JP2001264179A - Infrared filter and imaging device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an infrared image of good quality having a large S/N. SOLUTION: An infrared filter 5 is constituted to increase an attenuation amount of transmitting infrared ray at a center as compared with that at a peripheral edge. The filter 5 is disposed between a cold shield opening 3a and an infrared detector 4. An infrared ray amount passed via the opening 3a is constantly reduced at the peripheral edge of the detector 4. Since this reduced infrared ray amount is corrected by the filter 5, a uniform infrared ray amount is obtained by the detector 4 in a totally visual field region. Thus, an infrared image of good quality having no luminance difference can be obtained at the large S/N.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging apparatus for detecting infrared rays from a subject by an infrared detector and an infrared filter used in the imaging apparatus.

[0002]

2. Description of the Related Art In general, in a high-sensitivity infrared imaging apparatus for night vision or monitoring, a cooling element utilizing a photoconductive effect or a photovoltaic effect is used as an infrared detector. The detector in the apparatus is cooled to about -200 ° C. by liquid nitrogen or the like, and a cold shield (cold) also cooled to about −200 ° C. to minimize unnecessary radiation of infrared rays radiated from the inside of the apparatus. Shield).

FIG. 8 is a cross-sectional view showing a conventional infrared imaging apparatus. An optical system 2 including a condenser lens is incorporated in a lens barrel 1 to collect infrared rays radiated from a subject, The infrared light condensed by the optical system 2 is detected by an infrared detector 4 incorporated in a cold shield part 3 that shields heat, and an infrared image of a subject is obtained.

[0004] The cold shield part 3 is held in a vacuum dur 6 kept in a vacuum, and is configured to maintain the infrared detector 4 at an extremely low temperature. A member 7 having a property of transmitting infrared rays, such as sapphire, is fitted into the opening of the vacuum dewar 6 to maintain a vacuum.

The cold shield opening 3a has an advantage of blocking unnecessary infrared rays other than a subject image radiated from the inside of the lens barrel 1 or the like from reaching the infrared detector 4. There is a disadvantage that the amount of infrared light supplied to the light source 4 is limited.

If the diameter of the cold shield opening 3a is reduced, the ratio of unnecessary infrared rays radiated from the inside of the apparatus optical system or the like reaching the infrared detector 4 can be reduced as described above. , Signal to noise ratio (hereinafter,
S / N ratio) can be large and a good quality infrared image can be obtained.

However, the cold shield opening 3
If the aperture diameter of the aperture a is reduced, as shown by the broken line A in FIG. 8, the infrared rays that should reach the peripheral edge of the infrared detector 4 are also blocked. As compared with the infrared ray amount of P, the infrared ray amount at the end of the visual field, which is the peripheral portion, becomes smaller, and as shown in FIG. 9, the infrared ray amount at the peripheral portion side is reduced, which causes a luminance difference and deteriorates image quality.

Generally, the amount of infrared light at the center P of the visual field is set to 10
If the light amount at the end of the visual field is reduced to about 80 when the value is set to 0, it is possible to obtain an infrared image in which the entire image has substantially uniform brightness by sensitivity correction by so-called offset correction and gain correction in the image processing circuit. It can be done.

However, in order to obtain an infrared image with an improved S / N ratio, the opening diameter of the cold shield opening 3a is further reduced, and the ratio of the amount of light at the end of the visual field to the amount of infrared light at the center P of the visual field is 80%. If it further decreases, stable sensitivity correction may be difficult in the image processing circuit.

[0010]

As described above, in the conventional infrared imaging apparatus, there is a problem that the improvement in the S / N ratio causes a decrease in the amount of infrared light at the end of the visual field, thereby deteriorating the image quality.

[0011] Therefore, the present invention, under a large S / N,
An object of the present invention is to provide an imaging device capable of obtaining a high-quality infrared image and an infrared filter suitable for the imaging device.

[0012]

According to a first aspect of the present invention, there is provided an infrared filter having a light transmission characteristic in an infrared region.
It is characterized in that the amount of attenuation of transmitted infrared rays is increased.

A second invention relates to an infrared filter,
An infrared transmitting substrate that can transmit infrared light almost uniformly over the entire surface, and attached to the center of the infrared transmitting substrate,
An attenuating film for attenuating infrared light transmitted through the central portion.

According to a third aspect of the present invention, there is provided an infrared filter having a light transmission characteristic in an infrared region, wherein a plurality of substantially concentric infrared absorbing plates having different diameters are stacked on a common central axis. It is characterized by having done.

