JP2021081734A - Optical system and image capturing device - Google Patents

Abstract

To provide a fixed focus image capturing device that easily and inexpensively allows for increasing depth of field by attaching a removable light diffusion plate on an existing lens optical system, and to provide an optical system for the image capturing device.SOLUTION: An image capturing device includes: an optical system 210 comprising two or more lenses 212a-212d, an aperture stop 113 disposed between any two of adjacent lenses among the two or more lenses, and a light diffusion plate 115 disposed behind a rearmost last lens 212d; and an image element 120 disposed behind the light diffusion plate 115. The light diffusion plate 115 has a light diffusion surface 115b. Distance a from a front surface of the first lens 212a to the aperture stop 113 is larger than distance b from the aperture stop 113 to the image element 120.SELECTED DRAWING: Figure 18

Description

The present invention relates to an optical system and an imaging device, and more particularly to an optical system and an imaging device suitable for an information code reading device that reads an information code such as a barcode or a two-dimensional code.

Conventionally, in order to read information codes such as bar codes and two-dimensional codes, the focus lens of the optical system is moved to the focus position to focus, and the aperture aperture is reduced to increase the F value. A method of expanding the focus range by increasing the optical depth of field is known (see, for example, the background technology section of the specification of Patent Document 2).

There is also a method of intentionally increasing the spherical aberration of the optical system to increase the depth of field. Specifically, there is also a method of intentionally increasing spherical aberration by inserting a phase plate inside the optical system (see, for example, Patent Documents 1 and 2).

On the other hand, systems, methods, and media for recording images using an optical diffuser (light diffuser) have also been proposed, and the optical diffuser is arranged in the aperture of a camera lens (for example, Patent Documents). See 3).

Here, the depth of field and the sagittal and tangential that indicate the direction of the light beam will be described.

FIG. 22 is a schematic explanatory view of the depth of field.

As shown in this figure, a point on the subject surface O with an object distance s from the center of the lens is connected as a point on the image plane O'with an image distance s'from the center of the lens by a lens having an F value of F and a focal length f. It is imaged, but when it deviates back and forth from the image plane O', it forms an image as a circle. This circle is called a circle of confusion, and a circle with a maximum diameter of ε that is considered to be in focus is called a circle of permissible confusion. 'The scope of the side, alpha _1' image plane O which corresponds to the permissible circle of confusion and alpha ₂ that 'and the depth of focus alpha The combined'. Further, the range on the subject surface O side corresponding to the depth of focus α'is called the depth of field α by combining _{α 1} and α _2.

The tangential plane is a plane including an optical axis and a main ray, and corresponds to a radial direction from the center of the plane. The sagittal plane is a plane that includes the main ray and is perpendicular to the tangential plane, and corresponds to the tangential direction of the concentric circles.

Japanese Unexamined Patent Publication No. 2003-235794 International Publication No. 2009/1193838 Japanese Patent No. 5567692

However, in the prior art as disclosed in Patent Document 1 and Patent Document 2, it is necessary to intentionally design the optical system itself with a large aberration, which imposes a heavy load on the optical design. In addition, it cannot be used as a normal lens, and it is necessary to use a special optical system that is not versatile.

In addition, in the case of using a phase plate, although the spot diameter is made substantially uniform in the optical axis direction (near the depth of focus), the spot difference between the center and the periphery of the image cannot be completely matched. Aligning sagittal / tangential rays at each distance was also very difficult in terms of design.

Furthermore, as the F value increases with respect to the opening, the difference between the sagittal and tangier in the field of view increases, and the image state including the periphery within the imaging range does not become uniform during restoration in signal processing, and the screen. There was a performance disadvantage in the scene where code reading was required in the entire area.

In view of these problems of the prior art, an object of the present invention is to install a removable light diffuser in a pre-designed lens optical system as an imaging device without using a special optical design that takes a long time to develop. By doing so, it is possible to provide a fixed-focus type imaging device capable of easily expanding the depth of field at low cost and an optical system of such an imaging device.

