JP2006243609A - Autofocus device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an autofocus device of a hybrid AF system capable of preventing a main subject from getting out of focus in the midst of consecutive photographing. <P>SOLUTION: When the decision is made that a difference between a subject distance P detected in a step S11 and a previous subject distance P0 stored is larger than a predetermined value (th) in the midst of consecutive photographing, that is, when a range-finding area comes off from the main subject, focusing operation is performed not based on the subject distance P detected at that time but based on the previous subject distance P0. At such a time, since the previous subject distance P0 is the subject distance of the main subject, a picture where the main subject is brought into focus is taken. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hybrid autofocus apparatus capable of performing contrast detection AF and distance measurement AF.

  Conventionally, an electronic camera such as a digital still camera performs automatic focus adjustment (hereinafter referred to as AF) by using a focus evaluation value obtained by replacing a high-frequency component of an image captured by an image sensor with a sharpness. AF is known. Contrast detection AF is superior in focusing accuracy because it detects the in-focus state of the imaging surface itself, and it is not necessary to provide a separate focus detection sensor. This is also advantageous.

  However, since a plurality of samplings are required, the focusing operation takes time. For this reason, in order to improve the speeding up of the focusing speed, a hybrid AF type distance measuring device that can be used by switching between the above-described contrast detection AF and known outside light AF using a distance measuring sensor has been proposed. (For example, refer to Patent Document 1). In this distance measuring device, the two AF methods of contrast detection AF and external light AF can be appropriately switched based on the presence / absence of a shooting mode setting in which priority is given to shortening the focusing time, so that a scene where the time lag is not preferable However, it enables high-speed AF that never misses a photo opportunity.

JP 2001-255456 A

  However, since the distance measurement area in the external light AF is relatively narrow, the background is in focus when the distance measurement area is out of the subject when continuously shooting a moving subject. As a result, there is an inconvenience that an image whose subject is not in focus is included in a plurality of continuously shot frames.

An autofocus device according to a first aspect of the present invention includes an evaluation value calculation means for calculating a focus evaluation value of a subject image based on an imaging signal obtained by imaging a subject image formed by a photographing lens, and subject light. Detected by a distance measuring means that detects a subject distance by receiving light, a first autofocus means that performs a focusing operation by driving a focus lens of a photographing lens so that a focus evaluation value is maximized, and a distance measuring means There is no second autofocus means for performing a focusing operation based on the subject distance, setting means for setting a continuous shooting mode for continuously shooting a plurality of times by a continuous shooting command, and no continuous shooting mode is set by the setting means In this case, when the focusing operation is performed by the first autofocus unit and the continuous shooting mode is set by the setting unit, the first autofocus unit performs the initial shooting of the continuous shooting. After performing the focusing operation, after the second continuous shooting, the first control means for performing the focusing operation with the second autofocus means, and the memory for storing the subject distance corresponding to the focusing state at the time of the first shooting. And the difference between the subject distance detected by the distance measuring means and the subject distance stored in the storage means at the time of the second and subsequent photographing during the continuous photographing is determined as to whether or not the difference between the subject distance and the subject distance During the continuous shooting with the determination means, if (a) the determination means determines that the value is equal to or less than the determination value, the focusing operation is performed based on the subject distance detected by the distance measurement means, and is stored in the storage means. The subject distance detected is replaced with the subject distance detected by the distance measuring means. When the determination means determines that it is not less than the determination value, the focusing operation is performed based on the subject distance stored in the storage means. Sase Characterized by comprising a second control means.
According to a second aspect of the present invention, there is provided an autofocus device comprising: an evaluation value calculating means for calculating a focus evaluation value of a subject image based on an imaging signal obtained by imaging a subject image formed by a photographing lens; Detected by a distance measuring means that detects a subject distance by receiving light, a first autofocus means that performs a focusing operation by driving a focus lens of a photographing lens so that a focus evaluation value is maximized, and a distance measuring means There is no second autofocus means for performing a focusing operation based on the subject distance, setting means for setting a continuous shooting mode for continuously shooting a plurality of times by a continuous shooting command, and no continuous shooting mode is set by the setting means In this case, when the focusing operation is performed by the first autofocus unit and the continuous shooting mode is set by the setting unit, the first autofocus unit performs the initial shooting of the continuous shooting. After the second focusing operation, after the second continuous shooting, the first control unit performs the focusing operation with the second autofocus unit, and (a) the distance measuring unit detects the second continuous shooting. When the difference between the subject distance and the subject distance corresponding to the in-focus state at the first shooting is larger than the determination value of the subject distance change, the focusing operation is performed based on the subject distance at the first shooting, and (b ) The difference between the subject distance detected by the distance measuring unit at the time of the third and subsequent shootings of the continuous shooting and the subject distance detected by the distance measuring unit at the first and second shootings before the shooting, And a second control unit that performs a focusing operation based on a subject distance one time before the shooting when the determination value is larger than each of the determination values.

