JP2001257945A - Optical low-pass filter attaching structure for image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the thickness of an optical low-pass filter(LPF) provided between an image pickup lens and an image pickup device and to secure a wider space between the image pickup lens and the image pickup device. SOLUTION: A planar solid-state imaging device 13 is embedded on the base of a recessed part 12 of a casing 11. Transparent cover glass 15 is fitted and adhered to a step part 14, which is formed at the edge of the recessed part 12, by an adhesive agent. Nitrogen is sealed into the easing 11. An optical LPF 16 formed by sticking lithium niobate plates 16a and 16b is stuck on the surface of the cover glass 15 on the side of the solid-state imaging device 13 while using ultraviolet setting resins.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device for suppressing a moire generated as a pseudo signal when a stripe pattern of a subject and a pixel pitch of an image sensor are close to each other in an image pickup apparatus provided in a digital camera or a video camera, for example. The present invention relates to a low-pass filter mounting structure.

[0002]

2. Description of the Related Art Conventionally, there is known an apparatus using an image pickup apparatus such as a digital camera in which an optical low-pass filter (spatial frequency filter) is provided between an image pickup lens and the image pickup apparatus. The optical low-pass filter is a filter for preventing a moiré caused by a beat between a pixel pitch of an image sensor and a spatial frequency of a subject, and restricts a spatial frequency of light incident on the image sensor to obtain an image obtained by an imaging device. Image quality can be improved.

According to the configuration in which the optical low-pass filter is provided, a space corresponding to the thickness of the optical low-pass filter must be provided between the imaging lens and the imaging device, which is a great obstacle in optical design.

[0004]

SUMMARY OF THE INVENTION The present invention reduces the thickness of an optical low-pass filter provided between an image pickup lens and an image pickup device, and mounts the optical low-pass filter so that a wider space can be secured between the image pickup lens and the image pickup device. The aim is to get the structure.

[0005]

According to the present invention, there is provided an optical low-pass filter mounting structure for an image pickup apparatus, wherein a solid-state image sensor is provided in a casing, a cover glass for covering the solid-state image sensor is mounted on the casing, and the inside of the casing is exposed to outside air. In an image pickup apparatus in which a space between a peripheral edge portion of a cover glass and a casing is sealed so as to be shielded from light, an optical low-pass filter is provided between the cover glass and the solid-state image pickup device.

The optical low-pass filter is preferably affixed to the surface of the cover glass on the side of the solid-state image sensor with an ultraviolet curing resin. The optical low-pass filter is, for example, a flat member smaller than the cover glass. The optical low-pass filter is provided in parallel with the solid-state imaging device, and is preferably formed from a plurality of birefringent plates.

In order to improve the performance of the optical low-pass filter, for example, a birefringent plate is integrally provided in parallel with the cover glass on the side opposite to the solid-state image sensor of the cover glass.
At this time, for example, an infrared cut filter is provided in close contact between the birefringent plate and the glass cover. This can prevent the infrared cut filter from deteriorating due to moisture absorption.

[0008] The birefringent plate, for the purpose of reducing its thickness,
It is preferably formed from a plate-like lithium niobate. Further, for example, an infrared cut coat is applied to one surface of the birefringent plate. Thereby, the space for the thickness of the infrared cut filter can be further saved.

The cover glass is, for example, an infrared cut filter. By using the cover glass also as the infrared cut filter, space can be saved by the thickness of the infrared cut filter.

For example, an infrared cut filter is provided between the optical low-pass filter and the cover glass or on the surface of the optical low-pass filter on the solid-state image sensor side in close contact.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. 1 and 2 show an image pickup apparatus using an optical low-pass filter mounting structure using lithium niobate. In addition, FIG.
It is sectional drawing which follows the II-II line.

The casing 11 of the image pickup device has a flat box shape, and has a thin flat plate-shaped concave portion 12. A flat solid-state imaging device 13 is embedded in the bottom surface of the concave portion 12. A step 14 is formed on the periphery of the recess 12 so as to surround the entire recess 12. A transparent cover glass 15 is fitted into the step portion 14 and covers the solid-state imaging device 13. The peripheral portion of the cover glass 15 is fixed to the step portion 14 with an adhesive, whereby the space between the peripheral portion of the cover glass 15 and the casing 11 is sealed. That is, the inside of the casing 11 is shut off from the outside air, and nitrogen is sealed in the inside.

