JP2017207450A - Imaging optical system and imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging optical system capable of effectively utilizing a pixel number held in an image pick-up device.SOLUTION: An imaging optical system 101 includes: an image formation optical system 10 configured to condense light L from a subject Q to form an image at an image formation position 15; an aperture diaphragm 20 arranged in the image formation position 15; a lens array 31 arranged closer to an image than the aperture diaphragm 20 and having a plurality of lenses 32; and an image pick-up device 40 arranged at a position conjugate to the aperture diaphragm 20 interposing the lens array 31 and having a light-receiving surface 41 configured to receive light flux L' having penetrated the lens array 31. The lenses 32 are aligned on an XY plane vertical to an optical axis O of the lenses and have respectively different lens intervals in two directions orthogonal to each other and vertical to the optical axis O.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an imaging optical system and an imaging apparatus.

An imaging device called a plenoptic camera is known that can arrange a lens array at the image side position of the imaging optical system, acquire the position information and direction information of the light beam, and change the focus position of the image after shooting. (See, for example, Patent Documents 1 and 2).
As an application technique of such an image pickup apparatus, there is a technique called a spectroscopic camera in which a spectral filter is inserted in an optical path to divide light according to wavelength and a plurality of spectra acquire images simultaneously (for example, Patent Documents 3 to 6) reference).

In the spectroscopic camera, the position information of the light beam is recorded on the sensor surface of the image sensor as the position of the lens of the lens array and the direction information of the light beam is received as color information. The aperture stop and the sensor surface are conjugate to each other, and an intermediate image at the aperture stop is projected onto the sensor surface as a conjugate image.
Incidentally, in order to improve the resolution of color information, it is necessary to project as many images as possible on the sensor surface, but the resolution of position information decreases in inverse proportion to the size of the conjugate image.
For this reason, there has been a demand for a technique that makes the maximum use of the number of pixels of the image sensor.

  The present invention has been made in view of the above problems, and an object thereof is to provide an imaging optical system that effectively uses the number of pixels of an imaging element.

  In order to solve the above-described problem, an imaging optical system according to the present invention includes an imaging optical system that focuses a light beam from a subject and forms an image at an imaging position, an aperture stop disposed at the imaging position, A lens array that is disposed on the image side of the aperture stop and includes a plurality of lenses, and a light receiving surface that is disposed at a position conjugate with the aperture stop across the lens array and that receives a light beam transmitted through the lens array The lens is arranged on a plane perpendicular to the optical axis of the lens, and has different lens intervals in two directions perpendicular to the optical axis and perpendicular to each other.

  According to the imaging optical system of the present invention, the number of pixels of the imaging element can be effectively used.

1 is a diagram illustrating an example of an overall configuration of an imaging apparatus according to an embodiment of the present invention. It is a top view which shows an example of a structure of the aperture stop shown in FIG. It is a top view which shows an example of a structure of the lens array which concerns on embodiment of this invention. It is a top view which shows an example of a structure of the filter array which concerns on embodiment of this invention. It is a top view which shows an example of a structure of the image pick-up element which concerns on embodiment of this invention. It is a schematic diagram which shows an example of the optical path which concerns on embodiment of this invention. It is a figure which shows the difference of the optical path length in each lens position in embodiment of this invention. It is a correlation diagram which shows the change of the focal distance by the incident wavelength of the lens in embodiment of this invention. It is a correlation diagram which shows an example of the effective focal distance which considered the length of the wavelength of the lens in embodiment of this invention. It is a top view which exaggerates the difference in a lens diameter as an example.

  As an example of an embodiment of the present invention, FIG. 1 shows a schematic configuration of a spectroscopic camera 100 as an imaging apparatus.

As shown in FIG. 1, the spectroscopic camera 100 includes an imaging optical system 101 having a first group 1, a second group 2, and a third group 3.
The spectroscopic camera 100 includes a first group 1 including an imaging optical system 10 that focuses light L as a luminous flux from a subject Q and forms an image at an imaging position 15, and an aperture stop 20 disposed at the imaging position 15. And a second group 2 including a field lens 22 disposed on the image side of the aperture stop 20.
The spectroscopic camera 100 is arranged with a third group 3 disposed on the image side of the aperture stop 20 and a position conjugate with the aperture stop 20 with the third group 3 interposed therebetween. The imaging device 40 includes a light receiving surface 41 that receives light.
In the following description, the direction in which the optical axis O ′ of the imaging optical system 10 extends is the Z direction, and among the directions perpendicular to the Z direction, the vertical direction is the Y direction, and the directions perpendicular to the Z direction and the Y direction. The horizontal direction is defined as the X direction. In addition, it is desirable that the center of the image sensor 40 and the optical axis O ′ of the imaging optical system 10 are arranged to coincide with each other.

