JP2005092085A - Focus detecting method and focusing method, and focus detecting device and focusing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily improve the accuracy of focusing without photographer's intention. <P>SOLUTION: Focusing is performed by a phase difference detection system (S101), and focusing is performed by a contrast detection system (S102), then a difference between respective focusing positions is detected and stored (S103). Then, the conversion coefficient of the phase difference system is updated (S104). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to focus detection and adjustment in a photographing apparatus such as a silver salt / digital still camera or a video camera.

  Conventionally, many proposals have been made and realized in which a light beam that has passed through a photographing lens is re-imaged on a sensor to automatically adjust the focus. These are classified into two typical methods, and are called a blur method and a shift method. At present, a method of detecting a relative positional shift in an image signal on a pair of sensors called a shift method is common in a single-lens reflex camera or the like.

  First, the above-described shift method will be briefly described with reference to FIG. As shown in FIG. 18, the basic components are a field mask (MSK) and a field lens (FLDL) arranged in the vicinity of a planned image formation surface on which a subject image is formed by a photographic lens (LNS), and a porous film is provided behind the field mask. A secondary optical system (AFL-a, b) having a diaphragm (DP-a, b) and a secondary imaging lens, and a plurality of photoelectric conversion element arrays (SNS-a, b) arranged behind it. is there.

  With this configuration, two subject images formed by light beams that have passed through two different pupil regions (PUP-a, b) of the photographic lens are re-imaged on different photoelectric conversion element arrays, and the relative relationship between the two subject images. An automatic focus detection device is realized by utilizing the fact that the target positional relationship changes depending on the focus state of the photographic lens.

  The “deviation amount” that is the relative positional relationship between the two subject images described above can be obtained by obtaining the correlation. An example of a calculation method for specifically obtaining this will be described with reference to FIG.

  The area U (the sum of the smaller values of the A image and B image) of the AND region of the two subject images (A image and B image) shown in FIG. 19 is converted into one image (A image in this example) as a photoelectric conversion element. Each pixel (1 bit) is shifted and the maximum value is obtained. If the A image and the B image coincide with each other, the maximum value is inevitably obtained. Therefore, the shift amount that brings about the maximum value is the relative shift amount between the A image and the B image.

  In these focus detection apparatuses, the distance between the centers of gravity of the two pupil regions becomes the base line length in triangulation, and the relative shift amount on the photoelectric conversion element and the focus shift amount of the photographing (objective) lens (hereinafter referred to as defocus amount). ).

  For example, since the lens interval of the secondary imaging lens is different between the optical axis of the photographing lens and the optical axis, a focus detection device having a conversion coefficient for each different lens interval of the secondary imaging lens has been proposed ( For example, see Patent Document 1.)

  In addition, a focus detection device has been proposed in which a calculation range is determined from an image signal of a photoelectric conversion element array and a conversion coefficient corresponding to the contrast center of gravity is obtained by calculation (see, for example, Patent Document 2).

  Furthermore, the conversion coefficient is not a problem if there is no vignetting in the focus detection light beam, but vignetting of the light beam may occur depending on the brightness of the photographing lens. On the other hand, a focus detection apparatus using a conversion coefficient corresponding to the brightness of the photographing lens has been proposed (see, for example, Patent Document 3).

  On the other hand, the blur method described above is also called a contrast detection method, and is often used in video movie equipment (camcorder) for video recording and electronic still cameras. This blur method is different from the above-described shift method, that is, a method of detecting a phase difference, and generally uses an image sensor as a focus detection sensor. This is a method in which focusing on the information (contrast information) of the high frequency component of the output signal of the image sensor, and the position of the photographing lens having the largest evaluation value is used as the in-focus position. However, as it is said to be a hill-climbing method, it is necessary to calculate the evaluation value while moving the photographic lens by a small amount and move it until it is found that the evaluation value is the maximum as a result, and it is not suitable for high-speed focus adjustment operation. Has been. However, since it is evaluated from the signal of the image sensor itself, a high accuracy can be obtained.

  On the other hand, a method for realizing compatibility between the above-described shift method and blur method using a line sensor for focus detection is disclosed (for example, see Patent Document 4).

