JP2763428B2 - Auto focus device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camera-integrated VTR.
The present invention relates to an improvement of a focus adjustment device used for the above-described method.

[0002]

2. Description of the Related Art In recent years, as a focus method used for video movies and the like, a contrast of a screen is detected by using a high frequency component of a video signal, and a focus lens is drive-controlled so that the contrast is maximized. Get focus,
So-called hill-climbing autofocus is the mainstream.

On the other hand, as a focus device, an inner focus method is becoming mainstream in place of the conventional front lens focus. This inner focus method drives the master lens that is a part of the relay system lens in the lens group, and is used to drive a large-diameter heavy lens that cannot achieve a short focusing distance in the front lens method. Disadvantages such as the necessity of a large motor are eliminated, and furthermore, it is possible to perform focusing in the full range from 0 m to infinity 至.

[0004] On the other hand, however, a focus (focusing) shift occurs during zooming, so that it must be corrected. The amount of correction of the focus (focus) shift varies greatly depending on the focal length and the distance to the subject, and at present, there is no one that has been completely corrected. To the focus (focus) correction when the zoom in inner looks focused method described here refers to the zoom tracking. As an example of performing this zoom tracking, there is a method of directly using the above-described hill-climbing method. Hereinafter, this will be described.

FIG. 6 shows the structure of a conventional contrast method using an inner focus type lens group and its output video signal. In the figure, reference numeral 1 denotes an inner focus type lens barrel, 101 denotes a fixed focusing front lens, 102 denotes a variator for zooming, that is, a magnification change, and 103 denotes an image plane correction accompanying movement of the variator 102. Is a master lens used for focusing, which is a part of a relay system lens. These lenses are generally a plurality of lens groups, but in the present case, they are expressed as a single lens for convenience.

[0006] Reference numeral 2 denotes a CCD, which converts incident light from the outside into the lens barrel 1 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. . Next, reference numeral 401 denotes an HPF (high-pass filter), which passes a signal of a certain frequency or higher of the luminance signal a, is amplified by the amplifier 404, and an LPF (low-pass filter) 405 cuts unnecessary high-frequency components. This L
The output of the PF 405 is sent to the detector 406 and becomes smooth as a waveform, converted into a digital signal by the A / D converter 407, and digitally added by the adder 408. The digital addition output Y is sent to the control circuit 5 as a focus evaluation value (an index indicating a focused state). Where H
The focus detection circuit 4 is constituted by the PF 401 to the adder 408.

Reference numeral 6 denotes a motor driver, and a control circuit 5
The variator 102 is moved by driving the zoom motor 7 on the basis of the zoom command from. Similarly, reference numeral 9 denotes 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.
4 is driven to move the stepping motor 10. 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. 11 is a detection knowledge switch you detect the end point of the movable range of the master lens 104, made of the ON at the point where the master lens 104 is focused on an object at infinity, the movement of the master lens of this point as a reference The quantity is expressed.

Next, the operation will be described with reference to FIGS. First, the basic hill climbing method will be described. The subject light incident through the lens barrel 1 is C
The signal is converted into an electric signal by the CD 2 and becomes a video signal A via the camera signal processing circuit 3. The luminance signal component (FIG. 7 (a)) is guided to the focus detection circuit 4, and first, the HPF
At 401, only a predetermined high frequency component is extracted (FIG. 7B). Next, after being amplified by the amplifier 404, L
The band is limited by the PF 405 (FIG. 7C), and the detector 40
6 is detected. (FIG. 7 (d)). Further, the image data is converted into a digital value by the A / D converter 407, and a predetermined area in one screen shown in 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 the high frequency component. The upper Symbol high frequency components since correspond with the contrast of the screen, the maximum when the master lens 104 as maximum contrast, i.e. the focus lens is in focus decreases as shifted from the focal point. 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 10 so that the focus evaluation value Y is always maximized, and drives the master lens 104 to a focal point.

Note that the difference between y ₁ and y _{2 in} FIG.
401 determined by the difference in the cutoff frequency of the cutoff frequency such that y ₁ <y ₂ in FIG. 8 is selected. In this way, a hill-climbing autofocus operation is achieved.

Next, the operation at the time of zooming will be described.
The 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 operation. At this time, the focal point moves as the variator 102 moves, 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, the correction using only the compensator 103 cannot perform all the corrections. As a result, as shown in FIG. 9, the master lens according to the movement of the variator 102 for each distance to the subject, that is, according to the focal length. 104
If you do not move it, you will not be in focus. 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 for doing this, the above-described hill-climbing method 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.
Assuming a theoretical tracking curve of 1 m to the subject shown in FIG. 11 and actually taking the tracking using the hill-climbing method as shown by the curve f, that is, moving from the wide-angle side to the telephoto side. Given the above, at the start of zooming, the distance to the subject is not known. Therefore, if the above-mentioned hill-climbing method is used, the focus evaluation value for judging the in-focus state will follow up where the focus evaluation value becomes large. A tracking curve is assumed as if it were present, and tracking is performed to maintain a focused state at the time of zooming.

