JP3239343B2 - Focus position detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus position detecting apparatus suitable for use in an automatic focusing mechanism of an optical device such as a microscope, a video camera or a still camera.

[0002]

2. Description of the Related Art In an optical apparatus such as a microscope, a video camera or a still camera, an image of an object is formed on a predetermined image plane by an objective optical system.
Imaging is performed using a two-dimensional imaging device such as a CD. Such an optical device is provided with an auto-focus mechanism in order to always clearly form an image of an object on a predetermined imaging plane. An important part of the autofocus mechanism is a focus position detection device for detecting a position shift (focus shift) between the image formed by the objective optical system and the original image plane.

FIG. 5 shows a conventional focus position detecting device. In FIG. 5, light from a sample 1 as an object to be observed is condensed by an objective lens 2, and a part of the condensed light is The light is separated by the splitter 3 and reaches the observation surface 4. When the sample 1 is focused on the objective lens 2, an image of the sample 1 is formed on the observation surface 4 by the objective lens 2, and this image is photoelectrically converted by, for example, a two-dimensional image sensor. On the other hand, the light transmitted through the beam splitter 3 is further split into two by the half prism 5, and the split light is incident on the light receiving surfaces of light receiving elements 6A and 6B such as line sensors.

In a state where the sample 1 is focused on the objective lens 2, an image of the sample 1 by the objective lens 2 is formed on the imaging surfaces 7A and 7B by the light split into two by the half prism 5, respectively. Assuming that an image is formed, one light receiving element 6A is disposed at a position away from the objective lens 2 by an interval Δ with respect to the image forming surface 7A, and the other light receiving element 6B is provided on the image forming surface 7B. On the other hand, it is arranged at a position separated by an interval Δ in the direction approaching the objective lens 2. In this case, the specimen 1 and the objective lens 2 are set so that the distribution of the imaging light flux from the specimen 1 detected by the light receiving element 6A is equal to the distribution of the imaging light flux from the specimen 1 detected by the light receiving element 6B.
The image blur on the light receiving element 6A and the image blur on the light receiving element 6B become equal by performing an operation such as changing the interval between the light receiving elements 6A and 6B. That is, a clear image of the specimen 1 is formed on the imaging surfaces 7A and 7B.
A clear image of the specimen 1 is formed on the observation surface 4 at the same time.

[0005]

In the prior art as described above, when the objective lens 2 is replaced with another objective lens, the half of the objective lens after replacement is changed due to differences in magnification and numerical aperture NA. The numerical aperture NA 'on the prism 5 side is different from the numerical aperture of the objective lens 2 previously. Its numerical aperture NA '
The degree of blurring of the image at the position where the light receiving elements 6A and 6B are arranged, that is, at the position defocused from the original imaging plane, is different due to the difference. For this reason, there is a disadvantage that the precision of focusing differs depending on the objective lens.

Further, since the brightness of the image is proportional to the square of the numerical aperture NA 'of the objective lens on the half prism 5 side, if the numerical aperture NA' is different, the brightness of the image on the light receiving surfaces of the light receiving elements 6A and 6B is changed. Will differ greatly. Therefore, when the objective lens is replaced, the light receiving element 6
In order to match the sensitivity characteristics of A and 6B, it is necessary to replace an ND filter or the like disposed in the middle of the optical path, or to change the brightness of the light source for illuminating the sample 1, and the operation becomes complicated. There was an inconvenience.

SUMMARY OF THE INVENTION In view of the above, the present invention provides a focus position detecting apparatus in which the brightness of an image for detection does not change and the detection accuracy of defocus does not change even when the objective optical system is replaced. With the goal.

