JP5057505B2 - Visibility correction filter glass manufacturing method - Google Patents

Description

  The present invention is used in color correction filters for digital still cameras (hereinafter referred to as DSCs), color video cameras, and the like, and transmits the visible region and corrects the visibility with a sharp cut characteristic and a near ultraviolet cut characteristic near 700 nm. The present invention relates to a method for producing filter glass.

Conventionally, solid-state imaging devices such as CCDs and CMOSs used in DSCs and color video cameras have spectral sensitivity ranging from the visible region to the near infrared region near 1100 nm. Therefore, since good color reproducibility cannot be obtained as it is, it is necessary to correct to normal human visibility using a filter that absorbs the infrared region. This filter uses a filter glass in which CuO is added to a phosphate glass or a fluorophosphate glass so as to selectively absorb near-infrared wavelengths. This filter glass contains CuO containing a large amount of P ₂ O ₅ as an essential component, and exhibits a blue-green color by forming Cu ²⁺ ions coordinated to a large number of oxygen ions in an oxidizing molten atmosphere. It has a near infrared cut characteristic.

  Among the filter glasses, phosphate-based glass has insufficient weather resistance, so it causes weathering on the polished glass surface. System glass is mainly used.

As a typical near-infrared cut filter glass made of CuO-fluorophosphate glass, the one described in Patent Document 1 is known as a typical one, and the sharp cut property at 600 to 700 nm is enhanced to absorb at 700 to 1200 nm. In order to strengthen the strength, there is one described in Patent Document 2 in which a specific amount of V ₂ O ₅ is added to a CuO-fluorophosphate glass.

Japanese Patent Laid-Open No. 1-219037 Japanese Patent Laid-Open No. 10-194776

As described above, a solid-state imaging device such as a CCD or CMOS has a spectral sensitivity ranging from the visible region to the near infrared region near 1100 nm, and also has sensitivity in the near ultraviolet region. The transmittance curve of a fluorophosphate glass filter containing Cu ²⁺ ions as described in the above patent document does not transmit a wavelength of approximately 300 nm or less, and the transmittance increases rapidly in the wavelength range of 300 nm to 400 nm, It is a curve that gradually falls from 600 nm to 700 nm. When the transmittance in the visible region is set to a certain level or more, it has a characteristic of slightly transmitting the longer wavelength side exceeding 900 to 1000 nm. For this reason, it may be difficult to make the human visibility and the color reproducibility of the photographed image completely coincide with each other only by absorption by the glass filter.

In such a case, the near-ultraviolet region and the near-infrared region are further cut by using a dielectric multilayer film in combination. The dielectric multilayer film is composed of an alternating laminated film of titanium dioxide (TiO ₂ ) as a high refractive index layer and silicon dioxide (SiO ₂ ) as a low refractive index layer, and is formed on the surface of a near infrared cut filter glass. In some cases, a low-pass filter may be formed by vacuum deposition or sputtering on the surface of a crystal plate built in the camera. The transmission characteristic of the infrared cut film by the dielectric multilayer film is that light having a wavelength of about 400 nm or less and 700 nm or more is reflected and hardly transmitted, and 400 to 700 nm is transmitted with respect to light incident perpendicularly to the film formation surface. . As a result, in an optical system that combines absorption by a glass filter and reflection by a dielectric multilayer film, a transmittance curve that transmits 400 to 600 nm at a high rate, gradually decreases from 600 to 700 nm, and does not transmit 700 nm or more. The characteristics can be drawn and approximated to human visibility.

