JPS63176072A - Automatic focusing system - Google Patents

Abstract

PURPOSE:To realize an exact focusing without being influenced by a disturbance by continuing the focusing while focus voltage, which is taken out several times after the level of the focus voltage falls suddenly by more than the prescribed level, is neglected. CONSTITUTION:When, for instance, a man passes in front of a camera, the focus voltage E falls suddenly as shown by an alternate long and short dash line, and as a differential voltage DELTAE comes steeply large, a sign alters. Then, a fact that the disturbance has arisen is detected by the largeness of the level change of the differential voltage DELTAE. Namely, when the level Ln of the differential voltage DELTAE is >=six times, for instance, of the level Ln-1 of the differential voltage DELTAE, calculated just before it, it is decided that the focus voltage E is fluctuated by the disturbance. In this case, considering the influence of the disturbance to exist, the focus voltage through the several times of sampling after it, is neglected, and a focus lens is made to move as it does, by keeping the state before the disturbance arose.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an autofocus system used in various video cameras, etc., and in particular can realize accurate focusing without being affected by changes in focus voltage caused by external disturbances. This is how it was done.

(Prior art) Conventionally, attention has been paid to the fact 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 referred to as the focal voltage. An autofocus device is known that performs focusing such that the focus voltage is discretely taken out and the focus voltage is driven to the maximum level to bring the position of the lens to the just-focus position by driving the focus lens.

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 literature such as the Technical Report of the Television Society published in November 1957, page 675.

(Problems to be Solved by the Invention) By the way, in the above-mentioned mountain climbing servo system, a difference voltage is detected by sequentially comparing the levels of focus voltages taken out discretely, and the focus is determined based on the level and sign of the difference voltage. The point of maximum voltage level, that is, the just-focus position is detected.

In other words, the focal voltage changes exponentially as the focus lens moves in the optical axis direction, so the level of the differential voltage decreases near the just-focus position, and the focus lens passes through the just-focus position. At this stage, the sign of the differential voltage changes from positive to negative or from negative to positive, and by detecting this change, the just-in-focus position is detected.

By the way, when a person or a car crosses in front of the camera, or when there is so-called image skipping due to a lens driving device, the level of the focal voltage suddenly drops temporarily.

According to the conventional hill-climbing servo system, there is a problem in that a peak point caused by a drop in the focal voltage due to such disturbance is mistakenly determined to be the just-focus position.

(Means for Solving the Problems) The present invention has been made in view of the above-mentioned actual circumstances, and provides an autofocus method that can realize accurate focusing without being affected by changes in focal voltage caused by disturbances. The purpose is to

In order to achieve this objective, the present invention discretely extracts a predetermined high-frequency component of a video signal obtained by photographing a subject as a focal voltage, and, based on this focal voltage, directs the focus lens in the optical axis direction. This is an autofocus method that performs focusing by moving the lens, and if the level of the focal voltage suddenly drops above a predetermined level, the focusing voltage that has been extracted several times thereafter is ignored and focusing is continued. The present invention provides an autofocus method characterized by the following.

(Function) According to the autofocus method as described above, even if the focus voltage fluctuates due to disturbance, focusing will not be adversely affected by this fluctuation, and accurate focusing can be achieved.

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

FIG. 1 is a block diagram showing the configuration of an autofocus device for realizing the autofocus method according to the present invention, and this autofocus device is composed of an ahocal lens 5 and a focus lens (master lens) 1. It is equipped with an optical system 6.

Focusing is performed by moving the focus lens 1 in a predetermined direction along the optical axis (in the six directions of arrows) by a pulse motor 2, and the focus lens 1 is moved at the same time as the start of focusing. The moving distance of the focus lens 1 is detected by an O-tary encoder provided on the pulse motor 2, and is supplied to the control circuit 3 as position information S1.

