JPH0239779A - Automatic focus adjustor - Google Patents

Abstract

PURPOSE:To promptly and stably execute an automatic focus regulating action for any focal distance and diaphragm value by calculating sensitivity by means of focal distance information and diaphragm information, and optimizing a focusing motor speed and S/H timing based on the sensitivity. CONSTITUTION:Encoder information is inputted to a computing element 18, and the sensitivity corresponding to a condition at such a time is operated. In the computing element 18, according to an information table shown in a fiture set in a ROM beforehand, sensitivity S is operated from a lens focal distance f1 and a diaphragm value Fi. In the computing element 18, the sensitivity obtained by referring to the table of sensitivity information Si is inputted to a motor speed converter 19. In the motor speed converter 19, a motor speed deciding circuit 10 converts the logical motor speed expressed according to the control level of the motor outputted corresponding to a focusing degree by a motor speed deciding circuit 10 into a practical physical motor speed Vi conforming to the speed control information table.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic focus adjustment device suitable for use in video cameras and the like.

[Conventional technology]

Traditionally, automatic focus detection devices used in video cameras and other video equipment extract high-frequency components from the video signal obtained from the image sensor and drive the photographic lens in such a way that this high-frequency component is maximized. A method for performing focusing is known.

Such an automatic focus adjustment method does not require special optical components for focus adjustment, and has advantages such as being able to accurately focus even on distant objects. This type of automatic focus adjustment method will be explained using FIG. 10.

2 is a focusing lens, which is moved in the optical axis direction by a lens drive motor 12 to perform focusing. Reference numeral 2 denotes a variable magnification lens which changes the focal length of the photographing optical system by moving in the optical axis direction. 3 is an aperture which is controlled by an IG meter 14 to pass an appropriate amount of light.

The light passing through this lens group forms an image on the imaging surface of the image sensor 4, is charged and converted into an electric signal, and is output as a video signal. This video signal is amplified to a predetermined level by an amplifier 5, inputted to the camera's process circuit (not shown), and converted into a standard television signal, as well as an aperture driving I.
The signal is input to an iris driver 15 that drives and controls the G meter 14 and a band pass filter (E, P, F) 6.

The iris driver 15 detects the level of the video signal so that the level is always constant at an optimum value.

A signal is sent to the IG meter 14 to drive the aperture 3.

The BPF 6 extracts high-frequency components from the video signal, and the gate circuit 7 extracts only the signal corresponding to the focus detection slope set on a part of the screen, which is detected by the detector 8. After that, the sample and hold circuit 9 performs vertical synchronization. Sample and hold is performed at intervals synchronized with integral multiples of the signal. Based on this held signal, the motor speed determination circuit 10 sets the speed of the focusing motor 12 according to the degree of focus. That is, the motor driver 13 is instructed to vary the motor speed so that it becomes faster when the blur is large and slow when the blur is small. Further, the motor direction determination circuit 11 sets the driving direction of the motor in the direction in which the output of the sample and hold circuit 9 is maximized.

In other words, the so-called hill-climbing control, which is known from the past, is performed.
2, and the focusing lens 1 is adjusted in conjunction with the driving.

[Problem that the invention seeks to solve]

By the way, when the focusing lens 1 is moved from close range to infinity, the output of the sample-and-hold circuit 9 shows a mountain shape that reaches its maximum value at the in-focus point, as shown in FIG. 11(b). If you move the variable magnification lens 2 from this state so that the focal length becomes longer, the shape of the mountain will be as shown in the figure (
As shown in a), it becomes steep near the focus. On the other hand, when the variable magnification lens 2 is moved so that the focal length is shortened, the shape of the mountain becomes a gentle curve throughout the range of movement of the lens, as shown in FIG. 3(C). On the other hand, when the aperture 3 is opened compared to the initial state shown in Figure (b), the shape of the mountain becomes as shown in Figure (a).
When the aperture 3 is closed, it becomes a sharp, steep shape, and becomes a gentle curve as shown in the same figure (C). This phenomenon occurs because the depth of field changes by changing the focal length and aperture value.

