JP2008191575A - Focus detector and imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a focus detector capable of setting a storage time for each focus detection area with simple constitution and an imaging device including the same. <P>SOLUTION: The storage time of each line sensor is controlled by the setting of a control register 203a. The control register 203a includes a limit time setting register for setting a limit time and a range finding point timer limit specifying register for specifying a type of the limit time setting register. Thus, the scale of the control register is reduced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a focus detection device for detecting a focus state in a plurality of focus detection areas and an imaging device including the focus detection device.

  A phase difference detection type focus detection device is known as one of focus detection devices used in an autofocus camera. In the phase difference detection method, a light beam from a subject that has passed through a different optical path of the main optical system is split by a pupil splitting optical system, and the split light beam is imaged on a pair of line sensors. The focus state in the focus detection area in the photographing screen is detected from the two image interval values of the paired subject images detected in step S2.

  In addition, in the phase difference detection type focus detection device, a plurality of pairs of focus detection areas corresponding to a plurality of focus detection areas in the shooting screen are detected in order to detect a subject image located in a wider area of the shooting screen. A focus detection apparatus capable of so-called multipoint distance measurement in which a line sensor is provided to detect a subject image has also been proposed.

  Here, in such a phase difference detection type focus detection apparatus, charge accumulation in the line sensor is monitored by a monitor sensor disposed in the vicinity of the line sensor, and the output of the monitor sensor has reached a predetermined value. Control is performed to end the accumulation operation of the corresponding line sensor. In such accumulation control, a limit time of accumulation operation is set, and when this limit time is reached, the accumulation operation is forcibly performed even if the accumulation amount of each line sensor does not reach the predetermined value. It is also done.

In the case of such accumulation control, for example, in a scene where the luminance of the background subject is higher than that of the main subject such as a night scene, the sensor output in the focus detection area corresponding to the main subject is insufficient depending on how the limit time is set. In some cases, the accumulation operation may end. Therefore, in the method of Patent Document 1, the method of limiting the accumulation time is changed between night scene shooting and normal shooting. That is, in Patent Document 1, in the case of normal shooting that is not night scene shooting, based on the storage time at the location where the storage operation is completed in a plurality of focus detection areas within a range that does not exceed a preset limit time. A limit time is set, and in the case of night scene shooting, the accumulation operation is terminated according to a preset long time limit regardless of the accumulation time at the location where the accumulation operation is terminated.
JP 2004-70099 A

  Here, in Patent Document 1, the limit time of the accumulation operation is common to all focus detection areas, but this may not be sufficient.

  For example, in the above-described night scene or backlight scene, a case where a bright background subject and a dark main subject are mixed in one focus detection area can be considered. In particular, when the main subject is a person, it is preferable that the focus state of the face portion (particularly the pupil portion) can be detected instead of the focus state of the boundary portion with the bright background. When the main subject is mixed, the line sensor reacts to a bright background subject, the monitor sensor output reaches the threshold value, and the accumulation operation ends with insufficient sensor output in the portion corresponding to the pupil portion. There is a possibility that. In such a focus detection area, it is necessary to continue the accumulation operation regardless of the output of the monitor sensor.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a focus detection device capable of setting an accumulation time for each focus detection area with a simple configuration and an imaging device including the focus detection device. To do.

  In order to achieve the above object, a focus detection apparatus according to a first aspect of the present invention includes a plurality of line sensors provided corresponding to a plurality of focus detection areas, and the line sensor for each of the plurality of line sensors. A detector that detects that the amount of received light has reached a certain amount, a control register that sets a limit time of accumulation operation for each of the plurality of line sensors, an output of the detector, and a setting of the control register And a control unit for controlling the end of the accumulation operation for each line sensor.

  In order to achieve the above object, an imaging apparatus according to the second aspect of the present invention includes an imaging unit that captures a subject image to obtain image data, and an optical system that forms the subject image on the imaging unit. A plurality of line sensors provided corresponding to a plurality of focus detection areas, a detector that is arranged for each of the plurality of line sensors and detects that the amount of light received by the line sensor has reached a certain amount, and A control register for setting a limit time of the accumulation operation for each of the plurality of line sensors; and a control unit for controlling the end of the accumulation operation for each of the line sensors based on the output of the detector and the setting of the control register. A focus detection device that calculates the focus state of the optical system in each focus detection area from the output of each line sensor, and the optical system according to the calculation result of the focus state A focus adjustment unit that performs focus adjustment, and having a recording unit for recording image data obtained by the imaging unit.

  According to the present invention, it is possible to provide a focus detection device capable of setting an accumulation time for each focus detection area with a simple configuration and an imaging device including the focus detection device.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[First Embodiment]
First, a first embodiment of the present invention will be described. FIG. 1 is a diagram illustrating a configuration of a digital single-lens reflex camera (hereinafter, abbreviated as a camera as appropriate) as an example of an imaging apparatus according to the first embodiment of the present invention. The camera of FIG. 1 includes an interchangeable lens 101 and a camera body 110.

