JPH08201729A - Optical element, photographic optical system and photographic device - Google Patents

Abstract

PURPOSE: To provide an optical element which has a function to cut IR rays and a function as an optical low-pass filter and can be easily produced at a low cost by forming an optical low-pass filter on a plate which cuts all or almost all light in an IR region. CONSTITUTION: A plate 2a consists of a plastic material which does not transmit light in an IR region. A phase grating 2b having a periodical structure and a function as optical low-pass filter is formed from a plastic material into one body on the surface of the plate 2a facing to an afocal lens group 3c. The phase grating 2b has a repeating structure of trapezoids. As for the material for the plate 2a, well-known one is used, and for example, a material containing metal salts essentially comprising copper salt and a copolymer obtd. by copolymn. of phosphate group-contg. monomers and mixture of monomers copolymerizable with the first monomers can be used. As for the material to form the phase grating, for example, an acryl or epoxy resin can be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element, a photographing optical system and a photographing device, and more particularly to a photographing system which obtains image information by discretely sampling spatial image information by a solid-state image sensor, a pickup tube or the like. The present invention relates to an optical element, a photographing optical system, and a photographing device such as a video camera or an electronic camera.

[0002]

2. Description of the Related Art In recent years, various imaging systems have been developed for obtaining image information by optically spatially sampling a subject image with a solid-state imaging device or a pickup tube in a video camera, an electronic camera or the like. This type of solid-state image pickup device, image pickup tube, and the like have high spectral sensitivity in the long wavelength region, and therefore need to block light in the infrared region. Therefore, in the conventional image pickup system, a filter that blocks light in the infrared region is inserted in the image pickup optical system. Further, when the image information is obtained using a solid-state image sensor or the like, if the subject includes a high frequency component exceeding ½ of the sampling frequency, a structure or false color that the subject does not originally have occurs and the image Deteriorate. Therefore, in the conventional imaging system, an optical low-pass filter for blocking high frequency components is inserted in the system. The filter for blocking the light in the infrared region is
Conventionally, it is made of glass having a characteristic of blocking a predetermined wavelength range, and an optical low-pass filter that uses the birefringence of quartz has been used.

[0003]

However, in the above-described conventional example, since the photographing system has the infrared cut filter, the optical low-pass filter, and the lens as separate members, the size and weight of the photographing system as a whole are small. Both increased, and there was a problem in terms of cost.

Therefore, an object of the present invention is to provide an optical element having a function of blocking infrared rays and an optical low-pass filter function, which is low in cost and easy to manufacture.

[0005]

In order to achieve the above object, the first invention of the present application is characterized in that an optical low-pass filter is formed on a flat plate that blocks all or most of light in the infrared region. Is an optical element.

The second invention of the present application is an optical element characterized in that a lens is formed on a flat plate that blocks all or most of the infrared light.

The third invention of the present application is an optical element characterized in that an optical low-pass filter and a lens are formed on a flat plate that blocks all or most of light in the infrared region.

According to the first to third inventions of the present application, an infrared ray cutting function, a function as an optical low pass filter, and / or
Alternatively, a low-cost optical element having a function as a lens can be provided.

A fourth invention of the present application is a photographic optical system comprising the optical element of the first to third inventions of the present application.
This makes it possible to provide a compact and low-cost photographing optical system.

A fifth invention of the present application is an imaging apparatus characterized by taking an image of an object using the optical element of the first to third inventions of the present application or the taking optical system of the fourth invention of the present application. This makes it possible to provide a small-sized and low-cost image pickup apparatus.

[0011]

1 and 2 are views showing a first embodiment of the present invention, which will be described below with reference to the drawings.

Reference numeral 3 is a rear focus zoom lens composed of four groups and nine elements, 3a is a fixed lens group fixed to a lens barrel (not shown), 3b is a moving lens group for zooming, and 3c.
Is an afocal lens group fixed to the lens barrel, and 3d
Is a moving lens group for focusing. In the present invention, the zoom type of the lens is not particularly limited.

Reference numeral 1 is a diaphragm, 2 is an optical element according to the present invention, and 6 is an image pickup element such as a CCD. 2a is a flat plate made of a plastic material that does not transmit light in the infrared region. On the surface of the flat plate 2a on the side of the afocal lens group 3c, a phase grating 2b made of a plastic material and having a periodic structure having an optical low pass filter function is integrally formed with the flat plate 2a. The structure of the phase grating 2b is shown in FIG.
It has a trapezoidal repeating structure as shown in.

