Patent Application
20160041311
The present invention relates to an imaging device including an image processing section which is configured to connect multiple images with respective different view fields formed on a single solid state imaging sensor and to output an image on a single sheet, and relates to a compound eye optical system used for it.
In recent years, thin type mobile terminals each equipped with an imaging device, represented by smart phones, tablet type personal computers, and the like, have spread rapidly. However, the imaging device mounted on such a thin type mobile terminal is required to be thin and compact while having high resolution. In order to respond to such a request, the overall length of imaging lenses has been shortened by the optical design, and precision in manufacturing has been improved so as to cope with an increase in error sensitivity due to the shortened overall length. However, with the conventional constitution in which an image is obtained with a combination of a single imaging lens and an imaging sensor, there may be a limitation. Accordingly, an optical system which changes the concept of the conventional optical system will be expected.
In contrast, in an optical system called a compound eye optical system, an imaging region of an imaging sensor is divided, multiple lenses (hereafter, called ommatidium lenses) are disposed for the respective divided imaging regions, and images obtained by the divided imaging regions are processed so as to output a final image. Such a compound eye optical system has been received a lot of attention in order to cope with a request to make an imaging device thinner (refer to PTL1).
However, any of various kinds of compound eye optical systems proposed up to now has not be able to achieve an optical system of a ultra-thin type with high image quality. Description is given to the reasons. One of the factors which deteriorate optical performances includes an image surface curvature. The image surface curvature means a state where an image surface is curved, that is, a state where an image surface is shown with a broken line in
Herein, in an optical system of a view field division type, as an ommatidium lens is arranged closer to a periphery, the view angle of a light flux entering the ommatidium lens becomes larger. Accordingly, a range of an image forming position deviation associated with a view angle change becomes larger. For example, in
In many optical systems of a view field division type, in order to improve performance degradation due to this image surface curvature, a lens surface (or a lens group) of an ommatidium lens arranged on a periphery (other than the center) is made to eccentric so as to incline the curved image surface, thereby creating a state where an image is in-focus in a usable photographing range (refer to Patent Document 1). With this method, a focus position may be improved. However, as shown in
The present invention has been achieved in view of the problems of the conventional techniques, and an object of the present invention is to provide a compound eye optical system which can acquire a high quality image by solving the problem of aberration in an optical system of a view field division type and can attain an imaging device of an ultra-thin type, and to provide an imaging device employing it.
A compound eye optical system according to the present invention is a compound eye optical system for use in an imaging device which includes an image processing section configured to connect images formed with respective different view fields on a single solid state imaging sensor so as to output an image formed on a single sheet, and comprises an array lens including multiple lenses which are formed integrally into a single sheet and have respective different optical axes, wherein multiple ommatidium lenses configured to form images correspondingly to respective view fields are constituted by the lenses of the array lens, and at least one of Formula (1) and Formula (2) is established.
·h—c>·h—d (1)
·v—c>·v—d (2)
·h_c: the horizontal direction photographing range of a central ommatidium lens located on a central side of the array lens
·h_d: the horizontal direction photographing range of a peripheral ommatidium lens located closer to a peripheral side of the array lens rather than the central ommatidium lens
·v_c: the vertical direction photographing range of the central ommatidium lens located on the central side of the array lens
·v_d: the vertical direction photographing range of a peripheral ommatidium lens located closer to the peripheral side of the array lens rather than the central ommatidium lens
On the assumption that the horizontal direction maximum photographing angle which enters an ommatidium lens is made to ·h_max, the minimum photographing angle is made to ·h_min, the vertical direction maximum photographing angle is made to ·v_max, and the minimum photographing angle is made to ·v_min, a horizontal direction photographing range in the photographing range of an ommatidium lens can be expressed as ·h=|tan·h_max−tan ·h_min|, and a vertical direction photographing range can be expressed as ·v=|tan·v_max−tan·v_min|. That is, Formula (1) means that the horizontal direction photographing range of a central ommatidium lens is equal to or more than the horizontal direction photographing range of a peripheral ommatidium lens, and Formula (2) means that the vertical direction photographing range of a central ommatidium lens is equal to or more than the vertical direction photographing range of a peripheral ommatidium lens.