In order to achieve the above object, the image pickup apparatus of the present invention comprises two or more lenses, an aperture arranged between any two adjacent lenses of these lenses, and the frontmost first lens of the lenses. An optical system having an optical element arranged in front of the lens and an imaging element arranged behind the final lens at the rearmost of the lenses are provided, and the optical element has a light diffusing surface. The first distance from the front surface of the first lens to the aperture is smaller than the second distance from the aperture to the image pickup element. Further, the third distance from the light diffusing surface to the diaphragm and the first distance may satisfy the relationship of 0 ≦ the first distance ≦ the third distance.

Alternatively, the image pickup apparatus of the present invention is arranged behind two or more lenses, an aperture arranged between any two adjacent lenses of these lenses, and the rearmost final lens of the lenses. It is provided with an optical system having an optical element and an image pickup element arranged behind the optical element, and the optical element has a light diffusing surface, and the front surface of the first lens which is the frontmost of the lenses. The first distance from the aperture to the aperture is larger than the second distance from the aperture to the image pickup element. Further, the third distance from the light diffusing surface to the diaphragm and the second distance may satisfy the relationship of 0 ≦ the third distance ≦ the second distance.

Here, the "front" is the side where the light rays are incident on the optical system (subject side), and the "rear" is the side where the light rays are emitted from the optical system (image sensor side).

According to the image pickup device having such a configuration, by installing a removable light diffusing plate in the existing lens optical system, it is possible to realize a fixed focus type image pickup device that can easily expand the depth of field at low cost. be able to.

In the image pickup apparatus of the present invention, an image restoration processing unit that performs image processing and restoration processing on the image data acquired by the image sensor, and a restoration image output unit that outputs an image restored by the image restoration processing unit. May be further provided.

Here, the image restoration processing unit may have a Wiener filter or an FIR filter created from a pattern of a point image function diffused and incident on the image pickup device, but the filter is not limited to these filters. Further, the light diffusing surface may have, for example, a point-symmetrical ring structure and a discontinuous height pitch shape or a lens shape, but is not limited to these shapes.

The optical system of the present invention is arranged in front of two or more lenses, an aperture arranged between any two adjacent lenses of these lenses, and the frontmost first lens of the lenses. The optical element includes an optical element, and the optical element has a light diffusing surface, and a first distance from the front surface of the first lens to the aperture is arranged behind the final lens which is the rearmost of the lenses. It is characterized in that it is smaller than the second distance from the image pickup element to the aperture.

Alternatively, the optical system of the present invention is arranged behind two or more lenses, an aperture arranged between any two adjacent lenses of these lenses, and the rearmost final lens of the lenses. The optical element has a light diffusing surface, and the first distance from the front surface of the frontmost first lens of the lens to the aperture is arranged behind the optical element. It is characterized in that it is larger than the second distance from the image pickup element to the aperture.

According to the optical system having such a configuration, it is possible to realize an optical system suitable for the above-mentioned imaging device.

According to the image pickup device of the present invention, by installing a removable light diffusing plate in the existing lens optical system, it is possible to realize a fixed focus type image pickup device that can easily expand the depth of field at low cost. it can.

Further, according to the optical system of the present invention, it is possible to realize an optical system suitable for the above-mentioned imaging device.

