JP2005233985A - Auto-focus camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To more surely focus at the time of predicting a moving body. <P>SOLUTION: In a state where a shutter button 56 is half-depressed, a distance to a specified object lying at a closest position is repeatedly measured by a CPU 46 based on the output of a passive sensor 44. And also, when the shutter button 56 is fully depressed, the focal point of the specified object is detected by the CPU 46 based on the output of an image sensor 18. Further, whether a change of an object field before and after the shutter button 56 is fully depressed satisfies a prescribed condition is judged by the CPU 46 based on the measurement result of the object distance by the passive sensor 44 and the detection result of the focal point by the image sensor 18. When the judgement result is affirmative, focusing is performed based on the measurement result of the object distance. On the other hand, when the judgement result is negative, focusing is performed based on the detection result of the focal point. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an autofocus camera, and more particularly to an autofocus camera that adjusts focus by using an external light AF method and a contrast AF method in combination.

An example of a conventional autofocus camera of this type is disclosed in Patent Document 1. According to this prior art, passive AF and active AF are prepared as AF methods, and passive AF is selected when so-called moving object prediction is performed. As a result, a good focus adjustment directed to the moving subject is realized.
JP 2001-4909 A [G02B 7/28 7/34 7/32 G03B 13/36]

  However, the moving object prediction is to predict the position of the subject at the time of photographing with reference to the movement of the subject until the photographing operation is performed. For this reason, when the subject moves outside the assumed range before and after the shooting operation, the focus cannot be adjusted well in the moving object prediction.

  Therefore, a main object of the present invention is to provide an autofocus camera that can realize more reliable focus adjustment for a moving subject.

  The autofocus camera according to the present invention is a measuring means for repeatedly measuring the distance to the specific subject at the nearest position based on the output of the first sensor when the shooting command is not issued, and the result of the specific subject when the shooting command is issued. Focus detection means for detecting the focus based on the output of the second sensor, and the change in the object scene before and after the shooting command is issued based on the measurement result of the measurement means and the detection result of the focus detection means is a predetermined condition The determination means for determining whether or not the first condition is satisfied, the first adjustment means for adjusting the focus based on the measurement result of the measurement means when the determination result of the determination means is positive, and the determination result of the determination means are negative Second adjusting means for adjusting the focus based on the detection result of the in-focus detection means.

  The measurement means repeatedly measures the distance to the specific subject existing at the nearest position based on the output of the first sensor when the imaging command is not issued. The in-focus detection unit detects the in-focus point of the specific subject based on the output of the second sensor when a shooting command is issued. The determining means determines whether or not a change in the object scene before and after the shooting command is issued satisfies a predetermined condition based on the measurement result of the measuring means and the detection result of the in-focus detection means. If the determination result of the determination means is affirmative, the first adjustment means adjusts the focus based on the measurement result of the measurement means. On the other hand, if the determination result of the determination unit is negative, the second adjustment unit adjusts the focus based on the detection result of the in-focus detection unit.

  If the change in the scene before and after the shooting command is issued satisfies a predetermined condition, it is considered that the measurement result of the measurement means is highly reliable, and the focus is adjusted based on the measurement result of the measurement means. On the other hand, if the change in the field before and after the shooting command is issued does not satisfy the predetermined condition, the reliability of the measurement result by the measurement means is regarded as low, and the focus is adjusted based on the detection result of the in-focus detection means Is done. Thereby, the focus can be adjusted more reliably at the time of moving object prediction.

  The autofocus camera according to the invention of claim 2 is dependent on claim 1, wherein a plurality of areas are assigned to the object scene, and the predetermined condition is the same before and after the shooting command is issued for the area where the specific subject exists. Including the area condition. Whether or not the area where the specific subject exists is the same before and after the shooting command greatly affects the reliability of the measurement result of the measuring means. Therefore, such an area condition is imposed.