For this reason, in the past, even if the optimal focus adjustment operation could be performed at a certain aperture value or focal length (generally at the maximum aperture or when the variable magnification lens was at the telephoto end), changing the aperture value or focal length would result in an optimal focusing operation. This caused undesirable movements such as extremely slow focusing, or too fast focusing, which caused hunting at the focused point.

〔the purpose〕

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide an automatic focus adjustment device that can perform automatic focus adjustment at high speed and smoothly regardless of the focal length or aperture state.

[Means for solving problems]

In order to achieve the above-mentioned object, according to the present invention, there is provided an extraction means for extracting a signal according to the degree of focus from an imaging signal outputted from an imaging means, and an extraction means for extracting a signal according to a focus degree from an imaging signal outputted from an imaging means; A driving means for driving a focusing lens of an optical system to a focused point, information regarding sensitivities of the optical system in a plurality of states and extraction timings of the extraction means according to each of the plurality of sensitivities, and driving of the driving means. It is characterized by comprising a control information table storing at least one type of control information, and a calculation means for detecting sensitivity regarding the optical system and comparing it with the control information table to set focus control information for the optical system. shall be.

C Effect] According to the present invention, the sensitivity is calculated from the focal length information and the aperture information, and the focusing motor speed is adjusted based on this sensitivity.
By optimizing the S/H timing, fast and stable self-blade focusing can be performed at any focal length or aperture value.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the automatic focus adjustment device of the present invention shown in the figures will be described in detail.

〔Example〕

FIG. 1 is a diagram showing the configuration of a first embodiment of the present invention. In this figure, the same reference numerals are used for the same components as in the conventional example shown in FIG. 8, and the explanation thereof will be omitted. In FIG. 1, 16 is a zoom encoder that detects the position of the variable magnification lens, and 17 is an iris encoder that detects the operating state of the diaphragm 3, that is, the opening of the diaphragm. These encoder information are input to the computing unit 18, and the sensitivity is computed according to the situation at that time. This computing unit 18
Now, the second
According to the information table shown in the figure, the lens focal length f I (+=1.2.=n) and the aperture value FI (i=1.2.
2゜...n), the magnitude relationship of each focal length for calculating the sensitivity S is f,>F2>...>f, and fl
is the longest focal length in this system, and the relationship between this longest focal length and an arbitrary focal length f+ can be expressed as follows.

Also, the size relationship of the aperture value F is F, <F2<...F.

, F is the smallest aperture value (open aperture) in this system, and this minimum aperture value Fl and any aperture value F
The relationship with 1 is Fl=2I□IF, (i=2....n)
・・・・・・・・・・・・ It can be expressed as (2).

The sensitivities S, , S2, . In this arithmetic unit 18, sensitivity information S1 in FIG.
The sensitivity determined by referring to the table is input to the motor speed converter 19. The motor speed converter 19 converts the logical motor speed, which represents the motor speed outputted from the motor speed determination circuit 10 in accordance with the degree of focus, into a third control step.
This is for converting into an actual physical motor speed v1 according to the speed control information table shown in the figure.

In FIG. 3, MS, . . . MS 2m are output from the motor speed discrimination circuit 10 and are 12 logical motor speeds of the lens drive motor, and these logical motor speeds are:
For example, if the motor speed can be switched to multiple stages depending on the position of the focusing lens relative to the in-focus point, it is important to know which stage the focusing lens is at depending on the degree of focus, and at what speed it should be driven. This information indicates whether there is a focus point, and can also be viewed as lens position information with respect to the focal point. The information table for controlling the actual speed of the motor shown in FIG.
It is stored in advance in the OM and is referenced when necessary.

In FIG. 3, the logical motor speeds MS, . . . M S
To explain the relationship between 2n and MS211, MS211-1
．． ...MS2. By changing the logical motor speed in the order of MS, the motor speed is gradually reduced (i.e., the lower the focus degree is, and the larger the deviation from the focus point, the faster the motor speed is (, the closer to the focus point As V,
The relationship is V2<...<V4n.

V,,V2. ...y4n is the output of the motor speed converter 19 and is the actual physical motor drive speed determined from the logical motor speed MSi and the sensitivity S+ according to the motor speed information table shown in FIG. When the sensitivity S1 is highest, the logical motor speed MS.

