JP3065699B2 - Focus position detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus position detecting device such as a microscope.

[0002]

2. Description of the Related Art In a conventional focus position detecting apparatus for a microscope, a one-dimensional image sensor is disposed at in-focus and out-focus positions before and after an image forming point. The high-frequency component of the image output from the image sensor becomes maximum when an image is formed on the image sensor. From this, assuming that the high-frequency component outputs from the in-focus and out-focus image sensors with respect to the movement of the sample stage are symmetrical with respect to the image forming point, the difference between the high-frequency components of the two outputs is calculated by taking the difference between the high-frequency components. The crossing point is the imaging point.

As described above, it is assumed that the output of the in-focus and out-of-focus image sensors is completely symmetrical with respect to the image forming point when the zero crossing point is the image forming point. However, in the conventional arrangement and configuration, there is a difference between the sizes of the images on both sensors (the image on the in-focus image sensor is smaller than the image on the out-focus image sensor). A difference occurs in the amount of information that can be captured, and the out-of-focus image has a lower spatial frequency distribution, so its high-frequency component output is small. -The crossing point does not correspond exactly to the imaging point.

For this reason, Japanese Patent Publication No. 61-13722 discloses a
In the first and second image sensors, the size of the light image received by the first image sensor and the size of the light image received by the second image sensor are adjusted for focusing. The above problem is solved by newly providing a magnification correcting optical system in order to make it almost equal to.

[0005]

However, in such a conventional technique, an optical component is newly added in order to make the in-focus image and the out-focus image uniform in size. There is also a problem.

The focus position detection apparatus of the present invention has been made in view of such a problem, and an object thereof is to provide a focus position detection apparatus capable of performing accurate detection without adding a new optical component. A position detecting device is provided.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an imaging optical system and two object images in the vicinity of a predetermined imaging plane of the imaging optical system. Two image sensors and the two image sensors
An optical system for projecting the two object images, and a focus position detecting device that detects the degree of focus of the imaging optical system based on the outputs of the two image sensors. The pixel size and pixel pitch of the light receiving portion of the sensor are configured to have a fixed ratio between the two image sensors.

[0008]

That is, in the present invention, since the pixel size and the pixel pitch of the light receiving portion of each image sensor for photographing two object images are configured to have a fixed ratio between the two image sensors, a new optical sensor is used. The focus position detection error can be eliminated without providing any components.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the basic concept of the present invention is shown in FIG.
This will be described with reference to FIG.

In FIG. 1A, reference numeral 1 denotes an image forming optical system, and reference numerals 3 and 3 'denote two image sensors for picking up two object images near a predetermined image forming plane. Reference numeral 4 denotes an optical system for projecting the two objects onto the two image sensors. Reference numerals 2 and 2 ′ denote planned image planes of the image forming optical system 1.

FIG. 1B shows an image pickup surface of the two image sensors 3 and 3 'by taking a line sensor of 10 pixels as an example. The image pickup surface of the image sensor 3 has a pixel size. The pixel pitch is p in a and b in the vertical and horizontal order.
The image pickup surface of the image sensor 3 'has pixel dimensions of ka and kb in the vertical and horizontal order, and a pixel pitch of kp.
As described above, the present invention is characterized in that the ratio of the pixel size and the pixel pitch between the two image sensors is set to a constant value k.

That is, in the present invention, when an object image is incident, the image sensor 3, the image sensor 3,
An in-focus image and an out-focus image are formed on 3 ', and the out-focus image is k times the in-focus image. k is determined by the imaging optical system 1, but is 1.1 or more in a normal microscope. Further, since the image pickup surfaces of the two image sensors 3 and 3 'are formed as shown in FIG. 1B, an in-focus image is picked up with the pixel size and pixel pitch shown in the lower part of FIG. 1B. The out-focus image k times as large as the in-focus image is imaged at a pixel size and pixel pitch k times as shown in the upper part of FIG. Therefore, two object images having a magnification ratio of k times can be captured with the same level of resolution with respect to the spatial frequency distribution originally possessed by the object. Hereinafter, a first embodiment of the present invention will be described in detail with reference to FIG.

