JPH0421277A - Focus adjustment device - Google Patents

Abstract

PURPOSE:To attain zoom tracking with excellent focus accuracy over the entire zoom range by adopting the mount climb method for a position where the mount climb method is effective for the accuracy and utilizing a tracking curve in response to the distance of an object afterward. CONSTITUTION:The mount climb method is used for a position where the focus depth is comparatively deep and zoom tracking is implemented along a tracking curve prepared in advance from the focal distance when the focus depth starts being shallow. When the focus starts from fo and reaches fn, a tracking curve in the most vicinity is selected from a ROM 51 depending on the position of a master lens 104 and a master lens 104 is moved along the selected tracking curve.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a focus adjustment device for a video camera or the like.

[Conventional technology]

In recent years, the focus method used for video movies, etc. detects the contrast of the screen using the high-frequency components of the video signal, and then drives and controls the focus lens so that this contrast is maximized to obtain a focused point. So-called mountain climbing autofocus is the mainstream.

On the other hand, as a focus device, an inner focus system is becoming mainstream, replacing the conventional front lens focus. This inner focus method drives internal lenses such as relay lenses and convensators in the lens group, and requires a large motor to drive large diameter and heavy lenses that cannot be achieved due to the short focusing distance of the front lens method. Disadvantages such as usage are eliminated, and it also has the feature of being able to focus over a full range from close range Om to infinity (2).

However, on the other hand, focus shifts occur when zooming, so
Must be corrected.

The amount of correction for this out-of-focus varies greatly depending on the focal length and the distance to the subject, and there is currently no camera that has completely corrected it. Here, focus correction during zooming in the inner focus method described above is called zoom tracking. As an example of performing this zoom tracking, there is a method that uses the mountain climbing method described above as is. This will be discussed below.

FIG. 2 shows the configuration of a contrast method process using an inner focus lens group and its output video signal.

In the figure, 1 represents an inner focus type lens barrel, 101 is a fixed front lens for condensing, 1
02 is a variator for zooming, that is, variable power; 103 is a compensator; and 104 is a mask lens that is part of a relay lens and is used for focusing. These lenses are generally a group of multiple lenses, but in this book, for convenience, they are expressed as one lens.

2 is a COD which converts the light incident on the lens barrel 1 from the outside into an electrical signal and sends it to the camera signal processing circuit 3, from which a video signal A and a luminance signal a are respectively taken out. . Next, 401 is an HPF (bypass filter), through which signals of a certain frequency or higher of the luminance signal a pass through, are amplified by an amplifier 404, and unnecessary high frequency components are cut by an LPF (low pass filter) 405.

The output of this LPF 405 is sent to a detector 406 where it becomes a smooth waveform, converted into a digital signal by an A/D converter 407, and digitally added by an adder 408. This digital addition output Y becomes a focus evaluation value (an index representing the state of focus) and is sent to the control circuit 5.

Here, the HPF 401 to the adder 408 constitute the focus detection circuit 4.

A motor driver 6 drives the zoom motor 7 based on a zoom command from the control circuit 5 to move the variator 102. Similarly, 9 is a mask lens 1 for focusing.
A stepping motor driver is used to drive a stepping motor 10 that moves the 04, and is driven based on a focus command from a control circuit 5. Also, 8 is variator 1
It detects the position of lens 02, that is, the focal length, and is composed of a potentiometer, and the lens position is read by a potential that corresponds one-to-one. Reference numeral 11 denotes an end point detection switch that detects the end point of the movable range of the master lens 104, which is turned ON when the master lens 104 is focused on an object at infinity, and the amount of movement of the mask lens is determined based on this point. represents.

Next, the operation will be explained.

First, I will explain the basic mountain climbing method.

The object light incident through the lens barrel 1 is transmitted to the CCD 2.
The signal is converted into an electrical signal by the camera signal processing circuit 3 and becomes a video signal. Of these, luminance signal component a (third
In Figure (a)), the focus detection circuit 4
At 01, only a predetermined high frequency component is extracted (FIG. 3(b)).

Next, the high frequency component is amplified by an amplifier 404, band-limited by an LPF 405 (FIG. 3(C)), and detected by a detector 406 (FIG. 3(d)).

Further, the A/D converter 407 converts it into a digital value, and the adder 408 converts it into a 1
The values of a predetermined area (FIG. 6) on the screen are added and output as a focus evaluation value Y.

In other words, the focus evaluation value Y is an integral value of high frequency components.

Furthermore, since the above-mentioned high frequency component corresponds to the contrast of the screen, the contrast is maximum, that is, when the mask lens 104 as a focus lens is at the in-focus point, it is at its maximum, and it decreases as it deviates from the in-focus point. Therefore, the focus evaluation value Y changes as the mask lens 104 moves.
Figure 4 shows the characteristics of a mountain shape. The control circuit controls the stepping motor 10 to drive the mask lens 104 to the in-focus point so that the focus evaluation value Y is always the maximum.

Note that the difference between y and y in FIG. 4 is determined by the difference in cutoff frequency of the HPF 401, and the cutoff frequency is selected by V+<')'2. In this way, mountain climbing autofocus operation is achieved.

Next, the operation during zooming will be explained.

A zoom signal is sent from the control circuit 5 to the motor driver 6 to drive the zoom motor 7. Following this zoom motor drive, the variator 102 moves on the optical axis and performs a magnification change action. At this time, movement of the focus occurs as the variator 102 moves, but the compensator 103, which is mechanically connected via a cam or the like, simultaneously moves on the optical axis and operates to correct the movement of the focus.

However, it is not possible to make all the corrections by using only the convencator 103, and as a result, as shown in FIG. Without it, you won't be able to focus.

Therefore, in order to focus during zooming, the mask lens 104 may be moved along a so-called tracking curve shown in FIG.

