JPH06214150A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To high accurately perform automatic focusing with a simple constitution without being influenced by aberration and flare at all. CONSTITUTION:A field stop 4 restricting the illuminated area of an object surface 7 to a size which is nearly conjugate to the image pickup surface 11' of an image pickup element 11 is provided on transmission illuminating systems 1, 2a, 3, 2b and 4-6, and also index irradiation optical systems 8, 9, 13, 12, 10, and 14-16 performing irradiation with index light whose wavelength band is nearly equal to that of object illuminating light from the transmission illuminating systems 1, 2a, 3, 2b, and 4-6 are provided on an area other than the area of the object surface 7 illuminated by the transmission illuminating systems 1, 2a, 3, 2b, and 4-6; furthermore, light receiving optical systems 8, 9, 13, 10, 17, and 18 receiving the index light reflected at the object surface 7 in a state where they separate the index light from illuminating light are provided: and an image on the object surface 7 is focused on the image pickup surface 11' of the image pickup element 11 based on a signal from the video camera 18 of the light receiving optical systems 8, 9, 13, 10, 17, and 18.

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 for microscopes and the like.

[0002]

2. Description of the Related Art As a conventional device of this type, Japanese Patent Laid-Open No.
There is one described in Japanese Patent Publication No. 202708. This is a transmission illumination system that illuminates the object surface with illumination light, an observation system that forms an image of the illuminated object on the object projection surface with an objective lens, and an index light with a wavelength different from the illumination light through the objective lens. An index irradiation system that forms an image on the object plane, a pupil classification prism that divides the index image reflected on the object plane into two at the pupil position of the objective lens, and the divided first light flux is received at the image formation position. Based on the output of the first detector, the second detector that receives the divided second light flux at its image forming position, and the output of the detector, the distance between the object plane and the objective lens is controlled to form an object image of the object image. It is an autofocus device having an interval control means for focusing on a surface. And 2 in the pupil plane
Since the divided light information includes the same pattern information, the pattern information common to both is erased by the calculation, and only the focus error information is provided, so that accurate focus control that is not affected by the pattern is possible. Become.

The above publication also describes that light in the same wavelength region can be used by amplitude-modulating the illumination light for an object and the illumination light for index irradiation at different frequencies.

[0004]

The illumination light for the object and the illumination light for the index irradiation are different wavelength bands, for example, the illumination light for the object uses a light source in the vicinity of 400 to 600 nm, and the illumination light for the index irradiation is 800 nm. When a light source is used, the influence of aberration is unavoidable in the lens portion where both light sources pass in common. In other words, in order to improve the resolution of the observation system, the aberration correction of the objective lens is adjusted to 400
When it is best near 600 nm, the aberration at the wavelength of the illumination light for index irradiation becomes large. As a result, the index image is distorted, and a good autofocus state cannot be obtained. Also,
In the objective lens and other lens groups, an antireflection coating is applied to the lens surface in order to suppress the occurrence of flare, but it is difficult for this antireflection coating to perform good antireflection in a wide wavelength band. Therefore, if antireflection is performed on the wavelength of the light source of the illumination light for the object, the effect cannot be expected in the wavelength band of the illumination light for index irradiation. Also,
When the illumination light between objects having the same wavelength and the index irradiation illumination light are used by performing the amplitude modulation, although the optical problem caused by the difference in the wavelengths of the two illumination lights is solved, the modulation, There is a problem that the configuration for demodulation serves as an index. The present invention has been made in view of such conventional problems, and an object of the present invention is to make it possible to perform highly accurate autofocus with a simple configuration without being affected by aberrations and flares. .

[0005]

In order to solve the above problems, in the present invention, the object illuminating means is provided with a light flux limiting member for limiting the illumination area of the object to a size substantially conjugate with the image pickup surface of the image pickup means. In addition to providing the index illuminating means for illuminating the index light in the wavelength band substantially equal to the object illuminating light outside the illumination area of the object by the object illuminating means, the index light reflected on the object surface is received separately from the illumination light. The light receiving means and the control means for matching the object surface with the image pickup surface of the image pickup means are provided based on the output of the light receiving means.

[0006]

As described above, according to the present invention, the illumination light of the object and the index light can be made into the light of the same wavelength band with a simple structure, and therefore, the accurate light can be obtained without being affected by the aberration and the flare. Autofocus operation becomes possible.

