JP2005157197A - Light quantity controller, optical device and photographing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light quantity controller in which optical performance degradation by an influence of minute thickness components of a filter member is reduced and which performs successful light quantity control in the light quantity controller using the filter member which attenuates light quantity and whose transmittance of light is different depending on a place, and to provide an optical device (lens device) and a photographing device. <P>SOLUTION: In the light quantity controller which is provided with a diaphragm constituted of a plurality of diaphragm blades S11, S12 and the filter member P1 fixed to at least one of the plurality of diaphragm blades and whose transmittance of light used for attenuating the light quantity of light passing an opening is different depending on the place, and which changes area in an opening area of the opening by relative transfer of the plurality of diaphragm blades and controls the light quantity, it is constituted so that the filter member is arranged so as to cover a part of the opening area including an optical axis of the opening in an open state of a diaphragm. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a light amount adjustment device, an optical device (lens device), and a photographing device that are suitable for a photographing device such as a video camera or a digital still camera, and particularly suppresses deterioration of optical performance even in an image pickup device having a small pixel pitch. It relates to possible technologies.

In a photographing optical system of a photographing apparatus such as a video camera, a light amount adjusting device that adjusts a light amount by changing an aperture diameter formed by a plurality of diaphragm blades is used. In such a diaphragm device, if the aperture diameter becomes too small, optical performance deterioration due to light diffraction becomes a problem.
In view of this, in order to prevent the aperture diameter from becoming too small even under bright subject conditions, a light amount adjusting device using both a diaphragm blade and an ND (Neutral Density) filter has been proposed and put into practical use.
For example, in Patent Document 1, an ND filter is affixed to an aperture blade so as to be positioned within an aperture formed by aperture blades, and the ND filter has a plurality of regions each set to have a uniform transmittance. There is disclosed a diaphragm device in which the transmittance is set to increase in order from the outside to the inside.
Further, in Patent Document 2, an ND filter whose transmittance is continuously changed by shading is used to move a mechanical aperture blade from the open position to a predetermined aperture area, and small aperture control below a certain aperture value. A throttling device is disclosed in which a filter part having a high transmittance enters the opening in order.
Japanese Patent Application Laid-Open No. 2004-228561 describes an influence on the optical performance given by the transmittance of an ND filter having a plurality of density regions, and discloses an imaging apparatus having an exposure control mechanism that takes measures.

In these conventional ones, the main cause of the optical performance deterioration in the intermediate stop state from the open position to the small stop is the influence of diffraction due to the difference in the transmittance of the ND filter covering the opening formed by the stop blades. It is considered to be dominant, and measures are taken against the influence of diffraction focusing on the transmittance and area of each region of the ND filter having a plurality of density regions.
Furthermore, as a conventional example using an ND filter, for example, in Patent Document 4, two ND filters are used, and in order to eliminate ghosts generated by reflection between the ND filters, the ND filters are not parallel to each other. What has been disclosed is disclosed.
Patent Document 5 discloses an ND filter that forms a filter by forming a large number of halftone dots.

By the way, the cause of the optical performance deterioration in the intermediate aperture state is not only the influence of diffraction due to the ND filter transmittance difference, which is a problem in the conventional example, but also the transmitted wavefront phase difference due to the thickness component of the ND filter. It has an influence.
As described above, it is empirically known that the optical performance deteriorates when a part of the aperture opening is covered with a thick filter, and these are described in Patent Document 6, Patent Document 7, Patent Document 8, and the like. Is disclosed. However, there is an analysis of how the thickness component of the filter affects the optical performance, but a more optimal measure for disposing it in the optical system is not disclosed.

On the other hand, as a workaround for the influence of the thickness of the ND filter on the optical performance, in Patent Document 9, an ND filter having a transparent part and a part whose transmittance changes continuously or stepwise is fixed to a circular shape. A configuration has been proposed in which the diaphragm aperture is movable so as to cover the entire aperture, and the amount of transmitted light is adjusted.
Japanese Patent No. 2592949 Japanese Patent Laid-Open No. 52-117127 JP 2000-106649 A Japanese Patent Laid-Open No. 5-281591 JP 2000-352736 A JP 2003-121900 A JP 2003-240919 A JP 2003-241254 A JP-A-6-265971

  However, in the above-mentioned Patent Document 9, an ND filter having a transparent part and a part whose transmittance changes continuously or stepwise is used, and this ND filter is moved in a state of covering all the fixed circular aperture openings to transmit light quantity. Therefore, the ND filter covers all of the aperture, and thus has a problem that the transmittance is lowered.

