JPH0419702A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To enable an expensive automatic focusing operation which is accurate with small storage capacity by storing only representative values of locus data for correcting focus movement in zooming. CONSTITUTION:This device is provided with a storage means 6 which divides a focusing-possible range into plural areas by object distances and stores one representative focus movement locus data of each area, and a specific offset is added to representative data in zooming to drive a focusing lens 105. This storage means 6 obtains the representative data for correcting the focus movement in the zooming without increasing the circuit scale. Further, a controller 5 drives the focusing lens 51 so that the focus movement in the zooming is corrected, thereby moving the focusing lens 105. Consequently, the excellent automatic focusing device which causes no defocusing even when the movement quantity of the focus is varied with the object distance in the zooming is obtained nearly without increasing the circuit scale.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an autofocus device for a video camera or the like.

[Conventional technology]

Figure 8 shows a conventional autofocus device, so-called hill-climbing autofocus, which detects the contrast of the screen using the high-frequency components of the imaging signal and performs focusing by driving and controlling the lens to maximize the contrast. This is an example of the device, and in the figure, 101 is a front lens for focusing, 102 is a variator for variable magnification,
103 is a convencator for image plane correction, and 104 is a relay lens for image formation, which constitute the zoom lens 1. These lenses are generally a group of multiple lenses, but in this case, for convenience, they are expressed as one lens. 2 is a CCD which converts incident light from the zoom lens 1 into an electric signal and sends it to a camera signal processing circuit 3, from which a video signal a and a luminance signal are respectively taken out.

Next, 401 is a BPF (band pass filter), through which a signal with a frequency in a certain band of the luminance signal passes, and a detector 40
2, the waveform is smoothed by A/D converter 40.
3, it is converted into a digital signal. The digital signals from the A/D converter 403 are digitally added by an adder 404 and sent to the control circuit 5 as a focus evaluation value C which is used for mountain climbing control. BPF here
401 to adder 404 constitute the focus detection circuit 4.

A first motor driver 7 drives the first motor 10 for the front lens 101 based on a control circuit 50 command. Similarly, 8 is the second motor driver, which drives the variator 1.
02 is driven based on the command from the control circuit 5. Usually first motor 10. second motor 1
2, DC motors are often used.

Note that 9 is a first sensor that detects the position of the front lens, and the position is detected by observing brush noise of the first motor 10, and 11 is a focal point that detects the position of the variator lens. The second sensor 11 for distance detection is composed of a sliding resistor or the like, and in this case, the position is detected by reading a predetermined potential that corresponds one-to-one with the lens position.

Next, the operation will be explained.

The object light incident through the zoom lens 1 is C0D
2 is converted into an electrical signal by the camera signal processing circuit 3.
After that, it becomes a video signal a. Of these, the luminance signal component b(
In FIG. 9(a), the BP is guided to the focus detection circuit 4.
As seen in F401 (FIG. 9 (c)), only high frequency components are extracted.

Next, after being detected by the detector 402 (FIG. 9(C)), A
The /D converter 403 converts the value into a digital value, and the adder 404 adds the values of a predetermined area in one screen, and outputs the result as a focus evaluation value C. Since the above-mentioned high frequency component corresponds to the contrast of the screen, the contrast is maximum, that is, the maximum when the focus lens is at the in-focus point, and decreases as it deviates from the in-focus point. Therefore, as the focus lens moves, the focus evaluation value C exhibits a mountain-shaped characteristic as shown in FIG. 11. The control circuit 5 controls the first motor 10 so that the output signal C is always at the maximum. , drives the front lens 101 to the in-focus point. Autofocus operation is achieved in this way.

Furthermore, the operation during zooming will be explained. A zoom signal is sent from the control circuit 5 to the second motor driver 8 , and this motor driver 8 drives the second motor 12 . Following the drive of this motor 12, the variator 102 moves on the optical axis and performs a magnification change action. At this time, a focus movement occurs as the variator 102 moves, but a compensator 103 mechanically connected via a cam or the like simultaneously moves on the optical axis and operates to correct the focus movement.

Incidentally, as an autofocus method for conventional photographic lenses, a front lens focus method has been widely used in which the front lens of a zoom lens is driven in the optical axis direction to achieve focus, as shown in FIG. Reasons for this include the fact that the structure is relatively simple and that manual focusing operations are easy to perform. However, on the other hand, there are disadvantages such as the short focusing distance, the need to drive a heavy lens with a large diameter, which tends to require a large motor, and the need to handle with care as the rotating parts are exposed. There was also.

Compensators,
A so-called inner focus method is considered in which focusing is performed by driving an internal lens such as a relay lens in the optical axis direction. By applying the inner focus method, the above problem can be solved, so that, for example, it becomes possible for the operator to focus on a nearby object from an infinite distance without any intervention. However, in the case of the inner focus method, the focusing lens is located further back on the optical axis than the zooming lens, so as shown in Fig. The mechanical correction method cannot handle objects at all distances because the amount of movement of the focal point (that is, the amount of movement of the focusing lens) is different.

