JP2016145943A - Focus adjustment apparatus, imaging apparatus, control methods for such apparatuses, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focus adjustment apparatus capable of reducing the effects of brightness of ambient environments when a subject including a point light source is photographed.SOLUTION: The focus adjustment apparatus comprises: an acquisition means for acquiring plural pieces of image data while changing the image formation position of the subject; photometric means for measuring the luminance of the subject including the point light source; determination means for determining an exposure condition to acquire the plural pieces of image data based on the measured luminance; evaluation value acquisition means for acquiring an evaluation value indicative of the focusing degree for each of plural image formation positions, using the acquired plural pieces of image data; focusing position determination means for determining the focusing positions based on the evaluation values; and setting means for setting a photographing mode to photograph the point light source subject at an illuminance lower than a predetermined illuminance. The determination means, when the photographing mode is determined, determines the exposure condition such that a predetermined range of exposure values is obtained by decreasing the exposure values with respect to the correct exposure to acquire the photographed image based on the measured luminance, with the plural pieces of image data allowed to be acquired.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a focus adjustment apparatus, an imaging apparatus, a control method thereof, and a program.

  2. Description of the Related Art Conventionally, an imaging apparatus equipped with an automatic focus adjustment (also referred to as AF) function for automatically focusing is known. In the AF function, for example, when using the contrast of a subject, an evaluation value (also referred to as an AF evaluation value) representing the degree of focus is calculated while moving the focus lens position, and this AF evaluation value is maximum (the subject contrast is maximum). Move the focus lens to the position. However, if the contrast is low due to low or high illuminance, taking the focus lens position on the horizontal axis and the AF evaluation value on the vertical axis, the shape does not form an appropriate mountain shape, and the optimum focus lens position is accurately determined. May not be able to ask for.

  For such a problem, a technique for determining the reliability of automatic focus adjustment (AF) based on an AF evaluation value is known. Patent Document 1 proposes a method of repeating the process of changing the exposure condition without performing focus adjustment until AF reliability becomes high when it is determined that the reliability based on the AF evaluation value is low. . Since the focus lens can be moved based on the AF evaluation value when it is determined that the AF reliability is high by repeatedly changing the exposure condition, the accuracy of the AF function can be improved.

JP 2011-257758 A

  However, when performing astronomical photography, the brightness of the celestial object (point light source subject) itself is almost constant regardless of the shooting location, but the brightness of clouds and air varies depending on the surrounding lighting and weather, so the shooting location The photometric value varies depending on the weather. For this reason, when the exposure condition is changed as in the prior art, if the integrated value of the image signal (that is, the photometric value) is used, it reacts not with the brightness of the celestial object but with the brightness of the surroundings of the camera. In some cases, the exposure conditions cannot be determined appropriately. In addition, when setting an exposure condition suitable for photographing a point light source subject, the area of the point light source subject may be saturated, and the exposure condition suitable for the photographing may not always be appropriate as the AF exposure condition.

  The present invention has been made in view of the above-mentioned problems of the prior art. That is, a focus adjustment device, an imaging device, a control method thereof, and a program capable of performing appropriate automatic focus adjustment with reduced influence of brightness due to the surrounding environment when shooting including a point light source subject The purpose is to provide.

  In order to solve this problem, for example, the focus adjustment apparatus of the present invention has the following configuration. That is, an acquisition unit that exposes an image sensor at a plurality of imaging positions while changing an imaging position in an optical axis direction of an optical image of a subject, acquires a plurality of image data for focus adjustment, and a point light source subject. A photometric means for measuring the brightness of the subject including the light, a determining means for determining an exposure condition for acquiring a plurality of image data for focus adjustment based on the brightness measured by the photometric means, and a plurality of acquired in the exposure condition Using the image data, an evaluation value acquisition unit that acquires an evaluation value representing the degree of focus for each of the plurality of imaging positions, a focus position determination unit that determines a focus position based on the evaluation value, and a predetermined value Setting means for setting a shooting mode for shooting a point light source subject at an illuminance lower than the predetermined illuminance, and the determining means receives a plurality of image data for focus adjustment when the shooting mode is set. Take In such a state, the exposure amount is decreased with respect to the appropriate exposure for obtaining the actual captured image obtained based on the measured luminance, and the exposure condition is determined so as to be in a predetermined exposure amount range. It is characterized by.

  According to the present invention, it is possible to perform appropriate automatic focus adjustment in which the influence of brightness due to the surrounding environment is reduced when shooting including a point light source subject.

1 is a block diagram illustrating a functional configuration example of a digital camera as an example of a focus adjustment apparatus according to a first embodiment of the present invention. 6 is a flowchart showing a series of operations of the photographing operation according to the first embodiment. The figure which shows an example of the program diagram used for the AF process which concerns on Embodiment 1. FIG. 5 is a diagram illustrating an example of a relationship of an AF evaluation value signal with respect to a focus lens position according to the first embodiment. 7 is a flowchart showing a series of shooting operations according to the second embodiment. The flowchart which shows a series of operation | movement of the astronomical photography estimation process which concerns on Embodiment 2. FIG.

(Embodiment 1)
Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. In the following, an example in which the present invention is applied to a lens-integrated digital camera capable of automatic focus adjustment will be described as an example of a focus adjustment device. However, the present invention can be applied not only to the focus adjustment function in a lens-integrated digital camera but also to the focus adjustment function in an interchangeable lens and a digital single-lens reflex camera. Further, the focus adjustment function according to the present invention may be applied not only to the digital camera body but also to an interchangeable lens unit. Furthermore, in the following description, the focus adjustment function at the time of shooting will be described as an example, but it can also be applied as a focus adjustment function at the time of live view.

(Configuration of digital camera 1)
FIG. 1 is a block diagram illustrating an example of a functional configuration of a digital camera 1 as an example of the focus adjustment apparatus of the present embodiment. One or more of the functional blocks shown in FIG. 1 may be realized by hardware such as an ASIC or a programmable logic array (PLA), or may be realized by a programmable processor such as a CPU or MPU executing software. May be. Further, it may be realized by a combination of software and hardware. Therefore, in the following description, even when different functional blocks are described as the operation subject, the same hardware can be realized as the subject.

