JP3165709B2 - Lens control 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 lens moving speed control device for focusing in a zoom lens used for an image pickup device such as a video camera.

[0002]

2. Description of the Related Art There are various types of zoom lenses conventionally used for video cameras and the like. FIG. 5 shows the configuration of a conventional zoom lens, in which 1 is a front lens group for performing focus adjustment by moving in the optical axis direction, 2 is a variator lens group for zooming, and 3 is a variator lens group. A compensator lens group for keeping the imaging surface constant when zooming is performed, and a variator lens group 2
The compensator lens group 3 moves during zooming while maintaining a predetermined relationship.

[0003] Reference numeral 4 denotes a lens group for forming an image;
2 shows an image forming plane on which an image sensor such as a CD is arranged. The so-called front focus lens which performs focusing with the front lens group shown in FIG. 5 is a mechanical cam for obtaining this predetermined relationship because the interlocking relationship between the variator lens and the compensator lens is constant. It was common to link mechanically using rings.

On the other hand, unlike a front lens focus lens,
A type of lens called a so-called inner focus or rear focus that performs focusing by a lens group behind a variator lens is known.

FIG. 6 shows an example of this type of rear focus zoom lens. The front lens group is fixed, and the variator lens group 2 and the compensator lens group 3 have the front focus lens shown in FIG. A predetermined interlock is performed using a mechanical cam ring or the like as in the case of the lens group. 4
(Or a part of 4) is a lens group for focusing.
When the focus lens group is disposed behind the variable power lens in this way, it is necessary to move the lens group 4 during zooming even if the object distance is kept constant, and to take the lens group 4 according to the focal length. The position changes according to the subject distance.

FIG. 7 shows a focusing position for each subject distance in accordance with the focal length of the lens group 4 shown in FIG. In the figure, the horizontal axis represents the focal length, and “W” is the wide end “T” of the zoom lens and the telephoto end. The vertical axis indicates the position of the lens group 4, and indicates the position at which each curve (or straight line) indicated by 6 to 10 is in focus at each focal length with respect to a certain distance. Is a subject distance of 50 cm, 7 is 1
m and 8 are 2 m, 9 is 10 m, and 10 is the focusing locus at the ∞ distance.

Further, when the lens group 4 is in a wide and extended (moving toward the subject side) position as shown by a point 11, it is possible to focus on a distance immediately before the lens.

FIG. 1 shows an example of the configuration of another inner focus lens. In this case, the lens group 1, the variator lens 2, and the diaphragm 12 move in the direction of the arrow when zooming from wide to tele, and 4A is a fixed lens group and 4B is a focus lens group.

In this case, since there is no lens group of the correction system (lens group corresponding to 3 in FIG. 6) linked in a predetermined relationship behind the variator lens 2, the graph shown in FIG. It becomes as shown in. For example, 13 is 50
cm, 14 is 1 m, 15 is 2 m, 16 is 10 m, and 17 is a focusing locus of ∞ distance.

A lens having such characteristics as shown in FIG. 8 includes a lens group 1 and a diaphragm 12 in FIG.
May be fixed so that only the lens group 2 moves during zooming.

As described above, in the case of a lens type called an inner focus or a rear focus, focusing can be performed at a short distance as compared with a front lens focus lens, and the lens can be downsized depending on the lens type. However, even if the object distance does not change during zooming, the position of the focal plane moves, so that blurring during zooming does not occur. It is necessary to maintain such a relationship correctly according to the distance.

As a method of preventing the out-of-focus state due to such a zoom operation, the following method can be considered.

First, there is a combination with a TTL type automatic focusing device. For example, in an automatic focusing device of a video camera, a method is known in which a peak of a high-frequency component of an imaging signal of a CCD or the like is used as a focus position.

FIG. 10 shows the principle. When the horizontal axis indicates the position of the lens group for focus adjustment and the vertical axis indicates the high-frequency component (focus voltage) of the imaging signal, the peak of the focus voltage is indicated at the position indicated by the arrow in the figure. Is the position of the focusing lens.

FIG. 11 shows an example of a method of obtaining the focal voltage F shown in FIG.

FIG. 11A shows an actual imaging visual field.
0 is the angle of view, 18 is the range (distance measuring frame) 19 from which a video signal for performing automatic focus adjustment is taken out is the subject.

