JP2003029138A - Autofocusing method and ultraviolet microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an autofocusing method which is capable of stably and efficiently detecting a focusing position under all conditions, and to provide a UV microscope. SOLUTION: This autofocusing method has an objective optical system (13) for observing a sample (12), driving means (20) for adjusting the relative distance between the sample (12) and the objective optical system (13) and imaging means (17) for converting the optical image from the sample (12) formed by the objective optical system (13) to a video signal and detects the focusing position by using the data obtained from the video signal described above, in which the relative distance between the sample (12) and the objective optical system (13) is regulated to a range, where the video signal is obtainable and a contrast value is determined, after the video signal is subjected to smoothing processing, then the position, where the contrast value is maximum, is determined as the focusing position.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an automatic focusing method and an ultraviolet microscope.

[0002]

2. Description of the Related Art In automatic focusing of a microscope, an active automatic focusing method using a laser is generally used.

On the other hand, as an automatic focusing method using a video signal, a contrast method for accumulating the brightness difference between adjacent pixels in an image as a differential value and a method using a standard deviation of brightness values are known. As an example in which these are applied, in Japanese Patent Laid-Open No. 5-236315, a value obtained by superimposing differential values of adjacent pixels for several lines is used as a contrast index value, and the influence of dust or scratches on an observation target is used. Has been reduced.

Further, in Japanese Patent Laid-Open No. 6-337357, it is assumed that the image having a better focus has a larger variation in the luminance distribution, and the standard deviation is obtained from the histogram of the luminance vs. frequency of the image, and the value becomes the maximum position. Is the focal position. Further, in Japanese Patent Laid-Open No. 2000-266995, contour components are extracted from the difference between an original image and an image obtained by delaying the image by a certain phase, and the difference between the maximum value and the minimum value in the image is detected. Show an autofocus method by contrast that is not affected by noise.

[0005]

However, in the active automatic focusing method, it is necessary to use a long-wavelength laser of 780 nm or the like, and in an ultraviolet microscope that must have an imaging performance specialized for ultraviolet light, There is a problem that the optical performance for obtaining a high resolution by the short wavelength light is affected.

Further, the conventional automatic focusing method using a video signal as described above is effective for low-magnification observation in which the pattern of the observation object is large and observation in which the contrast of the observation object is clear. However, for high-magnification observation or low-contrast image observation in which the pattern change in the visual field is small, there is a high probability that the focus position will be erroneously detected or cannot be found due to the influence of noise components.

In particular, when the total magnification of the objective lens and the imaging lens becomes as high as 500, the pattern change appearing in the field of view becomes extremely slight depending on the object to be observed.
Therefore, the change in the contrast value for use in autofocus becomes indistinguishable compared to the accumulation of the change in the noise component in the flat portion of the image, and it is difficult to detect the position where the contrast value has a clear peak. It will be difficult.

Further, in an image with a low contrast such as a semiconductor wafer having a protective film, the change in the contrast value of the edge component in the image to be noticed is very small and it is buried in the offset change amount. It becomes difficult to detect the position where the value clearly has a peak.

An object of the present invention is to provide an automatic focusing method and an ultraviolet microscope capable of stably and efficiently detecting a focused position under all circumstances.

[0010]

In order to solve the problems and achieve the object, the automatic focusing method and the ultraviolet microscope of the present invention are configured as follows.

(1) In the automatic focusing method of the present invention, an objective optical system for observing a sample, driving means for adjusting a relative distance between the sample and the objective optical system, and the objective optical system. An image pickup means for converting an optical image of the sample formed by the above into a video signal, wherein the video signal is obtained in an automatic focusing method for detecting a focus position using data obtained from the video signal. The relative distance between the sample and the objective optical system is adjusted within a certain range, the video signal is subjected to smoothing processing, and then the contrast value is obtained. The position where the contrast value is the maximum is the focus position.

(2) In the automatic focusing method of the present invention, an objective optical system for observing a sample, driving means for adjusting the relative distance between the sample and the objective optical system, and the objective optical system. An image pickup means for converting an optical image of the sample formed by the above into a video signal, wherein the video signal is obtained in an automatic focusing method for detecting a focus position using data obtained from the video signal. The relative distance between the sample and the objective optical system is adjusted within a certain range, and the increase / decrease judgment of the contrast value obtained from the video signal and the increase / decrease judgment of the dispersion value obtained from the video signal are combined to obtain a focus position. To detect.