  The zoom lens group 2 is a lens group that forms a photographing optical system together with the focus lens group 3, and performs a zooming operation (zooming operation) of the photographing optical system under the control of the third motor driving unit 20. Further, the focus lens group 3 changes the focusing position of the optical image formed on the image sensor 5 by changing the imaging position in the optical axis direction of the optical image of the subject under the control of the second motor drive unit 19. . The diaphragm 4 is a diaphragm that changes the amount of light transmitted through the zoom lens group 2 and the focus lens group 3 under the control of the first motor. The photographic lens barrel 31 is a lens barrel including the zoom lens group 2, the focus lens group 3, and the diaphragm 4.

  The image sensor 5 includes a solid-state image sensor (also referred to as an image sensor) such as a CMOS (Complementary Metal Oxide Semiconductor), for example, and photoelectrically converts an optical image of a subject that has passed through the imaging optical system and formed on the image sensor into an electrical signal. To do. The imaging unit 6 receives the electrical signal photoelectrically converted by the imaging device 5 and performs various image processing to generate a predetermined image signal.

  The A / D conversion unit 7 includes, for example, an A / D conversion circuit, converts the analog image signal output from the imaging unit 6 into a digital image signal (image data), and outputs the digital image signal. The VRAM 8 includes a storage medium such as a semiconductor memory, and temporarily stores the image data output from the A / D conversion unit 7. The D / A converter 9 reads the image data stored in the VRAM 8, converts it into an analog signal, and converts it into a form suitable for reproduction output.

  The display unit 10 includes an image display device such as a liquid crystal display device (LCD), and displays the image data output from the D / A conversion unit 9. The storage memory 12 is a non-volatile storage medium such as a semiconductor memory, and stores image data processed by the compression / decompression unit 11. In addition, the compression / decompression unit 11 has a compression function for performing compression processing and encoding processing of image data in order to read out the image data temporarily stored in the VRAM 8 and make it suitable for storage in the storage memory 12. In addition, the image data stored in the storage memory 12 has a decompression function for performing a decoding process, a decompression process, and the like to obtain an optimum form for reproducing and displaying the image data.

  The AE processing unit 13 and the AF processing unit 14 perform calculations for performing automatic exposure (AE) processing and automatic focusing (AF) processing on the image data output from the A / D conversion unit 7, respectively. And outputs each calculation result to the control unit 15. The timing generator (TG) 16 generates a predetermined timing signal for controlling the operation timing of the imaging unit 6 and the imaging element driver 17.

  The control unit 15 includes, for example, a CPU or MPU, and controls each unit of the entire digital camera 1 by, for example, developing and executing a program stored in the EEPROM 25 in a work area of a RAM (not shown).

  The image sensor driver 17 includes a control function for controlling the image sensor 5 at the timing generated by the TG 16. The aperture drive motor 21 is a motor that drives the aperture 4 and controls the aperture according to a control signal output from the first motor drive unit 18. The focus drive motor 22 is a motor that drives the focus lens group 3, and controls the lens position of the focus lens in accordance with a control signal for the focus lens output by the second motor drive unit 19. The zoom drive motor 23 is a motor that drives the zoom lens group 2, and the third motor drive unit 20 includes a control function that drives and controls the zoom drive motor 23.

  The operation unit 24 is an operation unit including various switches, a dial, or a touch panel for operating the digital camera, detects a user operation, and transmits a detection result or operation content. The various switches include a main power switch for starting the digital camera 1 to supply power, a release switch for starting a shooting operation (storage operation), a playback switch for starting a playback operation, and a zoom lens group 2 of the shooting optical system. It includes a zoom switch that moves and moves the zoom. The release switch generates a first stroke (hereinafter referred to as SW1) for generating an instruction signal for starting an AE process and an AF process performed prior to a photographing operation, and a first stroke for generating an instruction signal for starting an actual exposure operation. It has a two-stage switch with two strokes (hereinafter SW2).

  The EEPROM 25 is an electrically rewritable read-only memory in which programs for performing various controls and the like and data used for performing various operations are stored in advance. The battery 26 includes a detachable battery and provides power to each part of the digital camera.

  The strobe light emitting unit 28 has a light emitting element, and emits light in response to an instruction from the switching unit 27 that controls flash light emission. The LED 29 includes a light emitting element such as an LED or a display element, for example, and displays a warning. The speaker 30 includes a mechanism for converting an electric signal into sound, and generates sound guidance and warning according to an instruction from the control unit 15.

  The AF auxiliary light generation unit 33 is a lighting unit that includes a light source such as an LED, for example, and illuminates all or a part of the subject when performing AF processing. The AF auxiliary light driving unit 32 includes a control function for driving the AF auxiliary light generating unit 33 in accordance with an instruction from the control unit 15. The shake detection sensor 35 includes, for example, an acceleration sensor that detects camera shake, and the shake detection unit 34 includes a function of processing a signal of the shake detection sensor 35. The face detection unit 36 detects the face position and the size of the face from the image data output from the A / D conversion unit 7 and outputs the detection result to the control unit 15. The motion vector detection unit 37 acquires The amount of movement of the subject on the image is obtained from a plurality of image data at different times.

  The storage memory 12 includes a storage medium that stores image data and the like. Various types such as a fixed type or a card shape or a stick shape, including a semiconductor memory such as a card type flash memory which is detachably attached to the apparatus, and a magnetic storage medium such as a hard disk or a floppy disk Can be included.

  A basic operation of the digital camera 1 having the above-described configuration will be described.

  First, the optical image of the subject that has passed through the taking lens barrel 31 of the digital camera 1 is adjusted on the light amount by the diaphragm 4 and then formed on the light receiving surface of the image sensor 5. The formed optical image is converted into an electrical signal by photoelectric conversion processing by the image sensor 5 and is output to the imaging unit 6. The imaging unit 6 performs predetermined signal processing on the input analog electrical signal to generate a predetermined image signal. The generated image signal is converted into a digital image signal (image data) by the A / D converter 7 and then temporarily stored in the VRAM 8. The image data stored in the VRAM 8 is converted into an analog image signal in a form suitable for display by the D / A conversion unit 9 and then displayed as an image on the display unit 10. On the other hand, the image data stored in the VRAM 8 is also output to the compression / decompression unit 11. The image data is subjected to compression processing by the compression / decompression unit 11, further converted into image data in a form suitable for storage, and stored in the storage memory 12.

