JPS59107315A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To execute with high accuracy automatic focusing even in case of a sample whose contrast is low by providing a generating means of an interference fringe, and setting a position where a peak value of a variable density level of every one period of the interference fringe takes the maximum value, as a focused point position. CONSTITUTION:A light emitted from a light source 21 is split into two luminous fluxes by a beam splitter 22, and an interference fringe is generated by a light reflected by a sample 1 and a light reflected by a reference light mirror 24. A shutter 25 is provided between the beam splitter 22 and the reference light mirror 24, the shutter 25 is opened at the time of focusing, the light of the light source 21 is reflected by the reference light mirror 24, and it is closed when observing a sample 20, and the light of the light source 21 is shielded between the beam splitter 22 and the reference light mirror 24. Also, this device is provided with an objective lens 23, a slit 27 installed on a real image surface of the sample 20, a photoelectric multiplier tube 28 for converting a light passing through the slit 27 to an electric signal, a scanning mirror 26, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to automatic focusing of optical devices such as microscopes.

Conventional Structure and Problems There is a conventional automatic focusing device of this type that takes advantage of the fact that the high frequency component contained in the video signal is at its maximum at the in-focus position. Its specific configuration is shown in FIG. In a microscope in which a sample 1 is illuminated by a light source 3 and a 1TV camera 8 is provided on a real image plane formed by an objective range 2 and a focusing lens 4, a control circuit for inventing a control signal as a reference for the timing of a periodic signal of the 1Tv camera 8. 16, a differentiating circuit 9 that differentiates the video signal obtained by the 1Tv camera 8, a rectifying circuit 1o that rectifies this differentiated signal, an integrating circuit 11 that integrates this rectified signal, and an integrating circuit 11 before the sampling period. A holding circuit 12 that holds the output, and a comparison circuit 13 that compares the output value of the holding circuit 12 and the output value of the integrating circuit 11.
The output of the comparator circuit 13 causes the motor control circuit 1 to
4 drives a motor 6 via a motor drive circuit 15, and a feeding device 7 connected to the motor 6 follows the focusing lens 4 supported by a parallel spring 5 to the position where the output value of the integrating circuit 11 is the maximum value. Control.

Such an automatic focusing device has the disadvantage that when the contrast of the real image is low, the S/N ratio decreases and the focusing accuracy deteriorates because it is heavily influenced by noise.

OBJECTS OF THE INVENTION In view of the above-mentioned drawbacks, it is an object of the present invention to provide an apparatus that performs accurate autofocus without being affected by noise even when the contrast of a real image is low.

Structure of the Invention The present invention relates to an imaging device or a photoelectric conversion device provided on a real image plane of a sample or behind the real image plane, a means for generating interference fringes of the sample, and a periodicity of the density level of the interference fringes obtained by the device. and a control means that detects the peak value of each cycle and performs follow-up control to the position where the density level peak value is maximum.If the coherent light is not good, the coherent range is narrow, and within the coherent range, the By focusing on the fact that the peak values of the interference fringe shading levels are different, and by setting the position where the maximum value of the interference fringe shading levels for each period is the focal point position, the focusing accuracy is independent of the contrast of the real image. This has the effect of enabling highly accurate automatic focusing even for images with low contrast.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a front view showing an embodiment of the present invention. In FIG. 2, 2o is a sample, 21 is a light source that illuminates the sample, 22 is a beam splinter, and 24 is a reference light mirror. The light emitted from the light source 21 is transmitted to the beam splitter 2
2, the light reflected by the sample 1 and the light reflected by the reference beam mirror 24 generate interference fringes.

26 is a shutter, which is provided between the beam splinter 32 and the reference beam mirror 24. Shutter 26
is opened during focusing, the light from the light source 21 is reflected by the reference light mirror, and is closed when observing the sample 2o, and the light from the light source 21 is blocked between the beam splitter 22 and the reference light mirror 24. 23 is an objective lens, 27 is a slit placed on the real image plane of the sample 20 by the objective lens 23, and 28 is a photomultiplier tube that is provided behind the slit 27 and converts the light passing through the slit 27 into an electrical signal. be. 26 is a scanning mirror provided between the objective lens 23 and the slit 27 on the optical axis. 29 is a slide table, and sample 2
0 and move it up and down slightly.

31 is a motor, and a feed screw 30 is connected to the output shaft.

32 is the peak value P1.32 of the density level of one cycle of interference fringes shown in FIG. P2. This is a peak value detection circuit that detects P3. The peak value detection circuit 32 outputs the peak value of the gray level to the holding circuit 33 and the comparison circuit 34. The holding circuit 33 holds the peak value of the gray level inputted from the peak value detection circuit 32, and outputs the peak value - period before to the comparison circuit 34. The comparison circuit 34 is the peak value detection circuit 32
The gray level peak value input from the holding circuit 33 is compared with the gray level peak value input from the holding circuit 33 one cycle before. 35 is a motor control circuit that controls the rotational direction of the motor 31 so that the peak value of the gray level input from the detection circuit 33 to the comparison circuit 34 is larger than the peak value of the gray level input from the holding circuit 33; 36 is a motor drive circuit that drives the motor 31.

Next, the principle of the focusing point in the automatic focusing wave apparatus configured as shown in FIG. 2 will be explained with reference to FIG. 4.