It is a block diagram which shows the schematic structure of the image pickup apparatus 100 which concerns on Embodiment 1 of this invention. It is an enlarged cross-sectional view of the optical system 110 of the image pickup apparatus 100. It is a schematic block diagram of the optical system 110 for demonstrating the principle of the depth of field expansion. (A) is a perspective view of the light diffusing plate 115. (B) is a front view of the light diffusing plate 115. (C) is a partial cross-sectional view of the light diffusing plate 115. (D) is a partial cross-sectional perspective view of the light diffusing plate 115A which is a modification of the light diffusing plate 115. (A) and (b) are diagrams showing the relationship between the distance and the point spread function (PSF) in the case where the optical system 110 does not have the light diffusing plate 115 and in the case where the optical system 110 does not have the light diffusing plate 115. (A) is a schematic explanatory view of the diffusion angle σ of the light diffusion plate 115. (B) is a graph showing the angular distribution of PSF on the image sensor 120. (A) is a schematic explanatory view of an image restoration filter used in the image restoration processing unit 150. (B) is an equation showing a Wiener filter as an example of a restoration filter. (A) is a schematic configuration diagram of the optical system 110 for explaining the performance deterioration due to the in-screen image height of the optical system 110 when the aperture 113 is open. (B) is a graph illustrating the spatial frequency characteristics of the MTF. (C) is a graph illustrating the change of MTF due to the image height for each sagittal and tangier, respectively. (D) is a graph illustrating the spatial frequency characteristics of the MTF for each sagittal and tangier, respectively. (A) is a schematic block diagram of the optical system 110 for explaining the performance deterioration due to the in-screen image height of the optical system 110 when the F value is large. (B) is an image diagram in the case where the performance deterioration of the tangier is large with respect to the sagittal. (C) is a graph illustrating the change of MTF due to the image height for each sagittal and tangier, respectively. (D) is a graph illustrating the spatial frequency characteristics of the MTF for each sagittal and tangier, respectively. It is the schematic which shows the specific design example of the optical system 110. It is the optical data of the design example. (A) and (b) are graphs illustrating the optical characteristics of the case without the light diffusing plate 115 and the case with and without the light diffusing plate 115, respectively. It is an optical simulation result when there is a light diffusing plate 115. In (a), when the optical system 110 has a relationship of a> b (not applicable to the first embodiment), the change in MTF due to the image height is simulated for each sagittal and tangier around the image sensor 120, respectively. This is the obtained graph. (B) is a graph obtained by simulating the spatial frequency characteristics of the MTF for each sagittal and tangier of the axis center and the periphery on the image sensor 120 in the same case. In (a), when the optical system 110 has a relationship of a <b (corresponding to the first embodiment), the change in MTF due to the image height is obtained by simulation for each of the peripheral sagittals and tangiers on the image sensor 120. It is a graph. (B) is a graph obtained by simulating the spatial frequency characteristics of the MTF for each sagittal and tangier of the axis center and the periphery on the image sensor 120 in the same case. In (a), when the optical system 110 has a relationship of a> b (not applicable to the first embodiment) and the F value is large (F8.0), the change in MTF due to the image height is measured in the periphery on the image sensor 120. It is a graph obtained by simulation for each sagittal and tangier of. (B) is a graph obtained by simulating the spatial frequency characteristics of the MTF for each sagittal and tangier of the axis center and the periphery on the image sensor 120 in the same case. In (a), when the optical system 110 has a relationship of a <b (corresponding to the first embodiment) and the F value is large (F8.0), the change in MTF due to the image height is measured around the image sensor 120. It is a graph obtained by simulation for each sagittal and tangier. (B) is a graph obtained by simulating the spatial frequency characteristics of the MTF for each sagittal and tangier of the axis center and the periphery on the image sensor 120 in the same case. It is sectional drawing of the optical system 210 of the image pickup apparatus which concerns on Embodiment 2 of this invention. In (a), when the optical system 210 has a relationship of a <b (not applicable to the second embodiment), the change in MTF due to the image height is simulated for each sagittal and tangier around the image sensor 120, respectively. This is the obtained graph. (B) is a graph obtained by simulating the spatial frequency characteristics of the MTF for each sagittal and tangier of the axis center and the periphery on the image sensor 120 in the same case. In (a), when the optical system 210 has a relationship of a> b (corresponding to the second embodiment), the change in MTF due to the image height is obtained by simulation for each of the peripheral sagittals and tangiers on the image sensor 120, respectively. It is a graph. (B) is a graph obtained by simulating the spatial frequency characteristics of the MTF for each sagittal and tangier of the axis center and the periphery on the image sensor 120 in the same case. (A) is a cross-sectional view of an optical system 110A which is a modification of the optical system 110 of the image pickup apparatus 100 according to the first embodiment of the present invention. (B) is a cross-sectional view of the optical system 210 of the image pickup apparatus according to the second embodiment of the present invention. It is a schematic explanatory drawing of the depth of field.

Hereinafter, some embodiments of the present invention will be described with reference to the drawings.

