TW201730658A - Photographing apparatus and photographing method - Google Patents

Abstract

A photographing apparatus includes a light source configured to radiate light; a focusing optical system configured to change a path of light reflected by an object; a capturing unit configured to capture an image of the object formed by the focusing optical system; and a distance adjustment unit configured to adjust a distance between the focusing optical system and the object. The capturing unit captures an image of the object every time the distance between the focusing optical system and the object changes by a predetermined interval, wherein the predetermined interval is set to be smaller than the size of a depth of field of the focusing optical system.

Description

Shooting device and shooting method

The present invention relates to a photographing apparatus and a photographing method, and relates to an autofocus technique of a photographing apparatus.

In a laser processing process, etc., it is important to clearly photograph the surface of an object. In order to improve the sharpness of the image, it is necessary to perform an operation of aligning the focus position of the focusing optical system to the object, and the above operation is referred to as an autofocus operation.

The autofocus operation is a job of changing the distance between the focusing optical system and the object while finding the distance position for realizing a clear image. That is, in the autofocus process, it is necessary to change the distance between the focusing optical system and the object to perform a plurality of shooting operations.

However, previously, in order to obtain an image without shaking in a plurality of shooting jobs, an image was taken in a stationary state. However, in this case, the delay time required for the vibration of the waiting device to disappear is consumed, and thus there is a problem that it is difficult to perform the autofocus operation at high speed. Further, when the autofocus operation is performed in the moving state, the sharpness of the image is lowered, so that it is difficult to find an accurate focus position.

[Problem to be Solved by the Invention] According to an exemplary embodiment, an autofocus operation of a photographing device can be performed accurately and quickly. [Means for solving the problem]

In one aspect, an imaging apparatus includes: a light source, illumination light; a focusing optical system that changes a path of light reflected by the object; and an imaging unit that captures the object formed by the focusing optical system And a distance adjusting unit that adjusts a distance between the focusing optical system and the object; and each time the distance between the focusing optical system and the object changes by a specific interval, the imaging unit captures the object The image of the object, the specific interval described above is set to be smaller than the depth of the depth of the focus optical system.

The imaging unit can capture an image of the object in a global shutter manner.

The distance adjusting unit may change the distance between the object and the focusing optical system at a constant speed in at least one section.

The speed at which the distance adjusting unit changes the distance between the object and the focusing optical system satisfies the formula 1, Equation 1 (V1 = magnitude of the speed of change of the distance between the object and the focusing optical system, f = number of times of imaging per unit time of the imaging unit in the equal speed section, DOF = depth of field of the focusing optical system).

The speed at which the distance adjusting unit changes the distance between the object and the focusing optical system satisfies the formula 2, V1< Equation 2 (V1 = magnitude of change in distance between the object and the focusing optical system, DoF = depth of field of the focusing optical system, E = exposure time per frame of the imaging section).

The exposure time per frame of the above shooting section can satisfy the formula 3, Equation 3 (E = exposure time per frame of the imaging unit, A _pixel = pixel area of the imaging unit, M = magnification, V2 _max = maximum value of the relative vibration velocity between the imaging unit and the object).

The imaging device may further include an encoder that senses a change in a distance between the object and the imaging unit to generate an electrical signal.

The imaging device may further include a control unit that generates a synchronization signal to the imaging unit based on the electrical signal generated by the encoder.

The imaging device may further include a processor that receives the image of the object captured by the imaging unit and captures the sharpness of the image.

The processor can determine a distance between the object that captures the image with the highest definition and the focusing optical system as a focus distance.

The processor can determine the focus distance by using Equation 4 according to the sharpness value of the image. Equation 4 (H = distance between the focusing optical system and the object in the focused state, H _i = distance between the focusing optical system and the object at the ith shot in which the highest sharpness is measured, H _{i - 1} = distance between the focusing optical system and the object at the i-1th shot, H _{i + 1} = distance between the focusing optical system and the object at the i+1th shot, C _i = measured Sharpness value of the i-th captured image with the highest resolution, C _{i - 1} = sharpness value of the i-1th captured image, C _{i + 1} = sharpness is the clarity of the i+1th captured image Degree).

The range in which the distance adjusting unit changes the distance between the object and the focusing optical system can be determined by Equations 5 and 6, and H-D-δ<X<H+D+δ... Equation 5 Equation 6 (X = distance between the support of the object and the focus point of the focusing optical system, H = predicted thickness of the object, D = thickness deviation of the object, δ = acceleration interval, V1 = maximum speed, a = acceleration).

In another aspect, a photographing method is provided, comprising the steps of: irradiating light to an object; and concentrating light reflected by the object by a focusing optical system; adjusting the focusing optical system and the above a step of distance between the objects; and a step of capturing an image of the object every time the distance between the focusing optical system and the object changes by a specific interval; and the specific interval is set to be smaller than the above Focus on the depth of field of the optical system.

In the step of adjusting the distance, the distance between the object and the focusing optical system may be changed at a constant speed in at least one interval.

In the step of adjusting the distance, the imaging unit may capture an image of the object at a fixed time interval in a section in which the distance between the object and the focusing optical system is changed at a constant speed, and the object and the object The speed at which the distance between the focusing optical systems changes satisfies the formula 1, Equation 1 (V1 = magnitude of the speed of change of the distance between the object and the focusing optical system, f = number of times of shooting per unit time of the imaging unit in the equal speed section, DoF = depth of field of the focusing optical system, α is equal to 0.1 < Any real number with α < 0.5).

In the step of adjusting the distance, the speed of changing the distance between the object and the focusing optical system may satisfy the formula 2, V1< Equation 2 (V1 = magnitude of change in distance between the object and the focusing optical system, DoF = depth of field of the focusing optical system, E = exposure time per frame of the imaging section).

The above-described photographing method may further include the step of sensing a change in the distance between the object and the photographing portion to generate an electrical signal.

The above shooting method may further include the step of generating a synchronization signal to the imaging unit based on the electrical signal.

The above imaging method may further include the step of receiving an image of the object captured by the imaging unit and capturing the sharpness of the image.

The above shooting method may further include the step of determining the focus distance by the formula 4 according to the sharpness value of the image, Equation 4 (H = distance between the focusing optical system and the object in the focused state, H _i = distance between the focusing optical system and the object at the ith shot in which the highest sharpness is measured, H _{i - 1} = distance between the focusing optical system and the object at the i-1th shot, H _{i + 1} = distance between the focusing optical system and the object at the i+1th shot, C _i = measured Sharpness value of the i-th captured image with the highest resolution, C _{i - 1} = sharpness value of the i-1th captured image, C _{i + 1} = sharpness is the clarity of the i+1th captured image Degree). [Effect of the invention]

According to an embodiment, the photographing device can perform an autofocus operation while a distance between the object and the focusing optical system changes. Therefore, the photographing device can shorten the time required for auto focus.

