WO2019207874A1 - Optical glass, optical element using same, optical system, interchangeable lens for camera, and optical device - Google Patents

Abstract

Provided is an optical glass containing, on a mass basis: 10-30% of SiO₂; 6-20% of B₂O₃; 25-50% of Nb₂O₅; 15-30% of K₂O; 0-8% of TiO₂; 0-8% of P₂O₅; 0-4% of RO (wherein R represents at least one selected from the group consisting of Ca, Sr, Ba and Zn); and 0-10% of Li₂O. The ratio (TiO₂/Nb₂O₅) of the TiO₂ content to the Nb₂O₅ content is 0-0.3.

Description

Optical glass, optical element using the same, optical system, interchangeable lens for camera, and optical apparatus

The present invention relates to an optical glass, an optical element using the optical glass, an optical system, an interchangeable lens for a camera, and an optical device. The present invention claims the priority of Japanese Patent Application No. 2018-082588 filed on April 23, 2018, and for the designated countries where weaving by reference of documents is permitted, the contents described in the application are as follows: Incorporated into this application by reference.

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

JP 2009-286670 A

The first aspect of the present invention is, in mass percentage, SiO ₂ : 10 to 30%, B ₂ O ₃ : 6 to 20%, Nb ₂ O ₅ : 25 to 50%, K ₂ O: 15 to 30%, TiO ₂ : 0 to 8%, P ₂ O ₅ : 0 to 8%, RO (wherein R represents at least one selected from the group consisting of Ca, Sr, Ba and Zn): 0 to 4 _{%, Li 2 O: 0 ~} 10%, a ratio of TiO ₂ with respect to _{Nb 2 O 5 (TiO 2 /} Nb 2 O 5) is 0 to 0.3, the optical glass.

The second aspect of the present invention is an optical element using the above-described optical glass.

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

4th aspect of this invention is the interchangeable lens for cameras containing the above-mentioned optical system.

A fifth aspect of the present invention is an optical device including the above-described optical system.

FIG. 1 is a perspective view of an imaging apparatus including an optical element using the optical glass according to the present embodiment. 2A and 2B are schematic views of another example of an imaging apparatus including an optical element using the optical glass according to the present embodiment, and FIG. 2A is a front view of the imaging apparatus. FIG. 2B is a rear view of the imaging apparatus. FIG. 3 is a block diagram illustrating an example of a configuration of a multiphoton microscope including an optical element using the optical glass according to the present embodiment. FIG. 4 is a graph plotting λ ₅ and ν _d of each example and each comparative example. FIG. 5 is a graph in which ΔP _{g, F} and ν _d of each example and each comparative example are plotted. Figure 6 is a graph plotting P _{g, F} and [nu _d of Examples and Comparative Examples.

Hereinafter, an embodiment of the present invention (hereinafter referred to as “the present embodiment”) will be described. The following embodiments are examples for explaining the present invention, and are not intended to limit the present invention to the following contents.

The optical glass according to the present embodiment is a SiO ₂ —B ₂ O ₃ —Nb ₂ O ₅ —K ₂ O-based optical glass, and has a mass percentage of SiO ₂ : 10 to 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 is Ca And represents at least one selected from the group consisting of Sr, Ba, and Zn.): 0 to 4%, Li ₂ O: 0 to 10%, and the content of TiO ₂ with respect to the content of Nb ₂ O ₅ The ratio (TiO ₂ / Nb ₂ O ₅ ) is 0 to 0.3.

In this specification, unless otherwise specified, the content of each component is assumed to be% by mass with respect to the total weight of the glass in terms of oxide composition. As used herein, the oxide equivalent composition means that oxides, composite salts, etc. used as raw materials for glass constituent components are all decomposed and changed to oxides when melted, and the total mass of the oxides is 100%. It is the composition which described each component contained in glass.

Conventionally, microscopic observation using ultraviolet light such as a fluorescence microscope has been actively performed. As a material for optical glass used in such an optical device, a glass material having a high transmittance in the ultraviolet region or the like is desired. Moreover, in an optical system in such an optical apparatus, chromatic aberration is corrected (achromaticity) by combining glass materials having different refractive indexes and dispersions. From the viewpoint of performing such achromaticity, high dispersion is achieved. A glass material having a small partial dispersion ratio while having a small Abbe number is desired.

