JPH01162075A - Auto-focus system - Google Patents

Abstract

PURPOSE:To execute an exact and speedy focusing by inverting a focus lens moving direction when a focus voltage to be detected does not achieve a reference voltage value in a prescribed time after a focusing start. CONSTITUTION:A control circuit 3 successively executes the sampling of a focus voltage E, which accompanies a moving in the optical axis direction of a focus lens 1, in each field after the focusing start (in each 1/60 seconds in case of an NTSC system). This control circuit 3 stores a peculiar number for a detectable minimum value Emin of a detector 11, etc., or plural reference voltage values SEn, which is the integer number-fold of the constant-fold value of this minimum value Emin and respective reference voltage values SEn. When the focus voltage E and any one of the reference voltage values SEn are not coincident in a prescribed time (t), the moving direction of the focus lens 1 is inverted at a time point to achieve the prescribed time. Thus, since an unnecessary time can be reduced as much as possible, a time to be needed for the focusing can be shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an autofocus system used in various video cameras and the like, and is particularly concerned with an autofocus system that enables reliable and quick focusing.

(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. By driving the focus lens so that this focal voltage becomes the maximum level, the position of this lens is set to 1? 2. Description of the Related Art An autofocus device that performs focusing to match a stop focus position is known.

This focusing method is known as the so-called mountain-climbing servo method, and this method is described in NHK Technical Research Report 11rI40, Volume 17, No. 1, Volume 86, Page 21, or 1982. Year 1
This is explained in detail in documents such as the Television Society Technical Report ED No. 675 released in January.

(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 sampled and the levels are successively compared. The focus lens is moved in a predetermined direction by detecting the presence or absence of out-of-focus and the direction of the just-in-focus position based on the magnitude relationship between the focus voltages at two points.

Therefore, when the amount of change in the focal voltage with respect to the amount of lens movement becomes small, such as when photographing a low-contrast subject, or when the sampling range is too far from the just-focus position, the above-mentioned The difference value (differential voltage) level obtained by level comparison is too small, and it takes time to detect the direction of the just-focus position, and as a result, the above-mentioned hill-climbing servo method cannot be performed reliably and quickly. There is a problem.

(Means for Solving the Problems) The present invention has been made in view of the above-mentioned circumstances, and has an object to perform reliable and quick focusing even when the change m of the focal voltage with respect to the movement of the lens is small. The purpose is to provide an autofocus method that allows for

In order to achieve this objective, the present invention extracts a predetermined high-frequency component of a video signal obtained by photographing a subject as a focal voltage, and combines this focal voltage with a plurality of preset reference voltage values. This is an autofocus method that performs focusing by moving the focus lens in the optical axis direction based on the result of comparison with the reference voltage. If the focus voltage does not reach the reference voltage value, the moving direction of the focus lens is reversed, and after the reversal, the focus lens returns to the focusing position, and if the focus voltage does not reach the reference voltage value again within the predetermined time, the focus lens is focused again. The present invention provides an autofocus method characterized in that focusing is completed by returning to a starting position.

(Function) According to the autofocus method as described above, as long as the focal voltage is within a detectable range, reliable and rapid focusing can be performed regardless of the amount of change in the focal voltage with respect to the amount of movement of the lens. can.

(Embodiment) Hereinafter, a preferred embodiment of the autofocus system according to the present invention will be described in detail with reference to FIGS. 1 to 6.

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 (mask lens) 1. It is equipped with an optical system 6.

Focusing is performed by moving the focus lens 1 in a predetermined direction (arrow A-B direction) along the optical axis using a pulse motor 2, which is a moving means in this embodiment. The focus lens 1 is moved at the same time as focusing starts, and the position of the focus lens 1 on the optical axis is detected by a rotary encoder provided on the pulse motor 2 and controlled as position information $1. It is designed to be supplied to circuit 3.

In addition, the dancing image 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 is photoelectrically converted into an electrical video signal S2 by an image sensor 7 using a charge-coupled device (charge-coupled device) or the like.

This video signal @S2 is amplified by an amplifier 8 and supplied to a camera circuit (not shown), etc., and is also supplied to a bandpass filter (BPF) 9, which receives a predetermined signal from the video signal S2. The high-frequency components of are extracted and supplied to an automatic gain control circuit (AGC) 10.

Then, the automatic gain control circuit 10 performs gain control on the high-frequency component and then supplies it to a detector (DET) 11. A focal voltage E as shown in the figure is detected.

Here, the focus voltage E corresponds to the definition of the reproduced image obtained by reproducing the video signal S2, and is 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.

Then, the control circuit 3 controls the focus voltage E accompanying the movement of the focus lens 1 in the optical axis direction every field (176 in the case of the NTSC system) from the start of focusing.
Sequential sampling is performed every 0 seconds).

Moreover, this control circuit 3 has a plurality of reference voltage values SE that are integral multiples (for example, odd multiples) of the minimum value E min that can be detected by the detector 11 or the like or a constant multiple of this minimum value E min.
n, and a unique number (corresponding to n) for each reference voltage value SEn.

Furthermore, time data S4 is supplied to this control circuit 3 from a timer 13.

This timer 13 is incremented by a clock pulse of a predetermined frequency at the same time as the start of focusing. The predetermined time is detected.

The operation of the timer 13 is controlled by a timer control signal S5 supplied from the control circuit 3, and the timer 1
The contents of 3 are reset at the end of focusing and when a predetermined period of time has elapsed from the start of focusing.

Then, this control circuit 3 sequentially compares the levels of each of the reference voltage values SEn and the focal voltage E detected as described above, and when these match within a predetermined time specified by the time data S4, Then, only the number unique to the matched reference voltage value is read out.

