JP4779383B2 - Digital camera - Google Patents

Description

  The present invention relates to a focus detection device that detects a focus adjustment state of a photographing optical system using a phase difference detection method and a contrast detection method, and a digital camera including the focus detection device.

  It is known to utilize the advantages of both the phase difference detection method and the contrast detection method, in which after the photographic lens is driven near the focal point by the phase difference detection method, the focus adjustment state is finely adjusted by the contrast detection method. (For example, refer to Patent Document 1). In this case, a phase difference type AF sensor using a photoelectric conversion element such as a CCD line sensor detects only a part of the subject light on the shooting screen, but in the case of a contrast type imaging device, the entire shooting screen is detected. Subject light is detected, and a focus evaluation value is calculated using a signal in an image area corresponding to the focus detection area.

JP 2001-281530 A

  Incidentally, a storage type sensor such as a CCD is used for the AF sensor and the image sensor. In the accumulation type sensor, it is necessary to determine the accumulation time in accordance with the amount of incident light and to control so as to obtain an appropriate level signal. If the accumulation time is not appropriate and is too short, the output level is lowered, leading to a decrease in detection accuracy, or the cause of detection failure. On the other hand, if the accumulation time is too long, the output becomes saturated and cannot be detected.

  For example, consider a case where the subject brightness of the subject region detected by the AF sensor is lower than other regions of the shooting screen. In this case, if the accumulation time ExT of the image sensor is set to an appropriate value for the entire photographing screen based on the subject luminance information of the entire screen obtained from the photometric sensor, it corresponds to the low-luminance subject captured by the AF sensor. The output signal is low. For this reason, there is a problem that the focus adjustment cannot be performed with high accuracy by the contrast detection method.

According to a first aspect of the present invention, a digital camera according to a first aspect of the present invention detects a subject-type light corresponding to a focus detection area set in a photographing screen by the storage-type image pickup device and a storage-type image pickup device that picks up subject light that has passed through the photographing optical system. A storage type photoelectric conversion element, focus information calculation means for calculating focus information representing a focus adjustment state of the photographing optical system based on an output signal from the storage type photoelectric conversion element, and an image pickup signal of the storage type image pickup element An evaluation value calculating means for calculating a focus evaluation value based on a signal corresponding to the focus detection area, and an object corresponding to the entire shooting screen or a range of a predetermined area larger than the focus detection area in the shooting screen Photometric means for measuring light and outputting a photometric signal, and storage time of the storage type photoelectric conversion element when detecting subject light corresponding to the focus detection area Based on the first control means for controlling the accumulation of the storage type image sensor when acquiring the imaging signal to calculate the focus evaluation value, and based on the photometric signal of the photometric means, And a second control means for controlling accumulation of the accumulation type image pickup device.

  According to the present invention, since the accumulation type image pickup element is subjected to accumulation control based on the accumulation time of the accumulation type photoelectric conversion element, it is possible to perform appropriate accumulation control for the accumulation type image pickup element. The focus evaluation value calculation can be performed with high accuracy on the subject captured by the camera.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an embodiment of the present invention, and is a block diagram showing a main configuration of an AF digital camera provided with a focus detection apparatus according to the present invention. In the AF digital camera shown in FIG. 1, the mirror unit 2 is provided between the image sensor 3 and the photographing lens 1, and in a state where no photographing is performed (non-photographing state), as shown in FIG. Are arranged on the optical axis. The focus of the photographic lens 1 is adjusted by driving the focus lens of the photographic lens 1 by the motor 13. The motor 13 is driven and controlled by the lens drive control unit 8.

  The mirror unit 2 includes a half mirror 201 and a total reflection mirror 202, and a part of the subject luminous flux that has passed through the photographing lens 1 is reflected by the half mirror 201 and guided to the photometric sensor 9 in a non-shooting state. The photometric sensor 9 detects the subject luminous flux reflected by the half mirror 201 and acquires the luminance information of the subject from the detection result. The obtained subject luminance information is output to the accumulation time setting unit 7. On the other hand, the subject luminous flux that has passed through the half mirror 201 is reflected by the total reflection mirror 202 and guided to the AF sensor 5. On the other hand, at the time of photographing, the mirror unit 2 is retracted from the optical axis, and the subject luminous flux that has passed through the photographing lens 1 reaches the image sensor 3.

