JPH0416810A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To enable invariably accurate focusing control without defocusing even if the surface of an object is finely uneven by driving an objective and the object relatively in the direction of the optical axis of the objective according to the representative position and size of a spot image which are detected by a detecting means. CONSTITUTION:A line sensor 20 is so arranged that when the object 18 to be observed is at the focusing position of the objective 16, the smallest spot image is formed on a nearly center element of the line sensor 20. The output of the line sensor 20 is supplied to an arithmetic and control unit 21, which finds the representative position X and size l of the spot image formed on the line sensor 20 and drives a sample base 17 in the optical axis direction of the objective 16 through a driving device 22 having a stepping motor, etc., according to those values X and l to perform the focusing control automatically. Consequently, even when the surface of the object 18 is finely uneven, the focusing control can accurately be performed at all times without causing any defocusing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The second invention relates to an automatic focusing device for an optical instrument such as a telescope.

[Conventional technology]

An automatic focusing device that uses a measurement light beam to automatically focus on an object being observed with an optical instrument is disclosed in West German Patent No. 3, for example.
219503 C2, West German Patent Publication No. 2102922
Disclosed in the issue.

In these conventional automatic focusing devices, the light beam from the measurement light source is transmitted through one side of the pupil of the objective lens and focused on the object, and the spot image is received by a photodetector after passing through the objective lens. The position is detected and automatic focusing is performed by driving the object or objective lens in the optical axis direction according to the deviation between the representative position and the representative position of the spot image incident on the photodetector during focusing. There is. That is, X is the representative position of the spot image that enters the photodetector during focusing. Assuming that the representative position of the actually incident spot image is X, as shown in FIG. 8, the object or objective lens is driven so that X=X0 for automatic focusing. [Problem to be Solved] However, in the conventional automatic focusing device described above, a photodetector receives an image of a spot formed on an object and detects its representative position. Therefore, as shown in FIG. 9, if there are minute irregularities on the surface of the object 1, even if the maximum gap depth of the irregularities is sufficiently small compared to the focal depth of the objective lens 2, Irregularities or objects!
? ! ! If the spot is smaller than the spot of the measuring light beam formed on the surface of 11, or if the spot is located at the boundary between the spot and the uneven part, the reflected light will be scattered by the uneven part and the light will be out of focus. The light intensity distribution of the spot image formed on the photodetector is shown as a curve in FIG. However, there is a problem in that the camera may be out of focus. In Fig. 10, the curved line indicates the light intensity distribution when the spot image formed on the photodetector is focused when there are no minute irregularities on the surface of the object 1, and in this case, the center of gravity position X and X
Matches o.

In this way, with conventional automatic focusing devices, if there are minute irregularities on the surface of the object, the focus will be off. When observing a continuous object without scanning it,
There is a problem that a focus shift occurs during scanning, making it impossible to make accurate observations, and that the observer's eyes become extremely tired.

This invention was made by focusing on such conventional problems, and even if there are minute irregularities on the surface of the object,
It is an object of the present invention to provide an automatic focusing device that is appropriately configured so as to be able to always accurately control focusing without causing focus deviation.

[Means and effects for solving the problem] In order to achieve the above object, the present invention projects a light beam from a measurement light source onto an object through one side of the pupil of an objective lens, and projects the spot image onto the object. An automatic focusing device that receives light through a lens and a photodetector, and controls focusing by relatively driving the objective lens and the object in the optical axis direction of the objective lens based on the output thereof, the photodetector means for detecting the representative position and size of the spot image formed on the photodetector based on the output of the photodetector; The lens and the object are configured to be relatively driven in the optical axis direction of the objective lens to control focusing.

〔Example〕

FIG. 1 shows a first embodiment of the invention. This embodiment is applied to an epi-illumination type microscope, in which a light beam from a measurement light source 11 such as a semiconductor laser is made into a parallel light beam by a collimator lens 12, and then passed through a polarizing beam splitter 13.1, 74 and a wavelength plate 14. The measurement light beam is reflected by the dichroic mirror 15 and is incident on one side of the pupil of the objective lens 16 to be focused on the observation object 18 placed on the sample stage 17 .

