JPH04280173A - Automatic focus adjusting device - Google Patents

Abstract

PURPOSE:To attain always stable automatic focus detection under any condition with immunity to the effect of external disturbance such as hand blur by providing a prescribed motor stop period when a large fog is discriminated in the vicinity of focus. CONSTITUTION:This device is provided with a modulation means 6 changing periodically the image forming state at a light receiving face of an image pickup means 2, a detection means detecting a signal in response to a focus from the image pickup signal outputted from the image pickup means 2, an extract means 10 extracting a reply signal E6 of the modulation means 6 from an output of the detection means, an output means outputting a stop signal SOFF for a prescribed period, a selection means 19 selecting either the extract means, the detection means or the output means, and driving means 15, 16 driving a focusing lens 1 of an optical system to the focus based on the signal selected by the selection means 19.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focus adjustment device suitable for use in video cameras and the like.

[Background technology] In recent years, automatic focus detection devices (hereinafter referred to as AF) have become essential for imaging devices such as video cameras. An automatic focus detection method that extracts and evaluates a signal according to sharpness and performs a focus detection operation of an optical system is attracting attention.

There are various types of this type of AF system, but first, the basic circuit configuration of an AF device to which the present invention can be applied will be explained with reference to FIG. A subject image is formed by a focusing lens 1, formed on an imaging surface of an imaging device 2 such as a CCD, and photoelectrically converted into a video signal. The image sensor 2 is periodically vibrated in the optical axis direction by an image sensor drive circuit 6 driven at the timing of a reference clock generated by a timing generation circuit 5, causing a slight change (wobbling) in the imaging state. The video signal photoelectrically converted by the image sensor 2 is amplified by the preamplifier 3, and subjected to predetermined processing such as γ correction, blanking processing, and addition of a synchronization signal in the process circuit 4, and converted into a standardized standard video signal. At the same time, the signal is input to the bandpass filter 7. A bandpass filter 7 extracts a high frequency component that changes depending on the in-focus state of the video signal, that is, sharpness, and then a gate 8 extracts a signal corresponding to a focus detection area set at a predetermined position on the screen. Only the signal S0 is passed through, rectified by the peak detection circuit 9, held at its peak, and outputted as a signal S0. Then, the synchronous detection circuit 10 performs synchronous detection at the timing of the reference clock generated by the timing generation circuit 5, thereby obtaining a signal S1 representing the in-focus state in response to minute wobbling in the optical axis direction of the image sensor 2. . In addition, the peak detection circuit 9 output,
S0 is delayed by 1V (V is a vertical synchronization period) in a 1V delay circuit 11, and compared with S0 in a comparator circuit 12 to generate a signal S that determines whether you are currently climbing or descending a mountain.
1 is obtained. Furthermore, the signal S0 is also input to the mode determination comparator 13, and when the value of the signal S0 is larger than the threshold value VH, the switch 14 is switched to the signal S1 side, and the signal S1 in response to wobbling is sent to the motor driver 15. By applying this voltage and driving the motor 16 to move the focusing lens 1, automatic focusing operation in a closed loop mode is performed. On the other hand, when the signal S0 is smaller than VH, the switch 14 is also switched to the mountain climbing signal S2 side, and the motor driver 15
Automatic focusing is performed in mountain climbing mode without using wobbling.

Next, the automatic focus adjustment operation will be further explained using FIG. 6. FIG. 6A shows the output level S0 of the peak detection circuit 9 with respect to the position of the focusing lens 1 when in focus/out of focus. When the focusing lens position is closer than the in-focus point, a response signal AN to the wobbling of the image sensor is detected. Further, when the focusing lens position is located on the far side than the in-focus point, a response signal AF to wobbling of the image sensor is detected. At the time of focus, a response signal AM is detected. Since the phase is opposite when the lens is on the near-distance side and on the long-distance side, front focus and rear focus information can be obtained. When these signals are synchronously detected using the reference timing of the output of the timing generation circuit 5, a signal S1 shown in FIG. 6(b) is obtained. In other words, the AN at close range is in phase with the reference timing, so a positive signal is output as the synchronous detection output S1, and the AF at long distance is in reverse phase with the reference timing, so a negative signal is output as the synchronous detection output S1. be done. Further, when in focus, the signal S1 becomes approximately 0 level. Therefore, this signal S1
By inputting this into the motor drive circuit 15, the motor 16 can be driven. The above is an explanation of the motor driver input in closed loop mode. However, the signal S1 has a drawback; when the signal becomes very blurred, S0 in FIG. 6(a) becomes small, and the output of S1 in FIG. 6(b) also becomes small, resulting in a slow motor speed. Therefore, S0 is V
When the voltage is lower than H, S1 is not used, but a comparison signal S2 compared with S0 1V earlier as shown in FIG. 6(c) is used. This signal S2 is a comparator output, so it has a constant value and has only the sign that should drive the lens. The above is mountain climbing mode. The motor drive circuit 15 operates the motor from a short distance to a long distance when a positive signal is input, and from a long distance to a short distance when a negative signal is input, proportional to the absolute level of the signals S1 and S2. to move the focusing lens at the same speed. Therefore, when the focusing lens is out of focus, it moves rapidly toward the in-focus point at a speed of S2, and when it approaches the in-focus point, it converges at a speed of S1 to the in-focus point where S1 becomes zero, thereby performing automatic focus adjustment. It will be done.

