JP2001111870A - Image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image pickup device that can effectively eliminate the spatial frequency component in the vicinity of a half of a sampling frequency without the need for a crystal low pass filter. SOLUTION: This image pickup device is provided with an image pickup lens system 10, a light receiving element array 12 that has a plurality of light receiving elements placed at a prescribed element interval, and a signal processing circuit 14 that processes a signal supplied from the light receiving element array. The image pickup lens system 10 includes an aperture 11 and a composite planar lens 21 that is placed in the vicinity of the aperture 11 and has a lens plane consisting of a plurality of spherical surfaces whose spherical centers are placed at positions symmetrical to an optical axis or a plurality of rotary aspherical planes whose rotation axes are placed at positions symmetrical to the optical axis. The distance between the spherical centers or the rotary axes of the composite planar lens 21 is selected so that the interval of split images formed on the light receiving element array 12 with lights passing through a plurality of the spherical surfaces or the rotational aspherical surfaces is nearly equal to the element interval of the light receiving element array 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging device such as a video camera and an electronic still camera, and more particularly to a miniaturized imaging device capable of effectively removing moiré.

[0002]

2. Description of the Related Art Generally, in an imaging apparatus using a light receiving element array using a periodic array of light receiving elements such as a CCD, a subject image is formed on the light receiving element array and the image is formed at a predetermined spatial frequency. Sampling and outputting image information. At this time, the sampling frequency of the light receiving element is 1 /
When two or more spatial frequency components are included, moiré and false colors occur. In other words, with respect to an object having a spatial frequency up to 1/2 of the sampling frequency, the image information can be correctly reproduced.
A frequency component of / 2 or more is reproduced as false information, which causes moire and false colors. This phenomenon is generally known as aliasing distortion of the sampling theorem.

[0003] In order to prevent such moiré and false colors, in a conventional imaging apparatus, an optical low-pass filter made of quartz (hereinafter, referred to as a quartz low-pass filter) is disposed immediately before a light receiving element. . By passing through the quartz low-pass filter, a spatial frequency component of サ ン プ リ ン グ or more of the sampling frequency included in the subject image is removed.

FIG. 14 is a diagram showing an optical system of a conventional image pickup apparatus using a crystal low-pass filter 82. The crystal low-pass filter 82 is inserted before the light receiving element array (imaging surface) 12, more precisely, before the cover glass 13 that covers the light receiving element. Normally, the crystal low-pass filter 82 is a combination of two first and second crystals (not shown). The first crystal uses the birefringence of the crystal to separate the image at a position separated by the pixel interval D of the light receiving element. As a result, the response is reduced to zero near half the sampling frequency. The second crystal separates the image so that the separation width of the image becomes D / 2, and makes the response zero at a spatial frequency of one time the sampling frequency.

The principle will be described with reference to FIGS. FIG. 15A shows an image with a spatial frequency of サ ン プ リ ン グ of the sampling frequency, and FIG. 15B shows an image with a spatial frequency of ４ (double the wavelength) divided into two images on a CCD. It is a figure for explaining the case where it formed an image.

For example, if the pixel interval of the CCD array is D, the sampling frequency fs is 1 / D (mm ^-1 ). In the example of FIG. 15, since 10 pixels are arranged per unit length, the sampling frequency fs is 10. now,
An image having a spatial frequency of (1/2) fs, that is, a frequency of 5 is separated into two images with a separation width D equal to the pixel interval and formed. Then, the two images are formed at positions shifted by exactly one pixel. When these images are combined, the contrast becomes zero, and the output of the spatial frequency component near 1/2 of the sampling frequency at which the moiré is most noticeable is eliminated.

On the other hand, even if an image having a spatial frequency of 2.5 (1/4 of the sampling frequency) is separated into two with a separation width D corresponding to the pixel interval D, as shown in FIG. In addition, the combined output of the two images maintains the spatial frequency 2.5 originally possessed by the images. That is, for an image whose spatial frequency is lower than １ ／ of the sampling frequency, correct image information can be maintained and output even if the separated images are combined.