  For example, when a reproduction switch (not shown) in the operation unit 24 is operated and turned on, the reproduction operation is started. The image data stored in a compressed form in the storage memory 12 is subjected to a decoding process or an expansion process by the compression / decompression unit 11 and then output to the VRAM 8 and temporarily stored therein. Further, the stored image data is converted into an analog signal by the D / A conversion unit 9 and displayed as an image on the display unit 10.

  Further, the image data digitized by the A / D conversion unit 7 is output to the AE processing unit 13, the AF processing unit 14, and the face detection unit 36 separately from the VRAM 8 described above. The AE processing unit 13 performs arithmetic processing such as cumulative addition on the luminance value of the input image data. Thereby, an AE evaluation value (for example, a photometric value) corresponding to the brightness of the subject is calculated, and the calculation result is output to the control unit 15. That is, the AE processing unit 13 serves as a photometric unit.

  The AF processing unit 14 inputs image data and performs AF processing. Specifically, the AF processing unit 14 applies a high-pass filter (HPF) to image data corresponding to a partial area (also referred to as an AF frame) of the screen, and extracts a high-frequency component of the AF frame. Then, an arithmetic value such as cumulative addition is performed to calculate an evaluation value (AF evaluation value signal) representing the degree of focus corresponding to the contour component amount on the high frequency side. That is, the AF processing unit 14 serves as an evaluation value acquisition unit. The AF frame may be an arbitrary part including the central part in the image area, the part and a plurality of parts adjacent to the part, or a plurality of parts distributed discretely in the image area. . As described above, the AF processing unit 14 also serves as a high-frequency component detection unit that detects a predetermined high-frequency component from the image data generated by the image sensor 5 in the course of performing the AF processing.

  When the image data is input, the face detection unit 36 detects a part characterizing the face such as eyes and eyebrows from the image, and obtains the position or area of the person's face on the image. Furthermore, the face detection unit 36 obtains the size and inclination of the face based on the positional relationship such as the part characterizing the detected face and the distance between them.

  A predetermined timing signal is output from the TG 16 to the control unit 15, the imaging unit 6, and the imaging element driver 17, and the control unit 15 performs various controls in synchronization with the timing signal. The imaging unit 6 inputs a timing signal from the TG 16 and performs various image processing such as separation of color signals in synchronization with the timing signal. Further, the image sensor driver 17 drives the image sensor 5 so as to synchronize with the timing signal of the TG 16.

  The control unit 15 controls the first motor driving unit 18 based on the photometric value calculated by the AE processing unit 13 and appropriately adjusts the aperture amount of the aperture 4 to perform AE control. Further, the control unit 15 controls the second motor driving unit 19 based on the AF evaluation value signal calculated by the AF processing unit 14 to move the focus lens group 3 to an appropriate in-focus position and perform AF control. Further, when a zoom switch (not shown) in the operation unit 24 is operated, the control unit 15 controls the third motor driving unit 20 according to the operation amount of the zoom switch to appropriately move the zoom lens group 2. Then perform the zooming operation of the photographic optical system. Note that the control unit 15 may further calculate the AF evaluation value signal instead of the AF processing unit 14.

(Shooting operation in the digital camera 1)
Next, a shooting operation according to the present embodiment will be described with reference to the flowchart shown in FIG. In the following, the operation of acquiring the AF evaluation value while driving the focus lens group 3 to a predetermined position is scanned, the interval of the position of the focus lens for acquiring the AF evaluation value is the scan interval, and the number of AF evaluation values is acquired. This is called the number of scan points. The focus lens moving range for acquiring the AF evaluation value is set as a scan range, and the scan range is determined by the product of the scan interval and (number of scan points-1). Further, the combination of the aperture value of the aperture 4 for the AF process, the storage time of the image sensor and the amplification factor is also referred to as an AF exposure condition.

  In this photographing operation, the output of the image signal is started from the image sensor 5 when the main power switch of the operation unit 24 is turned on, for example, when the user sets the operation mode of the digital camera 1 to the photographing (recording) mode. Start at the point. Then, the control unit 15 is executed by controlling each unit of the digital camera 1.

  In step S <b> 201, the control unit 15 causes the display unit 10 to display an image formed on the image sensor 5 as an image. As described above, the subject image formed on the image pickup device 5 is stored in the VRAM 8 as image data via the image pickup unit 6 and the A / D conversion unit 7, and then the image data is displayed on the display unit 10 ( Live view display).

  In S202, the control unit 15 determines whether or not the shooting mode is set to a shooting mode for shooting a celestial object excluding the sun and the moon (also referred to as celestial shooting mode). The control unit 15 determines the shooting mode based on the switch state of the operation unit 24 or a preset setting value, and performs normal shooting processing when determining that the astronomical shooting mode is not set. Then, the process proceeds to S230. On the other hand, if the controller 15 determines that the astrophotography mode is set, the process proceeds to S203.

  When the process proceeds to S230, the control unit 15 performs normal shooting processing. The control unit 15 causes the storage memory 12 to store image data acquired under appropriate conditions by performing AE processing, AF processing, and the like according to the operation of the release switch by the user. When the control unit 15 stores the image data in the storage memory 12, the control unit 15 ends a series of processes related to photographing.

  In S203, the control unit 15 determines whether or not an instruction to start AF processing (also referred to as celestial AF) for the celestial object has been made by a user operating a button for starting AF processing for the celestial object (celestial AF start button). To do. When it is determined that the celestial AF start button has not been operated, the control unit 15 proceeds to S210, whereas when it is determined that the celestial AF start button has been operated, the process proceeds to S204.

  In S204, the control unit 15 acquires a photometric value. The photometric value includes an output value (for example, subject luminance value) of the AE processing unit 13 with respect to image data acquired from the image sensor, an accumulation time of the image sensor 5 when the output value is acquired, a signal amplification factor, and an aperture of the aperture 4 Calculated based on the value. The accumulation time of the image sensor 5 may be appropriately read as exposure time, and the signal amplification factor as film sensitivity.

