JPH07114463B2 - Auto focusing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an auto-focusing method used for various video cameras and the like, and is particularly capable of performing reliable and quick focusing.

(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 shooting a subject corresponds to the definition of the reproduced image, and the voltage of this high frequency component is used as the focal voltage. There is known an autofocus device which performs focusing such that the position of the lens is matched with the just focus position by driving the focus lens so that the focus voltage becomes the maximum level.

And, such a focusing system is known as a so-called hill climbing servo system, and this system is NHK Technical Research Report Sho. 40, Vol. 17, No. 1, Vol. 86, page 21, or Showa. It is explained in detail in the literature such as the Technical Report of the Television Society published in November 1957, ED No. 675.

(Problems to be Solved by the Invention) In the hill-climbing servo system as described above, the focus voltages at two points which are temporally (positionally) displaced from each other are sampled, and the levels are sequentially compared. The focus lens is moved in a predetermined direction by detecting the presence / absence of a focus shift and the direction of the just focus position according to the magnitude relationship of the focus voltage.

Therefore, when the amount of change in the focus voltage with respect to the lens movement amount is small, as in the case of shooting a low-contrast subject, or when the sampling range is too far from the just focus position, the level is set as described above. The difference value (difference voltage) level obtained by comparison is too small, and it takes time to detect the direction of the just focus position, and as a result, the hill climbing servo system as described above cannot be performed reliably and promptly. There is a point.

(Means for Solving Problems) The present invention has been made in view of the above-mentioned circumstances, and ensures reliable and quick focusing even when the amount of change in the focus voltage with respect to the amount of movement of the lens is small. It is an object of the present invention to provide an autofocusing method capable of

Then, in order to achieve this object, the present invention sequentially extracts a predetermined high frequency component of a video signal obtained by photographing an object as a focus voltage En for each predetermined period. It is an auto-focusing method in which a plurality of reference voltage values set in 3 are sequentially compared, and the focusing lens 1 is moved in the optical axis direction to perform focusing based on the comparison results. When the focus voltage En detected within the predetermined time t set by the control means 3 does not reach any reference voltage, the moving direction of the focus lens 1 is reversed to the focusing start position direction, and after the reverse rotation, The focus voltage does not reach the reference voltage value even when the focus lens 1 reaches the 2t position for a predetermined time beyond the focusing start position. In this case, the present invention provides an autofocusing method, characterized in that the focus lens 1 is returned to the focusing start position to end the focusing.

(Operation) According to the auto-focusing method as described above, if the focus voltage is within a detectable range, reliable and quick focusing can be performed regardless of the amount of change in the focus voltage with respect to the movement amount of the lens. it can.

(Embodiment) A preferred embodiment of the autofocusing method according to the present invention will be described in detail below with reference to FIGS. 1 to 6.

FIG. 1 is a block diagram showing the configuration of an autofocus device for realizing the autofocusing method according to the present invention. The autofocus device is composed of an afocal lens 5 and a focus lens (master lens) 1. The optical system 6 is provided.

Focusing is performed by moving the focus lens 1 in a predetermined direction (arrows A and B directions) in the optical axis direction by a pulse motor 2 which is a moving unit in the present embodiment. 1 is moved simultaneously with the start of focusing. The position of the focus lens 1 on the optical axis is detected by a rotary encoder provided in the pulse motor 2 and is used as position information S _{1 by the} control means. It is adapted to be supplied to a certain control circuit 3 (hereinafter referred to as control circuit 3).

Further, the imaging light from the subject that is incident through the optical system 6 as described above is the CCD that is the imaging means in this embodiment.
It is photoelectrically converted into an electric video signal S ₂ by the image pickup device 7 using a (charge coupled device) or the like.

Then, the video signal S ₂ is amplified by an amplifier 8 and supplied to a camera circuit (not shown) and the like, and is also supplied to a bandpass filter (BPF) 9. The bandpass filter 9 outputs the video signal S ₂ from the video signal S _2. A predetermined high frequency component is extracted and supplied to the automatic gain control circuit (AGC) 10.

