JP2014021313A - Optical system and image capturing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical system suitable for enhancing image quality over an entire range of object distance and for reducing size.SOLUTION: When image recovery processing is applied to an image, produced by having an image sensor capture an object image formed by an optical system, by using an image recovery filter having filter values corresponding to aberration of the optical system, the optical system satisfies: 1<|Δyum+Δylm|/|Δyui+Δyli|<12 and 2<|(Δyum+Δylm)|/2 p<6. Δyum represents an amount of lateral aberration of the d-ray in a 70% upper light flux that reaches an 80% image height when focused at an intermediate object distance, Δylm represents an amount of lateral aberration of the d-ray in a 70% lower light flux that reaches the 80% image height when focused at the intermediate object distance, Δyui represents an amount of lateral aberration of the d-ray in the 70% upper light flux that reaches the 80% image height when focused at an infinite object distance, Δyli represents an amount of lateral aberration of the d-ray in the 70% lower light flux that reaches the 80% image height when focused at the infinite object distance, and P represents a pixel pitch of the image sensor.

Description

  The present invention relates to an optical system used in an imaging apparatus such as a digital still camera or a video camera, and more particularly to an optical system suitable for an image restoration process performed on an image generated by imaging.

  An image obtained by imaging a subject with an imaging device such as a digital camera has image degradation caused by spherical aberration, coma aberration, field curvature, astigmatism, etc. of the photographing optical system (hereinafter simply referred to as an optical system). A blur component is included as a component. Such a blur component is generated when a light beam emitted from one point of a subject to be collected again at one point on the imaging surface when an aberration is not caused and there is no influence of diffraction is formed by forming an image with a certain spread.

  The blur component here is optically represented by a point spread function (PSF), and is different from blur due to focus shift. In addition, color bleeding in a color image can also be said to be a difference in blurring for each wavelength of light with respect to axial chromatic aberration, chromatic spherical aberration, and chromatic coma aberration of the optical system. Further, the lateral color misregistration can be said to be a positional misalignment or a phase misalignment due to a difference in imaging magnification for each wavelength of light when the lateral chromatic aberration is caused by the optical system.

An optical transfer function (OTF) obtained by Fourier transforming the point spread function (PSF) is frequency component information of aberration and is represented by a complex number. The absolute value of the optical transfer function (OTF), that is, the amplitude component is called MTF (Modulation Transfer Function), and the phase component is called PTF (Phase Transfer Function). MTF and PTF are frequency characteristics of an amplitude component and a phase component of image degradation due to aberration, respectively. Here, the phase component is expressed as the phase angle by the following formula. Re (OTF) and Im (OTF) represent the real part and the imaginary part of the OTF, respectively.
PTF = tan ⁻¹ (Im (OTF) / Re (OTF))
As described above, since the optical transfer function (OTF) of the optical system deteriorates the amplitude component and the phase component of the image, each point of the subject becomes asymmetrically blurred like coma aberration in the deteriorated image. .

  In addition, lateral chromatic aberration is generated by acquiring, for each color component, an image for each color component whose imaging position is shifted due to a difference in imaging magnification for each wavelength of light, according to the spectral characteristics of the imaging device. At this time, not only the image formation position is shifted between the color components such as RGB, but also the image formation position shift for each wavelength, that is, the spread of the image due to the phase shift occurs in each color component. For this reason, the chromatic aberration of magnification is not simply a color shift of a parallel shift, but in this specification, the color shift is described as being the same as the chromatic aberration of magnification.

  As a method for correcting the deterioration of the amplitude component (MTF) and the deterioration of the phase component (PTF) in the deteriorated image (input image), a method using information on the optical transfer function of the optical system is known. This method is also called image restoration or image restoration. Hereinafter, processing for correcting (reducing) a deteriorated image using information of the optical transfer function of the optical system is referred to as image restoration processing (or simply restoration processing). . As will be described in detail later, as one of image restoration processing methods, a convolution method is known in which a real-space image restoration filter having an inverse characteristic of the optical transfer function is convoluted with an input image (convolution). Patent Document 1). Patent Document 2 discloses a method for performing image processing (image restoration) while retaining a filter coefficient for correcting image degradation.

  Further, in Patent Document 3, spherical aberration is generated to obtain a desired resolution (MTF width) in order to perform good image recovery even for images obtained by imaging subjects with different object distances. A method is disclosed.

JP 2005-509333 A JP 2010-56992 A JP 2011-028166 A

  In general, it is difficult to reduce the variation of the aberration of the optical system due to the object distance. For this reason, if importance is placed on the performance in a state in which the object distance is infinite, the aberration in the state in which the object distance is in focus tends to deteriorate.

  On the other hand, if it is assumed that image restoration is performed, a certain amount of aberration of the optical system can be allowed, and as a result, it is possible to easily improve the image quality over the entire object distance of the optical system. . In addition, in order to reduce the size of the optical system, it is possible to reduce the size of the optical system by correcting image degradation due to aberration caused by increasing the refractive power of each lens group constituting the optical system by image restoration. You can also

  However, if the image restoration strength is too high, the noise component contained in the deteriorated image is emphasized. Further, if the allowable amount of aberration of the optical system is too large, image deterioration cannot be sufficiently corrected even if image restoration is performed. For example, if the curvature of field is too large among the aberrations, the image plane will fall on the image sensor due to manufacturing errors of the lenses that make up the optical system or the image sensor will fall, and the "single blur" is an asymmetry in resolution Becomes prominent. In this case, even if image restoration is performed, blurring cannot be corrected satisfactorily.

