JP3621941B2 - Manufacturing method of ND filter, light quantity diaphragm device and camera having this ND filter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing an ND filter, a light quantity reduction device having the ND filter, and a camera, and more particularly to a method for manufacturing an ND filter having a gradation density distribution suitable for use in a photographing system such as a video camera or a still video camera. The present invention relates to an ND filter, and a light quantity diaphragm device having these ND filters.
[0002]
[Prior art]
In order to control the amount of light incident on a solid-state image sensor such as a silver salt film or a CCD, the light amount diaphragm device is provided in the optical path of the photographing optical system so as to narrow the light amount smaller when the object field is bright. It is configured.
Therefore, when shooting a clear or high-brightness field, the aperture becomes a small aperture, which is easily affected by the hunting phenomenon of the aperture and light diffraction, resulting in degradation of image performance.
As a countermeasure against this, a film-like ND (Neutral Density) filter is attached to the aperture blade so that the aperture of the aperture is enlarged even if the brightness of the object field is the same.
[0003]
In recent years, as the sensitivity of the image sensor has improved, the density of the ND filter is increased to further reduce the light transmittance, and the aperture of the diaphragm is increased even if the brightness of the object field is the same. . However, when the density of the ND filter is increased in this way, the light amount difference between the light a passing through the ND filter and the light b not passing through the ND filter in the state shown in FIG. There are drawbacks such as "shading" phenomenon and resolution reduction. In order to solve this drawback, it has become necessary to adopt a structure in which the transmittance of the ND filter increases gradually toward the center of the optical axis.
[0004]
In FIG. 7, reference numerals 706A, 706B, 706C, and 706D denote lenses constituting the photographing optical system 706, reference numeral 707 denotes a solid-state image sensor, and reference numeral 708 denotes a low-pass filter. Reference numerals 711 to 714 denote members constituting the diaphragm device, 711 is an ND filter, and diaphragm blades 712 and 713 are opposed to each other, and the two diaphragm blades form a substantially rhombic opening. The ND filter is usually bonded to the diaphragm blade. Reference numeral 714 denotes a diaphragm blade support plate.
[0005]
In general, as a method for producing an ND filter, a film-like material (cellulose acetate, PET (polyethylene terephthalate), vinyl chloride, etc.) is mixed with an organic dye or pigment that absorbs light, and kneaded. There is a type in which an organic dye or pigment that absorbs light is applied to the material. In these manufacturing methods, it is possible to produce a filter having a uniform density, but it is extremely difficult to produce a filter (gradation filter) of a type in which the density changes in the same filter.
[0006]
Regarding such a density variable type (gradation type) ND filter, the present inventors have already proposed a method for producing a density variable type (gradation type) ND filter by microphotography (Patent Documents 1 to 3). 3).
Further, as a method for manufacturing a gradation filter, there is a method in which an elliptical gradation filter is manufactured by a vacuum deposition method (see Patent Document 4).
Further, as a countermeasure for the high image quality, a single density ND filter is bonded to a plurality of diaphragm blades and driven to change the density from a portion where the single density filter does not overlap a plurality of overlapping portions. There is something that made it possible.
[0007]
[Patent Document 1] Japanese Patent No. 2754518 (Japanese Patent Laid-Open No. 05-281593)
[Patent Document 2] Japanese Patent No. 2771078 (Japanese Patent Laid-Open No. 06-095208)
[Patent Document 3] Japanese Patent No. 2771084 (Japanese Patent Laid-Open No. 06-175193)
[Patent Document 4] Japanese Patent Application Laid-Open No. 11-38206
[Problems to be solved by the invention]
By the way, in the video camera at the time when Patent Documents 1 to 3 were proposed, the image quality was improved by the ND filter produced by these methods. However, in recent years, the CCD has been further improved in sensitivity, size, and height. Due to the image quality, the image quality may be deteriorated due to the influence of light scattering by the silver salt particles, particularly when used under special conditions (for example, in a small aperture state under backlight).
[0009]
Further, the gradation filter manufacturing method described in Patent Document 4 has a drawback that the density cannot be changed in a very small region (for example, a change from 3% to 80% transmittance in a range of 3 mm).
Further, in the method of changing the density from the overlapping portion and the portion that does not overlap with each other even if the single concentration filter is driven by adhering and driving the single density ND filter in the conventional example described above, There are disadvantages such as an increase in cost due to an increase in the number of ND filters, and an increase in thickness due to the presence of a plurality of ND filters on the diaphragm blades, which makes it impossible to cope with recent miniaturization and space saving.
