JP2013041027A - Optical filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical filter made of a multiple-density ND filter including a gradient type with excellent optical characteristics and allowing easy production.SOLUTION: A fine rugged structure 32 being rugged with a variable height or pitch is consecutively formed on a transparent resin substrate 31, and an ND film 33 made of a multilayer film is formed on the fine rugged structure 32, so that transmittance is varied according to the height or pitch of the fine rugged structure 32. Accordingly, by forming on the transparent resin substrate 31 in which the height or pitch of the fine rugged structure 32 is consecutively varied, an ND filter having density variation is manufactured.

Description

  The present invention relates to an optical filter used in a photographing apparatus such as a camera or an optical apparatus.

  Conventionally, an aperture device for adjusting the amount of light is incorporated in an optical device such as a digital camera or a video camera. This diaphragm device adjusts the amount of light incident on a solid-state imaging device such as a CCD by opening and closing the diaphragm blades. When the object field is bright, the diaphragm device is further narrowed down.

  Therefore, when shooting a clear or high-luminance subject, the aperture for attenuating the light becomes a small aperture, but if the aperture is too small, the light is diffracted by the aperture and the captured image is degraded. It may cause. Further, as the sensitivity of a solid-state imaging device such as a CCD becomes higher, the amount of light needs to be further attenuated, and this tendency of image deterioration becomes remarkable.

  Therefore, as a countermeasure against this problem, a film-like ND (Neutral Density) filter is attached to the diaphragm blades as a light quantity adjusting member, so that the quantity of light is attenuated while the diaphragm aperture is large. Specifically, an ND filter made of a different member from the diaphragm blade is attached to a part of the diaphragm blade via an adhesive, and when the subject has high brightness, the ND filter is positioned on the optical axis. This limits the amount of light passing through. As a result, it is possible to avoid narrowing down until the aperture opening becomes too small, and the aperture opening can be maintained at a constant size.

  Further, an ND filter having a density gradient is used as the light amount adjustment function, and the light amount can be further adjusted by moving the ND filter. An ND filter having this density gradient is called a gradation ND filter, and for example, as shown in Patent Document 1, is produced by copying from a master plate having a density distribution onto a silver salt film. Further, as shown in Patent Document 2, a film is formed using a slit mask to form a density distribution, or a method of forming a density distribution by ejecting ink by an ink jet method as shown in Patent Document 3 or the like. Can be produced.

  FIG. 17 is a schematic cross-sectional view of a conventional gradation type ND filter 1, in which dielectric layers 3a and light absorption layers 3b having different thicknesses are alternately stacked on a transparent resin substrate 2, and the film thickness is formed on the outermost layer. The ND film 3 made of the outermost layer 3c made of a dielectric layer having a uniform thickness is formed. Further, an antireflection film 4 having a uniform film thickness is formed on the back surface of the transparent resin substrate 2.

JP-A-6-95208 JP 2004-61900 A JP 2004-246305 A

  In recent years, image sensors composed of solid-state image sensors used in imaging devices such as digital cameras and video cameras have been improved in sensitivity, and the density of ND filters has been increased accordingly.

  However, when the density of the ND filter is increased, unevenness in the amount of light due to the presence or absence of the filter at the filter tip in the opening may increase, and image quality may deteriorate. Therefore, it has become common to use a gradation ND filter whose density continuously decreases toward the tip of the filter.

  However, according to the method shown in Patent Document 1, silver salt particles contained in the silver salt film may cause scattering and image quality deterioration. Moreover, in the method shown in Patent Document 2, in order to reduce the surface reflection of the ND filter, first, a film is formed using a slit mask, and further, an antireflection film having a uniform thickness on the surface layer without using the slit mask. As a result, the production process takes time. In addition, the method disclosed in Patent Document 3 has a problem that the spectral characteristics of the ink are inferior to those of the deposited film at present.

  In the gradation ND filter 1 shown in FIG. 17, it is preferable that the outermost layer 3c has a uniform thickness up to the gradation part in order to reduce reflection even in the gradation part. For this purpose, as shown in FIG. 18A during deposition, a film is formed up to a layer before the outermost layer 3c with a predetermined interval between the transparent resin substrate 2 attached to the jig 11 and the deposition mask 12. To do. Subsequently, as shown in (b), the vapor deposition mask 12 is removed, and the outermost layer 3c is formed to a certain thickness.

  However, in this method, in order to remove the vapor deposition mask 12, it must be once taken out of the vapor deposition chamber, and it takes a long working time.

