JP2005266676A - Variable optical low pass filter and image pickup unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost and small-sized variable optical low pass filter. <P>SOLUTION: Four sides of a parallel plane plate 6 are held by a support frame 10 so as to keep airtightness, and the support frame 10 is supported by a flexible support member 12 so as to keep airtightness of a space between an imaging device 3 and the parallel plane plate 6. The parallel plane plate 6 (the support frame 10) is vibrated by small-sized actuators 21 and 22. The actuators 21 and 22 are arranged between a surface including the parallel plane plate 6 (the support frame 10) and a surface including a substrate 11 having the imaging device 3 mounted thereon. The parallel plane plate 6 is made of optical glass having no birefringent properties. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical low-pass filter used with an image sensor and an imaging unit including the optical low-pass filter.

  When an optical image is picked up using an image sensor, an optical low-pass filter that removes a frequency component equal to or higher than a predetermined frequency included in the optical image is used. The cutoff frequency of the optical low-pass filter is determined according to the pixel pitch of the image sensor. The pixel pitch is determined by the size of the pixels constituting the image sensor, but also changes depending on the resolution of the image. For example, when a high resolution image is obtained using all the pixels of the image sensor, the pixel pitch becomes fine, and when a low resolution image is obtained by performing pixel thinning of the image sensor, the pixel pitch is apparently coarse. Thus, when the resolution of the image is changed, it is necessary to change the cutoff frequency of the optical low-pass filter in accordance with the changed pixel pitch. Patent Documents 1 and 2 each disclose a technique for making the cutoff frequency of an optical low-pass filter variable. The technique described in Patent Document 1 inserts a filter member on the optical path from the imaging optical system to the incident surface of the imaging element, and rotates the filter member about its rotation axis to thereby set the cutoff frequency by the filter member. It is something to change. The technology described in Patent Document 2 is to obtain an low-pass filter effect by connecting an actuator to the image sensor chip itself and shifting the image position by causing the image sensor to vibrate during exposure.

JP 2000-69339 A Japanese Patent Laid-Open No. 6-189318

  The technique of Patent Document 1 requires a large space for the rotation of the filter member, resulting in an increase in size of the apparatus. Further, since the space between the image sensor and the filter is not hermetically sealed, dust or the like may be attached. In the technique of Patent Document 2, a large number of drive components are arranged in the same space as the image sensor chip. Since it is difficult to make many parts completely dust-free, when the parts are moved, dust attached to the parts may float in the package in the image sensor chip. Further, dust or the like may be generated due to wear of parts by driving. Furthermore, if the image sensor chip itself is moved, a burden is imposed on the bonding wire of the image sensor chip.

The variable optical low-pass filter according to the first aspect of the present invention maintains the hermeticity of the space formed between the optical member and the image pickup element that picks up the optical image of the optical member and the light beam that has passed through the optical member. A flexible support member that supports the relative angle of the member and the image sensor so as to be changeable, and an actuator that drives the optical member to change the relative angle are provided.
According to a second aspect of the present invention, in the variable optical low-pass filter according to the first aspect of the present invention, the actuator is configured so as to be disposed on a mounting member on which the imaging element is mounted.
According to a third aspect of the present invention, in the variable optical low-pass filter according to the second aspect, the actuator is configured to be disposed between the surface including the mounting member and the surface including the optical member.
According to a fourth aspect of the present invention, in the variable optical low-pass filter according to the second or third aspect, the optical member is held by the frame member so as to have a sealing property, and the interval between the mounting member and the frame member is changed. The actuator is configured to change the relative angle according to the above.
According to a fifth aspect of the present invention, in the variable optical low-pass filter according to the first aspect, the actuator is configured so as to be integrally formed with the package of the image sensor.
According to a sixth aspect of the present invention, in the variable optical low-pass filter according to the fifth aspect, the actuator is configured to be disposed between a surface including the bottom surface of the package and a surface including the optical member.
According to a seventh aspect of the present invention, in the variable optical low-pass filter according to the fifth or sixth aspect, the optical member is held by the frame member so as to be hermetically sealed, and the distance between the package and the frame member is changed. The actuator is configured to change the relative angle.
An imaging unit according to an eighth aspect of the present invention includes the variable optical low-pass filter according to any one of claims 5 to 7 and an imaging element, and the variable optical low-pass filter and the imaging element are integrated. It is characterized by that.

