JP2011114722A - Imaging apparatus, and electronic device - Google Patents

Abstract

Provided are an imaging apparatus and an electronic apparatus that can simplify an optical system and can reduce costs, and can prevent a decrease in depth expansion function even when a diaphragm diameter is changed.
A variable stop 214, an aberration control optical system 210 having an aberration control function for intentionally generating aberration, an image sensor 220, and an image processing device 240 for forming a primary image into a high-definition final image, The aberration characteristic of the aberration control optical system 210 has a characteristic to be rotated around the optical axis, and the variable diaphragm 214 is also configured to form a substantially circular shape at the optical axis center even when the aperture is changed. Regardless of the aperture of the aperture 214, the aperture has at least one inflection point in the refractive index of spherical aberration within the aperture.
[Selection] Figure 4

Description

  The present invention relates to an imaging apparatus and an electronic apparatus that include an imaging device and includes an optical system.

In response to the digitization of information, which has been rapidly developing in recent years, the response in the video field is also remarkable.
In particular, as symbolized by a digital camera, a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) sensor, which is a solid-state imaging device, is used for the imaging surface in place of a conventional film.

  As described above, an imaging lens device using a CCD or CMOS sensor as an imaging element is for taking an image of a subject optically by an optical system and extracting it as an electrical signal by the imaging element. In addition to a digital still camera, It is used in video cameras, digital video units, personal computers, mobile phones, personal digital assistants (PDAs), image inspection devices, industrial cameras for automatic control, and the like.

FIG. 25 is a diagram schematically illustrating a configuration and a light flux state of a general imaging lens device.
The imaging lens device 1 includes an optical system 2 and an imaging element 3 such as a CCD or CMOS sensor.
In the optical system, the object side lenses 21 and 22, the diaphragm 23, and the imaging lens 24 are sequentially arranged from the object side (OBJS) toward the image sensor 3 side.

In the imaging lens device 1, as shown in FIG. 25, the best focus surface is matched with the imaging element surface.
FIGS. 26A to 26C show spot images on the light receiving surface of the imaging element 3 of the imaging lens device 1.

  In addition, imaging devices have been proposed in which light beams are regularly dispersed by a phase plate and restored by digital processing to enable imaging with a deep depth of field (for example, Non-Patent Documents 1 and 2 and Patent Documents). 1-5).

USP 6,021,005 USP 6,642,504 USP 6,525,302 USP 6,069,738 JP 2003-235794 A

“Wavefront Coding; jointly optimized optical and digital imaging systems”, Edward R. Dowski, Jr., Robert H. Cormack, Scott D. Sarama. “Wavefront Coding; A modern method of achieving high performance and / or low cost imaging systems”, Edward R. Dowski, Jr., Gregory E. Johnson.

In the imaging devices proposed in the above-mentioned documents, it is assumed that the OTF when the above-described phase plate is inserted into a normal optical system is almost constant with respect to the object distance, and the contrast is normal optical. It deteriorates more than the system.
For example, in the application of a sensing camera such as a code reader, such a deterioration in contrast causes a deterioration in reading rate.
In addition, in a camera that requires contrast, such as a digital camera or a portable terminal camera, noise is increased by applying image processing such as convolution to improve the deteriorated contrast.
However, it is difficult to suppress the deterioration of contrast in optical design using a phase plate.

In the depth extension optical system, the aberration control element is disposed in the vicinity of the stop of the optical system and exerts a depth extension action.
Here, when trying to use in an environment where the brightness changes, in the optical system with a fixed aperture, it will be handled by the signal control of the image sensor and signal processing system. Has the disadvantage of being limited.

Therefore, a conventional optical system often incorporates a system that mechanically controls the amount of light taken through the lens.
In many cases, the amount of light is adjusted by opening and closing wings that are mechanically operated to block light.

  However, when the above method is applied to a depth extension optical system, the depth extension function depends on the change of the aperture shape due to the variable aperture, so that the depth extension function is lost or the efficiency is significantly reduced. There is.

  An object of the present invention is to provide an imaging apparatus and an electronic apparatus that can prevent the depth expansion function from being lowered even if the aperture diameter is changed.

  An image pickup apparatus according to a first aspect of the present invention includes an aberration control optical system including an aberration control unit having an aberration control function for generating spherical aberration, and a substantially circular aperture centered on the optical axis to form the aberration control. A variable aperture that restricts the light beam passing through the optical system and makes the aperture variable; and the aberration control optical system and an image sensor that captures a subject image that has passed through the variable aperture, and the aberration control unit includes: The generated aberration is rotationally symmetric about the optical axis and has at least one inflection point of the spherical aberration.

  An electronic apparatus according to a second aspect of the present invention includes an imaging device, and the imaging device is centered on an optical axis and an aberration control optical system including an aberration control unit having an aberration control function for generating spherical aberration. A variable aperture that forms a substantially circular aperture and restricts a light beam passing through the aberration control optical system, and the aperture is variable. The aberration control section has at least one inflection point of the spherical aberration, and the generated aberration is rotationally symmetric about the optical axis.

  According to the present invention, it is possible to simplify the optical system, and it is possible to prevent the depth extension function from being lowered even if the aperture diameter is changed.

