JPH05107451A - Autofocusing device - Google Patents

Abstract

PURPOSE:To enhance the tracking (focusing) accuracy at the time of zooming, in a video movie in which an inner focusing lens is adopted. CONSTITUTION:The tracking curve at the time of zooming of an inner focusing lens is different for each subject distance. Accordingly, if the focusing lens is moved along the tracking curve at the time of zooming, focusing condition is maintained; however, on the wide-angle side (f0 to fm) (not shown), the depth of focus is deep, and the purposed tracking curve cannot be selected. Therefore, when zooming is carried out in this condition, focusing cannot be assured. Thus, in this region, tracking is carried out by wobbling so as to transfer to a tracking curve that has been previously prepared at the point fm (not shown).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a VTR with a built-in camera.
The present invention relates to an improvement of a focus adjustment device used for the above.

[0002]

2. Description of the Related Art In recent years, as a focus system used for video movies and the like, the contrast of the screen is detected by using the high frequency component of the video signal, and the focus lens is driven and controlled so as to maximize the contrast. Get the focus,
So-called mountain climbing auto focus is the mainstream.

On the other hand, as a focus device, an inner focus system is becoming mainstream instead of the conventional front lens focus. This inner focus method drives internal lenses such as relay lenses and compensators in the lens group, and it requires a large motor to drive a large-diameter lens that cannot achieve a short focusing distance in the front lens method. It has the feature that the disadvantages such as the need of the camera are eliminated, and that it is possible to focus in a full range from a close range of 0 m to infinity ∞.

However, on the other hand, a focus (focus) shift occurs during zooming, and therefore it must be corrected. The correction amount of this focus (focus) shift largely changes depending on the focal length and the distance to the subject, and there is no complete correction yet. Correcting the focus at the time of zooming in the inner focus method described above is called zoom tracking. As an example of performing this zoom tracking, there is a method of using the above-mentioned hill climbing method as it is. This will be described below.

FIG. 6 shows a configuration of a conventional contrast method processing using an inner focus type lens group and a video signal output from the lens group. In the figure, reference numeral 1 denotes an inner focus type lens barrel, 101 is a fixed condensing front lens, 102 is a variator for zooming, that is, zooming, and 103 is an image plane correction accompanying movement of the variator 102. Reference numeral 104 denotes a master lens used for focusing, which is a part of a relay lens. These lenses are generally a group of a plurality of lenses, but in this case, they are represented as one lens for convenience.

Reference numeral 2 denotes a CCD, which converts light incident on the lens barrel 1 from the outside into an electric signal, and the electric signal is sent to a camera signal processing circuit 3 to extract a video signal A and a luminance signal a respectively. .. Next, 401 is an HPF (high-pass filter), which passes a signal having a frequency equal to or higher than the luminance signal a, is amplified by an amplifier 404, and an unnecessary high-frequency component is cut by an LPF (low-pass filter) 405. This L
The output of the PF 405 is sent to the detector 406 and becomes a smooth waveform, converted into a digital signal by the A / D converter 407, and digitally added by the adder 408. This digital addition output Y is sent to the control circuit 5 as a focus evaluation value (index indicating the focus state). Where H
The focus detection circuit 4 is configured by the PF 401 to the adder 408.

Further, 6 is a motor driver, which is a control circuit 5.
The zoom motor 7 is driven on the basis of the zoom command from to move the variator 102. Similarly, 9 is a stepping motor driver, which is driven based on a focus command from the control circuit 5, and which is a master lens 10 for focusing.
The stepping motor 10 for moving 4 is driven. Reference numeral 8 denotes a potentiometer for detecting the position of the variator 102, that is, the focal length, which is read at a potential corresponding to the lens position on a one-to-one basis. Reference numeral 11 denotes a detection switch for detecting an end point of the movable range of the master lens 104, which is turned on when the master lens 104 is focused on a subject at infinity. Represents the amount of movement.

Next, the operation will be described with reference to FIGS. 6 to 11. First, the basic hill climbing method will be explained. The subject light incident through the lens barrel 1 is C
It is converted into an electric signal by the CD 2 and becomes a video signal A through the camera signal processing circuit 3. The luminance signal component (FIG. 7A) of them is guided to the focus detection circuit 4, and first, the HPF is detected.
In 401, only the predetermined high frequency component is extracted (FIG. 7 (b)). Then, after being amplified by the amplifier 404, L
The band is limited by the PF 405 (FIG. 7C), and the detector 40
It is detected at 6. (FIG.7 (d)). Further, it is converted into a digital value by the A / D converter 407, and the predetermined area in one screen shown in (h) of FIG.
The value of (i) is added and output as the focus evaluation value Y. That is, the focus evaluation value Y is an integrated value of high frequency components. Further, since the high frequency component corresponds to the contrast of the screen, the maximum contrast, that is, the maximum when the master lens 104 as the focus lens is in the focus, decreases as the focus shifts. Therefore, the focus evaluation value Y exhibits a mountain-shaped characteristic as shown in FIG. 8 as the master lens 104 moves. The control circuit 5 controls the stepping motor 1 so that the focus evaluation value Y is always maximized.
By controlling 0, the master lens 104 is driven to a focal point.