  According to the present invention, it is possible to provide a compact variable optical low-pass filter that prevents intrusion and generation of dust and the like to the image sensor and does not impose a driving burden on the image sensor, and an image pickup unit having the variable optical low-pass filter.

The best mode for carrying out the present invention will be described below with reference to the drawings.
(First embodiment)
FIG. 1 is a diagram for explaining a main configuration of an imaging apparatus including a variable optical low-pass filter according to the first embodiment of the present invention. In FIG. 1, the imaging apparatus includes an actuator 2, an imaging element 3, an actuator driver 4, a control circuit 5, a parallel plate 6, an image processing circuit 7, a memory 8, and a setting operation member 9.

  The control circuit 5 inputs a signal output from each block in the imaging apparatus, performs a predetermined calculation, and outputs a control signal based on the calculation result to each block.

  The image sensor 3 is constituted by a CCD image sensor or the like. The image sensor 3 captures an image of a subject light beam that has passed through the objective lens 1 and outputs an image signal to the image processing circuit 7. The image processing circuit 7 includes an A / D conversion circuit, and converts an analog imaging signal into a digital signal.

  The image processing circuit 7 performs image processing such as white balance adjustment on the image data after digital conversion, and also performs compression processing for compressing the image data after image processing in a predetermined format. The memory 8 includes a memory card that can be attached to and detached from the imaging apparatus. In the memory 8, image data after image processing is recorded.

  The setting operation member 9 includes a release switch interlocked with the operation of a release button (not shown), an image mode switching switch (not shown), and the like, and sends an operation signal corresponding to each switch to the control circuit 5. Here, the “image mode” includes a high-definition mode that effectively uses pixels provided in the image sensor 3 and a pixel thinning mode that performs pixel thinning at a predetermined ratio. In the high definition mode, for example, an image of 6 million pixels is obtained, and in the pixel thinning mode, an image of 1.5 million pixels is obtained.

  The parallel plate 6 is made of optical glass that does not have birefringence, and is disposed on the optical path from the objective lens 1 to the imaging surface of the imaging device 3. The parallel plate 6 is configured such that the tilt angle with respect to the imaging surface of the imaging device 3 can be adjusted by driving the actuator 2. The actuator 2 is composed of a laminated piezoelectric element or the like, and expands and contracts according to a drive signal supplied from the actuator driver 4. When the actuator 2 repeatedly expands and contracts, the parallel plate 6 vibrates.

  The actuator driver 4 generates a drive signal for the actuator 2 in accordance with the control information for the parallel plate 6 transmitted from the control circuit 5, and outputs this drive signal to the actuator 2. The control information of the parallel plate 6 includes data indicating the vibration direction, amplitude, and frequency when the parallel plate 6 is vibrated.

  The present invention is characterized by a variable optical low-pass filter constituted by the actuator 2, the parallel plate 6 and the image sensor 3 of the image pickup apparatus.

  FIG. 2 is a diagram illustrating details of the variable optical low-pass filter. In FIG. 2, the image sensor 3 is mounted on a substrate 11. The parallel plate 6 has a shape (for example, a rectangle) corresponding to the planar shape of the imaging surface 31 of the image sensor 3 and is held by the support frame 10 so that the four sides of the parallel plate 6 are kept airtight. The support frame 10 is supported by the flexible support member 12. The flexible support member 12 is made of, for example, black silicon rubber. The flexible instruction member 12 is attached to the support frame 10 around the parallel plate 6 so as not to interfere with the subject light beam transmitted through the parallel plate 6, and the subject light beam incident on the imaging surface 31 of the image sensor 3. It is bonded to the image pickup device 3 around the image pickup surface 31 so as not to interfere. Thereby, the space surrounded by the parallel flat plate 6 (support frame 10), the flexible support member 12, and the image sensor 3 is kept hermetically sealed, and dust, water vapor, and the like from outside the space do not enter.

