JPH07248451A - Device for automatically detecting focus - Google Patents

Abstract

PURPOSE:To surely detect a focus even from a subject image showing a contrast characteristic having plural subpeaks like the subject image in a phase difference microscopic examination and to improve a focusing speed and focusing precision without enlarging a device. CONSTITUTION:A high frequency component is extracted from image signals of conjugate front/rear light images outputted from an image sensor by a high- pass filter 30, and frequency characteristics incorporated in the frequency band of the high-pass filter and nearly symmetrical to the focusing are extracted by band-pass filters 31, 32. Then, a difference value between contrast values of the front/rear light images in the high-pass filter and the difference value between the contrast values of the front/rear light images in the band-pass filter are obtained based on a prescribed evaluation function, and focusing search is performed based on these difference values.

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 for optical equipment such as a microscope.

[0002]

2. Description of the Related Art An optical device such as a camera processes a video signal obtained by capturing an image of a subject with an image sensor to calculate a defocus amount, and an autofocus (hereinafter An automatic focus detection device that performs control (abbreviated as AF) is used.

Various focus detection methods have been considered in such various optical devices. For example, JP-A-5
Japanese Patent Laid-Open No. 9-182409 describes a focus detection method focusing on high frequency components of a video signal.

Such a focus detection device handles a contrast value appearing in a high frequency component of a video signal as a defocus amount and performs focus detection. That is, as shown in FIG. 12, the contrast value appearing in the high frequency component of the video signal has the characteristic that the contrast value becomes maximum at the in-focus point, and the contrast value decreases as the defocus amount increases. Therefore, by utilizing this characteristic, AF control is performed by a so-called hill-climbing servo system.

Further, Japanese Patent Application Laid-Open No. 64-42416 discloses a so-called optical path difference type AF control. In this focus detection method, a front pin / pin showing characteristics similar to those shown in FIG. The contrast characteristic of the rear pin is used.

The above-mentioned focus position detecting device basically has light receiving elements such as image sensors arranged at two positions before and after the planned image forming surface, and corresponds to the contrast of the light receiving image picked up by each light receiving element. The AF control is performed by operating the servo mechanism of the optical system based on the signal.

FIG. 13 shows a contrast signal of an optical image (this blurred image is referred to as a front focus image) picked up by a light receiving element arranged in front of the reference image forming plane, and a light receiving image arranged after the reference image forming plane. The characteristics of the optical image picked up by the element (this blurred image is referred to as the back focus image) and the contrast signal are shown.

As shown in the figure, the contrast value of the front focus image becomes maximum at the stage Z position slightly away from the in-focus point to the + side, and the contrast of the rear focus image is slightly away from the in-focus point to the stage Z at the stage Z. Maximum at position. At this time, since the two sensors before and after the in-focus point are arranged at the same distance from the conjugate reference image plane, the place where the maximum value of the contrast between the front focus image and the rear focus image is the same distance from the focus point. Become.

Further, FIG. 14 shows the rear pin contrast value (A).
The characteristic of the signal (hereinafter referred to as an S-shaped curve) obtained by subtracting the front pin contrast value (B) from is shown. FIG. 14
As shown in, the in-focus point coincides with the point where the value of (AB) becomes zero. This point is called the cross point, and the object is OB.
(A-B) is positive when the subject is closer than the focus, and (A-B) when the object is far from the OB focus.
B) is negative.

In the AF control by the optical path difference method, the difference between the contrast values of the front-focused / rear-focused images is calculated, and the object or the imaging lens is moved in the direction according to the polarity of the difference value.
This operation is repeated until the difference between the contrast values of the front focus / rear focus is close to zero.

On the other hand, recently, automatic focusing technology has also been applied in the field of microscopes. In a microscope, the optical conditions for forming a subject image by the microscopic method are very different,
There are various contrast characteristics of the subject image.

In particular, the contrast characteristic of the subject image in the phase contrast microscope has a shape having a plurality of peaks (hereinafter referred to as sub-peaks) in addition to the focusing peak, as shown in FIG.

