JP4900134B2 - Focus adjustment device, camera - Google Patents

Description

  The present invention relates to a focus adjustment device and a camera including the focus adjustment device.

  Conventionally, a contrast detection method that detects the contrast of a subject image captured by an image sensor while changing the focus adjustment state of the photographic lens, and moves the photographic lens to the peak position when it passes through the focus position (contrast peak). Autofocus is widely used. (See Patent Document 1)

JP 2003-241074 A

  In such contrast detection type autofocus, there is a problem that when the lens is moved to the peak position, focus adjustment cannot be performed with high accuracy due to the influence of backlash.

Focusing device according to the invention of claim 1 includes a first focus detection means contrast method for detecting the focus evaluation value based on contrast of the image by the imaging optical system in association with the focusing position of the imaging optical system, A second focus detection unit of a phase difference detection system that detects a defocus amount based on a shift amount of a pair of images due to a light beam passing through different positions of an exit pupil of the imaging optical system in association with the focus adjustment position; Calculation means for obtaining a defocus amount corresponding to the focus evaluation value of the contrast, and target defocus for setting the defocus amount corresponding to the focus adjustment position when the focus evaluation value shows a peak value as a target defocus amount An amount setting unit; and a focus adjustment control unit that performs focus adjustment control on the imaging optical system so that the target defocus amount is detected by the second focus detection unit; Characterized in that it comprises a.
According to a second aspect of the present invention, in the focus adjustment apparatus according to the first aspect, a half mirror that divides the light beam that has passed through the imaging optical system so as to be guided to the first focus detection unit and the second focus detection unit, respectively. Is further provided.
According to a third aspect of the present invention, in the focus adjustment apparatus according to the first or second aspect, the target defocus amount is the smallest defocus amount among the plurality of defocus amounts detected by the second focus detection unit. It is characterized by being larger than.
According to a fourth aspect of the present invention, in the focus adjustment apparatus according to any one of the first to third aspects, the target defocus amount setting unit is configured to detect the image after the peak value of the focus evaluation value is detected. The target defocus amount is set before focus adjustment control of the optical system .
According to a fifth aspect of the present invention, there is provided a camera comprising the focus adjustment device according to any one of the first to fourth aspects .

  According to the present invention, it is possible to eliminate the influence of backlash and perform focus adjustment with high accuracy.

  FIG. 1 is a configuration diagram of a camera according to an embodiment of the present invention. The camera shown in FIG. 1 includes a camera body 1 and a photographing lens 2 that is a photographing optical system. The camera body 1 includes a half mirror 11, a focus detection device 12, an image sensor 13, a signal processing unit 14, a control unit 15, and a focus adjustment unit 16. The taking lens 2 is composed of various lenses including a focus adjustment lens.

  The half mirror 11 divides the light beam that has passed through the photographing lens 2 so as to be guided to the focus detection device 12 and the image sensor 13, respectively. The light beam from the photographic lens 2 that has passed through the half mirror 11 is guided to the image sensor 13 and forms a subject image on the image sensor 13. The image sensor 13 captures the subject image thus formed and outputs an image signal to the signal processing unit 14. For example, a CMOS (Complementary Metal Oxide Semiconductor) type, a CCD (Charge Coupled Device), or the like is used as the imaging element 13.

  The signal processing unit 14 performs analog-digital conversion processing on the imaging signal output from the imaging device 13 to convert the imaging signal into image data. At this time, predetermined image processing may be performed as necessary. Based on the image data acquired in this way, the signal processing unit 14 further calculates the contrast value of the subject image in association with the focus adjustment position of the photographic lens 2, that is, the position of the focus adjustment lens in the photographic lens 2. This contrast value represents a focus evaluation value related to the focus adjustment state of the photographic lens 2. That is, the image sensor 13 and the signal processing unit 14 detect the focus evaluation value based on the contrast of the image by the photographing lens 2 as the first focus adjustment state of the photographing lens 2. The image data and the contrast value acquired by the signal processing unit 14 are output to the control unit 15.