It is an external view which shows an example of the information code reader as an electronic device which concerns on embodiment of this invention. It is a figure which shows the example of an information code. It is a block which shows the structural example of the imaging device applied to the information code reader of FIG. It is a figure which shows the basic composition of the imaging lens unit which forms the aberration control optical system containing the variable aperture_diaphragm | restriction which concerns on this embodiment. It is a figure which shows the structural example of the six iris variable aperture diaphragms which can hold | maintain an open part circularly at the time of open and half open which concern on this embodiment. It is a figure which shows the structural example of two iris variable apertures which cannot hold | maintain an open part circularly at the time of half open as a comparative example. It is an image figure of PSF by the iris variable iris diaphragm concerning this embodiment. It is an image figure of PSF by the variable aperture of a comparative example. It is a figure which shows the basic composition of the imaging lens unit which forms the aberration control optical system containing the variable aperture_diaphragm | restriction by the liquid crystal element which concerns on this embodiment. It is a figure for demonstrating the structural example and function of the external dependence type aberration control element which concern on this embodiment. It is a figure for demonstrating the basic composition of the liquid crystal device applicable as a variable aperture. It is a figure for demonstrating control operation | movement of the aperture diameter by a liquid crystal device. It is a figure for demonstrating the spherical aberration generation amount of the aberration control optical system which concerns on this embodiment, Comprising: It is a figure which shows the relationship between a sensor and PSF when an image pick-up element (sensor) is fixed. It is a figure for demonstrating the spherical aberration generation amount of the aberration control optical system which concerns on this embodiment, Comprising: It is a figure which shows the relationship between a sensor and PSF when an aberration control optical system is fixed. It is a figure which shows the state of MTF with respect to the defocus of the normal optical system and the aberration control optical system which concerns on this embodiment. It is a figure which shows that MTF with respect to a defocus can be performed for 2 minutes in the arbitrary frequencies in the aberration control optical system which suppressed the high frequency OTF fluctuation | variation. It is a figure which shows that MTF with respect to a defocus can be divided into 2 by the arbitrary frequency in the aberration control optical system which suppressed the OTF fluctuation | variation of the low frequency. It is a figure which compares and shows the spherical aberration by the difference in aperture diameter, and the depth of this optical system in a defocus MTF, and a normal optical system. It is a figure which compares and shows the defocus MTF of the normal optical system by the difference in aperture diameter, and the aberration control optical system which concerns on this embodiment. It is a figure for demonstrating the MTF correction process in the image processing apparatus which concerns on this embodiment. It is a figure for demonstrating concretely the MTF correction process in the image processing apparatus which concerns on this embodiment. It is a figure which shows the response (response) of MTF when an object exists in a focus position in the case of a normal optical system, and when it remove | deviated from a focus position. It is a figure which shows the response of MTF when an object exists in a focus position and remove | deviates from a focus position in the case of the optical system of this embodiment which has an aberration control element. It is a figure which shows the response of MTF after the image process of the imaging device which concerns on this embodiment. It is a figure which shows typically the structure and light beam state of a general imaging lens apparatus. FIG. 26A is a diagram showing a spot image on the light receiving surface of the imaging element of the imaging lens device of FIG. 25, where FIG. In the case (Best focus), (C) is a diagram showing each spot image when the focal point is shifted by -0.2 mm (Defocus = -0.2 mm).

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

FIG. 1 is an external view showing an example of an information code reader as an electronic apparatus according to an embodiment of the present invention.
2A to 2C are diagrams illustrating examples of information codes.
FIG. 3 is a block diagram illustrating a configuration example of an imaging apparatus applicable to the information code reading apparatus of FIG.
Here, an information code reader is illustrated as an apparatus to which the imaging apparatus of the present embodiment is applicable.

As shown in FIG. 1, the information code reader 100 according to the present embodiment has a main body 110 connected to a processing device such as an electronic register (not shown) via a cable 111, for example, a reflectance printed on a reading object 120. It is a device that can read the information code 121 such as a different symbol or code.
As an information code to be read, for example, a one-dimensional bar code 122 such as a JAN code as shown in FIG. 2A, a stack-type CODE 49 as shown in FIGS. 2B and 2C, Alternatively, a two-dimensional barcode 123 such as a matrix type QR code can be used.

In the information code reading apparatus 100 according to the present embodiment, an illumination light source (not shown) and an imaging apparatus 200 as shown in FIG.
As will be described in detail later, the imaging apparatus 200 applies an aberration control surface or aberration control element to the optical system, intentionally generates aberration (spherical aberration in the present embodiment) by the aberration control element, and focuses. It has a depth extension function.
In addition, the imaging apparatus 200 has a variable stop, the aberration control optical system has a characteristic to be rotated around the optical axis, and the variable stop also forms a substantially circular shape at the center of the optical axis even when the aperture is changed. An aberration control optical system system configured to be used is adopted, and an information code such as a one-dimensional barcode such as a JAN code and a two-dimensional barcode such as a QR code is accurately read with high accuracy. It is configured to be possible.

In addition to the above-described configuration, the imaging apparatus 200 has a modulation transfer function (MTF: Modulation Transfer Function) for defocus. In order for the aberration control function to exhibit depth expansion, the imaging apparatus 200 can be opened even if the aperture diameter changes. Employs a system called an aberration control optical system that has at least one inflection point in the aperture, and it can accurately identify one-dimensional barcodes such as JAN codes and information codes such as two-dimensional barcodes such as QR codes. It can be read with high accuracy.
The imaging apparatus 200 employs an aberration control optical system that enables one to have one or more peaks in the main image plane shift region of an arbitrary frequency, thereby enabling depth expansion while suppressing a decrease in the MTF peak value. In addition, an information code such as a one-dimensional barcode such as a JAN code and a two-dimensional barcode such as a QR code can be accurately read with high accuracy.