[0007]

FIG. 1 is an optical layout diagram of an embodiment of the present invention. The light source 1 is a light source that emits a light flux having a predetermined wavelength, and the light emitted from the light source 1 is a lens 2 a, an aperture stop 3, and a lens 2.
b, the field stop 4, the infrared cut filter 5, and the condenser lens 6 are transmitted, and the object plane 7 is illuminated. The illumination area of the object plane 7 is an area in which the aperture of the field stop 4 is imaged on the object plane 7 by the lens 6. This system 1, 2a, 3, 2
b, 4, 5, and 6 constitute a transillumination system as an object illuminating means. The image on the object plane 7 is formed on the image pickup surface (corresponding to the object projection plane) of the image pickup device 11 by the objective lens 8 and the lens 10. On the image pickup surface of the image pickup device 11,
A part of the object illuminated by the transillumination system is formed as an image of the object. Here, the shape of the aperture of the field stop 4 is such that an area 40 ′ that is substantially the same as the image pickup surface 11 ′ is illuminated on the image pickup surface of the image pickup element 11 shown in FIG. 6A.
The illumination area (40 in FIG. 5) on the object plane 7 is the imaging plane 11 ′.
It is set to be almost conjugate with. Indicator light source 1
The irradiation light of No. 6 passes through the condenser lens 15 and two slits 14a, 14 of the index plate 14 whose plan view is shown in FIG.
Illuminate b. The index light that has passed through the two slits of the index plate 14 passes through the condenser lens 10, the infrared cut filter 12, and the half mirror 13 and then is reflected by the half mirror 9, whereby the optical axis is bent at a right angle and the objective lens. By 8, the index slit image is projected on the object plane 7. The two slits formed in the index plate 14 are the object plane 7
It is provided at a position where an index slit image is formed at two locations outside the above illumination area. The index light on which the index slit image has been formed is reflected by the object plane 7, passes through the objective lens 8 again, is reflected by the half mirror 9 to have its optical path bent at a right angle, and then is reflected again by the half mirror 13. The optical path is bent at a right angle, passes through the lens 10, and is split into two by the pupil splitting prism 17 arranged on the pupil plane. As shown in FIG. 3, the two-divided luminous flux forms an image pickup surface 1 of the video camera 18.
8'on the slit images 140a ', 140' for indices, respectively.
The configuration is such that a ", 140b ', and 140b" are imaged.

As described above, by combining the wavelength characteristics of the light sources 1 and 16 and the wavelength selection characteristics of the infrared cut filters 5 and 12, the illumination light of the object and the index light can be set to have substantially the same wavelength characteristics. FIG. 2 is a diagram for explaining the image formation state of the index slit image formed on the image pickup surface 18 ′ of the video camera 18 after being divided by the pupil division prism 17. When the object plane 7 is below the in-focus position with the positions P ₁ and P ₂ of the index slit image as a boundary when the object plane 7 is in the in-focus position, they are separated from the positions P ₁ and P _2. If the portion shown in FIG. 2a deviated in the direction becomes a light beam, and conversely, if the object plane 7 is above the in-focus position, the positions P ₁ and P ₂
The portions shown in FIG. 2b, which are shifted toward each other, become light beams. Therefore, the image forming position of the index slit image on the image pickup surface 18 'of the video camera 18 moves in a direction toward or away from each other due to the vertical movement of the object plane.

FIGS. 3A, 3B and 3C illustrate a case where the moving state of the index slit image 40 shown in FIG. 2 is picked up by a video camera. Figure 3 (a) shows
When the object plane 7 is above the in-focus position,
FIG. 3B shows a case where the object plane 7 is at the in-focus position, and FIG.
(C) shows the case where the object plane 7 is below the in-focus position.