  Therefore, in order to realize high image quality and miniaturization over the entire object distance of the optical system on the premise of image restoration, it is necessary to consider how to generate aberrations suitable for image restoration. Patent Documents 1 to 3 do not describe any aberration of the optical system suitable for such image restoration. In Patent Document 3, spherical aberration is generated to obtain a desired MTF width, while the resolution is greatly deteriorated in the meridional direction and the sagittal direction on the MTF peak image plane. For this reason, it is necessary to increase the gain of image restoration. As a result, noise increases and it is difficult to obtain good image quality.

  The present invention is based on the premise of performing image restoration, an optical system suitable for high image quality and miniaturization over the entire object distance, and imaging that performs image restoration on an image obtained by imaging using the optical system Providing equipment.

The optical system according to one aspect of the present invention is capable of focus adjustment, and according to the aberration of the optical system with respect to an image generated by imaging an object image formed by the optical system with an imaging device. When image restoration processing is performed using an image restoration filter having a filter value, the following condition is satisfied.
1 <| Δyum + Δylm | / | Δyui + Δyli | <12
2 <| (Δyum + Δylm) | / 2p <6
However, an image height of 80% of the maximum image height of the optical system is set to 80% image height, and an upper line and an underline passing through a position of 70% of the effective light beam diameter among meridional rays passing through the optical system are 70% respectively. When overline and 70% underline,
Δyum is the amount of lateral aberration of the d-line in the 70% upper line that reaches 80% image height in the focused state with respect to the intermediate object distance.
Δylm is the amount of lateral aberration of the d-line among the 70% underline that reaches 80% image height in the focused state with respect to the intermediate object distance.
Δyui is the amount of lateral aberration of the d-line among the 70% upper line that reaches 80% image height in the focused state with respect to the object distance at infinity,
Δyli is the lateral aberration amount of the d-line among the 70% underline that reaches 80% image height in the focused state with respect to the object distance at infinity,
P is the pixel pitch of the image sensor,
The intermediate object distance is
(Focal distance of the entire optical system / diagonal length of the image sensor) × 520
It is.

  An image sensor that captures an object image formed by the optical system and an output from the image sensor are generated, and the image has a filter value corresponding to the aberration of the optical system. An imaging apparatus having an image processing unit that performs image restoration processing using an image restoration filter also constitutes another aspect of the present invention.

  According to the present invention, it is possible to realize an optical system capable of improving image quality and downsizing over the entire object distance while generating aberrations suitable for image restoration. In addition, a small-sized imaging device capable of obtaining a high-quality image can be realized by performing imaging and image restoration processing using this optical system.

1 is a cross-sectional view at the wide-angle end of an optical system that is Embodiment 1 (Numerical Example 1) of the present invention. FIG. 4 is a longitudinal aberration diagram in a focused state with respect to an infinite object distance at the wide-angle end and an intermediate focal length of the optical system of Example 1. FIG. 6 is a longitudinal aberration diagram and a lateral aberration diagram in a focused state with respect to an infinite object distance at the telephoto end of the optical system of Example 1. FIG. 6 is a longitudinal aberration diagram and a lateral aberration diagram in a focused state with respect to the closest object distance at the telephoto end of the optical system of Example 1. FIG. 6 is a longitudinal aberration diagram and a lateral aberration diagram in a focused state with respect to an intermediate object distance at the telephoto end of the optical system of Example 1. Sectional drawing in the wide angle end of the optical system which is Example 2 (numerical example 2) of this invention. FIG. 7 is a longitudinal aberration diagram in a focused state with respect to an infinite object distance at the wide-angle end and the telephoto end of the optical system according to Example 2. FIG. 10 is a longitudinal aberration diagram and a lateral aberration diagram in a focused state with respect to an infinite object distance at an intermediate focal length of the optical system of Example 2. FIG. 6 is a longitudinal aberration diagram and a lateral aberration diagram in a focused state with respect to the closest object distance at an intermediate focal length of the optical system of Example 2. FIG. 10 is a longitudinal aberration diagram and a lateral aberration diagram in a focused state with respect to an intermediate object distance at an intermediate focal length of the optical system of Example 2. Sectional drawing in the wide angle end of the optical system which is Example 3 (numerical example 3) of this invention. FIG. 10 is a longitudinal aberration diagram in a focused state with respect to an infinite object distance at the wide-angle end and intermediate focal length of the optical system according to Example 3. FIG. 10 is a longitudinal aberration diagram and a lateral aberration diagram in a focused state with respect to an infinite object distance at the telephoto end of the optical system of Example 3. FIG. 10 is a longitudinal aberration diagram and a lateral aberration diagram in a focused state with respect to the closest object distance at the telephoto end of the optical system of Example 3. FIG. 7 is a longitudinal aberration diagram and a lateral aberration diagram in a focused state with respect to an intermediate object distance at the telephoto end of the optical system of Example 3. The figure explaining the image restoration filter used in the image restoration process which the optical system of each Example presupposes. The figure explaining correction | amendment of the point image by the said image restoration process. The figure explaining the correction | amendment of the amplitude and phase by the said image restoration process. The lateral aberration figure which shows how to generate the aberration on the assumption of the image restoration process in each example. FIG. 2 is a block diagram illustrating a configuration of an imaging apparatus including an optical system according to each embodiment.

  Embodiments of the present invention will be described below with reference to the drawings.

First, prior to description of specific embodiments, definitions of terms used in each embodiment and image restoration processing will be described.
"Input image"
The input image is a digital image generated by using an output from an imaging element obtained by photoelectrically converting a subject image formed by a photographing optical system in the imaging apparatus. This digital image is an image deteriorated in accordance with an optical transfer function (OTF) including aberration information of a photographing optical system constituted by an optical element such as a lens or an optical filter. The imaging element is configured by a photoelectric conversion element such as a CMOS or CCD. The photographing optical system may include a mirror (reflection surface) having a curvature. Further, the photographing optical system may be detachable (exchangeable) with respect to the imaging device. In the imaging apparatus, an imaging system is configured by an imaging device and a signal processing circuit that generates a digital image (input image) using an output of the imaging device.