Furthermore, the present applicant has proposed a focus detection apparatus that can obtain an evaluation value of a phase difference detection method while being an image sensor (see, for example, Patent Documents 5 and 6).
JP-A-63-172210 JP-A-8-94916 Japanese Patent Laid-Open No. 61-18911 JP 59-146010 A JP 2000-156823 A JP 2001-305415 A

  The countermeasure against the problem of the conversion coefficient in the above-described shift method focuses on the position of the focus detection area on the photographing screen and the brightness of the photographing lens. However, when the position on the shooting screen is set largely off the optical axis, the degree of vignetting changes depending not only on the brightness of the shooting lens but also on the exit pupil of the shooting lens. Can no longer be obtained.

  20 and 21 are diagrams for explaining the vignetting condition. FIG. 20 is a diagram illustrating the state of the focus detection light beam at the exit pupil of the photographing optical system, and is the focus detection light beam on the optical axis (0) without any vignetting.

  On the other hand, FIG. 21 is a diagram showing the degree of vignetting at two points (h and i) outside the optical axis, where h is a point on the Y axis (up and down in the drawing), and two images of the focus detection light beam. On the other hand, vignetting occurs almost evenly. However, at the point i displaced in the X-axis (left and right direction on the paper surface), a more complicated vignetting is performed. As a result, the distance between the centers of gravity of the two images changes, and the conversion coefficient also changes in a complicated manner.

  According to the focus detection and adjustment method of the present invention, a photoelectric conversion step of photoelectrically converting a pair of light images emitted from the same part of the subject and input via different paths, and detection from the pair of photoelectrically converted light images A first focus adjustment step for adjusting the objective lens to the in-focus position based on the relative shift amount and a conversion coefficient for converting the relative shift amount into the focus shift amount of the objective lens, and a pair of photoelectrically converted light A second focus adjustment step for adjusting the objective lens to a focus position based on contrast information detected from the image, and the conversion coefficient is updated based on the focus positions adjusted in the first and second focus adjustment steps, respectively. And an updating process.

  In addition, the focus detection and adjustment apparatus of the present invention includes a photoelectric conversion unit that photoelectrically converts a pair of light images emitted from the same portion of the subject and input via different paths, and a pair of photoelectrically converted light images. A first focus adjusting means for adjusting the objective lens to the in-focus position based on a relative deviation amount detected from the lens and a conversion coefficient for converting the relative deviation amount into a focus deviation amount of the objective lens, and a photoelectrically converted pair Second focus adjusting means for adjusting the objective lens to the in-focus position based on the contrast information detected from the optical image of the first image, and the conversion coefficient based on the in-focus positions adjusted by the first and second focus adjusting means, respectively. And updating means for updating.

  According to the present invention, it is possible to easily improve the focus adjustment accuracy without the photographer's intention. Therefore, the effectiveness of the phase difference detection method capable of performing a quick autofocus operation with a short distance measurement time can be sufficiently extracted.

  The best mode for carrying out the invention will be described below in detail with reference to the drawings. In the following, after focus detection and adjustment by the phase difference detection method, focus detection and adjustment by the contrast detection method are performed, and the difference between the detection adjustment results is stored and learned, and the conversion coefficient is updated by the phase difference detection method. An electronic still camera will be described as an example of an image capturing apparatus that learns the correct conversion coefficient for each image capturing and easily improves the focus adjustment accuracy without the photographer's intention.

  FIG. 1 is a block diagram illustrating a structure of an electronic still camera in the embodiment. In FIG. 1, 1 is a photographing lens, 2 is a shutter having a diaphragm function, 3 is an image sensor for converting an optical image into an electrical signal by a CCD or C-MOS, and 4 is a known camera signal process such as gamma correction. A process circuit 5 is an A / D converter that converts the analog output of the process circuit 4 into a digital signal, 6 is an image compression circuit that compresses image data by adaptive discrete cosine transform (ADCT), and 7 is an image compression circuit 6. This is a changeover switch for switching between transmission of image data compressed by the above and image data bypassing the image compression circuit 6 (not compressed).