[0010]
Therefore, the present invention has a method for manufacturing an ND filter having a gradation density distribution in which the uniformity of the light quantity is improved and the spectral characteristic is flat at each density, and the ND filter, and can cope with high image quality. An object of the present invention is to provide a simple light quantity diaphragm device and camera.
[0011]
[Means for Solving the Problems]
The present invention provides a method for manufacturing an ND filter having a gradation density distribution, an ND filter, and a light quantity diaphragm device and a camera having these ND filters, which are configured as follows.
The manufacturing method of the ND filter according to the present invention has a sawtooth shape for forming a gradation density distribution on a film other than the outermost layer when manufacturing an ND filter by forming at least two kinds of films on a substrate. The slit mask is revolved integrally with the substrate to form a film, and the outermost layer film is formed without using the mask.
In addition, the light quantity reduction device and the camera of the present invention are characterized by using the ND filter manufactured by the ND filter manufacturing method.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific embodiments of the present invention will be described, but the present invention is not limited to these specific embodiments. In particular, in the following description of FIG. 3 and the like, a case where a vacuum deposition method is used as an example of a method for forming an ND filter is described. However, the present invention is applied to a sputtering method, an inkjet printing method, and a spray method. The same effect can be obtained also in the above, and since these film forming methods are generally known, the description is omitted here.
[0013]
FIG. 3 is a simplified diagram of the inside of a chamber in a vacuum vapor deposition machine used as an example for explaining this embodiment. In FIG. 3, 101 is a vapor deposition umbrella, 102 is a substrate on which a film is formed, 103 is a vapor deposition source, 104 Is a base material on which film formation is actually performed, and 105 is a substrate jig for fixing the base material 104.
In addition, the substrate 102 described in the present embodiment is a state in which the base material 104 is set on the substrate jig 105 as shown in FIG.
[0014]
FIG. 4 is a diagram showing a slit type mask as an example for explaining this embodiment. In FIG. 4, 106 is a slit type mask, 107 is a width between slits in the slit type mask, and 108 is a substrate. It is the distance from the slit mask.
[0015]
In the vacuum vapor deposition method used in this embodiment, the substrate in the chamber is provided on the vapor deposition umbrella 101 as shown in FIG. 3, and the substrate 102 rotates with the vapor deposition umbrella 101 to form a film. By providing, for example, a sawtooth-shaped slit-type mask as shown in FIG. 4A on the film forming side of the substrate 102, the vapor deposition particles to be vapor deposited are determined from the positional relationship between the vapor deposition source 103 and the substrate 102. The film can pass through the slit and reach the substrate 102, or is blocked by the slit mask and cannot reach the substrate 102, and a film thickness distribution as shown in FIG. 5A is obtained.
[0016]
Here, the reason why the sawtooth shape as shown in FIG. 4 is used for the slit mask will be described.
The mask shape used for the slit-type mask is expected to vary depending on the density distribution to be created, but the target density distribution in this embodiment is a gradation density distribution in which the transmittance is gradually reduced or increased. It is. Such density distribution is considered to be the most general specification in consideration of the application of the ND filter. Specifically, for example, the distribution has transmission characteristics as shown in FIG. In order to create an ND filter that satisfies this specification, it is necessary to obtain a density distribution as shown in FIG. Since the concentration and the film thickness have a linear relationship, in other words, it can be said that it is necessary to obtain a film thickness distribution as shown in FIG.
[0017]
20A is a comb-shaped slit mask shape, FIGS. 20B and 20C are simulation examples of film thickness distribution when the slit mask is comb-shaped, and FIG. 20D is a straight-line type. FIG. 20E shows an example of a film thickness distribution simulation when the slit mask is linear.
As can be seen from the simulation results, in the linear mask as shown in FIG. 20D, the bottom of the film thickness distribution swells and rises as shown in FIG. 20E, and FIG. It is not possible to obtain a film thickness distribution as indicated by. In order to improve this, if a comb-shaped mask as shown in FIG. 20 (a), which has a greater influence of wraparound than the straight type, is used, an inflection point appears as shown in FIG. 20 (b). In order to solve this problem, it is necessary to take a sufficient distance between the substrate and the mask. However, if this distance is increased, the distribution at the maximum value of the film thickness is undulated as shown in FIG. Further, in the case of a comb-tooth shape, the film thickness distribution in the Δy-axis direction on the substrate is not constant, and it is extremely undulated, and it is generally difficult to keep it within specifications.
