JP6045231B2 - FOCUS ADJUSTMENT DEVICE, IMAGING DEVICE, AND IMAGING DEVICE CONTROL METHOD - Google Patents

Description

  The present invention relates to a focus adjustment device, an imaging device, and an imaging device control method used for a digital camera or the like.

  2. Description of the Related Art Conventionally, a phase difference detection method is generally well known as an automatic focusing device for a camera. In the phase difference detection method, a light beam from a subject that has passed through different exit pupil regions of the photographing lens is imaged on a pair of line sensors of the AF sensor. The defocus amount of the photographing lens is detected by calculating the relative position of the pair of subject images obtained by photoelectric conversion by the pair of line sensors, and the photographing lens is driven based on this.

  Various techniques for performing continuous shooting with a camera having this type of automatic focus adjustment device are disclosed in patent documents and the like.

  For example, Patent Document 1 discloses a technique for shortening the accumulation time by preferentially operating a high-sensitivity sensor during continuous shooting because high-speed continuous shooting cannot be performed when the signal accumulation time of the line sensor between the frames is increased. It is disclosed.

JP-A-6-186473

  However, in the technique disclosed in Patent Document 1 described above, when the luminance of the subject is extremely high, the sensor is strongly influenced by light shot noise, and a good SN ratio cannot be obtained. Since the AF sensor circuit amplifies the accumulated signal including noise by the signal amplifying circuit, the noise is also amplified together, and the output becomes a poor SN ratio.

(Object of invention)
An object of the present invention is to provide a focus adjustment device, an imaging device, and an imaging device capable of detecting an optimal defocus amount even in a scene where high-speed defocus detection is required or not. It is to provide a control method.

In order to achieve the above object, the focus adjustment apparatus of the present invention is configured by arranging a plurality of pairs of line sensors that respectively receive light that has passed through different pupil regions of a photographing lens for forming a subject image. A focus setting sensor, sensitivity setting means for setting the sensitivity for each pair of line sensors, and signals of which pair of line sensors of the plurality of pairs of line sensors. A selection unit that selects whether to use, a defocus amount detection unit that detects a defocus amount using signals of a pair of line sensors selected by the selection unit, and the defocus amount based on the detected defocus amount. In a focus adjustment apparatus having a lens driving means for driving a photographic lens, it has an operation mode setting means for switching between a first operation mode and a second operation mode. The first operation mode is a mode in which the multiple pairs of line sensors are set to different sensitivities and signals are accumulated simultaneously, and the second operation mode is set to the same sensitivity for the multiple pairs of line sensors. In this mode, the signal is accumulated a plurality of times with different sensitivities.

  According to the present invention, it is possible to detect the optimum defocus amount regardless of whether the scene requires high-speed defocus detection or not.

It is a block diagram of the digital camera which concerns on the Example of this invention. It is a block diagram of the optical system in an Example. It is a figure which shows arrangement | positioning and AF frame of the line sensor in an Example. It is a figure which shows the structure of the AF sensor of an Example. It is a figure explaining the control method of the PB signal and accumulation time in an Example. It is a circuit diagram of the pixel which comprises the line sensor in an Example. 7 is a timing chart showing the operation of the circuit of FIG. It is a figure which shows the accumulation time and output voltage when a brightness | luminance is made constant. It is a flowchart of the focus adjustment operation | movement in an Example. It is a flowchart of the reliability determination in an Example. It is a flowchart of the defocus detection calculation in an Example. It is the figure which showed the relationship between the brightness | luminance of a to-be-photographed object, and S / N ratio. It is a figure for demonstrating reliability determination. It is a figure for demonstrating an image coincidence degree. It is a figure for demonstrating the image surface position prediction and lens drive of a photographic lens in moving object imaging | photography.

  The mode for carrying out the present invention is as described in the following examples.