Therefore, in Japanese Patent Laid-Open No. 56-35111, scanning is performed within a predetermined range from the distance at which the maximum peak is detected to detect whether there is a peak smaller than the maximum peak, and AF control is performed based on this detection signal. Is described. Furthermore, as the AF control in the phase contrast microscope,
For example, some focus on a specific spatial frequency component in a phase-difference microscope and perform AF control.

[0014]

However, the above-described automatic focusing technique may be erroneously recognized as a focusing point for a contrast characteristic having a plurality of subpeaks. Very difficult to do.

Experiments and simulations have revealed that the main factor that causes a sub-peak in the contrast characteristic of a subject image in a phase-difference microscope is annular illumination by a ring slit.

The ring slit causes the following phenomenon. (1) The depth of focus increases. (2) Side slope increases.

(3) The specific spatial frequency intensity of the spatial frequencies included in the subject image increases despite the increase of the defocus amount within the depth of focus. 16 to 18 show the MT of the above (3) in the phase contrast microscope.
The F (Modulation Transfer Function) simulation result model is shown.

The parameters in the figure are obtained by converting the spatial frequency [line / mm] of the subject image into the electrical frequency [Hz] from the pixel pitch and scan rate of the image sensor, and the electrical frequency and the spatial frequency are proportional. Have a relationship.

The vertical axis represents the MTF relative value indicating the intensity, and the horizontal axis represents the defocus amount. Further, FIGS. 16 to 18 show the magnification of the phase difference objective lens for each parameter.

From these figures, regardless of the magnification of the phase difference objective lens, the intensity of any spatial frequency (electrical frequency) component vibrates and attenuates as the defocus amount increases. At each magnification, the higher the frequency is, the faster the intensity is attenuated and the shorter the cycle of vibration is. Further, at the same frequency, the intensity of the phase difference is attenuated more quickly as the magnification of the phase difference objective lens increases, and the period of vibration becomes shorter.

Due to the above-described damped vibration of intensity, a sub-peak phenomenon occurs in which the contrast value increases despite the increase in the defocus amount. If the conventional hill-climbing servo method is applied to the contrast characteristic having such a sub-peak, the sub-peak may be determined to be in focus, which may cause a problem such as the AF control ending in an incomplete state. There is.

Further, with reference to FIGS. 19 and 20, let us consider a case where the optical path difference type AF control is applied to the case of the phase difference spectroscope. FIG. 19 shows the contrast characteristics of the front pin / rear pin in the phase contrast microscope. As shown in the figure, the contrast characteristics of the phase contrast microscope have maximum values (B, B ', C in the figure) in addition to the maximum values (A, A'in the figure) at the focal point of the front focus / rear focus. , C ′). As shown in the figure, A and A'are the maximum points of the contrast value of the front pin / rear pin.

FIG. 20 shows an S-shaped curve created from the contrast characteristics of the front and rear pins in FIG. S shown in the figure
When AF control is applied using a curve, M1 in the figure
When there is a subject at the point, (1) the sign of the S-curve is positive, so move the stage or shooting lens in the (D1) direction, and (2) zero cross the S-curve at the false focus (a). AF occurs at the false focus (a) because points are generated.
Control is complete. Will be.

However, the false focus point (a) is at a position different from the original focus point, and the AF control ends in an incomplete state. When a subject is present at M3 in FIG. 20, the conventional AF control regards the false focus point (b) as the focus point, resulting in incomplete AF.

That is, complete focus detection is possible with conventional AF control only when the subject is within the range of M2.
Therefore, it is difficult to apply the conventional optical path difference method to the phase difference spectroscope.

On the other hand, it is conceivable that the sensors of the front pin and the rear pin are separated from the reference focusing point so that the contrast curves of the front pin and the rear pin do not overlap each other, and the characteristics as shown in FIG. 21 are provided.