In Ia, Ib, and Ic in FIGS. 3A, 3B, and 3C, the geometric patterns on the object plane 7 are transmitted illumination systems 1, 2a, 3, 2b, 4, and. The area of the area 4c ′ is changed to the shape of the aperture of the field stop 4 by 5 and 6 (image sensor 1
1 is almost the same as the shape of the light receiving surface 11 '). In addition, FIG.
In (b) and (c), 140a ′ and 140a ″ are reflection images on the object plane 7 of the slit 14a of the index plate 14, 1
40b 'and 140b "are slits 14b of the index plate 14
3 is a reflection image of the object surface 7 of FIG. The video camera 18
Index slit images 140a ′, 140a ″, 140
The geometric patterns Ia, Ib, and Ic of the object plane 7 are also imaged together with b ′ and 140b ″, but the scanning line L1 for scanning the index slit images 140a ′ and 140a ″ and the index pattern by the image processing described later. Slit images 140b ', 140
The intervals of the respective slit images are obtained from the image signal of the scanning line L2 that scans b ″.

FIG. 7 shows a servo system from the video signal 19 which is the output of the video camera 18, the horizontal synchronizing signal 20 and the vertical synchronizing signal 21 to the DC motor 34 for autofocus drive. An amplifier 22 for amplifying 19; a high-pass filter 23 for differentiating the output of the amplifier 22; a peak hold circuit 24 for performing peak detection of the differentiated two slit image waveforms for indexes; a sample and hold circuit 25; and a timing pulse generation circuit. Two
6, an edge detection circuit 27, a gated circuit 28, a synchronization circuit 29 for measuring the distance between the edges of the two peak slit-detected index images, and a sawtooth wave generation circuit 3
0, a sample-and-hold circuit 31 obtains a motor control target signal and inputs it to one input terminal of an arithmetic circuit 32. On the other hand, the output voltage of the tacho generator 35 is amplified by the preamplifier 36, and the feed back signal smoothed through the low pass filter 37 is input to the other input terminal of the arithmetic circuit 32, and the control signal generated by the arithmetic circuit 32 is used. The motor drive circuit 33 drives the DC motor 34 to relatively move the object plane 7 and the objective lens 8 to perform autofocus control.

The operation of the apparatus will be described in detail below. In the present device, the images of the two slits 14a and 14b of the index plate 14 are index projection systems 16, 15, 14, 10, 12, 13,
When the images are projected on the geometric pattern formed on the object plane 7 by 9, 8 and the images are in focus, the images of the slits 14a, 14b and the object projection image 39 are captured by the video camera 18 and the image. Focus on element 11 (FIG. 3)
(C), FIG. 6). When the object plane 7 is vertically displaced from the in-focus position, as shown in FIGS. 3A and 3B, the index slit images 140a ′, 140a ″, 140.
b ′ and 140b ″ move in the opposite direction in the left-right direction, that is, the two-divided index slit images 140a ′ and 14b.
0a ″, 140b ′, and 140b ″ move away from or closer to each other depending on the focus state (see FIG. 2).
Then, in the in-focus state, the index slit is in the in-focus state at an intermediate position (P ₁ and P _{2 in} FIG. ₂ ). The optical principle according to this embodiment is described in JP-A 1-202070.
Since it is the same as that described in Japanese Patent Publication No. 8, the detailed description is omitted. An object projection image 40 ″ illuminated by the transillumination system (1, 2a, 3, 2b, 4, 5, 6, 7) is also formed on the imaging surface 18 ′ of the video camera 18 (FIG. 3).
(A), (b) (c)). However, this object projection image 4
0 "is the transmitted illumination system (1, 2a, 3, 2b, 4, 5,
In the field stop 4 of (6, 7), the illumination range is slits 14a, 1
4b images 140a ', 140a ", 140b', 140
It is restricted so that it does not overlap with b ".
As shown in FIG. 6, the illumination range required for the image pickup surface 11 ′ of the image pickup element is determined so as to be ensured within the necessary minimum range. However, since the illumination range cannot be narrower than the range of the image pickup surface 11 ′ of the image pickup device, as shown in FIG. 6, the images 140a ′, 140a ″ of the slits 14a, 14b, 1
The slits 40a ′ and 140b ″ have two slit shapes formed near the periphery of the light flux shown in FIG. 4 so as not to overlap the image pickup surface 11 ′. Images 140a of the slits 14a and 14b imaged by the video camera 18a. ', 140
a ", 140b ', 140b" and the projected image 39 of the object
Is converted into a video signal 19 (FIG. 8 (a)), and the amplifier 2
Entered in 2.

