JPH0442108A - Focus adjustor - Google Patents

Abstract

PURPOSE:To obtain a precise focusing state over the entire area of zooming by deciding the distance to a subject at the time of power variation and moving a focus lens group according to the best movement track from a storage means. CONSTITUTION:A ROM 51 is stored with movement tracks of a master lens 104 which are preset according to the distance to the subject, i.e. tracking curves. Position information on the master lens 104 is represented as the operation quantity of a stepping motor 10. When the zooming to a telephoto side is started from specific focal length, intervals of the respective tracking curves are wide, so the distance to the subject can easily be estimated from the positions of the master lens 104 corresponding to those focal length values; and the zooming is performed by utilizing the tracking curve corresponding to the distance and then the high-accuracy, excellent focusing state can be held over the entire range of the zooming.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a focus adjustment device applied to, for example, autofocus of a camera-integrated video tape recorder (hereinafter referred to as a video movie).

[Prior art] In recent years, focusing methods for video movies, etc.
Mountain-climbing autofocus has become mainstream, in which the high-frequency components of the video signal are extracted, the contrast of the screen is detected, and the focus lens group is driven and controlled to maximize the contrast. It's coming.

On the other hand, the focus device, that is, focus adjustment 1! As for t11, the inner focus method is becoming mainstream instead of the front lens focus method. This inner focus method drives the internal lenses in the lens group, such as the relay lens and compensator.Compared to the front lens focus method, the lens can be driven by a small motor that allows for a shorter focusing distance. Although it has excellent features such as being able to focus over a full range from close range Om to infinity, it does cause out-of-focus when zooming.

Zoom tracking is necessary to correct this.

The amount of correction for such out-of-focus changes greatly depending on the focal length and the distance to the subject, and perfect correction is difficult.

As an example of zoom tracking, a method using the above-mentioned mountain climbing method as is can be considered, and this will be explained below.

Fig. 5 is a block diagram showing the configuration of a mountain climbing autofocus device. In the figure, (1) is an inner focus type lens barrel, and a fixed front lens (101).
Variator for zoom (102) This variator (
a compensator (103) that corrects the image plane due to the movement of the lens (102); a master lens (104) that is part of a relay lens and is used for focusing;
It is equipped with Although each lens is made up of a plurality of lens groups, it is expressed as one lens here.

(2) is a CCD that converts the light incident on the lens m cylinder (1) from the outside into an electrical signal, and converts the light incident on the lens m cylinder (1) into an electrical signal, and
), and a video signal (A) and a luminance signal (a) are respectively extracted. (4) is a focus detection circuit, which includes a bypass filter (hereinafter referred to as HPF) (401) that passes signals above a certain frequency of the luminance signal (a);
Amplification @ (404), a low-pass filter (hereinafter referred to as LPF) (405) that cuts unnecessary high-frequency components, and a detector (40B) that makes the output of this LPF (405) a gentle waveform. , an A/D converter (40G) that converts the output of this detector (40G) into a digital signal.
7) and an adder (408) that performs digital addition, and the digital addition output (Y) from the adder (408) serves as a focus evaluation value, that is, an index representing the state of focus. and is sent to the control circuit (5).

(8) is a motor driver, which drives the zoom motor (7) based on the zoom command from the control circuit (5);
Move the variator (102). (9) At step t, stepper motor try/go, the stepping motor (
10) to move the mask lens (104).

(8) is a switch that detects the position of the /heliator (1o2), that is, the focal length, and is composed of a potentiometer, and can be read at a potential corresponding to the lens position and l versus l.

(II) is an end point detection switch that detects the end point of the or movement range of the mask lens (+04).
4) is turned ON at the point when the subject at infinity is focused on, and the movement value of the mask lens (+04) is expressed with this point as a reference.

Next, the operation of the above configuration will be explained using FIGS. 5 to 10.

First, we will explain the basic mountain climbing autofocus operation.

The subject light incident through the lens barrel (1) is CC
The signal is converted into an electrical signal by D (2), and a video signal (^) and -degree signal (a) are extracted through a camera signal processing circuit (3). Among them, the luminance signal component (a) as shown in FIG. 5(a) is guided to the focus detection circuit (4), and first,
In the HPF (40+) of this focus detection circuit (4), only predetermined high frequency components as shown in FIG. 5(b) are extracted.

Next, after being amplified by an amplifier (404), the LPF (404)
05), the band is limited as shown in Figure 5(c), and the detector (
406), the wave is detected as shown in FIG. 5(d). moreover,
The A/D converter (407) manually converts the value into a digital value, and the adder (408) adds the value of a predetermined area (S) in one screen shown in (H) in FIG. 9 to perform focus evaluation. Output as value (Y).