FIG. 16 is a graph showing the MTF (modulation transfer function) characteristics of the quartz low-pass filter 82 as a function of the spatial frequency. The MTF characteristics of the crystal 1 and the crystal 2 constituting the crystal low-pass filter 82 are indicated by broken lines, respectively.
The TF characteristic is shown by a solid line. The MTF characteristic of the crystal 1 becomes zero when the spatial frequency is fS / 2, that is, 1/2 of the sampling frequency at which moire is most noticeable. On the other hand, in order to reduce a spatial frequency component higher than 1/2 of the sampling frequency, the quartz crystal 2 forms a separated image so that the separation width of the image becomes D / 2. As a result, the response becomes zero at one time the sampling frequency. When crystal 1 and 2 are synthesized,
As indicated by the solid line 3, high frequency components that cause moiré and false colors can be effectively reduced.

[0009]

However, a low-pass filter made of quartz is expensive and requires a space to be provided in the optical path of an image forming optical system, which is a major constraint on miniaturization of an image pickup apparatus. Had become.

In addition to using a low-pass filter made of quartz, a method of reducing a frequency component equal to or more than 1/2 of the sampling frequency of the light-receiving element included in the subject image is as follows. And a method of inserting a lenticular are known. The method using a diffraction grating forms a multiple image by diffraction, but has a drawback such that fringes appear on an imaging surface when a small aperture is used. The method using a lenticular separates an image by refraction. However, there is a problem in that many ridge lines are present in the structure, and sagging of the ridge line affects image quality. In addition, any of these methods restricts miniaturization of the imaging device, similarly to a low-pass filter made of quartz.

Another approach is disclosed in Japanese Patent Laid-Open No. 7-325.
Japanese Patent Publication No. 269 discloses a technique in which wedge-shaped prisms having different inclination directions are arranged in the middle of an imaging optical system to separate an image by refraction. In this method, a step occurs because the height of the wedge-shaped prism surfaces having different inclination directions is different from each other at the boundary line, and diffraction light is conspicuous in a high-contrast subject.

As still another method, Japanese Patent Application Laid-Open No. 10-21 / 1998
No. 0371 discloses that an aberration is intentionally left in an imaging optical system,
1 of sampling frequency of light receiving element included in subject image
Disclosed is a method of reducing frequency components equal to or higher than / 2.
However, this method has a narrow range of use because the effect varies depending on the aperture and the focus position.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image pickup apparatus capable of reducing the size of the apparatus and effectively removing moiré which causes deterioration in image quality.

Another object of the present invention is to provide an image pickup apparatus capable of removing moiré stably under any photographing conditions without being affected by opening and closing of the aperture.

[0015]

SUMMARY OF THE INVENTION The present invention provides a compound surface lens having a lens surface composed of a plurality of spherical surfaces on which respective spherical centers are located in a predetermined relationship with respect to the optical axis, or in a predetermined relationship with respect to the optical axis. A compound surface lens having a lens surface composed of a plurality of rotating aspherical surfaces where respective rotation axes are located is used. The curved surfaces of the plurality of spherical or rotating aspheric surfaces are all equal.

That is, in order to achieve the above object, an image pickup apparatus according to the present invention comprises an image pickup lens system, a light receiving element array composed of a plurality of light receiving elements arranged at a constant element interval, and a light receiving element array. The imaging lens system includes a signal processing circuit that processes the supplied signal, and the imaging lens system includes a stop and the complex surface lens positioned near the stop. The distance between the sphere centers of the plurality of spherical surfaces or the distance between the rotation axes of the plurality of rotating aspheric surfaces constituting the complex surface lens is formed on the imaging surface by light passing through each of the plurality of spherical surfaces or the rotating aspheric surfaces. The image separation interval is set so as to be substantially equal to the light receiving element interval of the light receiving element array.

By forming one lens surface of the lens in the imaging lens system with two or more spherical surfaces or rotating aspheric surfaces, an extra optical element can be inserted between the imaging lens system and the light receiving element array. The separated image can be easily formed on the imaging array. Therefore, it is possible to omit the optical element that has been conventionally inserted in the middle of the imaging optical system, and it is possible to sufficiently reduce the size of the imaging device.

Since the distance between the spherical centers of the plurality of spherical surfaces or the distance between the rotation axes of the rotating aspherical surfaces is set so that the interval between the separated images substantially matches the interval between the light receiving elements of the light receiving element array.
It is possible to effectively reduce a spatial frequency component near 1/2 of the sampling frequency.