(3) The ultraviolet microscope of the present invention comprises an ultraviolet objective optical system for observing a sample, driving means for adjusting the relative distance between the sample and the ultraviolet objective optical system, and the driving means. After the adjustment, an image pickup means for converting an optical image from the sample formed by the ultraviolet objective optical system into a video signal, and a contrast value obtained by performing a smoothing process on the video signal, and the contrast value is the maximum. And a control unit for setting a position at which is a focus position.

(4) The ultraviolet microscope of the present invention comprises an ultraviolet objective optical system for observing a sample, driving means for adjusting the relative distance between the sample and the ultraviolet objective optical system, and the driving means. After the adjustment, an image pickup means for converting an optical image from the sample formed by the ultraviolet objective optical system into a video signal, an increase / decrease determination of a contrast value obtained from the video signal, and a dispersion value obtained from the video signal. The control means detects the in-focus position in combination with the increase / decrease determination.

As a result of taking the above-mentioned means, the following effects are achieved.

(1) According to the automatic focusing method of the present invention, the contrast value is calculated by subjecting the sampled data to obtain automatic focusing by performing a kind of smoothing process for preserving the edge. When performing, the luminance change due to the noise component is excluded while leaving the contrast change of the observation target in the image, and a clear peak having the maximum contrast value can be obtained.

(2) According to the automatic focusing method of the present invention, by combining the increase / decrease determination of the contrast value and the increase / decrease determination of the variance value, the focusing operation is performed in the focusing direction or in the opposite direction. It is possible to make a stable determination as to whether or not it is.

(3) According to the ultraviolet microscope of the present invention, the contrast value is calculated by subjecting the sampled data in order to obtain the automatic focus to a seed smoothing process which keeps the edges in advance. At this time, while leaving the contrast change of the observation target in the image, the change in luminance due to the noise component is excluded, and a clear peak having the maximum contrast value can be obtained.

(4) According to the ultraviolet microscope of the present invention, by combining the increase / decrease judgment of the contrast value and the increase / decrease judgment of the dispersion value, whether the focusing operation is in the focusing direction or in the opposite direction. Can be stably determined.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 is a block diagram showing a configuration of a microscope to which an automatic focusing method according to a first embodiment of the present invention is applied.

In FIG. 1, an observation target sample 12 is placed on a stage 11 which is movable in the Z-axis direction. The beam splitter 1 is placed on the observation optical axis of the objective lens 13.
4, an imaging lens 15, and an image sensor 17 are arranged. Further, the illumination device 16 is arranged so that its illumination optical axis is orthogonal to the observation optical axis at the beam splitter 14.

The control device 18 includes an A / D conversion circuit 181,
The memory 182 and the CPU 183 are provided, and these are connected to the bus 184. The CPU 183 is connected to the stage 11 via the stage drive device 20, and the A / D conversion circuit 181 is connected to the image sensor 17. Further, the control device 18 has a display monitor 19
Are connected.

In FIG. 1, the illumination light emitted from the illumination device 16 is reflected by the beam splitter 14,
The sample 12 to be observed is irradiated through the objective lens 13. Along with the irradiation, the reflection image from the observation target sample 12 is projected on the image sensor 17 via the objective lens 13, the beam splitter 14, and the imaging lens 15.

The projected image is converted into an electric signal by the image sensor 17, and the A / D in the controller 18 is converted.
Converted to a digital signal by the conversion circuit 181,
It is stored in the memory 182 via the bus 184. The image stored in the memory 182 is displayed on the display monitor 19.

The CPU 183 extracts the data of the designated area from the image data stored in the memory 182,
An evaluation calculation for obtaining a contrast index is performed. CPU1
83 sends a control signal to the stage driving device 20 via a serial communication terminal (not shown) based on the result of the evaluation calculation, and moves the stage 11 in the vertical direction (observation optical axis direction) by the stage driving device 20. The focal distance is obtained by changing the relative distance between the observation sample 12 and the objective lens 13.

FIG. 2 is a flow chart showing the procedure of the focusing operation of the microscope configured as described above. The procedure of the focusing operation will be described below with reference to FIG. When the operator gives an instruction to start the operation from an operation unit (not shown), step S
At 1, the CPU 183 moves the stage 1 in the upward direction (+ Z) and positions it at the designated start position. Step S
2, the CPU 183 displays an image of the observation target sample 12 captured by the image sensor 17 at the start position in A /
It is stored in the memory 182 via the D conversion circuit 181.

