JP2003215439A - Focus detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a focus detector which restarts the driving of a lens in a close-range direction when a focus evaluated value is decreased after stopping the driving of the lens. <P>SOLUTION: An AF digital camera is provided with a photographic lens 1, a solid-state image pickup element 2, an A/D converter 3, a memory 4, an image processing circuit 5, an external recording circuit 6, a control circuit 8, a motor 13, a focus control mechanism 14 and a CPU 12. The CPU 12 divides the driving mode of a focus lens to a scanning mode, a restarting mode and a hill-climbing mode, and the relation of respective driving amounts is set to Ms≥Mr≥Mm. In the scanning mode, the focus lens is driven from a long distance side to the close-range side in a fixed direction. In the restarting mode, the driving of the focus lens focused and stopped is restarted to search a new focusing position. In the climbing mode, the driving direction of the focus lens is decided according to the change of the focus evaluated value. The CPU 12 sets the lens driving direction to the close-range side in the scanning mode and the restarting mode. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus detection device for a camera.

[0002]

2. Description of the Related Art There is known a focus detecting device for picking up an image of a subject using an image pickup device such as a CCD and detecting an adjustment state of a focus position by a photographing lens based on an image pickup signal output from the image pickup device. Among them, the focus detection method called the hill climbing method is designed to maximize the data of the high frequency component of the frequency of the image pickup signal, that is, the focus evaluation value while moving the taking lens forward and backward with respect to the in-focus position in the optical axis direction. The focus position is detected. In the mountain climbing method, since the photographing lens is always driven, the followability with respect to the movement of the subject is improved, but a lot of power is consumed for driving the lens. Therefore, when the focus evaluation value becomes equal to or higher than a predetermined value, it is considered to be in focus and the driving of the taking lens is stopped once, and when the focus evaluation value is lower than the predetermined value, the driving of the taking lens is restarted.

[0003]

When the driving of the taking lens is restarted, it is not known whether the focus evaluation value has decreased due to the subject approaching the camera or the focus evaluation value has decreased due to the subject moving away from the camera. Generally, the following two situations can be considered as situations in which the lens drive is restarted after focusing. 1. When a focused subject moves 2. When the camera is panned by another subject In the case of 1 above, the subject often approaches the camera,
In the case of 2, the closest subject is likely to be the main subject. Therefore, when the lens driving is restarted, it is possible to avoid unnecessary lens driving when the lens driving direction is set to the close side.

An object of the present invention is to provide a focus detection device in which the driving direction is set to the close side when the lens driving is restarted.

[0005]

A focus detection apparatus according to the present invention comprises an image pickup device for picking up a subject image through a taking lens, and an evaluation value calculation circuit for calculating a focus evaluation value using an image pickup signal output from the image pickup device. And a drive signal output circuit that outputs a drive signal for driving the photographing lens to the close-up side and the long-distance side so that the focus evaluation value calculated by the evaluation value calculation circuit is maximized, and is calculated by the evaluation value calculation circuit. And a control circuit that controls the drive signal output circuit to stop the output of the drive signal to the photographing lens according to the focus evaluation value and restart the output of the drive signal to the photographing lens from the direction of driving the photographing lens to the close side. By providing, the above-mentioned object is achieved. The control circuit may control the drive signal output circuit so as to switch and output the two types of drive signals according to a change in the focus evaluation value calculated by the evaluation value calculation circuit. The control circuit outputs (1) a drive signal for driving the photographing lens at the first drive speed when the focus evaluation value calculated in the past by the evaluation value calculation circuit monotonously decreases, and (2) the evaluation value. Controlling the drive signal output circuit so as to output a drive signal for driving the photographing lens at a second drive speed higher than the first drive speed when the focus evaluation value calculated by the arithmetic circuit decreases by a predetermined value or more. You can also The control circuit may restart the output of the drive signal to the photographing lens when the focus evaluation value calculated in the past by the evaluation value calculation circuit monotonously decreases.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an AF (autofocus) digital camera according to an embodiment of the present invention. In FIG. 1, the digital camera includes a taking lens 1, a solid-state image sensor 2, an A / D converter 3, a memory 4, an image processing circuit 5, an external recording circuit 6, and an AE.
/ AWB processing circuit 7, control circuit 8, bandpass filter 9, integrating circuit 10, AF arithmetic circuit 11
, A motor 13, and a focus control mechanism 14. Among these, the AE / AWB processing circuit 7, the bandpass filter 9, the integrating circuit 10, and the AF arithmetic circuit 11
Are configured in the CPU 12.