  The interchangeable lens 101 is configured to be detachable from the camera body 110 via a camera mount (not shown) provided on the front surface of the camera body 110. The interchangeable lens 101 includes a focus lens 102, a lens driving unit 103, and a lens CPU 104.

  The focus lens 102 is a lens for focus adjustment included in the photographing optical system. The focus lens 102 is driven in the optical axis direction (the direction of arrow A in FIG. 1) by the lens driving unit 103, and adjusts the focal position of the photographing optical system. As a result, a light beam from a subject (not shown) that has passed through the photographic optical system forms a focused image on the image sensor 124 in the camera body 110.

  The lens driving unit 103 is composed of, for example, a driving mechanism including a driver and an ultrasonic motor. The focus lens 102 is driven in response to a control signal from the lens CPU 104.

  The lens CPU 104 is a control circuit that controls the lens driving unit 103 and the like. The lens CPU 104 can communicate with the system controller 123 in the camera body 110 via the communication connector 105. For example, various lens data that is stored in advance in the lens CPU 104 and used for calculation of defocus amounts such as manufacturing variation information of the focus lens and aberration information of the focus lens is transmitted from the lens CPU 104 to the system controller 123.

  The camera body 110 includes a main mirror 111, a finder optical system including a focusing screen 112, a pentaprism 113, and an eyepiece lens 114, a sub mirror 115, a condenser lens 116, a total reflection mirror 117, a separator diaphragm 118, and a separator lens 119. An AF optical system, a temperature sensor 120, an AF sensor 121, an AF controller 122, a system controller 123, an image sensor 124, and a recording unit 125 are configured.

  The main mirror 111 is a mirror that is configured to be rotatable and that has a central portion formed of a half mirror. When the main mirror 111 is in the down position (shown position), the main mirror 111 reflects a part of a light beam from a subject (not shown) that enters the camera body 110 via the interchangeable lens 101 and transmits a part thereof. On the focusing screen 112, the light beam reflected by the main mirror 111 is imaged. The pentaprism 113 causes the subject image formed on the focusing screen 112 to enter the eyepiece lens 114 as an erect image. The eyepiece 114 enlarges the subject image from the pentaprism 113 so that the user can observe it. In this way, the state of the subject (not shown) can be observed.

  The sub mirror 115 is installed on the back surface of the half mirror portion of the main mirror 111, and reflects the light beam transmitted through the half mirror portion of the main mirror 111 in the direction of the AF optical system.

  The condenser lens 116 of the AF optical system condenses the light beam reflected by the sub mirror 115 and formed on a primary imaging surface (not shown) and makes it incident in the direction of the total reflection mirror 117. The total reflection mirror 117 reflects the light beam from the condenser lens 116 toward the AF sensor 121. Separator stop 118 is disposed in front of AF sensor 121 and divides the light beam from total reflection mirror 117 into pupils. The separator lens 119 condenses the luminous flux divided by the separator diaphragm 118 and causes the AF sensor 121 to re-image. The temperature sensor 120 is installed in the vicinity of the separator lens 119 as shown in FIG. 2, for example, detects the ambient temperature of the separator lens 119, and outputs it to the AF controller 122. As the temperature sensor 120, for example, a known temperature sensor such as a thermistor can be used.

  The AF sensor 121 converts the subject image that has been pupil-divided with parallax and re-imaged into an electrical signal (subject image signal) and outputs it to the AF controller 122. Here, the AF sensor 121 is configured to be able to detect a focus state in a plurality of focus detection areas (ranging points) in the shooting screen. The AF controller 122 controls the operation of the AF sensor 121 and calculates, from the subject image signal output from the AF sensor 121, a two-image interval value of a pair of subject images obtained by pupil division by, for example, correlation calculation. The defocus amount of the focus lens 102 at each distance measuring point is calculated from the calculated two image interval values, and is output to the system controller 123.

  The system controller 123 controls the operation of the camera shown in FIG. For example, the system controller 123 transmits the defocus amount from the AF controller 122 to the lens CPU 104 during automatic focus adjustment (AF) of the focus lens 102. The lens CPU 104 adjusts the focus of the focus lens 102 based on the defocus amount. Further, at the time of shooting, the system controller 123 performs various image processing on the subject image signal obtained by the image sensor 124 and then records the image data obtained thereby in the recording unit 125.

  When the main mirror 111 is retracted from the illustrated position, the image sensor 124 converts a subject image formed through the photographing optical system into an electrical signal.

  The release button 126 gives an instruction to start AF and an instruction to start shooting to the system controller 123. When the release button 126 is pressed halfway, the 1st release switch is turned on and an AF start instruction is given to the system controller 123. In addition, when the release button 126 is fully pressed, the 2nd release switch is turned on to give an instruction to start photographing to the system controller 123.

