JPH04360112A - Automatic focusing system - Google Patents

Abstract

PURPOSE:To accomplish automatic focusing based on output from one or a few photodetectors. CONSTITUTION:This system is provided with a photoelectric conversion part 1, an image-formation part 2 which forms the image of an object on the conversion part 1, a focus shifting plate 3 which is constituted of a light transmissive material having specified thickness and which is allowed to get in and out of an optical path between the conversion part 1 and the image-formation part 2 to shift a position where the image of the object is formed, a focus divergence detection part 4 which detects the fluctuation amount E of the output from the conversion part 1 caused by allowing the plate 3 to get in and out of the optical path, and a focusing control part 5 which controls the focusing of the image-formation part 2 in a direction where the fluctuation amount E is reduced based on the fluctuation amount E. Then, the photoelectric conversion part 1, the image-formation part 2, and the focus shifting plate 3 are constituted of a member which makes infrared rays symmetric.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing system, and more particularly to an automatic focusing system that automatically focuses on an object within a field of view. Generally, it is preferable for an imaging device to use a method (passive type) in which the focus is automatically adjusted based on an image signal that enters the field of view. Nowadays, two-dimensional imaging devices (such as CCDs) are easily available in the visible light region, so automatic focus adjustment can be performed based on two-dimensional processing of image signals. On the other hand, in the long-wavelength infrared region, it is still difficult to obtain two-dimensional high-speed imaging devices, and for this reason, infrared imaging devices mechanically scan the field of view with respect to a line of light-receiving elements. method is adopted. Therefore, in such an imaging device, it is desired to provide a method for automatically adjusting the focus based on the output of one or a small number of light receiving elements.

0002

2. Description of the Related Art Conventional infrared imaging devices do not have a suitable passive automatic focusing method, so the operator manually operates the focusing control button while looking at the display screen to obtain a clear image. . However, it is necessary to manually adjust the focus every time the distance to the object changes, which places a heavy burden on the operator. In particular, manual focus adjustment of infrared imaging devices used by aircraft pilots is problematic in that overloading the pilot can lead to serious accidents.

0003

SUMMARY OF THE INVENTION As described above, the conventional infrared imaging apparatus has a problem in that focus adjustment is performed manually, which places a heavy burden on the operator. An object of the present invention is to provide an automatic focus adjustment method that can automatically adjust the focus based on the output of one or a small number of light receiving elements.

0004

[Means for Solving the Problems] The above problems are solved by the configuration shown in FIG. That is, the automatic focus adjustment method of the present invention consists of a photoelectric conversion section 1, an imaging section 2 that forms an image of an object on the photoelectric conversion section 1, and a light transmitting material having a predetermined thickness. a focus shift plate 3 that is inserted into and taken out of the optical path between the image forming unit 2 and shifts the image formation position of the object; and a focus shift plate 3;
a focus shift detection section 4 that detects a variation E in the output of the photoelectric conversion section 1 due to the insertion and removal of the lens; and a focusing control section that controls the focusing of the imaging section 2 in a direction in which the variation E is reduced based on the variation E. 5.

[0005]

[Operation] The automatic focus adjustment method of the present invention utilizes the fact that the imaging position of the object is shifted by inserting a light transmitting material 3 of a predetermined thickness in the optical path between the photoelectric conversion section 1 and the imaging section 2. It is something. For example, if the light ray (solid line) from the object is coming from an infinite distance but the imaging section 2 focuses on a nearby object, the image of the object will be focused in front of the photoelectric conversion section 1. I image it. In this state, the image diameter on the light-receiving surface becomes wider than when focused, and becomes larger than the size of the light-receiving surface, so the output of the photoelectric conversion unit 1 becomes relatively small. In this state, for example, if a focusing plate 3 with a predetermined thickness that is optically denser than the surroundings (higher refractive index) is inserted, the image of the object will be shifted to the position shown by the dotted line in the figure and will be formed. As a result, the imaging diameter becomes smaller and approaches the size of the light receiving surface. Therefore, in this case, the output of the photoelectric conversion section 1 is increased by inserting the focus shift plate 3. This relationship holds true as long as the focus position of the image forming section 2 is in front of the object, so when the output of the photoelectric conversion section 1 increases when the focus shift plate 3 is inserted, the focus position of the image forming section 2 increases. By controlling the focusing so that the focal position is moved further away, the imaging section 2 can finally be focused on the object.