However, in such a method, a driving mechanism for changing each sensor position of the front pin / rear pin depending on the magnification of the most shadow lens is required, resulting in an increase in cost and an increase in size due to the complexity of the device. .

Therefore, a method of scanning a predetermined range around the peak to surely move it to the maximum peak as in JP-A-56-35111 is conceivable. However, this method requires a scanning time, so It has the drawback of lowering the focal speed.

Further, as shown in FIGS. 16 to 18, the appearance position of the sub-peak varies depending on the spatial frequency of the subject and the magnification of the objective lens, and therefore the scan width cannot be determined unconditionally, which is not suitable for AF.

Further, in the method of focusing on the unique spatial frequency component in the phase contrast spectroscope, the above points are cleared, but the extraction frequency is constant even if the objective lens magnification changes, so that it is sufficient. There is a possibility that the focus accuracy may not be obtained. Furthermore, depending on the extracted frequency component, the MTF may be asymmetrical with respect to the in-focus point in front and rear defocus.

22 to 25 show defocus characteristics of the relative MTF of the phase difference objective lens 10 × with respect to the spatial frequency. In these figures, the vertical axis shows the relative MTF value and the horizontal axis shows the defocus amount. The relative MTF characteristic at the spatial frequency of FIG. 22 is almost symmetrical with respect to the in-focus point (δ = 0), but the symmetry becomes higher as the frequency increases as shown in FIG.
It becomes like. For this reason, if the extraction frequency component is kept constant, the focusing accuracy may decrease.

Therefore, according to the present invention, it is possible to reliably detect the focus even from a subject image having a contrast characteristic having a plurality of sub-peaks like a subject image in a phase contrast microscope.
Moreover, it is an object of the present invention to provide an automatic focus detection device having high focusing speed and high focusing accuracy without increasing the size of the device.

[0033]

According to a first aspect of the present invention, a subject is irradiated with annular slit light, and direct light and diffracted light from the subject are transmitted through a retardation film and made incident on an image sensor. In an automatic focus detection device that performs a focus search for a subject based on image signals of conjugate optical images before and after output from the image sensor, it has a function of extracting high-frequency components from the image signal output from the image sensor. A high-pass filter, a band-pass filter that is included in the frequency band of the high-pass filter from the image signal output from the image sensor, and has a function of extracting a frequency characteristic that is substantially symmetrical with respect to focusing, and the high-pass filter and the band-pass filter Based on the specified evaluation function, the contrast values of the front and rear optical images from the A focus servo means having a function of obtaining a difference value and a difference value of contrast values of front and rear optical images in a bandpass filter, and performing a focus search based on both of these difference values is achieved. It is an automatic focus detection device to be tried.

According to the second aspect, the bandpass filter has a function of switching the filter constant according to the types of the retardation film and the annular slit light. According to the third aspect, the bandpass filter has a function of switching the filter constant according to the sum of the respective contrast values of the conjugate optical images before and after, or the magnitude of any of these contrast values.

According to the fourth aspect, the focusing servo means performs the focusing search based on only the difference value of the contrast values in the high-pass filter in the case of a spectroscope other than the phase difference spectroscope, while the phase difference spectroscope is used. In this case, it has a function of performing a focus search based on the results of both the contrast value difference in the high-pass filter and the contrast value difference in the band-pass filter.

[0036]

According to the first aspect of the present invention, when an annular slit light is applied to a subject, and the direct light and the diffracted light from the subject are transmitted through the retardation film and incident on the image sensor, the image sensor outputs the light. Image signals of the preceding and following conjugate optical images are output. The high-frequency component of this image signal is extracted by the high-pass filter, and the image signal is included in the frequency band of the high-pass filter by the band-pass filter, and the frequency characteristic that is substantially symmetrical with respect to the focus is extracted.

Then, based on a predetermined evaluation function, the front and rear optical images from the high pass and band pass filters are contrasted with each other by the difference between the contrast values of the front and rear optical images in the high pass filter and the contrast of the front and rear optical images in the band pass filter. The difference value of the values is obtained, and the focusing search is performed based on both of these difference values.

