JPS6326082A - Automatic focussing device for video camera - Google Patents

Abstract

PURPOSE:To move a focussing lens to a just focussing position at high speed by minutely oscillating an oscillating lens in a period even number times one field period and using a focal point voltage at two points having a time difference half said period. CONSTITUTION:The oscillating lens 6 is minutely oscillated so as to have an amplitude of 2d in an optical axis direction by an oscillating means 3 using a piezoelectric element, for instance, the period of the four field period of a television signal treated by a video camera and an oscillation speed of a rectangular shape wave. A microcomputer 4 calculates distance (x) to the just focussing position P of the focussing lens 1 from the values of the focal point voltage E(x+d) at the two points, an E(x-d) amplitude value 2d and an inclination factor (a) and supplies the data of this distance (x) to a controller 5. Thereby, the focussing can be carried out extremely rapidly and correctly.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an autofocus device used in various video cameras and the like, and is capable of performing focusing quickly and efficiently.

(Prior Art) Conventionally, it has been known that the voltage level of the high frequency component of a video signal obtained by photographing a subject is the voltage level of the reproduced image.
Focusing on the fact that it corresponds to I degree, we extract the voltage of this high frequency component as the focal voltage and drive the focus lens so that this focal voltage reaches the maximum level, bringing the lens position to the just focus position. An autofocus device that performs focusing to match objects is known.

This focusing method is known as the so-called mountain-climbing servo method, and this method is described in the NHK Technical Research Report, Vol. This is explained in detail in literature such as the Technical Report of the Society of Television Engineers published in November 2015, page 675.

(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, during the time it takes for the focus lens to reach the just-focus position, the lens must be moved while constantly comparing the levels as described above.
There is a problem in that the lens cannot be moved to a just-focus position at high speed and the time required for focusing is long.

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 problem) Unreleased i was made in view of the actual situation as described above.
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 involve movement 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. This is an autofocus device that performs focusing by obtaining a distance lx to a just-focus position P and moving the focus lens 1 using a moving means 2 so that this distance MX becomes 0, A photographing means 3 that performs minute photographing at a period that is an even multiple of one field period in the camera, and the amplitude of the focal voltmeter t- and the minute 11iiU at two points having a time difference of half the period within one photographing. The controller comprises a calculator Q4 that calculates the distance x from the value 2d and the slope coefficient a of the focal voltage E, and a control signal generating means 5 that outputs a control signal S2 corresponding to the calculated distance x. By supplying the signal S2 to the moving means 2, the focus lens 1 is moved to the just-focus position P.

(Function) In the autofocus device configured as described above, the focal voltage E(x+d) at the above two points.

E(x - d > , S width value 2d, and slope coefficient a), the distance x to the just focus position P of the focus lens 1 can be immediately obtained, and thereby the focus lens 1 can be moved to the just focus position P. It can be moved at high speed.

Therefore, the time required for focusing can be shortened, and rapid focusing can be achieved.

Furthermore, since no photographing takes place in the vicinity of the just-focusing device P, the conventional problem of unnaturalness of the reproduced image caused by the photographing of the focus lens 1 can be solved, and reliable focusing can be achieved. be able to.

(Embodiments) Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS. 1 to 4.

As shown in FIG. 1, the autofocus device according to this embodiment has an optical system 7 including a focus lens (master lens) 1 and a vibration lens 6. Focusing is performed by appropriately moving the lens in the optical axis direction (in the direction of the arrow) using a pulse motor 2 serving as a moving means.

In addition, in this embodiment, the vibration lens 6 has an amplitude of 2 in the optical axis direction using a vibrator Q3 using a piezo element, for example.
The d0 period is a four-field period of the television signal handled by the video camera, and the vibration speed is minutely vibrated in a rectangular waveform.

On the other hand, imaging light from a subject that enters through the optical system 7 is photoelectrically converted into a development signal S1 by an image play element 8 such as a CCD (charge coupled device).

This video signal S1 is supplied to a camera circuit (not shown) via an amplifier 9, and is also supplied to a filter circuit 1.
0, and a predetermined high frequency component is extracted by this filter circuit 10.

Then, this high-frequency component is gain-controlled to a predetermined level by an automatic gain control circuit (AGC) 11 having a time constant of at least 4 field periods, and then detected by a detector 12.
This is extracted as a focal voltage E as shown in FIG.

This focal voltage E is supplied via an A/D (analog-digital) converter 13 to a microcomputer 4, which is a performance means in this embodiment.

Here, the focal voltage E detected and extracted by the detector 12 by the minute imaging of the vibration lens 6 is the third
As shown in the figure, it is extracted as a rectangular waveform voltage signal with a period of four field periods.

Then, the microcomputer 4 generates a focal voltage E (x + d) at two points having a time difference of two field periods, which is a half of the period of one vibration in the micro vibration.
Sample and capture E (x − d ).

Further, a drive signal @S3 for vibrating the vibration means 3, which is output from the controller 5 which is the control signal generator Q in this embodiment, is supplied to the microcomputer 4 as data regarding the imaging width value 2d. Ru.

Further, the microcomputer 4 is supplied with data on the value of the slope coefficient a, which indicates the slope of the focal voltage E, as shown in FIG. 2, from the color detector 14.

