JP3658068B2 - Imaging device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an imaging apparatus that guides light from an imaging object to an imaging element in which a plurality of photoelectric conversion elements are arranged via an imaging lens and captures an image of the imaging object.
[0002]
[Prior art]
In a conventional imaging device, a plurality of photoelectric conversion elements are arranged in one or two dimensions to form an imaging element, light from an imaging object is directly guided to the imaging element by an imaging lens, and the imaging object is placed on the imaging element. Form an image of In each photoelectric conversion element of the image sensor, an electrical signal corresponding to the input is generated and output to the image processing apparatus. Thus, the image of the imaging object is read by the same number of pixels as the photoelectric conversion element.
[0003]
[Problems to be solved by the invention]
By the way, an imaging apparatus is desired to be able to capture an image with a wider dynamic range than before. This “dynamic range” indicates the range from the minimum density to the maximum density that can be captured when an image is captured by an imaging device. According to an imaging device with a wide dynamic range, an original can be reproduced with excellent reproducibility. However, as the dynamic range becomes narrower, it becomes impossible to capture images better.
[0004]
As a main factor for narrowing the dynamic range, ghosts and scattering by an imaging lens have been conventionally known. As a result of various studies by the inventor of the present application, in addition to ghosts and scattering, peripheral diffraction waves (its contents and dynamics) The effect on the range will be described later), and it was found that the dynamic range was narrowed. Hereinafter, the influence of the peripheral diffraction wave on the dynamic range will be described with reference to FIG.
[0005]
For example, when the density measurement of the minute black spot 2 formed on the document 1 is performed by a conventional imaging apparatus, an image plane illuminance distribution as shown in FIG. 5B is obtained on the imaging element. Here, it is assumed that there is no ghost light or scattered light.
[0006]
Considering only incident light (illumination light) propagating according to the laws of geometrical optics, a part of the incident light is shielded by the minute black spot 2, while the rest is reflected by the original surface other than the minute black spot 2, and is on the light receiving element side. Proceed to For this reason, the illuminance distribution in the image sensor becomes zero corresponding to the minute black spot 2 completely as shown by the solid line in FIG. Take a high value. For this reason, the range from the lowest level to the highest level (corresponding to the dynamic range) that can be detected by the image sensor is Rg.
[0007]
However, the image plane illuminance at the image sensor actually has a distribution as shown by the one-dot chain line in FIG. This is due to the influence of Boundary Diffraction Wave, and a diffraction image is formed on the image sensor as a result of combining the incident optical wave and the peripheral diffracted wave. is there.
[0008]
The “peripheral diffracted wave” is a diffracted wave generated from an end of light when incident on the diffractive object. In the imaging apparatus configured as described above, the diaphragm of the imaging lens corresponds to a diffractive object, and peripheral diffraction waves are generated from the edge of the diaphragm. Here, when viewed from the image sensor side, it seems that peripheral diffraction waves are generated from the edge of the pupil of the imaging lens. This peripheral diffracted wave is described in detail in, for example, page 670 of “Principle of optics II (by Max Born & Emil Wolf, translated by Toru Kusagawa and Hideaki Yokota; Tokai University Press)”. However, in “Optical Principle II”, “Boundary Diffraction Wave” is translated as “boundary diffracted wave”, but it is the same as “peripheral diffracted wave”.
[0009]
When a diffraction image is formed by the influence of the peripheral diffracted wave in this way, the image plane illuminance at the position corresponding to the minute black spot 2 does not become zero, but increases by ΔR, and the dynamic range Rg + d in this case is the peripheral diffraction. It becomes narrower by ΔR than the dynamic range Rg when the wave is ignored.
[0010]
The present invention is intended to overcome the above-described problems in the prior art, and an object thereof is to provide an imaging apparatus having a wide dynamic range by removing peripheral diffraction waves generated from the edge of the pupil of the imaging lens.