  Next, a focus detection apparatus as a main part of the present embodiment will be described. FIG. 3 is a block diagram showing details of the configuration of the AF sensor, AF controller, and system controller of FIG.

  In FIG. 3, the AF sensor 121 includes a pixel unit 201, an analog processing unit 202, and a digital processing unit 203.

  The pixel unit 201 includes a line sensor unit 201a and a monitor sensor unit 201b. The line sensor unit 201a is configured by arranging a plurality of line sensors that receive a light beam divided by the separator lens 119 in correspondence with the distance measuring points. The light beam received by each line sensor is an electrical signal (subject image signal). And output to the analog processing unit 202. The monitor sensor unit 201b includes a plurality of monitor sensors arranged corresponding to each line sensor in order to monitor the accumulation operation status of each line sensor. Each monitor sensor detects a light beam equivalent to the light beam received on average by each line sensor as an electrical signal and outputs it to the digital processing unit 203.

  FIG. 4A is a diagram showing an example of the ranging point arrangement, and FIG. 4B is a line sensor unit and a monitor sensor unit for detecting the focus state in the ranging point arrangement shown in FIG. It is a figure which shows the example of a structure. Here, the example of FIG. 4B is an example in which one distance measuring point is composed of two islands in the horizontal direction and the vertical direction. The focus state of one island is detected by a pair of line sensors of a standard part and a reference part. For example, when focusing on the distance measuring point 2b in FIG. 4A, the focus state at the distance measuring point 2b is as follows: a pair of the reference unit horizontal sensor 11 and the reference unit horizontal sensor 12, the reference unit vertical sensor 13 and the reference unit vertical. Detected by a pair of sensors 14. In addition, monitor sensors 15 are arranged in the vicinity of each horizontal sensor and vertical sensor, and the accumulation operation status of the corresponding line sensors is monitored. Here, in the example of FIG. 4B, a monitor sensor is provided corresponding to each line sensor. However, since line sensors in the same island generally control accumulation in the same accumulation time, the reference unit and the reference unit You may make it provide a monitor sensor only in any one.

  The analog processing unit 202 performs analog processing such as correlated double sampling (CDS) and gain adjustment on the subject image signal output from each line sensor of the pixel unit 201 and outputs the subject image signal to the AF controller 122.

  The digital processing unit 203 includes a control register 203a, a timer 203b, and a sequencer 203c.

  The control register 203a is a register for setting the limit time of the accumulation operation for each distance measuring point. Here, the limit time of the accumulation operation is set for each distance measuring point, and can be selected from two types of maximum accumulation time and minimum accumulation time. For the distance measurement point for which the maximum accumulation time is selected, the accumulation operation of the corresponding line sensor is terminated when the maximum accumulation time has elapsed even if the output of the monitor sensor does not reach the predetermined value. On the other hand, for the distance measurement point for which the minimum accumulation time is selected, the accumulation operation of the corresponding line sensor is continued until the minimum accumulation time elapses even if the output of the monitor sensor reaches a predetermined value. The control register 203a will be described in detail later.

  The timer 203b measures the limit times of the accumulation operation set for each distance measuring point in the control register 203a, and notifies the sequencer 203c when each limit time is counted. The sequencer 203c controls the accumulation operation of each line sensor of the pixel unit 201 from the output of the timer 203b and the output of each monitor sensor of the pixel unit 201.

  In FIG. 3, the AF controller 122 includes a sequencer 211, a timer 212, an accumulation time register 213, an AD converter (ADC) 214, and a memory 215.

  The sequencer 211 as a control unit receives various control signals such as an accumulation start instruction signal for starting an accumulation operation at each distance measuring point and a signal for setting the control register 203a in response to a control signal from the system controller 123. A signal is supplied to the AF sensor 121. The timer 212 measures the accumulation time of each distance measuring point. The accumulation time register 213 holds the accumulation time for each distance measuring point measured by the timer 212. In other words, the accumulation time register 213 receives an accumulation end timing signal output from the sequencer 203c of the AF sensor 121 at each end of the accumulation operation at each distance measuring point, and stores the accumulation time counted by the timer 212 at that time. Hold for each distance measuring point.

  The ADC 214 converts the subject image signal output as analog data from the analog processing unit 202 of the AF sensor 121 into a digital signal. The memory 215 temporarily holds the digital subject image signal from the ADC 214. The digital subject image signal held in the memory 215 is used for calculating the defocus amount.

  Next, the control register 203a will be described in more detail. FIG. 5 is a diagram showing the configuration of the control register 203a. Here, the control register 203a in FIG. 5 has a limit time corresponding to each of the distance measuring points 2b, 2c, 2d, 3a, 3b, 3c, 3d, 3e, 4b, 4c, and 4d shown in FIG. Shows a configuration in which can be set.

  As shown in FIG. 5, the control register 203a includes three types of registers: a distance measuring point timer limit designation register, a limit time setting register, and a maximum / minimum selection register. Hereinafter, these registers will be described in detail.