  The image pickup device 3 is an area sensor for performing focus adjustment by photographing and contrast detection, and a storage type sensor such as a CCD or a CMOS is used. The AF sensor 5 is also a storage type sensor such as a CCD or CMOS, but a line sensor is generally used. The level of the imaging signal output from the accumulation type sensor differs depending on the amount of light incident on each pixel of the sensor, and the output signal level increases as the amount of light increases. Reference numeral 10 denotes a control unit of the image sensor 3, which performs accumulation control, image signal read-out control, and the like when imaging is performed by the image sensor 3. The AF sensor is also provided with a control unit 11 that performs similar control.

  When shooting, the accumulation time setting unit 7 is used for shooting so that the exposure amount to the image sensor 3 is optimized based on the entire shooting screen obtained by the photometric sensor 9 or subject luminance information of a predetermined area. The accumulation time ExT is set, and the accumulation time ExT is output to the control unit 10. The control unit 10 causes the image sensor 3 to start and end accumulation based on the input photographing accumulation time ExT.

  In the case of performing the focus adjustment operation, in the present embodiment, the focus adjustment by the phase difference detection method based on the output signal of the AF sensor 5 and the focus adjustment by the contrast detection method based on the video signal of the imaging element 3 for photographing are performed. Use in combination. Specifically, when the release button of the camera is half-pressed, a signal from the AF sensor 5 is acquired with the mirror unit 2 disposed on the optical axis. The accumulation time AFT of the AF sensor 5 at this time is calculated by the accumulation time setting unit 7. As an accumulation time determination method, for example, the monitor sensor 12 is disposed in the vicinity of the AF sensor 5 and the calculation is performed based on the output of the monitor sensor 12 or the like. For example, the output values of the monitor sensor 12 from the start of accumulation are integrated, and when the integrated value reaches a predetermined level, the accumulation operation of the AF sensor 5 is terminated.

  The output signal of the AF sensor is input to the defocus amount calculation unit 6, and the defocus amount calculation unit 6 calculates a defocus amount that is focus information by a phase difference detection method. The calculated defocus amount is input to the lens drive control unit 8, and the lens drive control unit 8 drives the motor 13 to move the focus lens to a lens position based on the defocus amount. As a result, the focus lens of the photographing lens 1 is disposed in the vicinity of the in-focus position.

  Next, when the release button of the camera is half-pressed, the mirror unit 2 is retracted from the optical axis, the image is picked up by the image sensor 3, and the video signal is input to the evaluation value calculator 4. Although details will be described later, the accumulation time IAFT at this time is different from the above-described accumulation time for photographing ExT. The evaluation value calculation unit 4 extracts a high frequency component in a predetermined band based on the video signal in the focus detection area. Then, the absolute value of the extracted high-frequency component is integrated to calculate a focus evaluation value related to the subject image in the focus detection area. The calculated focus evaluation value is input to the lens drive control unit 8, and the lens drive control unit 8 performs focus adjustment by driving the focus lens of the photographing lens 1 based on the focus evaluation value. The focus lens driven to the vicinity of the in-focus position by the adjustment operation using the phase difference detection method described above is further accurately adjusted by the focus adjustment operation using the contrast detection method.

  FIG. 2 shows an example of the focus detection area set in the photographing screen 20, and one focus detection area 21 is set in the center of the screen. Reference numeral 22 denotes an area detected by the AF sensor 5. The focus evaluation value described above is calculated based on the imaging signal in the focus detection area 21. In order to obtain the focus evaluation value with high accuracy, the area of the focus detection area 21 needs to be increased to some extent. In general, the focus detection area 21 has a larger width (vertical width in the case of FIG. 2) than the detection area 22 of the AF sensor 5 composed of line sensors.

  By the way, when the detection signal of the AF sensor 5 is acquired, the detection is performed with the accumulation time AFT based on the output signal of the monitor sensor 12 described above. The monitor sensor 12 detects the subject light flux in the detection region 22, and the accumulation time AFT is determined based on the subject light flux so that the output signal level of the AF sensor 5 becomes appropriate. On the other hand, the photometric sensor 9 outputs luminance information based on the subject luminous flux of the entire shooting screen to the storage time setting unit 7, and the shooting storage time ExT is determined so that the exposure amount at the time of shooting is optimized. Therefore, when the focus evaluation value is calculated using only the video signal in the focus detection area 21 in the center of the screen, the signal level may be inappropriate for obtaining an accurate focus evaluation value.

