JPS63177105A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To increase the response speed of focusing operation and to reduce oscillating operation almost at a focusing point by controlling an optical system to the focusing point with a past focus signal, a current focus signal, and a predicted focus signal. CONSTITUTION:A mountain-climbing circuit predicts a future focus voltage from plural focus voltages of previous fields and the focus voltage of the current field and generates a driving signal for driving the driving motor 18 of a focusing lens 2 according to the predicted value. A monostable multivibrator (MM) 12 and a sample pulse generating circuit 13 receive a vertical synchronizing signal from a camera circuit 5 and generate sampling pulses at specific timing. Namely, the value of the focus voltage D of a future field (i+1) and/or the value of the focus voltage E of the field (i+2) right before it is predicted from a specific arithmetic expression (e.g. quadratic function for prediction) by using the focus voltage (focus signal) C of the current field (i) and the focus voltages of at least two precedent fields, and this predicted value is used to control the motor 18. Consequently, vibrations of the lens at the peak of a mountain are reduced or eliminated.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an automatic focusing device.

[Conventional technology]

In recent years, video cameras have been using the so-called mountain-climbing servo method (e.g. , NHK Technical Research, 1965, Vol. 17, No. 1, Volume 86, No. 21-37
An automatic focusing device is known. Specifically, in this mountain climbing method, the focusing lens drive motor is rotated in the direction in which the focus signal indicating the degree of focus increases, and then the motor is rotated in the same direction as if climbing a mountain until the focus signal begins to decrease. direction.

When the focus signal starts to decrease, reverse the motor.

By repeating this, the focusing lens will reach the in-focus point.

[Problem that the invention seeks to solve]

With conventional automatic focusing devices like this,
The focus signal of the current field and the previous field are compared, and the focusing lens is controlled in the direction where the focus signal becomes larger. Therefore, in order to know the in-focus point, the peak of the focus signal must be crossed once. Therefore, there is a considerable overrun state, and a slight deviation from the focused point or vibrations before and after the focused point are unavoidable. Furthermore, since the speed of the motor is controlled by one temporally immediately preceding focus signal, the timing of motor speed control tends to be delayed by one tempo, which is also a cause of large vibrations before and after the in-focus point.

In view of this problem, a method has been considered in which the amount of lens drive until reaching the peak value is calculated from a plurality of past focus signals, and the speed of the lens is controlled according to the amount of drive. If the peak is far away, the calculated drive amount is not necessarily accurate, and the focus may be incorrect, resulting in a lack of reliability.

The present invention therefore aims to eliminate these drawbacks and to present an automatic focusing device that reduces or eliminates lens vibrations on mountain tops.

Means for Solving Problem c] The automatic focusing device according to the present invention is an automatic focusing device that automatically controls an optical system to a focused point using a focus signal that takes an extreme value at a focused point, and holding means for holding the signal value;
゛ Prediction means for predicting one or more future focus signals according to a predetermined prediction formula from the current focus signal and the past focus signal from the holding means; and control means for controlling the system to a focused point.

[Effect]

Since the prediction means predicts the result of adjusting the optical system, control corresponding to the extreme value, that is, the focused focus, can be given to the optical system driving means even if the focus signal does not exceed the extreme value. As a result, the response speed of the focusing operation is increased, and the vibration operation near the in-focus point is alleviated or eliminated.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 6 is a schematic block diagram of a hill-climbing automatic focusing device to which the present invention is applied, and FIG. A block diagram of an embodiment of the circuit 16 is shown, and FIG. 2 is an explanatory diagram illustrating focal voltage values in successive fields.

In FIG. 6, light from a subject 1 passes through a focusing lens 2, forms an image on a photoelectric conversion means (for example, a CCD image sensor) 3, and is converted into an electrical signal. The output signal as a video signal outputted from the photoelectric conversion means 3 is applied to a processing circuit (hereinafter referred to as a camera circuit) 5 of a video camera via an amplifier 4, and is also applied to a bandpass filter (hereinafter referred to as a camera circuit) 5 for focus detection. BPF)6 is also applied. BPF
6 extracts high □ frequency components from the video signal, and gate circuit 7
send to

The window pulse forming circuit 8 receives the horizontal synchronizing signal HD and vertical synchronizing signal VD separated from the video signal from the camera circuit 5, and generates a window that cuts out a preset area (for example, the center of the screen) in one screen. form a signal. The gate circuit 7 allows only the human signal in the screen area designated by this window signal to pass through. Gate circuit 7
The output of is detected by a detection circuit (DET) 9, and the detection output is integrated by an integration circuit 10. The output voltage of the integrating circuit 10 represents the amplitude value of a high frequency component in a designated area within the screen, and is hereinafter referred to as a focal voltage. This focal voltage indicates the definition, that is, the contrast, of the shadow image, and as described above, takes the maximum peak value at the focal point and decreases before and after that.

The rising circuit 16 predicts the future focus voltage from the plurality of focus voltages of the previous field and the focus voltage of the current field, and forms a drive signal for driving the drive motor 18 of the focusing lens 2 according to the predicted value. . Mono multivibrator (MM) 12 and sample pulse forming circuit 1
3 receives the vertical synchronization signal VD from the camera circuit 5 and forms a sampling pulse at a predetermined timing.