  As shown in FIG. 3, the imaging apparatus 200 of the information code reading apparatus 100 includes an aberration control optical system 210, an imaging element 220, an analog front end unit (AFE) 230, an image processing device 240, a camera signal processing unit 250, and an image display. A memory 260, an image monitoring device 270, an operation unit 280, and a control device 290 are provided.

  FIG. 4 is a diagram showing a basic configuration of an imaging lens unit that forms an aberration control optical system including a variable stop according to the present embodiment.

The aberration control optical system 210 </ b> A supplies an image obtained by photographing the subject object OBJ to the image sensor 220.
In the aberration control optical system 210A, a first lens 211, a second lens 212, a third lens 213, a variable aperture 214, a fourth lens 215, and a fifth lens 216 are arranged in order from the object side.
In the aberration control optical system 210A of this embodiment, a fourth lens 215 and a fifth lens 216 are connected. That is, the lens unit of the aberration control optical system 210A of the present embodiment is configured to include a cemented lens.

The aberration control optical system 210A of the present embodiment is configured as an optical system to which an aberration control surface as an aberration control unit having an aberration control function for intentionally generating aberration is applied.
In this embodiment, it is necessary to insert an aberration control surface in order to generate only spherical aberration. As an aberration control effect, an aberration control element as a separate element may be inserted.
An example of this is shown in FIG. 4 and includes a normal optical system including an aberration control surface (third lens R2 surface).
The aberration control surface here refers to a lens surface that includes the aberration control effect of the aberration control element. The aberration control surface 213a is preferably adjacent to the variable stop 214.

The aberration characteristics of the aberration control optical system 210A of the present embodiment have a depth of focus expansion effect (function) even when the aperture of the variable stop 214 changes.
In the aberration control optical system 210A of the present embodiment, the aberration control function unit has at least one inflection point of spherical aberration, with the generated spherical aberration being rotationally symmetric about the optical axis.
In other words, the aberration control function unit formed by the aberration control surface or the aberration control element has an inflection point of spherical aberration within the aperture regardless of the aperture of the variable stop 214.
The variable diaphragm 214 is formed of an iris diaphragm that has a plurality of wings and whose aperture is variable by making these wings movable, or a liquid crystal element (liquid crystal device), for example.
As will be described later, the variable aperture formed by the liquid crystal device changes the aperture by changing the transmission portion and the light shielding portion.

As described above, in this embodiment, the aberration control optical system 210A has a characteristic to be rotated around the optical axis, and the variable diaphragm 214 also forms a substantially circular shape at the optical axis center even when the aperture is changed. Configured to do so. The reason is as follows.
The distribution of the PSF changes as the shape of the diaphragm changes. Therefore, the restoration filter designed based on the PSF obtained by the aberration control characteristics to be rotated around the optical axis may not be able to effectively exhibit the restoration function if the shape of the diaphragm changes.
In order for the aberration control function to exhibit depth expansion, it is necessary to have at least one inflection point in the aperture diameter even if the aperture diameter changes.
Therefore, in this embodiment, the aberration control optical system 210A basically has a characteristic to be rotated around the optical axis, and has an inflection point at any aperture diameter of the variable aperture. The opening diameter is configured to have a substantially circular shape with the optical axis as the center.

Here, the aberration control optical system 210A can select a plurality of F values by changing the aperture of the variable stop 214, and any of the selectable F values depends on the effect of the aberration control element or the aberration control surface. It is possible to perform depth extension.
The aberration characteristic of the aberration control optical system 210 </ b> A of the present embodiment has at least one (one or more) inflection points within the effective diameter of the variable stop 214.
Further, the aberration characteristic of the aberration control optical system 210A of the present embodiment is that the light beam in the case of the minimum aperture diameter having the effect of extending the depth of focus by the aberration control function from the region through which the light beam passes when the variable aperture 214 has an open aperture. It has one or more inflection points in the region excluding the region through which passes.
In other words, the aberration characteristics of the aberration control optical system 210A of this embodiment are the F value expected to have a depth expansion effect, the region of the aberration control surface through which the light beam passes at the brightest F value, and the darkest F value. There are one or more inflection points between the areas of the aberration control surface through which light passes.

In the aberration control optical system 210A of the present embodiment, the main image that is not pseudo-resolved at a predetermined frequency is set such that the PSF spans two or more pixels by using an aberration control optical system including an aberration control surface having an aberration control function. This is configured as a depth extension optical system having two or more peaks with respect to defocusing in the surface shift region.
In a depth extension optical system using a general optical wavefront modulation function, the base of one peak is expanded in the MTF characteristics to expand the depth. In exchange for this, the peak value of the MTF characteristics decreases.
In the present embodiment, by having a plurality of peaks using the aberration control function, depth extension can be realized while suppressing a decrease in peak value.
By appropriately controlling the spherical aberration, it is possible to extend the depth without performing image restoration processing.
Specifically, the aberration control optical system 210A of the present embodiment divides the MTF peak for defocus into a plurality of parts (here, divided into two) by an aberration control element that mainly generates spherical aberration or an aberration control surface. Can control the change of OTF in the out-of-focus state and can extend the depth. In order to divide the peak, an inflection point is given to the spherical aberration.