The taking lens 1 includes a focus lens (not shown) for adjusting the focus position so that the subject image passing through the lens is formed on the image pickup surface of the solid-state image pickup device 2. The solid-state image sensor 2 is, for example, a CCD, and accumulates a signal charge for each pixel according to the intensity of light of a subject image formed on the imaging surface. A timing signal is supplied from the control circuit 8 to the solid-state image sensor 2. The signal charge accumulated in the solid-state image pickup device 2 is swept out by the timing signal and sent to the A / D converter 3 as an image pickup signal. Note that the solid-state image sensor 2 is a MOS instead of a CCD.
You may comprise using a sensor, CID, etc.

The A / D converter 3 converts an analog signal into a digital signal and outputs the converted image data to the memory 4. The image data is temporarily stored in the memory 4 and then output to the image processing circuit 5. The image processing circuit 5 includes a signal processing circuit such as a gain control circuit, an AE integration circuit, a luminance signal generation circuit, and a color difference signal generation circuit. The image processing circuit 5 performs image processing such as contour compensation and gamma correction on the digitally converted image data. Image processing circuit 5
Further, the image data subjected to the image processing is data-compressed in a predetermined compression format (for example, JPEG method) and output to the external recording circuit 6. The external recording circuit 6 records and reads the compressed data on an external storage medium (not shown) such as a CF memory card that is attached to and detached from the digital camera. The image processing circuit 5 also performs decompression processing when reading and decompressing the compressed data recorded in the external storage medium.

The control circuit 8 generates and sends a timing signal to the solid-state image pickup device 2. The CPU 12 is connected to the control circuit 8, the image processing circuit 5, the memory 4, etc., and is used for focus detection (AF) and photometry (A) of the digital camera.
E), various calculations such as white balance adjustment (AWB), and sequence control of camera operation are performed. Various operation signals are input to the CPU 12 from a release switch (not shown) or the like.

The focus detection processing performed by the above digital camera will be described. The image pickup signal output corresponding to each pixel of the solid-state image pickup device 2 has a different signal level according to the intensity of light incident on each pixel. CPU12
Of the image data output from the solid-state imaging device 2 and stored in the memory 4 described above reads out the data for focus detection from the memory 4 by designating a predetermined address where the data is stored. A high-frequency component is extracted from the focus detection data read from the memory 4, and a focus evaluation value is calculated. Specifically, the focus detection data is passed through a bandpass filter 9 to extract a desired frequency component contained in the image data, and the absolute value of the extracted signal is integrated by an integrating circuit 10 to obtain a focus evaluation value. .

FIG. 2 is a diagram showing an example of the relationship between the position of a focus lens (not shown) in the taking lens 1 and the focus evaluation value. In FIG. 2, the horizontal axis is the position of the focus lens, and the vertical axis is the focus evaluation value. The lens position D1 that maximizes the focus evaluation value is the focus position of the focus lens with respect to the main subject.

The AF calculation circuit 11 focuses so as to maximize the calculated focus evaluation value, that is, to maximize the contrast by eliminating the blurring of the edge of the subject image captured by the solid-state image sensor 2. The lens drive signal is output to the motor 13. When the motor 13 rotates, the focus control mechanism 14 moves the focus lens forward and backward in the optical axis direction. The AF calculation circuit 11 drives the focus lens in the direction of ∞ (far distance) when the focus lens is driven in the closest direction of FIG. 2 and the focus evaluation value decreases. Further, the AF calculation circuit 11 drives the focus lens in the close-up direction when the focus evaluation value decreases by driving the focus lens in the ∞ direction. That is, the focus lens is alternately driven in the close-up direction and the ∞ direction with the position (focus position D1) at which the focus evaluation value is maximized.

