JP6387381B2 - Autofocus system, method and image inspection apparatus - Google Patents

Description

  The present invention relates to an autofocus technique, and more particularly to an autofocus system and method capable of instantaneous focusing and an image inspection apparatus to which these are applied.

  Conventional precision inspection includes ordinary optical devices (eg, line scan cameras, area scan cameras, etc.), captures images of the surface of the subject, analyzes the captured images using computer image processing technology, and detects foreign matter on the surface of the subject. Or, a defect such as a pattern abnormality is detected. However, in the inspection apparatus, it may be difficult to capture an image of the surface of the subject so that the subject does not move, and if the moving state occurs and the position of the subject is changed, a focus shift occurs.

  For example, when inspecting a precision subject (for example, a panel), an air floating table is provided for some precision subjects in order to suppress scratches or fouling by the transport conveyor during the subject transportation process. To avoid coming into direct contact with the lower plane. When attempting to inspect a subject with such a conveyance process, the subject floats above the table by the action of air floating, and the height floats to a predetermined range value (for example, 300 μm). However, the depth of field of a general camera is about 35 μm, and the inspection object cannot be accurately controlled within the range of the depth of field. Therefore, when the focus is inspected according to the air floating table, it is necessary to quickly and effectively focus on the subject floating on the table, and it is necessary to provide such a focusing method.

US Pat. No. 6,677,565 US Pat. No. 7,247,827 US Pat. No. 7,297,910 US Pat. No. 8422031 Taiwan Patent Application Publication No. I369508 Specification Taiwan Patent Application Publication No. I521295 Specification

  In view of the above problems, an object of the present invention is to provide an autofocus system, a method, and an image inspection apparatus that are different from the conventional ones.

  In order to achieve the above object, the autofocus system of the present invention projects a part of the linear speckle on the subject via the objective lens, and images the subject and a part of the linear speckle. The target image is obtained by capturing, and the length, width and position of a part of the linear speckle in the target image are acquired by using image processing technology, and one of the linear speckles in the acquired target image is obtained. The state in which the subject is in focus is determined based on the length, width, and position of the unit, and the objective lens is quickly adjusted to the position for focusing on the subject based on the determination result.

  Specifically, the autofocus system of the present invention includes a linear light source, an objective lens, a light shielding member, an image sensor, and a focus adjustment module. The linear light source is, for example, a linear laser speckle. A linear speckle like this is generated. A part of the linear speckle is incident on the objective lens, and a part of the linear speckle is projected onto the subject. The light blocking member is provided in an optical path between the linear light source and the objective lens, partially blocks the linear speckle, and allows only a part of the linear speckle to enter the objective lens. The image sensor is used to capture a subject and a part of a linear speckle to obtain a target image. The focus adjustment module determines the state in which the subject is in focus based on the length, width, and position of a part of the linear speckle in the target image, and the distance between the objective lens and the subject based on the determination result Adjust.

  The focus adjustment module of the autofocus system of the present invention determines that the subject is already in focus when it is determined that the length and width of a part of the linear speckle in the target image have decreased to a predetermined limit value. judge. The focus adjustment module also allows the subject to be closer to the objective lens than the focal point of the objective lens when a part of the linear speckle in the target image is located on one side of a predetermined reference point related to the focused state. It is determined that the subject is located, and when a part of the linear speckle in the target image is located on the other side of the reference point, it is determined that the subject is located farther from the objective lens than the focal point of the objective lens.

  The autofocus system of the present invention is preferably configured to include a converging lens, a reflecting mirror, a first spectroscope, a second spectroscope, and an imaging lens positioned in front of the image sensor. Linear speckles emitted from a linear light source are incident on the incident surface of the convergent lens. The light shielding member is provided between the exit surface of the converging lens and the reflecting mirror. The reflecting mirror reflects a part of the linear speckle to the first spectroscope. The first spectroscope reflects the linear speckle to the objective lens, and allows the reflected light reflected from the subject to the objective lens and a part of the linear speckle to pass therethrough. The second spectroscope is located between the first spectroscope and the imaging lens, and reflects the reflected light from the objective lens entering through the first spectroscope and a part of the linear speckle to the imaging lens. . The imaging lens can generate the target image described above by the image sensor by converging the reflected light and a part of the linear speckle to form an image on the detection surface of the image sensor.

  The autofocus system of the present invention may further include a driving device. The driving device is connected to the focus adjustment module and moves the objective lens based on the determination result of the focus adjustment module to adjust the distance between the objective lens and the subject.

