JPH08320430A - Automatic focus detector - Google Patents

Abstract

PURPOSE: To provide an automatic focus detector capable of exactly detecting a focusing state even when few object exists on the surface of the object or a photoelectric transducer is slightly inclined. CONSTITUTION: In this automatic focus detector provided with an illuminating optical system by which an object surface is irradiated with a light beam from a light source, an image forming optical system dividing a light beam reflected on the object surface into two light beams having an optical path difference, forming the image of one light beam on a first image forming position and the image of the other beam on a second image forming position and a photoelectric transducer arranged between both image forming positions and receiving two light beams, the detector is provided with a scanning area setting part 10, using a CCD area sensor 5 as the photoelectric transducer and setting two scanning areas being two-dimensionally scanned by the CCD area sensor 5, and a control circuit for performing focusing control by comparing the high frequency components of two light beams received by two scanning areas set by the setting part 10. The images of object included in two light beams are surely received by two scanning areas of the CCD area sensor 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focus detection device that can be used in optical instruments such as microscopes.

[0002]

2. Description of the Related Art As a conventional automatic focus detection device, for example, a light source, an irradiation optical system for irradiating light from the light source onto an object surface, and reflected light from the object surface into two light fluxes having an optical path difference. Splitting, one of the two light beams is imaged at the first image forming position, and the other of the two light beams is imaged at the second image forming position deviated in the optical axis direction with respect to the first image forming position. Two light fluxes received by the photoelectric conversion element, which are provided with an imaging optical system and a photoelectric conversion element which is arranged between the first imaging position and the second imaging position and which receives the optical images of the two light fluxes. (2
One optical image) into two electric signals, extract only the high-frequency components of each electric signal, integrate the absolute values, obtain the difference between the two integrated values to obtain the focus deviation signal, and based on this signal It is known that the focus state is detected by the above-mentioned method. A CCD line sensor 70 as shown in FIG. 7 is used as the photoelectric conversion element.
The CCD line sensor 67 has a plurality of elements arranged in a line, and is configured so that electric signals photoelectrically converted from the respective elements are output in time series (sequentially).

[0003]

However, in the above-mentioned prior art, as a photoelectric conversion element, a CC as shown in FIG. 7 is used.
Since the D line sensor 70 is used, (1) When there are few objects on the object plane, the object images 71a, 72 included in the two light fluxes (two optical images) 71, 72 having the optical path difference.
In some cases, a may not be received by the CCD line sensor 70, and in this case, the in-focus deviation signal cannot be obtained.
In-focus state cannot be detected, and (2) CCD
If the line sensor 70 is slightly tilted as shown in FIG. 7, the two optical images 71 and 72 received by the CCD line sensor 70 do not coincide with each other, so that the in-focus state cannot be accurately detected.

The present invention has been made in view of the above circumstances, and its object is to accurately detect the in-focus state even when there are few objects on the object surface or when the photoelectric conversion element is slightly tilted. It is an object of the present invention to provide an automatic focus detection device capable of performing the above.

[0005]

In order to solve the above-mentioned problems, the automatic focus detection device according to the invention of claim 1 comprises a light source,
An irradiation optical system that irradiates the object surface with light from this light source, and splits the reflected light from the object surface into two light beams having an optical path difference, and forms one of the two light beams at a first imaging position. And an image forming optical system that forms the other of the two light beams at a second image forming position that is displaced in the optical axis direction with respect to the first image forming position, and the first image forming position and the second combination. An automatic focusing device that is disposed between the image position and a photoelectric conversion element that receives the two light fluxes, and detects a focus state by comparing optical information of the two light fluxes obtained by the photoelectric conversion element. In the detection device, the photoelectric conversion element is configured to be two-dimensionally scannable, and the scanning area setting means for setting two scanning areas for two-dimensionally scanning by the photoelectric conversion element, and the scanning area setting means. 2 of the photoelectric conversion elements set By comparing the optical information of the two light beams received by the scanning area determined focus deviation signal, and a control circuit for performing focus control based on the focus error signal.

In the automatic focus detection device according to the present invention, the scanning area setting means is configured to two-dimensionally scan two scanning areas of the photoelectric conversion element, which are separated by a predetermined distance. .

In the automatic focus detection device according to the third aspect of the present invention, the control circuit compares the two optical information obtained in one corresponding scanning line in the two scanning areas with each other to obtain a focus shift. Integrating means is included to integrate the signal for all scan lines in the scan area.