Moreover, the imaging device can obtain a clear image even if the auto focus is dynamically achieved. The photographing device can capture at least one image taken during the dynamic autofocus process within the depth of field of the focusing optical system.

Further, the imaging device corrects the accurate focus distance in accordance with the sharpness value of the image, whereby the accuracy of the autofocus operation can be improved.

In the following drawings, the same reference numerals are given to the same components, and the size of each component may be exaggerated in the drawing for clarity and convenience of description. On the other hand, the embodiments described below are merely examples, and various modifications can be made according to the embodiments.

The first and second terms can be used to describe various constituent elements, but the constituent elements are not limited by the terms. The above terms are used only for the purpose of distinguishing one component from another component.

As long as the other meanings are not clearly stated in the text, the singular expression includes the plural expression. In addition, when a part is "included" to a certain component, unless otherwise stated, it means that it may include other components, and does not mean that other components are excluded.

Further, terms such as "parts" and "modules" described in the specification refer to units that process at least one function or operation.

FIG. 1 is a view showing an imaging device 100 of an exemplary embodiment.

Referring to Fig. 1, an imaging apparatus 100 of an exemplary embodiment may include: a light source 110; a focusing optical system 120 that changes a path of light reflected by the object 10; and an imaging unit 140 that captures an object formed by the focusing optical system 120. The image of the object 10; and the distance adjusting portion 130 adjust the distance between the focusing optical system 120 and the object 10.

Light source 110 can illuminate light. Light emitted from the light source 110 can be irradiated to the object 10 through a specific optical system. FIG. 1 shows an example in which light emitted from the light source 110 travels in parallel light. However, the embodiment is not limited thereto, and an optical system through which light emitted from the light source 110 passes may be differently configured. Further, the light emitted from the light source 110 can be directly irradiated to the object 10 without passing through the optical system.

The focusing optical system 120 can be changed to the path of the light reflected by the object 10. The light whose path is changed by the focusing optical system 120 can be incident on the image sensor of the imaging unit 140. In FIG. 1, the focusing optical system 120 is shown in a manner separate from the imaging unit 140, but the embodiment is not limited thereto. The focusing optical system 120 may also be included inside the imaging unit 140. In this case, the distance adjusting unit 130 can change the distance between the focusing optical system 120 and the object 10 by moving the imaging unit 140. Focusing optics 120 can have a particular focusing distance. Therefore, when the focusing optical system 120 maintains an appropriate distance from the surface of the object 10, the imaging unit 140 can obtain a clear image of the object 10.

The object 10 may include a wafer, a semiconductor wafer, or the like as an object to be photographed, and is not limited thereto. The object 10 is not fixed in thickness due to the roughness of the surface. Further, the distance between the surface of the object 10 and the focusing optical system 120 is not fixed depending on the flatness of the support surface S1 of the support object 10. Therefore, in order to clearly obtain an image of the object 10, the imaging device 100 needs to appropriately adjust the distance between the object 10 and the focusing optical system 120. The process of adjusting the distance between the focusing optical system 120 and the object 10 in order to clearly obtain an image of the object 10 by the photographing apparatus 100 is referred to as an auto focusing process.

The distance adjusting portion 130 can change the distance between the object 10 and the focusing optical system 120 during the autofocusing process. The distance adjustment unit 130 can move the support surface S1 on which the object 10 is attached. As another example, the distance adjustment unit 130 can move the focusing optical system 120. When the focusing optical system 120 is built in the imaging unit 140, the distance adjusting unit 130 can also move the imaging unit 140. Also, the distance adjusting portion 130 can change the distance between the focusing optical system 120 and the object 10 by simultaneously moving the focusing optical system 120 and the supporting surface S1.

In order to change the distance between the object 10 and the focusing optical system 120, the distance adjusting unit 130 can move a moving body having a large mass including the focusing optical system 120, the imaging unit 140, and the support surface S1. The moving body may be the focusing optical system 120, the imaging unit 140, the support surface S1, and the like that the distance adjustment unit 130 moves to achieve auto focus. During the acceleration/deceleration of the moving body by the distance adjusting unit 130, vibration due to the inertial force occurs. For example, when the imaging device 100 captures the semiconductor object 10, the imaging unit 140 becomes larger in quality due to the equipment attached thereto, and the mass of the moving body becomes large. At this time, when the distance adjustment unit 130 accelerates and decelerates the imaging unit 140, the imaging unit 140 generates vibration due to the inertial force.

According to the comparative example, the image of the object 10 can be imaged in a state where the interval between the focusing optical system 120 and the object 10 does not change. For example, after the focusing optical system 120 is moved to a specific position, an image of the object 10 can be imaged while the focusing optical system 120 is stationary. At this time, in order to obtain a clear image, the imaging unit 140 needs to wait for several tens of ms to several hundreds of ms after the focusing optical system 120 moves and stands still until the vibration due to acceleration and deceleration disappears, and then image capturing is performed.

For example, when the lens system with magnification M and the camera whose horizontal and vertical dimensions are px and py are taken at the optimal focus distance, when the vibration velocity vector is set to (vx, vy, vz), A clear image can only be obtained if vx*E<px/M, vy*E<py*M, and vz*E<DOF are satisfied. Here, E refers to the exposure time of the imaging unit 140, and DOF refers to the depth of field DOF of the focusing optical system 120, which will be described in detail in the following description.

However, the manner of the above comparative example may be disadvantageous for high speed shooting. In order to find an accurate focus position, it is necessary to compare the sharpness of an image obtained by changing the distance between the focusing optical system 120 and the object 10 to various distances. However, whenever an image is obtained, the vibration due to acceleration and deceleration is reduced, so the standby time is required until vx*E<px/M, vy*E<py*M, and vz*E<DOF are satisfied. In addition, the autofocus process becomes longer due to the above standby time. For example, when the mass of the moving body exceeds 30 kg, a standby time of 400 ms or more is required each time an image is taken. Therefore, the delay time required to obtain an image after 10 movements and at rest is 4 seconds or longer. This delay time becomes a factor that makes it difficult to achieve high-speed shooting.