The reflected light of the measurement light beam focused on the observation object 18 passes through the objective lens 16 and is reflected by the dichroic mirror 15, and the return light from the observation object 18 is passed through the quarter-wave plate 14.
The light is made incident on the polarized beam splitter 13 through the polarized beam splitter 13. Here, the observation target 18 that enters the polarization heam splitter 13
The return light from the
Since the light passes twice, the plane of polarization of the returning light differs by 90 degrees from the plane of polarization of the outgoing light, and it is reflected by the polarization heam splinter 13. Observation object 1 reflected by the second polarized beam beam 1 Lusota 13
The return light from 8 is received by a line sensor 20 via an imaging lens 19.

The line sensor 20 includes an objective lens 16 and an observation target 18.
The observation target object 1
The line sensor 20 is arranged so that the smallest spot image is formed at an element approximately in the center of the line sensor 20 when the lens 8 is in the in-focus position with respect to the objective lens 16.

The output of the line sensor 20 is supplied to the arithmetic and control unit 21, which determines the representative position X and size l of the spot image formed on the line sensor 20, and
A drive device 22 having a stepping motor etc. based on
The sample stage 17 is driven in the optical axis direction of the objective lens 16 via the lens 16 to automatically control the focus.

The image of the observation object 18 is formed at an imaging position 24 by an observation imaging lens 23 via an objective lens 16 and a dichroic mirror 15, so that it can be observed visually or with a TV camera or the like.

The operation of this embodiment will be explained below with reference to the flowchart shown in FIG.

First, the arithmetic and control unit 21 determines the representative position X and size l of the spot image projected onto the line sensor 20 based on the output of the line sensor 20 (block 31).

Here, in the front focus state where the focal point of the objective lens 16 is located in front of the observation object 18 (on the objective lens 16 side), the return light from the observation object 18 becomes convergent light, so as shown in 3A. The spot image 25 formed on the line sensor 20 moves from the representative position Moving. In addition, in the rear bin state where the focal point of the objective lens 16 is located behind the observation object 18, the return light from the observation object 18 becomes diverging light, so the spot image 25 formed on the line sensor 20 is The spot moves from the representative position X0 at the time of focus to the other side, increasing in size as the focus shift increases. I wanted to, line sensor 2
The light amount distribution of the spot image formed on 0 is as shown in FIG. 3B depending on the focal state.

As the representative position X of the spot image 25 formed on the line sensor 20, its center of gravity position or median position is determined. Here, if the number of elements of the line sensor 20 is n, and the photoelectric output of each element is y, then the center of gravity position X can be found as follows, and the median position X is
and x+1 by interpolation.

In addition, a spot image 25 formed on the line sensor 20
The magnitude l is determined by counting the number of elements whose output exceeds the threshold level, as shown in FIG.

After determining the representative position X and size l of the spot image projected on the line sensor 20, next, the representative position X and the preset representative position X at the time of focusing are determined. Find the absolute value of which difference,
IX-X. It is determined whether l≦△X (block 32).

Here, IX-X. When l≦ΔX, it is determined that the object to be observed 18 or the objective lens 16 is in the focused position, and the current position is maintained without supplying a drive signal to the drive device 22, and the process moves to block 31. return. On the other hand, I
X-X. When I>ΔX, it is determined that the in-focus position is not reached, and X-X. The front focus and rear focus are determined from the polarity of the calculation result, and a drive signal is supplied to the drive device 22 accordingly to drive the sample stage 17 one step in the direction to correct the focus shift (
Block 33) and the representative position X1 and size of the spot image 25 after the drive! Find + (block 34)
.