  The image inspection apparatus of the present invention can further include an image capturing device and illumination means, in addition to the autofocus system. The illumination means provides illumination to the subject, and the image capturing device immediately captures an image of the subject when it is determined that the subject is in focus by the focus adjustment module of the autofocus system.

  The illumination means of the image inspection apparatus of the present invention can include a spectroscope and a lighting fixture. The spectroscope and the first and second spectroscopes of the autofocus system are arranged coaxially. The spectroscope is used to illuminate a subject by receiving visible light from a lighting fixture and reflecting the visible light toward the subject.

  The image inspection apparatus of the present invention can further include a lens filter. The lens filter is provided between the image capturing device and the spectroscope of the illumination unit. For this reason, it is possible to prevent a part of the linear speckle reflected from the subject from entering the image capturing device.

And the autofocus method of the present invention comprises:
Using a linear light source to generate one linear speckle (a);
Projecting only a part of the linear speckle onto the subject via the objective lens (b);
(C) obtaining a target image by capturing an image of a subject and a part of a linear speckle with an image sensor;
Determining a state in which the subject is in focus based on the length, width, and position of a portion of the linear speckle in the target image; and
And (e) adjusting the distance between the objective lens and the subject based on the determination result of step (d).

  The autofocus system and the autofocus system method according to the present invention are based on one of the linear speckles while determining the distance to the subject based on the length and width of a part of the linear speckles in the captured target image. Determine whether the subject is in focus by determining whether each of the length and width of the part is reduced to the limit value, or based on the position of a part of the linear speckle, Whether the subject is above or below the focus (whether the subject is above or below the in-focus state) is determined. With this configuration, the present invention can realize quick focusing only by speckle image processing with a simple geometric shape, and the number of pixels of an image necessary to be processed by an algorithm responsible for image processing. Can be less. Furthermore, it is possible to effectively reduce the situation where the center of gravity position of the speckle luminance distribution is relatively accurate and has little fluctuation, and the center of gravity position fluctuates left and right due to non-uniform speckle luminance distribution.

It is a schematic diagram which shows the system of the image inspection apparatus of this invention. It is a schematic diagram which shows the target image obtained in the state which the autofocus system of this invention combined with the different focus. It is a schematic diagram which shows the target image obtained in the state which the autofocus system of this invention combined with the different focus. It is a schematic diagram which shows the target image obtained in the state which the autofocus system of this invention combined with the different focus. It is a schematic diagram which shows the target image obtained in the state which the autofocus system of this invention combined with the different focus. It is a schematic diagram which shows the target image obtained in the state which the autofocus system of this invention combined with the different focus.

  FIG. 1 shows an image inspection apparatus 100 according to an embodiment of the present invention. The image inspection apparatus 100 according to the present embodiment captures an image by photographing the surface of the subject 4 and detects a wrinkle on the subject 4 based on the captured image (foreign matter or pattern abnormality on the subject surface). It is used to perform inspection to detect).

  The image inspection apparatus 100 includes an autofocus system 1, an image capture unit 2, an illumination unit 3, and an image inspection unit 20. The autofocus system 1 is used for focusing on the subject 4. The image capturing means 2 is used to capture the image of the subject 4 after the autofocus processing by the autofocus system 1 is finished, capture the image, and obtain a clear inspection image. The illumination unit 3 is used to provide illumination necessary when the image capturing unit 2 captures an image of the subject 4. The image inspection means 20 is connected to the image capture means 2 to receive the image to be inspected from the image capture means 2, and detects defects such as foreign matter or pattern abnormality from the image to be inspected by computer image processing technology. Used for.

  The autofocus system 1 includes a linear light source 5, an optical assembly 6, an image sensor 7, a focus adjustment module 8, a driving device 9, and an objective lens 10. The linear light source 5 is used to generate linear speckles such as linear infrared laser speckles. The optical assembly 6 includes a converging lens 61, a light blocking member 62, a reflecting mirror 63, a first spectroscope 64, a second spectroscope 66, and an imaging lens 67, and is linearly emitted from the linear light source 5. The speckle passes through these sequentially and reaches the imaging lens 67.

