JPH0980301A - Auto focus device - Google Patents

Abstract

(57) An object of the present invention is to provide an autofocus device capable of selecting an optimum focus detection sensitivity and focus detection range without being influenced by the design of an observation optical system. In an autofocus device in which index image light reflected by an object surface and transmitted through an objective lens 8 is made incident on a pupil splitting prism 33 and is further received by light receiving position detecting elements 34a, 34b, a pupil splitting prism is provided. By selecting the light shielding shape of the variable light shielding plate 32 that shields a part of the light beam incident on 33, the light amount distribution of the light received on the light receiving position detection elements 34a and 34b is optimized, and the desired focus detection sensitivity and focus detection range are set. obtain.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autofocus device used in a microscope or the like.

[0002]

2. Description of the Related Art Japanese Unexamined Patent Publication No.
The one disclosed in Japanese Patent No. 202708 is known.
This device is a focus detection optical system that projects an index image onto an object plane and obtains the distance between the object plane and the objective lens from the reflected light of a geometric pattern formed on the object plane within the range illuminated by the index image. Is used. The geometric pattern is divided into two by a pupil division prism placed at a position where a pupil is formed by the reflected light flux, and an optical detection element (for example, PS
D), two-split SPD (silicon photodiode), a pair of CCD linear sensors, or a pair of CCs
Two index images are formed on a light receiving element such as a D area sensor. In these index images, the light amount center of gravity of the image forming position on the light receiving element moves substantially in proportion to the distance between the object plane and the objective lens, so that the position of the light amount center of gravity due to the light amount distribution of each of the two index images is shifted. The distance between the object plane and the objective lens can be obtained by calculation from the output of the light receiving element. Therefore, the object plane can be matched with the in-focus position by controlling this interval.

[0003]

However, the conventional autofocus device has a problem that the detection sensitivity and the detection range are uniquely determined by the NA (numerical aperture) of the focus detection optical system. That is, when the NA of the focus detection optical system is small, the shift of the center of gravity of the amount of light captured on the light receiving element is relatively small, and the detection sensitivity is lowered.
When the NA of the focus detection optical system is large, the detection sensitivity is high but the detection range is narrow. Therefore, when the object plane deviates from the focal plane by a certain amount or more, the detection range is exceeded and the autofocus function is activated. Disappear. Therefore, in the conventional device, the NA itself of the focus detection optical system must be changed when the detection sensitivity is lowered to widen the focus detection range. Generally, the focus detection optical system also shares the optical components of the observation optical system such as the objective lens, but since the specifications of the observation optical system are usually given priority, the NA of the focus detection optical system may not be set to an appropriate value. is there. That is, in the conventional device, the focus detection sensitivity and the focus detection range are uniquely determined by the NA of the focus detection optical system, and as a result, these factors are determined by the convenience of the observation optical system, and an appropriate autofocus function is secured. hard.

An object of the present invention is to provide an autofocus device capable of selecting an optimum focus detection sensitivity and focus detection range.

[0005]

The invention described in claim 1 is applied to an autofocus device for obtaining information corresponding to a deviation between a reference position and an actual position of an object 7. Then, an index irradiating means for forming an image of the index light on the object plane through the objective lens 8, a dividing means 33 for dividing the index image light reflected by the object surface and transmitted through the objective lens 8 into two at a pupil position, and a dividing means 33. Light blocking means 3 for blocking a part of the incident light flux
2, a first light receiving means 34a for receiving the first light flux of the index image light split by the splitting means 33 at the image forming position, and a second light flux of the index image light split by the splitting means 33. An autofocus device comprising: a second light receiving means 34b for receiving light at an image position; and an extracting means for extracting information from the light quantity distribution of the light flux received by the first and second light receiving means 34a, 34b. According to a second aspect of the present invention, in the autofocus device according to the first aspect, the light shielding shape of the light shielding means 32 is variable.

According to the first aspect of the invention, the light fluxes received by the first and second light receiving means 34a, 34b depend on the light-shielding shape of the light-shielding means 32 for blocking a part of the light flux entering the splitting means 33. Creates a light distribution. According to the second aspect of the invention, the light quantity distribution of the light flux received by the first and second light receiving means 34a and 34b changes according to the change in the light blocking shape of the light blocking means 32.

Incidentally, in the section of means and action for solving the above problems for explaining the constitution of the present invention, the drawings of the embodiments are used for making the present invention easy to understand. It is not limited to.