  The distance measuring point timer limit specifying register as the second register is a 4-bit register that holds data for specifying the type of limit time setting register applied to each distance measuring point. Here, in the example of FIG. 5, data for two distance measuring points can be held in one distance measuring point timer limit designation register.

  First, data for each of the distance measuring point 2b and the distance measuring point 2c is set in the distance measuring point 2b / 2c timer limit designation register. That is, the upper 2 bits of the value set in the distance measuring point 2b / 2c timer limit designation register indicate data corresponding to the distance measuring point 2b, and the lower 2 bits indicate data corresponding to the distance measuring point 2c.

  Similarly, data for each of the ranging point 2d and the ranging point 3a is set in the ranging point 2d / 3a timer limit designation register. Further, data for each of the distance measuring points 3b and 3c is set in the distance measuring points 3b and 3c timer limit designation register. In the distance measuring point 3d / 3e timer limit designation register, data for each of the distance measuring point 3d and the distance measuring point 3e is set. In the distance measuring points 4a and 4b, the timer limit designation register is set with data for each of the distance measuring points 4a and 4b. Further, data for the distance measuring point 4c is set in the distance measuring point 4c timer limit designation register. Since the number of distance measuring points is 11, the lower 2 bits of the distance measuring point 4c timer limit designation register are not used.

  FIG. 6 is a diagram showing the relationship between the data set in the distance measuring point timer limit designation register and the limit time setting register selected by the data. Here, xx in FIG. 6 indicates the number of the distance measuring point.

  As shown in FIG. 6, the upper or lower 2 bits of data in the ranging point timer limit specification register are used for selecting the limit time setting register 1, for selecting the limit time setting register 2, and for selecting the limit time setting register 3. Assigned to. That is, the limit time setting register 1 is selected when the upper or lower 2 bits of the ranging point timer limit designation register are “00”, and the limit time setting register 2 is selected when the data is “01”. In the case of “10”, the limit time setting register 3 is selected. As will be described later, since only three types of limit time setting registers are provided, “11” is prohibited. If the number of limit time setting registers is four, “11” is also used.

  The limit time setting register as the first register is composed of two 4-bit registers to form one limit time setting register. FIG. 7 is a diagram showing the relationship between the data set in the limit time setting register and the limit time set thereby. Here, x in FIG. 7 indicates the number of the limit time setting register. The example of FIG. 7 shows an example in which the limit time can be set at intervals of 2 ms from the minimum time 2 ms (00000000) to the maximum time 512 ms (11111111).

  In the maximum / minimum time determination register, data for determining whether the limit time set in each of the limit time setting registers is used as the maximum limit of the accumulation time or the minimum limit of the accumulation time is set. . In the example of FIG. 4, since there are three types of limit time setting registers, only the upper 3 bits are used. FIG. 8 is a diagram showing a relationship between data set in the maximum / minimum time determination register and settings corresponding to the data. Here, x in FIG. 8 indicates the number of the limit time setting register. As shown in FIG. 8, the limit time held in the limit time setting register corresponding to the case where the data of the maximum / minimum time determination register is “0” is treated as the maximum accumulation time, and the limit corresponding to the case of “1”. The limit time held in the time setting register is treated as the maximum accumulation time.

  For example, among the 11 distance measuring points shown in FIG. 4 (a), the maximum accumulation time of the distance measuring points 2b, 2c, 2d, 3a, 3e, 4b, 4d, and 4e, which are neighboring distance measuring points, is set to 10 ms. The case where the maximum accumulation time of the distance measuring points 3b, 3c, 3d, which are distance measuring points near the center, is set to 50 ms will be described.

First, “0000” is set to address 7 and “0100” is set to address 8 in order to set 10 ms in the limit time setting register 1. In order to set 50 ms in the limit time setting register 2, “0001” is set in the address 9 and “1000” is set in the address 10.
Next, data is set in the distance measuring point timer limit designation register. In the above example, “0000” is assigned to address 1, “0000” is assigned to address 2, “0101” is assigned to address 3, “0100” is assigned to address 4, “0000” is assigned to address 5 is “0000” 0000 "is set. That is, “00” is set to the bit corresponding to the distance measuring point for setting 10 ms, and “01” is set to the bit corresponding to the distance measuring point for setting 50 ms.
Finally, since the limit time is handled as the maximum accumulation time, “00” is set in the upper 2 bits of the address 13.

  By configuring the control register as shown in FIG. 5, the number of registers can be reduced. For example, when it is attempted to set a limit time for each distance measurement point for the 11 distance measurement points shown in FIG. 4A, (limit time setting register) 8 bits × (number of distance measurement points) 11 = 88 bits are required. On the other hand, when the control register is configured as shown in FIG. 5, it can be configured by (timer limit designation register for each ranging point) 24 bits + (limit time setting register) 8 bits × 3 types = 48 bits. . In this way, it is possible to keep the required 88 bits to 44 bits. Since the line sensor used for the AF sensor usually uses a CCD process, the transistor size tends to increase. Therefore, it can be considered that even a reduction of 40 bits has a large effect on the chip size.