In FIG. 11B, FIG. 11A shows a state of a subject in a distance measuring frame. (B) is a video signal (Y signal) of the subject shown in (a). When this signal is differentiated, it becomes a waveform as shown in (c), and further as an absolute value, it becomes as shown in (d). Then, the label F of the signal (e) obtained by sampling and holding this becomes the focal voltage.

FIG. 12 is a block diagram showing a camera in which such an automatic focusing device and an inner focus lens are combined. An image pickup device such as a CCD is arranged at an image forming position of No. 5, and thereafter, a luminance signal Y
Is formed, and information in the focus detection frame is used as a focus detection (AF) circuit 21.
It is taken in. In the AF circuit, by the above-described method and the like,
The focus voltage is obtained, and this value and the focusing lens 4B
If the focus is out of focus or out of focus, it is determined whether the type of blur is front focus or rear focus, etc. Based on the result of this determination, the motor 22 for driving the focus lens is driven in a predetermined direction.

However, it is extremely difficult to accurately control the position of the lens group 4B during zooming and remove blurring only from the distance measurement result of the automatic focusing device using such an image pickup signal.

That is, as shown in FIG. 9, in the vicinity of the telephoto and at a long distance, the movement of the focus lens group is large (that is, the slope of the curve is steep) with respect to a small change of the horizontal axis (a small change of the variator). . This indicates that if the distance measurement operation of the automatic focusing device is not performed quickly and accurately, the situation will be immediately out of focus.

However, in general, in the case of an automatic focusing device using an image pickup signal, the interval at which the distance measurement result is obtained is restricted by the field period, so that it is as short as 1/6.
It is about 0 seconds.

Therefore, there is a limit to the "raw speed", and in practice, not all distance measurement results every 1/60 second can be accurately obtained, and the moving speed of the focus lens to be further selected is optimum at one time. It is difficult to transform.

From the above considerations, in general, in the configuration as shown in the block diagram of FIG. 12, out-of-focus blur during zooming cannot be removed at the telephoto end unless measures such as extremely lowering the zoom speed are taken. .

Therefore, as a second means for removing out-of-focus during zooming, the data of the focus trajectory shown in FIGS. 7 and 9 is calculated by using the formula, position data, or the moving speed of the focus lens according to the zooming speed. The data stored in the CPU in the form of data, etc., and the drive contents of both the zoom motor that drives the variator lens and the focus motor that drives the focus lens based on information on the focal length and the position of the focus lens during zooming are stored in this memory. A method of determining the content can be considered.

For example, as shown in FIGS. 7 and 9,
Small areas I, II, II as shown in FIG. 13 in the map in which the horizontal axis indicates the focal length and the vertical axis indicates the focus lens position
I, IV, the moving speed of the variator lens in the horizontal axis while divided ... into when the V _V, method to keep memory speed V _F to be movement of the focusing lens in each region, by the applicant, It is disclosed in JP-A-1-280709. In this case seeking V _F by differentiating the focus trajectory passes through the center point of the small region. This V _V ,
In case of performing zooming with V _F, upon zooming from the telephoto to the wide direction, but can maintain a focus it is under the condition that the subject distance is not changed during zooming, last during zooming from the wide to telephoto direction It will be difficult to maintain focus up to that point.

The reason is that, as is clear from FIGS. 7 and 9, the distance between the trajectories representing the in-focus point from the curve corresponding to each subject distance, for example, from ∞ to 1 m, which is divided into a wide range at the telephoto end, is large on the wide side. Due to the depth of field, the light converges within a narrow range (the difference in the focal point position decreases). On the other hand, when the depth width based on the permissible circle of confusion under the aperture value on such a map is obtained, in the case of the inner focus lens,
In many cases, the width is substantially constant regardless of the focal length. Therefore, in the in-focus state on the wide side (within the depth but the true focus is unknown), it is not always located on the true focus locus, so the focus lens position at that time is known. However, if the curve diverges on the tele side, an accurate curve is not always traced, and the focal point on the tele side cannot be determined accurately.

As described above, it is difficult to prevent blurring during zooming even if the object distance does not change with the inner focus lens. Generally, the above two methods, namely, TTL using an image pickup signal, are used. It is common to remove blur using an in-zoom algorithm that uses a type of autofocus device and a memory of the focus trajectory in the map.