  An object of the present invention is to solve the above-described problems and provide a multi-density optical filter including a gradation type that can be easily produced and has excellent optical characteristics.

  In order to achieve the above object, an optical filter according to the present invention continuously forms a minute uneven shape on the surface of a transparent substrate, and forms an ND film composed of a plurality of layers of inorganic hard films on the uneven shape. However, the uneven shape is characterized in that at least one of pitch and height is changed.

  According to the optical filter according to the present invention, by continuously forming a concavo-convex shape in which at least one of pitch and height is different on a transparent resin substrate in advance, and forming an ND film including a light absorption layer thereon, Regions having different transmittances can be formed according to the uneven shape.

1 is a configuration diagram of an imaging apparatus according to Embodiment 1. FIG. It is a schematic cross section of an ND filter. It is a perspective view of a fine concavo-convex structure. It is explanatory drawing of the manufacturing method of a fine uneven structure. It is a schematic cross section of a fine concavo-convex structure. It is sectional drawing of the vapor deposition jig | tool of ND filter. It is a schematic diagram of a chamber. It is a film | membrane block diagram of a ND filter. It is a film | membrane schematic diagram of the ND filter of a modification. It is explanatory drawing of a mode that a vapor deposition film is laminated | stacked on a fine concavo-convex structure. It is a model figure explaining that a vapor deposition film is formed on a fine concavo-convex structure, and the transmittance changes due to a deviation in film thickness. 6 is a schematic cross-sectional view and a concentration distribution diagram of an ND filter of Example 2. FIG. It is a density distribution figure of ND filter which uses Ti for a light absorption layer. It is explanatory drawing which cut | disconnected the ND filter by press release. 6 is a schematic cross-sectional view and a concentration distribution diagram of an ND filter of Example 3. FIG. 6 is a schematic cross-sectional view and a concentration distribution diagram of an ND filter of Example 4. FIG. It is a schematic cross section of a conventional gradation ND filter. It is explanatory drawing of the preparation methods of the conventional gradation ND filter.

  The present invention will be described in detail based on the embodiment shown in FIGS.

  FIG. 1 is a configuration diagram of an image pickup apparatus according to the first embodiment. A light amount adjusting device 25 is provided in lenses 21 to 24 as an image pickup optical system, and a solid-state image pickup device 27 including a low-pass filter 26, a CCD, and the like behind the lens 21-24. Are arranged sequentially. In the light quantity adjusting device 25, a pair of aperture blades 29 a and 29 b are movably attached to the aperture blade support plate 28. An ND filter 30 is bonded to the diaphragm blade 29a for the purpose of reducing the amount of light passing through the substantially rhombic opening formed by the diaphragm blades 29a and 29b.

  In addition to this, the imaging device is provided with a control circuit (not shown) that drives the light amount adjustment device 25 and processes the imaging output signal of the solid-state imaging device 27.

  Note that the ND filter 30 may be advanced and retracted independently from the aperture blades 29a and 29b.

  FIG. 2 is a schematic cross-sectional view of the ND filter 30. A fine concavo-convex structure 32 is formed on a transparent resin substrate 31 made of a biaxially stretched PET (polyethylene terephthalate) resin film having a plate thickness of 100 μm. Further, an ND film 33 including a dielectric layer 33a, a light absorption layer 33b, and a dielectric layer 33c is formed on the transparent resin substrate 31 and in the gap and the upper portion of the fine concavo-convex structure 32. An antireflection film 34 is formed on the back surface of the transparent resin substrate 31.

  In Example 1, biaxially stretched PET is used for the transparent resin substrate 31. However, it is also possible to use a film-like resin substrate having transparency and mechanical strength other than PET. For example, PEN (polyethylene naphthalate), acrylic resin, polycarbonate, polyimide resin, norbornene resin, polystyrene, polyvinyl chloride, polyarylate, polysulfone, polyethersulfone, polyetherimide, and the like can be used.

  The plate thickness of the transparent resin substrate 31 is preferably as thin as possible while maintaining the rigidity of the ND filter 30. Specifically, the plate thickness is preferably 300 μm or less, more preferably 50 to 100 μm.

  FIG. 3A is a perspective view of the fine concavo-convex structure 32, which is also referred to as a “Moth eye” structure in which conical protrusions 35 are continuously arranged at equal intervals on the transparent resin substrate 31. It is. In addition to the conical shape shown in (a), the shape of the protruding portion 35 is a quadrangular pyramid-shaped protruding portion 36 shown in (b), or another polygonal pyramid shape, and further an inverted conical concave portion 37 shown in (c). It is good.

