JPS63284512A - Auto-focusing device - Google Patents

Abstract

PURPOSE:To eliminate the change of the shape of a reception light spot due to the variance of reflectivity of an object to improve the focusing precision by detecting reception light spot positions on respective light receiving elements by output signals from first and second light receiving parts and adding these outputs to turn the distance ring of a photographic lens. CONSTITUTION:An auto-focusing device consists of a first optical system consisting of a light emitting element 1 and a projection lens 3, two light reception optical systems consisting of light reception position detecting elements omitted in the figure and light receiving lenses, a processing circuit 4, a motor 5, and a potentiometer 6. Respective reception light sot positions are detected in first and second computing elements 24 and 25 by output signals from light receiving elements 10 and 11 of light reception optical systems of this device. Outputs of computing elements 24 and 25 are added by an adder 26, and the output of the adder 267 is supplied to a subtractor 27 together with a set voltage Vc from the potentiometer 6. A distance ring 1 of a photographic lens 9 is turned by the output of a driving circuit 30 in accordance with the output of the adder 26 to focus the lens 9 on the object.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an automatic focusing device suitable for use in video cameras, etc., and particularly an infrared automatic focusing device with excellent single focus performance. Regarding equipment.

[Conventional technology]

Conventionally, various techniques for automating various adjustment mechanisms of video cameras have been proposed and implemented, and the operability has been rapidly improved. As for the adjustment mechanism for focusing on the subject, various automatic focusing devices have been proposed that automatically perform this adjustment, and an example is an automatic focusing device using infrared rays (for example, (Japanese Unexamined Patent Publication No. 57-20708).

This method uses the principle of triangulation; a subject is irradiated with infrared rays emitted by a light-emitting element, the reflected light is received by a light-receiving element, and the image is adjusted to the subject according to the light-receiving state of the light-receiving element. This is to determine the deviation from the focused state. This light-receiving element is separated from the two light-receiving sections and moves in conjunction with the extending operation of the imaging lens. If each light receiving part of such a light receiving element is irradiated with an equal amount of reflected light (that is, when the amounts of light received by the two light receiving parts are equal, hereinafter this is referred to as the amount of received light being balanced), The in-focus state is determined from the detection output of this light-receiving element, and the imaging lens is also positioned to focus on this subject. When the amount of light received by the light-receiving element is not balanced, the light-receiving element moves so that the amount of light received is balanced,
Along with this, the imaging lens also moves to focus.

[Problem that the invention seeks to solve]

By the way, when a subject is irradiated with infrared rays from a light emitting element on the video camera side, a portion of the infrared rays may not be reflected back to the video camera depending on the subject or the position of the subject within the field of view of the video camera. When a subject is completely irradiated with infrared rays, the irradiation area (i.e., the projected spot) will be circular, and if the reflectance within this projected spot is approximately uniform, the amount will be uniform throughout the projected spot. A reflection occurs. However, when focusing on a subject that is made up of a combination of areas with different reflectances, such as a black and white pattern, the amount of reflected light in some parts of the projection spot on the subject is sufficiently small compared to other parts. ,
The light-receiving spot generated by the light-receiving element has a circular shape with a portion missing. Furthermore, if a portion of the projection spot on the object extends beyond the boundary of the object, there is no reflected light from this extended portion. Therefore, in this case as well, a portion of the circular light receiving spot on the light receiving element is missing.

As described above, when the light receiving spot of the light receiving element has a partially chipped shape, there is a problem in that an error occurs in focus determination and the performance of the automatic focusing device is deteriorated.

In other words, detecting the amount of light received by each light-receiving part of the light-receiving element to detect the out-of-focus of the imaging lens means that the center of gravity of the light-receiving spot on the light-receiving element is the reference position (i.e., the center of gravity of the light-receiving spot The purpose is to detect the degree of deviation from the center of gravity of this light receiving spot in a focused state when the shape is circular (at this time, the amounts of light received by the two light receiving sections are balanced).

So, taking as an example an automatic focusing unit mounted on a FL, 2x6x video camera lens, the base line length is 30cm and the focal length of the light receiving lens is 25cm. In the case of , the movement range of the center of gravity of the light receiving spot from infinity to close distance is approximately α81111
becomes. On the other hand, the diameter of the light-receiving spot is approximately α4tm, and the amount of change in the center of gravity due to the lack of the light-receiving spot K is at most α
2m, the total movement range of the light receiving spot is 174
It will extend to On the other hand, in terms of focusing accuracy, the permissible amount of variation in the center of gravity position is 0.02 square meters, and the effect of a chip in the shape of the light-receiving spot on accuracy is extremely large.