  In S205, the control unit 15 determines whether the illuminance at the time of image data acquisition (that is, at the time of shooting) is lower than a predetermined illuminance based on the acquired photometric value. If the illuminance at the time of shooting is lower than the predetermined illuminance, the control unit 15 determines that the illuminance is low and proceeds to S206. If the illuminance at the time of shooting is equal to or higher than the predetermined illuminance, the control unit 15 determines that the illuminance is not low. Then, the process proceeds to S220. If it is determined that the light intensity is not low, it means that the environment is not a desired environment for photographing a celestial body due to the influence of the moon or the illumination on the ground. For this reason, in S220, the control unit 15 drives the focus lens group 3 to a fixed point, and then proceeds to S210. Note that the fixed point here is, for example, a focus obtained by further correcting a positional shift due to temperature or camera posture based on the position of the focus lens group 3 that is in focus at infinity at each zoom position, which is measured at the time of manufacture. This is the position of the lens group 3 (infinity adjustment position). Further, in S220, the control unit 15 may display on the display unit 10 that the environment is not suitable for the astronomical photographing mode due to the influence of the moon, illumination on the ground, or the like in order to inform the user that the celestial AF has failed. .

  In S206, the control unit 15 determines the aperture value of the aperture 4 for AF processing, the storage time of the image sensor, and the amplification factor (also referred to as AF exposure conditions).

  In general, when performing astronomical photography, the sky may become bright due to the influence of illumination light from buildings or the like in urban areas. When clouds are present, the sky may become bright because the moonlight or city lights are reflected on the clouds. In such a case, the exposure of the celestial object may be insufficient by measuring the brightness of the sky or clouds that have become bright rather than the brightness of the celestial object (point light source subject). That is, there is a possibility that an AF evaluation value for appropriately operating AF with respect to a celestial body cannot be obtained due to insufficient signal amount when performing AF processing.

  On the other hand, in the astronomical photography in the mountainous area, the number of visible celestial bodies can be increased because the influence of ambient lighting etc. is reduced compared to the case of urban areas, but the proportion of celestial bodies in terms of area is Since it is small, exposure to the celestial body may become too large by metering the dark sky. For this reason, when the signal for a bright celestial body is saturated, the AF evaluation value may be higher in a state slightly blurred than the original focused state, and there is a possibility that a correct focused position cannot be obtained.

  For this reason, first, the control unit 15 obtains a combination of an aperture value, an accumulation time, and an amplification factor that provide appropriate exposure based on the photometric value acquired in S204. Then, a combination of an aperture value, an accumulation time, and an amplification factor is determined so that the predetermined exposure amount is smaller than the obtained combination. However, when determining the aperture value, accumulation time, and amplification factor combination that reduces the predetermined exposure amount, the control unit 15 determines that the combination is selected from a predetermined range.

  For example, the control unit 15 first determines a combination of an aperture value, an accumulation time, and an amplification factor that further reduces, for example, the seven-step exposure amount, from the obtained combination of the aperture value, the accumulation time, and the amplification factor. The combination for reducing the exposure amount of the predetermined amount in this way is a combination of the aperture value, the accumulation time, and the amplification factor for obtaining an exposure amount suitable for shooting (also referred to as main shooting to distinguish from AF). This is because the combination of the aperture value, the accumulation time, and the amplification factor for obtaining an exposure amount suitable for AF processing is different. This is not a problem even if the signal of a bright celestial image of 1st to 2nd stars is saturated in the actual captured image, but rather a dark celestial body such as 3 to 6th stars can be recognized on the image. It may be preferable to become like this. On the other hand, in the image for AF processing, when the signal of a bright celestial image is saturated, for example, as described in Japanese Patent Application Laid-Open No. 2012-141457, a slightly out-of-focus state is In some cases, the evaluation value becomes high and the correct in-focus position cannot be obtained. Therefore, in the present embodiment, during AF processing, a combination of an aperture value, an accumulation time, and an amplification factor that are optimal under the condition where the predetermined exposure amount is reduced is obtained, and the signal of a bright celestial image is not saturated. Like that.

  A combination of the aperture value, the accumulation time, and the amplification factor is obtained based on the program diagram shown in FIG. In FIG. 3, the vertical axis represents the aperture value (Av), the horizontal axis represents the storage time (Tv) of the image sensor, and the diagonal line represents the exposure value (Ev). The thick solid line represents the brightness of the subject with the optimum exposure. Show. For example, when the Av value is 3 and the Tv value is −2, the brightness of the subject with proper exposure is Ev value = 2.

  The upper and lower limits of the program diagram may be determined in advance based on experiments and the like, assuming the typical astronomical scene and taking into account the brightness of the celestial bodies included in the AF frame and the number thereof. The upper limit value on the program in this embodiment is, for example, that the aperture value is F2.8 (Av value = 3), the accumulation time is 1 second (Tv value = 0), and the amplification factor at this time is equivalent to ISO100 (Sv = 5). This combination, for example, assumes that AF processing is performed on a scene where there are many relatively bright first-class stars, second-class stars, and planets in the AF frame. This is for determining an exposure amount that does not cause saturation of pixel values in the AF frame. On the other hand, the lower limit value on the program is that the aperture value is F2.8 (Av value = 3) and the accumulation time is 4 seconds (Tv value = -2), and the amplification factor at this time is equivalent to ISO800 (Sv = 8) It is. This combination assumes, for example, a case where AF processing is performed on a dark scene in which there are not many first-class stars, second-class stars, and planets in the AF frame, or there are few and many third-class stars or less. Even in such a scene, a predetermined exposure amount is ensured.

  Further, when the combination of the aperture value, the accumulation time and the amplification factor obtained by reducing the predetermined exposure amount is not within the range of the program diagram shown in FIG. 3 (when the exposure amount exceeds the upper limit or falls below the lower limit), Use a combination that will be the upper limit or lower limit of the program diagram (clip).

  When the control unit 15 determines the aperture value, the accumulation time, and the amplification factor used during the AF process, the process proceeds to S207.