  Note that the bit size of each register constituting the control register is not limited to that shown in FIG. 5, but can be selected according to the trade-off between the number of distance measuring points, the limit time setting resolution, and the chip size. It is.

  FIG. 9 is a flowchart showing processing at the time of AF in the first embodiment. FIG. 9 illustrates an example in which the maximum accumulation time is set as the limit time in the control register 203a. An example of setting the minimum accumulation time will be described in a second embodiment described later.

  When the process of FIG. 9 is started, first, the AF controller 122 initializes the control register 203a of the AF sensor 121 (step S100). As an example, when a maximum accumulation time of 300 ms is set for each distance measuring point, the control register 203a is set by first setting 300 ms in the limit time setting registers 1 to 3 ("1001" in the addresses 7, 9, and 11). “0101” is set to the addresses 8, 10, and 12). Next, a value indicating the limit time setting register 1 is set in each ranging point timer limit specification register (“0000” is set in the addresses 1 to 6). Further, the maximum / minimum time determination register is set so that the limit time set in the limit time setting register 1 is used as the maximum accumulation time (the highest bit of the maximum / minimum time determination register is set to “0”). ). After completion of such initialization, the AF controller 122 enters a standby state.

  After initialization of the control register 203a, the system controller 123 determines whether or not the user has pressed the release button 126 halfway to turn on the 1st release switch (step S101). If the first release switch is turned on in step S101, the system controller 123 sends an AF execution instruction to the AF controller 122. In response to this, the AF controller 122 starts the accumulation operation of each distance measuring point of the AF sensor 121 (step S102).

  The sequencer 203c of the AF sensor 121 monitors the output of each monitor sensor of the monitor sensor unit 201b and the output of the timer 203b, and the output of the monitor sensor reaches a predetermined value or the timer 203b measures the maximum accumulation time. If this happens, the accumulation of the corresponding distance measurement points is terminated, and the AF controller 122 is notified that the accumulation of the corresponding distance measurement points has been completed. In response to this, the AF controller 122 detects the accumulation time counted by the timer 212, and holds the detected accumulation time in the accumulation time register 213 for each distance measuring point (step S103).

  Next, the AF controller 122 determines whether or not the accumulation operation at all distance measuring points has been completed (step S104). If it is determined in step S104 that the accumulation operation has not been completed at all distance measuring points, the process returns to step S103 and waits. On the other hand, when the accumulation operation at all distance measuring points is completed in the determination in step S <b> 104, the AF controller 122 sends a subject image signal readout instruction to the AF sensor 121. Thereby, the electric charge accumulated in each line sensor of the AF sensor 121 is read as an electric signal (step S105). Next, the AF controller 122 corrects an offset due to a dark current component or the like in the subject image signal read from the AF sensor 121 (step S106). Here, the generation time of the dark current is determined by the timing of completion of accumulation of the line sensor at each distance measuring point and the charge transfer timing from the line sensor. These can be detected by measuring the accumulation time for each distance measuring point by the timer 212 of the AF controller 122. Since the dark current also changes depending on the temperature, the temperature around the line sensor is measured in advance, and the dark current component in the subject image signal is obtained from the measured temperature and the generation time of the dark current. The subject image signal is level-shifted so that

  Next, the AF controller 122 performs illuminance correction for correcting the non-uniformity of the photodiode output constituting each line sensor of the AF sensor 121 (step S107). For this correction, for example, correction data is obtained from the illuminance variation of the line sensor when a uniform luminance surface is observed, and the corresponding subject image signal is corrected by this correction data.

  Next, the AF controller 122 calculates a two-image interval value by correlation calculation from the subject image signal output from the line sensor that makes a pair of the standard portion and the reference portion in the island (step S108). Thereafter, the AF controller 122 detects the contrast of the subject image in order to determine the reliability of the correlation calculation result (step S109). Then, the AF controller 122 determines the reliability of the correlation calculation result by determining whether or not the contrast of the subject image is sufficiently high (step S110).

  If it is determined in step S110 that the contrast of the subject image is low, that is, the reliability of the correlation calculation result is low, the AF controller 122 updates the gain in the analog processing unit 202 of the AF sensor 121. Sends an instruction to increase the gain (step S111). After that, the process returns to step S102, and the ranging point accumulation operation is resumed. On the other hand, if it is determined in step S110 that the contrast of the subject image is high, that is, the reliability of the correlation calculation result is high, the AF controller 122 determines whether or not the current scene is a backlight scene. (Step S112). This determination is, for example, determined as a backlight scene when the luminance difference between the subject image signals output from the line sensors corresponding to each distance measuring point is extremely large (for example, the luminance difference LV10 or more). In the case of a backlight scene, it is determined that the dark subject is the main subject.