  By the way, in recent years, in a DSC or the like using an image sensor with a high pixel count, a purple outline blur called purple fringe is recognized in a photographed image due to chromatic aberration of a lens system. . In other words, the refractive index of a medium such as glass that constitutes an optical element has a property that depends on the wavelength of light, and even for the same medium, the refractive index for visible light, the refractive index for near ultraviolet light, and the refraction for near infrared light. It is different from the rate. Due to this property, when light passes through the glass optical element, the shorter wavelength light is refracted more strongly, and the longer wavelength light is less refracted. The infrared optical path is branched, and near ultraviolet rays are focused on the near side and near infrared rays are focused on the rear side relative to the focal position of visible light (axial chromatic aberration). At the position where the light beam branched in this way reaches the photoelectric conversion surface of the image sensor, the chromatic aberration becomes a two-dimensional deviation, and this deviation becomes a blur radius due to near ultraviolet rays or near infrared rays, and blurring occurs. Cause. In particular, in an image sensor with a high pixel count, the influence of chromatic aberration is easily recognized as the pixel size is reduced, and the influence is more likely to occur in the peripheral part than in the center part of the captured image. In other words, the problem of contour blur due to chromatic aberration can be said to be a problem that has become apparent as the number of pixels of the image sensor increases.

  The above-mentioned dielectric multilayer film cuts light in the ultraviolet region and infrared region by reflection, but the dielectric multilayer film changes its reflection characteristics depending on the incident angle of the light beam, so that it transmits light incident on the film surface perpendicularly. Even light with a wavelength of 0 may not be completely reflected with respect to obliquely incident light and may be transmitted. For this reason, the outline blur due to chromatic aberration cannot be eliminated, and the influence is likely to occur at the periphery of the image where the light incident obliquely on the image sensor increases. In addition, when the light reflected by the dielectric multilayer film becomes stray light in the optical system and enters the dielectric multilayer film obliquely again, it reaches the photoelectric conversion surface of the image sensor and changes the color of the photographed image such as false color. It will cause disturbance.

  Therefore, if light in the ultraviolet region or infrared region can be cut by glass absorption without relying on the dielectric multilayer film, the adverse effects can be eliminated even if these unnecessary lights are incident obliquely. As the method, since the above-mentioned CuO-fluorophosphate glass originally has absorption in the ultraviolet region, it is conceivable to increase the amount of CuO added in order to enhance absorption in the near ultraviolet region. FIG. 4 shows a transmittance curve of a conventional CuO-fluorophosphate glass in which the amount of CuO added is changed. This is a comparative glass to be described later, in which curve 9 is added with 2 parts by mass of CuO and curve 10 is added with 5 parts by mass of CuO with respect to 100 parts by mass of the mother glass made of fluorophosphate glass. is there. As can be seen from FIG. 4, when the amount of CuO added is increased, the absorption in the near infrared region increases with the absorption in the near ultraviolet region, and the cut pattern of 600 to 700 nm moves to the short wavelength side. That is, the cut characteristics in the near-ultraviolet region and the near-infrared region cannot be controlled independently only by changing the CuO addition amount.

  The near-ultraviolet or near-infrared cut pattern of the visibility correction filter that is actually used in DSCs and video cameras is determined according to the sensitivity characteristics of each CCD or CMOS or the design of the camera. It is desirable that the cut characteristic in the ultraviolet region and the cut characteristic in the near infrared region can be controlled independently.

  The present invention has been made in consideration of such circumstances, and a filter glass used for correcting the visibility of a solid-state imaging device has a near-ultraviolet absorption characteristic, and a near-infrared absorption characteristic and a near-ultraviolet absorption characteristic. An object of the present invention is to provide a method capable of stably supplying independently changeable glass. It is another object of the present invention to provide a visibility correction filter glass that can reduce disturbances in a captured image such as blurring caused by near-ultraviolet chromatic aberration of a lens system.

In order to solve the above problems, the present invention provides 0.02 to 0.5 parts by mass of V ₂ O ₅ in an outer ratio with respect to 100 parts by mass of the basic glass made of CuO-fluorophosphate glass. And 0.1 to 10 parts by mass of a compound component that acts as an oxidant with respect to V is added and melted , and the basic glass is in mass% and P ₂ O ₅ 10 to 60%. AlF ₃
0 to 20%, RF (R is at least one of Li, Na, and K) 1 to 30%, R′F ₂ (R ′ is at least one of Mg, Ca, Sr, and Ba) 10 to 75% , (
However, it contains 0.5 to 12 parts by mass of CuO as an outer portion with respect to 100 parts by mass of the base glass having a total of 90% or more of the total components composed of oxides up to 70% of the total fluoride weight). The component that acts as an oxidizing agent for V is any one selected from nitric acid compounds, sulfuric acid compounds, peroxides, perchloric oxides, and chloric acids of the metal elements constituting the basic glass. It is added in the above form .