  The color component of the input image has, for example, information on RGB color components. For handling color components, other commonly used color spaces such as brightness, hue and saturation expressed in LCH, and luminance and color difference signals expressed in YCbCr can be selected and used. . As other color spaces, for example, XYZ, Lab, Yuv, JCh can be used, and color temperature can also be used.

The input image or the recovered image (output image) includes a shooting state (in other words, a state of a focal length, an aperture value, a focused subject distance (object distance), etc., at the time of shooting that generated the input image. Shooting state information as information indicating (shooting conditions) can be attached. Various correction information for correcting the input image can also be attached. When an input image is output from an imaging device to an image processing device provided separately and image restoration processing is performed by the image processing device, shooting state information and correction information may be attached to the input image. preferable. In addition to being attached to the input image, the shooting state information and the correction information can be directly or indirectly transferred from the imaging apparatus to the image processing apparatus by communication.
"Image recovery processing"
An input image (degraded image) generated by imaging by an imaging device is g (x, y), an original undegraded image is f (x, y), and is a Fourier pair of an optical transfer function (OTF). When the point spread function (PSF) is h (x, y), the following equation is established. * Indicates convolution (convolution integration or sum of products), and (x, y) indicates coordinates (position) on the input image.
g (x, y) = h (x, y) * f (x, y)
When this equation is Fourier transformed into a display format on the frequency plane, it becomes a product format for each frequency as shown in the following equation. H is a Fourier transform of the point spread function (PSF) h and corresponds to the optical transfer function (OTF). G and F are Fourier transforms of g and f, respectively. (U, v) indicates the coordinates on the two-dimensional frequency plane, that is, the frequency.
G (u, v) = H (u, v) · F (u, v)
In order to obtain the original image from the deteriorated image generated by imaging, both sides of the above equation may be divided by H as follows.
G (u, v) / H (u, v) = F (u, v)
F (u, v), that is, G (u, v) / H (u, v) is subjected to inverse Fourier transform to return to the actual surface, whereby a restored image that is the original image f (x, y) is obtained. .

Here, when R is a result of inverse Fourier transform of H ⁻¹ , the original image f (x, y) is similarly obtained by performing convolution processing on the actual image as in the following equation. A recovered image can be obtained.
g (x, y) * R (x, y) = f (x, y)
This R (x, y) is an image restoration filter. When the input image is two-dimensional, generally the image restoration filter is also a two-dimensional filter having taps (cells) corresponding to the respective pixels of the two-dimensional image. In general, as the number of taps (cells) of the image restoration filter increases, the image restoration accuracy improves. Therefore, depending on the required image quality as an output image, image processing capability as an image processing device, aberration characteristics of the photographing optical system, etc. Set the number of taps that can be realized.

  Since the image restoration filter needs to reflect at least aberration characteristics, the image restoration filter is completely different from a conventional edge enhancement filter (high-pass filter) of about 3 taps each in horizontal and vertical directions. In addition, the image restoration filter is generated based on the optical transfer function (OTF) including aberration information of the photographing optical system, so that both the amplitude component and the phase component in the deteriorated image (input image) are accurately corrected. can do.

  In addition, the actual input image includes a noise component. For this reason, when an image restoration filter created by taking the perfect reciprocal of the optical transfer function (OTF) as described above is used, not only the degraded image is restored, but also the noise component is greatly amplified. This is because the MTF is raised so that the MTF (amplitude component) of the imaging optical system is returned to 1 over the entire frequency when the amplitude of noise is added to the amplitude component of the input image. MTF, which is amplitude degradation due to the photographing optical system, returns to 1, but the power spectrum of the noise component also rises at the same time. As a result, noise is amplified according to the degree to which the MTF is raised, that is, the recovery gain.

Therefore, when there is noise, a good image cannot be obtained as a viewing image. This can be expressed as follows: N represents a noise component.
G (u, v) = H (u, v) .F (u, v) + N (u, v)
G (u, v) / H (u, v) = F (u, v) + N (u, v) / H (u, v)
With respect to this point, for example, a method of controlling the degree of recovery according to the intensity ratio (SNR) of the image signal and the noise signal as in the Wiener filter shown in Expression (1) is known.

  M (u, v) represents the frequency characteristic of the Wiener filter, and | H (u, v) | represents the absolute value (MTF) of the optical transfer function (OTF). In this method, for each frequency, the recovery gain is suppressed as the MTF is small, and the recovery gain is increased as the MTF is large. In general, since the MTF of the photographing optical system is high on the low frequency side and low on the high frequency side, this is a method of substantially suppressing the recovery gain on the high frequency side of the image signal.

  The image restoration filter will be described with reference to FIG. The number of taps of the image restoration filter is determined according to the aberration characteristics of the photographing optical system and the required image restoration accuracy.

  In FIG. 16A, an 11 × 11 tap two-dimensional image restoration filter is shown as an example. In FIG. 16A, values (coefficient values) in each tap are omitted, but one cross section of this image restoration filter is shown in FIG. A value in each tap of the image restoration filter shown in FIG. 16B is set based on information on various aberrations of the photographing optical system described above. The distribution of the tap values of the image restoration filter serves to return the signal value (PSF) spatially spread by the aberration to an original one point ideally.

  In the image restoration process, the value of each tap of the image restoration filter is convolved (also referred to as convolution integration or product sum) with respect to each pixel corresponding to each tap in the input image. In the convolution process, in order to improve the signal value of a certain pixel, the pixel is matched with the center of the image restoration filter. Then, the product of the signal value of the input image and the tap value (coefficient value) of the image restoration filter is taken for each corresponding pixel of the input image and the image restoration filter, and the sum is replaced with the signal value of the central pixel.

