JPH09185019A - Optical low-pass filter and image formation system having the filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain specific low-pass effect while simplifying the whole image formation system by using a resin material which cuts off infrared light for a substrate, and providing a grating which is sectioned in a trapezoid shape and has a periodic pattern at least in one direction on the surface of the substrate. SOLUTION: The optical low-pass filter 2 is constituted by using the resin material which cuts off nearly all or the majority of infrared light such as a plastic material containing metal ions for the substrate 21 and providing the phase grating 22 which is sectioned in the trapezoid shape and arranged at a specific period on the surface of the substrate. Then luminous flux which passes through the phase grating 22 is diffracted to obtain the low-pass effect. In addition to the trapezoid sectional shape, a repetitive pattern of triangular shapes, a sine waveform, etc., which is formed at a repetition pitch in at least one direction is applicable to the phase grating 22. The optical low-pass filter may be formed by injection molding using a metal mold or casting, or by cutting a block of resin directly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical low-pass filter and an image forming system having the same, and, for example, in a video camera or an electronic still camera, the image information is CCD.
The present invention relates to an optical low-pass filter suitable for forming an image on the surface of an image pickup device such as the above and an image forming system having the same.

[0002]

2. Description of the Related Art In recent years, in the field of video cameras, electronic cameras and the like, various systems have been proposed in which a solid-state image sensor is used to spatially sample a subject image to obtain image information.

Generally, in an image forming system using a solid-state image pickup device having a discrete pixel structure, image information is optically spatially sampled to obtain an output image. In this case, if the subject includes a high spatial frequency component equal to or higher than the sampling frequency, a false signal such as a structure or a hue that the subject does not have occurs. That is, frequency components that cannot be sampled by the imaging system (frequency components exceeding the Nyquist frequency) cannot be reproduced as image information, and cause so-called waveform distortion (aliasing), moire fringes, false colors, etc. Is coming. Therefore, conventionally, an optical low-pass filter is arranged in a part of the image forming system to limit the high spatial frequency component of the subject. As the optical low-pass filter at this time, a filter utilizing the birefringence of quartz, an element utilizing diffraction formed by forming a phase grating on a flat plate, and the like are used.

Further, in an image forming system using a fixed image pickup device, the solid-state image pickup device exhibits high spectral sensitivity in the long wavelength region.
An infrared light cut filter that blocks light in the infrared region is provided in the optical path. A flat glass plate containing metal ions is used as an infrared light cut filter that blocks light in the infrared region at this time.

Conventionally, when a crystal plate is used as a case where an optical low-pass filter or an infrared light cut filter is provided in the optical path, the infrared light cut filter is sandwiched between them and arranged as a unit in front of the CCD. . When a phase grating is used as an optical low pass filter,
It is provided in the optical path separately from the infrared light cut filter.

Various types of optical low-pass filters and image-forming systems having the same have been proposed in the past. For example, Japanese Patent Publication No. 52-22247 proposes an optical low-pass filter using a phase grating. Has been done.

[0007]

The optical low pass filter using a quartz plate and the infrared light cut filter containing metal ions are made of different materials. For this reason, there has been a problem that the optical total length of the image forming system becomes long because it has been conventionally manufactured independently and provided in the optical path of the image forming system.

On the other hand, since the phase grating type optical low-pass filter and the infrared light cut filter are separately provided in the optical path, the imaging system using them requires a lot of space in the optical path. In addition, since the number of planes increases, an optical ghost is likely to occur, and the number of assembling steps increases.

According to the present invention, when a solid-state image pickup device is used as an image pickup means to obtain image information, a substrate for forming a pattern for obtaining a low pass effect is appropriately set to simplify the entire image forming system and to obtain a predetermined image. It is an object of the present invention to provide an optical low-pass filter capable of obtaining the low-pass effect of (1) and effectively cutting out a significant infrared light, and easily obtaining good image information, and an imaging system having the optical low-pass filter.