  According to the present invention, it is possible to stably produce glass that can absorb near-ultraviolet rays in addition to the absorption characteristics of near-infrared rays. Therefore, in the imaging optical system using the glass obtained by the present invention, unnecessary. Ultraviolet rays do not reach the image sensor, and it is possible to reduce disturbance of the captured image due to outline blurring or stray light ultraviolet rays caused by near ultraviolet chromatic aberration. In addition, since the near-ultraviolet cut characteristic and the near-infrared cut characteristic can be controlled independently, a filter having characteristics suited to the image sensor used in combination with the glass obtained by the present invention can be provided. Contributes to improved color reproducibility.

The present invention achieves the above-mentioned object by the above-described configuration, and the reason why the content of each component constituting the glass in the present invention is limited as described above will be described below.

First, the reason why the CuO-fluorophosphate glass is used as the basic glass is that, as described above, the absorption characteristics in the near-infrared region due to Cu ²⁺ ions coordinated to oxygen ions are necessary for correcting the visibility.

V ₂ O ₅ shows absorption in the ultraviolet region in fluorophosphate glass, so it is added as an ultraviolet absorber, but if it is less than 0.02 parts by mass relative to 100 parts by mass of the basic glass, absorption in the near ultraviolet region The effect is not sufficient, and when added over 0.5 parts by mass, absorption appears in the visible region and the visible transmittance is greatly reduced. Preferably it is 0.05-0.3 mass part, More preferably, let a lower limit be 0.1 mass part.

V ₂ O ₅ is known to have a strong absorption in the ultraviolet region in the state of V ⁵⁺ in the glass, V ⁵⁺ is among the components in the glass, particularly easily reduced by other transition metals, It changes to V ⁴⁺ and V ³⁺ which have no absorption in the ultraviolet region. For this reason, there exists a fault that an ultraviolet-ray absorption characteristic is weakened and is not stabilized. Examples of transition metals that coexist in glass include Cu, which is an essential component as a near-infrared absorber, and Fe and Ti that are mixed as impurities from raw materials, but since Fe and Ti that are mixed as impurities are in trace amounts. The effect is small, and the effect of Cu is large.

In Patent Document 2 described above, a glass in which a small amount of V ₂ O ₅ is added to a CuO-fluorophosphate glass is disclosed, but under normal melting conditions, V ions in the glass are caused by the influence of Cu or F. It becomes V ⁴⁺ and shows absorption around 1000 nm, and the ultraviolet absorption characteristics due to V ⁵⁺ cannot be expressed stably. Therefore, in Patent Document 2 introduces a _V 2 _{O 5} for the purpose of enhancing the absorption at 700 to 1200 nm.

In the present invention, by adding the above-mentioned predetermined amount of V ₂ O ₅ and adding 0.1 to 10 parts by mass of a compound component that acts as an oxidant to V and melting it, the UV absorption characteristics by V ⁵⁺ are stabilized. It was made to express. In this case, the compound component that acts as an oxidizing agent for V is any one selected from nitric acid compounds, sulfuric acid compounds, peroxides, perchloric oxides and chloric acids of the metal elements constituting the basic glass in the present invention. One or more forms, for example, LiNO ₃ , MgSO ₄ , BaO ₂ , KClO ₄ , NaClO ₃ , NaLiNO ₃ , Sr (NO ₃ ) ₂ , Li ₂ SO ₄ , BaSO, as shown in the Examples below. ₄ , Na ₂ O ₂ , K ₂ O ₂ , Ca (ClO ₄ ) ₂ , LiClO ₄ , KClO ₃ , Ba (ClO ₃ ) _{2 and the} like are preferably added. When added as a glass component compound, these cations finally remain in the glass to form the glass, so there is no waste of raw materials used, and V is oxidized relatively stably through the melting process. It acts as an agent, and as a result, the ultraviolet absorption characteristics by V ⁵⁺ can be stabilized. In addition, since it does not exhibit absorption at a specific wavelength, there is an advantage that the transmittance characteristic as the visibility correction filter intended by the present invention is not disturbed.

