JP2507144B2 - Focus adjustment device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement of a focus adjusting device used in a camera-integrated VTR or the like.

[Conventional technology]

In recent years, as a focus method 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 drive-controlled so as to maximize the contrast, so-called a so-called focus point is obtained. Mountain climbing auto focus is the mainstream.

On the other hand, as a focus device, an inner focus method is becoming mainstream instead of the conventional front focus.

This inner focus method drives internal lenses such as a relay lens and a compensator in the lens group, and the in-focus short distance in the front lens method cannot be short.
Disadvantages such as the need for a large motor to drive a heavy lens with a large diameter are eliminated, and it has the feature that it is possible to focus in a full range from 0m to infinity at infinity.

However, on the other hand, a focus (focus) shift occurs during zooming, so 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 here is called zoom tracking. As an example of performing this zoom tracking, there is a method of directly using the above-described hill climbing method.

 This will be described below.

FIG. 2 shows a configuration of a conventional contrast method processing using an inner focus type lens group and a video signal which is an output thereof.

In the figure, 1 represents an inner focus type lens barrel, 101 is a front lens for condensing light, 102 is a variator for zooming, that is, magnification change, and 103 is a variator 102.
Compensator for correcting the image plane associated with the movement of the
Is a master lens used for focusing, which is a part of the 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 incident light from the outside into the lens barrel 1 into an electric signal, and the electric signal is a camera signal processing circuit 3
And the video signal A and the luminance signal a are respectively taken out. 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.

The output of the LPF 405 is sent to the wave 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 (index indicating the focus state).

Here, the focus detection circuit 4 is configured by the HPF 401 to the adder 408.

A motor driver 6 drives the zoom motor 7 based on a zoom command from the control circuit 5, and a variator 10 is provided.
Move 2 Similarly, 9 is a stepping motor driver, which is driven based on a focus command from the control circuit 5 and drives a stepping motor 10 that moves the master lens 104 for focusing. A potentiometer 8 detects the position of the variator 102, that is, the focal length, and is read at a potential corresponding to the lens position on a one-to-one basis. Reference numeral 11 is a detection switch for detecting the 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, and the movement amount of the master lens is based on this point. Represented.

Next, the operation will be described with reference to FIGS. 2 to 7. First, the basic hill climbing method will be explained. The subject light incident through the lens barrel 1 is converted into an electric signal by the CCD 2 and becomes a video signal A through the camera signal processing circuit 3. The luminance signal component (Fig. 3 (a)) of them is guided to the focus detection circuit 4, and first, only a predetermined high frequency component is extracted in the HPF 401 (Fig. 3 (b)). Next, after being amplified by the amplifier 402, the band is limited by the LPF 405 (FIG. 3 (c)) and detected by the detector 406 (FIG. 3 (d)). Further, the value is converted into a digital value by the A / D converter 407, and the adder 408 adds the value of a predetermined area in FIG. 6 (i) shown in FIG. It is output as (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. 4 as the master lens 104 moves. The control circuit 5 controls the stepping motor 10 so that the focus evaluation value (Y) always becomes maximum, and drives the master lens 104 to the in-focus point.

The difference between y ₁ and y ₂ in FIG. 4 is determined by the difference in cutoff frequency of the HPF401, 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 drive of the zoom motor, and performs a zooming action. At this time, the movement of the focal point occurs 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. Focus will not be reached unless 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 for doing this, the hill climbing method described above is used with a slightly longer zoom time. That is,
Now, take the case where the distance to the subject is 1 m as an example. The theoretical tracking curve w with a distance of 1 m to the subject shown in FIG. 7 is hypothesized, and actually, tracking is 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 this, the distance to the subject is unknown at the start of zooming. Therefore, if the above-mentioned hill climbing method is used, it follows that the focus evaluation value for determining the in-focus state becomes large, so even if the distance to the subject is not known as a result, it is as if the tracking curve is an index. The tracking curve is virtually taken as if there is an object, and the in-focus state at the time of zooming is assumed.

[Problems to be Solved by the Invention]

Since the conventional apparatus is configured as described above, it is hard to say that the focus evaluation value always reflects the focus state when the subject content changes due to the change in the angle of view during zooming.

Therefore, it is sometimes determined that the subject is in focus by mistake, and it is difficult to accurately correct the focus shift.

The present invention has been made in order to solve the above problems, and an object of the present invention is to provide a focus adjusting device with very few focusing errors and extremely high accuracy.

[Means for solving the problem]

The focus adjusting device according to the present invention moves the master lens based on the relative ratio of the in-focus evaluation values that have passed through two HPFs at a place where the depth of focus is comparatively deep, and a certain focal length where the depth of focus starts to become shallow. From the position, zoom tracking is performed along a tracking curve prepared in advance.

[Action]

According to the present invention, with the above-described configuration, the optimum tracking curve prepared in advance can be selected without using any special means, so that the focusing accuracy during zooming is improved.

〔Example〕

An embodiment of 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, 402 is an HPF (high-pass filter) 2,
As shown in FIG. 10, the cutoff frequency is set higher than that of HPF1. Further, 403 is a switch for switching between HPF1 and HPF2 to output, and 14 is a calculation circuit for calculating the focus evaluation value obtained by switching the switch 403, and ROM (read-out) which is a data memory as a storage means. An only memory) 51 is connected to the control circuit 5.

Next, the operation will be described with reference to FIGS. 1, 4, and 8 to 11.