<Embodiment 1>
FIG. 1 is a block diagram showing a schematic configuration of an image pickup apparatus 100 according to a first embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of the optical system 110 of the image pickup apparatus 100. In the following description, the side where the light rays are incident on the optical system 110 (which is also the subject side) is "front" (left in the figure), and the side where the light rays are emitted from the optical system 110 is "rear" (in the figure). Right).

As shown in FIG. 1, the image pickup device 100 uses an optical system 110 having two or more lenses, an image pickup element 120 arranged behind the optical system 110, and an analog signal output from the image pickup element 120. An image processing unit that has an A / D converter 130 that converts to a digital signal, a RAW image memory 141, and a convolution calculation unit 142, and performs image processing on the image data of the digital signal output from the A / D converter 130. An image restoration processing unit 150 having 140, a deconvolution calculation unit 151, and performing restoration processing on the image data after image processing by the image processing unit 140, and an image restored by the image restoration processing unit 150 are output. It includes a restored image output unit 160.

Examples of the image sensor 120 include, but are not limited to, a CCD sensor, a CMOS sensor, a MOS sensor, and the like. If the image sensor 120 can directly output a digital signal instead of an analog signal, the A / D converter 130 can be omitted.

The image processing unit 140 and the image restoration processing unit 150 do not necessarily have to be independent, and may be integrated into one.

Further, as shown in FIG. 2, the optical system 110 has a mount portion 111a at the rear end and a filter groove 111b on the inner surface of the front end portion, and has a replaceable cylindrical lens barrel 111 and the inside of the lens barrel 111. The first lens 112a, the second lens 112b, and the third lens (final lens) 112c arranged in order from the front, the aperture 113 arranged immediately before the second lens 112b, and the holder screwed into the filter groove 111b. It is provided with a light diffusing plate 115 held by 114.

Here, the distance a and the distance b defined as follows in the optical system 110 are characterized in that a <b.

a: From the front surface (first surface) of the frontmost first lens 112a to the aperture 113 b: From the aperture 113 to the image sensor 120 (imaging surface) As the mount portion 111a of the lens barrel 111, for example, C mount is mentioned. However, it is not limited to this.

The first lens 112a and the third lens 112c are convex lenses, and the second lens 112b is a concave lens, but the combination is not limited to this, and the total number of lenses is not limited to three.

Although the diaphragm 113 is an aperture diaphragm, its arrangement is not necessarily limited to the position shown in the drawing.

Since the light diffusing plate 115 held by the holder 114 can be removed by turning it in a direction in which the screw into the filter groove 111b is loosened, it is easy to replace it with another light diffusing plate, an optical element, or the like.

FIG. 3 is a schematic configuration diagram of an optical system 110 for explaining the principle of increasing the depth of field. FIG. 4A is a perspective view of the light diffusing plate 115. FIG. 4B is a front view of the light diffusing plate 115. FIG. 4C is a partial cross-sectional view of the light diffusing plate 115. FIG. 4D is a partial cross-sectional perspective view of the light diffusing plate 115A, which is a modified example of the light diffusing plate 115. 5 (a) and 5 (b) are diagrams showing the relationship between the distance and the point spread function (PSF) depending on whether the optical system 110 does not have the light diffusing plate 115 or not.

As shown in FIG. 3, the light diffusing plate 115 arranged at the foremost surface of the optical system 110 is formed as a light diffusing surface 115b whose front surface 115a is flat but its rear surface diffuses light. As shown in FIGS. 4A to 4C, the cross section of the light diffusing surface 115b has a continuous shape with jagged edges at discontinuous height pitches, and has a point-symmetrical ring structure. However, the cross-sectional shape is not limited to this, and for example, a lens shape such as the light diffusing plate 115A shown in FIG. 4D may be used. Further, although not shown, a binary shape or a diffraction grating shape may be used. As the material of the light diffusing plate 115 and the light diffusing plate 115A, a material such as resin or glass that can be molded with a mold or the like is preferable.