  One of the actuators 21 and 22 is fixed to the substrate 11 and the other is fixed to the support frame 10. When the actuators 21 and 22 are displaced according to the drive signal from the actuator driver 4 (FIG. 1), the support frame 10 is tilted, and the tilt angle of the parallel plate 6 with respect to the imaging surface 31 is changed. The actuator 2 (FIG. 1) is arranged at four locations corresponding to the four sides of the parallel plate 6. Of these, two actuators 21 and 22 are shown in FIG. 2, and the other two are not shown. Omitted.

  In FIG. 2, the actuators 21 and 22 are mounted between a surface including the parallel plate 6 (support frame 10) and a surface including the substrate 11 on which the image sensor 3 is mounted in the direction of the optical axis of the objective lens 1. . Accordingly, no member constituting the variable optical low-pass filter is disposed closer to the objective lens 1 than the parallel plate 6 (support frame 10), and is close to the front surface (objective lens 1 side) of the parallel plate 6. It is possible to arrange a focal plane shutter (not shown).

  FIG. 3 is a diagram for explaining an optical operation by the variable optical low-pass filter of FIG. 2, and FIG. 3 (a) shows a state in which the optical low-pass filter operation is not performed. In FIG. 3A, subject light from the subject 13 is collected by the objective lens 1 and passes through the parallel plate 6. In this case, the displacement of the actuator 2 is adjusted so that the parallel plate 6 is parallel to the imaging surface of the imaging device 3. The light beam that has passed through the parallel plate 6 forms a subject image 14 a on the imaging surface of the imaging device 3.

  FIG. 3B is a diagram illustrating the first low-pass filter operation state. When the actuator 2 is driven, the parallel plate 6 is inclined with respect to the imaging surface of the imaging device 3. When the parallel plate 6 is tilted, the subject image formed on the imaging surface of the image sensor 3 moves according to the refractive index of the material constituting the parallel plate 6, the thickness of the parallel plate 6, and the tilt angle of the parallel plate 6. To do. When the actuator 2 is driven to vibrate the parallel plate 6 (support frame 10) so that the parallel plate 6 alternately repeats the states of FIGS. 3A and 3B, the parallel plate 6 is connected to the imaging surface of the image sensor 3. The image is vibrated like the subject image 14b.

  FIG. 3B shows an example in which the parallel plate 6 is driven so that the subject image vibrates in the horizontal direction of the screen (image displacement occurs). When vibration for at least one period is applied to the parallel plate 6 (support frame 10) during the charge accumulation time (that is, exposure time) in the image pickup device 3, an optical low-pass filter effect with respect to the horizontal direction of the screen is caused by the generated image shift. . This filter effect can suppress so-called color moire and luminance moire. Note that the amplitude of vibration applied to the parallel plate 6 (support frame 10) is determined by the control circuit 5 in accordance with the set image mode. That is, the amount of image shift required according to the presence or absence of the thinning process and the degree of thinning is calculated, and the amplitude required to generate this amount of image shift is determined. Since the pixel pitch is coarse in the pixel thinning mode, the amplitude of the vibration applied to the parallel flat plate 6 (support frame 10) is made larger than in the high definition mode. By increasing the amplitude of vibration, an optical low-pass filter effect corresponding to the case where the cutoff frequency is lowered can be obtained. Data indicating the relationship between the image shift amount and the amplitude is stored in the control circuit 5 in advance.

  FIG. 3C is a diagram illustrating the second low-pass filter operation state, in which the parallel plate 6 is driven so that the subject image vibrates in the horizontal and vertical directions of the screen (image shift occurs). It is an example. When vibrations corresponding to at least one horizontal / vertical period are applied to the parallel plate 6 (support frame 10) during the charge accumulation time (that is, the exposure time) in the image pickup device 3, the horizontal and vertical directions of the screen are caused by the generated image displacement. An optical low-pass filter effect occurs for each of the above.