  An autofocus camera according to a third aspect of the invention is dependent on the second aspect, further comprising a calculation unit that calculates a distance to a specific subject based on the focal point detected by the focal point detection unit, and the predetermined condition is that the photographing is performed It further includes a distance condition that a difference between the distance measured by the measuring unit and the distance calculated by the calculating unit immediately before the command is issued is equal to or less than a threshold value.

  When the distance to the specific subject is greatly different before and after the shooting command, the reliability of the measurement result by the measuring means is lowered. Therefore, such a distance condition is imposed.

  The autofocus camera according to the invention of claim 4 is dependent on claim 3, and the measurement means measures the distance to the subject belonging to each of the plurality of areas, and the plurality of measurement measures measured by the measurement execution means. A distance detecting means for detecting the shortest distance from the distances is included. Thereby, the distance to the specific subject can be accurately measured.

  The autofocus camera according to the invention of claim 5 is dependent on claim 4 and includes first area specifying means for specifying an area corresponding to the shortest distance detected by the distance detecting means from a plurality of areas, and focus detection. Second area specifying means for specifying an area corresponding to the focal point detected by the means from a plurality of areas is further provided. Thereby, the area to which the specific subject belongs can be specified accurately.

  An autofocus camera according to a sixth aspect of the invention is dependent on the first aspect, further comprising a calculation unit that calculates a distance to the specific subject based on the focal point detected by the focal point detection unit, and the predetermined condition is that the photographing is performed It includes a distance condition that the difference between the distance measured by the measuring means and the distance calculated by the calculating means immediately before the command is issued is equal to or less than a threshold value.

  An autofocus camera according to a seventh aspect of the invention is dependent on any one of the first to sixth aspects, further comprising third adjusting means for adjusting the focus each time a measuring operation is performed by the measuring means, and the in-focus detecting means is And a focus changing means for changing the focus in a specific range narrower than the maximum range in which the focus can be changed. As a result, the focal point of the specific subject can be detected in a short time when the shooting command is issued.

  An autofocus camera according to an eighth aspect of the invention is dependent on any one of the first to ninth aspects, further comprising time detection means for detecting a measurement time by the measurement means, wherein the first adjustment means is detected by the time detection means. The adjustment operation is performed with reference to the measurement time.

  The autofocus camera according to the invention of claim 9 is dependent on any one of claims 1 to 8, wherein the measuring means measures the distance to the specific subject by the phase difference detection method, and the focusing detection means is adjusted by the contrast detection method. Detect focus.

  An autofocus camera according to a tenth aspect of the invention is dependent on any one of the first to ninth aspects, and further comprises a recording means for recording an object scene image photographed in response to a photographing command on a recording medium.

  A focus control program according to an invention of claim 11 is a focus control program executed by a processor of an autofocus camera, and (a) when a shooting command is not issued, a distance to a specific subject present at the nearest position is determined by a first sensor. (B) When a shooting command is issued, the focal point of the specific subject is detected based on the output of the second sensor, and (c) the measurement result of step (a) and the step (b ) And whether or not the change in the object scene before and after the shooting command is issued satisfies a predetermined condition, and if (d) the determination result of step (c) is affirmative The focus is adjusted based on the measurement result of (a), and (e) when the determination result of step (c) is negative, the focus is adjusted based on the detection result of step (b). As in the first aspect, the focus can be adjusted more reliably when the moving object is predicted.

  According to the present invention, since the focus is adjusted by a different method according to the change in the object scene before and after the shooting command is issued, the focus can be adjusted more reliably when the moving object is predicted.

  The above object, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

  With reference to FIG. 1, a digital camera 10 of this embodiment includes a zoom lens 12, a focus lens 14, and an aperture unit 16. The optical image of the object scene is irradiated on the light receiving surface, that is, the imaging surface of the image sensor 18 through these members. On the imaging surface, a charge corresponding to the optical image of the subject, that is, a raw image signal is generated by photoelectric conversion.