The difference between y ₁ and y _{2 in} FIG.
The cutoff frequency of 401 is determined, and the cutoff frequency is selected so that y ₁ <y _{2 in} FIG. In this way, the hill-climbing autofocus operation is achieved.

Next, the operation during zooming will be described.
A zoom signal is sent from the control circuit 5 to the motor driver 6 to drive the zoom motor 7. The variator 102 moves on the optical axis in accordance with the driving of the zoom motor, and performs a zooming action. At this time, the movement of the focal point occurs along with the movement of the variator 102, but the compensator 103 mechanically connected via a cam or the like simultaneously moves on the optical axis and moves so as to correct the focal point movement.

However, all the corrections cannot be made by the correction of only the compensator 103, and as a result, as shown in FIG. 9, the master lens is moved according to the movement of the variator 102 for each distance to the object, that is, according to the focal length. 104
Focus will not be reached unless is moved. Therefore, in order to focus during zooming, the master lens 104 may be moved along a so-called tracking curve shown in FIG.

As an example of a method of doing this, the hill climbing method described above is used with a slightly longer zoom time. That is, the case where the distance to the subject is 1 m is taken as an example. The theoretical tracking curve w with a distance of 1 m to the subject shown in FIG. 11 is assumed, and tracking is actually performed by using the hill climbing method as shown by the curve f, that is, moving from the wide-angle side to the telephoto side. Considering, the distance to the subject is unknown at the start of zooming. Therefore, if the above-mentioned hill-climbing method is used, the focus evaluation value for determining the in-focus state will be chased.
As a result, even if the distance to the subject is not known, the tracking curve is virtually tracked as if there is a tracking curve that serves as an index, and tracking is performed to maintain the in-focus state during zooming.

As described above, many inventions have been filed for the focus adjusting method of the lens called the rear lens or the inner focus method, including the above-mentioned conventional example. However, what can be said in common with these prior inventions is that it is not clarified how, when zooming from the wide-angle end to the telephoto side, it is possible to perform zooming while maintaining the in-focus state.

That is, the operation has been described only for the case where the zoom is performed again during the middle of the zoom or the case where the zoom is performed from the telephoto side to the wide-angle side. This is because the subject distance can be easily grasped and tracking is extremely easy.
To put this a little more briefly, for example, the tracking curve shown in FIG. 9 is considerably close to the wide-angle end (for example, the tracking curve for the subject distance of 1 m and the tracking curve for 2 m are extremely close to each other). Therefore, it is impossible to select a tracking curve corresponding to the subject distance first because the focus master lens easily moves to the adjacent curve due to a minute movement and the depth of field is deep. .. Under the present circumstances, it is not clear in the prior invention how to perform optimal tracking or how to grasp the distance to the subject when zooming from such a state to the telephoto side.

[0015]

Since the conventional focus adjusting device is configured as described above, the focus evaluation value when the subject content changes due to the change in the angle of view during zooming indicates the constant focus condition. I didn't want to reflect it. Therefore, there is a problem that it is difficult to correct the system in some cases because it is sometimes mistakenly determined that the subject is in focus.

The present invention has been made in order to solve the above-mentioned problems, and when zooming from the wide-angle side to the telephoto side, there is little focusing error and extremely accurate zoom tracking is possible. The purpose is to obtain a regulator.

[0017]

A focus adjusting device according to the present invention comprises a filter means for extracting a high frequency component from a picked-up image signal during a magnification change operation, and an output of the filter means is integrated over a predetermined period. And a first means for performing a wobbling operation by determining the amount of movement of the focus lens based on the result of the comparing means, and a comparing means for comparing the output of the integrating means with the output after a fixed time. A plurality of movement paths of the focus lens are prepared for each distance of the subject, and second movement means for storing the movement amount of the focus lens for each predetermined focal length with respect to each movement trajectory. The means and the second means are used together to move the focus lens during the zooming operation.

[0018]

According to the present invention, since the optimum tracking curve prepared in advance can be selected without using any special means by the above-mentioned structure, the focusing accuracy at the time of zooming is improved.