The focus detection processing by the focus detection device of the AF digital camera described above is called a hill climbing method. In the hill-climbing focus detection process, a focus evaluation value is repeatedly calculated from image data repeatedly captured by the solid-state image sensor 2. The AF camera maximizes the focus evaluation value when the newly calculated focus evaluation value has not changed from the previously calculated focus evaluation value (strictly speaking, when the amount of change is less than the predetermined value). The drive of the focus lens is stopped within a predetermined range from the in-focus position.

The AF camera restarts the drive of the focus lens when the focus evaluation value changes while the drive of the focus lens is stopped. The present invention is such that, when the drive of the focus lens stopped in the hill climbing focus detection process is restarted, the drive direction of the focus lens is set to the close side.

CPU 12 of the AF digital camera described above
The AF processing performed in step 3 will be described with reference to the flowchart in FIG. The process shown in FIG. 3 is started when the main switch (not shown) of the camera is powered on. In step # 1, the CPU 12 initializes data and flags required for AF processing,
Go to 2. At this time, the CPU 12 sets the lens driving mode to the scan mode. The scan mode is a mode in which the focus lens is driven in a fixed direction from, for example, the ∞ (far distance) side to the close side. It is suitable for driving the focus lens at high speed up to the position where the focus evaluation value changes.

In step # 2, the CPU 12 calculates the focus evaluation value VF _val from the image data for focus detection stored in the memory 4, and proceeds to step # 3. In step # 3, the CPU 12 acquires the position of the focus lens. The position of the focus lens is acquired by inputting information indicating the lens position from the focus control mechanism 14. The CPU 12 acquires the average LPav of the position of the focus lens when the image data used in the calculation of step # 2 is accumulated in the solid-state image sensor 2 and the current position LP of the focus lens, and then acquires step # 4. Go to.

In step # 4, the CPU 12 performs a process for determining the lens drive mode, and proceeds to step # 5. In addition to the scan mode described above, the lens drive mode includes a hill climbing mode and a restart mode. The mountain climbing mode is a mode in which the driving direction of the focus lens is determined according to the change in the focus evaluation value. The focus lens is moved to a position close to the in-focus position, and the focus evaluation value changes due to the movement of the focus lens. The restart mode is a mode in which the drive of the focus lens stopped after focusing is restarted to search for a new focus position.
Details of the process for determining the lens drive mode will be described later.

In step # 5, the CPU 12 makes a focus determination and proceeds to step # 6. The focus determination is performed based on the calculated focus evaluation value VF _val , the amount of change in the focus evaluation value VF _val compared to the previously calculated focus evaluation value, the current focus lens position LP, and the like.

In step # 6, the CPU 12 performs a process of determining the drive amount M and drive direction of the focus lens, and proceeds to step # 7. Details of the process for determining the driving amount M and the driving direction of the lens will be described later.
In step # 7, the CPU 12 outputs a focus lens drive instruction to the motor 13 so as to drive the focus lens in the drive amount M and the drive direction determined in step # 6, and returns to step # 2. As a result, the focus lens is driven in the instructed drive direction with the instructed drive amount M.

In the process shown in FIG. 3, the focus evaluation value VF _val is calculated from the image data for focus detection (step #
The lens drive mode (step # 4), the lens drive amount M and the drive direction (step # 6) are determined for each 2), and the focus lens is driven with the determined drive amount M and drive direction (step # 7). The operation is repeated. The lens driving amount M is the amount by which the focus lens is driven by one driving instruction to the motor 13. That is, the focus lens moves back and forth in the optical axis direction by repeating the step driving with the driving amount M.
The moving speed of the focus lens is increased or decreased by changing the driving amount M per step driving.