For example, JP-A-3-4187 by the present applicant
In No. 8, it is determined whether the out-of-focus direction is the front focus or the rear focus based on the phase of the change of the focus voltage when the CCD is slightly displaced in the optical axis direction by a piezo actuator or the like.
Based on this determination result, in addition to the above-mentioned speed, the content of the speed for correcting the front focus and the rear focus is also stored in memory for each of the above-described small areas, and a method of selecting an optimum speed among them is disclosed. ing.

In this case, it is possible to completely remove out-of-focus during zooming from the wide direction to the telephoto direction.
Costs are reduced by using piezo actuators, etc.
A problem arises in size and power saving.

In addition to a method of detecting a front pin and a rear pin by a so-called modulation method, the optical member is slightly changed to an optical axis method using a piezo actuator or the like as a means for knowing the direction of blur when out of focus. There is known a so-called trial method in which a focus lens is first moved to one of them, and a determination is made based on whether a change in a focus voltage at that time has increased or decreased.

In general, when a front pin and a rear pin are detected by a trial method, a longer time is required for the determination as compared with the modulation method, and it is difficult to make a quick determination.

[0032]

As is apparent from the above description, it is necessary to determine the direction of the front focus and the rear focus by using a trial method and to remove the blur generated in the inner focus type lens. Since the focusing lens needs to keep changing its position according to the focal length and subject distance, it is necessary to set and switch the speed of the focus motor quite finely in order to move the focus lens to the front or rear focus side for the time being. Required. In order to properly obtain the change in the focus voltage, it is necessary to set the speed of the focus motor in consideration of the change in the depth of focus due to the lower value. However, the method of remembering the speed used for each small area as described above has been insufficient.

[0033]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is characterized in that a zoom lens and a focal position accompanying the movement of the zoom lens are provided. When the focus lens to be corrected and the zoom lens are not moved, the value is 0. During the driving of the zoom lens, the reference speed determined by the positions of the zoom lens and the focus lens is changed to the depth of field and the focus state. Control means for driving the focus lens based on the speed corrected accordingly.

[0034]

Another feature of the present invention is that the control means controls the information relating to the depth of field to F _NO , the coefficient relating to the focus state to K, and the reference speed determined by the positions of the zoom lens and the focus lens to V _C. If the amount of change in the reference speed V _C is ΔV _C , the moving speed V of the focus lens
Is calculated by the following equation: V = V _C + F _NO × K × ΔV _C.

[0036]

According to the present invention, the optimum speed corrected for various conditions such as variations in the speed of the zoom lens, the depth of field, the position of the zoom lens, the front focus, the rear focus, and the focus state corresponding to the degree of focus, etc. Focus lens driving can be realized, and in setting the moving speed of the focus lens during zoom operation of the inner focus lens, fine speed change suitable for the trial method is possible, regardless of shooting conditions, Blur during zooming from the wide to the telephoto direction can be greatly improved, and a small size, low power consumption and low cost can be realized.

[0037]

FIG. 1 is a block diagram of an AF system for an inner focus type lens in a form suitable for carrying out the present invention. In the figure, 101, 102, 104
The lens groups A and 104B correspond to 1, 2, 4A and 4 in FIG.
B is the same as each lens group.

The mirror frame 118 of the variator lens group 102
Is provided integrally with a brush portion 119 for position detection, and the variator is moved so that a variable resistor or a gray code pattern is printed on the substrate 12.
The brush part 119 slides on the zero. The focal length is detected by capturing this output by the zoom encoder circuit 123, and the information is captured by the system control required CPU 133.

When detecting the position of the focus lens 104B, for example, a stepping motor is used as the focus motor 127, and the number of drive pulses given to this step motor is taken into the CPU 133 from the focus motor drive pulse detector 124. It becomes possible to know.

The video signal output from the image sensor 121 enters the AF device 122, which detects the value of the focus voltage and takes it into the CPU 133.

In the CPU 133, the zoom encoder 12
3 and information on the position of the zoom lens and the focus lens detected by the focus motor drive pulse detector 124, information on the focus voltage, the operation status of the zoom switch 132, and the memory 134 in charge of the focus locus data in the map. 136 are respectively stored.
Zoom motor 1 based on speed, direction and area data
29 and the drive contents of the focus motor 127 are determined.
The motors are driven via drivers 128 and 126 of the respective motors so that the focus lens traces on the focus locus of FIG. However, the zoom motor may be driven at a fixed speed at a predetermined voltage.

