JP2006146031A - Camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a camera capable of performing focus detection of a high speed with high accuracy not affected by a change with lapse of time in a camera which performs focus detection of a phase difference system. <P>SOLUTION: The subject light from a taking lens 2 is divided to two by a main mirror 3, and one of the divided light is made incident on an imaging element 8 for contrast AF and a portion of the other of the divided light is guided to a focus detector 61 for phase difference type AF and is made incident on an AF sensor provided therein. The imaging data for a contrast system output from the imaging element 8 and the imaging data for a phase difference system output from the focus detector 61 are synchronously acquired and the focus detection of the phase difference system is corrected on the basis of the change in the maximum contrast evaluation value obtained from the data and a defocusing amount. Consequently, the phase difference system focus detection free of the erroneous correction due to mismatching of the object subject can be performed with high accuracy. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a camera that performs focus detection using a phase difference method and a contrast method.

  Conventionally, a hybrid AF type camera having both a distance measuring sensor such as a phase difference type focus detection sensor and a contrast type focus detection sensor has been proposed (for example, see Patent Document 1). The phase difference type focus detection has a high detection speed, while the contrast type focus detection has a high detection accuracy. Therefore, by using the hybrid AF method, a camera with a high detection speed and high accuracy can be realized.

  Further, there is known a method of correcting a change with time of the distance measuring sensor using a result of contrast-type focusing (see, for example, Patent Document 2).

JP 2003-227996 A JP 2003-279844 A

  However, in the above-described method for correcting change with time in Patent Document 2, the contrast-type image acquisition timing used for correction is different from the phase-difference image acquisition timing, and thus correction may not be performed accurately. Further, if such a situation is to be excluded, there is a drawback that restrictions on the subject become severe and it is difficult to obtain a correction opportunity.

According to a first aspect of the present invention, there is provided a camera according to a first aspect of the present invention, comprising: a light dividing unit that divides subject light that has passed through the photographing lens into first light and second light; , A contrast evaluation value calculating means for calculating a contrast evaluation value based on an output signal of the first image sensor, a first control means for performing a contrast type focus adjustment based on the contrast evaluation value, and a subject by the second light A second image sensor for detecting an image, focus detection value calculation means for calculating a focus detection value by a phase difference method based on an output signal of the second image sensor, and a first at the time of focus adjustment based on a contrast evaluation value Synchronous detection by the second image sensor is performed in synchronization with detection of the image sensor, and the focus detection value is calculated based on the calculation result of the focus detection value calculation means based on the output signal of the second image sensor at the time of synchronization detection. Correction data calculation means for calculating correction data for correction, a memory for storing correction data, a focus detection value is corrected by the correction data stored in the memory, and focus adjustment is performed based on the corrected focus detection value And a second control means for performing the above.
According to a second aspect of the present invention, in the camera according to the first aspect, the synchronization detection is performed by a photographing instruction, and correction data is calculated by the correction data calculating means for each photographing instruction.
According to a third aspect of the present invention, in the camera according to the first or second aspect, an image pickup device of an image recording image pickup unit is used as the first image pickup device.
According to a fourth aspect of the present invention, in the camera according to the first or second aspect, each of the first imaging element and the second imaging element is optically conjugate with the light receiving portion of the first imaging element and the imaging surface of the image recording imaging means. Contrast calculated by an output signal output at the time of synchronous detection from an image sensor having a smaller pixel pitch in the light-receiving unit projection image and having a smaller pixel pitch when projected onto a smooth surface. Based on the evaluation value, there is provided judgment means for judging whether or not to rewrite the correction data stored in the memory.
According to a fifth aspect of the present invention, in the camera according to the fourth aspect, the high-frequency component of the output signal output at the time of synchronous detection is extracted from the image sensor having the smaller pixel pitch in the light-receiving unit projection image, and the contrast of the high-frequency component is extracted. High frequency contrast calculation means for calculating an evaluation value is provided, and the determination means determines that the correction data stored in the memory is not rewritten when the contrast evaluation value calculated by the high frequency contrast calculation means is larger than a predetermined reference value. .
According to a sixth aspect of the present invention, in the camera according to any one of the first to fifth aspects, the first light is guided and an observation optical system for observing the subject image is provided, via at least a part of the observation optical system. A part of the guided first light is detected by the first image sensor.
A seventh aspect of the invention is the camera according to any one of the first to fifth aspects, further comprising display means for displaying a subject image obtained by the first image sensor.