  Therefore, the present invention reduces the optical performance deterioration due to the influence of the minute thickness component of the filter member and performs good light amount adjustment in the light amount adjusting device using the filter member that attenuates the light amount and has different light transmittance depending on the location. It is an object of the present invention to provide a light amount adjusting device, an optical device (lens device), and a photographing device that can perform the above.

The present invention provides a light amount adjusting device, an optical device (lens device), and a photographing device configured as follows.
That is, the light amount adjusting device of the present invention includes an aperture configured by a plurality of aperture blades for forming an aperture,
A filter member fixed to at least one of the plurality of diaphragm blades and used for attenuating the amount of light passing through the aperture, the transmittance of which varies depending on the location. In the light amount adjusting device that adjusts the light amount by changing the area of the opening area of the opening by a simple movement, the filter member covers a part of the opening area including the optical axis of the opening in the open state of the diaphragm. It is characterized by being arranged. In the conventional one, when the filter enters the diaphragm, the phenomenon differs between light passing through the filter and light passing through a portion without the filter, depending on the thickness of the filter. For this reason, the image quality formed on the image plane is affected and a defect occurs. On the other hand, according to the above configuration of the present invention, the filter member covers the optical axis of the photographing lens when the diaphragm is opened, and the principal ray of the lens passes through the filter side. This reduces the image quality degradation. Specifically, by setting the filter member to cover 51% or more of the aperture area when the diaphragm is opened, the influence of light passing through a portion without the filter is reduced, and deterioration in imaging performance can be prevented. Become. Further, when narrowing from the release, the area of the filter portion with respect to the opening area further increases, so that the state becomes favorable.
Furthermore, it is desirable that the filter member covers 51% or more and 95% or less of the opening area when the aperture is opened.
Further, the filter member is configured such that the transmittance varies depending on the location of the filter, so that the difference between the amount of light passing through a portion without a filter such as a single concentration filter and the amount of light passing through a portion is different. It is possible to prevent the occurrence of a large amount, and it is possible to eliminate the occurrence of unevenness in the amount of light on the captured screen.
Furthermore, in order to eliminate such unevenness in the amount of light, it is desirable that the density of the filter changes gently with respect to the direction in which the filter is inserted.
Moreover, the light quantity adjustment apparatus of this invention can take the structure which has a several area | region in which the said filter member differs in the transmittance | permeability formed of the multilayer film. By making the filter member with a multilayer film in this way, when the density change is made with a filter, the density change can be controlled freely to some extent, and the thickness of the filter necessary for adding the density can be reduced. . Thereby, the influence which the said filter inserted in a photographic optical system exerts decreases, and deterioration of optical performance can be decreased. Moreover, it is desirable that the multilayer film has a layer that reduces reflection. Conventionally, the presence of a flat plate such as a filter in a photographing optical system has caused ghost and flare. Therefore, it is possible to reduce the ghost and flare by forming an antireflection film by forming the filter with a multilayer film structure.
Further, in order to obtain an appropriate transmitted wavefront phase difference for reducing optical performance deterioration due to the influence of a minute thickness component, the transmitted wavefront phase difference is set to {1 ± (1/5)} λ or {2 A layer for setting to be in the range of ± (1/5)} λ can be formed.
Further, if the transmittance of the filter covering 51% or more of the opening area is low, the transmitted light amount of the entire lens is reduced, and TNo becomes dark, which is not preferable. For this reason, the part with the highest transmittance of the filter member has a transmittance of 75% or more, and more desirably 90% or more.
Furthermore, it is desirable that the multilayer film has a layer that reduces reflection.
Further, the transmitted light amount adjusting means can be configured to be inclined in the vertical direction with respect to the photographing screen. When shooting with a normal camera, especially when shooting a moving picture such as a video camera, the recorded image is viewed on a TV monitor or the like when viewed. At this time, the upper side photographed by the camera coincides with the upper side of the monitor. At this time, the light source that most affects the ghost generated by the filter is mostly sunlight or light, but all of them are probabilistically present on the upper side of the screen. Therefore, it is possible to effectively fly out of the shooting screen by tilting the filter up and down. Although it is possible to fly by tilting left and right, it is not preferable because the tilting angle increases and the size of the optical system increases.
Further, if the filter itself is disposed obliquely with respect to the optical axis, the plurality of diaphragm blades of the transmitted light amount adjusting means may be disposed perpendicular to the optical axis.
Further, in the present invention, by using the light amount adjusting device of the present invention described above, an optical device (lens device) or a photographing device that can be reduced in size with less generation of ghosts and flares can be realized. Is possible.