  The direction of vibration applied to the parallel plate 6 (support frame 10) described above is determined in correspondence with the direction of pixel arrangement in the image sensor 3. That is, if the pixel arrangement direction is the horizontal direction and the vertical direction, the image shift direction for obtaining the optical low-pass filter effect is also the horizontal direction and the vertical direction.

The first embodiment described above will be summarized.
(1) The four sides of the parallel plate 6 are held by the support frame 10 so as to keep the airtightness, and the support frame 10 is flexible and flexiblely supported so as to keep the airtightness of the space between the image sensor 3 and the parallel plate 6. Supported by member 12. By obtaining hermeticity, dust or water vapor from outside the space does not enter the imaging surface side of the imaging device 3.

(2) Since the support frame 10 is supported by the flexible support member 12, the actuator 2 that vibrates the parallel plate 6 (support frame 10) can be reduced in size. If the support frame 10 is not supported by the flexible support member 12, the actuator 2 needs to have both a function of supporting the support frame 10 and a function of generating vibration, and the actuator 2 having a large size and high strength is required. End up. On the other hand, in the present embodiment, an actuator having at least a vibration generating function is sufficient, and thus a small actuator 2 can be used.

(3) Since the actuator 2 (21, 22) reduced in size by the above (2) is provided between the surface including the parallel flat plate 6 (support frame 10) and the surface including the substrate 11 on which the imaging device 3 is mounted. Among the members constituting the variable optical low-pass filter, there is no member disposed so as to protrude from the parallel plate 6 (support frame 10) toward the objective lens 1 side. For this reason, a focal plane shutter (not shown), a focusing mechanism (not shown), and the like can be disposed in the vicinity of the front surface of the parallel plate 6 (objective lens 1 side), and the imaging apparatus can be reduced in size and weight. Is possible. In addition, maintenance work such as cleaning can be easily performed.

(4) Since the optical member is configured using the parallel plate 6 made of general optical glass, the cost can be reduced as compared with the case where the optical member is configured using a birefringent material. Moreover, since the parallel flat plate 6 made of general optical glass has a better antireflection effect when the antireflection coating is applied than the birefringent material, the parallel flat plate 6 itself may cause ghost and flare. Less is. Furthermore, the parallel plate 6 is less susceptible to aging deterioration (for example, change in spectral transmittance, turbidity, etc.) of the material (optical glass) as compared with the case where a photoelastic member or a liquid prism is used, and the ambient temperature of the material. It is hard to be affected by changes in

(5) Since the parallel plate 6 is vibrated, it becomes difficult for foreign matters such as dust to adhere to the parallel plate 6 itself.

  In the above description, the image shift direction for obtaining the optical low-pass filter effect is made to coincide with the pixel arrangement direction in the image pickup device 3, but the image shift direction by the low-pass filter according to the present invention is not necessarily equal to the pixel arrangement direction. You don't have to.

  In the above description, an example in which a multilayer piezoelectric element is used as the actuator 2 has been described. However, instead of the multilayer piezoelectric element, a single layer piezoelectric element to which an actuation (displacement) amount increasing mechanism is added, or a monomorph / bimorph piezoelectric element. An element may be used.

  You may comprise an actuator with a voice coil motor instead of a piezoelectric element. FIG. 4 is a diagram illustrating a configuration example of a variable optical low-pass filter when a voice coil motor is used. 4, the same components as those in FIG. 2 are denoted by the same reference numerals as those in FIG. A difference from FIG. 2 is that a part of the support frame 10a constitutes a voice coil motor. The voice coil motor is provided in place of the actuators 21 and 22 in FIG.

  A coil 2 ′ is wound around a part of the support frame 10 a, and the coil 2 ′ is disposed in the magnetic field generated by the magnet 2 ″. The magnet 2 ″ is fixed on the substrate 11. When a current flows through the coil 2 ′ by the actuator driver, the voice coil motor drives the support frame 10a in the vertical direction in FIG. FIG. 4 shows a state in which a downward force is applied to the left coil 2 ′ and an upward force is applied to the right coil 2 ′.