Thereafter, the video signal 19 is high pass.
A differential waveform is obtained by the filter 23 (FIG. 8B).
In the timing pulse generation circuit 26, the images 140a ′, 140a ″, 14 of the slits 14a, 14b shown in FIG.
The timing at which the rasters L1 and L2 (the position of which is predetermined by design) that crosses 0b ′ and 140b ″ is scanned is detected, the peak hold circuit 24 and the sample and hold circuit 25 are operated, and the rasters L1 and L2 are scanned. Images 140a ', 1 of the slits 14a, 14b
The left edge portion of 40a ", 140b ', 140b" is detected. Image 140 of slit 14a divided into two
a ′, 140a ″ and the image 140 of the slit 14b
Two left edges of b ′ and 140b ″ are detected, and a pulse synchronized with this position is output from the edge detection circuit 27 (FIG. 8C). These two pulses are passed through the gate circuit 28. It is input to the sawtooth wave generation circuit 30 and the sample and hold circuit 31. In the sawtooth wave generation circuit 30, the output rises in proportion to the time in synchronization with the first pulse, and the sample and hold circuit 31 outputs the second pulse. Output V of the sawtooth wave generation circuit 30 in synchronization with the pulse
By holding the two pulse intervals t to the voltage v
And is input to one input terminal of the arithmetic circuit 32 as a servo target voltage of the DC motor 34. Arithmetic circuit 32
Compares with the output voltage of the tacho generator 35 (actually, the voltage passed through the preamplifier 36 and the low-pass filter 37), controls the DC motor 34, and relatively moves the object plane 7 and the objective lens 8, The object plane 7 is always in focus.

[0014]

As described above, according to the present invention, the illumination area of the object and the object irradiation position of the index light are configured so as not to overlap with each other, and are separated by the image pickup means of the object and the index light receiving means. Since light is received, it is possible to use light of the same wavelength band with a simple configuration.

[Brief description of drawings]

FIG. 1 is an optical system layout of an embodiment of the device according to the present invention.

FIG. 2 is a diagram showing a reaching area of index light split by a pupil splitting prism on an imaging surface of a video camera.

FIG. 3 is a diagram showing an image formation state on an image pickup surface of a video camera.

FIG. 4 is a plan view of an index plate.

FIG. 5 is a diagram showing an illumination area of an object plane.

FIG. 6 is a diagram showing a state of an image on an image sensor.

FIG. 7 is a block diagram of an electric signal processing circuit.

FIG. 8 is a waveform timing chart showing main waveforms in the block diagram of FIG. 7.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 light source 2a, 2b lens 3 aperture stop 4 field stop 5 infrared cut filter 6 condenser lens 7 object plane 8 objective lens 9 half mirror 10 lens 11 image sensor 11 'light receiving surface of image sensor 11 infrared cut filter 13 half mirror 14 index plates 14a and 14b slits 15 condenser lens 16 index light source 17 pupil division prism 18 video camera 18 'imaging surface of video camera 18 video signal 20 horizontal sync signal 21 vertical sync signal 22 amplifier 23 high-pass filter 24 peak Hold circuit 25 Sample and hold circuit 26 Timing pulse generation circuit 27 Edge detection circuit 28 Gate circuit 29 Synchronous circuit 30 Sawtooth wave generation circuit 31 Sample and hold circuit 32 Arithmetic circuit 33 Motor drive circuit 4 DC Motor 35 Tacho Generator 36 Preamplifier 37 Low-pass Filter 40 Illumination Area on Object Surface 40 'Area in which Object Projection Image Occurs 40 "Object Projection Image 140a', 140a" 140b ', 140b "Slit Image for Index Ia, Ib , Ic Object plane pattern image L1, L2 Scan line

Claims (1)

[Claims] 1. An apparatus comprising: an illuminating means for illuminating an object surface with illuminating light; and an observation system for forming an image of the illuminated object on an object projection surface by an objective lens and capturing the image by an image capturing means. The illumination means is provided with a light flux limiting member that limits the illumination area of the object by the illumination means to a size conjugate with the image pickup surface of the image pickup means, and the illumination light is passed through an objective lens to areas other than the illumination area of the object by the illumination means. Index irradiation means for forming an index light of a wavelength band substantially coincident with the object surface on the object surface, and a light receiving means for separating the index light reflected by the object surface from the illumination light by the illumination means and receiving the light.
An autofocus device comprising: a control unit that focuses the object plane on an image pickup surface of the image pickup unit based on an output of the light receiving unit.