[0018]
On the other hand, with a sawtooth-shaped slit mask shape, it is possible to improve the rise of the bottom of the film thickness distribution closer to that shown in FIG. In comparison, since the wraparound in the Δy-axis direction on the substrate is uniform, these problems can be solved. Regarding the film thickness distribution in the Δy-axis direction, even if it is a sawtooth type, it cannot be made completely constant as in the case of a comb-tooth type. Since it is almost uniform, by setting the distance between the substrate and the slit mask and the width of the slit optimally, it is possible to obtain a result sufficient to satisfy the specifications.
[0019]
FIG. 5 (a) is a result of actually performing a film thickness distribution simulation using the sawtooth / linear slit mask shown in FIG. 4 (a). FIG. 5 (b) is a graph of FIG. 5 (a). FIG. 5C-1 is a bird's-eye view of the position in the vapor deposition umbrella, and FIG. 5C-2 is a cross-sectional view of the position in the vapor deposition umbrella. . Reference numeral 9 denotes a substrate position in the vapor deposition umbrella 1.
[0020]
The film thickness distribution shown in FIG. 5A naturally varies depending on the substrate position 109 in the deposition umbrella, the width 107 between the slits of the mask, the distance 108 between the substrate and the mask, the mask shape, and the like. Become a thing. Accordingly, by adjusting the width 107 between the slits of the mask, the distance 108 between the substrate and the mask, the mask shape and the like, the thin film formed on the substrate can obtain an arbitrary gradation film thickness distribution.
An increase in the film thickness means that the film density is increased and the transmittance is decreased. Therefore, obtaining an arbitrary film thickness distribution is, in other words, an object of the present invention, an arbitrary gradation. It can be said that the concentration distribution is obtained.
[0021]
Further, the shape of the slit mask for producing such an arbitrary gradation density distribution is a sawtooth / linear slit mask having a shape as shown in FIG. 5 (a) has been described together with the simulation results. Actually, as shown in FIGS. 4 (b) and 4 (c), the shape of the sawtooth is not limited to a straight line, but may be a curved shape. The rate of change can be varied. Furthermore, although the mask shape example shown in FIG. 4 has a symmetrical shape with respect to one convex portion, it is not always necessary to be so and an asymmetric case may be considered, and the gradation density distribution of the ND filter to be manufactured. It is expected that it will vary widely.
[0022]
By using the sawtooth slit mask described in this embodiment, it is possible to produce a gradation ND filter having a flat spectral characteristic at each density, and can meet various needs for gradation changes. Furthermore, environmental stability can be improved by performing heat treatment after vapor deposition.
In addition, an increase in reflectivity due to changes in antireflection conditions, which occurs when the film thickness partially changes, is also suppressed. By using this, an aperture device with improved uniformity in the amount of light can be obtained, which can handle high image quality. It is possible to obtain a diaphragm device that can respond.
[0023]
【Example】
Examples of the present invention will be described below, but the present invention is not limited to these examples.
In this example, first, on the PET base material (hereinafter referred to as a PET base material) having a thickness of 75 μm, from the first layer to the frontmost layer in the film configuration shown in FIG. As shown in the figure, Al ₂ O ₃ .Ti _x O _y was alternately laminated to form a film.
In this example, the slit mask was arranged as shown in FIG. 4 using the sawtooth / linear type of FIG.
As the film generation method, the vacuum deposition method was selected because the film thickness can be controlled relatively easily and the scattering is very small in the visible wavelength range.
As the material of the base material, PET having high heat resistance (glass transition point Tg), high transparency in the visible wavelength range, and low water absorption was selected.
[0024]
Next, the slit mask was removed, and the outermost layer was formed with an optical film thickness n × d (where n is a refractive index and d is a mechanical film thickness) and a constant film thickness under the condition of 1 / 4λλ: 540 nm. The refractive index n of the outermost layer film was selected to be 1.5 or less in the visible wavelength range. Specifically, MgF ₂ was used.
[0025]
As described above, after film formation from the first layer to the outermost layer, heat treatment was performed in air at a temperature of 110 ° C. for 1 hour. The reason why 110 ° C. is selected is that the effect of environmental stability is insufficient when the temperature is less than 100 ° C., and when the temperature exceeds 130 ° C., problems such as thermal degradation of the base material and cracks in the film occur. Accordingly, the heat treatment temperature is suitably between 110 ° C and 130 ° C.
[0026]
In order to investigate the environmental stability, the plastic ND filter was subjected to a standing test at 60 ° C. and 85% for 240 hours, and the transmittance before and after the test was measured. . As a reference, when the same environmental test was performed on the sample without heat treatment, and the transmittance before and after the test was measured, it increased by about 2%.
The cause of such a phenomenon is that the substrate temperature during vacuum deposition is low.
