JP5400396B2 - Imaging device - Google Patents

Description

  The present invention relates to a technique for improving the accuracy of an autofocus operation when an optimum distance measuring point is automatically selected from a plurality of distance measuring points.

  2. Description of the Related Art Conventionally, there is an image pickup apparatus having an autofocus (AF) function that automatically performs focusing at the time of shooting. There are several methods for realizing this AF function, but the TTL phase difference method widely adopted in single-lens reflex cameras and the like has a feature that distance measurement is possible only at a fixed position within a predetermined screen. Have. Therefore, it is often equipped with a so-called multi-point ranging AF sensor in which a plurality of ranging points are arranged in advance so that a plurality of positions on the screen can be measured.

  An imaging apparatus having a plurality of distance measuring points normally includes a “ranging point arbitrary selection mode” and a “ranging point automatic selection mode”. The “ranging point arbitrary selection mode” is a mode in which focusing control is performed on a certain ranging point selected by the user from a plurality of ranging points. Further, the “ranging point automatic selection mode” is a mode in which focusing control is performed by automatically selecting a ranging point for performing focusing control according to the state of the subject on the camera side. Regarding the automatic distance measurement point selection mode, basically, after obtaining the distance measurement results of all the distance measurement points, an optimal one point is selected based on these distance measurement results. That is, when performing automatic selection of distance measurement points, it is desirable that there are distance measurement results for all distance measurement points.

  As an AF function, there is a continuous AF mode that keeps the subject in focus. The continuous AF mode is particularly effective for moving subjects, predicts subject movement by continuously measuring distances in the time direction, and focuses on the time lag from distance measurement to shooting. It is a function to perform. In order to perform accurate prediction, it is desirable that the distance measurement results can be sampled with high density in the time direction.

  As can be seen from the above, in the automatic AF point selection and continuous AF mode, it is necessary to calculate the distance measurement results of all the AF points at high speed.

  On the other hand, in the TTL phase difference method, considering the degree of freedom of composition at the time of shooting, it is desirable to arrange more distance measuring points with higher density. For this reason, there is a configuration in which one long line sensor is finely divided into blocks to increase the number of distance measuring points.

  As an example, an AF line sensor configured to have five distance measuring points by dividing one long line sensor into five as shown in FIGS. 1A to 1D will be described. Here, in order to make the explanation easy to understand, each ranging point is numbered with Line 1 to Line 5 from the left side in the drawing.

  FIG. 1A is an example in which one line is simply divided into five. Thus, although five distance measuring points can be configured, the line length per distance measuring point is shortened, and there is a problem that the defocus range that can be detected is narrowed.

  Therefore, if an attempt is made to construct five distance measuring points while keeping the line length per distance measuring point to be longer than a certain length, it will inevitably overlap across a plurality of distance measuring points as shown in FIG. 1B. The pixel that ends up comes out. Therefore, a method is known in which accumulation control of the long line sensors is performed collectively, and the corresponding blocks are extracted from the read image signal and used for focus detection calculation.

  Patent Document 1 calculates a distance measurement result in a certain block division, and determines whether or not distance conflict occurs at these distance measurement points, and if it is determined that distance conflict occurs. The technique of changing the block division and redoing the focus detection calculation is disclosed. If the pixel area (block) used for the focus detection calculation is shifted as in Patent Document 1, the position of the distance measuring point can be changed variously.

  However, if there is a pixel that overlaps a plurality of distance measuring points by simply changing the region of the pixel used for focus detection, the accumulation control optimized for each line cannot be performed. If the accumulation control is not optimized for each line, a reliable image signal cannot be obtained, and there is a problem that accurate focus detection cannot be performed.

  As a specific example, a case where a specific pattern as shown in FIG. 1C comes to Line 1 and Line 2 will be described. If optimal accumulation control is performed for Line 1 when such a pattern is used as an object, an image signal with sufficient amplitude cannot be obtained for Line 2, so that an accurate focus detection result cannot be obtained. Conversely, when optimal accumulation control is performed on Line 2, the image signal of Line 1 is saturated, and again, a reliable focus detection result cannot be expected.

