JP3187871B2 - Focus detection 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 focus detection device, and more particularly to a focus detection device that performs focus detection using a video signal.

[0002]

2. Description of the Related Art A technique for performing in-focus detection using a video signal is disclosed in NHK Technical Report Vol. 17, No. 1, Ishida et al. There is a method (generally referred to as a hill climbing method). Referring to the relationship diagram between the frequency component and the lens defocus in FIG. 14, this method uses the fact that the high frequency component of the video signal increases near the in-focus point compared with the vicinity of the non-focus point, and the high-frequency component peaks. become (Korea sharpness degree is increased) in particular focused, extracted frequency components from the video signal, and drives the optical system to a higher frequency component position.

A method of moving an optical system to two or more predetermined positions, detecting frequency components at those positions, and detecting a focal point by taking a ratio of the frequency components is disclosed in Japanese Patent Laid-Open No. Hei. 275916. FIG.
FIG. 5 is a diagram illustrating a relationship between a frequency component ratio and a defocus characteristic with respect to an MD curve (curve of a frequency component and a lens defocus characteristic) illustrated in FIG.

However, this method requires two photographic optical systems.
Unless it is moved to more than the position, the focal point cannot be detected, which is not preferable in use. Therefore, the above problem can be solved by providing two sensors having a predetermined optical path difference in the camera body and obtaining the frequency component ratio from the outputs of these two sensors.

[0005]

By the way, the above-mentioned 2
In the system using two sensors, the system shown in FIG.
The relationship between the frequency component ratio and the defocus amount as shown in FIG. 5 needs to be stored as a table.
Since this relationship is defined by the optical path difference between the two sensors, when this imaging optical system is mounted on another camera body, the optical path difference between the two sensors in the camera body is designed. If they are not the same, accurate focus detection cannot be performed.

Actually, such an optical path difference should be set in accordance with the AF function (accuracy priority or speed priority) of the camera. Therefore, it is not preferable to set this to a common value for all cameras. However, storing a table of a plurality of frequency component ratios vs. defocus amounts in the memory in the photographing optical system in accordance with the plurality of types of optical path difference values causes a problem that the storage capacity increases.

In such a system, it is common to detect an approximate focus position by using a low-frequency component of a video signal and then obtain an accurate focus position by using a high-frequency component. However, in this frequency switching method,
At least two tables of frequency component ratio versus defocus amount must be stored for low frequency and high frequency.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has a table corresponding to the key difference between two sensors in a plurality of types of camera bodies, and two types of frequency component ratios versus defocus amounts by frequency switching. It is an object of the present invention to provide a focus detection device having high systematicity with a small storage capacity without storing the table.

[0009]

That is, according to the present invention, the light distribution of a subject passing through a photographing optical system is photoelectrically converted in at least two different places of the photographing optical system.
A photoelectric conversion element that outputs a photoelectric conversion signal; frequency detection means for extracting frequency components from the photoelectric conversion signal output from the photoelectric conversion element; and frequency components corresponding to the two locations detected by the frequency detection means. Frequency component ratio detecting means for determining a ratio, and an optical path of the photoelectric conversion element
Interval value output means for outputting a value corresponding to the length; and calculating the defocus amount of the photographing optical system from the ratio of the frequency components .
Function storage means for storing a plurality of function formulas used for the purpose, and set in accordance with the imaging optical system and used for the function formula.
Coefficient storage means for storing coefficients to be used, and said frequency component
The value of the frequency component ratio obtained by the ratio detection means is determined in advance.
Comparing means for comparing with the set value and outputting a comparison result;
Stored in the function storage means according to the output result of the comparison means.
Select at least one function expression from the multiple
And a plurality of parameters stored in the coefficient storage means.
Selection means for selecting at least one coefficient from a number
And the function, coefficient and frequency selected by the selection means
The value of the ratio of the components, and the value output from the interval value output means
Characterized by comprising the defocus amount calculation means for calculating a defocus amount using the distance value.

[0010]

In the in-focus point detecting apparatus according to the present invention, the light distribution of the object passing through the photographing optical system is photoelectrically converted at least at two different positions of the photographing optical system, and the photoelectric conversion signal is converted into a photoelectric conversion signal. Output from the conversion element. Frequency components are extracted from the photoelectric conversion signals output from the photoelectric conversion elements by frequency detection means. The ratio of the detected frequency components corresponding to the two locations is obtained by frequency component ratio detection means, and the ratio of the optical path length of the photoelectric conversion element is calculated.
The corresponding value is output from the interval value output means. In addition,
From the frequency component ratio, the defocus amount of
A plurality of function expressions used for operation are stored in function storage means.
Stored in the camera and set according to the shooting optical system.
Coefficients used in the function expression are stored in coefficient storage means.
Then, the frequency obtained by the frequency component ratio detecting means
The value of the component ratio is compared with a predetermined value by the comparing means.
The comparison result is output. Output of the comparison means
A plurality of function expressions stored in the function storage means according to the result
At least one function expression is selected by the selection means.
And a plurality of coefficients stored in the coefficient storage means.
At least one coefficient is selected from. And
The function, coefficient and frequency component selected by the selection means
And the interval output from the interval value output means.
The defocus amount is calculated by the defocus amount calculation means using the value .

An embodiment of the present invention will be described below with reference to the drawings. First, an outline of the present invention will be described. The invention
Shows the light distribution of the subject through the interchangeable shooting optical system,
At two places near the planned focal plane of the above-mentioned photographing optical system,
A photoelectric conversion element that performs photoelectric conversion and outputs a photoelectric conversion signal.
And from the photoelectric conversion signal output from this photoelectric conversion element
Frequency detecting means for extracting each frequency component;
Numbers corresponding to the two locations detected by the number detection means
Frequency component ratio detecting means for obtaining a ratio of wave number components;
The defocus amount of the imaging optical system is calculated from the ratio of the wave number components.
The coefficient used for the function
A memory provided in the above-mentioned photographing optical system for storing for each interval amount.
Storage means, the coefficient according to the interval amount, and the frequency
Defocuser that calculates the amount of defocus based on the ratio of components
And an amount calculation means. And
In the in-focus point detecting apparatus according to the present invention, the light passes through the photographing optical system.
The light distribution of the subject is 2 near the planned focal plane of the photographing optical system.
Each part is photoelectrically converted, and each frequency component is detected.
Is done. The frequency components corresponding to the two detected locations are detected.
The ratio of the minute and the ratio of this frequency component
The coefficients used in the function for calculating the focus amount
It is stored for each interval amount. And, according to the above interval amount
Defocus based on the ratio of
The quantity is calculated.

FIG. 1 is a block diagram showing the concept of a camera to which a focus detection device is applied as a first embodiment of the present invention. In the figure, the lens side is an optical system 1
And a driving unit 2 for driving the optical system 1 and a case where the frequency component ratio and the defocus amount at a predetermined optical path difference are approximated to a plurality of functions based on the frequency component and the defocus amount of the optical system 1. A storage unit 3 for storing coefficients.

On the main body side, a photoelectric conversion element 4, a frequency detection section 5 for detecting a specific frequency component from the output of the photoelectric conversion element 4, and an output obtained by a predetermined optical path difference from the frequency detection section 5 Frequency component ratio detector 6 for detecting the ratio of
And a defocus amount calculation unit 7.

In the focus detection device having such a configuration,
When a light beam from a subject passes through the optical system 1, the light distribution of the subject is converted into an electric distribution by the photoelectric conversion element 4.
Then, the specific frequency component is detected from the output of the photoelectric conversion element 4 by the frequency detection unit 5, and the ratio of the output obtained from the frequency detection unit 5 with a predetermined optical path difference is detected by the frequency component ratio detection unit 6. You.

The defocus amount calculation unit 7 uses a coefficient as a parameter based on the output value of the frequency component ratio detection unit 6, information indicating the type of the optical system 1, predetermined optical path difference information, and a coefficient switching value. A specific function is set from a plurality of stored functions, a coefficient of the specific function is set from the storage unit 3, and a defocus amount is calculated based on the set approximate function. In addition, the defocus amount calculation unit 7 receives the current position of the optical system 1 from the drive unit 2, calculates a drive amount of the optical system 1 based on the current position, and drives the optical system 1 through the drive unit 2.
Further, based on the frequency component of the optical system 1 and the defocus amount, a coefficient when the frequency component ratio and the defocus amount at a predetermined optical path difference are approximated by a plurality of functions is stored at least for each optical path difference and each frequency. 3 is stored. Next, the frequency component versus defocus characteristic will be described with reference to FIG. The method of detecting the focal point based on the frequency component ratio is disclosed in detail in Japanese Patent Application Laid-Open No. 2-275916, and a schematic expression is shown here.

The ratio of the specific frequency components of the two screens at a predetermined optical path difference is determined by the relationship between the position of the optical system and the position of the optical system independent of the frequency components of the object. S1 (ω) = O (ω) * L1 (ω) S2 (ω) = O (ω) * L2 (ω) S1 (ω) / S2 (ω) = L1 (ω) / L2 (ω) where * : Multiplication O (ω): Subject frequency component L1 (ω), L2 (ω): Optical system frequency transfer characteristic S1 (ω), S2 (ω): Detection frequency component. Next, as a second embodiment of the present invention, an example in which the in-focus point detecting device is applied to a camera will be described.

FIG. 3 is a diagram showing a schematic configuration of this camera as a second embodiment. Optical system 1 with camera 10
The luminous flux that has passed through is split into a finder system and an AF detection system by a main mirror (M mirror) 11 composed of a half mirror only in the central periphery. The luminous flux guided to the finder system is guided to the finder 12. The light beam guided to the AF detection system is guided to a beam splitter 14 by a sub-mirror (S mirror) 13, and further converted to an electric signal via a sensor 15.

FIG. 4 shows a block diagram of the camera shown in FIG. The camera includes a lens 16 and first and second sensor CCDs 17 and 18 for converting light beams having different optical path lengths passing through the lens 16 into electric signals.
(Having a sensor optical path difference ds with the film equivalent surface interposed therebetween). Also, this camera uses the sensor CC
In addition to an A / D conversion circuit 19 for converting the signals of D17 and D18 into digital signals, a memory 20 and a lens 16, the first and second sensor CCDs 17 and 18, and a CPU (central processing unit) 21 for controlling the memory 20 Is provided.

The CPU 21 calculates the coefficients of a plurality of functions that approximate the relationship between the ratio of the frequency components of the lens 16 and the defocus, and the frequency component ratio that switches the approximated functions.
A memory 20 for storing the intervals and frequencies of the first and second sensor CCDs 17 and 18 and a specific frequency component extracted from a digital signal from the A / D conversion circuit 19 to obtain a frequency component ratio; The relative defocus amount is detected based on the coefficient from 20. Further, the lens 16
The driving amount of the lens 16 is calculated on the basis of the positional information of the first and second sensors CCD1 and CCD2.
Drives 7 and 18 are controlled. The operation of the camera configured as described above will be described with reference to a flowchart as a main sequence in FIG.

When the operation is started, initialization is performed in step S1, and then it is determined in step S2 whether the first release is turned on. If the first release is off, this sequence ends. If the first release is on, the process proceeds to step S3 to determine whether the second release is on.

In step S3, if the second release is on, the flow advances to step S4 to execute a shutter and winding sequence, and then returns to step S1. On the other hand, if the second release is off in step S3, the process proceeds to step S5, where the subroutine program AF is executed.

Thereafter, in step S6, the focusing flag GF
(The flag GF is GF = 1 when the lens 16 is at the in-focus position, and GF = 0 when the lens 16 needs to be driven out of focus). In step S6, if GF = 1, the process returns to step S1, and if GF = 0, the process proceeds to step S7, where the lens 16 is driven to the position specified by the subroutine program AF. FIG. 6 shows a sequence of the subroutine program AF shown in FIG.

When the subroutine program AF is started, initialization is performed (step A1), and then the characteristics of the lens 16 and the lens 1 are communicated with the lens 16.
No. 6 is detected (step A2). Then, integration of the first and second sensor CCDs 17 and 18 is performed (step A3), and after integration, the signals of the first and second sensor CCDs 17 and 18 are read out (step A).
4).

The read signal is transmitted to A in real time.
/ D converted and stored as digital data (step A5). The digital data is subjected to a masking process (Gaussian mask; multiplying a Gaussian distribution coefficient by a pixel signal to remove a detection error due to discontinuity at both ends of the signal at the sensor) (step A6). based on the frequency of the position information and the lens 16 of the lens 16 at A2 is set to the detection frequency f1, the frequency f1 to be detected digitally processed at CPU 21 (discrete
Discrete Fourier Transform; Discrete Fourier
Transform ) detects the detection frequency f1 (step A7).

Next, the ratio (MTFR1) of the frequency components from the two sensors having the predetermined optical path difference is detected (step A8), and the MTFR and the predetermined value ε1 (included in the information of the lens 16 and detected at the frequency f1) Are different) (step A9).

If | MTFR1-1 | <ε1 is not satisfied, information on MTFR1 and the lens 16 (function switching M
The defocus amount at the detection frequency f1 is calculated from the TFR1 value and the coefficient of the function by a predetermined function approximation (step A10). Then, the drive amount L1 of the lens 16 is calculated based on the calculated defocus amount and the current position of the lens 16 (step A11).

On the other hand, in step A9, | MT
If FR1-1 | <ε1, it means that the lens 16 is already near the focal point. That is, the detection frequency is changed based on the information of the lens 16 in order to increase the focus detection accuracy, and the detection frequency f2 is higher than f1.
(F2 is a frequency at which the interval between the two sensors is smaller than Z0 of the characteristics of the lens frequency component and the defocus amount shown in FIG. 7) (step A1).
2). Next, the detection frequency f2 is detected by digital processing (DFT) (step A13), and the ratio (MT) of the frequency components from the two sensors having a predetermined optical path difference is detected.
FR2) is detected (step A14).

Thereafter, the MTFR2 and the predetermined value ε2 (included in the information of the lens 16 and differ depending on the detection frequency f2)
Are compared (step A15). Where | MTFR
If 2-1 | <ε2, MTFR2 and lens 16
(The function switching MTFR1 value, function coefficient) 2, the defocus amount at the new detection frequency f2 is calculated by a predetermined function approximation (step A16). Next, the driving amount L2 of the lens 16 is calculated based on the calculated defocus amount and the current position of the lens 16 (step A1).
7) After the drive amount of the lens 16 is calculated, the focusing flag GF is set to GF = 0 (step A18).

On the other hand, in step A15, | MTF
If R2-1 | <ε2, the focusing flag GF is GF = 1.
(Step A19), and after the focusing flag GF is set, the subroutine program AF is terminated.
FIG. 7 is a diagram showing a specific frequency component and a defocus characteristic of the lens at a specific frequency of the lens used in the embodiment.

In the figure, the vertical axis represents the frequency component of the lens (normalized to 1 when focusing on an ideal subject), and the horizontal axis represents the defocus amount of the lens. The lens frequency component M0 is set in consideration of noise, and the defocus amount from the focal point at that time is set to Z0. The defocus amount is determined according to the position of the object point (subject) and the position of the lens 16. Here, when the detection frequency f1 is set to f10 and used, the defocus amount corresponds to the region corresponding to Z0 to Z1 (from the position where the lens 16 corresponds to the infinity or the closest position, the defocus amount on one side where the defocus amount is large). (Position where the amount is Z1). When the detection frequency f1 is set to f11 higher than f10 and used, the focus amount is Z1.
(A position where the lens 16 has substantially the same defocus amount Z2 on both the infinity side and the closest side from the defocus amount on one side with a large defocus amount from Z1)
It is. If the detection frequency f1 is set to f12, which is higher than f11, the defocus amount is substantially equal to the area near Z2 (the lens 16 is substantially the same defocus amount Z2 on both the infinity side and the closest side). Position). FIG. 8 shows comparison values ε1, ε2 for the MTFR.
FIG. 4 is a diagram for explaining settings.

In the figure, ε1 is a switching point between the detection frequencies f1 and f2, and is determined in consideration of a difference between two optical paths and an S / N ratio of a signal. Ε2 is determined in consideration of the focusing accuracy (determined by the F number (F _No ) of the lens) and the S / N of the signal. Next, calculation of the defocus amount of the lens 16 will be described with reference to the flowchart shown in FIG.

A plurality of functions that approximate the relationship between the MTFR corresponding to the detection frequency and the defocus amount are function switching M
It is expressed by a hyperbola and a linear function with the TFR value as a boundary (FIG. 1
0 shows a relational expression). In the lens having the characteristics shown in FIG. 2, the function switching MTFR value is k = 1 and the MTF is
If R> k, the defocus amount d is d = C + B / (MTFR + A) (1); C = −2.36 B = 3.09 A = 0.31 If MTFR> k, the defocus amount d is d = D * MTFR + E (2); D = −2.2 E = 2.2

Now, when the defocus calculation of the subroutine program is started, MT at the detection frequency is calculated.
The F ratio detection values MTFR1 and MTFR2 are input to the MTFR (step B1). Next, the MTFR is compared with the function switching value k (step B2). Where M
If TFR> k, the function obtained by the above equation (1) is set (step B3), and then the coefficients A, B, and C are set from the information of the lens 16 (step B4).

On the other hand, in step B2, the MTF
If not R> k, the function obtained by the above equation (2) is set (step B5). Then, coefficients D and E are set based on the information of the lens 16 (step B6). Thereafter, the defocus amount d is calculated by a predetermined function (step B7), and the process exits this subroutine program. FIG. 11 is a subroutine for explaining communication of lens data.

When the lens data communication of this subroutine program is started, a signal of two sensor intervals ds is transmitted from the camera to the lens together with a communication start signal (step C1). Next, data on the focus detection together with the communication start signal from the lens to the camera (detection frequency f, function switching MTFR value k, M at that frequency)
The TFR comparison value ε and the function coefficients A, B, C, D, and E) are repeatedly transmitted only for the frequencies stored in the lens (step C2). Then, the current lens position is communicated to the camera (step C3), thereby exiting this subroutine program.

With this configuration, it is possible to provide an in-focus point detection device which is fast and simple with little information even for a plurality of lenses and does not depend on the state of the subject. In this embodiment, DFT processing is used for frequency detection, but any processing (digital filter, analog filter) capable of detecting a narrow band may be used. In the above-described example, the detection frequency is switched three times according to the lens position. However, the detection frequency may be further reduced. In addition, a plurality of detection frequencies may be used within a range satisfying the condition (FIG. 7).

Further, other optical path length changing means such as changing the optical path length by driving a time-division lens may be used. For example, one sensor may be used, and the position of the sensor may be moved by a relay lens or the like. Although the film equivalent surface is sandwiched at the center, it is not always necessary to sandwich it at the center. Further, the arrangement of the sensors may be as follows.

That is, as shown in FIG. 12A, a film equivalent surface is sandwiched between the sensors I and II,
12B, the sensor II is disposed on the film equivalent surface, and the sensor I, II or the sensor II III has the shortest interval and the sensors I and III have the longest interval.
May be the shortest, and the sensors I and III may be the longest. Therefore, they are arranged equivalently to those shown in FIGS. 12A and 12B, and the accuracy is guaranteed at the shortest distance between the sensors.
At the time of large defocus, a sensor having a long sensor interval may be used. Further, the sensor may be downsized by the reduction optical system.
Further, the coefficient may be obtained without changing the hyperbolic expression (2) by merely changing the coefficient of the linear function of the expression (1). Next, a third embodiment of the present invention will be described. FIG. 13 shows a block configuration as a third embodiment. The same parts as those in FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted.

In the figure, the main body side has sensor CCDs 17 and 18 for converting light beams having different optical path lengths passing through the lens 16 into electric signals, respectively (having a sensor optical path difference ds across the film equivalent surface). And these sensor CCD
An A / D circuit 19 for converting the signals 17 and 18 into digital signals, a specific frequency is extracted from the digital signals of the sensor CCDs 17 and 18, and the same frequency component ratio (MTF
R) and a main CPU (MCPU) 21a for controlling the integration and reading of the sensor CCDs 17 and 18.

On the other hand, the lens side detects the amount of defocus based on the lens 16 based on a plurality of functions that approximate the relationship between the ratio of the frequency component of the lens 16 and the defocus for each detection frequency and sensor interval. It has a lens CPU (LCPU) 21b for calculating the drive amount based on the current position information, and a memory 20 for storing the coefficients of the function for each frequency. In the third embodiment, since the sequence other than the lens data communication is performed in the same manner as the above-described second embodiment, the description is omitted here.

With this configuration, the approximation function can be optimized for each lens, and by storing information on the lens side, the memory capacity of the main body can be reduced. Therefore, it is possible to provide a high-speed and simple focus detection device.

[0042]

As described above, according to the present invention, spatial frequency components are extracted from two video signals having different in-focus states, the ratio is approximated to a plurality of functions, and only the coefficients of the functions are stored. It is possible to provide an in-focus detection device which can reduce the amount of data and can easily cope with an interchangeable lens. Further, since a plurality of functions are switched based on the value of the ratio of the detected spatial frequencies, highly accurate in-focus detection can be performed using an optimal approximate function.

Further, by storing the function on the lens side,
There is no need to define a function unique to the lens on the camera body side, and a highly accurate focus detection device can be provided with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the concept of a camera to which a focus detection device is applied as a first embodiment of the present invention.

FIG. 2 is a diagram showing characteristics of frequency components versus defocus.

FIG. 3 is a diagram showing a schematic configuration of a camera to which a focus detection device is applied in a second embodiment of the present invention.

FIG. 4 is a block diagram of the camera shown in FIG. 3;

FIG. 5 is a flowchart illustrating the operation of the second embodiment.

FIG. 6 is a sequence of a subroutine program AF of FIG. 5;

FIG. 7 is a diagram showing a specific frequency component and a defocus characteristic of the lens at a specific frequency of the lens.

FIG. 8 is a diagram for explaining setting of comparison values ε1 and ε2 relating to MTFR.

FIG. 9 is a flowchart illustrating an operation of calculating a defocus amount.

FIG. 10 is a diagram showing a relational expression for obtaining a plurality of functions approximating a relation between an MTFR corresponding to a detection frequency and a defocus amount.

FIG. 11 is a subroutine for explaining communication of lens data.

FIG. 12 is a diagram showing an arrangement relationship between an equivalent surface of a film and a sensor.

FIG. 13 is a block diagram of a camera to which a focus detection device is applied according to a third embodiment of the present invention.

FIG. 14 is a diagram showing a relationship between frequency components and lens defocus.

15 is a diagram illustrating a relationship between a frequency component ratio and a defocus characteristic with respect to an MD curve (a curve of a frequency component and a lens defocus characteristic) illustrated in FIG. 14;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical system, 2 ... Drive part, 3 ... Storage part, 4 ... Photoelectric conversion element, 5 ... Frequency detection part, 6 ... Frequency component ratio detection part, 7 ...
Defocus amount calculation unit, 10 camera, 11 main mirror (M mirror), 12 finder, 13 sub mirror (S mirror), 14 beam splitter, 15 sensor, 16 lens, 17 first sensor CCD, 18 ...
Second sensor CCD, 19 A / D conversion circuit, 20 memory, 21 CPU (central processing unit), 21a main CPU (MCPU), 21b lens CPU (LCP)
U).

Claims (1)

(57) [Claims] 1. A light distribution of a subject passing through a photographing optical system,
A photoelectric conversion element for performing photoelectric conversion at at least two different positions of the photographing optical system and outputting a photoelectric conversion signal, and frequency detecting means for extracting frequency components from the photoelectric conversion signal output from the photoelectric conversion element And frequency component ratio detecting means for calculating the ratio of the frequency components corresponding to the two places detected by the frequency detecting means, and an interval value for outputting a value corresponding to the optical path length of the photoelectric conversion element
Output means, a function for storing a plurality of function formulas used to calculate the defocus amount of the imaging optical system from the ratio of the frequency components, storage means, and is set according to the imaging optical system, Used in the above function expression
Coefficient storing means for storing the coefficient of the frequency component ratio obtained by the frequency component ratio detecting means.
A ratio that compares a value with a predetermined value and outputs the comparison result
Comparison means and the function storage means according to the output result of the comparison means.
At least one function expression from a plurality of remembered function expressions
As well as a plurality of stored in the coefficient storage means.
Selector for selecting at least one coefficient from among the coefficients
A stage, a function expression, a coefficient and a frequency component selected by the selection means.
And the interval output from the interval value output means.
Focusing detection apparatus characterized by comprising: a defocus amount calculation means for calculating a defocus amount using the value.