  The pitch P of the concave / convex pattern of the fine concavo-convex structure 32 is preferably about 10 to 2000 nm, and in Example 1, it is set to 300 nm.

  As means for forming the protrusions 35 and 36 and the recess 37 constituting the fine concavo-convex structure 32, for example, there are the following methods.

  (1) A method of transferring the fine concavo-convex structure 32 to the surface of the transparent resin substrate 31 by applying heat or pressure using a fine concavo-convex structure mold having a shape opposite to that of the fine concavo-convex structure 32.

  (2) A method of forming the fine relief structure 32 directly on the surface of the transparent resin substrate 31 using a semiconductor manufacturing technique.

  (3) A method of forming a film with a solidifiable material on the surface of the transparent resin substrate 31 and closely adhering a fine concavo-convex structure mold having a shape opposite to the fine concavo-convex structure 32 to solidify the solidifiable material.

  In Example 1, the fine concavo-convex structure 32 is formed by using the method (3) that is excellent in shape transferability and productivity and that gives little heat to the transparent resin substrate 31.

  The solidifiable material is not particularly limited, but a UV curable resin is preferable, and examples thereof include urethane-based, acrylic-based, epoxy-based, and urethane acrylate-based resins. In Example 1, UV curable polymethyl methacrylate is used to form the fine concavo-convex structure 32.

  FIG. 4 is an explanatory view of a method for producing the fine concavo-convex structure 32. First, a solidifiable material 43 is applied onto the fine concavo-convex structure mold 42 formed on the transfer mold 41. FIG. Subsequently, after the transparent resin substrate 31 is brought into close contact with the surface to which the solidifiable material 43 is applied, the solidifiable material 43 is solidified by irradiating UV light from the transparent resin substrate 31 side, and finally the transparent resin substrate 31. Is released from the transfer mold 41.

  Various methods for forming the fine uneven structure mold 42 of the transfer mold 41 are known. For example, using a photolithography technique using electron beam drawing or laser interferometry used in semiconductor manufacturing, or forming a predetermined fine concavo-convex structure on a glass material, Ni plating is performed, and the plating layer is peeled off to form a mold. An electroforming method or the like can also be used.

  FIG. 5 is a schematic cross-sectional view of the fine concavo-convex structure 32, and the height of the protrusions of the fine concavo-convex structure 32 formed on the transparent resin substrate 31 is changed so as to increase toward A, B, C and the right side of the page. It has a structure to do. At this time, as the fine concavo-convex structure mold 42, a deeper hole is formed in a portion where the height of the fine concavo-convex structure 32 is higher.

  The fine concavo-convex structure mold 42 formed in Example 1 is not limited in shape, height, pitch, pattern, or the like. Moreover, when the surface shape of the fine concavo-convex structure 32 formed on the transparent resin substrate 31 was measured with an atomic force microscope (AFM), the height h changed continuously from 50 to 500 nm, and the concavo-convex with a pitch of 300 nm. A pattern was formed. Moreover, since the skirt part of the projection part 35 is (phi) 300 nm, if the pitch is 300 nm, the skirt part of the projection part 35 will adjoin without leaving | separating.

As shown in FIG. 2 using the thus-prepared transparent resin substrate 31 and using a vacuum deposition method, an inorganic hard film ND film 33 comprising a dielectric layer 33a, a light absorption layer 33b, and a dielectric layer 33c. Is deposited. The material of the dielectric layer 33a, the light absorption layer 33b, and the dielectric layer 33c is not particularly limited, and the dielectric layers 33a and 33c are Al ₂ O ₃ , TiO ₂ , SiO ₂ , MgF ₂ , Nb ₂ O ₃ , Ta A simple substance such as ₂ O ₅ , HfO ₂ , ZrO ₂ or a mixture thereof can be used. However, the dielectric layer 33c as the outermost layer is preferably made of SiO ₂ or MgF ₂ having a small refractive index. Further, as the light absorbing layer _{33b, CeO 2, HfO 2,} Pr 2 O 3, Sc 2 O 3, Tb 2 O 3, TiO 2, Nb 2 O 5, Ta 2 O 5, Y 2 O 3, ZnO, Unsaturated oxides formed by depositing ZrO ₂ or the like in a high vacuum state without introducing oxygen gas, metals such as Ti, Cr, and Ni, oxides and alloys thereof, absorption materials thereof, and dielectric materials described above A mixture with can be used.