  If it is determined in step S112 that the scene is a backlight scene, the AF controller 122 determines whether the accumulation control result is appropriate (step S113). This determines that the accumulation control result is not appropriate when AF is performed on the contour of a person or the like. An example of the determination method in step S113 will be described. For example, in a backlight scene as shown in FIG. 10A, people are arranged at the distance measuring points 3d and 3e. In such a scene, paying attention to the line sensor output at the distance measuring point 3d, the output is as shown in FIG. That is, in the sensor output, the output of the face portion is relatively smaller than the output of the background portion. In the case of such sensor output, it is determined that the accumulation control result is not appropriate because AF is performed in the vicinity of the face outline, not the human pupil. Then, as shown in FIG. 10C, the accumulation time is lengthened so that the contrast necessary for AF can be obtained in the face.

  If it is determined in step S113 that the accumulation control result is not appropriate, the AF controller 122 sends an instruction to turn off the accumulation control by the monitor sensor at the corresponding distance measurement point, and resets the limit time of each distance measurement point. An instruction is sent to set (step S114). Thereafter, the process returns to step S102, and the ranging point accumulation operation is performed again.

The resetting of the limit time will be described. First, for a distance measuring point including a main subject portion such as a person like the distance measuring point 3d in FIG. 10A, the accumulation time is lengthened so that the contrast necessary for AF is obtained in the main subject portion. That is, about this distance measuring point,
(Output level at which necessary contrast can be obtained) / (Current output level of main subject) × (Accumulation time at distance measuring point (main subject))
The accumulation control is performed according to the maximum accumulation time obtained by the above. On the other hand, for other distance measuring points, accumulation control is performed with the accumulation time of the distance measuring points (for example, the distance measuring point 3c) around the distance measuring point including the main subject portion as the maximum accumulation time. Note that accumulation control according to the minimum accumulation time may be performed for the main subject portion.

  Here, the processing of step S112 to step S114 is mainly processing for AF with respect to a person in backlight. Therefore, it may be performed only in the portrait photographing mode.

  If the accumulation control result is appropriate in the determination in step S113, the AF controller 122 selects a distance measurement point and calculates the defocus amount of the focus lens 102 at the selected distance measurement point (step S113). S115). The selection of the distance measuring point here may be performed by selecting the closest distance measuring point among the highly reliable distance measuring points, for example. After calculating the defocus amount, the system controller 123 transmits the calculated defocus amount to the lens CPU 104. The lens CPU 104 drives the focus lens 102 by controlling the lens driving unit 103 based on the defocus amount (step S116). Thereafter, when the user fully presses the release button 126, the operation proceeds to the photographing operation.

  As described above, according to the first embodiment, by changing the setting of the control register built in the AF sensor, the accumulation time of each line sensor in the AF sensor capable of measuring a plurality of distance measuring points is individually set. Can be set. Further, by setting the limit time by a combination of the distance measuring point timer limit designation register and the limit time setting register, it is possible to reduce the number of registers necessary for configuring the control register.

[Modification]
Hereinafter, modifications of the first embodiment will be described. In step S1 of FIG. 9, the initial value of the limit time is the same for each line sensor, but when the distance measuring point to be measured is known (focusing on the center distance measuring point in the shooting screen). In the case of distance measurement, or when a user selects a distance measurement point), the maximum accumulation time may be different between the distance measurement point that is the distance measurement target and the distance measurement point that is not the distance measurement target. FIG. 11 shows processing for varying the maximum accumulation time for each distance measuring point.

  In FIG. 11, as an example, at initialization, the maximum accumulation time of distance measurement points to be distance measurement objects is set to 300 ms, and the maximum accumulation time of other distance measurement points is set to 50 ms (step S200). In this case, 300 ms is set in the limit time setting register 1 and 50 ms is set in the limit time setting register 2, and in each distance measuring point timer limit designation register, the limit time is set in the bit indicating the distance measuring point to be measured. A value indicating the setting register 1 is set, and a value indicating the limit time setting register 2 is set to bits indicating other distance measuring points. Further, the maximum / minimum time determination register is set so that the limit times set in the limit time setting register 1 and the limit time setting register 2 are used as the maximum accumulation time. After completion of such initialization, the AF controller 122 enters a standby state.

  Here, in FIG. 11, the processing from step S200 to step S213 after step S200 is substantially the same as that in FIG. Note that the selection of the distance measurement points in step S213 is performed when there are a plurality of distance measurement points to be distance measurement objects.

  According to the modification described above, it is possible to obtain the contrast necessary for AF by lengthening the maximum accumulation time of the distance measurement points, and for the distance measurement points other than the distance measurement objects, the maximum accumulation time. Can be shortened to minimize the accumulation time.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. The second embodiment is an example in which a minimum accumulation time is set for each distance measuring point. Since the configuration is the same as that of the first embodiment, description thereof is omitted.