  8 is a microphone for external audio input, 9 is a noise reduction circuit for reducing noise of the audio signal output from the microphone 8, 10 is an A / D converter for converting the analog output of the noise reduction circuit 9 into a digital signal, and 11 is An audio compression circuit that compresses audio data using adaptive differential PCM (DPCM) or the like, and 12 is a change-over switch that switches transmission of audio data compressed by the audio compression circuit 11 and audio data that bypasses the audio compression circuit 11.

  Reference numeral 13 denotes a buffer memory that temporarily stores at least image data (video signal) and audio data (audio signal), and can read out the temporarily stored data (signal) at a desired speed by a memory control circuit described later. is there.

  A memory control circuit 14 controls the A / D converters 5, 10, the image compression circuit 6, the audio compression circuit 11, the changeover switches 7 and 12, and the buffer memory 13. Here, when the image data is compressed, the image data compressed by the image compression circuit 6 is buffered under the control of the memory control circuit 14 when the image data output from the A / D converter 5 is not compressed. It is written in the memory 13. When the audio data is compressed, the audio data compressed by the audio compression circuit 11, and when the audio data is not compressed, the audio data output from the A / D converter 10 is controlled by the memory control circuit 14. Is written to.

  Reference numeral 15 denotes a memory card or hard disk, which will be described later, or an interface (I / F) with an external device, 16 a memory card, and 17 a hard disk. Reference numeral 18 denotes a connector on the camera body side, which electrically connects the memory card 16 or the hard disk 17 to the camera body.

  The recording area of the memory card 16 includes a management data area 19 and an information data area 20, and information in these areas is read and written from the camera body via the interface 21 and the connector 22 on the memory card 16 side. Information on the write protect (write prohibition) 23 can also be read from the camera body via the interface 21 and the connector 22. Here, the interface 21 includes a control circuit such as a CPU and an MPU, a nonvolatile memory such as a ROM and an EEPROM, a RAM, and the like, and controls the memory card 16 based on a predetermined program.

  On the other hand, the storage area of the hard disk 17 includes a management data area 24 and an information data area 25. Information in these areas is read and written from the camera body via the interface 26 and the connector 27. The interface 26 includes a control circuit such as a CPU and an MPU, a nonvolatile memory such as a ROM and an EEPROM, and a RAM. The interface 26 controls the hard disk 17 based on a predetermined program.

  28 is a shutter driving circuit for driving the shutter 2, 29 is a lens driving circuit for driving a focusing lens in the photographing lens 1, 30 is a distance measuring circuit for adjusting the focus of the photographing optical system to the subject, and 31 is a brightness of the subject. A photometric circuit to be measured, 32 is a flash, and 33 is a temperature detection circuit, which detects the temperature of the recording medium and the presence or absence of freezing or condensation.

  Reference numeral 34 denotes a power supply control circuit for detecting and controlling the state of the power supply, and reference numeral 35 denotes a power supply unit, which includes a battery, a DC-DC converter, a switch for switching energized blocks, and the like, and is controlled by the power supply control circuit 34. The power supply control circuit 34 detects the presence / absence of a battery, the type of battery, and the remaining battery level, and controls the power supply unit 35 based on the detection result and instructions from a system control circuit described later.

  Reference numeral 36 denotes a display device that displays the camera operation state (number of shots, etc.), and 37 is a control memory that stores shooting operation constants, variables, and the like of the system control circuit 39.

  Reference numeral 38 denotes a switch group for inputting various operation instructions to a system control circuit described later. The switch group 38 includes, for example, a main switch 40, a distance measuring and metering switch 42 that is closed by a first stroke of the release button 41, and instructs distance measurement and metering by the distance measuring circuit 30 and the metering circuit 31, and a release button. A recording switch 43 that is closed by the second stroke 41 and instructs to record a photographed image on the memory card 16 or the hard disk 17, and a single (S) mode for photographing one or one set, a plurality of consecutive sheets. Or, a mode switch 44 for selecting one of a continuous (C) mode for performing a plurality of sets of photographing and a self-timer photographing mode, a one-shot mode for performing a focus adjustment operation only once, and a servo mode for performing continuously. Switch 45 to be selected, number of recorded images, distinction between frame recording / field recording, aspect ratio, pixel configuration, compression method, pressure An image mode switch 46 for selecting an image recording method such as a rate (in the figure, it is written as a single switch, but is composed of a plurality of switches), an erasing mode is selected, and erasing is executed. There are an erasing switch 47 for instructing, an audio recording main switch 48 for designating on / off of audio recording, and an audio recording execution switch 49 for instructing execution of audio recording.