  In S207, the control unit 15 changes the drive mode of the image sensor 5 and the display of the display unit 10. The control unit 15 changes the drive mode of the image sensor 5 to the horizontal / vertical non-addition drive mode for celestial AF, and changes the display on the display unit 10 from the live view display so far to the display in celestial AF. . The reason for changing the display on the display unit 10 is that the accumulation time of the image sensor 5 during celestial AF may become longer in units of seconds, and the AF time becomes longer according to the number of scan points. In addition, the update rate of the display unit may be slowed by the celestial AF. In this way, it is possible to prevent the user from misinterpreting as a failure or the like during celestial AF. At this time, the control unit 15 may calculate the time required for the AF process and further display the elapsed time or the remaining time of the AF process. When the control unit 15 changes the drive mode of the image sensor 5 and the display of the display unit 10, the process proceeds to S208.

  In S208, the control unit 15 controls the focus lens group 3 to control the operation of the AF process. First, scanning according to the present embodiment will be described with reference to FIG. 4 in which the horizontal axis represents the focus lens position and the vertical axis represents the AF evaluation value. In the scan in the present embodiment, a relatively narrow range is scanned around the infinity adjustment position of the focus lens group 3 (position measured at the time of manufacture and corrected for positional deviation). Especially when scanning very dark objects such as celestial bodies, the accumulation time for obtaining the AF evaluation value for one screen may be several seconds, so the time required for scanning is fatal by limiting the scan range. Can be prevented from becoming longer. The scan interval is set as wide as possible so that the in-focus position can be searched. For example, the scan interval is set to about 3 to 5 times the depth obtained by the open aperture value (the aperture value in the most open state). The number of scan points is determined according to the difference between the environment where the infinity adjustment position was measured at the time of manufacture and the environment during shooting (and during AF processing). For example, in the present embodiment, the environment at the time of manufacturing, such as measuring at a predetermined temperature with the camera horizontal, is recorded, and the ambient temperature and the internal temperature of the taking lens barrel 31 are simultaneously measured by a thermometer (not shown). To do. At this time, the control unit 15 can increase or decrease the number of scan points by comparing the temperatures and camera postures during AF processing and manufacturing.

  For example, when the number of scan points is 7, the control unit 15 acquires the output (AF evaluation value signal) of the AF processing unit 14 while moving the focus lens position to each point, and the focus at which the AF evaluation value is maximized. Determine the lens position. More specifically, the control unit 15 first controls the focus drive motor 22 via the second motor drive unit 19 to move the focus lens group 3 to the scan start position (“A” in FIG. 4). . The control unit 15 drives the focus lens group 3 to each scan position, and when the drive of the focus lens group 3 ends at the scan end position (“B” in FIG. 4), the acquired AF evaluation value is maximized. (C in FIG. 4) is obtained. Thereafter, the control unit 15 drives the focus lens group 3 to a position where the AF evaluation value is maximized. In this manner, the control unit 15 also serves as a focus position determination unit in addition to the focus position drive control unit.

  The acquisition of the AF evaluation value can be performed at predetermined scan intervals without performing the stop positions of all the focus lens groups 3 in order to speed up the AF process. That is, in the example shown in FIG. 4, AF evaluation values may be acquired at points a1 to a3. In such a case, the in-focus position C may be estimated by performing an interpolation process using the point where the AF evaluation value becomes the maximum value and the points before and after the point. Specifically, when the position of the focus lens group 3 is X1, the AF evaluation value is the maximum value Y1 (a1), and the AF evaluation values acquired at the front and rear positions X2 and X3 are Y2 (a2) and Y3, respectively. In the case of (a3), the position X0 of the in-focus position C is obtained as follows. Note that Y1> Y3 and Y1 ≧ Y2.

  Further, the reliability of the AF evaluation value may be evaluated before obtaining the point (C in FIG. 3) at which the AF evaluation value becomes the maximum value by the interpolation processing described above. When the reliability is sufficiently high, the point at which the AF evaluation value becomes the maximum value is obtained, and it is determined that the celestial AF is successful. In addition, about the reliability determination method of AF evaluation value, since the method described, for example in patent 0435422 or patent 04185741 can be used, description is abbreviate | omitted.

  In addition, the number of scan points when the elevation angle is about 30 ° ± 15 ° C. and the temperature is normal temperature is set to 7 points, for example. At this time, when the elevation angle is almost horizontal (for example, less than about ± 15 degrees) and the ambient temperature at the time of manufacture and the temperature at the time of photographing of the photographing lens barrel 31 are substantially equal (for example, the difference is within 2 degrees). May further reduce the number of scan points. The output (AF evaluation value signal) of the AF processing unit 14 is acquired while moving the focus lens group 3 from the “A ′” point to the “B ′” point shown in FIG. The focus lens group 3 is driven to that position. On the other hand, if you are shooting near the zenith, or if the shooting temperature is very high or low, such as when it is very different from the manufacturing environment, increase the scan range by increasing the number of scan points to 9 or more. Yes. The number of scan points is determined in this way when it is highly probable that astronomical photography is performed while avoiding a long time for celestial AF until the possibility of performing astronomical photography is low. This is to achieve both of capturing the in-focus position.

  In S209, the control unit 15 controls the imaging device 5 so that the driving mode of the imaging device 5 is returned from the driving mode for celestial AF to the driving for displaying the live image, and the display on the display unit 10 is also returned to the display of the live image. At this time, the control unit 15 displays the success or failure of the celestial AF on the display unit 10 in order to notify the user of the success or failure of the celestial AF performed in S208. If the celestial AF is successful, for example, the LED 29 is turned on and at the same time a process such as displaying a green frame on the screen of the display unit is performed. On the other hand, if the celestial AF is not successful, the LED 29 is blinked and a process such as displaying a yellow frame on the display unit 10 is performed.

  In S210, the control unit 15 acquires the state of SW1, and determines whether SW1 is on. If it is determined that SW1 is on, the process advances to S211 to execute the astronomical AE process. . On the other hand, if it is determined that SW1 is not turned on, the process returns to S201 again to perform live view display on the display unit 10.