  According to the present invention, synchronization detection by the second imaging element is performed in synchronization with detection of the first imaging element during focus adjustment based on the contrast evaluation value, and based on the output signal of the second imaging element at the time of synchronization detection. Since the focus detection value by the phase difference method is corrected by the correction data, highly accurate phase difference focus detection can be performed.

  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 a camera according to the present invention, and is a diagram showing a schematic configuration of a focus detection relationship of a single-lens reflex digital still camera 1. The taking lens 2 that forms an image of the subject light beam on the image pickup surface of the image pickup device 5 includes a focus lens (not shown) that adjusts the focal position.

  The subject luminous flux that has passed through the photographing lens 2 and the diaphragm 11 is reflected by the main mirror 3 toward the viewfinder screen 4. The finder screen 4 is disposed at a position optically conjugate with the imaging element 5 on which a subject image is formed, and the subject image is formed on the finder screen 4. When the camera is released, the main mirror 3 is flipped upward, and the light beam that has passed through the photographing lens 2 forms an image on the image sensor 5 through the open shutter 10. As the image sensor 5, a CCD image sensor, a MOS type image sensor, a CID, or the like is used.

  The light beam L transmitted through the finder screen 4 is reflected by the roof surface 6 a of the pentaprism 6 and reaches the surface 6 b of the pentaprism 6. In the present embodiment, a hologram 7 which is a reflection diffraction grating is attached to the surface 6b of the pentaprism 6, and a silver-deposited reflector 12 is closely attached to the back side of the hologram 7. Yes. In FIG. 1, the hologram 7 and the reflecting plate 12 are illustrated apart from the surface 6b for easy understanding, but in actuality, they are provided in close contact with the surface 6b. The reflecting plate 12 constitutes a third reflecting surface that reflects the subject light flux to the viewfinder eyepiece 9.

  By the way, in the conventional pentaprism, the surface 6b constituting the third reflecting surface is vapor-deposited on the silver, and the light beam incident on the surface 6b is reflected to the finder eyepiece 9. On the other hand, in the pentaprism 6 of the present embodiment, the light beam L that has reached the surface 6 b passes through the surface 6 b and enters the hologram 7. The hologram 7 has an imaging function of diffracting light L1 having a predetermined wavelength so as to be guided in a predetermined direction and forming an image of the light beam L1. The image sensor 8 is disposed at the imaging position of the subject image formed by the hologram 7. That is, a part (light having a predetermined wavelength) L1 of the light beam L is guided toward the image pickup device 8 by the diffraction action of the hologram 7, and forms a subject image on the image pickup surface. The light L2 having a wavelength other than the predetermined wavelength is transmitted through the hologram 7 and reflected toward the viewfinder eyepiece 9 by the reflecting plate 12 serving as the third reflecting surface.

  As the image pickup device 8, an area type CCD image pickup device, a CMOS device, or the like is used. The light receiving surface (imaging surface) of the image sensor 8 is optically conjugate with the screen surface of the finder screen 4 and the imaging magnification is different, but the subject image imaged on the image sensor 5 is conjugate with the subject image. Projected onto the imaging surface. Although not shown in FIG. 1, the finder optical system is also provided with an AE photometric element 15 (see FIG. 5) that receives scattered light from the finder screen 4 via the pentaprism 6.

  The central part of the main mirror 3 is composed of a half mirror, and a sub mirror 60 is provided on the back side of the half mirror part. The sub mirror 60 reflects the light beam transmitted through the half mirror part of the main mirror 3 and guides it to the focus detection device 61 provided at the bottom of the camera. Although details of the focus detection device 61 will be described later, focus detection by the phase difference method is performed using detection data of the focus detection device 61. As will be described later, in the camera according to the present embodiment, the AF operation is performed using both the phase difference type focus detection based on the detection data of the focus detection device 61 and the contrast type focus detection based on the imaging data of the image sensor 8 described above. Like to do.

  FIG. 2 is a perspective view showing the configuration of the focus detection device 61. The focus detection device 61 includes a field mask 62, a field lens 63, a separator lens 64, and an AF sensor 65. In the case of this camera 1, it has one AF area in the center of the object field, and the AF sensor 65 is provided with a pair of line sensors 65a and 65b corresponding to this AF area.

