JP2006350188A - Autofocus device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To appropriately set a focus area even when switching a focus detection system in a device where a plurality of focus areas are grouped in hybrid AF. <P>SOLUTION: When the group Gr1 is selected, focus detection of the focus areas Ar8 to Ar11 in the group is performed by a phase difference detection system, and a focusing lens is driven based on the result of the focus detection. Before the focusing lens reaches a focusing position, the device is switched to contrast AF. In the contrast AF, a zone Zn1 involving the areas Ar8 to Ar11 becomes the focus area. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an autofocus (automatic focus adjustment) apparatus capable of focus adjustment by two methods.

  As a camera focus adjustment method, there are mainly a phase difference detection method adopted in a single-lens reflex camera and a contrast method adopted in a video camera or the like. The contrast method has higher focusing accuracy than the phase difference detection method, but has a drawback that it takes time to focus. Therefore, there is a camera that realizes high-speed and high-precision AF control by performing focus adjustment by a phase difference detection method first and switching to a contrast method immediately before the focusing lens reaches a target position (for example, Patent Document 1). ). The focus adjustment performed by the two methods in this way is called hybrid AF.

JP 2004-109690 A

  In the hybrid AF, when shifting from the phase difference detection method to the contrast method, there is a possibility that appropriate AF cannot be performed if the selected area is relatively small or the subject is out of the area.

The present invention provides a first focus detection means and a second focus detection for detecting a focus adjustment state of a photographing optical system in a plurality of focus detection areas set in a field screen of the photographing optical system by different methods. Part of a plurality of focus detection areas in a focus adjustment apparatus comprising: a means for adjusting a focus of a photographing optical system based on a focus adjustment state by at least one of the first and second focus detection means When the selection means capable of selecting a group as a group and the first focus detection means are used, the focus adjustment state is detected for each focus detection region belonging to the group selected by the selection means, and the second focus detection is performed. When using the means, control means is provided for controlling the focus adjustment state to be detected for an area including each focus detection area belonging to the selected group.
According to the second aspect of the present invention, the first focus detection unit detects the focus adjustment state by weighting a part of the focus detection regions belonging to the group selected by the selection unit as the priority region, and the second focus detection region. When the focus adjustment state is detected by the focus detection means, the focus adjustment state detected for the portion corresponding to the priority region among the included regions is weighted.

  According to the present invention, a part of a plurality of focus detection areas can be selected as a group, and when using the first focus detection means, the focus adjustment state is detected for each focus detection area belonging to the selected group. At the same time, when the second focus detection means is used, the focus adjustment state is detected for the area including each focus detection area belonging to the selected group. Even when the subject is out of the focus area, the subject can be focused.

An embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a configuration diagram of a digital camera system in the present embodiment. The photographing lens 10 includes a plurality of lens groups 11 to 13 including a focusing lens 12. Part of the subject luminous flux that has passed through the photographing lens 10 is reflected by the main mirror 21 and guided to the finder optical system 22. A part of the light beam transmitted through the main mirror 21 is reflected by the sub mirror 23 and guided to the focus detection device 24.

  An imaging element 25 such as a CCD or CMOS is provided at the rear of the mirrors 21 and 23. When the mirror is raised, imaging by the imaging element 25 becomes possible. The image sensor 25 receives the light beam transmitted through the photographing lens 10 and photoelectrically converts it to output an electrical image signal. The image signal is subjected to various processes (including A / D conversion) by the image processing circuit 26 and then recorded as digital image data on a recording medium (not shown).

Next, automatic focus adjustment control in this embodiment will be described.
FIG. 2 is a diagram showing the focus area superimposed on the shooting screen. As shown in the drawing, eleven focus areas Ar1 to Ar11 are set, and the focusing lens 12 is driven based on the focus adjustment state of any selected area. The area may be selected manually by the photographer or automatically determined by the camera.

  In this embodiment, eleven focus areas are grouped as a group of areas Gr1 to Gr7 composed of a plurality of areas shown in FIGS. 2B to 2H, and one of the groups is selected. It can be done. The group selection unit 29 in FIG. 1 selects any group according to the operation of the photographer, and sends selection information to the calculation unit 24c and the image processing unit 26 described later. Hereinafter, this mode is referred to as a group selection mode, and the selected group is referred to as a selection group.