  The imaging optical system 10 is a condensing optical system having at least one positive power lens, and forms an intermediate image at the imaging position 15.

The second group 2 includes an aperture stop 20 disposed at the imaging position 15 and a field lens 22 disposed on the image side of the aperture stop 20.
As shown in FIG. 2, the aperture stop 20 is a field stop having an opening 21 that is a rectangular field defining region having an aspect ratio of X: Y = 4: 3. The aperture stop 20 has a function as a light quantity limiting unit for limiting the incident light quantity of the light L condensed by the imaging optical system 10.
The field lens 22 is a convex lens arranged in the vicinity of the imaging position 15 on the + Z direction side in order to improve the light collection efficiency of the light L that has passed through the opening 21.
The field lens 22 deflects the light L that has passed through the opening 21 so as to approach the direction parallel to the Z direction, thereby preventing the light L from being unnecessarily scattered and improving the utilization efficiency of the light L. It is the condensing means for making it. The field lens 22 is a single convex lens in this embodiment, but may be composed of a plurality of lenses. In this embodiment, the field lens is used. However, instead of the field lens, a collimating lens or the like may be used to change to parallel light.
The field lens 22 may be disposed between the aperture stop 20 and the lens array 31. However, in order to deflect the light L that has passed through the aperture 21 so as to approach the direction parallel to the Z direction. Is preferably in the vicinity of the aperture stop 20.

  In the following description, the term “near” means that the optical design is close within a range that does not change the optical design. For example, when the term “near the imaging position 15” is used, Indicates that the position is within the range of the position including the design error and tolerance.

  As shown in FIG. 1, the third group 3 includes a lens array 31 in which a plurality of lenses 32 are arranged side by side on an XY plane, and a plurality of lenses having different wavelength transmission characteristics that are arranged on the + Z side of the lens array 31. And a filter array 33 serving as a spectroscopic unit having the spectroscopic filter 34.

As shown in FIG. 3, the lens 32 is an aspherical lens supported by the lens array 31 in a two-dimensional arrangement on the XY plane. The lens optical axis O of the lens 32 is parallel to the Z axis.
Lens 32, the X-direction are arranged at a distance L ₁ between the lens optical axis O to each other and are spaced apart by a distance L ₂ between the lens optical axis O to each other in the Y direction. In other words, the distance between the lenses in the X direction of the lens 32 is _{L 1,} the distance between the lenses in the Y direction of the lens 32 is _{L 2.}
Further, the aspect ratio of the lens interval in this embodiment is equal to the aspect ratio of the opening 21 and also to the aspect ratio of the light receiving surface 41 of the image sensor 40 described later, and the aspect ratio is L ₁ : L ₂ = 4: 3. is there.
In this embodiment, 16 lenses of 4 rows and 4 columns are arranged in this embodiment, and are divided into groups A, B, C, and D as shown in FIG.

  As shown in Table 1 described later, the lens 32 has a lens surface R1 on the −Z direction side and a lens surface on the + Z direction side of each lens 32 depending on the wavelength transmission characteristics of the spectral filter 34 to which each lens 32 corresponds. The focal length f is set to be different depending on the curvature with R2.

As shown in FIG. 4, in the filter array 33, spectral filters 34 having different wavelength transmission characteristics are arranged in an array on the XY plane. Each spectral filter 34 is arranged corresponding to each group of A, B, C, and D of the lens 32, and the position is determined so that the light L from each lens 32 to which the same reference numeral is attached enters. Is done.
That is, the spectral filter 34 is a spectroscopic unit that splits each light L that has passed through the corresponding lens 32 and transmits only a specific wavelength region according to the wavelength transmission characteristics of the spectral filter 34.
The spectral filter 34 is preferably an optical filter such as a bandpass filter. In the present embodiment, only the case where the spectral filter 34 is provided is shown, but the spectral filter 34 may not be provided. In this case, a plurality of images having no difference in wavelength λ are formed on the light receiving surface 41 of the image sensor 40 described later, so that distance information to the subject Q can be acquired instead of color information.