In a compound eye optical system, as described in the above-mentioned conventional techniques, as compared with a central ommatidium lens, the image forming performance of a peripheral ommatidium lens tends to deteriorate. An amount of image surface curvature in a photographing range can be made smaller by narrowing the photographing range of a peripheral ommatidium lens as compared with the photographing range of a central ommatidium lens. Accordingly, an amount of eccentric of a lens surface (or a lens group) can be made smaller. As a result, the ommatidium lens can be made to have little defocus and a good image forming performance, and it becomes possible to constitute a compound eye optical system with a good image forming performance. In the case where the photographing range of an ommatidium lens arranged in the vicinity of a periphery is narrowed on the condition that the photographing ranges of a compound eye optical system is not changed, it is necessary to widen the photographing range of an ommatidium lens arranged in the vicinity of a center. However, since the lens arranged in the vicinity of a center has a margin in image forming performance comparatively relative to a lens arranged in the vicinity of a periphery, if the photographing range is made wide somewhat, deterioration in image forming performance does not become a large problem.
An imaging device according to the present invention includes the compound eye optical system, a solid state imaging sensor, and an image processing section.
According to the present invention, it becomes possible to provide a compound eye optical system which can acquire a high quality image by solving the problem of aberration in an optical system of a view field division type and can attain an imaging device of an ultra-thin type, and to provide an imaging device employing it.
a) and 1(b) are illustrations for describing an image surface curvature.
a) and 3(b) are illustrations for describing correction of an image surface curvature by inclining a lens.
a) and 6(b) are plan views for describing a positional relationship between a compound eye optical system and an imaging region.
a) is a schematic diagram showing a photographing range of a comparative example,
a), 8(b), 8(c), and 8(d) are diagrams where respective MTF values in photographing ranges D1, V1, H1, and C in comparative examples are graphed respectively.
a), 9(b), 9(c), and 9(d) are diagrams where respective MTF values in photographing ranges D1, V1, H1, and C in examples are graphed respectively.
Hereafter, description is given to a compound eye optical system according to the present invention and an imaging device using it. The compound eye optical system is an optical system in which multiple lens systems are arranged in a form of an array for a single imaging sensor, and the compound eye optical system is usually classified into a super resolution type in which each of the multiple lens systems is configured to image the same view field and a view field division type in which each of the multiple lens systems is configured to image a respective different view field. A compound eye optical system according to the present invention is configured to connect multiple images with the respective different view fields and to output a synthesized image formed on a single sheet. Accordingly, the compound eye optical system corresponds to the view field division type configured to form multiple images with the respective different view fields.
As shown in
The object side lenses and the image side lenses formed respectively on the lens arrays LA1 and LA2 are stacked separately in the respective optical axis directions, thereby forming multiple ommatidium lenses configured to form multiple images with the respective different view fields on an imaging surface SS (for example, a photoelectric conversion unit of a solid state imaging device) of a single imaging sensor SR.
In
The first embodiment is constituted to perform a view field division in a matrix form of 5×5. Accordingly, as can be seen from
·h—c>·h—d (1)
·v—c>·v—d (2)
As shown in
As shown in
Hereafter, description is further given concretely to examples suitable for the above-mentioned compound eye optical system by showing construction data and by comparing them with comparative examples. The examples shown in here are numerical examples corresponding to the above-mentioned embodiments, and the optical constitution diagram (
The area arrangement of the ommatidium lens Ln in the examples and the comparative examples is shown in Table 1. The ommatidium lenses Ln are arranged at 5×5 positions, and a whole optical system L0 is arranged at three positions. However, since the ommatidium lenses Ln are arranged symmetrically in vertical and horizontal directions, only nine positions (C, V1, V2, H1, H2, D1 D2, VD, and HD) are shown (common with the comparative examples).
