Aberration estimation device, aberration estimation method, program, and storage medium

Abstract

To estimate the aberration of an optical system accurately in a short time on the basis of a plurality of light intensity distributions.SOLUTION: An aberration estimation device has a light source unit 101 that includes a first light source and a second light source that illuminate an optical system to be inspected 102; and an estimation unit that estimates the aberration of the optical system to be inspected 102 on the basis of light intensity distributions of the first and second light sources obtained through the optical system to be inspected 102. The first and second light sources are different from each other in position in an optical axis direction of the optical system to be inspected 102 and a direction perpendicular to the optical axis direction.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an aberration estimation device, an aberration estimation method, a program, and a storage medium that estimate the aberration of an optical system using the light intensity distribution.

Background Art

[0002] In order to evaluate and guarantee the performance of optical devices, the optical systems in optical devices such as cameras and telescopes are estimated for aberration. In order to estimate the aberration of an optical system, a method is known in which light is irradiated onto the optical system, and the aberration of the optical system is estimated based on the light intensity distribution obtained through the optical system.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, a method is disclosed in which a driving device is used to drive a sensor and an optical system to obtain light intensity distributions at a plurality of defocus positions, and the aberration is obtained based on the plurality of light intensity distributions. However, in the estimation method of Patent Document 1, the longer the number of light intensity distributions acquired to improve the estimation accuracy, the longer it takes to drive the sensor and the optical system.

[0005] In view of the above problems, an object of the aberration estimation device in the present invention is to estimate the aberration of an optical system with high accuracy in a short time based on a plurality of light intensity distributions.

Means for Solving the Problems

[0006] The aberration estimation device of the present invention includes a light source unit including a first light source and a second light source that illuminate a test optical system, and an estimation unit that estimates the aberration of the test optical system based on the respective light intensity distributions of the first and second light sources obtained through the test optical system. The first and second light sources are characterized in that their positions in the optical axis direction of the test optical system and in the direction perpendicular to the optical axis direction are different from each other.

Effects of the Invention

[0007] According to the present invention, it is possible to provide an aberration estimation device and an aberration estimation method capable of estimating the aberration of an optical system with high accuracy in a short time based on a plurality of light intensity distributions.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Modes for Carrying Out the Invention

[0009] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The same members in each figure are denoted by the same reference numerals, and redundant descriptions are omitted.

[0010] FIG. 1 is a schematic diagram of an aberration estimation apparatus 100 according to the present embodiment. The aberration estimation apparatus 100 according to the present embodiment includes a light source unit 101, an image sensor 103, a computer 104, and a display unit 105, and measures (estimates) the wavefront aberration of the optical system to be measured 102.

[0011] Here, the optical system to be measured 102 may be the optical system alone to be measured, or a combination of the optical system to be measured and the image sensor 103. For example, when the object to be measured is a camera lens or a telescope, the optical system to be measured 102 is the camera lens or the telescope itself. Further, the object to be measured may be an element or device in which an optical system and an image sensor are integrated, such as a camera for a mobile phone.

[0012] The light emitted from the light source unit 101 is imaged on the image sensor 103 by the optical system to be measured 102 to form an optical image. The image sensor 103 acquires the light intensity distribution of the optical image formed by the optical system to be measured 102. The image sensor 103 is, for example, a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal-Oxide Semiconductor) sensor.

[0013] As a modification in the present embodiment, the light intensity distributions of a plurality of light sources obtained through the optical system to be measured may be acquired using the image sensor included in the measurement object. In this case, the image sensor 103 in the aberration estimation apparatus 100 is not essential. In this case, at least the computer 104 is communicably connected to the information on the light intensity distribution obtained by the image sensor included in the measurement object. Note that the communication means may be wired or wireless.

[0014] The computer 104 estimates the aberration of the optical system 102 to be inspected by performing an estimation calculation on the acquired light intensity distribution. The computer 104 includes control means for controlling the imaging device 103. The computer 104 also includes calculation means for performing an estimation calculation on the light intensity distribution acquired by the imaging device 103.

[0015] Note that the control means and the calculation means (estimation unit) may be included in one computer or may be individual devices. For example, it may be configured to execute an estimation calculation using a server existing on the cloud through a network as a calculation device. Note that the acquired light intensity distribution may be stored by the computer 104 or a data holding device (not shown). The display unit 105 is, for example, a liquid crystal display or a projector. The display unit 105 displays the acquired aberration and the like.

[0016] If necessary, the acquired aberration may be used to evaluate and adjust the optical system 102 to be inspected.

[0017] Since this embodiment can be mathematically modeled, it can be implemented as a software function of a computer system. Here, the software function of the computer system includes a programming (program) including executable code. The software code is executable on a general-purpose computer. During the operation of the software code, the code or related data records are stored within a general-purpose computer platform. However, in other cases, the software is stored elsewhere or loaded into a suitable general-purpose computer system. Therefore, the software code can be held as one or more modules in at least one machine-readable medium (storage medium).

[0018] The light source unit 101 has a plurality of light sources and illuminates the optical system 102 to be inspected. In this embodiment, the light source is preferably a point light source. A point light source is an element from which light diverges from a minute area, and for example, a member having a minute opening such as a pinhole can be used. The end of an optical fiber also functions as a point light source. It is also possible to use a minute white circle drawn on a flat base of a black body or minute luminescent paint. In this case, although there is a separate illumination source for illuminating the base, these scatterers and light emitters can be regarded as light sources.