Then, the automatic gain control circuit 10 supplies the high frequency component to the detector (DET) 11 after gain control, and the detector 11
At, the focus voltage E as shown in FIG. 2 corresponding to the predetermined high frequency component of the video signal S ₂ is detected.

Here, the focus voltage E corresponds to the definition of the reproduced image reproduced from the video signal S ₂ , and becomes maximum when the focus lens 1 is at the just focus position P.

The focus voltage E is the A / D (analog-digital) converter 1
It is digitized at 2 and supplied to the control circuit 3.

Then, the control circuit 3 sequentially samples the focus voltage E that accompanies the movement of the focus lens 1 in the optical axis direction every one field (every 1/60 seconds in the case of the NTSC system) from the start of focusing.

The control circuit 3 also includes a plurality of reference voltage values SEn that are the minimum detectable value Emin of the detector 11 or the like or an integer multiple (for example, an odd multiple) of a value that is a constant multiple of this minimum value Emin, and each reference voltage. A unique number (corresponding to n) is stored in the value SEn.

In addition, the control circuit 3 receives time data from the timer 13.
S ₄ is supplied.

The timer 13 is incremented by a clock pulse of a predetermined frequency at the same time when focusing is started, and the control circuit 3 controls the time data of the timer 13.
A predetermined time from the start of focusing is detected by S ₄ , that is, the count value of clock pulses.

The operation of the timer 13 is controlled by a timer control signal S ₅ supplied from the control circuit 3, and the content of the timer 13 is such that a predetermined time set in advance by the control circuit 3 has elapsed from the end of focusing and the start of focusing. It will be reset when you do.

The control circuit 3 then sequentially compares the levels of the reference voltage values SEn with the focus voltage E detected as described above,
When these match within the predetermined time defined by the time data S _4, only the number unique to the matched reference voltage value is read.

Here, the control circuit 3 stores the magnitude relation between the reference voltage values associated with the numbers unique to each reference voltage value, and the reference voltage value associated with the newly read number is read before that. If it is larger than the reference voltage value related to the number, it is determined that the focus lens 1 has not reached the just focus position P, and the control signal S ₃ for continuously moving the focus lens 1 is driven by the motor. circuit
Supply to 14.

On the other hand, the control circuit 3 fetches the position information S ₁ indicating the position ln of the focus lens 1 at this time when the focus voltage En at the same level as each reference voltage value SEn is detected.

In the present embodiment, the focus voltage is taken into the control circuit 3 as discrete information for each field. Therefore, in this embodiment, the captured value is the reference voltage value SE.
Assuming that the focus voltage En detected when n is first exceeded has reached the reference voltage value SEn, the focus voltage E at this time
n and the position information S ₁ are taken in.

In addition, in the autofocus device as described above, the first
As shown in FIG. 3, when the focus lens 1 is moved in the direction of arrow A in FIG.
Reference voltage value SEmax taken as having reached SEmax
If the unique number is detected twice in succession, the just focus position P is in the middle of these two detection positions.

Therefore, when the same number is read twice, if the focus lens 1 is moved to a position between the two detection positions X and Y, the focus lens 1 will be read.
The position of can be matched with the just focus position P.

Therefore, the control circuit 3 calculates, based on the position information S ₁ ,
In such a case, the focus lens 1 is moved in the opposite direction (first
By supplying a control signal S ₃ for returning a predetermined amount {(XY) / 2} in the direction of arrow B in the drawing) to the motor drive circuit 14, the pulse motor 2 is rotated in the opposite direction for focusing. Do.

Further, as shown in FIG. 4, when the number read as described above is at a level smaller than the number read previously, the detected position before that is the just focus position P. .

Therefore, in such a case, the focus lens 1
Can be made to coincide with the just focus position P by returning to the previous detection position.

Also in this case, as in the case described above, the control circuit 3
Supplies a control signal S ₃ for moving the focus lens 1 in the opposite direction based on the position information S ₁ to the motor drive circuit 14 for focusing.

