JP2000209510A - Image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a small-sized image pickup device that copes with image pickup of both visual and infrared regions without the use of a changeover means for a filter such as insertion/removal of an infrared ray cut filter. SOLUTION: The image pickup device is configured with an image forming optical system 1 on an optical axis A of an image pickup optical path, an optical low pass filter with an infrared ray cut coat 3 formed thereto, and a CCD(charge coupled device) 4 that applies photoelectric conversion to an incident light to obtain a picked-up image. In the case of photographing under visual light condition, while an infrared ray cut filter is turned at a maximum angle (e.g. 45 degrees turning), a characteristic of transmitting visual rays and cutting infrared rays can be obtained, and the photographing under the usual visual rays is conducted. In the case of using this image pickup device for an infrared ray camera such as a night vision camera, the light up to the infrared ray region can be transmitted by decreasing the amount of turning.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging apparatus capable of photographing in both a visible region and an infrared region.

[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.

In recent years, imaging devices such as video cameras capable of imaging even in the near-infrared or infrared region have been put to practical use. This is to switch by inserting and removing an infrared cut filter in the optical path.For example, in an image pickup apparatus, an infrared cut filter such as a colored glass is inserted into the image pickup optical path at the time of photographing in the visible light region, and an infrared ray is cut. At the time of photographing an area, the infrared cut filter is removed from the optical path (Japanese Patent Laid-Open No. 52523/1982).
No. 3). Also, a configuration for switching between a visible light cut filter and an infrared cut filter has been devised (Japanese Patent Application Laid-Open No. 61-1986).
-13974). The switching of the imaging environment is performed by these configurations.

However, the insertion and removal of the infrared cut filter and the switching of the filter have disadvantages in that the number of components increases, the size of the mechanism must be increased, and the optical path length increases.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and does not use a filter switching means such as insertion / removal of an infrared cut filter. It is an object of the present invention to obtain a small-sized imaging device compatible with imaging.

[0007]

SUMMARY OF THE INVENTION The present invention focuses on the fact that the blocking characteristic of a multilayer infrared cut coat depends on the angle of incidence on the infrared cut coat, and uses this as an imaging device for both visible light and infrared light. And is characterized by the following configurations.

More specifically, an infrared cut filter comprising a visible light transmitting plate having a multilayer infrared cut coat formed between an image forming optical system and an image pickup device arranged along the optical axis, and an optical low-pass filter. An imaging device in which filters are arranged, wherein the multilayer infrared cut coat is:
In a state of being rotated by a maximum amount within a predetermined rotation range from a plane perpendicular to the optical axis, it is configured to obtain a characteristic of transmitting visible light and blocking infrared light, and light in the infrared region as the rotation amount decreases. An imaging device configured to transmit light is disclosed.

According to a second aspect of the present invention, there is provided an image pickup apparatus in which an optical low-pass filter having a multilayer infrared cut coat formed on a front surface or a back surface is arranged between an image forming optical system arranged along an optical axis and an image pickup device. The optical low-pass filter is rotatable within a range of 0 to 45 degrees from a plane perpendicular to the optical axis, and the multilayer infrared cut coat transmits visible light while being rotated by the maximum amount of the rotation range. An image pickup apparatus is configured to obtain a characteristic of blocking infrared light, and is configured to transmit light in an infrared region as the rotation amount decreases.

In either configuration, visible light is transmitted and infrared light is blocked when the visible light transmitting plate having the multilayer infrared cut coat or the optical low-pass filter having the multilayer infrared cut coat is rotated by the maximum amount. In this state, normal visible light imaging is performed. When used as an infrared camera such as a night vision camera, infrared light is transmitted by reducing the rotation amount.

As described above, the transmittance characteristics (filter characteristics) of the multilayer infrared cut coat depend on the angle of incidence on the infrared cut coat. Hereinafter, a change in the transmittance characteristic with respect to the light incident angle using Sample A and Sample B is shown in a graph.