  In the center of the field mask 62, a rectangular opening 62a is formed as a field stop corresponding to the AF area. The light beam that has passed through the opening 62a is divided into two by separator lenses 64a and 64b arranged side by side in the horizontal direction, and formed on the pair of line sensors 65a and 65b, respectively. FIG. 3 is a diagram illustrating an example of output signals from the line sensors 65a and 65b. The horizontal axis represents the pixel number of the line sensor (that is, the pixel position), and the vertical axis represents the output signal level. A pair of subject images formed on the line sensors 65a and 65b approach each other in a so-called front pin state in which the photographing lens 2 forms a sharp image of the subject in front of the primary imaging plane (subject side), and conversely In a so-called rear pin state in which a sharp image of the subject is connected after the primary image plane, they move away from each other.

  Then, when the subject images formed on the line sensors 65a and 65b have a predetermined interval, a sharp image of the subject is positioned on the primary imaging plane. The defocus amount is obtained by obtaining the distance between the subject images. That is, this subject image is photoelectrically converted by the line sensors 65a and 65b to be converted into electrical signals, and these signals are processed to obtain the relative distance between the pair of subject images, thereby forming a sharp image by the photographing lens 2. It is determined in what direction and how far the position to be determined is from the primary imaging plane. The defocus amount at this time is used as an index indicating the focus adjustment state of the photographing lens 2.

  By the way, for example, when a change in position deviation or the like occurs in the separator lenses 64a and 64b due to a change over time, the defocus amount obtained by the above-described calculation may differ from the actual defocus amount. As will be described later, in the present embodiment, an accurate defocus amount is obtained by correcting the defocus amount by the above calculation using the image data of the image sensor 8 described above. The primary imaging plane described above is configured to coincide with a position optically equivalent to the imaging element 5 for photographing.

  FIG. 4 is a block diagram for explaining a control system of the camera 1 shown in FIG. The signal processing circuit 21 performs processing such as gain adjustment and noise removal on the analog image signal read out from the image pickup device 5 for photographing and then performs A / D conversion, and further performs white balance adjustment, contour compensation, and gamma. Perform processing such as correction. The compression / decompression circuit 22 compresses the original image and decompresses the compressed image in a predetermined compression format (for example, JPEG method).

  The buffer memory 23 is a memory that temporarily stores original image data after imaging and image data after compression, and SRAM, VRAM, SDRAM, or the like can be used. The memory card 24 is a detachable recording medium for recording images, and a flash memory or the like can be used. The shutter drive device 25 opens and closes the shutter 10 with an actuator, and the aperture drive device 26 opens and closes the aperture 11 with an actuator. The lens driving device 27 drives the focus lens of the photographing lens 2 by an actuator.

  The signal processing circuit 31 is a signal processing circuit related to the contrast AF imaging device 8, and performs A / D conversion after performing processing such as gain adjustment and noise removal on the analog image signal read from the imaging device 8. I do. The processed signal is input to the controller 28 and temporarily stored in the buffer memory 23.

  The controller 28 includes a microcomputer and peripheral components such as a ROM, a RAM, and an A / D converter, and performs focus adjustment control, exposure control, flash light emission control, imaging control, and the like. The controller 28 includes a band pass filter 32 relating to the output signal of the image sensor 8, an integration circuit 33, and an AF control circuit 34. The controller 28 is connected to a half-press switch 29 that is turned on when a shutter button (not shown) is half-pressed, a release switch 30 that is turned on when the shutter button is fully pressed.

  Of the image data stored in the buffer memory 23 from the signal processing circuit 31, focus detection data, that is, data in the AF area is read from the buffer memory 23 and input to the bandpass filter 32. The bandpass filter 32 extracts a predetermined high frequency component from the spatial frequency of the focus detection image data. In the integration circuit 33, integration is performed with respect to the absolute value of the extracted high frequency component. This integrated value is used as a contrast evaluation value during focus adjustment.

  FIG. 5 is a diagram illustrating the relationship between the position of a focus lens (not shown) provided in the photographing lens 2 and the contrast evaluation value. In FIG. 5, the horizontal axis represents the position of the focus lens, and the vertical axis represents the contrast evaluation value. The lens position P with the maximum contrast evaluation value corresponds to the focus position of the focus lens. The AF control circuit 34 shown in FIG. 4 maximizes the contrast so that the contrast evaluation value calculated by the integration circuit 32 is maximized, that is, the blur of the edge of the subject image captured by the image sensor 8 is eliminated. In this way, the lens driving device 27 is controlled to move the focus lens in the optical axis direction.