In the construction data of an ommatidium lens Ln (position: C) which is rotational symmetric around the optical axis AX, as face data, face number, radius of curvature r (mm), axial face distance d (mm), index of refraction nd in terms of d line (wavelength: 587.56 nm), and Abbe's number vd in terms of d line are shown sequentially in the order from a column on the left side. Further, in the construction data of an ommatidium lens Ln (position: V1, VD, D1, V2, D2, HD, H2, and H1) which is an eccentric optical system, as face data, face number, radius of curvature r (mm), axial face distance d (mm), and Y eccentricity (mm) are shown sequentially in the order from a column on the left side. The notation “90 degree rotation” on an ommatidium lens Ln means that a state where a face produced in accordance with the construction data is rotated by 90 degree around Z axis becomes the state of the lens. Therefore, in relation to an eccentric direction and a free curved surface coefficient, it becomes the same with the case where X and Y are replaced with each other (the H direction corresponds to the X direction, and the V direction corresponds to the Y direction).
In the central ommatidium lens Ln (position: C) which is rotational symmetric around the optical axis AX, an aspherical surface being rotational symmetric around the optical axis AX is used, and the aspherical surface is defined by the following formula (AS) using a local orthogonal coordinate system (X, Y, Z) in which an apex of its surface is made to the original point. In each of the peripheral ommatidium lenses Ln (position: V1, VD, D1, V2, D2, HD, H2, and H1) which is an eccentric optical system, a free curved surface is used, and the free curved surface is defined by the following formula (FS) using a local orthogonal coordinate system (X, Y, Z) in which an apex of its surface is made to the original point. As aspherical surface data, aspherical surface coefficients are shown, and as free curved surface data, free curved surface coefficients are shown (however, A (j, k) is represented by Xj·Yk). Further, the coefficient of an item where there is no notation is 0; in all the aspherical surfaces, K=0; in both the X and Y directions in all the free curved surfaces, K=0; and in all the data, E−n=×10−n.
Z=(C0·h2)/[1+·{1−(1+K)·C02·h2}]+·(A1·h1) (AS)
Z=(C0·h2)/[1+·{1−(1+K)·C02·h2}]+·{A(j,k)·Xj·Yk} (FS)
In the above formulas,
H: Height (h2=X2+Y2) in the vertical direction to the Z axis (the optical axis AX),
Z: Amount of a displacement in the Z axis direction at a position with a height of h (on the basis of an apex of a surface),
C0: Curvature on an apex of a surface (an inverse number of a radius of curvature r),
K: Conic constant,
Ai: i-th order aspherical surface coefficient, and
A(j, k): j-th in X and k-th in Y free curved surface coefficient.
The followings are the construction data of examples.
.892E−01
indicates data missing or illegible when filed
indicates data missing or illegible when filed
Y
indicates data missing or illegible when filed
1E+01
Y2:
indicates data missing or illegible when filed
.492E−01
E+03
94E+03
indicates data missing or illegible when filed
.760E+01
indicates data missing or illegible when filed
The followings are the construction data of comparative examples. In the comparative examples, the respective photographing ranges of the ommatidium lenses are equal to each other. Except it, the constitutions are the same as the constitutions of Examples.
7E−01
E+01
indicates data missing or illegible when filed
.923E+03
indicates data missing or illegible when filed
Y2
indicates data missing or illegible when filed
8E−01
E+02
indicates data missing or illegible when filed
2E+01
indicates data missing or illegible when filed
51E+01
indicates data missing or illegible when filed
a) is a schematic diagram showing a photographing range of a comparative example,
Herein, with reference to Table 4, since ·h_c=0.38 and ··_c=0.20 in the central ommatidium lens (c1) in the example, the relationship with the photographing range of each of the peripheral portions is as follows.