A number of inventions, including the above-mentioned prior art, have been filed for the method of adjusting the focus of a lens called the rear lens or inner focus method. However, what can be said in common with these prior arts is that, when zooming from the wide-angle end to the telephoto side, it is not clear how zooming can be performed while maintaining the in-focus state.

That is, the operation is described only when zooming is performed again in the middle of zooming or when zooming from the telephoto side to the wide-angle side. In this method, the subject distance can be easily grasped, and tracking is extremely easy.
To put it a little more simply, for example, the tracking curve near the wide-angle end of the tracking curve shown in FIG. 9 is quite close (for example, the tracking curve at a subject distance of 1 m and the tracking curve at 2 m are extremely close). Therefore, it is impossible to first select a tracking curve corresponding to the subject distance because the focus master lens easily moves to the next curve due to a minute movement, and furthermore, the depth of field is deep. . At present, it has not been clarified in the prior invention how to perform optimal tracking or how to grasp the distance to the subject when zooming to the telephoto side from such a state.

[0015]

Since the conventional focus adjusting device is configured as described above, the focus evaluation value when the subject content changes due to a change in the angle of view at the time of zooming always shows the focus state. It was nice that it was reflected. Therefore, there is a problem that it is sometimes determined that focusing is erroneously performed, and it is difficult to perform correction with high accuracy .

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has a focus capable of achieving extremely accurate zoom tracking with little focusing error when zooming from the wide-angle side to the telephoto side. The aim is to obtain an adjusting device.

[0017]

A focus according to the present invention
Scan equipment is, Masutaren for the zoom lens and focus
Inner focus type lens device having
Converts subject light incident on the lens device into a video signal
Converting means for converting a luminance signal component of the video signal into a predetermined
Focus detection method that integrates the area and generates a focus evaluation value
And a comparator for comparing the focus evaluation value with a predetermined reference value.
And the master based on the comparison result of this comparison device.
Depending on the means to move the lens and the distance to the subject
Storage means for storing a plurality of tracking curves.
When driving the above zoom lens,
Now, move the master lens up to the specified focal length.
Wobbling operation and the focus
Drive while detecting the focal point based on the evaluation value
Closely related to the master lens at the focal length of
While sorting the tracking curve from the storage means,
The master lens above corresponds to the selected tracking curve.
Drive .

[0018]

According to the present invention, in a deep range of the depth of focus,
The master lens up to the specified focal length.
Bring operation is performed, and the focus
Drive while performing focus detection by value,
The focal length is close to the master lens.
The racking curve is selected from the storage means, and
The above master lens corresponding to the separated tracking curve
Is driven, so that an optimal tracking curve prepared in advance can be selected without using any special means, so that the focusing accuracy at the time of zooming is improved.

[0019]

【Example】

Embodiment 1 FIG. Hereinafter, the present invention will be described with reference to the drawings. FIG. 1 shows a focus adjustment apparatus according to an embodiment of the present invention. In the figure, reference numeral 14 denotes a comparison circuit for comparing focus evaluation values obtained from a focus detection circuit 4, and a data memory as 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 of FIG. At this time, assuming that the distance to the subject is 2 m, the master lens 104 may be moved along the tracking curve Z of 2 m. However, actually, in the range of the focal length f _{0 to} f _n1 , the depth of focus is so deep that it is impossible to determine the distance to the subject.
Even if a tracking curve is prepared for each distance in advance, it is not known which curve to use. Therefore, in the range of the focal length 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 so much, and tracking is performed in this part by the evaluation value judgment by wobbling.

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 magnitude judgment of the focus evaluation value Y obtained before and after the original focal point. When the focal length starts from f ₀ and reaches f _n1 , a tracking curve starting from the position closest to 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 is shown in FIG.

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

Here, the h and j fields are during the movement of the master lens 104, and the h field is in front of the reference ideal line L, that is, in the direction in which the master lens 104 is extended. The master lens 104 is moved in the returning direction. In the fields i and k, the focus evaluation value Y of the corresponding field in the measurement period is obtained from the focus detection circuit 4 in FIG. That is, assuming that the reference ideal line L in FIG. 4 is the focal point, the front focus (focus) and the rear focus (focus) can be determined by comparing the focus evaluation values Y of the i and k fields, and at the same time, the defocus amount Can also be determined.

