JP4006241B2 - Optical low-pass filter and optical apparatus having the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical low-pass filter and an optical apparatus having the optical low-pass filter, and is suitable for an imaging optical system that performs imaging with an imaging element having pixels with a predetermined pitch, such as an optical system for a video camera and an optical system for a digital still camera. is there.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an optical system (imaging optical system) such as a video camera or a digital still camera that performs imaging using an image sensor having pixels with a predetermined pitch, such as a CCD or MOS, has a high-frequency pattern on a subject and pixels of the image sensor. An optical low-pass filter is used to remove moire that occurs during the period.
[0003]
In order to remove moire, generally, an optical low-pass filter made of a parallel plate of a single crystal of crystal is inserted on the image plane side of the main imaging optical system to cut off the high-frequency component of the subject. In addition, various types of optical low-pass filters have been proposed.
[0004]
For example, in Japanese Patent Application Laid-Open No. 1-916, the applicant of the present invention is an optical device in which a diffraction grating is formed by a thin film on an optical member disposed at or near the pupil of an imaging optical system, and a low-pass effect is obtained by the diffraction action thereby. A low-pass filter is proposed. In addition to this, the applicant of Japanese Patent Application Laid-Open No. 9-288254 similarly divided a light-transmitting surface of an optical member arranged in the pupil of the imaging optical system or in the vicinity thereof into a plurality of areas to form a propeller-like surface. An optical low-pass filter that is formed and obtains a low-pass effect by the refraction action thereby is proposed. Similarly, in Japanese Patent Application Laid-Open No. 7-325269, the light passage surface of the optical member is divided into a plurality of areas to form a split prism-like surface having a twisted relationship with respect to the optical axis. An optical low-pass filter that obtains a low-pass effect by action is proposed.
[0005]
[Problems to be solved by the invention]
Optical low-pass filters consisting of parallel plates made of a single crystal of crystal are generally joined by changing the optical axis of a plurality of quartz crystals, making it difficult to manufacture, and providing space for placement in the optical system. There was a tendency to grow. In addition, an optical low-pass filter using a diffractive action can provide a good low-pass effect, but it is necessary to manufacture a fine diffraction grating.
[0006]
An object of the present invention is to provide an optical low-pass filter capable of obtaining a good optical low-pass effect with a simple configuration and an optical apparatus having the same.
[0007]
[Means for Solving the Problems]
An optical device according to a first aspect of the present invention includes an imaging device having pixels with a certain pitch,
An imaging optical system for forming an image on the imaging element;
In an optical apparatus having an optical low-pass filter disposed at or near the pupil of the imaging optical system,
The optical low-pass filter has a whole area on one side of the substrate that is divided by one straight line as a first small area, and the other side of the one straight line. the when the second small region, by giving a phase difference to transmitted light by applying a thin film on the two small areas, and to obtain a low-pass effect,
When the phase difference between the small regions is θ and the dominant wavelength of light passing through the small regions is λ,
λ / 4 ≦ θ ≦ 3λ / 4
It is characterized by satisfying.
[0008]
An optical device according to a second aspect of the present invention is an image sensor having pixels with a certain pitch;
An imaging optical system for forming an image on the imaging element;
In an optical apparatus having an optical low-pass filter disposed at or near the pupil of the imaging optical system,
The optical low-pass filter is formed by dividing the second straight line on one side of the first straight line when the entire region through which light passes on the substrate surface is divided by the first straight line and the second straight line intersecting each other. The whole of one side is a first small area, the other side of the first straight line is the second side of the second straight line is the second small area, the one side of the first straight line is the second straight line. third lower region of the other side, when the other side of the second straight line on the other side of the first straight line and the fourth sub-area, position the passing light by applying a thin film on the four small regions While giving a phase difference to obtain a low-pass effect,
A phase difference of λ / 2 is given to light passing through the first small area and light passing through the second small area,
The light passing through the second small region and the light passing through the third small region are given a phase difference of λ,
The light passing through the third small region and the light passing through the fourth small region are given a phase difference of λ / 2,
It is characterized in that no phase difference is given to the light passing through the fourth small region and the light passing through the first small region.
[0009]
According to a third aspect of the present invention, in the first or second aspect of the present invention, the optical low-pass filter has a refractive action.
[0010]
According to a fourth aspect of the present invention, in the first aspect of the present invention, the optical low-pass filter is provided on a surface of the imaging optical system having a curvature at or near the pupil. It is said.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic view of a main part of an optical system having an optical low-pass filter according to the present invention. In FIG. 1, reference numeral 1 denotes a photographing optical system, which includes a zoom lens and a single focal length lens. L is the optical axis of the imaging optical system 1, 2 is a stop, 3 is the imaging surface of the imaging device 4 having pixels with a predetermined pitch, and an image is formed on the imaging surface. Of the plurality of lenses constituting the imaging optical system 1, the image-side surface (a surface close to the diaphragm 2, that is, near the pupil) 1GR of one lens 1G is divided into a plurality of areas in terms of area. In the present embodiment, as shown in FIG. 2, the region 1a and 1b are divided into two regions (first and second small regions), and a light-transmitting thin film is formed in each region. A low-pass effect is obtained by providing a predetermined phase difference θ between 1a and 1b.
