JP3104990B2 - Auto focus device - Google Patents

Description

The present invention relates to a video camera that performs a focusing operation by extracting a high-frequency component from a captured video signal, and more specifically,
The present invention relates to an auto-focusing device that can reduce fluctuations of a focusing lens during focusing according to an object to be photographed.

(Prior Art) First, a conventional video camera autofocus apparatus will be described with reference to FIGS.

FIG. 4 is a flowchart showing the focusing operation procedure. FIG. 5 is a graph showing the relationship between the focus signal level and the lens position in the focusing process.

The level of the focus signal obtained by integrating the high frequency components extracted from the video signal is compared by moving the focusing lens back and forth to determine the moving direction (step).
Next, the focusing lens is moved in the determined direction to climb the peak of the focus signal level (step). When the focus signal level starts to decrease, it is determined that the vehicle has passed the top of the mountain, and the direction of movement is reversed to reach the top of the mountain (step). At this point, the focusing operation is completed, and thereafter, it is determined whether to start the focusing operation again (step).

FIG. 6 is a graph showing an example of a change in the level of the focus signal at the time of focusing.

As long as the focus signal level is within the preset threshold range, a clear image can be obtained without moving the focusing lens, but once the focus signal level goes out of the threshold range, the focusing operation is performed again. Is activated.

The case where the camera is restarted includes, for example, a sharp movement of a subject or a fluctuation of a photographing range of a camera, and the focusing lens fluctuates more than necessary.

In consideration of such a case, the conventional video camera is provided with an AF release button or a manual focus button for stopping the AF operation.

(Problems to be Solved by the Invention) By turning on the AF release button and the like, it is possible to prevent a malfunction of the focusing lens due to the movement of the subject and the like, and to suppress a temporarily generated screen blur and wasteful power consumption. Because it can be.

However, there is a drawback in that, even if AF release is set, if the user immediately pans or shoots another subject, the AF operation must be restarted by pressing the button again.

The object of the present invention is to eliminate the above disadvantages, and after focusing,
In a situation where the focus signal level is considerably unstable, a stabilization switch that can be manually operated by the photographer's judgment enables stable shooting without restarting even if the subject is slightly changed or camera shake, It is an object of the present invention to provide an auto-focusing apparatus with good operability that can smoothly shift to shooting of the next separate subject without performing a special operation such as an operation of an AF release button.

(Means for Solving the Problems) In order to achieve the above object, an autofocus apparatus according to the present invention moves the focus lens so that the level of a focus signal extracted from a captured video signal is maximized. In an autofocus device of a video camera performing a focusing operation, AF detection means for extracting a high-frequency signal from the video signal to obtain one focus signal output, and fixing after a focus lens reaches a maximum position of the focus signal level A restart determination unit that determines whether or not the focus signal level exists within a range of the first threshold value that has been set, and shifts to a focusing operation again when the focus signal level is out of the range; A switch capable of setting a second threshold value wider than the threshold value range, wherein the second threshold value is fixed when the switch is operated; It is configured to replace place to have value.

After the focus signal level exceeds the second threshold value and the focusing operation is restarted, the second threshold value is set to the first threshold value unless the switch is pressed. It is configured to return.

(Example) Hereinafter, the present invention will be described in more detail with reference to the drawings.

FIG. 1 is a circuit block diagram showing an embodiment of an autofocus device for a video camera according to the present invention. Light from a subject (not shown) is condensed by the taking lens 1 and forms an image on the CCD 3. The output of the CCD 3 is transmitted to the camera processing circuit 4, where it is processed into a video signal to which a synchronization signal and the like are added.

The video signal generated by the camera processing circuit 4 is sent to a circuit for storing on a magnetic tape (not shown).
It is also sent to the AF detection circuit 5.

The AF detection circuit 5 extracts and integrates the high frequency components of the video signal to generate a focus signal.

The control circuit 6 determines the level of the focus signal sent from the AF detection circuit 5 to control the moving direction and movement of the focus lens for a series of focusing operations, and further detects the top of the level and returns to that position. And outputs a control signal to the motor drive circuit 7 to stop the motor.