According to an exemplary embodiment, in order to achieve faster autofocus, the imaging unit 140 may capture an image of the object 10 while the distance between the focusing optical system 120 and the object 10 changes. In other words, the imaging unit 140 can capture an image of the object 10 while at least one of the object 10 and the focusing optical system 120 is not in a stopped state. Therefore, after the moving body is stationary, there is no need to wait for the vibration due to the acceleration and deceleration to disappear, so that the time required for the autofocus can be shortened.

The imaging unit 140 can image the object 10 in a global shutter manner. Here, the global shutter mode refers to a method in which all pixels are simultaneously exposed to obtain an image. Conversely, a rolling shutter method is to obtain an image for one line or a group of pixels, and obtain an image by time difference between the remaining pixels. When the imaging unit 140 images the object 10 in the global shutter mode, a clear image can be obtained even if there is external vibration.

The sharpness of the image captured by the imaging unit 140 changes due to the change in the distance between the object 10 and the focusing optical system 120. When the sharpness of the image captured by the imaging unit 140 is maximized, the distance between the object 10 and the focusing optical system 120 can be referred to as a focal length. Even if the distance between the object 10 and the focusing optical system 120 does not completely coincide with the above-described focal length, the sharpness of the image captured by the imaging unit 140 does not largely change. That is, even if the distance between the object 10 and the focusing optical system 120 changes within a certain section in the vicinity of the focal length, the sharpness of the image is not greatly affected. As described above, the region in which the sharpness of the image is held is referred to as the depth of field (DOF) of the focusing optical system 120.

In the autofocus process, the distance between the focusing optical system 120 and the object 10 can be adjusted to the depth of field DOF of the focusing optical system 120. However, when the imaging unit 140 captures an image while the distance between the object 10 and the focusing optical system 120 changes, the image cannot be captured when the focus point is within the depth of field DOF. Therefore, it is impossible to obtain a sharp image at the time of auto focusing, so it is difficult to find an accurate auto focus position. In order to solve the above problem, each time the distance between the collecting optical system 120 and the object 10 is changed by a certain interval, the imaging unit 140 may image an image of the object 10. Also, the above specific interval may be set to be smaller than the size DOF of the depth of field of the focusing optical system 120.

FIG. 2 is a view showing a position of a captured image of the imaging unit 140 during autofocusing. In FIG. 2, the case where the focusing optical system 120 is moved is exemplarily shown, but the embodiment is not limited thereto. For example, the distance between the focusing optical system 120 and the object 10 can also be changed by moving the support surface S1 of the object 10.

Referring to FIG. 2, each time the distance between the focusing optical system 120 and the object 10 is changed by a certain interval Δh, the imaging section 140 will image an image of the object 10. In addition, the specific interval Δh may be set smaller than the size of the depth of field DOF of the focusing optical system 120. The above specific interval Δh may be fixedly maintained during the autofocusing process, or may be slightly changed. However, even if the specific interval Δh changes, the size thereof may be smaller than the size of the depth of field DOF of the focusing optical system 120. Therefore, even if imaging is performed in the middle of the change in the distance between the object 10 and the focusing optical system 120, at least one shooting can be performed in the depth of field DOF.

In order to increase the work speed of the auto focus, the distance adjusting portion 130 can change the distance between the object 10 and the focusing optical system 120 within a specific range. FIG. 3 is a view showing a range in which the distance between the object 10 and the focusing optical system 120 is changed by the distance adjusting unit 130.

Referring to FIG. 3, the distance adjusting portion 130 can move the focus point P of the focusing optical system 120 within a specific region. The distance adjusting unit 130 can move the focus point P of the focusing optical system 120 around the position L2 of the predicted height H of the object 10 from the surface L1 of the support surface S1. For example, the distance adjustment unit 130 can move the focus point P of the focusing optical system 120 to satisfy Equation 1.

[Expression 1] HD -δ< X < H+D +δ

Here, X = the distance between the support surface of the object and the focus point of the focusing optical system, H = the predicted thickness of the object, D = the thickness deviation of the object, and δ = the acceleration interval.

FIG. 4 is a diagram exemplarily showing that the moving speed of the focus point P changes with time. In FIG. 4, the horizontal axis represents time, and the vertical axis represents the relative speed (moving speed of the focus point P) between the focusing optical system 120 and the object 10.

Referring to Fig. 4, the relative speed between the focusing optical system 120 and the object 10 is gradually increased before time t1. At this time, the relative speed can be increased with a fixed acceleration a. The acceleration section is a section in which the distance adjustment unit 130 accelerates the movement of at least one of the focusing optical system 120 and the object 10 .

As an example, during a period from time t0 to t1, the focus point P of the focusing optical system 120 can be moved from the surface L1 of the support surface S1 to the height H-D-δ to the height H-D. The distance δ that moves within the acceleration interval can be expressed by Equation 2.

[Expression 2]

In Equation 2, δ represents the magnitude of the distance moved during the acceleration time, a represents the magnitude of the acceleration, and V represents the terminal speed based on the acceleration, that is, the magnitude of the maximum speed.

From time t1 to time t2, the relative speed between the focusing optical system 120 and the object 10 can be maintained at a fixed size V1. As an example, during a period from time t1 to t2, the focus point P of the focusing optical system 120 can be moved from the surface L1 of the support surface S1 to the height H-D to the height H+D. Further, from time t2 to time t3, the relative speed between the focusing optical system 120 and the object 10 is gradually reduced. At this time, as an example, the relative speed can be gradually reduced with a specific acceleration -a. Further, during a period from time t2 to t3, the focus point P of the focusing optical system 120 can be moved from the surface L1 of the support surface S1 to the height H+D to the height H+D+δ. The distance adjustment unit 130 sets the movement range of the focus point P in consideration of the predicted height H and the thickness deviation D of the object 10, whereby the speed at which the focus distance is sought becomes faster and more accurate.

While the focus point P has moved from the surface L1 of the support surface S1 to the height H-D to the height H+D, the imaging unit 140 may image the image of the object 10 a plurality of times. At this time, the focus point P can be moved at a constant speed, and the magnitude V1 of the moving speed can depend on the exposure time of the imaging unit 140. Here, the exposure time refers to a time when the imaging unit 140 is exposed to light in order to obtain an image when performing one shooting. The exposure time can be adjusted by the time that the light source 110 illuminates the light. As another example, the exposure time may be adjusted by a shutter or a diaphragm located inside the imaging unit 140.