As described above, depth expansion can be realized for selection of a plurality of apertures by appropriately providing one or more, preferably two or more inflection points in the spherical aberration.
As described above, among the F values expected to have a depth expansion effect, the region of the aberration control surface through which the light beam passes at the brightest F value and the aberration control surface through which the light beam passes at the darkest F value. It is desirable to have one or more inflection points between regions.
By adopting this configuration, even when the F value is changed, it is possible to efficiently obtain the depth extending action.

Here, a specific configuration example of the variable diaphragm 214 will be described.
FIGS. 5A and 5B are diagrams showing a configuration example of six iris variable diaphragms that can hold the open portion in a circular shape when opened and half-opened according to the present embodiment.
FIG. 5A shows the open state, and FIG. 5B shows the half-opened state.
FIGS. 6A and 6B are diagrams showing a configuration example of two iris variable diaphragms that cannot hold the open portion in a circular shape when half open, as a comparative example.
FIG. 6A shows the opened state, and FIG. 6B shows the half opened state.

According to this embodiment, the iris variable diaphragm 214A has six iris blades 214-1 to 214-6.
Each of the iris feathers 214-1 to 214-6 is configured to be rotatable around the rotation axes AX <b> 1 to AX <b> 6 under the control of a drive control system (not shown).
The rotational range of each of the iris wings 214-1 to 214-6 is restricted by the movement of the pins BS <b> 1 to BS <b> 6 inserted into the long holes of the iris wings 214-1 to 214-6 by the long holes HL <b> 1 to HL <b> 6. It is a range.
Thereby, the aperture is continuously or stepwise changed between the open state and the minimum aperture state in FIG.

As a comparative example, a variable diaphragm 214B shown in FIGS. 6A and 6B has two wings 214-7 and 214-8.
This comparative example is a type of variable diaphragm that narrows into a triangular shape when the diaphragm is squeezed from the open state.

7A and 7B are image diagrams of PSFs with the iris variable aperture according to the present embodiment.
7A shows the PSF in the aperture state of FIG. 5A, and FIG. 7B shows the PSF in the aperture state of FIG. 5B.
8A and 8B are image diagrams of PSFs with a variable aperture according to a comparative example.
8A shows the PSF in the aperture state of FIG. 6A, and FIG. 8B shows the PSF in the aperture state of FIG. 6B.

In the variable stop of the comparative example, the PSF is circular in the open state, but in the half open state, the light beam is cut into a triangle by the stop. Therefore, the light beam passing through the aberration control surface near the stop is inevitably cut off.
As a result, the light beam having the depth extending action is cut nonuniformly with respect to the chief ray.
That is, as shown in FIG. 8 (A), the PSF that was circular when opened (FIG. 7) becomes a triangle as shown in FIG. Can no longer be generated.

  On the other hand, in the variable aperture 214A of the present embodiment, the PSF by the aperture that maintains a circular shape when half-opened is a circular PSF similar to that when opened as shown in FIG. 7A, as shown in FIG. 7B. It is possible to maintain the same depth expansion action when opened.

  Next, an example in which an externally dependent aberration control element formed by a liquid crystal element is applied to the variable diaphragm will be described.

  FIG. 9 is a diagram illustrating a basic configuration of an imaging lens unit that forms an aberration control optical system including the liquid crystal element according to the present embodiment.

The aberration control optical system 210B in FIG. 9 is configured as an optical system to which an aberration control element having an aberration control function for intentionally generating aberration is applied.
Specifically, instead of the third lens 213 and the aberration control unit 213a, an externally dependent aberration control element 217 formed by a liquid crystal element is applied.
Then, as will be described later, the variable diaphragm 214b is formed by a liquid crystal device (liquid crystal element) from the viewpoint of responsiveness.

The aberration characteristics of the aberration control optical system 210B are configured such that the aberration control function of the aberration control optical system can be changed according to the change in the aperture of the variable stop 214b.
The aberration control optical system 210B of the present embodiment has at least one inflection point in the refractive index of spherical aberration within the aperture regardless of the aperture of the variable stop 214b.
Then, the difference in refractive index from the central portion at the inflection point of the refractive index increases from the central portion of the optical axis OX toward the peripheral portion.
Further, the difference in refractive index between the inflection point and the optical axis central portion increases as the aperture of the variable stop 214b decreases.

As described above, in the aberration control optical system 210B, the externally dependent aberration control element 217 is applied as an element that can change the aberration control function of the aberration control optical system in accordance with the change in the aperture of the variable stop 214. Yes.
The externally dependent aberration control element 217 depends on the outside for the expression, the degree of expression, and the non-expression of the aberration control function having the function of changing the aberration of imaging on the light receiving surface of the imaging element 220 by the imaging lens.
The externally dependent aberration control element 217 has good imaging performance when the aberration control optical system 210B is in focus when the aberration control function is controlled to the non-expressed state by the control device 290. When the expression state is controlled, the aberration control optical system 210B is in a state where the depth is expanded.
When the aberration control function is exhibited, the degree of expression of the aberration control function of the externally dependent aberration control element 217 changes in accordance with the change of the variable stop 214b under the control of the control device 200.

  10A and 10B are diagrams for explaining a configuration example and functions of the externally dependent aberration control element according to the present embodiment.