Further, since the lens surface composed of a plurality of spherical surfaces or rotating aspheric surfaces is arranged at a position close to the stop, even when the stop is stopped down, light is uniformly incident on each of the plurality of spherical surfaces or rotating aspheric surfaces. Thus, the separated image can be surely separated by a distance equal to the element interval and formed on the light receiving element array. That is, it becomes possible to stably reduce the frequency components near 1/2 of the sampling frequency under any photographing conditions.

The number of spherical or rotating aspherical surfaces constituting the complex surface lens is, for example, 2, 4, 8, or the like. In either case, the curved surfaces have the same shape.

In the features of the present invention, "in a predetermined relationship with respect to the optical axis" means, for example, a positional relationship symmetrical with respect to the optical axis.

When the number of spherical surfaces or rotating aspherical surfaces constituting the compound lens surface is two, the lens is set such that the spherical center or the rotating axis is symmetrically separated from the optical axis in the horizontal or vertical direction. I do. In this case, it is possible to reduce a spatial frequency component near 1/2 of the sampling frequency in either the horizontal direction or the vertical direction.

This lens can be used by rotating it by 45 °. In this case, since the separated image to be formed is symmetrical at an oblique position, the distance between the spherical centers or the distance between the rotation axes is set so that the distance between the separated images is √2 times the distance between the light receiving elements. This makes it possible to effectively reduce the spatial frequency components near half the sampling frequency in both the horizontal and vertical directions.

When the number of spherical or rotating aspheric surfaces is set to 4, as shown by the solid line in FIG. The removing effect can be achieved with a single lens surface.

The compound surface lens of the present invention can be mass-produced by, for example, molding using a mold. Further, the cutting machine such as a curve generator may be used to manufacture a single product.

Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the drawings.

[0027]

Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment> FIG. 1 is a schematic block diagram showing a configuration of an imaging apparatus 100 according to a first embodiment of the present invention.

The imaging apparatus 100 includes an imaging lens system 10 and
A light receiving element array 12 and a signal processing circuit 14 are provided. As shown in FIG. 2, the imaging lens system 10 includes an aperture 11
And a composite surface lens 21 including two spherical surfaces each having a spherical center at a position symmetrical with respect to the optical axis, which is located closest to the stop 11, and forms a subject image on the light receiving element array 12. The light receiving element array 12 is composed of a plurality of light receiving elements (not shown) arranged at a constant element interval, and converts a light image formed by the imaging lens system into an electric signal by photoelectric conversion. The electric signal is supplied to the signal processing circuit 14, where the electric signal is subjected to digital processing, for example, and output as a video signal. Imaging device 10 according to the first embodiment of the present invention
0 further includes a drive circuit 18 and a controller 16. The controller 16 drives the light receiving element array,
In addition to controlling the timing of supplying an electric signal to the signal processing circuit 14, the timing of performing signal processing by the signal processing circuit 14 and the like are controlled. The drive circuit 18 supplies a clock pulse or the like to the light receiving element array 12 to drive the light receiving element array 12 according to a control command of the controller 16.

FIG. 2 is an optical path diagram of an optical system from the imaging lens system 10 to the light receiving element array 12 in FIG. The imaging lens system 10 shown in FIG. 2 has a so-called Tessar type lens configuration, and includes an aperture 11. In the present invention, the lens surface closest to the stop 11, that is, in the example of FIG. 2, the lens surface closest to the subject of the cemented lens positioned on the imaging surface side of the stop is formed of two spherical surfaces. In the first embodiment of the present invention, a lens having a lens surface composed of these two spherical surfaces is called a compound surface lens. The light receiving element array 12
It is covered with a cover glass 13 to protect its surface. The pixel interval D of the array is, for example, 0.005 mm.
In this case, the sampling frequency is 1 / 0.005
(Mm ⁻¹ ).

As apparent from FIG. 2, the imaging apparatus according to the first embodiment of the present invention includes an extra optical element between the imaging lens system 10 and the light receiving element array 12 (and the cover glass 13). Not at all. As a result, the optical path length can be reduced as compared with the conventional imaging device shown in FIG. 14, and the overall size of the imaging device can be reduced.
Furthermore, since there is no restriction to take a large distance from the last surface of the imaging lens system to the imaging plane, that is, so-called back focus, the imaging lens system can be designed to be small, and the entire imaging apparatus can be further downsized.