[0008]

1 to 11 show an optical microscope to which an embodiment of an autofocus device according to the present invention is applied. In FIG. 1, visible light emitted from an observation light source 1 passes through a lens 2, a lens 3, a field stop 4, an infrared cut filter 5, and a condenser lens 6 to illuminate an object 7. The illumination light transmitted through the object 7 passes through the objective lens 8, the dichroic mirror 9 transmits light of wavelengths other than infrared light, and further passes through the lens 10 on the image pickup device 11 at a position conjugate with the surface position of the object 7. Form an object plane image on. The above optical path is the observation system optical path 12.

On the other hand, the index light source 21 emits light having a wavelength from the infrared region to visible light, and this light is condensed by the condenser lens 22 and illuminates the index 23. Index 2 made of glass plate
A chromium vapor deposition pattern serving as a shielding portion 23b is formed on the surface of No. 3, and a rectangular transparent portion 23a is formed at the center. The light transmitted through the transparent portion 23a having the index shape is transmitted through the lens 24, further transmitted through the half mirror 25, and is incident on the visible cut filter 26. Then, only the infrared light passes through the visible cut filter 26, is reflected by the dichroic mirror 9, and the optical path is bent downward by 90 degrees. The bent index light enters the objective lens 8 to form an index image on the surface of the object 7. Since the optical system is configured so that the index 23, the surface of the object 7, and the image sensor 11 all have a conjugate positional relationship, when the index image is focused on the surface of the object 7, the surface of the object 7 is reflected by the image sensor 11. The fine pattern of is imaged. That is, the surface of the object 7 is located at the focal plane of the observation system optical path 12.

The index image projected on the surface of the object 7 is the object 7
The light is reflected by the surface of and is transmitted through the objective lens 8. Further, it is reflected by the dichroic mirror 9 and transmitted through the visible cut filter 26. Of this transmitted light, the half mirror 25
Then, a half of the light amount is reflected, transmitted through the lens 31, and enters the variable light shielding plate 32. The variable light shielding plate 32 is composed of a liquid crystal panel, and the shielding portion and the transmission portion can be arbitrarily set by selectively applying a voltage to the elements of the panel. The index light emitted from the lens 31 is blocked in the vicinity of the pupil by the variable light blocking plate 32 to block the light flux in the area of the shielded portion, and is then split into two by the pupil splitting prism 33 placed at the pupil position. Detection element 34a
The other enters the optical position detecting element 34b. When the index image incident on the optical position detecting elements 34a, 34b is focused on the optical position detecting elements 34a, 34b, the surface of the object 7, the index 23 and the optical position detecting elements 34a, 34b are detected.
This is when the positions of are in a conjugate relationship. Indicator light source 2
1 to the surface of the object 7, and further the optical position detecting element 34a,
The optical path leading to 34b is the focus detection system optical path 35.

The optical position detecting elements 34a and 34b are PSDs that output two signals.
Is to output the output signals A1 and B1, and the optical position detecting element 34b is to output the output signals A2 and B2, respectively. PS
The centroids G1 and G2 of the light applied to D (distance from the center of the light receiving surface to the centroid of the applied light) are: G1 = (A1-B1) / (A1 + B1) G2 = (A2-B2) / (A2 + B2) ) Is required.

4 and 5 show electric signal processing blocks of the autofocus device according to this embodiment. The output signal A1 of the optical position detection element 34a is impedance-converted by the amplifier 41, and the output signal B1 is impedance-converted by the amplifier 42, respectively, and input to the subtractor 43 and the adder 44. The outputs of the subtractor 43 and the adder 44 are input to the divider 45 to obtain the output signal d1 = (A1-B1) / (A1 + B1). d1 indicates the distance from the center of the light receiving surface of the optical position detecting element 34a to the center of gravity of the emitted light.

On the other hand, the output signal A2 of the optical position detecting element 34b is impedance-converted by the amplifier 46 and the output signal B2 is input by the amplifier 47, and is input to the subtracter 48 and the adder 49. The outputs of the subtractor 48 and the adder 49 are input to the divider 50 to obtain the output signal d2 = (A2-B2) / (A2 + B2). d2 indicates the distance from the center of the light receiving surface of the optical position detecting element 34b to the center of gravity of the emitted light.