However, as a characteristic of general optical glass, the partial dispersion ratio (P _{g, F} ) with respect to the Abbe number (ν _d ) tends to increase as the dispersion increases. Therefore, the optical glass having high dispersion has a problem that the relationship between the Abbe number and the partial dispersion ratio greatly deviates from the linear relationship (reference line) in the positive direction, and the positive anomalous dispersion becomes large.

In this regard, the optical glass according to the present embodiment has high dispersion and a low partial dispersion ratio (P _{g, F} ) with respect to the Abbe number (ν _d ). Further, the optical glass according to the present embodiment has a high transmittance in a wide region including the ultraviolet light region. Furthermore, as a preferable aspect of the present embodiment, for example, 1.60 ≦ n _d ≦ 1.80, 25 ≦ ν _d ≦ 35, and n _d ≦ −0.04 × ν _d +3.00. In the medium refractive index high dispersion region, 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. An optical glass satisfying the relationship of 0030 × ν _d +0.6900 can be realized.

Such an optical glass has a high internal transmittance of ultraviolet light and a low partial dispersion ratio (P _{g, F} ) with respect to the Abbe number (ν _d ), and the relationship between the Abbe number and the partial dispersion ratio is linear. It is controlled to approximate the relationship (reference line). That is, the optical glass has a small deviation of the partial dispersion ratio from the reference line in the positive direction and low positive anomalous dispersion. Further, internal transmittance of the ultraviolet region, the refractive index with respect to the Abbe number _{(ν d) (n d)} , the partial dispersion ratio Abbe number _{(ν d) (P g,} F) also has a unique optical glass Is possible. Since the optical glass according to the present embodiment has such characteristics, it can sufficiently satisfy the above-described requirements.

Hereinafter, the component composition of the optical glass according to the present embodiment will be described.

SiO ₂ is an oxide that forms glass and can improve devitrification resistance. On the other hand, if it is contained in a large amount, the meltability tends to deteriorate and the Abbe number tends to increase. From this viewpoint, the content is 10 to 30%. Further, 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. Further, the refractive index can be lowered with respect to the Abbe number. On the other hand, when it is contained in a large amount, the devitrification resistance is lowered, and the Abbe number tends to be increased. From this viewpoint, the content is 6 to 20%. The upper limit of the content may be 19% or 18%. Further, 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. Further, the refractive index can be lowered with respect to the Abbe number. On the other hand, when it is contained in a large amount, devitrification resistance and meltability are lowered, the partial dispersion ratio with respect to the Abbe number is increased, and the transmittance tends to be deteriorated. From this viewpoint, the content is 25 to 50%. Further, the upper limit of the content is preferably 49%, more preferably 48%. Further, 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 with respect to the Abbe number. Further, the transmittance can be improved. On the other hand, when it is contained in a large amount, the devitrification resistance is lowered and the Abbe number tends to be increased. From this viewpoint, the content is 15 to 30%. Further, the upper limit of the content may be 26% or 22%. Moreover, the lower limit of the content may be more than 15% and may be 15.5%.

TiO ₂ is an optional component that can lower the refractive index relative to the Abbe number when it exceeds 0%. On the other hand, if it is contained in a large amount, the transmittance tends to deteriorate. From such a viewpoint, the content is 0 to 8%. The upper limit of the content may be 6% or 4%. Moreover, the lower limit of the content may be over 0% or 1%.

Incidentally, when the content of TiO ₂ with respect to the content of _Nb 2 _{O 5} is too large, the transmittance tends to decrease. From this viewpoint, the content ratio of TiO ₂ to the content of _{Nb 2 O 5 (TiO 2 /} Nb 2 O 5) is 0 to 0.3. Further, the upper limit value of the ratio may be 0.25 or 0.24. Further, the lower limit value of the ratio may be greater than 0 or 0.01.

P ₂ O ₅ is an optional component that lowers the refractive index relative to the Abbe number when it exceeds 0%. On the other hand, when it is contained in a large amount, the partial dispersion ratio with respect to the Abbe number increases, and the Abbe number tends to increase. From such a viewpoint, the content is 0 to 8%. Moreover, the upper limit of the content may be 7% or 6%. Moreover, the lower limit of the content may be over 0% or 1%.

