JPS62119511A - Focus detector - Google Patents

Abstract

PURPOSE:To detect a focus with a high accuracy by providing a reduction optical system having a positive refracting power between an objective lens or a barrel lens and a projection lens, preferably, on the image surface side of the middle between them. CONSTITUTION:The light emitted from light emitting elements 16 and 17 alternately passes minute lenses 14 and 15 and is turned by a prism 13 and passes a beam splitter 29 and is projected on the image surface by a projection lens 12 and is projected on a sample through a reduction lens 11, a barrel lens 10, and an objective lens 9. The light reflected from the sample passes the objective lens 9, the barrel lens 10, the reduction lens 11, and the projection lens 12 and is reflected on the beam splitter 20 to form a spot on a light receiving element 19 by a detecting lens 18. A polarizing beam splitter may be used as the beam splitter 20, and a quarter-wave plate is arranged in a proper position between the beam splitter and the object if the polarizing beam splitter is used. Thus, the focus is detected accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a focus detection device suitable for optical instruments and medical instruments such as cameras, microscopes, rigid endoscopes, and fundus cameras.

[Conventional technology]

Conventionally, this type of focus detection device has adopted a light projection detection method in order to obtain a focus detection device with good responsiveness and high precision. Infrared light has been used. The chromatic aberration between facing visible light and infrared light is very different, and some kind of correction mechanism is required, which has been a big problem, especially in microscopes that are used by replacing objective lenses with different chromatic aberration corrections.

For example, in Japanese Patent Application Laid-Open No. 58-217909, it was necessary to provide a lens system that can move a certain distance in the optical axis direction to adjust the focal position of the infrared light.

FIG. 12(a) shows how an image is formed by the objective lens X, in which the solid line represents visible light and the dotted line represents infrared light. FIG. 12 fbl shows how an image is formed by an objective lens Y different from that described above. The visible light image can be created at the same position M, but the infrared light image can be created at a different position (
NX, N,). This is because the magnification and amount of chromatic aberration correction differ depending on the objective lens. As a result, the infrared light from the laser diode (LD) enters the detector with a deviation, and is determined to be in an out-of-focus state. Therefore, it was necessary to move and adjust the correction lens C as shown in FIG. 12 (C1).

[Problem that the invention seeks to solve]

As mentioned above, in the conventional example, the focal position shift of infrared light has been adjusted by moving the correction lens, but since the focal position shift differs for each objective lens, it is necessary to adjust the focus position of infrared light every time the objective lens is replaced. I had to move the correction lens. In view of the above problems, it is an object of the present invention to provide a focus detection device that does not require lens adjustment.

[Means and effects for solving the problem] This device has a positive refractive power between the objective lens or barrel lens and the image plane formed by the lens, preferably from the center to the image plane side. By providing a reduction optical system and reducing the positional shift of images caused by infrared light that are produced at different positions by different objective lenses, it is possible to eliminate the need for lens adjustment in the focus detection method using infrared light. By simply adjusting the electrical system of the signal processing circuit constituting the focus detection device, the focus can be detected with high accuracy in response to the use of various different objective lenses.

〔Example〕

Before entering into a detailed description of the present invention, the basic principles of the focal position detection method and reduction optical system applied to the present invention will be explained.

First, the basic principle of the focal position detection device applied to the present invention will be explained with reference to FIGS. 1 and 2 (objective lens).
It passes through a position P that is conjugate to the image plane of ■, and beam splitter 4.
After passing through the imaging lens (objective lens) 1, the light flux A is formed as a point image Q on the object 2 at the focal position. If the object 2 is a scatterer, the point image Q becomes a light beam that fills the full aperture of the imaging lens 1 and forms a point image Q on the light receiving element 3 placed on the image plane.
imaged as. Further, when the object 2 is a mirror surface, the light beam becomes a beam B and is imaged on the light receiving element 3 as a point image Q'. On the other hand, the point image by the light emitting element 8 is similarly formed on the light receiving element 3 as a point image Q' after passing through the microlens 6 (luminous flux B
reference). Therefore, it can be seen that in the focused state, both the point image by the light emitting element 7 and the point image by the light emitting element 8 are exactly the same point image on the light receiving element 3.