  According to the present invention, even when the object to be captured by the distance measuring means is deviated from the main subject during continuous shooting, the obtained plurality of captured images include an image in which the main subject is not in focus. Problems can be prevented or reduced.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of the present invention, and is a block diagram of a digital still camera equipped with an autofocus device. The photographic lens 1 is provided with a focusing lens (not shown) for adjusting the focus, and the focus of the photographic lens 1 is adjusted by driving the focusing lens with a focus motor 9. In general, a stepping motor is used as the focus motor 9, and open loop control is performed by pulse driving from the CPU 8.

  The subject image formed by the photographic lens 1 is projected on the imaging surface of the imaging device 2, and the imaging device 2 outputs an electrical signal corresponding to the light intensity of the subject image formed on the imaging surface. By performing focus adjustment by driving the focusing lens by the focus motor 9, a focused subject image is formed on the imaging surface. A CCD image sensor, a MOS type image sensor, or the like is used as the image sensor 2, and an image signal output from the image sensor 2 is input to the analog signal processing unit 3.

  The analog signal processing unit 3 is provided with a CDS circuit, an AGC circuit, a color separation circuit, and the like. The CDS circuit performs correlated double sampling (CDS) processing for reducing noise of the imaging signal, and the AGC circuit performs gain adjustment. Thus, auto gain control (AGC) processing for adjusting the level of the image signal is performed. The imaging signal processed by the analog signal processing unit 3 is converted from an analog signal to a digital signal by the A / D converter 4.

  The A / D converted signal is input to the digital signal processing unit 5 and the CPU 8. The digital signal processing unit 5 includes signal processing circuits such as a gain control circuit, a luminance signal generation circuit, and a color difference signal generation circuit, and performs various functions such as edge enhancement, gamma correction, and white balance adjustment on the input imaging signal. Perform image processing. The imaging signal input to the digital signal processing unit 5 is temporarily stored in the buffer memory 11, read out from the buffer memory 11 for each process described above, and the processed signal is stored in the buffer memory 11 again. The buffer memory 11 is a frame memory that can store data for a plurality of frames imaged by the imaging device 2.

  The distance measuring unit 10 is an external light AF type distance measuring device that performs known passive distance measurement and active distance measurement, and includes a light receiving lens provided separately from the photographing lens 1 and subject light captured via the light receiving lens. A distance measuring sensor for receiving light is provided. The distance measurement unit 10 receives subject light in response to a command from the CPU 8 and calculates distance measurement data based on the output of the distance measurement sensor. The calculation result is output to the CPU 8.

  The CPU 8 that controls the entire camera also includes an AE calculator 81, an external light AF calculator 82, a contrast AF calculator 83, and the like. The AE calculation unit 81 performs automatic exposure calculation based on the imaging signal from the A / D converter 4. The external light AF calculation unit 82 calculates the subject distance based on the distance measurement data from the distance measurement unit 10, and further converts the calculated subject distance into the driving amount of the focusing lens. The contrast AF calculation unit 83 extracts a predetermined high frequency component from the spatial frequency of the image data in the AF area by a band pass filter or the like, and calculates the focus evaluation value by integrating the absolute value of the extracted high frequency component. .

  When performing external light AF, the focus motor 9 is driven based on the focusing lens drive amount calculated by the external light AF calculation unit 82, and the focus adjustment operation of the photographing lens 1 is performed. When performing contrast detection AF, the focus adjustment operation is performed by moving the focusing lens to a lens position where the focus evaluation value calculated by the contrast AF calculation unit 83 reaches a peak. In the AE calculation and AF calculation, calculation is performed using imaging signals of the entire image pickup area of the image pickup device 2 or a part of the area (for example, the center of the screen, the center of each fixed area, the top, bottom, left, and right). Do.