One example of how to do this is to take a slightly longer zoom time and use the hill climbing method described above. Let's take as an example a case where the distance to the subject is 1 meter. Assuming a theoretical tracking curve 7 with a distance of 1 m to the subject shown in Fig. 7,
In reality, as shown in (force), tracking is performed using the mountain climbing method. In other words, considering that the camera moves from the wide-angle side to the telephoto side, the distance to the subject is not known at the start of zooming. Therefore, if you use the hill-climbing method described above, you will be tracking the point where the focus evaluation value that determines the in-focus state becomes large, so even if you do not know the distance to the subject, you can track it as if it were an index. Tracking is performed using a virtual tracking curve as if a curve existed, and the in-focus state during zooming is maintained.

[Problem to be solved by the invention]

Since the conventional apparatus is configured as described above, it is difficult to say that the focus evaluation value always reflects the focus state when the subject content changes due to a change in the angle of view during zooming. Therefore, there are times when it is mistakenly judged that the focus is on.
It was difficult to make accurate corrections.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an extremely accurate focusing device with fewer focusing errors.

[Means to solve the problem]

In the focus adjustment device according to the present invention, at a relatively deep depth of focus, the hill-climbing method is used as before, and from a certain focal length position where the depth of focus begins to become shallow, the focus adjustment device follows a tracking curve prepared in advance. This is to perform zoom tracking.

[Effect]

In this invention, with the above-described configuration, an optimal tracking curve prepared in advance can be selected without using any special means, so that focusing accuracy during zooming is improved.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

Regarding the configuration of one embodiment of the present invention, as shown in FIG. 1, a ROM 51 which is a data memory is connected to the control circuit 5 as a storage means, and other parts are the same as the conventional configuration example. .

Next, the operation will be explained.

Let us now assume that zoom tracking is performed from the wide-angle side to the telephoto side along the tracking curve shown in FIG. At this time, if the distance to the subject is 2 m, the master lens 104 may be moved along a 2 m tracking curve. However, in reality, in the range of focal length f0 to f□, the depth of focus is deep and it is impossible to judge the distance to the subject.
Even if tracking curves are prepared for each distance in advance, it is difficult to know which curve to use. Therefore, in this range of focal lengths f0 to f2, where the depth of focus is deep, the angle of view and the content of the subject do not change much and are stable, so tracking is performed in this area using the hill-climbing method described above.

In other words, the focus evaluation value Y represents the in-focus state with fairly high accuracy, and the amount of movement of the mask lens 104 is also relatively small. Then, when the focal length starts from fo and reaches f7, the tracking curve starting from the closest one is selected from the ROM 51 according to the position of the mask lens 104 at that point, and from then on, the tracking curve starts along this selected trunking curve. At the same time, the mask lens 104 is moved.

This situation is shown in FIG.

Here, the data format of the tracking curve prepared and stored in advance in the ROM 51 is the data format of the mask lens 104.
It is expressed by the amount of movement of the driving stepping motor 10. In other words, the unit movement amount of the mask 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 mask lens 104. The ROM 51 uses the above data format, and has a tracking curve for each distance of the subject, and for each tracking curve, the data is calculated for each predetermined distance, as shown in Fig. 8 by fMI+fn□,... The amount of movement of the mask lens 104 is stored as the number of steps of the stepping motor 10.

In FIG. 9, the absolute position of the mask lens 104 is expressed by the number of steps of the stepping motor 10, and the focal length is read and expressed from the potential of the potentiometer 8 in a one-to-one correspondence. In addition, the line indicated by the broken line Go to
At that point, the tracking curve changes to the one with a subject distance of 2 m.

In the above embodiment, a stepping motor was used for the focusing mask lens, but the same effect can be obtained by using a DC motor.

Further, the location where the hill climbing method changes to the tracking curve prepared in advance may be arbitrarily selected depending on the system.

〔Effect of the invention〕

As described above, according to the focus adjustment device according to the present invention,
The hill-climbing method is used only where accuracy can be achieved, and thereafter a tracking curve according to the subject distance is used, making it possible to perform zoom tracking with high focusing accuracy over the entire zoom range.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a focus adjustment device according to an embodiment of the present invention, FIG. 2 is a conventional block diagram, FIG. 3 is a diagram explaining the operation of a focus detection circuit, and FIG. 4 is a diagram explaining a mountain climbing operation. Figure, 5th
The figure shows an example of the movement locus of the focus lens during zooming in the inner focus method, FIG. 6 is a diagram explaining the focus area, and FIGS. 7 and 8 are diagrams explaining the focus adjustment method of the present invention. FIG. 9 is a diagram showing the focal length versus the number of steps of the stepping motor. In the figure, 1 is a lens barrel, 101 is a front lens, 1
02 is a variator, 103 is a convencator, 104 is a master lens, 2 is a CCD, 3 is a camera signal processing circuit,
4 is a focus detection circuit, 401 is an HPF, 404 is an amplifier,
405 is an LPF, 406 is a detector, 407 is an A/D converter, 408 is a charger, 5 is a control circuit, 6 is a motor driver, 7 is a zoom motor, 8 is a focal length detection sensor,
51 is a ROM. Note that the same reference numerals in the figures indicate the same or equivalent parts.

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 and integrated over a predetermined period of time. a focus detecting means; a lens moving means for moving the lens system based on the output of the focus detecting means; a plurality of moving trajectories of the focus lens group are prepared for each distance to the subject during magnification changing operation; A focus adjustment device comprising a storage means for storing the movement amount of the focus lens group for each predetermined focal distance with respect to the trajectory, a focus lens movement means by the focus detection means, and a focus adjustment device based on the storage contents of the storage means. A focus adjusting device characterized in that a focus lens group is moved in combination with means for moving a lens.