JPH05281459A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To enable highly precise zoom tracking by simple constitution as to a video camera which uses an inner focus type zoom lens. CONSTITUTION:A focus adjusting device which detects the high-band component level of an image pickup signal obtained from an image pickup element 2 as a focus evaluation value (y) and decides the point where the focus evaluation value (y) becomes maximum as a focusing position uses the inner focus type zoom lens which uses pulse motors 52 and 10 to drive a variator lens 102 for zooming and a master lens 104 for focusing respectively; and the zoom position and focus position are controlled with the numbers of driving pulses of the pulse motors 52 and 10 respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus adjusting device used in a camera-integrated VTR or the like.

[0002]

2. Description of the Related Art In recent years, a focus system used in video cameras and the like detects the contrast of a screen by using a high frequency component of a video signal and drives and controls a focus lens so that the contrast becomes maximum. The so-called hill-climbing autofocus method that obtains a focused point is the mainstream.

As a focus device for a zoom lens, an inner focus system is becoming mainstream instead of the conventional front lens focus system. This inner focus type zoom lens drives the rear group inside the lens such as the relay lens and compensator in the lens group. Disadvantages such as the need for a large motor to drive the lens have been eliminated, and it has the feature of being able to focus in a full range from a close range to infinity.

However, this inner focus type zoom lens needs to be corrected because a focus shift occurs during zooming. The correction amount of this focus shift largely changes depending on the focal length and the distance to the subject. Therefore, the current situation is that good correction cannot be made unless the detection accuracy of these is increased. Performing focus correction during zooming using this inner focus method is called zoom tracking.

FIG. 3 is a block circuit diagram showing the structure of a conventional focusing device using a hill-climbing autofocus system. Reference numeral 1 is an inner focus system zoom lens.
1 is a fixed front lens for condensing, 102 is a variator for zooming, 103 is a compensator for correcting the image plane accompanying movement of the variator 102, and 104 is a part of a relay lens used for focusing. These are master lenses, and these lenses consist of multiple lens groups.
Here, one lens is used.

Reference numeral 2 denotes a CCD, which converts the subject image formed by the zoom lens 1 into an electric signal. Reference numeral 3 denotes a camera signal processing circuit, which is a video signal V and a luminance signal Y (see FIG.
(A)) is output. Reference numeral 401 denotes a high-pass filter (hereinafter referred to as “HPF”), which passes a component b (FIG. 4A) of the luminance signal Y having a certain frequency or higher. Reference numeral 404 is an amplifier, and 405 is a low-pass filter (hereinafter referred to as “LPF”), which outputs a signal c (FIG. 4C) in which unnecessary high frequency components of the output signal of the amplifier 404 are cut. 406
Is a detector which detects the output signal c of the LPF 405 and outputs a signal d having a gentle waveform (FIG. 4 (d)). 407
Is an A / D converter that converts the input signal d into a digital signal. An adder 408 digitally adds the data in the focus detection area set at the center of the screen. This digital addition output y serves as a focus evaluation value (an index representing a focused state). The HPF 401 to the adder 408 described above constitute the focus detection circuit 4.

Reference numeral 5 is a control circuit to which the digital addition output y is input, and reference numeral 6 is a motor driver, which drives a zoom motor 7 for moving the variator 102 based on a zoom command from the control circuit 5. A pulse motor 9 is a pulse motor 1 for moving the master lens 104 for focusing.
0 is driven based on the focus command from the control circuit 5. A potentiometer 8 detects the position of the variator 102, that is, the focal length, and outputs a potential signal corresponding to the lens position on a one-to-one basis.

Reference numeral 11 denotes an end point detection switch for detecting an end point of the movable range of the master lens 104.
Is ON at a position where an object at infinity is in focus, and the amount of movement of the master lens 104 is represented with this position as a reference. Reference numeral 13 is a data memory, which is a data memory for storing the movement locus of the master lens 104 during zoom movement, that is, the tracking curve.

First, focus adjustment of this type of apparatus by the hill climbing method will be described. The subject light incident through the zoom lens 1 is converted into an electric signal by the CCD 2 and becomes a video signal V through the camera signal processing circuit 3.
The luminance signal component Y (FIG. 4A) of the video signal V is guided to the focus detection circuit 4, and the HPF 401 first extracts the signal b (FIG. 4B) of the predetermined high frequency component.
This signal b is amplified by the amplifier 404 and then the LPF 40
The band is limited by 5 (FIG. 4C) and detected by the detector 406 (FIG. 4D).

Further, the data is converted into a digital value by the A / D converter 407, and the data in the focus detection area of the screen ratio 1/9 to 1/4 located at the center of the screen is added by the adder 408 to obtain the focus. It is output as the evaluation value y. That is, the focus evaluation value y is the integrated value of the high frequency components, and since this high frequency component corresponds to the contrast of the screen, the maximum contrast, that is, the master lens 104.
Is the maximum value when is at the in-focus point, and becomes smaller as it deviates from the in-focus point. Therefore, the focus evaluation value y has a mountain-shaped characteristic as shown in FIG. 5 as the master lens 104 moves. The control circuit 5 controls the pulse motor 10 so that the focus evaluation value y is always the maximum, and drives the master lens 104 to the in-focus point.