RO (R represents one or more selected from the group consisting of Ca, Sr, Ba, and Zn) is an optional component that lowers the partial dispersion ratio relative to the Abbe number when it exceeds 0%. On the other hand, when it is contained in a large amount, the devitrification resistance is lowered, and the refractive index with respect to the Abbe number tends to increase. From this point of view, the total content of components corresponding to RO is 0 to 4%. Further, the upper limit of the total content may be 3% or 2%. Further, the lower limit of the total content may be more than 0% or 0.3%.

Li ₂ O is an optional component that lowers the partial dispersion ratio relative to the Abbe number and improves the transmittance when it exceeds 0%. On the other hand, when it is contained in a large amount, the devitrification resistance decreases, the Abbe number increases, and the refractive index with respect to the Abbe number tends to increase. From this viewpoint, the content is 0 to 10%. Further, the upper limit of the content may be 8% or 7%. Moreover, the lower limit of the content may be over 0% or 1%.

Na ₂ O is an optional component that lowers the partial dispersion ratio relative to the Abbe number and improves the transmittance when it exceeds 0%. On the other hand, when it is contained in a large amount, the devitrification resistance decreases, the Abbe number increases, and the refractive index with respect to the Abbe number tends to increase. From this viewpoint, the content is 0 to 10%. Further, the upper limit of the content may be 8% or 7%. Moreover, the lower limit of the content may be over 0% or 1%.

ZrO ₂ is an optional component that lowers the partial dispersion ratio relative to the Abbe number without increasing the Abbe number when it exceeds 0%. On the other hand, when it is contained in a large amount, the devitrification resistance is lowered, and the transmittance tends to deteriorate. From this viewpoint, the content is 0 to 12%. Moreover, the upper limit of the content may be 10% or 8%. Moreover, the lower limit of the content may be over 0%, or 1%.

Ta ₂ O ₅ is an optional component that keeps the Abbe number low when it exceeds 0%. On the other hand, when it is contained in a large amount, the devitrification resistance tends to be lowered. From this viewpoint, the content is 0 to 12%. Moreover, the upper limit of the content may be 10% or 8%. Moreover, the lower limit of the content may be over 0%, or 2%.

WO ₃ is an optional component that keeps the Abbe number low when it exceeds 0%. On the other hand, if it is contained in a large amount, the transmittance tends to deteriorate. From such a viewpoint, the content is 0 to 5%. Further, the upper limit of the content may be 4% or 3%. Moreover, the lower limit of the content may be over 0% or 1%.

Sb ₂ O ₃ is an optional component effective for clarifying and homogenizing glass when it contains more than 0%. From such a viewpoint, the content is preferably 0 to 1%.

Not only each component mentioned above but other arbitrary components can also be added in the range which does not hinder achievement of the target optical glass in this embodiment.

The optical glass according to the present embodiment having the above-described component composition is highly dispersed, has a high internal transmittance in a wide region including the ultraviolet region, and has a partial dispersion ratio with respect to the Abbe number (ν _d ) ( _{Pg, F} ) is low. In particular, such characteristics can be maintained even in a medium refractive index high dispersion region.

Hereinafter, suitable characteristics of the optical glass in the present embodiment will be described.

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

Next, as a preferable aspect of the optical glass according to the present embodiment, one in which the refractive index (n _d ) and the Abbe number (ν _d ) satisfy the relationship represented by the following formula (1) can be given.
n _d ≦ −0.04 × ν _d +3.00 (1)

Among them, the refractive index (n _d ) is in the range of 1.60 to 1.80, and the Abbe number (ν _d ) is such that the desired characteristics can be more satisfactorily exhibited even in the medium refractive index high dispersion region. Examples thereof include those in the range of 25 to 35 and satisfying the relationship represented by the formula (1).

And the optical glass which concerns on this embodiment has a high ultraviolet light transmittance. For example, from the viewpoint of utilization of ultraviolet light and usefulness for achromatization, an optical glass having good transmittance in the ultraviolet light region and a low partial dispersion ratio with respect to the Abbe number can be obtained. A preferred specific example thereof is an optical glass having a wavelength (λ ₅ ) at which the internal transmittance is 5% is 355 nm or less.