  The characteristics of the image restoration processing in the real space and the frequency space will be described with reference to FIGS. 17 and 18. In FIG. 17, (a) shows the PSF before image restoration, and (b) shows the PSF after image restoration. Further, (a) in (M) of FIG. 18 shows the MTF before image restoration, and (b) in (M) shows the MTF after image restoration. Further, (a) in FIG. 18 (P) shows the PTF before image restoration, and (b) in (P) shows the PTF after image restoration. The PSF before image restoration has an asymmetric spread, and due to this asymmetry, the PTF has a non-linear value with respect to the frequency. Since the image restoration process amplifies the MTF and corrects the PTF to zero, the PSF after the image restoration is symmetrical and sharp.

  The image restoration filter can be created by inverse Fourier transform of a function designed based on the inverse function of the optical transfer function (OTF) of the photographing optical system. For example, when a Wiener filter is used, a real space image restoration filter that is actually convolved with the input image can be created by performing inverse Fourier transform on Equation (1).

  Also, since the optical transfer function (OTF) changes according to the image height (position on the image) of the imaging optical system even under the same imaging conditions, the image restoration filter is changed and used according to the image height. Is done.

  In the following, an optical system capable of adjusting the focus (photographing optics), which has been provided with high image quality and miniaturization over the entire object distance by giving aberration that causes image degradation suitable for correction by the above-described image restoration processing. Specific examples of the system will be described as Examples 1 to 3 (Numerical Examples 1 to 3).

  1, 6, 11, and 11 show cross sections at the wide-angle end of the optical systems of Examples 1 to 3. FIG. The arrows described below each group (L1 to L6, SP) in the figure indicate the movement of each group from the wide-angle end to the telephoto end. All of the optical systems of Examples 1 to 3 are zoom lenses capable of zooming. However, even if zooming is not possible, the focus lens group is moved to bring the focusing surface and the imaging surface (sensor surface). Any other embodiment of the present invention can be used as long as it is a single-focus optical system that can be matched with each other.

  FIGS. 2A and 2B are longitudinal aberration diagrams in a focused state with respect to the infinity object distance (infinity end) at the wide-angle end and the intermediate focal length of the optical system of Example 1, respectively. . FIGS. 3A and 3B show longitudinal aberration diagrams and lateral aberration diagrams in a focused state with respect to an infinite object distance at the telephoto end of the optical system of Example 1, respectively. The longitudinal aberration diagram shows spherical aberration, astigmatism, distortion and lateral chromatic aberration. The lateral aberration diagram shows the lateral aberration at the center of the screen and the lateral aberration at 80% image height (which will be described later). FIGS. 4A and 4B are longitudinal aberration diagrams and lateral aberration diagrams in a focused state with respect to the closest object distance (closest end) at the telephoto end of the optical system of Example 1, respectively. ing. Further, FIGS. 5A and 5B show a longitudinal aberration diagram and a lateral aberration diagram in a focused state with respect to the intermediate object distance at the telephoto end of the optical system of Example 1, respectively.

  FIGS. 7A and 7B are longitudinal aberration diagrams in a focused state with respect to an infinite object distance at the wide-angle end and the telephoto end of the optical system of Example 2, respectively. FIGS. 8A and 8B show a longitudinal aberration diagram and a lateral aberration diagram in a focused state with respect to an object distance at infinity at the intermediate focal length of the optical system of Example 2, respectively. FIGS. 9A and 9B show a longitudinal aberration diagram and a lateral aberration diagram in a focused state with respect to the closest object distance at the intermediate focal length of the optical system of Example 2, respectively. Further, FIGS. 10A and 10B show a longitudinal aberration diagram and a lateral aberration diagram in a focused state with respect to the intermediate object distance at the intermediate focal length of the optical system of Example 2, respectively.

  FIGS. 12A and 12B are longitudinal aberration diagrams in a focused state with respect to an infinite object distance at the wide-angle end and the intermediate focal length of the optical system of Example 3, respectively. FIGS. 13A and 13B show a longitudinal aberration diagram and a lateral aberration diagram in a focused state with respect to an infinite object distance at the telephoto end of the optical system of Example 3, respectively. FIGS. 14A and 14B show a longitudinal aberration diagram and a lateral aberration diagram in a focused state with respect to the closest object distance at the telephoto end of the optical system of Example 3, respectively. Further, FIGS. 15A and 15B show a longitudinal aberration diagram and a lateral aberration diagram in a focused state with respect to the intermediate object distance at the telephoto end of the optical system of Example 3, respectively.

  In the cross-sectional views of the zoom lenses, L1 to L6 indicate first to sixth lens groups, respectively. GB indicates a glass block such as an optical filter or a color separation prism, and SP indicates an aperture stop. IP indicates an image plane.

  In each aberration diagram, d and g indicate aberrations of d-line and g-line, respectively. ΔM and ΔS indicate aberrations on the meridional image surface and the sagittal image surface, respectively. Further, in the lateral aberration diagram, S indicates the sagittal ray aberration, and M indicates the meridional ray aberration. The lateral chromatic aberration is indicated by the g-line.

The optical system (lens as a photographing optical system) of each embodiment is a filter corresponding to the aberration of the optical system with respect to an image generated by imaging an object image formed by the optical system with an imaging device. It is assumed that image restoration processing is performed using an image restoration filter having a value. In this case, the optical system of each example satisfies both the following conditions (1) and (2). In the conditions (1) and (2), the image height is 80% of the maximum image height of the optical system, in other words, the sensor size that is the size of the image sensor from the center of the image sensor (screen) toward the periphery. The image height corresponding to 80% of the image is 80% image height. In addition, an upper line and an underline passing through 70% of the effective light beam diameter of the meridional ray passing through the optical system are defined as a 70% upper line and a 70% underline, respectively.
1 <| Δyum + Δylm | / | Δyui + Δyli | <12 (1)
2 <| (Δyum + Δylm) | / 2p <6 (2)
However,
Δyum is the amount of lateral aberration of the d-line in the 70% upper line that reaches 80% image height in the focused state with respect to the intermediate object distance.
Δylm is the amount of lateral aberration of the d-line among the 70% underline that reaches 80% image height in the focused state with respect to the intermediate object distance.
Δyui is the amount of lateral aberration of the d-line among the 70% upper line that reaches 80% image height in the focused state with respect to the object distance at infinity,
Δyli is the lateral aberration amount of the d-line among the 70% underline that reaches 80% image height in the focused state with respect to the object distance at infinity,
P is the pixel pitch of the image sensor.

