component that, when contained in excess of 0%, reduces the partial dispersion ratio relative to the Abbe number without increasing the Abbe number. On the other hand, when contained in a large amount, the stability against devitrification tends to decrease and the transmittance tends to deteriorate. From this viewpoint, the content is 0 to 12%. The upper limit of the content may be 10% or 8%. The lower limit of the content may be more than 0% or 1%.

Ta ₂ O ₅ is an optional component that maintains a low Abbe number when contained in an amount exceeding 0%. On the other hand, when contained in a large amount, the stability against devitrification tends to decrease. From this viewpoint, the content is 0 to 12%. The upper limit of the content may be 10% or 8%. The lower limit of the content may be more than 0% or 2%.

_WO3 is an optional component that maintains the Abbe number low when it is contained in an amount exceeding 0%. On the other hand, when it is contained in a large amount, the transmittance tends to deteriorate. From this viewpoint, the content is 0 to 5%. The upper limit of the content may be 4% or may be 3%. The lower limit of the content may be greater than 0% or may be 1%.

Sb ₂ O ₃ is an optional component that is effective for clarifying and homogenizing the glass when it is contained in an amount exceeding 0%. From this viewpoint, the content is preferably 0 to 1%.

In addition to the above-mentioned components, other optional components can be added as long as they do not interfere with achieving the optical glass desired in this embodiment.

The optical glass according to this embodiment having the above-mentioned component composition has high dispersion, high internal transmittance over a wide range including the ultraviolet light range, and a low partial dispersion ratio (P _g,F ) relative to the Abbe number (ν _d ). In particular, these characteristics can be maintained even in the medium refractive index high dispersion range.

The following describes the preferred properties of the optical glass in this embodiment.

First, from the viewpoint that the optical glass according to this embodiment is suitable for use in the medium refractive index, high dispersion region, the preferred refractive index (n _d ) for this region is in the range of 1.60 to 1.80, and the preferred Abbe number (ν _d ) is in the range of 25 to 35.

Next, a suitable embodiment of the optical glass according to this embodiment is one in which the refractive index (n _d ) and the Abbe number (ν _d ) satisfy the relationship expressed by the following formula (1).
n _d ≦-0.04×ν _d +3.00...(1)

Among the above, those that can better exhibit the desired characteristics even in the medium refractive index high dispersion region include those having a refractive index (n _d ) in the range of 1.60 to 1.80, an Abbe number (ν _d ) in the range of 25 to 35, and satisfying the relationship expressed by formula (1).

The optical glass according to this embodiment has a high ultraviolet light transmittance. For example, from the viewpoint of the utility of ultraviolet light and achromatization, the optical glass can have a good transmittance even in the ultraviolet light region and a low partial dispersion ratio to the Abbe number. A preferred example of such an optical glass is one in which the wavelength (λ ₅ ) at which the internal transmittance is 5% is 355 nm or less.

Further, a specific preferred example of this embodiment is an optical glass having an anomalous dispersion value (ΔP _g,F ) of 0.0080 or less. The anomalous dispersion value is an index of anomalous dispersion, and a specific definition will be given later.

Conventionally, particularly in the medium refractive index, high dispersion region, there has been a problem in that as the dispersion of the optical glass increases, the anomalous dispersion value (ΔP _g,F ) increases. Taking this into consideration, a preferred specific example of the present embodiment is one in which the partial dispersion ratio (P _g,F ) and the Abbe number (ν _d ) satisfy the relationship expressed by the following formula (2).
P _g,F ≦-0.003ν _d +0.6900...(2)

An even more preferred embodiment of the optical glass according to this embodiment satisfies the relationship expressed by formula (2) above, has a wavelength ( _λ5 ) at which the internal transmittance is 5% of 355 nm or less, and has an anomalous dispersion value (ΔPg _,F ) of 0.0080 or less. Optical glass having all of these characteristics has a high internal transmittance for ultraviolet light even in the medium refractive index high dispersion region, and has a low partial dispersion ratio ( _Pg,F ) to the Abbe number ( _νd ).