The output signals d1 and d2 are input to the subtracter 51, and d1-d2, which is the relative distance between the index images formed on the two optical position detecting elements 34a and 34b, is output. In addition to amplifying this output with the amplifier 52,
The low-pass filter 53 removes the high-frequency component and inputs it to the adder 54 which is the addition part of the servo circuit. Adder 5
4, the motor control circuit 55, the DC motor 56, the tacho generator 57 and the low pass filter 58 form a negative feedback servo loop. Therefore, the sample mounting Z stage 59 is drive-controlled in the Z direction using the output signal of the low-pass filter 53 as a reference signal so that the surface of the object 7 fixed to the sample mounting Z stage 59 is at the focal position.

FIGS. 6A and 6B show three examples in which the arrangement of the shield portion and the transmission portion of the variable light shield plate 32 are different, respectively, A type (FIG. 6A), B type (FIG. 6B) and C type (FIG. 6B). 6 (c)). The A type has a strip-shaped shielding portion in the central portion, the B type has a strip-shaped transparent portion in the central portion, and the C type has the entire transparent portion.

<C Type> FIGS. 7A to 7C show the image formation state of the index image on the optical position detecting elements 34a and 34b when the variable light-shielding plate 32 is the C type. The variable light-shielding plate 32 does not block the index light, and the index light is directly incident on the pupil division prism 33, which corresponds to a state equivalent to that of the conventional device. As shown in FIG. 8A, in the focused state, the index image is focused on the surface of the object 7, and the reflected light is applied to the pupil division prism 33 without being blocked by the variable light shielding plate 32. . Therefore, a perfect pupil is formed here. As a result, the index image is focused on the optical position detecting elements 34a and 34b using all the light fluxes. At this time, the center of gravity of the index image is at the center of the light receiving surface, and d1 = 0 and d2 = 0.

In the front focus state shown in FIG. 8B, that is, in the state in which the index image is focused before reaching the surface of the object 7,
As shown in FIG. 7B, the optical position detecting element 34a is out of focus, and is closer to the minus side (FIG. 7B).
At the left side of), an index image is created. Similarly, an index image can be formed on the optical position detecting element 34b in a defocused state and in the positive direction. In FIG. 7B, d1 = −2.0 and d2 = + 2.0.

In the rear focus state shown in FIG. 8C, that is, in the state where the index image is focused after passing through the surface of the object 7,
As shown in FIG. 7 (c), an index image is formed on the optical position detecting element 34a in a defocused state and in the positive direction. Similarly, an index image can be formed on the optical position detecting element 34b in a defocused state and toward the minus side. In FIG. 7C, it can be seen that d1 = + 2.0 and d2 = −2.0, which are opposite to the front pinned state. In this way, the positional relationship between the image formation position of the index image and the surface of the object 7 changes, so that the magnitude relationship between d1 and d2 changes. The distance D between the actual surface position of the object 7 and the focal position where the surface of the object 7 should originally be can be expressed as a function of d1−d2: D = f (d1−d2), and is commonly known as shown in FIG. It is shown by a two-dimensional curve called an S curve.

<A type> FIGS. 10A to 10C show the image formation state of the index image on the optical position detecting elements 34a and 34b when the variable light shielding plate 32 is of A type. In the focused state shown in FIG. 8A, the index image is focused on the surface of the object 7. This reflected light passes through the lens 31 and is blocked by the variable light-shielding plate 32 at a strip-shaped region (see FIG. 6A) extending parallel to the ridgeline of the pupil division prism 33. Therefore, the index light incident on the pupil division prism 33 is eclipsed in a band-shaped region centered on the ridgeline near the center of the pupil, but the index image is detected by the optical position detecting element in the in-focus state even with an imperfect pupil. Focus on 34a, 34b. At this time, the center of gravity of the index image is located at the center of the light receiving surface, and d1 = 0 and d2 = 0.

In the front pin state shown in FIG.
As shown in (b), an index image is formed on the optical position detecting element 34a in a defocused state and toward the minus side. Similarly, an index image can be formed on the optical position detecting element 34b in a defocused state and in the positive direction. This index image is clearly different from the front focus state in the C type, has a smaller area, and the positions of the centers of gravity on the optical position detecting elements 34a and 34b are closer to the minus side and the plus side, respectively, d1 = -2. 5, d2 = + 2.5. This is the pupil splitting prism 33 of the light flux of the index image.
This is because the variable light-shielding plate 32 blocks the portion close to the ridgeline.

In the rear pin state shown in FIG.
As shown in (c), an index image is formed on the optical position detection element 34a in a defocused state and in the positive direction.
Further, similarly, an index image can be formed on the optical position detecting element 34b in a defocused state and toward the minus side. This index image has a smaller area than the C type, and the barycentric positions on the optical position detecting elements 34a and 43b are closer to the plus side and the minus side, respectively, and d1 = + 2.5, d2 = It becomes -2.5.