  When displaying a real-time moving image of the object scene, that is, a through image, on the LCD monitor 38, the CPU 46 instructs the driver 24 to open the aperture and instructs the driver 26 to repeat pre-exposure and thinning-out reading. The driver 24 opens the aperture of the aperture unit 16, and the driver 26 repeatedly executes pre-exposure of the image sensor 18 and thinning readout of the raw image signal generated thereby. Pre-exposure and thinning readout are executed in response to a vertical synchronizing signal generated every 1/30 seconds. As a result, a low-resolution raw image signal corresponding to the optical image of the subject is output from the image sensor 18 at a frame rate of 30 fps.

  The output raw image signal of each frame is subjected to a series of processes of noise removal, level adjustment and A / D conversion by the CDS / AGC / AD circuit 28. Thereby, raw image data which is a digital signal is obtained. The signal processing circuit 30 performs processing such as white balance adjustment, color separation, and YUV conversion on the raw image data output from the CDS / AGC / AD circuit 28 to generate image data in YUV format. The generated image data is written into the SDRAM 34 by the memory control circuit 32 and then read out from the SDRAM 34 by the same memory control circuit 32. The video encoder 36 converts the image data read out by the memory control circuit 32 into a composite video signal conforming to the NTSC format, and supplies the converted composite video signal to the LCD monitor 38. As a result, a through image of the subject is displayed on the monitor screen.

  Of the image data generated by the signal processing circuit 30, Y data is given to the luminance evaluation circuit 40 for exposure control. The luminance evaluation circuit 40 integrates the Y data for each frame to obtain a luminance evaluation value. The CPU 46 fetches the luminance evaluation value obtained by the luminance evaluation circuit 40 in response to the vertical synchronization signal, and updates the exposure time set in the driver 26 based on the luminance evaluation value. Thereby, the brightness of the through image is adjusted.

  When the zoom key 60 is operated while the through image is displayed, the CPU 46 commands the driver 20 to drive the zoom lens 12. The zoom lens 12 is moved in the optical axis direction by the driver 20. The angle of view of the through image displayed on the LCD monitor 38 changes in response to the operation of the zoom key 60.

  When the shutter button 56 is half-pressed, exposure control for recording is performed based on the luminance evaluation value output from the luminance evaluation circuit 40. At this time, not only the exposure time set in the driver 26 but also the aperture amount set in the driver 24 is adjusted.

  When such exposure control is completed, the focus is adjusted according to the passive AF method and the contrast AF method. Note that the CPU 46 gives a movement command to the driver 22 for focus adjustment. The focus lens 14 is moved in the optical axis direction by the driver 22.

  Regarding the passive AF, the optical image of the object scene is irradiated to the linear sensor 44c through the optical lens 44a, and is irradiated to the linear sensor 44d through the optical lens 44b. Image signals output from the linear sensors 44c and 44d are given to the CPU 46. There is a deviation (phase difference) between the image captured by the linear sensor 44c and the image captured by the linear sensor 44d. The CPU 46 measures the distance to the subject by triangulation using this phase difference, and detects the focal point based on the measured distance.

  Regarding contrast AF, the AF evaluation circuit 42 integrates the Y data output from the signal processing circuit 30 for each frame period to obtain an AF evaluation value. The CPU 46 captures the obtained AF evaluation value in response to the vertical synchronization signal, and detects the focal point based on the captured AF evaluation value.

  In passive AF, high-speed focus adjustment is possible, but accuracy is low. With contrast AF, high-accuracy focus adjustment is possible, but adjustment takes time. Therefore, in this embodiment, the focus lens 14 is moved to the vicinity of the focal point detected by the passive AF, and then the focus lens 14 is set to the focal point by the contrast AF. Thereby, high-speed and high-precision focus control is realized.

  When the zoom magnification is high, the distance to the subject of interest is close, the brightness of the object field is insufficient, or the macro mode is selected with the mode key 58, the focus is set only by contrast AF. Is adjusted. Details will be described later.