In addition, the imaging light from the subject that enters through the optical system 6 as described above is transmitted to the COD, which is the imaging means in this embodiment.
The image signal is photoelectrically converted into an electrical video signal $2 by an image sensor 7 using a charge coupling element (1 charge coupling element) or the like.

Then, this video signal S2 is amplified by an amplifier 8 and supplied to a recording circuit (not shown), etc., and is also passed through an automatic gain control circuit (AGC) 9 to a bandpass filter <BP>.
F) Supplied to 10.

This bandpass filter 10 extracts a predetermined high frequency component from the video signal S2 and supplies it to a detector (DET) 11.

The detector 11 obtains a focal voltage E as shown in FIG. 2, which corresponds to a predetermined high-frequency component of the video signal S2.

Here, this focus voltage E corresponds to 111 degrees of the reproduced image obtained by reproducing the video signal Sg, 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 12 and supplied to the control circuit 3.

The control circuit 3 sequentially samples the focal voltage E associated with the movement of the focus lens 1 in the optical axis direction for each field from the start of focusing.

Next, this control circuit 3 calculates a differential voltage ΔE by sequentially comparing the levels of each focus voltage sampled sequentially, and determines the just focus position P by detecting the magnitude and sign change of the level of this differential voltage ΔE. To detect.

Based on this detection result, the control circuit 3 supplies a pulse signal of a predetermined number of pulses as an rtsm signal S3 to the pulse motor 2 to rotate it. As a result, the focus lens 1 is brought into just focus position rI.
Get closer to the IP.

Here, the focal voltage E sharply drops as shown by the dotted line in FIG. 2, for example, when a person passes in front of the camera. In such a case, the differential voltage ΔE suddenly increases and its sign changes.

Therefore, in this embodiment, the presence of the above-mentioned disturbance is detected based on the magnitude of the level change of the differential voltage ΔE.

That is, in this embodiment, the level LO of the differential voltage ΔE is the level 1-n of the previously calculated differential voltage ΔE.
If it is, for example, six times or more of -1, it is determined that the focal voltage E has fluctuated due to disturbance.

If it is determined that such a disturbance has occurred,
It is thought that this disturbance has an effect. After that, the focus voltage obtained by sampling several times is ignored, and the state before the disturbance is maintained, and the focus lens 1 is moved as it is.

Thereafter, based on the sampled focus voltage E as described above (the hill-climbing servo is restored), the just focus position @P is detected.

As described above, according to the autofocus device according to the present embodiment, by continuing focusing while ignoring the focal voltage sampled when a disturbance occurs, the peak value caused by this disturbance can be determined to be the just focus position. There will be no misjudgment.

Note that in this embodiment, the focus lens 1 was moved as it was when a disturbance occurred, but by stopping this movement, the discontinuous portion of the focus voltage curve can be reduced, and more accurate focusing can be achieved. It can be realized.

Furthermore, the determination of whether or not there is a disturbance is not limited to the method of this embodiment.

(Effects of the Invention) As is clear from the above description, the present invention discretely extracts a predetermined high-frequency component of a video signal obtained by photographing a subject as a focal voltage, and adjusts the focus lens based on this focal voltage. This is an autofocus method that performs focusing by moving the focus voltage in the optical axis direction, and if the level of the focus voltage suddenly drops to a predetermined level or more, the focus voltage that has been extracted several times thereafter is ignored and focusing is performed. By continuing, accurate focusing can be achieved without being affected by external disturbances.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a graph showing the relationship between focal voltage and lens position. . 1... Focus lens, 2... Pulse motor, 3
...ilJ 111 circuit. 1 Sea J

Claims (1)

[Claims] Focusing is performed by discretely extracting a predetermined high-frequency component of a video signal obtained by photographing a subject as a focal voltage, and moving a focus lens in the optical axis direction based on this focal voltage. The autofocus method is characterized in that when the level of the focus voltage suddenly drops to a predetermined level or more, the focus voltage taken out several times thereafter is ignored and focusing is continued. Focus method.