As shown in FIG. 9, it can be seen that the S curve obtained in the case of the A type has a gentler slope than that in the case of the C type, and the focus detection sensitivity is improved.

<B Type> FIGS. 11A to 11C show the image formation state of the index image on the optical position detecting elements 34a and 34b when the variable light-shielding plate 32 is of B type. As shown in FIG. 8A, the index image is focused on the object plane 7 in the focused state. This reflected light is reflected by the lens 31.
In the variable light-shielding plate 32, only the strip-shaped region (see FIG. 6B) extending parallel to the ridgeline of the pupil division prism 33 is transmitted, and the other part is blocked. However, even with an incomplete pupil, the index image is focused on the optical position detecting elements 34a and 34b in the focused state. At this time, the center of gravity of the index image is located at the center of the light receiving surface, and d1 = 0 and d2 = 0.

In the front pin state shown in FIG.
As shown in (b), an index image is formed on the optical position detecting element 34a in a defocused state and toward the minus side. Similarly, an index image can be formed on the optical position detecting element 34b in a defocused state and in the positive direction. These index images are different from the front pin state in C type,
The area is smaller, and the center of gravity is closer to the center of the light receiving position detecting elements 34a and 34b, and d1 = -1.0 and d2 = + 1.0. This is the pupil splitting prism 33 of the light flux of the index image.
This is because only the light flux in the portion close to the ridge line is used and the other portions are shielded by the variable light shielding plate 32.

In the rear pin state shown in FIG.
As shown in (c), an index image is formed on the optical position detection element 34a in a defocused state and in the positive direction.
Further, similarly, an index image can be formed on the optical position detecting element 34b in a defocused state and toward the minus side. This index image has a smaller area than that of the C type, and the center of gravity is closer to the center of the light receiving position detecting elements 34a and 34b, and d1 = + 1.0 and d2 = -1.0. .

As shown in FIG. 9, the S curve obtained in the B type has a steeper slope than that in the C type. That is, d1-d for defocus of the same size
The change in the value of 2 is smaller than that of the C type. Therefore, in the B type, the focus detection sensitivity is lower and
It can be seen that the focus detection range has expanded.

As described above for the A type, B type, and C type, in the autofocus device of the present embodiment, the light is incident on the optical position detecting elements 34a, 34b according to the light shielding pattern of the variable light shielding plate 32. The amount of movement of the center of gravity of the light flux changes. Therefore, the variable light-shielding plate 3
The focus detection sensitivity and the focus detection range are changed by switching the voltage applied to 2, and the same effect as changing the NA of the focus detection optical system can be obtained.

Although three types of light-shielding patterns have been described above, the shape of the light-shielding portion is not limited to these examples. For example, when the variable light-shielding plate 32 is a D-type light-shielding pattern shown in FIG. 6D, the S-curve depends on the distance between the transmission part and the center (line corresponding to the ridgeline of the pupil division prism). The inclination of changes.

When the autofocus device according to the present embodiment is used, the focal position can be efficiently adjusted by the procedure described below. First, coarse adjustment is performed with the type B selected and the focus detection range expanded. Then, switch to type A and make fine adjustments with the focus detection sensitivity increased to achieve accurate focus alignment. As described above, when the positional deviation from the focus is large, the detection sensitivity is lowered to take it into the focus detection range, and after the rough adjustment is made, the detection sensitivity is increased to perform a high-sensitivity autofocus operation, and the sample mounting Z A fine height adjustment of the stage 59 is possible. In this way, it is possible to simultaneously satisfy the contradictory conditions of increasing the focus detection sensitivity and expanding the focus detection range in the conventional autofocus device.

When a relay lens is inserted in the observation optical system to make the magnification of the observation optical system variable, the S curve is switched in conjunction with the magnification so that the focus detection sensitivity is the focus obtained at that magnification. It is also possible to set the value corresponding to the depth. That is, generally, when observing at a low magnification, the depth of focus becomes deep, and the focus detection sensitivity can be lowered as compared with the case of observing at a high magnification. If the S-curve is automatically switched by changing the light-shielding pattern of the variable light-shielding plate, the focus detection range is expanded at a low magnification, and as a result, even if the unevenness on the object surface is relatively large, the focus alignment can be performed. A margin is secured, and good autofocus operation is possible. It should be noted that the feature of the conventional technique (Japanese Patent Laid-Open No. 1-2202708) that the non-uniformity of the reflectance of the surface of the object surface and the presence or absence of a pattern do not affect the autofocus operation is
Not lost in the present invention.