[0019]

【Example】

Example 1. The present invention will be described below with reference to the drawings. FIG. 1 shows a focus adjusting apparatus according to an embodiment of the present invention. In the figure, 14 is a comparison circuit for comparing focus evaluation values obtained from a focus detection circuit 4, and a data memory as a storage means. A certain ROM (Read Only Memory) 51 is connected to the control circuit 5.

Next, the operation will be described with reference to FIGS. Now, it is assumed that zoom tracking is performed from the wide angle side to the telephoto side along the tracking curve in FIG. At this time, if the distance to the subject is 2 m, the master lens 104 may be moved along the tracking curve Z of 2 m. However, in practice, the depth of focus is deep in the range of the focal lengths f _{0 to} f _n1 and the distance to the subject cannot be determined.
Even if a tracking curve is prepared for each distance in advance, it is not known which curve should be used. Therefore, in the range of the focal lengths f _{0 to} f _n1 where the depth of focus is deep, the angle of view and the content of the subject do not change much, so tracking is performed by evaluation value determination by wobbling in this portion.

That is, the master lens 104 is moved by the wobbling operation shown in FIG. 4, and the master lens 104 moves while correcting the moving direction according to the result of the judgment of the focus evaluation value Y obtained before and after the original focusing point. Then, when the focal length starts from f ₀ and becomes f _n1 , the tracking curve that starts closest to the position of the master lens 104 at that point is selected from the ROM 51, and thereafter, along the selected tracking curve. The master lens 104 is moved. This state is shown in FIG.

The wobbling operation will be described with reference to FIG. L represents a reference ideal line, which is the minimum (infinity; 10 m or more) and maximum (1 m) of the amount of extension of the master lens 104 on the telephoto side of the tracking curve shown in FIG.
A subject distance of 3 m, which is the middle of m), is assumed. h,
Each of i, j, and k indicates an operation during one field period. All operations are performed on the basis of one field, and four fields form one wobbling cycle.

Here, the fields h and j are the movement period of the master lens 104, and the field h is the front side with respect to the reference ideal line L, that is, the direction in which the master lens 104 is extended. On the contrary, the field j is the rear side, that is, The master lens 104 is moved in a direction in which it does not extend. The i and k fields are the focus evaluation values Y of the corresponding fields during the measurement period.
From the focus detection circuit 4 of FIG. That is, assuming that the reference ideal line L in FIG. 4 is the in-focus point, the front focus (focus) and the rear focus (focus) are found by comparing the focus evaluation values Y of the fields i and k, and at the same time, the defocus amount is obtained. Can also be determined.

Now, when a zoom signal is sent from the control circuit 5 of FIG. 1 to the motor driver 6 and the motor driver 6 drives the zoom motor 7, the variator 102 is moved to start the zooming operation to the telephoto side. Is h, i, j, k in FIG.
As shown in, the stepping motor 10 is driven via the stepping motor driver 9 by the focus command for each field. Thereby, the movement of the master lens 104 and the measurement of the focus evaluation value Y of the output from the focus detection circuit 4 are repeated. At this time, the master lens 104 is stopped in the measurement field. Then, the focus evaluation value Y obtained every other field is judged by the comparison circuit 14 to be larger or smaller.

When the focus evaluation values Y obtained in the fields i and k are respectively I and K, if the focus evaluation value Y of the above judgment result is (1) I to K, the current master lens is almost the same. If the position of 104 is the in-focus point, (2) If I> K, the in-focus point is the position where the master lens 104 is extended further. (3) If I <K, the in-focus point is the position where the master lens 104 is not extended further than the current position. , Operates according to this condition.

This can be shown by the focus evaluation value of FIG. 5, and the amount of defocus seen from the original focus point (top of the mountain) is represented by i "and k". In addition, FIG. 5 shows the case of the above (2). As can be seen from FIG. 5, it is preferable that the focus evaluation values Y in the fields of i and k are equal, that is, the condition of i ″ = k ″ and I = K, and as a result, the above (2)
I> in the case of i ″ <k ″ in FIG.
In the period of h'in the next field, the movement amount of the master lens 104 (for example, several steps in the step width of the stepping motor) is increased to further extend the amount, and the return amount is reduced in the field of J'to correct the focal point. It will be possible. This state is shown by m in FIG. The reference theoretical line corrected by this is shown as L.

The focus lens position in FIG. 4 is represented by the number of steps of the stepping motor 10,
2, 3, ... Mean the first step, the second step, and the third step.