  FIG. 6 is a cross-sectional view of a vapor deposition jig 51 for forming the ND film 33 on the transparent resin substrate 31. The vapor deposition jig 51 is fixed together with a vapor deposition pattern forming mask 52 through a pin or the like (not shown) so that the surface on which the fine concavo-convex structure 32 is formed on the transparent resin substrate 31 faces the film formation surface.

  FIG. 7 is a configuration diagram of a chamber of a vacuum evaporation machine for forming the ND film 33 on the transparent resin substrate 31. A vapor deposition source 54 is provided in the chamber 53 and a rotatable dome 55 is provided. In this rotating dome 55, a vapor deposition pattern 51 shown in FIG. 6 in which a vapor deposition pattern forming mask 52 having an opening at a film forming portion and a transparent resin substrate 31 are set is arranged. The transparent resin substrate 31 fixed to the vapor deposition jig 51 rotates around the Z axis of the chamber 53 together with the rotating dome 55 to form a film.

In Example 1, the ND filter 30 having the film configuration shown in FIG. 8 was manufactured using Al ₂ O ₃ as the dielectric layer 33a, TiOx as the light absorption layer 33b, and SiO ₂ as the dielectric layer 33c.

  Since the height of the fine concavo-convex structure 32 formed on the transparent resin substrate 31 continuously changes as shown in FIG. 5, when the ND film 33 is formed on the fine concavo-convex structure 32 as shown in FIG. Depending on the height of the fine concavo-convex structure 32, the transmittance also changes.

Further, as shown in FIG. 8, an antireflection film 34 made of TiO ₂ and SiO ₂ is formed on the back surface side of the transparent resin substrate 31, but an ND film 33 may be formed instead.

  In addition, as shown in FIG. 9, the fine uneven structure 32 may be provided on each of both surfaces of the transparent resin substrate 31, and the ND film | membrane 33 may be formed on these.

  FIG. 10 is an explanatory diagram when the ND film 33 is formed on the fine concavo-convex structure 32. As shown to (a), the some projection part 35 is formed on the transparent resin substrate 31, and the vapor deposition material 33 'flies with a certain kinetic energy. For this reason, the vapor deposition material 33 ′ traveling from above has a high probability of continuing to move even if it reaches the slope of the protrusion 35 and fixing in the valleys between the protrusions 35. That is, as shown in (b), as for the thickness of the ND film 33 which is a vapor deposition film, the valley is thicker (t2), and the top of the protrusion 35 is thinner (t1).

  FIG. 11 is an explanatory diagram showing that the transmittance changes due to the film thickness distribution in the fine region. (A) shows a state where there is no film thickness distribution, that is, a deposited film is formed on a plane, and (b) shows a state where there is a film thickness distribution, that is, a deposited film is formed on the fine concavo-convex structure 32 and the fine concavo-convex structure is formed. The film thickness of the valley part of 32 is thick, and the film thickness of the top part is thin.

First, let M be the minute unit of the deposited film shown in FIG. 11A, d be the width, L be the thickness, and T be the transmittance of the deposited film with the thickness L. Given the small areas A and B of the width d, the incident light I ₀ is I _0/2 respectively in the minute areas A and B, each amount of transmitted light I ₁ and I _2, and the whole of the minute areas A and B The amount of transmitted light is I ₁₂ . The total thickness of the deposited film in each region and L · x, the deposited film on a plane are formed (a), since the minute areas A and B are the film thickness of equal total transmitted light quantity I ₁₂ is The following formula.
I ₁₂ = (I _0/2 ) · T ^x · 2

On the other hand, in FIG. 11B, the deposition film volume adhering to the entire area of the minute regions A and B is the same as that of FIG. 11A, but the unevenness occurs in the film thickness due to the unevenness as described above. And B have different film thicknesses. Therefore, the transmitted light amounts I ₃ and I ₄ in the micro regions A and B are different, and as a result, the total transmitted light amount I ₃₄ is the sum of the transmitted light amounts I ₃ and I ₄ . As shown in FIG. 11, in the minute regions A and B, assuming that the vapor deposition film corresponding to the film thickness y of the minute region B is biased and adhered to the minute region A, the total transmitted light amount I ₃₄ is expressed by the following equation.
I ₃₄ = (I _0/2 ) · {T ^{(x + y)} + T ^(xy) }

Comparing the transmitted light amounts I ₁₂ and I ₃₄ , the total transmitted light amount I ₃₄ has a larger value, that is, if there is a deviation in film thickness in the micro regions A and B, the transmittance is higher than the uniform film thickness. I understand.

