JPH03204276A - Automatic focus adjustment device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic focus adjustment device, and more particularly to an automatic focus adjustment device that utilizes a video signal suitable for use in a video camera or the like.

[Conventional technology]

Generally, the focus adjustment range of a video camera or the like is configured such that a distance of about 1.2 m from the camera is set as the closest end, and objects existing in a range from there to an infinite distance are brought into focus.

However, in recent years, as video cameras have become popular in homes as consumer devices, opportunities to take pictures in relatively narrow spaces have increased, and the minimum shooting distance of video cameras has been made even smaller than the conventional 1.2 m, allowing There is a growing demand for cameras that can take pictures closer to objects. In response to this demand, it is possible to design the lens of a video camera to double the amount of movement of the focusing lens compared to conventional devices, thereby shortening the distance at the closest point that can be photographed to about 0.6 m.

[Problem to be solved by the invention]

However, in the video camera etc. mentioned above,
Reducing the distance of the closest end in an optical system causes several disadvantages.

First, since the amount of movement of the force single lens increases, the responsiveness of the automatic focusing device to the entire lens movement range becomes relatively poor. For example, if you conventionally perform vanning on a subject that exists at the closest end of 1.2 m from infinity, and it takes 3 seconds to move the lens to focus, then the distance at the closest end is 0. As 6m,
It takes about 6 seconds to focus on a subject at that distance.

This length of time significantly deteriorates operability and poses a practical problem.

The second problem is malfunction of the focusing device caused by false resolution of the lens. In other words, by shifting the focus of the lens (and for subjects with high spatial frequencies, the phase of 18
An imaging phenomenon that is shifted by 0° occurs.

This is false resolution. In automatic focus adjustment devices that use video signals, in-focus is determined when the high-frequency components in the video signal reach a maximum value. According to this method, even in the state of false resolution, the maximum value is determined. Takes a value. therefore,
The lens is determined to be in focus when there is false resolution, and the lens stops. This phenomenon occurs frequently when the amount of lens defocus is large, and when the minimum shooting distance is 1.2 m, which is the same as before, false resolution does not occur due to the depth of field. However, if the minimum shooting distance is 0.6m, false resolution will occur,
The lens may stop and remain out of focus.

[Means for solving problems]

The present invention has been made with the aim of solving the above-mentioned problems, and is characterized by a focus adjustment means that adjusts the focus by changing the imaging position based on a signal corresponding to the degree of focus. a means for switching the movement range of the focus adjustment means into a first movement area and a second movement area that includes the first movement area and further extends toward the closest side; and the focus adjustment means. When the means cannot focus in the first movement area, the focus adjusting means is moved to the close side and focus adjustment is performed in the second movement area, and when the focus is brought into focus, and a control means for maintaining this state.

[Effect]

This allows the same automatic focus adjustment as before in normal distance ranges, and also enables quick focus without malfunction even when focusing on very close ranges, creating an automatic focus adjustment device that does not require complicated operations. It can be realized.

Further, when performing focus adjustment, the distance range in which the focus adjustment lens is located can be detected and focus adjustment can be performed in accordance with the distance range, so that a quick and highly accurate focus adjustment operation can be performed.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an automatic focus adjustment device according to the present invention will be described in detail below with reference to the drawings.

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

In the figure, l is a focusing lens group (hereinafter referred to as a focusing lens) that performs focus adjustment, and is moved from an infinity position to a close-up position by a motor 2, for example, 0.
It is configured to be movable so as to be able to focus up to a 6 m position, and the movement position information is detected by the focus encoder 5. FIG. 2 shows the movement range of this focusing lens 1, and the normal automatic focusing operation is in the range from infinity ω to the closest end of 1.2 m, and the short range range (described later) is 1.2 m.
Areas of 2 to 0.6 m are each allocated. The details will be described later. Reference numeral 3 indicates a variator lens, and reference numeral 4 indicates a convencator lens. A cam (not shown) performs zooming along a cam locus shown by a dotted line in the figure. Focal length information resulting from this zooming is detected by the zoom encoder 6.

Reference numeral 7 denotes an aperture unit that adjusts the amount of light incident on an image sensor, which will be described later, and its aperture value is detected by an aperture encoder 8. 9 is a master lens, and 10 is a CCD that photoelectrically converts the subject image formed on the imaging surface and outputs a video signal.
11 performs gamma correction, blanking processing, addition of a synchronization signal, etc. to the video signal output from the image sensor.
This is a camera signal output circuit that performs predetermined processing and outputs a standardized video signal such as NTSC.