Reference numeral 1 denotes an imaging optical system, and reference numeral 3 denotes an image sensor that captures two object images in the vicinity of a predetermined imaging plane. The projection optical system 4 projects two object images onto the image sensor 3, and is composed of a half mirror and a mirror, a prism, or the like. The correction circuit 5 is a circuit that corrects a fixed pattern noise, a dark current component, and the like with respect to the output of the image sensor 3, and corrects each pixel in synchronization with an external clock signal. The variable gain amplifier 6 controls the gain by an external control signal. The A / D converter 7 performs A / D conversion in synchronization with an external clock signal. The driver 8 receives a clock signal from the outside, converts the clock signal into a signal that can drive the image sensor 3, and supplies the signal to the image sensor 3. The memory circuit 9 temporarily stores a video signal read at high speed. The accumulation is performed in synchronization with an external clock signal. The timing controller 10 includes a correction circuit 5, a variable gain amplifier 6, an A / D converter 7, a driver 8,
A clock signal or the like is supplied to each of the memory circuits 9.

The CPU 11 includes a timing controller 1
0, read image data from the memory circuit 9,
It calculates the focus evaluation and outputs the result. The display circuit 12 displays the calculation result of the focus evaluation of the CPU 11 to the user of the focus detection device.

FIG. 3 is a diagram showing a light receiving portion of the image sensor 3. In this embodiment, a line sensor as shown is used. 20 pixels 21 for receiving the in-focus image
0, 20 pixels 22 for receiving the out-of-focus image
0 are arranged on the same straight line. The size of the pixels 21 is vertical a and horizontal b, and is arranged at a pitch p. The size of the pixels 22 is vertical a ', horizontal b' and arranged at a pitch p '.

Accordingly, the light receiving area has a length b and a width l for an in-focus image, and has a length b 'and a width l' for an out-of-focus image. Where a, b, p, l, a ',
b ', p', l 'satisfy the following relationship. a ′ = ka b ′ = kb p ′ = kp l = 200 × p− (p−a) l ′ = 200 × p ′ − (p′−a ′) In the above equation, k is a constant determined by the imaging optical system. In this embodiment, the value is about 1.2. The operation of the present embodiment will be described below with reference to FIGS.

An object image incident on the image forming optical system 1 is converted into an in-focus image,
It is projected as an out-of-focus image. FIG. 4A shows an example of the pattern of this projected image. The horizontal axis indicates the physical position of the line sensor in the pitch direction. As shown in the figure, the luminance distributions of the in-focus image and the out-focus image have different levels and sizes. The size of the out-focus image is k times the size of the in-focus image,
The level is 1 / k ² of the in-focus image Double is the level of the out-of-focus image. k is a constant determined by the imaging optical system.

Since the accumulation time of the image sensor 3 is made appropriate by the timing controller 10, the output of the image sensor 3, which photoelectrically converts the object image, is output as shown in FIG.
(B), the size of the in-focus image and the size of the out-focus image are the same. When the output of the image sensor 3 is corrected by the correction circuit 5, FIG.
The signal is as shown in FIG. The in-focus image and the out-focus image have an error such as ΔE in FIG. 4C due to the sensitivity error of the sensor, the error of the light amount division ratio of the optical system 4, and the like. At this time, the output level can be made uniform as shown in FIG. 4D by changing the gain when outputting the out-of-focus image. As described above, the object image is suitable for calculation for focus evaluation without newly adding an optical component.

Here, the CPU 11 sends a control signal to the timing controller 10 to start and end the image storage of the image sensor 3 and to start reading the stored image data. When the reading of the image data starts, the variable gain amplifier 6
Data converted to a more appropriate state is output in a time series. The output of the variable gain amplifier 6 is an A / D converter 7
Is sequentially converted into digital data and stored in the memory circuit 9 as image data. When the reading of the image data is completed, the timing controller 10 sends an end signal to the CPU 11 as a status signal.

The CPU 11 further reads out image data from the memory circuit 9, performs an operation for evaluating the degree of focus, and displays the result on the display circuit 12. As the display, any one of the three types of front focus, rear focus, and focus may be displayed, or the distance to the focus position may be displayed.