After that, the size l of the spot image 25 before l step driving is
and the size 1' after driving (block 35).
, f'≦l, it is determined that the lens is truly driven in the focusing direction, and the process returns to block 32 as x=x', p=x'<block 36), and the above operations are repeated. On the other hand,! ! '>i, it is determined that the drive is not in the focusing direction, that is, it is affected by the scattered light, and the sample stage 17 is moved to the previous step position via the drive device 22, that is, one step before the drive. (block 37).

Note that the driving amount of one step by step driving is set in advance so that it is smaller than the range of the depth of focus.

After that, the representative position X' and size of the spot image 25 again! ! w1 is determined (block 38), and IX"-XI≦△X is determined based on the representative position X"" and the previously determined representative position X at the step drive position (block 39).
) When IX"-XI≦ΔX, it is determined that the observation target 18 is in the focused position with respect to the objective lens 16, and the current position is maintained without supplying a drive signal to the drive device 22. Then, return to block 38 and find that IX'“−XI>ΔX
When , it is determined that it is not at the in-focus position, and x=x'“,
l! =12" (block 40) as block 32
Return to , and repeat the above operation.

Therefore, according to this embodiment, for example, as shown in FIG. 4, a flat area a, a lower flat area b,
When scanning a specimen 45 having a region C having fine irregularities on almost the same plane as the region C by moving in the direction shown by the arrow, the following operation is performed.

First, in area a, when the representative position The loop of blocks 32→33→34→35→36→32 is repeated several times to control the focus, and then the loop of blocks 32→31 maintains the focused state. That is, if the specimen surface is flat, it is impossible for p'>p in block 35, so focusing is controlled by the loop of blocks 32→33→34→35→36→32.

After that, when scanning begins in area A, it is initially in a front-focus state due to the difference in level from area a, so as shown in FIG. 5B, it becomes X''Xo (l The size of the spot image also increases, or after that, by the same operation as in area a, focusing is controlled so that X=Xo and the size of the spot image becomes the minimum.

Next, when entering region C, even though it is in the focused state, due to scattered light due to minute irregularities on the specimen surface, Xf-Xo (IX-X) as shown in FIG. 5C.

>ΔX), the size f of the spot image also increases. In this case, first, in the block 33, the sample stage 17
However, since this one-step drive is in the direction of defocusing from the in-focus position, the size l' of the spot image is always larger than before the drive. Therefore, after that, in block 37, the step position before driving, that is, the focus position is returned, and the absolute value IX'"-X(
] When X'-XI≦ΔX, it is determined that the image is in focus, and the driving device 22 is maintained in a stopped state through a loop of blocks 38→39, and the in-focus state is maintained. In addition, IX'“XI
>ΔX, the process returns to block 32 via block 40, and a focusing operation is performed based on the determination that IX-X, l≦ΔX.

In this way, according to this embodiment, the sizes of the spot images 25 before and after step driving are compared (6'≦l) to determine whether the driving direction is correct or not, and if the driving direction is incorrect, Return to the previous step position, find the representative position X' of the spot image 25 at that position again, and calculate the absolute value IX of the difference between the representative positions before and after step driving at the same step position.
”-XI or By focusing on a plane and then scanning, it is possible to always accurately control focus without being affected by minute irregularities. Further, since one line sensor 20 is used and the representative position X and size l of the spot image 25 are determined based on its output, the optical system can be constructed easily and at low cost.

FIG. 6 shows a second embodiment of the invention. In this embodiment, in the configuration shown in FIG.
The return light from the observation object 18 through the half mirror 51
The light is divided into two by the line sensor 20 and the other is received by the semiconductor device detector (PSD) 52. Based on the output of the line sensor 2o, the size of the spot image is adjusted to the output of the PSD 52. The representative position of the spot image is detected based on this, and the other configurations are the same as in the first embodiment. In this way, if the size and representative position of the spot image are detected based on the output of an independent detector, the calculation speed can be increased, so that quick focusing control is possible.