  Originally, with respect to the subject as shown in FIG. 1C, if the accumulation is performed for a short time so that the image signal does not saturate for Line 1 and sufficient amplitude is obtained for Line 2, In both cases, a reliable image signal can be obtained and is ideal. However, since there are overlapping regions on both lines, it is impossible to obtain an optimal image signal for both lines in a single accumulation operation.

Therefore, by switching between a divided pattern A having three distance measuring points and a divided pattern B having two distance measuring points from one long line sensor as shown in FIG. A distance point can be configured. Since there is no overlapping pixel in each division pattern, it is possible to perform accumulation control optimized for each line individually. Therefore, with this method, it is necessary to accumulate a plurality of times, but many distance measuring points can be arranged with high density.
JP-A-8-15603

  However, in this configuration, there is a problem that it takes time because it is necessary to accumulate a plurality of times as many as the number of division patterns in order to obtain distance measurement results of all distance measurement points. In particular, when high-speed continuous shooting is performed in the continuous mode of automatic ranging point selection, the time available for AF is limited. For this reason, each time imaging is performed, accumulation with a plurality of block division patterns cannot be performed, and distance measurement results for all distance measurement points cannot be obtained, so accurate distance measurement point automatic selection can be performed. There is no problem.

  Therefore, the present invention has been made in view of the above-described problems, and an object thereof is to improve the accuracy of autofocus when performing continuous shooting in the automatic selection of the distance measuring point and the continuous AF mode. .

In order to solve the above-described problems and achieve the object, an imaging apparatus according to the present invention is an imaging apparatus having a plurality of focus detection areas with respect to an object field, and performs autofocus by a phase difference method. one focus of the line sensor is divided into a plurality of divided areas so divided areas adjacent to partially overlap their respective one of the divided regions of the plurality of focus detection areas A first focus detection area group composed of an autofocus sensor corresponding to a detection area , a divided area of the plurality of divided areas of the autofocus sensor that do not overlap with each other, and the first focus detection area at least one focal point of the second group of focus detection area consisting of divided regions do not differ overlapping the divided areas constituting a group Based on the image signal obtained by a group of exit region and a focus adjustment means for performing autofocus control, the focus adjustment means, if a continuous shooting mode for performing continuous shooting, depending on the continuous shooting speed The image signal from the first focus detection region group and the image signal from the second focus detection region group are switched and used, or the image signal from the first focus detection region group is used. And whether to use both of the image signals from the second focus detection area group and performing autofocus control.

  According to the present invention, it is possible to improve the accuracy of autofocus when performing continuous shooting in the AF point automatic selection and continuous AF mode.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
In the first embodiment, a digital single-lens reflex camera having 33 distance measuring point arrangements (focus detection area arrangements) as shown in FIG. 2A with respect to the object field in the viewfinder is taken as an example. I will explain.

  This distance measuring point has a configuration having two block division patterns (divided areas) as shown in FIG. 2B that overlap each other while filling the gap between the distance measuring points. For easy understanding, the left block division pattern in FIG. 2B is assumed to be A mode, and the right block division pattern is assumed to be B mode. In the drawing, a predetermined number of distance measuring points that can be measured in the B mode are indicated by diagonal lines, and a line area used for focus detection is indicated by gray. FIG. 2C is a diagram in which the lines of each ranging point in the A mode and the B mode are displayed so as to overlap each other, and each mode is laid out so that a partial area is overlapped so as to fill the gap between the ranging points. This makes it possible to arrange a plurality of ranging points at high density.

  FIG. 3 is a cross-sectional view of the digital single-lens reflex camera in the present embodiment.

  In FIG. 3, reference numeral 101 denotes a camera body, and a photographing lens 102 is mounted on the front surface thereof. The photographing lens 102 can be exchanged, and the camera body 101 and the photographing lens 102 are also electrically connected via a mount contact group 112. Further, a diaphragm 113 is arranged in the photographing lens 102 so that the amount of light taken into the camera can be adjusted.