According to the present invention, in a light amount adjusting device that uses a filter member that attenuates the amount of light and has different light transmittance depending on the location, optical performance deterioration due to the influence of a minute thickness component of the filter member is reduced and good light amount adjustment is performed. Therefore, it is possible to realize a light amount adjusting device that can perform the above-described operation.
In addition, if the light amount adjusting device of the present invention is used in a photographing optical system of a photographing device that forms an image on an image pickup device, it is possible to obtain good image information even with an image pickup device having a small pixel pitch. Thus, it is possible to realize a lens system in which ghosts and flare generated by the device and the image sensor are reduced.

Hereinafter, a light amount adjusting device (aperture device) according to an embodiment of the present invention will be described.
Prior to the description, first, how the transmitted wavefront phase difference affects the image will be described.
First, what phenomenon occurs optically when a filter having a thickness covers a part of the aperture opening will be described with reference to FIG.
6A to 6E show a case where a filter P and an aperture stop S are arranged in front of the non-aberration ideal lens L (on the object side), and parallel rays that are plane waves of monochromatic light having a wavelength λ are incident. A point image intensity distribution Q in the vicinity of the geometrical optical imaging point I is shown.

  FIG. 6A shows a state where the filter P is zero in thickness and does not affect the transmitted wavefront. In this case, the intensity distribution Q is a diffraction image based on the relationship between the F number F and the wavelength λ of the light beam (see “Wavefront optics for lens design” written by Toru Kusagawa, Tokai University Press). When the stop S has a circular aperture, a point image having a radius of 1.22Fλ is formed, and ring-shaped weak diffracted light is formed around the point image. Here, a thick filter is inserted into a region on the lower side of the paper surface of the filter P corresponding to 1/3 of the aperture of the stop S, and the transmitted wavefront phase difference is (1/4) as shown in FIG. When set to λ, a mountain appears as if two point images having substantially the same intensity overlap.

Further, when the filter is inserted to make it 50%, as shown in FIG. 6C, the intensity distribution Q becomes an image intensity distribution of two points that are completely separated in the vertical direction within the paper surface. This is because the amount of light that passes through a portion of the pupil that does not have a filter out of the light that is to be collected at the geometrical optical imaging point I is equal to the amount of light that passes through the filter.
When the filter P is further inserted to 70%, the amount of light passing through the filter increases as shown in FIG. As a result, the amount of light passing through the portion without the filter is weakened and the intensity on the filter passing side is increased.

Further, when the filter P is completely inserted, the total light quantity passes through the filter as shown in FIG. 6E, so that the transmitted wavefront phase difference matches and the converted optical path length according to the filter thickness also matches. The focus position is the same. As a result, the intensity distribution Q again becomes a diffraction image of one point image and returns to the same state as in FIG.
From the above, it can be seen that the optical performance is good to be 51% or more at which the point image intensity of one side becomes strong.

Next, examples of the present invention will be described.
[Example 1]
In Example 1 of the present invention, the light intensity adjusting device (aperture device) is configured by applying the above-described configuration of the present invention.
FIG. 1 shows a configuration of a light amount adjusting device (aperture device) of the present embodiment. In FIG. 1, FIG. 1 (A) shows an open aperture state, FIG. 1 (B) shows an intermediate aperture state, and FIG. 1 (C) shows a minimum aperture state.
In FIG. 1, S11 and S12 are diaphragm blades for forming a diaphragm aperture, and the aperture area can be changed by relatively moving the diaphragm blades.
P1 is an ND filter (filter member), which is affixed and fixed to the diaphragm blade S12. Therefore, as the diaphragm blades S11 and S12 move relative to each other, the area where the ND filter P1 covers the opening changes.

FIG. 2 shows the configuration of an ND filter that is one of the components of the light amount adjusting device (aperture device) of the present embodiment. In FIG. 2, in the ND filter P1, a region N22 having a predetermined transmittance is formed on one surface of the substrate B1, and a region N23 having a transmittance different from that of the region N22 is formed on a part of the other surface. Therefore, the transmittance is different between the case where the light passes only through the region N22 and the case where the light passes through both the regions N22 and N23, and the transmittance is greater when the light passes through only the region N22.
For the substrate B1, a synthetic resin film such as cellulose acetate, polyethylene terephthalate (PET), vinyl chloride, or an acrylic resin is used. The main reasons for using a synthetic resin film are that the specific gravity is light and that it is difficult to break even if processed thinly. Here, the thickness of the substrate B1 is about 100 μm to 50 μm.