As the oxidizing agent, MnO ₂ , Cr ₂ O ₃ , CeO _{2 and the} like are also known, but depending on the amount added, absorption inherent to these components may appear. For example, CeO ₂ contains CuO-containing fluorine. When coexisting with V ions in a phosphate glass, V shifts the redox equilibrium of Ce in the oxidation direction, and V itself is reduced to V ⁴⁺ or V ³⁺ having no absorption in the ultraviolet region. Since it has been found by experiments by the inventor, it is not suitable for the purpose of the present invention. Therefore, in the present invention, it is necessary to add 0.1 to 10 parts by mass of a compound component that acts as an oxidizing agent for V and melt.

If the component acting as an oxidizing agent for V is less than 0.1 parts by mass with respect to 100 parts by mass of the basic glass, the effect of maintaining the redox balance of V at V ⁵⁺ is not sufficient, and 10 parts by mass If it exceeds, foaming at the initial stage of melting becomes excessive and bubbles may remain in the glass, which is not preferable as glass for optical filters. Preferably it is 0.5-8 mass parts.

Next, components constituting the basic glass will be described. P ₂ O ₅ is a main component that forms a network structure of glass, but if it is less than 10%, vitrification is difficult, and if it exceeds 60%, the chemical durability is lowered and there is a concern about the influence of weathering in long-term use. Is done. Preferably it is 20 to 50%.

AlF ₃ is an effective component for improving the chemical durability of the glass, but if it exceeds 20%, the meltability of the glass decreases. Preferably it is 1 to 15%.

  LiF, NaF, and KF shown as RF are effective components for introducing fluorine into glass and lowering the melting temperature and viscosity. However, when the total amount of RF is less than 1%, the effect cannot be obtained. If it exceeds 50%, the chemical durability is remarkably lowered. Preferably it is 5 to 25% of range.

MgF ₂ , CaF ₂ , SrF ₂ , and BaF ₂ shown as R′F ₂ are effective in stabilizing the glass without reducing chemical durability, but the total amount of R′F ₂ is 10 If it is less than%, it is difficult to vitrify, and if it exceeds 75%, the tendency to devitrify becomes remarkable. Preferably it is 20 to 60% of range.

  Moreover, even if up to 70% of the total amount of metal fluoride constituting the mother glass is replaced with a metal oxide, desired spectral characteristics and chemical durability can be obtained.

As described above, a glass having a total of 90% or more of components composed of P ₂ O ₅ , AlF ₃ , RF, and R′F ₂ (including a metal oxide substituted with a metal fluoride) is referred to as a mother glass in the present invention. The mother glass can be a glass composed of the above components, but in addition to the above components, a substance that does not impair the properties of the visibility correction filter glass, such as ZnF ₂ , ZrF ₄ , LaF _3, etc. For the purpose of improving the meltability and adjusting the thermal expansion coefficient, it can be incorporated in the range of up to 10%.

  CuO is an essential component for cutting near-infrared rays, but it is an outer split with respect to 100 parts by mass of the mother glass, and if it is less than 0.5 parts by mass, the near-infrared absorbing effect is not sufficient, and if it exceeds 12 parts by mass. The transmittance in the visible range is also lowered, and the glass becomes unstable and devitrification increases. Preferably it is 1-10 mass parts. In general, in the visibility correction in a DSC or color video camera, a cut pattern in which the wavelength at which the transmittance is 50% in the near infrared region is in the range of 590 nm to 670 nm, and in many cases is in the range of 610 nm to 650 nm, is preferably used. Further, in order to ensure good color reproducibility and incident light quantity, the transmittance at a wavelength of 500 nm is at least 80% or more, more preferably 85% or more, for a single glass not coated with an antireflection film or the like. preferable. On the other hand, in order to reduce the influence of near-ultraviolet rays with which the image sensor has sensitivity, the wavelength at which the transmittance is 50% in the near-ultraviolet spectral transmittance is on the long wavelength side of 360 nm or more, more preferably 370 nm or more. It is preferable.