FIG. 4 is a flow chart for explaining the flow of processing for determining the lens drive mode. Step # 1
At 01, the CPU 12 determines whether or not focusing is stopped. The CPU 12 makes an affirmative decision in step # 101 if the focus lens drive is stopped and the focus lens drive is stopped, and proceeds to step # 105, and makes a negative decision in step # 101 if the focus lens drive is not stopped. And proceeds to step # 102. The drive stop of the focus lens is determined to be stopped when the focus stop flag is set to 1, and is driven when the focus stop flag is set to 0. The focus stop flag when the process of FIG. 3 is started is set to the initial value 0.

In step # 102, the CPU 12
Determines whether the currently set lens drive mode is the hill climbing mode. The CPU 12 proceeds to step # 10 when the lens drive mode is set to the mountain climbing mode.
Affirmative determination is made for 2, the process of FIG. 4 is terminated, and the process proceeds to step # 5 of FIG. In this case, the mountain climbing mode is continued. On the other hand, when the lens driving mode is not set to the mountain climbing mode, the CPU 12 makes a negative determination in step # 102, and proceeds to step # 103.

In step # 103, the CPU 12
Determines whether the focus evaluation value VF _val is greater than or equal to a predetermined value CL _{t h1} . If VF _val ≧ CL _th1 is established, the CPU 12 makes an affirmative decision in step # 103 to determine in step # 104.
Go to. In this case, since it is assumed that the focus evaluation value changes due to the movement of the focus lens, the mountain climbing mode is suitable. On the other hand, the CPU 12
_{If val} ≧ CL _th1 is not established, a negative decision is made in step # 103, the processing in FIG. 4 is terminated, and step # 103 in FIG.
Go to 5. In this case, since the focus evaluation value VF _val is small, the focus evaluation value VF _val is small and is easily affected by noise, and the drive direction of the focus lens may be erroneously determined in the mountain climbing mode. Therefore, the scan mode or the restart mode set at this point is continued.

In step # 104, the CPU 12
Sets the lens drive mode to the hill climbing mode, ends the processing in FIG. 4, and proceeds to step # 5 in FIG. In step # 105, the CPU 12 determines whether or not to restart focusing. The CPU 12 determines whether or not the focus evaluation value VF _val has decreased by a predetermined value CL _th2 or more compared to the focus evaluation value at the time of focus determination. The CPU 12 compares the focus evaluation value at the time of focus determination (step # 5) with the focus evaluation value VF _val.
Is less than the predetermined value CL _th2 , step # 105
Is affirmatively determined, the focus stop flag is set to 0, and the process proceeds to step # 106. In this case, driving of the focus lens is restarted. On the other hand, the CPU 12 sets the focus evaluation value VF _val to a predetermined value CL _{th2 as} compared with the focus evaluation value at the time of focus determination.
If it has not decreased more than the above, a negative determination is made in step # 105, the processing in FIG. In this case, focusing stop is continued.

In step # 106, the CPU 12
Checks the change in the focus evaluation value every predetermined time after the focus determination (step # 5). FIG. 5 is a diagram showing a state in which the focus evaluation value gradually decreases due to the movement of the subject after the focus is stopped. In FIG. 5, the horizontal axis represents time and the vertical axis represents the focus evaluation value. Time t0 is the time when the focus determination is made. The focus evaluation value that was VF (t0) at time t0 gradually decreases as the subject moves over time. The CPU 12 is in a monotonically decreasing state in which the state in which the focus evaluation value is smaller than the focus evaluation value at the immediately preceding time point continues, that is, VF (t0)> VF (t1)> VF (t2)> VF (t.
When 3) is established, the affirmative decision is made in step # 106 and the operation proceeds to step # 107. However, the focus evaluation value at time t1 is VF (t1), the focus evaluation value at time t2 is VF (t2), and the focus evaluation value at time t3 is VF (t3).