The moving speed of the focus point P (the magnitude of the speed change speed of the object 10 and the focusing optical system 120) V1 can satisfy the formula 3.

[Expression 3]

In Equation 3, V1 = the magnitude of the change speed of the distance between the object and the focusing optical system, DOF = depth of field DOF of the imaging section, and E = exposure time per frame of the imaging section. Further, α is a real number satisfying 0 < α < 1, and can be changed according to the optical performance of the imaging unit 140.

If the focus point P moves too fast, the focus point P will be separated from the depth of field DOF while the image capturing unit 140 is shooting one frame. Therefore, as in Equation 3, the focus point P can be prevented from deviating from the depth of field DOF by the exposure time required for shooting by limiting the moving speed of the focus point P.

In the autofocusing process, even if the distance between the focusing optical system 120 and the object 10 is moved at a constant speed, fine vibration is generated in a direction perpendicular to the direction of the distance between the focusing optical system 120 and the object 10. Therefore, if the exposure time per frame of the imaging unit 140 becomes too long, the sharpness of the image is lowered by the vibration between the focusing optical system 120 and the object 10. In order to prevent the sharpness of the image from being lowered, the movement between the focusing optical system 120 and the object 10 is performed within one pixel of the imaging unit 140 during each frame exposure time. In order to satisfy the above, the exposure time per frame of the imaging section 140 can satisfy the formula 4.

[Expression 4]

In Equation 4, E = exposure time per frame of the imaging unit 140, A _pixel = pixel area of the imaging unit 140, M = magnification, V2 _max = maximum value of relative vibration velocity between the imaging unit 140 and the object 10 .

As shown in the equation 4, if the exposure time E of the imaging unit 140 is restricted, it is possible to prevent the sharpness of the image from being lowered due to the horizontal vibration between the imaging unit 140 and the object 10. For example, in the case of capturing a wafer in a normal wafer grooving process, the field of view (FOV) of the imaging unit 140 needs to be 240 um×180 um to 480 um×360 um, and optical resolution is required. It is 1.2 um or less. When the maximum velocity V2 _max of the vibration between the imaging unit 140 and the object 10 is 0.2 mm/s, it is required to be in accordance with Equation 4 in an environment where the pixel size is 4.8 um × 3.6 um and the magnification is 10 times. Exposure time within approximately 2 ms. In addition, the output power of the light source 110 required to obtain an image may vary according to the exposure time E. For example, the smaller the exposure time E per frame of the imaging unit 140, the greater the light output power required by the light source 110. For example, if the exposure time of the field of view (FOV) of 480 um x 360 um is about 2 ms, the minimum output power required by the light source 110 would be about 0.2 W.

While the focus point P is moving from the surface L1 of the support surface S1 to the height H-D to the height H+D at the constant velocity V1, the imaging unit 140 can image the image of the object 10 at a fixed time interval. Since the imaging section 140 captures an image of the object 10 at a fixed time interval, an image can be obtained each time the focus point P is moved by a fixed distance. At this time, the moving speed of the focus point P (the relative speed between the object 10 and the focusing optical system 120) V1 and the number of times of photographing per unit time of the imaging unit 140 can satisfy the formula 5.

[Expression 5]

In Equation 4, V1 = the magnitude of the change speed of the distance between the object 10 and the focusing optical system 120, f = the number of times of shooting per unit time of the imaging unit 140 in the constant velocity section, DOF = depth of field DOF of the focusing optical system 120 . Further, α is a real number satisfying 0 < α < 1, and can be changed according to the optical performance of the imaging unit 140.

Referring to the formula 5, the product of the moving speed V1 of the focus point P and the reciprocal of the number of shots f of the photographing portion 140 may become smaller than the size DOF of the depth of field DOF of the focusing optical system 120. Therefore, even when the focus point P is moved while the focus point P is being moved, at least one shot can be taken when the focus point P is in the depth of field DOF range of the focus optical system 120. In addition, the focus distance can be derived from a sharp image captured within the depth of field DOF range.

As an example, in the case of an imaging device used in a conventional wafer groove, the DOF value may be approximately 10 μm < DOF < 20 μm. In addition, in order to achieve more accurate photographing, the value of the above α*DOF may be required to be approximately 5 μm or less. Therefore, V1/f<5 um can be satisfied according to Equation 5. As an example, in the case of f = 40 Hz, it is necessary to satisfy V1 ≤ 0.2 mm/s, and in the case of f = 80 Hz, V1 ≤ 0.4 mm/s is satisfied. The above values are only examples and may vary depending on the operating environment.

When the focus point P is located within the depth of field DOF of the focusing optical system 120, a clear image can be obtained. Further, when the image pickup apparatus 100 of the embodiment obtains the clear image described above, it can be determined that automatic focusing is achieved. Referring again to FIG. 1, the photographing apparatus 100 may include a processor 160 to evaluate the sharpness of an image photographed by the photographing section 140. The processor 160 can transmit and receive information to the imaging unit 140 by wireless communication or wired communication.

The processor 160 of FIG. 1 can receive image information captured by the imaging unit 140. Further, the processor 160 can transmit the operation setting information of the imaging unit 140 to the imaging unit 140. The imaging unit 140 can change the operation mode of the imaging unit 140 by receiving the operation setting information from the processor 160. For example, the processor 160 can transmit setting information such as the exposure time E per frame, the number of times of shooting f per unit time, and the like to the imaging unit 140. Further, the imaging unit 140 can receive the setting information and change the exposure time E per frame and the number of imaging times f per unit time based on the setting information. Further, the processor 160 can automatically determine the setting information of the imaging unit 140 based on the above Equations 1 to 5. However, the embodiment is not limited to this. For example, the processor 160 can also receive the setting information of the imaging unit 140 by input from the user. To this end, the processor 160 can provide an input interface for inputting setting information. The above input interface can be provided in a button mode or a touch screen manner.

The processor 160 may include an application program for performing the above functions, and various databases (DB: Database, hereinafter referred to as "DB") built internally or externally depending on the situation. The DB may be formed inside or outside of the processor 160.

As shown in FIG. 3, while the focus point P moves from the surface L1 of the support surface S1 to the H-D height to the H+D height, the imaging unit 140 can transmit the image captured a plurality of times to the processor 160. The processor 160 can evaluate the sharpness of the image received from the photographing section 140. For example, the processor 160 may evaluate the sharpness of each image to convert the number of components.