  When the shutter button 56 is fully pressed, the photographing process is executed. The CPU 46 instructs the driver 26 to perform one main exposure and one full pixel readout, and instructs the JPEG codec 48 to perform image compression. The driver 26 performs the main exposure on the image sensor 18 and reads the raw image signal obtained thereby from the image sensor 18. The read raw image signal is subjected to the same processing as described above by the CDS / AGC / AD circuit 28 and the signal processing circuit 30. The obtained YUV format image data is written into the SDRAM 34 by the memory control circuit 32.

  The JPEG codec 48 reads image data from the SDRAM 34 through the memory control circuit 32, performs JPEG compression on the read image data, and writes the compressed image data, that is, JPEG data, into the SDRAM 34 through the memory control circuit 32. The CPU 46 reads the JPEG data obtained in this way from the SDRAM 34 through the memory control circuit 32, and records the JPEG file including the read JPEG data on the recording medium 52 through the I / F circuit 50.

  When the moving object prediction mode is selected by the mode key 58, the distance measurement by the passive AF is repeatedly executed when the shutter button 56 is half pressed. The measured distance and measurement time are registered in the history table 46t. When the shutter button 56 shifts from the half-pressed state to the fully-pressed state, the distance of the subject during the main exposure is predicted with reference to the history table 46t. The focus lens 14 is set at a position corresponding to the predicted distance, and when the setting is completed, the same photographing process as described above is executed. Note that when an unexpected change occurs in the object scene before and after the shutter button 56 is fully pressed, focus adjustment using contrast AF is executed instead of moving object prediction. Details will be described later.

  Specifically, the CPU 46 executes processing according to the flowcharts shown in FIGS. Note that a control program corresponding to these flowcharts is stored in the flash memory 54.

  First, the through image processing system is activated in step S1 of FIG. Specifically, the driver 26 is instructed to repeat pre-exposure and thinning-out reading. As a result, a through image is output to the LCD monitor 38.

  In step S3, it is determined whether or not the shutter button 56 has been half-pressed. In step S5, it is determined whether or not the zoom key 60 has been operated. When neither the shutter button 56 nor the zoom key 60 is operated, through image AE processing is executed in step S9. Thereby, the exposure time is adjusted. When the AE process is completed, the process returns to step S3. When the zoom key 60 is operated, YES is determined in step S5, and zoom processing is performed in step S7. As a result, the zoom lens 12 moves in the optical axis direction. When the zoom process is completed, the process returns to step S3.

  If the shutter button 56 is half-pressed, YES is determined in step S3, and recording AE processing is executed in step S11. Thus, the exposure time and the aperture amount are adjusted so that the optimum exposure amount can be obtained. In step S13, it is determined whether or not the shooting condition is suitable for passive AF, and the determination flag flg1 is set to “0” or “1” depending on the determination result. That is, if the shooting condition is not suitable for passive AF, the determination flag flg1 is set to “0”, and if the shooting condition is suitable for passive AF, the determination flag flg1 is set to “1”.

  If the determination flag flg1 is “0”, NO is determined in step S15, and contrast AF is executed in step S17. If the determination flag flg1 is in the set state, the process proceeds from step S15 to step S19, and it is determined whether the moving object prediction mode is selected. If the moving object prediction mode is not selected, passive AF and contrast AF are executed in steps S21 and S23, respectively.

  When passive AF and contrast AF are used together, the focus lens 14 moves at high speed in the vicinity of the focal point by passive AF, and is set to the focal point by contrast AF. When only contrast AF is performed, the focus lens 14 is set to a focal point at a predetermined speed.

  When the process of step S17 or S23 is completed, the operation state of the shutter button 56 is determined in steps S25 and S27. As long as the shutter button 56 is half-pressed, the processes in steps S25 and S27 are repeated. When the operation of the shutter button 56 is released, YES is determined in the step S27, and the process returns to the step S3. If the shutter button 56 is fully pressed, YES is determined in the step S25, and the photographing process is executed in a step S29. A JPEG file storing JPEG data corresponding to the subject image is recorded on the recording medium 52 by the photographing process. When the photographing process is completed, the process returns to step S1.