If Kere light diffusion plate 115 is Do, as shown in FIG. 5 (a), the spot diameter on the image pickup device 120 only deviate slightly from the in-focus distance light will spread largely. On the other hand, the light diffusion plate 115 Ah lever, as shown in FIG. 5 (b), the spot diameter on the image pickup device 120 also deviates from the in-focus distance hardly spread. That is, the light diffusing plate 115 having the light diffusing surface 115b can make the light spread (bokeh characteristic) on the image sensor 120 substantially constant in the distance direction.

FIG. 6A is a schematic explanatory view of the diffusion angle σ of the light diffusion plate 115. FIG. 6B is a graph showing the angular distribution of PSF on the image sensor 120.

As shown in FIG. 6A, the diffusion angle σ of the light diffusion plate 115 is defined as the light spread angle on the image sensor 120 from the exit pupil surface of the lens. The diffusion angle σ (bokeh width) can be calculated by the following equation based on the distance Z from the exit pupil surface of the lens to the image sensor 120, the light spread angle 2σ, and the diffusion width W on the image sensor 120.

σ = tan ^-1 (W / Z)
Here, the angular distribution of the PSF on the image sensor 120 is a substantially Gaussian distribution as shown in FIG. 6 (b).

FIG. 7A is a schematic explanatory view of an image restoration filter used in the image restoration processing unit 150. FIG. 7B is an equation showing a Wiener filter as an example of the restoration filter.

As shown in FIG. 7A _{, the observed image f is obtained by multiplying the original image f 0} by PSF (k) as a blur characteristic and adding noise (n). This relationship can be expressed by the following equation in the spatial domain.

f ₀ * k + n = f
Further, in the frequency domain, it can be expressed by the following equation.

F ₀・ K + N = F
Here, F ₀ , K, N, and F correspond to the original image, PSF, noise, and observed image, respectively.

Therefore, it is possible to generate a restored image f _r from the observed image f by following the reverse process. Specifically, the restoration filter (H) in the frequency domain that follows the reverse process is calculated in advance, and the restoration image F _r can be generated by multiplying the observation image F by the restoration filter (H). Since this is a general content for those skilled in the art, detailed description thereof will be omitted.

If the bokeh characteristic is uniform in the screen (within the image height of the image sensor 120), the restored image will also be in focus and uniform.

As the restoration filter (H), for example, a Wiener filter as shown in FIG. 7B can be applied, but the restoration filter (H) is not limited to this. Instead, if an FIR filter is used, the FFT calculation becomes unnecessary by approximating the spatial calculation in the Wiener filter, which has the effect of shortening the processing time.

FIG. 8A is a schematic configuration diagram of the optical system 110 for explaining the performance deterioration due to the in-screen image height of the optical system 110 when the aperture 113 is open. FIG. 8B is a graph illustrating the spatial frequency characteristics of the MTF. FIG. 8C is a graph illustrating changes in MTF due to image height for each sagittal and tangier, respectively. FIG. 8D is a graph illustrating the spatial frequency characteristics of the MTF for each sagittal and tangier, respectively.

As shown in FIG. 8A, when an element such as a light diffusing plate 115 or a phase plate is inserted into the optical system 110, performance deterioration occurs due to the in-screen image height as shown in FIG. 8B. In particular, as shown in FIGS. 8 (c) and 8 (d), the difference between the sagittal and the tangential in the field of view becomes an issue.

FIG. 9A is a schematic configuration diagram of the optical system 110 for explaining the performance deterioration due to the in-screen image height of the optical system 110 when the F value is large. FIG. 9B is an image diagram in the case where the performance deterioration of the tangier is larger than that of the sagittal. FIG. 9C is a graph illustrating changes in MTF due to image height for each sagittal and tangier, respectively. FIG. 9D is a graph illustrating the spatial frequency characteristics of the MTF for each sagittal and tangier, respectively.

In the optical system 110 shown in FIG. 8 (a), when a larger F value, as shown in FIG. 9 (a), the performance degradation due to intra image height becomes large further. For example, when the original image f ₀ is a cross character, blurring appears only above and below the horizontal bar, as shown in FIG. 9B. Further, as shown in FIGS. 9 (c) and 9 (d), the difference between the sagittal and the tangier in the field of view is larger than that of FIGS. 8 (c) and 8 (d), respectively. ..