As shown in FIG. 5, the image sensor 40 is a rectangular light-receiving element having a length-to-width ratio, that is, an aspect ratio of 4: 3.
The image sensor 40 is arranged side by side on the surface of the image sensor 40 on the −Z direction side, and has a plurality of rectangular light receiving surfaces 41 that receive the light L transmitted through the lens 32.
Similar to the spectral filter 34 or the lens 32, the light receiving surface 41 is arranged in groups of A, B, C, and D. The light receiving surfaces 41 are arranged side by side in a manner in which the surface of the image sensor 40 is divided into 16 parts. That is, the aspect ratio of the light receiving surface 41 is equal to the aspect ratio 4: 3 of the image sensor 40.
As described above, the aspect ratio of the light receiving surface 41 and the ratio of the lens intervals L ₁ and L ₂ of the lens 32 coincide with each other, so that the lens 32 and the light receiving surface 41 are arranged to face each other.
Accordingly, the light L grouped by A, B, C, and D of the corresponding lens 32 is incident on the light receiving surface 41, respectively. The light receiving surface 41 is disposed in the vicinity of the focal point F at which the intermediate image formed at the imaging position 15 is condensed again by the third group 3 including the lens 32 to form an image.

  A method for acquiring image information including color information of the subject Q using the spectroscopic camera 100 having such a configuration will be described.

The light L spreading from the subject Q is incident on the first group 1 of the spectroscopic camera 100 and forms an intermediate image at the imaging position 15 of the imaging optical system 10.
An aperture stop 20 is disposed in the vicinity of the imaging position 15, and unnecessary light that is not imaged by the aperture stop 20 is excluded.
The light L that has passed through the opening 21 is deflected by the field lens 22 in the direction along the optical axis O ′ of the first group 1.

When the light L enters the lens array 31, the light L is divided according to the positions of the lenses 32 arranged on the lens array 31.
The light L transmitted through each lens 32 is transmitted only by a component having a specific wavelength λ (nm) by the spectral filter 34, and forms an image on the light receiving surface 41 disposed at a position corresponding to each lens 32. .
In other words, a spectral filter 34 having different wavelength transmission characteristics is disposed between the lens array 31 and the image sensor 40, and the light flux L having different wavelength λ (nm) bands toward the respective light receiving surfaces 41. Irradiate.

Since the light beam L ′ is imaged on the light receiving surface 41, images having different wavelengths λ (nm) are formed on the light receiving surface 41 of the image sensor 40 for the same subject Q as shown in FIG. .
For example, in the present embodiment, since 16 light receiving surfaces 41 are formed on the image sensor 40, 16 images of the subject Q having different wavelengths λ (nm) are formed.
With this configuration, the spectroscopic camera 100 can capture a plurality of images having different color information of the subject Q.

  Although not described in the present embodiment, the spectroscopic camera 100 can obtain an image in which the color information of the subject is accurately reproduced by combining the plurality of images. In the present embodiment, the number of light receiving surfaces 41 is 16 in 4 rows and 4 columns. However, as long as there are a plurality of light receiving surfaces 41, the number of light receiving surfaces 41 may be 9 of 3 × 3, or any other number.

As described above, in order for the spectroscopic camera 100 to accurately obtain an image of the subject Q, the light beams L ′ that have passed through the respective lenses 32 need to form an image on the light receiving surface 41.
This point will be described in more detail.
First, as shown in FIG. 1, the lens array 31 and the image sensor 40 are arranged to face each other, and the distance Z ₁ between the lens array 31 and the image sensor 40 is constant.

However, as exaggeratedly shown in FIG. 6, the light beam L ′ transmitted through the lens array 31 is light flux L ′ between the vicinity of the optical axis O ′ that is near the center of the image sensor 40 and the peripheral portion of the image sensor 40. There are different amount corresponding optical path length Z ₂ inclined from the optical axis O '.
Specifically, the light flux L ′ incident on the light receiving surface 41 of the group A, the light beam L ′ incident on the light receiving surfaces 41 of the groups B, C, and D, and the central portion near the optical axis O ′ of the image sensor 40. in the optical path length Z ₂ are different as shown in FIG.

  Further, the refractive index N of the lens 32 is N = 1.53 with respect to the d-line of sodium (wavelength λ = 589.3 nm), but the refractive index N has wavelength dependency. That is, the focal length f of the lens 32 varies depending on the wavelength λ of the transmitted light beam L ′ as shown in FIG.

In view of the problems as described above, the distance to the focal point F of the lens 32, that is, the focal length f, as shown in Table 1, is a spectral filter corresponding to each group A, B, C, D and the lens 32. It is desirable to determine in consideration of the 34 wavelength transmission characteristics.
Further, in the present embodiment, the wavelength λ of the light beam L ′ transmitted through the spectral filters 34 arranged in the respective groups A, B, C, and D is taken into consideration, and the effective focal length is set as shown in FIG. Is done.