  When a group is selected, only focus areas belonging to the selected group are targets for focus detection. For example, when the group Gr1 in FIG. 2B is selected, focus detection is performed on the four areas Ar8 to Ar11, and any area is selected from the detection results based on a predetermined algorithm, and the selection is performed. Focus adjustment is performed based on the focus detection result of the area.

  The focus adjustment is a hybrid AF based on a phase difference detection method and a contrast method. The focus detection device 24 in FIG. 1 is of a phase difference detection type, and includes a pair of line sensors 24a provided for the focus area and a re-image that divides the incident light beam into pairs and re-images on the line sensors 24a. The imaging optical system 24b and a calculation unit 24c that calculates the defocus amount corresponding to the focus shift amount for each area based on the output (focus detection signal) of the line sensor 24a. As shown in FIG. 3, in the present embodiment, a pair of line sensors 24a is provided corresponding to each of the eleven focus areas Ar1 to Ar11.

  The calculation unit 24 c calculates a lens drive signal for bringing the focusing lens 12 to the in-focus position based on the calculated defocus amount, and sends this to the lens drive unit 28. The lens driving unit 28 includes a focus motor, a motor driving circuit, and the like, and drives the focusing lens 12 in the optical axis direction based on a lens driving signal to perform focus adjustment.

  On the other hand, contrast-based focus adjustment (hereinafter referred to as contrast AF) focuses on the fact that there is a correlation between the degree of image blur and contrast, and uses that the contrast of the image is maximized when it is in focus. Focusing. For this reason, the image signal imaged by the image sensor 25 is acquired, and the magnitude of the contrast is evaluated by the magnitude of the high frequency component of the image signal. The evaluation value calculation unit 27 extracts a high-frequency component of a predetermined band from a signal corresponding to the focus area from the image signal obtained by imaging, and integrates the absolute value of the extracted high-frequency component. Focus evaluation value.

  The focus evaluation value is an amount that changes in accordance with the contrast of the image, in other words, the focus adjustment state of the focusing lens 12, and becomes the maximum value (peak value) when the contrast becomes maximum after focusing. Therefore, by obtaining a lens position where the focus evaluation value reaches a peak and bringing the focusing lens 12 to that position, it is possible to focus on the subject in the focus area.

  FIG. 4 is a diagram showing the displacement of the focus evaluation value according to the position of the focusing lens 12. A hill-climbing method is known as a method for finding the peak position (focusing point). In the hill-climbing method, a focus evaluation value is calculated for each predetermined sampling pitch while moving the focusing lens 12, and the focus evaluation value is compared with the same evaluation value (stored value) at the previous sampling each time the calculation is performed. If the current evaluation value is higher than the previous evaluation value, the peak is approaching, and sampling is continued while moving the focusing lens 12 in the same direction. If the current evaluation value is smaller than the previous evaluation value, the focus lens 12 is moved in the opposite direction because it is far from the peak. By repeating this operation, the focusing lens 12 can be finally brought to the peak position (the peak of the mountain).

As described above, the contrast AF performs focus adjustment using the image signal actually captured by the image sensor 25. Therefore, while focusing accuracy is high, it takes time to find the peak position. In particular, when the initial lens position is far from the peak position, it is necessary to start mountain climbing from the foot, and it takes a lot of time to focus. On the other hand, the phase difference detection method described above performs focus detection with the focus detection device 24c arranged at a position different from that of the image sensor 25. Therefore, the focus detection accuracy is lower than that of the contrast method. Since the target position of the focusing lens can be grasped in advance, the focusing lens can be brought to the target position at high speed.
In view of the above points, in the present embodiment, hybrid AF using the above two methods is performed to achieve both accuracy and speed in focus adjustment. This will be specifically described below.

  FIG. 5 shows focus adjustment control in the group selection mode, which is executed by the calculation unit 24c, the image processing unit 26, the evaluation value calculation unit 27, and the like. It is assumed that the focus area group has already been selected.