[0019] Note that the light generation region (generation surface) in the light source does not necessarily have to be strictly a point. Since the image formed by the optical system 102 to be inspected has a spread due to diffraction limit, aberration of the optical system 102 to be inspected, etc., it is sufficient that the size of the geometric optical image of the light source is smaller than these wave-optical spreads. The specific member of the light source is not limited to the above, and any element in which light emission, scattering, and light emission occur in a minute area may be used. Also, the center of the light source in each embodiment means the center on the light emission surface.

[0020] The light source unit 101 in the aberration estimation apparatus 100 in FIG. 1 is composed of a light source (first light source) 1011, a light source (second light source) 1012, and a light source (third light source) 1013. The light sources 1012 and 1013 are different from the light source 1011 in their positions in the optical axis direction of the optical system to be inspected and in the direction perpendicular to the optical axis direction. That is, they are arranged at different object heights and different defocus positions. The light source 1011 in FIG. 1 is located on the optical axis of the optical system 102 to be inspected. At the time of measurement, it is preferable that the optical system 102 to be inspected is arranged so that the light emitted from any one of the point light sources is condensed on the imaging element (light receiving unit) 103. In other words, the light source 1011 and the imaging element 103 are in a conjugate relationship by the optical system 102 to be inspected.

[0021] Also, hereinafter, a light source that is in a conjugate relationship with the image sensor 103 by the optical system under test 102 is referred to as a reference light source, and a light source other than the reference light source is referred to as a peripheral light source. In FIG. 1, the light source 1011 that is the reference light source is located on the optical axis of the optical system under test 102, but the position of the reference light source is not limited to this. The position of the reference light source in this embodiment is preferably a point on the conjugate plane that is in a conjugate relationship with the image sensor 103 by the optical system under test 102. However, it is not necessary to be in an exact conjugate relationship, and a state with a certain amount of defocus may be acceptable. A deviation in arrangement within a range that does not deviate from the imaging state for which the optical system under test 102 is to be evaluated is allowed.

[0022] There are two types of defocus, object-side defocus that represents the deviation in the optical axis direction between the focus position and the object (subject), and image-side defocus that represents the deviation in the optical axis direction between the image formed with the light-receiving part (image sensor) and the image. Hereinafter, for the sake of clarity, both are described separately. However, since the two can be converted according to the imaging relationship, the conditions for object-side defocus can be converted into the conditions for image-side defocus, and vice versa. Also, when simply expressed as defocus, it refers to a state where the image is deviated in the optical axis direction with respect to the position of the image sensor 103, and the cause is not specified.

[0023] The peripheral light source group consists of at least one or more light sources. In FIG. 1, only the light sources 1012 and 1013 are shown, but the light sources included in the peripheral light source group are not limited to two. The peripheral light source group is arranged such that the positions in the optical axis direction of the optical system under test and in the direction perpendicular to the optical axis direction are different from those of the reference light source. As a result, the peripheral light source group is imaged with a different image height and a different image-side defocus from the image of the reference light source by the optical system under test 102. By adopting such a configuration, a plurality of point images with different defocus can be obtained without a driving device. Therefore, based on the plurality of light intensity distributions, the aberration of the optical system can be estimated with high accuracy in a short time.

[0024] Also, the peripheral light source group is preferably arranged on the object side (a position farther from the imaging element 103 than the reference light source) and on the image side (a position closer to the imaging element 103 than the reference light source) with respect to the reference light source. By adopting such a configuration, it is possible to obtain light intensity distributions defocused by the defocus amounts of positive and negative respectively. As a result, the aberration of the optical system 102 to be inspected can be accurately estimated. For example, as shown in FIG. 1, the light source 1012 is arranged at a position closer to the imaging element 103 than the reference light source, and the light source 1013 is arranged at a position farther from the imaging element 103 than the reference light source. Hereinafter, defocus in the direction from the object side to the image side is defined as positive.

[0025] Furthermore, the peripheral light source group preferably consists of two or more light sources, and the positions in the optical axis direction of the optical system 102 to be inspected and in the direction perpendicular to the optical axis direction are different from each other. By obtaining the light intensity distributions of a plurality of optical images formed by such a peripheral light source group, the accuracy of the estimation calculation can be improved.

[0026] The details of the arrangement of each light source in the light source unit 101 according to the present embodiment will be described with reference to FIG. 2. FIG. 2 is a cross-sectional view including the optical axis of the optical system 102 to be inspected and the reference light source (light source 1011). The region represented in gray in FIG. 2 is a region that satisfies the conditional expressions (1) to (3) described later. The plurality of light sources of the light source unit 101 according to each embodiment are preferably arranged so as to satisfy any one or more of the following conditional expressions (1) to (3).

[0027] Although only the cross-section passing through the optical axis is shown in FIG. 2, actually, the space obtained by rotating the gray region in FIG. 2 around the optical axis as the rotation axis is the region that satisfies the conditional expressions (1) to (3). Also, in the present embodiment, the light source 1011 arranged on the optical axis is used as a reference, but it is not limited thereto. By satisfying the above-described conditional expressions with an arbitrary light source arranged outside the optical axis, the respective effects can be achieved.

[0028] Since the images of the light sources arranged within the depth of field range of the optical system under test can be regarded as having substantially the same shape, each light source is preferably arranged at a defocused position with an interval of object-side defocus amount larger than the depth of field range of the optical system under test.