In step S3, the CPU 183 causes the memory 1
Image data D1 to Dn for a predetermined n pixels on the designated sampling line are extracted from the image stored in 82. The sampling line is set, for example, by a horizontal line and a vertical line having a constant width that intersect at the center of the screen.

In step S4, the CPU 183 selects the image whose luminance value is the median value of the three pixels among the image data Di-1, Di, Di + 1 of the three adjacent pixels in the image data D1 to Dn. Let the data be Mi. The CPU 183 sequentially shifts the image data Mi pixel by pixel along the sampling line (i = 1, 2, ...) And then sequentially obtains the image data Di at each center, and replaces the obtained image data Mi with the obtained image data Mi. In step S5, the CPU 183 obtains the contrast index value Cz at the stage position from the replaced image data.

In step S6, the CPU 183 calculates the Z coordinate of the stage 11 from which the next image data should be acquired,
In step S7, it is determined whether the Z coordinate is within the search range. If it is within the search range, step S
If the search range is exceeded, the CPU 183 moves the stage 11 to the Z coordinate where the contrast index value Cz is maximized, and ends the series of focusing operation processes. In this way, while moving the stage 11 up and down, the contrast index value is obtained at each position, and the process of finding the maximum position is performed.

In normal automatic focusing, since the center of the screen is focused on, the sampling line is arranged so that the image data in the center of the screen is weighted. However, a plurality of sampling lines may be set not only in the central portion of the screen but also in the screen for totaling, or may be areas instead of lines.

In the contrast index value thus obtained, the fluctuation due to the noise component is removed, and the contrast index value at the in-focus position and the contrast index value at the out-of-focus position are likely to have a relative difference.

FIG. 3 is a graph showing the relationship between the contrast index value and the relative distance between the sample and the objective lens in an image having a relatively high contrast. In FIG. 3, reference numeral 61 is data obtained by performing the smoothing processing shown in the above-described focusing operation procedure and then calculating the contrast index value,
Reference numeral 62 is data obtained by calculating the contrast index value without smoothing processing. The brightness difference between adjacent image data is used to calculate the contrast index value.

Although the peak position which should be the in-focus position can be calculated with the data of 62 as well, the difference between the data at the in-focus position and the data at the out-of-focus position is clear in the data of 61. Therefore, it can be seen that the possibility of erroneous determination is reduced.

FIG. 4 is a graph showing the relationship between the contrast index value and the relative distance between the sample and the objective lens in an image with low contrast. In FIG.
Reference numeral 63 is data obtained by calculating the contrast index value after performing the above-described smoothing processing, and 64 is data obtained by calculating the contrast index value without the smoothing processing. The brightness difference between adjacent image data is used to calculate the contrast index value.

With the data of 64, it is difficult to calculate the peak position which should be the in-focus position, and there is a possibility of making an erroneous determination. And the data at the out-of-focus position can be clearly distinguished, and stable determination of the in-focus position can be performed.

According to the first embodiment, before the contrast index value is calculated, the data of each pixel is replaced with the median value of the adjacent pixels to maintain the contrast information of the edge portion in the image. However, it is possible to remove the influence of the noise component in the flat portion of the image. This makes it possible to highlight only the information to be extracted for automatic focusing in an image with a small pattern change or an image with a low contrast.

Further, in the first embodiment, the median value of three adjacent pixels is taken, but when sampling is performed on a line, it is possible to use 5 adjacent pixels or the like, or the area is sampled. In this case, adjacent 3 × 3 pixels may be used. Further, the replacement of the pixel data may be any kind of smoothing processing that maintains the edge portion, not the median value. For example, a method of obtaining an average value of the brightness of one pixel and an adjacent pixel and replacing the data of the one pixel with the average value only when the difference between the one pixel and the average value exceeds a threshold value. May be

(Second Embodiment) The structure of a microscope to which the automatic focusing method according to the second embodiment is applied is the same as that of the first embodiment.

FIG. 5 is a flowchart showing the procedure of the focusing operation of the microscope according to the second embodiment. The procedure of the focusing operation will be described below with reference to FIG. When the operator issues an operation start instruction from an operation unit (not shown),
In step S11, the CPU 183 moves the stage 1 to a specified position (a predetermined start position when the operation starts). In step S12, the CPU 183 stores the image of the observation target sample 12 captured by the image sensor 17 at the designated position in the memory 182 via the A / D conversion circuit 181.

In step S13, the CPU 183 calculates the contrast index value Cz on the designated sampling line from the image stored in the memory 182, and in step 14, the CPU 183 extracts the contrast index value Cz from the image stored in the memory 182. The variance value Dz of the image data on the sampling line is calculated.