  When the release button is half-pressed, this program is started, and focus adjustment is first performed using a phase difference detection method. That is, focus detection is performed by the focus detection device 24 on all focus areas in the selected group (step S1), and the defocus amount of each area is calculated from the result (step S2). Then, a specific area is selected from these defocus amounts based on a predetermined algorithm (step S3), and the moving amount and moving direction of the focusing lens 12 are calculated based on the defocus amount of the selected area (step S3). S4) The driving of the focusing lens 12 is started (step S5). For example, in the close priority algorithm, the defocus amount of the focus area in the selected group is compared to determine the area where the closest subject exists, and the focusing lens 12 is driven based on the defocus amount of the area. .

  After starting the lens drive, focus adjustment is performed by the phase difference detection method until the subject enters the depth of field. The depth of field is calculated in advance from information (focal length and aperture value) of the photographing lens 10 and distance measurement data, and the lens driving is continued until the lens position falls within the range. The lens driving may be continued until the defocus amount falls within a predetermined value.

  Thereafter, the process waits until the release button is fully pressed (step S7). When the release button is fully pressed, the mirrors 21 and 23 are raised (step S8). As a result, imaging by the image sensor 25 becomes possible, and contrast adjustment (mountain climbing) focus adjustment is started. First, an image is picked up by the image pickup element 25 (step S9), and an image signal corresponding to the focus zone is obtained (step S10).

  The focus zone here means an area for calculating a focus evaluation value in contrast AF. That is, in the present embodiment, in contrast AF, the focus area group (selected group) in which the defocus amount is detected in the phase difference detection method is not taken over as it is, but in the selection area as surrounded by a broken line in FIG. .. Are reset as zones Zn1 to Zn7... Containing each focus area, and a focus evaluation value is obtained based on an image signal in this area. The focus zone is a single partial area that includes all focus areas (areas in the phase difference detection method) belonging to the selected group and does not include other focus areas. For example, if the selected group is a group Gr1 (FIG. 2B) composed of areas Ar8 to Ar11, the T-shaped partial region Zn1 becomes the focus zone. If the selected group is a group Gr2 (FIG. 2C) composed of areas Ar3, Ar5 to Ar7, Ar9, the cross-shaped partial region Zn2 becomes the focus zone.

  In order to obtain an image signal corresponding to the focus zone, for example, in the case of an address reading type image pickup device such as a CMOS, the address corresponding to the zone may be designated and read and A / D converted. In the case of a sequential readout type imaging device such as a CCD, only the signal corresponding to the zone is A / D converted, and the rest is discarded. In any case, it is not necessary to handle the entire image, and only the signal corresponding to the zone is required, so that the processing can be performed in a short time.

  Next, the focus evaluation value of the image signal of the extracted focus zone is calculated (step S11), and this is compared with the previous evaluation value to determine the moving direction of the focusing lens 12, and only a predetermined pitch in that direction is determined. The lens is driven (step S12). Since the calculation of the evaluation value applies only to the signal corresponding to the zone, the calculation time can be shortened.

  The processes in steps S9 to S12 are repeated until the focusing lens 12 reaches the peak position. When the focusing lens 12 reaches the peak position, it is determined that the focusing lens 12 is in focus and shooting is performed, and image data is recorded on the recording medium (step S13). → S14).

  As described above, in this embodiment, since focus adjustment is first performed by the phase difference detection method, the focusing lens 12 is already in the vicinity of the in-focus position (near the top of the mountain) at the start of contrast AF. Therefore, the lens driving range until the focusing lens 12 is brought to the peak position can be shortened to the minimum, and the number of focus evaluation value calculations and comparisons can be reduced accordingly. Therefore, the time required for focusing can be greatly reduced. Further, since focusing is finally performed by contrast AF, focusing accuracy is high.

  In addition, in the present embodiment, the focus zone in the contrast AF includes the focus area in the selected group, that is, includes all of these and does not include other areas. Since it is an area, it is possible to focus on a subject existing in the zone even when the subject deviates from the area while the lens is being driven, which greatly contributes to prevention of blurring due to movement of the subject or camera movement.