Here, the sharpness of the image may be an evaluation amount determined according to the degree of defocusing when the image is captured. For example, an image captured in a state where the focus point P is out of the depth of field DOF of the focusing optical system 120 is an image captured in a state in which the degree of defocus is severe. In addition, the image captured in a state where the degree of defocus is more severe includes a portion that is relatively blur, and thus it can be evaluated that the above-described sharpness is low. Conversely, an image captured when the focus point P is located within the depth of field DOF or near the depth of field DOF is an image captured in a state where the degree of defocus is relatively low. In addition, the image captured in a state where the degree of defocus is low includes less blur portions, and thus can be evaluated as having higher definition.

By way of illustration, processor 160 may evaluate the sharpness by analyzing the difference in brightness between pixels of the image. For example, if there are more blurred portions in the image, the difference in brightness between pixels will decrease. Therefore, the processor 160 can evaluate that the sharpness of the image is low when the difference in brightness between pixels is small. Conversely, if the image is sharp, the portion of the light and dark that changes sharply between the pixels will increase. Therefore, the more the area where the amount of change in brightness and darkness between pixels of the image is large, the processor 160 can determine that the sharpness of the image is higher.

The processor 160 can determine the image with the highest definition among the images received from the photographing unit 140. Further, when the image with the highest definition is captured, it can be determined that the distance between the object 10 and the focusing optical system 120 is close to the focusing distance. For example, the processor 160 may receive N images from the photographing section 140 and evaluate the sharpness of the i-th image therein to be the highest. Then, the processor 160 can obtain the conclusion that the distance between the object 10 and the focusing optical system 120 is closest to the focusing distance when the ith image is captured.

In order to find an accurate focus position based on the sharpness of the image evaluated by the processor 160, it is necessary to know the relative distance between the focusing optical system 120 and the object 10 at the time point when each image is captured. That is, there is a need for a method in which the position of the focusing optical system 120 and the object 10 is known every time the imaging unit 140 captures an image.

FIG. 5 is a diagram showing an imaging device 200 of another exemplary embodiment.

Referring to FIG. 5, the photographing apparatus 200 of the exemplary embodiment may further include an encoder 250 that senses a change in the distance between the object 10 and the photographing section 140 to generate an electrical signal. The remaining components have been described in the imaging device 100 of Fig. 1, and therefore the overlapping description will be omitted.

The encoder 250 can be interlocked with the distance adjustment unit 130. The encoder 250 can sense the state of the distance adjusting portion 130 to generate a telecommunication signal based on the above state. For example, each time the distance adjustment unit 130 changes the distance between the object 10 and the imaging unit 140 by a certain interval, the encoder 250 generates an electrical signal. As another example, the encoder 250 can self-sensing the amount of change in the distance between the object 10 and the focusing optical system 120 to generate a pulse signal.

FIG. 6 is a diagram exemplarily showing an electric signal generated by the encoder 250.

Referring to Fig. 6, each time the distance between the object 10 and the focusing optical system 120 is changed by a certain interval, the encoder 250 generates a pulse signal. The frequency at which the pulse signal is generated may vary according to the depth of field DOF of the focusing optical system 120. For example, the amount of change in the distance when the arbitrary i-th pulse is generated and when the (i+1)th pulse is generated may be set smaller than the size of the depth of field DOF of the focusing optical system 120 or the same as the size of the depth of field DOF of the focusing optical system 120. Only by setting the distance interval at which the encoder 250 generates the pulse signal to be smaller than the depth DOF of the focusing optical system 120, the positional change of the focus point P between adjacent shots can be set smaller than the size of the depth of field DOF.

In FIG. 6, the pulse signal is shown as an example of the electrical signal generated by the encoder 250, but the embodiment is not limited thereto. For example, the encoder 250 can also generate different kinds of electrical signals according to the distance between the object 10 and the focusing optical system 120. In this case, processor 160 may internally include an algorithm to parse the electrical signals generated by encoder 250.

The operation of the imaging unit 140 can be synchronized by the pulse signal of the encoder 250. For example, the imaging unit 140 may count the number of pulses of the pulse signal received from the encoder 250. Further, each time the number of pulses is increased by a specific number, the imaging unit 140 captures an image of the object 10. Moreover, the processor 160 can count the number of pulses of the pulse signal received from the encoder 250. In addition, the processor 160 can know the focus optical system 120 and the object 10 at the time point when the image with the highest sharpness is captured, based on the number of pulses counted from the time when the image capturing unit 140 receives the image with the highest sharpness. The distance between them.

FIG. 7 is a diagram showing an imaging device 300 of another exemplary embodiment.

Referring to FIG. 7, the photographing apparatus 300 of the embodiment may further include a control section 355 that generates a synchronization signal to the photographing section 140 based on the electric signal generated by the encoder 250. The control unit 355 can receive the electrical signal generated by the encoder 250. In addition, the control unit 355 can generate a synchronization signal to the imaging unit 140 based on the electrical signal received from the encoder 250. Whenever the distance between the focusing optical system 120 and the object 10 changes by a certain interval, the control section 355 generates a synchronization signal based on the electrical signal supplied from the encoder 250. The imaging unit 140 is synchronized by the above-described synchronization signal, so that each time the distance between the focusing optical system 120 and the object 10 is changed by a specific interval, an image of the object 10 is captured. In addition, the above specific interval may be set to be smaller than the depth of field DOF of the focusing optical system 120.

Further, the processor 160 can receive the synchronization signal from the control unit 355, and when the imaging unit 140 captures an image, the distance between the object 10 and the focusing optical system 120 can be known. In FIG. 7, the processor 160 and the control unit 355 are shown in separate blocks. However, in FIG. 7, only the two configurations are shown in terms of functional separation, and the processor 160 and the control unit 355 are not limited to being separated by hardware. For example, the processor 160 and the control unit 355 can share the same hardware resources and perform their respective functions. Moreover, the processor 160 and the control unit 355 can also be separated into different devices.

FIG. 8 is a view exemplarily showing the synchronization signal generated by the control unit 355. In FIG. 8, the upper graph shows the pulse signal generated by the encoder 250, and the lower graph shows the synchronization signal generated by the control unit 355.

Referring to FIG. 8, each time the number of pulse signals received from the encoder 250 is increased by a specific amount, the control unit 355 generates a pulse signal as a synchronization signal. In FIG. 8, the control unit 355 generates an example of a pulse signal every time the number of pulse signals received from the encoder 155 changes in units of three. However, the embodiment is not limited to this. For example, the number ratio between the pulse signal generated by the control unit 355 and the pulse signal generated by the encoder 250 may be smaller than the number shown in FIG. 8 or larger than the number shown in FIG.