[0011]
[Means for Solving the Problems]
The invention of claim 1 is an imaging apparatus that guides light from an imaging object to an imaging element in which a plurality of photoelectric conversion elements are arranged via an imaging lens, and captures an image of the imaging object. In order to achieve the object, the plurality of photoelectric conversion elements have a plurality of openings corresponding one-to-one, and only light incident on the openings among the light from the imaging lens is guided to the photoelectric conversion elements. A blocking unit that blocks incident light other than the aperture, and each of the blocking units and the imaging lens are arranged in a one-to-one correspondence with the plurality of apertures. Projection means having a plurality of projection elements formed in the vicinity of the corresponding aperture, and the diameter of the aperture is made smaller than the projected image of the pupil of the imaging lens projected in the vicinity of the aperture.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram showing an embodiment of an imaging apparatus according to the present invention. FIG. 2 is a partially enlarged perspective view of the imaging apparatus of FIG. In this imaging apparatus, an imaging lens 10, a microlens array 20 having a plurality of microlenses 21, a microaperture array plate 30 having a plurality of microapertures 31, and a plurality of photoelectric conversion elements 41 are arranged one-dimensionally in the X direction. The image pickup device 40 is arranged in this order. Note that the same number of microlenses 21 and microapertures 31 as the photoelectric conversion elements 41 are provided, and the microlenses 21 are arranged one-dimensionally in the X direction while corresponding to the microapertures 31 in a one-to-one manner. The apertures 31 are one-dimensionally arranged in the X direction while corresponding one-to-one with the photoelectric conversion elements 41. Thus, in this embodiment, the micro lens 21, the micro aperture 31, and the photoelectric conversion element 41 correspond to each other on a one-to-one basis.
[0013]
As shown in FIG. 1, the imaging lens 10 receives light L from the imaging target and collects the light L at a position P on the imaging element 40 side to form an aerial image of the imaging target.
[0014]
The microlens array 20 is disposed at this position P. For this reason, the linear aerial image extending in the X direction is separated by the plurality of microlenses 21 provided in the microlens array 20. In particular, since an electrical signal output from each photoelectric conversion element 41 corresponds to one pixel of an image picked up by the image pickup element 40, an image separated by each microlens 21 corresponds to a pixel. The lens array 20 separates the aerial image of the object to be imaged.
[0015]
The light from the microlenses 21 passes through the corresponding microapertures 31 and enters the corresponding photoelectric conversion elements 41 to form divided images. In this embodiment, the microlens 21 projects an image of the aperture (pupil) 11 of the imaging lens 10 on or near the corresponding microaperture 31, and the microlens 21 functions as a projection element.
[0016]
In this embodiment, as shown in FIG. 3, the diameter D of each micro aperture 31 formed on the micro aperture array plate 30 is set smaller than the size of the image I of the diaphragm 11 of the imaging lens 10. Therefore, the peripheral diffraction wave BDW generated from the edge of the diaphragm 11 of the imaging lens 10 can be blocked by the micro aperture array plate 30. This will be described in detail with reference to FIG.
[0017]
As shown by the broken line in FIG. 1, the peripheral diffraction wave BDW generated from the edge of the diaphragm 11 propagates to the micro aperture array plate 30 side through the micro lens 21. Here, when the image I of the diaphragm 11 of the imaging lens 10 formed on the micro aperture array plate 30 is observed, the edge of the diaphragm 11 appears to shine. The reason why the edge of the diaphragm 11 looks shining as described above is due to the peripheral diffraction wave BDW generated from the edge of the diaphragm 11 of the imaging lens 10 as apparent from the above description. In this embodiment, since the diameter D of each micro aperture 31 is made smaller than the image I of the diaphragm 11 as described above, the peripheral diffraction wave BDW is blocked by the micro aperture array plate 30 and the peripheral diffraction wave BDW is imaged. Propagation to the element 40 side is prevented. Therefore, it is possible to prevent the peripheral diffracted wave BDW from passing through the micro aperture 31 of the micro aperture array plate 30 and entering the image sensor 40, and the influence of the peripheral diffracted wave BDW can be eliminated.