In step S15, the CPU 183 compares the contrast index value Cz with the contrast index value Cz-1 at the previous position (Z coordinate) of the stage 11,
As a result, if it has decreased (Cz-1> Cz), one decrease flag is set in step S18.

If the reduction flag is not reduced in the step S15 (Cz-1≤Cz) and the reduction flag is set at the previous position (Z coordinate) of the stage 11 in the step S16, the step is executed. In S17, the CPU 183 compares the dispersion value Dz with the dispersion value Dz-1 at the previous position (Z coordinate) of the stage 11, and if the dispersion value is decreased as a result (Dz-1> Dz), In step S18, one decrease flag is set.

After the decrease flag is set in step S18, or when the decrease flag is not set at the previous position (Z coordinate) of the stage 11 in step S16, or when the decrease flag is decreased in step S17. If not (Dz-1 ≦ Dz), in step S19,
The CPU 183 calculates the number of set decrease flags. If the designated number N (for example, 2 to 4) is not reached, the CPU 183 determines that the stage 1
The movement direction (downward, -Z) of 1 is held, the next designated position (Z coordinate) is calculated, all decrease flags are cleared, and the process returns to step S11 to repeat the above process.

If it is determined in step S19 that the number of decrease flags is greater than or equal to the designated number N, step S21.
Then, the CPU 183 reverses the moving direction of the stage 11 (upward, + Z), calculates the next designated position (Z coordinate) in step S22, and in step S23, the CPU 183.
Moves the stage 1 in the upward direction (+ Z) to the designated position. In step S24, the CPU 183 stores the image of the observation target sample 12 captured by the image sensor 17 at the designated position in the memory 182 via the A / D conversion circuit 181.

In step S25, the CPU 183 calculates the contrast index value Cz on the designated sampling line from the image stored in the memory 182, and in step 26, the CPU 183 extracts the contrast index value Cz from the image stored in the memory 182. The variance value Dz of the image data on the sampling line is calculated.

In step S27, the CPU 183 compares the contrast index value Cz with the contrast index value Cz-1 at the previous position (Z coordinate) of the stage 11,
As a result, if it has decreased (Cz-1> Cz), one decrease flag is set in step S30.

If it is not decreased (Cz-1≤Cz) in step S27 and the decrease flag is set at the previous position (Z coordinate) of the stage 11 in step S28, In S29, the CPU 183 compares the dispersion value Dz with the dispersion value Dz-1 at the previous position (Z coordinate) of the stage 11, and if the dispersion value is decreased as a result (Dz-1> Dz), In step S30, one decrease flag is set.

After the reduction flag is set in step S30, or when the reduction flag is not set at the previous position (Z coordinate) of the stage 11 in step S28, or when the reduction flag is reduced in step S29. If not (Dz-1 ≦ Dz), in step S31,
The CPU 183 calculates the number of set decrease flags. If the designated number N (for example, 2 to 4) is not reached, in step S32, the CPU 183 sets the stage 1
The next designated position (Z coordinate) is calculated while holding the movement direction (+ Z) of 1, and the above process is repeated by returning to step S23.

If the number of decrease flags is equal to or more than the designated number N in step S31, step S33.
Then, the CPU 183 moves the stage 11 to a position where the maximum contrast index value is obtained, and ends a series of focusing operations.

The processing of steps S22 to S33 may be performed after returning the stage 11 to the position (Z coordinate) where the first reduction flag is set. Alternatively,
In step S19, when the number of decrease flags is equal to or more than the specified number N, a series of focusing operation processing is ended, and the position where the contrast index value reaches the peak (the contrast index value decreases before and after that) 11 may be moved.

The number of times the decrease flag is not set continuously is monitored. If the decrease flag is not set more than the specified number of times, it is considered that the focus position is still reached, and when the decrease flag is set. Alternatively, the stage 11 may be positioned at a position where the contrast index value has reached its peak on the assumption that the focus position has been passed, and the series of focusing operation processes may be ended. In the second embodiment,
The contrast index value is calculated by the same method as in the first embodiment.

FIG. 6 is a graph showing the relationship between the contrast index value and the dispersion value data with respect to the relative distance between the sample and the objective lens. In FIG. 6, 81 is a contrast index value, and 82 is dispersion value data.
The contrast index value and the variance value generally become larger as the image is in focus, but the increase / decrease situation does not necessarily interlock between images taken at constant intervals (Z direction) due to noise conditions and the like. An example of the focus search procedure will be described below with reference to FIG.