In this case, according to the second aspect, the filter constant can be switched in the bandpass filter according to the types of the retardation film and the annular slit light. According to the third aspect, the filter constant can be switched by the sum of the respective contrast values for the front and rear optical images that are conjugate in the bandpass filter, or the magnitude of either of these contrast values.

Further, according to the fourth aspect, in the focusing servo means, if the spectroscope other than the phase difference spectroscope is used, the focus search is performed based only on the difference value of the contrast values in the high-pass filter, In the case of the phase difference microscope, the focus search is performed based on the results of both the difference value of the contrast value in the high pass filter and the difference value of the contrast value in the band pass filter.

[0040]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an automatic focus detection device. The microscope in this embodiment is provided with a stage 10 that can move an object S, which is an observation sample, in the vertical direction. An opening is formed on the stage 10 for transmitted illumination.

The illumination light generated by the transmissive light source 11 is formed into ring-shaped illumination light by the ring slit 12, and the ring-shaped illumination light illuminates the subject S from below through the stage opening by the condenser lens 13. ing.

On the optical axis above the subject S, the objective lens 14 for phase difference spectroscope is arranged. The phase difference microscope objective lens 14 has a phase difference film formed in a ring-shaped region on which the annular illumination light enters. The light flux that has passed through the objective lens 14 for phase contrast spectroscope is branched by the eyepiece prism 15, and one light flux is guided to the eyepiece lens 16.

The light flux from the phase difference spectroscopic objective lens 14 split by the eyepiece prism 15 passes through the imaging lens 17 and then enters the optical path difference prism Q to be split into two parallel light fluxes. The CCD sensor 1S is arranged at a position where two object light images (front pinned image and rear pinned image) having different optical path differences on the light receiving surface and conjugate with each other with respect to the planned focal plane are projected.

The CCD sensor 18 outputs an analog image signal having a voltage corresponding to the amount of incident light of the projected light image and the storage time. The output of the CCD sensor 1S is subjected to analog processing such as amplification and filter processing in an analog processing section 19 described later, digitized by an A / D converter 21, and then incorporated into a memory 22. This memory 2
The stored contents of No. 2 can be read from the arithmetic circuit 23.

The arithmetic circuit 23 calculates the contrast value of the subject image using the digital signal of the subject image stored in the memory 22, and the bit data representing the contrast value is C.
It has a function of transmitting to the PU 24.

The CPU 24 monitors via the A / D converter 21 whether the analog image signal of the subject image output from the CCD sensor 18 is suitable for the range of the analog processing section 19, and the analog image signal of the subject image. Has a function of transmitting, to the timing generator 25, an instruction to set a storage time suitable for the range when the range is not suitable for the analog processing unit 19.

The CPU 24 has a function of obtaining a stage drive amount such that the contrast values of the front and rear pins are substantially the same based on the contrast values of the front and rear pins from the arithmetic circuit 23 and transmitting it to the drive circuit 26. have.

Further, the CPU 24 has an external controller 27.
It has a function to receive information such as AF start / stop, current microscopic method, objective lens magnification, etc. The drive circuit 26 receives the drive signal from the CPU 24 and drives the stage 10.

As shown in FIG. 2, the analog processing section 19 includes a high-pass filter (HPF) 30 used in general microscopy and phase-difference microscopy and band-pass filters (BPF) used only in phase-difference microscopy. ) 31, 32 and two analog switches 33, 3 for switching the filters
It is composed of four.

Of these, two types of BPFs are provided: a BPF 31 used when the phase difference objective lens magnification is low and medium, and a BPF 32 used when the magnification is high. Furthermore, the selection of which filter is used is made by the analog switches 33 and 34 for the signal from the CPU 24.