  FIG. 1 is a block diagram illustrating a configuration of a digital camera as an imaging apparatus according to an embodiment of the present invention. A signal input circuit 204, an image sensor (image sensor) 206, and an AE sensor 207 for detecting a switch group 214 for various camera operations are connected to the camera microcomputer (hereinafter referred to as CPU) 100. . A shutter control circuit 208 for controlling the shutter magnets 218a and 218b and the AF sensor 101 are also connected. Further, a signal 215 is transmitted to the photographing lens 300 (see FIG. 2) via the lens communication circuit 205, and the focal position and the aperture are controlled. The operation of the camera is determined by the setting of the switch group 214.

  The AF sensor 101 includes a line sensor. By controlling the AF sensor 101 by the CPU 100, the defocus amount is detected from the contrast distribution of the subject obtained by the line sensor, and the photographing lens 300 (see FIG. 2). Control the focal position of the.

  The CPU 100 controls the AE sensor 207 to detect the luminance of the subject, and determines the aperture value and shutter speed of the photographic lens 300. Then, the aperture value control, lens drive control, and lens information acquisition are performed via the lens communication circuit 205. Further, the shutter speed is controlled by adjusting the energization time of the magnets 218 a and 218 b via the shutter control circuit 208, and the photographing operation is performed by controlling the image sensor 206.

  In the CPU 100, there is a storage circuit 209 such as a ROM storing a program for controlling the camera operation, a RAM for storing variables, and an EEPROM (electrical erasing and writable memory) for storing various parameters. Built in.

  Next, the optical configuration of the digital camera will be described with reference to FIG. Most of the light beam from the subject incident through the photographing lens 300 is reflected upward by the quick return mirror 305 and formed on the finder screen 303 as a subject image. The user of the digital camera can observe this image through the pentaprism 301 and the eyepiece lens 302. A part of the photographic light beam passes through the quick return mirror 305, is bent downward by the rear sub-mirror 306, passes through the field mask 307, the field lens 311, the stop 308, and the secondary imaging lens 309, and the AF sensor (focus detection sensor). ) 101 is imaged. The focus state of the photographic lens 300 can be detected by processing an image signal obtained by photoelectrically converting this image. At the time of shooting, the quick return mirror 305 jumps up, and the total luminous flux is imaged on the image sensor 206, and the subject image is exposed.

  A focus detection method in the focus detection unit (in FIG. 2, composed of an optical system from the field mask 307 to the secondary imaging lens 309 and the AF sensor 101 in FIG. 2) is a known phase difference detection method. Then, it is possible to detect the focus state of a plurality of different areas in the screen.

  Here, the relationship between the line sensor on the AF sensor 101 and the AF frame in the shooting screen will be described with reference to FIGS. 3 (a) to 3 (c).

  FIG. 3A is a diagram illustrating the arrangement of the line sensors of the AF sensor 101. The line sensors 102-1a and 102-2a are arranged adjacent to each other in parallel so that the positions of the line sensors 102-1a and 102-2a are relatively shifted from each other by 1/2 pixel (in a staggered arrangement). ). Similarly, the line sensors 102-1b and 102-2b are arranged adjacently in parallel so that the positions of the line sensors 102-1b and 102-2b are relatively shifted from each other by 1/2 pixel (staggered). Are arranged). The line sensors 102-1a and 102-1b and the line sensors 102-2a and 102-2b are paired by the secondary imaging lens 309, and constitute the line sensors 102-1 and 102-2. The line sensors 102-1 and 102-2 are a pair of line sensors that receive light that has passed through different pupil regions of the photographing lens 300, and detect a phase difference between two images output from the pair of line sensors. By doing so, the defocus amount is detected. Similarly, the line sensors 102-3 and 102-4 and the line sensors 102-5 and 102-6 are also staggered. That is, a plurality of pairs of two line sensors that are shifted from each other in the longitudinal direction of the line sensor are arranged.