[0008]

A focus position detecting apparatus according to the present invention comprises: an objective optical system (2) for condensing light from an object (1) to form an image of the object (1); Photoelectric detector (13) for photoelectrically detecting the image formed by 2)
A focus position detecting device for detecting an image forming position of the objective optical system (2), wherein the focus position detection device is formed between the objective optical system (2) and the photoelectric detector (13) by the objective optical system (2). Re-imaging optical system (8a, 8b,
8c), and the re-imaging optical system includes a first optical system (8a, 8b) for condensing light from the objective optical system (2).
And a second image forming an image of the light collected from the first optical system.
Optical system (8c) and relay image formed by the second optical system
To generate a first relay image and a second relay image
And an optical path splitting prism (12), a photoelectric detector (1
3), when viewed with the objective optical system in focus,
The first optical system is arranged before and after the imaging position of the second optical system,
The first optical system and the first optical system on a surface conjugate with the pupil plane of the objective optical system (2) formed between the optical system and the second optical system;
Between the second optical system, the first relay image thereof and the second relay image thereof.
The diaphragm means (10) is arranged at a position where the relay image is telecentric .

In this case, at least some of the optical elements (8a1, 8a2) of the first optical system are configured to be movable, and by moving the movable optical elements, the objective optical system (2) is moved.
The conjugate between the pupil plane (9) and the arrangement surface of the aperture means (10) may be maintained. Further, the movable optical element (8d, 8e) of the first optical system may be a Galileo system.

[0010]

According to the present invention, for example, as shown in FIG. 1, an image (7) formed by the objective optical system (2) is once relayed by the re-imaging optical system (8a, 8b, 8c). Is done. The diaphragm means (10) is located at a position conjugate with the pupil plane (9) of the objective optical system (2) in the optical path of the re-imaging optical system.
Is arranged, the numerical aperture NA 'of the re-imaging optical system on the image (11A) side can be kept constant by the aperture means (10). Thereby, even when the objective optical system (2) is replaced, the accuracy of focusing can be made constant on the light receiving surface of the photoelectric detector (13). The brightness on the photoelectric detector (13) depends on its numerical aperture N.
Since it is determined by the square of A. ', the brightness on the light receiving surface of the photoelectric detector (13) can be made constant by the aperture means (10).

Further, at least a part of the optical elements (8a1, 8a2) of the first optical system is configured to be movable, and by moving these movable optical elements, the pupil plane (9) of the objective optical system (2) is moved. When the objective lens system (2) is replaced and the position of the pupil plane (9) is changed, the conjugate of the diaphragm means (10) with the arrangement surface of the diaphragm means (10) is maintained. The arrangement plane is conjugate with the pupil plane of the objective optical system after the exchange. Therefore, the image-side numerical aperture NA 'of the re-imaging optical system is kept constant.

When the movable optical element (8d, 8e) of the first optical system is a Galileo system, when the objective optical system (2) is replaced and the position of the pupil plane changes, By moving the Galileo system, the squeezing means (10)
Is conjugated to the pupil plane of the objective optical system after replacement. Even in this case, the magnification of the image (11A) of the object re-imaged by the re-imaging optical system does not change, and the accuracy of detection of defocus is maintained constant.

It is desirable that the diaphragm means (10) is arranged at a position where the image (11A) relayed by the re-imaging optical system is telecentric on the image side. With such an arrangement, even if defocus occurs, the photoelectric detector (13)
Since the size of the image at does not change, the detection accuracy of the defocus is kept constant.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a focus position detecting device according to the present invention will now be described.
An embodiment will be described with reference to FIGS. The present embodiment is applied to, for example, an autofocus mechanism of a microscope that can be used by exchanging various objective lenses. FIG. 1 shows a schematic configuration of the present embodiment. In FIG. 1, a beam splitter 3 is arranged between an objective lens 2 and an image 7 of a specimen 1 as an observation object by an objective lens 2. An image forming light beam from the objective lens 2 branched by the beam splitter 3 is guided to an observation surface 4. In a state where the sample 1 is focused on the objective lens 2, an image of the sample 1 is formed on the observation surface 4, and a light receiving surface of, for example, a two-dimensional image sensor is arranged on the observation surface 4. .