On the surface of the cover glass 15 on the solid-state image sensor 13 side, lithium niobate (L) as a birefringent plate is provided.
N) An optical low-pass filter 16 constituted by laminating two plates 16a and 16b is adhered. Two L
The N plates 16a and 16b are arranged so that the directions of image shift due to birefringence are different. The optical low-pass filter 16 is placed on the cover glass 15 in a state where an adhesive made of an ultraviolet curable resin is applied to the entire surface thereof, and is fixed to the cover glass 15 by irradiating the ultraviolet light.

The optical low-pass filter 16 is a plate-like member having substantially the same size as the solid-state image sensor 13 and is opposed to the solid-state image sensor 13 in parallel. The surface of the optical low-pass filter 16 is slightly smaller than the cover glass 15. A gap having substantially the same size as the thickness of the optical low-pass filter 16 is formed between the optical low-pass filter 16 and the solid-state imaging device 13.

Although a quartz plate may be used as the optical low-pass filter 16, the optical low-pass filter using the quartz plate is thicker than the one using the LN plate. The depth is larger than the thickness of the quartz plate and is not limited to the one that does not interfere with the image sensor 13. On the other hand, in the first embodiment, the optical low-pass filter 16 has a configuration in which an LN plate, which is much thinner than a quartz plate, is bonded to the optical low-pass filter 16. There is an advantage that there are many.

The shape and size of the optical low-pass filter 16, the size of the gap between the optical low-pass filter 16 and the solid-state image sensor 13, and the like can be changed as needed.

FIG. 3 is a diagram schematically showing the positional relationship between the image pickup device shown in FIGS. 1 and 2 and the infrared cut filter 20.

The infrared cut filter 20 is disposed between the imaging lens (not shown) and the cover glass 15, and is supported by a support member (not shown). The infrared cut filter (light absorption type infrared cut filter) 20 is a rectangular flat plate having substantially the same dimensions as the optical low-pass filter 16 and is disposed substantially parallel to the cover glass 15, and the center thereof coincides with the optical axis of the imaging optical system. I do. The light transmitted through the imaging lens enters the imaging device via the infrared cut filter 20, and the infrared cut filter 20 absorbs light in the infrared wavelength region. Thereby, the solid-state imaging device 13 can detect the image of the subject with a more natural color.

As described above, the first embodiment of the present invention is as follows.
Cover glass 1 provided on casing 11 of imaging device
5 has an optical low-pass filter 16 attached to the back surface. That is, since the optical low-pass filter 16 is disposed in the space formed between the cover glass 15 and the solid-state imaging device 13, the optical low-pass filter between the imaging lens and the imaging device is not changed so much. Can be reduced in space corresponding to the thickness. Thereby, the degree of freedom of the space near the optical axis of the imaging lens is increased, and the configuration is simplified. Also, LN
The plate has a problem in that it has pyroelectricity and adsorbs dust such as dust around it, thereby deteriorating the quality of a captured image. However, in the first embodiment, since the optical low-pass filter 16 is disposed in the casing 11 sealed from the outside air,
Optical low-pass filter 1 using LN plates 16a and 16b
No dust or the like adheres to the image pickup device 6, and the image quality of the image obtained by the imaging device can be improved.

Next, a second embodiment of the present invention will be described with reference to FIG. Since the configuration of the second embodiment is substantially the same as that of the first embodiment, only portions different from the first embodiment will be described.

In the second embodiment, an infrared cut filter 15 'is used as the cover glass 15 in the first embodiment.
The optical low-pass filter 16 is formed by laminating three LN plates 16a, 16b, and 16c.

As a result, the same effect as that of the first embodiment can be obtained, and it is not necessary to provide the infrared cut filter 20 between the imaging lens and the imaging device as in the first embodiment. The space for the thickness of the infrared cut filter 20 between the lens and the imaging device can be further reduced.

FIG. 5 shows a third embodiment of the present invention. A third embodiment will be described with reference to FIG.

In the third embodiment, the infrared cut filter 20 disposed outside the cover glass 15 in the first embodiment is disposed inside the cover glass 15 similarly to the optical low-pass filter 16. Was done,
Other configurations are substantially the same as those of the first embodiment.