[0008]

In the automatic focus detection device according to the present invention, the photoelectric conversion element can be two-dimensionally scanned, and two photoelectric conversion elements having the optical path difference in the two scanning areas set by the scanning area setting means. Since the light beam is received, even when there are few objects on the object plane, the images of the object included in the two light beams can be reliably received by the two scanning regions of the photoelectric conversion element, and the photoelectric conversion element is slightly tilted. Even if
Two coincident optical images can be received in the two scanning areas of the photoelectric conversion element.

In the automatic focus detection device according to the present invention, the scanning area setting means two-dimensionally scans two scanning areas of the photoelectric conversion element which are separated by a predetermined distance, so that the entire surface of the photoelectric conversion element is two-dimensionally scanned. The scanning time and the signal processing time are shortened as compared with the case of scanning manually, and the focused state can be detected at high speed.

In the automatic focus detection device according to the third aspect of the present invention, the focusing means is a focusing deviation signal obtained by comparing the two optical information obtained by the corresponding one scanning line in the two set scanning areas. Is integrated for all the scanning lines in each scanning region, so that a high-level focusing deviation signal can be obtained over a wide range.

[0011]

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

FIG. 2 shows an optical system of an automatic focus detection apparatus for a microscope according to an embodiment of the present invention, and FIG. 1 shows a block diagram of a control circuit for performing focus control used in the apparatus. .

The automatic focus detection device for a microscope shown in FIG. 2 has a light source 1, a half mirror 2 and an objective lens 3, and irradiating optics for irradiating the object surface 4a of an object 4 with light from the light source 1. The system and the reflected light from the object surface 4a are divided into two light fluxes having an optical path difference, one of the two light fluxes is imaged at the first imaging position x, and the other of the two light fluxes is first imaged. It is arranged between the first image forming position x and the second image forming position y and an image forming optical system for forming an image at a second image forming position y which is displaced in the optical axis direction with respect to the position x, and has an optical path difference. The photoelectric conversion element 5 receives two light fluxes (two optical images). The imaging optical system includes an objective lens 3 which forms an image of reflected light from the object surface 4a, and a half prism 6 which divides the reflected light from the object surface 4a passing through the objective lens 3 into a transmitted light and a reflected light.
And a half prism 7 that splits the light reflected by the half prism 6 into two light beams having an optical path difference. The reflected light from the object surface 4a that has passed through the half prism 6 is imaged on an image surface (not shown), and this image surface can be observed by an observation optical system.

When the object plane 4a is at the in-focus position (position B in FIG. 2), XY = 0 (X: first image forming position x
The distance between the photoelectric conversion element 5 and the light receiving surface of the photoelectric conversion element 5, Y: the distance between the second image forming position y and the light receiving surface) is adjusted in advance.

As the photoelectric conversion element 5, a CCD area sensor capable of two-dimensional scanning is used. This C
As shown in FIG. 5, the CD area sensor 5 includes N scanning lines (for example, from the first scanning line L1 to the twentieth scanning line L20) in which n (for example, 10) elements are arranged in one row. 20 scanning lines), and the electric signals photoelectrically converted from the respective elements of the scanning lines L1 to L20 are output in time series (sequentially). In FIGS. 4 and 5, reference numeral 5a denotes a virtual center line 5.
The left half of the CCD area sensor 5 is divided by 0, and the reference numeral 5b indicates the right half of the CCD area sensor 5. Further, in FIGS. 4 and 5, one of the two optical images 41 receives light in the left half of the light receiving range 5a, and the other of the two optical images receives in the right half of the light receiving range 5a.
Light is received in each of b.

The control circuit shown in FIG. 1 has two scanning areas which are two-dimensionally scanned by the CCD area sensor 5 (a scanning area within the light receiving area 5a in the left half and a scanning area within the light receiving area 5b in the right half). The scanning area setting unit 10 capable of arbitrarily setting the area) is provided. The scanning area setting unit 10 may, for example, scan the second scanning line L in the left half light receiving range 5a.
The scanning area from the 2nd to 9th scanning lines can be set, and the scanning area from the 12th scanning line L12 to the 19th scanning line can be set within the right half light receiving range 5b. Further, the scanning area setting unit 10 has timings controlled by a timing control circuit 18, which will be described later, and for each scanning line, A1 to C1 of FIG.
Electric signal 3 photoelectrically converted according to the amount of received light
1 or 31 'is read and output.