In this embodiment, a relay lens system composed of a lens 8a, a lens 8b, and a lens 8c (which is represented by a "relay lens system 8") is disposed above the beam splitter 3 in this order. , Specimen 1
Is formed again to form a relay image 11A. In this case, the conjugate plane of the pupil plane (Fourier transform plane) 9 of the objective lens 2 by the lenses 8a and 8b is formed between the lens 8b and the lens 8c, and the conjugate plane with the pupil plane 9 is formed. The aperture 10 is arranged at the position. The aperture 10 limits the numerical aperture NA ′ of the relay lens system 8 on the image 11A side to a predetermined value. Thus, even when the objective lens 2 is exchanged, as long as the pupil plane of the objective lens after the exchange is at the same position as the pupil plane 9, the light flux passing through the aperture 10 and forming the relay image 11A by the lens 8c is obtained. The numerical aperture is always constant.
Therefore, the detection accuracy of the defocus does not change, and the brightness of the detection relay image 11A does not change.

Since the defocus cannot be detected only by the configuration of FIG. 1, an optical system as shown in FIG. 2 is arranged next to the lens 8c. FIG. 2 shows an image 7 from the objective lens 1 of FIG.
FIG. 2 shows an example of an optical system. In FIG. 2, an optical path splitting prism 12 is disposed on a rear end lens 8c of the relay lens system 8. The optical path splitting prism 12 is formed by bonding a slope of a prism having a parallelogram cross section to a slope of a prism having a right-angled triangle and a bonding surface 12a.
Is a half mirror surface.

In this arrangement, the light beam emitted from the lens 8c is reflected by the half mirror surface 12 of the optical path splitting prism 12.
The relay image 11A is formed by a light beam that has been divided into two by a and transmitted through the half mirror surface 12a. Further, the light beam reflected by the half mirror surface 12a is
The cross section inside is totally reflected by the other inclined surface 12b of the parallelogram prism, and the totally reflected light beam causes a relay image 11 to be formed.
B is imaged. Each of the relay images 11A and 11B is obtained by re-imaging the image 7 by the relay lens system 8.

In FIG. 1, when the sample 1 is focused on the objective lens 2, in FIG. 2, one relay image 11A is formed at a predetermined interval from the optical path dividing prism 12, and the other relay image 11A is formed. The relay image 11B is formed inside the optical path splitting prism 12, and an intermediate position between the image forming position of the relay image 11A and the image forming position of the relay image 11B is set outside the optical path splitting prism 12. Then, the light receiving surface of the light receiving element 13 such as a one-dimensional CCD or a line sensor is arranged at an intermediate position therebetween. That is, the sample 1 is the objective lens 2
In the state in which the light is focused, the optical path length from the light receiving surface of the light receiving element 13 to the relay image 11A is equal to the optical path length from the light receiving surface of the light receiving element 13 to the relay image 11B. Therefore, the light receiving element 13 receives the blurred image of the relay image 11A and the blurred image of the relay image 11B, and focuses the sample 1 by, for example, equalizing the light amount distribution of both. Note that a two-dimensional image sensor or the like may be used as the light receiving element 13.

In the example of FIG. 2, the arrangement surface of the stop 10 between the lens 8b and the lens 8c is the same as the objective lens 1 of FIG.
Is conjugate with the pupil plane 9 of FIG. Further, it is desirable that the position of the stop 10 is a position where the relay images 11A and 11B are telecentric, that is, near the position of the front focal plane of the lens 8c. Thus, the relay images 11A and 11B
Is made to be telecentric, so that the relay image 11A on the light receiving surface of the light receiving element 13 can be obtained even if a defocus occurs.
And 11B have the same blurred image magnification. Therefore, the blur states of the images before the relay image 11A and after the relay image 11B are almost completely equal, and the focusing accuracy is increased.

Next, a second embodiment of the present invention will be described with reference to FIG. In this embodiment, the configuration of the relay lens system 8 in the embodiment of FIG. 2 is changed. In FIG. 3, portions corresponding to those in FIG. 2 are denoted by the same reference numerals, and detailed description thereof will be omitted. FIG. 3 shows the optical system of the present example following the image 7 of FIG. 1. In FIG. 3, a lens 8a1 movable along the optical axis AX and along the optical axis AX in order from the image 7 toward the stop 10. The movable lens 8a2 and the fixed lens 8b. Other configurations are the same as those in FIG. Then, the relay images 11A and 11B are re-imaged from the image 7 by a relay lens system including the lenses 8a1, 8a2, 8b, and 8c (this is also called a “relay lens system 8”).