  FIG. 3B shows an example of the arrangement of the line sensor 102-1a and the line sensor 102-2a. Here, in order to make the explanation easy to understand, each pixel is composed of five pixels. The line sensor 102-1a includes photodiodes (light receiving units) 60-U1 to 60-U5, and the line sensor 102-2a includes photodiodes (light receiving units) 60-L1 to 60-L5. The photodiodes 60-U1 to 60-U5 and the photodiodes 60-L1 to 60-L5 are arranged at the same pixel pitch. As will be described later, the pixel includes a switch, a capacitor, and an amplifier circuit in addition to the photodiode. However, in FIG. 3B, switches, capacitors, and amplifier circuits are omitted, and only the photodiode and the element isolation region 61 are shown. The switches, capacitors, and amplifier circuits are provided in the light shielding layer 62, and are formed adjacent to the photodiode formation region.

  FIG. 3C is a diagram showing the arrangement of AF frames displayed in the viewfinder 400 and the AF visual field 404 by the line sensor on the AF sensor 101. The AF frame 401 includes the line sensor 102-1 and the line sensor 102-2, the AF frame 402 includes the line sensor 102-3 and the line sensor 102-4, and the AF frame 403 includes the line sensor 102-5 and the line sensor 102-6. Each is arranged. By arranging two sets of line sensors close to each other in one AF frame and halving the pixel pitch equivalently (by staggering), it is possible to improve focus detection accuracy for a high-frequency subject.

  A detailed circuit configuration of the AF sensor 101 will be described with reference to a block diagram of FIG. The subject image formed by the secondary imaging lens 309 is photoelectrically converted by the line sensors 102a and 102b and accumulated as electric charges. The accumulated charge is output as a voltage by the amplifier circuit. The line sensors 102a and 102b have a sensitivity setting circuit 103 for each line. The line selection circuit 104 selects one line among a plurality of lines of the line sensors 102a and 102b. And it has the function to transmit the accumulation | storage signal of a line sensor to the PB contrast detection circuit mentioned later.

  The PB contrast detection circuit 105 detects the largest signal (hereinafter referred to as Peak signal) and the smallest signal (hereinafter referred to as Bottom signal) among the pixel signals of the line selected by the line selection circuit 104. Then, a difference signal (hereinafter referred to as a PB signal) between the Peak signal and the Bottom signal is output to the accumulation stop determination circuit 106.

  FIG. 5 is a diagram showing the relationship between the signal amount of the PB signal, which is an output signal from the PB contrast detection circuit 105, and the accumulation time. The accumulation time 0 is the accumulation start timing, and the PB signal increases as time elapses. The accumulation stop determination circuit 106 compares and determines the PB signal and the accumulation stop level. When the PB signal becomes larger than the accumulation stop level, an accumulation stop signal is output to the line sensors 102a and 102b in order to stop accumulation of pixels in the line selected by the line selection circuit 104. Further, the CPU 100 outputs an accumulation end signal and line information for which accumulation has been completed to the CPU 100. If the PB signal does not reach the target value within a predetermined time, an accumulation stop signal is output to the line sensors 102a and 102b in order to forcibly stop the accumulation.

  The pixel signals accumulated by the line sensors 102 a and 102 b are output to the output circuit 108 as pixel signals for each pixel by driving the shift register 107 by the CPU 100. The output circuit 108 extracts a contrast component from the pixel signal, performs processing such as amplification, and outputs the processed signal to an A / D converter (not shown) of the CPU 100.

  FIG. 6 shows a specific circuit diagram of the pixels constituting the line sensor. In FIG. 6, the line sensor includes a sensor pixel circuit unit and a noise removal circuit unit. The sensor pixel circuit unit includes a photodiode PD, capacitors CL, CPD, CS, a current source 1, a current source 2, MOS transistors M1, M2, M3, M4, and M5, and switches SWRES, SWSENS, and SWCH. The noise removal circuit unit includes a capacitor CCLAMP, an amplifier circuit AMP1, and switches SWPTS1, SWPTS2, SWPTN1, SWPTN2, SWCLAMP, and SWPHn. The voltage VRES is a reset potential, and the voltage VCLAMP is a clamp potential. The output VOUT is connected to the line selection circuit 104. The capacitance CPD is a parasitic capacitance generated by a photodiode, a MOS transistor, a switch, a wiring, or the like. The switches SWRES, SWSENS, SWCH, SWPTS1, SWPTS2, SWPTN1, SWPTN2, SWCLAMP, and SWPHn are respectively turned on / off by signals φRES, φSENS, φCH, φPTS1, φPTS2, φPTN1, φPTN2, φCLAMP, and φPHn.

