JPH07294801A - Automatic focus adjustment device - Google Patents

Abstract

(57) [Abstract] [Purpose] To obtain an automatic focusing device that enables a high-speed focus, reduces power consumption associated with a focusing operation, and enables an efficient focusing operation. A so-called auto-correlation has a photographing system having a diaphragm means for selectively mounting a plurality of openings and one opening in a light path by a diaphragm switching means, a photoelectric conversion element, a focus lens driving means, and the like. When the focus detection of the shooting system is performed using the two focus detection methods in the order of the method and the mountain climbing method, the shooting-related conditions are set in advance, and when the conditions are satisfied, the focus is determined only by the autocorrelation method. A focusing operation is performed using a motion-based signal. The condition is a value related to a focal length, an aperture value, a depth of focus, and a high-speed mode changeover switch.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focus adjusting device, and more particularly to an automatic focus adjusting device used in an optical device such as a still video camera having a photoelectric conversion element as a focus sensor.

[0002]

2. Description of the Related Art Conventionally, a so-called autocorrelation focusing method using a photoelectric conversion element as a focusing sensor and a hill climbing method as a method of an automatic focusing device suitable for miniaturization built in an optical device such as a still video camera. The focus method is known.

The autocorrelation focusing method will be described with reference to FIGS. As shown in FIG. 5A, an aperture 52 having two openings 52a and 52b of different sizes shown in FIG. 5B is inserted in the optical path of an optical system (photographing lens) 51.
At this time, if the focus is deviated as shown in FIG.
The two object blurs shown in (C) are formed to deviate from each other. The optical device takes in one field of the image and takes the autocorrelation of the horizontally scanned signal. Then, the autocorrelation coefficient as shown in FIG. 6 is obtained, and the temporal correlation of τ _c showing the maximum peak value of the autocorrelation coefficient value C (τ) in the region excluding τ = 0 of the autocorrelation coefficient is obtained. The distance corresponds to the lateral shift amount of the two images, and it is necessary to obtain the focus shift amount from this value and the crossing angle α of the light beams from the two openings 52a and 52b entering the photoelectric conversion element 53, and to focus from that amount. The moving amount of the special focus lens is calculated.

On the other hand, the two deviated subject images have different brightness because of different aperture sizes. Therefore, from the order of brightness of the two images, it is possible to know whether the image is front-focused or rear-focused.
The moving direction of the lens can also be determined. Thus, the moving amount and the moving direction of the focus lens necessary for focusing are determined, and if the focus lens is driven according to this, focusing can be obtained. The flow chart of this system is shown in FIG.
This method has the advantage that the focusing time is short.

Next, regarding the mountain climbing focusing system, reference is made to Junichi Ishida, Yasushi Fujimura; "Automatic Focus Adjustment of Television Camera by Mountain Climbing Servo System", NHK Technical Research, Volume 17, No. 1 (Sho 40). The technology is disclosed. The main points of this method will be described with reference to FIGS. The diaphragm 82 provided in the optical system (photographing lens) 81 in this case is as shown in FIG.
As shown in (B), it has a single aperture used for normal photographing. At this time, when the focus is deviated as shown in FIG. 8A, one blurred subject image is formed on the photoelectric conversion element 53 as the image pickup means as shown in FIG. 8C. The optical device takes in the image for one field, takes out a high frequency component based on the process shown in FIG. 9, and integrates for one field to obtain a focus evaluation value. (This value corresponds to the sharpness).

Next, the optical device moves the focus lens by a small amount, and the focus evaluation value is obtained again based on the same process. Then, the magnitude is compared with the previous focus evaluation value, and if the focus evaluation value becomes large, it is determined that the focus is approaching, and the peak is obtained as shown in FIG. Therefore, this system is characterized in that high focusing accuracy can be obtained.

[0007]

In the auto-correlation focusing method, when the focus lens moves to the position obtained by calculation due to variations in lens processing, etc., a slight focus shift occurs on the focus surface. There is. Further, since it is difficult to obtain correlation in the vicinity of the in-focus position, high focusing accuracy may not be obtained when starting from the vicinity of the in-focus position.

Further, in the hill climbing focusing method, the focusing position is obtained by moving the focus lens in small increments, so that the default
When the amount of waste is large, there is a problem that it takes time to focus.

According to the present invention, when the focus detection of the photographic system is performed by using the two focus detection methods in the order of the so-called autocorrelation focus method and the hill-climbing focus method, the conditions regarding the photography are set in advance,
When this is satisfied, a high-speed focus is made possible by performing the focusing operation using the signal based on the focusing operation only by the autocorrelation focusing method, and the power consumption associated with the focusing operation is reduced. An object of the present invention is to provide an automatic focusing device that enables an efficient focusing operation.