In this embodiment, the focus voltage (focus signal) of the current field i
C and its smaller value (both are the focal voltage B of the two previous fields)
(Field 1-1) and A (Field 1-2), the value of the future focus voltage of field i+1 and/or the focus of the future field i+2 according to a predetermined calculation formula (for example, a prediction formula of a quadratic function). The value of voltage E is predicted and the remoter 18 is controlled based on this predicted value.

In FIG. 1, a sample and hold circuit 11 samples and holds the output of an integrating circuit 10 for each field using a sampling pulse from a sample pulse forming circuit 13. Reference numeral 19 denotes a circuit for correcting noise components of the focal voltage sample value C° from the sample-and-hold circuit 11. The correction circuit 19
-'l.

Given the predicted focal voltage D' of field i predicted from the focal voltage of i-1, the focal voltage C(=(αC.

+βD' ”)/2). However, α+β=1. On the output side of the correction circuit 19, a delay circuit 20 and a delay circuit 21 for one field are connected in cascade, and the delay circuit 20
outputs the focus voltage B of the previous field t-1, and the output of the delay circuit 21 outputs the focus voltage A of the field i-'l before the previous field. The prediction circuit 22 receives the focal voltage A, the focal voltage B, and the focal voltage C, and calculates the focal voltage E of the next field i+1 and the focal voltage E of the next field i+2 based on a known calculation formula, for example, a prediction formula of a quadratic function. Form.

This function of the prediction circuit 22 can be easily implemented using a commercially available microprocessor.

The predicted focus voltage of the prediction circuit 22 is applied to the correction circuit 19 via the delay circuit 27 for one field, and is used for correction by the correction circuit 19. Due to the delay circuit 27, the two input voltages of the correction circuit 19 should have the same or close values.

The top determination circuit 23 determines whether or not the next field i+l will be in focus based on the focus voltage C of the current field i and the predicted focus voltage E, and if it is determined that the next field will be in focus, it will issue a motor stop signal. is sent to the motor drive circuit 26. The predicted focus voltage is greater than the current focus voltage C and the predicted focus voltage E
If it is larger than , the next field i+l is in focus, and the motor 18 is already rotating toward the state of field i+l, so a motor stop signal is issued at this point.

A specific circuit example of this summit determination circuit 23 is shown in FIG.
A comparator circuit 27 compares the predicted focus voltage E and the predicted focus voltage, and a comparison circuit 2 compares the predicted focus voltage and the current focus voltage C. Then, the AND circuit 29 outputs a motor stop signal when D is thicker than C (and larger than E).

The motor direction determination circuit 24 receives the focus voltage B of the previous field i-1, the focus voltage C of the current field i, and the predicted focus voltage of the next field i+l, and determines the direction in which the motor 18 should be rotated. That is, focal voltage B; C, D
For example, when B<C<D, the motor 18 is rotated in the normal direction, and when B>C>D, the motor 18 is rotated in the reverse direction. A specific circuit example of the motor direction determination circuit 24 is shown in FIG. 4. In FIG. 4, the comparison circuit 30 outputs an H signal when B>C, and the comparison circuit 31 outputs an H signal when C>D. Therefore, the AND circuit 34 outputs an H signal when B>COD. Further, the comparison circuit 32 outputs an H signal when B<C, and the comparison circuit 33 outputs an H signal when C<D.
Therefore, the AND circuit 35 outputs an H signal when B<C<D. NAND circuit 36 and 37
constitutes a flip-flop. AND circuit 34 and same 3
Since the outputs of 5 do not become H at the same time, the NAND circuit 36 outputs H when the output of the AND circuit 35 is H.
Therefore, when the output of the AND circuit 34 is H, the output becomes L. This output of the NAND circuit 36 becomes the motor direction signal.

The motor speed determination circuit 25 determines the focal voltage B of the previous field i-1, the focal voltage C of the current field i, and the next field.
A signal indicating the rotational speed of the motor 18 is generated in response to the focal voltage of i+l. That is, when the difference D-C is larger than the difference C-B, since the focal voltage curve is convex downward, it can be determined that the peak is far away, and the rotational speed of the motor 18 is increased. On the other hand, when the difference D-C is smaller than C-B, the focal voltage curve is upwardly convex, so it can be determined that the peak is near, and the rotational speed of the motor 18 is reduced.

A specific example of this motor speed determination circuit 25 is shown in FIG.
In FIG. 5, the subtraction circuit 38 calculates C-B, the subtraction circuit 39 calculates D-C, and the comparison circuit 40 calculates C-B.
8 and the output of the subtraction circuit 39 are compared. The output of the comparison circuit 40 is converted to one of two values by an inverter 41 and becomes a motor speed signal.