[0029] Here, according to the wave optics imaging theory, when the object-side numerical aperture of the optical system under test 102 is NAo and the wavelength of the light source is λ [nm], the depth of field DOF of the optical system under test is expressed by Equation 1. [Equation 1] DOF = λ / NAo 2

[0030] In order to arrange each light source at a defocused position with an interval of object-side defocus amount Df [mm] larger than the depth of field range of the optical system under test, when the minimum amount of the distance in the optical axis direction between the centers of each light source is Δzmin [mm], 1 / NAo 2 ≦ |Δzmin| / λ (1) Also, the object-side numerical aperture NAo can be obtained by NAo = 1 / 2FM using the F-number and magnification M of the optical system under test. Hereinafter, it is assumed that the F-number is about 1 to 8 generally used for photographic lenses.

[0031] For example, in the case of a wide-angle lens, since the magnification is about 50 times, in order to estimate the aberration of the wide-angle lens, it is preferable to satisfy the conditional expression (1a). 640000 ≦ |Δzmin| / λ (1a)

[0032] Also, in the case of a photographic lens having a standard focal length used for portrait photography etc., since the magnification is about 30 times, in order to estimate the aberration of the photographic lens having a standard focal length, it is preferable to satisfy the conditional expression (1b). 230000 ≦ |Δzmin| / λ (1b)

[0033] Furthermore, in the case of a telephoto lens etc., since the magnification is small at about 5 times, in order to estimate the aberration of the telephoto lens, it is preferable to satisfy the conditional expression (1a). 6400 ≤ |Δzmin| / λ (1c)

[0034] However, if Δzmin is made too large, the apparatus will become large-sized. Also, if Δzmin is made too large, depending on the light source used, the light intensity distribution of the light source may decrease. Therefore, it is preferably set to 1000 mm ≤ |Δzmin|. Thus, in order not to make the apparatus too large-sized and to accommodate optical systems in a wide wavelength range, it is more preferable that the plurality of light sources in the light source unit 101 satisfy (1b) rather than (1a), and (1c) rather than (1b).

[0035] Next, in order to avoid the overlap of a plurality of point images, it is preferable that each light source be arranged at a distance such that the object height is greater than or equal to the spread due to the defocus of each point image. The spread angle of the point image is expressed as sin -1 (NAo) when converted to the object space. Therefore, in the geometric arrangement shown in FIG. 2, the angle θ [°] formed by the straight line connecting the centers of any two light sources and the optical axis is expressed by Equation 2. [Equation 2-1] sin -1 (NAo) ≤ θ ≤ 180° - sin -1 (NAo)

[0036] By satisfying this condition, the overlap between the plurality of light sources can be avoided. In order to estimate the aberration with high precision, it is desirable that each point image be completely separated from each other, but it is not necessary to be strictly separated, and a partial region may overlap. For example, even if there is an overlap of about 10% between the point images, the present invention will function. When expressed by an equation, it becomes Equation 2-2. [Equation 2-2] 0.9sin -1 (NA o ) ≤ θ ≤ 180° - 0.9sin -1 (NA o )

[0037] Here, assuming a general photographic lens with a reduction magnification of about 5 times and an F-number of 1 or more, 5.2 ≤ θ ≤ 174.8 (2) By arranging a plurality of light sources so as to satisfy conditional expression (2), the point images of the respective light sources can be spatially separated. As a result, by lighting the plurality of light sources at once and performing imaging, it becomes possible to collectively acquire a plurality of point images having different defocus amounts. By adopting such a configuration, it is not necessary to perform a process of separating a plurality of point images, and the time for the estimation process can be shortened.

[0038] When a plurality of light sources are arranged at mutually different object heights, since the influence of vignetting varies according to the object height, different light intensity distributions are obtained. For example, when using the pupil function of a point image to estimate aberration, since it is assumed that the shape of the pupil function of the point image coincides with the shape of the actual pupil function of the point image, an error occurs in the estimated aberration if the vignetting used for the estimation is different from the vignetting of the actual optical system. Therefore, in order to satisfy a desired estimation accuracy, it is preferable to reduce the influence of vignetting.

[0039] Here, a desired estimation accuracy is δ0, a difference in object height between the reference light source 1011 and the surrounding light sources is Δh, an amount of vignetting that changes according to Δh is Δr, and an amount of estimation error δ that occurs at that time is represented by Equation 3. [Equation 3] δ(Δr(Δh)) ≤ δ0

[0040] The relationship between the object height and the estimation error in the present embodiment will be described with reference to FIG. 3. FIG. 9 is a diagram showing the relationship between the object height and the estimation error, and represents an estimation error δ(h) that occurs when the object height h at which the peripheral light source group in the present embodiment is installed is changed. The vertical axis in FIG. 9 is the RMS residual obtained using the root mean square (RMS), and the horizontal axis is the object height h [cm].

[0041] As the object height h in Fig. 3 increases, the aperture eclipse generated by the optical system under test increases, so the larger the object height h, the larger the estimation error. Generally, as an index of the accuracy of aberration, it is desirable that the estimation error δ be 100 mλ or less. Therefore, the object height in this embodiment is preferably 180 mm or less. Furthermore, since the imaging magnification M in this embodiment is 20 times, when expressed as a function of the imaging magnification M, the object height is preferably 9M [mm] or less. Assuming that the reduction magnification of the optical system to which the aberration estimation apparatus of this embodiment is applied is 100 times or less (M ≤ 100), the object height is preferably 900 mm or less. When estimating aberration with higher accuracy, the object height is preferably 270 mm or less.

