JP2004048615A - Imaging optical element and imaging optical instrument using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging optical element by which color image synthesis can be performed even in the case of a short-distance object. <P>SOLUTION: The imaging optical element has a lens array having four lenses arranged on one surface of a planar transparent substrate. The four lenses are arranged by making two lenses into one set and arranged so that two lenses in each set become symmetrical about a point on a lens formation surface of the transparent substrate. A light shielding film is covered and a circular opening is provided on a lens formation surface and a lens non-formation surface of the lens array. Color filters 32 of three primary colors (R, G, B) are provided in circular openings of an optical incident surface. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an imaging optical element and an imaging optical device using the same, and more particularly to an imaging optical element suitable for use in a digital camera and an imaging optical device using the same.
[0002]
[Prior art]
In recent years, so-called digital cameras that can record high-definition images using a solid-state electronic imaging device such as a CCD have become widespread. Further, such digital cameras are required to be further reduced in size, weight, and definition. An imaging optical system used in a digital camera is required to be small, simple, and have high imaging performance in order to utilize the performance of a high-resolution solid-state electronic imaging device.
[0003]
In a normal imaging optical system, an object light is condensed using a single lens, and an image is formed on a solid-state imaging device via a color filter. The color filter is usually provided on a solid-state imaging device.
[0004]
In order to further reduce the thickness of the digital camera, an imaging optical element using a lens array in which a plurality of lenses having a short focal length are arranged is used instead of a single lens.
[0005]
FIG. 1 shows an example of such an imaging optical element. (A) is a plan view, and (B) is a sectional view taken along line XX ′ of (A). The imaging optical element 10 includes a lens array 16 having four lenses 14 arranged on one surface of a flat transparent substrate 12. Such a lens array 16 is one in which a lens is mounted on a transparent substrate, or one in which a transparent substrate and a lens are integrally formed. The four lenses 14 are a set of two lenses, and the two lenses of each set are arranged so as to be point-symmetric on the lens forming surface of the transparent substrate 12. Each optical axis of the four lenses is equidistant from the center of symmetry.
[0006]
The lens forming surface and the lens non-forming surface of the lens array 16 are covered with a light-shielding film 18 made of a light-absorbing film in order to shield light transmitted through portions other than the lens in order to increase the contrast of the formed image. Is done. However, the lens forming surface is provided with a first circular opening 19 having a diameter smaller than the lens diameter in the lens portion and coaxial with the optical axis of the lens, and the lens non-forming surface is coaxial with the optical axis of the lens. A second circular opening 20 is provided. The first circular opening 19 and the second circular opening 20 have the same diameter. Furthermore, the whole is covered with the antireflection film 22.
[0007]
In a digital camera, the imaging optical element as described above is arranged with the lens forming surface facing the solid-state imaging device and the lens non-forming surface (which is a light incident surface) parallel to the light receiving surface of the solid-state imaging device. Thus, an imaging optical device is configured. FIG. 2 shows the imaging optical device thus configured. For simplicity of illustration, the imaging optical element 10 shows only the lens array 16. In the figure, reference numeral 24 denotes a solid-state imaging device. On the light receiving surface of the solid-state imaging device 24, three primary color filters 26 are provided in the imaging region corresponding to each lens.
[0008]
According to the imaging optical device as described above, a color image can be formed by combining images formed by the respective lenses. Further, since the light incidence surface of the imaging optical element 10 is flat, a short working distance can be obtained.
[0009]
[Problems to be solved by the invention]
In the conventional imaging optical device described above, four color filters are provided on the light receiving surface of the solid-state imaging device. As shown in FIG. 2, when a long-distance subject is imaged, an image of the subject is formed on each color filter 26 corresponding to each lens. However, since the image formation position varies depending on the position of the subject, there is a problem that, in the case of a close-range subject, the image formation position deviates from the color filter 26 as shown in FIG. .
[0010]
An object of the present invention is to provide an imaging optical element which has solved the above-described problems and an imaging optical device using the same.
[0011]
Another object of the present invention is to provide an imaging optical element capable of obtaining an image with high contrast and an imaging optical device using the same.
[0012]
Still another object of the present invention is to provide an imaging optical element capable of obtaining a fine image and an imaging optical device using the same.
[0013]
[Means for Solving the Problems]
A first aspect of the present invention is an imaging optical element, a flat transparent substrate having a plurality of lenses arranged on one surface, and provided on a surface of the transparent substrate on which the lenses are arranged, A first light-shielding film having a first opening smaller than a lens diameter, and a second opening provided on a surface of the transparent substrate opposite to a surface on which the lenses are arranged, and corresponding to each of the lenses; A second light-shielding film; and three primary color filters provided in the second opening.
[0014]
According to the present invention, the plurality of lenses are arranged such that two lenses form one set, and the two lenses of each set are point-symmetric with respect to one center of symmetry. Each optical axis of the plurality of lenses is equidistant from the center of symmetry.
[0015]
A second aspect of the present invention is an imaging optical device. In this imaging optical device, the solid-state imaging device, the light-receiving surface of the solid-state imaging device, the surface on which the lens is formed, and the light-receiving surface of the solid-state imaging device, the surface on which the lens is formed And an imaging optical element arranged so that the opposite surface is parallel.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 3 shows an embodiment of the imaging optical element of the present invention. (A) is a plan view, and (B) is a sectional view taken along line YY 'of (A).
[0017]
The image forming optical element 30 of this embodiment has three primary colors (R, G, and R) in the second circular aperture 20 on the light incident surface opposite to the lens forming surface of the conventional image forming optical element 10 described with reference to FIG. B) A color filter 32 is provided, and the other structure is the same as that of the imaging optical element of FIG. Therefore, the same components as those in FIG. 1 are denoted by the same reference numerals.
[0018]