When the light source 21 shown in FIG. 2 is an incoherent light such as a non-rogen light bulb, the coherent range is narrower than that of a coherent light such as a laser beam, and the density level of the interference fringes varies from the light source 21 to the reference light. The distance to the mirror 24 is maximum when the distance from the light source 21 to the sample 2o is equal. Therefore, as the sample 20 is moved in the direction of arrow A as shown in FIG.
The interference fringes are the clearest at position B, where the distances to zero are the same, and after passing through position B, the interference fringes gradually become unclear. The slit 2
When detected by a photomultiplier tube based on changes in the amount of light passing through 7, the detection signal has a waveform as shown in FIG. If the position of the reference light mirror is set in advance so that the peak value of the density level of the interference fringes is maximized when the sample is in focus, automatic detection can be performed by detecting the maximum value of the peak value of the density level of the interference fringes. The focus is powerful.

Note that the maximum value of the peak value of the density level can be obtained from either the bright part or the dark part of the interference fringe, so it is sufficient to detect either one.

Next, the operation of this embodiment will be explained.

The shutter 25 is opened, and the light from the light source 21 is split by the beam splitter 22 into two beams: the light that irradiates the sample 2o, and the light that hits the reference beam mirror and is reflected. The scanning mirror 26 is stationary, and the motor control circuit 35 drives the motor 31 via the motor drive circuit 36. At this time, the density level of the interference fringe caused by the light reflected from the sample 20 and the light reflected from the reference beam mirror 24 is photoelectrically converted by a photomultiplier tube, and the peak value of the density level of one period of the interference fringe is detected by the peak value detection circuit 32. To detect. Peak value inspection.

The output circuit 32 outputs the gray level peak value to the holding circuit 33 and the comparison circuit 34. The holding circuit 33 outputs the peak value of the gray level one cycle before to the comparison circuit 34, and the comparison circuit 34 compares both values. When the gray level peak value input from the peak value detection circuit 32 to the comparison circuit 34 is larger than the gray level peak value input from the holding circuit 33 one period before the interference fringe, the control circuit 35 controls the motor 1
Rotate in the same direction as 1. Conversely, when the peak value of the density level one period before the interference fringe input from the holding circuit 33 is smaller, the control circuit 35 reverses the motor 11. The gray level peak value of the holding circuit 33 is updated when the comparison circuit 34 completes the comparison.

At the position where the gray level level value outputted from the peak value detection circuit 32 takes the maximum value, the motor 31 repeats inversion, or
If the motor 31 is stopped at this position, the focus is on the sample 1. Also, in order to prevent malfunctions due to the influence of noise etc. when no interference fringes appear, the output value of the peak value detection circuit 32 is If the level is below a certain level, reversing of the motor 31 is prohibited.

Close the shutter 25 when the focus is on the sample 2o,
If the light going to the reference beam mirror 24 is blocked, the interference fringes disappear.) By scanning the sample 20 with the scanning mirror 26, the sample 2o can be observed.

As described above, the interference fringe generating means, the photoelectric converter, the interference fringe peak value detection circuit, the holding circuit that holds the peak value and outputs the peak value - period before, and the output of the peak value detection circuit Focusing accuracy can be improved by providing a comparison circuit that compares the peak value output from the holding circuit with the peak value of one cycle before, and a motor control circuit that performs follow-up control to the position where the peak value of the interference fringe density level is the maximum value. Highly accurate automatic focusing is possible regardless of the contrast of the real image of the sample.

Although the embodiment of the present invention uses an optical head that combines a photomultiplier and mechanical scanning, a television camera or a diode array may also be used.

Focusing is still performed by slightly moving the sample, but it is also possible to move the optical head or the lens system.

In the embodiment of the present invention, the scanning mirror is stopped when focusing, but focusing may be performed while rotating the scanning mirror.

In the embodiment of the present invention, the peak value of the interference fringe density level detected by the peak value detection circuit is compared with the peak value of one cycle before, but the peak value of the interference fringe density level input to the holding circuit is The maximum value of is held by the holding circuit,
The interference fringe shading level peak value detected by the peak value detection circuit is compared with the maximum value of the previously detected shading level peak value, and control is automatically performed to follow the maximum value of the interference fringe shading level peak value. Even if focusing is performed, it is included in the present invention.

Effects of the Invention By providing a means for generating interference fringes and focusing on the position where the peak value of the density level for each period of the interference fringes takes the maximum value [4], the focusing accuracy can be adjusted to the contrast of the real image of the sample. High-precision automatic focusing can be performed even on samples with low contrast, which is highly effective.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing the configuration of a conventional autofocus device;
The figure is an explanatory diagram showing the configuration of the first embodiment of the automatic focusing device according to the present invention, Fig. 3 is an explanatory diagram showing the shading level of interference fringes, and Figs. FIG. 20... Sample, 21... Light source, 22...
... Beam splitter, 23 ... Objective lens, 24 ... Reference light mirror, 28 ... Photomultiplier tube, 32 ... Peak value detection circuit, 33・
...Holding circuit, 34...Comparison circuit, 36
...Motor control circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 1 Figure 2 Figure 3 Figure 4 (cL) 8

Claims (2)

[Claims] (1) An imaging device or a photoelectric conversion device provided at the real image plane of the sample, or at the rear of the real image plane, means for generating interference fringes on the sample, and a means for generating interference fringes for each cycle of the density level of the interference fringes obtained by the device. An automatic focusing device comprising a control means for detecting a peak value and performing follow-up control to a position where the density level peak value is maximum. (2) The control means includes a peak value detection circuit that detects the peak value of the interference fringe density level for each cycle, and holds the peak value detected by the peak value detection circuit, and stores the peak value of -cycle before. a holding circuit that outputs an output; a comparison circuit that compares a gray level peak value output from the peak value detection circuit with a peak value output from the holding circuit one cycle before; and a comparison circuit that outputs the peak value from the peak value detection circuit. 2. The automatic focusing device according to claim 1, further comprising a servo mechanism that follows a position where the peak value is larger than the peak value output from the holding circuit one cycle before.