FIG. 3 is a diagram showing the shape of the compound surface lens 21 according to the first embodiment of the present invention by contour lines.
The lens 21 according to the first embodiment includes a spherical surface 1 and a spherical surface 2
Having. The spherical centers of the respective spherical surfaces are located at a predetermined relationship with respect to the optical axis, that is, at positions symmetrical from the optical axis and separated from each other by a distance d. The image formed by the lens 21 is
An image is formed on the imaging surface 12 at a distance D that matches the pixel interval D. This is shown in detail in FIG.

In FIG. 4, for convenience of explanation, other lens elements of the imaging lens system 10 shown in FIG. 2 are omitted. Further, the composite surface lens 21 is shown as a plano-convex lens.
The spherical center of the spherical surface 1 of the lens 21 is located on the same side as the spherical surface 1 with respect to the optical axis, and the spherical center of the spherical surface 2 is located on the same side as the spherical surface 2. The two spherical centers are separated by a distance d at positions symmetrical with respect to the optical axis. Light incident on the spherical surface 1 forms a subject image on the imaging surface 12 on the same side as the spherical surface 1 with respect to the optical axis. The light incident on the spherical surface 2 forms an object image on the imaging surface 12 on the same side as the spherical surface 2 with respect to the optical axis. The two subject images are formed at a pixel interval D of the light receiving element array 12 (0.005 mm in the first embodiment).

The distance between the spherical centers of the two spherical surfaces is set to a value such that the interval between separated images formed on the light receiving element array 12 matches the pixel interval D, regardless of the lens shape employed. You. For example, when a plano-convex lens is used as shown in FIG. 4, the distance d between the spheres is equal to the interval D between the separated images (d = D), so that d = 0.005 mm.
In the case of other shapes, d is determined by the entire lens system, that is, the radius of curvature, the surface interval, the refractive index, and the like of all surfaces so that the separation image interval matches the pixel interval D. Note that the spherical surface 1 and the spherical surface 2 have the same radius of curvature r regardless of the type of the compound lens.

The compound lens surface of the compound lens 21 is located closest to the stop 11. For example, when the complex surface lens according to the first embodiment is applied to a home video camera, the distance from the apex of each spherical surface of the complex surface lens 21 to the stop surface is about 0.5 mm to 1 mm. By arranging the compound lens surface in the vicinity of the aperture in this manner, even when the aperture is most narrowed, the amount of light incident on the two spherical surfaces can be made uniform and an accurate separated image can be formed on the imaging surface. Will be possible. This is shown in FIG.

FIG. 5 has the same configuration as FIG. 4 except for the aperture of the diaphragm 11. As described above, the two spherical surfaces are symmetrical with respect to the optical axis. If the aperture diameter is minimized,
Light incident on the lens 21 is concentrated at the center of the lens. Since two spherical surfaces symmetrical with respect to the optical axis are located in the immediate vicinity of the stop, light having substantially the same amount of light as the spherical surface 1 and the spherical surface 2 is guided, and an image formed on the imaging surface at a pixel interval D is also provided. It has approximately equal light intensity. As a result of synthesizing the two separated images having substantially equal light intensities, spatial frequency components in the vicinity of 1/2 of the sampling frequency can be surely canceled out, and the cause of moire can be reliably removed. As described above, according to the configuration of the first embodiment of the present invention, the cause of moiré can be reliably removed regardless of a change in imaging conditions, so that a stable effect in image formation can be achieved.

FIG. 6 shows a composite surface lens 31 which is a modification of the bispherical lens shown in FIG. In the lens 21 of FIG.
The spherical centers of the two spherical surfaces were located at positions symmetrical from the optical axis, that is, on the same side as the corresponding spherical surfaces.
On the other hand, the spherical centers of the two spherical surfaces of the lens 31 shown in FIG. 6 are located at a position crossing the optical axis, that is, a symmetrical position shifted in the direction in which the two spherical surfaces are overlapped.
For this reason, the spherical center 1 of the spherical surface 1 is located on the spherical surface 2 side,
Is located on the spherical surface 1 side.

FIGS. 7 and 8 show the state of image formation of a separated image when the complex surface lens 31 is used. FIG. 7 is an optical path diagram in a state where a normal aperture position is set, and FIG. 8 is a state where the aperture is reduced to a minimum.
Regardless of the state of the diaphragm 11, an image formed by light passing through the spherical surface 1 is formed on the imaging surface on the spherical surface 2 side, and an image formed by light passing through the spherical surface 2 is formed on the imaging surface by the spherical surface 1
Imaged on the side. The interval between the two images is equal to the pixel interval D. As described in connection with the description of the lens 21, since the compound lens surface is located immediately near the stop 11, the amounts of incidence on the spherical surfaces 1 and 2 become uniform, and when the separated images are combined, the sampling frequency Can be accurately canceled out. Thus, the composite surface lens 31 in which the spherical centers of the two spherical surfaces are crossed can also achieve the same effect as the case where the spherical centers of the two spherical surfaces are arranged away from the optical axis as shown in FIG. it can.