  In S211, the control unit 15 performs astronomical AE processing. In the celestial AE process, the aperture value of the aperture 4, the accumulation time of the image sensor, and the amplification factor (that is, the exposure condition during the main photographing) that are properly exposed during the main photographing are determined based on the photometric value acquired in S204. To do. As described above, even if the image of a bright celestial image of 1st to 2nd stars may be saturated in the captured image, it is preferable that a dark celestial body such as 3rd to 6th stars is recognized on the image. Therefore, an exposure condition that can photograph a dark celestial body of 3-6 mag stars is selected. Note that a photometric value may be acquired from the AE processing unit 13 at the beginning of the process of this step.

  In S212, the control unit 15 acquires the state of SW2, and determines whether SW2 is on. If it is determined that SW2 is on, the process proceeds to S213. If it is determined that SW2 is not turned on, the process returns to S201.

  In S213, the control unit 15 ends the series of processes after performing the exposure process for performing the imaging set in S211. On the other hand, if it is determined that SW2 is not turned on, the control unit 15 returns the process to S201 and causes the display unit 10 to display a live image.

  Note that the program diagram of FIG. 3 is merely an example, and different program diagrams can be used if various conditions are different, for example, the open F value of the photographing lens barrel is different. Further, the above-described upper limit value and lower limit value can be appropriately adjusted according to the difference in the program diagram, optimization for the use environment, and the like.

  As described above, in the present invention, in the AF processing when the mode for photographing the starry sky is set, an aperture value and an accumulation time that reduce the predetermined exposure amount from the appropriate exposure for obtaining the actual captured image. In addition, the combination of the amplification factors (that is, the exposure conditions) is obtained, and the exposure conditions for the AF processing and the actual photographing are made different. Furthermore, exposure conditions suitable for astronomical photography are set within a predetermined range. By doing so, it is possible to perform appropriate automatic focus adjustment with reduced influence of brightness due to the surrounding environment when shooting including a point light source subject. In particular, the saturation of the point light source subject can be prevented and the necessary exposure amount can be secured, and more accurate AF processing can be performed.

(Embodiment 2)
Next, Embodiment 2 will be described. In Embodiment 2 of the present invention, based on the outputs from the motion vector detection unit 37, shake detection unit 34, AF processing unit 14, and AE processing unit, it is first estimated whether or not a celestial object is being imaged in the astrophotography mode. Then, it is determined whether or not to perform the celestial AF process according to the estimated result. For this reason, the configuration of the digital camera 1 is the same as that of the first embodiment, and the shooting operation according to the present embodiment is also common except for an astronomical shooting estimation process described later. For this reason, the same configurations and steps will be denoted by the same reference numerals, and redundant description will be omitted, and differences will be mainly described.

  Hereinafter, the shooting process of the digital camera 1 according to the present embodiment will be described with reference to FIG. Similarly to the first embodiment, the main photographing process is started when, for example, the user sets the operation mode of the digital camera 1 to the photographing (recording) mode, and is executed by the control unit 15 controlling each part of the digital camera 1. .

  The control unit 15 performs the processes of S201 to S202. If the control unit 15 determines in S202 that the astronomical shooting mode is set, the process proceeds to S501.

  In S501, the control unit 15 acquires a photometric value. The photometric value is obtained based on the output value (for example, subject luminance value) of the AE processing unit 13, the accumulation time of the image sensor 5 when the output value is acquired, the signal amplification factor, and the aperture value of the aperture 4.

  In S502, the control unit 15 performs an astronomical object estimation process to be described later, and estimates whether or not a celestial object is being photographed. Then, in S503, when it is estimated that the celestial object is captured, the control unit 15 proceeds to S504, and when it is estimated that the celestial object is not photographed, the control unit 15 proceeds to S505. When the process proceeds to S505, the control unit 15 determines whether the illuminance at the time of shooting is lower than a predetermined illuminance from the photometric value acquired in S501. If the illuminance is low, the process proceeds to S220. A process of driving the focus lens group 3 to a fixed point is performed. On the other hand, if the illumination is not low, the process proceeds to S230 to perform normal shooting.

  In S504, the control unit 15 determines whether or not the celestial AF start button has been operated by the user to instruct the start of the AF process for the celestial object. When it is determined that the celestial AF start button has not been operated, the control unit 15 proceeds to S210. On the other hand, when it is determined that the celestial AF start button has been operated, the control unit 15 proceeds to S206.

  The subsequent processes in S206 to S213 are performed in the same manner as in the first embodiment, and a series of operations of the main photographing process is finished.

(A series of operations related to astrophotography estimation processing)
Next, a series of operations related to the astrophotography estimation process performed in S502 will be described with reference to FIG.

  In S601, the control unit 15 determines whether the illuminance at the time of shooting is lower than a predetermined illuminance based on the photometric value acquired in S501. If the controller 15 determines that the illumination is not low, the process proceeds to S620. When it is determined that the illuminance is lower than the predetermined illuminance, the output signal of the shake detection unit 34 is acquired in S602.

  In step S603, the control unit 15 determines whether a tripod is used for shooting. The control unit 15 determines whether or not the tripod is used based on the time-series change of the output signal acquired from the shake detection unit 34. For example, the control unit 15 compares the camera shake amount of the digital camera 1 with a threshold value for determining the use of a tripod. If the control unit 15 determines that shooting is performed using the tripod, the process proceeds to S604. On the other hand, if it is determined that the shooting is not performed using a tripod, the process proceeds to S620. More specifically, the control unit 15 determines that the tripod is used when the time-series change of the output signal value of the shake detection unit 34 is smaller than the threshold value and the absolute value thereof is also smaller than the threshold value. In fact, even if you are not using a tripod, it is determined that you are using a tripod if it is fixed to some equipment. However, the time-series change period to be taken into consideration is set to a long time of several seconds or more so that it is not determined that a tripod is used when the amount of camera shake is small in handheld shooting.

  In step S604, the control unit 15 acquires the output signal of the motion vector detection unit 37, and in step S605, the control unit 15 uses the acquired output signal of the shake detection unit 34 and the acquired output signal of the motion vector detection unit 37 to generate an image. Find the movement of the subject above. The movement of the subject on the image is obtained from the relative relationship between the output signal of the motion vector detection unit 37 and the output signal of the shake detection unit 34. Therefore, the movement of the subject on the image obtained in this step is the movement of the subject on the image when there is no camera shake (that is, the actual movement of the subject).

