JPS62272218A - Autofocusing device - Google Patents

Abstract

PURPOSE:To attain rapid and smooth focusing by calculating a focusing distance on the basis of a focus voltage obtained at the time of photographing an object and a focus voltage obtained after the passage of prescribed time to control a focusing lens position. CONSTITUTION:A focus voltage E(X) corresponding to the focusing distance X of a high frequency component in a video signal obtained through a detector 10 at the time of photographing the object and a focus voltage E(X+m) obtained after the passage of the prescribed time required when a focusing lens 1 is moved by a distance (m) are supplied to a microcomputer 3 through an A/D converter 11. The focusing distance (X) is calculated by operation based upon the equality I and converted into a lens movement control signal. Thus, the automatic focusing of the lens 1 can be rapidly and smoothly executed without vibrating movement. In the equation, (a) is a constant factor relating to the inclination of a focus voltage curve.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an autofocus device used in various video cameras, etc., and is capable of performing focusing reliably and quickly. be.

(Prior Art) Conventionally, attention has been paid to the fact that the voltage level of the high-frequency component of a video signal obtained by photographing a subject corresponds to the N fineness of the reproduced image edge, and the voltage level of this high-frequency component has been developed. An autofocus device is known that performs focusing by extracting a focal voltage as a focal voltage and driving a focusing lens so that the focal voltage reaches a maximum level so that the position of the lens coincides with the just-focus position.

This method of focusing is described in Volume 17, Issue 1, Volume 1, Volume 86, Page 21, or 1982.
Television Society Technical Report ED No. 675 published in November
It is explained in detail in the literature such as page 7.

(Problems to be Solved by the Invention) By the way, in the above-mentioned mountain climbing servo system, the focal voltages at two points that are temporally (positionally) shifted from each other are successively compared in level, and the level of the focal voltage at these two points is compared. The force lens is moved in a predetermined direction by detecting the presence or absence of focus shift and the direction based on the magnitude relationship of the focus voltage.

Therefore, until the focus lens reaches the just-focus position, the lens must be moved while constantly comparing the levels as described above, and the lens cannot be moved to the just-focus position at high speed, making it difficult to focus. The problem is that it takes a long time.

Further, near the just-focus position, the focus lens converges to the just-focus position while taking pictures in the optical axis direction, which causes an unnaturalness to the reproduced image.

(Means for solving the problems) The present invention has been made in view of the above-mentioned circumstances,
It is an object of the present invention to provide an autofocus device that moves the focus lens to a just-focus position at high speed and does not cause vibration of the focus lens near the just-focus position.

In order to achieve this object, the present invention, as shown in FIG. Just focus IP
This is an autofocus device that performs focusing by moving the focus lens 1 with a motor 2 so that the distance wiX becomes 0. ) and a focal voltage E (x+m) after a predetermined period of time has elapsed to obtain a distance X to the just-focus position P of the focus lens 1, and output a control signal S2 corresponding to this distance X. and the above-mentioned bacteriostatic signal S2
The motor 2 is driven by:

(Function) In the autofocus device configured as described above, the focus voltage E(X) at the start of focusing and the focus voltage E(X+m) at the elapse of a predetermined time are immediately brought to the just focus position P of the focus lens 1. distance
As a result, the above focus lens 1
can be moved to the just-focus position P at high speed.

Therefore, the time required for focusing can be shortened.

Further, since no photographing or the like occurs in the vicinity of the just-focus position IP, the conventional problem of unnaturalness of reproduced images due to vibration of the focus lens 1 can be solved.

(Example) Hereinafter, a preferred example according to the present invention will be described in detail using FIGS. 1 and 2.

The autofocus device according to the present embodiment includes an optical system 6 composed of an ahocal lens 5 and a focus lens (mask lens) 1, as shown in FIG.
Focusing is performed by moving the focus lens 1 in the direction of the optical axis (in the six directions of arrows) by a pulse motor 2, and the focus lens 1 is moved simultaneously when focusing is started. .

Furthermore, imaging light from a subject that enters through the optical system 6 as described above is photoelectrically converted into an electrical video signal S1 by an imaging device 7 using a COD (charge coupled device) or the like.