As shown in FIGS. 10A and 10B, the externally dependent aberration control element 217 can be constituted by a liquid crystal element (liquid crystal lens) 217a, for example.
The liquid crystal lens 217a can change the light collection state by switching the voltage applied to the element.
For example, when a voltage is applied by the control device 290, as shown in FIG. 10A, the liquid crystal lens 217a is controlled to have an aberration control function, and the aberration control optical system 210B is in a multi-focus state.
On the other hand, when the voltage application is stopped (or set to a lower level than the manifestation state) by the control device 200, as shown in FIG. 10B, the liquid crystal element 217a has the aberration control function controlled to the non-expression state, and the aberrations The control optical system 210B is in a single focus state.
In the present embodiment, when the liquid crystal lens 217a is in the manifestation state, the degree of expression of the aberration control function changes in accordance with the change of the variable diaphragm 214b under the control of the control device 200.
In controlling the degree of expression of the aberration control function, the voltage applied to the liquid crystal lens 217a is changed, for example, linearly or stepwise.
As a result, the liquid crystal lens 217a changes in the multi-focus state according to the change in the applied voltage.

In the present embodiment, the variable iris 214b can employ the iris feather variable iris shown in FIG. 5, but the externally dependent aberration control element 217 is formed of the liquid crystal lens 217a as in this example. In this case, it is desirable to form the variable aperture with a liquid crystal device from the relationship of responsiveness.
The variable diaphragm 214 formed by a liquid crystal device will be described below.

For example, as shown in FIG. 11, the liquid crystal device 300 basically includes pixels formed by switching transistors TSW, liquid crystal elements LQD, and storage capacitors CS arranged in a matrix.
The source of the switching transistor TSW is connected to the signal line LSG, and the gate is connected to the scanning line LSCN.
Then, a signal line driver and a scanning line driver (not shown) are driven by the control device 200 to control light transmission and light shielding in the plurality of pixels PXL. Can be obtained.

The aberration control function described above means a function for intentionally generating aberration.
Aberrations can be extended in depth without performing image restoration processing, particularly by appropriately controlling spherical aberration.
Specifically, in the present embodiment, it is possible to control the change of the OTF in the out-of-focus state by dividing the focus of the defocus MTF. In order to divide the focus, the spherical aberration has an inflection point.
By configuring the externally dependent aberration control element 217 for controlling the aberration with the liquid crystal lens 217a and the hybrid configuration with the variable stop 214b, it becomes easier to control the spherical aberration.

Here, the aberration control optical system 210B having the above-described configuration can select a plurality of F values by changing the aperture diameter, and in any of the selectable F values, the depth is expanded by the effect of the aberration control function. .
Therefore, the refractive index of the liquid crystal lens 217a when the depth is extended is from the central portion (intersection with the optical axis OX) to the peripheral portion, and at least one inflection point of the refractive index within the aperture. To have.
In this embodiment, the difference in refractive index from the central portion at the inflection point of the refractive index is configured to increase from the central portion toward the peripheral portion.
Usually, the light beam that has passed through the stop has a larger angle difference (NA is larger) on the image plane with the light beam that has passed through the peripheral part.
That is, in a normal optical system, the depth of focus becomes shallower as the beam bundle has a larger NA. Therefore, it is desirable to increase the amount of generated aberration (spherical aberration) in order to cancel this.
In the present embodiment, the difference in refractive index from the central portion at the inflection point of the refractive index is configured to increase as the F value becomes darker. This is because the darker the F value, the longer the depth of focus, and a large amount of aberration is required to achieve a corresponding depth expansion.

Further, in the aberration control optical system 210B, similarly to the aberration control optical liquid 210A, an aberration control optical system including an aberration control surface having an aberration control function is used so that the PSF extends over two pixels or more, and a predetermined frequency is set. The MTF characteristic for defocusing is configured as a depth extension optical system having two or more peaks in a main image plane shift region that is not falsely resolved in FIG.
In a depth extension optical system using a general optical wavefront modulation function, the depth is extended by making the MTF characteristic with respect to the object distance substantially constant. However, in this case, the peak value of the MTF characteristic is lowered.
In the present embodiment, by having a plurality of peaks using the aberration control function, depth extension can be realized while suppressing a decrease in peak value.
By appropriately controlling the spherical aberration, it is possible to extend the depth without performing image restoration processing.
Specifically, the aberration control optical system 210B of the present embodiment divides the MTF peak for defocus into a plurality of parts (here, divided into two) by an aberration control element that mainly generates spherical aberration or an aberration control surface. Can control the change of OTF in the out-of-focus state and can extend the depth. In order to divide the peak, an inflection point is given to the spherical aberration.
As described above, depth expansion can be realized for selection of a plurality of aperture diameters by appropriately giving two or more inflection points to the spherical aberration.
As described above, among the F values expected to have a depth expansion effect, the region of the aberration control surface through which the light beam passes at the brightest F value and the aberration control surface through which the light beam passes at the darkest F value. It is desirable to have one or more inflection points between regions.
By adopting this configuration, even when the F value is changed, it is possible to efficiently obtain the depth extending action.

  Hereinafter, the characteristic configuration and function of the aberration control optical systems 210A and 210B according to the present embodiment will be described in more detail.

  FIGS. 13A and 13B and FIGS. 14A and 14B are diagrams for explaining the spherical aberration generation amount of the aberration control optical system according to the present embodiment. FIG. 13 shows the relationship between the sensor and the PSF when the imaging element (sensor) is fixed, and FIG. 14 shows the relationship between the sensor and the PSF when the aberration control optical system is fixed.