The control unit 355 can know the interval between the focusing optical system 120 and the object 10 based on the electrical signal received from the encoder 250. Further, the control unit 355 can control the operation mode of the distance adjustment unit 130 based on the interval between the focus optical system 120 and the object 10 described above.

The control unit 355 can control the distance adjustment unit 130 such that the focus point P moves within the range satisfying the formula 1. At this time, values such as H, D, δ, etc. in Equation 1 can be input through the input face of the processor 160. The processor 160 can transmit the input set value to the control unit 355. The control unit 355 can determine how the distance adjustment unit 130 operates by comparing the received set value with the distance value obtained from the electrical signal received from the encoder 250.

For example, if the control unit 355 receives the point H-D-δ=0.64 mm from the processor 160, the end point H+D+δ=0.96 mm, and the iso-speed V1=0.2 mm/s in the constant-speed motion section, the control unit 355 can focus on The control signal is transmitted to the distance adjusting unit 130 in such a manner that the height of P becomes the position of H-D-δ = 0.64 mm. Further, if the height of the focus point P becomes H-D-δ = 0.64 mm, the control unit 355 can transmit a movement end interrupt signal to the processor 160. Further, when the control unit 355 receives the autofocus start command from the processor 160, the control unit 355 can adjust the height of the focus point P to a position of H-D-δ=0.64 mm based on the electric signal received from the encoder 250, at an equal acceleration a. (=V1/Δt) 0.667 mm/s2 is accelerated from speed 0 to speed V1 0.2 mm/s and moved from the position of H-D=0.7 mm to the position of H+D=0.9 mm at speed V1 0.2 mm/s. The acceleration -a (= -0.667 mm / s2) is decelerated and stops at the position of height H + D + δ = 0.96 mm. In addition, the control unit 355 can transmit a mobile end interrupt signal to the processor 160. Further, when the height of the focus point P becomes H + D = 0.9 mm from the position of H - D = 0.7 mm, the control unit 355 can generate a pulse signal at intervals of 5 μm. Further, the imaging unit 140 can image the object 10 by synchronizing the pulse signals. The above numerical values are merely examples and may vary depending on the embodiment.

FIG. 9 is a view showing a change in height of the focus point P corresponding to time.

In Fig. 9, the vertical axis represents the height of the focus point P, and the horizontal axis represents time. For convenience, the state in which the auto focus starts is indicated as the origin.

The processor 160 can evaluate the sharpness of the N images received from the photographing section 140. In addition, the processor 160 can determine the ith image with the highest definition among the N images. Moreover, the processor 160 can know the height H _{i of the ith} shot based on the signal received from the control unit 355 or the encoder 250. In addition, the focus point P can be moved to the above-described height H _i .

Referring to Fig. 9, at t ₀ to t ₁ , the focus point P can perform an acceleration motion. As an example, at time t ₀ , the height of the focus point P is 0 in the graph, but may actually be H-D-δ shown in Equation 1. Also, at time t ₁ , the height of the focus point P may be H-D. The time Δt required to accelerate the motion may vary depending on the magnitude of the constant velocity V1 and the acceleration a.

At time t ₁ to t _N , the focus point P can be moved at a constant speed. In the constant velocity motion interval, the height of the focus point P can be changed from H-D to H+D. In the section where the focus point P performs the constant velocity motion, the imaging unit 140 captures an image of the object 10 every time the focus point P moves by a certain interval Δh. The specific interval Δh is set to be smaller than the depth of field DOF of the focusing optical system 120, whereby at least one shot can be achieved within the depth of field DOF.

In the equal-speed motion section, photographing is performed at specific distance intervals, so that the image of the object 10 can be photographed at a specific time interval of 1/f. The time required for the imaging unit 140 to transmit image data to the processor 160 may be less than the above-described time interval 1/f. In Fig. 9, t _i is the time at which the i-th shot is achieved in the constant velocity interval. Further, H _i is the height of the focus point P when the i-th shot is taken in the constant speed section. After N shots are taken in the equal speed range, the focus point P can be decelerated. The focus point P can be stopped at the height H+D+δ.

FIG. 10 is a graph showing the relationship between the height of the focus point P and the sharpness of the image.

Referring to Fig. 10, the sharpness C _i at the height H _i at which the i-th shot is taken may have the highest value. The processor 160 may determine the height H _i of the image captured with the maximum sharpness _Ci value as the auto focus distance among the plurality of sharpness values. The manner in which the processor 160 determines the auto focus distance is not limited thereto. For example, processor 160 may further consider the adjacent H _i H _{i - 1,} each of the clarity value C at the height H _{i + 1 i - 1,} C _{i + 1} for correcting autofocus distance.

FIG. 11 is a diagram showing the processor 160 correcting the auto focus distance.

Referring to FIG. 11, the processor 160 may calculate the height _Hmax of the image that obtains the maximum sharpness _Cmax . As shown in FIG. 11, the distance does not change continuously photographed image of the object 10, and therefore will not maximum height H _max of the captured image in image sharpness. However, in practice, the interval between H _{i - 1} , H _i , and H _{i + 1} is very narrow, so that the focus can be estimated by a quadratic function while the height of the focus point P changes from H _{i - 1} to H _{i + 1} . The relationship between the height of the point P and the sharpness of the image. Further, by the above approximation method, H _{i - 1} , H _i , H _{i + 1} and C _{i - 1} , C _i , C _{i + 1} can be expressed by Equation 7 to Formula 9.

[Expression 7]

[Expression 8]

[Expression 9]

Further, the sharpness can be obtained C _max is the maximum height H _max of the image obtained inflection point to a quadratic function as shown in Equation 7 is a formula 9 i.e. -b / 2a. When the height H _max =−b/2a is obtained from Equations 7 to 9, it can be expressed as Equation 10.

[Expression 10]

Each processor 160 may calculate the height _{H i - 1, H i,} H i + 1 obtained image sharpness _{C i - 1, C i,} C i + 1 in accordance with the preferred formula above calculated 10 focusing distance above the height H _max and H _max is determined as the auto-focusing distance. When the processor 160 determines the autofocus distance H _max , the distance adjustment unit 130 can change the distance between the object 10 and the focusing optical system 120 such that the distance between the focus point P and the support surface of the object 10 becomes H _max . .