~Actual motor speed V1~V4 corresponding to M S 2n
n is selected, but the sensitivity is S2. ..., S2n, the change in focus degree with respect to the amount of lens movement becomes smaller, so the physical motor speeds are respectively v2 to V2n+1 + corresponding to MS1-M52n.
..., V2n to V4n are selected and the motor speed is increased. As a result, even if the sensitivity changes, this can be corrected by the motor speed, and the time taken to reach the in-focus point and changes in characteristics near the in-focus point can be corrected.

In this way, the speed command value V converted from the logical motor speed to the actual physical motor speed by the motor speed converter 19 is supplied to the motor driver 13, which drives and controls the motor 12 to drive the focusing lens I. drive and perform automatic focus adjustment. As a result, when the sensitivity S1 is high and the peak of the characteristic curve indicating the degree of focus is steep, the focusing lens 1 is moved at a slow speed, and when the sensitivity is low and the peak is gentle, the focusing lens 1 is moved at a slower speed. It is possible to drive the focusing lens 1 at a high speed, and optimum speed control is possible according to the sensitivity.

This operation is shown by the characteristic curve in FIG. When the sensitivity S is plotted on the horizontal axis and the physical motor speed v1 is plotted on the vertical axis, if the sensitivity S is plotted at equal intervals, the motor speed increases exponentially as the sensitivity decreases. The scale in FIG. 4 is not accurate, but is for general understanding, and is shown compressed in the direction of motor speed.

However, it can be understood from the figure that as the sensitivity S1 decreases, the physical motor speed Vi increases, and that the sensitivity-speed curve shifts with the logical motor speed MSi serving as a parameter.

According to this embodiment, the sensitivity S in FIG.
, ~S 2n are set, for example, in 6 stages, and the value is doubled at each stage, that is, S+ is set to S, and S
The ratio with zn is l/32. That is, the aperture value Fl is 6 for each of 36 combinations when the focal length f+ of the variable magnification lens is changed in 6 steps.
Since an information table in which one of the stage position sensitivities S and -S6 is set is created in advance, there is no need to perform calculations every time a detection is performed (the calculation speed can be greatly improved). In general, the sensitivity when the apertures F, I and the focal length r1 are set can be determined by, for example, - for boat fishing, Fo = open aperture value So, and positional sensitivity when the aperture is open.

For example, in the table for motor speed control shown in FIG. 3, six levels of sensitivity are set from 81 to S2n, and each physical motor speed is V.

There are 12 settings from V4n to V4n. This speed can also be set so as to sequentially double the speed for each of vl + V 2+ (Vl = V
, The lower limit of the motor speed is set to the maximum speed at which the motor can be stopped stably without causing hunting or the like at the focal point. However, these speed values are determined by taking into consideration the characteristics of the motor, the configuration and scale of the optical system, and the signal processing system for focus detection, and are not universal values, but may be determined as appropriate during design. Determined based on the various conditions mentioned above. This will be explained later in the third embodiment.

In the embodiment described above, the theoretical motor speed MS+ and aperture value Fl depend on the lens position relative to the focal point.

A case has been described in which the speed of the focusing lens driving motor is controlled with reference to an information table based on the sensitivity determined according to the focal length f1, thereby allowing optimal control of the automatic focusing device. Optimum control of the automatic focus adjustment device can also be achieved by changing the sampling interval for detecting the degree of focus by the sample hold circuit 9 from the video signal instead of the speed.

A second embodiment of the present invention in which the sampling interval for detecting the degree of focus is varied will be described in detail below.

FIG. 5 shows a block diagram of a video camera in this second embodiment. In this figure, the same reference numerals are used for the same components as those of the conventional example shown in FIG. 8 and the first embodiment shown in FIG. 1, and the explanation thereof will be omitted.

The calculation unit 18 uses the outputs of the zoom encoder 16 and the iris encoder 17 to obtain the sensitivities 81 to S2n based on the sensitivity information table shown in FIG. 2, which is the same as in the first embodiment described above. be.

The sensitivity S1 corresponding to the current aperture value F1° focal length information f1 determined by the calculator 18 is input to the sample hold timing generator 20 of the sample hold circuit 9. This sample hold timing generator 2
0 is equipped with a sampling timing information table for giving a sampling interval tI according to the sensitivity as shown in FIG. 6, and by comparing the input sensitivity S1 with this information table, the appropriate Find the sampling interval tl.