  Of the light flux that has passed through the photographic lens 2, the light flux reflected by the half mirror 11 is input to the focus detection device 12. The focus detection device 12 defocuses the focus adjustment state of the photographic lens 2 in association with the focus adjustment position of the photographic lens 2, that is, the position of the focus adjustment lens in the photographic lens 2 by a known phase difference detection method using pupil division. Detect the amount. That is, the focus detection device 12 sets the defocus amount based on the shift amount of the pair of images due to the light beams passing through different areas of the exit pupil of the photographing lens 2 as the second focus adjustment state of the photographing lens 2, as described above. Detection is performed by a method different from that of the element 13 and the signal processing unit 14. The defocus amount calculated in the focus detection device 12 is output to the control unit 15.

  As described above, the imaging device 13, the signal processing unit 14, and the focus detection device 12 each detect the focus evaluation value and the defocus amount based on the image obtained by the photographing lens 2. Therefore, it is possible to detect the focus evaluation value and the defocus amount that accurately reflect the focus adjustment position of the photographic lens 2.

  The control unit 15 records the image data output from the signal processing unit 14 on a recording medium (not shown). Thus, the subject is photographed by recording the image data based on the light from the subject obtained in the image sensor 13 on the recording medium. Further, the control unit 15 executes autofocus processing based on the defocus amount output from the focus detection device 12 and the contrast value output from the signal processing unit 14. By executing this autofocus process, the control unit 15 determines the drive amount of the focus adjustment lens in the photographing lens 2 and outputs a drive signal corresponding to the drive amount to the focus adjustment unit 16. The specific content of the autofocus process executed by the control unit 15 will be described in detail later.

  The focus adjustment unit 16 drives the focus adjustment lens of the photographing lens 2 using a drive mechanism (not shown) based on the drive signal output from the control unit 15. As a result, the focus adjustment position of the photographic lens 2 is changed to perform focus adjustment, and the subject is brought into focus.

  When a release button (not shown) in the camera body 1 is half-pressed by the photographer, the control unit 10 executes an autofocus process, and the focus of the photographic lens 2 is adjusted. At this time, the defocus amount is detected by the focus detection device 12 while changing the focus adjustment position of the photographing lens 2, and the contrast value is determined by the signal processing unit 14 based on the imaging signal output from the imaging device 13. Detected. Thereafter, when the release button is fully pressed, the half mirror 11 is retracted from the optical path of the photographic lens 2 and a subject image is captured by the image sensor 13. The captured subject image is recorded on the recording medium.

  Next, the contents of the autofocus process will be described. In the autofocus process, the control unit 15 first sets the target position (target lens position) of the focus adjustment lens of the photographing lens 2 based on the contrast value output from the signal processing unit 14. Next, a defocus amount (target defocus amount) corresponding to the set target lens position is obtained based on the defocus amount output from the focus detection device 12. Thereafter, the lens drive amount is calculated based on the defocus amount obtained at the current focus adjustment position of the photographic lens 2 and the obtained target defocus amount, and the focus adjustment is performed on the drive signal corresponding to the calculated lens drive amount. To the unit 16. Based on the drive signal output in this way, the focus adjustment unit 16 drives the focus adjustment lens by an amount corresponding to the lens drive amount, and changes the focus adjustment position of the photographing lens 2.

  When the focus adjustment lens is driven as described above, the control unit 15 monitors the defocus amount detected by the focus detection device 12 and compares it with the target defocus amount. If the detected defocus amount does not coincide with the target defocus amount, a lens drive amount corresponding to the difference is obtained and a drive signal is output to the focus adjustment unit 16. By repeating this control until the target defocus amount is obtained, the focus of the photographic lens 2 is adjusted.

  In autofocus using a normal contrast detection method, focus adjustment accuracy is reduced due to the effect of backlash that occurs when the drive direction changes. However, since the focus adjustment lens is driven so that the target defocus amount can be obtained by performing the autofocus process as described above, the focus of the photographing lens 2 is highly accurate without being affected by backlash. Adjustments can be made. In addition, the target defocus amount is obtained based on the target lens position set based on the contrast value, and the focus adjustment lens is driven to obtain the target defocus amount. Compared with the focus, the focus of the photographic lens 2 can be adjusted with high accuracy.