[0042] From the above, when the difference between the maximum reference light source 1011 that satisfies the above formula 3 and the surrounding light sources is Δhmax, 900 mm ≥ Δhmax (3) By arranging a plurality of light sources to satisfy the conditional expression (3), the influence of the aperture eclipse can be sufficiently reduced, so that the aberration in the optical system under test can be accurately obtained.

[0043] In this embodiment, since a plurality of light sources are arranged at different object heights, the aberration of the light from each light source and the aberration in the point image obtained from the light from the reference light source are different. Since the aberrations in the point images obtained from each light source are different from each other, the aberration estimated from the light intensity distribution based on the point image formed by each light source has an error with respect to the true aberration. Here, the arrangement for reducing this error will be described.

[0044] When it is assumed that the aberration of the optical system under test with respect to the reference light source is estimated, the difference component between the aberration of the point image in the surrounding light source group and the aberration of the point image in the reference light source is defined as the amount of aberration variation. Even when there is an amount of aberration variation, in order to accurately estimate the aberration of the point image in the reference light source, it is preferably arranged such that the signs of the amounts of aberration variation are different from each other. By adopting such a configuration, the estimation error caused by the influence of the amount of aberration variation generated by the object height can be reduced.

[0045] Here, the sign of the amount of aberration variation and the arrangement of the light sources will be described.

[0046] For example, the amount of coma aberration variation is approximately proportional to the object height h, and the amount of spherical aberration variation increases approximately proportionally to the square of the object height h. Hereinafter, the arrangement of a plurality of light sources for reducing the influence on the light intensity distribution due to the aberration variation depending on the object height will be described.

[0047] A generalized explanation for higher-order aberrations will be given using FIG. 4. FIG. 4 is a diagram in which the positions of the light sources are projected onto a plane perpendicular to the optical axis through the reference light source 1011.

[0048] In FIG. 4, the light source 1012 is installed at a positive position on the x-axis, and the light source 1013 is installed at a position rotated by an angle φ around the x-axis with the optical axis (reference light source 1011) as the center. At this time, the relationship between the wavefront aberration (first wavefront aberration) of the point image formed by the light emitted from the light source 1012 through the optical system under test 102 and the wavefront aberration (second wavefront aberration) of the point image formed by the light emitted from the light source 1013 through the optical system under test 102 will be described. Note that the position of the light source 1012 in FIG. 4 is not limited to the x-axis. The angle φ in the present embodiment may be represented by the angle formed by the line segment connecting the position of the light source 1012 and the optical axis and the line segment connecting the position of the light source 1013 and the optical axis.

[0049] If the object height difference between the reference light source 1011 and the surrounding light sources is sufficiently small, the amount of variation of the second wavefront aberration corresponds to the wavefront aberration obtained by rotating the amount of variation of the first wavefront aberration by φ.

[0050] Next, the preferred arrangement of the light sources will be described using FIG. 5. FIG. 5 is a diagram showing an example of wavefront aberration.

[0051] The wavefront aberration representing the coma aberration shown in FIG. 5(a) is an aberration whose sign of the amount of variation is inverted every 180° rotation. Therefore, by arranging the light source 1012 and the light source 1013 at positions rotated by approximately 180° around the optical axis, wavefront aberrations with different signs of the amount of coma aberration variation can be obtained.

[0052] The wavefront aberration representing the astigmatism shown in FIG. 5(b) is an aberration in which the sign of the amount of variation is inverted every 90° rotation. Therefore, by arranging the light source 1012 and the light source 1013 at positions rotated by approximately 90° about the optical axis, wavefront aberrations with different signs of the amount of variation of the astigmatism can be obtained.

[0053] The wavefront aberration representing the astigmatism shown in FIG. 5(c) as an example of higher-order aberration is an aberration in which the sign of the amount of variation is inverted every 60° rotation. Therefore, by arranging the light source 1012 and the light source 1013 at positions rotated by approximately 60° about the optical axis, wavefront aberrations with different signs of the amount of variation of the coma aberration can be obtained.

[0054] In addition, in order to reduce the influence of higher-order aberrations with higher precision, it is preferable that each light source is arranged at a finer angle. For example, by arranging the peripheral light sources at positions rotated by approximately 90° about the optical axis, not only the astigmatism in which the sign of the amount of variation is inverted every 90° rotation described above, but also the influence of the coma aberration in which the sign of the amount of variation is inverted every 180° rotation can be reduced with higher precision. Also, the influence of higher-order coma aberration represented by the 14th and 15th terms of the Fringe Zernike polynomial can be reduced.

[0055] Also, by arranging the peripheral light sources at positions rotated by approximately 45° about the optical axis, the influence of the aberration in which the sign of the amount of variation changes at 45° rotation represented by the 17th term of the Fringe Zernike polynomial can be suppressed. The higher-order astigmatism represented by the 10th term of the Fringe Zernike polynomial shown in FIG. 5(c) does not change the sign variation amount at every 45° rotation. However, by arranging the light sources at different angles, the amount of variation of the aberration generated for each point image is distributed to each component of the 10th and 11th terms. Even if the sign of the amount of variation of the wavefront aberration simply does not change, if the light sources are arranged so that the aberration variation is different between the plurality of obtained point images, the estimation error can be reduced by the averaging effect. Therefore, the estimation accuracy can be improved by performing calculations using the point images obtained by the light sources arranged at a plurality of angles.