  In the image sensor 3 and the AF sensor 5 using the accumulation type sensor, the accumulation time when the subject luminance is low is set longer than that when the subject luminance is high so that a sufficient signal level can be obtained. For example, when the detection area 22 is dark but the subject has sufficient brightness for the entire screen, the accumulation time AFT of the AF sensor 5 is set so that an appropriate signal level can be obtained for the dark detection area 22. On the other hand, since the image capturing accumulation time ExT is set so that the signal level is appropriate based on the luminance of the entire screen, it is likely to be shorter than the accumulation time AFT of the AF sensor 5.

  As described above, in the conventional focus detection apparatus, imaging is performed with the same shooting accumulation time ExT as that during shooting, and the focus evaluation value is calculated based on the video signal in the focus detection area 21 at that time. Therefore, the accumulation time ExT is shorter than the appropriate value for the subject in the detection area 22 captured by the AF sensor 5, and the output signal corresponding to the subject is low. As a result, the subject captured by the AF sensor 5 cannot be accurately focused, or the contrast of the subject in the detection area 22 cannot be obtained, and the focus is adjusted with the contrast of another subject in the focus detection area 21. There is a problem of being broken.

  Therefore, in the present embodiment, when imaging for calculating the focus evaluation value is performed, the accumulation time of the image sensor 3 when acquiring the focus evaluation value based on the luminance of the subject captured by the AF sensor 5. IAFT was set. FIG. 3 is a flowchart for explaining the focus adjustment operation. The focus adjustment operation shown in FIG. 3 starts, for example, when the release button of the camera is pressed halfway.

  In step S <b> 1, the accumulation time setting unit 7 sets the accumulation time AFT of the AF sensor 5. The setting is performed so as to be an optimum value for the AF sensor 5 based on the output of the monitor sensor 12 provided in the vicinity of the AF sensor 5 as described above. In step S2, the AF sensor 5 accumulates based on the accumulation time AFT set in step S1, and the defocus amount calculation unit 6 calculates the defocus amount DF based on the output signal of the AF sensor 5.

  In step S3, the lens drive control unit 8 determines whether or not the defocus amount DF calculated in step S2 is within a predetermined amount set in advance. This predetermined amount is for determining the switching timing from the focus adjustment operation by the phase difference detection method to the focus adjustment operation by the contrast detection method, and it is determined whether or not the current lens position is sufficiently close to the focus position. The determination is based on the focus amount DF.

  If it is determined in step S3 that the defocus amount DF is within the predetermined amount, the process proceeds to step S5. On the other hand, if it is determined in step S3 that the defocus amount DF is larger than the predetermined amount, the process proceeds to step S4, and the photographing lens 1 is driven by the defocus amount DF. If the process of step S4 is completed, the process returns to step S2, and detection by the AF sensor 5 is performed again to calculate the defocus amount DF. Then, the processes in steps S2 to S4 are repeatedly executed until the lens position is sufficiently close to the in-focus position and the defocus amount DF is determined to be within the predetermined amount.

In step S5, the accumulation time setting unit 7 sets the accumulation time IAFT of the image sensor 3 when performing focus adjustment by the contrast detection method. In the present embodiment, the accumulation time IAFT is calculated by the following equation (1) based on the accumulation time AFT set for the AF sensor 5. In Expression (1), αc is a sensitivity ratio between the AF sensor 5 and the image sensor 3. That is, since the contrast of the same subject as that captured by the AF sensor 5 is to be detected, when the sensitivity ratio is equal, the imaging element 3 is imaged in the same accumulation time as that of the AF sensor 5.
IAFT = αc × AFT (1)

  In step S <b> 6, imaging is performed by the imaging device 3 using the accumulation time IAFT set in Expression (1), and the focus evaluation value is calculated by the evaluation value calculation unit 4 based on the video signal in the focus detection area 21. The calculated focus evaluation value is sent to the lens drive control unit 8, where it is stored together with the lens position data. By using the accumulation time IAFT of Expression (1), an appropriate output video signal is output from the image sensor 3 to the same subject as the subject for which the AF sensor 5 has performed focus detection by the phase detection method, and the accurate detection is performed. A focus evaluation value can be obtained.