  Reference numeral 103 denotes a main mirror, which is a half mirror. The main mirror 103 is obliquely arranged on the photographing optical path in the finder observation state, and reflects the photographing light beam from the photographing lens 102 to the finder optical system, while the transmitted light enters the AF unit 105 via the sub mirror 104. In the photographing state, the evacuation is taken out of the photographing optical path.

  The AF unit 105 is a phase difference detection type AF sensor having a ranging point layout as shown in FIG. 2A. Since the focus detection by the phase difference method is a known technique, the specific operation is omitted here, but the following operation is performed. That is, an image signal is acquired by forming a secondary image formation surface of the photographing lens 102 on a focus detection line sensor (autofocus sensor) in the AF unit 105, and the focus adjustment state of the photographing lens 102 is detected. Based on the detection result, a focusing lens (not shown) is driven to perform automatic focus adjustment (autofocus control).

  Reference numeral 108 denotes an image sensor, 106 denotes an optical low-pass filter, and 107 denotes a focal plane shutter.

  Reference numeral 109 denotes a focusing plate disposed on a planned image forming surface of the photographing lens 102 constituting the finder optical system, and reference numeral 110 denotes a pentine optical path changing pentaprism. Reference numeral 114 denotes an eyepiece, and the photographer can confirm the photographing screen by observing the focus plate 109 from here. Reference numeral 111 denotes an AE unit which is used for photometry.

  Reference numeral 115 denotes a release button, which is a two-stage push-in switch having a half-pressed state and a fully pressed state. When the release button 115 is pressed halfway, preparatory operations such as AE and AF operations are performed, and when the release button 115 is fully pressed, the image sensor 108 is exposed to perform shooting processing. Hereinafter, the state where the switch is half pressed is described as a state where SW1 is turned on, and the state where the switch is fully pressed is described as a state where SW2 is turned on.

  Reference numeral 116 denotes a display unit, which is attached to the back surface of the camera body 101. The display unit 116 is generally constituted by a liquid crystal panel so that an image taken by the photographer can be directly observed.

  Reference numeral 120 denotes a control unit that controls the overall operation of the camera body 101, and controls related to imaging operations and autofocus are also performed here.

  Next, the operation of the camera in this embodiment will be described using the flowchart of FIG.

  In step S401, if the AF point automatic selection mode (the mode for automatically selecting a distance measuring point expected to be present) is the continuous AF mode and the continuous shooting mode is set, step S402 is set. Go to and read the continuous shooting speed (frame speed).

  Step S403 is a step of waiting for the user to turn on SW1. The system waits until SW1 is turned on. When SW1 is turned on, the process proceeds to step S404, and the focus adjustment operation is continuously performed. In the focus adjustment operation here, in order to determine where the subject is in the viewfinder (automatic selection of ranging points), the ranging results at all ranging points are required. For this reason, AF in A mode and B mode are alternately performed in order, it is determined which distance measurement point the subject is always present, and the focus is not shown so as to focus on the distance measurement point. Drive the focusing lens. This focus adjustment operation is repeated until it is detected that SW2 is turned on, which is an operation for accepting the start of photographing from the user. When SW2 is turned on, the process proceeds to step S406.

  Step S406 is a step of switching AF accumulation control during continuous shooting according to the frame speed read in step S402 before entering the actual continuous shooting operation. If the frame speed read in step S402 is equal to or greater than the predetermined speed stored in the camera, only one of the A mode and B mode AF is performed for one frame shooting, and the mode is switched alternately for each frame. Steps S407 to S411 which are AF sequences are performed by switching between. This is because, when the frame speed is high, the time allocated to single frame shooting is shortened, and naturally the time that can be used for AF also decreases. If the A and B modes are forcibly stored within a predetermined time, the accumulation will be insufficient and accurate range finding results will not be obtained. This time becomes too long, resulting in a drop in frame speed. For this reason, when the frame speed is equal to or higher than the predetermined speed, the sampling rate of the distance measurement result decreases. However, AF is performed in only one mode for each shooting, and appropriate distance measurement is performed by alternately switching the mode. Enable automatic point selection.