On the other hand, FIG. 2 shows an out-of-focus state, in which the point image produced by the light emitting element 7 passes through the microlens 5, passes through a position P that is conjugate with the image plane of the imaging lens 1, passes through the beam splitter 4, and then passes through the imaging lens. (Objective lens) 1 becomes a light beam and is formed as an out-of-focus point image QA on an object 2 that is not at the in-focus position. Note that the in-focus position is indicated by 2°. When the object 2 is a scatterer, the point image QA becomes a luminous flux equal to the aperture of the imaging lens 1 and is an out-of-focus point image Q,' on the light receiving element 3.
is formed as. If the object 2 is a mirror surface, the light beam C becomes a light beam C and is formed on the light receiving element 3 as an out-of-focus point image QA'. On the other hand, after the point image by the light emitting element 8 passes through the microlens 6, it similarly appears on the object 2 as an out-of-focus point image QB.
After that, an out-of-focus point image QR' is formed on the light-receiving element 3. 7
The point images QA' and Q[l' of the light-emitting element 8 are formed at different positions, or at the same position when in focus.

Here, when the light emitting element 7 and the light emitting element 8 are blinked alternately, the position of the point image on the light receiving element 3 does not change at the in-focus point, but when the point image is out of focus, the point image on the light receiving element 3 alternates between QA' ,
QB' and a change in position occurs. Therefore, when focusing, it is sufficient to move the imaging lens 1 (object 2 in the case of a microscope) so that the point image on the light receiving element 3 does not move.

Furthermore, it is possible to determine front focus and rear focus and to measure defocus (2) from the moving direction and amount of movement of the point image. Especially when the amount of defocus is small, the light emitting element 7 and the light emitting element 8
The angle formed by the luminous flux is θ.

If the moving amount of the point image is δ, the defocus amount d on the image side is calculated by the following formula d = −□ +11
It can be determined from 2 tan-. Note that although the discussion has been made above as a point image, it does not necessarily have to be a point image.

Next, the basic principle of the reduction optical system applied to the present invention will be explained. FIG. 3 +al shows how an image is formed by the barrel lens O having a focal length fT, and the solid line is visible light, and a visible light image is formed at a position M at f7 from the barrel lens O. The dotted line is infrared light for objective lens X, which is 0.2 f from visible light image M.
The image is formed with a shift of □ (N), and the dashed line is the objective lens Y.
In the case of infrared light, the image is formed with a further shift of 0.4 f (N,).

At this time, if the magnification of the visible light image is β, then the objective lens
The infrared light image obtained by the objective lens Y is 1.2β times larger, and the infrared light image obtained by the objective lens Y is 1.6β times larger.

Fig. 3 tb+ shows a case where a convex lens C with a focal length of 2f is provided at a position 0.2f ahead of the visible light image M, and in this case, the infrared light image NX by the objective lens X is 0.1f from M.
At a position behind 3fT, an infrared light image N by the objective lens Y,
0.13 f is focused at the rear position, and the image magnification becomes β and 1.22 β, respectively. By arranging a convex lens between the barrel lens O and the visible light image M in this way, the positional shift of the infrared light image due to the objective lenses X and Y can be reduced from 0.4f when the convex lens C is not arranged. It can be reduced to 0.13 fT, and the change in image magnification is also small.

Figure 3 (C1 shows the case where a convex lens C' with a focal length of 0.2 fT is placed 0.2 fT ahead of the visible light image M, and the infrared light image NX by the objective lens X is 0.07
In front of f, an infrared light image N by objective lens Y is focused at a position 0.05 fT ahead of M. The image magnification is 0.5β for the visible light image and 0 for the infrared light image by objective lenses X and Y.
．． 33β and o, 25β. After all, if a reduction optical system consisting of a convex lens system is disposed between the barrel lens O and the visible light image M, the position of the infrared light image due to the difference in objective lenses; η deviation can be reduced to 0.
02 f, and the change in image magnification is also small, which is very convenient.

Here, as shown in Figure 4 (al), when a reduction lens C with a focal length f projects a virtual image at a distance a from the lens surface to a position b, the formula holds true.The relationship between a and b in this case Figure 4 (bl
3(b) and 3(C) mentioned above in this graph.
The range indicated by the dotted line satisfies the conditions explained using the IO diagrams. In other words, even if a changes significantly, b changes little.

This tendency is particularly noticeable when b is close to the focal length of the reduction lens. In practice, when the rear focal point of the reduction lens is made to approximately coincide with the imaging plane, the rear principal point will be closer to the rear than the center of the barrel lens and the imaging plane, that is, about 2 points from the center of the barrel lens. It is desirable to use a lens system with the following focal length in such a way that the rear focal point is not too far away from the image plane.

By providing a reduction optical system between the objective lens or barrel lens and its image forming surface, as in the case of a double series, the positional deviation of the infrared light image can be reduced. By simply adjusting the electrical system, it is possible to provide a focus detection device that can be used with a variety of different objective lenses.