The intermediate object distance is
(Focal distance of the entire optical system / diagonal length of the image sensor) × 520
It is. Strictly speaking, the diagonal length of the imaging element means the diagonal length of the effective imaging area of the imaging element.

  Conditions (1) and (2) are based on the premise that image restoration is performed, and high image quality is obtained in the entire object distance (infinite object distance to nearest object distance), and a small optical system is realized. It is a condition.

  When the object distance changes, the focal plane deviates from the position of the image sensor (hereinafter also referred to as the sensor position), so it is common to move the focus lens group so that the focal plane coincides with the sensor position. . However, when the focus lens group is moved, the relative relationship between the focus lens group and the other lens groups changes, so that the aberration variation when the object distance changes increases. In particular, the variation in field curvature increases. In addition, since the spherical aberration and the field curvature shift while the focus lens group moves from the in-focus position for the object distance to the in-focus position for the closest object, the focal planes on and off the axis are different. As a result, the image quality at the sensor position deteriorates.

  The variation in curvature of field at the time of changing the object distance has a relationship that when the curvature of field at an object distance is optically corrected, the curvature of field at other object distances deteriorates. For this reason, in an optical system that does not assume the conventional image restoration, in order to improve the optical performance over the entire object distance, the variation in the field curvature accompanying the change in the object distance remains, and the object There is a design that balances the entire distance.

  In an optical system in which such image plane fluctuations remain, it is possible to correct curvature of field associated with a change in object distance by intentionally generating coma. FIG. 19A shows a representative lateral aberration diagram from the in-focus state for the object distance at infinity to the in-focus state for the closest end. In the lateral aberration at the center of the screen in this figure, since the spherical aberration is smaller than that of a general optical system, the image plane on which the MTF peaks on the axis (hereinafter referred to as the MTF peak image plane) is the focal plane. Almost matches.

  On the other hand, at 80% image height, the meridional image plane is over, and the off-axis MTF peak image plane is shifted from the on-axis MTF peak image plane. This is because the underline of the meridional ray is generated in the minus direction. For this reason, as shown in FIG. 19 (B), it is possible to improve the over tendency of the entire meridional image plane by generating an upward line of the meridional ray in the minus direction.

  And coma aberration deteriorates and resolution deteriorates along with improvement in field curvature fluctuation, but by correcting resolution degradation by image recovery, good image quality is achieved while improving field curvature fluctuation. can do.

  As described above, it is possible to achieve an optical system in which the curvature of field at the time of change in the object distance is corrected by correcting image degradation caused by coma aberration by image restoration.

  Condition (1) limits the ratio of the amount of coma aberration generated between the in-focus state for the intermediate object distance and the in-focus state for the object distance at infinity. When the value of the condition (1) exceeds the upper limit, coma is excessively generated in a focused state with respect to the intermediate object distance, and the image is significantly deteriorated. Further, if the value of the condition (1) is less than the lower limit, the coma aberration in the focused state with respect to the intermediate object distance is small, and it becomes difficult to correct the variation in field curvature due to the change in the object distance. It is not preferable.

It is more desirable to set the range of the condition (1) as follows.
1 <| Δyum + Δylm | / | Δyui + Δyli | <10 (1) ′
Condition (2) is a condition regarding the image quality of the optical system. If the value of condition (2) is less than the lower limit, the amount of coma is small, and it is difficult to correct fluctuations in field curvature accompanying changes in object distance, which is not preferable. On the other hand, when the value of the condition (2) exceeds the upper limit, the coma generated is too large, and the image before the image restoration process is significantly deteriorated. Therefore, even if the image restoration process is performed, a good restored image cannot be obtained, or as a result of extremely strengthening the image restoration, an image with enhanced noise is obtained.
It is more desirable to set the range of the condition (2) as follows.
2 <| (Δyum + Δylm) | / 2p <5 (2) ′
As described above, in this embodiment, the intermediate object distance is
(Focal distance of the entire optical system / diagonal length of the image sensor) × 520
And When the object distance exceeds the intermediate object distance, for example, the focal length of the entire optical system becomes larger than the diagonal length of the image sensor used in the third embodiment. At this time, the intermediate object distance increases and becomes close to an infinite object distance. For this reason, it becomes difficult to reduce the fluctuation of the field curvature accompanying the change in the object distance. If the intermediate object distance is less than this, the focal length of the entire optical system becomes small with respect to the diagonal length of the image sensor used in the first and second embodiments. At this time, the intermediate object distance becomes small and close to the nearest edge distance. For this reason, it becomes difficult to reduce the fluctuation of the field curvature accompanying the change in the object distance.

  The conventional optical system is not designed in consideration of how to generate coma aberration suitable for image restoration unlike the optical systems of the embodiments. In other words, the conventional zoom lens is not premised on performing image restoration, and even if the condition (1) or (2) is satisfied in a part of the intermediate region of the object distance, This is an optical system whose optical performance cannot be corrected.

  Each of the optical systems of Examples 1 to 3 includes, in order from the object side, a first lens unit L1 having a positive refractive power and a second lens unit L2 having a negative refractive power.