On the other hand, if the imaging unit 2 is focused at infinity even though the light ray from the object is coming from the perigee, the image of the object will be on the back side of the photoelectric conversion unit 1. It forms an image. In this state, the image diameter on the light-receiving surface becomes wider than when focused, and becomes larger than the size of the light-receiving surface, so the output of the photoelectric conversion section 1 becomes relatively small. If the focus shift plate 3 as described above is inserted in this state, the image of the object will be formed with a further shift to the rear position, resulting in an even larger image diameter. Therefore, in this case, the output of the photoelectric conversion section 1 is reduced by inserting the focus shift plate 3. This relationship holds true as long as the focal position of the imaging section 2 is far away from the object, so if the output of the photoelectric conversion section 1 becomes low when the focal shift plate 3 is inserted, the focal position of the imaging section 2 will be lower. By controlling the focusing so that the focal position becomes close, the imaging section 2 can finally be focused on the object.

[0007] Preferably, the photoelectric conversion section 1, the imaging section 2, and the focus shift plate 3 are constructed of members that are symmetrical with respect to infrared rays, thereby realizing the above-mentioned automatic focus adjustment in the scanning infrared imaging device.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 2 is a diagram showing the configuration of the automatic focusing system of the embodiment. In the figure, 1 is an infrared light receiving element array (DET), 11 to 13 are video amplifiers provided for each light receiving element, and 21 is an infrared optical system array. a focal section, 22 an infrared scanning mirror, 23 a scanning mirror drive motor, 24 an infrared optical system imaging section, 3 a focus shift plate, 31 a rotation transmission mechanism section, 32 a focus shift plate drive motor, 33 is a photo encoder directly connected to the rotating shaft of the drive motor 32;
41 is a defocus detection unit; 41 is a low-pass filter (LPF) for removing noise components from the video signal VS; 42
is an A/D converter, 43 and 44 are registers, 45 and 46 are subtracters, 47 is a center clipping circuit, 47a is a comparator (CMP), 47b is a switch circuit, and 48 is D
49 is a timing generation circuit, 51 is a focusing drive section, and 52 is an afocal section drive motor.

The focus shift plate drive motor 32 is rotating at a predetermined speed, and in this state, the photo encoder 33 outputs an encode signal PE corresponding to the rotation angle, and inputs it to the timing generation circuit 49. Timing generation circuit 4
9 generates various timing signals based on the encode signal PE. For example, the sawtooth wave scanning signal SAW is output at a rate of four cycles per one rotation of the motor 32, and the scanning mirror 22 thus makes four reciprocations. Further, a sampling signal SP is output near the center of each return path of the scanning mirror 22, so that the A/D converter 42 samples the video signal VS near the center in the field of view of each return path. Furthermore, the timing generation circuit 49 outputs a transfer signal XP in synchronization with the sampling signal SP, whereby each A/D conversion output is sequentially shifted into the registers 43 and 44.

By the way, since the focus shift plate 3 is inserted in every other return pass of the scanning mirror 22, as will be described later, the sampling data when the focus shift plate 3 is inserted is stored in the register 43 again. The registers 44 each hold sampling data when the focus shift plate 3 is not inserted. The subtracter 46 is activated by the subtraction activation signal EN outputted from the timing generation circuit 49 at this point, and performs an operation of subtracting the contents of the register 44 from the contents of the register 43. Note that at this time, the subtracter 45 uses the register 44
The reason for subtracting the offset (OFS) from the contents will become clear from the explanation below.

The comparator 47a compares the absolute value |E| of the error signal E output from the subtractor 46 with a predetermined threshold th, and outputs a switch signal when |E|<th.
This causes the switch circuit 47b to change the connection from the a side to the b side. That is, the center clipping circuit 47 has |E|<
When it is not th, the error signal E is output as is, and |E|<
At the time of th, the output is clipped to 0 to prevent occurrence of servo hunting due to minute errors. In this way, the error signal E or 0 is D/A converted by the D/A converter 48 and input to the focusing drive section 51.

The focusing drive section 51 receives an error signal E.
The direction (polarity) in which the error signal E becomes smaller according to the input of
The motor 52 is driven to
automatically adjusts to focus on the object. FIG. 3 is a diagram showing the configuration of the focus shift plate of the embodiment, and (A) of FIG.
3 is a front view of the focus shift plate seen from the side of the image forming section 24 in FIG. 2, and FIG. 3B is a bottom view of FIG. 3A. In the figure, the focus shift plate 3 is made of infrared transmitting material (
For example, two blades 3a, 3 made of germanium)
b is symmetrical with respect to the rotation axis, allowing smooth rotation. The focus shift plate 3 rotates, for example, in the direction of arrow C, and one rotation corresponds to four reciprocations of the scanning mirror 22. Dividing this into four quadrants (1) to (4), there is no blade in the first and third quadrants, blade 3b is in the second quadrant, and blade 3b is in the fourth quadrant.
Each quadrant has a blade 3a. Therefore, the focus shift plate 3 is inserted once every two reciprocations of the scanning mirror 22.