In both the compound surface lens 21 shown in FIG. 3 and the compound surface lens 31 shown in FIG. 6, the position of the spherical center of the spherical surface constituting the compound lens surface is symmetric with respect to the optical axis. When the spherical center position is asymmetrical with respect to the optical axis, for example, when the shape of the lens surface shown in FIG. 9 is adopted, a separated image can be formed at a position separated by the pixel interval D. This is because the interval between the separated images is determined by the interval between the spherical centers. However, in the case of the asymmetric compound surface lens shown in FIG. 9, the amount of light incident on the two spherical surfaces at the time of the small aperture becomes uneven, and the light intensity of the separated image differs. For this reason, when the separated images are combined, the light intensity of one of the images is superior, and the component of サ ン プ リ ン グ of the sampling frequency cannot be effectively canceled. In addition, the occurrence of aberration becomes asymmetric, and the effect of reducing the spatial frequency component in the vicinity of １ ／ of the sampling frequency becomes asymmetric, so that a sufficient moiré reduction effect cannot be obtained as a whole lens. Therefore, it is preferable that the composite surface lens used in the imaging apparatus of the present invention is configured such that the spherical center of the spherical surface constituting the composite surface is symmetric with respect to the optical axis.

The position of the spherical center is not necessarily limited to the pixel arrangement direction (ie, the horizontal or vertical direction) as long as it is symmetric with respect to the optical axis. For example, as shown in FIG. 10, by rotating the compound surface lens 21 of FIG.
The spherical centers may be arranged so as to be symmetrical in the oblique direction with respect to the optical axis. In this case, by two spherical surfaces,
It is possible to cut a spatial frequency component in the vicinity of 1/2 of the sampling frequency simultaneously in both the horizontal direction and the vertical direction. However, the horizontal direction (x direction) and the vertical direction (y
Direction), a separated image must be formed so as to be separated by a pixel interval D, so that the distance between spherical centers is set so that the separated image itself has an interval of √2D.

When manufacturing the above-described composite surface lens, whether the spherical centers constituting the composite surface are separated (FIG. 3) or overlapped (FIG. 6) is selected depending on the processing method. That is, when the lens is directly ground by a curve generator or the like, the shape of the lens surface must be selected so that the grindstone does not interfere with the surface other than the surface to be ground. Specifically, in the case of manufacturing a lens having a composite surface by grinding, it is preferable to overlap the spheres as shown in FIG. 6, and in the case of forming a lens having a concave composite surface by grinding, separate the spheres. Is preferred.

When the lens is manufactured by molding, it is preferable to select the shape of the lens surface when processing the mold surface so that the grindstone does not interfere with the other surface when processing one spherical mold. .

In any of the manufacturing methods, the spherical centers of two or more spherical surfaces are arranged so as to be symmetric with respect to the center point of the lens, and the radii of curvature of all spherical surfaces are set to be equal.

According to the compound surface lens according to the first embodiment of the present invention, the cause of moiré can be eliminated by itself without the need for an auxiliary optical element. That is, by forming a composite lens surface with two spherical surfaces and forming a separated image at a distance equal to the pixel interval D, a spatial frequency component near 1/2 of the sampling frequency at which the influence of moire is most likely to occur is cut. Can be.

By arranging the compound lens surface of the compound surface lens having such a configuration in the vicinity of the stop, moiré can be stably reduced irrespective of the position of the stop, that is, photographic conditions. High quality images can be achieved.

<Second Embodiment> In a second embodiment of the present invention, a case will be described in which a compound surface lens composed of four spherical surfaces is used. In the second embodiment, the compound surface lens is also called a four spherical lens.

That is, the lens system used in the image pickup apparatus according to the second embodiment is located in the vicinity of the stop 11 and the stop 11, and the respective ball centers are positioned in a predetermined relationship (symmetric relationship) with respect to the optical axis. And a compound surface lens having a lens surface composed of four spherical surfaces.