In FIG. 5, the infrared cut filter 20
Is an optical low-pass filter in which three LN plates 16a, 16b, and 16c are attached to the surface of the infrared cut filter 20 on the solid-state imaging device 13 side. 16 is further bonded. Thereby, the same effect as in the second embodiment can be obtained. In addition, infrared cut filters generally have hygroscopicity,
This results in quality degradation. However, in the third embodiment, the infrared cut filter 20 is provided in the casing 11 sealed from the outside air, and is disposed between the cover glass 15 and the optical low-pass filter 16, so that the quality of the infrared cut filter 20 due to moisture absorption is reduced. No degradation problem occurs.

Next, a fourth embodiment of the present invention will be described with reference to FIG. In the fourth embodiment, in the first embodiment, an infrared cut filter 20 is attached to the outer surface of the cover glass 15 (the surface opposite to the solid-state imaging device 13), and an LN plate 16d is further provided thereon. It is the thing which stuck. That is, in the fourth embodiment, the LN plate 16d, the infrared cut filter 2
0, a cover glass 15, and an optical low-pass filter 16 are stacked in this order on the filter and the cover glass. Therefore,
In the fourth embodiment, there is no need to separately provide an infrared cut filter as in the first embodiment.

In the present embodiment, the optical low-pass filter 16 is composed of several LN plates, but may be a combination of a quartz plate and an LN plate as described above. Further, the LN plate 16d functions as an optical low-pass filter having a low pass spatial frequency in cooperation with the optical low-pass filter 16, so that the L
The number of the N plates to be bonded is reduced, and the LN plate 16
d may be plural.

As described above, according to the fourth embodiment,
Since the optical low-pass filter 16 is disposed in the space formed between the cover glass 15 and the solid-state imaging device 13,
A large space between the imaging lens and the imaging device can be secured by the thickness of the optical low-pass filter 16. Thereby, the degree of freedom of the space near the optical axis of the imaging lens increases. In addition, the infrared cut filter 20
Since the infrared cut filter is sandwiched between the glass cover 15 and the LN plate 16d, the problem of quality deterioration due to moisture absorption of the infrared cut filter can be prevented as in the third embodiment. In the fourth embodiment, an optical low-pass filter having desired characteristics is desired to be formed. However, when the depth of the concave portion is insufficient, the configuration of the third embodiment shown in FIG. 5 cannot be adopted. It is effective for

Next, a fifth embodiment of the present invention will be described with reference to FIG. The fifth embodiment is different from the second embodiment in that an infrared cut filter and a cover glass 15 ′ are used.
The LN plate 16d is stuck on the outside of. The infrared cut filter 15 ′ also serving as a cover glass is made of one LN
It is shielded from the outside air by the plate 16d, and the problem of moisture absorption of the infrared cut filter does not occur. As described above, also in the fifth embodiment, the same effect as in the fourth embodiment can be obtained, and a wider space is secured between the imaging lens and the imaging device because the infrared cut filter is used as the cover glass. can do.

FIG. 8 is a sectional view showing the structure of the sixth embodiment. In the sixth embodiment, an infrared cut coat is applied to the outer surface 15s of the cover glass 15 in the first embodiment. In the configuration of the sixth embodiment, the same effects as those of the first embodiment can be obtained. In the sixth embodiment, since the infrared cut filter is applied to the surface of the cover glass 15 in place of the infrared cut filter 20, the space for the infrared cut filter 20 can be saved, and the space between the imaging lens and the imaging device can be reduced. Space can be secured more widely. Further, the infrared cut coat has no problem of quality deterioration due to moisture absorption.

FIG. 9 is a sectional view showing the structure of the seventh embodiment. In the seventh embodiment, an LN plate 16d is attached to the outside of the cover glass 15 of the first embodiment, and the LN plate 16
An infrared cut coat is applied to the outer surface 16d 'of the line d. In the configuration of the seventh embodiment, the same effect as in the fourth embodiment can be obtained. Further, in the seventh embodiment, since the infrared cut filter is used instead of the infrared cut filter, the space for the infrared cut filter 20 can be saved similarly to the sixth embodiment, and A wider space between the imaging devices can be ensured, and the problem of quality deterioration due to moisture absorption of the infrared cut filter is eliminated.