12 is a gate circuit that gates the video signal output from the image sensor 10, sets a focus detection area on the imaging screen, and allows only signals corresponding to the detection area to pass; 13;
14 is a bypass filter (hereinafter referred to as HPF) that extracts a high frequency component used for detecting the focus state from the video signal corresponding to the focus detection area extracted by the gate circuit 12, and 14 is a high frequency component output from the HPF 13. 15 is a peak hold circuit that holds the peak value of the output level of the detection circuit 14 in one field period, and 16 is a peak hold circuit that holds the output level of the peak hold circuit 15 in one field period. A delay circuit 17 is a differential circuit that compares the current output of the peak hold circuit 15 with the output of the peak hold circuit 15 from the previous l field outputted from the delay circuit 16, and outputs a signal according to the difference. , 18 is an A/D conversion circuit that converts the analog output signal of the differential circuit 17 into a digital signal, and 19 is an auto/manual focus adjustment switch (hereinafter referred to as A/D conversion circuit).
20 is a one-shot focus switch (hereinafter referred to as O3T switch), 21 is a motor drive circuit that drives the focusing lens drive motor 2 according to commands from a system control circuit, which will be described later, and 22 is a focus encoder. 5. Various encoder information of the zoom encoder 6 and aperture encoder 8 and a focus signal according to the degree of focus outputted from the A/D conversion circuit 18, as well as the A/M switch 19 and the O3T switch 20.
This is a system control circuit that inputs operation command information, calculates this information, and outputs control information for controlling the focusing lens drive motor 2 to the motor drive circuit 21, and is configured by a microprocessor. .

Next, the operation of the automatic focus adjustment device according to the present invention will be explained step by step with reference to FIGS. 3 and 4.

FIG. 3 is a diagram showing patterns of focusing lens movement ranges in each operation mode and focusing operations according to the operating states of the A/M switch and O3T switch in this embodiment.

Also, Fig. 4 shows the A/M switch 19 and the O8T switch 20.
3 is a flowchart for explaining a control algorithm for focus adjustment operation with respect to the operating state of the camera.

(1) When the automatic focus adjustment mode is selected by the A/M switch and the O5T switch is off, (1)
), the movement range of the focusing lens l that can perform automatic focusing operation is 1.2 from infinity to the closest point.
m range and performs normal autofocusing operations.

That is, high-frequency components of the video signal corresponding to the focus detection area set on the imaging surface by the gate circuit 12 and HPF 13 are extracted from the video signal output from the image sensor 10, circuit 15
The peak level is detected at the field period. This change in peak level is processed by the delay circuit 16. Differential circuit 1
7 and converted into a digital signal via the A/D conversion circuit 18 and then supplied to the system control circuit 22.

Further, position information of the focusing lens l and aperture value information of the aperture 7 are also detected by the focus encoder 5 and the aperture encoder 8, respectively, and are supplied to the system control circuit.

The system control circuit 22 includes the A/D conversion circuit 18
The driving circuit 2 analyzes the change in the peak hold value for each field of the high frequency component outputted from the high frequency component and the direction of the change, and drives the focusing lens l to the in-focus point.
Outputs a control signal to 1. That is, by detecting the difference for each field, and driving the focusing lens l in the direction in which the current peak value is larger than the previous one based on the polarity, the difference becomes 0, and then by detecting the reversal of the polarity of the difference value, the peak In other words, it is possible to detect the focal point where the hold value is maximum. This focus detection method itself is known as the so-called "mountain climbing servo method J", and further explanation thereof will be omitted.

Furthermore, when the focusing lens 1 is moved to the close side and stopped at the focused point on the close side, which will be described later, the above-mentioned high frequency component, which changes in accordance with the movement of the focusing lens 1, will reach the peak position. Then, the focusing lens l is stopped.

(2) When the A/M switch is set to manual and the O8T switch is off, as shown in (2) in Figure 3,
In manual focus adjustment mode, the focus lens l remains stationary and is not driven, and focus adjustment can only be performed manually.

(3) When the A/M switch is manual and the O8T switch is on, the so-called one-shot automatic focusing mode is activated, as shown in (3) in Figure 3, and the focusing lens automatically focuses once. After l stops, it does not restart and goes into manual focus adjustment mode.

The operating range of the focusing lens l at this time is the entire range from infinity to the closest end of 0.6 m.

(4) Next, when the O5T switch is turned on, the automatic focus adjustment mode is activated over the entire range from infinity to the closest end of 0.6 m, and the automatic focus adjustment operation is performed by driving the focusing lens l from the current position to the closest position.

Then, by switching from the normal moving area autofocus mode to the full range autofocus mode, and driving the focusing lens drive motor 2 at maximum speed while searching for a subject at a closer distance, responsiveness is improved. can be improved.