SUMMARY OF THE INVENTION An object of the present invention is to solve this problem and provide an automatic focusing device that can improve the accuracy of focus determination even if a portion of the light receiving spot on the light receiving element is missing.

[Means for solving problems]

In order to achieve the above object, the present invention provides a first light emitting section consisting of a projection lens and a light emitting element, and a first light receiving section fixedly disposed on both sides of the light emitting section and consisting of a light receiving lens and a light receiving element. a second light receiving section; a first and a second arithmetic unit that respectively detect the position of the light receiving spot on the second light receiving section; It includes an adder that adds the output voltages of the second arithmetic unit, and drives the distance ring of the imaging lens system according to the output voltage of the adder.

[Effect]

1st. Since the second light receiving sections are arranged on both sides of the light emitting section, the light receiving spot positions on the light receiving elements of these light receiving sections move in opposite directions as the distance to the subject changes. On the other hand, the first. The shape of the light-receiving spot obtained on the light-receiving element of the second light-receiving section is the same, and therefore, if a chip occurs in the shape of the light-receiving spot, the direction of change in the light-receiving spot position due to this chip in each light-receiving element will change. are the same.

1st. The output voltage obtained by the second arithmetic unit includes the amount of variation in the light receiving spot position due to the missing light receiving spot.
The direction of this amount of variation is the direction of the amount of variation in the light receiving spot position due to a change in distance to the subject. If the outputs of the second light receiving section are the same, the directions will be opposite to each other. Therefore, the first
．． By adding the output voltages of the second arithmetic unit, the amount of variation in the light receiving spot position due to the chipping of the light receiving spot shape is offset, and it is possible to detect the light receiving spot position that accurately represents the distance to the subject.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

First, referring to FIG. 2, a video camera equipped with an automatic focusing device according to the present invention will be described.

In the figure, the automatic focusing device is an infrared light emitting diode (
(hereinafter referred to as IRED) 2 and a projection lens 3.
Although not shown, the projection optical system includes two sets of light receiving optical systems including a light receiving position detection element (hereinafter referred to as PSD) and a light receiving lens, a processing circuit 4, a motor 5, and a potentiometer 6.

Light from an object (not shown) is incident on an image sensor (not shown) through the imaging lens system 9, and the image of the object formed on the image sensor is converted into a video signal. This video signal is output from the video camera and is also supplied to the electronic viewfinder 8, so that the image within the field of view can be monitored.

On the other hand, under the control of the processing circuit 4, the IRED emits infrared light. This infrared light is irradiated onto the subject through the projection lens 3, and the reflected light is incident on two sets of light receiving optical systems, respectively. These output signals of the PSD of the light receiving optical system are supplied to the processing circuit 4, where they are processed together with the output signal of the potentiometer 6 representing the position of the distance ring 1 in the imaging lens system 9. Detected. A signal representing the amount of defocus is supplied to the motor 5 as a drive signal, and the rotation of the motor 5 is transmitted to the distance ring 1 via the gear 7. This is K, imaging lens system 9
The distance ring 1 rotates so that the distance ring 1 focuses on the subject.

Figure 3 shows the positional relationship of the light receiving optical system with respect to the projection optical system in Figure 2, where 10° and 11 are PSD,
12. 15 is a light receiving lens, 14 is a subject, and parts corresponding to those in FIG. 2 are given the same reference numerals.

In FIG. 3, two sets of light receiving optical systems are fixedly arranged, one on each side of the projection optical system, so that their optical axes are parallel to the optical axis of the projection optical system.

The light-receiving lenses 12.15 of these light-receiving optical systems are provided on the same plane with the same focal length, and PSDlo, 11 is provided at the focal position of the light-receiving lenses 12.15, respectively.

Now, when the IRED 2 emits infrared light, this infrared light is irradiated onto the subject 14, and the reflected infrared light is reflected by the light receiving lens 1.
2.15 and is received by PSDlo, 11. IR
Assuming that the spot shape of the infrared light emitted by the ED is circular, when the reflectance of the subject is uniform, PSDlo, 11
The spot shape of the reflected infrared light received is also circular.