  In the ND filter 30 of Example 2 manufactured as shown in FIG. 12A, the fine uneven structure 32 in which the height is changed to several groups stepwise from 50 to 500 nm is formed on the transparent resin substrate 31. An ND film 33 is formed thereon. (B) shows the position and the height of the fine relief structure 32, and (c) shows the relationship between each position and optical density. The optical density OD is calculated by OD = −logT (T is transmittance). According to (c), it can be seen that the optical density continuously changes depending on the position, resulting in a gradation ND filter.

  In addition, when materials having different extinction coefficients are used for the light absorption layer 33b, gradation ND filters having different density change widths can be manufactured. For example, when Ti is used, as shown in FIG. 13, a gradation ND filter having a density change different from that in FIG. 12C can be produced.

  Finally, as shown in FIG. 14, the ND filter 30 can be obtained by pressing the transparent resin substrate 31 on which the ND film 33 is formed.

  According to the first embodiment, by changing the pattern of the fine concavo-convex structure 32 formed on the transparent resin substrate 31, the optical density can be formed even when the ND film 33 having a uniform thickness is formed thereon. Therefore, the film forming process that has been divided into two processes can be completed only once.

  FIG. 15A is a schematic cross-sectional view of the ND filter 30 ′ of the third embodiment. Using the transparent resin substrate 31 in which the pitch of the fine uneven structure 32 is changed between 300 and 800 nm, the ND filter 30 ′ is manufactured by the same method as in the first embodiment. (B) shows the position and the pitch of the fine relief structure 32, and (c) shows the relationship between each position and the optical density OD.

  As can be seen from this result, the gradation ND filter 30 ′ whose density changes can also be produced by changing the pitch of the fine relief structure 32.

  FIG. 16A is a schematic cross-sectional view of the ND filter 30 ″ of Example 4. The transparent structure in which the fine concavo-convex structure 32 has a region where the height is 50 nm and the height is 500 nm. Using the resin substrate 31, the ND filter 30 ″ is manufactured by the same method as in the first embodiment. (B) shows the position and the height of the fine relief structure 32, and (c) shows the relationship between each position and the optical density OD.

  As can be seen from this result, a multi-density ND filter composed of a plurality of uniform density portions can be produced.

  In Examples 1 to 3, the height of the fine relief structure 32 was changed, and in Example 4, the pitch was changed with the height of the fine relief structure 32 being constant. In addition, both the height and pitch of the fine concavo-convex structure 32 can be changed, that is, at least one of the pitch and height may be changed.

  The present invention can be widely applied as an ND filter used in an imaging apparatus such as a digital camera or a video camera.

21-24 Lens 25 Light quantity adjusting device 27 Solid-state imaging device 28 Diaphragm support plate 29a, 29b Diaphragm 30, 30 ', 30 "ND filter 31 Transparent resin substrate 32 Fine uneven structure 33 ND film 33a, 33c Dielectric layer 33b Light Absorbing layer 33 ', 33 "Vapor deposition material 34 Antireflection film 35, 36 Protrusion 37 Recess 41 Transfer mold 42 Fine uneven structure type 43 Solidifiable material 51 Vapor deposition jig 52 Vapor deposition pattern forming mask 53 Chamber 54 Vapor deposition source 55 Rotating dome

Claims (6)

  A minute uneven shape is continuously formed on the surface of a transparent substrate, and an ND film composed of a plurality of layers of inorganic hard films is formed on the uneven shape, and the uneven shape changes at least one of pitch and height. An optical filter characterized by having been made.   The optical filter according to claim 1, wherein at least one of the pitch and the height of the uneven shape continuously changes.   The optical filter according to claim 1, wherein at least one of the pitch and height of the concavo-convex shape is a fine concavo-convex structure having a visible light wavelength or less.   The optical filter according to claim 1, wherein the inorganic hard film includes a light absorption layer.   The optical device according to any one of claims 1 to 4, wherein the filter includes a diaphragm blade having an opening and a filter that adjusts the amount of light that moves forward and backward in the opening. A light amount adjusting device comprising a filter.   An imaging apparatus comprising: an imaging optical system; a solid-state imaging device; and the light amount adjusting device according to claim 5.

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