Furthermore, as a preferable specific example of the present embodiment, an optical glass having an anomalous dispersion value (ΔP _{g, F} ) of 0.0080 or less can be given. The anomalous dispersion value is an index of anomalous dispersion, and a specific definition will be described later.

Conventionally, there is a problem that the anomalous dispersion value (ΔP _{g, F} ) increases as the dispersibility of the optical glass increases, particularly in the medium refractive index high dispersion region. As a specific example, 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)

As a more preferable aspect of the optical glass according to the present embodiment, the wavelength (λ ₅ ) satisfying the relationship represented by the above formula (2) and having an internal transmittance of 5% is 355 nm or less. Yes, the anomalous dispersion value (ΔP _{g, F} ) is 0.0080 or less. An optical glass having these characteristics also has a high internal transmittance of ultraviolet light and a low partial dispersion ratio (P _{g, F} ) with respect to the Abbe number (ν _d ) even in a medium refractive index high dispersion region. .

The optical glass according to the present embodiment having the above-described characteristics can be suitably used as an optical element used in an optical device or the like, for example. Such optical elements include mirrors, lenses, prisms, filters, and the like. Examples of the optical system including such an optical element include an objective lens, a condenser lens, an imaging lens, and an interchangeable lens for a camera. Furthermore, these optical systems can be suitably used for optical devices such as imaging devices such as interchangeable lens cameras and non-lens interchangeable cameras, and microscopes such as multiphoton microscopes. Such an optical device is not limited to the above-described imaging device and microscope, and includes a video camera, a teleconverter, a telescope, binoculars, monoculars, a laser rangefinder, a projector, and the like. Examples of these will be described below.

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

The imaging device 1 is a so-called digital single-lens reflex camera (lens interchangeable camera), and the photographing lens 103 (optical system) includes an optical element having the optical glass according to the present embodiment as a base material. A lens barrel 102 is detachably attached to a lens mount (not shown) of the camera body 101. Then, light passing through the photographing lens 103 of the lens barrel 102 is imaged on a sensor chip (solid-state imaging device) 104 of a multichip module 106 disposed on the back side of the camera body 101. The 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 mounted on the glass substrate 105 as a bare chip.

FIG. 2 is a schematic diagram of another example in which the optical device is an imaging device. 2A is a front view of the imaging device CAM, and FIG. 2B is a rear view of the imaging device CAM.

The imaging device CAM is a so-called digital still camera (lens non-exchangeable camera), and the photographing lens WL (optical system) includes an optical element having the optical glass according to the present embodiment as a base material.

When the imaging device CAM presses a power button (not shown), the shutter (not shown) of the photographing lens WL is opened, and the light from the subject (object) is condensed by the photographing lens WL and arranged on the image plane. An image is formed on the image sensor. The subject image formed on the image sensor is displayed on the liquid crystal monitor M arranged behind the image pickup device CAM. The photographer determines the composition of the subject image while looking at the liquid crystal monitor M, and then depresses the release button B1 to capture the subject image with the image sensor, and records and saves it in a memory (not shown).

The imaging device CAM is provided with an auxiliary light emitting unit EF that emits auxiliary light when the subject is dark, a function button B2 used for setting various conditions of the imaging device CAM, and the like.

<Multiphoton microscope>
FIG. 3 is a block diagram illustrating an example of the configuration of the multiphoton microscope 2.

The multiphoton microscope 2 includes an objective lens 206, a condensing lens 208, and an imaging lens 210. At least one of the objective lens 206, the condensing lens 208, and the imaging lens 210 includes an optical element that uses the optical glass according to the present embodiment as a base material. Hereinafter, the optical system of the multiphoton microscope 2 will be mainly described.

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

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

The beam adjusting unit 203 has a function of adjusting the beam diameter of the ultrashort pulse light incident from the pulse dividing device 202 according to the pupil diameter of the objective lens 206, the wavelength of the multiphoton excitation light emitted from the sample S, and the ultrashort wavelength. Function to adjust the focusing and divergence angle of ultrashort pulse light to correct axial chromatic aberration (focus difference) with the wavelength of the pulsed light, while the pulse width of ultrashort pulse light passes through the optical system In order to correct the spread due to the velocity dispersion, a pre-chirp function (group velocity dispersion compensation function) for imparting the reverse group velocity dispersion to the ultrashort pulse light is provided.