In addition, focusing lens 1 can be adjusted by operating the O3T switch.
The range of movement can be changed, so even if the lens stops at a false focus position due to false resolution,
By operating the O8T switch, the focusing lens is moved further to the close side and set to the in-focus point, and the moving range of the focusing lens is switched to another movement range, and the focusing lens group is moved to the true in-focus position. be able to.

The above operation will be explained based on the flowchart in FIG.

In the figure, after the control flow starts, the A/M switch 19 is used to determine whether auto or manual is selected as the focus adjustment operation.
), if auto is selected, check 0N10FF of the O3T switch (S2) and confirm that the O3T switch is OFF.
If so, search for the focal point in the normal range from infinity to close 1.2 m, perform automatic focus adjustment,
When the in-focus point is detected, the focusing lens l is stopped (S13° S14.515). After the focusing lens 1 is stopped at the in-focus point, it returns to Sl and performs control again according to the state of the A/M switch.

If the O5T switch was turned on in S2, the automatic focus adjustment mode will be activated, and it will be necessary to determine whether the current position is in focus (S3), and if it is, the focusing lens will be turned on.
(S7). If the focus is not in focus, drive the focusing lens l in the closest direction, and move from infinity ω to close 0.6m.
The automatic focus adjustment operation is performed within the entire area of , and is repeated until the in-focus point is detected (S4. S5. S6). When the in-focus point is detected, stop focusing lens 1 (
S7). When the focusing lens 1 stops, the timer TII is activated to start counting, and the elapsed time T of the timer TII is compared with the threshold value Tlh. If T, has not reached the threshold value T+h, the area where the focusing lens 1 is currently located is determined (5IO), and if it is not within the short distance area, the process returns to S9 and the focusing lens is positioned within the normal area. Continue counting the time.

If the focus lens has moved within the short range area before T1 reaches the threshold at 510, the timer Tll is reset and stopped (5ll), and the process returns to S5 to perform automatic focus adjustment operation within the entire area. I do.

In addition, in S9, if TI>Tlh, that is, more than the threshold value T+h has elapsed since the focusing lens l was moved into the normal area, the timer TII is stopped and reset, and the process goes to S13, where the automatic Shift to focus adjustment operation.

On the other hand, if the O5T switch is not operated when manual is selected with Sl, the focusing lens 1 is usually moved over the entire short distance range (0.6 m - (1)) to adjust the focus (520), and when manual is selected, the O5T switch is turned on. When set to , automatic focus adjustment is performed for the entire area (S17).
After focusing and stopping the focusing lens, it does not restart (so-called one-shot autofocus) and enters manual mode (S18, S19°520). and S
1 and performs control according to the state of the A/M switch.

As described above, according to the present invention, the A/M switch and the O5
Depending on the operating state of the T switch, the focus adjustment mode can be optimally set according to the situation at that time. In other words, if you operate the OST switch in manual mode to perform one-shot autofocus, the camera will automatically focus to the in-focus point in all areas, including the close range, and then enter manual focus adjustment mode, and operate the O3T switch in auto mode. For example, automatic focus adjustment is performed in all areas including the close range, and after stopping the lens at the focal point, the area where the lens is located is determined, and the focus adjustment mode is adjusted depending on the time the lens is located in that area. The video camera is configured to operate as if switching between the two, and does not require complicated operations, providing extremely good operability in a video camera that performs real-time shooting.

〔Effect of the invention〕

As described above, according to the focus adjustment device of the present invention, the movement range of the focusing lens includes a normal range where focus adjustment is performed in normal operation, and a short range range where focusing is possible to a closer distance than the normal range. Since the focus adjustment operation mode can be changed according to the situation without complicated operations, it is possible to quickly shoot even when there is false resolution etc., especially for close-up subjects. The automatic focus adjustment operation can be optimally controlled depending on the conditions at the time.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of an example of a video camera to which the focusing device of the present invention is applied, Fig. 2 is a diagram for explaining the movement area of the focusing lens, and Fig. 3 shows focusing in each focusing mode. FIG. 4 is a flowchart showing a control algorithm for focusing operation in the present invention.

Claims (1)

[Scope of Claims] Focus adjustment means for adjusting the focus by changing the imaging position based on a signal corresponding to the degree of focus; a movement range of the focus adjustment means being a first movement area; means for switching to a second moving area set to include a moving area of
It is characterized by comprising a control means for moving the focus adjustment means to the close side, performing focus adjustment in the second moving region, and maintaining the focus state when the focus state is reached. Automatic focus adjustment device.