  Image data that has been subjected to a series of processing by the digital signal processing circuit 5 and stored in the buffer memory 11 is recorded in an external storage medium 14 such as a memory card via a recording / reproducing signal processing circuit 13. When recording image data in the external storage medium 14, data compression is generally performed in a predetermined compression format, for example, the JPEG method. The recording / reproduction signal processing circuit 13 performs data compression when recording image data on the external recording medium 14 and data expansion processing when reading compressed image data from the external storage medium 14. The recording / playback signal processing circuit 13 also includes an interface for performing data communication with the external storage medium 14.

  Reference numeral 7 denotes a display device for displaying a subject image. For example, an LCD monitor using liquid crystal is used. In the shooting mode, the image signal picked up by the image pickup device 2 at predetermined time intervals is subjected to signal processing by the analog signal processing circuit 3, the A / D converter 4, and the digital signal processing circuit 5, and then the buffer memory. 11 and transferred to the VRAM 6, and an image based on the image data stored in the VRAM 6 is displayed on the display device 7. When image data stored in the external storage medium 14 is displayed on the display device 7, the image data read from the external storage medium 14 is transferred to the VRAM 6 and reproduced and displayed on the display device 7. The operation unit 12 for performing operation instructions and various settings by the user is provided with a release button, a setting button for setting a continuous shooting mode, and the like, for example.

<< Description of AF processing operation >>
2 and 3 are flowcharts for explaining the AF processing operation, and the flowchart of FIG. 3 shows processing following the processing of FIG. The AF process starts when the CPU 8 detects that the release button provided on the operation unit 12 is half-pressed. When the AF process starts, the external light AF process is performed in step S1, and then the contrast detection AF process is performed in step S2.

  FIG. 4 is a diagram for explaining the movement of the focusing lens in the processes of steps S1 and S2. A curve L1 shows the relationship between the lens position of the focusing lens and the focus evaluation value. There is a correlation between the degree of blur of the subject image formed on the imaging surface of the image sensor 2 and the contrast, and the contrast of the image becomes maximum when the image is focused. The level of contrast can be evaluated by a focus evaluation value obtained by extracting a high-frequency component of the imaging signal, and D1 at which the focus evaluation value reaches a peak is the focus lens position.

  In contrast detection AF, the focusing lens is normally shifted by a predetermined amount toward the infinity (∞) side or the close side, and the focus evaluation value calculated at that time is compared with the focus evaluation value before movement. If the focus evaluation value after movement is larger, it is considered that the resolution (focusing degree) tends to increase with respect to the movement direction, and the focusing lens is further moved in the same direction. Calculate and compare If the focus evaluation value after movement is smaller, the degree of focusing tends to be lower in the moving direction, so the same calculation and comparison are performed by moving the focusing lens in the reverse direction. By performing hill-climbing AF in which such processing is repeated, a focus position where the focus evaluation value is maximized is searched.

  In this way, when focus adjustment is performed using only contrast detection AF, the search is performed while moving by a predetermined amount in the direction in which the focus evaluation value increases from the in-focus search start point, so that the peak is detected. It is necessary to search a wide range. For example, when the search start position is at the infinity end and the peak position is near the close end, the search range becomes substantially the same as the drivable range as shown in FIG.

  On the other hand, in the case of the hybrid AF method in which contrast detection AF and external light AF are combined, the focusing lens is moved to the vicinity of the focusing lens position D1 by the external light AF processing in step S1 described above, and then in step S2. The peak of the focus evaluation value is searched by contrast detection AF processing. In this case, since the search start position is in the vicinity of the lens position D1, the search range in the contrast detection AF is narrower than in the case of (a), and the search time can be shortened. As a result, the total focusing time can be shortened compared to the case of only contrast detection AF.

  In step S3, it is determined whether or not the release button has been fully pressed. If it is determined that the release button has been fully pressed, the process proceeds to step S4 to perform a shooting and recording operation. On the other hand, if it is determined in step S3 that the release button has not been fully pressed, the series of AF processing ends. In step S5, it is determined whether or not the continuous shooting mode is set via the operation unit 12. If it is set, the process proceeds to step S10 in FIG.