  If YES is determined in the step S19, a moving object prediction process is executed in a step S31. When the operation of the shutter button 56 is canceled during the moving object prediction process, the execution flag flg2 is set to “0”. When the shutter button 56 is fully pressed during the moving object prediction process, focus control is executed and the execution flag flg2 is set to “1”.

  In step S33, the state of the execution flag flg2 is determined. If the execution flag flg2 is “0”, the process returns to step S3. If the execution flag flg2 is “1”, the photographing process is executed in step S35. When the photographing process is completed, the process returns to step S1.

  The passive AF determination process in step S13 is executed according to a subroutine shown in FIG. Prior to the description, three focus areas F0 to F2 are allocated to the scene H as shown in FIGS. 2 (A) to 2 (C). The AF evaluation value is obtained for each of the focus areas F0 to F2. The positional relationship between the focus areas F0 to F2 and the detection area M of the passive sensor 44 changes according to the zoom magnification.

  In step S41 of FIG. 10, the zoom magnification is compared with the threshold value TH1. If the zoom magnification is greater than or equal to the threshold value TH1, the detection area M is regarded as straddling only the focus area F1, as shown in FIG. 2A, and the determination flag flg1 is set to “0” in step S57 to prohibit passive AF. Set to. The reason why passive AF is prohibited in the positional relationship shown in FIG. 2A is that passive AF may cause misadjustment when the subject of interest belongs to the focus area F0 or F2.

  On the other hand, if the zoom magnification is less than the threshold value TH1, the detection area M is regarded as straddling the focus areas F0 to F2 as shown in FIG. 2B or 2C, and the process proceeds to step S43. In step S43, areas M0, M1, and M2 that overlap with the focus areas F0, F1, and F2 in the detection area M are specified as effective areas. As shown in FIG. 3, the flash memory 54 stores an effective area table 54t describing the relationship between the zoom magnification and the effective areas M0 to M2. In step S43, the effective areas M0 to M2 corresponding to the current zoom magnification are specified with reference to the effective area table 54t.

  In step S45, the distance to the subject belonging to each of the specified effective areas M0 to M2 is measured based on the output of the passive sensor 44, and in the subsequent step S47, the shortest distance is specified from the obtained three distances. To do.

  In step S49, it is determined whether or not the specified shortest distance is less than the threshold value TH2. In step S51, it is determined whether or not the macro mode is selected. In step S53, the brightness of the object scene is set to the threshold value TH3. It is determined based on the output of the luminance evaluation circuit 40 whether or not it is less than the threshold value. If YES is determined in at least one of steps S49, S51, and S53, the determination flag flg1 is set to “1” in step S55 to permit passive AF. On the other hand, if NO is determined in all of steps S47, S49, and S51, the determination flag flg1 is set to “0” in step S57 to prohibit the passive AF.

  The reason why the passive AF is prohibited when the distance to the subject is short and when the macro mode is selected is that the influence of the positional deviation of the passive sensor 44 and the image sensor 18 cannot be ignored as the distance to the subject is short. is there. The reason why passive AF is prohibited when the brightness of the object scene is insufficient is that the accuracy of the passive sensor 44 decreases as the object scene becomes darker. When the process of step S53 or S55 is completed, the process returns to the upper hierarchy routine.

  The moving object prediction process in step S31 is executed according to a subroutine shown in FIGS.

  First, in steps S61 to S65, processing similar to that in steps S43 to S47 described above is performed. In step S67, referring to a timer (not shown), the time when the process of step S63 is performed is acquired. In step S69, the shortest distance specified in step S65 and the time acquired in step S67 are registered in the history table 46t shown in FIG. In step S71, the focus area to which the subject with the shortest distance belongs is specified as the area FP in the focus areas F0 to F2, and in step S73, the focus lens 14 is moved to a position corresponding to the shortest distance.