In this embodiment, a known material can be used for the flat plate 2a, for example, Japanese Patent Laid-Open No. 6-11822.
A copolymer obtained by copolymerizing a phosphoric acid group-containing monomer as shown in 8 and a mixed monomer composed of a monomer copolymerizable therewith, and a metal salt containing a copper salt as a main component. There is a material containing and.

Further, the position where the phase grating is provided need not be on the afocal lens group 3c side, and the position on which the optical element 2 is arranged may be on the object side instead of the image plane side of the diaphragm 3. Furthermore, the structure of the phase grating 2b is not limited to a trapezoidal shape, but a triangular shape,
The shape may be a sine wave and is not particularly limited.

As a material for forming the phase grating, a plastic material having a good spectral characteristic with respect to the wavelength range used in the photographing lens 1 (visible light range in the present invention) can be used. There is a system resin. The method of forming this phase grating is not particularly limited.

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

Next, a second embodiment will be described with reference to FIG.

In FIG. 3, the components having the same reference numerals as those in FIG. 1 have the same functions, and therefore the description thereof will be omitted.

Reference numeral 4 is an optical element according to the second embodiment of the present invention. 4a is a flat plate made of a material that does not transmit light in the infrared region, like the flat plate 2a in the first embodiment. Four
Reference numeral b is a lens formed of a plastic material on both sides of the flat plate 4a. As a result, the optical element 4 has a function as an afocal lens group in the photographing optical system 3 and a function as an infrared cut filter.

Further, both surfaces of the optical element are coated with a known antireflection film (not shown).

Reference numeral 5 is a phase grating type optical low-pass filter. However, the present embodiment is not particularly limited to the phase grating type optical low pass filter,
A conventional crystal low pass filter may be used.

As the optical element of this embodiment, not only the structure of this embodiment, but also a structure in which a convex lens and a concave lens as shown in FIGS. 4A to 4E are combined, or FIG.
It may have a structure in which a Fresnel lens is formed as shown in (F), and is applicable not only to the afocal lens group as in the present embodiment but also to any lens of the photographing optical system used. That is clear.

If the photographing optical system shown in the first and second embodiments is applied to an actual video camera or electronic still camera, a compact and low-cost photographing device can be provided.

By combining the first and second embodiments, an optical element having both an optical low pass filter function, an infrared cut filter function and a lens function as shown in FIG. 5 can be realized.

[0026]

As described above, according to the present invention,
The infrared cut filter function, the optical low-pass filter function, and the lens function can be arranged as the same member in the photographing system, and the photographing system as a whole can be downsized and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an optical element according to a first embodiment of the present invention.

FIG. 3 is a diagram illustrating a second embodiment of the present invention.

FIG. 4 is a diagram illustrating an optical element according to a second embodiment of the present invention.

FIG. 5 is a diagram illustrating an optical element having both an optical low-pass filter function, an infrared cut filter function, and a lens function.

[Explanation of symbols]

 1 Aperture 2 Optical element of the first embodiment of the present invention 2a Flat plate 2b Phase grating 3 Photographing optical system 4 Optical element of the second embodiment of the present invention 4a Flat plate 4b Lens 5 Optical low-pass filter 6 Image sensor

Claims (13)

[Claims] 1. An optical element comprising an optical low-pass filter formed on a flat plate that blocks all or most of light in the infrared region. 2. The optical element according to claim 1, wherein the optical low-pass filter is a phase grating. 3. The optical element according to claim 2, wherein the phase grating has a regular structure in at least one direction. 4. The optical element according to claim 3, wherein a cross section of each of the protrusions forming the phase grating in the direction showing the regular structure is trapezoidal. 5. The optical element according to claim 1, wherein the phase grating is made of a plastic material. 6. The optical element according to claim 1, wherein the optical low-pass filter is an amplitude grating. 7. An optical element having a lens formed on a flat plate that blocks all or most of light in the infrared region. 8. The optical element according to claim 7, wherein the lens is a convex lens and / or a concave lens. 9. The optical element according to claim 7, wherein the lens is a Fresnel lens. 10. An optical element comprising an optical low-pass filter and a lens formed on a flat plate that blocks all or most of light in the infrared region. 11. The optical element according to claim 1, wherein the flat plate is made of a plastic material. 12. A photographing optical system comprising the optical element according to claim 1. 13. An image taking apparatus, which takes an image of an object using the taking optical system according to claim 12.