[0010]

The optical low-pass filter of the present invention comprises: (1-1) a substrate made of a resin material that blocks infrared light, and a section of which has a trapezoidal cross section and is periodic in at least one direction. It is characterized in that a grating having a target pattern is provided and a light flux passing through the grating is diffracted to obtain a low-pass effect.

(1-2) A substrate made of a resin material that blocks infrared light, a grating having a triangular cross-section is provided on the surface thereof and having a periodic pattern in at least one direction, and a light flux passing through the grating. Is characterized by diffracting to obtain a low-pass effect.

(1-3) A substrate is made of a resin material that blocks infrared light, a grating having a sinusoidal cross section and a periodic pattern in at least one direction is provided on the surface of the substrate, and a light flux passing through the grating. Is characterized by diffracting to obtain a low-pass effect.

Particularly, in the structural requirements (1-1), (1-2) or (1-3), it is characterized by being manufactured by injection molding using a (1-3-1) mold. (1-3-2) It is characterized by being manufactured by cast molding using a mold. (1-3-3) It is characterized by being manufactured by cutting a resin material that blocks infrared light.

(1-4) A resin material for blocking infrared light is used as a substrate, an amplitude grating is provided on the surface thereof, and a light beam passing through the amplitude grating is diffracted to obtain a low-pass effect. There is.

Particularly, in the structural requirements (1-1) to (1-4), (1-4-1) the resin material is a plastic material containing metal ions. (1-4-2) The resin material is characterized by being a thermoplastic resin. (1-4-3) The resin material is an ultraviolet curable resin.

The image forming system of the present invention comprises the requirements (1-1) to (1)-
It is characterized in that at least one optical low-pass filter of (1-4) is used.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of a main part of a first embodiment of an image forming system having an optical low-pass filter of the present invention, and FIG. 2 is a main part of the first embodiment of an optical low-pass filter of the present invention. It is a perspective view.

In the figure, reference numeral 3 denotes an image forming system, which is composed of a rear focus type zoom lens in the present embodiment, but is not particularly limited to this type of optical system.

In the figure, 3a is a first group of positive refractive power, 3b is a second group of negative refractive power, 3c is a third group of positive refractive power, 3d.
Denotes a fourth group having a positive refractive power. An aperture stop 1 is arranged in front of the third lens group 3c. Reference numeral 2 is an optical low-pass filter, which is arranged in front of the diaphragm 1. Reference numeral 6 is a solid-state image pickup device as an image pickup means.

In the present embodiment, the material of the lenses constituting each lens group may be either inorganic glass or organic glass and is not particularly limited.

In FIG. 1, during zooming from the wide-angle end to the telephoto end, the second group 3b is moved to the image plane side as shown by the arrow, and the fourth group 3d is moved to change the image plane due to zooming. Correcting. Further, a rear focus type is adopted in which the fourth group 3d is moved along the optical axis for focusing.

The solid curve 4a and the dotted curve 4b of the fourth group shown in the same figure are images at the time of zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and a near object, respectively. The movement locus for correcting the surface variation is shown. The first
The first and third groups are fixed during zooming and focusing.

In the present embodiment, the fourth lens group 3d is moved to correct the image plane variation due to zooming, and the fourth lens group 3d is also corrected.
Is moved to focus. In particular, as shown by curves 4a and 4b in the same figure, the zoom lens is moved so as to have a convex locus toward the object side when zooming from the wide-angle end to the telephoto end. Thereby, the space between the third and fourth units is effectively used, and the overall length of the lens is effectively reduced.

In the present embodiment, when focusing from an object at infinity to a near object at the telephoto end, for example, the fourth lens unit is moved forward as indicated by a straight line 4c in FIG.

Optical low-pass filter 2 of this embodiment
As shown in FIG. 2, a substrate 21 is made of a resin material such as a plastic material containing metal ions that blocks most or most infrared light, and a predetermined trapezoidal cross section is formed on the surface of the substrate 21. The phase gratings 22 arranged in a cycle are provided. Then, the light flux passing through the phase grating is diffracted to obtain the low-pass effect.