When the position of the pupil plane (corresponding to the pupil plane 9 in FIG. 1) of the objective lens is changed by exchanging the objective lens before the image 7, the lens 8a1 and the lens 8a2 are respectively moved. By independently moving along the optical axis AX,
The conjugate between the pupil plane and the plane where the aperture 10 is arranged is maintained. Thereby, even when various objective lenses are exchanged and used, the numerical aperture NA ′ of the imaging light beam incident on the light receiving element 13 from the lens 8c is maintained at a constant value,
Defocus detection accuracy is maintained constant. In this regard, in general, a high-magnification objective lens has a relatively low focusing accuracy due to a small numerical aperture on the image side with respect to the magnification, but
If the detection accuracy of the defocus is set in accordance with the aperture 10 of the numerical aperture on the image side of the high-magnification objective lens, a constant detection accuracy can be obtained even when the objective lens is replaced.

As in the present embodiment, the lenses 8a1 and 8a2, which are part of the relay lens system 8, are moved so as to be able to cope with a wide range of fluctuations in the position of the pupil plane (entrance pupil) of the objective lens. For example, even when the position fluctuation of the entrance pupil is large as in a microscope, the accuracy of focusing can be kept constant. Further, the brightness of the relay images 11A and 11B is always kept constant by the stop 10, and the saturation phenomenon of the light receiving element 13 does not occur. Therefore, it is not necessary to adjust the brightness of the light source for illuminating the sample.

Next, for example, when the light beam from the lens 8b to the lens 8c via the stop 10 is a parallel light beam,
Lens 8a1, lens 8a2 between image plane 7 and aperture 10
And the combined focal length of the lens system including the lens 8b and the lens 8b is f. The movable lens 8a1 is moved so that the combined object-side principal point of the lens system including the lens 8a1, the lens 8a2, and the lens 8b is always located at a distance f from the image plane 7.
And the movable lens 8a2 is moved. If you do this,
When the position of the pupil plane (entrance pupil) of the objective lens before the image 7 changes, the position of the plane (exit pupil) conjugate to the pupil plane is changed without changing the positions of the relay images 11A and 11B. 10 can be maintained. Needless to say, the exit pupil in this case is most preferably telecentric, which improves the focusing accuracy.

Next, a third embodiment of the present invention will be described with reference to FIG. This embodiment also differs from the embodiment of FIG. 2 in the configuration of the relay lens system 8. In FIG. 4, portions corresponding to FIG. 2 are denoted by the same reference numerals, and detailed description thereof will be omitted. FIG. 4 shows an optical system of this example following the image 7 of FIG. 1. In FIG. 4, a fixed lens 8b and a concave lens 8d movable along the optical axis AX are arranged in order from the image 7 toward the stop 10. And a movable convex lens 8e is arranged along the optical axis AX. The concave lens 8d and the convex lens 8e move integrally along the optical axis AX as a Galileo system. Other configurations are the same as those in FIG. Then, the relay images 11A and 11B are re-imaged from the image 7 by a relay lens system including the lens 8b, the concave lens 8d, the convex lens 8e, and the lens 8c (also referred to as a “relay lens system 8”).

In this case, the light beam from the image 7 is converted into a parallel light beam by the lens 8b, and this parallel light beam is further converted into a concave lens 8
The light is converted into a parallel beam having a large diameter by a Galileo system composed of d and the convex lens 8e. Then, the parallel light flux emitted from the Galileo system reaches the lens 8c via the stop 10. That is, the space between the lens 8b and the Galileo system is a parallel system, and the space between the Galileo system and the lens 8c is also a parallel system. Therefore, even when the Galileo system including the concave lens 8d and the convex lens 8e is moved along the optical axis AX, the positions and magnifications of the relay images 11A and 11B do not change.

In addition, when the position of the pupil plane (entrance pupil) is changed due to the exchange of the objective lens, the Galileo system is moved accordingly, so that the plane (exit pupil) conjugate with the pupil plane is changed. The position can be maintained on the arrangement surface of the diaphragm 10. Therefore, the focusing accuracy is more stably maintained.