FIG. 10 is a schematic view showing a specific design example of the optical system 110. FIG. 11 is optical data of the design example. 12 (a) and 12 (b) are graphs illustrating the optical characteristics of the case without the light diffusing plate 115 and the case with and without the light diffusing plate 115, respectively. FIG. 13 is an optical simulation result when the light diffusing plate 115 is present.

As shown in FIGS. 10 and 11, this design example is a triplet lens having a focal length f = 20 mm and an F value = 3.0, a distance to a subject of 300 mm, and a viewing radius of 38.4 mm. The diffusion angle of the light diffuser is 0.1 °.

The items in the second and subsequent columns of the optical data indicate the radius of curvature, the spacing, the material, and the surface radius, respectively. The radius of curvature of infinity means that it is a plane.

In the second and subsequent lines of the optical data, # 0 is the subject, # 1 is the front surface of the light diffusing plate 115, # 2 is the diffusing surface of the light diffusing plate 115, # 3 and 4 are both sides of the first lens 112a, and # 5 is the aperture. 113, # 6 and 7 are both sides of the second lens 112b, # 8 and 9 are both sides of the third lens 112c, # 10 is the distance (space) from the third lens 112c to the image sensor 120, and # 11 is the image sensor 120. Corresponds to each.
FIG. 12A shows the optical characteristics when the light diffusing plate 115 is not present, and FIG. 12B shows the optical characteristics when the light diffusing plate 115 is present.

Further, FIG. 13 shows the spot diameters on the axis center and the periphery on the image sensor 120 in the defocus range in the optical axis direction, and it can be seen that the spot diameters are substantially uniform also in the axis center and the periphery.

FIG. 14A simulates the change in MTF due to the image height for each sagittal and tangier around the image sensor 120 when the optical system 110 has a relationship of a> b (not applicable to the first embodiment). It is a graph obtained by each. FIG. 14B is a graph obtained by simulating the spatial frequency characteristics of the MTF for each sagittal and tangier of the axis center and the periphery on the image sensor 120 in the same case.

Further, FIG. 15A shows that when the optical system 110 has a relationship of a <b (corresponding to the first embodiment), the change in MTF due to the image height is changed for each sagittal and tangier around the image sensor 120. It is a graph obtained by simulation. FIG. 15B is a graph obtained by simulating the spatial frequency characteristics of the MTF for each sagittal and tangier of the axis center and the periphery on the image sensor 120 in the same case.

Although already described above with reference to FIGS. 8 (c) and 8 (d), when the optical system 110 has a relationship of a> b, as shown in FIG. 14 (a), a sagittal in the field of view. And the difference between tangential and tangential becomes large. In particular, if the tangential MTF is significantly reduced around the visual field, there is a risk that the normal reading of the two-dimensional code will be hindered.

On the other hand, when the optical system 110 has a <b relationship as in the first embodiment, as shown in FIG. 15 (a), the sagittal and tangier MTFs are maintained high up to the periphery of the visual field, and both are maintained. Since the difference is extremely small, there is no risk of interfering with the reading of the two-dimensional code.

FIG. 16A shows the change in MTF due to the image height on the image sensor 120 when the optical system 110 has a relationship of a> b (not applicable to the first embodiment) and the F value is large (F8.0). It is a graph obtained by simulation for each sagittal and tangier around. FIG. 16B is a graph obtained by simulating the spatial frequency characteristics of the MTF for each sagittal and tangier of the axis center and the periphery on the image sensor 120 in the same case.

Further, FIG. 17A shows the change in MTF due to the image height when the optical system 110 has a relationship of a <b (corresponding to the first embodiment) and the F value is large (F8.0). It is a graph obtained by simulation for each sagittal and tangier around the above. FIG. 17B is a graph obtained by simulating the spatial frequency characteristics of the MTF for each sagittal and tangier of the axis center and the periphery on the image sensor 120 in the same case.

Although already described above with reference to FIGS. 9 (c) and 9 (d), when the optical system 110 has a relationship of a> b, as shown in FIG. 16 (a), a sagittal in the field of view. The difference between the tangier and the tangier becomes even larger, and there is a high risk that the normal reading of the two-dimensional code will be hindered, especially due to a large decrease in the MTF of the tangier around the visual field.