  Here, a method of setting the target lens position based on the contrast value and obtaining the target defocus amount corresponding to the target lens position based on the defocus amount will be described with reference to a specific example of FIG. As shown in FIG. 2, for example, it is assumed that the contrast value Con (n) and the defocus amount Def (n) are detected when the position of the focus adjustment lens is the lens position P (n). Further, the contrast value Con (n + 1) and the defocus amount Def (n + 1) are detected at the lens position P (n + 1), and the contrast value Con (n + 2) and the defocus amount Def (n + 2) are detected at the lens position P (n + 2). Is detected.

  Based on the contrast values Con (n), Con (n + 1), and Con (n + 2) that are discretely detected by the signal processing unit 14 with respect to changes in the lens position, the control unit 15 is in a state where the photographing lens 2 is in focus. The maximum contrast value Con (max) indicating that is obtained. At this time, as shown in FIG. 2, the contrast value Con (n + 1) having the highest detected contrast value is centered to interpolate a portion where no contrast value is detected by three-point interpolation. Find the peak of the value. The contrast value at this peak is taken as the maximum contrast value Con (max). Here, the maximum contrast value Con (max) indicating the in-focus state is determined based on the three contrast values Con (n), Con (n + 1), and Con (n + 2). The maximum contrast value may be obtained based on the above contrast value.

  After obtaining the maximum contrast value Con (max) as described above, the control unit 15 obtains the lens position P (t) corresponding to the maximum contrast value Con (max). This lens position P (t) is set to the target lens position of the focus adjustment lens. The control unit 15 sets the target lens position P (t) based on the contrast values Con (n), Con (n + 1), and Con (n + 2) thus detected.

  When the target lens position P (t) is set as described above, the control unit 15 then defocus amounts Def (n), Def (n + 1) and Def (n + 2) discretely detected by the focus detection device 12. ) To obtain a target defocus amount Def (t) corresponding to the target lens position P (t). At this time, as shown in FIG. 2, the target defocus amount Def (t) is obtained by interpolating a portion where the defocus amount is not detected. In this way, the contrast value, that is, the defocus amount corresponding to the focus adjustment position when the first focus adjustment state indicates the in-focus state, that is, the second focus adjustment state, is set as the target focus adjustment state.

  Based on the target defocus amount Def (t) obtained as described above, the control unit 15 calculates the lens drive amount and outputs a drive signal corresponding to the lens drive amount to the focus adjustment unit 16. Here, the target defocus amount Def (t) is determined based on the three defocus amounts Def (n), Def (n + 1), and Def (n + 2), but three or more defocus amounts are determined. The target defocus amount may be obtained based on the focus amount.

  FIG. 3 shows a flowchart of the autofocus process executed in the control unit 15. In step S10, the control unit 15 acquires the contrast value output from the signal processing unit 14 at the current focus adjustment position. In step S20, the control unit 15 acquires the defocus amount output from the focus detection device 12 at the current focus adjustment position. At this time, the contrast value and the defocus amount may be acquired while moving the focus adjustment lens.

  In step S30, the control unit 15 determines whether or not the peak of the contrast value has passed based on the contrast value acquired in step S10. If the peak of the contrast value is passed, that is, if the contrast value that has been increasing has started to decrease, the process proceeds to step S50. On the other hand, if it has not yet passed the peak of the contrast value, the process proceeds to step S40.

  In step S40, the control unit 15 outputs a drive signal to the focus adjustment unit 16, thereby moving the focus adjustment lens and changing the focus adjustment position of the photographing lens 2 by a predetermined amount. If step S40 is performed, it will return to step S10. Accordingly, the contrast value and the defocus amount are acquired while changing the focus adjustment position of the photographing lens 2 until the peak of the contrast value is passed.