In the above-described embodiment, the present invention is applied to an autofocus mechanism of a microscope in which an objective lens can be exchanged. In addition, for example, various interchangeable lenses having different aperture F values are exchanged and used. The present invention is similarly applied to an autofocus mechanism such as a video camera and a still camera. As described above, the present invention is not limited to the above-described embodiment, and can take various configurations without departing from the gist of the present invention.

[0028]

According to the present invention, the numerical aperture on the rear side of the re-imaging optical system can always be kept constant by the aperture means arranged at a position conjugate with the pupil plane of the objective optical system. Of the image on the light receiving surface can be kept constant.
That is, the detection accuracy of the defocus by the photoelectric detector can be constant regardless of the type of the objective optical system. Also, since the numerical aperture is fixed by the aperture means, the brightness of the image relayed by the re-imaging optical system on the photoelectric detector is always constant, and when a light source for illuminating an object is used. To
There is an advantage that it is not necessary to adjust the brightness of the light source due to the sensitivity of the photoelectric detector.

In the case where the movable optical element constituting the first optical system is moved to maintain the conjugate between the pupil plane of the objective optical system and the arrangement surface of the diaphragm means, the objective optical system can be replaced. Therefore, even if the position of the pupil plane changes, the accuracy of detecting the defocus by the photoelectric detector can be kept constant. Further, when the movable optical element is a Galileo system, even if the Galileo system is moved so as to maintain the conjugate between the pupil plane of the objective optical system and the arrangement plane of the diaphragm means, the re-imaging optical system may be used. Since the relayed image does not change, the defocus detection accuracy is more stably maintained.

[Brief description of the drawings]

FIG. 1 is a partially omitted light path diagram showing the entire configuration of a first embodiment of a focus position detecting apparatus according to the present invention.

FIG. 2 is an optical path diagram showing a configuration after a relay lens system according to a first embodiment.

FIG. 3 is an optical path diagram showing a configuration after a relay lens system according to a second embodiment of the present invention.

FIG. 4 is an optical path diagram showing a configuration after a relay lens system according to a third embodiment of the present invention.

FIG. 5 is an optical path diagram showing an entire configuration of a conventional focus position detecting device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 sample 2 objective lens 7 image of sample 1 8a, 8b, 8c lens 9 pupil surface of objective lens 10 aperture 11A, 11B relay image 12 optical path splitting prism 13 light receiving element

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-2-1809 (JP, A) JP-A-2-6709 (JP, A) JP-A-63-65415 (JP, A) JP-A-4- 98233 (JP, A) JP-A-4-174410 (JP, A) JP-A-4-338711 (JP, A) JP-A-5-72467 (JP, A) Japanese Utility Model Application No. 57-133018 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) G02B ^7/ 28-7/36

Claims (3)

(57) [Claims] 1. An objective optical system comprising: an objective optical system that collects light from an object to form an image of the object; and a photoelectric detector that photoelectrically detects an image formed by the objective optical system. In a focus position detection device that detects an imaging position of an optical system, a re-imaging optical system that re-images an image of an object formed by the objective optical system between the objective optical system and the photoelectric detector is provided. Disposed, the re-imaging optical system, a first optical system for condensing light from the objective optical system, a second optical system for imaging the condensed light from the first optical system, A relay image formed by the second optical system
To generate a first relay image and a second relay image
An optical path splitting prism , wherein the photoelectric detector is in a state where the objective optical system is in focus.
When viewed from the above, it is arranged before and after the imaging position of the second optical system.
It is, in the pupil plane conjugate with the plane of said objective optical system is formed between the second optical system and the first optical system, and the first optical system
Between the first relay image and the second optical system.
Position where the second relay image is telecentric
A focus position detecting device , wherein a stop means is arranged in the focusing position. 2. A conjugate between a pupil plane of the objective optical system and an arrangement plane of the diaphragm means by moving at least a part of the optical elements of the first optical system and moving the movable optical elements. 2. The focus position detecting device according to claim 1, wherein 3. The focus position detecting device according to claim 2, wherein the movable optical element of the first optical system is a Galileo system.