In A1 to C1 of FIG. 3, an electric signal 31
Is a signal (optical information) output from each element of one scanning line (for example, the scanning line L3) in one scanning region shown in FIG. 5 in time series, and the electric signal 31 'is the other scanning region. It is a signal (optical information) that is output in time series from each element of one scanning line (for example, the scanning line L13 corresponding to the scanning line L3) in the inside. And
In B1 in FIG. 3, the object plane 4a is in the in-focus position (position B in FIG. 2)
A1 and C1 in the figure are the object plane 4a.
3A and 3B respectively show the states at positions A and C in FIG. 2 which are deviated from the in-focus position.

The control circuit further includes a DC offset removing circuit 11 for removing a DC component from the output signal of the scanning region setting section 10, an amplifier 12 for amplifying the output signal of the DC offset removing circuit 11, and an output signal of the amplifier 12. And a bandpass filter 13 for extracting a high frequency component (optical information representing the contrast of the optical images 41 and 42) and outputting a signal 32 or 32 'shown by A2 to C2 in FIG. 3, respectively. A2 to C2 in FIG. 3 correspond to A1 to C1 in FIG. 3, respectively.

The control circuit further includes an absolute value circuit 14 for detecting the absolute value of the output signal of the bandpass filter 13,
An integrator 15 for integrating the output signal of the absolute value circuit 14 and 2
It is provided with one sample hold circuit 16 and 17 and a timing control circuit 18.

The timing control circuit 18 controls the operation timings of the scanning area setting section 10, the integrator 15, and the two sample hold circuits 16 and 17.

The timing control circuit 18 includes a scanning area from the second scanning line L2 to the ninth scanning line L9 and a scanning area from the twelfth scanning line L12 to the nineteenth scanning line L19 by the scanning area setting unit 10. When and are set, the second scan line L2 and the twelfth scan line L12, 3 corresponding to the scan line L2
Th scan line L3, 13 corresponding to scan line L3
The operation timing of the scanning area setting unit 10 is controlled so that the electrical signal 31 or 31 'is output from each scanning line in the order of the thirteenth scanning line L13 ... And the nineteenth scanning line.

Further, the timing control circuit 18
Operates the integrator 15 when the electric signal 31 is output from each of the second to ninth scan lines L2 to L9, and a signal indicating an integrated value at this time (A3 to C in FIG. 3).
The signal 33) shown in FIG.
In addition, the integrator 15 is operated when the electrical signal 31 'is output from each of the 12th to 19th scanning lines L12 to L19, and a signal indicating the integrated value at this time (A3 to FIG. The other sample-hold circuit 17 holds the signal 33 'shown at C3.

The control circuit further compares the output signals of the sample and hold circuits 16 and 17 (signals representing integrated values), and the signal representing the difference (represents the amount of deviation of the object 4 from the in-focus position). With a focus shift signal, one corresponding scan line in the two scan areas set, for example, scan line L
3, the differential amplifier 19 for outputting the signal 61) of FIG. 6 obtained by signal processing the electric signals 31, 31 'from L13.
And an integrator circuit 20 which integrates the focus shift signal 61 from the differential amplifier 19 for all the scanning lines in each scanning area and outputs a focus shift signal 62 (see FIG. 6), and the object to be inspected 4
And a focusing motor 22 for controlling the relative position of the objective lens 3 in the optical axis direction, and a motor control circuit 20 for controlling the focusing motor 22 by an output signal from the integrating circuit 20.

Next, the operation of the embodiment having the above configuration will be described.

The light from the light source 1 is applied to the object surface 4a via the half mirror 2 and the objective lens 3. The reflected light from the object surface 4a passes through the objective lens 3, the half mirror 2 and the half prism 6, and is then split by the half prism 7 into two light beams having an optical path difference. One of the two light beams is imaged at the first image forming position x, and the other of the two light beams is imaged at the second image forming position y which is displaced in the optical axis direction with respect to the first image forming position x. As a result, the two light fluxes having the optical path difference (the two optical images 41 and 4 shown in FIGS.
2) One and the other are received within the light receiving range 5a in the left half and the light receiving range 5b in the right half of the CCD area sensor 5, respectively.