As described above, according to the infrared filters according to the first to third aspects of the present invention, the amount of transmitted infrared light is greater at the peripheral portion than at the central portion. When employed in an imaging device, the difference in the amount of infrared light at the peripheral portion with respect to the central portion is corrected, and S / S
It is possible to obtain a high-quality infrared image with uniform brightness while maintaining N.

According to a fourth aspect of the present invention, there is provided an optical system for collecting infrared rays from a subject image, a cold shield unit for introducing the infrared rays through the optical system and shielding unnecessary infrared radiation.
An image pickup apparatus comprising: a detector for detecting infrared rays from the subject through an opening of the cold shield portion; wherein the first to third inventions are provided between the cold shield opening and the detector. The infrared filter according to any one of the inventions is arranged.

As described above, in the fourth invention, the infrared filter according to the first to third inventions is disposed between the cold shield opening and the infrared detector. The amount of infrared light at the peripheral portion, which has been reduced by the opening, is corrected, and the infrared detector can maintain a large S / N and obtain a high-quality infrared image by making the amount of infrared light uniform in the radial direction.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An infrared filter according to the present invention and an embodiment of an image pickup apparatus using the same will be described below in detail with reference to FIGS. Note that the same components as those of the conventional configuration shown in FIG. 8 are denoted by the same reference numerals, and detailed description is omitted.

FIG. 1 is a block diagram showing an embodiment of an imaging apparatus using an infrared filter according to the present invention. In FIG. 1, an optical system 2 for condensing infrared light radiated from a subject is incorporated in a lens barrel 1, and the infrared light passing through the optical system 2 has a property of transmitting infrared light at the opening of a vacuum dual 6. It is supplied to the infrared detector 4 through the member 7, the cold shield opening 3a, and the infrared filter 5 sequentially.

As shown in the side view of FIG. 2, the infrared filter 5 is an infrared transmitting substrate 5 made of sapphire or the like.
An infrared absorbing film 52 is formed such that an alloy or the like is adhered to the first surface by vacuum evaporation or the like so that the film thickness is smaller at the peripheral portion than at the central portion.

Since the infrared filter 5 has an infrared absorbing film 52 made of an alloy thin film or the like, the infrared transmission characteristic of the infrared filter 5 is, as shown in FIG. In this case, the transmittance is low and the amount of attenuation of infrared rays is large, while the transmittance is high and the amount of attenuation of infrared rays is small in the visual field end region which is the peripheral portion.

On the other hand, since the cold shield opening 3a reduces the amount of incident infrared light at the peripheral portion as described above, the amount of infrared light is opposite to the characteristic of the infrared filter 5, as shown in FIG. The characteristic is large in the center P portion and small in the peripheral end portion of the visual field.

The amount of incident infrared light that reaches the infrared detector 4 is represented by the product of the amount of infrared light that enters through the cold shield opening 3a and the transmittance of the infrared filter 5, and the infrared detector 4 uses the cold shield opening 3a. Is corrected by the infrared transmittance of the infrared filter 5, and the characteristic that the total amount of infrared light is uniform from the field center P to the field end as shown in FIG. 5 can be obtained.

Therefore, the infrared detector 4 detects a subject image having a uniform amount of infrared light over the entire visual field region, and improves the S / N ratio by the cold shield unit 3 and produces a high-quality infrared image with little luminance difference. Obtainable.

In the first embodiment, since the infrared absorbing film 52 of the infrared filter 5 is formed by vapor deposition whose film thickness can be easily adjusted, the optimum characteristic pattern for compensating the infrared transmitting characteristic in the cold shield portion 3 is obtained. Can be easily formed. Further, in the infrared filter 5 shown in FIG. 2, the film thickness is deposited on the infrared transmitting substrate 51 such as sapphire glass so as to change its film thickness continuously from the central portion (the center P of the visual field) to the peripheral portion. As shown in FIG. 6, the same effect can be obtained by vapor deposition so that the film thickness changes stepwise.

In any case, according to the first embodiment, the amount of infrared rays reaching the infrared detector 4 varies depending on the area (field of view) due to the opening 3a of the cold shield part 3. Since the infrared filter 5 is provided so as to perform the correction, the difference in the amount of infrared rays can be suppressed at least within a range where the sensitivity correction (offset correction or gain correction) of the infrared detector 4 is possible, and a large S / N is secured. In addition, a high-quality image with a small difference in luminance can be obtained.

Next, in the above-described first embodiment, the infrared filter 5 is formed by vapor deposition of an alloy so that the film thickness changes relatively continuously. However, the infrared filter 5 has substantially concentric circles having different diameters. The same effect can be obtained even when a plurality of infrared absorbing plates each having a shape are stacked on a common central axis.