By repeatedly performing the above-described imaging, imaging signal processing, focus degree evaluation calculation, and display of the focus degree evaluation result,
A focus indicator capable of displaying the degree of focus in real time can be configured. It is needless to say that an automatic focusing device can be configured by performing a focusing operation (automatic focusing operation) based on the evaluation result of the degree of focusing. In the embodiment of the present invention, the in-focus image detecting section and the out-of-focus image detecting section are formed on the same silicon substrate in order to facilitate the alignment between the imaging optical system 1 and the image sensor 3. It is also possible to detect the focus image with a separate image sensor. Next, a second embodiment of the present invention will be described with reference to FIG.

In this embodiment, a focus evaluation area is selected using a two-dimensional area sensor as an image sensor. The block configuration of the system is the same as that of the first embodiment shown in FIG. 2, and the shape of the light receiving surface of the image sensor is as shown in FIG.
It is as shown in. The in-focus image light receiving pixels 23 are arranged 200 × 200 = 40000 pixels, and the out-of-focus image light receiving pixels 24 are arranged 200 × 200 = 40000 pixels. The size of the pixels 23 is arranged at pitches Px and Py in the vertical and horizontal C, and the size of the pixels 24 is arranged at the pitches Px 'and Py' in the vertical and horizontal C '.

Generally, Px = Py and Px '= Py' so that the sampling pitches in the x and y directions are equal.
Set to. And C, C ', Px, Py, Px', P
y ′ satisfies the following relationship. C ′ = kC Px ′ = kPx (Py ′ = kPy) In the above equation, k is a constant determined by the imaging optical system as in the first embodiment, and is about 1.2.

In this embodiment, similarly to the first embodiment, image data in an appropriate state is written into the memory circuit 9. Here, when the focus evaluation area is selected, the number of in-focus image data and the number of out-of-focus image data can be made to correspond equally, thereby simplifying the calculation by the CPU 11 and the loading of the image data from the memory circuit 9. Can be. If the pixel size and pixel pitch of the in-focus image detection area and the out-of-focus image detection area are equal, loading and calculating pixel data of the same part of the object image at the time of area selection becomes very complicated.

[0025]

As described in detail above, according to the present invention,
In-focus image,
The focus position detection error due to the difference in the size of the out-of-focus image can be removed, and its space reduction effect,
The cost reduction effect is very large.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams for explaining a basic concept of the present invention.

FIG. 2 is a diagram showing a configuration example of a focus position detection device according to the present invention.

FIG. 3 is a diagram showing a light receiving section of the image sensor in detail.

4A is a diagram showing a pattern of a photographed image, FIG. 4B is an output waveform diagram of an image sensor whose accumulation time has been adjusted, and FIG. FIG. 4D is a corrected output waveform diagram of the image sensor, and FIG. 4D is an output waveform diagram in which two levels are made the same by changing a gain.

FIG. 5 is a diagram showing a light receiving section of an image sensor according to a second embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Imaging optical system, 2, 2 '... Planned imaging surface, 3, 3' ... Image sensor, 4 ... Projection optical system, 5 ... Correction circuit, 6 ... Variable gain amplifier, 7 ... A / D converter , 8 ... Driver, 9 ... Memory circuit, 10 ... Timing controller,
11 CPU, 12 display circuit. 21, 22, 23, 2
4: Pixel.

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Yasuaki Takahama 2-43-2 Hatagaya, Shibuya-ku, Tokyo Inside Olympus Optical Industrial Co., Ltd. (56) References JP-A-58-92908 (JP, A) Sho-59-94720 (JP, A) JP-B-43-10265 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B ^7/ 28-7/40

Claims (2)

(57) [Claims] An image forming optical system, two image sensors for picking up two object images in the vicinity of a predetermined image forming plane of the image forming optical system, respectively, and the two object images are applied to the two image sensors. An optical system for projecting, and a focus position detecting device that detects a degree of focus of the imaging optical system based on outputs of the two image sensors, a light receiving unit of each image sensor that captures the two object images Wherein the pixel size and the pixel pitch are set to have a fixed ratio between the two image sensors. 2. The in-focus position detecting device according to claim 1, wherein the light receiving portions of the two image sensors are formed on the same semiconductor substrate.