  As shown in FIG. 4, when the actuator is constituted by a voice coil motor, the voice coil motor is arranged between a surface including the parallel flat plate 6 (support frame 10) and a surface including the substrate 11 on which the imaging device 3 is mounted. Therefore, the imaging device can be downsized. Further, by configuring the voice coil motor with a part of the support frame 10a, it is possible to obtain the effects of cost reduction and reduction in size / weight by reducing the number of parts.

(Second embodiment)
FIG. 5 is a diagram illustrating a configuration example of a variable optical low-pass filter according to the second embodiment of the present invention. In FIG. 5, the image pickup device package 17 bonds the image pickup device chip 15 on the image pickup device substrate 16 and bonds the image pickup device chip 15 and the wiring pattern formed on the image pickup device substrate 16 together. Packaged.

  The variable optical low-pass filter is integrated with the image sensor package 17. That is, the support frame 10b holds the four sides (in the case of a square) of the parallel flat plate 6 so as to maintain hermeticity, and maintains the hermeticity of the space sandwiched between the parallel flat plate 6 (support frame 10b) and the imaging element chip 15. The support frame 10b is supported by a flexible flexible support member 12a. The flexible support member 12a in this case is made of an adhesive or the like that retains flexibility even after bonding. That is, the support frame 10b (parallel plate 6) is integrated with the image sensor package 17 by adhesion. When the image pickup device package 17 with the parallel flat plate 6 (support frame 10b) integrated in this way is mounted on the substrate 11, the wiring of the image pickup device chip 15 is connected to the wiring on the substrate 11 via the image pickup device terminal 18. Connected with pattern.

  The actuator 2 a is integrated with the image sensor package 17 by being mounted on the image sensor package 17. When the actuator 2 a is mounted on the imaging device package 17, the actuator 2 a is connected to the wiring pattern on the substrate 11 via the actuator terminal 19. A signal for driving the actuator 2a is supplied from an actuator driver 4 (not shown) through this wiring. The actuator 2a is composed of a laminated piezoelectric element or the like, and adjusts the inclination angle of the parallel plate 6 (support frame 10b) with respect to the imaging surface of the imaging element chip 15.

As described above, according to the second embodiment, the following operational effects can be obtained.
(1) The parallel plate 6 (support frame 10b), the actuator 2a, and the image pickup device package 17 are integrated. If the parallel plate 6 (support frame 10b) and the actuator 2a are integrated with the image pickup device package 17 before the image pickup device package 17 is mounted on the substrate 11, the parallel plate 6 is mounted after the image pickup device package 17 is mounted on the substrate 11. Compared with the case where the (support frame 10b) and the actuator 2a are assembled on the image sensor, the cost can be reduced and the workability can be improved. Moreover, the effect of miniaturization / lightening is also acquired by setting it as an integrated structure.

(2) Since the support frame 10b is supported by the flexible support member 12a, the actuator 2a that vibrates the parallel plate 6 (support frame 10b) can be reduced in size as in the first embodiment.

(3) Since the small actuator 2a is disposed between the surface including the parallel flat plate 6 (support frame 10b) and the surface including the bottom surface of the image pickup device package 17, the variable optical low-pass as in the first embodiment. There is no need to arrange the members constituting the filter on the objective lens side. As a result, a focal plane shutter (not shown), a focusing mechanism (not shown), and the like can be disposed in the vicinity of the front surface (objective lens 1 side) of the parallel plate 6, and the imaging apparatus can be made compact. become.

  In the above description, an example in which a parallel plate 6 made of general optical glass having no birefringence is used as an optical member has been described, but an optical element having birefringence is used instead of the parallel plate 6. Also good. In this case, since the optical low-pass filter effect of a predetermined frequency can be obtained without vibrating the optical member, the actuator is not driven and the cut-off frequency is lowered when the cut-off frequency need not be changed. Only the actuator needs to be driven. Thereby, power consumption can be reduced.