  Linear speckles emitted from the linear light source 5 are incident on the incident surface of the converging lens 61. The light shielding member 62 is provided on the optical path of the linear light source 5 and the objective lens 10, that is, on the optical path along which the linear speckle proceeds, and more specifically, provided between the exit surface of the converging lens 61 and the reflecting mirror 63. It is done. The light shielding member 62 partially blocks the linear speckle and causes only a part of the linear speckle to enter the objective lens 10. For example, the light shielding member 62 shields half or nearly half of the linear speckle and allows the other half or nearly half of the linear speckle (part of the linear speckle) to enter the objective lens 10. To do. The reflecting mirror 63 is used to reflect a part of the linear speckle to the first spectroscope 64. The first spectroscope 64 reflects a part of the linear speckle from the reflecting mirror 63 to the objective lens 10. In the present embodiment, half or nearly half of the linear speckles emitted from the linear light source 5 are blocked by the light shielding member 62, so that the objective lens 10 actually has only the half of the linear speckles that are not blocked. Upon receipt of a part, a part of the linear speckle is projected onto the subject 4. Since the illumination light emitted from the illumination unit 3 is also projected onto the subject 4 via the objective lens 10, the reflected light reflected from the subject 4 and part of the linear speckle reflected from the subject 4 are , Both are reflected by the subject, enter the objective lens 10, and pass through the first spectroscope 64. The second spectroscope 66 is located between the first spectroscope 64 and the imaging lens 67, and the reflected light from the first spectroscope 64 and a part of the linear speckle enter and the imaging lens 67. Used to reflect on The imaging lens 67 is located in front of the image sensor 7 (between the second spectroscope 66 and the image sensor 7), and converges reflected light and a part of the linear speckle to detect the detection surface of the image sensor 7 ( The image is formed on the imaging surface. The image sensor 7 is an image sensor such as a CCD sensor or a CMOS sensor, and outputs an image formed through the imaging lens 67. The output image includes a target of the subject 4 and a part of the linear speckle. Includes images. That is, the image sensor 7 is used to capture an image of the subject 4 and a part of the linear speckle and obtain a target image.

  The focus adjustment module 8 is connected to the image sensor 7 to receive the target image, perform image processing and analysis, and generate parameters such as the length, width and position of a part of the linear speckle in the target image ( Extract. Then, based on the obtained parameters, the current focusing state of the subject 4 (for example, whether the subject 4 is located at the focal point of the objective lens 10 or above or below the focal point) is determined. Thus, the position of the objective lens 10 can be adjusted based on the determination result of the focus adjustment module 8. That is, the focus adjustment module 8 determines the focus state of the subject 4 based on the length, width, and position of a part of the linear speckle in the target image, and drives the drive device 9 based on the determination result. Thus, the objective lens 10 is moved, and the distance between the objective lens 10 and the subject 4 is adjusted.

  More specifically, based on the imaging principle, a part of the linear speckle in the target image becomes longer and thicker as the position of the subject 4 is farther from the focal point of the objective lens 10. Conversely, the closer the subject 4 is to the focal point, the shorter and thinner part of the linear speckle in the target image. When the subject 4 is located above the focal point (assuming that the subject 4 shown in FIG. 1 is in focus, the subject 4 is closer to the objective lens 10 than in the focused state. 1), the position of a part of the linear speckle is located on one side (for example, the left side) of the reference point, and the subject 4 is located below the focal point (subject 4). 1 is away from the objective lens 10 and is positioned below the in-focus state in FIG. 1), the position of a part of the linear speckle is on the other side (for example, the right side) of the reference point. To position. Further, when the length and width of a part of the linear speckle in the target image gradually decrease to the limit value, it indicates that the subject 4 has already reached the focal point. At this time, the linear shape in the target image A part of the speckle will look like one speckled speckle.