That is, if the output of the comparison circuit 40 is positive or zero (D-C≧C-B)
When , the output of the inverter 41 becomes L, and the comparator circuit 40
When the output of inverter 41 is negative (DC<C-8), the output of inverter 41 becomes H. The motor drive circuit 26 rotates the motor 18 at high speed when this motor speed signal is L, and
Rotate at low speed when .

Next, the operation of the circuit shown in FIG. 1 will be explained. The sample-and-hold circuit 11 outputs a hold value C' of the focal voltage for each field. The correction circuit 19 has this sample
In addition to the focal voltage from the hold circuit 11, the delay circuit 27
The predicted focal voltage D' of field i predicted using the focal voltage of fields i-3゜i-2, i-1 is also input, and the correction circuit 19 calculates C=C= for appropriate α and β. The focal voltage C' of the current field i is corrected by αC'+βD, where α+β=1.

Since C' has a value different from the original output value due to noise, a predetermined weight is applied to correct the noise.

This eliminates the occurrence of errors, abnormalities, or delays in focusing operations due to noise while climbing a mountain. In addition, correction circuit 1
The correction calculation in 9 is not limited to the above example, and may be other calculations.

The prediction circuit 22 receives the output C of the correction circuit 19 and the delay circuit 2.
From the outputs A and B of 0.21, the focal voltage of the next field i+1 and the successive field i+2 is calculated based on the quadratic function, E
Predict. The peak determination circuit 23 determines whether or not the focal voltage reaches its peak as described above from the current value C and the predicted value E, and if it reaches the peak, sends a motor stop signal to the motor drive circuit 26. The motor direction determination circuit 24 sends a direction signal indicating the rotation direction of the motor 18 to the motor drive circuit 26, and the motor speed determination circuit 25 sends a direction signal indicating the rotation direction of the motor 18.
A speed signal indicating the rotational speed of the motor is sent to the motor drive circuit 26. Motor drive circuit 26 controls motor 18 according to these signals.

In the illustrated example, the past focal voltage is held by the one-field delay circuit 20.21, but the analog value (or
/digital value after D conversion), and performs sampling/
BBD or CCD elements may be used that respond to sampling pulses from pulse forming circuit 13 and transfer them to adjacent cells.

Furthermore, the output of the motor speed determination circuit 25 may be applied to the prediction circuit 22 so that the motor speed, that is, the sampling interval of the focal signal may be taken into consideration during prediction.This function and the above-mentioned functions of the prediction circuit 22 may be , which can be easily achieved by numerical operations on a microprocessor. In the illustrated example, three focus voltages are input to the prediction circuit 22 and the focus voltages of the next field and the field after that are predicted using a quadratic equation. More precise predictions may be made using polynomials.

In the above explanation, focus detection using high frequency components of a video signal in a video camera was taken as an example. The present invention can be similarly used for other photographic devices such as eye reflex cameras and electronic still cameras as long as they can obtain signals. Further, the output of the top determination circuit may be used to switch to another focus detection method with higher focus detection accuracy. In this embodiment, both motor speed control and summit determination are performed, but it goes without saying that one of them may be performed using another method.

〔Effect of the invention〕

As can be easily understood from the above explanation, according to the present invention, since the future focus signal is predicted, there is no time lag in controlling the focusing drive means, and there is no time lag in the control of the focusing drive means. Unnatural movements caused by noise are also eliminated.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of an example of the focus judgment/control part which is the main part of the automatic focusing device according to the present invention, and FIG.
The operation explanatory diagrams of the circuit shown in the figure, FIG. 3, FIG. 4, and FIG. 5 are as follows:
A diagram showing a specific example of the partial circuit in FIG. 1, and FIG. 6 shows a basic configuration block diagram of an automatic focusing device to which the present invention is applied. 1-*Subject 2--Focusing lens 3-
Image sensor 4.-Amplifier 5.-Camera circuit 6.-Band pass filter 7.-Gate circuit 8.--Window circuit 9.-Detection circuit io-Integrator circuit 11.-
・Sample/hold circuit 12・−・Mono multivibrator 13−・Sample/pulse forming circuit 16・
- Mountain climbing circuit 18 - Motor 19 - Correction circuit 20
．． 21--Delay circuit 22--Prediction circuit 23--Top determination circuit 24--Motor direction determination circuit 25-Motor speed determination circuit 26--Motor drive circuit 27.2
8... Comparison circuit 20.21... Delay circuit 29-
・AND circuit 30.31.32.33・-・Comparison circuit 34.35・−・AND circuit 36°37・−N A
ND circuit 38.39 - Subtraction circuit 40 - Comparison circuit 41 - Inverter Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5

Claims (2)

[Claims] (1) An automatic focusing device that automatically controls an optical system to a focused point using a focus signal that takes an extreme value at the focused point, and includes a holding means for holding a past focus signal value, and a current focus signal and the holding means. prediction means for predicting one or more future focus signals according to a predetermined prediction formula from past focus signals from the past focus signals;
An automatic focusing device comprising: control means for controlling an optical system to a focused point using a current focus signal and a predicted focus signal. (2) The automatic focusing device according to claim (1), further comprising a correction means for correcting a current focus signal with a previously predicted focus signal at a corresponding time point.