In this information table, the size relationship of each sampling interval is 1. <12<...<tn, that is, the higher the sensitivity S1 is, the shorter the sampling interval t1 is, and conversely, the lower the sensitivity S+ is, the shorter the sampling interval t1 is.
The settings are such that it makes the . The sampling interval t1 determined by the sample and hold timing generator 20 is input to the sample and hold circuit 9, and the sample and hold interval for the high frequency component of the video signal is controlled. In other words, when the sensitivity is high, by shortening the sampling interval, the relative change rate of the degree of focus for each sampling is reduced, and the speed of the focusing lens drive motor 12 is relatively slowed down, thereby increasing the degree of focus. Perform a hill-climbing motion that matches the steepness of the characteristic, and conversely, when the sensitivity is low, increase the sampling interval (by doing so, increase the rate of change in the degree of focus for each sampling and increase the relative motor speed). Do the same as you did and perform mountain climbing motions that are suitable for a gentle mountain.

Furthermore, the relationship between the above-mentioned sensitivity S and the sampling interval t is shown in FIG. Since the sensitivity S is set at equal intervals, an exponential characteristic is obtained.

The sampling intervals t1...tzn are set, for example, so that the intervals are doubled, doubled, etc., that is, expressed as arbitrary t+=t, X2'-'. Considering the characteristics of the video signal, it is preferable in terms of design to set the shortest sampling interval to 1/60 second of the vertical synchronization period.

In this way, the sample and hold circuit 9 samples and holds, for example, the amount of high frequency components in the video signal, and the focusing lens 3
In an automatic focus adjustment system that drives the camera, when the sensitivity S+ is high, the sampling interval t1 is set to perform fine detection to prevent focusing lens overshoot, hunting, etc., and when the sensitivity is low, the detection interval is lengthened. It is possible to reliably detect the displacement of the degree of focus by using the lens, and to solve problems such as the focusing lens stopping due to a small displacement or requiring a long time to move to the in-focus point.

FIG. 8 shows a third embodiment of the automatic focus adjustment device of the present invention. This embodiment controls the speed of the focusing lens driving motor 12 according to the sensitivity in the first embodiment shown in FIG. 1, and the sampling according to the sensitivity in the second embodiment shown in FIG. This shows a device that performs both interval control and spacing control.

As shown in the figure, the sensitivity S+ calculated by the calculator 18 that calculates the sensitivity according to the information table is transmitted to the sample hold timing generator 20 and the motor speed converter 19.
The information is input to both of the above and compared with a motor speed information table and a sampling timing information table configured in a ROM (not shown) provided internally or externally, respectively.

Logical motor speed M S + is sample and hold generator 2
Also supplied to 0. Then, in the motor speed information table, the logical motor speed is converted into actual physical motor speed information (■1) according to the sensitivity level S+, and outputted to the motor driver 13 that controls the focusing lens drive motor 12, and the sampling timing information is In the table, the sampling interval t'+ corresponding to the input sensitivity is supplied to the sample and hold circuit 9, and the sample and hold timing is controlled as described above.

FIG. 9 shows a motor speed information table and a sampling timing information table in this embodiment. Each control value is selected depending on which sensitivity S1 and logical motor speed MS, so those on the same table Illustrated as Each sensitivity Si, logical motor speed M
The actual physical motor speed is shown on the left and the sampling interval 1+ is shown on the right, respectively for S+. The actual motor speed is set in the range of v1 to Vm (V and Il are the maximum speeds), and the sampling interval is set in the range of 1/1 to t'2n-□+1. As mentioned before, the maximum speed vm of the motor increases with the speed of the motor (due to motor noise, durability, etc., it is not possible to set it to a large value without limit, and considering these conditions, Set to the highest speed within the range.

Therefore, even if V+ is set to be 2'-1 times vI, ■□ must be the upper limit, and everything beyond this must be constant at vm. After vrn becomes constant, a substantial response is taken by changing the sampling interval t'+ in order to relatively increase the motor speed.