The difference between the characteristics y1 and y2 in FIG.
The case where the cutoff frequencies of the HPF 401 are different is shown. In this way, the hill-climbing autofocus operation is achieved.

Next, the operation during zoom movement will be described. When the zoom signal is sent from the control circuit 5 to the motor driver 6 and the zoom motor 7 is driven, the variator 10
2 moves on the optical axis to perform a zooming action. At this time, the focus also moves as the variator 102 moves, but the compensator 103 mechanically connected via a cam or the like simultaneously moves on the optical axis to correct the focus movement.

However, all the corrections cannot be made by the correction of the compensator 103 alone, and as a result, as shown in FIG. 6, the master lens 104 must be moved in accordance with the movement of the variator 102 for each distance to the subject. I'm not impatient. Therefore, in order to focus during zooming,
It is necessary to move the master lens 104 along a so-called tracking curve shown in FIG.

By the way, in the recent lens construction, the compensator 103 is omitted in order to reduce the size and weight.
The operation of this compensator 103 is controlled by the master lens 104.
The method of leaving it to the mainstream is becoming mainstream. The zoom tracking curve at this time has a large inflection point as shown in FIG. In the following explanation, this compensator 1
The case of the method without 03 will be described.

Next, an example of a method for performing such zoom tracking will be described. FIG. 8 is an enlarged view of the point P of the zoom tracking curve in FIG. 7, and shows the movement locus of the master lens 104 during zoom movement. Here, the data format of the tracking curve stored in the data memory 13 is the pulse motor 1 for driving the master lens 104.
It is stored with a movement amount of 0.

That is, since the unit movement amount of the master lens 104 is represented by one step of the pulse motor 10, the number of steps driven by the pulse motor 10 is the absolute position of the master lens 104. In this format, there is a tracking curve for each subject distance, and each tracking curve has a predetermined focal length, that is, the positions f1, f2, f3, ... F9 of the variator 102 shown in FIG.
The amount of movement of the master lens 104 at is stored as the number of steps of the pulse motor 10. At this time, the position of the variator 102 is read with the potential of the potentiometer 8 in a 1: 1 relationship.

Therefore, the position of the variator 102 is detected by the potentiometer 8 during zoom movement, and the pulse motor 10 is driven according to the amount of extension of the master lens 104 at the detected position. Therefore, with respect to the ideal tracking curve l1 in FIG.
Has a step-like movement trajectory. In FIG. 8, the master lens 104 is extended one step at each position of the variator 102, f2, f3, ..., F8. As described above, tracking is performed during zoom movement, and focus movement is corrected.

[0018]

The conventional autofocus device is constructed as described above, but especially in zoom tracking during zoom movement, the variator 10 is used.
2 and the position detection accuracy of the master lens 104 are not increased, good zoom tracking cannot be performed, and a potentiometer with high resolution and a small linearity deviation is required.

The present invention has been made to solve the above problems, and an object thereof is to obtain an autofocus device capable of performing highly accurate zoom tracking with extremely simple control during zoom movement. To do.

[0020]

A feature of the present invention is that a pulse motor is also used for the zoom motor, and both the movement of the variator and the movement of the master lens are driven by the pulse motor.

[0021]

Since the pulse motor can be controlled by the number of drive pulses, it is possible to easily perform control with excellent variator position detection resolution and detection accuracy without using a potentiometer.

[0022]

1 is a block circuit diagram showing an embodiment of the present invention. In the figure, reference numeral 52 denotes a zoom pulse motor for moving the variator 102, which is driven by the pulse motor driver 51 based on a command from the control circuit 5.
Reference numeral 53 is a zoom end point detection switch for detecting the moving end point of the variator 102, and 54 is a signal line for guiding the vertical synchronizing signal Vs from the camera signal processing circuit 3 to the control circuit 5.

Further, the data memory 13 stores the position data of the variator 102 on the tracking curve as the moving amount of the zoom pulse motor 52. In other words, this is the same as the driving method of the master lens 104,
The movement amount of the variator 102 is the zoom pulse motor 52.
Is represented by the number of driving steps, and this number of steps is the absolute position of the variator 102. The pulse motor 10
Will be referred to as a "focusing pulse motor" in order to distinguish it from the zooming pulse motor 52, but the operation is the same as that of the conventional example.

FIG. 9 is a sectional view showing an embodiment of the variator driving mechanism, and shows a structure in which the variator 102 is driven by the rotation of the screw screw 60 directly connected to the shaft of the zoom pulse motor 52. According to this configuration, the unit movement amount of the variator 102 is determined by the total movement amount of the variator 102 in the zoom area, the feed pitch of the screw screw 60, and the rotation angle of the zoom pulse motor 52 per step.