For example, it is assumed that the image sensor 220 is a sensor having a certain pixel pitch. In this case, in the present embodiment, it is necessary to generate spherical aberration and make the PSF larger than one pixel PXL.
As shown in FIGS. 13A and 14A, even if spherical aberration is generated with a size that allows the PSF to be accommodated in one pixel PXL, it is the same as a normal optical system. In the normal optical system, the size of the center PSF at the focus position is generally minimum.
On the other hand, in the aberration control optical systems 210A and 210B according to the present embodiment, as shown in FIG. 13B, the PSF is controlled not to be out-of-focus but to a size that does not fit in one pixel PXL even at the focus position. The

Next, selection of an image sensor (sensor) suitable for the aberration control optical system will be described.
For example, if there is an aberration control optical system having a certain PSF size, it is preferable to select a sensor whose pixel pitch is smaller than the size of the PSF, as shown in FIG.
If a pixel pitch larger than the PSF is selected, it becomes the same as the normal optical system, which is in focus. Therefore, in this case, the effect of spherical aberration of the aberration control optical system cannot be obtained effectively.

FIGS. 15A to 15C are diagrams illustrating the MTF state with respect to the defocus of the normal optical system and the aberration control optical system according to the present embodiment.
FIG. 15A shows the MTF state with respect to the defocus of the normal optical system, FIG. 15B shows the MTF state with respect to the defocus of the aberration control optical system according to the present embodiment, and FIG. The MTF state with respect to the defocus of the depth extension optical system in which the MTF characteristic with respect to the object distance is substantially constant is shown.

In a normal optical system, as shown in FIG. 15A, there is one focus position at the center. The second mountain on both sides falls and flips, resulting in false resolution.
Therefore, the area to be resolved is a main image plane shift area MSAR indicated by shading. When the depth of one peak of the normal optical system is extended, the MTF is greatly deteriorated as shown in FIG.

Therefore, in the MTF for the defocus of the aberration control optical system according to the present embodiment, as shown in FIG. 15B, the single peak PK1 in the normal optical system is divided into two peaks PK11 and PK12. ing.
It can be seen that although the MTF is slightly degraded, the depth is increased by about 2 times due to the division into two, and the degradation is suppressed more than the depth extension of one peak.

  FIGS. 16A to 16C and FIGS. 17A to 17C show that the MTF for defocus can be divided into two at an arbitrary frequency by a spherical aberration curve (curve) in the aberration control optical system of the present embodiment. FIG.

  FIGS. 16A to 16C show that the MTF for defocus can be divided into two at an arbitrary frequency in the aberration control optical system in which high-frequency OTF fluctuation is suppressed, and FIG. 16A shows the spherical aberration curve. FIG. 16B shows the state of the MTF peak in the main image plane shift area area MSAR at low frequency, and FIG. 16C shows the state of the MTF peak in the main image plane shift area area MSAR at high frequency. Is shown.

  FIGS. 17A to 17C show that the MTF for defocus can be divided into two at an arbitrary frequency in the aberration control optical system in which the low-frequency OTF fluctuation is suppressed. FIG. 17A shows the spherical aberration curve. FIG. 17B shows the state of the MTF peak in the main image plane shift area area MSAR at a low frequency, and FIG. 17C shows the MTF peak state in the main image plane shift area area MSAR at a high frequency. Indicates the state.

As can be seen from FIGS. 17A to 17C, in order to increase the depth of the low frequency, the amplitude of the spherical aberration may be increased.
A defocus MTF having an arbitrary frequency can be divided into two by controlling the amplitude. That is, the depth of an arbitrary frequency can be expanded.

In the present embodiment, the low frequency and high frequency for defocus are defined as follows.
A frequency that is half or more of the Nyquist frequency determined from the pixel pitch of the solid-state imaging device (imaging device 220) to be used is a high frequency, and a frequency lower than half is a low frequency.
However, the Nyquist frequency is defined as follows.
Nyquist frequency = 1 / (pixel pitch of solid-state image sensor × 2)

18A to 18C are diagrams showing spherical aberration and defocus MTF due to a difference in aperture diameter, and a comparison between the present optical system and a normal optical system in depth.
FIG. 18A shows a state in which the aperture is opened, FIG. 18B shows a state in which the aperture is stopped in the middle, and FIG. 18C shows a state in which the aperture is stopped.

In the state where the aperture is opened most, as shown in FIG. 18A, since light rays pass through the aberration control surface near the aperture having a plurality of inflection points, a plurality of inflection points are also formed in the spherical aberration curve. Have.
Even if the aperture is narrowed from there, as shown in FIGS. 18B and 18C, the depth expansion action can be continued until at least one inflection point remains.

FIGS. 19A to 19C are diagrams showing a comparison of the defocus MTFs of the normal optical system and the aberration control optical system according to the present embodiment due to the difference in aperture diameter.
FIG. 19A shows a state in which the variable aperture is opened, FIG. 19B shows a state in which the variable aperture is stopped in the middle, and FIG. 19C shows a state in which the variable aperture is stopped.

In FIGS. 19A to 19C, shaded portions indicate depth regions.
As can be seen from FIGS. 19A to 19C, in order to have the same level of depth expansion effect regardless of the selectable F value (diaphragm aperture), as the aperture diameter decreases, the distance from the center increases. A larger optical modulation amount at the same position is better.

The characteristic configuration, function, and effect of the optical system according to the present embodiment have been described above.
Hereinafter, the configuration and functions of other components such as the image sensor and the image processing unit will be described.

For example, as shown in FIG. 4, the imaging element 220 includes a parallel plane plate (cover glass) 221 made of glass and an imaging surface 222 of an imaging element made up of a CCD or a CMOS sensor in this order from the fourth lens 216 side. ing.
Light from the subject OBJ via the aberration control optical system 210A is imaged on the imaging surface 222 of the imaging element 220.
Note that the subject dispersion image captured by the image sensor 220 is an image in which a deep light beam and a blurred portion are formed without being focused on the image sensor 220 by the aberration control surface 213a or the externally dependent aberration control element 217. is there.