FIG. 5 shows a first embodiment in which the present invention is applied to a microscope optical system using a focusing device based on the above principle.
In the figure, 9 is an objective lens, 1o is a barrel lens, 11 is a reduction lens, 12 is a lens that projects an infrared light spot, 13 is a prism, 14.15 is a microlens, and 16.17 is a light emitting device such as a laser diode. 18 is a detection lens, 19 is a light receiving element, and 20 is a beam splitter.

The light emitted alternately from the light emitting elements 16 and 17 passes through microlenses 14 and 15, is redirected by a 1m reprism 13, passes through a beam splitter 20, is projected onto an image plane by a projection lens 12, and is further passed through a reduction lens 11. ．． Barrel lens 1
0. It passes through the objective lens 9 and is projected onto the sample. The light reflected from the sample passes through the objective lens 9 again. Barrel lens 10. The light passes through the reduction lens 11 and the projection lens 12, is reflected by the beam splinter 20, and is generated by the detection lens 18 to form a spot on the light receiving element 19. A polarizing beam splitter may be used as the beam splitter 20, but in that case, an A wavelength plate is disposed at an appropriate position between the beam splitter and the object.

FIG. 6 shows the signal processing circuit of the first embodiment. First, the detailed structure of the light receiving element 19 will be explained with reference to FIG. 7. Reference numeral 30 denotes a high resistance S.

A substrate, 31 a p-type resistance layer, 32 an n+ layer, 33 a common electrode, 34 and 35 electrodes, and the surface layer exhibits a photoelectric effect due to a pn junction. Therefore, when light enters the p-type resistance layer 3I as shown in the figure, the output currents from the electrodes 34 and 35 are 1 and 6, respectively, depending on the position of incidence.
is obtained. Here, the distance between the electrodes 34 and 35 is set to 1.
The resistance is Re, the distance from the electrode 34 to the light incident position is X, its partial resistance is RX, and the photocurrent generated by the incident light is I. Then, Rff Re becomes, and if the resistance layer is uniform, the following equation can be obtained j2
− x β l Therefore,
Output current IA of electrode 3135, 1. By performing the calculation from lA-I-IIl#, the human position of the light, that is, the distance 1ii1fx, is determined regardless of the human energy, that is, the amount of incident light. Incidentally, the amount of incident light is obtained from the following equation 1% (51).

Again in FIG. 6, 21.21' is a current amplifier for amplifying the output currents IA and In from the two electrodes 34 and 35 of the light receiving element 19, and the outputs are VA and V.

22 is a subtracter that calculates (VA VR), 23 is (V
An adder 24 calculates (VA -V, ).
* ) / (v → -VB > (corresponds to formula (4))
This is a divider that performs the calculation.

Reference numeral 25 denotes a control circuit for controlling a drive circuit 26 that removes the DC bias component from the output signal of the divider 24 and then moves the stage according to the output signal.The circuit configuration is, for example, as shown in FIG. It has become. That is, 3G is a rectifier circuit, 37 is a differentiation circuit, 38 is a comparator, 3
Reference numeral 9 denotes a zero level detection circuit, in which the AC output signal from the divider 24 is converted into a DC signal by a rectifier circuit 36, and a positive/negative determination is made by a comparator 38 via a differentiation circuit 37, so that the signal decreases while If the signal is increasing, the stage driving direction is reversed, and the zero level detection circuit 39 detects that the signal has become "zero", and the focus is established. This is detected and the drive of the stage is stopped.

Note that 27 is a drive circuit that causes the light emitting elements 16 and 17 to blink alternately.

Since the focus detection device according to the present invention is configured as described above, first, the light source 16 is
．． 17, the divider 24 outputs a signal with a constant amplitude as shown in FIG. 9(a), for example, in the out-of-focus state. Here, the amplitude of this signal is a measure of deviation from the in-focus point, and a modulus amplitude of -0 means that the object is in focus. Therefore, when the stage is moved little by little along the optical axis, the output signal of the divider 24 becomes
The signal changes to the one shown in Figure fbl or Figure 9 (C1).

If this signal is rectified and smoothed by the rectifier circuit 36, it will change to a signal as shown in Figure 9+d) or Figure 9 (el).Therefore, if this signal is differentiated by the differentiator circuit 37, the signal will change. The slope of the envelope of If negative, drive times 1
1826 is allowed to operate as it is, and if it is positive, an inverted signal is applied to the lens drive circuit 26, thereby moving the stage toward the focal point. Then, if the movement of the stage is stopped when the amplitude becomes -0, the in-focus state is achieved.