  In step S50, the control unit 15 calculates the maximum contrast value by the method as described above based on the contrast value acquired in step S10 executed so far. Thereby, the maximum contrast value Con (max) in FIG. 2 is obtained.

  In step S60, the control unit 15 sets a target lens position corresponding to the maximum contrast value calculated in step S50. Thereby, the target lens position P (t) in FIG. 2 is set.

  In step S70, the control unit 15 performs the target defocus corresponding to the target lens position set in step S60 by the method described above based on the defocus amount acquired in step S20 executed so far. Calculate the amount. Thereby, the large target defocus amount Def (t) in FIG. 2 is obtained.

  In step S80, the control unit 15 moves the focus adjustment lens according to the target defocus amount calculated in step S70. At this time, as described above, the control unit 15 calculates the lens drive amount based on the defocus amount and the target defocus amount obtained at the current focus adjustment position of the photographic lens 2, and sends the drive signal to the focus adjustment unit 16. By outputting, the focus adjustment lens is moved, and the focus adjustment position is changed.

  In step S <b> 90, the control unit 15 acquires the defocus amount output from the focus detection device 12. In step S100, the control unit 15 compares the defocus amount acquired in step S90 with the target defocus amount calculated in step S70, and determines whether the target defocus amount has been acquired. If the target defocus amount is not acquired, the process returns to step S80 to move the focus adjustment lens until the target defocus amount is acquired. When the target defocus amount is acquired, the flowchart of FIG. 3 ends. In this way, the autofocus process is executed.

According to the embodiment described above, the following operational effects are obtained.
(1) The camera body 1 uses the imaging device 13 and the signal processing unit 14 to set the first focus adjustment state of the photographic lens 2, that is, the focus evaluation value based on the contrast value of the subject image, as the focus adjustment position of the photographic lens 2. Detect in association. Further, the focus detection device 12 associates the second focus adjustment state of the photographic lens 2, that is, the defocus amount with the focus adjustment position of the photographic lens 2 in a manner different from that of the image sensor 13 and the signal processing unit 14. To detect. Then, the control unit 15 sets the second focus adjustment state corresponding to the focus adjustment position of the photographing lens 2 when the first focus adjustment state indicates the in-focus state as the target focus adjustment state (steps S50 to S50). S70) The focus adjustment lens is driven by the control unit 15 and the focus adjustment unit 16 so that the focus adjustment state of the target set by the focus detection device 12 is detected, and the photographing lens 2 is adjusted in focus (step S80). It was decided. Since it did in this way, the influence of a backlash can be eliminated and the focus adjustment of the photographic lens 2 can be performed accurately.

(2) The image pickup device 13, the signal processing unit 14, and the focus detection device 12 detect the first focus adjustment state and the second focus adjustment state, respectively, based on the image by the photographing lens 2. . Since it did in this way, a 1st focus adjustment state and a 2nd focus adjustment state can be correctly matched and detected with respect to the focus adjustment position of the photographic lens 2. FIG.

(3) The image sensor 13 and the signal processing unit 14 detect a focus evaluation value based on the contrast of the image taken by the photographing lens 2 as the first focus adjustment state. Moreover, the focus detection apparatus 12 detects the defocus amount based on the shift amount of the pair of images due to the light beams passing through different positions of the exit pupil of the photographing lens 2 as the second focus adjustment state. By applying to such a combination of detection methods, each detection method can be effectively controlled.

(4) In step S80, the control unit 15 and the focus adjustment unit 16 respond to the lens driving amount based on the second focus adjustment state and the target focus adjustment state obtained at the current focus adjustment position of the photographing lens 2. The focus adjustment position of the taking lens 2 was changed. Thus, the focus adjustment lens can be accurately adjusted to a position where the set target focus adjustment state can be obtained.