  The operation of the above circuit will be described with reference to the timing chart of FIG. First, the sensitivity is set by φSENS. When φSENS is at a low level, SWSENS is turned off, only the capacitor CPD is connected to the transistor M1, and the sensor is set to high sensitivity. When φSENS is at a high level, SWSENS is turned on, capacitors CPD and CL are connected to the transistor M1, and the sensor is set to low sensitivity. Hereinafter, the operation when the low sensitivity is set will be described.

The switches SWRES, SWCH, SWPTN1, SWPTN2, and SWCLAMP are turned on to reset the capacitors CL, CS, and CCLAMP. Thereafter (after pixel reset), the switches SWRES, SWPTN2, and SWPTN1 are sequentially turned off. At this time, the offset voltage of the sensor pixel circuit unit is VOS1, the offset voltage of the amplifier circuit AMP1 is VOS2, and the noise voltage generated by turning off the switch SWRES is VN1. Then, the capacity CCLAMP is
VCP = (VRES + VOS1 + VOS2 + VN1) −VCLAMP
The charge corresponding to is charged and noise is stored. Further, the SWPTS1 is turned on to connect the capacitor CCLAMP and the amplifier circuit AMP1, and then the SWCLAMP is turned off to complete the noise storing operation.

Next, the switches SWPTS2 and SWPHn are turned on to start signal accumulation. When the accumulation signal is S, the output VSENS of the sensor pixel circuit unit is expressed by the following equation.
VSENS = VRES + VOS1 + VN1 + S
Further, the input VIN of the amplifier circuit AMP1 is subtracted by the noise voltage stored in the capacitor CCLAMP described above, and is expressed by the following equation.
VIN = VSENS−VCP = S−VOS2 + VCLAMP
Therefore, the sensor output VOUT is expressed by the following equation.
VOUT = VIN + VOS2 = S + VCLAMP

  As described above, noise can be removed from the accumulated signal at the time of signal output by the noise removal circuit unit, and highly accurate PB contrast detection can be performed.

  At the end of the accumulation, the switch SWCH is turned off to hold the charge in the capacitor CS.

  When reading a signal, a line sensor read by the line selection circuit 104 is selected, and SWPHn is sequentially turned on by a signal from the shift register 107, and the signal is output to the output circuit 108. At this time, an accumulated signal from which noise has been removed by the noise removing circuit unit is obtained as in signal accumulation.

  FIG. 8 shows the relationship between the accumulation time and the output voltage when the luminance is constant. The accumulation time 0 is the accumulation start timing, and the output voltage increases as time elapses. The slope of the output voltage of the run sensor set to high sensitivity is larger than the slope of the output voltage of the line sensor set to low sensitivity.

  The operation of the focus adjustment apparatus configured as described above will be described in detail based on the flowchart of FIG.

  In this embodiment, it is assumed that the continuous shooting mode is set and servo control suitable for continuous shooting of a moving subject is set. At the time of servo control, as shown in FIG. 15, the defocus amount is continuously detected even during continuous shooting, and the lens drive amount is updated. Furthermore, the change of the image plane position obtained from the past multiple detection defocus amounts and the driving amount of the photographing lens is regarded as a predetermined function according to time, and the function is obtained by a statistical method to predict the driving of the photographing lens. It is carried out. That is, assuming that the exposure operation is performed at the point A in FIG. 15, the lens drive by adding the moving object prediction correction amount to the defocus amount at the next focus adjustment is completed before the next exposure, so that the exposure from the last focus adjustment is performed. The subject can be focused in anticipation of the movement of the subject during the release time lag until the start of.

  When a focus adjustment start signal is received by operating the switch group 214, the focus adjustment operation is started by controlling the AF sensor 101 from the CPU 100. Here, for example, it is assumed that the AF frame 401 shown in FIG. 3C is selected.