  Reference numeral 39 denotes a system control circuit, which corresponds to an instruction from the switch group 38, detection of the type of recording medium attached to the camera body and the state of the recording medium (remaining storage capacity, etc.), and other detection devices for the camera body described above. Performs overall control of the camera body. For example, according to the detection result of the distance measuring circuit 30, the focusing lens of the photographing lens 1 is driven by the lens driving circuit 29 to control the photographing lens 1 in a focused state. Further, the system control circuit 39 performs control such as determining the opening time of the shutter 2 by the shutter driving circuit 28 so that the optimal exposure amount is obtained based on the photometric result of the photometric circuit 31.

  Reference numeral 50 denotes a connector which connects an external device such as a personal computer or a printer with a wired interface represented by USB (Universal Serial Bus) or IEEE1394. Not only the wired interface but also a wireless interface such as IrDA or Bluetooth may be used.

  Next, the image sensor 3 in the present embodiment will be described. In the present embodiment, a CMOS process compatible sensor (hereinafter abbreviated as a CMOS sensor), which is one of the amplification type solid-state imaging devices, is used as the imaging element 3.

  One of the features of this CMOS sensor is that the MOS transistor of the light receiving portion and the MOS transistor of the peripheral circuit can be formed in the same process, so that the number of masks and the process steps can be greatly reduced as compared with the CCD. It is done. Taking advantage of this feature, in this embodiment, two photoelectric conversion units are configured in one pixel, and two floating conversion regions (hereinafter referred to as FD regions) and source follower amplifiers conventionally provided in each photoelectric conversion unit are converted into two photoelectric conversions. Only one is formed in the part, and two photoelectric conversion parts are connected to the FD region via the MOS transistor switch.

  Accordingly, the charges of the two photoelectric conversion units can be transferred to the FD region simultaneously or separately, and the signal charges of the two photoelectric conversion units can be added or not added only at the timing of the transfer MOS transistor connected to the FD region. Easy to do. Using this structure, the first addition output mode for performing photoelectric conversion output by the light beam from the entire exit pupil of the imaging optical system and the photoelectric conversion output by the light beam from a part of the exit pupil of the imaging optical system are separately performed. The non-addition output mode to be performed can be switched. In the addition output mode in which signals are added at such a pixel level, a signal with less noise can be obtained as compared with a method of adding signals after they are read out.

  FIG. 2 is a diagram illustrating a circuit configuration of the area sensor unit in the image sensor. In the example shown in FIG. 2, the two-dimensional area sensor has 2 columns × 2 rows of pixels. However, in practice, the number of pixels is increased to obtain a practical resolution.

In FIG. 2, reference numerals 101 and 151 denote first and second photoelectric conversion units each including a MOS transistor gate and a depletion layer under the gate, 102 and 152 are photogates, 103 and 153 are transfer switch MOS transistors, and 104 is a reset MOS transistor. , 105 is a source follower amplifier MOS transistor, 106 is a vertical selection switch MOS transistor, 107 is a source follower load MOS transistor, 108 is a dark output transfer MOS transistor, 109 is a light output transfer MOS transistor, and 110 is a dark output storage capacitor C _TN , the bright output accumulation capacitor C _TS, 112 and 154 are vertical transfer MOS transistors 111, 113 and 155 vertical output line reset MOS transistor, the differential output amplifier 114, 115 is the vertical scanning unit, 116 horizontal scanning unit der .

  FIG. 3 is a cross-sectional view showing the structure of the light receiving section (for example, 130-11) shown in FIG. The light receiving units 130-21, 130-12, and 130-22 have the same structure. In FIG. 3, 117 is a P-type well, 118 and 158 are gate oxide films, 119 and 159 are first-layer poly-Si, 120 and 150 are second-layer poly-Si, and 121 is an n + FD region.