The filter characteristics of the BPFs 31 and 32 are
As shown in FIGS. 3 to 5, at each phase difference objective lens magnification, the MTF is set so as to be able to extract a frequency component that is symmetrical in front and rear defocus with respect to the in-focus point. That is, at high magnification (40 ×, 60 ×), the MTF characteristics are symmetrical, and for high magnification BPF 32 and low / medium magnification (10 ×, 20 ×) M
Two types of B of low-to-medium magnification BPF31 with symmetrical TF characteristics
It has a PF configuration. The filter constants of each of the two BPFs are determined with reference to FIGS. 16 to 18 and 22 to 25.

Next, the operation of this embodiment configured as described above will be described with reference to FIG. External controller 27
When AF is started by the signal from (step S
1) The CPU 24 detects the spectroscopic method and the objective lens magnification which have been externally input to the controller 27 by the spectrographer in the next step S2. Next, in step S3, the CPU 24 switches the analog switch 34 so that the image signal is on the HPF 30 side in any speculum.

After switching the analog switch 34 in this manner, the CPU 24 reads the analog signal output from the CCD sensor 18 in step S4, and the analog signal from the sensor 18 is adapted to the analog processing section 19 in the next step S5. Check if there is.

If the range does not match as a result of this check, the CPU 24 issues a command to the timing generator 25 to set the accumulation time so that the range matches. In this operation, the signal of the sensor 18 is the analog processing unit 19
It is repeated until the range is matched.

If the range is compatible, the CPU 24
Calculates the contrast value of the front focus image and the rear focus image according to a predetermined evaluation function in accordance with the signal from the sensor 18 in the next step S6, and calculates the difference between the rear focus contrast value and the front focus contrast value in step S7.

When this difference amount is equal to or larger than a predetermined value α, C
In steps S8 and S9, the PU 24 calculates the drive direction of the stage 10 from the sign of the difference, that is, the magnitude relationship between the front pin contrast value and the rear pin contrast value, and calculates the drive amount from the absolute value of the difference amount to drive the stage.
This stage driving operation is repeated until the difference between the rear focus contrast value and the front focus contrast value becomes ± α or less.

The AF operation ends here with a spectroscope other than the phase difference spectroscope. However, the current microscopic method and the objective lens magnification, which have been previously input by the spectrographer into the external controller 27, are set to CP.
When the U24 detects in step S10 and recognizes that the current spectroscopic method is the phase difference, the CPU 24 determines in step S10.
In step 11, the analog switches 33 and 34 are switched. That is, the analog switch 34 is set to the phase difference filter side, and B according to the above-described objective lens magnification is used.
The analog switch 33 is switched to the PF side.

In the case of the phase difference spectroscope, the CPU 24 calculates the difference in the contrast between the front focus image and the rear focus image through the phase difference spectroscopic BPF in step S12. If this difference is less than or equal to the threshold value β, Since the front focus image and the rear focus image can be determined to have a conjugate relationship with respect to the planned in-focus plane, the MTF characteristics are substantially equal, and thus the in-focus state is determined.

On the other hand, when the difference between the two is β or more, the CPU
No. 24 has different MTF characteristics in steps S13 and S14, and it is determined that the front focus image and the rear focus image do not have a conjugate relationship with the planned focus plane, that is, are out of focus.

When it is determined that the focus is out of focus, the CPU 24 switches the analog switch 34 to the HPF side again, and further drives the stage in the same direction as the scan direction in which the stage position where the focus determination is performed is reached to perform the AF operation. Resume. In this operation, the difference between the back focus contrast value and the front focus contrast value is a predetermined value α or less, and the front focus contrast value and the rear focus contrast value in the frequency band extracted by the phase difference spectroscopic BPF are the predetermined value β or lower. Only when both of the conditions are satisfied, the focus is considered, and the process is repeated until the AF operation is completed.