Sample A has an infrared cut coat formed on one surface of one quartz plate. Infrared cut coat is T
a thin film of iO2 and SiO2 repeatedly formed,
It has a total of 32 layers, and is designed so that the wavelength at which the transmittance becomes 50% is 650 nm when the light incident angle is 0 degree. FIG. 5 shows a sample A at a light incident angle of 0 degree.
FIG. 7 is a graph showing the change in the transmittance characteristic with respect to the light incident angle when the angle is 20 degrees, FIG. 7 is a graph when the angle is 35 degrees, FIG. 8 is a graph when the angle is 45 degrees, and FIG. .

Sample B, like Sample A, has an infrared cut coat formed on one surface of a single quartz plate. The infrared cut coat is formed by repeatedly forming a thin film of TiO2 and SiO2, has a total of 32 layers, and has a wavelength of 650 nm at which the transmittance becomes 50% at a light incident angle of 45 degrees.
It is designed to be. 10 shows a sample B at a light incident angle of 0 degree, FIG. 11 shows a case at 20 degrees, FIG. 12 shows a case at 35 degrees, FIG. 13 shows a case at 45 degrees, and FIG.
6 is a graph showing changes in transmittance characteristics with respect to a light incident angle at the time of degrees.

In both samples, it can be seen that the transmittance characteristic shifts to the shorter wavelength side in accordance with the rotation angle. By making use of such characteristics to make the infrared cut filter (infrared cut coat) rotatable with respect to the optical axis, it is possible to perform imaging in the visible light region and the infrared light region.

That is, the transmittance characteristic of the infrared cut filter (infrared cut coat) is set in advance to the long wavelength (infrared) side, and in this state, it is used as a night vision imaging apparatus for imaging up to the infrared region. At the time of imaging only in the visible light region, the image is rotated by a predetermined angle to block infrared light and used only in the visible light region.

In order to set the filter characteristic (light transmission area) of the infrared cut filter (infrared cut coat) on the long wavelength (infrared) side, each layer thickness is set to a value obtained by dividing a design wavelength by a predetermined value. Generally, each film thickness is set in the range of 1/8 to 1/4 of the design wavelength. That is, when the design wavelength is set on the long wavelength side, the thickness of each layer increases.

However, if the rotation angle is too large, a wavelength region having a reduced transmittance appears even in the wavelength range of the transmission region. For example, in the graphs of FIGS. 9 and 14 rotated by 55 degrees in both samples, the transmittance of light of a part of the wavelength is reduced even in the transmission region, and the imaging quality is reduced. In any of the samples, at a rotation of up to 45 degrees, almost practical transmittance characteristics are obtained.

When the infrared cut filter is rotated, the effective range of the filter is narrowed. For example, if the effective range of the filter without rotation is 100%, 45
When rotated by degrees, the effective range is about 70%, and when rotated by 60 degrees, the effective range is reduced by half to 50%. The lower limit of the practical effective range is about 70%. If the lower limit is not reached, the size of the filter is increased, and the size of the imaging apparatus is increased, which is not preferable.

In the actual design, it is necessary to determine the material and thickness of the multilayer film so that the transmittance characteristics when the light incident angle is the maximum (in this example, 45 degrees) as shown in Sample B are good. There is.

The rotating mechanism may be manually operated with a knob or rotated by a 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.

[0021]

Embodiments of the present invention will be described with reference to the drawings. FIGS. 1 and 2 are schematic views showing an image pickup apparatus. FIG. 1 is a schematic view when an image is captured in a visible light region, and FIG. 2 is a schematic view when an image pickup range is extended to an infrared light region. FIG.
FIG. 1 is a schematic perspective view of an imaging device used in the present invention, and is a diagram illustrating a rotation mechanism of an optical low-pass filter on which an infrared cut coat 3 is formed.