Now, when a zoom signal is sent from the control circuit 5 of FIG. 1 to the motor driver 6, the motor driver 6 drives the zoom motor 7, moves the variator 102, and starts a variable power operation to the telephoto side. Are h, i, j, k in FIG.
As shown in (1), a stepping motor 10 is driven via a stepping motor driver 9 by a 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 determined by the comparison circuit 14 to be larger or smaller.

Here, assuming that the focus evaluation values Y obtained in the respective fields i and k are I and K, respectively, if the focus evaluation value Y of the above determination result is (1) I to K, the current master lens is almost present. If the position of 104 is the focal point, (2) if I> K, the focal point has further extended the master lens 104. If (3) I <K, the focal point returns the master lens 104 further than the current position.
It operates according to this condition.

This can be represented by the focus evaluation value in FIG. 5, and the defocus amount as viewed from the original focal point (the top of the mountain) is represented by i ″, k ″. FIG. 5 shows the case (2). As can be seen from FIG. 5, it is preferable that the focus evaluation values Y in the i and k fields be equal, that is, the condition of I = K and i = K, and as a result, the above (2)
If I> K , i ″ <k ″ in FIG. 5, the moving amount of the master lens 104 ( for example, several steps with the step width of the stepping motor, etc.) during the period h ′ of the next field in FIG. ) Is increased and further extended, and
If the amount of return is reduced in the field of J ', correction to the focal point can be performed. This situation is indicated by m in FIG. Further, the reference theoretical line thus corrected is indicated as L '.

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

The above state is shown in FIG. 3 as the movement locus of the master lens 104. This is advantageous because a focus correction operation can be obtained that is not affected by the subject distance and is not easily affected by a change in focus evaluation value due to a change in magnification.

The data format of the tracking curve prepared in advance stored here in ROM51 is represented by moving amount of 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 becomes the absolute position of the master lens 104. In the ROM 51, while taking the above data format, a tracking curve is provided for each distance to the subject, and each tracking curve is provided for each predetermined distance, that is, as shown by f _n1 , f _n2 ,... In FIG. The moving amount of the master lens 104 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 corresponding to 1: 1 from the potential of the potentiometer 8.

In FIG. 3, a line indicated by a broken line x is
When the absolute position of the step motor 10 by the focal length f ₀ mm at the wide-angle side went a zoom to the telephoto side from the place of "2", to go as far as the focal length f _n1 while detecting the focal point in the wobbling, the This indicates that the point changes to a tracking curve with a subject distance of 2 m.

Incidentally, it goes without saying that the amount of movement of the master lens 104 during the periods h and j in FIG. That is, the amount of movement is regulated by the information of the iris (aperture; not shown). In addition, the wobbling operation of the entire zoom area is extremely controlled in consideration of the steepness of the tracking curve on the telephoto side shown in FIG. Had difficult drawbacks.

In the above embodiment, the stepping motor is used for the master lens for focusing. However, the same effect can be obtained with a DC motor. Further, the point where the focus point is detected by the relative ratio and transitions to the tracking curve prepared in advance may be arbitrarily selected according to the system. Further, the number of tracking curves prepared in advance may be any number according to the accuracy. Further, the accuracy is improved by preparing a plurality of HPFs for extracting the high frequency components 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 (for one field).

[0034]

As described above, according to the focus adjusting apparatus according to the present invention, in a place where the distance to the subject is very difficult to determine, tracking is performed by detecting the focal point by wobbling, and thereafter, the tracking is performed according to the subject distance. Since the configuration is such that the tracking curve is used, zoom tracking with good focusing accuracy is possible regardless of zooming from any point over the entire zoom range.

[Brief description of the 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 an operation of wobbling.

FIG. 5 is a diagram illustrating a focused state by wobbling.

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

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

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

FIG. 9 is a diagram illustrating a tracking curve at the time of zooming by the inner focus method.

FIG. 10 is a diagram illustrating zones of evaluation values.

FIG. 11 is a diagram illustrating a state of zoom tracking by a hill-climbing method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inner focus 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 Fixed light condensing Front lens 102 Variable power 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)

(57) [Claims] 1. A zoom lens and a master for focusing
Inner focus type lens device having a lens
And converts the subject light incident on the lens device into a video signal.
Converting means for converting the luminance signal component of the video signal
Focus that accumulates for a predetermined area of and generates a focus evaluation value
Detecting means for comparing the focus evaluation value with a predetermined reference value
Based on the comparison result of the comparison device and the comparison device,
The means to move the master lens and the distance to the subject
Storage means for storing a plurality of corresponding tracking curves;
When driving the zoom lens, the depth of focus is
In the range, the master lens up to the predetermined focal length
Wobbling operation, and when it is extended and returned,
Drive while performing focus detection based on the focus evaluation value.
Close relationship with the master lens at a given focal length
When a certain tracking curve is selected from the storage means,
The above master corresponding to the selected tracking curve
An autofocus device characterized by driving a lens .