That is, the focal point j market value (Y) is the integral value of the high frequency component. In addition, this high frequency component corresponds to the contrast of the screen, so when the contrast is maximum, that is,
It is maximum when the mask lens (+04) serving as a focus lens is at the focal point, and decreases as it deviates from the one focal point. Therefore, the focus evaluation value (Y) exhibits a mountain-shaped characteristic as shown in FIG. 7 as the master lens (lo4) moves.

The control circuit (5) controls the stepping motor (10) to drive the master lens (104) to the in-focus point so that the focus evaluation value (Y) is always maximized.

The difference between yl and y2 in Figure 7 is that HPF (401)
The cutoff frequency is determined by the difference in the cutoff frequencies of yl and X, and the cutoff frequency is selected when yl<v2.

Next, the operation during zooming will be explained.

A zoom signal is sent from the control circuit (5) to the motor Drino (6) to drive the zoom motor (7).

As the zoom motor (7) is driven, the variator (102) moves on the optical axis and performs a magnification change action.At this time, as the variator (102) moves, the focal point However, by simultaneously moving on the optical axis with the force ζ of a compensator (103) mechanically connected via a cam etc., it operates to compensate for the movement of the focal point.

If only the compensator +1031 is moved, not all corrections can be made, and as shown in Fig. 8, the mask lens ( +041
In order to achieve focus during zooming, it is necessary to move the mask lens (1041) along a tracking curve as shown in FIG. 8.

As an example of how to do this, take a slightly longer zoom time,
The mountain climbing method described above is used.

In other words, let us take as an example a case where the distance to the subject is Im. Assume a theoretical tracking curve (wa) with a distance of 1 m to the subject shown in Figure 10, and actually express it in (force):
The mountain climbing method is used for tracking.

In other words, considering moving from the wide-angle side to the telephoto side, the distance to the subject at the start of zooming is unknown. Therefore, if you use the hill climbing method described above, the focus evaluation value used to determine the in-focus state will be large. As a result, even if you do not know the distance to the subject, you can track it by imagining the tracking curve as if there was a tracking curve that serves as an index, and you can check the accuracy when zooming. It will maintain focus.

[Problems to be Solved by the Invention] Since the conventional focus adjustment device is configured as described above, the focus evaluation value reflects the in-focus situation when the content of the subject changes due to changes in the angle of view during zooming. Therefore, there is a problem in that it may be mistakenly determined that the subject is in focus even when it is not, and it is difficult to achieve accurate focusing.

This invention was made in order to solve the above-mentioned problems, and includes a focus adjustment r that can obtain a highly accurate focusing state over the entire zoom range during zooming.
The purpose is to provide ta.

[Means for Solving the Problems] A focus adjustment device according to the present invention determines the distance to a subject during zooming, and based on the determination result, determines the movement trajectory of a plurality of focus lens groups stored in a storage means. The present invention is characterized in that one of the focus lens groups is selected and the focus lens group is moved based on the movement locus of the selected one.

[Function] According to the present invention, the optimal one among a plurality of movement trajectories is selected according to the distance to the subject during zooming, and the focus lens is moved based on it, so that the focus during zooming is It is possible to improve accuracy.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described based on the drawings.

FIG. 1 is a block diagram showing the configuration of an autofocus device according to an embodiment of the present invention.
The difference from the conventional example shown in the figure is that the ROM (51), which is a data memory as a storage means, is connected to the control circuit (5), and the other configurations are the same as the fifth FA. The same reference numerals are given to the five parts, and detailed explanation thereof will be omitted.

As shown in FIG. 2, the ROM (511) stores a plurality of preset mask lens (+041) movement trajectories, that is, tracking curves, according to the distance to the subject. The storage method, that is, the data format, is the focal length at the potential obtained from the focal length detection switch (8) and the amount of movement of the mask lens + 1041 represented by the number of steps of the stepping motor (10). The positional information of the lens +1041 is expressed by the amount of operation of the stepping motor (10).

This is because the unit movement amount of the mask lens f+041 is expressed by l steps of the stepping motor (10), and the number of steps driven by the stepping motor (10) becomes the absolute position of the mask lens (+041).

Next, the operation of the configuration described in F will be explained.

Now, we will explain the case where the lens barrel (1) with the tracking curve shown in Fig. 2 zooms from the wide-angle side to the telephoto side when zooming9.If the distance to the subject at this time is 2m, then the tracking curve M of 2m will be explained. By moving the mask lens fl integration 4 along Al, the in-focus state during zooming can be maintained.

In this way, if the distance to the subject is known, the above focusing operation is possible, but if it is not known, simply preparing a tracking curve is of no use. I will explain how to solve this problem.