The imaging devices 100, 200, and 300 of the exemplary embodiments have been described above with reference to FIGS. 1 through 11. Hereinafter, an imaging method using the above-described imaging devices 100, 200, and 300 will be described. All of the technical features of the above-described imaging devices 100, 200, and 300 can be applied to the imaging methods described below, and overlapping descriptions will be omitted.

Figure 12 is a flow chart showing a photographing method of an exemplary embodiment.

Referring to FIG. 12, the photographing method may include the steps of: irradiating light S1110; using step focusing optical system 120 to condense light reflected by the object 10, and adjusting the distance between the focusing optical system 120 and the object 10. Step S1130; and a step S1140 of capturing an image of the object 10 each time the distance between the focusing optical system 120 and the object 10 is changed by a specific interval.

In step S1110, the light source 110 can be used to illuminate the object 10 with light. The light source 110 can adjust the irradiation time of the light in a manner corresponding to the specific exposure time E. As another example, the light source 110 may be continuously irradiated with light, and the aperture of the imaging unit 140 may operate in accordance with the exposure time E described above. Further, the exposure time E can be determined by Equation 4 in consideration of the pixel size of the imaging unit 140, the magnification, and the maximum vibration velocity between the focusing optical system 120 and the object 10.

In step S1120, the light reflected by the object 10 can be collected by the focusing optical system 120. Focusing optics 120 can have a particular depth of field DOF. The sharpness of the image formed by the light of the focusing optical system 120 changes depending on whether or not the focus point P is located at the above-described depth of field.

In step S1130, the relative distance between the focusing optical system 120 and the object 10 can be changed. In step S1130, the distance adjustment unit 130 can make the range of movement of the focus point P satisfy the above Equations 1 and 2.

In step S1140, the imaging unit 140 can capture an image of the object 10 a plurality of times while the focus point P is moving. Whenever the distance between the focusing optical system 120 and the object 10 changes by a certain interval Δh, the imaging unit 140 captures an image of the object 10. Also, the specific interval Δh described above may be set to be smaller than the depth of field DOF of the focusing optical system 120. Thereby, even if the imaging is performed in an environment in which the imaging unit 140 moves, a clear image can be captured at least once.

Figure 13 is a flow chart showing a method of photographing of another exemplary embodiment.

Referring to FIG. 13, the photographing method may further include a step S1135 of generating a pulse signal according to a change in the distance between the focusing optical system 120 and the object 10. The pulse signal can be generated by the encoder 250 shown in FIG. As another example, the pulse signal may be generated by the control unit 355 of FIG. 7 that receives the electrical signal of the encoder 250. The operation of the distance adjusting unit 130 can be controlled based on the above-described pulse signal. Further, the imaging unit 140 can be synchronized based on the pulse signal.

Figure 14 is a flow chart showing a method of photographing of still another exemplary embodiment.

Referring to FIG. 14, the photographing method may further include the steps of: capturing the sharpness of the image captured by the photographing portion 140, and the step S1160 of capturing the focus distance based on the sharpness value of the image.

In step S1150, the processor 160 may receive an image from the imaging unit 140 to evaluate the sharpness of each image. In addition, the sharpness of each image evaluated can be converted into a numerical value.

In step S1160, the processor 160 may determine the focus distance according to the sharpness value of the image. As an example, the height H _i of the ith shot that achieves the highest definition can be determined as the focus distance. As another example, as shown in FIG. 11, the processor 160 may also calculate the sharpness C _{i - 1} , C _i , C _{i + 1} of the images obtained at the heights H _{i - 1} , H _i , H _{i + 1} , respectively. The height H _{max is} determined as the autofocus distance in accordance with the optimum focus distance H _max calculated according to the above formula 10.

The imaging devices 100, 200, and 300 of the exemplary embodiments and the imaging methods using the imaging devices 100, 200, and 300 have been described above with reference to FIGS. 1 through 14. According to the embodiment, the autofocus operation can be realized while the distance between the object 10 and the focusing optical system 120 changes to shorten the time required for the autofocus. Also, even if autofocus is dynamically achieved, at least one image is captured within the depth of field of the focusing optical system 120, whereby a clear image can be obtained. Further, the accurate focus distance is corrected in accordance with the sharpness value of the image, whereby the accuracy of the autofocus operation can be improved.

In the above description, various matters are specifically described, but these matters are not intended to limit the scope of the invention, and should be construed as an example of a preferred embodiment. Therefore, the scope of the invention should not be limited by the illustrated embodiments, but should be defined by the technical idea recited in the claims.

1/f‧‧ ‧ time interval
10‧‧‧ objects
100, 200, 300‧‧‧ camera
110‧‧‧Light source
120‧‧‧Focus optical system
130‧‧‧Distance Adjustment Department
140‧‧‧Photography Department
160‧‧‧ processor
250‧‧‧Encoder
355‧‧‧Control Department
C _i ‧‧‧The sharpness value of the i-th captured image with the highest resolution
C _{i + 1} ‧‧‧ clarity value of the _{i +} 1th captured image
C _{i - 1} ‧‧‧ clarity value of the i-1th captured image
C _max ‧‧‧maximum clarity
D‧‧‧ thickness deviation of the object
H‧‧‧Distance between the focusing optical system and the object in the focused state
H _i ‧‧‧The distance between the focusing optical system and the object at the ith shot of the highest sharpness
H _{i + 1} ‧‧‧Distance between the focusing optical system and the object at the _{i +} 1th shot
H _{i - 1} ‧‧‧Distance between the focusing optical system and the object at the i-1th shot
H _max ‧‧‧Maximum image height
L1‧‧‧ surface
L2‧‧‧ position
P‧‧‧ Focus point
S1‧‧‧ support surface
S1110～S1160‧‧‧Steps
t, t0, t1, t2, t3, t ₀ , t ₁ , t ₂ , t _i , t _N , t _{i - 1} , t _{i + 1} , t _f ‧‧‧
V1‧‧‧The speed of change in the distance between the object and the focusing optical system δ‧‧‧Acceleration interval Δh‧‧‧interval Δt‧‧‧

Fig. 1 is a view showing an image pickup apparatus of an exemplary embodiment. FIG. 2 is a view showing a position of a captured image of an imaging unit during autofocusing. 3 is a view showing a range in which the distance between the object and the focusing optical system is changed by the distance adjusting unit. FIG. 4 is a diagram exemplarily showing that the moving speed of the focus point changes with time. Fig. 5 is a view showing an image pickup apparatus of another exemplary embodiment. Fig. 6 is a view exemplarily showing an electric signal generated by an encoder. Fig. 7 is a view showing an image pickup apparatus of still another exemplary embodiment. Fig. 8 is a view exemplarily showing a synchronization signal generated by a control unit. FIG. 9 is a view showing a change in height of a focus point corresponding to time. Fig. 10 is a graph showing the relationship between the height of a focus point and the sharpness of an image. Fig. 11 is a view showing the processor correcting the auto focus distance. Figure 12 is a flow chart showing a photographing method of an exemplary embodiment. Figure 13 is a flow chart showing a method of photographing of another exemplary embodiment. Figure 14 is a flow chart showing a method of photographing of still another exemplary embodiment.