FIG. 11 shows a four spherical lens 41 used in the second embodiment. The spherical centers of the respective spherical surfaces are located on the same side as the corresponding spherical surfaces with respect to the optical axis, and are symmetrical to each other. In this case, the distance d between the centers of the adjacent spherical surfaces is determined so that the interval between separated images formed on the imaging surface matches the pixel interval D.

When the four spherical lens 41 is used, it is possible to remove a spatial frequency component near 1/2 of the sampling frequency in both the horizontal direction and the vertical direction of the imaging surface. Therefore, moire can be prevented more effectively, and a high-quality image can be generated.

FIG. 12 is a diagram of a compound surface lens 51 which is a modification of the tetraspherical lens shown in FIG. This lens configuration corresponds to FIG. 6, and the spherical centers of the four spherical surfaces are shifted in the direction in which they overlap each other, and are located at positions that cross the optical axis. More specifically, the spherical center of the spherical surface 1 is located on the diagonal surface of the spherical surface 3, and the centripetal of the spherical surface 2 is located on the diagonal surface of the spherical surface 4. Similarly, the center of the spherical surface 3 is located on the diagonal surface of the spherical surface 1, and the center of the spherical surface 4 is located on the diagonal surface of the spherical surface 2. With this configuration, FIG.
The same effect as that of the lens can be achieved. That is, it is possible to form separated images separated by a distance equal to the pixel interval D in both the horizontal direction and the vertical direction of the imaging surface, and remove a spatial frequency component near 1/2 of the sampling frequency.

FIG. 13 is a view showing a composite surface lens 61 which is still another modification of the tetraspherical lens shown in FIG. In this modification, four spherical centers are arranged on the same straight line orthogonal to the optical axis.

More specifically, the spherical surface forming the lens 61 is rotated in a counterclockwise direction by a first spherical surface, a second spherical surface, a third spherical surface, and a fourth spherical surface.
Assuming spherical surfaces, the spherical centers of these spherical surfaces are arranged in the longitudinal direction of FIG. 13 in the order of the spherical center of the first spherical surface, the spherical center of the fourth spherical surface, the spherical center of the second spherical surface, and the spherical center of the third spherical surface. In this state, the third and fourth ball centers are alternately inserted between the first and second ball centers. The distance between the spherical center of the first spherical surface and the spherical center of the second spherical surface adjacent thereto is d. The distance between the spherical center of the third spherical surface and the spherical center of the fourth spherical surface adjacent thereto is also d, but deviates by exactly d / 2 from the distance between the first and second spherical centers on a straight line perpendicular to the optical axis. Position.

In the example of FIG. 13, the separated image formed by the four spherical lenses is formed along the vertical direction of the light receiving element array. That is, an image by the first spherical surface, an image by the fourth spherical surface, an image by the second spherical surface, and an image by the third spherical surface are formed in order from the top. The interval between the first spherical image and the second spherical image matches the pixel interval D, and the interval between the fourth spherical image and the third spherical image also matches the pixel interval D. Therefore, the interval between adjacent separated images is の of the pixel interval, that is, D / 2.

When these images are combined, the spatial frequency component that is one time the sampling frequency and the spatial frequency component that is one half the sampling frequency become almost zero. 1) are reduced to a considerable extent. This is the same effect as the low-pass filter using two crystals described in connection with FIG. 16, and has a configuration in which the contrast of an image whose half cycle is finer than D can be reduced. Therefore, a clear image can be generated by more effectively preventing moire and false colors.

In the case of the second embodiment of the present invention, by changing the shape of the lens surface of one lens of the imaging lens system without inserting an extra element such as an optical filter into the optical path of the imaging optical system, An effect similar to that of a low-pass filter using two crystals can be achieved. That is, when the compound lens surface is constituted by four spherical surfaces whose spherical centers are staggered, in addition to a component near 1/2 of the sampling frequency,
Since the high frequency component of 1/2 or more can be greatly reduced, it is possible to generate a higher quality image.

Also in the second embodiment, similarly to the first embodiment, the compound lens surface is located closest to the stop. This is because light is evenly incident on each spherical surface even when the aperture is small.
The radii of curvature of the four spherical surfaces are the same.