As described above, according to the first embodiment, in the case of focusing, the intensities of the frequency bands in which the front and rear defocus characteristics of the MTF characteristic are symmetrical, and the contrast values are almost the same before and after. Match. That is, the in-focus characteristics shown in FIG. 4 are obtained. On the other hand, in the case of out-of-focus, the front focus image and the rear focus image deviate from either the front focus or the rear focus with respect to the planned focal plane as shown in FIG. Even if the total contrast values of all the frequencies of the front and rear images are the same, the front and rear contrast values at the extraction frequencies shown in the arrow range in the figure are different from each other. AF in the phase contrast microscope becomes possible.

Further, in this embodiment, the focusing search is performed by driving the stage, but the same effect can be obtained by driving the stage. Further, in this embodiment, H
Although the stage drive amount is not changed when determining the focus of the front focus image and the rear focus image extracted by the PF, once the focus determination is made by the magnitude of the front focus contrast value and the rear focus contrast value by the BPF. If the stage drive amount is controlled to be larger than normal one or two times, the risk of repeated out-of-focus determination by the BPF is reduced.
The focusing speed becomes high, and the effect of the present invention can be improved.

The phase-difference BPF of the present invention has two types of low-, medium-magnification and high-magnification settings according to the phase-difference objective lens. If the filter constant of the BPF is configured to be switched by the CPU, the AF control with higher accuracy becomes possible. In this embodiment, the BPF is analog,
If this is digitally configured by an arithmetic circuit or a CPU, it can be implemented without adding special hardware.

Further, focusing determination for phase difference such as switching of analog switch is about once or twice after AF is started, so that the focusing speed can be made almost equal to that of other spectroscopic methods. Therefore, for a subject that has multiple sub-peaks in addition to the focusing peak of the contrast characteristics of the subject, such as a phase-contrast speculum, it is possible to perform high-speed and high-precision AF control without complicating the device by the optical path difference optical system Becomes

Further, since the objective lens data is provided in advance, the constant of the bandpass filter is changed even if the objective lens is exchanged, so that A can be used for various objective lenses.
F correspondence is possible.

By providing a switching means for the phase difference spectroscope and other spectroscopes, it is possible to perform AF on all speculums including the phase difference speculum. Next, a second embodiment of the present invention will be described.

The configuration of the optical system and AF device of this embodiment is the first
This is similar to the embodiment, and detailed description thereof is omitted. As shown in FIG. 7, the analog processing section 19, which is a feature of the present embodiment, includes phase difference spectroscopic filters BPF40 and BPF41.
It is composed by. The filter constants of these BPFs 40 and 41 have the following characteristics.

(1) The extraction frequency MTF characteristic is symmetrical in front and rear defocus with respect to focusing. (2) The phases of the damping vibrations of the extraction frequency MTF characteristics of the BPFs 40 and 41 are shifted by about a half cycle in the vicinity of the focus, and the cycles are different.

If two kinds of BPFs as described above are prepared, when one has a small relative MTF and a low contrast value, the contrast value of one BPF becomes a certain level or more.
Next, the operation of the present embodiment configured as described above will be described with reference to FIG.
Will be explained.

A is generated by a signal from the external controller 27.
When F is started, the CPU 24 detects the spectroscopic method and the objective lens magnification which have been input to the external controller 27 by the spectrographer in advance in step S21, and in step S22, in any case of speculums. The analog switch 44 is switched so that the image signal is on the HPF 42 side.

After switching the analog switch 44, the CPU
24 reads the analog signal of the CCD sensor 18 in step S23, and checks whether the analog signal of the sensor 18 is suitable for the analog processing section 19 in the next step S24.

If the range does not match, the CPU 24
Issues a command to the timing generator 25 to set the storage time so that the range fits. This operation is repeated until the signal of the sensor 18 matches the range of the analog processing section 19.

If the range is suitable, the CPU 24
In step S25, the contrast value of the front focus image and the rear focus image is calculated according to a predetermined evaluation function in accordance with the signal from the sensor 18, and in the next step S26, the difference between the rear focus contrast value and the front focus contrast value is calculated.