  If the shutter button 56 is half-pressed, YES is determined in the step S75, and the process returns to the step S61. Therefore, while the half-pressed state continues, distance measurement using the passive sensor 44 is repeatedly executed, and the measured shortest distance and measurement time are sequentially registered in the history table 46t.

  When the operation of the shutter button 56 is released, NO is determined in steps S75 and S77, the execution flag flg2 is set to "0" in step S79, and the process returns to the upper hierarchy routine.

  If the shutter button 56 is fully pressed, YES is determined in the step S77, and a minute contrast AF process is executed in a step S81. Here, contrast AF is executed in a range of “2α” centered on the current position of the focus lens 14.

  When the AF evaluation value characteristics of the focus areas F0, F1 and F2 change along the curves CRV0, CRV1 and CRV2 shown in FIG. 5, and the focus lens 14 moves in the range of “2α” centered on the lens position Pc, In the small contrast AF, only the in-focus FP1 is detected among the in-focus FP0 to FP2. On the other hand, the AF evaluation value characteristics of the focus areas F0, F1, and F2 change according to the curves CRV0 ′, CRV1 ′, and CRV2 ′ shown in FIG. 6, and the focus lens 14 is in a range of “2α” centered on the lens position Pc ′. In the case of movement, the in-focus FP0 ′ and FP1 ′ are detected from the in-focus FP0 ′ to FP2 ′ in the minute contrast AF.

  In step S83, it is determined whether or not a plurality of in-focus points are detected by the minute contrast AF. If “NO” here, the process proceeds to a step S87 as it is, but if “YES”, the focus point on the closest end side is specified in a step S85, and then, the process proceeds to a step S87. In step S87, the focus area corresponding to the focused point of interest (the only focused point detected by the minute contrast AF or the focused point specified in step S85) is specified as the area FC, and in step S89, the focused point of focus is set. The distance to the corresponding subject is calculated.

  In step S91, it is determined whether or not the focus areas FP and FC match each other. In step S93, it is determined whether or not the difference between the shortest distance specified in the immediately preceding step S65 and the distance calculated in step S89 is equal to or less than a threshold value TH4. The threshold value TH4 may be changed according to the moving speed of the subject when the shutter button 56 is half-pressed.

  If YES is determined in both steps S91 and S93, the process proceeds to step S95, and the distance to the subject when performing the photographing process (main exposure) is predicted with reference to the history table 46t. In step S97, the focus lens 14 is moved to a position corresponding to the predicted distance. When the movement is completed, the execution flag flg2 is set to “1” in step S101, and then the process returns to the upper layer routine.

  On the other hand, if it is determined NO in either one of steps S91 and S93, the focus lens 14 is set as the focused focal point in step S99, the execution flag flg2 is set to “1” in step S101, Thereafter, the process returns to the upper hierarchy routine. That is, when the focus areas FP and FC do not coincide with each other or when the distance difference is larger than the threshold value TH4, the moving object prediction is stopped and the focus adjustment according to the contrast AF (micro contrast AF) is executed. .

  As shown in FIG. 7A, when the child CL moving in the object scene H according to the motion vector AX1 is photographed in the moving object prediction mode, the focus is obtained by repeating the passive AF when the shutter button 56 is half-pressed. Follows the child CL. The history table 46t stores measured distances and measurement times.

  As shown in FIG. 7B, the motion vector AX2 representing the motion of the child CL before and after the shutter button 56 is fully pressed is equal to the motion vector AX1, and as a result, the focus area to which the child CL belongs is determined by the shutter button 56. If the difference between the distance measured last by passive AF and the distance measured by minute contrast AF is equal to or less than the threshold TH4 before and after being fully pressed, YES is determined in steps S91 and S93. The focus is adjusted with reference to the history table 46t.