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

For example, in the case of fluorescence observation of the sample S, the fluorescent dye in which the sample S is stained is multiphoton excited in the vicinity of the irradiated region of the sample S with the ultrashort pulse light and in the vicinity thereof. Fluorescence having a shorter wavelength than the pulsed light (hereinafter referred to as “observation light”) is emitted.

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

The observation light reflected by the dichroic mirror 205 enters the fluorescence detection unit 207. The fluorescence detection unit 207 includes, for example, a barrier filter, a PMT (photomultiplier tube), and the like, receives observation light reflected by the dichroic mirror 205, and outputs an electrical signal corresponding to the amount of light. . Further, the fluorescence detection unit 207 detects observation light over the observation surface of the sample S as the ultrashort pulse light is scanned on the observation surface of the sample S.

On the other hand, the observation light that has passed through the dichroic mirror 205 is descanned by a scanning unit (not shown), passes through the dichroic mirror 204, is condensed by the condenser lens 208, and is at a position almost conjugate with the focal position of the objective lens 206. It passes through the provided pinhole 209, passes through the imaging lens 210, and enters the fluorescence detection unit 211.

The fluorescence detection unit 211 includes, for example, a barrier filter, a PMT, and the like, receives the observation light imaged on the light receiving surface of the fluorescence detection unit 211 by the imaging lens 210, and outputs an electric signal corresponding to the light amount. In addition, the fluorescence detection unit 211 detects the observation light over the observation surface of the sample S as the ultrashort pulse light is scanned on the observation surface of the sample S.

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

Further, the observation light emitted from the sample S in the direction opposite to the objective lens 206 is reflected by the dichroic mirror 212 and enters the fluorescence detection unit 213. The fluorescence detection unit 213 includes, for example, a barrier filter, a PMT, and the like, receives observation light reflected by the dichroic mirror 212, and outputs an electrical signal corresponding to the amount of light. Further, the fluorescence detection unit 213 detects observation light over the observation surface of the sample S as the ultrashort pulse light is scanned on the observation surface of the sample S.

The electrical signals output from the fluorescence detection units 207, 211, and 213 are input to, for example, a computer (not shown), and the computer generates an observation image based on the input electrical signal and generates the generated observation. Images can be displayed and observation image data can be stored.

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

<Production of optical glass>
The optical glass according to each example and each comparative example was produced by the following procedure. First, glass raw materials such as oxides, hydroxides, carbonates, phosphoric acid compounds (phosphates, orthophosphoric acids, etc.), and nitrates so as to have the chemical compositions (mass%) shown in Tables 2 to 10. Was weighed. Next, the weighed raw materials were mixed, put into a platinum crucible, melted at a temperature of 1100 to 1400 ° C. for about 1 hour, and homogenized with stirring. Then, after lowering to an appropriate temperature, each sample was obtained by casting into a mold or the like and gradually cooling.

<Measurement of refractive index of optical glass>
The refractive index (n _d ) of each sample was measured using a precise refractive index measuring instrument (manufactured by TRIOPTICS; “Spectro Master HR”). Then, the Abbe number (ν _d ) and the partial dispersion ratio (P _{g, F} ) were calculated using the obtained actual measurement values. In addition, the value of the refractive index used for the calculation was set to the seventh decimal place.

<Measurement of internal transmittance of optical glass>
The transmittance of each sample was measured using an ultraviolet-visible near-infrared spectrophotometer (manufactured by Hitachi High-Tech Science Co., Ltd .; “UH4150”). The internal transmittance was calculated from the difference in transmittance between the 12 mm thick sample and the 2 mm thick sample. In addition, the description of “devitrification” in the table indicates that when glass was manufactured, measurement was impossible due to devitrification of the glass (that is, it cannot be used as optical glass). Show.

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

The anomalous dispersion value (ΔP _{g, F} ) is an index indicating anomalous dispersion and was calculated by the following method. First, two glass types “NSL7” and “PBM2” (both OHARA Glass Co., Ltd.) having the Abbe number (ν _d ) and the partial dispersion ratio (P _{g, F} ) shown in Table 1 were used as reference materials. .