[0056] Furthermore, by arranging the peripheral light sources at positions rotated about the optical axis by approximately 60° each, the influence of the astigmatism with the sign of the fluctuation amount reversing every 60° rotation can be reduced with higher precision. Also, by arranging the peripheral light sources at positions rotated about the optical axis by approximately 30° each, the influence of astigmatism and the like can be reduced with even higher precision.

[0057] In this embodiment, the rotation amount is set to 360 / n° (n is an integer) per rotation, but it is not limited thereto. Even if the light sources are not arranged exactly every 360 / n°, the estimation error can be reduced by the averaging effect. Even when the number of light sources to be arranged is small, the above-described effect can be obtained by setting the angle φ formed by at least two of the plurality of light sources to 30° or more.

[0058] Here, when the angle formed by the line segment connecting the light source 1012 and the optical axis of the optical system under test 102 shown in FIG. 4 and the line segment connecting the light source 1013 and the optical axis of the optical system under test 102 is φ [°], 30° ≤ φ (3) By arranging a plurality of light sources so as to satisfy the conditional expression (3), the point images formed by the plurality of light sources can be spatially separated. As a result, it becomes possible to collectively acquire a plurality of point images with different defocuses by lighting the plurality of light sources at once and performing imaging. With such a configuration, it is not necessary to perform a process of separating the plurality of point images, and the time for the estimation process can be shortened.

[0059] Hereinafter, preferred embodiments of the present invention will be described in detail.

[0060] [Example 1] The aberration estimation apparatus 100 according to Example 1 will be described with reference to FIG. 6.

[0061] The light source unit 101 in this embodiment has a laser light source 106, an optical fiber branching element 107, a light quantity adjustment element 108, and the end faces of three optical fibers. The light emitted from the laser light source 106 is guided to the optical fiber branching element 107 by the optical fiber. The light emitted from the laser light source 106 in this embodiment is assumed to have a wavelength of about 524 nm. The optical fiber branching element 107 divides the light into three optical fibers. The three optical fibers have a light quantity adjustment element 108 for adjusting the light quantity. Also, the end faces of these three optical fibers respectively correspond to the light sources 1011, 1012, and 1013 in this embodiment.

[0062] In this embodiment, the light source 1011 is a reference light source and is installed on the optical axis. The light sources 1012 and 1013 are installed such that their positions in the optical axis direction of the optical system under test and in the direction perpendicular to the optical axis direction with respect to the reference light source are different from each other. In this embodiment, the object heights of the peripheral light source group (light sources 1012 and 1013) are 2 cm and -2 cm respectively, and the object-side defocus amounts are 10 cm and -10 cm. Also, in this embodiment, the light emitted from the light source unit 101 is reduced by 20 times by the optical system under test 102 and imaged on the imaging element 103.

[0063] Next, a flowchart of the aberration estimation method by the aberration estimation device 100 in each embodiment will be described with reference to FIG. 7.

[0064] In step S1, the optical system under test 102 is installed such that the center of the reference light source and the imaging element 103 are conjugate. Note that the installation of the optical system under test 102 is not limited to this, and the optical system under test 102 may be arranged such that all of the plurality of light sources are defocused with respect to the imaging element 103.

[0065] In addition, the light source unit 101 is preferably configured to be adjustable according to the optical system 102 to be inspected. By driving a plurality of light sources in the optical axis direction and the direction perpendicular to the optical axis according to the aperture diameter and focal length of the optical system 102 to be inspected, the aberration of the optical system 102 to be inspected can be accurately estimated. Note that step S1 may be performed by an operator or may be automated by the apparatus.

[0066] In step S2, the light intensity distribution of each point image formed by the light emitted from the light source unit 101 through the optical system 102 to be inspected is acquired. When the light source unit 101 is configured such that the point images do not overlap, all the light sources can be turned on simultaneously, and the light intensity distribution of each point image can be acquired based on a single image. Further, when separating the overlap of the point images by time division, the light sources to be turned on may be sequentially changed, and a plurality of light intensity distributions may be acquired in synchronization with the lighting timing. Furthermore, the light intensity distribution acquired in step S2 is stored in the computer 104 as necessary.

[0067] Note that it is only necessary to be able to acquire the light intensity distribution of each point image separately, and this method is not limited. For example, when using light sources of different wavelengths, all the light sources may be turned on simultaneously, and the light intensity distribution of each point image may be acquired from a single image. Further, when acquiring the light intensity distribution of each point image from a single image, the image may be separated into images corresponding to each light source by image processing as necessary. When performing the image processing for separation, the point images may be separated based on the position calibrated in advance, or the center position of the point image may be calculated and separated based on that. When the overlap of the point images is separated by wavelength, the pixels corresponding to each color of the camera may be extracted.

[0068] In addition, as a method of making the positions of the first and second light sources different from each other in the optical axis direction of the optical system under test and the direction perpendicular to the optical axis direction, it is conceivable to drive the optical system under test and the light source unit. However, when moving at high speed, the accuracy tends to decrease, and when moving at low speed, it takes time. Therefore, when acquiring the light intensity distribution of each of the plurality of light sources, it is preferable not to drive the light source unit or the optical system under test. In other words, it is preferable that the light source unit and the optical system under test are fixed while step S2 is being executed.