In FIG. 6, A4 is a contrast index value at the focus search start position (-200), and when the initial moving direction of the stage 11 is downward (-Z), the next stage 1
The contrast index value at the Z position (-300) of 1 is A5
Becomes Here, since A5 <A4, the decrease flag is set at the Z position (−300) having the data of A5, and it is recognized that the stage 11 is moving away from the focus.

Next, the stage 11 is further moved downward by the same distance to obtain data A6. Here A6>
However, since the decrease flag is set at the position of A5, the variance value data B6 is the previous data B5.
Compare with. As a result, since the number has decreased, it is considered that the stage 11 is moving away from the focus, and the decrease flag is set. Then, the result of accidentally giving a low contrast index value in A6 is not used as it is, so that the direction to the in-focus position is not erroneously recognized.

When the designated number N is set to 2, since the decrease flag is set twice in succession here, for example, the stage 11 is moved to the Z position (one position upward from the focus search start position (-200)). -100) and obtain data A3. Further, the stage 11 is moved upward by a designated interval to obtain the data A2, A1, and A0. At the time when A0 is obtained, the decrease flag is set twice in succession, so the focus search operation is stopped and the maximum value is reached. The stage 11 is moved to the Z position (0) where A2 is obtained, and the process ends.

According to the second embodiment, by simultaneously monitoring the indexes of different properties, it becomes difficult to be influenced by the fluctuation of the illumination light quantity and the noise, and the focus search progresses in the focus direction, or It is possible to efficiently and stably judge whether or not the stage 11 is moving in the direction away from, and it is possible to suppress the time for leading the stage 11 to the focus position. Further, by performing the smoothing processing shown in the first embodiment and then implementing the automatic focusing method of the second embodiment, more stable focusing can be realized.

(Third Embodiment) FIG. 7 is a block diagram showing the configuration of an ultraviolet microscope to which the automatic focusing method according to the third embodiment of the present invention is applied. In FIG.
The same parts as are denoted by the same reference numerals. The ultraviolet microscope is a microscope that uses light in the ultraviolet region including deep ultraviolet as illumination light for observation. In the ultraviolet microscope shown in FIG.
The automatic focusing method described in the first embodiment or the second embodiment is applied.

In FIG. 7, an observation target sample 12 is placed on a stage 11 which is movable in the Z-axis direction. On the observation optical axis of the ultraviolet objective lens 131, the beam splitter 14, the imaging lens 15, and the ultraviolet light image sensor 1 are provided.
71 are arranged. Further, the illumination device 16 is arranged so that its illumination optical axis is orthogonal to the observation optical axis at the beam splitter 14 via the ultraviolet light filter 30.

The controller 18 includes an A / D conversion circuit 181,
The memory 182 and the CPU 183 are provided, and these are connected to the bus 184. The CPU 183 is connected to the stage 11 via the stage drive device 20, and the A / D conversion circuit 181 is connected to the ultraviolet light image sensor 17.
Connected to 1. Further, a display monitor 19 is connected to the control device 18.

In FIG. 7, the illumination light emitted from the illuminating device 16 passes only the ultraviolet light by the ultraviolet filter 30, is reflected by the beam splitter 14, passes through the ultraviolet objective lens 131, and passes through the sample 12 to be observed. Is irradiated. Along with the irradiation, the reflection image from the observation target sample 12 is projected on the ultraviolet light image sensor 171 via the ultraviolet light objective lens 131, the beam splitter 14, and the imaging lens 15.

The projected image is converted into an electric signal by the ultraviolet light image sensor 171, converted into a digital signal by the A / D conversion circuit 181 in the control device 18, and stored in the memory 182 via the bus 184. It The image stored in the memory 182 is displayed on the display monitor 1
9 is displayed.

The CPU 183 extracts the data of the designated area from the image data stored in the memory 182,
An evaluation calculation for obtaining a contrast index is performed. CPU1
83 sends a control signal to the stage driving device 20 via a serial communication terminal (not shown) based on the result of the evaluation calculation, and moves the stage 11 in the vertical direction (observation optical axis direction) by the stage driving device 20. The focal position is obtained by changing the relative distance between the observation sample 12 and the ultraviolet objective lens 131.

Generally, the ultraviolet microscope must be designed so that the aberration is optimally corrected at around 250 nm in order to exhibit the image forming performance by the short wavelength light.
However, since the wavelength of the laser used for active autofocusing is generally longer than that, when the optical design is performed in consideration of the laser wavelength, it has a considerable influence on the imaging performance with ultraviolet rays.