  In this embodiment, the FD region 121 is connected to the first photoelectric conversion unit 101 and the second photoelectric conversion unit 151 via the transfer switch MOS transistors 103 and 153. In the example shown in FIG. 3, the first photoelectric conversion unit 101 and the second photoelectric conversion unit 151 are drawn apart from each other. However, the boundary portion is actually very small, and the first photoelectric conversion unit 101 and the first photoelectric conversion unit 101 are practically used. The two photoelectric conversion units 151 may be considered to be in contact with each other.

  Reference numeral 122 denotes a color filter that transmits light in a specific wavelength range, and reference numeral 123 denotes a microlens for efficiently guiding a light beam from the imaging optical system to the first and second photoelectric conversion units.

  FIG. 4 is a plan view showing the arrangement of the pixels of the image sensor, the photoelectric conversion units, and the color filters. Here, only 4 columns × 4 rows are extracted and shown. Each pixel including the light receiving portion and the MOS transistor is laid out in a substantially square shape and is arranged adjacent to the grid. The light receiving units 130-11, 130-21, 130-12, and 130-22 described above with reference to FIG. 2 are located in the pixels 71-11, 71-21, 71-12, and 71-22, respectively. Here, it is represented as 72-11, 72-21, 72-12, 72-22.

  In this area sensor, R (red), G (green), and B (blue) color filters are alternately arranged in each pixel to form a Bayer array in which four pixels are a set. In this Bayer arrangement, the overall image performance is improved by arranging more G pixels that are easily felt when the observer views the image than the R and B pixels. In general, in this type of image sensor, the luminance signal is generated mainly from G, and the color signal is generated from R, G, and B.

  As described above, each pixel has two photoelectric conversion units, and R, G, and B shown in FIG. 4 are photoelectric conversion units including red, green, and blue color filters. 2 represents the distinction between the first photoelectric conversion unit and the second photoelectric conversion unit. For example, R1 means a first photoelectric conversion unit having a red color filter, and G2 means a second photoelectric conversion unit having a green color filter.

  Further, in each pixel, in order to effectively use the light beam emitted from the imaging optical system, it is necessary to provide a condensing lens in each light receiving unit and deflect light that is to reach other than the light receiving unit to the light receiving unit. Become. For this reason, a microlens is provided in front of the image sensor. The microlens of each pixel is an axisymmetric spherical lens or aspherical lens in which the center of the light receiving portion and the optical axis approximately coincide with each other, each having a rectangular effective portion, and having a light incident side as a convex shape in a lattice shape They are closely arranged.

  The power of each microlens is set so as to project each light receiving portion of the imaging element onto the exit pupil of the imaging optical system. At this time, the projection magnification is set so that the projected image of each light receiving unit is larger than the exit pupil of the stop of the imaging optical system, and the relationship between the amount of light incident on the light receiving unit and the stop of the imaging optical system is approximately linear. . As a result, shooting according to the subject brightness is possible, and focus detection is also possible by operating the two photoelectric conversion units separately.

  Next, a sensor driving method in the embodiment will be described. As described above, by dividing the photoelectric conversion unit into two, the accumulated charges in the two regions can be easily added or not added. Therefore, the operation in the addition mode is performed for imaging and luminance calculation, and the operation in the non-addition mode is performed for focus detection.

First, the outline of the charge accumulation operation of the image sensor will be described with reference to FIGS. To extend the depletion layer under the photo gate 102, 152, the control pulse FaiPG _00, a positive voltage is applied to the φPG _e0. During storage, the FD region 121 is fixed to the power source V _DD by setting the control pulse φR ₀ high to prevent blooming. When photons hν are irradiated and carriers are generated under the photogates 102 and 152, electrons are accumulated in a depletion layer under the photogates 102 and 152, and holes are discharged through the P-type well 117.

  An energy barrier by the transfer MOS transistor 103 is formed between the photoelectric conversion unit 101 and the FD region 121, and an energy barrier by the transfer MOS transistor 153 is formed between the photoelectric conversion unit 151 and the FD region 121. For this reason, electrons are present under the photogates 102 and 152 during photocharge accumulation. Thereafter, if the horizontal scanning unit is scanned and the charge accumulation operation is performed in the same manner, the charge is accumulated in all the photoelectric conversion units.