On the other hand, when the optical system 110 has a relationship of a <b as in the first embodiment, as shown in FIG. 17A, the sagittal and tangier MTFs are maintained high up to the periphery of the visual field, and both of them are maintained. Since the difference is extremely small, there is no risk of interfering with the reading of the two-dimensional code.

According to the first embodiment described above, since the spot size can be made substantially uniform over the entire image height including the periphery of the image, it is possible to obtain a good image with an enlarged depth of field even in the restored image. It will be possible.

Since the existing optical system is used, the configuration of the optical system can be simplified, the spot size in the entire image can be made substantially uniform, and the restored image in signal processing can be provided with a better image. It is possible. In addition, the light diffusing plate can be used as an additional part for ready-made lenses without newly designing and molding a lens dedicated to increasing the depth of field and without molding a mold that requires an initial cost. , It is possible to build a system at a very low cost.

When installed in inspection equipment such as factories, the best position (cover) because the depth of field is deep in advance if the phase plate is incorporated inside the optical system as in the prior literature mentioned in the background technology section. While it is difficult to adjust the focus to the center of the depth of field), according to the first embodiment of the present invention, the initial adjustment of the focus position can be performed with the light diffusing plate 115 removed, and there is no detailed optical knowledge. However, the setting can be done easily.

In addition, when using an inspection camera, there is a lot of steady vibration in the factory, and it is conceivable to increase the F value to increase the depth of field or increase the shutter speed. However, if the F value is increased, the brightness becomes insufficient, and it becomes difficult to realize a high-speed shutter speed that can suppress the influence of vibration. According to the first embodiment of the present invention, the depth of field can be expanded without changing the F value (brightness).

<Embodiment 2>
An imaging device in which the optical system 110 of the imaging device 100 according to the first embodiment is replaced with an optical system 210 having a different configuration will be described below as the second embodiment of the present invention. The same components and the like are designated by the same reference numerals, and the differences will be mainly described.

FIG. 18 is a cross-sectional view of the optical system 210 of the image pickup apparatus according to the second embodiment of the present invention.

As shown in FIG. 18, the optical system 210 has a mount portion 211a at the rear end and a filter groove 211b on the inner surface in the vicinity thereof, and has a replaceable cylindrical lens barrel 211, and the front inside the lens barrel 211. The first lens 212a, the second lens 212b, the third lens 112c, and the fourth lens (final lens) 212d arranged in order from the first lens 212a, the aperture 113 arranged immediately before the fourth lens 212d, and the filter groove 211b are screwed into the filter groove 211b. It is provided with a light diffusing plate 115 held by the holder 114.

Here, the distance a and the distance b defined as follows in the optical system 210 are characterized in that a> b.

a: From the front surface (first surface) of the frontmost first lens 212a to the aperture 113 b: From the aperture 113 to the image sensor 120 (imaging surface) In FIG. 19 (a), the optical system 210 has a <b relationship. In the case of (not applicable to the second embodiment), it is a graph obtained by simulation for each of the peripheral sagittals and tangentials on the image sensor 120, respectively, for the change in MTF due to the image height. FIG. 19B is a graph obtained by simulating the spatial frequency characteristics of the MTF for each sagittal and tangier of the axis center and the periphery on the image sensor 120 in the same case.

Further, FIG. 20A shows a change in the MTF due to the image height for each sagittal and tangier around the image sensor 120 when the optical system 210 has a relationship of a> b (corresponding to the second embodiment). It is a graph obtained by simulation. FIG. 20B is a graph obtained by simulating the spatial frequency characteristics of the MTF for each sagittal and tangier of the axis center and the periphery on the image sensor 120 in the same case.

When the optical system 210 has a relationship of a <b, as shown in FIG. 19A, the difference between the sagittal and the tangential in the field of view becomes large. In particular, if the tangential MTF is significantly reduced around the visual field, there is a risk that the normal reading of the two-dimensional code will be hindered.