[0005]

[Problem to be Solved by the Invention] However, according to the above example, it is possible to switch between the closed-loop mode that uses the response of the modulation signal and the so-called mountain climbing mode that does not use the response of the modulation signal using only the level of the bandpass filter output. Because of this, when the bandpass filter output S0 generally decreases due to camera shake, etc., the camera accidentally enters mountain climbing mode, even though it should have stayed close to focus and remained in closed loop mode. , on the other hand, it moves away from the focal point, resulting in blurring.

[0006]

[Means for Solving the Problems] The present invention has been made for the purpose of solving the above-mentioned problems, and is characterized by periodically changing the imaging state on the light receiving surface of the imaging means. a modulation means, a detection means for detecting a signal according to the degree of focus from among the imaging signals output from the imaging means, an extraction means for extracting a response signal of the modulation means from the output of the detection means, and a fixed time period. output means for outputting a stop signal; selection means for selecting one of the extraction means, the detection means, and the output means; An object of the present invention is to provide an automatic focusing device equipped with a driving means for driving the object.

Another feature of the present invention is that the first detection means detects a signal corresponding to the degree of focus from among the image pickup signals output from the image pickup means, and the first detection means detects that the focus point is near. a second detection means; a focus adjustment means for performing focus adjustment according to the output of the first detection means; The automatic focus adjustment device further comprises a control means for outputting a stop signal for a certain period of time to the focus adjustment means when the output of the first detection means changes by a predetermined amount of change or more.

[0008]

[Operation] As a result, the drive control of the focus adjustment motor can be performed optimally using the response signal of the modulation means without being affected by temporary camera shake or disturbances such as noise, regardless of the shooting conditions. Good automatic focus detection operation can be achieved under all conditions.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of an automatic focus adjustment device according to the present invention will be described in detail with reference to the respective figures.

FIG. 1 is a block diagram showing the configuration of an embodiment of an automatic focus detection device according to the present invention. Note that the structures indicated by reference numerals 1 to 12 and 14 to 16 have the same structure and operate in the same manner as those shown in FIG.

The image signal output from the preamplifier 3 is
The signal is input to the edge width detection circuit 17 at the same time as it is input to the band pass filter 7 . In the edge width detection circuit,
It outputs an electrical signal (edge width signal) proportional to the width of the edge portion of the subject image (large when it is blurred and smallest when it is in focus). This edge width signal is transmitted to the synchronous detection circuit 10.
The signal E6 is inputted into the mode determination circuit 18 at the same time as a signal E6 representing the in-focus state in response to minute wobbling in the optical axis direction of the image sensor 2 is obtained. The mode determination circuit generates a switching signal for the switch 19 based on the input object edge width signal.The switch 19 generates signals E6 and S1 and a signal SOFF for stopping the motor.
An automatic focus detection operation is performed by selecting one of them and applying it to the motor driver.

The edge width signal is used here simply because the high frequency components extracted by a band pass filter etc.
Although it changes greatly depending on contrast and brightness, this edge width signal is a signal normalized to the brightness level, so it is less affected by brightness and contrast, and changes only depending on the degree of focus. This is because the purpose is to use this signal to reliably distinguish between the vicinity of the in-focus point and the state of large blur.

Next, the operation of the edge width detection circuit 17 will be explained using FIGS. 2 and 3. FIG. 3 shows the internal configuration of the edge width detection circuit 17. A signal E0 input to the edge width detection circuit 17 is differentiated by a differentiation circuit 21 and outputs a differential signal E1. This differential signal E1 is converted to an absolute value by an absolute value circuit 22, and a gate circuit 23 extracts only the signal corresponding to the focus detection area on the screen. This signal is
It is integrated by an integrator 24 over a certain specific width, and becomes the denominator input to a divider 25. Also, the output signal of the gate 23 is the divider 2
This becomes the numerator input of 5. Then, the output of the divider 25 is peak held in a peak hold circuit 26 in order to obtain the maximum value, thereby obtaining the edge width. That is, for each integration period of the integrator 24, a peak value obtained by dividing the peak value of that period by the integrator output is held. FIG. 3 is a diagram showing signals E0 to E4 for in-focus edges and out-of-focus edges having different contrasts. (b-1)
-(f-1) are in-focus edges, and (b-2) to (f-2) are out-of-focus edges. As can be seen from this figure, the final output E4 represents the width of the edge (that is, the degree of focus) without depending on the contrast.