  However, if the motion vector AX2 changes as shown in FIG. 8A and, as a result, the focus area to which the child CL belongs differs before and after the shutter button 56 is fully pressed, NO is determined in step S91. The focus is set to the focal point specified by the minute contrast AF. If the motion vector AX2 changes as shown in FIG. 8B, and the difference between the distance measured last by the passive AF and the distance measured by the minute contrast AF exceeds the threshold value TH4, the step It is determined NO in S93. The focus is set to the focal point specified by the minute contrast AF.

  The focus is adjusted by contrast AF instead of passive AF because the movement of the child CL in FIG. 8 (A) and FIG. 8 (B) is an unexpected movement of the moving object prediction. This is because the focus can be adjusted better.

  In addition, when the child CL suddenly approaches the front of the camera as shown in FIG. 8B, the distance to the child CL is initially greater than the threshold value TH2 when the shutter button 56 is half-pressed. When the shutter button 56 is fully pressed, the distance to the child CL may be less than the threshold value TH2. Below the threshold TH2, the influence of the positional deviation between the passive sensor 44 and the image sensor 18 cannot be ignored. The reason for performing the focus adjustment according to the contrast AF in FIG.

  As can be seen from the above description, when the shutter button 56 is half-pressed, the CPU 46 repeatedly measures the distance to the specific subject present at the nearest position based on the output of the passive sensor 44 (S61 to S65). The CPU 46 also detects the focal point of the specific subject based on the output of the image sensor 18 when the shutter button 56 is fully pressed (S81 to S83). Further, the CPU 46 determines whether the change in the object scene before and after the shutter button 56 is fully pressed is a predetermined condition based on the measurement result of the object distance using the passive sensor 44 and the detection result of the in-focus point using the image sensor 18. It is determined whether or not the condition is satisfied (S91, S93). If the determination result is affirmative, the focus is adjusted based on the measurement result of the subject distance. On the other hand, if the determination result is negative, the focus is adjusted based on the focus detection result.

  That is, if the change in the field before and after the shutter button 56 is fully pressed satisfies a predetermined condition, it is considered that the measurement result of the subject distance using the passive sensor 44 is high, and the focus is determined based on the measurement result. Is adjusted. On the other hand, when the change in the scene before and after the shutter button 56 is fully pressed does not satisfy the predetermined condition, it is considered that the reliability of the measurement result by the passive sensor 44 is low, and the in-focus detection using the image sensor 18 is performed. The focus is adjusted based on the result. Thereby, the focus can be adjusted more reliably at the time of moving object prediction.

  In this embodiment, when the focus is adjusted, only the focus lens 14 is moved in the optical axis direction, but the image sensor 18 is moved in the optical axis direction instead of the focus lens 14 or together with the focus lens 14. You may make it move. In this embodiment, passive AF is adopted as one of AF methods, but active AF may be adopted instead of passive AF.

It is an illustration figure which shows the structure of one Example of this invention. (A) is an illustrative view showing the positional relationship between the object field and the detection area of the passive sensor when the zoom magnification is set to the telephoto side, and (B) is an object image when the zoom magnification is set to an intermediate value. It is an illustration figure which shows the positional relationship of the detection field of a field and a passive sensor, (C) is an illustration figure which shows the positional relationship of the field of view and the detection area of a passive sensor when zoom magnification is set to the wide angle side. is there. It is an illustration figure which shows an example of the effective area table applied to the FIG. 1 Example. It is an illustration figure which shows an example of the log | history table applied to the FIG. 1 Example. It is a graph which shows an example of the change of AF evaluation value with respect to a lens position. It is a graph which shows another example of the change of AF evaluation value with respect to a lens position. (A) is an illustrative view showing an example of an object scene immediately before the shutter button is fully pressed, and (B) is an illustrative view showing an example of an object scene immediately after the shutter button is fully pressed. (A) is an illustrative view showing another example of the scene immediately after the shutter button is fully pressed, and (B) is an illustrative view showing another example of the scene immediately after the shutter button is fully pressed. FIG. It is a flowchart which shows a part of operation | movement of CPU applied to the FIG. 1 Example. It is a flowchart which shows a part of other operation | movement of CPU applied to the FIG. 1 Example. It is a flowchart which shows a part of other operation | movement of CPU applied to the FIG. 1 Example. FIG. 12 is a flowchart showing yet another portion of behavior of the CPU applied to the embodiment in FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Digital camera 12 ... Zoom lens 14 ... Focus lens 16 ... Aperture unit 18 ... Image sensor 40 ... Luminance evaluation circuit 42 ... AF evaluation circuit 44 ... Passive sensor 46 ... CPU