The optical glass according to this embodiment having the above-mentioned characteristics can be suitably used as an optical element for use in optical devices. Such optical elements include mirrors, lenses, prisms, filters, and the like. Examples of optical systems including such optical elements include objective lenses, condenser lenses, imaging lenses, and interchangeable lenses for cameras. Furthermore, these optical systems can be suitably used in optical devices such as imaging devices, such as interchangeable lens cameras and non-interchangeable lens cameras, and microscopes, such as multiphoton microscopes. Such optical devices are not limited to the imaging devices and microscopes described above, but also include video cameras, teleconverters, telescopes, binoculars, monoculars, laser range finders, projectors, and the like. Examples of these are described below.

<Imaging device>
FIG. 1 is a perspective view of an example of an optical device used as an imaging device.

The imaging device 1 is a so-called digital single-lens reflex camera (interchangeable lens camera), and the photographing lens 103 (optical system) is equipped with an optical element whose base material is the optical glass according to this embodiment. A lens barrel 102 is detachably attached to a lens mount (not shown) of a camera body 101. Light passing through the photographing lens 103 of the lens barrel 102 is imaged on a sensor chip (solid-state image sensor) 104 of a multi-chip module 106 arranged on the rear side of the camera body 101. This sensor chip 104 is a bare chip such as a so-called CMOS image sensor, and the multi-chip module 106 is, for example, a COG (chip on glass) type module in which the sensor chip 104 is bare-chip mounted on a glass substrate 105.

Figure 2 is a schematic diagram of another example in which the optical device is an imaging device. Figure 2(a) shows a front view of the imaging device CAM, and Figure 2(b) shows a rear view of the imaging device CAM.

The imaging device CAM is a so-called digital still camera (a camera with non-interchangeable lenses), and the photographing lens WL (optical system) is equipped with an optical element whose base material is the optical glass according to this embodiment.

When the power button (not shown) of the imaging device CAM is pressed, the shutter (not shown) of the taking lens WL is opened and light from the subject (object) is collected by the taking lens WL and focused on the imaging element arranged on the image plane. The subject image focused on the imaging element is displayed on the LCD monitor M arranged behind the imaging device CAM. After the photographer decides on the composition of the subject image while looking at the LCD monitor M, he or she presses the release button B1 to capture the subject image with the imaging element, which is then recorded and saved in memory (not shown).

The imaging device CAM is equipped with an auxiliary light emitting unit EF that emits auxiliary light when the subject is dark, a function button B2 that is used to set various conditions for the imaging device CAM, etc.

<Multiphoton microscope>
FIG. 3 is a block diagram showing an example of the configuration of the multiphoton microscope 2. As shown in FIG.

The multiphoton microscope 2 includes an objective lens 206, a condenser lens 208, and an imaging lens 210. At least one of the objective lens 206, the condenser lens 208, and the imaging lens 210 includes an optical element having the optical glass according to this embodiment as its base material. The following description will focus on the optical system of the multiphoton microscope 2.

The pulsed laser device 201 emits ultrashort pulsed light, for example, with a near-infrared wavelength (approximately 1000 nm) and a pulse width in femtosecond units (e.g., 100 femtoseconds). The ultrashort pulsed light immediately after being emitted from the pulsed laser device 201 is generally linearly polarized in a predetermined direction.

The pulse splitting device 202 splits the ultrashort pulse light and emits the ultrashort pulse light with a higher repetition frequency.

The beam adjustment unit 203 has a function of adjusting the beam diameter of the ultrashort pulse light incident from the pulse splitter 202 to match the pupil diameter of the objective lens 206, a function of adjusting the focusing and divergence angles of the ultrashort pulse light to correct the axial chromatic aberration (focus difference) between the wavelength of the multiphoton excitation light emitted from the sample S and the wavelength of the ultrashort pulse light, and a pre-chirp function (group velocity dispersion compensation function) of giving the ultrashort pulse light an inverse group velocity dispersion to correct the pulse width of the ultrashort pulse light that widens due to group velocity dispersion while passing through the optical system.