Then, this microcomputer 4 receives the focal voltages E (X + d >, E (X − d
) Distance @y from the value of the amplitude value 2d and the tilt coefficient a to the just-focus position P of the focus lens 1.

is calculated, and the data of this distance x is supplied to the controller 5.

This controller 5 controls the supplied distance lx and the distance
control signal S2 of a predetermined number of positive or negative pulses according to the sign of
is supplied to the pulse motor 2.

Then, the pulse motor 2 rotates in a predetermined direction by a predetermined number of rotations in response to the control signal S2, moves the focus lens 1 to the just-focus position P, and finishes focusing.

Next, the calculation method in the calculation means 4 will be explained.

First, the just focus position P of the focus lens 1
The focal voltage when the distance to
It can be approximated by the following equation: b6-(ax)2...(1).

Note that in equation (1), a is the slope coefficient of the focal voltage E, and b
is a variable that changes depending on the subject.

Next, by differentiating the above equation (1), E-(x)=-2a"bxe-"2・((2JThese(
From equation 1) and equation (2).

On the other hand, when the focus lens 1 is vibrated with a small amplitude 2d, the following formula holds true.

In addition, the above E(×) is ...(5) can be replaced with

Therefore, by substituting equations (4) and (5) into equation (3) above, we get:

Therefore, the microcomputer 4 calculates the focal voltages E(x-d), 'E(x+d), ffi width 2d at the two points supplied.
By calculating the value of the slope coefficient a of the focus voltage E based on the above equation (7), the distance x to the just-focus position P of the focus lens 1 can be immediately calculated.

In addition, in the above equation (7), the focus lens 1
Focus voltages at two points E (X - d), E (x + d) depending on the positional relationship between and the just focus position P
The sign of the calculated distance flx differs because the magnitude relationship changes.

Therefore, the positional relationship between the focus lens 1 and the just-focus position P can be determined based on the sign of the distance lx calculated as described above, and the direction in which the focus lens 1 is to be moved can be known.

Moreover, the above-mentioned slope coefficient a is calculated based on the fact that the F value of the lens is the focal length WBf.
It is generally known that it is a function that is inversely proportional to the frequency fe of the object, that is, the cutoff frequency of the filter circuit 10.

Therefore, by inputting information on the focal length [ into the a calculator 14 and supplying data such as F(Vi) from the aperture 15 of the optical system 7, the above-mentioned inclination coefficient a can be calculated.

As described above, according to this embodiment, the distance 11x to the just-focus position P of the focus lens 1 and the positional relationship between the focus lens 1 and the just-focus position P can be immediately calculated by calculating each necessary value. By rotating the pulse motor 2 based on this, focusing can be performed extremely quickly and accurately.

Furthermore, in this embodiment, by setting the moving speed of the focus lens 1 to have a rectangular waveform, the focal voltage at one minute vibration also becomes a rectangular waveform as shown in FIG.

Therefore, even if the sampling timing in the microcomputer 4 changes slightly, the required focal voltage E at two points
(x−d), E(x+d) can be obtained.

By the way, the above equation (4) holds true when the amplitude value 2d is relatively small compared to the slope coefficient a.

However, when the amplitude value 2d becomes large, the above equation (4) no longer holds true, and the distance X calculated using the calculation method described above differs from the actual distance! It (straightness) does not match as shown in FIG. 4, and an error occurs.

This error increases as the photographing width 2d increases, and particularly increases as the distance 11jlix between the focus lens 1 and the just-in-focus position IP increases.

On the other hand, if the amplitude value 2d is made too small, the differential voltage Δ
Since the value of E (x + d) - E (x - d)) becomes small, the number of effective digits of the calculated distance MX decreases, causing an error.

A non-linear processing circuit is provided between the roller 5 and the distance calculated by the microcomputer 4! By performing non-linear processing on the direct value of ltX and converting it into the true value, the above-mentioned amplitude value 2d can be increased to a certain extent without generating an error.

(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.

Furthermore, since the focus lens is moved smoothly even in the vicinity of the just-focus position, it is possible to prevent unnaturalness from occurring in 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 time chart showing focal voltage within one vibration. FIG. 4 is a graph showing the relationship between the amplitude value and the calculated distance. DESCRIPTION OF SYMBOLS 1... Focus lens, 2... Moving means (pulse motor), 3... Vibrating means, 4... Calculating means (microcomputer), 5... Control signal generating means (controller),
6... Perturbation lens, E... Focus voltage, a... Slope coefficient, d... Half of the amplitude value, E (x - d)
・E (x + d)... Focal voltage at two points. Patent applicant: Japan Victor Co., Ltd. Representative: Kunito Umiki ~). =J', 1 O 1 Illustration 3Fa

Claims (1)

[Claims] A high-frequency component of a video signal obtained by photographing a subject is extracted as a focal voltage, and a distance to the just-focus position of a focus lens is obtained based on this focal voltage, and this distance is determined to be 0. An autofocus device for a video camera that performs focusing by moving the focus lens using a moving means, the vibrating means for slightly vibrating the vibrating lens at a period that is an even number multiple of one field period in the video camera; , calculation means for calculating the distance from the focal voltage at two points having a time difference of half the period within one vibration, the amplitude value of the micro vibration, and the slope coefficient of the focal voltage; and the calculated distance. and a control signal generation means for outputting a control signal according to the movement means, and the focus lens is moved to a just-focus position by supplying the control signal to the movement means. focus device.