JP2000206325A - Infrared ray cut filter and imaging device by using infrared ray cut filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an infrared ray cut filter capable of fine adjustment of a characteristic of the infrared ray cut filter after forming a multi-layer film, and an imaging device by using the infrared ray cut filter. SOLUTION: This imaging device is composed by arranging, on an optical axis A of an imaging optical path, an image formation optical system 1, an optical low-pass filter 2 on which an infrared ray cut coat 3 is formed, and a CCD (charge coupled element) 4 for executing photoelectric conversion of incident light and for obtaining an imaging image. The optical low-pass filter 2 is composed so that the face of incidence can be rotated by 0-20 degrees from the face vertical to the optical axis A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared cut filter used for a video camera and an electronic still camera, and an image pickup apparatus using the infrared cut filter.

[0002]

2. Description of the Related Art A general video camera is composed of a coupling optical system, an infrared cut filter, an optical low-pass filter, and an image pickup device such as a CCD in the order perpendicular to the optical axis from the object side. For a subject having color information close to the pixel pitch of an imaging device such as a CCD, a pseudo signal different from the original video information is generated in the imaging device, and a moiré phenomenon in which colors are blurred in an output video may occur. An optical low-pass filter is used to block and attenuate the spatial frequency components related to such a pseudo signal.

Incidentally, an imaging device such as a CCD has a relatively wide sensitivity characteristic, and in addition to light in the visible region,
Partially responds to light in the infrared region. However, in an imaging apparatus used for normal subject photographing, infrared incident light becomes stray light, which causes a reduction in resolution, image spots and unevenness, and adversely affects color reproducibility.

[0004] In order to eliminate such adverse effects, infrared cut filters have been used, and conventionally, colored glass has often been used. Also recently, Al2O
3. A multilayer infrared cut coat (hereinafter, referred to as an infrared cut coat) in which a dielectric such as TiO2, SiO2, etc. is formed in multiple layers has been increasingly used. In this method, for example, an infrared cut coat is formed on the surface of an optical low-pass filter by means of vapor deposition or the like.With such a configuration, the entire optical path length is shortened, the number of components is reduced, and the size of the imaging device is reduced. It is also considered to aim.

[0005] The above infrared cut coat has several tens of dielectric thin films laminated, but has a problem that it is difficult to obtain stable characteristics because the blocking characteristics shift to longer wavelengths after the film formation. As a countermeasure against this, it is common to form a film in advance in anticipation of the above-mentioned wavelength shift amount. However, since the shift amount itself also varies, there is a problem that the yield with respect to required characteristics is reduced.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an infrared cut filter which makes it possible to finely adjust the characteristics of an infrared cut coat after forming a multilayer film; It is an object of the present invention to obtain an imaging device using a cut filter.

[0007]

SUMMARY OF THE INVENTION The present invention has been made by paying attention to the fact that the transmittance characteristic (filter characteristic) of an infrared cut coat depends on the angle of incidence on the infrared cut coat. It is characterized by a configuration.

According to a first aspect of the present invention, there is provided an infrared cut filter inserted into an image pickup optical path, wherein the infrared cut filter is formed of a visible light transmitting plate having a multilayer infrared cut coat formed thereon. It is characterized in that it can be rotated by a predetermined angle from a plane perpendicular to the axis.

According to a second aspect of the present invention, there is provided an image pickup apparatus wherein at least an infrared cut filter made of a visible light transmitting plate having a multilayer infrared cut coat formed thereon is arranged in front of an image pickup optical path of the image pickup device. The cut filter can be rotated by a predetermined angle from a plane perpendicular to the optical axis of the imaging optical path.

As described above, the transmittance characteristics of the infrared cut coat depend on the light incident angle on the infrared cut coat. FIGS. 5 and 6 are graphs each showing a change in transmittance characteristics (filter characteristics) with respect to a light incident angle on the infrared cut coat. Each is an optical low-pass filter configured to obtain a desired light separation pattern by bonding three quartz plates having predetermined light separation characteristics. An infrared cut coat is formed on one side, and an antireflection film is formed on the other side. are doing. Infrared cut coat is TiO2, SiO
2 are repeatedly formed, and have a total thickness of about 3 μm in a 32-layer configuration. In FIG. 6, an infrared cut coat is formed slightly thinner as a whole than that shown in FIG. 5 so as to correspond to different required characteristics (wavelength range to be cut off).

In both graphs, A is when the rotation angle with respect to a plane perpendicular to the optical axis is 0 degree, B is 5 degrees, C is 10 degrees, D is 15 degrees, and E is These data are for the case of the same 20 degrees, and it can be seen that the filter characteristics move to the shorter wavelength side in accordance with the rotation angle. By making use of such characteristics, the infrared cut filter (infrared cut coat) can be rotated about the optical axis,
Fine adjustment of transmittance characteristics can be performed.