This video signal S1 is amplified by an amplifier 8 and supplied to a recording circuit (not shown), and is also passed through an automatic gain control circuit (AGC) 13 to a bandpass filter (B).
PF)9.

This bandpass filter 9 extracts a predetermined high frequency component from the video signal S1 and supplies it to the detector 10.

The detector 10 obtains a focal voltage E as shown in FIG. 2, which corresponds to the high frequency component of the video signal $1.

Here, the focus voltage E corresponds to the definition of the reproduced image obtained by reproducing the video signal S1, and becomes maximum when the focus lens 1 is at the just-focus position P.

The focal voltage E is digitized by an A/D (analog-digital) converter 11 and supplied to the microcomputer 3, which is the calculating means in this embodiment.

In this embodiment, the microcomputer 3 takes in the focal voltage E(X) at the start of focusing and the focal voltage E(x+m) after a predetermined time has elapsed, performs arithmetic processing as described later, and adjusts the focus voltage of the focus lens 1 just right. The distance X to the focus position flP is calculated, and a control signal $2 having the number of pulses corresponding to this distance X is output.

This control signal S2 is supplied to a drive circuit 12 that rotationally drives the motor 2, and rotates the motor 2 by a predetermined amount in a predetermined direction. As a result, the focus lens 1 moves to the just-focus position P, and focusing ends.

Next, the arithmetic processing of the microcomputer 3 in this embodiment will be explained.

First, the curve of the focal voltage E shown in FIG. 2, that is, the relationship between the focal voltage E and the distance X to the just-focus position P of the focus lens 1 is E(X) = b e
−”x)2 (1) It can be approximated by the following formula.

In this equation (1), a is a coefficient that determines the slope of the focal voltage E curve, and b is a coefficient that determines the maximum value of the focal voltage E curve.

In addition, the focal voltage E (X+m) after a predetermined time elapses is E (x+m):B @-t a (x+m)+
2...(2) becomes.

Note that m in this equation (2) indicates the moving distance of the focus lens 1 in the predetermined time as shown in FIG. 3, and this X indicates the number of pulses to the motor 2 or The microcomputer 3 can count the number of output pulses from the attached 0-Tari encoder.

-(ax)2+a2(x2+2mx+m2) e becomes.

Also, if we take the logarithm of this equation (3), becomes.

Therefore, when this equation (4) is solved for X, it becomes.

In this way, the focal voltage E at the start of focusing
(x), focal voltage E (x+
By taking the logarithm of the value divided by m), the distance X to the just-focus position P of the focus lens 1 can be determined.

Further, this value has a positive or negative sign, and the direction in which the focus lens 1 should be moved is determined by this sign.

As a result, according to this embodiment, the focus lens 1
Focusing is started based on the distance x 1 between and the just focus position P at the start of focusing, and the relative position of the just focus position P with respect to the focus lens 1, that is, whether it is located in front or behind in the optical axis direction. It can be determined based only on the focal voltage E (X) at the time and the focal voltage E (X+m) at the elapse of a predetermined time.

Therefore, based on the results obtained as described above, the distance
By supplying the drive circuit 12 with a control signal S2 that controls the rotation of the motor 2 so as to set the value to 0, the focus lens 1 can be moved at high speed to the just-focus position P.

Further, the focus lens 1 does not vibrate near the just focus position P, and the focus lens 1
smoothly reaches the just-focus position P based on the control signal S2.

By the way, in the above embodiment, only a microcomputer was used as the arithmetic means 3, but in addition to this microcomputer, it is also possible to provide a divider that executes the above equation (3) or a log circuit that executes the above equation (4). , . . . (6) may be executed. This can reduce the processing load on the microcomputer, making it easier to design and manufacture the microcomputer.

Also, the above (instead of formula 3, You may use the following formula.

And when using this formula (7), becomes.

In addition, from the Television Society Technical Report ED No. 675 Page 7, the value of a in the above (a formula and (8) formula) is a function of the focal length 11i, the subject frequency (e, and the F value of the lens, etc.) It has been known.

Regarding the focal length f, the value of a is inversely proportional to f2 in the case of the front lens focusing method, and is unrelated in the case of the rear lens focusing method.

Furthermore, as a result of practice using actual lenses, it has been found that the value of a is proportional to fe and inversely proportional to the F value of the lens.