In the case of the present invention in which the position information of the focus lens is read by the number of steps of the stepping motor, the position information disappears when the power is turned off. Absent. Therefore, when the main switch SW131 is turned on, the power-on reset 130 controls another switch (not shown) to return the focus lens group 104B to the starting position, and restarts counting.

Next, the setting of the focus lens driving speed in the present invention will be described.

According to the present invention, as shown in FIG. 13, the movement area of the zoom lens and the focus lens is divided into a plurality of small areas, and each area correctly traces the locus differentiated at the center point. This is similar to the above-mentioned prior application by the present applicant in that only the speed V _C is stored, but in the case of the present invention, the stored trace speed is corrected according to various conditions. This is characterized in that the optimum focus lens driving speed is calculated.

[0045] In the present invention, the the final focus lens driving speed V _F, is calculated by the following equation. V _F = X × (V _C + K × F _NO × ΔV _C ) At this time, the moving speed of the zoom lens is V _C determined by design.
Is set (voltage setting) by design on the basis of which is determined. However, the zoom lens moving speed may have an error.

In this equation, X is a coefficient for correcting the deviation of the moving speed of the variator lens from the design value,
F _NO is used to correct the focus detection sensitivity based on the depth of field with the correction coefficient of the aperture value FN ₀ . K is a coefficient determined by the CPU 133 from a plurality of signals including the focus voltage. When the focus lens is driven in the front focus direction from the state where the focus trajectory is traced during the zoom operation (+), the rear focus is determined. When the focus lens is driven in the direction, the sign becomes (-), and its absolute value determines the speed difference from the trace speed. The [Delta] V _C is the minimum amount of change in the differential trace speed and speed of use.

In the present invention, by driving the focus lens based on this equation, the variation in the speed of the zoom lens, the depth of field, the position of the zoom lens, the front focus,
It is possible to realize focus lens driving at an optimum speed corrected for various conditions such as a back focus and a focus state such as a degree of focus, and to set a moving speed of the focus lens during a zoom operation of the inner focus lens. In addition, it is possible to change the speed finely suited to the trial method, greatly improve the blur during zooming from wide to tele of the inner focus lens regardless of the shooting conditions, and reduce the size and power consumption. It is possible to realize a small and low cost.

Hereinafter, an algorithm for determining the focus lens driving speed based on the above equation will be described.

According to the present invention, the CPU 1
The lens control is performed by a control program stored in 33. Specifically, the drive speed of the focus lens is determined according to a flowchart shown in FIG.

Hereinafter, the flowchart of FIG. 2 will be described.

In step 201, an automatic focus adjustment routine in the CPU 133 starts. Step 202 ~
Step 203 is an initial reset step for the first round only after the control is started. In step 202, the flag A and the flag T are set to high. Step 203
Then, the value F of the focus voltage at that time is stored in the memory as F ₀ .

Steps 204 to 215 correspond to the aperture value F _NO for calculating V = V _C + F _NO × K × ΔV _C , which is a feature of the present invention, and the zoom lens and focus stored in each area of FIG. This corresponds to the processing of determining the reference follow-up speed V _C of the focus lens according to the lens position and taking in the focus voltage value F for each V. In the present flow, the above-mentioned calculation of X of V = X × (V _C + F _NO × K × ΔV _C ) is omitted for convenience of explanation.

In step 204, it is determined whether or not the photographer is operating the zoom switch 131. If the zoom switch 131 has been pressed, step 205
The flag Z is set to Hi, and the positions of the two groups of zoom lenses 102 are detected in step 206. Then step 2
At 07, in the case of the example of FIG.
The absolute position of B is detected. .. Are determined in Step 208 from the positions of the variator lens group and the focus lens group captured in Steps 206 and 207, and the speed V in the small area determined in Step 209 is determined in Step 208. The stored value of _C is read from memory.

On the other hand, if the zoom operation has not been performed in step 204, the flag Z is set in step 210.
Is set to Low, and the zoom motor is stopped (only when it has been driven up to that time).

In step 211, the focus motor drive speed V _C = 0. That is, in the present invention, in use the speed of the focus motor zoom, regardless except during _{zooming, V = V C + F NO} · K to calculate at · [Delta] V _C of the formula was used as a base, except when zooming V _C = It will be set to 0. That is, when the zoom operation is not performed, there is no displacement of the focal plane due to the zoom operation, so that the correction of the focus lens is unnecessary as long as the lens is in focus.