According to a third or fourth aspect of the present invention, the visible light transmitting plate is a quartz optical low-pass filter,
The rotation angle may be 0 to 20 degrees from a plane perpendicular to the optical axis.

As is well known, a quartz optical low-pass filter uses birefringence characteristics for separating incident light into ordinary light and extraordinary light in the filter, and the separation width determines the filter characteristics. Therefore, by rotating the quartz optical low-pass filter that has formed the multilayer infrared cut filter,
Although it is conceivable that the separation width deviates from a predetermined value and deteriorates the filter characteristics, the difference between the refractive index of air and the refractive index of the quartz optical low-pass filter is also combined, so that the rotation angle is set from a plane perpendicular to the optical axis. It was found that the deviation could be suppressed to a practical level when the angle was within 45 degrees. However, in the case of fine adjustment of the filter characteristics in the infrared cut filter, it is practically possible to sufficiently adjust the rotation by about 0 to 20 degrees. As is clear from the data shown in FIGS. 5 and 6, the filter performance also decreases as the rotation angle increases. Therefore, a more preferable rotation range is about 0 to 15 degrees.

According to a fifth aspect of the present invention, there is provided an imaging apparatus in which at least an imaging optical system, a quartz optical low-pass filter, and an imaging device are arranged in this order along the optical axis,
A multilayer infrared cut coat is formed on the front surface or the back surface of the quartz optical low-pass filter, and the quartz optical low-pass filter is 0 to 2 from a surface perpendicular to the optical axis.
It may be configured to be rotatable in a range of 0 degrees.

According to a sixth aspect of the present invention, there is provided an infrared cut filter including a visible light transmitting plate having a multilayer infrared cut coat formed between an image forming optical system and an imaging device arranged along the optical axis. An imaging device in which optical low-pass filters are arranged, wherein the infrared cut filter may be configured to be rotatable by a predetermined angle from a plane perpendicular to the optical axis. In this configuration, since the infrared cut filter and the optical low-pass filter are separated, the optical low-pass filter is not rotated. Therefore, in setting the maximum rotation angle of the infrared cut filter, it is not necessary to consider the deterioration of the low-pass filter characteristics.

The rotation mechanism may be manually operated by a knob, or may be rotated by driving means such as an actuator. The optical low-pass filter may be based on a birefringence effect or may be based on a diffraction grating.

[0017]

Embodiments of the present invention will be described with reference to the drawings. 1 and 2 are schematic diagrams showing an image pickup apparatus. FIG. 2 shows a state of fine adjustment of an optical low-pass filter on which an infrared cut coat 3 is formed. FIG. 3 is a schematic perspective view of an image pickup apparatus used in the present invention, and is a diagram illustrating an example of a rotation mechanism of an optical low-pass filter on which an infrared cut coat 3 is formed.

The image pickup apparatus includes an image forming optical system 1 on an optical axis A of an image pickup optical path, an optical low-pass filter 2 having an infrared cut coat 3 formed thereon, and a CCD (charge-coupled device) for photoelectrically converting incident light to obtain a picked-up image. Elements) 4 are arranged. The imaging optical system 1 includes a plurality of lenses.
The optical low-pass filter 2 is composed of a plurality of quartz plates, and is combined with quartz plates having different light separation directions so as to obtain a desired light separation pattern as a whole, and is attached with an adhesive or the like. The infrared cut coat provided on the front of the optical low-pass filter is SiO2, TiO2, Al2O
3, a dielectric thin film of ZrO2 or MgF2 or the like is appropriately combined with a plurality of layers.

In this embodiment, Al2O3, S
A combination layer of iO2 and TiO2 is repeatedly formed by a vacuum deposition method, and has a thickness of about 3 μm as a whole. In addition, the thickness of each one layer is about 0.1 μm,
This makes it possible to selectively reflect only the light in the infrared region and transmit the visible light very efficiently by utilizing the interference effect of the light of the thin film.

The optical low-pass filter 2 on which the infrared cut coat 3 is formed is configured to be rotatable by 0 to 20 degrees from a plane whose incident surface is perpendicular to the optical axis. This rotation angle θ can be set to a larger rotation angle, but considering the actual infrared cut filter characteristics and the characteristics of the optical low-pass filter, the above range is a practically effective range. As described above, 0 to 15 degrees is a more preferable range from the viewpoint of filter characteristics.

As shown in FIG. 3, for example, the rotating mechanism may be such that the optical low-pass filter 3 is installed on a rotating table 51 and rotated by external energy from the driving mechanism 5, or a knob is provided to allow manual adjustment. It may be. Needless to say, the rotation may be a rotation in the opposite direction.

As described above, the transmittance characteristic of the infrared cut coat depends on the incident angle, and the plate surface is inclined (rotated) with respect to the optical axis on the basis that the infrared cut coat surface is perpendicular to the optical axis. Accordingly, the transmittance characteristic shifts to the short wavelength side, that is, the visible light side. By utilizing this characteristic, fine adjustment after the installation of the infrared filter becomes possible. The infrared cut coat may be provided on the back side of the optical low-pass filter.