In this way, focus detection is performed by the JW of the present invention.
Since the apparatus of the present invention does not require a pupil dividing means, the optical system is simple, and since only one light-receiving element is required, the signal processing system is simple and adjustment is easy. Since the optical system and the signal processing system are both simple, the overall configuration is simple, and as a result, it can be easily incorporated into optical equipment and medical equipment. Furthermore, since a semiconductor device detector is used as the light receiving element, signals can be input in real time, resulting in improved focusing speed. Further, if the magnification of the system including the objective lens is β, the moving amount d' of the stage can be determined from equation (1) as follows: δ d ' - (61 θ 2 β2 tan -).

FIG. 10 shows a flowchart when a simple microprocessor is used as the control circuit 25. First, the light emitting element 16 is turned on and the point image position QA' at that time is input, and then the light emitting element 17 is turned on. Then, input the point image position QB' at that time. Next, the difference (image shift) δ−QA
Find 'QB'. The sign of δ indicates the direction of defocus (front focus, rear focus), and the absolute value of δ corresponds to the amount of defocus. Next, equation (1) is calculated, the image shift δ is converted to defocus ld, and focusing can be obtained by driving the stage.

At this time, if the defocus ID is large, the light flux from the light emitting elements 16, 17 that is reflected back from the object is eclipsed by the lens frame, etc., and the amount of light decreases.

Therefore, when the defocus amount d is large, the light receiving element 1
9 detects the light @(Vn +VB), and drives the stage so that this value increases, and the light receiving element 1
9 can detect the positions of point images Qll' and Qll', the focusing speed can be increased. Note that the light emitting elements T-16 and I7 are 1'f 1ffl lamps.

Any LED, laser, semiconductor laser, etc. may be used, but for practical purposes, red 1.1. ED, red (a semiconductor laser is suitable. Also, one light receiving element need not be a semiconductor device detector, but an image sensor such as a so-called CCD type or MOS type) may be used.

Next, as a second embodiment, a case where the principle described in 1-1 is applied to a single-lens reflex camera will be described.

FIG. 11 shows the optical system, 40 is an imaging lens, 41 is a beam splitter provided in a quick return mirror, 42 is a mirror, 43 is a reduction lens, 44 is a beam splinter, 45 is a light receiving element, 46 .47 is a microlens, and 48.49 is a light emitting element. As described above, an optical system similar to that shown in FIG. 5 is installed in a single-lens reflex camera.

In this case, the signal processing system shown in the first embodiment can be used as is by replacing the part that drives the stage with a structure that drives the lens, so a detailed explanation of its structure and operation will be omitted.

〔Effect of the invention〕

” - As mentioned above, according to the present invention, when used in a microscope, for example, an objective lens with a magnification ranging from very low to high magnification (for example, 1χ
It is possible to provide a focus detection device that responds very quickly to objects (from 150X to 150
There is an advantage that focus detection can always be performed with a positive value only by electrical adjustment of the circuit.

[Brief explanation of drawings]

Figures 1 and 2 are diagrams showing the basic principle of the focus detection device;
3 and 4 are explanatory diagrams of the state of image formation when a reduction lens system is provided and their relationship graphs, and FIG. 5 is a diagram showing a first embodiment equipped with a reduction optical system according to the present invention. , FIG. 6 is a diagram showing the signal processing circuit of the embodiment described in -, FIG. 7 is a diagram showing the structure of the light receiving element in the optical system, and FIG.
- A diagram showing the configuration of the control circuit in the distribution υ processing circuit, Figure 9 is a diagram showing the signal processing process by the above control circuit, and Figure 10 is the case where microphone 11 is used as the control circuit. FIG. 11 is a diagram showing the optical system of the second embodiment, and FIG. 12 is an explanatory diagram of the state of image formation in the conventional example. 9... Objective lens, 10... Lens barrel lens, 11
゜43...reducing lens, 12...projection lens,
13...prism, Im 15,46.47...
...Minute lens, 16.1.7.48.49...Light emitting element, 18...Detection lens, 19.45...
・Photodetector, 20.41.44...Beam splinter, 21゜21'...Current amplifier, 22...Subtractor, 23...Adder, 24...Divider , 25
...control circuit, 26..., lens drive circuit, 27
...Drive circuit, 40, 0. Imaging lens, 42
····mirror. Figure 1 & 0 Figure 17 Figure 4' i Figure 1

Claims (2)

[Claims] (1) In a focus position detection device that detects the focal position by causing an image position shift using light beams passing through different paths in an optical system, the image formation by the objective lens or barrel lens and the lens By providing a reduction optical system with positive refractive power between the surface and the surface, and reducing the positional deviation of the infrared light images that are focused at different positions by different objective lenses, it is possible to focus using infrared light. A focus detection device characterized by performing detection. (2) The focus detection device according to claim (1), wherein the rear principal point position of the reduction optical system is closer to the imaging plane than the intermediate position between the objective lens or barrel lens and the imaging plane formed by the lens. .