  In S606, the control unit 15 determines whether or not the obtained movement is a celestial movement based on the movement of the subject on the image obtained in S604. If it cannot be determined that the movement is a celestial movement, the process proceeds to S620. For example, the control unit 15 determines whether or not the movement of the subject obtained in time series is moving in the same direction in the same direction for a certain period or more. That is, the movement of the celestial body is determined based on the magnitude of the movement of the subject on the image (the amount of movement of the bright spot within the screen) and its mode (the method of moving the bright spot). If the control unit 15 determines that the object moves, the process proceeds to S607.

  In step S <b> 607, the control unit 15 acquires an AF evaluation value signal from the AF processing unit 14. However, the AF evaluation value signal acquired here is not the AF evaluation value corresponding to the above-described contour component amount on the high frequency side, but the integrated value (AF of the luminance signal within the AF frame not passing through the high-pass filter (HPF)). The three AF evaluation values are the evaluation value YI), the maximum value (AF evaluation value YP), and the difference between the maximum value and the minimum value (AF evaluation value MM).

  The AF evaluation value YP can be affected by noise simply by taking the maximum value. For this reason, in this embodiment, for example, signal values are rearranged in descending order from the maximum value of the signal in the AF frame without passing through the HPF, and from the maximum value to several percent (for example, 2%) of the number of pixels in the AF frame. A value obtained by taking the average of these may be used as the AF evaluation value YP. Similarly, since the AF evaluation value MM can be influenced by noise included in the signal, for example, the signal values are arranged in ascending order from the minimum value of the signal in the AF frame without passing through the HPF, and the number of pixels in the AF frame is determined from the minimum value. A value obtained by averaging values up to several% (for example, 2%) may be used as the minimum evaluation value YB. The difference between the AF evaluation value YP and the minimum evaluation value YB obtained in this way may be used as the AF evaluation value MM. In the present embodiment, the control unit 15 acquires the three AF evaluation values obtained by the AF processing unit 14, but the control unit 15 uses the three AF evaluation values based on the signal values obtained from the AF processing unit 14. You may ask for.

  In S608, the control unit 15 determines whether the acquired AF evaluation value YI is small. The control unit 15 determines that the AF evaluation value YI is small when the AF evaluation value YI is smaller than a predetermined threshold TI. Here, in the case of astronomical photography, the AF evaluation value YI is assumed to be small because most of the subject is a dark sky. If the controller 15 determines that the AF evaluation value YI is small, the process proceeds to S609. If the controller 15 determines that the AF evaluation value YI is large, the process proceeds to S620.

  In S609, the control unit 15 determines whether the AF evaluation value YP is large. The control unit 15 determines that the AF evaluation value YP is large when the AF evaluation value YP is larger than a predetermined threshold value TP. Here, when shooting a celestial object in astrophotography, the AF evaluation value YP is assumed to be a value close to the maximum value of the signal output value. When it is determined that the AF evaluation value YP is large, the control unit 15 proceeds the process to S610, and when it is determined that the AF evaluation value YP is small, the process proceeds to S620.

  In step S610, the control unit 15 determines whether the AF evaluation value MM is large. When the AF evaluation value MM is larger than a predetermined threshold TM, it is determined that the AF evaluation value MM is large. Here, in the case of astronomical photography, since there are dark sky and bright celestial bodies within the AF frame, it is assumed that the AF evaluation value MM, which is the difference between them, is large. That is, the control unit 15 estimates whether or not the astrophotography is performed from the tendency of the AF evaluation value acquired in S607. If the controller 15 determines that the AF evaluation value MM is large, the process proceeds to S611. If the controller 15 determines that the AF evaluation value MM is small, the process proceeds to S620.

  In S <b> 611, the control unit 15 acquires the elevation angle of the digital camera 1 using the output of the shake detection unit 34. Here, the acquisition of the elevation angle of the digital camera 1 can be performed by measuring a shake in the pitch direction over time in shake detection, for example. . If the digital camera 1 detects upward deflection in the pitch direction when the digital camera 1 is directed upward, and then detects no downward deflection in the pitch direction that cancels out the magnitude of the upward deflection, at that time It can be estimated how much the digital camera 1 is facing upward (elevation angle). In the case of astronomical photography, it is assumed that there is a certain degree of elevation angle. Therefore, in this embodiment, the elevation angle is determined on the assumption that at least the digital camera 1 will not face downward in astronomical photography. That is, in S612, the control unit 15 compares the obtained elevation angle of the digital camera 1 with a predetermined elevation angle threshold value (for example, 0) to determine whether the elevation angle is equal to or greater than the threshold value. If the controller 15 determines that the acquired elevation angle is greater than or equal to the threshold, the process proceeds to S613. If the controller 15 determines that the acquired elevation angle is less than the threshold, the process proceeds to S620.

  In step S613, the control unit 15 estimates that the current shooting is astronomical shooting, returns the processing to the caller, and waits for the celestial AF start button to be pressed. On the other hand, in S620, it is presumed that it is not astronomical photography, and in S621, control is performed to notify the display unit 10 of a warning. For example, the display unit 10 displays that there is a possibility of shooting an object other than the celestial body in the astrophotography mode. However, in addition to displaying a warning by characters on the display unit 10, notification of the warning may be performed by a method such as changing the display of an LED or the like.

  As described above, in the present embodiment, the movement of the subject on the image, the maximum or minimum value of the AF evaluation value, and the elevation angle of the digital camera are acquired, and an estimation process is performed to determine whether or not astronomical photography is being performed. I did it. In this way, even when the shooting mode is set to the astronomical shooting mode, it is possible to prevent unconditionally performing the astronomical AF process and performing an AF process that takes a relatively long time.