In the read state, the control pulses φPG ₀₀ , φPG _e0 , control pulses φTX ₀₀ , φTX are used so that the barriers under the transfer MOS transistors 103 or 153 are eliminated and the electrons under the photogates 102 and 152 are completely transferred to the FD region 121. Set _e0 .

  Next, the reading operation of the image sensor will be described using the timing chart shown in FIG. This timing chart is for the non-addition output mode in which the two photoelectric conversion units are independently output, and is used for reading the focus detection image.

First, the horizontal output line is reset by setting the control pulse φL to high by the timing output from the horizontal scanning unit 116. Further, the control pulses φR ₀ , φPG ₀₀ , φPG _e0 are set high, the reset MOS transistor 104 is turned on, and the first-layer poly Si 119 of the photogate 102 is set high. At time T ₀ , the control pulse φS ₀ is set high, the selection switch MOS transistor 106 is turned on, and the light receiving unit 130-11 is selected. Next, the control pulse φR _{0 is set} to low, the reset of the FD region 121 is stopped, the FD region 121 is set in a floating state, and the gate and source of the source follower amplifier MOS transistor 105 are made through, and at time T ₁ , the control pulse φT _{N is set} to high, and the dark voltage in the FD region 121 is output to the storage capacitor C _TN 110 by the source follower operation.

Next, in order to perform photoelectric conversion output of the first photoelectric conversion unit, the control pulse φTX ₀₀ of the first photoelectric conversion unit is set to high and the transfer switch MOS transistor 103 is turned on, and then the control pulse φPG _{00 is set} to low at time T ₂ . Lower. At this time, a voltage relationship is preferable in which the potential well that has spread under the photogate 102 is raised so that photogenerated carriers are completely transferred to the FD region 121.

At time T ₂ , charges from the photoelectric conversion unit 101 of the photodiode are transferred to the FD region 121, so that the potential of the FD region 121 changes according to light. At this time, since the source follower amplifier MOS transistor 105 is in a floating state, the potential of the FD region 121 is output to the storage capacitor C _TS 111 with the control pulse φT _S being high at time T ₃ . At this time, the dark output and the light output of the first photoelectric conversion unit are stored in the storage capacitors C _TN 110 and C _TS 111, respectively, and the control pulse φH _C at the time T ₄ is temporarily high, and the vertical output line reset MOS transistor 113 and 155 is turned on to reset the vertical output line, and in the vertical transfer period, the dark output and light output of the pixel are output to the vertical output line by the scanning timing signal of the vertical scanning unit 115. If the differential output V _OUT is obtained by the differential amplifier 114 of the storage capacitors C _TN 110 and C _TS 111, a signal with good S / N from which random noise and fixed pattern noise of the pixel are removed can be obtained.

The optical charge of the light receiving section 130-12 is being accumulated in the accumulation capacitor C _TN and C _TS husband simultaneously receiving section 130-11 s, the read is delayed by one light-receiving portion of the timing pulses from the vertical scanning unit 115 The data is read out to the vertical output line and output from the differential amplifier 114. Since it is the difference in timing pulse of one light receiving portion, the accumulation time of both can be regarded as substantially the same.

After outputting a bright output to the accumulation capacitor C _TS 111, to turn on the reset MOS transistor 104 a control pulse .phi.R ₀ as high, resetting the FD region 121 to the power supply V _DD.

After the vertical transfer of the first photoelectric conversion unit is completed, the second photoelectric conversion unit is read. In the reading of the second photoelectric conversion unit, the control pulse φR _{0 is set} to low, the resetting of the FD region 121 is stopped, the FD region 121 is set in a floating state, and the gate-source between the source follower amplifier MOS transistor 105 is set to through. a control pulse .phi.T _N and high at time T _5, to output a dark voltage of the FD region 121 again to the storage capacitor C _TN 110 by the source follower operation.

In order to perform photoelectric conversion output of the second photoelectric conversion unit, lowering after conducting the transfer switch MOS transistor 153 to control pulse .phi.TX _e0 of the second photoelectric conversion unit as a high, a control pulse FaiPG _e0 at time T ₆ as low.