In steps 212 and 213, the latest content of the focus voltage F ₀ is sent to F ₁ , and the latest F is newly incorporated in F ₀ and updated. That is, F ₀ is the current focus voltage,
F1 is the value of the focus voltage ₁ V before. Step 2
At 14, the aperture value FNO is read, and at step 215, the value is converted to a value used in the above equation.

There are various known methods for detecting the aperture value. For example, there is a method of disposing a hall element in an aperture meter. There is a method of converting the output of the Hall element from A / D, and obtaining an aperture value from a conversion formula, a conversion table, or the like created in the CPU in advance. Further, in the equation for obtaining V, what value F _NO should be actually calculated differs depending on how many times the aperture is set as a reference for ΔV _C. For example, when the aperture value is F = 1.0,
If you use the actual aperture value as it is. Theoretically, in order to keep the speed at which the circle of confusion changes, the coefficient F _NO may be changed in proportion to the aperture value. Such a conversion may be performed. For example, the data used when calculating the K is, depending on whether you are using up data for any previous point in time, it is also considered if not decide the coefficient F _NO by the ratio of a simple aperture.

At step 216, the flag A is determined. Although the flag A is set high in step 202,
This means that the direction (rear focus, front focus) is not known when the focus is out of focus or when the focus is changed to out of focus.
Similarly, when the direction is unknown, step 217 and subsequent steps are performed.
This is for passing through the routine up to 39.

Since the present embodiment is a trial-type automatic focusing apparatus, first, the driving direction for "moving the focus lens 104B in any direction" is determined in step 217. Determining the sign of K in the calculation formula corresponds to this. In this embodiment, a random number table is used for the determination. Next, at step 218, the state of the flag C is determined. The flag C is used to increase the speed of "moving for the time being" in order to send the focus lens at a high speed when the signal change is not sufficient to perform the direction determination and the focus lens is considered to be large. In the first cycle, the flag C is Low, and the initial setting speed for “moving for the time being” is set at step 220, in this example, | K |
= 1. This value differs depending on how ΔV _C is set. For example, the distance measurement of the NTSC video camera is performed every three fields of 1/60 sec (1/20 sec), and the focus is adjusted. When the blur determination capability of the apparatus is an aperture value of 1.0, the number of pulses of the step motor is about 1 pulse, and the permissible circle of confusion (a circle of confusion where humans can perceive blur) is about 3 pulses from the true focus. However, when the coefficient F _NO is configured to use the actual aperture value as it is, a change of about 1 to 2 pulses in 1/20 sec is desirable. That is, 20-40p
This is more true if ps is calculated as K × ΔV _{C in the} correction term. For example, ΔV _C = 30 is set.

Actually, in this setting, the focusing lens driving speed V when F2.0, K = 1, and V _C = 200 pps during zooming is V = 200 + 2.0 × 1 × 30.
= 260 pps is calculated as the usage speed.

At step 221, such a calculation is performed. At step 222, the presence or absence of a zoom operation is determined.
The zoom and focus motors start driving at the same time. Step 224 is not for zoom operation, and only the focus motor is driven.

At step 225, the flag T is determined.
The flag T is high only immediately after the power is turned on.
In this case, the processing returns to Step 204 after being set to Low. That is, immediately after the power is turned on, since the contents of the focus voltages F ₀ and F ₁ are not the focus voltages detected by changing the positions of the lenses, the conditions for performing the correct direction determination are not complete,
This is to postpone the focus state determination process once.

In the second and subsequent rounds, since the flag T is low in step 226 of the first round, the flow proceeds to step 228 according to the determination in step 225. First, F ₀ is compared with a predetermined threshold value F _th1. When F ₀ is small, the flag C is set to Hi, and the value of | K | is increased through step 219 to increase the speed. The fact that F ₀ is small means that the focal voltage is extremely low and the state of blur is large, so that it seems that a sufficient difference between F ₀ and F ₁ cannot be obtained, so the acceleration is accelerated. It is. However, the focus voltage F does not always exceed F _th1 if the direction is wrong even if the vehicle is accelerated. Therefore, it is desirable that this portion be further smoothed by including other judgment items, but is omitted here because it is not the essence of the present invention.