FIG. 7 shows a third embodiment of the invention. In this embodiment, in the configuration shown in FIG. 6, the return light from the observation object 18 reflected by the polarizing beam splitter 13 is divided into two by a half mirror 51, and one of the two is divided by the imaging lens 51.
5, the line sensor 20 receives the light, and the other light passes through the imaging lens 56 and is received by the PSD 52.The other configuration is the same as that of the second embodiment. With this configuration, in addition to being able to obtain the same effects as in the second embodiment, by decreasing the focal length of the imaging lens 55, the rate of change in the size of the spot image can be increased.
By increasing the focal length of the imaging lens 56, the projection magnification can be increased and the positional displacement sensitivity of the spot image can be increased.

Note that the present invention is not limited only to the embodiments described above, and numerous modifications and changes are possible. For example, in the embodiments described above, focusing is controlled by driving the sample stage 17, or by driving the objective lens 16, or by driving both the objective lens 16 and the sample stage 17. It can also be configured like this. In addition, in the above embodiment, the distance between the objective lens and the object was changed by step driving, so the driving amount for one step was preset to be smaller than the depth of focus range, but the detected Depending on the difference between the position X and the representative position Xo at the time of focus, the block 33 in FIG. 2 may be driven not in steps but in -degrees. In this way, faster focusing control becomes possible. Furthermore, the present invention is not limited to epi-illumination type microscopes, but can be effectively applied to automatic focusing of other microscopes or optical instruments other than microscopes.

〔Effect of the invention〕

As described above, according to the present invention, a photodetector receives an image of a spot projected onto an object through one side of the pupil of an objective lens, and determines the representative position and size of the spot image based on the output. The objective lens and the object are driven relatively in the optical axis direction of the objective lens based on the representative position and size of the detected spot image to control focusing. Even if there are minute irregularities on the surface, the focus can always be controlled accurately without causing defocusing.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention, FIG. 2 is a flowchart showing its operation, and FIGS. 3 A and B are representative positions and sizes of spot images on the line sensor shown in FIG. 1. Figure 4 is a diagram showing how the specimen is scanned; Figures 5A, B, and C are diagrams for explaining the focusing operation for the specimen shown in Figure 4; Figure 6 is a diagram showing how the specimen is scanned; FIG. 7 is a diagram showing a second embodiment of the invention, FIG. 7 is a diagram showing a third embodiment, and FIGS. 8, 9, and 10 are diagrams for explaining the conventional technology. 11 - Measurement light source 12 - Collimator lens 13 Polarizing beam splitter 14 - 1/4 wavelength plate 15 - Dichroic mirror 16 - Objective lens 17 - Sample stage 18 = - Observation object 19 - Imaging lens 20 Line sensor 21 - Arithmetic control Device 22 - Drive device
23 Observation imaging lens 24-imaging position 2
5- Spot image 45- Specimen 51 Half mirror 52- Semiconductor device detector (PSD) 55. 56 --- Imaging lens 1 Figure 3 Figure 4 Figure 2 Figure 5

Claims (1)

[Claims] 1. A light beam from a measurement light source is projected onto an object through one side of the pupil of an objective lens, and the spot image is received by a photodetector through the objective lens, and based on the output. An automatic focusing device that controls focusing by relatively driving the objective lens and the object in the optical axis direction of the objective lens, the automatic focusing device comprising: means for detecting the representative position and size of the spot image detected by the detection means, and based on the representative position and size of the spot image detected by the detection means, the objective lens and the object are relative to each other in the optical axis direction of the objective lens. An automatic focusing device characterized in that the automatic focusing device is configured to perform focusing control by driving the automatic focusing device. 2. The automatic focusing device according to claim 1, wherein a line sensor is used as the photodetector, and the representative position and size of the spot image are detected based on the output thereof. 3. A line sensor and a semiconductor device detector are used as the photodetector, and each of the line sensor and the semiconductor device detector receives the spot image,
2. The apparatus according to claim 1, wherein the size of the spot image is detected based on the output of the line sensor, and the representative position of the spot image is detected based on the output of the semiconductor device detector. Autofocus device.