  In step S800, the set continuous shooting speed is determined. If the continuous shooting speed is faster than the predetermined amount stored in the digital camera, the first operation for simultaneously storing signals by setting the line sensors corresponding to the AF frame 401 to different sensitivities for one frame shooting The mode (steps S801 to S805) is executed.

  In step S801, the line sensor 102-1 is set to high sensitivity, and the line sensor 102-2 is set to low sensitivity.

  In the next step S802, the CPU 100 controls the AF sensor 101, and simultaneously starts signal accumulation operations by the line sensor 102-1 and the line sensor 102-2. Then, in the next step S803, an accumulation stop determination operation is performed. The CPU 100 detects an accumulation stop signal output from the AF sensor 101. Then, the operation in step S803 is repeated until the accumulation stop signal is detected. If the accumulation stop signal is detected, the process proceeds to the signal reading operation in step S804. In step S804, a pixel signal reading operation is performed. In step S805, the reliability of the read pixel signal is determined.

  A flowchart of the reliability determination process is shown in FIG. In the reliability determination, the reliability of the pixel signal is determined from the contrast and luminance information of the subject, and the line sensor is selected based on the determination result. Here, the reliability determination of the pixel signal will be described. FIG. 12 shows the relationship between the brightness of the subject and the SN ratio of the AF sensor output.

  FIG. 12A is a diagram when the contrast of the subject is higher than a predetermined value Cth. When the brightness of the subject is high, accumulation control is performed so that the PB signal is constant, so the SN ratio is a constant value. In this luminance range, light shot noise is dominant. Since the line sensor set to low sensitivity has a larger dynamic range of the pixel portion than the line sensor set to high sensitivity, the luminance at which the SN ratio is constant is high, and the influence of light shot noise is also small. For this reason, the SN ratio at high luminance is larger than that of the line sensor set to high sensitivity. Here, the luminance at which the SN ratio of the line sensor is low sensitivity sensor> high sensitivity sensor is L1.

  When the luminance of the subject is low, the PB signal amount of the line sensor does not reach the accumulation stop level within a predetermined accumulation time, and the accumulation is forcibly stopped. Below the luminance at which the accumulation is forcibly stopped, the SN ratio of the AF sensor output deteriorates rapidly. This is because noise due to dark current, noise generated in the circuit, and the like do not change while the signal amount decreases. The line sensor set to high sensitivity has a low luminance at which accumulation is forcibly stopped, and the SN ratio at low luminance is larger than that of the line sensor set to low sensitivity. Here, the luminance at which the SN ratio of the line sensor is high sensitivity sensor> low sensitivity sensor is L2.

  When the luminance of the subject is between L1 and L2, the SN ratio of the line sensor set to low sensitivity and the line sensor set to high sensitivity is approximately the same, and improves as the luminance increases.

  FIG. 12B is a diagram when the contrast of the subject is equal to or less than a predetermined value Cth. When the contrast of the subject is low, the signal from the line sensor is a contrast component of the subject, so the amplitude is small. For this reason, it is easily affected by light shot noise at high luminance, dark current at low luminance and noise caused by the circuit, and the SN ratio is deteriorated as a whole. In addition, when the luminance ratio of the line sensor at the time of high luminance is L3> L3> L3, the luminance becomes low luminance sensor> high luminance sensor. On the other hand, when the luminance of the line sensor at the time of low luminance is L4 where L4 is the luminance where high sensitivity sensor> low sensitivity sensor, L2 <L4.

  FIG. 13 shows the relationship between the contrast and brightness of the subject, the sensitivity of the line sensor, and the calculation accuracy of defocus detection. When the contrast of the subject is low, the influence of various noises becomes large, and the luminance range in which defocus detection calculation with high reliability can be performed with each sensitivity setting becomes narrow.

  As described above, in the first operation mode (S801 to S805), signal accumulation is performed at least once during the period from the end of exposure for the previous photographic frame to the start of exposure for the current photographic frame. .