At step 229, the flag C is set to Low. In step 230, ΔF = F ₀ −F ₁ is calculated in order to detect the direction of the trial method (back focus or front focus).
In step 231, a comparison is made _between | ΔF | and ΔF _th1 . ΔF _th1 is a threshold value for discriminating _between in-focus and out-of-focus, and if | ΔF | falls below this threshold value, it is determined that focusing has been achieved. In the case of focusing, the flag A is set to Lo at 232 and 233.
w, taking action to set the flag B to Hi, and focusing on F ₀ →
Storing the F _K serving as a reference for unfocused judgment. Flag Lo
By setting w and B to Hi, step 21 will be performed next.
According to the determinations of steps 6 and 240, the flow of steps 241 to 244 is performed. In step 231, | ΔF |> Δ
When it is determined that F _th1 , the sign of ΔF is identified in step 235 because the direction can be determined. If ΔF is positive, the sign of K is kept as it is (step 23).
7) If it is negative, it is inverted (step 236). Thus, the direction of the correction speed with respect to the reference speed V _C of the focus lens is determined.

After the direction is determined, the flags A and B are set to low in steps 238 and 239. As a result, the steps 216 and 240 are executed from the next round to execute the step 245.
Subsequent out-of-focus → Enters a routine for focusing.

If the determination in step 231 is No, and it is determined that focusing has been achieved, steps 204 to 215 proceed as described above from the next round, and reach step 241. Since focus is achieved, K = 0. That zooming is V = V _C, and the focus lens is composed only of the drive to correct the deviation of the focal plane due to zooming. The focus motor is stopped except during zooming.

In step 242, the absolute value of the difference between the current focus voltage and the focus voltage F _K at the time of the focus determination and ΔF
_th2 is compared. ΔF _th2 is a threshold for judging in-focus → out-of-focus (or there is a signal change), and means restarting after in-focus. The determination in step 242 is N
If o, the process directly proceeds to step 258; if Yes, the flag B is set to L
OW, the flag A is set to Hi (steps 243 and 24).
4) From now on, the determination in step 216 leads to step 2
To reach 17.

If the determination in step 231 is Yes and the camera is out of focus and the directions of the front and rear pins are determined,
In the next lap, the result in Step 240 is No, and Step 24
It reaches 5. In step 245, ΔF = F ₀ −F ₁ is calculated, the sign is confirmed in step 246, and if negative, the flag A is set to Hi in step 247, and then the process returns to step 217 again. This determination also takes into consideration that ΔF is not always kept positive (even if the rotation direction of the motor is correct) due to noise or the like. For example, an algorithm that makes the determination true when the number of determinations is equal to or more than a predetermined number out of a predetermined number of times may be considered, but the simplest form is used here because it is not the essence of the present invention.

Steps 248, 251 and 252 are steps for determining the degree of out-of-focus and changing the speed. F _th2 is below the focal voltage.
In larger threshold than the above-mentioned F _th1, if there are F ₀ between F _th1 and F _th2 determination is No and in step 248, the absolute value of K in step 249 is 3 and settings. That is, when the out-of-focus direction is known out of focus and the blur is considerably large. Since F _th3 are considered moderately blurred by time greater than F _th2, when the F ₀ is in the F _th3 and F _{th 2} in step 250 | is set to = 2 | K. or,
When F ₀ is larger than F _th2 but ΔF is larger than the above-mentioned ΔF _th1 which is the focus determination threshold value, | K | = 1 in step 253 because the degree of blurring is small. When the in-focus state is determined in step 252, it is determined that focusing has been achieved from out of focus. In step 254, K is set to 0, and the same operation as in steps 232 to 234 is performed in step 25.
Perform at 5-257.

In step 258, the actual speed V of the focus lens is calculated based on the equation (1) based on the value of K determined by the above processing. Note that the focus motor speed is determined, for example, in step 221 or 258.
It is set at the time of passing, and is switched to the latest V calculated at the time when step 204 is entered.

As described above, according to the present invention, the speed of the focus motor is calculated and calculated by the above-described formula of V = V _C + F _NO · K · ΔV _C irrespective of whether the zoom is being performed or not. Accordingly, (a) V can be set by using the routine of the same trial method basically at the time of zooming and at the time other than zooming (when zooming is not performed, V _C = 0 may be set).
(B) By appropriately setting ΔV _C , F _NO
Regardless of this, it is possible to easily set V so that the circle of confusion has the same condition according to the state of blurring (F _NO is converted into a coefficient). (C)
By changing K, there is an advantage that a fine speed change is possible, and the occurrence of out-of-focus blur in zooming from wide to tele when using the inner focus lens can be suppressed as much as possible.

In the first embodiment of the present invention, | K | =
The example in which the speed is determined using 0 to | K | = 3 has been described. However, in order to perform the fine speed control, which is a feature of the present invention, more finely and smoothly, the ΔV _C must be set in the first embodiment. Instead of the value ΔV _C = 30 in the example shown in the description of the example, a small value such as ΔV _C = 5 is set, and | K | is set over a wider range (for example, | K | = 0 to 1).
00) It is conceivable to use them properly.

In determining such a fine K, it is not a flowchart of an IF sentence as shown in FIG. 2 but a fuzzy suitable one which has been actively applied to a control system in recent years.

In the first embodiment, the type of the signal for obtaining the focal voltage is considered to be one. In the second embodiment, for example, the signal ES corresponding to the width of the edge portion of the subject image as shown in FIG. It is assumed that two signals, ie, and a high frequency component FV, are obtained. The edge width signal ES performs focus detection by utilizing the fact that the edge width becomes narrower as approaching the focal point. The edge width is set to Δx, and when ES = 1 / Δx is used, the edge peaks at the focal point. As shown in the figure, ES has a characteristic of having a sharp characteristic near the focus, and FV has a gentler characteristic. The method for detecting these signals is known in Japanese Patent Application Laid-Open No. Sho 62-103616 and the description thereof is omitted. FIG. 4 shows an example of a rule for determining the K value by fuzzy inference in this case.

For example, when the sign of the current K is positive, ES indicates a large value, and dES (ΔF of the change with respect to ES) is positive. However, when the absolute value is small, there is a high possibility that the vehicle is at the top of a mountain. Since the focus is considered to be close, the content of the reel marked with a circle indicates that the sign of K is positive and the speed content is small.

In practice, Es, dES,
An input membership function is given to each of FV, dFV, and (the amount of change in FV) K, and an output membership function is given to K that is output as a repair.

When fuzzy inference is introduced in determining K as in this example, V = V _C +
That is, fine speed control can be performed using the calculation formula of F _NO · K · ΔV _C.

That is, rather than simply determining the value of K based on the threshold value, K = 0, and determining the value of K while including an ambiguous element in addition to K, thereby performing more natural control. Can be.

In the above-described first and second embodiments, the method of determining the coefficient K among the expressions V = V _C + F _NO · K · ΔV _C for determining the speed of the focus lens has been described. V = X × introducing a correction term for zoom motor speed
The speed calculation method in the case of (V _C + F _NO · K · ΔV _C ) will be described.

As described above, when practicing the present invention, V _C
Taking the method memory the values for each individual regions divided into small areas, yet in the case where V _C represents the speed of the focus motor, actually calculated in V _C is as follows. The horizontal axes in FIGS. 7 and 9 can be replaced with the time axis on the assumption that the variator moves at a constant speed, instead of the variator position (focal length). That is, the center point of the area is represented by (t, g) (t is the time required to reach the variator position when the wide end is assumed to be 0, and g is the focus lens position).
(T). Therefore, the value obtained by differentiating f (t) is pp
It is converted into s order, so that V _C of the region is shown.

Accordingly, in order to make the variation of the circle of confusion constant even when the zoom speed changes, the value of X obtained by the design zoom speed t _Z and the actual zoom speed t _Z ′ is obtained. The value of t _Z ′ / t _Z is given by (V _C + F _NO · K · Δ
It can be seen that V _C ) needs to be multiplied. In doing this, it is necessary to know t _Z '. As a method of detecting t _Z ′, a method of predicting by measuring a change in unit time of a volume encoder can be considered. actually,
When the power is turned on, the minute distance zoom motor is actually moved to calculate t _Z ′ to obtain X, and thereafter that value is used.
While the zoom operation is being performed, the rate of change of the encoder output is continuously measured, and t _Z ′ is updated. The latest X is used for the correction. Such methods are conceivable.

[0082] Particularly in this invention, since it is required in the zoom value of V _C is accurate, in fact, the calculation of the X becomes indispensable.

In order to more accurately grasp X calculated in the third embodiment, a step motor may be used as the zoom motor.

In each of the first to third embodiments of the present invention, V
_C is based on the premise that the V _C stored in each of the small areas as shown in FIG. 13 is read and used in the maps as shown in FIGS. 7 and 9. 1
It is also conceivable that the respective cam trajectories such as 4 and 15 are stored as points on the trajectory (A / D values of the zoom encoder, step motor addresses). In this case, the time difference Δt between the time when the current zoom encoder value was first shown and the time when the previous zoom encoder value was first shown, the current step motor address and the future zoom encoder value It is conceivable that Δy / Δt is obtained from the difference Δy of the address to be taken by the stepping motor when the value reaches the value and is set as V _C. X in the V _C in this case
Correction of X for V _C so will have been considered also becomes unnecessary. (If you want to consider X only for the correction term, V =
V _C + X · F According to _NO · K · may be a [Delta] V _C) as described above present invention, wherein the determination of the speed of the focus motor of the inner focus lens _{V = V C + F NO ·} K · ΔV C
Alternatively, by determining V = X × (V _C + F _NO · K · ΔV _C ), the algorithm for determining the speed of the focus motor at the time of zooming and other speeds can be unified (V _C = 0 at the time of no zooming). By changing K, fine speed control can be supported. By the aperture value F _NO consideration, F
_It is easy to set the speed so that the speed of the circle of confusion changes is substantially constant regardless of _NO . Features such as In particular, when a fuzzy inference algorithm or the like is combined, fine speed control according to various situations is possible but effective.

[0085]

As described above, according to the present invention,
When the zoom lens is not moved, the value is 0. During the driving of the zoom lens, the reference speed determined by the positions of the zoom lens and the focus lens is determined based on the speed corrected according to the depth of field and the focus state. By controlling the focus lens drive speed, fine-grained speed changes suitable for the trial method are possible regardless of the presence or absence of the zoom operation, regardless of the shooting conditions. Blur during zoom operation in the telephoto direction can be greatly improved, high-quality automatic focusing can be performed, and small size, low power consumption and low cost can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a positional configuration when a lens control device according to the present invention is applied to a video camera.

FIG. 2 is a flowchart showing a focus lens speed control algorithm according to the present invention.

FIG. 3 is a characteristic diagram showing a relationship between a focus lens position and a focus voltage according to another embodiment of the present invention.

FIG. 4 is a diagram for explaining rules when fuzzy inference according to another embodiment of the present invention is applied.

FIG. 5 is a diagram illustrating an example of a zoom lens that performs focus adjustment by driving a front lens.

FIG. 6 is a diagram illustrating an example of a rear focus (inner focus) type zoom lens.

7 is a characteristic diagram showing a locus of a focus position of the focus lens according to a zoom position in the rear focus zoom lens shown in FIG.

FIG. 8 is a diagram showing another example of a rear focus (inner focus) type zoom lens.

9 is a characteristic diagram showing a locus of a focus position of the focus lens according to a zoom position in the rear focus zoom lens shown in FIG.

FIG. 10 is a characteristic diagram illustrating a relationship between a focus lens position and a focus voltage.

FIG. 11 is a diagram for explaining a method of obtaining a distance measurement area and a focus voltage in an imaging screen.

FIG. 12 is a block diagram showing an example of a rear focus lens type camera provided with an automatic focusing device.

FIG. 13 is a map in which a zoom lens position (focal length) is plotted on the horizontal axis, a focus lens position (subject distance) is plotted on the horizontal axis, and a focus lens driving speed according to the focal length is divided into a plurality of small areas and stored. FIG.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Kunihiko Yamada, Canon, Inc. 3- 30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-3-41878 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 5/232 G02B 7/28

Claims (2)

(57) [Claims] 1. A zoom lens, a focus lens that corrects a focal position accompanying movement of the zoom lens, and 0 when the zoom lens is not moved, and focuses on the zoom lens while the zoom lens is being driven. A lens control device comprising: a control unit that drives the focus lens based on a speed obtained by correcting a reference speed determined by a position of a lens according to a depth of field and a focus state. 2. The control means according to claim 1, wherein said control means is FNO for information relating to the depth of field, K is a coefficient relating to a focus state, VC is a reference speed determined by the positions of a zoom lens and a focus lens, and VC is a reference speed. ΔVC
Then, the moving speed V of the focus lens is expressed as V =
A lens control device configured to calculate according to VC + FNO × K × ΔVC.