When this difference amount is greater than or equal to a predetermined value α, C
The PU 24 determines the sign of the difference in steps S27 and S28,
That is, the driving direction of the stage 10 is calculated from the magnitude relationship between the front focus contrast value and the rear focus contrast value, and the drive amount is calculated from the absolute value of the difference amount, and the stage is driven.
This stage driving operation is repeated until the difference between the rear focus contrast value and the front focus contrast value becomes ± α or less.

The AF operation ends here in a spectroscope other than the phase difference spectroscope. However, when the CPU 24 detects in step S29 the current microscopic method pre-input by the spectrograph to the external controller 27 and recognizes that the current microscopic method is a phase difference, the CPU 24 determines in step S30 that the analog switch is an analog switch. 44 is switched to the phase difference filter input side, and further the analog switch 43 is switched to the BPF (A) input side.

If the sum of the front pinned image contrast value and the rear pinned image contrast value through this filter is less than or equal to the predetermined value β, the CPU 24 proceeds to step S32 and switches the analog switch 43 to the BPF (B) input side, and step S
33 BPF (A) 40 or BPF (B) 41
The difference between the back-focused image contrast value and the front-focused image contrast value via is calculated, and if this difference is less than or equal to the threshold value γ, it is determined that focus is achieved, and the AF operation is ended.

On the other hand, when the difference between the two is γ or more, it is determined that the lens is out of focus, the analog switch 44 is switched to the HPF side again, and in the same scanning direction as the stage position where the focus determination is performed. Further, the stage is driven to restart the AF operation.

This operation is performed under the condition that the difference between the rear pin contrast value and the front pin contrast value is a predetermined value α or less, and the rear pin contrast value and the front pin contrast value in the frequency band extracted by the phase difference spectroscopic BPF are the predetermined value γ. Repeat until both of the following conditions are met:

As described above, according to the second embodiment, when the contrast value is low as shown in FIG. 9 by using a plurality of types of BPFs 40 and 41, the BPFs are switched to move to (a) and (b) MTF. Can be increased to improve the focusing accuracy.

Further, as shown in FIG. 10, even if the contrast values happen to coincide with each other due to the optical path difference as shown in (c), the BPF
By switching between the two, it is possible to improve the focusing accuracy because the confirmation as to whether the front pin and the rear pin are in the conjugate position is doubled as in (d). In this case, as shown in FIG. 11, the contrast difference value by BPF (A) 40 and B
If a focusing search is performed using both results of the contrast difference value by the PF (B) 41, the focusing speed will be slightly reduced, but as described above, it is necessary to check whether the front pin and the rear pin are in the conjugate position. Since it is doubled, focusing accuracy can be increased.

Further, in the present embodiment, when the difference becomes γ or less, the AF operation is ended, but when further focusing accuracy is required, the frequency band of the BPF is further changed and the MTF characteristic with respect to the focusing is obtained. Selects a more symmetrical band, front pin,
This requirement can be satisfied by making the threshold value of the difference between the rear pin contrast values as small as possible.

By varying the filter constant of the band-pass filter that matches the frequency characteristic of the subject, it becomes possible to deal with AF for various subjects. By providing the switching means for the phase difference spectroscope and the other spectroscope, it is possible to perform AF on all speculums including the phase difference speculum. It should be noted that the present invention is not limited to the above embodiments, and various modifications can be made.

[0083]

As described in detail above, according to the present invention, it is possible to reliably detect the focus even from a subject image having a contrast characteristic having a plurality of sub-peaks such as a subject image in a phase-contrast spectroscope. It is possible to provide an automatic focus detection device that can improve the focusing speed and the focusing accuracy without increasing the size.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of an automatic focus detection device according to the present invention.

FIG. 2 is a specific configuration diagram of an analog processing unit in the device.

FIG. 3 is a diagram showing a contrast value with respect to a subject position.

FIG. 4 is a diagram showing MTF characteristics when focused.