The image pickup apparatus comprises an image forming optical system 1 on the optical axis A of the image pickup optical path, an optical low-pass filter 2 having an infrared cut coat 3 formed thereon, and a CCD (charge-coupled) 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 45 degrees from a plane whose incident surface is perpendicular to the optical axis. This rotation angle can be set to a larger rotation angle, but in consideration of 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 30 degrees is a more preferable range from the viewpoint of filter characteristics.

In such an imaging apparatus, when imaging in a visible condition, the infrared cut filter has a characteristic of transmitting visible light and blocking infrared light while rotating the infrared cut filter by a maximum amount (for example, 45 degrees). In this state, normal visible light imaging is performed. When used as an infrared camera such as a night-vision camera, the amount of rotation is reduced to transmit light up to the infrared light region.

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

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.

In this embodiment, since the optical low-pass filter and the infrared cut filter are separately provided and only the infrared cut filter is rotated, the change of the spatial frequency cutoff characteristic by rotating the optical low-pass filter is performed. Need not be considered.

[0029]

According to the present invention, a visible light transmitting plate having a multilayer infrared cut coat formed thereon or an optical low-pass filter having a multilayer infrared cut coat formed thereon is rotated by a maximum amount to transmit visible light and infrared light. It is configured to obtain a property of blocking light, and in this state, normal visible light imaging is performed.
When used as an infrared camera such as a night vision camera,
The infrared light is transmitted by reducing the rotation amount. Therefore, since there is no need to insert and remove the infrared cut filter as in the related art, it is possible to obtain a small-sized imaging device for both visible light and infrared light without increasing the size of the structure.

[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 graph showing an example of transmittance characteristics with respect to an incident angle.

FIG. 6 is a graph showing an example of transmittance characteristics with respect to an incident angle.

FIG. 7 is a graph showing an example of a transmittance characteristic with respect to an incident angle.

FIG. 8 is a graph showing an example of transmittance characteristics with respect to an incident angle.

FIG. 9 is a graph showing an example of transmittance characteristics with respect to an incident angle.

FIG. 10 is a graph showing another example of the transmittance characteristic with respect to the incident angle.

FIG. 11 is a graph showing another example of the transmittance characteristic with respect to the incident angle.

FIG. 12 is a graph showing another example of the transmittance characteristic with respect to the incident angle.

FIG. 13 is a graph showing another example of the transmittance characteristic with respect to the incident angle.

FIG. 14 is a graph showing another example of the transmittance characteristic with respect to the incident angle.

[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 Continued on the front page F term (reference) 2H048 GA01 GA19 GA24 GA25 GA33 GA51 GA61 GA66 5C022 AA15 AB13 AC42 AC51 AC74 5C024 AA01 AA06 EA08 FA01 GA11

Claims (2)

[Claims] 1. An image pickup apparatus in which an infrared cut filter and an optical low-pass filter each composed of a visible light transmitting plate on which a multilayer infrared cut coat is formed are arranged between an image forming optical system and an image pickup device arranged along an optical axis. The apparatus, wherein the multilayer infrared cut coat is configured to obtain a property of transmitting visible light and blocking infrared light in a state of being rotated by a maximum amount within a predetermined rotation range from a plane perpendicular to the optical axis, and An imaging device configured to transmit light in the infrared region as the rotation amount decreases. 2. An imaging apparatus comprising: a quartz optical low-pass filter having a multilayer infrared cut coat formed on a front surface or a back surface between an imaging optical system and an imaging device arranged along an optical axis; Quartz optical low-pass filter is 0 mm from the plane perpendicular to the optical axis.
To be rotatable in a range of up to 45 degrees, and the multilayer infrared cut coat is configured to obtain a characteristic of transmitting visible light and blocking infrared light in a state of being rotated by the maximum amount of the rotation range,
Further, an imaging apparatus configured to transmit light in an infrared region as the rotation amount decreases.