(5) The half mirror 11 divides the light beam via the photographing lens 2 so as to be guided to the image sensor 13 and the focus detection device 12, respectively. Since it did in this way, the detection of the 1st focus adjustment state by the image pick-up element 13 and the signal processing part 14 using the light beam which passed the same imaging lens 2, and the 2nd focus adjustment state by the focus detection apparatus 12 are carried out. Detection can be performed simultaneously. Therefore, the target focus adjustment state is easily obtained.

  In the above-described embodiment, the camera body 1 that performs autofocus processing and captures a subject image has been described. However, the present invention may be applied to a focus adjustment apparatus that performs only autofocus processing. Or it is good also as a camera provided with such a focus adjustment apparatus.

  In the embodiment described above, the contrast value is detected by the signal processing unit 14 and the defocus amount is detected by the focus detection device 12 when the focus adjustment lens is at the same focus adjustment position. However, the contrast value and the defocus amount may be detected at different lens positions. That is, if the contrast value and the defocus amount are detected in association with the lens position, the contrast value and the defocus amount can be associated with each other, so that the target defocus amount can be similarly obtained.

  Furthermore, in the embodiment described above, the target lens position corresponding to the maximum contrast value is set, and the defocus amount corresponding to the target lens position is set as the target defocus amount. It is not necessary. For example, the movement of the subject is predicted, and based on the prediction result, the lens position that is separated from the lens position corresponding to the maximum contrast value by the amount corresponding to the movement of the subject is set as the target lens position. The defocus amount corresponding to the target lens position may be set as the target defocus amount. In other words, the second focus adjustment state corresponding to the focus adjustment position other than when the first focus adjustment state indicates the in-focus state can be set as the target focus adjustment state.

  In addition, as an example of a phase difference detection type focus detection device, an example of a focus detection device independent of an image sensor has been shown, but photoelectric conversion that receives light by dividing a pupil of an imaging optical system in an imaging pixel array of the image sensor You may apply to the focus detection apparatus of the structure which mixed the focus detection pixel which has a part.

  The embodiments and modifications described above are merely examples, and the present invention is not limited to these contents as long as the features of the invention are not impaired. Other aspects conceivable within the scope of the technical idea of the present invention are also included in the scope of the present invention.

It is a block diagram of the camera by one embodiment of this invention. It is a figure which shows the specific example for demonstrating the method of setting a target lens position based on a contrast value, and calculating | requiring the target defocus amount corresponding to a target lens position based on a defocus amount. It is a flowchart of an autofocus process.

Explanation of symbols

1: camera body, 2: photographing lens, 11: half mirror, 12: focus detection device,
13: Image sensor, 14: Signal processing unit, 15: Control unit, 16: Focus adjustment unit

Claims (5)

The focus evaluation value based on contrast of the image by the imaging optical system and the first focus detection means contrast method to detect in correspondence with the focusing position of the imaging optical system,
A second focus detection unit of a phase difference detection system that detects a defocus amount based on a shift amount of a pair of images due to a light beam passing through different positions of an exit pupil of the imaging optical system in association with the focus adjustment position;
A calculation means for obtaining a defocus amount corresponding to the contrast focus evaluation value;
A target defocus amount setting means for setting a defocus amount corresponding to the focusing position when the focus evaluation value is a peak value as the target defocus amount,
Focusing device, characterized in that it comprises, a focusing control means for focusing controlling said imaging optical system so that the target defocus amount is detected by the second focus detection unit. The focus adjustment apparatus according to claim 1,
A focus adjustment apparatus , further comprising a half mirror that divides the light beam that has passed through the imaging optical system so as to be guided to the first focus detection unit and the second focus detection unit, respectively . The focusing apparatus according to claim 1 or 2,
The focus adjustment apparatus , wherein the target defocus amount is larger than a smallest defocus amount among the plurality of defocus amounts detected by the second focus detection unit . The focus adjustment apparatus according to any one of claims 1 to 3,
The target defocus amount setting means sets the target defocus amount after the peak value of the focus evaluation value is detected and before the focus adjustment control of the imaging optical system is performed. apparatus. The camera provided with the focus adjustment apparatus as described in any one of Claims 1-4 .

Images