  Such AF control is generally called “contrast method” AF operation. In the focusing operation using the contrast method, the contrast evaluation value is calculated by taking the shooting data, and the lens speed at which the contrast evaluation value is maximized is detected while comparing the calculated value with the immediately preceding calculation value. It has the disadvantage of being slow. On the other hand, there is an advantage that focusing with higher accuracy can be performed.

  Note that, as described above, integration is performed after passing through the band-pass filter 32 to obtain an evaluation value. However, local frequency components may be calculated by window function Fourier transform, wavelet transform, or the like to obtain an evaluation value.

  The AF control circuit 34 in FIG. 4 drives the focus lens in the ∞ (infinity) direction if the contrast evaluation value changes from increasing to decreasing while driving the focus lens in the closest direction in FIG. 5. Conversely, if the contrast evaluation value changes from increasing to decreasing while driving the focus lens in the ∞ direction, the focus lens is driven in the closest direction. By performing such control, the lens position P at which the contrast evaluation value is maximized as shown in FIG. 5 is detected.

  In the operation of detecting the lens position at which the contrast evaluation value is maximized, for example, if the imaging data is captured at a sufficiently fine driving distance interval from the beginning, if the lens position at which the contrast evaluation value is maximized is passed once, It is only necessary to return the focus lens to the maximum lens position and stop. Also, when the operation of turning the driving direction back and forth in the infinity direction and the close-up direction is repeated, the drive distance interval for capturing image data every time the driving direction is turned back is made finer, and the contrast when driving at a predetermined interval There is also a method of returning the focus lens to the lens position where the value is maximized and stopping. Furthermore, after performing the operation of driving the focus lens while capturing image data intermittently for a predetermined drive range, the maximum position is calculated from the contrast evaluation value based on the output data obtained during that time, and the focus is focused on that position. There is also a way to return the lens.

  The controller 28 is provided with an AF control circuit 66 that performs AF control by the above-described phase difference method based on detection data of the focus detection device 61, in addition to the AF control circuit 34 that performs AF control by the contrast method. When the half-press switch 29 is turned on, the controller 28 performs an AF operation as will be described later. Note that the correction value rewriting circuit 35 and the contrast determination circuit 36 provided in the memory 71, the correction value memory 72, and the controller 28 are components related to correction in the AF operation, and will be described in the correction operation described later.

[Explanation about AF operation of camera]
As described above, the camera according to the present embodiment includes the two AF control circuits 34 and 66 having different methods, and the focusing operation can be performed by using these AF control circuits 34 and 66 together. In that case, first, the focusing operation by the phase difference method is performed based on the detection result of the focus detection device 61, and then the highly accurate focusing operation by the contrast method is performed.

  In addition to the combined use, the AF operation may be performed only by the phase difference method or the contrast method depending on the situation. For example, when the subject has low luminance, focus detection cannot be performed using either the phase difference method or the contrast method. In such a case, as in a conventional silver salt type single-lens reflex camera, the auxiliary light is irradiated and the focusing operation is performed by the phase difference method. In addition, when the distance of the subject is changing as in moving body photography, it is impossible to accurately focus with the contrast method, which takes time for focus detection. In such a case, the focusing operation is performed only with the phase difference method. Like that.

  Further, an input operation unit that is an instruction unit for selecting a focus detection method may be provided in the camera so that the user can select a focus detection method. That is, the user may be able to select a combination of the phase difference method and the contrast method, only the phase difference method, or only the contrast method. For example, when it is desired to perform fast focus detection, a phase difference method may be selected.

[Description of correction in phase difference focus detection]
By the way, it is desirable that the in-focus position by the phase difference method coincides with the lens position P at which the contrast evaluation value reaches a peak. However, in actuality, there is a difference between the calculated defocus amount and the actual defocus amount due to an assembly error of the focus detection device 61, a change with time after the assembly, and the like, and the lens position is the peak position P (FIG. 5). The position is shifted from the reference). Therefore, in the present embodiment, the defocus amount based on the detection data of the focus detection device 61 is corrected by the method described below so that the focus operation start position A by the contrast method is always near the peak position P. I made it.

  As described above, in the focusing operation using the contrast method, the contrast evaluation value of the predetermined range H centering on the lens position A is first calculated and then the peak position P is detected (see FIG. 7A). ) Or a method of detecting the peak position P by repeatedly calculating the contrast evaluation value every time the focus lens is moved by a predetermined amount and moving the focus lens in the direction in which the contrast evaluation value increases from the lens position A. (See FIG. 7B).