  By the way, when the contrast detection AF operation is performed in step S2, the focusing lens is moved to the peak position of the focus evaluation value. In step S10, the subject distance is calculated from the lens position of the focusing lens after moving to the peak position, and the subject distance is stored in a storage unit (not shown) provided in the CPU 8. Alternatively, distance measurement may be performed when the contrast detection AF operation is completed, the subject distance at that time may be obtained, and this may be stored. This subject distance is stored as the previous subject distance P0.

  In step S11, the subject distance P is obtained by external light AF. In step S11, the process is stopped until the subject distance P is calculated, and the focusing lens moving process is not performed. In step S12, it is determined whether or not the release button is fully pressed. If it is determined that the release button is fully pressed, the process proceeds to step S13. If it is determined that the release button is not fully pressed, a series of AF processing ends. To do.

  In step S13, it is determined whether or not the absolute value “| P0−P |” of the difference between the stored previous subject distance P0 and the current subject distance P acquired in step S11 is greater than a predetermined value th. . If “| P0−P |> th” is determined in step S13, the process proceeds to step S14, the distance measurement error flag errflg is set to errflg = 1, and if “| P0−P | ≦ th” is determined, the process proceeds to step S15. Then, the distance measurement error flag errflg is set to errflg = 0, and the process proceeds to step S16.

  For example, if the ranging area is out of the background from the main subject during continuous shooting, or if some object crosses in front of the main subject, the change in P1 with respect to P0 is assumed from normal continuous shooting. Larger than the ones. FIG. 5 shows the relationship between the shooting frame and the subject distance in such a case. The horizontal axis represents the number of frames representing the number of frames during continuous shooting, and the vertical axis represents the subject distance in each frame. In the example shown in FIG. 5A, the distance measurement area is out of the main subject during the third frame processing, and the main subject is captured again after the fourth frame. In the example shown in FIG. 5B, the distance measurement area is out of the main subject during the third and fourth frame processing.

  In both cases of FIG. 5A and FIG. 5B, the difference “| P0−P |” from the subject distance of the second frame, which is the previous subject distance P0, is larger than the predetermined value th at the time of shooting the third frame. Is also getting bigger. The predetermined value th is an allowable value for determining whether or not the distance measurement area has been removed from the main subject during continuous shooting. In the case of “| P0−P |> th”, the predetermined value th is described above. It is determined that such a situation has occurred, that is, the distance measurement for which the subject distance P has been acquired is determined to be an error, and the distance measurement error flag errflg is set to errflg = 1.

  In step S16, it is determined whether or not the ranging error flag errflg is 1. If it is determined in step S16 that errflg = 1, the process proceeds to step S17 to set the previous subject distance P0 to the subject target position Px, and then proceeds to step S20. On the other hand, if it is determined in step S16 that errflg = 0, the process proceeds to step S18, where the current subject distance P is set as the subject target position Px, and then the process proceeds to step S19 where the subject distance P acquired this time is set. Stored as a new previous subject distance P0. In step S20, the focusing lens is moved to a lens position corresponding to the subject target position Px.

  After that, if the photographing operation process is performed in step S21, it is determined in step S22 whether or not the release button is fully pressed. If it is determined in step S22 that the full-pressing operation has been performed, the continuous shooting operation is continued, so that the process returns to step S11 to perform the next shooting, and the processing from step S11 to step S21 is repeated. On the other hand, if it is determined in step S22 that the full-pressing operation has not been performed, the series of AF processing ends.

  At the time of processing the first frame and the second frame in FIGS. 5A and 5B, the relationship between the subject distance P acquired in step S11 and the previous subject distance P0 in each case is “| P0−P | ≦≦ th ". Therefore, the process proceeds to step S13 and step S15, and the ranging error flag errflg is set to errflg = 0. Then, the process proceeds to step S16, step S18, step S19, and step S20, and the focusing lens is driven with the current subject distance P as the subject target position. At the start of the third frame processing, the subject distance acquired during the second frame processing is stored as the previous subject distance P0.