Now, two arbitrary scanning areas which are two-dimensionally scanned by the CCD area sensor 5 are set by the scanning area setting section 10 (for example, the entire surfaces of the left and right light receiving areas 5a and 5b are scanned). It has been set). At this time, the scanning area setting unit 10 first outputs the electric signal 31 (see A1 to C1 in FIG. 3) obtained on the first scanning line L1 in one scanning area 5a, and then the other scanning. An electric signal 31 '(see the same figure) obtained by the eleventh scan line L11 corresponding to the scan line L1 in the area 5b is output, and then obtained by the second scan line L2 in the scan area 5a. The electric signal 31 is output, and then the electric signal 31 'obtained on the 12th scanning line L12 corresponding to the scanning line L2 in the scanning area 5b is output. Similarly, the two scanning areas 5a,
The electric signals 32, 32 'obtained in one corresponding scanning line in 5b are alternately output, and finally the scanning line L2
The electric signal 32 'obtained at 0 is output.

When the signals 31 and 31 'are alternately output from the scanning area setting unit 10 in this way, the DC offset removing circuit 11 removes the DC component from the signals 31 and 31', and the amplifier 12 amplifies this signal. After that, when the bandpass filter 13 extracts the high frequency component, A2 to C in FIG.
Signals 32 and 32 ', respectively indicated by 2, are obtained. A2 signals 32 and 32 'become A1 signals 31 and 31', B2 signals 32 and 32 'become B1 signals 31 and 31', and C2 signals 32 and 32 'become C1 signals 31 and 31'. Corresponds to each. When the absolute value of the output signal of the bandpass filter 13 is detected by the absolute value circuit 14 and the output signal of the absolute value circuit 14 is integrated by the integrator 15, A3 to C3 in FIG.
33 and 33 ', which represent the integrated values respectively shown in FIG.
A3 signals 33 and 33 'become A2 signals 32 and 32',
B3 signals 33 and 33 'become B2 signals 32 and 32',
The signals 33 and 33 'of C3 correspond to the signals 32 and 32' of C2, respectively.

The signals 33 and 33 'of A3 to C3 correspond to the two optical images 41 and 42 (see FIG. 4), respectively.
The signal 33 is held by the sample hold circuit 16,
The signal 33 'is held by the sample hold circuit 17. The differential amplifier 19 compares the output signals of the sample and hold circuits 16 and 17 (the signals representing the integrated value) and outputs the out-of-focus signal 61 shown in FIG. This out-of-focus signal 61
Is a signal obtained for each corresponding one scanning line (for example, corresponding scanning lines L3 and L13) in the set two scanning regions. The integrating circuit 20 is the differential amplifier 1
The focus shift signal 61 from 9 is integrated for all the scanning lines in the scan area, and the focus shift signal 62 shown in FIG. 6 is output. The motor control circuit 21 controls the focusing motor 22 based on the focus shift signal 62 from the integrating circuit 20. That is, the motor control circuit 21 determines that the focus shift signal 62 is 0.
The focusing motor 22 is controlled to control the relative position between the object 4 and the objective lens 3 in the optical axis direction of the imaging optical system.

As described above, in the automatic focus detection apparatus according to the above-described embodiment, the object to be inspected in the optical axis direction of the imaging optical system is adjusted so that the focus shift signal 62 output from the integrating circuit 20 becomes zero. An automatic focusing operation is performed by controlling the relative position between the objective lens 3 and the objective lens 4 by the focusing motor 22.

According to the above-described embodiment, the CCD area sensor 5 can be two-dimensionally scanned, and the scanning area setting unit 10 can be used.
The two light beams (two optical images 41, 4 and 4) having an optical path difference in the two scanning areas of the CCD area sensor 5 set by
2) (see FIGS. 4 and 5), the image of the object included in the two optical images 41 and 42 can be reliably detected by the two scanning areas of the CCD area sensor 5 even when there are few objects on the object surface 4a. Can receive light. Further, even when the CCD area sensor 5 is slightly tilted as shown by the solid line in FIG. 4, two coincident optical images can be received in the two scanning areas of the CCD area sensor 5. Therefore, even if there are few objects on the object surface 4a or the CCD area sensor 5 is slightly tilted, the focus state can be accurately detected.

Further, according to the above embodiment, the integrating circuit 2
0 indicates the focus shift signal 61 from the differential amplifier 19 to the CCD
Since all the scanning lines in the two scanning areas of the area sensor 5 are integrated and the focusing deviation signal 62 shown in FIG. 6 is output, the focusing deviation is detected as apparent from FIG. The range can be widened.

In the above embodiment, the two scanning areas separated by a predetermined interval (for example, the interval m shown in FIG. 4) of the CCD area sensor 5 are two-dimensionally set by the scanning area setting unit 10. CCD if scanned
The scanning time and the signal processing time are shortened as compared with the case where the entire light receiving range of the area sensor 5 is two-dimensionally scanned, and the focused state can be detected at high speed.