The above-mentioned situation is shown in FIG. 3 as a movement locus of the master lens 104. This is advantageous because it makes it possible to obtain a focus correction operation that is not affected by a change in focus evaluation value due to a change in magnification regardless of the distance to the subject.

Here, the data format of the tracking curve preliminarily stored in the ROM 51 is represented by the amount of movement of the stepping motor 10 for moving the driving stepping motor 10 of the master lens 104. That is, the unit movement amount of the master lens 104 is represented by one step of the stepping motor 10. Therefore, the stepping number driven by the stepping motor 10 is the absolute position of the master lens 104. The ROM 51 has a tracking curve for each distance of the subject while taking the above data format, and for each predetermined distance to each tracking curve, that is, as shown by f _n1 , f _n2 , ... In FIG. Master lens 1
The movement amount of 04 is stored as the number of steps of the stepping motor 10.

In FIG. 3, the absolute position of the master lens 104 is represented by the number of steps of the stepping motor 10,
The focal length is read and represented by the potential of the potentiometer 8 corresponding to 1: 1.

Further, in FIG. 3, the line indicated by the broken line x is
When the absolute distance of the step motor 10 is zoomed from the position "2" to the telephoto side at the wide-angle side focal length f ₀ mm, the wobbling is performed to reach the focal length f _n1 while detecting the in-focus point. It is indicated that a point changes to a tracking curve with a subject distance of 2 m.

By the way, it goes without saying that the movement amount of the master lens 104 during the periods h and j in FIG. 4 is performed within the depth of focus where the wobbling operation is unnoticeable. That is, the movement amount is regulated by the information of the iris (aperture, not shown). Further, the wobbling operation over the entire zoom area is extremely controlled including the problem of the depth of focus where the inclination of the tracking curve on the telephoto side (the amount of extension of the master lens 104 per unit time) shown in FIG. 2 is steep. Had a difficult drawback.

In the above embodiment, the stepping motor is used as the master lens for focusing, but the same effect can be obtained with a DC motor. Further, the location where the tracking curve prepared in advance is changed from the focus detection based on the relative ratio may be arbitrarily selected according to the system. Further, the tracking curve prepared in advance may have a free number according to the accuracy. Further, it is more accurate to prepare a plurality of HPFs for extracting the high frequency component for obtaining the focus evaluation value Y. In this case, it is better to change the cutoff frequency of the HPF according to the situation or to obtain a plurality of filter outputs once (in one field).

[0034]

As described above, according to the focus adjusting device of the present invention, tracking is performed by the focus detection by wobbling in a place where the distance to the subject is very difficult to discriminate, and thereafter, according to the subject distance. Since the tracking curve is used, it is possible to perform zoom tracking with good focusing accuracy regardless of which point the zoom is performed over the entire zoom range.

[Brief description of drawings]

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

FIG. 2 is a diagram illustrating a zoom tracking curve in detail.

FIG. 3 is a diagram illustrating an operation of zoom tracking according to the present invention.

FIG. 4 is a diagram showing a wobbling operation.

FIG. 5 is a diagram illustrating a focused state due to wobbling.

FIG. 6 is a diagram showing a configuration of a conventional example.

FIG. 7 is a diagram illustrating an operation of a focus detection circuit.

FIG. 8 is a diagram showing a focused state due to a difference in HPF.

FIG. 9 is a diagram showing a tracking curve when zooming by an inner focus method.

FIG. 10 is a diagram showing evaluation value zones.

FIG. 11 is a diagram showing a state of zoom tracking by a mountain climbing method.

[Explanation of symbols]

 1 Inner focus type lens barrel 2 CCD 3 Camera signal processing circuit 4 Focus detection circuit 5 Control circuit 6 Motor driver 7 Zoom motor 8 Potentiometer 9 Stepping motor driver 10 Stepping motor 11 Detection switch 14 Comparison circuit 51 ROM 101 For fixed focusing Front lens 102 Variable variator 103 Compensator 104 Master lens 401 HPF 402 HPF 403 Switch 404 Amplifier 405 LPF 406 Detector 407 A / D converter 408 Adder

Claims (1)

[Claims] 1. A filter means for extracting a high frequency component from an imaged video signal during a magnification change operation, an integrating means for integrating the output of the filter means over a predetermined period, and an output of the integrating means after a predetermined time. And a first means for performing a wobbling operation for determining the movement amount of the focus lens based on the result of the comparison means, and a plurality of movement loci of the focus lens for each object distance. A second means for preparing and storing the movement amount of the focus lens for each predetermined focal length with respect to each movement locus is provided, and the zooming operation is performed by using the first means and the second means in combination. An autofocus device that sometimes moves the focus lens.