FIG. 6 is a diagram showing a state in which the focus evaluation value is sharply reduced by panning the camera to another object after the focus is stopped. In FIG. 6, the horizontal axis represents time and the vertical axis represents the focus evaluation value. Time t0 is the time when the focus determination is made. The CPU 12 compares the focus evaluation value VF (tn) with the focus evaluation value VF (tn-1) at the time immediately before by a predetermined value C.
If it decreases L _th3 above, i.e., VF (tn-1) -VF
When (tn) ≧ CL _th3 is satisfied, the negative determination is made in step # 106, and the process proceeds to step # 108.

In step # 107, the CPU 12
Sets the lens drive mode to restart mode (fine adjustment),
The process according to FIG. 4 is terminated and the process proceeds to step # 5 in FIG.
In step # 108, the CPU 12 sets the lens drive mode to the restart mode (coarse adjustment), ends the process in FIG. 4, and proceeds to step # 5 in FIG.

FIG. 7 is a flow chart for explaining the flow of processing for determining the drive amount and drive direction of the focus lens. In step # 201, the CPU 12
It is determined whether or not it is in focus. The CPU 12 makes an affirmative decision in step # 201 to proceed to step # 202 when the result of the in-focus determination (step # 5) shows that the in-focus state has been determined, whereas it negates step # 201 when the in-focus state has not been determined. It is determined and the process proceeds to step # 203. In step # 202, the CPU 12 sets the focus stop flag to 1 and sets the lens drive amount M to 0. Drive amount M
= 0 means stopping driving of the focus lens. CP
When the lens drive amount M is set to 0, U12 terminates the process shown in FIG. 7, and proceeds to step # 7 in FIG.

In step # 203, the CPU 12
Determines whether the set lens drive mode is the scan mode. The CPU 12 proceeds to step # 20 when the lens drive mode is set to the scan mode.
When the lens drive mode is not set to the scan mode, a negative determination is made in step # 203, and the process proceeds to step # 205.

In step # 204, the CPU 12
Sets the drive direction of the focus lens to the closest direction, sets Ms to the drive amount M of the focus lens, ends the processing in FIG. 7, and proceeds to step # 7 in FIG. In step # 205, the CPU 12 determines whether the set lens drive mode is the restart mode. The CPU 12 makes an affirmative decision in step # 205 if the lens drive mode is set to the restart mode to proceed to step # 206, and makes a negative decision in step # 205 if the lens drive mode is not set to the restart mode. And proceeds to step # 207. The case of proceeding to step # 207 is the case of the mountain climbing mode.

In step # 206, the CPU 12
Sets the drive direction of the focus lens to the close-up direction, sets Mr to the drive amount M of the focus lens in the restart mode (coarse adjustment), and sets Mr to the drive amount M of the focus lens in the restart mode (fine adjustment). / 2, respectively, and the process of FIG. 7 is terminated, and step # 7 of FIG.
Go to.

At step # 207, the CPU 12
3 sets the drive direction of the focus lens in the direction in which the focus evaluation value increases, sets Mm to the drive amount M of the focus lens, and ends the processing in FIG.
No. # 7. Here, the direction in which the focus evaluation value increases is the average LPa of the positions of the focus lens described above.
v, the current position LP of the focus lens, and the history of changes in the past focus lens position and focus evaluation value.

In step # 7 described above, the focus lens drive signal to the motor 13 is output according to the drive direction and drive amount M of the focus lens that has been set. When the lens drive amount M is 0, the motor 13
Is stopped. As a result, unnecessary focus lens driving is not performed during focusing, so that power consumption of the camera is reduced. The magnitude of the driving amount M is, for example, Ms ≧ Mr ≧ Mm
And

The moving speed at which the focus lens moves back and forth in the direction of the optical axis is the cycle in which steps # 2 to # 7 are repeated, and the lens drive amount M (Ms, M) per time.
r, Mm). The values of the cycle and the drive amount M (Ms, Mr, Mm) are set so that the focus lens moves back and forth smoothly.