  In either method, every time the focus lens is moved by a predetermined amount, imaging data is output from the imaging element 8, and a contrast evaluation value is calculated for each imaging data. In the present embodiment, the AF sensor 65 of the focus detection device 61 (see FIG. 2) is synchronized with the timing of outputting the imaging data from the imaging device 8 of FIG. 4 to the signal processing device 31 during the focusing operation by the contrast method. The detection data output from is acquired, and the obtained detection data is stored in the memory 71.

  Here, in the case of the image sensor 8 and the AF sensor 65 configured by a CCD, the synchronization means that the charge accumulation start time and the end time of the CCD are made the same. It should be noted that the synchronization does not necessarily need to be exactly the same, and there is no practical problem even if the time from the start to the end of storage is different.

  When the imaging data and the detection data output in synchronization are acquired in this way, a contrast evaluation value is calculated for each imaging data, and a maximum contrast evaluation value is obtained. When the AF control circuit 66 reads the detection data output in synchronization with the imaging data giving the maximum contrast evaluation value from the memory 71 and performs the phase difference type focus detection calculation, the maximum contrast evaluation value is obtained. The defocus amount is calculated.

  For example, when the focusing operation is performed by the method shown in FIG. 6B, as shown in FIG. 7A, the contrast evaluation values C1 to Cp at the respective lens positions during the focusing operation by the contrast method are obtained. can get. FIG. 7B shows the defocus amounts calculated from the detection data output in synchronization with the output of the imaging data, and the defocus amounts D1 to Dp are the contrast evaluation values C1 to Cp. It represents the defocus amount at the same lens position.

  The lens position A is a lens driving position (position determined to be in focus) by a phase difference focusing operation, and the defocus amount Da at the lens position A is Da = 0. When the focus lens drive in the focusing operation is sequentially performed, the contrast evaluation values are acquired in the order of C1, C2, Cp, and C3, and finally the focus lens is driven to the lens position P where the contrast evaluation value is the maximum. . The AF control circuit 66 calculates the defocus amount Dp at the lens position P based on the detection data output in synchronization with the imaging data giving the maximum contrast evaluation value Cp.

  In the example shown in FIGS. 7A and 7B, since the focus detection device 61 has a change with time, when the focus lens is at the lens position P, the defocus amount that should originally be Dp = 0 is Dp ≠. 0. The curve L in FIG. 8 is an example of the relationship between the original lens position and the defocus amount D, and the curve L ′ indicates the relationship between the lens position and the defocus amount D when there is a change over time. ing. In the example shown in FIG. 8, the curve L ′ is obtained by shifting the curve L to the right in the figure.

  In the initial setting before correction (described later) in the present embodiment, the defocus amount is calculated based on the curve L in FIG. Therefore, when the defocus amount is calculated when the focus lens is at the lens position B as shown in FIG. 8, what should originally be Db is calculated as Db '. When such a defocus amount Db ′ is obtained, the lens drive amount for moving the focus lens to the in-focus position is determined as the distance F (Db ′) from the lens position B to the lens position A. As a result, the focus lens is driven not to the lens position P where the maximum contrast evaluation value Cp is obtained but to the lens position A.

The lens driving amount F (Db ′) is larger than the lens driving amount F (Db) from the lens position B to the lens position P at which the maximum contrast evaluation value Cp is obtained, and the relationship of the following expression (1) is established. In the present embodiment, Dp ′ is used as correction data.
F (Db) = F (Db ′) − F (Dp ′)
≒ F (Db'-Dp ') (1)

  The correction data Dp ′ calculated by the AF control circuit 66 is once inputted to the correction value rewriting circuit 35. The correction value rewriting circuit 35 rewrites the correction data stored in the correction value memory 72 with the calculated correction data Dp ′ according to the determination result of the contrast determination circuit 36. That is, the correction value memory 72 is a memory for storing the correction data Dp ′ and is rewritten to new correction data Dp ′ one after another by the correction value rewriting circuit 35.

  When rewriting correction data, it is recommended to rewrite the correction data based on the most recent correction data, such as storing the correction data of the past several times close in time and taking the average value with them. Is preferred. Thereby, it is possible to mitigate the influence of variations in imaging data and detection data.