As shown in FIG. 3, the image sensor 220 forms an image captured by the aberration control optical system 210, and uses the analog front-end unit 230 as the primary image signal FIM of the electrical primary image information. Via a CCD or a CMOS sensor that is output to the image processing device 240.
In FIG. 3, the imaging element 220 is described as a CCD as an example.

The analog front end unit 230 includes a timing generator 231 and an analog / digital (A / D) converter 232.
The timing generator 231 generates the drive timing of the CCD of the image sensor 220, and the A / D converter 232 converts an analog signal input from the CCD into a digital signal and outputs it to the image processing device 240.

  The image processing device 240 constituting a part of the signal processing unit inputs a digital signal of a captured image coming from the AFE 230 in the previous stage, performs image processing such as edge enhancement, and the contrast reduced by the aberration of the aberration control optical system 201. The signal is improved and passed to the camera signal processing unit (DSP) 250 in the subsequent stage.

  The camera signal processing unit (DSP) 250 performs processing such as color interpolation, white balance, YCbCr conversion processing, compression, and filing, and stores the data in the memory 260 and displays the image on the image monitoring device 270.

  The control device 290 performs exposure control and has operation inputs from the operation unit 280 and the like, determines the operation of the entire system in accordance with those inputs, and controls the AFE 230, the image processing device 240, the DSP 250, and externally dependent aberration control. It controls the element 217, the variable diaphragms 214, 214b, etc., and governs the arbitration control of the entire system.

  Hereinafter, the configuration and functions of the optical system and the image processing apparatus according to the present embodiment will be described in detail.

  In the present embodiment, an aberration control optical system is employed to obtain high-definition image quality, and the optical system can be simplified and the cost can be reduced.

  As described above, the image processing device 240 receives the primary image FIM from the image sensor 220, performs image processing such as edge enhancement, and improves the contrast reduced by the aberrations of the aberration control optical systems 210A and 210B. To form a high-definition final image FNLIM.

The MTF correction processing of the image processing apparatus 240 is performed after edge enhancement, chroma enhancement, etc., using the MTF of the primary image, which is essentially a low value, as shown by a curve A in FIG. In the process, correction is performed so as to approach (reach) the characteristics indicated by the curve B in FIG.
A characteristic indicated by a curve B in FIG. 20 is a characteristic obtained when the wavefront is not deformed without using the aberration control surface or the aberration control optical element as in the present embodiment.
It should be noted that all corrections in the present embodiment are based on spatial frequency parameters.

In this embodiment, as shown in FIG. 20, in order to achieve the MTF characteristic curve B to be finally realized with respect to the MTF characteristic curve A with respect to the optically obtained spatial frequency, each spatial frequency is changed to each spatial frequency. On the other hand, as shown in FIG. 21, the original image (primary image) is corrected by applying strength such as edge enhancement.
For example, in the case of the MTF characteristic shown in FIG. 20, the curve of edge enhancement with respect to the spatial frequency is as shown in FIG.

  That is, a desired MTF characteristic curve B is virtually realized by performing correction by weakening edge enhancement on the low frequency side and high frequency side within a predetermined spatial frequency band and strengthening edge enhancement in the intermediate frequency region. To do.

As described above, the imaging apparatus 200 according to the embodiment basically includes the aberration control optical system 210 and the imaging element 220 that form the primary image, and the image processing apparatus 240 that forms the primary image into a high-definition final image. In this optical system, spherical aberration is intentionally achieved by providing a new aberration control element or by shaping the surface of the optical element such as glass or plastic for aberration control. An image with an increased depth of focus is generated, and such an image is formed on the image pickup surface (light receiving surface) of the image pickup element 220 including a CCD or a CMOS sensor, and the formed primary image is converted into an image processing apparatus. The image forming system obtains a high-definition image through 240.
In the present embodiment, the primary image from the image sensor 220 has a light flux condition with a very deep depth. For this reason, the MTF of the primary image is essentially a low value, and the MTF is corrected by the image processing device 240.

  Next, the response of the MTF of this embodiment and the normal optical system will be considered.

FIG. 22 is a diagram illustrating MTF responses when the object is at the focal position and when the object is out of the focal position in the case of a normal optical system.
FIG. 23 is a diagram illustrating the response of the MTF when the object is at the focal position and when the object is out of the focal position in the optical system of the present embodiment having the aberration control element.
FIG. 24 is a diagram illustrating a response of the MTF after image processing of the imaging apparatus according to the present embodiment.

As can be seen from the figure, in the case of an optical system having an aberration control surface or an aberration control element, even if the object deviates from the focal position, the change in the response of the MTF does not insert the aberration control surface or the aberration control element. Less than.
The image formed by the optical system is subjected to image processing by the subsequent image processing device 240, whereby the MTF response can be improved.
However, if noise increases when image processing is performed, it is preferable not to perform image processing that preferably improves the response of the MTF.
As described above, an optical system that intentionally generates aberration according to the purpose is referred to as an aberration control optical system.