As described with reference to FIG. 1, the four lenses 14 are formed as a set of two lenses on the transparent substrate 12, and the two lenses in each set are symmetric with respect to one point on the lens forming surface. To place. FIG. 4 shows an arrangement of the four lenses 14. Assuming that the transparent substrate 12 has a square shape, the transparent substrate 12 is arranged symmetrically in the diagonal direction with the center position 34 as the center of symmetry. If the four lenses are 14-1, 14-2, 14-3, and 14-4, respectively, the lenses 14-1 and 14-3 have a point-symmetric relationship, and the lenses 14-2 and 14-4 -4 have a point-symmetric relationship. The optical axes of all the lenses are equidistant from the center point 34 of symmetry.
[0019]
In addition to the point-symmetric arrangement as described above, it is necessary to arrange the lenses so that the images formed by the individual lenses do not overlap on the surface of the solid-state imaging device and do not protrude from the light-receiving surface of the solid-state imaging device. There is.
[0020]
FIG. 5 shows a lens non-formation surface of the imaging optical element 30. As described above, the second circular opening 20 is provided with three primary color (R, G, B) color filters. When the color filters are 32-1, 32-2, 32-3, and 32-4, respectively, the filters 32-1 and 32-3 are the same R color filter, and the filter 32-2 is the G color filter. The filter 32-4 is provided with a B color filter.
[0021]
FIG. 6 shows a state in which the imaging optical device 30 having the above-described configuration is arranged so that the incident surface thereof is parallel to the light receiving surface of the solid-state imaging device 24, and the imaging optical device is configured.
[0022]
In such an imaging optical device, even if the subject is a short-distance object, the color filter is provided in the lens array, so that the above-described problem of the related art does not occur, and the image is formed on the light receiving surface of the solid-state imaging device 24. A color image can be formed from two R color images, one G color image, and one B color image. In this case, the data of the two R color images is processed to specify the corresponding pixel position of the solid-state imaging device. Since the G color image and the B color image also have the same symmetrical positional relationship as the two R color images, the images are combined using the comparison result of the two R color images.
[0023]
In the above example, the two color filters are R color, but this may be G color or B color.
[0024]
In the imaging optical device described above, when the subject is at a short distance, a part of the light from the subject is blocked by the light shielding film 18 of the imaging optical element 30 and the second circular aperture provided with the color filter is provided. There is a possibility that the amount of light passing through 20 decreases and the contrast of the formed image deteriorates. In order to prevent this, as shown in FIG. 7, the shape of the opening in which the color filter is provided may be an elliptical shape extending toward the center point 34 of symmetry.
[0025]
FIGS. 8 and 9 are diagrams for explaining the consideration of the size of the oblong opening 36. FIG. 8 is a diagram showing the dimensions of the oblong opening 36, and FIG. 9 is a diagram for explaining the principle of the oblong opening.
[0026]
Oblong opening 36, as shown in FIG. 8, composed of a semicircular portion of the point A, the diameter d ₀ around the B, the central point A, a rectangular section between B. The diameter d ₀ is the same as the diameter of the first circular opening 19. The point B is the center on the side closer to the symmetry center point 34, the distance from the symmetry center point 34 to the point B is x, and the distance from the symmetry center point 34 to the point A is p.
[0027]
In the case of FIG. 7, the centers A and B of the respective oval openings are located on two orthogonal straight lines passing through the center point 34 of symmetry.
[0028]
As shown in FIG. 9, the distance from the short-distance subject to the incident surface of the imaging optical element, more precisely, the distance from the short-distance subject to the light-shielding film 18 on the non-lens forming surface, is 1; Assuming that the thickness is t, the refractive index of the lens array transparent substrate is n ₁ , and the refractive index of the surrounding medium (usually air) is n ₀ , the optical distance L between the subject and the lens 14 is:
[Equation 3]
L = {l + t (n ₁ / n ₀ )}
It is.
[0030]
Now, when the distance to the closest object camera can capture and l _min, in order to reduce the l _min, it is necessary to close the side of the center B near the symmetry center point 34 to the symmetry center point 34. However, if adjacent oval openings come into contact with each other, the light-shielding function is lost. Therefore, in the arrangement of the oval openings in FIG. 7, in order that adjacent oval openings do not touch, the distance x shown in FIG.
[0031]
(Equation 4)
x <d ₀ / √2
Must. On the other hand, the distance q between the two centers A and B of the oval opening is
[0032]
(Equation 5)
q = p−x
= P (1- _lmin / L)
Here, assuming that n ₀ = 1 and l _min １tn ₁ ,
[0033]
(Equation 6)
q = ptn ₁ / l _min
Is approximated. That is, one center A of the oval aperture is located at a distance p from the symmetric center point 34, which coincides with the optical axis of the lens 14, and the other center B is on a straight line C connecting the center A and the symmetric center point 34. At a distance of q from the center A. Oblong aperture is a circle of diameter d ₀ centered on the two points A and B obtained by connecting the two tangents parallel to the straight line C. However,
[0034]
(Equation 7)
q <p−d ₀ / √2
Therefore, the following relationship is required between the distance l _min and the parameters of the lens array.
[0035]
(Equation 8)
l _min > ptn ₁ / (p−d ₀ / √2)
As described above, by making the opening provided with the color filter an oblong opening, incident light can be effectively taken in regardless of the position of the subject, and an image with high contrast can be obtained.
[0036]
In the above embodiment, the case where the lens array is an imaging optical element having four lenses has been described. However, three or more pairs of two lenses are provided in a point symmetric arrangement, and all the lenses are arranged. May be arranged equidistant from the center of symmetry. According to the imaging optical device using such an imaging optical element, images can be synthesized by the same method as described above.
[0037]
【The invention's effect】
According to the present invention, the following effects can be obtained.
(1) Since an image is formed and combined using a different lens for each of the RGB colors, a bright color image can be obtained.
(2) Since the working distance is short irrespective of the subject distance by using a lens array having a short focal length, the digital camera can be downsized.
(3) An image with high contrast can be obtained because of the provision of the light shielding means capable of coping with a wide subject distance.
(4) Since a point-symmetric arrangement lens is used, accurate image composition is possible, and a fine image is obtained.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an example of a conventional imaging optical element.
FIG. 2 is a diagram illustrating an imaging optical device using the imaging optical element of FIG. 1;
FIG. 3 is a diagram showing one embodiment of an imaging optical element of the present invention.
FIG. 4 is a diagram showing an arrangement of lenses.
FIG. 5 is a diagram showing an arrangement of color filters.
FIG. 6 is a diagram showing an embodiment of the imaging optical device of the present invention.
FIG. 7 is a diagram showing an oval opening.
FIG. 8 is a diagram showing dimensions of an oblong opening.
FIG. 9 is a diagram for explaining the principle of an elliptical opening.
[Explanation of symbols]
10, 30 imaging optical element 12 flat transparent substrate 14 lens 16 lens array 18 light-shielding film 19 first circular opening 20 second circular opening 22 anti-reflection film 24 solid-state imaging device 26, 32 three primary color filters 34 symmetry Center point 36 Oval opening