  When performing the focusing operation by the phase difference method, the defocus amount D ′ is calculated based on the detection data from the focus detection device 61, and the lens driving amount F (D ′) at that time is calculated. Since this lens drive amount F (D ′) includes an error due to a change with time of the focus detection device 61 or the like, the correction data Dp ′ stored in the correction value memory 72 is used as in the equation (1). To correct. That is, the corrected lens driving amount F (D) is given by F (D) = F (Db′−Dp ′) ≈F (D ′) − F (Dp ′). Then, a focusing operation is performed using the corrected lens driving amount F (Db). As a result, the focus lens is moved to the lens position P where the contrast evaluation value C is the maximum value Cp.

  In the above-described example, when obtaining correction data, every time imaging data is output from the imaging device 8, detection data output from the focus detection device 61 is acquired and stored in the memory 71 in synchronization therewith. However, detection data may be acquired and stored every time imaging data is output a predetermined number of times. In this case, the detection data E at the acquisition time closest to the acquisition time of the imaging data giving the maximum contrast evaluation value Cp is read from the memory 71, the defocus amount De ′ based on the detection data E is calculated, and the defocus amount A lens driving amount F (De ′) corresponding to De ′ is calculated (see FIG. 9).

Since the lens drive amount F ′ from the output of the imaging data giving the maximum contrast evaluation value Cp until the detection data E is output is known, a defocus amount Ds corresponding to F ′ is calculated, and correction in this case The data becomes “Ds + De ′”, and this value is written in the correction value memory 72. When the defocus amount D ′ is obtained during the focusing operation by the phase difference method, the corrected lens driving amount F (D) is calculated by the following equation (2). In this case, the detection data acquired in synchronism is small, and the memory 71 does not require a large capacity.
F (D) = F (D′−Ds−De ′)
≒ F (D ')-F'-F (De') (2)

  The calculation of the correction data described above may be performed for each photographing operation, may be performed every time the photographing operation is performed a predetermined number of times, or may be performed at predetermined time intervals.

[Description of rewrite judgment operation]
Next, the correction data rewrite determination operation by the contrast determination circuit 36 will be described. In the rewriting determination operation performed here, it is determined whether or not the new correction data when rewriting by the correction value rewriting circuit 35 is reliable.

  By the way, it is desirable that the contrast type imaging device 8 has optically fine pixels so that focus detection can be performed even for a fine pattern. On the other hand, in the case of the AF sensor 65 which is an image sensor for phase difference method, in order to obtain a focus detection speed, the pixel is enlarged to some extent to shorten the accumulation time. Therefore, when the light receiving unit of the image sensor 8 and the light receiving unit of the AF sensor 56 are projected onto a surface optically conjugate with the imaging surface of the imaging image sensor 5, the pixel pitch of the projected image is generally a contrast method. The image sensor 8 has finer pixels.

  Therefore, when the contrast evaluation value of the high frequency component of the imaging data of the imaging device 8 is considerably large, it indicates that there is a fine pattern that cannot be captured by the AF sensor 65. That is, when the contrast evaluation value of the high-frequency component of the finer image sensor output is too large, the other image sensor cannot grasp the high-frequency information, resulting in a mismatch between the focus detection results of both. In this case, it is determined that the detection result is not reliable, and the correction data in the correction value memory 72 is not rewritten.

  When comparing the pixel pitches, the actual pixel pitches of the image sensor 8 and the AF sensor 65 are not compared, but the appearance on a surface optically conjugate with the image pickup surface of the image pickup device 5 for photographing. Compare the top pixel pitch. As shown in FIG. 1, the contrast type imaging device 8 and the finder screen 4 are in an optically conjugate positional relationship via a hologram 7 or the like on the optical path therebetween. For this reason, when the light receiving surface of the image sensor 8 is back-projected onto the finder screen 4 that is optically conjugate with the imaging surface of the image sensor 5 for photographing, an image is formed on the finder screen 4. That is, the projected image on the finder screen 4 becomes a projected image on a surface optically conjugate with the imaging surface of the imaging element 5 for photographing.

  On the other hand, the light receiving surface of the AF sensor 65 that is an imaging element for the phase difference method is conjugated to the primary imaging plane via the field lens 63 and the separator lens 64 as shown in FIG. Therefore, a back projection image of the light receiving surface of the AF sensor 65 is formed on the primary image forming surface through these optical elements. Since the primary imaging surface is optically conjugate with the imaging surface of the imaging device 5 via the sub-mirror 60, the back-projected image on the primary imaging surface is optically conjugate with the imaging surface of the imaging device 5. It corresponds to the projected image on the surface.