  If it is detected in step S411 that SW2 has been turned off, shooting is terminated in step S416.

  On the other hand, if the frame speed is slower than the predetermined speed in step S406, the process proceeds to steps S412 to S414 in which distance measurement is performed in both the A mode and the B mode for each frame shooting. This is because if the frame speed is slow, the time available for AF per frame increases, so there is room for AF in both modes A and B. When the frame speed is slow in this way, the ranging results of all ranging points are acquired before shooting, and automatic ranging point selection is performed to select the optimum ranging point based on this information. I can do it. If it is detected in step S415 that SW2 has been turned off, shooting is terminated in step S416.

(Second Embodiment)
A second embodiment of the present invention will be described with reference to the flowchart of FIG. Note that the hardware configuration of the camera in this embodiment is the same as that of the first embodiment, and an AF sensor having ranging point arrangements as shown in FIGS. 2A to 2C and a camera having a cross-sectional configuration as shown in FIG. To do.

  In the camera of the present embodiment, even when SW1 is not turned on (before SW1 is turned on), the lens is not driven, and “pre-AF” that executes only the distance measurement calculation (focus detection calculation) is performed. By performing pre-AF, it is possible to acquire subject information in advance (before the start of imaging), and it is possible to shorten the time until the lens is driven when SW1 is turned on.

  In step S501, if the AF point selection automatic AF mode is selected and the continuous shooting mode is set, pre-AF is repeated in steps S502 and S503. The pre-AF alternately performs both the A mode and the B mode, and stores the time required for accumulating all the latest n distance measuring points. n is a predetermined number of times determined in the camera.

  If SW1 is turned on in step S503, the process proceeds to step S504, and the focus adjustment operation is continuously performed. Here, the operation accompanied by the lens driving is actually performed. However, the time required for accumulating all the latest n distance measuring points together with the result recorded in step S502 by alternately switching between the A mode and the B mode. Record. This operation is repeated until SW2 is turned on in step S505. When SW2 is turned on, the process proceeds to step S506.

  Step S506 is a step of switching AF accumulation control during continuous shooting from the time taken for accumulation of all distance measuring points stored in steps S502 and S504. If the time required for AF sensor accumulation is short, distance measurement in both A mode and B mode can be performed for each photographing even if the frame speed is high. Conversely, if the time required for accumulation is long, 1 Only distance measurement in either the A mode or the B mode can be performed for each shooting.

  Therefore, in step S506, an average value of the accumulation times of all the latest n distance measuring points is calculated. Then, the average value Ta of the accumulation times of the distance measurement points having the longest accumulation time among the distance measurement points included in the A mode and the longest accumulation time of the distance measurement points included in the B mode. (Ta + Tb), which is the sum of the average values Tb of the distance measurement point accumulation times, is calculated. If (Ta + Tb) is equal to or longer than a predetermined time Tth (predetermined time) stored in the camera in advance, steps S507 to S510 for alternately switching the A mode and the B mode for each frame of continuous shooting are performed. If SW2 is turned off in S511, the shooting is terminated. Steps S507 to S510 are the same as steps S407 to S410 in FIG.

  On the other hand, if (Ta + Tb) is shorter than the predetermined time Tth stored in the camera in advance, the accumulation ends at a high speed. Therefore, accumulation in both the A mode and the B mode is performed before one image capture step S512 to S514. Proceed to Steps S512 to S514 are the same as steps S412 to S417 in FIG. If SW2 is turned off in step S515, the shooting is terminated.

  In this embodiment, (Ta + Tb) is calculated in step S506, and the AF accumulation control during continuous shooting is switched based on this. However, instead of (Ta + Tb), the average of the past n times of all ranging points is calculated. The case may be divided by using another numerical value that can evaluate the length of the accumulation time in both modes, such as the accumulation time Tave.