Further, in the above embodiment, a reference object is previously formed on the light receiving surface of the CCD area sensor 5 in the same manner as the two optical images 41 and 42 shown in FIG.
The distance m between the two optical images 41, 42 is stored in a memory unit (not shown). And when actually performing focus detection,
Two corresponding scan lines 5 separated by the stored distance m
If the scanning area setting unit 10 is configured to detect the high frequency components of the two optical images 41 and 42 at c and 5d, the scanning time and the signal processing time can be further shortened, and the focused state can be detected at a higher speed. can do.

It should be noted that in the above-described embodiment, it is possible to use another photoelectric conversion element configured to be two-dimensionally scannable instead of the CCD area sensor 5.

[0035]

As described above, according to the automatic focus detection device of the first aspect of the invention, the photoelectric conversion element can be two-dimensionally scanned, and the photoelectric conversion set by the scanning area setting means is performed. Since two light fluxes having an optical path difference are received in the two scanning areas of the element, the image of the object included in the two light fluxes can be reliably received by the two scanning areas of the photoelectric conversion element even when there are few objects on the object plane. You can
Even when the photoelectric conversion element is slightly inclined, it is possible to receive two coincident optical images in the two scanning regions of the photoelectric conversion element. Therefore, even if there are few objects on the object surface or the photoelectric conversion element is slightly tilted, the focus state can be accurately detected.

According to the automatic focus detection device of the second aspect of the invention, the scanning area setting means causes the two scanning areas of the photoelectric conversion element, which are separated by a predetermined distance, to be two-dimensionally scanned. The scanning time and the signal processing time are shortened as compared with the case where the entire surface of 2 is scanned two-dimensionally, and the focused state can be detected at high speed.

According to the automatic focus detection device of the third aspect of the present invention, the integrating means obtains by comparing the two optical information obtained by the corresponding one scanning line in the two set scanning areas. Since the focus shift signals generated are integrated for all the scanning lines in each scan area, a high level focus shift signal can be obtained over a wide range. Therefore, the focus shift detection range is widened.

[Brief description of drawings]

FIG. 1 is a block diagram of a control circuit which is a main part of an automatic focus detection device according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing an optical system of an automatic focus detection device according to an embodiment of the present invention.

FIG. 3 is a signal waveform diagram for explaining focusing control.

FIG. 4 is an explanatory diagram showing a state where the CCD area sensor is tilted.

FIG. 5 is an operation explanatory view showing a CCD area sensor.

FIG. 6 is a diagram showing an out-of-focus signal obtained by the automatic focus detection device according to one embodiment.

FIG. 7 is a CCD in a conventional automatic focus detection device.
It is a top view which shows a line sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 light source 4a object surface 5 CCD area sensor (photoelectric conversion element) 10 scanning area setting unit (scanning area setting means) 20 integrating circuit (integrating means) x first image forming position y second image forming position

Claims (3)

[Claims] 1. A light source, an irradiation optical system for irradiating an object surface with light from the light source, and a light beam reflected from the object surface is divided into two light beams having an optical path difference, and one of the two light beams is An image forming optical system that forms an image at a first image forming position and forms an image of the other of the two light fluxes at a second image forming position that is displaced in the optical axis direction with respect to the first image forming position; A photoelectric conversion element that is arranged between the image forming position and the second image forming position and receives the two light beams, and compares the optical information of the two light beams obtained by the photoelectric conversion element. In an automatic focus detection device for detecting a focus state, the photoelectric conversion element is configured to be two-dimensionally scannable, and scanning area setting means for setting two scanning areas to be two-dimensionally scanned by the photoelectric conversion element. And is set by the scanning area setting means. A control circuit for comparing the optical information of the two light beams received in the two scanning regions of the photoelectric conversion element to obtain a focus shift signal, and performing focus control based on the focus shift signal. An automatic focus detection device characterized in that 2. The automatic scanning apparatus according to claim 1, wherein the scanning area setting unit is configured to scan two scanning areas of the photoelectric conversion element, which are separated by a predetermined distance, two-dimensionally. Focus detection device. 3. The control circuit outputs an out-of-focus signal obtained by comparing two pieces of optical information obtained by corresponding one scanning line in each of the two scanning areas to all scanning in the scanning areas. The automatic focus detection device according to claim 1, further comprising integration means for integrating lines.