  The minimum accumulation time is set when, for example, a distance measurement point is designated by the user (when automatic distance measurement point selection is not performed). In such a case, as described in the modification of the first embodiment shown in FIG. 11, the accumulation time of the distance measurement points to be distance measurement objects is lengthened, and the accumulation of distance measurement points other than the distance measurement objects is accumulated. Although shortening the time is preferable in terms of shortening the AF time, there is a risk that the dark current at the distance measuring point where the accumulation was completed earlier increases accordingly. As described above, since the dark current is determined by the timing of completion of accumulation of the line sensor and the timing of charge transfer from the line sensor, the distance measurement target is within a range not exceeding the accumulation time of the distance measurement point to be distance measurement target. The dark current generation time is shortened by delaying the accumulation end timing of the other distance measuring points.

  FIG. 12 is a flowchart illustrating processing at the time of AF in the second embodiment. When the process of FIG. 12 is started, the AF controller 122 first initializes the control register 203a of the AF sensor 121 (step S300). After initialization of the control register 203a, the system controller 123 determines whether or not the user has pressed the release button 126 halfway to turn on the 1st release switch (step S301). If the first release switch is turned on in step S301, the system controller 123 sends an AF execution instruction to the AF controller 122. In response to this, the AF controller 122 starts the accumulation operation of each distance measuring point of the AF sensor 121 (step S302).

  The sequencer 203c of the AF sensor 121 monitors the output of each monitor sensor of the monitor sensor unit 201b and the output of the timer 203b, and the output of the monitor sensor reaches a predetermined value or the timer 203b measures the maximum accumulation time. If this happens, the accumulation of the corresponding distance measurement points is terminated, and the AF controller 122 is notified that the accumulation of the corresponding distance measurement points has been completed. In response to this, the AF controller 122 detects the accumulation time counted by the timer 212, and holds the detected accumulation time in the accumulation time register 213 for each distance measuring point (step S303).

  Next, the AF controller 122 determines whether or not the accumulation operation at all distance measuring points has been completed (step S304). If it is determined in step S304 that the accumulation operation has not been completed at all distance measuring points, the process returns to step S303 and waits. On the other hand, in the determination of step S304, when the accumulation operation at all the distance measurement points is completed, the AF controller 122 has reached the maximum accumulation time (300 ms) of the accumulation time of the distance measurement point to be measured, and the measurement. It is determined whether or not the minimum value of the accumulation time of distance measuring points that are not distance targets is equal to or less than a certain value (for example, 50 ms) (step S305). If it is determined in step S306 that the accumulation time of the distance measurement target has reached the maximum accumulation time, and the minimum accumulation time of the distance measurement points that are not the distance measurement object is equal to or less than a certain value, the measurement is performed. Assuming that the generation time of the dark current at the distance measurement point that is not the distance target is long, the value of the control register 203a is set so that the accumulation control based on the minimum accumulation time is performed at the distance measurement point that is not the distance measurement object at the next accumulation. Reset is performed (step S306). Thereafter, the process returns to step S302, and the distance measuring point accumulation operation is performed again.

  In resetting in step S306, first, the maximum / minimum time determination register is set so that the limit time set in the limit time setting register 1 is used as the minimum accumulation time (the highest level of the maximum / minimum time determination register). Set the bit to “1”). Next, the minimum accumulation time is set in a range that is longer than the original accumulation time and shorter than the accumulation time (300 ms) of the distance measurement target. In the example of FIG. 12, the minimum accumulation time is set to 250 ms. Further, a value indicating the limit time setting register 2 (the maximum accumulation time is set to 300 ms) is set to the bit of the distance measurement target in each distance measurement point timer limit designation register.

  In the determination in step S305, the accumulation time of the distance measurement target does not reach the maximum accumulation time (300 ms), or the minimum value of the distance measurement point accumulation time that is not the distance measurement object is a constant value (for example, 50 ms). If it exceeds, the AF controller 122 sends a subject image signal readout instruction to the AF sensor 121. Thereby, the electric charge accumulated in each line sensor of the AF sensor 121 is read out as an electric signal (step S307). Subsequent steps S308 to S315 are substantially the same as those in FIG.

  As described above, in the second embodiment, the accumulation control based on the minimum accumulation time is performed on the distance measurement point where the dark current generation time becomes long, so that measurement that is not a distance measurement object is performed as shown in FIG. The accumulation of distance points is continued until the minimum accumulation time has elapsed. As a result, it is possible to shorten the dark current generation time at the distance measurement points that are not the distance measurement object in a state in which the contrast at the distance measurement target object is sufficient.

  Although the present invention has been described above based on the embodiments, the present invention is not limited to the above-described embodiments, and various modifications and applications are naturally possible within the scope of the gist of the present invention. For example, in each embodiment described above, the accumulation time is set for each distance measuring point, but may be set for each island.