[0010]

The automatic focusing device of the present invention has the following configuration.

(1-1) A subject image is formed on a photoelectric conversion element by a photographing system having a diaphragm means for selectively mounting a plurality of openings and one opening in an optical path by a diaphragm switching means, By using the output signal from the photoelectric conversion element, the image formation state of the subject image is obtained by the calculating means, and by using the output signal from the calculating means, the focus lens of the photographing system is moved on the optical axis by the focus lens driving means. When moving and performing the focusing operation, a plurality of openings and one opening of the diaphragm unit are mounted in the optical path of the photographing system to perform the focusing operation.
When the focusing operation is performed in the order of the first focusing means and the second focusing means, the first focusing means and the second focusing means perform the focusing operation in the first focusing means. When the condition is satisfied, the focusing operation is performed only by the first focusing means.

In particular, (1-1-1) the preset condition relating to photographing is when the mode of the automatic focusing device is a high speed mode.

(1-1-2) The preset condition relating to photographing is that the value relating to the depth of field is equal to or greater than the preset range.

(1-1-3) The preset photographing condition is that the aperture value of the photographing system is equal to or larger than a preset value.

(1-1-4) The preset condition for photographing is that the focal length of the photographing system is equal to or less than a preset value.

(1-1-5) The preset photographing condition is that the value relating to the depth of field is equal to or more than a preset range, or the aperture value of the photographing system is equal to or more than the preset value. Or when the focal length of the imaging system is equal to or less than a preset value.

(1-1-6) In the first focus detection means, the image formation state of the subject image is determined from the autocorrelation of the plurality of subject images based on the light flux passing through the plurality of aperture openings of the aperture means. In the second focus detection means, the sharpness of the subject image on the photoelectric conversion element surface is compared and obtained for each field. It is characterized by such things.

[0018]

In the automatic focusing device according to the present invention,
It has two focusing means. The first focusing means is an autocorrelation focusing means, and the second focusing means is a hill climbing focusing means.

The focusing operation of this automatic focusing apparatus is performed as follows. First, as the first step, substantially focusing is realized by the autocorrelation focusing means.

At this time, a certain value (hereinafter referred to as D value) related to the depth of field is calculated from the brightness information, the focal length information and the subject distance information at that time, and this is larger than a preset threshold value. Or not. If the D value is larger than the threshold value, it is determined that the subject is within the required focusing accuracy, the subsequent focusing operation is stopped, and the process immediately proceeds to shooting and recording.

If the D value is smaller than the threshold value, it is determined that the subject is not within the required focusing accuracy, and then, as a second step, the hill-climbing focusing means is used for accurate focusing.

Further, in the present invention, a high-speed mode changeover switch is provided in the apparatus, and when the high-speed mode is selected, the first focusing means, that is, the autocorrelation focusing means, is used for substantially focusing. After focusing, the process immediately proceeds to shooting and recording without determining whether or not the subject is within the required focusing accuracy.

[0023]

FIG. 1 is a block diagram of the configuration of a first embodiment of the present invention.

In the figure, reference numeral 1 denotes a photographing lens (photographing system), which forms a subject image on the surface of the photoelectric conversion element 2. Shooting lens 1
Has a focusing lens 1-a and a variable power portion 1-b therein. The focusing lens 1-a is a taking lens 1.
In the optical axis direction, the object image is focused on the surface of the photoelectric conversion element 2, and the variable power portion 1-b is a plurality of lens elements of the lens elements constituting the taking lens 1. Moves relative to the optical axis to change the focal length f of the entire imaging system.

Reference numeral 8 denotes a focus lens driving means, which is C
Based on a command from the PU 12, the focus lens driving motor such as a stepping motor for moving the focus lens 1-a and the positions of the focus lens 1-a on the optical axis are detected, and the information is sent to the CPU 12. And a focus lens position detecting means for feedback.

Reference numeral 14 designates a variable power part driving means, which is used to change the focal length of the photographic lens 1 so as to change the focal length of the photographic lens 1.
The zoom lens has a zoom lens driving motor for moving -b along the optical axis and a zoom lens position detecting means for detecting the position of the variable power portion 1-b on the optical axis. Reference numeral 17 denotes a zoom switch, and when the photographer presses the switch, the CPU 12 issues a command to the variable magnification partial drive means 14 to change the focal length of the photographing lens 1.

The photoelectric conversion element 2 converts the subject image formed by the taking lens 1 into an electric signal.

