JPS62272217A - Autofocusing device - Google Patents

Abstract

PURPOSE:To attain rapid and smooth focusing by dividing twice the differential value of a focus voltage by a differential value to determine the focusing distance of a focusing lens. CONSTITUTION:The focus voltage E(x) of a high frequency component in a video signal obtained through a photographing element 7, an amplifier 8, and AGC13 a BPF9, an A/D converter 11, etc., and calculated on the basis of the quality I is supplied to a microcomputer 3. In the equality, (x) is a distance from the focusing lens 1 up to a focusing position and (a) and (b) are factor values relating to the voltage E(x) curve. The differential value and twice differential value of the voltage E(x) are calculated, the differential value is divided by the twice differential value to determine the distance (x) and the distance (x) is converted into a moving signal of the lens 1. Thus, the autofocusing of an image pickup device can be rapidly and smoothly attained.

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, it has been known that the voltage level of the high-frequency component of the video signal obtained by photographing a subject corresponds to the definition of the reproduced image, and the voltage of this high-frequency component is focused. An autofocus device is known that performs focusing such that the focus voltage is taken out as a voltage and the focus voltage is driven to the maximum level to drive the focus lens so that the position of the lens coincides with the just-focus position.

This focusing method is known as the so-called mountain-climbing servo method, and this method is described in the NHK Technical Research Report 1964, Volume 17, No. 1, Volume 86, Page 21, or the Showa This is explained in detail in documents such as the Technical Report of the Television Society of Japan published in November 1957, ED, page 675, 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 focal voltage at these two points is The focus lens is moved in a predetermined direction by detecting the presence or absence and direction of out-of-focus based on the magnitude relationship of the voltages.

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 on the just-focus position while vibrating in the optical axis direction, giving a reproduced image an unnatural appearance.

(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 extracts the high-frequency component of the video signal S1 obtained by photographing a subject as a focal voltage E, as shown in FIG. Just in focus M
This is an autofocus device that performs focusing by obtaining a distance X to P and moving the focus lens 1 using a motor 2 so that this distance X becomes O. The differential value,
The distance X to the just focus position P of the focus lens 1 is obtained by dividing by the twice differential value, and the calculation means 3 outputs a control signal S2 corresponding to this distance X. The motor 2 is driven.

(Function) In the autofocus device configured as described above, the focus voltage E at the start of focusing can move the focus lens 1 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 P, the conventional problem of unnatural reproduced images caused by 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 (master lens) 1, as shown in FIG.
Focusing is performed by moving the focus lens 1 in the optical axis direction (in the six directions of arrows) by a motor 2 such as a pulse motor, and the focus lens 1 is moved at the same time when focusing is started. It has become.

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

This video signal Sl 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 81.

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 only the focal voltage E at the time of starting focusing, performs arithmetic processing as described later, and calculates the distance X from which the focusing lens 1 reaches the just-focus position P. A control signal S2 with a pulse number corresponding to 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, such as the pulse motor, 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 expressed as follows. -(ax
)2 It can be approximated by the equation (1).

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.

Next, by differentiating the above equation (1) with respect to x, E(z)'==
−21L2xb e −”x)2...(2) It becomes.

Dividing the above equation ('2J) by equation (1) yields.

Moreover, if this (3 formula) is differentiated by X again, it becomes.

Then, dividing the above equation (3) by equation (4) yields.

Therefore, by dividing the differential value of the focal voltage E by the twice differential value, the distance @X to the just-focus position P of the focus lens 1 can be determined.

Note that the distance X in this case is a value to the just-focus position P of the focus lens 1 at the time of starting focusing.

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
The distance X 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 in the direction of the optical axis. It can be determined based only on the focal voltage E at the start.

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

Further, the focus lens 1 smoothly focuses on the just focus position Pfi based on the control signal S2 without causing the focus lens 1 to take a picture near the just focus position Pfi.
reach.

Also, from the Television Society of Japan Technical Report ED No. 675 page 7, the value of a in the above equation (4) is the focal length f,
It is known that it is a function of the frequency ie of the subject, the F value of the lens, etc.

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

Further, as a result of experiments using actual lenses, it was 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 focusing method, the value of a is as follows.In the case of the rear lens focusing method, the value of a is calculated in advance by calculating the above (equation 0 and equation (7)) and then calculating the value of fe, i. , F can be given to the microcomputer (3) to determine the value of a.

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

By the way, in the above embodiment, only a microcomputer was used as the calculation means 3, but by providing a differentiating circuit and a division circuit in addition to the microcomputer, the processing burden on the microcomputer can be reduced. design,
Manufacturing becomes easier.

Further, for example, by obtaining the distance JL1 of the focus lens 1 from the image sensor 7 in advance by counting the number of pulses to the rotary encoder or the motor 2, and adding this distance 11 to the distance X, The absolute distance L2 of the just-focus position P from the image sensor 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, and FIG. 2 is a graph showing the relationship with focal point 6 distance. 1... Focus lens, 2... Motor, 3...
Calculating means (microcomputer), 6... Optical system, E... Focus voltage, P... Just focus position, X... Distance to the just focus position of the focus lens. Figure 1 Figure 2 Procedural amendment August 12, 1988 1. Indication of the case 1986 Patent Application No. 115788 2. Name of the invention Autofocus device 3. Person making the amendment Relationship to the case Patent applicant Address: 3-12-4 Moriyacho, Kanayō-ku, Yokohama City, Kanagawa Prefecture
, Date of amendment order Voluntary amendment 5, Claims column of the specification to be amended, Detailed description of the invention column and 6, Contents of amendment (1) The scope of claims of the specification as attached. to correct. (2) "Focus lens" described in the following parts of the specification will be corrected to "focusing member." Specification page 4, line 8 to line 9, page 4 of the same book, line 10 to line 11, page 4 of the same book, line 1
Line 4 to line 15 of the same page, line 3 of page 5 of the same book, line 5 of page 5 of the same store, line 10 of page 5 of the same book, line 5 of page 5 of the same store, line 10 to page 4 of the same book Melon 13th row. (3) “Motor” described in the following parts of the specification is “
``means of transportation''. Page 4, line 11 of the specification, page 4, line 18 of the same book. (4) Specific force between page 13, line 6 and line 7 of page 13 [Note that the R@ element 7 described above may be used instead of the focus lens 1 as the focusing member, and this image carrier element 7 may be used as the focusing member. Focusing may be performed by moving in the optical axis direction. ” is inserted. (5) "Focus lens" described on page 13, line 19 of the specification is corrected to "focusing member (focus lens)." (6) “Motor” described on page 13, line 19 of the specification
is corrected as "transportation means (motor)". Attached Patent Claim: ``The a-acid component of the video signal obtained by photographing the subject is taken out as a focal voltage, the distance from this focal voltage to the just-focus position of the focusing member is obtained, and this distance becomes O. An autofocus device that performs focusing by moving the focus member in the optical axis direction using a moving means,

Claims (1)

[Claims] A high-frequency component of a video signal obtained by photographing a subject is extracted as a focal voltage, a distance from this focal voltage to the just-focus position of a focus lens is obtained, and this distance is set to 0. An autofocus device that performs focusing by moving the focus lens using a motor, the focus lens being adjusted by dividing the differential value of the focus voltage at a predetermined time during focusing by the twice differential value of the focus voltage. What is claimed is: 1. An autofocus device comprising: calculating means for obtaining a distance to a just-focus position and outputting a control signal according to the distance; and driving the motor in accordance with the control signal.