  In FIG. 10, in step S900, the CPU 100 determines whether the contrast of the subject is larger than a predetermined threshold based on the read signal. Here, the threshold value is Cth. If the contrast of the subject is greater than Cth, the luminance of the subject is determined in step S901. The luminance of the subject is calculated from the read signal and the accumulation time. Alternatively, the measurement result of the AE sensor 207 may be used. If the luminance is higher than L1 in step S901, the process proceeds to step S902, and the signal of the line sensor 102-2 set to low sensitivity is selected. If the luminance is lower than L2, the process proceeds to step S903, and the signal of the line sensor 102-1 set to high sensitivity is selected. If the luminance is not more than L1 and not less than L2, the process proceeds to step S904, and a value obtained by adding the signals of the line sensor 102-1 and the line sensor 102-2 is set as a pixel signal.

  If it is determined in step S900 that the contrast of the subject is Cth or less, the luminance of the subject is determined in step S905. If the luminance is higher than L3 in step S905, the process proceeds to step S906, and the signal of the line sensor 102-2 set to low sensitivity is selected. If the luminance is lower than L4, the process proceeds to step S907, and the signal of the line sensor 102-1 set to high sensitivity is selected. If the luminance is not more than L3 and not less than L4, the process proceeds to step S908, and a value obtained by adding the line sensor 102-1 and the line sensor 102-2 is set as a pixel signal.

  The CPU 100 that executes steps S902 to S904 and S906 to S908 constitutes a selection unit.

  Returning to FIG. 9, in step S800, if the continuous shooting speed is slower than the predetermined amount stored in the camera, the line sensor corresponding to the AF frame 401 is set to low sensitivity for each frame shooting and the signal is set. The second operation mode (steps S806 to S814) is performed in which accumulation is performed and the line sensor is set to high sensitivity and signal accumulation is performed again. That is, the second operation mode is a mode in which a plurality of pairs of line sensors are set to the same sensitivity and a plurality of signal accumulations are performed with different sensitivities each time.

  In FIG. 9, the CPU 100 executing step S800 corresponds to an operation mode setting unit.

  In step S806, the line sensors 102-1 and 102-2 are set to low sensitivity.

  In the next step S807, the AF sensor 101 is controlled by the CPU 100, and the signal accumulation operation by the line sensor 102-1 and the line sensor 102-2 is started. Then, in the next step S808, an accumulation stop determination operation is performed. The CPU 100 detects an accumulation stop signal output from the AF sensor 101. Then, the operation of step S808 is repeated until the accumulation stop signal is detected. When the accumulation stop signal is detected, the process proceeds to the signal reading operation of step S809.

  In step S810, the line sensors 102-1 and 102-2 are set to high sensitivity.

  In the next step S811, the CPU 100 controls the AF sensor 101, and starts signal accumulation operations by the line sensor 102-1 and the line sensor 102-2. Then, in the next step S812, an accumulation stop determination operation is performed. The CPU 100 detects an accumulation stop signal output from the AF sensor 101. Then, the operation in step S812 is repeated until the accumulation stop signal is detected. If the accumulation stop signal is detected, the process proceeds to the signal reading operation in step S813.

  In step S814, the reliability of the pixel signal read in steps S809 and S813 is determined.

  Reliability determination follows the flowchart of FIG. In Steps S902 and S906, when it is determined that the low sensitivity line is selected, a value obtained by adding the signals of the line sensors 102-1 and 102-2 read in S809 is set as a pixel signal. In steps S903 and S907, when it is determined that a high-sensitivity line is selected, a value obtained by adding the signals of the line sensors 102-1 and 102-2 read in step S813 is set as a pixel signal. In steps S904 and S908, when it is determined that both the low sensitivity line and the high sensitivity line are selected, the signals of the line sensors 102-1 and 102-2 read out in S809 and the signals read out in S813. A value obtained by adding the signals of the line sensors 102-1 and 102-2 is defined as a pixel signal.

  As described above, in the second operation mode (S806 to S814), signal accumulation with different sensitivities is performed between the end of exposure for the previous photographic frame and the start of exposure for the current photographic frame. Perform at least once each.

  In step S815, based on the result of the reliability determination, a defocus detection calculation is performed using the read pixel signal.