[0018]
Note that light that has passed through each micro aperture 31, that is, light that does not include the peripheral diffracted wave BDW, is incident on the corresponding photoelectric conversion element 41, and an electrical signal corresponding to the image separated by the micro lens array 20 is photoelectrically converted. Output from the conversion element 41. These electric signals are given to an image processing device (not shown), and predetermined image processing is executed.
[0019]
As described above, according to the imaging apparatus according to this embodiment, the peripheral diffraction wave BDW generated from the edge of the diaphragm (pupil) 11 of the imaging lens 10 is blocked by the micro aperture array plate 30 and the influence of the peripheral diffraction wave BDW. Therefore, the dynamic range of the image pickup apparatus can be expanded.
[0020]
In the above description, the imaging apparatus that captures a linear image (one-dimensional image) with the imaging element 40 in which the photoelectric conversion elements 41 are arranged one-dimensionally has been described. However, the application target of the present invention is limited to one-dimensional. However, the present invention can be applied to a two-dimensional imaging apparatus.
[0021]
FIG. 4 is a partial perspective view showing another embodiment of the imaging apparatus according to the present invention. The difference between this imaging device and the imaging device described above is that
(1) The photoelectric conversion elements 41 constituting the imaging element 40 are two-dimensionally arranged in the XY plane,
(2) The microlenses 21 and the micro apertures 31 are also two-dimensionally arranged so as to correspond to the photoelectric conversion elements 41 on a one-to-one basis in accordance with the two-dimensional arrangement of the photoelectric conversion elements 41. ,
The other basic configurations are the same.
[0022]
In the imaging apparatus configured as described above, an aerial image (two-dimensional) of an imaging target (not shown) is formed at the position P of the microlens array 20 by the imaging lens 10 (not shown in FIG. 4). Then, pixels are separated by the micro lens 21. Then, the light from the microlenses 21 enters the corresponding photoelectric conversion elements 41 via the corresponding microapertures 31, and the electric signals corresponding to the images separated by the microlens array 20 are converted into photoelectric conversion elements 41. To the image processing apparatus.
[0023]
Further, the peripheral diffracted wave BDW generated at the edge of the stop (pupil) 11 of the imaging lens 10 is propagated to the micro aperture array plate 30 via the micro lens 21 as in the above-described embodiment. It is blocked by the aperture array plate 30 and the propagation of the peripheral diffracted wave BDW to the image sensor 40 side is prevented. Therefore, it is possible to prevent the peripheral diffracted wave BDW from passing through the micro aperture 31 of the micro aperture array plate 30 and entering the image pickup device 40, and to eliminate the influence of the peripheral diffracted wave BDW. Also in the apparatus, the dynamic range can be expanded.
[0024]
In the above embodiment, the microlens 21 is provided as the projection unit. However, when the diameter of the microaperture 31 is set to be sufficiently small, the microaperture 31 functions as a pinhole of the pinhole camera. Fulfill. For this reason, the imaging device can be configured without providing the microlens 21 by sufficiently reducing the diameter of the microaperture 31.
[0025]
In the above embodiment, the micro-aperture 31 provided on the micro-aperture array plate 30 functions as an opening for guiding the light from the micro-lens 21 to the photoelectric conversion element 41, while the light incident on other than the micro-aperture 31 ( The peripheral diffracted wave (BDW) is blocked by the micro aperture array plate 30. That is, the micro aperture array plate 30 functions as a blocking means. However, the blocking means is not limited to the micro-aperture array plate 30, and the imaging device itself may function as the blocking means. For example, in a charge imaging element (CCD), a wiring pattern or the like is formed on the same plane as the photoelectric conversion element, but the surface is covered with a light shielding member except for the photoelectric conversion element, and light is incident only on the photoelectric conversion element. The light shielding member functions as a means. In this case, it is not necessary to provide the micro aperture array plate 30.
[0026]
【Example】
Next, an embodiment of the imaging apparatus in FIG. 1 will be described. The imaging apparatus according to this example includes the following components.
[0027]
<Image sensor 40>
This is a line sensor in which the pitch of the photoelectric conversion elements 41 is 25 μm.