Next, using FIG. 4, the mode determination circuit 18
The operation of the device will be explained with a focus on

[0015] When the flow starts in the same figure, first, in step 1, it is determined whether or not the object is in focus.
If it is in focus, the process proceeds to step 8, where the focusing lens is held in a stopped state, and then, in step 9, a restart determination is made.

[0016] If the focus is not in step 1,
Proceeding to step 2, the mode determination circuit 18 first compares the input edge width signal E5 with a predetermined threshold VE, and if E5 is greater than VE, the switch 19 selects the signal E6. Output (step
3) It is determined that the focal point is relatively close, and the closed loop mode using the wobbling response is set, the focusing lens is driven in step 4, and the process returns to the focus determination process in step 1. As a result, it is possible to perform a focus adjustment operation with high precision near the in-focus point.

In step 2, if E5 is less than or equal to VE, the process proceeds to step 5, where it is determined whether a predetermined period of time has elapsed. Until a certain period of time has elapsed, go to step 7, output a signal for selecting the signal SOFF with the switch 19, and then
Drive the focusing lens with ep4. Therefore, during this period, neither the signal related to the wobbling response nor the difference signal of the level of the high frequency component output from the comparator circuit 12 is supplied to the driver 15, and the focusing lens is stopped.

Further, in step 5, after a certain period of time has elapsed, the process proceeds to step 6, and outputs a signal for switching the switch 19 to select the difference signal S2 of the peak value of the level of the high frequency component output from the comparator circuit 12. ,
Proceed to step 4 and drive the focusing lens. Therefore, the focusing lens is driven by a focus detection operation that does not use a wobbling response.

Due to these operations, even if the edge signal E5 of the subject temporarily decreases due to camera shake, etc., the automatic focus adjustment operation is stable without immediately shifting from the closed loop mode to the mountain climbing mode for searching. can be done.

In this way, by using edge width signals that are not easily affected by contrast, brightness, etc., it is possible to accurately switch the automatic focus adjustment mode between when the subject is out of focus and when it is close to being in focus, and the state of the subject is always monitored. Good principal point adjustment operation can be performed regardless of the situation.

[0021]

As explained above, according to the automatic focus adjustment device of the present invention, the image sensor is modulated at a predetermined timing, a signal corresponding to the degree of focus is extracted from the image signal, and Now, in an automatic focusing device that drives the focusing lens based on the modulation response signal and the focusing degree signal when there is a large blur, a fixed motor stop period is set when it is determined that there is a large blur in the vicinity of focus. This has the effect that automatic focus detection can always be performed stably under all conditions without being affected by disturbances such as camera shake.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of an automatic focus adjustment device according to the present invention.

FIG. 2 is a configuration diagram of an edge width detection circuit in the present invention.

FIG. 3 is a diagram for explaining the operation of the edge width detection circuit in the present invention.

FIG. 4 is a flowchart for explaining mode switching in the present invention.

FIG. 5 is a configuration diagram of an automatic focusing device that is a premise for applying the present invention.

FIG. 6 is a diagram for explaining the operation of the device shown in FIG. 5;

Claims (2)

[Claims] 1. Modulating means for periodically changing the imaging state on the light receiving surface of the imaging means; detection means for detecting a signal according to the degree of focus from among the imaging signals output from the imaging means; extraction means for extracting a response signal of the modulation means from the output of the detection means; output means for outputting a stop signal for a certain period of time; and selection means for selecting one of the extraction means, the detection means, and the output means. . An automatic focusing device comprising: a driving means for driving a focusing lens of an optical system to a focused point based on a signal selected by the selecting means. 2. A first detection means for detecting a signal according to the degree of focus from among the image pickup signals output from the image pickup means, and a second detection means for detecting that the focus is near the focus point.
In a state where the focus adjustment means adjusts the focus according to the output of the first detection means and the second detection means detects that the focus is near, the output of the first detection means is An automatic focus adjustment device comprising: control means for outputting a stop signal for a certain period of time to the focus adjustment means when the change amount exceeds a predetermined amount.