[0069] In step S3, post-processing is executed by the computer 104 on the plurality of light intensity distributions obtained by separation, and the aberration of the optical system under test 102 is estimated.

[0070] The estimation calculation performed in step S3 can be executed by an intensity transport equation, optimization, Fourier iteration method, machine learning, or the like.

[0071] Optical devices for photographing general subjects such as cameras and telescopes are basically reduction optical systems. The optical image formed by the reduction optical system has a diffraction pattern finer than the pixel size of the image sensor 103, so that the light intensity distribution within the pixel is averaged by the image sensor 103 during imaging. Therefore, the light intensity distribution acquired through the reduction optical system does not have accurate optical image information. As a result, the accuracy of the acquired aberration may decrease.

[0072] Regarding this problem, a method of suppressing the influence of averaging by pixels by increasing the defocus amount of each light source with respect to the reference light source is conceivable. However, the larger the defocus amount of each light source with respect to the reference light source, the larger the size of the apparatus. Therefore, in the present embodiment, it is preferable that the aberration estimation calculation is performed using machine learning. By performing the estimation calculation using machine learning, the defocus amount of each light source with respect to the reference light source can be kept small, and the estimation accuracy can be maintained even when the number of light sources is small. That is, high-precision aberration estimation can be realized while keeping the apparatus small.

[0073] It is more preferable that the estimation calculation using machine learning enables correction processing for correcting the effects of vignetting and aberration that change due to differences in the relative object height of the light source.

[0074] For example, when using a multi-layer neural network as machine learning, each parameter such as weights and biases that make up the neural network is obtained by optimizing with a dataset of point images and aberration coefficients prepared in advance. With such a configuration, the multi-layer neural network in this embodiment can output the coefficients when the wavefront aberration of the optical system under test is expanded into Zernike coefficients, using the image of the light intensity distribution of the divided light source as input data. Furthermore, when optimizing the parameters of the network, it is more preferable to use learning data prepared in consideration of the change in the light intensity distribution due to the effects of vignetting and aberration that change due to differences in the relative object height of the light source.

[0075] In step S4, the display unit 105 displays the acquired aberration and the like.

[0076] By adopting such an aberration estimation method, it is aimed to estimate the aberration of the optical system with high accuracy in a short time based on a plurality of light intensity distributions.

[0077] Next, the aberration obtained by the method of Example 1 will be described with reference to FIG. 8. FIG. 8 is an example of the aberration estimated using the aberration estimation apparatus 100.

[0078] FIG. 8 shows the coefficients obtained by expanding the aberration with the Fringe Zernike polynomial. The broken line in FIG. 8 is the true aberration amount of the optical system under test 102, and the solid line is the aberration obtained by this embodiment. The true aberration amount can be obtained using simulation or the like. In FIG. 8, the solid line accurately reproduces the broken line, indicating that the aberration estimation apparatus 100 in this embodiment can acquire the aberration of the optical system under test 102 with high accuracy.

[0079] [Example 2] Next, the aberration estimation apparatus 100 according to Example 2 will be described. The configuration of the aberration estimation apparatus 100 in this example other than the light source unit 101 is the same as that in Example 1. Here, the configuration of the light source unit 101 in this example will be described with reference to FIG. 9. FIG. 9 is a diagram in which the positions of the light sources are projected onto a plane perpendicular to the optical axis through the reference light source.

[0080] The light source unit 101 in this example is composed of a reference light source (light source) 1011 and a peripheral light source group composed of eight light sources. In FIG. 9, in order to represent the difference in the installation positions in the optical axis direction, the light sources included in the peripheral light source group are illustrated as large circles with respect to the reference light source. Further, in order to represent the difference in the positive and negative defocus, the light source with positive object-side defocus is illustrated as a circle with a dark center, and the light source with negative object-side defocus is illustrated as a circle with a light center.

[0081] In this example, the peripheral light source group is arranged every 45°. Such a configuration is preferable in that the influence of the aberration described above can be reduced with high precision. Also, four of the peripheral light source group have positive defocus, and the remaining four have negative defocus. Thus, it is preferable that the peripheral light source group can be arranged such that the number of positive and negative defocuses is about the same.

[0082] Furthermore, a modified example of Example 2 will be described with reference to FIG. 10. FIG. 10 is a diagram in which the positions of the light sources are projected onto a plane perpendicular to the optical axis through the reference light source. FIG. 10(a) is different from FIG. 9 in that it has light sources arranged at different object heights in the peripheral light source group. FIG. 10(b) is different from FIG. 9 in that it illustrates the light sources with larger object-side defocus as larger circles in order to represent the difference in the absolute value of the defocus amount. FIG. 10(b) is different from FIG. 9 in that it has light sources arranged at different defocus positions in the peripheral light source group.

[0083] By adopting the configurations such as those shown in FIGS. 10(a) and 10(b), it is preferable in that robust estimation can be performed against changes in image height or defocus. Further, in FIG. 10, an example is shown in which light sources with only the object height or defocus different are arranged in the peripheral light source group, but the present invention is not limited thereto, and the light sources in the light source unit 101 may be arranged by combining FIGS. 10(a) and 10(b).

[0084] [Embodiment 3] Next, the aberration estimation apparatus 100 according to Embodiment 3 will be described. The configuration of the aberration estimation apparatus 100 in this embodiment other than the light source unit 101 is the same as that in Embodiment 1. Here, the configuration of the light source unit 101 in this embodiment will be described with reference to FIG. 11. FIG. 11 is a diagram in which the positions of the respective light sources are projected onto a plane perpendicular to the optical axis through the reference light source.