Another embodiment according to the present invention will be described with reference to FIG. FIG. 4 is a schematic diagram showing an image pickup apparatus, and has a configuration in which an optical low-pass filter and an infrared cut filter are separately provided. The same components as those in the above-described embodiment will be described using the same reference numerals. The imaging device includes an imaging optical system 1 and an infrared cut coat 7 on the optical axis of the imaging optical path.
In this configuration, an infrared cut filter 7 having zeros formed thereon, an optical low-pass filter 8, and a CCD 4 for photoelectrically converting incident light to obtain a captured image are arranged. The imaging optical system 1 includes a plurality of lenses. The infrared cut filter is composed of a visible light transmitting plate 6 such as transparent glass and an infrared cut coat 70.
It is constituted by combining a plurality of dielectric thin films of TiO2 alternately. The optical low-pass filter is configured by combining a plurality of quartz plates as described above.

In this embodiment, the optical low-pass filter and the infrared cut filter are separately provided, and only the infrared cut filter is rotated. Therefore, a change in characteristics due to the rotation of the optical low-pass filter is not taken into consideration. You may.

[0025]

According to the first to sixth aspects, an infrared cut filter made of an infrared cut coat inserted into an imaging optical path is rotatable by a predetermined angle from a plane perpendicular to the optical axis, and the infrared cut filter is rotated to rotate the infrared cut filter. The filter characteristics of the filter can be finely adjusted. Therefore, even after being incorporated in the imaging device, it is possible to finely adjust the filter characteristics to the optimum by rotating the infrared cut filter.

According to the third aspect, since the infrared cut coat is formed on the quartz optical low-pass filter, no separate visible light transmitting plate is required. Therefore, the entire optical path length can be shortened, and a small-sized imaging device can be obtained.

According to the fourth or fifth aspect, since the infrared cut coat is formed on the quartz optical low-pass filter, no separate visible light transmitting plate is required. Therefore, the entire optical path length can be shortened, and a small-sized imaging device can be obtained.

Conversely, if a configuration in which an infrared cut filter and an optical low-pass filter are separately provided is adopted, the amount of rotation of the infrared cut filter does not affect the characteristics of the optical low-pass filter, so that a wider range of adjustment is possible. .

[Brief description of the drawings]

FIG. 1 is a schematic view of an imaging device according to an embodiment of the present invention.

FIG. 2 is a schematic view of an imaging device according to an embodiment of the present invention.

FIG. 3 is a schematic perspective view of an imaging device according to an embodiment of the present invention.

FIG. 4 is a schematic view of an imaging device according to another embodiment of the present invention.

FIG. 5 is a transmittance characteristic graph when the light incident angle on the infrared cut filter is changed.

FIG. 6 is another transmittance characteristic graph when the light incident angle on the infrared cut filter is changed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Imaging optical system 2, 8 Optical low-pass filter 3, 70 Infrared cut coat 4 CCD 6 Visible light transmission plate 7 Infrared cut filter

 ──────────────────────────────────────────────────続 き The continuation of the front page F term (reference) 2H048 GA04 GA19 GA24 GA25 GA43 GA51 GA61

Claims (6)

[Claims] 1. An infrared cut filter inserted into an imaging optical path, wherein the infrared cut filter is made of a visible light transmitting plate having a multilayer infrared cut coat formed thereon, and is perpendicular to an optical axis of the imaging optical path. Infrared cut filter that can be rotated by a predetermined angle from. 2. An image pickup apparatus, comprising: at least an infrared cut filter formed of a visible light transmitting plate having a multilayer infrared cut coat formed on a front surface of an image pickup optical path of an image pickup device; An imaging device capable of rotating a predetermined angle from a plane perpendicular to an axis. 3. The infrared cut filter according to claim 1, wherein the visible light transmitting plate is a quartz optical low-pass filter, and the rotatable angle is 0 to 20 degrees. 4. The imaging apparatus according to claim 2, wherein the visible light transmitting plate is a quartz optical low-pass filter, and the rotatable angle is 0 to 20 degrees. 5. An imaging optical system along at least the optical axis,
A quartz optical low-pass filter, an imaging device arranged in the order of an imaging device, wherein a multilayer infrared cut coat is formed on the front surface or the back surface of the quartz optical low-pass filter, and the quartz optical low-pass filter is perpendicular to the optical axis. An imaging device that is rotatable within a range of 0 to 20 degrees from a plane. 6. An infrared cut filter composed of a visible light transmitting plate having a multilayer infrared cut coat formed thereon and an optical low-pass filter are respectively disposed between an imaging optical system and an imaging device arranged along the optical axis. An imaging device, wherein the infrared cut filter is rotatable by a predetermined angle from a plane perpendicular to the optical axis.