  The defocus detection calculation will be described with reference to the flowchart of FIG.

  First, in step S1001, the lens position is acquired.

  In the subsequent step S1002, optical information such as sensitivity necessary for automatic focus adjustment, best focus correction value, defocus amount per pulse, and the like is obtained from the photographing lens. These are performed by communicating from the CPU 100 to the taking lens.

  In the next step S1003, an image shift amount is calculated by performing a correlation operation, and a defocus amount D is obtained. The defocus amount and the actual lens driving amount are in a non-linear relationship, and are generally approximated by a function corresponding to the defocus amount. In addition, the amount handled in the actual payout is not the length but the focus pulse number P that is the drive waveform to the photographing lens.

  Since the CPU 100 has acquired the optical information necessary for conversion to the focus pulse number P in step S1002, the CPU 100 calculates the defocus amount D as described above in step S1003, and in the next step S1004, Conversion to the number P of focus pulses, which is a lens driving amount, is performed. The lens driving amount (focus pulse number P) necessary for focusing is obtained in this way, and in the subsequent step S1005, the image plane position and its detection time are stored in the storage circuit of the CPU 100, and in the next step S1006. Correction of the number of focus pulses of the predicted moving body is performed. This is based on the change of the image plane position obtained from the past multiple detection defocus amounts stored in the storage device of the CPU 100 and the driving amount of the photographing lens, with the lens position acquired in step S1001 as the origin. By assuming that the function is a predetermined function and calculating the function using a statistical method, correction is performed by determining the lens drive amount in anticipation of subject movement during the release time lag from the last focus detection until exposure is started. .

  Returning to FIG. 9, in step S816, the lens is driven based on the calculation result of the defocus detection, and the automatic focus adjustment is terminated.

  In this embodiment, the threshold for determining the contrast of the subject is one, but it may be plural. In this case, subsequent luminance determination is performed for each threshold value. Further, the luminance may be obtained by calculating from the accumulation time. Alternatively, the threshold value for determining the contrast of the subject is determined by an arithmetic expression and may be variable. Further, reliability determination may be performed based on the degree of image coincidence of the output signals of the respective sensors of the line sensor pair. The waveform in FIG. 14A has a high image coincidence between the line sensor pair and high reliability. The waveform in FIG. 14B has low image coincidence due to the influence of noise and the like, and has low reliability.

  As described above, in this embodiment, the focus adjustment operation is switched according to the continuous shooting speed.

  When the shooting speed is high, the time allocated for single frame shooting is shortened, so the time available for focus adjustment is also reduced, and the signal cannot be stored twice by switching the sensitivity. Further, if sensitivity is set using the result of the previous frame and signal accumulation is performed once, focus adjustment is performed with an inappropriate sensitivity when the luminance of the subject changes between photographing frames. In this embodiment, the two pairs of line sensors corresponding to one AF frame are set to different sensitivities so that the focus adjustment is performed using the sensitivity suitable for the luminance of the subject even in one signal accumulation. Can do. Furthermore, when the luminance of the subject is medium, the defocus calculation is performed by adding the signals of the two pairs of line sensors, so that focus detection with higher accuracy is possible. Also, even if the subject brightness is low or high and only the signals from a pair of line sensors are used, the focus adjustment is performed at a high sampling rate, so the subject movement prediction accuracy is high and sufficient. Precision focus adjustment is possible.

  When the shooting speed is slow, the time allotted for single frame shooting becomes longer, so the time available for focus adjustment also increases, and the signal can be stored twice by switching the sensitivity.

  In the present embodiment, by performing signal accumulation with two pairs of line sensors once with low sensitivity and high sensitivity, high-precision focus adjustment can be performed in a wide luminance range. Further, the signal accumulation between the photographing frames may be performed by alternately switching the number of times and the sensitivity without impairing the set photographing speed. As a result, focus adjustment at a high sampling rate is possible, prediction accuracy of subject movement is high, and higher-precision focus adjustment is possible.

  As mentioned above, although the preferable Example of this invention was described, this invention is not limited to these Examples, A various deformation | transformation and change are possible within the range of the summary.