[0085] The light source unit 101 in this embodiment is composed of a light source (reference light source) 1011 and a light source 1012. In FIG. 11(a), in order to represent the difference in the installation position in the optical axis direction, the light sources included in the peripheral light source group are shown as large circles with respect to the reference light source. In FIG. 11(a), the light source (first light source) 1011 and the light source (second light source) 1012 are different from each other in position in the optical axis direction of the optical system to be tested and in the direction perpendicular to the optical axis direction. Even if the reference light source is arranged at a position different from that on the optical axis as shown in FIG. 11(a), the aberration of the optical system 102 to be tested can be estimated. At this time, as shown in FIG. 11(a), it is preferable that the two light sources are arranged on a straight line including the optical axis. By adopting such a configuration, the influence of various aberrations when obtaining the aberration can be reduced.

[0086] In addition, in FIG. 11(b), in order to represent the difference in the sign of the defocus amount, the light source with a positive object-side defocus amount is illustrated as a circle with a dark color at the center, and the light source with a negative object-side defocus amount is illustrated as a circle with a light color at the center. Different from Example 1, the light source 1012 is defocused only by a negative object-side defocus with respect to FIG. 11(a). In FIG. 11(b), it is assumed that they are conjugate at the position on the optical axis (the intersection of x and y) via the imaging element 103 and the optical system to be tested 102. By arranging light sources defocused only by object-side defocuses with different signs at positions facing each other with the conjugate point as a reference, aberrations can be obtained with high precision.

[0087] [Other Embodiments] As described above, the preferred embodiments of the present invention have been described. However, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist thereof.

[0088] Here, a modified example of each embodiment will be described with reference to FIG. 12. In Examples 1 to 3, an example in which no optical element is arranged between the light source unit 101 and the optical system to be tested 102 has been shown, but the present invention is not limited to this. For example, an element that changes the traveling direction of light (an optical path changing element) such as a mirror or a beam splitter, or an optical element including a lens may be arranged in the optical path.

[0089] The light source unit 101 in the aberration estimation apparatus 100 of FIG. 12 is configured by arranging a mirror 109 and a beam splitter 110. The light emitted from the light source 1012 is guided to the optical system to be tested 102 via the mirror 109. Further, the light source 1013 is guided to the optical system to be tested 102 via the beam splitter 110. Here, 1012a and 1013a in FIG. 12 indicate the positions of virtual light sources formed by extending the light rays from the side of the optical system to be tested 102 (or the imaging element 103) when there is no optical path changing element. When there is an optical path changing element in the optical path, the same effect can be obtained if the characteristics described in each embodiment are possessed when it is assumed that there are light sources at the positions of the virtual light sources 1012a and 1013a.

[0090] The conditional expression (2) is used as a condition for avoiding the overlap of the spreads of a plurality of point images. However, the method for avoiding the overlap of the spreads of a plurality of point images is not limited to this. For example, the timing of turning on each light source may be changed, and an image may be acquired according to that timing. Even with this configuration, the processing time can be shortened compared to the case of using a driving device. Also, in this case, the aberration estimation device 100 needs to have an output control unit that changes the output of each light source over time.

[0091] Furthermore, if light sources of different wavelengths are arranged, a color camera is used as the imaging device 103, and images corresponding to each wavelength are extracted from the acquired image by arithmetic processing, then the images for each light source can be separated. At this time, since the aberration is different between each point image due to the different wavelengths, the estimation calculation executes a process of correcting the difference between the wavelengths.

[0092] In this embodiment, for the sake of easy explanation, the reference light source was described on (or near) the optical axis of the optical system under test. However, it is not limited to this. Even if the reference light source is arranged outside the optical axis of the optical system under test, the effects of each embodiment can be achieved. It is sufficient that the center of at least one of the plurality of light sources is in a substantially conjugate relationship with the imaging device 103 by the optical system under test 102. In each embodiment, the optical axis of the optical system under test was used as the reference axis when considering the arrangement constraints. However, when the reference light source is outside the optical axis, the straight line connecting the reference light source and the optical system under test can be considered as the reference axis.

[0093] In each embodiment, it is sufficient that the image used for the aberration estimation calculation is formed by the light from the light source, and it is not necessary for all the light sources constituting the light source unit 101 to be point light sources (or substantially point light sources). For example, it may have a light source for measuring the installation position of the optical system under test 102.

[0094] The present invention can also be implemented by supplying a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and causing one or more processors in a computer of the system or device to read and execute the program. It can also be implemented by a circuit (for example, ASIC) that realizes one or more functions.

[0095] Embodiments of the present invention include the following configurations.

[0096] [Configuration 1] A light source unit including a first light source and a second light source that illuminate a DUT optical system; An estimation unit that acquires an aberration of the DUT optical system based on the respective light intensity distributions of the first and second light sources obtained through the DUT optical system, The first and second light sources are characterized in that positions in the optical axis direction of the DUT optical system and in a direction perpendicular to the optical axis direction are different from each other. An aberration estimation device.

[0097] [Configuration 2] When a minimum amount of a distance in the optical axis direction of the DUT optical system between centers of the first and second light sources is Δzmin and a wavelength of the light source is λ, 640000≦|Δzmin| / λ The aberration estimation device according to Configuration 1, characterized in that the conditional expression is satisfied.