  When making the determination, the imaging data giving the maximum contrast evaluation value Cp is read from the buffer memory 33 in FIG. 1 and the high-frequency component is extracted by the band-pass filter 32. However, the high frequency component in this case is extracted at a higher frequency side than the high frequency component used when calculating the contrast evaluation value for contrast AF. This extraction reference frequency cannot be detected by the AF sensor 65 in consideration of the pixel pitches of the AF sensor 65 and the image sensor 8 projected onto a surface optically conjugate with the imaging surface of the imaging element 5 for photographing. The lower limit frequency of the high frequency component that seems to be. The contrast determination circuit 37 compares the extracted high-frequency component contrast evaluation value with a predetermined reference value. If the contrast evaluation value is larger than the reference value, the contrast determination circuit 37 determines that there is no reliability. Output to.

  Here, the reliability determination is performed only with the high-frequency component included in the imaging data of the imaging device 8 with the finer apparent pitch, but the contrast evaluation value based on the output of the AF sensor 65 that is the imaging device with the coarser pitch is used. The determination may be made by relative comparison. FIG. 10 shows a block diagram in such a case. The detection data stored in the memory 71 is processed by the band-pass filter 73 and the integrating circuit 74 to calculate a contrast evaluation value. The calculation result is input to the contrast comparison determination circuit 37. The contrast comparison / determination circuit 37 calculates the ratio between the contrast evaluation value based on the imaging data of the image sensor 8 and the contrast evaluation value output from the integration circuit 74. If the ratio is equal to or greater than a predetermined value, it is determined that there is no reliability as in the above-described determination, and the correction data in the correction value memory 72 is not rewritten.

  In the example described above, since the apparent pixel pitch is generally finer in the contrast type imaging element 8 than in the phase difference type AF sensor 65, such a case has been described. Even if it exists, this invention is applicable. Even in such a case, it is possible to determine whether or not the correction should be performed by evaluating the high frequency component of the output of the image sensor having a finer apparent pixel pitch.

  In the above, the reliability is determined based on whether or not the high-frequency component of the image sensor 8 having a fine pixel pitch is larger than the reference value. However, the reliability determination criterion is not limited to this. For example, there may be a case where the temperature or the camera posture has changed greatly or a shake has occurred, or the subject has changed like a moving object, and these may be used for reliability determination.

  In the camera shown in FIG. 1, the subject light is reflected by the main mirror 3 and the subject image is observed through the viewfinder eyepiece 9. However, the image is taken by the image sensor 8 as shown in FIG. The subject image may be displayed on the display device 100 such as an LCD, and the subject image may be observed. In the camera shown in FIG. 11, the image sensor 8 is disposed at a position where the finder screen 4 (see FIG. 1) is disposed, and a subject image is formed on the imaging surface of the image sensor 8 by the photographing lens 2. The imaging data output from the imaging element 8 is subjected to image processing by the processing circuit 101, and a subject image is displayed on the display device 100.

  The reflected light of the main mirror 3 is guided to the image sensor 8 and the contrast evaluation value is calculated based on the output value of the image sensor 8. For example, a part of the subject light is used for phase difference using a half mirror or a diffraction grating. The focus detection device 61 may be configured to guide the remaining subject light to the imaging element 5 for imaging, and the contrast evaluation value may be calculated using the output of the imaging element 5 for imaging.

As described above, the camera of the present embodiment can provide the following operational effects.
(A) The imaging data for the contrast method and the detection data for the phase difference method are output in synchronization, and the defocus amount at the focus lens position where the maximum contrast evaluation value is obtained from these data is obtained, and the defocusing is performed. Since the lens drive amount at the time of phase difference focusing operation is corrected based on the correction data obtained from the amount, it is possible to avoid erroneous correction due to mismatch of the target subject as in the past, and focus by the phase difference method Adjustment can be performed with high accuracy.
(B) When the contrast evaluation value of the high-frequency component of the image sensor with a smaller apparent pixel pitch is larger than the reference value, the correction data is not reliable and is not used for correction. It is possible to prevent erroneous correction due to the presence of a fine pattern in the subject that cannot be captured by the image sensor having the coarser pitch.

  In the correspondence between the embodiment described above and the elements of the claims, the main mirror 3 is the light splitting means, the image sensor 8 is the first image sensor, the AF control circuit 34 is the first control means, The AF sensor 65 is the second image sensor, the image sensor 5 is the image sensor of the image recording imaging means, the integration circuit 33 is the contrast evaluation value calculation means and the high-frequency contrast calculation means, and the AF control circuit 66 is the focus detection value calculation. Means, correction data calculation means and second control means, the correction value memory 72 is memory, contrast judgment circuit 36 and contrast comparison judgment circuit 37 are judgment means, display device 100 is display means, finder screen 4, pentagon The prism 6, hologram 7, reflector 12 and viewfinder eyepiece 9 constitute an observation optical system. In addition, the present invention is not limited to the above embodiment as long as the characteristics of the present invention are not impaired.