  In step S7, it is determined from the stored focus evaluation value whether the lens position of the focus lens provided in the photographing lens 1 has passed the lens position where the focus evaluation value reaches its peak. If it is determined in step S7 that the peak has been passed, the process proceeds to step S9. If it is determined that the peak has not been passed, the process proceeds to step S8. If the process proceeds to step S8, the focus lens is driven in step S8, and then the process proceeds to step S6 where the image pickup device 3 performs imaging to calculate a focus evaluation value.

  When the first contrast detection (imaging and focus evaluation value calculation) is performed from step S5 to step S6, contrast detection is performed at the lens position driven by focus adjustment by the phase difference detection method. When step S8 is executed for the first time, the focus lens is driven in the direction estimated from the defocus amount DF as the focus lens position. Until YES is determined in step S7, the processes in steps S6 to S8 are repeated. In the second and subsequent processes in step S8, the focus evaluation value is increased based on the stored focus evaluation value. The focus lens is driven in the direction of the estimated lens position.

  In step S9, based on the stored focus evaluation value and lens position, the lens position at which the focus evaluation value reaches its peak, that is, the focus lens position is calculated, and the focus lens of the photographing lens 1 is driven to the focus lens position. To do. In step S10, the accumulation time setting unit 7 calculates the photographing accumulation time ExT based on the detection result of the photometric sensor 9, and sets the accumulation time of the image sensor 3 to the photographing accumulation time ExT. In step S11, imaging is performed based on the imaging accumulation time ExT set in step S10, and a series of processing ends.

  In the present embodiment, since the imaging time IAFT for focus adjustment by the contrast detection method is set based on the accumulation time of the AF sensor 5 as in the above-described equation (1), the capturing of the AF sensor 5 is performed. It is possible to capture an image of a subject that is in an appropriate accumulation time. As a result, focus detection can be performed with high accuracy by the contrast detection method. In the above-described example, the focus evaluation value is calculated using the output signal of the image sensor 3 used for photographing. However, an image sensor for focus detection is provided separately from the image sensor 3, and the output signal of the image sensor You may make it acquire a focus evaluation value using. Although the AF sensor 5 detects the light flux through the photographing lens 1, a so-called external light passive system that does not involve the photographing lens 1 may be used.

  In the correspondence between the embodiment described above and the elements of the claims, the defocus amount calculation unit 6 is a focus information calculation unit, the photographing lens 1 is a photographing optical system, the control unit 10 is a control unit, and lens driving is performed. The control unit 8 constitutes an autofocus control unit. The above description is merely an example, and when interpreting the invention, there is no limitation or restriction on the correspondence between the items described in the above embodiment and the items described in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram illustrating an embodiment of the present invention, and is a block diagram illustrating a main configuration of an AF digital camera including a focus detection device according to the present invention. FIG. 3 is a diagram illustrating an example of a focus detection area set in a shooting screen 20. It is a flowchart explaining a focus adjustment operation | movement.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Shooting lens 3 Image pick-up element 4 Evaluation value calculating part 5 AF sensor 6 Defocus amount calculating part 7 Accumulation time setting part 9 Photometric sensor 10,11 Control part 12 Monitor sensor 21 Focus detection area 22 Detection area

Claims (2)

A storage-type image sensor that images subject light that has passed through the imaging optical system;
A storage type photoelectric conversion element for detecting subject light corresponding to a focus detection area set in a shooting screen by the storage type image sensor;
Focus information calculation means for calculating focus information representing a focus adjustment state of the photographing optical system based on an output signal from the storage photoelectric conversion element;
Evaluation value calculation means for calculating a focus evaluation value based on a signal corresponding to the focus detection area among the image pickup signals of the storage type image pickup device;
Metering means for metering subject light corresponding to an entire photographing screen or a range of a predetermined area wider than the focus detection area in the photographing screen and outputting a photometric signal;
The storage-type imaging device when acquiring the imaging signal to calculate the focus evaluation value based on the storage time of the storage-type photoelectric conversion device when detecting subject light corresponding to the focus detection area. First control means for controlling accumulation;
2. A digital camera comprising: a second control unit configured to perform accumulation control of the storage type image pickup device during a photographing operation based on a photometric signal of the photometry unit. The digital camera according to claim 1, wherein
The first control means performs accumulation control on the accumulation type image pickup element based on a sensitivity ratio between the accumulation type image pickup element and the accumulation type photoelectric conversion element and an accumulation time of the accumulation type photoelectric conversion element. Digital camera.

Images