The repetition frequency of the ultrashort pulsed light emitted from the pulsed laser device 201 is increased by the pulse division device 202, and the above-mentioned adjustment is performed by the beam adjustment unit 203. The ultrashort pulsed light emitted from the beam adjustment unit 203 is then reflected by the dichroic mirror 204 in the direction of the dichroic mirror 205, passes through the dichroic mirror 205, and is focused by the objective lens 206 to be irradiated onto the sample S. At this time, the ultrashort pulsed light may be scanned over the observation surface of the sample S by using a scanning means (not shown).

For example, when observing the fluorescence of sample S, the fluorescent dye with which sample S is stained undergoes multiphoton excitation in the area of sample S irradiated with the ultrashort pulsed light and in its vicinity, emitting fluorescence (hereinafter referred to as "observation light") with a wavelength shorter than that of the ultrashort pulsed light, which is an infrared wavelength.

The observation light emitted from the sample S in the direction of the objective lens 206 is collimated by the objective lens 206 and, depending on its wavelength, is reflected by or transmitted through the dichroic mirror 205.

The observation light reflected by the dichroic mirror 205 enters the fluorescence detection unit 207. The fluorescence detection unit 207 is composed of, for example, a barrier filter, a PMT (photomultiplier tube), etc., receives the observation light reflected by the dichroic mirror 205, and outputs an electrical signal according to the amount of light. In addition, the fluorescence detection unit 207 detects the observation light across the observation surface of the sample S as the ultrashort pulse light scans the observation surface of the sample S.

On the other hand, the observation light that passes through the dichroic mirror 205 is descanned by a scanning means (not shown), passes through the dichroic mirror 204, is focused by the focusing lens 208, passes through a pinhole 209 located at a position approximately conjugate to the focal position of the objective lens 206, passes through the imaging lens 210, and enters the fluorescence detection unit 211.

The fluorescence detection unit 211 is composed of, for example, a barrier filter, a PMT, etc., receives the observation light imaged on the light receiving surface of the fluorescence detection unit 211 by the imaging lens 210, and outputs an electrical signal according to the amount of light. In addition, the fluorescence detection unit 211 detects the observation light across the observation surface of the sample S as the ultrashort pulse light scans the observation surface of the sample S.

In addition, by removing the dichroic mirror 205 from the optical path, all observation light emitted from the sample S in the direction of the objective lens 206 can be detected by the fluorescence detection unit 211.

In addition, the observation light emitted from the sample S in the opposite direction to the objective lens 206 is reflected by the dichroic mirror 212 and enters the fluorescence detection unit 213. The fluorescence detection unit 213 is composed of, for example, a barrier filter, a PMT, etc., receives the observation light reflected by the dichroic mirror 212, and outputs an electrical signal according to the amount of light. In addition, the fluorescence detection unit 213 detects the observation light across the observation surface of the sample S as the ultrashort pulse light scans the observation surface of the sample S.

The electrical signals output from the fluorescence detection units 207, 211, and 213 are input, for example, to a computer (not shown), which can generate an observation image based on the input electrical signals, display the generated observation image, and store data of the observation image.

Next, examples of the present invention and comparative examples will be described. The present invention is not limited to these examples.

<Preparation of optical glass>
The optical glasses according to the examples and comparative examples were produced by the following procedure. First, glass raw materials such as oxides, hydroxides, carbonates, phosphate compounds (phosphates, orthophosphates, etc.), and nitrates were weighed out so as to obtain the chemical compositions (mass %) shown in Tables 2 to 10. Next, the weighed raw materials were mixed and charged into a platinum crucible, melted at a temperature of 1100 to 1400°C for about 1 hour, and stirred and homogenized. After that, the temperature was lowered to an appropriate level, and the mixture was cast into a mold or the like and slowly cooled to obtain each sample.