10‧‧‧ objects

100‧‧‧Photographing device

110‧‧‧Light source

120‧‧‧Focus optical system

130‧‧‧Distance Adjustment Department

140‧‧‧Photography Department

160‧‧‧ processor

D‧‧‧ thickness deviation of the object

H‧‧‧Distance between the focusing optical system and the object in the focused state

P‧‧‧ Focus point

S1‧‧‧ support surface

Claims (20)

An imaging device comprising: a light source that emits light to an object; a focusing optical system that changes a path of light reflected by the object; and an imaging unit that captures an image of the object formed by the focusing optical system And a distance adjusting portion that adjusts a distance between the focusing optical system and the object; and each time the distance between the focusing optical system and the object changes by a specific interval, the photographing portion is An image of the object is taken, the specific interval being set to be smaller than the depth of field of the focusing optical system. The imaging device according to claim 1, wherein the imaging unit captures an image of the object in a global shutter mode. The photographing apparatus according to claim 1, wherein the distance adjusting unit changes the distance between the object and the focusing optical system at a constant speed in at least one time interval. The photographing apparatus according to claim 3, wherein the speed at which the distance adjusting portion changes the distance between the object and the focusing optical system satisfies the formula 1, Equation 1 V1 = magnitude of the speed of change of the distance between the object and the focusing optical system, f = number of times of shooting per unit time of the imaging unit in the equal speed section, and DOF = depth of field of the focusing optical system. The photographing apparatus according to claim 1, wherein the distance adjusting portion changes a distance between the object and the focusing optical system to satisfy a formula 2, V1< ... Equation 2 V1 = magnitude of change in distance between the object and the focusing optical system, DoF = depth of field of the focusing optical system, E = exposure time per frame of the imaging section). The photographing device of claim 1, wherein the exposure time of each frame of the photographing portion satisfies the formula 3, Equation 3 E = exposure time per frame of the imaging unit, A _pixel = pixel area of the imaging unit, M = magnification, V2 _max = maximum value of the relative vibration velocity between the imaging unit and the object. The photographing device according to claim 1, further comprising an encoder that senses a change in a distance between the object and the photographing portion to generate an electrical signal. The imaging device according to claim 7, further comprising a control unit that generates a synchronization signal to the imaging unit based on the electrical signal generated by the encoder. The photographing apparatus according to claim 1, further comprising a processor that receives an image of the object photographed by the photographing unit and extracts sharpness of the image. The photographing apparatus according to claim 9, wherein the processor determines a distance between the object that photographs the image with the highest definition and the focusing optical system as a focus distance. The photographing apparatus of claim 9, wherein the processor determines a focus distance by a formula 4 according to a sharpness value of the image, Equation 4 H = distance between the focusing optical system and the object in the focused state, H _i = distance between the focusing optical system and the object at the ith shot in which the highest sharpness is measured, H _{i - 1} = distance between the focusing optical system and the object at the i-1th shot, H _{i + 1} = distance between the focusing optical system and the object at the i+1th shot, C _i = highest measured The sharpness value of the i-th captured image of the sharpness, C _{i - 1} = the sharpness value of the i-1th captured image, C _{i + 1} = the sharpness is the sharpness of the i+1th captured image value. The photographing apparatus according to claim 1, wherein the distance adjusting section changes a section of the distance between the object and the focusing optical system by the formula 5 and the formula 6, H- D-δ<X<H+D+δ... Equation 5 Equation 6 X = distance between the support of the object and the focus point of the focusing optical system, H = predicted thickness of the object, D = thickness deviation of the object, δ = acceleration interval, V1 = maximum speed, a = Acceleration. A photographing method comprising the steps of: irradiating light to an object; and concentrating light reflected by the object by a focusing optical system; adjusting between the focusing optical system and the object a step of distance; and each time the distance between the focusing optical system and the object changes by a specific interval, the photographing portion captures an image of the object; and the specific interval is set to be smaller than The depth of field of the focusing optical system. The photographing method according to claim 13, wherein in the step of adjusting the distance, a distance between the object and the focusing optical system is changed at a constant speed in at least one time interval. The photographing method according to claim 14, wherein in the step of adjusting the distance, the photographing portion is within a time interval of changing the distance between the object and the focusing optical system at a constant speed Obtaining an image of the object at a specific time interval, and a speed at which a distance between the object and the focusing optical system changes satisfies Equation 1, Equation 1 V1 = the magnitude of the change speed of the distance between the object and the focusing optical system, f = the number of times of shooting per unit time of the imaging unit in the equal speed interval, DoF = depth of field of the focusing optical system, α is equal to 0.1 < α Any real number of <0.5. The photographing method according to claim 14, wherein in the step of adjusting the distance, a speed at which a distance between the object and the focusing optical system is changed satisfies a formula 2, V1< ... Equation 2 V1 = magnitude of change in distance between the object and the focusing optical system, DoF = depth of field of the focusing optical system, and E = exposure time per frame of the imaging section. The photographing method of claim 14, further comprising the step of sensing a change in the distance between the object and the photographing portion to generate an electrical signal. The photographing method of claim 17, further comprising the step of generating a synchronization signal to the photographing unit based on the electrical signal. The photographing method according to claim 14, further comprising the step of receiving an image of the object photographed by the photographing unit and extracting a sharpness of the image. The photographing method of claim 19, further comprising the step of determining a focus distance by the formula 4 according to the sharpness value of the image, Equation 4 H = distance between the focusing optical system and the object in the focused state, H _i = distance between the focusing optical system and the object at the ith shot in which the highest sharpness is measured, H _{i - 1} = distance between the focusing optical system and the object at the i-1th shot, H _{i + 1} = distance between the focusing optical system and the object at the i+1th shot, C _i = highest measured The sharpness value of the i-th captured image of the sharpness, C _{i - 1} = the sharpness value of the i-1th captured image, C _{i + 1} = the sharpness is the sharpness of the i+1th captured image value.