The glass of the present invention can be produced as follows. First, the raw materials are weighed and mixed so that the obtained glass has the above composition range. This raw material mixture is placed in a platinum crucible, covered, and heated and melted at a temperature of 700 to 1000 ° C. in an electric furnace. After sufficiently stirring and clarifying, it is cast into a mold, slowly cooled, then cut and polished to form a flat plate having an inner thickness of 0.1 to 1 mm. Increasing CuO tends to make the glass unstable and easily devitrified. However, when melting with a crucible, the crucible is sealed with a lid made of platinum or the like to suppress the volatilization of the fluorine component, and within the crucible In order to eliminate the stagnation of the glass, devitrification of the glass can be suppressed by devising and strengthening the glass stirring method. The glass of the present invention does not cause any striae that cannot be removed in the subsequent polishing process through the melting and forming processes, and an optically homogeneous glass can be obtained.

  In addition, when melting glass using a platinum container, if there are many components that act as an oxidizing agent for V, the wear of the platinum is promoted and the life of the platinum container is shortened, or platinum-derived fine foreign matter is From this point, the amount of the component acting as an oxidizing agent for V is preferably within the above range.

Next, the glass of this invention is demonstrated in detail based on an Example. Examples of the present invention are shown in Table 1, and comparative examples are shown in Table 2. In addition, the composition in the table indicates the mother glass part in mass%, the CuO content is indicated by an outer ratio with respect to 100 parts by mass of the mother glass, and the compound component that acts as an oxidizing agent for V ₂ O ₅ and V is the mother glass. It is shown as an outer split with respect to 100 parts by mass of the basic glass made of CuO. The glass described in the table was weighed and mixed with the raw material powder so as to have the composition shown in the table, and melted at a temperature of 700 to 1000 ° C. using a platinum crucible. Then, the glass that has been sufficiently stirred and clarified is poured into a rectangular frame, sliced to a thickness of about 1 mm after slow cooling, and cut into 11 mm × 11 mm sizes, and fixed to the surface plate of the polishing apparatus 300 sheets at a time. Then, cerium oxide was used as an abrasive and optical polishing was performed until the thickness became 0.3 mm.

  Spectral transmittance was measured for the flat glass prepared as described above. Spectral transmittance is measured by using a UV-IR spectrophotometer V-570 manufactured by JASCO Corporation, which uses a diffraction grating in the optical system, and the glass is not coated with an antireflection film or the like. The rate was measured. As a result, the wavelengths at which the transmittance on the ultraviolet side of each Example and Comparative Example glass is 50% are shown in Tables 1 and 2, and the spectral transmittance curves of some examples are shown.

In FIG. 3 and Comparative Example No. The spectral transmittance curves of 11 glass are shown as curve 3 and curve 11. These samples have the same CuO content and V ₂ O ₅ content. 3 is the addition of BaO ₂ as a component that acts as an oxidizing agent for V. Since the CuO content is the same, the cut pattern on the near infrared side shows almost the same characteristics. In ^No. 3, absorption in the near ultraviolet region is greatly expanded by the action of V ⁵⁺ .

In FIG. 4, Comparative Example No. 12 and Comparative Example No. The spectral transmittance curves of 13 glasses are shown as curve 4, curve 12, and curve 13, respectively. Two comparative examples are shown in Example No. 4 containing the same amount of V ₂ O ₅ , but without adding a component that acts as an oxidizing agent for V. Comparative Example No. No. 13 has a higher CuO content. When the V ₂ O ₅ content increases, absorption also appears in the near ultraviolet region, but the addition of the oxidizing agent can shift the absorption in the near ultraviolet region to a longer wavelength side without changing the cut pattern in the near infrared region. it can.

In FIG. 6 and no. The spectral transmittance curves of the glass No. 7 are shown as curve 6 and curve 7, respectively. These samples are examples in which the contents of CuO, V ₂ O ₅ , and the oxidizing agent are different. By adjusting these infrared and ultraviolet absorption components, the transmittance in the visible range is kept high and the near-infrared and near-ultraviolet ranges are kept. It shows that the cut characteristics can be adjusted.