100 CPU
101 AF sensor 206 Imaging sensor 102-1 Line sensor 102-2 Line sensor 103 Sensitivity setting circuit

Claims (10)

A focus detection sensor configured by arranging a plurality of pairs of line sensors each receiving light that has passed through different pupil regions of a photographing lens for forming a subject image; and
Sensitivity setting means for setting the sensitivity for each pair of line sensors with respect to the plurality of pairs of line sensors,
Selecting means for selecting which pair of line sensors of the plurality of pairs of line sensors to use;
Defocus amount detection means for detecting a defocus amount using signals of a pair of line sensors selected by the selection means;
In a focus adjustment device having lens driving means for driving the photographing lens based on the detected defocus amount,
Having an operation mode setting means for switching between the first operation mode and the second operation mode;
In the first operation mode, the plurality of pairs of line sensors are set to different sensitivities, and signals are accumulated simultaneously.
The focus adjustment apparatus, wherein the second operation mode is a mode in which the plurality of pairs of line sensors are set to the same sensitivity and a plurality of signal accumulations are performed with different sensitivities each time.   The focus adjustment apparatus according to claim 1, wherein the plurality of pairs of line sensors are arranged adjacent to each other in the focus detection sensor. During continuous shooting, the operation mode setting means switches between the first operation mode and the second operation mode according to the continuous shooting speed,
In the first operation mode, signal accumulation is performed at least once during the period from the end of exposure to the previous photographing frame to the start of exposure to the current photographing frame,
In the second operation mode, signal accumulation at different sensitivities is performed at least once each from the end of exposure for the previous photographing frame to the start of exposure for the current photographing frame. The focus adjustment apparatus according to claim 1 or 2.   The operation mode setting means sets the first operation mode when the continuous shooting speed is higher than a predetermined speed, and sets the second operation mode when the continuous shooting speed is lower than the predetermined speed. The focus adjustment apparatus according to claim 1, wherein the focus adjustment apparatus is configured as described above. The selection means determines the reliability of the signal of the line sensor, and based on the determination result, which pair of line sensors of the plurality of pairs of line sensors is used to detect the defocus amount The focus adjustment apparatus according to claim 1, wherein the focus adjustment apparatus is selected. The selection unit determines the reliability of the signal of the line sensor from at least one information of luminance, contrast, image coincidence of the line sensor pair, and accumulation time, and based on the determination result, the plurality of pairs of lines 6. The focus adjusting apparatus according to claim 5, wherein a signal of which pair of line sensors among the sensors is used to detect the defocus amount.   3. The focus adjustment apparatus according to claim 2, wherein two pairs of line sensors adjacent to each other among the plurality of pairs of line sensors are arranged to be shifted from each other in a longitudinal direction of the line sensors.   8. The sensitivity setting unit according to claim 1, wherein the sensitivity setting unit sets the sensitivity of the line sensor by switching a capacitor for accumulating charges photoelectrically converted by the line sensor. Focus adjustment device.   An imaging apparatus comprising the focus adjustment apparatus according to claim 1. A focus detection sensor configured by arranging a plurality of pairs of line sensors that respectively receive light that has passed through different pupil regions of a photographic lens for forming a subject image, and among the plurality of pairs of line sensors selection means for selecting whether to use a signal of which a pair of line sensors, by using the signals of the pair of line sensors selected by said selecting means, and the defocus amount detecting means for detecting the defocus amount, is the detection a control method of an imaging device based on the defocus amount and a lens driving means for driving the photographing lens,
An operation mode setting step for switching between the first operation mode and the second operation mode;
A sensitivity setting step for setting sensitivity for each pair of line sensors with respect to the plurality of pairs of line sensors;
When switched to the first operation mode in the operation mode setting step, the plurality of pairs of line sensors are set to different sensitivities, and signals are accumulated simultaneously.
When switching to the second operation mode in the operation mode setting step, the plurality of pairs of line sensors are set to the same sensitivity, and a plurality of signal accumulations are performed with different sensitivities each time. Control method of imaging apparatus.

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