  2 to 6 show a target image 70 captured by the image sensor 7 during the autofocusing process of the autofocus system of the present invention. In each figure, one virtual intermediate line is displayed on the target image 70, and the first detection area 701 (left side area) and the second detection area 702 have the virtual intermediate line as a reference point (reference position). (Right area). The reference point that is divided into the left region 701 and the right region 702 is a predetermined reference related to the focus state, and as described above, for example, the subject 4 shown in FIG. 1 is in focus. This is the imaging position when the state is assumed. As shown in FIG. 2, the focus adjustment module 8 performs image processing and analysis on the target image 70 (this can be performed using a known image processing analysis technique), and then the line in the target image 70 is detected. Parameters such as the length, width and position of the part L1 of the speckle can be obtained. Further, from the analysis result in the target image 70, it can be determined that a part L1 of the linear speckle is relatively thick and long and is located on one side of the reference point (that is, the left side region 701). Accordingly, the focus adjustment module 8 determines that the subject 4 at this time is located above the current focus, and determines that the objective lens 10 needs to be moved upward in order to bring the subject 4 closer to the focus. To do. Based on such a determination result, the focus adjustment module 8 moves the objective lens 10 upward via the driving device 9. Thereafter, when the image sensor 7 captures the target image 70 again and the captured target image 70 is as shown in FIG. 3, the focus adjustment module 8 performs image processing and analysis on the target image 70 shown in FIG. After doing, it can be seen that it is relatively short, thin and similarly located in the left region 701 based on the parameters of the part L2 of the linear speckle. For this reason, the subject 4 at this time is positioned above the point where the focus is still in focus at the present time, but a part L2 of the linear speckle is shorter than before (FIG. 2). It is thin and it can be determined that the position is close to the focal point. The focus adjustment module 8 determines that the subject 4 can be brought closer to the focal point in FIG. 3 and the objective lens 10 needs to be moved further upward, and the objective lens 10 is further moved via the driving device 9. Move upward.

  When the target image 70 captured by the image sensor 7 is as shown in FIG. 6, the focus adjustment module 8 performs image processing and analysis on the target image 70 shown in FIG. Based on parameters such as the length, width, and position of the part L5, it can be seen that it is thick and long and is located on the other side of the reference point (that is, the right region 702). Therefore, the focus adjustment module 8 determines that the subject 4 at this time is located below the focal point at the present time, that is, the subject 4 is located below the paper surface in FIG. 1 than when the subject 4 is in focus. Can be determined. The focus adjustment module 8 moves the objective lens 10 downward in order to bring the subject 4 closer to the focal point, that is, to bring the objective lens 10 closer to the subject 4. Similarly, when the target image 70 captured by the image sensor 7 is as shown in FIG. 5, the focus adjustment module 8 determines that the subject 4 at this time is below the focus at the current time (the focus corresponding to the reference point). Although it is located below the position of the subject 4 in the state of being in alignment, it is determined that it is closer to the focal point than the previous one shown in FIG. 6 (a part L4 of the linear speckle is further shortened and thinned). judge. Since the focus adjustment module 8 can bring the subject 4 closer to the focus, the focus adjustment module 8 determines that the objective lens 10 still needs to move downward, and further lowers the objective lens 10 via the driving device 9. Move to.

  Next, when the target image 70 captured by the image sensor 7 is as shown in FIG. 4, the focus adjustment module 8 performs image processing and analysis on the target image 70 shown in FIG. Based on the parameters such as the length and width of the part L3 of the speckle, it can be determined that the length and width of the part L3 are reduced to the limit values. Therefore, the focus adjustment module 8 determines that the subject 4 at this time is currently in focus (positioned in focus). That is, FIG. 4 shows that the autofocus system 1 of the present invention has completed focusing of the subject 4. When the autofocus system 1 determines that the subject 4 is in focus, the autofocus system 1 immediately transmits a signal to notify the image capturing unit 2, and the image capturing unit 2 captures an image with respect to the subject 4. It is possible to obtain a clear image to be inspected.

  Referring again to FIG. 1, the driving device 9 is connected to the focus adjustment module 8, and based on the determination result of the focus adjustment module 8 until the autofocus system 1 completes focusing of the subject 4, The distance between the objective lens 10 and the subject 4 is adjusted by driving corresponding to the upward or downward movement.

  The illumination means 3 includes a spectroscope 31, a lighting fixture 32, and a collimator lens 33 provided between the spectroscope 31 and the lighting fixture 32. The spectroscope 31 of the illuminating means 3 and the first spectroscope 64 and the second spectroscope 66 of the autofocus system 1 are arranged coaxially and receive visible light from the illuminating device 32 and reflect it to the subject 4. Provide illumination light at.

  The image capturing means 2 includes an image capturing device 21, an imaging lens 22, and a lens filter 23. The image capturing device 21 is a photographing device, and is used to immediately capture an image on the subject 4 when the focus adjustment module 8 of the autofocus system 1 determines that the subject 4 has been focused. The content of the image captured by the image capturing device 21 is the subject 4 and includes a clear inspection image. The lens filter 23 is provided between the image capturing device 21 and the spectroscope 31 of the illumination unit 3, and filters light in a specific light wave band (in the present embodiment, indicates infrared laser speckle), thereby filtering It is possible to prevent a part of the shape speckle from entering the image capturing device 21.