Reference numeral 3 denotes a diaphragm member (diaphragm means), and this diaphragm member 3 has four diaphragms as shown in FIG.
That is, the diaphragm 3-a is an auto-correlation focusing diaphragm and is provided with two apertures having different sizes. Aperture 3-b, 3
Reference numerals -c and 3-d are diaphragms for photographing and focusing for climbing a mountain, and are provided with one opening (φ _j ) of different size. An aperture stop 3-d having the largest aperture is an aperture stop of the taking lens, and the latter two apertures are a middle aperture and a small aperture, respectively.
The diaphragm member 3 has, for example, a turret type structure, and one of the above four diaphragms is selectively mounted in the optical path depending on the situation. When the CPU 12 selects the auto-correlation focusing aperture 3-a, the aperture of the aperture 3-a
The two openings are mounted so as to be aligned in parallel to the horizontal scanning direction of the photoelectric conversion element 2 in a plane perpendicular to the optical axis. When other diaphragms are selected, the single aperture is mounted so that the approximate center is located on the optical axis.

A diaphragm switching means 9 is composed of a stepping motor or the like, and switches the diaphragm of the diaphragm member 3 based on a command from the CPU 12.

Reference numeral 4 is a photometric means for obtaining the brightness information of the subject. Reference numeral 5 denotes an image pickup circuit, which converts an electric signal obtained from the photoelectric conversion element 2 into a signal suitable for recording or calculation and outputs the signal. Reference numeral 6 is a recording means for recording the signal output from the image pickup circuit 5. Reference numeral 7 denotes a calculation means, which calculates and obtains the focus state of the subject image on the surface of the photoelectric conversion element 2 based on the signal output from the image pickup circuit 5.

Reference numeral 10 is a main power / mode selector switch, which switches the power of the entire apparatus ON / OFF and modes such as shooting and reproduction. Reference numeral 11 is a release switch for inputting the timing of the shooting operation at the time of shooting.
Switch 1 is turned on by the first stroke, and the first stroke
Switch 2 turns on with a second stroke that is larger than the stroke.

The CPU 12 turns on the blocks required for the mode set by the main power / mode changeover switch 10, and based on the signal from the release switch 11, the recording means 6, the image pickup circuit 5, and the photometry. Instructing the operation timing of the means 4, the calculation means 7, etc., and the focus lens driving means 8
Drive the focus lens 1-a via the
The position information of the shaving lens 1-a is obtained, the focus lens driving means 8 is controlled based on the signal of the calculating means 7, and the aperture switching means 9 is controlled based on the signals of the photometric element 4 and the calculating means 7. , Obtaining necessary information from each block to calculate the subject distance and depth of field of the subject, calculating the FNo of the taking lens 1, calculating the focal length, etc. based on the signal of each block. The operation signal is given to, received from, or operated in a necessary block.

Numeral 13 is a high-speed mode changeover switch, which is used when the photographer intends to photograph at high speed with less deviation of the photographing timing even if the focusing accuracy is lowered.

Reference numeral 15 denotes a threshold value storage means, which is a threshold value E to be compared with a D value related to the depth of field calculated by the CPU 12.
(F _i , φ _j ) is stored, for example, EEPR
Use OM.

The threshold value E (f
_i , φ _j ) is determined as follows. Perform the following experiments in advance. It is assumed that the focal length of the photographing lens is f _i and the diaphragm diameter suitable for photographing at that time is φ _j . In focus object distance when the focusing operation with the autocorrelation focusing scheme u, Renzude - if the size of the entrance pupil can be calculated from the data and phi _J and D _F, permissible circle of confusion between D _F and u Calculate the next near field depth D value using the diameter δ ′.

D = 2u ² δ '/ (f _{i DF} ) Then, the relationship between this D value and the focus shift at this point (after performing the autocorrelation focusing operation once) is examined. After this is experimentally obtained for many subjects, if the D value is larger than a certain threshold value, a threshold value at which the focus deviation can be allowed by the focusing operation only by the autocorrelation method is determined. This threshold may be one, or may be a plurality of values related to the focal length f _i and the aperture diameter φ _j . Therefore, this threshold is expressed as E (f _i , φ _j ).

FIG. 3 shows a flow chart at the time of photographing in the automatic focus adjusting device having the above structure, and the focusing operation of the subject will be mainly described.

First, when the main power / mode selector switch is set to the photographing mode (S1), the recording means 6 is ready to record the signal output from the image pickup circuit 5 by the operation signal of the CPU 12. It is initialized (S2). Next, the photographer determines the photographing composition of the subject using a known external viewfinder (not shown). Next, when the switch 1 of the release switch 11 is turned on (S3), the power supplies of the circuits of the photoelectric conversion element 2, the image pickup circuit 5, and the arithmetic means 7 are turned on (S4).

Next, the brightness of the subject is measured by the photometric means 4, and the information is sent to the CPU 12 (S5). At the same time, the diaphragm switching means 9 is driven by the operation signal of the CPU 12, and the autocorrelation focusing diaphragm 3-a of the diaphragm member 3 is mounted in the optical path of the taking lens (S6). Next, the speed of the electronic shutter suitable for the focusing means by the auto-correlation focusing method is determined by the CPU 12 based on the above-described subject photometric information, and the shutter speed determined by this is determined. The subject image is accumulated in the photoelectric conversion element 2 and then 1
A field, that is, an electric signal of a TV signal rate of 1/60 second per screen is taken in by the imaging circuit 5. This optical device performs autocorrelation focusing using this signal (S7) and drives the lens (S8).

Next, the CPU 12 determines the electronic shutter speed suitable for photographing based on the subject brightness information based on the program diagram of FIG. 4, and at the same time, selects one of the open diaphragm, the middle diaphragm and the small diaphragm. Is selected, and the aperture switching means 9 is driven to switch to the selected aperture (S9). This diaphragm member 3
Is switched during the vertical blanking period of the video signal so as not to affect the subject video signal taken from the photoelectric conversion element 2 into the image pickup circuit 5.

Next, it is judged whether or not the high speed mode is selected (S9 '), and if the high speed mode is selected, the process immediately proceeds to S12. If the switch 2 is on at this point, shooting / recording ( S13) is performed. If the normal mode is selected in S9 ', the process proceeds to S10'.

In S10 ', the CPU 12 first calculates the subject distance u in this state. That is, the focal length f _i is calculated from the previously stored data of the taking lens 1 and the zoom lens position information obtained from the zoom lens driving means 14, and the focal length f _i and the focus lens driving means 8 are calculated. The subject distance u is calculated using the obtained position information of the focus lens 1-a. Further, letting D _{F be} the size of the entrance pupil that can be calculated from the lens data, the focal length information, the focus lens information, and the aperture diameter φ _J , the following can be obtained using D _F , u and the permissible circle of confusion diameter δ ′. Calculate the D value.

D = 2u ² δ '/ (f _{i DF} ) This D value represents the depth of field at a short distance.

The D value obtained here is compared with the threshold value E (f _i , φ _j ) stored in the threshold value storage means 15 (S1).
0). If the D value is larger than the threshold value E (f _i , φ _j ), it is judged that the focusing error due to the autocorrelation method is acceptable,
Immediately proceed to S12. If D value is the threshold value E (f _i, φ _j)
If it is smaller, it is determined that the focusing error due to the autocorrelation method is unacceptable, and the process proceeds to the hill climbing focusing operation (S11). In S11, the electronic shutter speed determined above is determined.
The subject image is accumulated in the photoelectric conversion element 2 at
A video signal of a TV signal rate of / 60 seconds is sequentially captured by the image pickup circuit 5. This signal taken into the image pickup circuit 5 is converted into a signal suitable for the hill climbing focusing method, and is input to the arithmetic circuit 7. Based on this input signal, the calculating means 7 evaluates the in-focus state of the subject on the photoelectric conversion element 2 based on the hill-climbing in-focus method as described in the conventional example, and the CPU 12 determines this evaluation value. The focus lens driving means 8 is controlled by utilizing this, and the focus lens 1-a is driven to a position where the subject image is focused on the surface of the photoelectric conversion element 2.

Next, in S12, if the switch 2 of the release switch is turned on at this point, the photoelectric conversion element 2
The subject image stored in the image pickup circuit 5 is captured by the image pickup circuit 5. This signal taken in the image pickup circuit 5 is converted into a signal suitable for recording in the recording means 6 and recorded in the recording means 6 (S13). After the subject is recorded in this manner, the standby state is set in preparation for the next shooting.

[0046]

As described above, according to the present invention, when the focus detection of the photographing system is performed using the two focus detection methods in the order of the so-called autocorrelation focus method and the hill-climbing focus method, the conditions relating to the photography are set. If a preset value is satisfied, a high-speed focus is made possible by performing a focusing operation using a signal based on the focusing operation only by the auto-correlation focusing method, Thus, it is possible to achieve an automatic focus adjustment device that reduces power consumption and enables efficient focusing operation.

Others According to the present invention, after performing the focusing operation of the autocorrelation focusing method, the D value related to the depth of field is obtained, and if this is larger than the threshold value set by the experiment, the hill climbing method is selected. By omitting the focusing operation, it is possible to shoot with less time lag from the time the shooting button is pressed until recording, and thus the shift in shooting timing can be reduced. Further, in this case, since the time required for the entire focusing operation is shortened, the power consumption is reduced, and the optical recording device having the automatic focus adjustment device has a larger number of photographic images or a longer photographic time. The advantages such as

Further, when the photographer intends not to miss the photographing opportunity, if the photographer selects the high-speed mode by the high-speed mode changeover switch, the automatic focus adjusting device is the first. After focusing by the one-step autocorrelation focusing method, shooting and recording are performed immediately without determining the magnitude of the D value and the threshold value, so the time required for the entire focusing operation is further shortened.
Can respond to the photographer's intention.

As described above, according to the present invention, it is possible to achieve an automatic focusing apparatus which can achieve high-speed and accurate focusing, save power consumption, and have a good usability.

[Brief description of drawings]

FIG. 1 is a block diagram of the present invention.

FIG. 2 is a diaphragm member of the present invention.

FIG. 3 is a flowchart of the present invention.

[Figure 4] Program diagram

FIG. 5 is an explanatory diagram of a conventional autocorrelation focusing method. (A) Optical path diagram of autocorrelation focusing method (B) Aperture diagram of autocorrelation focusing method (C) Object diagram on focal plane of autocorrelation focusing method

FIG. 6 is an autocorrelation coefficient diagram of a conventional autocorrelation focusing method.

FIG. 7 is a flowchart of a conventional autocorrelation focusing method.

FIG. 8 is an explanatory view of a conventional mountain climbing focusing method (A) A mountain climbing focusing optical path diagram (B) A diaphragm drawing of the mountain climbing focusing method (C) A subject view on the focal plane of the mountain climbing focusing method

FIG. 9 is a flowchart for calculating a focus evaluation value in a conventional hill-climbing focusing method.

FIG. 10 is a focusing progress diagram of a conventional hill climbing focusing method.

[Explanation of Codes] 1 Photographic lens 1-a Focus lens 1-b Variable magnification part 2 Photoelectric conversion element 3 Aperture member 4 Photometric means 5 Imaging circuit 6 Recording means 7 Calculation means 8 Focus lens drive means 9 Aperture switching means 10 Main power supply / mode 11 Release switch Changeover switch 12 CPU 13 High-speed mode changeover switch 14 Variable magnification partial drive means 15 Threshold value storage means

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display area G03B 3/10

Claims (7)

[Claims] 1. A subject image is formed on a photoelectric conversion element by a photographing system having a diaphragm means for selectively mounting a plurality of openings and one opening in an optical path by a diaphragm switching means, and the photoelectric conversion is performed. By using the output signal from the element, the image formation state of the subject image is obtained by the calculating means, and by using the output signal from the calculating means, the focus lens driving means is used to focus the photographing system.
When the focusing lens is moved by moving the cas lens on the optical axis, a plurality of openings and one opening of the diaphragm means are mounted in the optical path of the photographing system to perform the focusing operation. When the focusing operation is performed in the order of the first focusing means and the second focusing means, the preset photographing is performed in the focusing operation by the first focusing means. An automatic focus adjusting device characterized in that a focusing operation is performed only by the first focusing means when a condition relating to is satisfied. 2. The automatic focusing device according to claim 1, wherein the preset condition relating to photographing is when the mode of the automatic focusing device is a high speed mode. 3. The preset conditions for shooting are:
The automatic focus adjustment device according to claim 1, wherein the value related to the depth of field is equal to or larger than a preset range. 4. The condition relating to the preset photographing is
The automatic focus adjusting device according to claim 1, wherein the aperture value of the photographing system is equal to or more than a preset value. 5. The preset condition for photographing is
2. The automatic focusing apparatus according to claim 1, wherein the focal length of the photographing system is equal to or less than a preset value. 6. The preset condition for photographing is
When the value related to the depth of field is greater than or equal to a preset range, or when the aperture value of the imaging system is greater than or equal to the preset value, or when the focal length of the imaging system is less than or equal to the preset value. 2. The automatic focusing apparatus according to claim 1, which is at least one of the following. 7. The image formation state of the subject image is obtained by the first focus detection means from the autocorrelation of the plurality of subject images based on the light flux passing through the plurality of aperture openings of the aperture means. 2. The automatic focus adjustment device according to claim 1, wherein the second focus detection means obtains the sharpness of the subject image on the surface of the photoelectric conversion element by comparing each field.