The motor drive circuit 7 drives the motor 8 according to the control signal to bring the focus lens 2 to a focus position. After focusing, the control circuit 6 detects whether or not the focus signal level is within the range of the threshold value. If the focus signal level is out of the range, the control circuit 6 performs the focusing operation again.

The threshold value of the control circuit 6 is set such that the focusing operation is not repeated frequently above and below a slight focus signal level, but rather becomes a relatively narrow range from a point where it interferes with photographing.

However, as described above, when the movement of the subject or the camera shake of the photographer is severe, the focusing operation is frequently performed. Therefore, the stabilizing switch 9 that can be turned on at the discretion of the photographer is provided. This stabilizing switch 9
Is turned on, the threshold value of the control circuit 6 becomes wider.

FIG. 2 is a diagram showing a state of a focus operation in response to a change in a focus signal level that moves with time and an operation of a stabilization switch.

In the figure, threshold values A and B indicate the threshold values of the control circuit 6 in the normal case and when the stabilization switch is turned on, respectively.

When the stabilization switch 9 is turned on after focusing, even if the focus signal lens fluctuates due to slight subject change or camera shake, stable shooting can be performed without restarting the focusing operation as long as the focus signal is within the range of the threshold B. And the focus lens becomes stable without moving.

However, when the shooting scene is changed by panning, the focus signal lens changes more than the threshold value B, so that the camera is restarted only at this time.

Then, after focusing, the threshold value is automatically returned to A, so that the tracking performance is not deteriorated.

FIG. 3 is a flowchart showing an operation procedure at the time of restart determination.

The control circuit 6 determines whether or not the stabilization switch is turned on (step 1). If it is not turned on, the threshold value A remains unchanged (step 2). If it is turned on, the threshold value is turned on. The value is set to B (step 3).

Then, it is monitored whether or not the focus signal level exceeds the range of the threshold value. If the level exceeds the threshold value, the focusing operation is performed again after a certain delay time (step 4).

(Effects of the Invention) As described above, according to the present invention, it is necessary to provide a stabilization switch capable of setting a threshold value range of a focus signal level that determines a range in which a focusing operation is to be restarted, by a manual operation. Accordingly, it is possible to prevent the screen from being blurred due to restart of the focusing operation. Moreover, after the threshold level is widened by the stabilization switch and restarted, the operation is automatically returned to the original threshold value, so that the operation for releasing the stabilization can be omitted.

Furthermore, since the operation contents of the control circuit need only be changed in addition to providing the stabilization switch, the present invention has a feature that the present invention can be implemented with a minimum number of additional components.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing an embodiment of an autofocus device for a video camera according to the present invention. FIG. 2 is a diagram showing a state of a focus operation in response to a change in a focus signal level that moves with time and an operation of a stabilization switch. FIG. 3 is a flowchart showing an operation procedure at the time of restart determination. FIG. 4 is a flowchart showing the focusing operation procedure. FIG. 5 is a graph showing the relationship between the focus signal level and the lens position in the focusing process. FIG. 6 is a graph showing an example of a change in the level of the focus signal at the time of focusing. DESCRIPTION OF SYMBOLS 1 ... Photography lens 2 ... Focus lens 3 ... CCD 4 ... Camera processing circuit 5 ... AF detection circuit 6 ... Control circuit 7 ... Motor drive circuit 8 ... Motor 9 ... Stabilization switch

Claims (2)

(57) [Claims] An autofocus apparatus for a video camera that performs a focusing operation by moving a focus lens so that a level of a focus signal extracted from a captured video signal is maximized. AF detection means for obtaining a focus signal output by extracting the focus signal; and a focus signal level within a fixed first threshold after the focus lens reaches the maximum position of the focus signal level. A restart judging unit for judging whether or not it is out of the range, and shifting to a focusing operation again when the value is out of the range; and a second threshold value wider than the first threshold value can be set An autofocus device, comprising: a switch, wherein the first threshold value is replaced with a fixed second threshold value when the switch is operated. 2. The method according to claim 1, wherein said second threshold value is set.
2. The autofocus apparatus according to claim 1, wherein after the focus signal level exceeds the threshold value and the focusing operation is restarted, the first threshold value is returned unless the switch is pressed.