Although the present invention has been described based on the first and second embodiments, the present invention is not limited to these embodiments. For example, the compound surface lens does not necessarily need to be arranged on the imaging surface side of the stop. When the multi-surface lens is located on the object side of the stop, a lens surface composed of two or more spherical surfaces is arranged near the stop. Accordingly, even at the time of a small aperture, light passing through each spherical surface can be uniformly guided to the next lens through the aperture, and a separated image with uniform light intensity can be formed on the light receiving element array. .

The number of spherical surfaces constituting the lens surface of the compound surface lens of the present invention is not limited to two or four. For example, three spherical surfaces may be used, and various configurations such as eight spherical surfaces can be adopted.

The composite surface lens of the present invention can provide the same effect as the case of a spherical surface even by a rotating aspherical surface having a rotating axis arranged in parallel with the optical axis.

[0060]

As described above, according to the image pickup apparatus of the present invention, the low-pass filter and its mounting parts can be eliminated without the need for a quartz low-pass filter. Therefore, assembling of the imaging device is facilitated, and the manufacturing cost can be reduced.

Further, according to the imaging apparatus of the present invention, a space for inserting a low-pass filter in the optical path of the imaging optical system is not required, and the apparatus can be downsized.

According to the imaging device of the present invention, since the low-pass filter can be removed, the surface reflection of the low-pass filter itself is eliminated. Therefore, reflection in the entire image pickup optical system is reduced, ghost and flare are reduced, and a better image pickup result can be obtained. Normally, if dust adheres to the low-pass filter placed immediately before the light receiving element, the shadow appears and deteriorates the image quality. However, the imaging apparatus according to the present invention can eliminate the possibility.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram illustrating a configuration of an imaging device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an optical path from an imaging lens shown in FIG. 1 to a light receiving element.

FIG. 3 is a first view of the present invention used in the imaging lens system of FIG. 2;
FIG. 2 is a diagram illustrating a configuration of a complex surface lens according to the embodiment and an image separation pattern on a light receiving surface.

FIG. 4 is an optical path diagram showing an image forming state of a separated image when the lens shown in FIG. 3 is used.

FIG. 5 is an optical path diagram showing an image formation state of a separated image in a state where the aperture is stopped down using the lens shown in FIG. 3;

6 is a diagram showing a configuration in which vertices of two spherical surfaces are crossed in a modification of the lens shown in FIG. 3, and a corresponding image separation pattern.

FIG. 7 is an optical path diagram showing an image forming state of a separated image when the lens of FIG. 6 is used.

FIG. 8 is an optical path diagram showing an image forming state in a state where the aperture is stopped down using the lens of FIG. 6;

FIG. 9 is a view showing still another modified example of the lens shown in FIG. 3 and its separation pattern.

10 uses the lens shown in FIG. 3 rotated by 45 °,
FIG. 4 is a separation pattern diagram when an image is separated in an oblique direction.

FIG. 11 is a diagram illustrating a configuration of a tetraspherical lens according to a second embodiment of the present invention and an image separation pattern thereof.

FIG. 12 is a diagram showing a modification of the complex surface lens shown in FIG. 11 and an image separation pattern thereof.

FIG. 13 shows another modification of the complex surface lens shown in FIG.
It is a figure showing the image separation pattern.

FIG. 14 is a diagram of an imaging optical system used in a conventional imaging device.

FIG. 15 is a diagram for explaining that a specific frequency component is reduced by overlapping a separation elephant;

FIG. 16 is a graph for explaining a high-frequency component reduction effect by a crystal low-pass filter.

[Explanation of symbols]

 Reference Signs List 80 imaging lens 11 aperture 12 light receiving element array (imaging surface) 13 cover glass 14 signal processing circuit 16 controller 18 drive circuit 21, 31, 41, 51, 61 composite surface lens 82 quartz low-pass filter 100 imaging device

Claims (1)

[Claims] A composite surface lens comprising a stop and a plurality of spherical surfaces located in the vicinity of the stop and having respective spherical centers located in a predetermined relationship with respect to the optical axis, or an optical axis located in the vicinity of the stop; An imaging lens system including a plurality of rotating aspheric surfaces each having a rotation axis positioned in a predetermined relationship with respect to the imaging lens system, and a light receiving element array having a plurality of light receiving elements arranged at regular element intervals And a signal processing circuit for processing a signal supplied from the light receiving element array, wherein the distance between separated images formed on the light receiving element array by light passing through each of the plurality of spherical or non-rotating aspherical surfaces is , The image pickup device being substantially equal to the element spacing.