  Through the above description, the focusing method of the present invention includes the following steps.

  Step (a): For example, one linear speckle such as a linear infrared laser speckle is generated. This step can be realized using the linear light source 5.

  Step (b): Only a part of the linear speckle is projected onto the subject 4 via the objective lens 10. At this time, the objective lens 10 is half of the linear speckle emitted from the linear light source 5, and at least a part of the laser light of the linear speckle is incident thereon. This step can be realized using the light shielding member 62.

  Step (c): A target image is obtained by capturing an image of the subject 4 and part of the linear speckle. This step can be realized using the image sensor 7.

  Step (d): A state in which the subject is in focus is determined based on the length, width, and position of a part of the linear speckle in the target image. This step can be realized by using the focus adjustment module 8.

  Step (e): The distance between the objective lens 10 and the subject 4 is adjusted based on the determination result of step (d), which is the determination result of the focused state. This step can be realized using the driving device 9.

  The autofocus system and autofocus system method of the present invention can be applied not only to the image inspection apparatus described above but also to an apparatus that needs to take an image, such as a smartphone having a camera function. is there.

  In summary, according to the autofocus system and the autofocus system method of the present invention, the determination as to whether or not the subject is in focus can be made directly from the target image. The target image captured by the image sensor 7 can obtain the length and width of a part of the linear speckle therein by using an image binarization process. Then, the distance of the distance to the focal point of the subject 4 is determined, and further, by determining whether or not the length and width of a part of the linear speckle have been reduced to the limit values, the subject 4 is brought into focus. It is determined whether it is positioned (in focus). Next, in the autofocus system and the autofocus system method of the present invention, the position of a part of the linear speckle in the target image, that is, the position of a part of the linear speckle in a focused state is used as a reference point. As described above, it is determined whether or not the subject 4 is positioned above or below the current focal point by determining the left side or the right side (or the left tilt or the right tilt) of the reference point. For this reason, it is not necessary to continuously acquire the rate of change in length of all the perspective positions and estimate the focal plane (the plane perpendicular to the optical axis passing through the focal point). In addition to this, the present invention uses linear speckles to determine the focused state compared to the conventional laser focus system that needs to handle the shape change of various light spots. Focusing only on simple geometric rectangles, the algorithm responsible for image processing requires a small number of image pixels, and the center of gravity of the speckle luminance distribution is relatively accurate and fluctuates. Therefore, it is possible to effectively reduce the situation in which the position of the center of gravity fluctuates left and right due to the uneven luminance distribution of the linear speckles.

  It should be noted that several persons can obtain sufficient teachings from the description of the above embodiments and can carry out the teachings, thereby ensuring that the contents of the present invention are different from the prior art and sufficiently have industrial applicability and inventive step. Can understand. Therefore, in order to meet the patent requirements, the present invention is filed based on the law.

1: autofocus system 10: objective lens 100: image inspection apparatus 2: image capturing means 20: image inspection means 21: image capturing apparatus 22: imaging lens 23: lens filter 3: illumination means 31: spectrometer 32: Lighting fixture 33: Collimating lens 4: Subject 5: Linear light source 6: Optical assembly 61: Converging lens 62: Light blocking member 63: Reflecting mirror 64: First spectroscope 66: Second spectroscope 67: Imaging lens 7: Image Sensor 70: Detection surface 701: First detection area 702: Second detection area 8: Focus adjustment module 9: Drive devices L1 to L5: Linear speckle

Claims (9)