FIG. 7 is a side view of an infrared filter 5 employed in a second embodiment of the image pickup apparatus according to the present invention. The infrared filter 5 has a light transmission characteristic in the infrared region and has different diameters. 531, 532,... 53
4) were bonded to each other so as to overlap the common central axis P.

Also with the infrared filter 5 having such a configuration, the transmission attenuation rate of the amount of infrared light at the end of the visual field is reduced, the amount of infrared light at the peripheral edge is increased, and the infrared light reaching the infrared detector 4 is equalized. Can be planned.

In this embodiment, the plurality of infrared absorbing plates 53 (531, 532,... 534) are bonded so as to overlap on the common central axis P. ., 534) may be formed, for example, by adopting a flexible sheet-like material and pasting the infrared-transparent substrate 51 such as sapphire glass in the first embodiment.

In the infrared filter 5, an absorption film having a high absorption rate is arranged near the center P of the visual field where the amount of incident infrared light is large, and an absorption film having a low absorption rate is realized in order to realize a high transmittance at the visual field end. It can also be configured to arrange a film.

Further, in the imaging apparatus according to the embodiment of the present invention, since the infrared filter is disposed inside the cold shield portion, unnecessary infrared light absorbed by the infrared filter is discharged to the outside as heat by the cold shield. As a result, a high-quality infrared image can be obtained without being re-emitted.

As described above, according to the imaging apparatus of the present invention, the infrared light from the subject detected by the infrared detector
The difference between the incident infrared dose at the center of the visual field and the edge of the visual field caused by the shielding at the cold shield opening can be corrected by an infrared filter so as to reduce the difference to a level that does not hinder sensitivity correction. / N, and a stable and high-quality infrared image having no luminance difference can be obtained.

[0034]

As described above, according to the present invention, S
It is possible to provide an imaging device having a good / N ratio and a high-quality infrared image with no luminance difference and an infrared filter used therewith, and the effect obtained in practical use is large.

[Brief description of the drawings]

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

FIG. 2 is a side view showing an infrared filter of the device shown in FIG.

FIG. 3 is an infrared transmittance characteristic diagram of an infrared filter of the device shown in FIG.

FIG. 4 is an infrared light quantity characteristic diagram at a cold seed opening of the apparatus shown in FIG. 1;

5 is an infrared light quantity characteristic diagram of the infrared detector of the device shown in FIG.

FIG. 6 is a side view of another infrared filter employed in the apparatus shown in FIG.

FIG. 7 is a side view showing an infrared filter used in a second embodiment of the imaging apparatus according to the present invention.

FIG. 8 is a cross-sectional view illustrating a conventional imaging device.

9 is an infrared light quantity characteristic diagram of the infrared detector of the device shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lens tube 2 Optical system 3 Cold shield part 3a Cold shield opening part 4 Infrared detector (detector) 5 Infrared filter 51 Infrared transmission board 52 Infrared absorption film 53,531-534 Infrared absorption plate 6 Vacuum dual 7 Transmit infrared rays Material with properties

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H04N 5/225 H04N 5/225 DE 7/18 7/18 NF term (reference) 2G065 AA04 AB02 BA37 BA38 BB20 BB24 BB26 BC10 CA01 CA16 DA01 DA20 2G066 BA23 BA32 BA46 BA48 BB01 CA08 CB01 5C022 AA01 AA15 AC55 AC64 5C054 AA01 CA05 CB00 CC01 EA01 HA18

Claims (6)

[Claims] 1. An infrared filter having a light transmission characteristic in an infrared region, characterized in that a central part has a greater attenuation of transmitted infrared light than a peripheral part. 2. An infrared transmitting substrate capable of transmitting infrared light substantially uniformly over the entire surface, and an absorbing film attached to a central portion of the infrared transmitting substrate and attenuating infrared light transmitted through the central portion. And an infrared filter. 3. The infrared filter according to claim 2, wherein the absorption film is made of an alloy thin film or the like. 4. An infrared filter having a light transmission characteristic in an infrared region, wherein a plurality of substantially concentric infrared absorbing plates having different diameters are stacked on a common central axis. And an infrared filter. 5. An optical system for condensing infrared light from a subject image, a cold shield unit for introducing the infrared light through the optical system and shielding unnecessary infrared radiation, and an opening of the cold shield unit. An imaging apparatus comprising: a detector for detecting infrared rays from the subject; the infrared ray according to any one of claims 1 to 4, between the cold shield opening and the detector. An imaging device, comprising a filter. 6. The imaging device according to claim 5, wherein the detector and the infrared filter are thermally shielded.