  Further, when the focal length f of each lens 32 is changed in this way, the F value of the lens 32, that is, the ratio between the focal length f and the lens diameter φ, which is the effective diameter of the light beam, is simply changed. It will be different.

The F value is a value indicating the degree of condensing of the light L incident on the lens 32, and serves as an index of the amount of light (illuminance) per area of the image.
In other words, if the F values are greatly different in each of the lenses 32, the image formed on the light receiving surface 41 has a significantly different light amount difference per area, so that accurate color information cannot be obtained. become.
In order to solve such a problem, when the focal length f of the lens 32 is individually changed, it is desirable to make the lens diameters φ different from each other as shown exaggeratedly in FIG.
In the present embodiment, in particular, the light amount difference is corrected by setting the lens diameter φ as shown in Table 1 as the effective diameter.

By the way, in such a spectroscopic camera 100, in order to improve the resolution of the color information of the subject Q, it is necessary to project as many images as possible by increasing the number of divisions of the surface of the image sensor 40. That is, the larger the number of light receiving surfaces 41, the better.
However, since the resolution of the position information of the subject Q decreases in inverse proportion to the size of the conjugate image, simply increasing the number of the light receiving surfaces 41 causes a problem that the reproducibility of the image of the subject Q itself deteriorates. .
Since the number of pixels on the surface of the image sensor 40 is finite, it is desirable to arrange the lens 32 so as to make maximum use of such pixels.

Therefore, the spectroscopic camera 100 collects the light L from the subject Q to form an image at the image forming position 15, the aperture stop 20 disposed at the image forming position 15, and the aperture stop 20. A lens array 31 that is disposed on the + Z direction side and includes a plurality of lenses 32, and a light receiving surface that is disposed at a position conjugate with the aperture stop 20 with the lens array 31 interposed therebetween, and that receives a light beam L ′ that has passed through the lens array 31. And an image sensor 40 having 41.
The lenses 32 are arranged on an XY plane perpendicular to the lens optical axis O of the lens 32, and have different lens intervals L in the X direction and the Y direction, which are two directions perpendicular to the lens optical axis O and orthogonal to each other. and a _{1, L 2.}
With this configuration, the pixels on the surface of the image sensor 40 can be effectively used to the maximum, and the utilization efficiency of the light L is good.

Further, in the present embodiment, a plurality of light receiving surfaces 41 are formed on the surface of the image sensor 40 in a rectangular shape with different aspect ratios. In addition, the lens intervals L ₁ and L ₂ are set so that the lens 32 is disposed to face each of the light receiving surfaces 41. Specifically, the lens interval ratio L ₁ : L ₂ is the aspect ratio L ₁ : L ₂ = 4: 3, similar to the aspect ratio of the light receiving surface 41 of the image sensor 40.
With this configuration, the pixels on the surface of the image sensor 40 can be effectively used to the maximum, and the utilization efficiency of the light L is good.

  In the spectroscopic camera 100, the aperture stop 20 and the light receiving surface 41 are conjugate, so that the image formed on the light receiving surface 41 is an image having the same shape as the shape of the opening 21 of the aperture stop 20.

Therefore, in the present embodiment, the aperture stop 20 has a rectangular opening 21 that is equal to the aspect ratio 4: 3 of the image sensor 40.
With such a configuration, the image formed on the light receiving surface 41 becomes an image having the same shape as the shape of the aperture 21 of the aperture stop 20 and an image having an aspect ratio of 4: 3 can be obtained, so that the resolution can be improved.

In the present embodiment, the spectroscopic camera 100 includes a field lens 22 disposed between the aperture stop 20 and the lens array 31.
With this configuration, the utilization efficiency of the light L incident on the lens array 31 is increased.

In the present embodiment, a filter array 33 including two or more spectral filters 34 having different wavelength transmission characteristics is disposed in the vicinity of the image side of the lens array 31, in other words, the + Z direction side.
With this configuration, the light L transmitted through the lens array 31 is extracted from the wavelength band of the specific wavelength λ by the spectral filter 34, so that the light receiving surface 41 of the image sensor 40 has a plurality of pieces of color information of the subject Q. An image is projected.

