JPS61143710A - Focus adjusting device - Google Patents

Abstract

PURPOSE:To speed up focusing even to the surface of a sample having a different in height by providing a means for offsetting the prescribed value of a reference in such a manner that an objective optical system is focused to the face different from the surface in the prescribed region of a sample by a servocontrol device. CONSTITUTION:The information quantity of contrast exist most in a part C and the focus is consequently matched with the part C if there is a rugged difference to the sample 4. The device which permits automatic focusing to the part A or part B and observation thereof by applying an offset to a zero crossing point level thereby deviating the focal position toward the optical axis direction by as much as the prescribed distance corresponding to the step between the parts A and B with respect to the part C, i.e., an offset generating means 16 is provided to a comparing differential circuit 16 in this stage. The quick focusing even to the surface of the sample having the difference in height is thus made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a focus adjustment device, and more particularly to an improvement in a focus adjustment device for a microscope.

(Background of the Invention) In an example of a conventional focus adjustment device for a microscope, one-dimensional image sensors are arranged at in-focus and out-of-focus positions before and after an imaging point. The high frequency component of the image output from the image sensor is at its maximum when an image is formed on the image sensor. Assuming that the high frequency component outputs from the in-focus and out-of-focus image sensors relative to the movement of the sample stage are symmetrical with respect to the imaging point, the zero crossing point is the imaging point by taking the difference between the high frequency components of both outputs. You can say that.

Therefore, if the sample stage is moved up and down by the servo device so as to obtain the zero crossing point, the image being observed can be accurately focused. However, the surface of the sample being observed is not necessarily a uniform surface, but has more or less irregularities. For this reason, the problem arises that the location where the zero crossing point can be obtained depends strongly on the concave or convex portions of the sample surface, and even if you try to observe the surface of the convex part inside the concave part, you can only observe the surface of the concave part. It wasn't in focus, which was extremely inconvenient.

(Objective of the Invention) An object of the present invention is to solve the above-mentioned drawbacks and to obtain a focusing device capable of quickly focusing even on a sample surface having height differences.

(Summary of the Invention) The present invention provides an objective optical system for observing a sample, and a predetermined value (zero crossing point 9) when the objective optical system is focused on the surface of a predetermined area of the sample. an electric circuit that generates an electric signal whose magnitude changes continuously according to changes in the distance between the surface and the objective optical system based on the value; In an apparatus having a servo device that adjusts the distance from the sample, the objective optical system is focused by the servo device on a surface slightly different from the surface of a predetermined area of the sample.
The technical point is to provide means for offsetting the predetermined value.

(Example) FIG. 1 shows Example 10 of the configuration of a focus adjustment device according to the present invention.
Indicates 0. Although Example ioo is applied to a metallurgical microscope using epi-illumination, it is possible to obtain a similar configuration even in the case of transmitted illumination. A stage up and down movement handle 2 moves the sample 4 on the stage 1 up and down to focus. An epi-illumination device 3 illuminates the sample 4. The illumination light reflected from the sample 4 is imaged by the objective lens 2. The illumination light that passes through the beam splitter 5 is focused on A, and the reflected light is focused on A'. A and A' shown in Figure 1
Assuming that the position is the focal position, an out-of-focus image sensor 6 is placed in the out-of-focus position at a distance t behind A', and an in-focus image sensor 7 is placed in the in-focus position at a distance t' in front of A'. ing. The image sensor 6 is an image sensor drive circuit 11
The optical image output is scanned by the sample and hold circuit 12.
and is passed through a band pass filter 13. The bandpass filter 13 extracts high frequency components of the optical image, and the effective value integrating circuit 14 integrates the effective values of the high frequency components during a predetermined period. The effective value integrated output is appropriately amplified by an amplifier 15 and then applied to one input trap of a differential amplifier circuit 16. On the other hand, image sensor 7
The above optical image output is also applied to the other input of the differential amplifier circuit 16 through the same electrical processing as described above. (In Fig. 1, the electrical signal processing system of the image sensor 7 is omitted because it is the same as the electrical signal processing system of the image sensor 6.) Fig. 2 shows the optical image on the image sensor and its electrical signal processing system. This shows how the target signal processing works. FIG. 2(A) shows the optical image on the 01-dimensional image sensor when the sample 4, which is made up of a single straight line, is moved up and down, and the central optical image is focused on the image sensor. The scanning of the image sensor is in the direction indicated by the arrow. Figure 2 (B) shows the optical-to-electrical conversion output of the optical image, Figure 2 (C) shows the high frequency component extracted from the output of the band pass filter 13, and Figure 2 (D) shows the output of the bandpass filter 13. Shows the effective value integral output. This is a curve that has a maximum value when an image is formed on an image sensor as shown in the figure.