  At the time of the next third frame process, the relationship with the subject distance of the second frame, which is the previous subject distance P0, is “| P0−P |> th”. Therefore, the process proceeds to step S13 and step S14, and the ranging error flag errflg is set to errflg = 1. Then, the process proceeds to step S16, step S17, and step S20, and the focusing lens is driven to focus with the previous subject distance P0, which is the subject distance acquired in the second frame, as the subject target position, and photographing is performed in step S21. That is, even if the distance measurement area is out of the main subject, an image in which the main subject is in focus can be taken.

  Next, since the processing of the fourth frame is different between FIGS. 5A and 5B, first, FIG. 5A will be described. In the case of FIG. 5A, since “| P0−P |> th”, the same processing as that in the third frame is performed. That is, the distance measurement error flag errflg is set to errflg = 1, and the process proceeds to step S16, step S17, and step S20 and is driven to focus with the previous subject distance P0 that is the subject distance acquired in the second frame as the subject target position. The Therefore, in the shooting in step S21, an image in which the main subject is in focus is shot. The processing for the fifth frame and thereafter is the same as that for the second frame, and an image in which the main subject is in focus is photographed.

  On the other hand, in the case of FIG. 5B, since “| P0−P | ≦ th”, the process proceeds to step S13 and step S15, and the distance measurement error flag errflg is set to errflg = 0. Then, the process proceeds to step S16, step S18, step S19, and step S20, and the focusing lens is driven with the current subject distance P acquired in the fourth frame as the subject target position. As a result, in the fourth frame, an image in which the main subject is in focus is captured.

  Note that the subject distance acquired in the fourth frame as the previous subject distance P0 is stored by the processing in step S19. Therefore, the processing of the next fifth frame is the same as the processing of the fourth frame in the case of FIG. 5A, but focusing is performed based on the subject distance acquired at the fourth frame which is the previous subject distance P0. Operation is performed. As a result, the image in the fifth frame is not in focus with respect to the main subject. The processing after the sixth frame is the same as the processing after the fifth frame in the case of FIG. 5A, and an image in which the main subject is in focus is photographed. As described above, in the situation shown in FIG. 5B, conventionally, an out-of-focus image is generated in two frames (third and fourth frames), but in this embodiment, one frame (5 Frame).

<Modification>
In the above-described embodiment, the case where the main subject is out of the distance measurement area as shown in FIG. 5 has been described. However, for example, when the main subject actually changes due to panning the camera during continuous shooting, for example. The detected subject distance changes as shown in FIG. In other words, when the main subject is out of the distance measurement area, the subject distance greatly changes to about two frames at most, but when panning is performed, the subject distance after panning as shown in FIG. The greatly changed state is continued.

  When the subject distance changes as shown in FIG. 6, in the process shown in FIG. 3, the previous subject distance P0 is not rewritten after the third frame, so the third and subsequent frames are also based on the subject distance of the second frame. There is an inconvenience that the focusing operation is performed. Therefore, in the modified example, the flowchart of FIG. 7 is used instead of the flowchart of FIG. Steps that perform the same processing as in FIG. 3 are assigned the same reference numerals as in FIG.

  In the modification shown in FIG. 7, the distance measurement error flag errflg is set in consideration of not only the previous subject distance P0 but also the subject distance P1 twice in advance. First, in step S100, the subject distance obtained in the first frame of continuous shooting is stored as the previous subject distance P0 and the previous subject distance P1. If it is determined in step S12 that the button is fully pressed and the process proceeds to step S103, the absolute value “| P0− of the difference between the previous subject distance P0 stored and the current subject distance P acquired in step S11. It is determined whether or not “P |” is greater than a predetermined value th. If “| P0−P | ≦ th” is determined in step S103, the process proceeds to step S106, and the ranging error flag errflg is set to errflg = 0. On the other hand, if it is determined that “| P0−P |> th”, the process proceeds to step S104.

  In step S104, it is determined whether or not the absolute value “| P1-P |” of the difference between the stored subject distance P1 and the current subject distance P acquired in step S11 is greater than a predetermined value th. . If “| P0−P | ≦ th” is determined in step S104, the process proceeds to step S106, the distance measurement error flag errflg is set to errflg = 0, and if “| P0−P |> th” is determined, the process proceeds to step S105. The distance measurement error flag errflg is set to errflg = 1. If the flag is set in each of steps S105 and S106, the process proceeds to step S107 in any case.