In the present embodiment, as shown in FIG. 2, the entire area where light on the substrate surface passes is divided by one straight line, and the entire one side of the straight line is defined as a first small area. The other side of the straight line is the second small region.
[0014]
FIG. 3 is an explanatory diagram showing the spot (point image) shape on the image plane 3 at the d-line according to the amount of the phase difference between the regions 1a and 1b. In FIG. 3, when the dominant wavelength at the time of photographing is λ, FIG. 3A shows a phase difference θ of 3λ / 4, FIG. 3B shows a phase difference θ of λ / 2, and FIG. The case where the phase difference θ is λ / 4 is shown. In any case, when converted to a simple single layer film, the region 1b in FIG. 2 corresponds to the direction in which the film thickness is thicker than the region 1a. (Λ = d line, wavelength 587.6 nm)
This phenomenon is caused by interference of light beams having a phase difference. For example, FIG. 3B shows that the intensity on the optical axis is zero due to interference of two light beams having a phase difference of λ / 2 and equal intensities. It has become.
[0015]
As shown in FIG. 3, the fact that the point image is divided into a plurality on the photographing surface 3 means that an optically similar effect to that of a conventional low-pass filter using a quartz plate can be obtained. It has such optical characteristics.
[0016]
In the present embodiment, the surface 1GR provided with a thin film in the vicinity of the stop 2 in the imaging optical system 1 has an optical action similar to that of an optical low-pass filter. Further, since the surface 1GR has a curvature at the same time, it also has a lens action (refractive action). The surface 1GR may be a flat surface.
[0017]
In this embodiment, for the sake of explanation, the result of the d-line monochromatic color as the wavelength of the light for photographing has been described. However, although white light has some blurring, it has the same effect as described above.
[0018]
However, as shown in FIG. 3, since the intensity distribution of the point image differs depending on the amount of phase difference in the pupil or a surface in the vicinity thereof, the above-described regions (when divided into two or more regions) When the phase difference between the regions) is θ, and the dominant wavelength is λ in the wavelength range of the light at the time of imaging,
λ / 4 ≦ θ ≦ 3λ / 4 (1)
It is preferable that the phase difference condition is satisfied.
[0019]
If the upper limit or lower limit of conditional expression (1) is exceeded, the intensity balance of the separated point images shown in FIG. 3 will be significantly lost and the low-pass effect will be diminished.
[0020]
The thin film formed on the lens surface 1GR may be formed by any method such as vapor deposition, sputtering, and chemical method.
[0021]
FIG. 4 is an explanatory view of the essential parts of Embodiment 2 of the optical low-pass filter of the present invention. As in the first embodiment, the optical low-pass filter of the present embodiment divides the pupil or the surface in the vicinity thereof among the lens surfaces of the imaging optical system 1 into a plurality of areas and provides a predetermined phase difference for each area. . In this embodiment, the surface is divided into four. The pupil division corresponding to the division of the surface 1GR is divided into four in the orthogonal direction as shown in FIG. Reference numerals 1a1, 1b1, 1c1, and 1d1 denote areas (first to fourth small areas) of the surface 1GR, respectively. FIG. 4B is an explanatory diagram showing the phase difference state of each region corresponding to FIG. FIG. 4C is a bird's-eye view showing the state of a monochromatic light point image on the imaging surface 3, and FIG. 4D is an explanatory diagram of the monochromatic light point image on the imaging surface 3. The phase difference between the regions is λ / 2 for each step.
In the present embodiment, as shown in FIG. 4, on one side of the first straight line when the entire region through which light passes on the substrate surface is divided by the first straight line and the second straight line that intersect each other. The whole of one side of the second straight line is a first small area, the other side of the first straight line and the whole one side of the second straight line is a second small area, one side of the first straight line The other side of the second straight line is a third small region, the other side of the first straight line is the other side of the second straight line, and the fourth small region is the other side.
[0022]
The phase difference between region 1a1 and region 1b1 is λ / 2, the phase difference between region 1b1 and region 1c1 is λ, the phase difference between region 1c1 and region 1d1 is λ / 2, and the phase difference between region 1d1 and region 1a1 Is 0.
[0023]
According to the present embodiment, as shown in FIG. 4D, it can be seen that the point image is divided into four on the imaging surface 3 and has a low-pass effect.