In the present embodiment, at least some of the lenses 32 have different focal lengths.
With this configuration, the optical path length between the vicinity of the optical axis O ′ of the image sensor 40 and the peripheral edge of the image sensor 40 is corrected, and the light L is correctly imaged on the light receiving surface 41. Shooting is possible.
Further, the focal length f of the lenses 32 having different focal lengths is determined so that the light L having the wavelength λ transmitted through the spectral filter 34 is imaged on the light receiving surface 41.
With this configuration, the light L transmitted through the lens 32 has an effect on the focal length due to the wavelength λ corrected by the difference in the focal length f of each lens 32, so that the light L on the light receiving surface 41 is not affected by the difference in the wavelength λ. Is imaged.

Furthermore, the lenses 32 having different focal lengths f have different lens diameters.
With such a configuration, the difference in the F value caused by the difference in the focal length f is corrected, and the light amount difference in each image of the subject Q imaged on the light receiving surface 41 is suppressed.

In the present embodiment, only the case where the aperture 21 of the aperture stop 20 has a rectangular shape has been described, but an elliptical shape in which the ratio of the major axis to the minor axis of the aperture 21 is equal to the aspect ratio 4: 3 of the image sensor 40 may be used.
With such a configuration, the image formed on the light receiving surface 41 becomes an image having the same shape as the shape of the aperture 21 of the aperture stop 20 and an image having an aspect ratio of 4: 3 can be obtained, so that the resolution can be improved.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments, and the present invention described in the claims is not specifically limited by the above description. Various modifications and changes are possible within the scope of the above.

For example, the third group of spectral filters may be disposed on the −Z direction side of the lens.
Further, the spectral filter may have a refractive index.
Further, there may be no field lens. In that case, since the spread angle of light becomes large, the image pickup device, the lens, and the like are enlarged, and the number of components is reduced, which contributes to cost reduction.
Particularly in the present embodiment, the aspect ratio of the image sensor is 4: 3, but other ratios such as 16: 9 may be used.

  In the above embodiment, only the spectroscopic camera including the spectroscopic filter has been described. However, the present embodiment may be applied to an image pickup apparatus using another image pickup optical system.

  The effects described in the embodiments of the present invention are only the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

DESCRIPTION OF SYMBOLS 1 1st group 2 2nd group 3 3rd group 10 Imaging optical system 15 Imaging position 20 Aperture stop 21 Aperture 22 Convex lens (field lens)
31 Lens array 32 Lens 33 Spectrometer (filter array)
34 Spectral filter 40 Image sensor 41 Light receiving surface 100 Imaging device (spectral camera)
101 Imaging optical system f Focal length φ Effective diameter (lens diameter)
Q Subject

JP 2014-206494 A Japanese Patent Laying-Open No. 2015-502523 Japanese Patent No. 5649702 JP2015-109667A WO2013-179620 JP 2006-344880 A

Claims (9)

An imaging optical system that focuses the light flux from the subject and forms an image at the imaging position;
An aperture stop disposed at the imaging position;
A lens array disposed on the image side of the aperture stop and including a plurality of lenses;
An imaging device that is disposed at a position conjugate with the aperture stop across the lens array and includes a light receiving surface that receives a light beam transmitted through the lens array;
Have
The imaging optical system, wherein the lenses are arranged on a plane perpendicular to the optical axis of the lens and have different lens intervals in two directions perpendicular to the optical axis and perpendicular to each other. The imaging optical system according to claim 1,
A plurality of the light receiving surfaces are formed on the surface of the imaging element in a rectangular shape with different aspect ratios,
The imaging optical system according to claim 1, wherein the lens interval is set so that the lenses are arranged to face each of the light receiving surfaces. The imaging optical system according to claim 2,
The image pickup optical system according to claim 1, wherein the aperture stop has an opening having a rectangular shape equal to the aspect ratio of the image pickup device or an elliptical shape having an equal ratio of the aspect ratio to the major axis and the minor axis. The imaging optical system according to any one of claims 1 to 3,
An imaging optical system comprising a convex lens disposed between the aperture stop and the lens array. The imaging optical system according to any one of claims 1 to 4,
An imaging optical system, wherein a spectroscopic unit including two or more spectral filters having different wavelength transmission characteristics is disposed on an image side or an object side of the lens array. The imaging optical system according to claim 5,
An imaging optical system, wherein at least some of the lenses have different focal lengths. The imaging optical system according to claim 6,
The imaging optical system according to claim 1, wherein the focal lengths of the lenses having different focal lengths are determined so that light having a wavelength transmitted through the spectral filter is imaged on the light receiving surface. The imaging optical system according to claim 6 or 7,
The imaging optical system, wherein the lenses having different focal lengths have different effective light beam diameters.   An imaging device comprising the imaging optical system according to any one of claims 1 to 8.

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