At time T ₆ , charges from the photoelectric conversion unit 102 of the photodiode are transferred to the FD region 121, so that the potential of the FD region 121 changes according to light. At this time, since the source follower amplifier MOS transistor 105 is in a floating state, the potential of the FD region 121 is output to the storage capacitor C _TS 111 with the control pulse φT _S being high at time T ₇ . At this time, since the dark output and the light output of the second photoelectric conversion unit are stored in the storage capacitors C _TN 110 and C _TS 111, respectively, the vertical output line reset MOS transistor is set with the control pulse φH _C at time T ₈ temporarily high. 113 and 155 are conducted to reset the vertical output line, and the dark output and light output of the pixel are output to the vertical output line by the scanning timing signal of the vertical scanning unit 115 in the vertical transfer period. Then, the differential output V _OUT of the second photoelectric conversion unit is obtained by the differential amplifier 114 of the storage capacitors C _TN 110 and C _TS 111.

With the above driving, reading of the first and second photoelectric conversion units can be performed independently. Thereafter, the horizontal scanning unit is scanned and the readout operation is performed in the same manner, whereby independent outputs of all the photoelectric conversion units can be obtained. That is, in the case of the next column, first, the control pulse φS ₁ is set high, then φR ₁ is set low, then the control pulses φT _N and φTX ₀₁ are set high, the control pulse φPG ₀₁ is set low, and the control pulse φT _S high, read out the signal of the first photoelectric conversion unit of the light receiving portion 130-21,130-22 a control pulse .phi.H _C as a temporary high. Subsequently, the control pulses φTX _e1 and φPG _e1 and the control pulse are applied in the same manner as described above, and the signals of the second photoelectric conversion units of the light receiving units 130-21 and 130-22 are read out.

  Next, an addition output mode for outputting a signal based on a light beam from all pupils of the objective lens by adding the signals of the first and second photoelectric conversion units in the FD region 121 will be described. This operation mode corresponds to image output by a normal image sensor.

FIG. 6 shows a timing chart in the case of adding the signals of the first and second photoelectric conversion units. In FIG. 5 in the non-addition mode described above, the timings of the control pulse φTX ₀₀ and the control pulse φTX _e0 and the control pulse φPG ₀₀ and the control pulse φPG _e0 are shifted. That is, in order to simultaneously read out from a first photoelectric conversion unit and the second photoelectric conversion unit of the light receiving unit 130-11, reads the noise component from the horizontal output line first control pulse .phi.T _N as high, and the control pulse .phi.TX ₀₀ and the control pulse φTX _e0 and control pulse φPG ₀₀ and control pulse φPG _e0 are simultaneously set to high and low, respectively, and transferred to the FD area 121. Thereby, it becomes possible to add the signals of the upper and lower photoelectric conversion units in the FD region 121 at the same time. Since signal addition is performed at the pixel level, the image is not affected by amplifier noise and an image with a high S / N ratio that cannot be obtained by addition after signal readout.

  With the driving method described above, the function as a light-receiving element for imaging and focus detection can be achieved with a single sensor.

  Here, regarding a method for adjusting the focus on a subject, a method for detecting a defocus amount, which is a focus shift amount of an imaging optical system, using a phase difference detection method that is a well-known technique will be described first.

  7A and 7B, for ease of understanding, the light beam incident on the first photoelectric conversion unit and the second photoelectric conversion unit are incident on the light receiving unit 72-11 illustrated in FIG. It is a figure which divides and shows each light beam. 122G represents that the color filter 122 that transmits light in a specific wavelength region in FIG. 3 transmits light in a wavelength region corresponding to G (green).

  FIG. 7A showing a light beam incident on the first photoelectric conversion unit, FIG. 7B shows a light beam incident on the first photoelectric conversion unit G1 when the light beam from the lower side of the figure enters the first photoelectric conversion unit G1. ), It can be seen that the light beam from above in the figure is incident on the second photoelectric conversion unit G2.