It is a figure which shows one Embodiment of the camera by this invention, and is a figure which shows schematic structure of the focus detection relationship of the single-lens reflex digital still camera. 3 is a perspective view showing a configuration of a focus detection device 61. FIG. It is a figure which shows the example of an output signal by line sensor 65a, 65b. 2 is a block diagram illustrating a control system of the camera 1. FIG. FIG. 6 is a diagram illustrating a relationship between a position of a focus lens provided in the photographing lens 2 and a contrast evaluation value. It is a figure explaining the focusing operation | movement by a contrast system, (a) shows a 1st example and (b) shows a 2nd example. It is a figure explaining the amount of defocusing, (a) shows the relationship between a lens position and contrast evaluation value C, (b) shows the relationship between a lens position and defocus amount D. It is a figure explaining the defocus amount when there exists a change with time. It is a figure explaining the defocus amount in the case of acquiring detection data every time imaging data is acquired a predetermined number of times. FIG. 6 is a block diagram when a contrast comparison / determination circuit 37 is provided. 3 is a block diagram of a camera that displays a subject image on the display device 100 based on imaging data of the imaging element 8.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Camera 2 Shooting lens 3 Main mirror 4 Finder screen 5,8 Image pick-up element 6 Penta prism 7 Hologram 9 Finder eyepiece 27 Lens drive device 28 Controller 32, 73 Band pass filter 33, 74 Integration circuit 34, 66 AF control circuit 35 Correction Value rewriting circuit 36 Contrast judgment circuit 37 Contrast comparison judgment circuit 60 Sub mirror 61 Focus detection device 65 AF sensor 100 Display device

Claims (7)

Light splitting means for splitting the subject light that has passed through the photographing lens into first light and second light;
A first image sensor for detecting a subject image by the first light;
Contrast evaluation value calculating means for calculating a contrast evaluation value based on an output signal of the first image sensor;
First control means for performing contrast focus adjustment based on the contrast evaluation value;
A second image sensor for detecting a subject image by the second light;
Focus detection value calculation means for calculating a focus detection value by a phase difference method based on an output signal of the second image sensor;
Synchronous detection by the second image sensor is performed in synchronization with detection of the first image sensor at the time of focus adjustment based on the contrast evaluation value, and the output signal from the second image sensor at the time of synchronization detection is used. Correction data calculation means for calculating correction data for correcting the focus detection value based on the calculation result of the focus detection value calculation means;
A memory for storing the correction data;
A camera comprising: second control means for correcting the focus detection value based on the correction data stored in the memory and performing focus adjustment based on the corrected focus detection value. The camera of claim 1,
The camera is characterized in that the synchronization detection is performed by a photographing instruction, and correction data is calculated by the correction data calculating means for each photographing instruction. The camera according to claim 1 or 2,
A camera characterized in that an image pickup device of an image recording image pickup means is used as the first image pickup device. The camera according to claim 1 or 2,
In the first image sensor and the second image sensor, the pixel pitches in the projected image of the light receiving unit when the respective light receiving units are projected onto a surface optically conjugate with the imaging surface of the image recording imaging unit are mutually equal. Is different,
Whether or not to rewrite correction data stored in the memory based on a contrast evaluation value calculated from an output signal output at the time of synchronization detection from an image sensor having a smaller pixel pitch in the light receiving unit projection image A camera comprising determination means for determining whether or not. The camera according to claim 4, wherein
A high-frequency contrast calculation means for extracting a high-frequency component of an output signal output at the time of synchronization detection from an image sensor having a smaller pixel pitch in the light-receiving unit projection image and calculating a contrast evaluation value of the high-frequency component;
The determination unit determines that the correction data stored in the memory is not rewritten when the contrast evaluation value calculated by the high-frequency contrast calculation unit is larger than a predetermined reference value. The camera according to any one of claims 1 to 5,
An observation optical system for guiding the first light and observing a subject image;
A camera, wherein a part of the first light guided through at least a part of the observation optical system is detected by the first image sensor. The camera according to any one of claims 1 to 5,
A camera comprising display means for displaying a subject image obtained by the first image sensor.

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