  In step S107, it is determined whether or not the ranging error flag errflg is 1. If it is determined in step S107 that errflg = 1, the process proceeds to step S108, and the previous subject distance P0 is set as the subject target position Px. On the other hand, if it is determined in step S107 that errflg = 0, the process proceeds to step S109 to set the current subject distance P as the subject target position Px. In the subsequent step S110, the focusing lens is moved to a lens position corresponding to the subject target position Px.

  In step S111, in preparation for the next continuous frame shooting, the previous subject distance P0 is stored as a new previous subject distance P1, and the subject distance P acquired this time is stored as a new previous subject distance P0. In step S112, photographing operation processing is performed. In step S113, it is determined whether or not the release button has been fully pressed. If it is determined in step S113 that the full-pressing operation has been performed, the continuous shooting operation is continued, so that the process returns to step S11 to shoot the next frame, and the processing from step S11 to step S112 is repeated. On the other hand, if it is determined in step S113 that the full-pressing operation has not been performed, the series of AF processes is terminated.

Next, a specific processing flow will be described for the case of FIG. 5A and the case of panning shown in FIG.
[In the case of FIG. 5A]
In the processing of the second frame, since the previous subject distance P0 and the previous subject distance P1 are both the subject distances acquired in the first frame, NO is determined in step S103 and the process proceeds to step S106, and the ranging error flag errflg is errflg = 0. Is set. As a result, the process proceeds to step S107, step S109, and step S110, and a focusing operation is performed based on the current subject distance P acquired in step S11. In step S112, an image focused on the main subject is captured. Note that the current subject distance is stored as the previous subject distance P0 by the processing in step S111.

  In the process of the third frame, the current subject distance P acquired in step S11 satisfies both “| P0−P |> th” and “| P1−P |> th”. Therefore, YES is determined in each of steps S103 and S104, and the distance measurement error flag errflg is set to errflg = 1 in step S105. Thereafter, the process proceeds from step S105 to step S107 and step S108 in order, and the subject distance of the second frame, which is the previous subject distance P0, is set as the subject target position Px. As a result, an image in which the main subject is in focus is obtained by photographing in step S112.

  In the processing of the next fourth frame, the previous subject distance P0 is the subject distance acquired in the third frame, and the subject distance P1 is the subject distance acquired in the second frame. Therefore, the relationship with the current subject distance P acquired in the fourth frame is “| P0−P |> th” and “| P1−P | ≦ th”. Therefore, the process proceeds in the order of step S103, step S104, and step S106, and the distance measurement error flag errflg is set to errflg = 0. Then, the process proceeds to step S107, step S109, and step S110, and the focusing lens is driven with the current subject distance P acquired at the fourth frame as the subject target position. As a result, an image focused on the main subject after panning is taken.

[In the case of FIG. 6]
The processing up to the fourth frame is the same as in the case of FIG. In the process of the fifth frame, the relationship between the current subject distance P acquired in step S11, the previous subject distance P0, and the previous subject distance P1 is “| P0−P | ≦ th”, “| P1-P | ≦ th”. Therefore, the process proceeds to step S103 and step S106, and the distance measurement error flag errflg is set to errflg = 0. Therefore, the process proceeds to step S107, step S109, and step S110, and the focusing lens is driven using the current subject distance P acquired in the fourth frame as the subject target position. As a result, an image focused on the main subject after panning is taken.

  Thus, in the above-described modification, an image focused on the target main subject (main subject before and after panning) can be taken except for the first frame after panning. Note that the situation shown in FIG. 5B is the same as in the case of the flow shown in FIG.

  In the case of a hybrid camera, the setting for single shooting can be set to hybrid AF, only contrast detection AF, or only ambient light AF. Steps S1 and S2 in FIG. 2 show processing when single shooting is performed by hybrid AF. For example, when only contrast detection AF is set, only step S2 is executed without performing step S1, and when only external light AF is set, only step S1 is executed without performing step S2. You should do it. When the first frame of continuous shooting is performed with external light AF, the subject distance detected at that time is stored in step S10.