  Note that the peak position may not be found by one contrast AF. In this case, the contrast AF is performed again, and the lens driving range at that time is set to a region before and after the in-focus position calculated from the focus detection result of the phase difference detection method. The width of the front and rear region is limited to a depth range determined by the focus position (distance) and information (focal length and aperture value) of the photographing lens 20. This is because the peak position is most likely to be within this range. As a result, the time required for another contrast AF can be shortened.

  Here, any of the focus areas in the selected group may be set as the priority area. FIG. 6 shows an example thereof, and the area indicated by the bold line is the priority area. The priority area can be freely set by the photographer. When the start of focus adjustment is commanded (for example, when a half-press operation is performed), the focus detection is performed by weighting the priority areas in the selected group using the phase difference detection method, and if focus detection is possible, The focusing lens is driven based on the focus detection result. After shifting to contrast AF, the image signal corresponding to the priority area among the image signals related to the focus zone is weighted in the same manner to calculate the focus evaluation value, and based on this, the lens is driven to focus.

  On the other hand, when focus detection by the phase difference detection method is impossible in the priority area, focus detection and lens driving are performed using another area in the selected group as the selection area. In this case, after shifting to contrast AF, a focus evaluation value is calculated from the entire image signal corresponding to the above-described focus zone, and lens driving is performed.

  By setting the priority area in this way, even if an object other than the main subject enters the outside of the priority area during lens driving, the object (main subject) in the priority area can be focused without being affected by it. .

  Even when the priority area is selected, when the peak position cannot be found by one contrast AF, the contrast AF is performed again. The lens driving range at that time is the focus of the phase difference detection method for the priority area. A region before and after the in-focus position calculated from the detection result (within a depth range) is used.

  Furthermore, as a measure when the peak position cannot be found by contrast AF, the depth information for each area is calculated from the focus detection results of several focus areas adjacent to the priority area, and the maximum value (far side subject) is calculated. It is conceivable that a range between the maximum value of the depth of field) and the minimum value (maximum value of the near-side depth of field) is set as the contrast AF lens driving range again. This is because there is a very high possibility that a subject to be focused exists during this time. By limiting the lens driving range of contrast AF in this way, the time until focusing can be shortened.

  In the above, the focus detection by the phase difference detection method and the focus adjustment based on the phase difference detection method are performed by half-pressing operation, and contrast AF is performed by full-pressing operation. You may shift to contrast AF during operation.

The block diagram of the camera system in one Embodiment. The figure explaining the focus zone in grouping of a focus area and contrast AF. The figure which shows the example of arrangement | positioning of the image sensor for focus detection. The figure which shows the relationship between a lens position and a focus evaluation value. 6 is a flowchart illustrating an example of focus adjustment control. The figure which shows the example which set the priority area in the focus zone.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Shooting lens 25 Image pick-up element 24 Focus detection apparatus 26 Image processing circuit 27 Evaluation value calculation part 28 Lens drive part 29 Group selection part Ar1-Ar11 Focus area Zn1-Zn7 Focus zone

Claims (2)

A first focus detection means and a second focus detection means for detecting a focus adjustment state of the photographing optical system in a plurality of focus detection areas set in a field screen of the photographing optical system by different methods; A focus adjusting apparatus comprising: a focus adjusting unit that performs focus adjustment of the photographing optical system based on a focus adjustment state by at least one of the first and second focus detection units;
Selection means capable of selecting a part of the plurality of focus detection areas as a group;
When using the first focus detection means, the focus adjustment state is detected for each focus detection region belonging to the group selected by the selection means, and when the second focus detection means is used. And a control means for controlling to detect the focus adjustment state for an area including each focus detection area belonging to the selected group.   The control means weights a part of the focus detection areas of the focus detection area belonging to the group selected by the selection means as a priority area, detects the focus adjustment state by the first focus detection means, and The weighting is performed on a focus adjustment state detected for a portion corresponding to the priority area in the included area when the focus adjustment state is detected by a second focus detection unit. The focus adjusting apparatus according to 1.

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