That is, as is clear with reference to FIG. 9, the sensitivity is 81.
The sampling interval t' + is kept constant at tJ 1 until ~S, n, and the sensitivity S, ~Sm and the motor logical speed MS.

-MSm, motor speeds v1 to vITl are selected.

However, for the sensitivity S m+1 ``''' S 2n in which the motor speed Vl exceeds v, n in calculation, vm is the upper limit, so everything is kept constant at vm, and the sampling interval t' i is changed to t'2 It is set to become gradually longer as ~t'2n-□+1.

Furthermore, when the logical motor speed M S + is MSm, the actual physical motor speed vrn is constant, corresponding to the change in sensitivity from 81 to Sn, and conversely, the sampling interval t' +
is changed from tJ 1 to t'2n-1. This allows the optimum physical motor speed and sampling interval to be selected and set on the table for any sensitivity.

That is, in the information table of FIG. 9, in region A, the sampling interval t'+ is kept constant and the actual speed Vl of the focusing lens driving motor 12 is varied in the range of v1 to Vm, and in region B, the motor speed is kept constant at vrn. By varying the sampling interval in two ranges from t' to t'n-+, optimum focus adjustment corresponding to sensitivity, that is, hill climbing operation in the focusing characteristic curve of FIG. 5 can be performed. Looking at this in FIG. 4, in each characteristic curve, the motor speed Vl is controlled to be constant over 7 m, which is indicated by the dotted line.

In addition, here in Figure 2, f and F are divided so that the sensitivity is doubled, but they may be divided finely or roughly (Fig. 3 and F are divided accordingly). The tables in Figures 5 and 7 are also detailed (you can divide them.
Physical motor speed v1, sampling interval tl, t
' , similarly, it does not prevent you from changing these settings.

In the block diagrams of the embodiments shown in FIG. 1, FIG. 4, and FIG. 6, for convenience of explanation, the information table of sensitivity S1,
Information table of motor speed v1, sampling interval t1
The above information tables have been described as being provided in the arithmetic unit 18, motor speed converter 19, and sample-hold timing generator 20, respectively, but in reality, they are centrally set in advance in a ROM (not shown). and control microcomputer.

This does not in any way preclude a configuration in which reference is made in response to a command.

〔effect〕

As described above, the present invention detects the sensitivity of any focal length and any aperture value, and sets either or both of the motor speed and focus sampling timing to the optimum value, thereby achieving high speed and Stable automatic focus adjustment becomes possible.

Control command values such as motor speed and sampling interval are then selected from an information table composed of optimal values for each pattern, greatly improving calculation speed.
Moreover, since the characteristics can be freely set according to the pattern, it can be applied to any model by simply changing the values in the information table. For example, even if the optical characteristics change due to interchangeable lenses, it can be adapted to any situation by changing the information table and programming.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the first embodiment, Fig. 2 is a diagram showing a sensitivity information table for determining the sensitivity of the first embodiment, and Fig. 3 is an actual physical diagram of the first embodiment. A diagram showing a motor speed information table for determining the motor speed, FIG. 4 is a characteristic diagram showing the relationship between sensitivity and physical motor speed, FIG. 5 is a block diagram of the second embodiment, and FIG. FIG. 7 is a characteristic diagram showing the relationship between sensitivity and sampling interval; FIG. 8 is a block diagram of the third embodiment; Figure 9 is a diagram showing an information table for determining the physical motor speed and sample timing of the third embodiment, Figure 10 is a block diagram of the conventional example, and Figure 11 is a diagram for explaining the principle of the automatic focus adjustment device. figure. Vz Vz zn Vz n + + zn 'Jzn VzrI+ 4 n Sz to S- 3° dimension 0 sonde Kairyo t ↑ S28 total σ de

Claims (1)

[Claims] Extracting means for extracting a signal according to the degree of focus from the imaging signal output from the imaging means; Driving means for driving the focusing lens of the optical system to the in-focus point based on the signal extracted by the extracting means. , a control information table storing at least one of the sensitivities of the optical system in a plurality of states, information regarding the extraction timing of the extraction means according to each of the plurality of sensitivities, and drive control information of the drive means; An automatic focus adjustment device comprising calculation means for detecting the sensitivity of the optical system and comparing it with the control information table to set focus control information for the optical system.