(Other embodiments)
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

DESCRIPTION OF SYMBOLS 3 ... Focus lens group, 4 ... Diaphragm, 5 ... Imaging device, 6 ... Imaging part, 10 ... Display part, 13 ... AE process part, 14 ... AF process part, 15 ... Control part, 18 ... 1st motor drive part, 24 ... operation unit, 37 ... motion vector detection unit

Claims (13)

Acquisition means for exposing the imaging device at a plurality of imaging positions while changing the imaging position in the optical axis direction of the optical image of the subject to acquire a plurality of image data for focus adjustment;
Photometric means for measuring the brightness of a subject including a point light source subject;
Determining means for determining an exposure condition for acquiring a plurality of image data for focus adjustment based on the luminance measured by the photometric means;
Using the plurality of image data acquired under the exposure conditions, an evaluation value acquisition unit that acquires an evaluation value representing the degree of focus for each of the plurality of imaging positions;
Focusing position determination means for determining a focusing position based on the evaluation value;
Setting means for setting a shooting mode for shooting the point light source subject at an illuminance lower than a predetermined illuminance;
In the state where a plurality of pieces of image data for the focus adjustment are acquired when the shooting mode is set, the determining unit is configured to obtain a proper captured image obtained based on the measured luminance. A focus adjustment apparatus, wherein an exposure condition is determined so that an exposure amount is reduced with respect to exposure and a predetermined exposure amount range is obtained.   The determining means reduces the exposure amount with respect to the appropriate exposure for obtaining the actual captured image, and as a result, when the decreased exposure amount exceeds the upper limit of the predetermined exposure amount range, the predetermined amount is determined. The upper limit of the exposure amount range, and when the reduced exposure amount is less than the lower limit of the predetermined exposure amount range, the lower limit value of the predetermined exposure amount range. The focus adjustment apparatus according to claim 1, wherein the exposure condition is determined.   The focus according to claim 2, wherein the determination unit determines a combination of an exposure time, an aperture value, and sensitivity of the image sensor as an exposure condition for acquiring a plurality of image data for focus adjustment. Adjusting device.   The predetermined exposure amount range is an exposure amount range for performing focus adjustment on the point light source subject in astronomical photography, and is included in a partial area on the image corresponding to the image data. The focus adjusting apparatus according to claim 3, wherein the focus adjusting apparatus has a range determined based on at least the distance.   The upper limit value of the predetermined exposure amount range is an exposure that does not saturate the luminance in the partial area on the image when the partial area on the image includes a point light source subject brighter than a predetermined equal star. The focus adjustment apparatus according to claim 4, wherein the focus adjustment apparatus is a quantity.   The lower limit value of the predetermined exposure amount range is such that when a partial point area on the image includes a dark point light source subject of a predetermined equal star or less, the luminance in the partial area on the image is predetermined. 6. The focus adjustment apparatus according to claim 4, wherein the exposure amount is higher than the luminance value. Further comprising estimation means for estimating whether or not a celestial object is shot based on at least one of the movement of the subject, the luminance in a partial region on the image corresponding to the image data, and the elevation angle of the imaging device;
The determining unit determines an exposure condition for acquiring a plurality of image data for the focus adjustment when the estimating unit determines that the object is photographed, and the estimating unit does not photograph the object. The focus adjustment apparatus according to claim 1, wherein if it is determined, an exposure condition for acquiring a plurality of pieces of image data for focus adjustment is not determined.   The said estimation means estimates whether the celestial body is image | photographed based on the moving amount and aspect in the screen of the bright spot in the one part area | region on the said image. Focusing device.   The estimating means is based on whether the integrated value of the luminance in a partial region on the image is less than a predetermined integrated value and the luminance in the region is higher than a predetermined value indicating the luminance of the point light source subject. The focus adjustment apparatus according to claim 7, wherein it is estimated whether or not a celestial body is photographed. An imaging means including the imaging element and capable of changing an imaging position in the optical axis direction;
The focusing device according to any one of claims 1 to 9,
The imaging apparatus is characterized in that the imaging position in the optical axis direction is changed according to the in-focus position determined by the in-focus position determining means. An acquisition step in which the acquisition means exposes the image sensor at a plurality of imaging positions while changing the imaging position in the optical axis direction of the optical image of the subject, and acquires a plurality of image data for focus adjustment;
A photometric step in which the photometric means measures the luminance of a subject including a point light source subject;
A determining step for determining an exposure condition for acquiring a plurality of image data for focus adjustment based on the luminance measured in the photometric step;
An evaluation value acquisition step for acquiring an evaluation value representing the degree of focus for each of the plurality of imaging positions, using the plurality of image data acquired under the exposure conditions,
An in-focus position determining means for determining an in-focus position based on the evaluation value;
A setting step for setting a shooting mode for shooting the point light source subject at an illuminance lower than a predetermined illuminance;
In the state in which a plurality of image data for the focus adjustment is acquired when the shooting mode is set, the determining step is appropriate for obtaining an actual captured image obtained based on the measured luminance. A method of controlling a focus adjusting apparatus, comprising: reducing an exposure amount with respect to exposure and determining an exposure condition so as to be within a predetermined exposure amount range. In a control method for an image pickup apparatus including an image pickup device and having an image pickup unit capable of changing an image formation position in an optical axis direction,
An acquisition step in which the acquisition means exposes the image sensor at a plurality of imaging positions while changing the imaging position in the optical axis direction of the optical image of the subject, and acquires a plurality of image data for focus adjustment;
A photometric step in which the photometric means measures the luminance of a subject including a point light source subject;
A determining step for determining an exposure condition for acquiring a plurality of image data for focus adjustment based on the luminance measured in the photometric step;
An evaluation value acquisition step for acquiring an evaluation value representing the degree of focus for each of the plurality of imaging positions, using the plurality of image data acquired under the exposure conditions,
An in-focus position determining means for determining an in-focus position based on the evaluation value;
A setting step of setting a shooting mode for shooting the point light source subject at an illuminance lower than a predetermined illuminance;
The imaging means has an imaging step of changing the imaging position in the optical axis direction according to the in-focus position determined by the in-focus position determining means,
In the state in which a plurality of image data for the focus adjustment is acquired when the shooting mode is set, the determining step is appropriate for obtaining an actual captured image obtained based on the measured luminance. A method for controlling an imaging apparatus, comprising: reducing an exposure amount with respect to exposure and determining an exposure condition so as to be within a predetermined exposure amount range.   The program for functioning a computer as each means of the focus adjustment apparatus of any one of Claim 1 to 9.