In the scanning infrared imaging device, approximately 70% of the first half of one cycle of the scanning mirror 22 is an image acquisition period (forward scanning period), and the remaining approximately 30% is a period during which the scanning mirror 22 returns (backward scanning period). ), and the video signal VS on the return trip is not used for video display. In this 30% backward scanning period,
Although the scanning direction is reversed, since the same field of view is being viewed, a reversely scanned video signal VS can be extracted. Therefore, by using a part of the remaining 30% of each period to alternately move the focus shift plate 31 in and out, and sample the video signal VS approximately in the middle of each return path, automatic focus adjustment is possible. Make use of it.

In the infrared light receiving element array 1, infrared light receiving elements are arranged in a vertical line as shown in the figure, and in this embodiment, the infrared light receiving element 1a located approximately in the center is also used for detecting defocus. Therefore, in this embodiment, the object to be controlled for focusing is located approximately at the center of the field of view. FIG. 4 is a diagram illustrating the function of the focus shift plate of the embodiment, and (A) of FIG. 4 shows a case where an image of the object is formed in front of the light receiving element 1a. This situation occurs when the optical system focuses on a nearby object even though the infrared rays (solid line) from the object are coming from an infinite distance. As is clear from the figure, in this state, the imaging diameter a on the light-receiving surface is larger than the size of the light-receiving element 1a, so the output of the light-receiving element 1a becomes relatively small. Therefore, when the focus shift plate 3 is inserted in this state, the image of the object is shifted backward to the position shown by the dotted line and formed, so the diameter of the image becomes small, b, which is the size of the light receiving element 1a in this example. are almost equal. Therefore, in the above state, there is a relationship in which the output of the light receiving element 1a increases due to the insertion of the focusing plate 3, and this relationship means that by gradually focusing the optical system on a distant object, the image of the object gradually changes. Even in the process of approaching the light receiving element 1a, a
>b holds true as long as there is a relationship. Therefore, by comparing the output of the light receiving element 1a according to the insertion and removal of the focus shift plate 3, it is possible to precisely guide the optical system to focus.

FIG. 4B shows a state where a=b, and in this state, the output of the light receiving element 1a is approximately the same regardless of whether the focus shift plate 3 is inserted or removed. This is the in-focus position for The output of the light receiving element 1a when the focus shift plate 3 is inserted is shown in (A) in FIG.
Even in the process from 1 to 4 (B) in FIG. 4, the maximum value is maintained at a substantially constant value.

FIG. 5 is a diagram illustrating the function of the focus shift plate of the embodiment, and (A) in FIG. 5 shows the case where the image of the object is formed behind the light receiving element 1a. This situation occurs when the optical system focuses on infinity even though the infrared rays (solid line) from the object are coming from the perigee. As is clear from the figure, in this state, the imaging diameter a on the light-receiving surface is larger than the size of the light-receiving element 1a, so the output of the light-receiving element 1a becomes relatively small. Therefore,
If the focus shift plate 3 is inserted in this state, the image of the object will be shifted further back to the position shown by the dotted line.
Its imaging diameter is b, which is even larger than the imaging diameter a. Therefore, in this case, the output of the light-receiving element 1a is further reduced by inserting the focus shift plate 3, and this relationship means that by gradually focusing the optical system on the perigee, the image of the object is gradually reduced. Even in the process of approaching the light receiving element 1a, this holds as long as the relationship a>b holds. Therefore, in this case as well, the light receiving element 1 corresponds to the insertion and removal of the focus shift plate 3.
By comparing the outputs of a, it becomes possible to bring the optical system into focus precisely.

FIG. 5B shows a state where a=b, and in this state, the output of the light receiving element 1a is approximately the same regardless of whether the focus shift plate 3 is inserted or removed. The relationship is the same as that in FIG. 4B at the focused position. Thus, according to this embodiment, it is possible to accurately focus on the object whether the infrared optical system is looking at a far point or near point from the object.

Note that the degree of deviation in image formation due to the insertion of the focus shift plate 3 depends on the thickness d of the focus shift plate 3. Therefore, if the thickness d is large, the convergence to the in-focus position is fast, but the focusing accuracy is limited. On the other hand, if the thickness d is small, the convergence to the in-focus position will be slow, but the focusing accuracy will be high. In addition, in FIGS. 4(A) and 5(B), a certain offset (OFS) occurs regarding the image forming point during focusing, but this reduces the light receiving area of the light receiving element 1a and If the thickness d of the shifting plate 3 is made small, the offset amount will also become very small. Alternatively, without reducing the light receiving area or the thickness d of the focus shift plate 3, as shown in FIG.
If the voltage corresponding to the offset (OFS) is subtracted from the output of the light receiving element 1a when the light receiving element 1a is not inserted, the offset imaging position in Fig. 4 (A) and Fig. 5 (B) can be moved to the right. It can be shifted.