  Further, the above-described embodiments include various stages of the invention, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some configuration requirements are deleted from all the configuration requirements shown in the embodiment, the above-described problem can be solved, and this configuration requirement is deleted when the above-described effects can be obtained. The configuration can also be extracted as an invention.

It is a figure which shows the structure of the digital single-lens reflex camera as an example of the imaging device which concerns on the 1st Embodiment of this invention. It is the figure which showed typically the secondary image formation system of AF optical system. FIG. 2 is a block diagram illustrating details of configurations of an AF sensor, an AF controller, and a system controller in FIG. 1. FIG. 4A is a diagram showing an example of the ranging point arrangement, and FIG. 4B is a line sensor unit and a monitor sensor unit for detecting the focus state in the ranging point arrangement shown in FIG. It is a figure which shows the example of a structure. It is a figure which shows the structure of a control register. It is a figure which shows the relationship between the data set to a ranging point timer limit designation | designated register, and the limit time setting register selected by it. It is a figure which shows the relationship between the data set to the time limit setting register, and the time limit set by it. It is a figure which shows the relationship between the data set to the maximum / minimum time judgment register, and the setting corresponding to the data. It is a flowchart shown about the process at the time of AF in the 1st Embodiment of this invention. FIG. 10A is a diagram illustrating an example of a backlight scene, and FIG. 10B is a diagram illustrating an example of the output of the AF sensor when the maximum accumulation time is not set in the backlight scene, and FIG. FIG. 6 is a diagram illustrating an example of an output of an AF sensor when a maximum accumulation time is set in a backlight scene. It is a flowchart shown about the process at the time of AF in the modification of the 1st Embodiment of this invention. It is a flowchart shown about the process at the time of AF in the 2nd Embodiment of this invention. It is a figure which shows the relationship between minimum accumulation time and dark current generation time.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101 ... Interchangeable lens, 102 ... Focus lens, 103 ... Lens drive part, 104 ... Lens CPU, 110 ... Camera body, 111 ... Main mirror, 112 ... Focusing screen, 113 ... Pentaprism, 114 ... Eyepiece, 115 ... Submirror, DESCRIPTION OF SYMBOLS 116 ... Condenser lens, 117 ... Total reflection mirror, 118 ... Separator aperture, 119 ... Separator lens, 120 ... Temperature sensor, 121 ... AF sensor, 122 ... AF controller, 123 ... System controller, 124 ... Image sensor, 125 ... Recording part 126 ... Release button 203a ... Control register

Claims (7)

A plurality of line sensors provided corresponding to a plurality of focus detection areas;
A detector for detecting that the amount of light received by the line sensor reaches a certain amount for each of the plurality of line sensors;
A control register in which the limit time of the accumulation operation for each of the plurality of line sensors is set;
A control unit for controlling the end of the accumulation operation for each line sensor based on the output of the detector and the setting of the control register;
A focus detection apparatus comprising: The control register includes a register in which determination information is set for the control unit to determine whether the limit time is the maximum accumulation operation time or the minimum accumulation operation time.
The focus detection apparatus according to claim 1, wherein the control unit determines the limit time as a maximum accumulation time or a minimum accumulation time according to the determination information, and controls the accumulation operation of the line sensor. When the control unit determines that the limit time is the maximum accumulation operation time, the accumulation operation time of the line sensor is not detected from the output of the detector without detecting the end of the accumulation operation of the line sensor. When the maximum accumulation operation time is reached, the above accumulation operation is terminated,
When it is determined that the limit time is the minimum accumulation operation time, even if the end of the accumulation operation of the line sensor is detected from the output of the detector, the accumulation operation time of the line sensor becomes the minimum accumulation operation time. The focus detection apparatus according to claim 2, wherein the accumulating operation is continued until it reaches. The control register is
A plurality of first registers for setting the limit time;
Among the plurality of first registers, a plurality of second registers for designating a first register in which a limit time to be set for each line sensor is set;
The focus detection apparatus according to claim 1, comprising:   5. The focus detection apparatus according to claim 4, wherein the second register is set with information for designating a plurality of line sensors in one register.   6. The focus detection apparatus according to claim 1, wherein the time limits for a plurality of line sensors provided corresponding to the same focus detection area are the same. An imaging unit that captures a subject image to obtain image data;
An optical system for forming the subject image on the imaging unit;
A plurality of line sensors provided corresponding to a plurality of focus detection areas; a detector disposed for each of the plurality of line sensors to detect that the amount of light received by the line sensor has reached a certain amount; A focus comprising: a control register in which a limit time of the accumulation operation for each line sensor is set; and a control unit that controls the end of the accumulation operation for each line sensor based on the output of the detector and the setting of the control register. A detection device;
A focus state calculation unit that calculates the focus state of the optical system in each focus detection area from the output of each line sensor;
A focus adjustment unit for adjusting the focus of the optical system according to the calculation result of the focus state;
A recording unit for recording image data obtained by the imaging unit;
An imaging device comprising:

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