(Third embodiment)
A third embodiment of the present invention will be described with reference to the flowchart of FIG. Again, the hardware configuration of the camera in this embodiment is the same as that of the first embodiment, and the AF line sensor having ranging point arrangements as shown in FIGS. Suppose you have a camera. Also in this embodiment, pre-AF is performed.

  Steps S601 to S605 are the same as steps S501 to S505 in FIG. 5, and if SW2 is turned on, the process proceeds to step S606.

  In step S606, the history of distance measurement results acquired and stored in steps S602 and S604 is analyzed. The movement tendency (moving direction) of the subject is determined by the direction of the optical axis of the photographic lens (the direction in which the subject approaches or moves away from the photographer) and the direction perpendicular to the optical axis (from the photographer in the viewfinder). It is determined which is more prominent (in the vertical and horizontal directions) (whether it is the subject), and AF accumulation control at the time of shooting is switched. Specifically, from the latest past n distance measurement results acquired in steps S602 and S604, the distance measurement point for which the subject was present is obtained for all n times, and a vector connecting the distance measurement points and the measurement points are obtained. The speed of movement of the subject in the direction perpendicular to the optical axis can be determined from the time interval for performing the distance. FIG. 7 shows an example in which the distance measurement point where the subject is present has changed in the latest six times. In steps S602 and S604, since the A mode and the B mode are alternately switched, the distance measurement points in FIG. 7 are also moved by the distance measurement points included in the A mode and the B mode. Alternating. At this time, the average moving speed Vxy in the direction perpendicular to the optical axis of the subject is obtained by using the vector in the figure and the time interval t for distance measurement.

It can be expressed as

  On the other hand, since the average moving speed Vz of the subject in the optical axis direction can be determined from the distance measurement results of the six distance measuring points in FIG.

It can be expressed as

  In step S606, the magnitudes of Vxy and Vz are compared, and if Vxy ≧ Vz, it is determined that the subject has a strong tendency to move in the direction perpendicular to the optical axis. For this reason, the distance measurement points are automatically selected based on the distance measurement results of all the distance measurement points so that the distance measurement points for performing the focus adjustment operation (focus detection operation) during the continuous shooting can be smoothly performed. Steps S607 to S609 are a sequence for performing distance measurement on all the distance measurement points. When SW2 is turned off in step S610, photographing is ended. Steps S607 to S609 are the same as steps S412 to S414 in FIG.

  On the other hand, if Vxy <Vz, the subject is considered to have a strong tendency to move in the optical axis direction. Therefore, in order to perform more accurate prediction, it is better to increase the sampling rate for AF during continuous shooting. desirable. Therefore, steps S611 to S618 are a sequence for performing AF accumulation control only in one of the modes A and B.

  Step S611 is a step for selecting which mode to fix. A distance measuring point at which the subject is considered to be present in the last distance measurement among the distance measurement results stored in steps S602 and S604. Ask for. If the distance measuring point is included in the A mode, the process proceeds to steps S612 to S614, and AF accumulation control is performed only in the A mode. If included in the B mode, the process proceeds to steps S615 to S617, and AF accumulation control is performed only in the B mode.

  In steps S612 to S617, since AF is performed only in one mode including the distance measuring point where the subject exists, high-speed AF is possible and the sampling rate for acquiring the distance measurement result is increased, so that accurate distance measurement is possible. become.

(Other embodiments)
The object of each embodiment is also achieved by the following method. That is, a storage medium (or recording medium) in which a program code of software that realizes the functions of the above-described embodiments is recorded is supplied to the system or apparatus. Then, the computer (or CPU or MPU) of the system or apparatus reads and executes the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention. Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but the present invention includes the following cases. That is, based on the instruction of the program code, an operating system (OS) running on the computer performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

  Furthermore, the following cases are also included in the present invention. That is, the program code read from the storage medium is written into a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer. Thereafter, based on the instruction of the program code, the CPU or the like provided in the function expansion card or function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

  When the present invention is applied to the above storage medium, the storage medium stores program codes corresponding to the procedure described above.