In this embodiment, the variable light-shielding plate 32 having a variable light-shielding pattern is used, but a light-shielding plate having a fixed light-shielding pattern may be used. By inserting such a light shielding plate into the focus detection optical system, the focus detection sensitivity and the focus detection range can be easily set to optimum values without being influenced by the design of the observation optical system. It is also possible to prepare a plurality of light-shielding plates having different light-shielding patterns and replace the light-shielding plates according to the observation conditions and the surface condition of the sample.

[0032]

According to the first aspect of the present invention, the index light incident on the first light receiving means and the second light receiving means is blocked by blocking a part of the index light incident on the dividing means by the blocking means. Since the amount of movement of the center of gravity of the light (the amount of movement for a fixed amount of defocus) can be adjusted, it is possible to select an appropriate focus detection sensitivity and focus detection range without being influenced by the design of the observation optical system. it can. According to the second aspect of the present invention, the shielding area of the blocking means can be changed. Therefore, after the focus detection sensitivity is lowered and the coarse adjustment is performed, the focus detection sensitivity is increased and the fine adjustment is performed efficiently. Also, high-sensitivity autofocus operation can be performed. Further, by changing the shielding area according to the depth of focus of the observation optical system, it is possible to select the optimum focus detection sensitivity and focus detection range according to the depth of focus.

[Brief description of drawings]

FIG. 1 is a diagram showing an optical microscope to which an embodiment of an autofocus device according to the present invention is applied, (a) showing an optical system of an optical microscope, and (b) showing a shape of an index.

FIG. 2 is a partially enlarged view of FIG.

FIG. 3 is a partially enlarged view of FIG. 1;

FIG. 4 is a diagram showing an electric signal processing block of the autofocus device according to the embodiment.

FIG. 5 is a diagram showing an electric signal processing block of the autofocus device according to the embodiment.

6A and 6B are diagrams showing a light-shielding pattern of a variable light-shielding plate of the autofocus device according to the embodiment, where FIG. 6A is a diagram showing an A type, FIG. 6B is a diagram showing a B type, and FIG. The figure which shows a type, (d) The figure which shows a D type.

FIG. 7 is a diagram showing an index image on the optical position detection element when the variable light-shielding plate has a C-type shielding pattern in the autofocus device according to the embodiment, and FIG. The figure which shows an index image, (b) the figure which shows the index image in the front focus state, (c) the figure which shows the index image in the back focus state.

8A and 8B are diagrams showing an index image of an object plane in the autofocus device according to the embodiment, FIG. 8A shows an index image in a focused state, and FIG. 8B shows an index image in a front focus state. And FIG. 6C is a diagram showing an index image in a rear focus state.

FIG. 9 is a diagram showing an S curve of the autofocus device according to the embodiment.

FIG. 10 is a diagram showing an index image on the optical position detecting element when the variable light-shielding plate has an A-type shielding pattern in the autofocus device according to the embodiment, and FIG. The figure which shows an index image, (b) the figure which shows the index image in the front focus state, (c) the figure which shows the index image in the back focus state.

FIG. 11 is a diagram showing an index image on the optical position detecting element when the variable light-shielding plate has a B-type shielding pattern in the autofocus device according to the embodiment, and FIG. The figure which shows an index image, (b) the figure which shows the index image in the front focus state, (c) the figure which shows the index image in the back focus state.

[Explanation of symbols]

 7 object 8 objective lens 32 variable light-shielding plate 33 pupil division prism 34a light receiving position detecting element 34b light receiving position detecting element

Claims (2)

[Claims] 1. An autofocus device for obtaining information corresponding to a positional deviation between a focal plane and an object plane, an index irradiating means for focusing the index light on the object plane through an objective lens, and the objective reflected by the object plane. A dividing unit that divides the index image light that has passed through the lens into two at a pupil position, a light-shielding unit that shields a part of the light beam that enters the dividing unit, and a first portion of the index image light that is divided by the dividing unit. A first light receiving means for receiving the light flux, a second light receiving means for receiving the second light flux of the index image light split by the splitting means, and light received by the first and second light receiving means. An autofocus device comprising: an extracting unit that extracts the information from a light amount distribution of a light flux. 2. The autofocus device according to claim 1, wherein the light blocking means has a variable light blocking shape.