<Measurement of the refractive index of optical glass>
The refractive index (n _d ) of each sample was measured using a precision refractive index measuring instrument ("Spectro Master HR" manufactured by TRIOPTICS). The Abbe number (ν _d ) and partial dispersion ratio (P _g,F ) were calculated using the actual measured values. The refractive index values used in the calculations were rounded down to seven decimal places.

<Measurement of internal transmittance of optical glass>
The transmittance of each sample was measured using an ultraviolet-visible-near infrared spectrophotometer (Hitachi High-Tech Science Corporation; "UH4150"). The internal transmittance was calculated from the difference in transmittance between a 12 mm thick sample and a 2 mm thick sample. Note that the description "devitrification" in the table indicates that measurement was impossible due to devitrification of the glass during production (i.e., it is impossible to use as optical glass).

<Evaluation of the dispersibility of optical glass>
The partial dispersion ratio (P _g,F ) is the ratio of (n _g -n _F ) to the primary dispersion (n _F -n _C ), where n _F is the refractive index of the glass for light with a wavelength of 486.133 nm (F line), n _C is the refractive index of the glass for light with a wavelength of 656.273 nm (C line), and n _g is the refractive index of the glass for light with a wavelength of 435.835 nm (g line).

The anomalous dispersion value (ΔP _g,F ) is an index showing anomalous dispersion, and was calculated by the following method: First, two types of glass, "NSL7" and "PBM2" (both are the names of glass types manufactured by OHARA CORPORATION), having the Abbe number (ν _d ) and partial dispersion ratio (P _g,F ) shown in Table 1, were used as reference materials.

Next, the partial dispersion ratio (Pg _,F ) was plotted on the vertical axis and the Abbe number ( _νd ) on the horizontal axis, with the straight line connecting the two points corresponding to the above-mentioned reference material as the reference line. The values of each example and each comparative example were plotted on the graph, and the difference between the vertical axis (partial dispersion ratio Pg _,F ) and the reference line was taken as ΔPg _,F . A partial dispersion ratio above the reference line is said to have positive anomalous dispersion, and a partial dispersion ratio below the line is said to have negative anomalous dispersion.

The equation for the baseline of this anomalous dispersion value (ΔP _g,F ) is P _g,F =0.641462+(−0.0016178)×ν _d (see the baseline in FIG. 6).

Tables 2 to 10 show the component composition (by mass), refractive index (n _d ), Abbe number (ν _d ), partial dispersion ratio (P _g,F ), the value of n _d +0.04×ν _d -3.00 as formula (i) (see formula (1)), the wavelength (λ ₅ ) at which the internal transmittance is 5%, the anomalous dispersion value (ΔP _g,F ), and the value of P _g,F +0.0030×ν _d -0.6900 as formula (ii) (see formula (2)) for each Example and Comparative Example.

If the value of formula (i) is 0 or a negative value, the relationship of formula (1) (n _d ≦−0.04×v _d +3.00) is satisfied. If the value of formula (ii) is 0 or a negative value, the relationship of formula (2) (P _g,F ≦−0.0030×v _d +0.6900) is satisfied.

FIG. 4 shows a graph plotting _λ5 vs. _vd for each Example and Comparative Example, FIG. 5 shows a graph plotting ΔPg _,F vs. _vd for each Example and Comparative Example, and FIG. 6 shows a graph plotting Pg _,F vs. _vd for each Example and Comparative Example.

*Formula (i)=n _d +0.04×ν _d -3.00
Formula (ii)=P _g,F +0.0030×ν _d -0.6900

From the above, it was confirmed that the optical glass of each Example had high internal transmittance and low partial dispersion ratio (P _g,F ) relative to Abbe number (ν _d ). In particular, even in the region where 1.60≦n _d ≦1.80, 25≦ν _d ≦35 and n _d ≦−0.04×ν _d +3.00 are satisfied, it was confirmed that there was little deviation from the reference line showing the relationship between the Abbe number and the partial dispersion ratio, and that the positive anomalous dispersion was low.