In addition, as a weather resistance test of the polished glass sample of each Example, it was kept under the conditions of a temperature of 60 ° C. and a relative humidity of 95%, and the time until the surface of the glass was altered was measured. As a result, it was judged that the glass of this example was able to withstand actual use without any change in the surface even after 1000 hours.

  FIG. 5 shows an example in which the visibility correction filter glass obtained by the method of the present invention is applied to an imaging optical system such as DSC. FIG. 5 is a cross-sectional view schematically showing an example of the configuration of the imaging optical system. The imaging optical system 30 is packaged via a photographing lens 31 for forming an image of a subject, a visual sensitivity correction filter 32, an optical low-pass filter 33 made of a quartz plate, etc., and a cover glass 34 with the same optical axis. An image sensor 36 enclosed in 35 is disposed. The subject light image formed on the photoelectric conversion surface 361 of the image sensor 36 by the photographing lens 31 is photoelectrically converted and output as an electrical video signal. The visibility correction filter 32 is made of glass obtained by the above-described method of the present invention, and has a characteristic of transmitting visible light and absorbing near infrared rays and near ultraviolet rays.

  When a light beam is incident on such an imaging optical system 30, the refractive index for visible light and the refractive index for near ultraviolet light of the photographing lens 31 are different, so that the optical path V of visible light and the optical path U of near ultraviolet light are illustrated. In an imaging optical system that branches in this manner and does not have a near-ultraviolet cut filter on the optical path, near-ultraviolet rays reach the image sensor 36 via optical paths U and U ′. As a result, in the photoelectric conversion surface 361 of the image sensor 36, a shift indicated by L in the drawing occurs. Since a general image sensor has sensitivity to near ultraviolet rays, the deviation L is recorded as an outline blur in an image.

  In the imaging optical system 30 using the visibility correction filter 32 obtained according to the present invention, visible light can be substantially transmitted and light having a wavelength of near-ultraviolet light or less can be substantially absorbed. However, near-ultraviolet rays branched into the optical path U are absorbed by the visibility correction filter 32 and do not reach the photoelectric conversion surface 361, thereby removing chromatic aberration caused by optical elements such as lenses. Thus, it is possible to reduce deterioration in image quality such as outline blur and false color in the captured image.

  At this time, when the central light beam reaching the center of the image sensor 36 is compared with the peripheral light beam reaching the periphery of the image sensor 36, the peripheral light beam contains more rays incident obliquely. The near-ultraviolet ray absorption amount of the filter 32 is such that as the length of the optical path through which the light passes through the filter increases, more light is absorbed. In this case, the optical path length is longer, and the peripheral light beam can absorb more light rays having a wavelength shorter than the near ultraviolet ray than the central light beam.

  The deviation L due to the chromatic aberration described above increases as the angle formed by the light beam with respect to the optical axis increases. Therefore, the chromatic aberration generated by near ultraviolet rays or the like increases toward the periphery of the photoelectric conversion surface 361, but as described above, it is oblique. Since the amount of absorption of near-ultraviolet rays by the visibility correction filter 32 increases as the peripheral light flux contains more light rays incident on the light, the influence of chromatic aberration can be effectively removed.

  In addition, for example, when an ultraviolet cut film made of a dielectric multilayer film is formed on the surface of the visibility correction filter 32 on the photographing lens 31 side, ultraviolet rays incident obliquely with respect to the film formation surface are reflected by the ultraviolet cut film. Even if it is transmitted without being transmitted, it is effectively absorbed by the visibility correction filter 32 as described above, so that it is possible to prevent or suppress the arrival of light having a wavelength of near-ultraviolet light or less to the photoelectric conversion surface 361. .

  The configuration of the imaging optical system shown in FIG. 5 is merely an example. For example, even if there is a change such as sandwiching the visibility correction filter between two quartz plates or replacing it with a cover glass, The effect of the visibility correction filter according to the invention does not change.