The sealing density of the film is greatly influenced by the substrate temperature at the time of film formation. If the temperature is low, the sealing density is low, and moisture, oxygen, etc. are easily transmitted. Therefore, the oxidation of Ti _x O _y itself as an absorption film is not performed. It is considered that the transmittance increases due to both the promotion and the low protective effect of a dielectric film such as an Al ₂ O ₃ film that protects it. It is considered that the environmental stability is improved by the heat treatment due to the “aging effect”.
[0027]
In general, when a glass substrate is used, the substrate temperature is 200 ° C. to 250 ° C., preferably about 300 ° C. for film formation.
However, when the substrate is plastic as in this case, it is necessary to form the film at a temperature at which the substrate does not cause thermal shrinkage, and the substrate temperature is limited to less than 150 ° C.
As shown in FIG. 5A, the film thickness distribution was almost the same as the simulation result.
However, the distribution is from the first layer to the eighth layer. The outermost layer has a constant film thickness.
[0028]
As an example, a pattern as shown in FIG. 2A is produced and cut into a substantially triangular shape, and then the cut filter 1 is attached to the blade 2 to obtain the state shown in FIG. The diaphragm device is the same as that described with reference to FIG. 7, and includes a plurality of diaphragm blades that are relatively driven to vary the size of the diaphragm aperture. One filter is is shown in Figure 2 (b), 0 is from where end surface to X ₁ X ₂ X ₃ is the concentration change region. X ₃ to X ₄ have the highest uniform density. X ₅ from X ₄ is an adhesive area for bonding the filter blade.
[0029]
In this embodiment, the configuration of the distance (X) and the film thickness is as shown in FIGS.
Further, the relationship between the distance (X) and the transmittance, and the distance (X) and the reflectance are as shown in FIGS.
Further, the spectral transmittance is as shown in FIG. 12, and the spectral reflectance is as shown in FIG.
As a result, the slit width is 0.05 m, the floating distance between the mask and the substrate is 0.01 m, the sawtooth length is 0.0075 m, and the sawtooth width is 0.0003 m.
[0030]
The relationship between the distance and the film thickness gradually increases as shown in FIG. 8, but this change tends to become gentler when the slit width is increased, and the uniform density region tends to increase as the floating distance increases. is there. In addition to these two parameters, a desired inclination state and a uniform density region can be controlled by five parameters such as a sawtooth shape, a sawtooth length 112 and a sawtooth width 113 as shown in FIG.
[0031]
(Comparative example)
Similarly to the example, the first to ninth layers having the film configuration shown in FIG. 6 were formed on a PET substrate having a material thickness of 75 μm by vacuum deposition.
The outermost layer was formed with an optical film thickness of n × d (where n is a refractive index d is a mechanical film thickness) of 1 / 4λλ: 540 nm. The refractive index n of the outermost layer film was selected to be 1.5 or less in the visible wavelength range. Specifically, MgF ₂ was used.
The slit mask was arranged as shown in FIG.
The mask used was (a) a sawtooth / linear type.
[0032]
As the film generation method, the vacuum deposition method was selected because the film thickness can be controlled relatively easily and the scattering is very small in the visible wavelength range.
As the material of the substrate, PET having high heat resistance (glass transition point Tg), high transparency in the visible wavelength range, and low water absorption was selected.
[0033]
As described above, after film formation from the first layer to the outermost layer, heat treatment was performed in air at a temperature of 110 ° C. for 1 hour. The reason for selecting 110 ° C. is the same as in the example.
Further, in order to investigate the environmental stability, when the plastic ND filter was subjected to a standing test at 60 ° C. and 85% for 240 hours in the same manner as in the above example, the same result as in the above example was obtained.
Further, as shown in FIG. 5A, the film thickness distribution was almost the same as the simulation result.
[0034]
In this comparative example, the configuration of the distance (X) and the film thickness is as shown in FIG. Further, the relationship between the distance and the transmittance and the distance and the reflectance at this time is as shown in FIGS.
Further, the spectral transmittance and the spectral reflectance are as shown in FIGS. 17 and 18, respectively. As a result, the slit width is 0.05 m, the floating distance between the mask and the substrate is 0.01 m, the sawtooth length is 0.0075 m, and the sawtooth width is 0.0003 m.
When the thickness of all layers is changed as in this comparative example, the antireflection conditions are not met, the reflectance increases, and the “ghost phenomenon” and “flare phenomenon” occur in terms of image quality.
[0035]
【The invention's effect】
According to the present invention, it is possible to realize an ND filter having a gradation density distribution with improved light quantity uniformity and flat spectral characteristics at each density.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a state in which a gradation ND filter obtained by the present invention is attached to a diaphragm blade.