On the other hand, when the optical system 210 has a relationship of a> b as in the second embodiment, as shown in FIG. 20 (a), the sagittal and tangier MTFs are maintained high up to the periphery of the visual field, and both are maintained. Since the difference is extremely small, there is no risk of interfering with the reading of the two-dimensional code.

The same effect as that of the first embodiment can be obtained by the second embodiment described above.

<About the modified example of each embodiment and the position of the light diffusing plate 115>
FIG. 21A is a cross-sectional view of the optical system 110A which is a modification of the optical system 110 of the image pickup apparatus 100 according to the first embodiment of the present invention. FIG. 21B is a cross-sectional view of the optical system 210 of the image pickup apparatus according to the second embodiment of the present invention. The optical system 110A is different from the optical system 110 in that the aperture 113 is arranged immediately after the second lens 112b, not immediately before.

When the distance a and the distance b satisfy the relationship of a <b as in the above-described first embodiment and FIG. 21 (a), especially when there is not a large difference between the distance a and the distance b, it is as follows. Including the distance c specified in the above, the relationship of 0 ≦ a ≦ c is satisfied. Further, it is preferable to make c as small as possible while satisfying this relationship.

c: From the light diffusing surface 115b of the light diffusing plate 115 to the aperture 113 As in the above-described second embodiment and FIG. 21 (b), when the distance a and the distance b satisfy the relationship of a> b, the distance a is particularly large. And when there is not a large difference in the distance b, the relationship of 0 ≦ c ≦ b is satisfied including the above distance c. Further, it is preferable to make c as small as possible while satisfying this relationship.

It should be noted that the present invention can be implemented in various other forms without departing from its gist or main features. Therefore, each of the above embodiments and examples is merely an example in every respect and should not be construed in a limited manner. The scope of the present invention is shown by the scope of claims, and is not bound by the text of the specification. Furthermore, all modifications and modifications that fall within the equivalent scope of the claims are within the scope of the present invention.

100 Imaging device 110 Optical system 110A Optical system 111 Lens barrel 112a First lens 112b Second lens 112c Third lens (final lens)
113 Aperture 114 Holder 115 Light diffuser 120 Image sensor 130 A / D converter 140 Image processing unit 141 RAW image memory 142 Convolution calculation unit 150 Image restoration processing unit 151 Deconvolution calculation unit 160 Restoration image output unit 210 Optical system 211 Lens mirror Cylinder 212a 1st lens 212b 2nd lens 212c 3rd lens 212d 4th lens (final lens)

Claims (6)

An optical system having two or more lenses, an aperture arranged between any two of these lenses adjacent to each other, and an optical element arranged behind the rearmost final lens of the lenses. ,
It is provided with an image sensor arranged behind the optical element.
The optical element has a light diffusing surface and has a light diffusing surface.
An image pickup apparatus characterized in that the first distance from the front surface of the frontmost first lens among the lenses to the diaphragm is larger than the second distance from the diaphragm to the image sensor. In the imaging device according to claim 1,
An imaging device characterized in that the third distance from the light diffusing surface to the diaphragm and the second distance satisfy the relationship of 0 < the third distance <the second distance. In the imaging device according to claim 1 or 2.
An image restoration processing unit that performs image processing and restoration processing on the image data acquired by the image sensor, and an image restoration processing unit.
An image pickup apparatus further comprising a restored image output unit that outputs an image restored by the image restoration processing unit. In the imaging device according to claim 3,
The image restoration processing unit includes an image pickup apparatus having a Wiener filter or an FIR filter created from a pattern of a point image function diffused and incident on the image pickup device. In the imaging apparatus according to any one of claims 1 to 4,
An imaging device characterized in that the light diffusion surface has a point-symmetrical circular structure and has a continuous shape , a lens shape , a binary grating shape, or a diffraction grating shape that is unevenly jagged in a cross-sectional view. With two or more lenses
With an aperture placed between any two of these lenses adjacent to each other,
The lens is provided with an optical element arranged behind the rearmost final lens.
The optical element has a light diffusing surface and has a light diffusing surface.
An optical system characterized in that the first distance from the front surface of the frontmost first lens among the lenses to the diaphragm is larger than the second distance from the image sensor arranged behind the optical element to the diaphragm. ..

Images