As described above, according to the present invention, the obtained glass exhibits stable near-ultraviolet absorption characteristics in addition to near-infrared light, and by adjusting the contents of CuO, V ₂ O ₅ and the oxidant component, the near-ultraviolet region is obtained. It is possible to independently control the cut characteristics and the near infrared cut characteristics. Even when the dielectric multilayer film is used in combination when the desired spectral characteristics cannot be obtained only by the absorption characteristics of the glass, when the glass obtained according to the present invention is used, the near ultraviolet due to the glass is higher than that of the conventional glass. Since the amount of absorption of unnecessary light such as a region increases, the influence of the light incident obliquely on the film formation surface described above can be reduced.

As described in detail above, the method for producing a visibility correction filter glass according to the present invention can stably provide near-ultraviolet absorption characteristics by a simple operation, and the glass obtained by this method is used as an imaging device. Can selectively and effectively absorb and remove unnecessary infrared rays and ultraviolet rays, which is useful for improving the color reproducibility of imaging devices such as DSCs and color video cameras. What is suitable as a filter can be provided.

Example No. 5 according to the present invention. 3 and Comparative Example No. It is a curve figure which shows the spectral transmittance curve of 11 glass. Example No. 5 according to the present invention. 4, Comparative Example No. 12 and Comparative Example No. It is a curve figure which shows the spectral transmittance curve of 13 glasses. Example No. 5 according to the present invention. 6 and no. FIG. 7 is a curve diagram showing a spectral transmittance curve of No. 7 glass. Comparative Example No. 9 and no. It is a curve figure which shows the spectral transmittance curve of 10 glass. It is typical sectional drawing which shows the structure of the imaging optical system to which the visibility correction filter glass which concerns on this invention is applied.

Explanation of symbols

3 Example glass No. 3 No. 3 spectral transmittance curve, 4. No. 4 spectral transmittance curve, 6. No. 6 spectral transmittance curve, 7. No. 7 spectral transmittance curve, 9 ... Comparative glass No. No. 9 spectral transmittance curve, 10 ... Comparative Example Glass No. No. 10 spectral transmittance curve, No. 11 Comparative glass No. No. 11 spectral transmittance curve, 12... Comparative glass No. 12 spectral transmittance curve, 13... Comparative Glass No. 13. Spectral transmittance curve, 30 ... Imaging optical system, 31 ... Lens, 32 ... Visibility correction filter, 33 ... Optical low-pass filter, 34 ... Cover glass, 36 ... Imaging element, 361 ... Photoelectric conversion surface

Claims (2)

V ₂ O ₅ is added in an amount of 0.02 to 0.5 parts by mass with respect to 100 parts by mass of the base glass made of CuO-fluorophosphate glass, and an oxidizing agent for V 0.1 to 10 parts by mass of a compound component acting as a melt , and the base glass is P ₂ O _{5 in} mass%.
10-60%, AlF ₃ 0-20%, RF (R is at least one of Li, Na, K) 1-30%, R′F ₂ (R ′ is at least of Mg, Ca, Sr, Ba) 1 type)
10% to 75% (however, up to 70% of the total amount of fluoride can be replaced with oxide), 100% by weight of the base glass is 90% or more, and CuO 0.5% A component containing 12 parts by mass and acting as an oxidant for V is a metal element constituting the basic glass, nitric acid compound, sulfuric acid compound, peroxide, perchloric oxide, and chloric acid. A method for producing a visibility correction filter glass, which is added in one or more forms selected from : The component that acts as an oxidizing agent for V is LiNO. ₃ , MgSO ₄ , BaO ₂ , KClO ₄ , NaClO ₃ , NaLiNO ₃ , Sr (NO ₃ ) ₂ , Li ₂ SO ₄ , BaSO ₄ , Na ₂ O ₂ , K ₂ O ₂ , Ca (ClO ₄ ) ₂ LiClO ₄ , KClO ₃ , Ba (ClO ₃ ) ₂ The method for producing a visibility correction filter glass according to claim 1, wherein the method is one or more selected from the group consisting of:

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