Claims (11)

Measuring means for repeatedly measuring the distance to the specific subject existing at the latest position based on the output of the first sensor when the imaging command is not issued;
In-focus detection means for detecting the in-focus point of the specific subject based on the output of the second sensor when the shooting command is issued;
Judgment means for judging whether a change in the object scene before and after the shooting command is issued satisfies a predetermined condition based on the measurement result of the measurement means and the detection result of the in-focus detection means;
First adjustment means for adjusting the focus based on the measurement result of the measurement means when the determination result of the determination means is affirmative; and detection of the in-focus detection means when the determination result of the determination means is negative An autofocus camera comprising second adjusting means for adjusting the focus based on a result. Multiple areas are assigned to the scene,
The autofocus camera according to claim 1, wherein the predetermined condition includes an area condition in which an area where the specific subject exists matches before and after the shooting command is issued. A calculation unit that calculates a distance to the specific subject based on the focal point detected by the focal point detection unit;
3. The predetermined condition further includes a distance condition that a difference between a distance measured by the measurement unit and a distance calculated by the calculation unit immediately before the photographing command is issued is equal to or less than a threshold value. Autofocus camera.   The measurement unit includes a measurement execution unit that measures a distance to a subject belonging to each of the plurality of areas, and a distance detection unit that detects a shortest distance from the plurality of distances measured by the measurement execution unit. The autofocus camera according to claim 3. A first area specifying means for specifying an area corresponding to the shortest distance detected by the distance detecting means from the plurality of areas; and an area corresponding to the focal point detected by the focal point detecting means. The autofocus camera according to claim 4, further comprising second area specifying means for specifying the area. A calculation unit that calculates a distance to the specific subject based on the focal point detected by the focal point detection unit;
The predetermined condition includes a distance condition that a difference between a distance measured by the measuring unit and a distance calculated by the calculating unit immediately before the photographing command is issued is equal to or less than a threshold value. Auto focus camera. A third adjusting means for adjusting the focus each time a measuring operation is performed by the measuring means;
7. The autofocus camera according to claim 1, wherein the focus detection unit includes a focus change unit that changes the focus in a specific range narrower than a maximum range in which the focus can be changed. It further comprises time detection means for detecting the measurement time by the measurement means,
The autofocus camera according to any one of claims 1 to 9, wherein the first adjustment unit performs an adjustment operation with reference to a measurement time detected by the time detection unit. The measuring means measures the distance to the specific subject by a phase difference detection method,
9. The autofocus camera according to claim 1, wherein the focus detection means detects the focus by a contrast detection method.   The autofocus camera according to claim 1, further comprising recording means for recording an object scene image photographed in response to the photographing command on a recording medium. A focus control program executed by a processor of an autofocus camera,
(a) When the shooting command is not issued, the distance to the specific subject existing at the nearest position is repeatedly measured based on the output of the first sensor,
(b) detecting the focal point of the specific subject based on the output of the second sensor when the shooting command is issued;
(c) Based on the measurement result of the step (a) and the detection result of the step (b), it is determined whether or not the change in the object scene before and after the shooting command is issued satisfies a predetermined condition. ,
(d) adjusting the focus based on the measurement result of step (a) when the determination result of step (c) is affirmative; and
(e) A focus control program for adjusting the focus based on the detection result of the step (b) when the determination result of the step (c) is negative.

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