  In the correspondence between the embodiment described above and the elements of the claims, the contrast AF calculation unit 83 is an evaluation value calculation unit, the distance measurement unit 10 and the outside light AF calculation unit 82 are distance measurement units, and the CPU 8 and the focus. The motor 9 constitutes first and second autofocus means, the operation unit 12 constitutes setting means, and the CPU 8 constitutes storage means, determination means, replacement means, and first and second control means. The above description is merely an example, and when interpreting the invention, there is no limitation or restriction on the correspondence between the items described in the above embodiment and the items described in the claims.

1 is a block diagram of a digital still camera equipped with an autofocus device according to the present invention. It is a flowchart for demonstrating AF process operation | movement. 3 is a flowchart showing an AF processing operation following the flowchart of FIG. 2. It is a figure explaining a movement of a focusing lens in processing of Steps S1 and S2. It is a figure which shows the relationship between an imaging | photography frame | piece and object distance. It is a figure which shows the relationship between the imaging | photography frame in the case of panning, and a to-be-photographed object distance. It is a figure which shows the flowchart in a modification.

Explanation of symbols

1 Shooting Lens 2 Image Sensor 8 CPU
DESCRIPTION OF SYMBOLS 9 Focus motor 10 Distance measuring part 12 Operation part 81 AE calculating part 82 Outside light AF calculating part 83 Contrast AF calculating part

Claims (2)

Evaluation value calculating means for calculating a focus evaluation value of the subject image based on an imaging signal obtained by imaging the subject image formed by the photographing lens;
Ranging means for detecting subject distance by receiving subject light;
A first autofocus means for performing a focusing operation by driving a focus lens of the photographing lens so that the focus evaluation value is maximized;
Second autofocus means for performing a focusing operation based on the subject distance detected by the distance measuring means;
A setting means for setting a continuous shooting mode for continuously shooting a plurality of times by a continuous shooting command;
When the setting unit does not set the continuous shooting mode, the first autofocus unit performs a focusing operation, and when the setting unit sets the continuous shooting mode, the first shooting of the continuous shooting is performed. A first control unit that performs a focusing operation with the second autofocusing unit after the second shooting of continuous shooting after performing the focusing operation with the autofocusing unit,
Storage means for storing the subject distance corresponding to the in-focus state at the time of the first shooting;
It is determined whether the difference between the subject distance detected by the distance measuring unit and the subject distance stored in the storage unit is equal to or less than a determination value of the subject distance change during the second and subsequent shootings during the continuous shooting. A determination means;
During the continuous shooting, (a) when the determination means determines that the value is equal to or less than the determination value, the focusing operation is performed based on the subject distance detected by the distance measurement means, and the storage means The stored subject distance is replaced with the subject distance detected by the distance measuring means, and (b) if the determination means determines that it is not less than or equal to the determination value, the object distance stored in the storage means is An autofocus device comprising: a second control unit that performs the focusing operation based on the second control unit. Evaluation value calculating means for calculating a focus evaluation value of the subject image based on an imaging signal obtained by imaging the subject image formed by the photographing lens;
Ranging means for detecting subject distance by receiving subject light;
A first autofocus means for performing a focusing operation by driving a focus lens of the photographing lens so that the focus evaluation value is maximized;
Second autofocus means for performing a focusing operation based on the subject distance detected by the distance measuring means;
A setting means for setting a continuous shooting mode for continuously shooting a plurality of times by a continuous shooting command;
When the setting unit does not set the continuous shooting mode, the first autofocus unit performs a focusing operation, and when the setting unit sets the continuous shooting mode, the first shooting of the continuous shooting is performed. A first control unit that performs a focusing operation with the second autofocusing unit after the second shooting of the continuous shooting after the focusing operation with the autofocusing unit,
(A) When the subject distance detected by the distance measuring means and the subject distance corresponding to the in-focus state at the first photographing are larger than the determination value of the subject distance change during the second continuous photographing. Performs the focusing operation based on the subject distance at the time of the first photographing, and (b) the subject distance detected by the distance measuring means at the time of the third and subsequent photographings and the one time before the photographing. And when the difference between the subject distances detected by the distance measuring means at the time of each previous photographing is larger than the determination value, the in-focus state is based on the subject distance one time before the photographing. An autofocus device comprising: a second control unit that performs an operation.

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