[0024]
FIG. 5 is an explanatory view of the essential parts of Embodiment 3 of the optical low-pass filter of the present invention. As in the first embodiment, the optical low-pass filter according to the present embodiment divides the pupil or the surface in the vicinity of the lens surface of the imaging optical system 1 into a plurality of areas and provides a predetermined phase difference for each area. ing. In this embodiment, the surface is divided into four diagonal sections. The pupil division corresponding to the division of the surface 1GR is divided into four in the orthogonal direction as shown in FIG. Reference numerals 1a2, 1b2, 1c2, and 1d2 denote areas of the surface 1GR, respectively. FIG. 5B is an explanatory diagram showing the state of the phase difference corresponding to FIG. 6A, FIG. 5C is a bird's-eye view showing the state of the point image of monochromatic light on the imaging surface 3, and FIG. FIG. 4 is an explanatory diagram of a point image of monochromatic light on the imaging surface 3. The phase difference in each region is λ / 2 at each step as in the embodiment of FIG.
[0025]
As shown in FIG. 5D, the point image becomes three deformed points, and a low-pass effect with directionality is obtained.
[0026]
As described above, according to each embodiment, the surface through which the pupil of the imaging optical system or light in the vicinity thereof is divided is divided into areas of a plurality of regions, and a predetermined phase difference is provided for each region by a thin film. The optical low-pass effect is obtained with a simple configuration and without taking up space.
[0027]
The thin film can be applied by vapor deposition or other known methods, and since no special material is used, it is advantageous in manufacturing compared to a conventional crystal low-pass filter and has a low-pass effect in terms of space. Is a surface, and the thickness is practically negligible. Therefore, it is very advantageous in terms of space compared to a conventional low-pass filter.
[0028]
This eliminates the restriction of lens back (back focus) when a conventional optical low-pass filter is used, so that the imaging optical system also has an effect that the degree of freedom in design increases and the size can be reduced.
[0029]
Furthermore, since the surface having the low-pass filter characteristic may be a curved surface, the surface can be used as a lens surface, and can be used as a kind of composite function surface.
[0030]
Next, an embodiment of a digital still camera using an optical system having an optical low-pass filter of the present invention as a photographing optical system will be described with reference to FIG.
[0031]
In FIG. 6, 10 is a camera body having an image sensor, 11 is a photographing optical system constituted by the optical system of the present invention, 12 is a strobe built in the camera body, 13 is an external viewfinder, and 14 is a shutter button. .
[0032]
In this way, by applying the optical system of the present invention to an optical apparatus such as a digital still camera, a small-sized optical apparatus having a good low-pass effect and high optical performance is realized.
[0033]
【The invention's effect】
According to the present invention, it is possible to achieve an optical low-pass filter capable of obtaining a good optical low-pass effect with a simple configuration and an optical apparatus having the optical low-pass filter.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a main part of an optical system according to a first embodiment of the present invention. FIG. 2 is an enlarged explanatory view of a part of FIG. 1. FIG. FIG. 4 is a schematic diagram of a main part of an optical low-pass filter according to a second embodiment of the present invention. FIG. 5 is a schematic diagram of a main part of the optical low-pass filter according to a third embodiment of the present invention. Schematic [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Imaging optical system 2 Aperture 3 Imaging surface of imaging device which has pixel of predetermined pitch 4 Imaging device

Claims (4)

An image sensor having pixels of a certain pitch;
An imaging optical system for forming an image on the imaging element;
In an optical apparatus having an optical low-pass filter disposed at or near the pupil of the imaging optical system,
The optical low-pass filter has a whole area on one side of the substrate that is divided by one straight line as a first small area, and the other side of the one straight line. the when the second small region, by giving a phase difference to transmitted light by applying a thin film on the two small areas, and to obtain a low-pass effect,
When the phase difference between the small regions is θ and the dominant wavelength of light passing through the small regions is λ,
λ / 4 ≦ θ ≦ 3λ / 4
Optical equipment characterized by satisfying An image sensor having pixels of a certain pitch;
An imaging optical system for forming an image on the imaging element;
In an optical apparatus having an optical low-pass filter disposed at or near the pupil of the imaging optical system,
The optical low-pass filter is formed by dividing the second straight line on one side of the first straight line when the entire region through which light passes on the substrate surface is divided by the first straight line and the second straight line intersecting each other. The whole of one side is a first small area, the other side of the first straight line is the second side of the second straight line is the second small area, the one side of the first straight line is the second straight line. third lower region of the other side, when the other side of the second straight line on the other side of the first straight line and the fourth sub-area, position the passing light by applying a thin film on the four small regions While giving a phase difference to obtain a low-pass effect,
A phase difference of λ / 2 is given to light passing through the first small area and light passing through the second small area,
The light passing through the second small region and the light passing through the third small region are given a phase difference of λ,
The light passing through the third small region and the light passing through the fourth small region are given a phase difference of λ / 2,
An optical apparatus satisfying that no phase difference is given to light passing through the fourth small region and light passing through the first small region.   3. The optical apparatus according to claim 1, wherein the optical low-pass filter has a refractive action.   The optical apparatus according to claim 1, wherein the optical low-pass filter is provided on a surface of the imaging optical system having a curvature at or near the pupil.

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