  FIG. 20 illustrates an imaging apparatus 10 that performs imaging using the optical system of each of the above-described embodiments as the imaging optical system 11. Reference numeral 12 denotes an image sensor, which is disposed at the position of the image plane IP shown in the sectional view of each zoom lens. An image processing unit 13 generates an image (input image) by performing various types of image processing on the output from the image sensor 12, and further performs image restoration processing on the image. Reference numeral 14 denotes a display / recording unit, which displays an image (recovered image) that has undergone image restoration processing by the image processing unit 13 on a monitor or records it on a recording medium such as a semiconductor memory.

  Hereinafter, specific numerical examples of each embodiment will be described.

  The optical system of Example 1 (Numerical Example 1) illustrated in FIG. 1 includes, in order from the object side, a positive first lens unit L1, a negative second lens unit L2, a positive third lens unit L3, and a negative fourth lens unit. The lens unit L4 includes a positive fifth lens unit L5, a negative sixth lens unit L6, and a glass block GB. An aperture stop SP is disposed closest to the image side in the third lens unit L3. In Example 1, the maximum image height is 21.635 mm. A full-size (24 mm × 36 mm) image sensor is arranged on the image plane IP. The pixel pitch of this image sensor is 6.4 μm.

  As can be seen from the longitudinal aberration diagrams in the in-focus state with respect to the object distance at infinity at the wide-angle end and the intermediate focal length shown in FIGS. 2A and 2B, the aberration is well corrected. Further, as can be seen from the lateral aberration diagrams in the focused state at the infinity end, the close end, and the intermediate object distance at the telephoto end shown in FIGS. 3 (B), 4 (B) and 5 (B), By producing coma aberration, the variation in field curvature over the entire object distance at the telephoto end is reduced.

The numerical values of Example 1 are shown below. ri (i = 1, 2, 3,...) indicates the radius of curvature of the i-th lens surface counted from the object side, and di indicates the i-th lens thickness or air interval. Ndi and νdi indicate the refractive index and Abbe number of the i-th lens material for the d-line. When the lens surface has an aspherical shape, the aspherical shape is a position in a direction orthogonal to the optical axis, where R is the radius of curvature of the central portion of the lens surface, X is the position (coordinates) in the optical axis direction. Let (coordinates) be Y and aspherical coefficients be Ai (i = 1, 2, 3,...)
X = (Y ² / R) / [1+ {1− (K + 1) (Y / R) ² } ^1/2 ]
+ A4Y ⁴ + A6Y ⁶ + A8Y ⁸ + A10Y ¹⁰ +...
It shall be represented by the following formula. e ± M means × 10 ^{± M.} Table 1 shows the relationship between Example 1 and the above-described conditions.
(Numerical example 1)
Unit mm
Surface data surface number rd nd νd Effective diameter
1 95.784 6.02 1.48749 70.2 56.00
2 737.461 0.18 55.50
3 102.717 2.10 1.61340 44.3 53.80
4 45.455 9.10 1.49700 81.5 50.97
5 2528.799 (variable) 50.29
6 -165.094 1.20 1.83481 42.7 25.20
7 55.232 3.29 24.32
8 -45.986 1.20 1.63854 55.4 24.28
9 53.394 2.97 1.84666 23.8 24.72
10 -414.048 (variable) 25.00
11 344.048 4.25 1.49700 81.5 25.60
12 -42.005 0.15 25.76
13 66.804 4.35 1.58913 61.1 25.41
14 -42.512 1.20 1.85026 32.3 25.09
15 -264.354 1.00 24.86
16 (Aperture) ∞ (Variable) 24.61
17 -48.251 1.20 1.70154 41.2 23.00
18 40.610 3.94 1.80518 25.4 23.66
19 -169.835 (variable) 23.80
20 -249.784 2.80 1.69680 55.5 25.20
21 -83.232 0.15 25.57
22 181.284 5.19 1.60311 60.6 25.75
23 -30.728 1.25 1.84666 23.8 25.66
24 -127.921 0.15 25.87
25 99.327 2.35 1.77250 49.6 25.86
26 -130.324 (variable) 25.60
27 74.930 1.20 1.88300 40.8 25.03
28 29.783 3.57 24.31
29 -112.308 2.85 1.80518 25.4 24.44
30 -31.068 4.56 24.80
31 -26.035 1.25 1.88300 40.8 24.41
32 ∞ 2.75 25.82
33 56.384 3.69 1.69895 30.1 29.16
34 967.801 (variable) 29.56
35 ∞ 1.13 1.51633 64.2 50.00
36 ∞ 0.20 50.00
37 ∞ 0.40 1.51633 64.2 50.00
38 ∞ (variable) 50.00
Image plane ∞

Various data zoom ratio 4.02
Wide-angle intermediate telephoto focal length 72.19 135.01 290.31
F number 4.28 4.75 5.94
Angle of View 16.68 9.10 4.26
Image height 21.64 21.64 21.64
Total lens length 185.42 214.97 239.40
BF 0.41 0.41 0.41

d 5 3.28 32.82 57.26
d10 25.74 13.79 1.08
d16 5.86 23.88 44.40
d19 18.36 12.28 4.46
d26 13.57 11.99 0.99
d34 42.58 44.16 55.16
d38 0.41 0.41 0.41

Entrance pupil position 46.11 111.44 201.54
Exit pupil position -91.42 -101.46 -118.76
Front principal point position 61.54 67.51 -215.38
Rear principal point position -71.79 -134.60 -289.90

Lens group data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
L1 1 130.99 17.40 0.81 -10.78
L2 6 -35.13 8.66 1.17 -5.10
L3 11 52.01 10.95 2.38 -5.00
L4 17 -141.89 5.14 -2.20 -5.16
L5 20 47.86 11.89 5.02 -2.27
L6 27 -51.14 19.87 3.63 -12.05
GB 35 ∞ 1.73 0.60 -0.60