Now, if you start zooming from a focal length between 11fn and fn6 in Fig. 2 and go to the telephoto side, [between n and fn6, the intervals between each tracking curve are wide, so the distance corresponding to these focal length values is It is possible to easily estimate the distance to the subject from the position of the master lens f1041, and from now on,
If you zoom using a tracking curve that corresponds to this distance, you can maintain good focus when zooming.

However, it is difficult to determine the distance to the subject, especially when zooming from the wide-angle end, that is, close to fO.This is because the depth of field is deep at the wide-angle end, and in addition to this, the distance to the subject corresponds to The amount of movement of the mask lens (104) is computationally small, and in some cases the stepping motor (l
O) One step of driving includes a considerable distance to the object, so the distance cannot be easily determined, and furthermore, blurring occurs when zooming from the wide-angle side to the telephoto side in this state.

FIG. 3 shows an enlarged view of the vicinity of fO on the wide-angle side of FIG. 8) is the focal length JIl value obtained from. Furthermore, each curve uses the distance to the subject as a parameter.

As can be seen from the figure, 1 of the steering motor (10)
Since the distance to the subject is covered by the amount of movement per step, it is not easy to determine the distance to the subject at the wide-angle end.This problem is solved in a first-order manner.

Now, assuming that the stepping motor (10) is at the second step, that is, the master lens (104) is focused and stopped at this position, the distance to the subject covered by this second step is 2 m, 3 m, and 4 m. becomes.

In other words, l is the stop F position of the mask lens (104).
This is because the coverage area extends from point P, which is the midpoint between the second step and the second step, to point Q, which is the midpoint between the second step and the third step. For example, when viewed from point P, ■
If there is an in-focus point closer to the step, it will be represented by the l-th step, so it returns to 0 and zooms toward the telephoto side from the second step of the current focusing stop position.

At this time, the mask lens (104) is immediately moved to the right by the stepping motor (10) to the third step. Then, up to the 15th position of the focal length, if you do not move beyond the 3rd step position and watch the in-focus state, that is, the focus evaluation value (Y) over time, the focal length will be as shown in Figure 4. Since the focus evaluation value (Y) when is f2 is the largest, this point indicates the in-focus state, and it can be determined that the distance to the subject is 3 m.

In this way, since the distance to the subject is determined immediately at the wide-angle end, extremely accurate determination results can be obtained without being affected by changes in the angle of view due to zooming.

In addition, in the above embodiment, the master lens for focusing (
Although the stepping motor (10) is used for the drive movement of the motor 100, a DC motor may be used under precise control and the same effect as in the above embodiment can be obtained.

Furthermore, any number of tracking curves may be stored in the ROM (51).

Furthermore, the smaller the amount of movement of the stepping motor (10) per step, the smaller the coverage range to the subject per step, and the more accurate the determination can be.

[Effects of the Invention] As described above, according to the present invention, when zooming, the distance to the subject can be accurately determined and the focus lens can be moved along the movement locus of @suit, so the zoom At times, highly accurate focusing can be achieved over the entire zoom range.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an autofocus device according to an embodiment of the present invention, FIGS. 2 and 3 are explanatory diagrams of the movement locus of the master lens during zooming in the present invention, and FIG. 4 is a block diagram showing the configuration of an autofocus device according to an embodiment of the present invention. 5 is a block diagram showing the configuration of a conventional autofocus device, FIG. 6 is a diagram explaining the operation of the focus detection circuit, and FIG. 7 is a diagram explaining the focus evaluation value in mountain climbing operation. Figure 8 is a diagram showing the movement trajectory of the master lens during zooming in the inner focus method, Figure 9 is a diagram showing the area where the focus evaluation value is obtained, and Figure 1θ is when tracking during zooming was performed while climbing a mountain. FIG. (1)...Lens barrel, (2)...CCD, (4)
... Focus detection circuit, (5) ... Control circuit, (7).
...Zoom motor, (8)...Focal length detection switch, (lO)...Stepping motor, (51)...
・ROM, (104)...Master lens. Note that the same reference numerals in the figures indicate the same or corresponding parts. Figure 1

Claims (1)

[Claims] (1) An inner focus type 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 that is extracted from the video signal for a predetermined period of time. a control means for controlling the lens system based on the output of the focus detection means; a lens movement means for moving the lens system by the control means; and a storage means for storing the movement amount of the focus lens group for each predetermined focal length corresponding to the movement locus of a plurality of focus lens groups prepared. Determine the distance to the subject, select a movement locus for the focus lens group from the storage means based on the determination result, and move the focus lens group by the movement means based on the selected movement locus. A focusing device characterized by comprising: