JP5012091B2 - Focus adjustment device - Google Patents

Description

  The present invention relates to a focus adjustment device that performs focus adjustment of an optical system using two types of focus detection methods with different methods, and an imaging device including the focus adjustment device.

  As an autofocus method used in an imaging apparatus such as a camera, it is based on phase difference AF that detects a defocus amount indicating a focus adjustment state of a photographing lens and performs focus adjustment, and a focus evaluation value obtained from contrast information of a subject image For example, there has been proposed a hybrid AF type camera that uses both the contrast AF method for adjusting the focus and performs the contrast AF after the phase difference AF (see, for example, Patent Document 1).

JP 2002-328293 A

  By the way, depending on the state of the subject, even if the defocus amount can be calculated by the first phase difference AF, there is a possibility that the peak position of the focus evaluation value that is regarded as the focus lens position in the subsequent contrast AF cannot be detected. However, the above-described conventional camera has a problem that such a case is not taken into consideration.

A focus adjustment device according to a first aspect of the present invention includes a first focus detection unit that detects focus information representing a focus adjustment state of the optical system based on an image of a light beam that has passed through a pair of regions of the optical system; Second focus detection means for detecting a focus evaluation value of the optical system based on contrast information of an image by the optical system when the focus adjustment lens of the optical system is driven and controlled with a predetermined step width in the optical axis direction; After the first control for driving the focus adjustment lens of the optical system to the first in-focus position based on the focus information by the first focus detection means, the focus evaluation value is detected by the second focus detection means. When the second control for driving the focus adjustment lens is performed and the in-focus position cannot be detected by the second control, based on new focus information by the first focus detection means. And control means for performing a third control for driving the focusing lens of the optical system to the second focus position Te, the control means includes a first focus position at the time of the first control, the third When the difference from the second in- focus position during control is smaller than a predetermined value, the predetermined step width of the second focus detection unit is narrowed, and the focus evaluation value is detected by the second focus detection unit. There rows fourth control for driving the focusing lens while performing the further the control means, said first focus position at the time of the first control, the second focus position at the time of the third control Is larger than the predetermined value, the focus adjustment is performed while the focus evaluation value is detected by the second focus detection means without changing the predetermined step width of the second focus detection means. a fifth control to drive the lens, characterized in row Ukoto.

  According to the present invention, even when the optical system cannot be focused to the in-focus state by the first focus adjustment, new focus information is detected by the first focus detection means at the lens position at that time, By executing the second focus adjustment based on the new focus information, the focus adjustment to the in-focus state can be performed more reliably.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an embodiment of an image pickup apparatus according to the present invention, and shows a configuration of a main part of a digital still camera. The camera shown in FIG. 1 includes a photographing optical system 1, a quick return mirror 2, a sub mirror 3, an image sensor 4, an AF drive motor 5, a phase difference AF detection unit 6, a control unit 10, a lens drive control unit 11, a focusing screen 12, A pentaprism 13 and an eyepiece 14 are provided. The control unit 10 includes an AF CCD control unit 101, a defocus calculation unit 102, a lens driving amount calculation unit 103, and a contrast calculation unit 104. SW1 is a half-push switch that is turned on by a half-press operation of a release button (not shown), and SW2 is a full-push switch that is turned on by a full-press operation of a release button.

  A photographing optical system 1 that forms a subject image on an imaging surface includes a plurality of lenses 1a, 1b, and 1c. The focus adjustment lens 1 b of the photographing optical system 1 is driven in the optical axis direction by the AF drive motor 5.

  The light beam from the photographic optical system 1 is reflected by the quick return mirror 2 and forms an image on the focusing screen 12 disposed at a position conjugate with the planned focal plane. The subject image formed on the focusing screen 12 is observed by the photographer via the pentaprism 13 and the eyepiece 14. At the time of photographing exposure, the quick return mirror 2 and the sub mirror 3 are retracted out of the optical path, and the subject light flux from the photographing optical system 1 enters the image sensor 4. A solid-state image sensor such as a CCD or a CMOS is used for the image sensor 4. Although not shown in FIG. 1, an infrared cut filter for cutting infrared light and an optical low-pass filter are disposed on the front surface of the image sensor 4.

  A part of the light beam incident on the quick return mirror 2 passes through a half mirror portion formed near the center of the quick return mirror 2, is reflected by the sub mirror 3, and enters the phase difference AF detection element 6. The phase difference AF detection element 6 is provided with an AF CCD sensor (not shown). The AF CCD sensor includes a pair of line sensors for receiving each light beam that has passed through a pair of partial areas on the pupil plane of the imaging optical 1 for each detection area. A signal output from the AF CCD sensor is input to the AF CCD control unit 101 of the control unit 10.

  The AF CCD control unit 101 controls the gain and accumulation time of the AF CCD sensor, determines a necessary area from a plurality of detection areas, reads out signals in the area, and calculates correction data. The defocus calculation unit 102 calculates a defocus amount representing a focus shift of the subject image from the calculation result of the AF CCD control unit 101. That is, the defocus calculation unit 102 performs a known correlation calculation based on the sensor signals of the pair of line sensors, calculates an image shift amount on the sensor, and uses the focus information of the photographing optical system 1 from the image shift amount. A certain defocus amount is calculated.

  Based on the defocus amount calculated by the defocus calculation unit 102, the lens drive amount calculation unit 103 calculates a lens target position that is a target when driving the focus adjustment lens 1b. The calculated lens target position is input to the lens drive control unit 11. The lens target position is a lens position where the defocus amount becomes zero when the focus adjustment lens 1b is driven to that position.

  On the other hand, the contrast calculation unit 104 of the control unit 10 receives an imaging signal of an imaging region corresponding to the detection area of the phase difference AF detection unit 6 among the imaging data output from the imaging element 4. The contrast calculation unit 104 extracts a high frequency component from the image pickup signal output from the image pickup device 4 and performs a known focus evaluation value calculation. In the in-focus state in which the photographing optical system 1 forms a sharp image on the imaging surface of the image sensor 4, the blur of the edge of the subject image is minimized and the contrast is maximized, so that the focus evaluation value is also maximized.

  The control unit 10 outputs a control signal based on the target lens position calculated by the lens drive amount calculation unit 103 and the focus evaluation value calculated by the contrast calculation unit 104 to the lens drive control unit 11. The lens drive control unit 11 adjusts the focus adjustment state of the photographic optical system 1 by controlling the AF drive motor 5 based on the control signal.

<< Focus Adjustment Operation in this Embodiment >>
Next, the focus adjustment operation in the present embodiment will be described with reference to the flowcharts of FIGS. A series of processing shown in this flowchart is performed by executing a focus adjustment processing program in the control unit 10. In step S101, it is determined whether or not the half-press switch SW1 for instructing the start of the focus adjustment operation is on. If it is determined to be on in step S101, the process proceeds to step S102 to start phase difference AF.

  In step S102, the defocus calculation unit 102 performs correlation calculation to calculate the defocus amount. The light beams that have passed through a pair of different areas of the photographic lens 1 are imaged on a pair of CCD line sensors provided in the phase difference AF detector 6. The defocus calculation unit 102 performs a known correlation calculation based on the sensor signal of the CCD line sensor, calculates an image shift amount on the sensor, and is focus information of the photographing optical system 1 from the image shift amount. Calculate the defocus amount.

  In step S103, it is determined whether or not focus detection is possible by the correlation calculation performed in step S102. For example, when the subject has a low contrast, the degree of correlation between a pair of data decreases, and the reliability of the correlation calculation value decreases. In such a case, since the focus adjustment accuracy is lowered, it is determined in step S103 that focus detection is impossible (NO), and the process proceeds to step S112.

  In step S112, a so-called scanning operation (search drive) is performed, and it is determined whether or not the lens position of the focus adjustment lens 1b is an end portion (closest end portion or infinity end portion) of the drive range.

  If it is determined in step S112 that the focus position is at the end of the drive range, the focus position cannot be detected by phase difference AF, and thus the process proceeds to step S113 to perform a non-focus process. As the out-of-focus processing, for example, the lens is stopped, and a warning display for notifying the user that the in-focus position cannot be detected is performed. On the other hand, if NO is determined in step S112, the process proceeds to step S114, the focus adjustment lens 1b is moved, and the process returns to step S102. In step S102, correlation calculation is performed at the position after the lens movement. Then, the process of S102 → S103 → S112 → S114 → S102 →... Is repeated until YES is determined in step S103 or until the lens position is determined to be an end in step S112. This is a so-called scanning operation.

  On the other hand, if YES is determined in the step S103, the process proceeds to a step S104, and the focus adjustment lens 1b is driven to the in-focus position based on the defocus amount calculated by the correlation calculation in the step S102. In step S105, the current lens position after movement is stored in a storage unit (not shown) of the control unit 10. In step S106, in order to perform contrast AF, the quick return mirror 2 is raised and retracted from the optical path. As a result, the subject image formed by the photographing optical system 1 is picked up by the image pickup device 4. At this time, if the imaging position of the photographing optical system 1 and the position of the imaging surface of the image sensor 4 coincide with each other, a focused subject image is captured. If there is a shift, a blurred image that is out of focus is captured.

  In step S107, as described above, the contrast calculation unit 104 calculates the contrast and calculates the focus evaluation value based on the imaging data acquired by the imaging device 4. In step S108, it is determined whether or not the peak position of the focus evaluation value can be detected based on the focus evaluation values obtained for the plurality of lens positions. Note that when step S106 → step S107 → step S108 is executed for the first time, and step S108 is executed for the first time, only one focus evaluation value has been calculated, so NO is determined in step S108 and the process proceeds to step S109. Conversely, if it is determined in step S108 that the focus position can be detected, the process proceeds to step S115, and the focus adjustment lens 1b is moved to a lens position (focus position) where the focus evaluation value reaches a peak.

  If NO is determined in step S108 and the process proceeds to step S109, it is determined in step S109 whether or not the peak position detection of the focus evaluation value in the contrast AF search range is completed. If it is determined in step S109 that the peak position detection in the search range has not ended, the process proceeds to step S116, and the focus adjustment lens 1b is moved by a predetermined amount. Thereafter, the process returns to step S107, and correlation calculation processing is performed on the moved lens position. Steps S107 → S108 → S109 → S116 → S107 are repeated until YES is determined in step S109.

  If it is determined in step S109 that the contrast AF in the search range has ended, the process proceeds to step S110. In this case, the phase difference AF from step S101 to step S104 indicates that the in-focus position could not be detected if the contrast AF was performed from the in-focus position even though the in-focus position was detected. Yes. For example, if the focus position is difficult to detect with contrast AF, if the subject suddenly moves between phase difference AF and contrast AF, or if the moving object has interrupted the subject In such a case, this situation can occur.

In such a case, the process proceeds from step S109 to step S110 and step S111, and a hybrid AF restart process is executed in step S111. In step S110, a lens driving amount X in contrast AF is calculated from the lens position stored in step S105 and the lens position at the end of contrast AF (that is, at the end of search). The calculated lens driving amount X is stored in the storage unit.

(Details of hybrid AF restart processing)
FIG. 3 is a flowchart showing details of the hybrid AF restart process in step S111. In step S201, the current lens position of the focus adjustment lens 1b when the contrast AF is completed is stored. Subsequent Step S202, Step S203, Step S211, and Step S212 perform the same processing as Step S102, Step S103, Step S112, and Step S114 in FIG. 2, respectively.

  That is, in step S202, the correlation calculation is performed based on the sensor signal output from the phase difference AF detection unit 6 at the current position, and the defocus amount is calculated. In step S203, it is determined whether or not focus detection is possible by the correlation calculation performed in step S202. If it is determined in step S202 that focus detection is possible, the process proceeds to step S204. On the other hand, if it is determined in step S202 that focus detection cannot be performed, the process proceeds to step S211 to determine whether or not the lens position of the focus adjustment lens 1b has reached the end of the drive range.

  If it is determined in step S211 that the end has not been reached, the process proceeds to step S212, the focus adjustment lens 1b is moved by a predetermined amount, and the process returns to step S202. On the other hand, if NO is determined in step S211, the process proceeds to step S210 to perform the above-described in-focus process. Also in the flowchart of FIG. 3, the process of S202 → S203 → S211 → S212 → S202 →... Is repeated until YES is determined in step S203 or the lens position is determined to be an end in step S211. Execute.

  If it is determined in step S203 that focus detection is possible and the process proceeds to step S204, the focus adjustment lens 1b is driven based on the defocus amount calculated in step S202. In step S205, a lens driving amount Y is calculated from the lens position stored in step S201 and the lens position after lens driving in step S204, and the lens driving amount Y and the lens driving amount X calculated in step S110 are calculated. It is determined whether or not the difference | Y−X | is smaller than a predetermined value δ.

  Here, the predetermined value δ is an amount corresponding to an error during AF. When | Y−X | <δ, the lens driving amount X at the first contrast AF in FIG. 2 and the lens driving amount Y at the second phase difference AF in FIG. 3 are substantially the same. It can be determined that the lens position at the start of the first contrast AF and the lens position at the end of the second phase difference AF are substantially the same position. That is, it can be determined that the in-focus position at the first phase difference AF and the in-focus position at the second phase difference AF are substantially the same, and it can be considered that the focus adjustment by the phase difference AF is reproducible. On the other hand, if | Y−X | ≧ δ, the in-focus position at the first phase difference AF and the in-focus position at the second phase difference AF are different, and the subject is between the first and second times. It can be considered that the distance has changed. Therefore, in this case, contrast AF is performed again from the lens position at the end of the second phase difference AF.

  Therefore, if it is determined in step S205 that | Y−X | <δ, the process proceeds to step S213, the focus adjustment lens 1b is stopped at the current lens position that is the in-focus position, and then the process returns to the flow of FIG. . On the other hand, if | Y−X | ≧ δ is determined in step S205, the process proceeds to step S206 to raise the quick return mirror 2 to perform contrast AF again.

  The subsequent steps S207, S208, S209, S214 and S215 are the same as the corresponding steps S107, S108, S109, S115 and S116 in FIG. In other words, the focus evaluation value is calculated by the contrast calculation unit 104 in step S207, and it is determined in the next step S208 whether or not the peak position of the focus evaluation value can be detected, that is, whether or not the focus position can be detected.

  If it is determined in step S208 that the in-focus position cannot be detected (NO), the process proceeds to step S209 to determine whether or not the peak position detection of the focus evaluation value in the contrast AF search range is completed. If it is determined in step S209 that the search range has not ended (NO), the process proceeds to step S215, the focus adjustment lens 1b is driven by a predetermined amount, and then the process returns to step S207. On the other hand, if it is determined in step S209 that the search range has ended (YES), the phase difference AF results vary, and the in-focus position cannot be detected even with contrast AF. The out-of-focus process similar to S113 is performed.

[Second example of hybrid AF restart processing]
FIG. 4 is a flowchart showing a second example regarding the hybrid AF restart process. 3 is different from the hybrid AF restart process of FIG. 3 described above, and the other processes are the same as the processes of the same reference numerals shown in FIG. In the hybrid AF restart process of FIG. 3, when it is determined in step S205 that | Y−X | <δ, the focusing operation is performed with priority given to the result of the phase difference AF. However, in the second example shown in FIG. 4, contrast AF is performed again regardless of the magnitude of the difference | Y−X |.

  In step S301, it is determined whether or not the lens drive amount difference | Y−X | is smaller than a predetermined amount λ. The predetermined amount λ may be the same as or different from the predetermined amount δ described above. Also in the case of the second example, when it is determined that | Y−X | <λ, it is determined that the lens position at the first phase difference AF and the lens position at the second phase difference AF are substantially the same. If it is determined that | Y−X | ≧ λ, it can be determined that the in-focus position of the first phase difference AF is different from the in-focus position of the second phase difference AF.

  If it is determined in step S301 that | Y−X | ≧ λ, the processing after step S206 is executed, and contrast AF is performed again from the lens position at the end of the second phase difference AF. On the other hand, if it is determined in step S301 that | Y−X | <λ, the process proceeds to step S302 to change the step width when driving the lens during contrast AF. For example, even if contrast AF is performed again with the same step width as the first contrast AF, there is a high possibility that the focus position cannot be detected in the same manner. Therefore, here, the peak position of the evaluation value is detected by reducing the step width. Improve the accuracy.

  If the step width is changed in step S302, the process proceeds to step S206, where the quick return mirror 2 is raised, and the second step after step S207 is performed with the changed step width. Also in this case, contrast AF is performed from the lens position at the end of the second phase difference AF.

  As described above, in the present embodiment, when the defocus amount is calculated by the first phase difference AF and the in-focus position is not detected by the first contrast AF, that is, the photographing optical system 1 by the hybrid AF. If the focus cannot be adjusted to the in-focus position, the second phase difference AF is performed at the current lens position, and the difference between the lens drive amount Y at that time and the lens drive amount X at the first contrast AF is performed. The focus was adjusted again according to the size of the lens. Therefore, even when focus adjustment cannot be performed at the in-focus position by the first phase difference AF and contrast AF, the focus adjustment lens 1b can be more reliably performed by performing the focus detection operation (phase difference AF and contrast AF) again. Can be driven to the in-focus lens position.

  Further, when the difference | Y−X | is smaller than the predetermined amount δ, that is, when the in-focus position by the first phase difference AF and the in-focus position by the second phase difference AF are substantially the same, the phase difference By performing focus adjustment based on the AF result, it is possible to focus more reliably even on a subject whose focus position is difficult to detect with contrast AF. Further, as in the second example shown in FIG. 4, when the difference | Y−X | is smaller than the predetermined amount λ, the step width in the second contrast AF is reduced to reduce the result of the second contrast AF. The detection of the focal position can be made more reliable.

  In the embodiment described above, the hybrid AF type focus adjustment device including the focus detection device that detects the subject light via the photographing optical system 1 and calculates the defocus amount has been described as an example. The present invention can be similarly applied to a hybrid AF type focus adjustment apparatus including a focus detection apparatus and a contrast type focus detection apparatus. Further, the contrast AF is performed using the imaging data of the imaging element 4 for photographing. However, a configuration in which an imaging element dedicated for contrast AF is separately provided may be used. Note that the present invention is not limited to the above embodiment as long as the characteristics of the present invention are not impaired.

It is a figure which shows one Embodiment of the imaging device by this invention. 6 is a flowchart for explaining a focus adjustment operation. It is a flowchart explaining the detail of a hybrid AF restart process. It is a flowchart which shows the 2nd example of a hybrid AF restart process.

Explanation of symbols

1: photographing optical system, 4: imaging device, 5: AF drive motor, 6: phase difference AF detection unit, 10: control unit, 11: lens drive control unit, 101: CCD control unit for AF, 102: defocus calculation , 103: Lens drive amount calculation unit, 104: Contrast calculation unit

Claims (1)

First focus detection means for detecting focus information representing a focus adjustment state of the optical system based on an image of a light beam transmitted through a pair of regions of the optical system;
Second focus detection means for detecting a focus evaluation value of the optical system based on contrast information of an image by the optical system when the focus adjustment lens of the optical system is driven and controlled with a predetermined step width in the optical axis direction;
After performing the first control for driving the focus adjustment lens of the optical system to the first in-focus position based on the focus information by the first focus detection means, the focus evaluation value of the second focus detection means is determined. When the second control for driving the focus adjustment lens is performed while detecting, and the focus position cannot be detected by the second control, the optical control is performed based on new focus information by the first focus detection means. Control means for performing third control for driving the focusing lens of the system to the second in-focus position ,
When the difference between the first in- focus position during the first control and the second in- focus position during the third control is smaller than a predetermined value, the control means narrowing the predetermined step width, it has rows fourth control for driving the focusing lens while performing detection of the focus evaluating value by said second focus detection means,
Furthermore, the control means detects the second focus when the difference between the first focus position during the first control and the second focus position during the third control is greater than the predetermined value. A focus adjustment device that performs a fifth control for driving the focus adjustment lens while detecting the focus evaluation value by the second focus detection means without changing the predetermined step width of the means. .

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