FIG. 5 is a diagram showing an MTF characteristic at the time of false focusing.

FIG. 6 is a flowchart of automatic focus detection.

FIG. 7 is a specific configuration diagram of an analog processing unit in the second embodiment of the automatic focus detection device according to the present invention.

FIG. 8 is a flowchart of automatic focus detection.

FIG. 9 is a diagram showing a relative MTF with respect to a defocus amount.

FIG. 10 is a diagram showing a relative MTF with respect to a defocus amount.

FIG. 11 is a flowchart of automatic focus detection.

FIG. 12 is a diagram showing a contrast value with respect to a stage position.

FIG. 13 is a diagram showing a contrast value with respect to a stage position.

FIG. 14 is a diagram showing a difference in contrast value between front and rear pins with respect to a stage position.

FIG. 15 is a diagram showing a contrast value with respect to a defocus amount in a phase contrast microscope.

FIG. 16 is a diagram showing a simulation result of MTF characteristics.

FIG. 17 is a diagram showing a simulation result of MTF characteristics.

FIG. 18 is a diagram showing a simulation result of MTF characteristics.

FIG. 19 is a diagram showing contrast characteristics of front pin / rear pin in the phase contrast microscope.

FIG. 20 is a diagram showing an S-shaped curve created from the contrast characteristics of the front pin / the rear pin.

FIG. 21 is a diagram showing a contrast amount with respect to a defocus amount.

FIG. 22 is a diagram showing a relative MTF with respect to a defocus amount.

FIG. 23 is a diagram showing a relative MTF with respect to a defocus amount.

FIG. 24 is a diagram showing a relative MTF with respect to a defocus amount.

FIG. 25 is a diagram showing a relative MTF with respect to a defocus amount.

[Explanation of symbols]

10 ... Stage, 11 ... Transmission light source, 12 ... Ring slit, 14 ... Phase contrast microscope objective lens, 18 ... CCD sensor, 19 ... Analog processing part, 21 ... A / D converter, 2
2 ... Memory, 23 ... Arithmetic circuit, 24 ... CPU, 25 ... Timing generator, 26 ... Drive circuit, 27 ... External controller, 30 ... High pie filter (HPF), 3
1, 32, 40, 41 ... Bandpass filter (BP
F), 33, 34, 43, 44 ... Analog switch, Q
... Optical path difference prism, S ... Subject.

Claims (4)

[Claims] 1. An object is irradiated with an annular slit light, and direct light and diffracted light from the object are transmitted through a phase difference film and made incident on an image sensor, and a conjugate front and rear output from the image sensor. In an automatic focus detection device that performs a focus search for the subject based on the image signal of the optical image of, a high-pass filter that extracts a high-frequency component from the image signal output from the image sensor, and an image output from the image sensor A bandpass filter that is included in the frequency band of the high-pass filter from the signal and extracts a frequency characteristic that is substantially symmetrical with respect to focus, and the front and rear optical images from the high-pass filter and the band-pass filter as a predetermined evaluation function. Based on the difference between the contrast values of the front and rear optical images in the high pass filter, the band pass filter An automatic focus detection device, comprising: a focus servo unit that obtains a difference value between contrast values of front and rear optical images in a filter and performs a focus search based on the difference values of both. 2. The automatic focus detection device according to claim 1, wherein the bandpass filter has a function of switching the filter constant according to the types of the retardation film and the annular slit light. 3. The band-pass filter has a function of switching a filter constant depending on the sum of contrast values of front and rear optical images having a conjugate relationship, or the magnitude of any of these contrast values. The automatic focus detection device according to claim 1. 4. The focusing servo means performs a focusing search based on only the difference value of the contrast values in the high-pass filter in the case of a spectroscope other than the phase difference spectroscope, while in the case of the phase difference spectroscope. The automatic focus detection device according to claim 1, further comprising a function of performing a focus search based on a result of both a difference value of contrast values in the high pass filter and a difference value of contrast values in the band pass filter.