The absolute value (MTF) of the OTF of the aberration control optical system shown in FIG. 23 is preferably 0.1 or more at the Nyquist frequency.
This is because, in order to achieve the OTF after restoration shown in FIG. 24, the gain is increased by image processing, but the noise of the sensor is also increased at the same time. Therefore, it is preferable to perform image processing without increasing the gain as much as possible at high frequencies near the Nyquist frequency.
In the case of a normal optical system, resolution is achieved if the MTF at the Nyquist frequency is 0.1 or more.
Therefore, if the MTF before image processing is 0.1 or more, it is not necessary to increase the gain at the Nyquist frequency in image processing. If the MTF before image processing is less than 0.1, the image after image processing becomes an image greatly affected by noise, which is not preferable.

As described above, according to the present embodiment, the variable aperture 214, the aberration control optical system 210 having an aberration control function for intentionally generating aberration, the image sensor 220, and the primary image are converted into a high-definition final image. The image processing apparatus 240 to be formed is included, and the aberration control function of the aberration control optical system can be changed in accordance with the change in the aperture of the variable stop 214.
The aberration control optical system 210 of the present embodiment has a characteristic to be rotated around the optical axis, and the variable diaphragm 214 is also configured to form a substantially circular shape at the optical axis center even when the aperture is changed. Is done.
The aberration control optical system 210 of this embodiment has at least one inflection point in the refractive index of spherical aberration within the aperture regardless of the aperture of the variable stop 214.
Then, the difference in refractive index from the central portion at the inflection point of the refractive index increases from the central portion of the optical axis OX toward the peripheral portion.
Further, the difference in refractive index between the inflection point and the optical axis central portion increases as the aperture of the variable stop 214 decreases.

  Therefore, according to the present embodiment, it is possible to prevent the depth extension function from being lowered even if the aperture diameter is changed, and it is possible to realize a good depth extension function even in a wide range of subject luminance.

  Further, according to the present embodiment, the aberration control optical system includes an aberration control optical system including an aberration control element having an aberration control function for intentionally generating an aberration, or including an aberration control surface having an aberration control function. Since the PSF is spread over two or more pixels, the MTF characteristic for defocus is formed as a depth extension optical system having two or more peaks in the main image plane shift region that is not falsely resolved at a predetermined frequency. The following effects can be obtained.

In this embodiment, by using the aberration control function to have a plurality of two or more peaks in the MTF characteristic for defocus, a general optical without an aberration control element while suppressing a decrease in peak value. Can extend the depth more than the system.
That is, according to the present embodiment, by appropriately controlling the spherical aberration, the depth can be expanded without performing the image restoration process, and a good image with appropriate image quality and less influence of noise is obtained. It becomes possible.

The imaging apparatus 200 according to the present embodiment can be used in an optical system that requires consideration for the small size, light weight, and cost of consumer devices such as digital cameras and camcorders.
In addition, the configuration of the aberration control optical system 210 can be simplified, manufacturing becomes easy, and cost reduction can be achieved.

  In addition to the digital still camera, the electronic apparatus to which the imaging apparatus 200 according to this embodiment can be applied includes an information reading device, a video camera, a digital video unit, a personal computer, a mobile phone, a PDA, an image inspection device, an automatic It can be applied to industrial cameras for control.

  DESCRIPTION OF SYMBOLS 200 ... Imaging device, 210 ... Aberration control optical system, 211 ... 1st lens, 212 ... 2nd lens, 213 ... 3rd lens, 213a ... Aberration control surface, 214, 214b: Variable aperture, 215: Fourth lens, 216: Fifth lens, 217: Externally dependent aberration control element, 217a: Liquid crystal element (liquid crystal lens), 220: Imaging Elements 230... Analog front end unit (AFE) 240... Image processing device 250... Camera signal processing unit 280. Image plane shift area.

Claims (8)

An aberration control optical system including an aberration control unit having an aberration control function for generating spherical aberration;
A variable aperture that forms a substantially circular aperture around the optical axis to limit the light flux that passes through the aberration control optical system, and the aperture is variable;
An imaging element that images the subject image that has passed through the aberration control optical system and the variable aperture;
The aberration control unit is
An imaging apparatus in which the generated aberration is rotationally symmetric about an optical axis and has at least one inflection point of the spherical aberration. The variable aperture is
The imaging apparatus according to claim 1, wherein the imaging device includes a plurality of wings, and the aperture is varied by making the wings movable. The variable aperture is
The imaging apparatus according to claim 1, wherein the imaging device is configured by a liquid crystal element, and the aperture is varied by changing a passage portion and a light shielding portion of the light flux. The aberration control unit is
The imaging apparatus according to claim 1, wherein the imaging device has an inflection point of the spherical aberration within the aperture regardless of the aperture of the variable aperture. The aberration control optical system is
The imaging apparatus according to claim 1, wherein an aberration control unit having the aberration control function is disposed adjacent to the diaphragm. The aberration control unit is
The imaging apparatus according to claim 1, further comprising a function of expanding a depth by generating spherical aberration. The imaging according to any one of claims 1 to 6, further comprising an image processing unit that performs image processing on an image signal obtained by the imaging element and improves an image characteristic that is deteriorated due to an aberration of the aberration control optical system. apparatus. Having an imaging device;
The imaging device
An aberration control optical system including an aberration control unit having an aberration control function for generating spherical aberration;
A variable aperture that forms a substantially circular aperture around the optical axis to limit the light flux that passes through the aberration control optical system, and the aperture is variable;
An imaging element that images the subject image that has passed through the aberration control optical system and the variable aperture;
The aberration control unit is
An electronic apparatus in which the generated aberration is rotationally symmetric about an optical axis and has at least one inflection point of the spherical aberration.

Images