When the subject 14 exists at infinity, the light receiving lens 1
The reflected infrared light passing through 2.13 becomes parallel to the infrared light projected through the projection lens 3. PSDIo at this time, 1
Taking the light receiving spot position on 1 as a reference, the subject 14
As it approaches the receiving lens 12.15 from infinity,
The light receiving spot position on PSDIo, 11 is as shown in the drawing.
change so that they are separated from each other. Therefore, by detecting the amount of change in the light receiving spot position from the reference position, the distance to the subject 14 can be determined based on the principle of triangulation.

Here, the light-receiving spot position refers to the position of the center of gravity of the light-receiving spot, and in the case of a circular spot, the position of the center point is the light-receiving spot position.

Therefore, now it is assumed that the reflectance of the subject 14 is uniform, and the PSD
The light receiving spot position PA on the object 10 is the light receiving spot position (that is, the reference position) P when the subject 14 exists at an infinite distance, as shown in FIG. 4(a)K.

It is assumed that the light receiving spot position on the PSD 11 is shifted by a distance xB from the reference position P2, as shown in FIG. 4(b). Then, the distance from the light receiving lens 12.13 to the subject 14 at this time is y, the focal length of the light receiving lens 12.13 is f1, the optical axis distance between the light receiving lens 12 and the projection lens 3 is tA1, the distance between the light receiving lens 13 and the projection lens is 3, the distances XA + XB can be expressed as follows.

Here, if 1A=4=t, then the following holds true. From this equation (3), the distance y to the subject 14
is obtained, and the distance ring 1 (FIG. 1) is rotated so that the imaging lens system 9 (FIG. 2) focuses at this distance y.

If the reflectance of the subject 14 is not uniform, even if the spot shape of the projected infrared light is circular, the spot shape of the received infrared light may not be circular. Now, suppose that the spot shape of the received infrared light is semicircular and a received light spot 15A is obtained on the PSD10 as shown in FIG. 5(a). ), a semicircular light receiving spot 15B is obtained on the PSD10 in the same direction as the light receiving spora) 15A.

Here, the subject 140 has a uniform reflectance and a light receiving spora) 1
If the shapes of 5A and 15B are circular, their center of gravity will be the center position PA and PB of the light receiving slot 15A and 15B, but if they are semicircular as shown, then the center of gravity of the light receiving slot 15A will be the center position of the light receiving slot 15A. P'A is shifted by a distance ΔXA from #PA by about % in the direction away from the reference position P, and the center of gravity position P- of the light receiving spot 15B is away from the reference position P.
2 by a distance ΔXB from position PB. Therefore, the light receiving spots 15A and 15B at this time
The light receiving spot position P'A.

The distances X'A and x'B from the reference positions p, , p2 of the P voice are respectively expressed as follows.

XA=XA+ΔxA −-・” −(4
)”B ””xB+ΔXB Town・
・--(5) Although the focal length of the light receiving lens 12.13 is equal to f, ΔxA = ΔXB, and the sum x'c of the distances x'A and x'B is expressed by equations (3) to (5)K Yes, it becomes. That is, the distance y to the subject 14 can be accurately detected, which is equivalent to Equation (3), and the shadow caused by the change in the shape of the light receiving spot is removed.

Next, an embodiment of the automatic focusing device according to the present invention, which specifically shows such arithmetic processing, will be described with reference to FIG. In this embodiment, the signal processing section corresponds to the processing circuit 4 in FIG. In the same figure, 16 to 19 are preamplifiers, 2
0 to 23 are detectors, 24 and 25 are arithmetic units, 26 is an adder, 27 is a subtracter, 28 is an AD converter, 29 is a microcomputer,
30.31 is a drive circuit, 52 is a reference voltage source, and the second
The same reference numerals are given to the parts corresponding to those in FIG.

The microcomputer 29 supplies a modulation signal to the drive circuit 30, which causes the IRED 2 to emit modulated infrared light. This infrared light is reflected by an object (not shown) and is received by the PSD lo, 11 through the light receiving lens 12.13.

PSDl 0 and 11 are two-split light receiving elements. P.S.D.
When a light-receiving spot occurs at l0, a photoelectric current of 1 AA modulated with an amplitude corresponding to the amount of light received is obtained from one light-receiving element, and a photoelectric current modulated with an amplitude corresponding to the amount of light received is also obtained from the other element. 'AA is obtained.