Figure 2 (E) shows the effective value integral output 2 on the out-of-focus image sensor and the in-focus image sensor.
2 and 23 as a function of the vertical movement of sample 4. Since the out-of-focus and in-focus positions are located above and below the imaging point, the output becomes a curve having its maximum value on the left and right of the imaging position in FIG. 2(E).

Since the output curves 22 and 23 are differentially added by the differential amplifier circuit 16, the difference signal becomes as shown by the solid line 21 in FIG. 2(E). If the output curves 22 and 23 are symmetrical with respect to the image point, the zero crossing point 24 of the difference signal curve 21 corresponds to the image point position. Therefore, if the difference signal is fed back to the servo motor 17 and the stage upper and lower handles 2 are driven, focus control becomes possible.

However, this control method assumes that the optical image output at the out-of-focus and in-focus positions is symmetrical, but in reality, the out-of-focus before and after the imaging point is symmetrical, as shown in Figure 3 (A). Images B and C on the in-focus have different sizes. In FIG. 3(A), 4 is a sample and 32 is an objective lens. If the length of the sensor is the same, the amount of information captured will be greater at the in-focus position. Furthermore, due to the nature of the objective lens, the out-of-focus image has poorer contrast, resulting in an effective value output as shown in FIG. 3(B). That is, the effective value output curve 36 of the out-of-focus image sensor 6 has a lower output level than the effective value output curve 37 of the in-focus image sensor T, and therefore the difference signal curve 38 does not zero-cross at the imaging point. In FIG. 3(B), the positional deviation between 24 and 24' becomes a focus error.

Therefore, in this embodiment, in order to eliminate this error, an image enlarging concave lens 8 is inserted in front of the in-focus image sensor T in FIG. 1. The configuration of this part is shown in Figure 3 (C). Let C be the image at the in-focus position before being magnified, and C' be the image magnified by the concave lens 8. And image B at out-of-focus position
By making the size of the image C' and the image C' the same, the outputs from both image sensors are symmetrical with respect to the image forming point, and the zero crossing point thereof corresponds to the focal position, making it possible to control with high precision.

By the way, in focus detection based on image contrast as in this embodiment, the magnitude of the electrical output also depends on the reflectance or transmittance of the sample 40. Therefore, as shown in FIG. 1, an output averaging circuit 1B averages the output of the image sensor, and the AGC circuit 19 is controlled by the average output value to control the gain of the amplifier 15. In this case, it is possible to cope with changes in the light image intensity due to changes in the magnification of the objective lens.

Now, using the apparatus configured as described above, the sample 4 is
When there are uneven steps as shown in FIG. 6, the amount of contrast information is greatest in the 0th part, so the 0th part is in focus. In such a case, in the present invention, by giving an offset to the zero-crossing point level, the focal position is shifted in the optical axis direction by a predetermined distance corresponding to the step difference between parts A and B with respect to part 0. The comparison differential circuit 16 is provided with a device that can automatically focus and observe the image, that is, an offset generating means 16a. When this device is not included, the automatic focusing device must be switched to manual mode and operated manually, which is extremely inconvenient.

(Effects of the Invention) The improved focus adjustment device disclosed above has the effect that more accurate focusing can be quickly performed on various samples.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an embodiment of a focus adjustment device applying the present invention to a metallurgical microscope, Fig. 2 is a diagram showing the state of electrical output in response to the vertical movement of the stage, and Fig. 3 is an in-focus diagram. FIG. 4 is a diagram showing the difference in the size of the optical image between the position and the out-of-focus position and a means for correcting the difference, and FIG. 4 is a diagram showing a sample with a step. [Explanation of symbols of main parts] Objective optical system...32 First image sensor...6 Second image sensor...T-concave lens...
・ 8 Electric circuit...11.12.13.14.15.
16.1B, 19 Servo device...17.2 Offset generating means...16a Applicant Nippon Kogaku Kogyo Co., Ltd. Figure 2

Claims (1)

[Scope of Claims] An objective optical system for observing a sample, and a predetermined value when the objective optical system is focused on the surface of a predetermined region of the sample, and a distance between the surface and the surface based on the predetermined value. an electric circuit that generates an electrical signal whose magnitude continuously changes according to a change in the distance between the objective optical system and the sample; and an electric circuit that adjusts the distance between the objective optical system and the sample so that the electric signal reaches the predetermined value. and a servo device, further comprising an offset generating means for offsetting the predetermined value so that the objective optical system is focused by the servo device on a surface different from the surface of the predetermined region of the sample. A focusing device featuring: