JPS61230111A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To perform stable focusing operation even during power variation by performing driving control over a focusing lens with dull sensitivity while a power variation detector detects the variable power being in process. CONSTITUTION:Part of luminous flux passing through the focusing lens 1 and a movable lens 2 for variable power is made incident on a focus detecting element 5 arranged at a position equivalent to an image pickup position through a mirror 3. A signal indicating the deviation between position information on the lens 2 obtained by a position detector 8 and the element 5 is inputted to an arithmetic control part and two pieces of position information obtained by the device Z at a specific interval of time are compared by a comparator 8 to detect the difference, and then the arithmetic control part performs the driving control over the driving motor Mf of the lens 1. Consequently, automatic focusing control is prevented from becoming unstable during the variable power and the automatic focusing operation is carried out stably even during the variable power.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention detects the deviation between the imaging position of a subject image and the imaging position by using a light beam transmitted through a focusing lens and a variable magnification movable lens. Regarding an automatic focusing device that drives and controls a focusing lens to correct this deviation (prior art) As an automatic focusing device as described above, a light beam that forms a subject image at a position that passes through a variable magnification movable lens is used. A mirror or half mirror is provided to split a part of the image, and the split light beam is made incident on a focus detection element placed at a position equivalent to the imaging position using an auxiliary optical system, thereby determining the imaging position of the subject image. A method for obtaining a shift signal of an electric signal representing a shift in the imaging position (Japanese Patent Application Laid-Open No. 59-5215) and a method for extracting a shift signal from the imaging position of an image sensor (Japanese Patent Publication No. 39-5265) are known. ing.

Such conventional automatic focusing devices have common problems as described below.

To explain an automatic focusing device configured using a focus detection element, the depth of focus eD of the photographing system, the focus deviation detection accuracy tB of the focus detection element, and the accuracy ε of the drive control accuracy of the focusing lens converted into focus deviation. , etc., a method has been put into practical use in which the allowable focus shift range [D] during automatic focus control is set and the focusing lens is driven and controlled until the detected focus shift amount ε becomes 1ε1≦D. ing. In this setting of D, the maximum amount of defocus that can remain ε=D is determined by the F value of the lens constituting the imaging system and the diameter of the minimum circle of confusion d of the image sensor. It is desirable that they be approximately equal, and if D>ε, the larger the difference, the more noticeable the image blurring will be on the image sensor due to the amount of residual defocus during automatic focusing control. It is desirable that The focusing lens is driven to correct the defocus that has occurred in a pseudo manner, resulting in a very unstable system. Furthermore, the control accuracy ε, of the focusing lens is preferably tw (p, If ε≧D, it will be difficult to accurately stop the focusing lens within the focusing range, resulting in an unstable system as described above.To summarize, the following relationship will result in good automatic focusing. This is a desirable condition for achieving the system.

ε8kuri, ε, (]), gD*l) ・・・・・・
(1) When the above system is applied to a zoom lens system, if defocus detection and magnification change are performed at the same time, it will be difficult to capture a subject image whose magnification changes continuously due to the change in magnification. The first step is to find the amount of defocus, and for this purpose the defocus detection accuracy during zooming, εB, is generally εs.
Since z > gs, it is no longer possible to maintain the conditions ε and <D described above, and the system becomes unstable. If the image is moved regardless of the focus, screen fluctuations caused by unnecessary focusing lens drive control will be superimposed on the continuous magnification change, and as a result, problems will easily occur in which the intention of the image will be lost. . This kind of problem also occurs in devices that extract shift signals from imaging signals.To solve this problem, a method that presses the focusing operation to stop during zooming (Japanese Patent Laid-Open No. 59-112) However, this method cannot cope with changes in subject distance during zooming, and for example, a moving subject is photographed without changing the proportion of the subject that occupies the screen too much7. Shooting that requires focusing and changing magnification at the same time is not possible. Such an automatic focusing device significantly reduces the value of the original automatic focusing device.

[Purpose of the invention]

The present invention was made to solve the above-mentioned problems of conventional automatic focusing devices, and prevents excessive movement of the focusing lens due to deterioration of focusing accuracy during zooming. [Structure of the Invention] The present invention provides an automatic focusing device that is stable even during zooming and performs nine focusing operations. If the focusing lens is driven and controlled with severe sensitivity, the out-of-focus signal during zooming will be distorted by the movement of the movable lens for zooming, and the accuracy of out-of-focus detection will be much worse than usual, resulting in excessive movement of the focusing lens. However, depending on the degree of deterioration in defocus detection accuracy during zooming, the focusing range can be expanded or the moving speed of the focusing lens during zooming can be slowed down. By controlling the drive of the focusing lens with low sensitivity, the condition shown in equation (1) above is maintained even during zooming, and as a result, focusing becomes stable. It was done after discovering what could be done.

The present invention detects the deviation between the imaging position of the subject image and the imaging position by using the light beam transmitted through the focusing lens and the variable magnification movable lens, and controls the driving of the focusing lens to correct this deviation. The automatic focusing device is provided with a magnification change detection device that detects that the magnification is changing, and while the magnification change detection device detects that the magnification is being changed, the drive control of the focusing lens is slowed down. 0 in an automatic focusing device that is characterized by the sensitivity The detection accuracy 182 is generally 1εs < gsz, and the degree of deterioration of the detection accuracy expressed as εsz/is is as follows: lateral magnification of the subject image is m, dm is the rate of change in lateral magnification per unit time, π is the rate of change in lateral magnification per unit time, and non-focal Assuming that the time required to detect this is ΔT, it tends to increase as the rate of change π of the multiplication factor increases and as the time ΔT required for detection increases. This can be expressed mathematically as follows:0 However, Xi is a parameter that provides subject conditions such as defocus detection logic, subject contrast, subject pattern, etc. The degree of increase is expressed as xl, which is the focus It changes depending on subject conditions such as shift detection logic, subject contrast, and subject pattern, and cannot be expressed in a simple functional form. It is possible to obtain the averaged value f(ΔT, π), which can be obtained through experiments using standard patterns or theoretical calculations. The degree of deterioration f(Δ+r, dm) obtained based on such experiments or considerations
The focus point WiDz during zooming is set using
Once it is detected that the movable lens for magnification is changing by some means described later, the focus range is set to (3) 2. It is desirable to realize a stable automatic focusing device by temporarily expanding the range from −D2 to D2, which satisfies the relationship shown in (1) The relationship ε8□<D2 corresponding to the condition ε,<DIC shown in 2. This makes it possible to recover and avoid instability of focus/zoom control caused by frequent out-of-focus range occurrences due to deterioration of focus detection accuracy during zooming. Even if you try to widen the focusing range, the focusing accuracy required during magnification changes is higher than when no magnification is performed, as the magnification of the image changes continuously and the resolution decreases, making it difficult to focus. Since the depth of field is also expected to be expanded, it is not necessary to increase the depth to that extent, and therefore it becomes possible to maintain a sufficiently satisfactory focusing accuracy.

In contrast to the above-described present invention, the conventional automatic focusing device has ε8. Also for −D〈ε8. <Since the focus lens was controlled in the range D, it was determined that the lens was out of focus due to the fluctuation of the shift signal K caused by the movement of the variable magnification lens, and the subject distance did not actually change. However, the focusing lens frequently moves, making the focusing unstable, causing image fluctuations due to focusing, and impairing the photographer's intention in creating the image.

〔Example〕

The present invention will be explained below with reference to the embodiments shown in FIGS. 1 to 5.

First, the automatic focusing device shown in FIGS. 1 and 2 will be explained.

The automatic focusing devices shown in FIGS. 1 and 2 are both provided with a mirror 3 that splits a part of the light beam that forms a subject image at a position where it passes through the focusing lens 1 and the variable magnification movable lens 2. The driving motor Mf of the focusing lens 1 is controlled by the position information outputted from the position detection device 2 of the auxiliary light lens 2 and the displacement signal outputted from the focus detection element 5 on the luminous flux divided by the mirror 3, and the displacement C of the displacement signal is calculated by -ε <D (D is a function of positional information).The configuration up to this point is the same as in conventional automatic focusing devices. However, the position detection device ZK uses an encoder, potentiometer, etc. In the figure, 6 is a master lens, 7 is an image sensor 0, and in the automatic focusing device shown in FIG. Two pieces of position information are stored so as to be updated sequentially, and the comparator 8 expands the two stored values to a range of ratio ε<Dz. In addition, in the automatic focusing device shown in Fig. 2, the variable 4FFT moving lens 2 is set to be moved by the drive motor Mz, and when the OR circuit 9 detects that there is a forward rotation or reverse rotation input to the zoom motor drive section, a hold is performed. Through the circuit, the allowable range of collapse is expanded in the same way as in the device of FIG.

By expanding the allowable deviation range determined by the arithmetic control unit during magnification changes, excessive driving of the focusing lens is prevented, and stable and effective focusing is achieved even during magnification changes. Next, FIG. 3, which shows a specific example of one arithmetic control section, will be explained.