According to the embodiment described above, the following operational effects can be obtained. (1) The drive mode of the focus lens is divided into a scan mode, a restart mode, and a hill climbing mode, and the relationship of the respective drive amounts is set to Ms ≧ Mr ≧ Mm. As a result, in the scan mode, the focus lens is moved at high speed to the position where the focus evaluation value changes, so that the time required for focusing is shortened. In the restart mode, the focus lens is moved at a lower speed than in the scan mode, so that it is possible to prevent the focus lens from moving too fast as compared with the change in the focus evaluation value. In the hill climbing mode, it becomes easy to perform the focus determination in which the focus is stopped so that the lens drive speed is further reduced to maximize the focus evaluation value. Furthermore, by reducing the drive amount Mm in the mountain climbing mode, it is possible to reduce the overrun when the focus is stopped. (2) The restart mode is divided into fine adjustment and coarse adjustment, and the drive amount of the focus lens during fine adjustment is set to 1/2 of the drive amount Mr of the focus lens during coarse adjustment. When the focus evaluation value monotonously decreases due to the movement of the subject after stopping focusing, the focus detection processing is performed by finely adjusting the position of the focus lens.
Focusing can be performed on the main subject without moving the focus lens too much. On the other hand, when the focus evaluation value sharply decreases due to the camera panning to another subject after the focus is stopped, the focus lens position is roughly adjusted to perform focus detection, so that the focus on the main subject quickly. Matching can be done. (3) In addition to the above (2), the focus lens is always driven to the close side in the restart mode. Generally, when the main subject moves after the focus is stopped, the subject often approaches the camera. Also, when the camera is panned to another subject, the closest subject is likely to be the main subject. Therefore, when the lens driving direction is set to the close side when the lens driving is restarted, focusing can be quickly performed, and unnecessary lens driving can be prevented to reduce power consumption accompanying lens driving.

In step # 103, it is determined whether or not the focus evaluation value VF _val is the predetermined value CL _th1 or more as a condition for setting the mountain climbing mode. Instead of this, the condition for setting the mountain climbing mode may be determined based on the magnitude of the inclination of the change with respect to the past focus evaluation value. In this case, the hill climbing mode is set when the magnitude of inclination exceeds a predetermined value.

The conditions for setting the mountain climbing mode may be determined as follows. Using another bandpass filter having a different passband from the bandpass filter 9, a frequency component different from that of the bandpass filter 9 is extracted to calculate the focus evaluation value, and the mountain climbing mode is set according to the magnitude of this calculation value. It is determined whether to do.

In the above description, the drive amount Ms in the scan mode is the largest and the drive amount Mm in the hill climbing mode is 1.
Although the driving amount Mr in the restart mode (coarse adjustment) is the smallest, it is in the middle of both, the magnitude of each driving amount may not be as described.

In the above description, the drive amount in the restart mode (fine adjustment) is set to Mr in contrast to the drive amount Mr in the restart mode (coarse adjustment).
However, the drive amount in the restart mode (fine adjustment) may be Mr or less.

Focus lens drive amount M (Ms, M
The values of r, Mm) are fixed values for each lens drive mode, but these values may be changed according to the calculated focus evaluation value.

In the above-described example, the data converted into the digital value by the A / D converter 3 is temporarily stored in the memory 4, the focus detection data is read from the memory 4, and the focus evaluation value is calculated. Alternatively, the focus evaluation value may be calculated by directly using the digital value output from the A / D converter 3 without passing through the memory 4.

In the example described above, the focus evaluation value decreases after focusing, and the drive of the focus lens is restarted in response to the decrease in the focus evaluation value. When the camera is panned to another subject, the focus evaluation value may increase. In this case, step # 1
At 06, the focus evaluation value VF (tn) changes by a predetermined value CL _th3 or more as compared with the focus evaluation value VF (tn-1) at the immediately previous time, that is, | VF (tn-1) -VF ( tn) ｜ ≧ CL
_{If th3} is satisfied, the determination in step # 106 is negative, and the process proceeds to step # 108.