Single lens Data lens Start surface Focal length
1 1 225.12
2 3 -134.81
3 4 93.02
4 6 -49.45
5 8 -38.51
6 9 56.02
7 11 75.60
8 13 44.76
9 14 -59.73
10 17 -31.26
11 18 41.05
12 20 177.91
13 22 43.97
14 23 -48.05
15 25 73.29
16 27 -56.69
17 29 52.52
18 31 -29.49
19 33 85.52
20 35 0.00
21 37 0.00

  The optical system of Example 2 (Numerical Example 2) illustrated in FIG. 6 includes, in order from the object side, a positive first lens unit L1, a negative second lens unit L2, a positive third lens unit L3, an aperture stop SP, The positive fourth lens unit L4 and the glass block GB are included. In Example 2, the maximum image height is 13.66 mm. An APS-C type image sensor (15.2 mm × 22.7 mm) is arranged on the image plane IP. The pixel pitch of this image sensor is 4.3 μm.

  As can be seen from the lateral aberration diagrams in the focused state at the infinity end, the close end, and the intermediate object distance at the intermediate focal length shown in FIGS. 8B, 9B, and 10B, the coma By producing aberrations, the variation in field curvature over the entire object distance at the intermediate focal length is reduced.

The numerical values of Example 2 are shown below. Table 1 shows the relationship between Example 2 and the above-described conditions.
(Numerical example 2)
Unit mm
Surface data surface number rd nd νd Effective diameter
1 219.691 1.98 1.84666 23.9 41.35
2 77.011 0.80 38.49
3 110.857 2.79 1.77250 49.6 38.45
4 -1566.128 0.29 37.69
5 57.811 3.26 1.77250 49.6 33.00
6 516.857 (variable) 31.76
7 * 1449.562 1.45 1.85400 40.4 29.52
8 * 17.597 6.32 23.53
9 -62.504 1.16 1.69100 54.8 23.28
10 79.992 0.17 23.14
11 27.282 2.67 1.94595 18.0 23.38
12 61.859 (variable) 22.95
13 * 15.625 3.02 1.85135 40.1 13.31
14 * 127.225 0.37 12.51
15 13.245 3.60 1.77250 49.6 11.81
16 2319.692 0.70 1.80518 25.4 10.32
17 8.119 1.97 8.97
18 -1265.485 1.74 1.48749 70.2 8.86
19 -42.123 0.98 8.75
20 (Aperture) ∞ (Variable) 8.53
21 ∞ (variable) 8.72
22 * 600.625 5.12 1.58313 59.4 27.51
23 * -35.796 (variable) 28.21
24 ∞ 1.21 1.51633 64.1 58.13
25 ∞ 1.51 58.13
26 ∞ 0.60 1.51633 64.1 58.13
27 ∞ (variable) 58.13
Image plane ∞

Aspheric data 7th surface
K = 7.95128e + 003 A 4 = -8.46681e-006 A 6 = 1.45376e-008
8th page
K = 3.72976e-001 A 4 = -1.13801e-005 A 6 = -4.49670e-009 A 8 = -4.98598e-010 A10 = 1.72434e-012
Side 13
K = -2.06246e-001 A 4 = -1.23394e-005 A 6 = 1.79103e-007 A 8 = -4.52541e-009 A10 = 2.60955e-011
14th page
K = -5.86105e + 001 A 4 = 8.28096e-006 A 6 = 1.05159e-007 A 8 = -2.30730e-009
22nd page
K = 1.81624e + 003 A 4 = -1.28722e-005 A 6 = 2.00678e-007 A 8 = -8.68491e-010
23rd page
K = 1.08981e + 000 A 4 = -2.12065e-005 A 6 = 2.34886e-007 A 8 = -9.22692e-010 A10 = 3.32500e-013

Various data zoom ratio 3.81
Wide-angle intermediate telephoto focal length 18.03 47.42 68.66
F number 2.88 4.57 5.94
Angle of view 33.69 15.83 11.25
Image height 12.02 13.45 13.66
Total lens length 87.58 100.81 110.99
BF 2.34 2.34 2.34

d 6 1.10 14.03 20.22
d12 23.85 6.03 0.99
d20 0.77 2.42 16.50
d21 11.46 29.23 23.11
d23 6.32 5.03 6.09
d27 2.34 2.34 2.34

Entrance pupil position 28.04 50.51 65.42
Exit pupil position -29.96 -94.15 -169.72
Front principal point position 36.01 74.62 106.68
Rear principal point position -15.69 -45.08 -66.32

Lens group data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
L1 1 81.28 9.10 3.63 -1.92
L2 7 -20.76 11.78 0.97 -8.20
L3 13 23.78 12.40 -5.10 -12.01
FC 21 ∞ 0.00 0.00 -0.00
L4 22 58.11 5.12 3.06 -0.18
GB 24 ∞ 3.32 1.35 -1.35

Single lens Data lens Start surface Focal length
1 1 -140.95
2 3 134.11
3 5 84.00
4 7 -20.87
5 9 -50.61
6 11 49.73
7 13 20.67
8 15 17.23
9 16 -10.12
10 18 89.34
11 22 58.11
12 24 0.00
13 26 0.00

  The optical system of Example 3 (Numerical Example 3) illustrated in FIG. 11 includes, in order from the object side, a positive first lens unit L1, a negative second lens unit L2, an aperture stop SP, a positive third lens unit L3, The lens includes a negative fourth lens unit L4, a positive fifth lens unit L5, and a glass block GB. In Example 3, the maximum image height is 3.875 mm. A 1 / 2.3 type (4.65 mm × 6.2 mm) imaging device is disposed on the image plane IP. The pixel pitch of this image sensor is 1.4 μm.