A linear light source for generating one linear speckle having a first portion and a second portion;
An objective lens for projecting the first part of the linear speckle on a subject, the first part of the linear speckle entering;
Provided in an optical path between the linear light source and the objective lens, shields the second part of the linear speckle and shields only the first part of the linear speckle on the objective lens Members,
An image sensor for capturing the subject and the first portion of the linear speckle to obtain a target image;
Connected to the image sensor, and obtaining, processing and analyzing the target image to identify the length, width and position of the first portion of the linear speckle in the target image; The focus state of the subject is determined based on the length, width, and position of the first portion of the linear speckle in the target image, and the distance between the objective lens and the subject is determined based on the determination result A focus adjustment module to adjust
Including
The first portion and the second portion are along the length of the linear speckle, and each of the first portion and the second portion has a length shorter than the length of the linear speckle. ,
When the first portion of the linear speckle in the target image becomes longer and wider, the focus adjustment module determines that the subject is away from the focus of the objective lens;
If the first portion of the linear speckle in the target image becomes shorter and narrower, the focus adjustment module determines that the subject is approaching the focus of the objective lens;
When the length and width of the first portion of the linear speckle in the target image are reduced to a predetermined limit value, the focus adjustment module determines that the subject is in focus,
When the first portion of the linear speckle in the target image is located on one side of a predetermined reference point set in advance in the target image, the focus adjustment module causes the subject to It is determined that the object lens is closer to the objective lens than the focal point of the objective lens,
When the first portion of the linear speckle in the target image is located on the other side of the reference point, the focus adjustment module causes the subject to be farther from the objective lens than the focal point of the objective lens. An autofocus system characterized by being determined to be in a position.   The autofocus system according to claim 1, wherein the linear light source generates linear laser speckle. A converging lens, a reflecting mirror, a first spectroscope, a second spectroscope, and an imaging lens;
The incident surface of the convergent lens is incident with the linear speckles emitted from the linear light source,
The light shielding member is provided between an exit surface of the convergent lens and the reflecting mirror, and the reflecting mirror reflects the first portion of the linear speckle to the first spectroscope,
The first spectroscope reflects the first portion of the linear speckle to the objective lens, and reflects the reflected light reflected from the subject to the objective lens and the first portion of the linear speckle. Allow to penetrate,
The second spectroscope is located between the first spectroscope and the imaging lens, and the reflected light from the first spectroscope and the first portion of the linear speckle are incident and the connection is made. Reflected on the image lens,
The image forming lens converges the reflected light and the first portion of the linear speckle to form an image on a detection surface of the image sensor in order to generate the target image. The autofocus system according to 1 or 2. A driving device for adjusting a distance between the subjects;
4. The autofocus according to claim 1, wherein the driving device is connected to the focus adjustment module and moves the objective lens based on a determination result of the focus adjustment module. 5. system. An autofocus system according to any one of claims 1 to 4, an image capturing device, and illumination means,
The illumination means provides illumination light to the subject;
The image capturing apparatus captures an image of the subject immediately when it is determined by the focus adjustment module of the autofocus system that the subject is in focus. The illumination means includes a spectroscope and a luminaire.
The spectroscope and the first spectroscope and the second spectroscope of the autofocus system are arranged coaxially,
The image inspection apparatus according to claim 5, wherein the spectroscope illuminates the subject by reflecting the visible light to the subject while visible light from the lighting fixture is incident thereon. A lens filter,
The lens filter is provided between the image capturing device and the spectroscope of the illumination unit, and the first portion of the linear speckle reflected from the subject is captured by the image capturing device. The image inspection apparatus according to claim 6, wherein this is prevented. Generating a linear speckle having a first portion and a second portion by a linear light source (a);
Projecting only the first portion of the linear speckle onto the subject via the objective lens (b);
Capturing an image of the subject and the first part of the linear speckle with an image sensor to obtain a target image;
By acquiring, processing and analyzing the target image, the length, width and position of the first portion of the linear speckle in the target image are specified, and the linear spec in the target image Determining the focus state of the subject based on the length, width and position of the first portion of the subject;
Adjusting the distance between the objective lens and the subject based on the determination result of the step (d);
Including
The first portion and the second portion are along the length of the linear speckle, and each of the first portion and the second portion has a length shorter than the length of the linear speckle. ,
In step (d),
If the first portion of the linear speckle in the target image becomes longer and wider, it is determined that the subject is moving away from the focus of the objective lens;
When the first portion of the linear speckle in the target image becomes shorter and narrower, it is determined that the subject is approaching the focus of the objective lens;
When the length and width of the first portion of the linear speckle in the target image are reduced to a predetermined limit value, it is determined that the subject is in focus,
When the first portion of the linear speckle in the target image is located on one side of a predetermined reference point set in advance in the target image, the subject is more than the focal point of the objective lens. It is determined that the position is close to the objective lens,
When the first part of the linear speckle in the target image is located on the other side of the reference point, it is determined that the subject is located farther from the objective lens than the focal point of the objective lens. An autofocus method characterized by that.   9. The method according to claim 8, further comprising the step of blocking the second portion of the linear speckle using a light shielding member and causing the first portion of the linear speckle to enter the objective lens. Autofocus method.

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