V1: ·h—c=·h—d,·v—c=·v—d,·h—d/·h—c=1,·v—d/·v—c=1
V2: ·h—c=·h—d,·v—c=·v—d,·h—d/·h—c=1,·v—d/·v—c=1
VD: ·h
—
c>·h
—
d,·v
—
c=·v
—
d,·h
—
d/·h
—
c=0.68,·v—d/·v—c=1
D2: ·h—c>·h—d,·v—c=·v—d,·h—d/·h—c=0.68,·v—d/·v—c=1
H2: ·h—c>·h—d,·v—c=·v—d,·h—d/·h—c=0.68,·v—d/·v—c=1
D1: ·h—c>·h—d,·v—c>·v—d,·h—d/·h—c=0.61,·v—d/·v—c=7
HD: ·h
—
c>·h
—
d,·v
—
c<·v
—
d,·h
—
d/·h
—
c=0.61,·v—d/·v—c=1.2
H1: ·h—c>·h—d,·v—c<·v—d,·h—d/·h—c=0.61,·v—d/·v—c=1.2
Therefore, the photographing ranges VD, D2, H2, D1, HD, and H1 of the peripheral portions satisfy the following formula (1), and the photographing range D1 of the peripheral portions satisfies the following formula (2). On the other hand, with reference to Table 5, the photographing range of the comparative examples is an equal division, and in the respective photographing ranges of all the peripheral portions, ·h_c=·h_d and ··_c=··_d.
·h—c>·h—d (1)
··—c>··—d (2)
a), 8(b), 8(c), and 8(d) are diagrams where respective MTF values in photographing ranges D1, V1, H1, and C in the comparative examples are graphed respectively.
Hereafter, preferable embodiments are explained collectively.
In the above-mentioned compound eye optical system, it is preferable that at least one of the formula (3) and the formula (4) is established.
0.9··h—d/·h—c·0.4 (3)
0.9···—d/··—c·0.4 (4)
In the case where the value of the formula (3) or the formula (4) is equal to or less than the upper limit value, it becomes possible to make an amount of an image surface curvature in the photographing range region smaller by narrowing the photographing range of the peripheral ommatidium lens relative to the photographing range of the central ommatidium lens. Accordingly, it becomes possible to make an amount of an eccentricity of a lens surface (or a lens group) smaller. As a result, it becomes possible to make an ommatidium lens which has little defocus and a good image forming performance, and it becomes possible to constitute a compound eye optical system with a good image forming performance. On the other hand, in the case where the value of the formula (3) or the formula (4) is equal to or more than the lower limit value, the photographing range of the central ommatidium lens is not likely to be taken too wide. Accordingly, it becomes possible to provide a compound eye optical system with a good optical performance in which an amount of an image surface curvature is not large also in the range photographed by the central ommatidium lens.
It is preferable to dispose three or more of the above-mentioned ommatidium lenses side by side in each of the horizontal direction and the vertical direction. With this constitution, the photographing range of each of the ommatidium lenses can be made small. Accordingly, it becomes possible to make an amount of an image surface curvature at the boundary of the photographing ranges smaller, and it becomes possible to enable a compound eye optical system to have a good image forming performance.
It is preferable that the above-mentioned ommatidium lens includes at least two lenses and at least one surface of the above-mentioned peripheral ommatidium lens includes a free curved surface. With this, it becomes possible to enable the compound eye optical system to have a good image forming performance.
It is preferable that the respective magnifications of the above-mentioned ommatidium lenses are almost the same with each other. With this, at the time of processing images formed via the respective ommatidium lenses, it becomes unnecessary to align or make the respective magnifications of the images uniform. Accordingly, connecting processing of the images becomes simple and the imaging device can be made low cost.
It is preferable to dispose a light shielding stop between the above-mentioned ommatidium lenses and an image surface. By disposing the light shielding stop, the constitution can be made so as to prevent light rays from entering a portion other than an imaging surface corresponding to each of the ommatidium lenses (to prevent a cross talk). Accordingly, the compound eye optical system can be made to have a good image forming performance.
It is clear for a person skilled in the art from the embodiments, the examples, and the technical concepts described in the present description that the present invention should not be limited to the embodiments and the examples described in the present description and includes another embodiment and modified examples. The description and example in the specification (description) are intended originally to show exemplification, and the scope of the present invention is shown by claims mentioned later.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-063922 | Mar 2013 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/056851 | 3/14/2014 | WO | 00 |