  As shown in FIG. 2, the regions N22 and N23 of the ND filter P1 have vapor-deposited layers having three roles on the film-like substrate B1. That is, the base coat layer 61 for setting the transmitted wavefront phase difference to a predetermined value ({1 ± (1/5)} λ or {2 ± (1/5)} λ), the transmittance uniformly regardless of the wavelength An ND layer 62 for dropping and an AR coating layer 63 for preventing surface reflection. The region N21 includes only the base coat 61 and the AR coat layer 63 without the ND layer 62.

The base coat layer 61 is formed by appropriately setting the film thickness of the dielectric film close to the refractive index of the substrate B1 such as Al ₂ O ₃ or SiO _{2 on} the substrate B1, thereby setting the transmitted wavefront phase difference to a desired value. doing. The ND layer 62 for lowering the transmittance is formed of a multilayer film and is set so as to reduce wavelength dependency. The ND layer 62 has a very small thickness in order to set a desired transmittance (desired density), and this is a main factor of the transmitted wavefront phase difference. The base coat layer 61 is for adjusting this to an appropriate transmitted wavefront phase difference. Then, an AR coating layer 63 for preventing surface reflection is deposited as a final layer. The AR coating layer 63 is formed by depositing a dielectric film such as MgF ₂ .

FIG. 3 shows the state of the transmitted wavefront that passes through the ND filter portion P1. Each area | region N22 and N23 in FIG. 3 sets each transmittance | permeability with a vapor deposition film. Then, by appropriately setting the film thickness of each region and the refractive index of the material, the transmitted wavefront phase difference including the manufacturing error is {1 ± (1/5)} λ or {2 ± (1/5)} λ. To be within the range.
Here, an appropriate transmitted wavefront phase difference for reducing optical performance degradation due to the influence of a minute thickness component means a case where the phase difference of light having a predetermined wavelength λ is in the vicinity of 0λ, 1λ, or 2λ. . In the present embodiment, “± (1/5) λ” is assumed as the range of “neighborhood”, and “near 0λ, 1λ, or 2λ” is expressed by an expression as follows.
{N ± (1/5)} λ (n = 0, 1, 2)
In order to minimize optical performance degradation, it is desirable to set the transmitted wavefront phase difference in the vicinity of 0λ ((1/5) λ or less). However, in order to make the transmitted wavefront phase difference in the vicinity of 0λ, it is necessary to provide a region for correcting the transmitted wavefront phase difference generated in the region N22 separately from the generation process of the region N22 and the region N23 because the region N22 has a predetermined thickness. is there. Therefore, in this embodiment, the transmitted wavefront phase difference is {1 ± (1/5)} λ or {2 ± (1 / .sup.1) using the base coat layer 61 that can be formed as part of the production process of the film constituting the region N23. 5) is set to be in the range of λ.

  The ND filter P1 is provided with a non-light-reducing region N21 and a predetermined transmittance region N22 on one surface of the substrate B1, and has the same transmittance as the non-light-reducing region N21 and region N22 on the other surface. A region N23 is provided. Therefore, the transmittance is the lowest when light passes through the region N22 and the region N23, the transmittance is the next lowest when the light passes through the region N21 and the region N22, and the transmittance is higher when the light passes through the region N21 and the region N21. Become the largest. As described above, the ND filter P1 of the present embodiment combines the vapor deposition ND film having two kinds of transmittances and sets three kinds of transmittances (concentrations).

[Example 2]
In Example 2 of the present invention, an optical system to which the light amount adjusting device of Example 1 was applied was configured. FIG. 4 shows the configuration of the optical system of the present embodiment.
In FIG. 4, reference numeral 10 denotes a photographing optical system constituted by a refraction system, a reflection system, a diffraction system, etc., 11 denotes a diaphragm for limiting light passing through the optical system 10 and adjusting brightness, and 12 is formed by the optical system 10. An image pickup device (photoelectric conversion device) such as a CCD or a CMOS that receives an object image to be received by a light receiving surface and converts it into an electrical signal. In this embodiment, the diaphragm 11 uses the light amount adjusting device described in the first embodiment.

  As described above, by using the light amount adjusting device as described in the first embodiment as an aperture of an optical system such as a photographing optical system, the influence of the transmitted wavefront phase difference of the ND filter when the aperture is reduced is reduced. Improvements can be made. In addition, it is possible to use an image sensor with a small pixel pitch.