It is a figure which shows the block division | segmentation of AF line sensor. It is a figure which shows the block division | segmentation of AF line sensor. It is a figure which shows the block division | segmentation of AF line sensor. It is a figure which shows the block division | segmentation of AF line sensor. It is a figure which shows AF line sensor and ranging point layout of the camera of embodiment of this invention. It is a figure which shows AF line sensor and ranging point layout of the camera of embodiment of this invention. It is a figure which shows AF line sensor and ranging point layout of the camera of embodiment of this invention. It is sectional drawing of the camera of embodiment of this invention. It is a flowchart which shows AF operation | movement of 1st Embodiment. It is a flowchart which shows AF operation | movement of 2nd Embodiment. It is a flowchart which shows AF operation of 3rd Embodiment. It is a figure which shows the example when there exists a to-be-photographed object's movement in the direction perpendicular | vertical to an optical axis in 3rd Embodiment.

105 AF unit 108 Image sensor

Claims (6)

An imaging apparatus having a plurality of focus detection areas with respect to a scene,
Line sensor for performing automatic focusing by the phase difference method is divided into a plurality of divided areas so divided areas adjacent to partially overlap their respective one of the divided regions of the plurality of focus An autofocus sensor corresponding to one focus detection area of the detection area;
The first focus detection area group composed of non-overlapping divided areas of the plurality of divided areas of the autofocus sensor, and the divided areas constituting the first focus detection area group are different from each other. and a focus adjustment means for performing autofocus control based on the image signal obtained by a group of at least one focus detection area of a group of second focus detection area consisting of divided regions not wrap,
When the focus adjustment unit is in a continuous shooting mode in which continuous shooting is performed, an image signal from the first focus detection area group and the second focus detection area group according to a continuous shooting speed. Auto-focus by selecting whether to use the image signal from the first focus detection area group or to use both the image signal from the first focus detection area group and the image signal from the second focus detection area group An imaging apparatus characterized by performing control. When the continuous shooting speed in the continuous shooting mode is equal to or higher than a predetermined speed, the focus adjusting unit detects an image signal from the first focus detection area group and the second focus detection area for each shooting . switching between image signals from a group in order, when the continuous shooting speed is slower than the predetermined speed, one of the image signal and the second focus detection from the group of the first focus detection area for each shooting The image pickup apparatus according to claim 1, wherein autofocus control is performed using both image signals from a group of regions . Instructing means for instructing start of autofocus is further provided, and the focus adjusting means performs focus detection calculation before the autofocus instruction by the indicating means, and a time required for the focus detection calculation before the start of photographing is a predetermined time. In the above case, the image signal from the group of the first focus detection area and the image signal from the group of the second focus detection area are sequentially switched for each photographing, and the focus detection calculation is performed. When the time is shorter than the predetermined time, autofocus is performed using both an image signal from the first focus detection area group and an image signal from the second focus detection area group for each photographing. The imaging apparatus according to claim 1, wherein control is performed. Instructing means for instructing the start of autofocus is further provided, and the focus adjusting means is configured to generate an image signal from the first focus detection area group and the second focus detection area group based on a moving direction of the subject. Switching between the image signals from the first focus detection area group and the image signals from the first focus detection area group and the image signal from the second focus detection area group. The imaging apparatus according to claim 1. The focus adjusting unit performs a focus detection calculation from before the autofocus instruction by the instruction unit, and based on a result of the focus detection calculation, the moving direction of the subject is mainly a direction along the optical axis of the photographing lens. The imaging apparatus according to claim 4, wherein when it is determined, a focus detection operation is performed using an image signal of a divided area corresponding to a focus detection area in which the subject is supposed to exist. The focus adjustment unit performs a focus detection calculation before the autofocus instruction by the instruction unit, and based on a result of the focus detection calculation, the subject moving direction is mainly a direction perpendicular to the optical axis of the photographing lens. If it is determined, autofocus control is performed using both the image signal from the first focus detection area group and the image signal from the second focus detection area group for each shooting. The imaging apparatus according to claim 4.

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