Subsequently, the partial dispersion ratio (P _{g, F} ) is taken on the vertical axis, the Abbe number (ν _d ) is taken on the horizontal axis, and a straight line connecting the two points corresponding to the above-mentioned reference material was taken as the reference line. And the value of each Example and each comparative example was plotted on the said graph, and the difference of the vertical axis | shaft (partial dispersion ratio _{Pg, F} ) with a reference line was set to (DELTA) Pg _{, F.} When the partial dispersion ratio is above the reference line, it is said to have positive anomalous dispersion, and when it is below the straight line, it has negative anomalous dispersion.

The equation of the base line of this anomalous dispersion value (ΔP _{g, F} ) is P _{g, F} = 0.641462 + (− 0.0016178) × ν _d (see the base line in FIG. 6).

Tables 2 to 10 show the composition (mass basis), refractive index (n _d ), Abbe number (ν _d ), partial dispersion ratio (P _{g, F} ), and formula (i) of each example and each comparative example. n _d + 0.04 × ν _d −3.00 (see formula (1)), wavelength (λ ₅ ) at which the internal transmittance is 5%, anomalous dispersion value (ΔP _{g, F} ), and formula (ii) ) Represents a value of P _{g, F} + 0.0030 × ν _d −0.6900 (see formula (2)).

If the value of equation (i) is 0 or a negative value, the relationship of equation (1) (n _d ≦ −0.04 × ν _d +3.00) is satisfied. Further, if the value of the formula (ii) is 0 or a negative value, the relationship of the formula (2) (P _{g, F} ≦ −0.0030 × ν _d +0.6900) is satisfied.

FIG. 4 shows a graph plotting λ ₅ and ν _d of each example and each comparative example, and FIG. 5 shows a graph plotting ΔP _{g, F} and ν _d of each example and each comparative example. 6 shows a graph plotting P _{g, F} and [nu _d of examples and Comparative examples.

* 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 a high internal transmittance and a low partial dispersion ratio (P _{g, F} ) with respect to the 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, the Abbe number and the part It was confirmed that the deviation from the reference line indicating the relationship of the dispersion ratio was small and the positive anomalous dispersion was low.

On the other hand, in each comparative example, the sample was devitrified, so that it could not be used as optical glass, the transmittance was poor, or the partial dispersion ratio was large and the positive anomalous dispersibility was high.

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

Claims (12)

1. In mass percentage,
   SiO ₂ : 10 to 30%,
   B ₂ O ₃ : 6 to 20%,
   Nb ₂ O ₅ : 25 to 50%,
   K ₂ O: 15-30%,
   TiO ₂ : 0 to 8%,
   P ₂ O ₅ : 0 to 8%
   RO (wherein R represents at least one selected from the group consisting of Ca, Sr, Ba and Zn): 0 to 4%,
   Li ₂ O: 0 to 10%,
   And
   The ratio of the content of TiO ₂ to the content of _{Nb 2 O 5 (TiO 2 /} Nb 2 O 5) is 0 to 0.3
   Optical glass.
2. In mass percentage,
   Na ₂ O: 0 to 10%,
   ZrO ₂ : 0 to 12%,
   Ta ₂ O ₅ : 0 to 12%,
   WO ₃ : 0-5%,
   Sb ₂ O ₃ : 0 to 1%
   The optical glass according to claim 1, wherein
3. The refractive index (n _d ) is in the range of 1.60 to 1.80.
   The optical glass according to claim 1 or 2.
4. The Abbe number (ν _d ) is in the range of 25 to 35,
   The optical glass according to any one of claims 1 to 3.
5. The refractive index (n _d ) and the Abbe number (ν _d ) satisfy the relationship represented by the following formula (1).
   The optical glass according to any one of claims 1 to 4.
   n _d ≦ −0.04 × ν _d +3.00 (1)
6. 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 5.
7. The anomalous dispersion value (ΔP _{g, F} ) is 0.0080 or less.
   The optical glass according to any one of claims 1 to 6.
8. 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 7.
9. An optical element using the optical glass according to any one of claims 1 to 8.
10. An optical system including the optical element according to claim 9.
11. An interchangeable lens for a camera including the optical system according to claim 10.
12. An optical device comprising the optical system according to claim 10.

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