On the other hand, in each of the comparative examples, the samples were devitrified and could not be used as optical glass, had poor transmittance, or had a large partial dispersion ratio and high positive anomalous dispersion.

1: Imaging device, 101: Camera body, 102: Lens barrel, 103: Shooting lens, 104: Sensor chip, 105: Glass substrate, 106: Multichip module, 2: Multiphoton microscope, 201: Pulse laser device, 202: Pulse splitting device, 203: Beam adjustment unit, 204, 205, 212: Dichroic mirror, 206: Objective lens, 207, 211, 213: Fluorescence detection unit, 208: Condenser lens, 209: Pinhole, 210: Imaging lens, CAM: Imaging device, WL: Shooting lens, EF: Auxiliary light emission unit, M: LCD monitor, B1: Release button, B2: Function button, S: Sample

Claims (17)

In mass percentage,
_SiO2 content : 10 % or more and 28% or less ,
_B2O3 content : 6 % or more and ₂₀ % or less ,
Nb ₂ O ₅ content : 25 % or more and 44.08% or less ,
K ₂ O content : 15 % or more and 30% or less ,
_P2O5 content : 0 % or more and ₈ % or less;
Optical glass. In mass percentage,
2. The optical glass according to claim 1, wherein the ratio of the TiO2 content to the Nb2O5 content (TiO2 _{/ Nb2O5} ) is 0 _{or more} and _{0.3 or} less . In mass percentage,
SiO ₂ Content: 10% or more and 28% or less,
B ₂ O ₃ Content: 6% or more and 20% or less,
Nb ₂ O ₅ Content: 25% or more and 44.08% or less,
K ₂ O content: 15% or more and 30% or less,
Nb ₂ O ₅ TiO relative to the content ₂ The ratio of the contents of TiO ₂ /Nb ₂ O ₅ ) is greater than or equal to 0 and less than or equal to 0.3;
Optical glass. In mass percentage,
P ₂ O ₅ Content: 0% or more and 8% or less;
The optical glass according to claim 3. In mass percentage,
Li ₂ O content: 0% or more and 10% or less,
TiO ₂ Content: 0% or more and 8% or less,
RO (wherein R is at least one selected from the group consisting of Ca, Sr, Ba and Zn)
(representing the total content): 0% or more and 4% or less
The optical glass according to any one of claims 1 to 4, wherein In mass percentage,
Na ₂ O content: 0% or more and 10% or less,
ZrO ₂ Content: 0% or more and 12% or less,
T ₂ O ₅ Content: 0% or more and 12% or less,
WO ₃ Content: 0% or more and 5% or less,
Sb ₂ O ₃ Content: 0% or more and 1% or less,
6. The optical glass according to claim 1, wherein The refractive index (n _d ) is in the range of 1.60 to 1.80 .
The optical glass according to any one of claims 1 to 6 . the Abbe number (ν _d ) is in the range of 25 or more and 35 or less ;
The optical glass according to any one of claims 1 to 7 . The refractive index (n _d ) and the Abbe number (v _d ) satisfy the relationship represented by the following formula (1):
The optical glass according to any one of claims 1 to 8 .
n _d ≦-0.04×ν _d +3.00...(1) The wavelength (λ ₅ ) at which the internal transmittance is 5% is 355 nm or less.
The optical glass according to any one of claims 1 to 9 . The anomalous dispersion value (ΔP _g,F ) is 0.0080 or less.
The optical glass according to any one of claims 1 to 10 . The partial dispersion ratio (P _g,F ) and the Abbe number (ν _d ) satisfy the relationship represented by the following formula (2):
P _g,F ≦-0.003ν _d +0.6900...(2)
The optical glass according to any one of claims 1 to 11 . An optical element comprising the optical glass according to any one of claims 1 to 12 . An optical system comprising the optical element according to claim 13 . An interchangeable lens for a camera comprising the optical system according to claim 14 . 15. A microscope objective comprising the optical system of claim 14. An optical device comprising the optical system according to claim 14 .

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