Here, this control circuit 3 stores the magnitude relationship between base*voltage values related to numbers unique to each reference voltage value, and reads out the reference voltage value thickness related to the newly read number before that. If the reference voltage value is larger than the reference voltage value associated with the number, it is determined that the focus lens 1 has not reached the just focus position P, and the control signal S3 is sent to the motor to continue moving the focus lens 1. Supplied to circuit 14.

On the other hand, when a focal voltage En... having the same level as each reference voltage value SEn... is detected, the control circuit 3 generates the above-mentioned position information indicating the position @JIn... of the focus lens 1 at this time. Import S1.

In this embodiment, the focal voltage is taken into the control circuit 3 as discrete information for each field. Therefore, in this embodiment, the captured values are each reference voltage value S
Focal voltage E detected when En is first exceeded
It is assumed that n has reached the reference voltage value SEn, and the focal voltage En and the position information S1 at this time are taken in.

In addition, in the autofocus device as described above, the third
As shown in the figure, when the focus lens 1 is moved in the direction of the arrow in Fig. 3, the reference voltage value S E max is taken as having reached the maximum reference voltage value 3 E max.
If a unique number for x is detected twice in succession, the just-focus position P will be located between these two detected positions.

Therefore, if the same number is read twice, move the focus lens 1 to the position of the two detections @ midway between X and Y, and the position of the focus lens 1 will be in just focus. It can be made to match the position P.

Therefore, based on the position information S1, the control circuit 3 moves the focus lens 1 in the opposite direction (direction of arrow B in FIG. 3) by a predetermined distance ff1(, (X-'/)/2).
) to the motor drive circuit 1.
4, the pulse motor 2 is rotated in the opposite direction to perform focusing.

Further, as shown in FIG. 4, if the number read out as described above is at a lower level than the number read out before, the previous detected position is the just focus position P.
It turns out that.

Therefore, in such a case, the focus lens 1
By returning the lens to the previous detection position, it can be brought into alignment with the just-focus position P.

In this case as well, the control circuit 3
is the focus lens 1 based on the position information S1.
Focusing is performed by supplying a control signal S3 to the motor drive circuit 14 to move the lens in the opposite direction.

As described above, according to this embodiment, the focus lens 1 can be moved to the just focus position P regardless of the level of the differential voltage as in the conventional case, and reliable focusing can be achieved.

In this way, the autofocus device according to this embodiment is
Since it is possible to read out a unique number for each reference voltage value SEn and continue to drive the focus lens 1 by 8 wJ based only on this number, even if the voltage difference between each focal voltage actually becomes smaller than the detection limit value, Reliable focusing can be performed even if

On the other hand, as shown in FIG. 5, if the focal voltage E does not match any of the reference voltage values SEn within a predetermined time based on the time data S4, that is, the amount of lens movement of the focal voltage at the sampling position If the change (2) is small, the direction of movement of the focus lens 1 is reversed when the predetermined time has elapsed.

Here, the amount of change in the focus voltage En with respect to the amount of lens movement becomes smaller as the distance from the just focus position P increases.
When moving in a direction away from this just focus position P at a position away from P, the focal voltage E detected in one field is based on ti! ; It takes a relatively long time to reach the voltage value SEn.

Therefore, within the predetermined time, the focal voltage E and the reference voltage value S are
If they do not match En, there is a high possibility that the focus lens 1 is moving away from the just focus position P.

Therefore, in such a case, the wasted time can be minimized by reversing the moving direction of the focus lens 1, so that the time used for focusing can be shortened.

If the focus voltage E detected within a predetermined time after the reverse rotation matches the reference voltage value, the focus lens 1 is moved to the just focus position P by performing the focusing operation as described above.

In this case, the direction of the just-focus position P with respect to the focus lens 1 is determined.

In addition, after the moving direction is reversed as described above, the focal voltage E remains at the reference voltage value S even within time 2, which is twice the predetermined time.
It may not match En.

In such a case, as shown in FIG. 6, the object has extremely low contrast, and focusing is essentially unnecessary, so the focusing lens 1 is returned to the focusing starting position and focusing is completed.

As described above, according to this embodiment, the time required for focusing can be shortened by omitting wasted time when photographing a low-contrast subject, and thereby rapid focusing can be achieved. .

In this embodiment, a unique number is stored for each reference voltage value SEn, but instead of this number, a unique code may be stored for each reference voltage value SEn.

(Effects of the Invention) As is clear from the above description, according to the present invention, as long as the focal voltage is within a detectable range, reliable focusing can be performed regardless of the level of the differential voltage, and low contrast Rapid focusing can be achieved when photographing a subject.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the autofocus system according to the present invention, Fig. 2 is a graph showing focal voltage, and Figs. 3 to 6 show the positional relationship between the position of the focus lens and the focal voltage. 3 is a graph showing a relationship between a corresponding focal voltage and a reference voltage value. 1... Focus lens, 2... Pulse motor, 3
...Control circuit, 13...Timer. Fig. 2 Fig. 8 Fig. 4 and Fig. 5 Ekyotomi 1 Fig. 6 Renakumi

Claims (1)

[Claims] A predetermined high-frequency component of a video signal obtained by photographing a subject is extracted as a focus voltage, and focus is performed based on the result of comparing this focus voltage with a plurality of preset reference voltage values. In an autofocus method that performs focusing by moving the lens in the optical axis direction, if the focus voltage detected within a predetermined time from the start of focusing does not reach one of the reference voltage values, the direction of movement of the focus lens If the focus voltage does not reach the reference voltage value again within the predetermined time after the focus lens returns to the focusing position after reversing, the focus lens is returned to the focusing start position and focusing is completed. An autofocus system characterized by the following.