As described above, according to the present 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 realized.

In this way, the autofocus device according to the present embodiment is
It is possible to read out a unique number for each reference voltage value SEn and continue moving the focus lens 1 based only on this number. Therefore, in the case where the differential voltage of each focus voltage is actually smaller than the detection limit value. Even if there is, reliable focusing can be performed.

On the other hand, as shown in FIG. 5, when the focus voltage E does not match any reference voltage value SEn within a predetermined time t from the start of focusing based on the time data S ₄ from the control circuit 3, That is, when the change amount of the focus voltage at the sampling position with respect to the level movement amount is small, the moving direction of the focus lens 1 is reversed when the predetermined time is reached.

Here, as shown in FIG. 5, the focus voltage En becomes less inclined as it moves away from the just focus position P. That is, since the amount of change with respect to the lens movement amount becomes small, when the focus lens 1 moves away from the just focus position P at a position away from the just focus position P, the focus voltage detected for each field. It takes a relatively long time for E to reach the reference voltage value SEn.

Generally, in a hill-climbing servo-type autofocus circuit used for a video camera or the like, when it is started and the descent is confirmed, it reverses to start hill climbing. That is, when the reference voltage value SEn is detected, it reverses and starts hill climbing.

Therefore, within the predetermined time t, the focus voltage E and the reference voltage value SE
If n does not match, there is a high possibility that the focus lens 1 is moving away from the just focus position P.

Therefore, in such a case, it is possible to reduce the useless time as much as possible by reversing the moving direction of the focus lens 1, so that the time required for focusing can be shortened.

When the focus voltage E detected within a predetermined time after the reversal coincides with 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.

Further, after the moving direction is reversed as described above, the focus voltage E remains at the reference voltage value SEn even within the time 2t which is twice the predetermined time.
May not match.

That is, there are cases where the focus lens 1 cannot be moved to the focusing position even when the focus lens 1 is reversed in the direction of the focusing start position and reaches the 2t position for a predetermined time beyond the focusing start position.

In such a case, as shown in FIG. 6, the subject has an extremely low contrast, and focusing is substantially unnecessary. Therefore, the focus lens 1 is returned to the focusing start position and the focusing is completed.

As described above, according to the present embodiment, the time required for focusing can be shortened by omitting the unnecessary time when photographing a low-contrast subject, etc., and thus quick focusing can be realized. .

In the present embodiment, a unique number is stored in each reference voltage value SEn, but each reference voltage value is stored in place of this number.
A code unique to SEn may be stored.

(Effect of the Invention) As is apparent from the above description, according to the present invention, if the focus voltage is within the detectable range, reliable focusing can be performed regardless of the level of the differential voltage, and the low contrast is achieved. It is possible to realize quick focusing when photographing the subject of.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the auto-focusing method according to the present invention, FIG. 2 is a graph showing a focus voltage, and FIGS. It is a graph which respectively shows the relationship between the corresponding focus voltage and a reference voltage value. 1 ... Focus lens, 2 ... Pulse motor, 3 ...
Control circuit, 13 ... Timer.

Claims (1)

[Claims] 1. A predetermined high-frequency component of a video signal obtained by photographing a subject is sequentially taken out as a focus voltage En for each predetermined period, and these focus voltages En and a plurality of preset preset voltage values are set by a control means 3. This is an autofocusing method of sequentially comparing with a reference voltage value and moving the focus lens 1 in the optical axis direction based on these comparison results to perform focusing, which is a predetermined value set by the control means 3 from the start of focusing. If the focus voltage En detected within the time t does not reach any of the reference voltages, the moving direction of the focus lens 1 is reversed to the focusing start position direction, and after reversing, the focus lens 1 starts the focusing. If the focus voltage does not reach the reference voltage value after reaching the 2t position for a predetermined time beyond the position, the focus lens An auto-focusing method, wherein 1 is returned to the focusing start position to end the focusing.