However, in the ultraviolet microscope constructed as shown in FIG. 7, the focusing performance with ultraviolet rays can be maximized and the automatic focusing can be performed. Also,
With an ultraviolet microscope, observation is performed at an optical magnification of about 200 to 500 times, so there may be little pattern change within one field of view depending on the observation target, but even in such an image, it is stable and efficient. A working autofocus method can be provided.

The present invention is not limited to the above-mentioned respective embodiments, and can be carried out by appropriately modifying it within the scope of the invention.

[0067]

According to the present invention, it is possible to provide an automatic focusing method and an ultraviolet microscope capable of stably and efficiently detecting a focused position under all circumstances. That is, it is possible to provide a simple and stable automatic focusing function that can be applied to high-magnification observation in which the pattern change of the observation target tends to be small and observation when the contrast of the observation sample is low. In particular, even in the case where the optical design does not match the laser wavelength of the active AF as in the case of an ultraviolet microscope, automatic focusing can be easily performed without sacrificing the optical performance.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a microscope to which an automatic focusing method according to a first embodiment of the present invention is applied.

FIG. 2 is a flowchart showing a procedure of a focusing operation of the microscope according to the first embodiment of the present invention.

FIG. 3 is a graph showing the relationship between the contrast index value and the relative distance between the sample and the objective lens according to the first embodiment of the present invention.

FIG. 4 is a graph showing the relationship between the contrast index value and the relative distance between the sample and the objective lens according to the first embodiment of the present invention.

FIG. 5 is a flowchart showing a procedure of a focusing operation of the microscope according to the second embodiment of the present invention.

FIG. 6 is a diagram showing the relationship between the contrast index value and the relative distance between the sample and the objective lens according to the second embodiment of the present invention;
And a graph showing the relationship between the variance value data.

FIG. 7 is a block diagram showing a configuration of an ultraviolet microscope to which an automatic focusing method according to a third embodiment of the present invention is applied.

[Explanation of symbols]

11 ... Stage 12 ... Sample to be observed 13 ... Objective lens 131 ... Ultraviolet objective lens 14 ... Beam splitter 15 ... Imaging lens 16 ... Lighting device 17 ... Image sensor 171 ... Ultraviolet light image sensor 18 ... Control device 181 ... A / D conversion circuit 182 ... memory 183 ... CPU 184 ... bus 19 ... Display monitor 20 ... Stage drive device 30 ... Ultraviolet light filter

Claims (4)

[Claims] 1. An objective optical system for observing a sample, driving means for adjusting a relative distance between the sample and the objective optical system, and an optical image from the sample formed by the objective optical system. An image pickup means for converting the image signal into a video signal, and an automatic focusing method for detecting a focus position using data obtained from the video signal, wherein the sample and the objective optical system are within a range where the video signal is obtained. The relative focusing distance is adjusted, the video signal is subjected to the smoothing process, the contrast value is obtained, and the position where the contrast value is the maximum is set as the in-focus position. 2. An objective optical system for observing a sample, driving means for adjusting the relative distance between the sample and the objective optical system, and an optical image from the sample formed by the objective optical system. An image pickup means for converting the image signal into a video signal, and an automatic focusing method for detecting a focus position using data obtained from the video signal, wherein the sample and the objective optical system are within a range where the video signal is obtained. Of the contrast value is determined by adjusting the relative distance of the image signal and the increase / decrease determination of the variance value obtained from the image signal are combined to detect the in-focus position. How to focus. 3. An ultraviolet objective optical system for observing a sample, drive means for adjusting a relative distance between the sample and the ultraviolet objective optical system, and the ultraviolet objective optical system after adjustment by the drive means. Imaging means for converting an optical image of the sample formed by the above into a video signal, and a contrast value is obtained after performing a smoothing process on the video signal, and the position where the contrast value is maximum is the in-focus position. An ultraviolet microscope characterized by comprising: 4. An ultraviolet objective optical system for observing a sample, drive means for adjusting a relative distance between the sample and the ultraviolet objective optical system, and the ultraviolet objective optical system after adjustment by the drive means. By combining the image pickup means for converting the optical image from the sample formed by the above into a video signal, the contrast value increase / decrease determination obtained from the video signal, and the variance value increase / decrease determination obtained from the video signal. An ultraviolet microscope comprising: a control unit that detects a focal position.