  The variable optical low-pass filter can be applied to “pixel shifting” for the purpose of apparently increasing the number of pixels constituting an image picked up by the image sensor, in addition to the purpose of suppressing the color moire and luminance moire described above. . In this case, the parallel plate 6 is not vibrated during the charge accumulation time in the image pickup device, but the charge accumulation of the image pickup device is started after the parallel plate 6 is set at a predetermined tilt angle before the charge accumulation of the image pickup device. . The tilt angle of the parallel plate 6 is maintained at least during the charge accumulation time in the image sensor. By synthesizing a plurality of picked-up images picked up by changing the inclination angle of the parallel plate 6, an image having a resolution finer than the pixel pitch formed on the image pickup device can be obtained. The tilt angle of the parallel plate 6 is determined by the control circuit 5 so as to generate an image shift amount corresponding to the pixel pitch of the image sensor.

  In the present embodiment, the example of driving the actuators arranged at both ends of the parallel plate has been described. However, a so-called cantilever in which one end of the parallel plate is fixed and the actuator arranged at the other end of the parallel plate is driven. The same applies to support.

  In the above description, an example in which the variable optical low-pass filter is used in combination with an imaging element such as a camera has been described. In addition to the camera, the projection type projector apparatus may be used in combination with a light valve.

  Correspondence between each component in the claims and each component in the best mode for carrying out the invention will be described. The optical member is constituted by, for example, a parallel plate 6. The mounting member is configured by, for example, the substrate 11. For example, the support frame 10 (10a, 10b) corresponds to the frame member. In addition, unless the characteristic function of this invention is impaired, each component is not limited to the said structure.

It is a figure explaining the principal part structure of the imaging device by 1st embodiment of this invention. It is a figure explaining the detail of a variable optical low-pass filter. (a) It is a figure which shows the state which is not performing the low-pass filter operation | movement. (b) It is a figure which illustrates the 1st low-pass filter operation state. (c) It is a figure which illustrates the 2nd low-pass filter operation state. It is a figure explaining the variable optical low-pass filter using a voice coil motor. It is a figure explaining the detail of the variable optical low-pass filter by 2nd embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Objective lens 2, 2a, 21, 22 ... Actuator 3 ... Imaging device 4 ... Actuator driver 5 ... Control circuit 6 ... Parallel plate 7 ... Image processing circuit 9 ... Setting operation member 10, 10a, 10b ... Support frame 11 ... Substrate 12, 12a ... flexible support member 15 ... imaging element chip 16 ... imaging element substrate 17 ... package

Claims (8)

An optical member;
A flexible structure that maintains the hermeticity of a space formed between the optical member and an image pickup device that picks up an optical image by the light beam that has passed through the optical member, and supports the relative angle between the optical member and the image pickup device in a changeable manner. A support member;
A variable optical low-pass filter, comprising: an actuator that drives the optical member to change the relative angle. The variable optical low-pass filter according to claim 1,
The variable optical low-pass filter, wherein the actuator is disposed on a mounting member on which the imaging element is mounted. The variable optical low-pass filter according to claim 2,
The variable optical low-pass filter, wherein the actuator is disposed between a surface including the mounting member and a surface including the optical member. The variable optical low-pass filter according to claim 2 or 3,
The optical member is held by a frame member so as to have a sealing property,
The variable optical low-pass filter, wherein the actuator changes the relative angle by changing an interval between the mounting member and the frame member. The variable optical low-pass filter according to claim 1,
The variable optical low-pass filter, wherein the actuator is formed integrally with a package of the imaging device. The variable optical low-pass filter according to claim 5,
The variable optical low-pass filter, wherein the actuator is disposed between a surface including a bottom surface of the package and a surface including the optical member. The variable optical low-pass filter according to claim 5 or 6,
The optical member is held by a frame member so as to have a sealing property,
The variable optical low-pass filter, wherein the actuator changes the relative angle by changing an interval between the package and the frame member. The variable optical low-pass filter according to any one of claims 5 to 7,
An imaging unit comprising: the imaging device, wherein the variable optical low-pass filter and the imaging device are integrated.

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