FIGS. 2A and 2B are diagrams for explaining a state in which the filter is not pressed when manufacturing a filter according to an embodiment of the present invention. FIG. 2A is a diagram showing a substantially triangular cutting pattern, and FIG. The figure which shows the structure of ND filter of.
FIGS. 3A and 3B are diagrams for explaining a method of manufacturing an ND filter by a vacuum deposition method according to an embodiment of the present invention. FIG. 3A is a configuration diagram inside a chamber of a vacuum deposition machine, and FIG. FIG.
FIGS. 4A and 4B are diagrams showing slit masks and mask shapes used in the embodiments and examples of the present invention. FIGS.
FIG. 5 is a diagram showing an example of a film thickness distribution simulation using a slit mask according to an embodiment of the present invention.
FIG. 6 is a view showing a film configuration of a vapor deposition ND filter for explaining the embodiment and examples of the present invention.
FIG. 7 is a diagram illustrating a photographing optical system used in a video camera for explaining a conventional technique.
FIG. 8 is a graph showing the relationship between distance and film thickness (from the first layer to the frontmost layer) in the example of the present invention.
FIG. 9 is a graph showing the relationship between distance and film thickness (9th layer) in an example of the present invention.
FIG. 10 is a graph showing the relationship between distance and transmittance in an example of the present invention.
FIG. 11 is a graph showing the relationship between distance and reflectance in an example of the present invention.
FIG. 12 is a graph showing spectral transmittance in an example of the present invention.
FIG. 13 is a graph showing spectral reflectance in an example of the present invention.
FIG. 14 is a graph showing the relationship between distance and film thickness (from the first layer to the final layer) in a comparative example.
FIG. 15 is a graph showing the relationship between distance and transmittance in a comparative example.
FIG. 16 is a graph showing the relationship between distance and reflectance in a comparative example.
FIG. 17 is a graph showing spectral transmittance in a comparative example.
FIG. 18 is a graph showing spectral reflectance in a comparative example.
FIG. 19 is a diagram showing an ideal gradation transmission / density distribution in the embodiment of the present invention.
FIGS. 20A and 20B are diagrams showing a simulation example using a comb-shaped slit mask according to an embodiment of the present invention, wherein FIG. 20A is a comb-shaped slit mask shape, and FIGS. 20B and 20C are slit masks; 4 is a simulation example of the film thickness distribution when the comb is a comb-tooth type, (d) is a linear slit mask, and (e) is a film thickness distribution simulation example when the slit mask is a linear type.
[Explanation of symbols]
1: ND filter 2: diaphragm blade 101: vapor deposition umbrella 102: substrate 103: vapor deposition source 104: base material 105: substrate jig 106: sawtooth-shaped slit mask 107: width between slits of mask 108: substrate and mask 109: substrate position 112 in the deposition umbrella 112: position on substrate Δx axis / Δy axis 113: sawtooth mask length 114: sawtooth mask widths 706A, 706B, 706C,
706D: Lens constituting the photographing optical system 706: Solid-state imaging device 708: Low-pass filter 711: ND filter 712, 713: Diaphragm blade 714: Diaphragm blade support plate

Claims (5)

When manufacturing an ND filter by forming at least two types of films on a substrate, a slit-shaped mask having a sawtooth shape is integrated with the substrate in order to form a gradation density distribution in a film other than the outermost layer. A method for producing an ND filter, comprising: forming a film by revolving the film and forming a film on the outermost layer without using the mask. 2. An arbitrary gradation density distribution is formed by adjusting a width between slits in the slit mask, a distance between the slit mask and the substrate, and a shape of the slit mask, respectively. 2. A method for producing the ND filter according to 1. The method further comprises the step of heat-treating the formed substrate in air at a temperature of 100 ° C. to 130 ° C. after forming the film of the outermost layer following the film other than the outermost layer. The manufacturing method of the ND filter of Claim 1 or Claim 2. A light quantity diaphragm comprising a plurality of diaphragm blades that are relatively driven to vary the size of the diaphragm aperture, and an ND filter for adjusting the light quantity disposed at least in part of the aperture formed by the diaphragm blades In the device
The said ND filter is comprised by the ND filter manufactured by the manufacturing method of any one of Claims 1-3, The light quantity diaphragming apparatus characterized by the above-mentioned. A camera, comprising: an optical system; a light amount diaphragm device according to claim 4 that limits an amount of light that passes through the optical system; and a solid-state imaging device that receives an image formed by the optical system.

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