[0028]
<Imaging lens 10>
The aperture is 20 mm and the focal length is 60 mm. (F number 3). Moreover, the shape of the stop is circular, and the imaging object is arranged at infinity.
[0029]
<Microlens array 20>
Ion exchange type flat microlenses are arranged in the X direction. Each flat microlens has a diameter of 20 μm and a focal length of 60 μm. (F number 3).
[0030]
<Micro aperture array plate 30>
The micro-apertures 31 having a diameter of 18 μm are arranged in the X direction at the same pitch (25 μm) as the pitch of the photoelectric conversion elements 41. Here, the diameter of the micro-aperture 31 is set to 18 μm because the size of the aperture of the imaging lens 10 projected onto the micro-aperture array plate 30 is φ20 μm when configured as described above.
[0031]
According to the imaging apparatus configured as described above, the peripheral diffraction wave BDW generated from the edge of the diaphragm 11 of the imaging lens 10 can be blocked by the micro aperture array plate 30, and the peripheral diffraction wave BDW is applied to the imaging element 40. Incidence can be prevented and the dynamic range of the imaging apparatus can be expanded.
[0032]
Since the aperture image is actually slightly expanded due to the Airy disk by the microlens array 20, the diameter of the microaperture 31 should be slightly reduced in order to eliminate the influence. For example, when the lens F-number is 3 and the wavelength λ = 0.55 mm, the radius r of the Airy disk is about 2 μm from r = 1.2 Fλ, and the aperture image has this spread. Therefore, when shielding the spread of light due to the Airy disk, the diameter of the micro aperture 31 should be 15 μm or less if a slight margin is provided.
[0033]
【The invention's effect】
As described above, according to the present invention, the plurality of photoelectric conversion elements are provided with blocking means having a plurality of openings corresponding one-to-one, and the plurality of projection elements are arranged between the blocking means and the imaging lens. It arrange | positions so that it may respond | correspond 1 to 1 to an opening, and the image of the pupil of an imaging lens is formed in the vicinity of a corresponding opening. Moreover, the diameter of the opening of the blocking means is made smaller than the projected image projected in the vicinity of the opening. For this reason, the peripheral diffracted wave generated from the edge of the pupil of the imaging lens can be blocked by the blocking means, the propagation of the peripheral diffracted wave to the imaging element can be prevented, and the dynamic range of the imaging apparatus can be expanded.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of an imaging apparatus according to the present invention.
FIG. 2 is a partially enlarged perspective view of the imaging apparatus of FIG.
3 is a diagram showing a relationship between a micro aperture and an image of a diaphragm of an imaging lens formed on the micro aperture array plate 30. FIG.
FIG. 4 is a partial perspective view showing another embodiment of the imaging apparatus according to the present invention.
FIG. 5 is a diagram illustrating an image plane illuminance distribution obtained when a minute black spot is imaged by a conventional imaging apparatus.
[Explanation of symbols]
10 Imaging lens 11 Aperture (pupil)
20 Microlens array (projection means)
21 Microlens (projection element)
30 Micro aperture array plate (blocking means)
31 Micro aperture (opening)
40 Imaging element 41 Photoelectric conversion element BDW Peripheral diffraction wave D Diameter (of micro aperture) I (Image of aperture of imaging lens) Image

Claims (1)

In an imaging device that guides light from an imaging object to an imaging element in which a plurality of photoelectric conversion elements are arranged via an imaging lens, and captures an image of the imaging object,
The plurality of photoelectric conversion elements have a plurality of openings corresponding one-to-one, and only light incident on the opening among the light from the imaging lens is guided to the photoelectric conversion element, and is incident on other than the opening. Blocking means for blocking light;
Each has a plurality of projection elements that are arranged in a one-to-one correspondence with the plurality of apertures between the blocking means and the imaging lens, and that form a pupil image of the imaging lens in the vicinity of the corresponding aperture. A projection means,
An imaging apparatus, wherein a diameter of the aperture is smaller than a projected image of a pupil of the imaging lens projected in the vicinity of the aperture.

Images