[Example 3]
In Example 3 of the present invention, an imaging apparatus to which the imaging optical system of Example 2 is applied is configured. FIG. 5 shows the configuration of the photographing apparatus of the present embodiment.
In FIG. 5, reference numeral 20 denotes a photographing apparatus main body, reference numeral 10 denotes a photographing optical system described in the second embodiment, and reference numeral 11 denotes an aperture configured by the light amount adjusting apparatus of the first embodiment.
Reference numeral 12 denotes an image sensor that receives a subject image formed by the photographing optical system 10, 13 denotes a recording medium that records the subject image received by the image sensor 12, and 14 denotes a viewfinder for observing the subject image.

As the finder 14, a finder of a type that observes a subject image displayed on a display element such as an optical finder or a liquid crystal panel can be considered. Alternatively, a large liquid crystal panel (not shown) may be provided to directly observe the panel.
In this way, by applying the imaging optical system described in the third embodiment to an imaging apparatus that forms a subject image on an imaging device such as a video camera or a digital still camera, the influence of the transmitted wavefront phase difference of the ND filter is affected. The image quality can be improved with less. In addition, it is possible to use an image sensor with a small pixel pitch.

Further, the transmitted light amount adjusting means is characterized by being inclined in the vertical direction with respect to the photographing screen. When shooting with a normal camera, especially when shooting a moving picture such as a video camera, the recorded image is viewed on a TV monitor or the like when viewed. At this time, the upper side photographed by the camera coincides with the upper side of the monitor. At this time, the light source that most affects the ghost generated by the filter is mostly sunlight or light, but all of them are probabilistically present on the upper side of the screen. Therefore, it is possible to effectively fly out of the shooting screen by tilting the filter up and down. Although it is possible to fly by tilting left and right, it is not preferable because the tilting angle becomes large and the photographic optical system becomes large.
In this way, by applying the configuration of the present invention to an optical apparatus such as a video camera, it is possible to realize an optical apparatus having a small size and high optical performance with little ghost and flare.

It is a figure which shows the structure of the light quantity adjustment apparatus in Example 1 of this invention. 3 is an enlarged cross-sectional view illustrating a configuration of an ND filter according to Embodiment 1. FIG. It is a figure which shows the mode of the phase of the wave front which permeate | transmitted the ND filter of the light quantity adjustment apparatus of Example 1. FIG. It is a figure which shows the structure of the optical system to which the light quantity adjustment apparatus of the said Example 1 in Example 2 of this invention is applied. It is a figure which shows the structure of the imaging device to which the imaging optical system of the said Example 2 in Example 3 of this invention is applied. . It is a figure for demonstrating the influence which the ratio which an ND filter covers aperture stop has on optical performance.

Explanation of symbols

S11, S12: Diaphragm blade P1: ND filter B1: Substrate 10: Imaging optical system 11: Diaphragm 12: Image sensor (photoelectric conversion element)
13: Recording medium 14: Finder 20: Image taking apparatus body N21, N22, N23: Area 61: Base coat layer 62: ND layer 63: AR coat layer

Claims (11)

A diaphragm composed of a plurality of diaphragm blades for forming an opening;
A filter member fixed to at least one of the plurality of diaphragm blades and used for attenuating the amount of light passing through the aperture, the transmittance of which varies depending on the location. In the light amount adjusting device that adjusts the light amount by changing the area in the opening region of the opening by gentle movement,
The light quantity adjusting device, wherein the filter member is disposed so as to cover a part of an opening region including an optical axis of the opening in the open state of the diaphragm.   The light amount adjusting device according to claim 1, wherein the filter member covers 51% or more of the area of the opening region.   The light amount adjusting device according to claim 1, wherein the filter member covers 51% or more and 95% or less of the area of the opening region.   The light amount adjusting device according to claim 1, wherein the filter member has a plurality of regions formed by a multilayer film and having different transmittances.   The light quantity adjusting device according to claim 4, wherein the multilayer film includes a layer that reduces reflection.   The multilayer film has a layer for setting a transmitted wavefront phase difference to be in a range of {1 ± (1/5)} λ or {2 ± (1/5)} λ. Item 6. The light quantity adjusting device according to Item 4 or Item 5.   5. The light amount adjusting device according to claim 1, wherein the filter member has a transmittance of 75% or more at a portion having the highest transmittance of the filter member.   5. The light amount adjusting device according to claim 1, wherein the filter member has a transmittance of 90% or more at a portion having the highest transmittance of the filter member.   The light amount adjusting device according to claim 1, wherein the filter member is disposed obliquely with respect to the optical axis.   An optical device comprising an optical system having the light amount adjusting device according to claim 1.   A photographing apparatus comprising a photographing optical system having the light amount adjusting device according to any one of claims 1 to 9.

Images