In FIG. 8, the tracking curve 11 has a focal length, that is, at the positions f5 to f9 of the variator 102, since the inclination is slightly steep with respect to f1 to f5, the accuracy of the movement amount of the variator 102 is doubled. The master lens 104 is extended. Variator 1 here
No. 02 position f5 to f9 unit movement amount f5 -f6, f6 -f
When ..f8-f9 corresponds to one step which is the minimum drive unit of the pulse motor 52 for zooming, f1 to f5
F1-f2, f2-f3, ... F4-f5 correspond to two steps.

In this embodiment, the movement of the variator 102 is carried out by driving the zoom pulse motor 52, but this driving timing is carried out in synchronization with the vertical synchronizing signal. The zoom pulse motor 52 is set to 1 each time a vertical synchronization signal is input.
It is driven step by step. This will be described with reference to the timing chart of FIG.

FIG. 2A shows a vertical synchronizing signal Vs obtained from the camera signal processing circuit 3 through a signal line 54. In synchronization with this, the zoom pulse motor 52 is first driven by one step (see FIG. b)), and stops at an intermediate position between the variator positions f1 and f2 (FIG. 2 (d)). At this point, the master lens 104 does not extend, so the focus pulse motor 10 is not driven.

Next, when the second Vs signal is input,
The pulse motor 52 for zooming is driven one step again,
Stop at the variator position f2. Next, when the zoom pulse motor 52 is driven by one step by the third Vs signal, the focus pulse motor 10 is driven by one step (FIG. 2 (c)) and the variator positions f2 and f2.
In the middle of 3, the master lens 104 stops at the point K in FIG.

The operation is continued in this manner, and after the zoom pulse motor 52 is driven one step by the 12th Vs signal at the position f8 of the variator 102 in FIG.
The focus pulse motor 10 is driven by one step (FIG. 2 (d)), and the master lens 104 stops at the position of f9 which is moved by seven steps as a result from the position of the variator position f1.

In the embodiment shown in FIG. 8, the case where the driving of the focus pulse motor 10 is one step with respect to the one step drive of the zoom pulse motor 52 has been described, but the zoom tracking shown in FIG. In a place where the curve has a large inclination, the driving of the focus pulse motor 10 may take several steps as compared with the one step drive of the zoom pulse motor 52. At this time, the focus pulse motor 10 may be continuously driven.

In the above embodiment, both the zoom pulse motor 52 and the focus pulse motor 10 are shown in FIG.
As shown in (b) and (d), one pulse drive moves one step.

The following modifications are possible in the above embodiment. (1) The minimum movement amount (movement amount per step) of the zoom pulse motor may be freely selected according to the system according to the movement amount of the variator in the entire zoom area, the required resolution, and the zoom time. (2) The drive timing of the zoom pulse motor is not limited to synchronization with the vertical synchronization signal,
A corresponding signal may be used. (3) When the driving amount of the focus pulse motor is large and it takes time to drive, the zoom pulse motor may be driven for each frame. (4) Although the focus pulse motor and the zoom pulse motor are driven at individual timings, they may be driven at the same timing.

[0033]

According to the present invention, since the pulse motor is used to move the variator, highly accurate zoom tracking can be realized, and an autofocus device can be obtained in which focus correction during zoom movement can be favorably performed over the entire zoom range. effective. In particular, since the amount of movement of the variator is determined by the number of drive pulses of the pulse motor, it is possible to obtain an effect that the zoom speed can be made constant and easily changed.

[Brief description of drawings]

FIG. 1 is a block circuit diagram of a focus adjustment apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation timing of the pulse motor of the embodiment of FIG.

FIG. 3 is a block circuit diagram of a conventional autofocus device for a video camera.

FIG. 4 is a waveform diagram of a focus detection circuit 4 of this conventional example.

FIG. 5 is a diagram showing an output characteristic of the focus detection circuit 4 when the HPF of the conventional example is switched.

FIG. 6 is a diagram showing a zoom tracking curve of a conventional example.

FIG. 7 is a diagram showing a zoom tracking curve of an autofocus device in which a compensator is omitted.

8 is a partially enlarged view of FIG. 7 and is a diagram for explaining the zoom tracking operation of the embodiment of FIG.

9 is a sectional view showing an example of a drive mechanism of the variator of the embodiment of FIG.

[Explanation of symbols]

 1 Inner focus type zoom lens 4 Focus detection circuit 5 Control circuit 10 Focus pulse motor 13 Memory circuit 52 Zoom pulse motor

Claims (2)

[Claims] 1. An autofocus device for an inner focus type zoom lens, wherein a variator is moved to change a focal length, and a master lens is moved to correct the movement of a focus, wherein the variator is moved. A pulse motor, a second pulse motor for moving the master lens, a focus detection circuit for detecting the level of a high frequency component of an imaged video signal obtained from an image sensor as a focus evaluation value, and the above-mentioned detection during zooming. A control circuit for controlling the position of the master lens by the hill climbing method so that the focus evaluation value becomes the maximum value, and the positions of the variator and the master lens are controlled as the number of steps of the first and second pulse motors. An autofocus device having a configuration. 2. The autofocus device according to claim 1, wherein the movement amount of the master lens with respect to the movement amount of the variator is switched according to the inclination of the tracking curve.