These photoelectric currents 'AA l ' AB are respectively preamplifier 1
6°17, only the modulated components are detected by the detectors 20 and 21, and a detected output which is a DC voltage of levels vAA and vAB according to the amplitude is obtained. The same goes for PSDl 1, by amplifying the photoelectric current 'BAl' BB with preamplifiers 18 and 19, and detecting the modulation components with detectors 22 and 23, the level corresponding to the amplitude of these modulation components is determined. DC detection outputs of vBA and vBB are obtained.

The detection outputs of the detectors 20 and 21 are supplied to the arithmetic unit 24, and the following calculation is performed. Levels vAA and vAB are each PS
It is proportional to the amount of light received by each element of D10, therefore,
The level vA expressed by equation (7) is the level vA when the subject is at an arbitrary distance, when the boundary between the two elements of PSDlo is the light receiving spot position (i.e., the reference position) when the subject is at infinity. is proportional to the light receiving spot position with respect to this reference position (specifically, as described above, the distance between the center of gravity of the light receiving spot and the reference position). Similarly, the detection output of the detectors 22 and 23 is
5, and the calculation is performed. The level VB expressed by this equation (8) is proportional to the distance between the reference position (boundary between two elements) in PSDll and the light receiving spot position.

Here, when the shape of the light receiving spot at PSDlo, 11 is circular, equations (7) and (8) are replaced by the above equation (1).
, Corresponding to (2), when it is not circular, the above formula (4
), corresponding to (5).

The calculation outputs of the calculation units 24 and 25 are added together by an adder 26. The output signal of the level (vA + VB) obtained by this is, as explained earlier, regardless of the shape of the light-receiving spot, that is, it is not affected by the unevenness of the light-receiving spot due to uneven reflectance of the subject, and has a correct circular shape. The light receiving spot is PSDl 0 .

The position of the light receiving spot obtained at No. 11 is shown. The addition output of the adder 26 is supplied to a subtracter 27.

On the other hand, a constant voltage is applied from the reference voltage source 32, and the potentiometer 6 operates in conjunction with the distance ring 1 (FIG. 1).
Level V proportional to the reciprocal of the focal position of the imaging lens system 9 (FIG. 1). Outputs the voltage of

This voltage is supplied to a subtracter 27, which outputs the difference voltage from the addition output from the adder 26. This differential voltage is converted into a digital value by the AD converter 28 and supplied to the microcomputer 29. When the digital value is less than a predetermined value, the microcomputer 29 determines that the imaging lens system 9 is in the focused state and maintains that state, and when the digital value is greater than the predetermined value, K is set to the front with the sign of the digital value. It is determined whether it is a pin or a rear pin, and a drive signal corresponding to the digital value is sent to the drive circuit 31 to drive the motor 5. As a result, the imaging lens system 9 is brought into focus.

Although one embodiment of the present invention has been described above, the present invention is not applied only to video cameras.

Furthermore, the spot shape of the infrared light projected from the light emitting section does not have to be circular.

〔Effect of the invention〕

As explained above, according to the present invention, even if the shape of the light receiving spot changes due to uneven reflectance of the subject,
The distance to the subject is accurately measured, greatly improving focusing accuracy.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of an automatic focusing device according to the present invention, FIG. 2 is an external view showing a video camera using the present invention, and FIG. 3 is an optical diagram of the embodiment shown in FIG. The block diagrams illustrating the system, FIGS. 4 and 5, are diagrams for explaining the operation of this embodiment. DESCRIPTION OF SYMBOLS 1... Distance ring, 2... Light emitting element, 3... Projection lens, 4... Processing circuit, 5... Motor, 6... Potentiometer, 7... Gear, 9... Imaging lens, 1
0.11... Light receiving element, 12.15... Light receiving element, 16-19... Preamplifier, 20-23... Detector, 24.25... Arithmetic unit, 26... Adder , 27
...Subtractor, 28...AD converter 5 Fig. 2 Fig. 5 Q 40 (1(b) Fig. 5

Claims (1)

[Claims] 1. One light emitting unit consisting of a projection lens and a light emitting element;
First and second light receiving sections, each consisting of a light receiving lens and a light receiving element, are fixedly arranged on both sides of the light emitting section, and each of the light receiving elements is activated by an output signal from the first and second light receiving sections. first and second arithmetic units for detecting the position of the light receiving spot; an adder for adding the outputs of the first and second arithmetic units; and a distance ring of the imaging lens is rotated according to the output of the adder. What is claimed is: 1. An automatic focusing device, comprising: means for moving the imaging lens, and focusing the imaging lens on a subject.