  As can be seen from the longitudinal aberration diagrams in the focused state with respect to the object distance at infinity at the wide-angle end and the intermediate focal length shown in FIGS. 12A and 12B, the aberration is corrected well. Further, as can be seen from the lateral aberration diagrams in the focused state at the infinity end, the close end, and the intermediate object distance at the telephoto end shown in FIGS. 13 (B), 14 (B) and 15 (B), By producing coma aberration, the variation in field curvature over the entire object distance at the telephoto end is reduced.

The numerical values of Example 3 are shown below. Table 1 shows the relationship between Example 3 and the above-described conditions.
(Numerical example 3)
Unit mm
Surface data surface number rd nd νd Effective diameter
1 112.067 1.80 1.80610 33.3 39.40
2 52.885 5.03 1.49700 81.5 35.90
3 -218.600 0.18 35.80
4 45.553 3.22 1.59282 68.6 34.70
5 131.490 (variable) 34.20
6 120.679 0.95 1.88300 40.8 19.70
7 8.615 4.92 14.10
8 -34.305 0.70 1.77250 49.6 13.90
9 28.642 0.20 13.80
10 16.947 2.30 1.92286 18.9 14.10
11 89.165 (variable) 13.80
12 (Aperture) ∞ (Variable) 6.68
13 * 9.778 4.30 1.55332 71.7 9.50
14 * -74.715 1.67 9.50
15 38.527 0.50 1.64769 33.8 9.00
16 10.092 0.37 9.00
17 13.822 0.50 1.80 400 46.6 9.00
18 8.013 2.11 1.48749 70.2 9.00
19 -31.006 (variable) 8.31
20 -564.447 0.70 1.48749 70.2 8.60
21 26.449 (variable) 8.70
22 20.740 2.25 1.78590 44.2 11.80
23 -55.591 1.26 1.94595 18.0 11.70
24 -1698.441 (variable) 11.60
25 ∞ 0.30 1.51633 64.1 20.00
26 ∞ 0.47 20.00
27 ∞ 0.50 1.51633 64.1 20.00
28 ∞ (variable) 20.00
Image plane ∞

Aspherical data 13th surface
K = -5.29634e-001 A 4 = -2.26010e-005 A 6 = 1.07748e-007 A 8 = -2.96223e-008 A10 = 7.23156e-010
14th page
K = -2.41360e + 002 A 4 = -2.87477e-005 A 6 = 3.05881e-007

Various data zoom ratio 33.54
Wide-angle intermediate telephoto focal length 4.42 12.77 148.25
F number 2.70 4.26 5.03
Angle of view 37.01 16.88 1.50
Image height 3.33 3.88 3.88
Total lens length 94.78 94.62 138.53
BF 0.53 0.53 0.53

d 5 0.92 17.42 62.79
d11 31.72 17.57 1.27
d12 12.69 0.50 3.21
d19 2.68 3.23 2.48
d21 3.22 5.67 24.20
d24 8.78 15.48 9.83
d28 0.53 0.53 0.53

Entrance pupil position 18.62 47.44 564.42
Exit pupil position -5771.10 -49.53 129.32
Front principal point position 23.04 56.95 883.31
Rear principal point position -3.89 -12.24 -147.72

Lens group data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
L1 1 82.06 10.23 2.82 -3.76
L2 6 -9.87 9.07 0.74 -6.39
SP 12 ∞ 0.00 0.00 -0.00
L3 13 18.85 9.45 -0.20 -7.09
L4 20 -51.81 0.70 0.45 -0.02
L5 22 28.04 3.51 -0.07 -1.98
GB 25 ∞ 1.27 0.50 -0.50

Single lens Data lens Start surface Focal length
1 1 -125.94
2 2 86.21
3 4 115.95
4 6 -10.55
5 8 -20.11
6 10 22.33
7 13 15.92
8 15 -21.26
9 17 -24.66
10 18 13.30
11 20 -51.81
12 22 19.47
13 23 -60.78
14 25 0.00
15 27 0.00

  Each embodiment described above is only a representative example, and various modifications and changes can be made to each embodiment in carrying out the present invention.

  It is possible to provide an optical system and an imaging apparatus that can achieve high image quality and downsizing over the entire object distance.

L1 First lens group L2 Second lens group IP Image plane (imaging device)

Claims (3)

An optical system capable of focusing,
When image restoration processing is performed on an image generated by imaging an object image formed by the optical system using an image sensor using an image restoration filter having a filter value corresponding to the aberration of the optical system And an optical system that satisfies the following conditions:
1 <| Δyum + Δylm | / | Δyui + Δyli | <12
2 <| (Δyum + Δylm) | / 2p <6
However, an image height of 80% of the maximum image height of the optical system is set to 80% image height, and an upper line and an underline passing through a position of 70% of the effective beam diameter of meridional rays passing through the optical system are 70% respectively. When overline and 70% underline,
Δyum is the amount of lateral aberration of the d-line in the 70% upper line that reaches the 80% image height in the focused state with respect to the intermediate object distance.
Δylm is a lateral aberration amount of the d-line among the 70% underline that reaches the 80% image height in a focused state with respect to the intermediate object distance,
Δyui is the amount of lateral aberration of the d-line in the 70% upper line that reaches the 80% image height in the focused state with respect to the object distance at infinity,
Δyli is the lateral aberration amount of the d-line among the 70% underline that reaches the 80% image height in a focused state with respect to the object distance at infinity,
P is the pixel pitch of the image sensor,
The intermediate object distance is
(Focal length of the entire optical system / diagonal length of the image sensor) × 520
It is.   2. The optical system according to claim 1, further comprising a first lens group having a positive refractive power and a second lens group having a negative refractive power in order from the object side. An imaging device for imaging an object image formed by the optical system according to claim 1 or 2,
An image processing unit that generates an image using an output from the image sensor and performs an image restoration process on the image using an image restoration filter having a filter value corresponding to the aberration of the optical system. An imaging apparatus characterized by the above.