[Problem to be solved by the invention]

Since the conventional autofocus device is configured as described above, when it is applied to an inner focus type zoom lens, it is difficult to accurately correct the movement of the focal point during zooming.

This invention was made to solve the above-mentioned problems. Even when zooming with an inner focus type zoom lens, the amount of movement of the focal point changes depending on the subject distance, the focus shift may cause blurring. To provide a good autofocus device that does not cause problems.

[Means to solve the problem]

The autofocus device according to the present invention divides the focusable range into a plurality of overhead areas divided by the subject distance, and is provided with a storage means for storing one focal point movement locus data representative of each area. In addition, during zooming, a predetermined offset is given to the representative data to drive the focus lens.

Further, the autofocus device according to the present invention corrects the focus movement of the inner focus lens during zooming, which changes depending on the subject distance, by moving the focus lens using hill climbing control, and also restarts the hill climbing method. The fixed value that prompts the camera is switched according to the distance to the subject.

(Operation) The storage means in the present invention provides representative data for correcting focus movement during zooming.

Further, the control device according to the present invention drives the focus motor and moves the focusing lens so as to correct focal movement during zooming.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an autofocus device according to a first embodiment of the present invention. In the figure, 101 is a fixed front lens for condensing light, and 105 is a part of a relay lens used for focusing. A master lens, 61 is a ROM as a storage means, 50 is a stepping motor driver that drives the stepping motor 51 based on a command from the control circuit 5, and 52 is an end point detection switch that detects the end point of the movable range of the master lens 105. . The rest is the same as the conventional example.

First, in FIG. 1, the front lens 101 is fixed and the master lens 105 operates as a focus lens, but since the normal focus operation is the same as that of the conventional example, a description thereof will be omitted here.

The focus operation during zooming will be described below. A zoom signal is sent from the control circuit 5 to the second motor driver 8 , and the second motor driver 8 drives the second motor 12 . According to the drive of this motor 12, the variator 10
2 moves on the optical axis and performs a magnification change action. Variator 102
A focal point shift occurs as the subject moves, and as shown in FIG. 2, the amount of shift varies depending on the subject distance. Therefore, when zooming, it is necessary to correct this focal shift by some means.

Now, data on the absolute position of the focus lens 105 corresponding to the focal lengths f0 to f detected by the focal length detection sensor 11 with respect to the object at the distance a to h shown in FIG. 2 is stored in advance in the ROM 61. It is assumed that it is stored in . Here, the absolute position of the focus lens 105 is stored in the ROM 61 and is expressed by the amount of movement from this point, based on the in-focus position for an object at infinity, that is, the point where the end point detection switch 52 is turned on. The data format is expressed by the amount of movement of the stepping motor 51. In other words, the unit movement amount of the focus lens 104 is represented by one step of the stepping motor 51. Note that the stepping motor 51 is controlled in an open loop, and the number of driven steps becomes the absolute position of the focus lens 105.

Now distance #! The subject is in focus at a focal length f (the absolute amount of extension of the focus lens 105 is mt), and f
When zooming up to Y, the control circuit 5 is
Of the focus correction data stored in 6! Take pictures of subjects that are further away! The data of the subject distance g closest to is selected and read out.

Then, a predetermined offset is given to the data to obtain focus correction data for the subject at a distance l. Therefore, from the focus lens extension amount mg when the subject distance g is f, let (mttm@,) be the offset amount when f, and thereafter subtract one step from the offset amount every time the f value changes to obtain O. Abort with. Therefore, the focus correction data for a subject at a distance l will be terminated at 14 as shown in FIG. 3, for example, in the case of m, . . . -m, 7=3 steps. Thereafter, the focus lens 105 is forcibly driven using the data of the subject distance g.

Note that since the purpose of this embodiment is to correct the movement of the focal point during zooming in an inner focus type zoom lens, the normal autofocus operation is not limited to the hill climbing method, but any other method may be used. . Further, in the above embodiment, the master lens is driven as the focus lens, but it may be configured to drive other lenses as long as it is a rear group lens after the variator. motor,
Alternatively, any motor with equivalent performance may be used.

FIG. 4 shows an autofocus device according to a second embodiment of the present invention. In the figure, 101 is a fixed front lens for condensing light, and 105 is a part of a relay lens used for focusing. 62 is a ROM as a storage means, and 15 is a stepping motor.
The motor is driven by the motor driver 13 based on a command from the control circuit 5, and moves the master lens 105. 14 is an end point detection switch that detects the end point of the movable range of the master lens 105. The other parts are the same as the conventional example.

First, in FIG. 4, the front lens 101 is fixed,
Although the master lens 105 operates as a focus lens, the normal focus operation is the same as that of the conventional example, so the explanation in this case will be omitted.

The focus operation during zooming will be explained below. A zoom signal is sent from the control circuit 5 to the second motor driver 8 , and this motor driver 8 drives the second motor 12 . According to the drive of the second motor 12, the variator 102
As the variator 102 moves on the optical axis and performs a magnification change action, a focal point shift occurs, but as shown in FIG. 5, the amount of shift varies depending on the subject distance. Therefore, when zooming, it is necessary to correct this focal shift by some means.