Claims (7)

A flat transparent substrate having a plurality of lenses arranged on one surface,
A first light-shielding film provided on a surface of the transparent substrate on which the lenses are arranged, the first light-shielding film having a first opening smaller than the lens diameter;
A second light-shielding film provided on a surface of the transparent substrate opposite to a surface on which the lenses are arranged, and having a second opening corresponding to each of the lenses;
Three primary color filters provided in the second opening;
An imaging optical element comprising: The plurality of lenses are arranged such that two lenses form one set, and two lenses of each set are point-symmetric with respect to one center of symmetry. The imaging optical element according to claim 1, wherein an optical axis is equidistant from the symmetry center point. 2. The imaging optical element according to claim 1, wherein two second apertures corresponding to at least one pair of two lenses having a point-symmetrical relationship are provided with color filters of the same color. The plurality of lenses are four, and two second openings corresponding to one pair of two lenses having a point-symmetric relationship are provided with color filters of the same color. 3. The imaging optics according to claim 2, wherein one of the two lenses is provided with a color filter of another color, and the other lens is further provided with a color filter of another color. element. The imaging optical element according to claim 1, wherein the second opening is an oval opening extending toward the center of symmetry. The second opening is four elliptical openings extending toward the center of symmetry, and these elliptical openings have two centers whose two circular portions are orthogonal to each other and pass through the center of symmetry. It is arranged to be located on the straight line of,
When the centers of the two circular portions of the elliptical opening are the first center near the center of symmetry and the second center is the center farther from the center of symmetry, respectively, the first center The distance q between the second center and

Where p is the distance between the center of symmetry and the second center,
t is the thickness of the transparent substrate,
n ₁ is the refractive index of the transparent substrate;
l _min is the distance between the surface of the transparent substrate on which the lenses are arranged and the closest subject;
And q is

Where d ₀ is the diameter of the two circular portions of the oblong opening,
The imaging optical element according to claim 4, wherein A solid-state image sensor;
The surface on which the lens is formed faces the light receiving surface of the solid-state imaging device, and the light receiving surface of the solid-state imaging device is arranged such that the surface on the opposite side to the surface on which the lens is formed is parallel. The imaging optical element according to any one of claims 1 to 6,
An imaging optical device comprising:

Images