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 focal lengths f _{0 to} f _n , and it is not possible to determine the distance to the subject, so which curve should be used even if tracking curves are prepared for each distance in advance? I don't understand. Therefore, in the range of the focal lengths f _{0 to} f _n where the depth of focus is deep, the angle of view and the content of the subject are stable without much change, and therefore tracking is performed in this portion by judgment based on the evaluation value.
That is, the relative ratio is calculated from the evaluation value obtained by the difference in the HPF cutoff frequency shown in FIG. 4, and the master lens 104 is moved according to this ratio. Then, when the focal length starts from f ₀ and becomes f _n , the master lens at that point
The tracking curve that starts closest to the position of 104 is selected from the ROM 51, and thereafter, the master lens 104 is moved along this selected tracking curve.
This is shown in FIG.

Here is the calculation of the relative ratio, but in FIG.
The HPF1 (401) is selected as the HPF, and the focus evaluation value at that time is y ₁ in FIG. Further, when the HPF2 is selected, the focus evaluation shall be y ₂ of Figure 4. here
HPF2 (402) shall have a higher cutoff frequency than HPF1. The characteristics of y ₁ and y ₂ of both are as shown in FIG.

When a zoom signal is sent from the control circuit 5 to the motor driver 6, the motor driver 6 drives the zoom motor 7, moves the variator 102, and starts the zooming operation to the telephoto side,
The control circuit 5 switches the switch 403 for each field as shown in FIG. 11, and calculates the focus evaluation values y ₁ and y ₂ obtained for each field to obtain the relative ratio. As can be understood from FIG. 4, when HPF2 having a high cutoff frequency is used, the focus evaluation value with respect to the unit movement amount from the focus tends to decrease. Therefore, it can be determined from this calculation result whether or not the focus is lost. That is, since the calculation result A = y ₂ ÷ y _{1 of the} calculation circuit 14 decreases when zooming is started and the focus moves away, an appropriate threshold value (for example, 80% of the average A value at the time of focusing, etc.) is obtained. ), The master lens 104 is extended by a predetermined width (for example, several steps with the step width of the stepping motor) and stopped, and then waits again until the division result A crosses the threshold value. This state is shown in FIG. 9 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 the change in the focus evaluation value due to the 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 movement 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 number of steps driven by the stepping motor 10 becomes 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, in FIG.
As indicated by f _n1 , f _n2 , ..., The amount of movement of the master lens 104 is stored as the number of steps of the stepping motor 10.

In FIG. 9, the absolute position of the master lens 104 is represented by the number of steps of the stepping motor 10, and the focal length is read from the potential of the potentiometer 8 in a 1: 1 correspondence.

Further, in FIG. 9, the line indicated by the broken line x is a relative ratio when zooming from the position where the absolute position of the step motor 10 is "2" to the telephoto side at the focal length f ₀ mm on the wide angle side. It shows that while the focus is detected, it goes to the focal length f _n , and at that point, the tracking curve shifts to a subject distance of 2 m.

Although the stepping motor is used as the master lens for focusing in the above embodiment, the same effect can be obtained with the 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.

Furthermore, the tracking curve prepared in advance may have a free number according to the accuracy.

〔The invention's effect〕

As described above, according to the focus adjustment apparatus of the present invention, tracking is performed by in-focus detection based on the relative ratio in a place where it is very difficult to determine the distance to the subject, and then the tracking curve according to the subject distance is used. With this configuration, 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 adjusting device according to an embodiment of the present invention, FIG. 2 is a diagram showing a configuration of a conventional example, FIG. 3 is a diagram explaining an operation of a focus detection circuit, and FIG. Fig. 5 is a diagram showing the in-focus state due to the difference in HPF, Fig. 5 is a diagram showing the tracking curve during zooming by the inner focus method,
FIG. 7 is a diagram showing a state of zoom tracking by the hill climbing method, FIG. 6 is a diagram showing zones of evaluation values, FIG. 8 is a diagram for explaining a zoom tracking curve in detail, and FIG. 9 is a zoom tracking of the present invention. FIG. 10 is a diagram showing the band of HPF, and FIG. 11 is a diagram explaining the operation of the present invention. In the figure, 1 is an inner focus type lens barrel, 101 is a fixed front lens for condensing, 102 is a variator for zooming, 103 is a compensator, 104 is a master lens, and 2 is
CCD, 3 is a camera signal processing circuit, 401 and 402 are HPFs, 403 is a switch, 404 is an amplifier, 405 is an LPF, 406 is a detector, and 407 is A.
/ D converter, 408 adder, 4 focus detection circuit, 5 control circuit, 6 motor driver, 7 zoom motor, 8
Is a potentiometer, 9 is a stepping motor driver, 10 is a stepping motor, 11 is a detection switch, 14 is an arithmetic circuit, and 51 is a ROM. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] 1. A photoelectric conversion unit that collects light from a subject by a lens system and converts the collected light into an image pickup signal, and a plurality of units that extract high frequency components of different bands from the image pickup video signal. The filter means, the means for integrating the output of the filter means over a predetermined period, and the calculating means for calculating the relative ratio of the outputs of the integrating means,
When the relative ratio becomes less than or equal to a predetermined value, a first means for moving the focus lens, and a plurality of movement paths of the focus lens at the time of zooming operation are prepared for each object distance, and for each movement path, A moving amount of the focus lens for each predetermined focal length
And a means for moving the focus lens by using the first means and the second means in combination during the zooming operation.