Now, data on the absolute position of the focus lens corresponding to the focal lengths f0 to f detected by the focal length detection sensor 11 with respect to the object at a distance of 1-n shown in FIG.
It is assumed that this information is stored in the ROM 62 in advance. Here, the absolute position of the focus lens is expressed by the amount of movement from this point, for example, based on the in-focus position for an object at infinity, that is, the point where the end point detection switch 14 is turned on.

Further, the data format stored in the ROM 62 here is represented by the amount of movement of the stepping motor 15. In other words, the unit movement amount of the focus lens is represented by one step of the stepping motor 15.

Note that the stepping motor 15 is controlled in an open loop, and the number of driven steps becomes the absolute position of the focus lens. Part of the data in the ROM 62 is shown in FIG.

Now, the focus is reached at the Y position shown in Figure 5 (focal length f2
．． When the focus lens position XV) is zoomed toward the telephoto side, the control circuit determines from the data stored in the ROM 62 that it belongs to the area , and sets a threshold value. The control circuit 5 constantly monitors the focus evaluation value C, and instructs the motor driver 8 to move the focus lens to the top of the evaluation value mountain during zooming using a hill climbing method, thereby driving the stepping motor 12. At this time, the threshold value for restarting the focus lens that has stopped at the in-focus point is 80% of the focus evaluation value C0 at that time in the case of area D3 as shown in Figure 7, and the change in focal length. When the focus evaluation value C falls below 80% of C6, the control circuit 5 restarts the focus lens, operates to detect the peak of the evaluation value, then stops, and sets the focus evaluation value at that time to 00. , and waits until the focus evaluation value falls below the 80% threshold again.

As shown in FIG. 7, the threshold for restarting is determined for each area defined by the subject distance. In other words, in a region where the amount of movement of the focal point is small with respect to a change in focal length, such as the region Do, the threshold value is set low, so that transient lens response can be avoided.

In the above embodiment, the relay system master lens 105 is driven as the focus lens, but other lenses may be driven as long as they are lenses after the variator 102.

Further, a DC motor or a motor having equivalent performance may be used as the focusing motor.

Further, the threshold value may be limited to the value shown in this embodiment.

〔Effect of the invention〕

As described above, according to the present invention, only the representative value of the locus data for correcting focus movement during zooming is stored, so that the storage capacity can be reduced and an inexpensive autofocus device with high accuracy can be provided.

Further, according to the present invention, during zooming, when the focus evaluation value falls below a predetermined threshold, the focus detection operation using the hill climbing method is restarted, and the threshold is switched according to the subject distance. , it is possible to perform good focus correction regardless of the distance of the subject, and an excellent autofocus device can be provided without requiring any special structure.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an autofocus device according to a first embodiment of the present invention, FIG. 2 is a diagram of a focus movement locus, and FIG.
4 is a diagram showing an example of focus correction data, FIG. 4 is a configuration diagram showing an autofocus device according to a second embodiment of the present invention, FIG. 5 is a diagram showing the operation of the embodiment of FIG. 4, and FIG. The figure shows the contents of the ROM 62, FIG. 7 shows an example of threshold setting, FIG. 8 shows the configuration of a conventional autofocus device, and FIG. 9 shows the output waveform of the conventional example. FIG. 10 is a diagram showing the characteristics of the focus evaluation value, and FIG. 11 is a diagram showing the focus movement locus with respect to the subject distance. In the figure, 1 is a zoom lens, 2 is a CCD, 4 is a focus detection circuit, 5 is a control circuit, 61.62 is a ROM, 12 is a motor, and 15.51 is a stepping motor. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (2)

[Claims] (1) An inner focus zoom lens that images a subject, a photoelectric conversion means that converts the light imaged by the zoom lens into a video signal, and extracts a predetermined high frequency component from the video signal and integrates it over a predetermined period of time. In an autofocus device comprising a focus detection means for controlling a lens system based on an output of the focus detection means, a control means for controlling a lens system based on an output of the focus detection means, and a lens drive means for driving the lens system by the control means, during a zooming operation, The movement trajectory of the focusing lens group is divided into a plurality of regions divided by the subject distance, and a storage means is provided for storing one movement trajectory representing each region for each predetermined focal length. An autofocus device characterized in that during a magnification change operation, a predetermined amount of offset is added to the stored contents of the storage means to move the focusing lens group. (2) an inner focus zoom lens that images a subject; a photoelectric conversion means that converts the light imaged by the zoom lens into a video signal; and a predetermined high frequency component extracted from the video signal and integrated over a predetermined period. an autofocus device comprising: a focus detection means for controlling the lens system; a control means for controlling the lens system by a hill climbing method based on the output of the focus detection means; and a lens drive means for driving the lens system by the control means; An autofocus device characterized in that part or all of the correction operation for the focus movement caused by the magnification change operation due to the movement of the system is performed by switching a certain value that prompts the restart of the hill climbing method according to the subject distance.