[0098] [Configuration 3] When the first and second light sources are projected onto a plane perpendicular to the optical axis of the DUT optical system, and an angle formed by a line segment connecting the first light source and the optical axis and a line segment connecting the second light source and the optical axis is φ [°], 30°≦φ The aberration estimation device according to Configuration 1 or 2, characterized in that the conditional expression is satisfied.

[0099] [Configuration 4] When an angle formed by a line segment connecting the center of the first light source and the center of the second light source and the optical axis of the DUT optical system is θ [°], 5.2≦θ≦174.8 An aberration estimation apparatus according to any one of Configurations 1 to 3, characterized by satisfying the following conditional expression.

[0100] [Configuration 5] The aberration estimation apparatus according to any one of Configurations 1 to 4, characterized in that the estimation unit acquires the aberration of the optical system under test based on the light intensity distribution using a multi-layer neural network.

[0101] [Configuration 6] The aberration estimation apparatus according to any one of Configurations 1 to 5, characterized in that the estimation unit acquires the aberration based on a change in the light intensity distribution caused by a difference in the positions of the first light source and the second light source.

[0102] [Configuration 7] The aberration estimation apparatus according to any one of Configurations 1 to 6, characterized in that the first and second light sources have different wavelengths from each other.

[0103] [Method 1] An aberration estimation method for estimating the aberration of an optical system under test, comprising: irradiating the optical system under test with light emitted by a first light source and a second light source, and acquiring the respective light intensity distributions of the first and second light sources through the optical system under test; acquiring the aberration based on the light intensity distribution, wherein the first and second light sources have different positions from each other in the optical axis direction of the optical system under test and in a direction perpendicular to the optical axis direction.

[0104] [Method 2] The aberration estimation method according to Method 1, characterized in that in the acquiring step, at least one of the first and second light sources and a light receiving unit that acquires the light intensity distribution are conjugately arranged through the optical system under test.

[0105] [Method 3] When the defocus amount from the object side to the image side direction is positive, The first light source is imaged at a position defocused by a positive defocus amount with respect to the light receiving unit by the optical system under test. The second light source is imaged at a position defocused by a negative defocus amount with respect to the light receiving unit by the optical system under test, according to the aberration estimation method described in Method 2.

[0106] [Configuration 8] A program characterized by causing a computer to execute the aberration estimation method according to any one of Methods 1 to 3.

[0107] [Configuration 9] A storage medium characterized by storing the program described in Configuration 8.

Explanation of Signs

[0108] 100 Aberration estimation device 101 Light source unit 102 Optical system under test 103 Image sensor

Claims

1. A light source unit including a first light source and a second light source for illuminating an optical system under test; An estimation unit that estimates an aberration of the optical system under test based on the respective light intensity distributions of the first and second light sources obtained through the optical system under test; The aberration estimation device, wherein the first and second light sources are different from each other in position in the optical axis direction of the optical system under test and in a direction perpendicular to the optical axis direction.

2. When a minimum amount of the distance in the optical axis direction of the optical system under test between the centers of the first and second light sources is Δzmin and the wavelength of the light source is λ, 640000 ≦ |Δzmin| / λ The aberration estimation device according to claim 1, characterized by satisfying the conditional expression.

3. When the first and second light sources are projected onto a plane perpendicular to the optical axis of the optical system under test, and an angle formed by a line segment connecting the first light source and the optical axis and a line segment connecting the second light source and the optical axis is φ [°], 30° ≦ φ The aberration estimation device according to claim 1 or 2, characterized by satisfying the conditional expression.

4. When an angle formed by a line segment connecting the center of the first light source and the center of the second light source and the optical axis of the optical system under test is θ [°], 5.2 ≦ θ ≦ 174.8 The aberration estimation device according to claim 1 or 2, characterized by satisfying the conditional expression.

5. The aberration estimation device according to claim 1 or 2, wherein the estimation unit estimates the aberration of the optical system under test based on the respective light intensity distributions of the first and second light sources using a multi-layer neural network.

6. The aberration estimation device according to claim 1 or 2, wherein the estimation unit estimates the aberration based on a change in the light intensity distribution caused by a difference in position between the first light source and the second light source.

7. The aberration estimation device according to claim 1 or 2, wherein the first and second light sources have different wavelengths from each other.

8. An aberration estimation method for estimating the aberration of a test optical system, comprising: irradiating the test optical system with light emitted by a first light source and a second light source, and obtaining the light intensity distribution of each of the first and second light sources through the test optical system; estimating the aberration based on the light intensity distribution; The aberration estimation method, wherein the positions of the first and second light sources are different from each other in the optical axis direction of the test optical system and in a direction perpendicular to the optical axis direction.

9. The aberration estimation method according to claim 8, wherein in the obtaining step, at least one of the first and second light sources and a light receiving unit for obtaining the light intensity distribution are conjugately arranged through the test optical system.

10. When the defocus amount from the object side to the image side direction is positive, the first light source is imaged at a position defocused by a positive defocus amount with respect to the light receiving unit by the test optical system, The aberration estimation method according to claim 9, wherein the second light source is imaged at a position defocused by a negative defocus amount with respect to the light receiving unit by the test optical system.

11. A program, characterized in that the computer executes the aberration estimation method according to any one of claims 8 to 10.

12. A storage medium, characterized in that it stores the program according to claim 11.

Images