In FIG. 3, the same reference numerals as in FIGS. 1 and 2 indicate the same functional members, and 10 is a circuit that calculates the amount of defocus and converts the amount of deviation into a voltage value. The voltage from the resistor 11.12 is compared with the voltage from the resistor 11.12 by the comparator 13.14. By switching the switch 16 with a signal, the voltage is v0+Δv when the magnification is not changed and vo−Δv1 is V when the magnification is being changed. +
Δ/.

■. -ΔV'. That is, when the magnification is not changed, the switch 16 connects the output terminal 11a of the resistor 11.12.
, 12a are connected to a comparator 13.14, respectively, so that the comparator 13.14 compares the output of the deviation calculation circuit 10 with VO+IV t Vo-IV.

Then, based on the input from the comparison quantity 13.14, the motor drive circuit 17 drives the drive motor according to the logic table below.Therefore, the system performs focusing control with an accuracy of -D ε<D. It will be done. Furthermore, when the signal from the magnification change detection section 15 is in the process of magnification change, the switch 16 is connected to the output terminal 1it of the resistor 11.12.
. Then, the motor drive circuit 1
7 drives the drive motor f similarly according to the logic table 0
As a result, focusing control is performed so as to satisfy -D2<g<D, (D2>D) Finally, the example shown in FIG. 4 in which a microcomputer is used for control will be described.

In FIG. 4, the same reference numerals as in FIGS. 1 to 3 indicate the same functional members, and reference numeral 18 inputs a signal from the main unit 15 and performs focusing control according to the flowchart shown in FIG. conduct.

Although the present invention has been described above with reference to the illustrated examples, the present invention is not limited to this, and the present invention can also be used to extract a shift signal from an output signal of an image sensor. It may also be possible to detect a change in the lens position information and, when the change is detected, to expand the reference range for K deviation determination as shown in FIG. In addition, methods that slow down the moving speed of the focusing lens during zooming, or methods that obtain shift signals by detecting the signal intensity of the image outline from the imaging signal, temporarily lower the detection threshold level during zooming. The object of the present invention can also be achieved by controlling the drive of the focusing lens with a lower sensitivity by lowering the sensitivity.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to prevent the occurrence of instability of automatic focusing control during zooming, which has been a problem with conventional automatic focusing devices, and This eliminates the inconvenience of not being able to focus on a moving subject while changing the magnification of the autofocus device, which has been forced to stop the autofocus function, and allows stable autofocus operation even while changing magnification. This provides an excellent effect of ensuring appropriate focusing accuracy.

[Brief explanation of drawings]

1 to 4 are schematic configuration diagrams each showing an example of the automatic focusing device of the present invention, and FIG. 5 is an operation flowchart of the microcomputer used in the automatic focusing device of FIG. 4. ...Focusing/Zoom, 2...Movable lens for variable magnification, 3...Mirror, 4...Auxiliary optical system, 5...Focus detection element, 6...Master lens, 7...・Image sensor, 8... Comparator, 9
...OR circuit, 2...position detection device for movable lens for variable magnification, Mf...
Focusing lens drive motor, M2... Drive motor for variable magnification movable lens, 10...
Misalignment calculation circuit, 11.12...Resistance, 13.14.
... Comparator, 15... Magnification change detection section, 16...
Switch, 17... Motor drive circuit, 18... Microcomputer. Patent applicant Konishiroku Photo Industry Co., Ltd. Figure 1 Figure 3 Figure 3 Figure 4v! J

Claims (5)

[Claims] (1) Automatically detects the deviation between the imaging position of the subject image and the imaging position by using the light beam transmitted through the focusing lens and the variable magnification movable lens, and controls the driving of the focusing lens to correct this deviation. The focusing device is provided with a magnification change detection device that detects that the magnification is being changed, and while the magnification change detection device is detecting that the magnification is being changed, the drive control of the focusing lens is controlled with low sensitivity. An automatic focusing device characterized by the following: (2) Claim 1, wherein the magnification change detection device stores two positional information of the movable lens for magnification change over time, and detects that the magnification is being changed based on the difference between the two stored values. Autofocus device as described. (3) A patent claim in which the movable lens for zooming is moved by a motor, and the zooming detection device detects that zooming is in progress based on the presence or absence of forward or reverse rotation input to the motor. The automatic focusing device according to item 1. (4) Any one of claims 1 to 3, wherein the means for controlling the drive of the focusing lens with low sensitivity is means for expanding the allowable range of deviation between the imaging position and the imaging position. An automatic focusing device described in Crab. (5) The automatic focusing device according to claim 4, wherein means for expanding the allowable range of deviation is activated for a certain period of time after the magnification change detection device detects that the magnification is being changed.