In the first and second embodiments, the optical low-pass filter is composed of two or three LN plates, but the number of LN plates may be one or four or more. . In the third and fourth embodiments, the infrared cut filter is provided between the cover glass 15 and the optical low-pass filter 16 or the LN plate 16d. However, when the optical low-pass filter 16 is composed of a plurality of LN plates. ,
You may stick | paste between LN boards and LN boards. In the configuration in which the infrared cut filter is provided inside the casing 11 as in the third embodiment, the infrared cut filter 20 may be attached to the surface of the optical low-pass filter 16 on the solid-state imaging device 13 side.

In the sixth and seventh embodiments, the infrared cut coat is applied to the outer surface of the cover glass 15 and the LN plate 16d. It may be applied to the surface on the 13th side. When the optical low-pass filter 16 is composed of a plurality of LN plates, an infrared cut coating is performed on a matching coat for bonding the LN plates, and the L
It may be applied between N plates. Also in the seventh embodiment, an infrared cut coat may be applied to the surface of the cover glass 15.

[0034]

As described above, according to the present invention, the thickness of the optical low-pass filter provided between the imaging lens and the imaging device can be reduced, and the space between the imaging lens and the imaging device can be secured more widely. Mounting structure can be obtained.

[Brief description of the drawings]

FIG. 1 is a plan view showing an image pickup apparatus using an optical low-pass filter mounting structure according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along the line II-II in FIG.

FIG. 3 is a diagram schematically illustrating a positional relationship between an imaging device and an infrared cut filter according to the first embodiment.

FIG. 4 is a diagram schematically illustrating a cross section of an imaging device using an optical low-pass filter mounting structure according to a second embodiment.

FIG. 5 is a diagram schematically illustrating a cross section of an imaging device using an optical low-pass filter mounting structure according to a third embodiment.

FIG. 6 is a diagram schematically illustrating a cross section of an imaging device using an optical low-pass filter mounting structure according to a fourth embodiment.

FIG. 7 is a diagram schematically showing a cross section of an imaging device using an optical low-pass filter mounting structure according to a fifth embodiment.

FIG. 8 is a diagram schematically illustrating a cross section of an imaging device using an optical low-pass filter mounting structure according to a sixth embodiment.

FIG. 9 is a diagram schematically illustrating a cross section of an imaging device using an optical low-pass filter mounting structure according to a seventh embodiment.

[Explanation of symbols]

Reference Signs List 11 casing 12 recess 13 solid-state imaging device 14 step 15 cover glass 15 'cover glass (infrared cut filter) 16 optical low-pass filter 16a, 16b, 16c, 16d lithium niobate plate (birefringent plate)

Claims (12)

[Claims] 1. A solid-state imaging device is provided in a casing, a cover glass for covering the solid-state imaging device is attached to the casing, and a space between a peripheral portion of the cover glass and the casing is shielded from outside air in the casing. An optical low-pass filter mounting structure for an image pickup device, wherein an optical low-pass filter is provided between the cover glass and the solid-state image pickup device in the image pickup device in which is sealed. 2. The optical low-pass filter mounting structure according to claim 1, wherein the optical low-pass filter is attached to a surface of the cover glass on the side of the solid-state image sensor with an ultraviolet curing resin. 3. The optical low-pass filter mounting structure according to claim 1, wherein the optical low-pass filter is a flat member smaller than the cover glass. 4. The optical low-pass filter mounting structure according to claim 1, wherein the optical low-pass filter is provided in parallel with the solid-state imaging device. 5. The optical low-pass filter mounting structure according to claim 1, wherein the optical low-pass filter is formed from a plurality of birefringent plates. 6. The optical low-pass filter mounting structure according to claim 1, wherein a birefringent plate is provided integrally with the cover glass on a side of the cover glass opposite to the solid-state imaging device. 7. The optical low-pass filter mounting structure according to claim 6, wherein the birefringent plate is provided in parallel with the cover glass. 8. The optical low-pass filter mounting structure according to claim 6, wherein an infrared cut filter is provided between the birefringent plate and the glass cover in close contact therewith. 9. The optical low-pass filter mounting structure according to claim 5, wherein the birefringent plate is formed of a plate-shaped lithium niobate. 10. The optical low-pass filter mounting structure according to claim 5, wherein an infrared cut coat is applied to at least one surface of the birefringent plate. 11. The optical low-pass filter mounting structure according to claim 1, wherein the cover glass is an infrared cut filter. 12. An infrared cut filter is provided between the optical low-pass filter and the cover glass or on a surface of the optical low-pass filter on the side of the solid-state imaging device. 3. The optical low-pass filter mounting structure according to 1.