The phase grating of the present embodiment can be applied to any cross-sectional shape other than a trapezoidal shape, such as a triangular shape or a sine wave shape, as long as it has a repeating pattern formed at a predetermined repeating pitch in at least one direction.

In the present embodiment, a known material can be used as the material for blocking all or most of the infrared light. For example, a copolymer obtained by copolymerizing a mixed monomer including a phosphoric acid group-containing monomer as disclosed in JP-A-6-118228 and a metal salt containing a copper salt as a main component are prepared. The material etc. which are contained can be applied.
It may also be a thermoreversible resin, a thermosetting resin, or an ultraviolet curable resin. Not limited.

The method of forming an optical low-pass filter with a material that blocks all or most of the light in the infrared region may be injection molding using a mold or cast molding, or a resin. This block may be directly formed by cutting. The present invention does not particularly limit this.

In the present embodiment, the optical low-pass filter is formed by the phase grating, but it is not limited to the phase grating and may be an amplitude grating.

The position where the optical low-pass filter is provided may not be on the object side of the diaphragm 1 but may be on the image plane side. In the image forming system of the present invention, the position where the optical low pass filter is provided is not particularly limited.

[0031]

As described above, according to the present invention, when a solid-state image pickup device is used as an image pickup means to obtain image information, an image is formed by appropriately setting a substrate on which a pattern for obtaining a low pass effect is formed. An optical low-pass filter that can obtain a desired low-pass effect while effectively simplifying the entire system and also effectively cuts infrared light, which is a leading one, and easily obtain good image information, and an imaging system having the optical low-pass filter. Can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic view of a main part of an image forming system having a low-pass filter of the present invention.

FIG. 2 is a perspective view of a main part of a low-pass filter according to the present invention.

[Explanation of symbols]

 1 Aperture 2 Optical Low Pass Filter 3 Imaging System 6 Solid-state Image Sensor 21 Substrate 22 Phase Grating

Claims (15)

[Claims] 1. A substrate made of a resin material that blocks infrared light,
An optical low-pass filter characterized in that a grating having a trapezoidal cross-section and having a periodic pattern in at least one direction is provided on the surface, and a light flux passing through the grating is diffracted to obtain a low-pass effect. 2. A substrate made of a resin material that blocks infrared light,
An optical low-pass filter characterized in that a grating having a triangular cross-section is provided on the surface thereof and having a periodic pattern in at least one direction, and a light beam passing through the grating is diffracted to obtain a low-pass effect. 3. A substrate made of a resin material that blocks infrared light,
An optical low-pass filter characterized in that a grating having a sinusoidal cross-section and having a periodic pattern in at least one direction is provided on the surface, and a light flux passing through the grating is diffracted to obtain a low-pass effect. 4. The optical low-pass filter according to claim 1, wherein the optical low-pass filter is manufactured by injection molding using a mold. 5. The optical low-pass filter according to claim 1, wherein the optical low-pass filter is manufactured by cast molding using a mold. 6. The method according to claim 1, wherein the resin material is manufactured by cutting a resin material that blocks infrared light.
2 or 3 optical low pass filters. 7. A substrate made of a resin material that blocks infrared light,
An optical low-pass filter characterized in that an amplitude grating is provided on the surface, and a light flux passing through the amplitude grating is diffracted to obtain a low-pass effect. 8. The optical low-pass filter according to claim 1, wherein the resin material is a plastic material containing metal ions. 9. The optical low-pass filter according to claim 1, wherein the resin material is a thermoplastic resin. 10. The optical low pass filter according to claim 1, wherein the resin material is an ultraviolet curable resin. 11. An image forming system, wherein the optical low pass filter according to claim 1 is provided in an optical path to form image information. 12. The image forming system according to claim 11, wherein the optical low-pass filter is provided near a diaphragm position. 13. The image forming system according to claim 11, wherein the position where the optical low-pass filter is provided is on the object side. 14. The image forming system according to claim 11, wherein the position where the optical low-pass filter is provided is on the image plane side. 15. The image forming system according to claim 11, wherein the image forming system is a rear focus type zoom lens.