FIG. 6 is a timing chart of auto-focusing control according to an embodiment. Auto-focusing control is performed when the optical system focuses on a nearby object even though the infrared rays from the object are coming from an infinite distance. It shows. In this case, the sampling signal SS obtained by inserting the focus shift plate 3 in the next fourth quadrant (4) is higher than the sampling signal SS in the first quadrant (1). The subtracter 46 outputs the error signal E during the period of the subtraction energizing signal EN, and the error signal E is larger than the threshold th.
A corresponding motor control signal MC is sent to the focusing control section 51, whereby the afocal section 21 is driven in a direction in which the error signal E becomes smaller. As a result, the sampling signal SS in the third quadrant (3) becomes higher, but in this example, it is still not sufficient, so the sampling signal SS in the next second quadrant (2) appears higher. As a result, the afocal part 2
1 is driven in the direction in which the error signal E is further reduced, and the afocal section 21 is thus guided to the in-focus position with respect to the object.

FIG. 7 is a timing chart of auto-focusing control according to the embodiment, and shows auto-focusing when the optical system is focused at infinity even though the infrared rays from the object are coming from the perigee. Shows control. In this case, the sampling signal SS obtained by inserting the focus shift plate 3 in the next fourth quadrant (4) is lower than the sampling signal SS in the first quadrant (1). The subtracter 46 outputs an error signal - during the period of the subtraction activation signal EN.
Since the error signal -E is larger than the threshold value th, the corresponding motor control signal -MC is sent to the focusing control section 51, thereby causing the afocal section 21
is driven in the direction in which the error signal -E becomes smaller. Although this increases the sampling signal SS in the third quadrant (3), it is still not sufficient in this example, so
Furthermore, the sampling signal SS in the next second quadrant (2)
appears lower. As a result, the afocal section 21 is driven in the direction in which the error signal -E is further reduced in the same manner as described above, and the afocal section 21 is thus guided to the in-focus position with respect to the object.

Note that in the above embodiment, a single light receiving element 1a
Although the focusing control is performed based on the outputs of the light receiving elements, the focusing control may be performed based on the outputs of a plurality of adjacent or discrete light receiving elements. Furthermore, in the above embodiment, a case has been described in which the focus shift plate 3 is optically denser than the surroundings (larger refractive index), but conversely, the focus shift plate 3 is optically coarser than the surroundings (lower refractive index). In this case, the insertion of the focus shift plate 3 brings the imaging position of the object closer to the imaging section 2, so the present invention can be realized by a concept opposite to that of the above embodiment.

[0022]

As described above, according to the present invention, the focus can be automatically adjusted based on the output of one or a small number of light receiving elements, and in particular, by applying the present invention to a scanning type infrared imaging device, This greatly reduces the operator's workload and enables safe navigation.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the basic configuration of the present invention.

FIG. 2 is a diagram showing the configuration of an automatic focus adjustment method according to an embodiment.

FIG. 3 is a diagram showing the configuration of a focus shift plate according to an embodiment.

FIG. 4 is a diagram illustrating the function of the focus shift plate of the embodiment.

FIG. 5 is a diagram illustrating the function of the focus shift plate of the embodiment.

FIG. 6 is a timing chart of auto-focusing control in the embodiment.

FIG. 7 is a timing chart of auto-focusing control in the embodiment.

[Explanation of symbols]

1 Photoelectric conversion section 2 Imaging section 3 Focus shift plate 4 Defocus detection section 5 Focusing control section

Claims (2)

[Claims] 1. A photoelectric conversion section (1), an imaging section (2) for forming an image of an object on the photoelectric conversion section (1), and a light transmitting material having a predetermined thickness. ) and imaging section (2)
The focus shift plate (3) is moved in and out of the optical path between the two to shift the imaging position of the object, and the variation (E) in the output of the photoelectric conversion unit (1) due to the focus shift plate (3) being moved in and out is detected. and a focusing control section (5) that performs focusing control of the imaging section (2) in a direction in which the variation (E) is reduced based on the variation (E). An automatic focus adjustment system featuring 2. The automatic focusing system according to claim 1, wherein the photoelectric conversion section (1), the imaging section (2), and the focus shift plate (3) are made of members that are symmetrical to infrared rays. .