Therefore, in the case of the front lens focus method, the value of a is f.

f2. F　　　　　　　　-(91 Then, In the case of the rear lens focusing method, becomes.

Therefore, the value of a can be obtained by determining in advance the values of the equations 0 and (10) above, and providing information regarding fe, f, and F to the microcomputer (3).

Note that the front lens focusing method is a method in which focusing is performed by moving the focus lens 1 located in front of the optical system 6, and the rear lens focusing method is a method in which focusing is performed by moving the focus lens 1 located in the rear of the optical system 6. This method performs focusing by

9. Also, the value of a can be found by finding an equation consisting of equation (4) above and solving equation (11) for a.

Next, other arithmetic processing by the microcomputer 3 will be explained.

First, by differentiating the above equations (1) and (2) with respect to X, E(X)'=-2a2xbe-"x)2'...αriE(
x 10m)'--2a2(x+m)be-"(x""
'---Q3.

Then, convert these equations (12) and (13) into (1)
Dividing by the formula and (2 formulas) yields.

Dividing these equations (14) by equation (15), we get E(X)' becomes.

Solving this equation (16) for X, we get m 1-Y “0”.

In this way, the focal voltage E at the start of focusing
The differential value of (x) is expressed as the focal voltage E after a predetermined time elapses
By dividing by the differential value of (X+m), the distance X to the just focus position P of the focus lens 1
can be found.

Then, by supplying the control signal S2 to the drive circuit 11 so that the distance X obtained in this way becomes O, it is possible to realize quick and reliable focusing as described above.

By the way, the absolute path 1 ft of the focus lens 1 from the image sensor 7 is obtained in advance by counting the number of output pulses of the rotary encoder and the number of pulses sent to the motor 2, and the distance X is added to this absolute distance 11. By adding, the absolute distance JL2 of the just-focus position P from the m-axis element 7 can be determined.

As a result, the distance between the camera equipped with this autofocus device and the subject can be determined, and this can be displayed on a viewfinder or the like or used for correction during zooming.

Further, in the above embodiment, an autofocus device using a rear lens focus method was described, but the same effect can be obtained even if the present invention is applied to an autofocus device using a front lens focus method. The distance X may be the distance to the just-focus position of the focus ring.

Further, in the above-described embodiment, the predetermined time during focusing is the time when focusing is started, but the present invention may be set immediately after or during the start of focusing.

(Effects of the Invention) As is clear from the above description, according to the present invention, the focus lens can be moved to the just-focus position at high speed, and the time required for focusing can be shortened.

In addition, since the focus lens is moved smoothly even near the just-focus position, it is possible to prevent unnaturalness on the reproduced image.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of an autofocus device according to the present invention, FIG. 2 is a graph showing the relationship between focal voltage and distance, and FIG. 3 is a diagram showing the focus lens of the embodiment shown in FIG. FIG. 3 is a diagram showing the relationship with the focus position. 1... Focus lens, 2... Motor, 3...
Calculating means (microcomputer), 6... Optical system, E... Focus voltage, P... Just focus position, X... Distance to just focus position of focus lens, m... Focus at a predetermined time. Lens transfer! ll distance. Patent applicant: Victor Japan Co., Ltd. Figure 1 Procedural Amendments August 12, 1982

Claims (1)

[Claims] 1) The high-frequency component of the video signal obtained by photographing the subject is extracted as a focal voltage, the distance from this focal voltage to the just-focus position of the focus lens is obtained, and this distance is determined to be 0. The autofocus device moves the focus lens using a motor to perform focusing, and the focus lens is brought into just focus based on a focus voltage at a predetermined time during focusing and a focus voltage after a predetermined time elapses. What is claimed is: 1. An autofocus device comprising: arithmetic means for obtaining a distance to a position and outputting a control signal according to the distance, the motor being driven by the control signal. 2) A patent characterized in that the distance to the just-focus position of the focus lens is obtained by taking the logarithm of the value obtained by dividing the focus voltage at a predetermined time during focusing by the focus voltage after a predetermined time elapses. An autofocus device according to claim 1. 3) The distance to the just-focus position of the focus lens is obtained by dividing the differential value of the focal voltage at a predetermined time during focusing by the differential value of the focal voltage after a predetermined time elapses. An autofocus device according to claim 1.