Correspondence between each component in the claims and each component in the embodiment of the invention will be described. The image pickup device is configured by, for example, the solid-state image pickup device 2. The evaluation value calculation circuit, the drive signal output circuit, and the control circuit are configured by the CPU 12, for example. The two types of drive signals correspond, for example, to a drive signal that drives the motor 13 with the drive amount Mr and a drive signal that drives the motor 13 with the drive amount Mr / 2. First
The drive speed of (1) corresponds to the drive speed of the focus lens according to the drive amount Mr / 2. The second drive speed is the drive amount Mr.
The drive speed of the focus lens by means of.

[0044]

As described in detail above, according to the present invention, a focus detection device for outputting a lens drive signal for driving the lens to the close-up side and the long-distance side according to the focus evaluation value,
When the lens driving is restarted, the driving direction is set to the close side. Thereby, for example, when the subject approaches while the lens drive is stopped, it is possible to quickly focus on the subject.

[Brief description of drawings]

FIG. 1 is a block diagram of an AF digital camera according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a relationship between a position of a focus lens in a photographing lens and a focus evaluation value.

[FIG. 3] AF performed by a CPU of an AF digital camera
It is a flow chart explaining the flow of processing.

FIG. 4 is a flowchart illustrating a flow of processing for determining a lens drive mode.

FIG. 5 is a diagram showing a state in which a focus evaluation value gradually decreases due to a subject moving after stopping focusing.

FIG. 6 is a diagram showing a state in which the focus evaluation value sharply decreases by panning the camera to another subject after stopping focusing.

FIG. 7 is a flowchart illustrating the flow of processing for determining the drive amount and drive direction of the focus lens.

[Explanation of Codes] 1 ... Shooting lens, 2 ... Solid-state imaging device, 3 ... A / D converter, 4 ... Memory,
5 ... Image processing circuit, 6 ... External recording circuit, 7 ... AE / AWB processing circuit, 8 ... Control circuit, 9 ... Bandpass filter, 10 ... Integration circuit, 11 ... AF arithmetic circuit 11, 12 ... C
PU, 13 ... Motor, 14 ... Focus control mechanism

Claims (4)

[Claims] 1. An image pickup device for picking up a subject image through a taking lens, an evaluation value calculation circuit for calculating a focus evaluation value by using an image pickup signal output from the image pickup device, and calculation by the evaluation value calculation circuit. A drive signal output circuit that outputs a drive signal that drives the photographing lens to the close-up side and the long-distance side so as to maximize the focus evaluation value, and the drive signal output circuit according to the focus evaluation value calculated by the evaluation value calculation circuit. And a control circuit for controlling the drive signal output circuit so as to stop the output of the drive signal to the photographing lens and restart the output of the drive signal to the photographing lens from the direction of driving the photographing lens to the close side. Focus detection device. 2. The focus detection device according to claim 1, wherein the control circuit drives the drive so as to switch and output two kinds of drive signals according to a change in the focus evaluation value calculated by the evaluation value calculation circuit. A focus detection device characterized by controlling a signal output circuit. 3. The focus detection device according to claim 2, wherein the control circuit has: (1) a first drive speed when the focus evaluation value calculated in the past by the evaluation value calculation circuit monotonically decreases. Output the drive signal to drive the shooting lens with, (2)
The drive signal for outputting the drive signal for driving the photographing lens at the second drive speed higher than the first drive speed when the focus evaluation value calculated by the evaluation value calculation circuit decreases by a predetermined value or more. A focus detection device characterized by controlling an output circuit. 4. The focus detection device according to claim 1, wherein the control circuit outputs a drive signal to the photographing lens when the focus evaluation value calculated in the past by the evaluation value calculation circuit monotonically decreases. A focus detection device characterized by restarting.