  That is, in the entire imaging device, the light beam incident on the second photoelectric conversion unit at any position of the area sensor unit is a light beam that passes through the left half of the exit pupil of the imaging optical system. On the other hand, the light beam incident on the first photoelectric conversion unit of the entire image pickup device may be considered as the left and right reversed with the optical axis L1 of the image pickup lens as the axis of symmetry. That is, the division of the exit pupil of the imaging optical system is as shown in FIG.

  In FIG. 8, 220 is an exit pupil of the imaging optical system. 221 is a first region on the exit pupil through which the light beam incident on the first photoelectric conversion unit of the image sensor passes, and 222 is a second region on the exit pupil through which the light beam incident on the second photoelectric conversion unit of the image sensor passes. It is an area. That is, the image signal obtained from the first photoelectric conversion unit and the image signal obtained from the second photoelectric conversion unit are both formed from a half light beam obtained by substantially dividing the exit pupil of the imaging optical system into two.

  In the optical system as described above, for example, when an object image is formed in front of the image sensor, the half light beam passing through the right side of the exit pupil is shifted to the left side on the image sensor, and the left side of the exit pupil is The passing half-beam shifts to the right. That is, a pair of image signals formed by a light beam that passes through each half of the pupil of the imaging optical system has a phase shifted in the left-right direction shown in FIG. 4 according to the imaging state of the object image. This is the shift method itself described with reference to FIG.

  Therefore, in order to obtain the above-described defocus amount, as described with reference to FIG. 19, the deviation amount that is the relative positional relationship between the two subject images may be obtained from the correlation.

  A specific focus detection and adjustment operation accompanied by a calibration operation in the focus detection apparatus having the above configuration will be described below. First, the focus adjustment operation (one-shot AF operation) in the one-shot mode in which the photographer performs one-time shooting will be described.

  FIG. 9 is a flowchart showing the one-shot AF operation. The one-shot AF operation is started when the photographer sets the one-shot AF mode with the switch 45 shown in FIG. 1 and turns on the distance metering switch at the first stroke of the release button 41.

  First, in step S101, a focus detection / adjustment operation by a phase difference detection method is performed. Details will be described later. In step S102, the focus detection / adjustment operation by the contrast detection method is performed after focusing by the phase difference detection method. Details will be described later. Next, in step S103, a difference in focus position between the phase difference detection method and the contrast detection method is detected and confirmed. In step S104, the conversion coefficient is updated using the phase difference detection method. Details will be described later. Thus, a series of one-shot AF operations are completed.

  FIG. 10 is a flowchart showing the AF operation by the phase difference detection method. First, in step S201, the accumulation operation of the sensor and the reading of accumulated charges are performed for focus detection. In step S202, the phase difference detection calculation for obtaining the image shift amount between the two images as described above is performed. Here, the image shift amount is α [bit]. Next, in step S203, conversion for obtaining the defocus amount (Δ [mm]) of the photographing optical system from the image shift amount α is performed. The conversion coefficient κ [mm / bit] is used for the conversion here. That is, the following equation is obtained.

Δ [mm] = κ [mm / bit] × α [bit]
The aim of the present invention is to improve the accuracy of the phase difference detection method by learning and updating the conversion count κ. Details of this will be described later.

  Next, in step S204, it is checked whether or not the current focus state is an in-focus state. Specifically, if the magnitude (absolute value) of the defocus amount Δ of the photographing optical system obtained in step S203 is equal to or less than a predetermined focus width Δo [mm], it is determined that the camera is in focus. If it is not in focus, the process proceeds to step S205, and the focus adjustment lens of the photographic optical system is driven in the direction and amount in which the defocus amount is eliminated.

  On the other hand, if it is in the focused state in step S204, the focus detection / adjustment operation by this phase difference detection method is terminated.

  FIG. 11 is a flowchart showing the AF operation by the contrast detection method. In the present embodiment, the contrast detection method AF is performed in the range of 5Fδ on the front side and the rear side from the in-focus position in the phase difference detection method AF, and in the range of 10Fδ. “5Fδ” is five times “Fδ”, and “Fδ” is a multiplication of the release aperture value “F” of the taking lens and “δ” which is the minimum resolution of the imaging system, which is generally called the minimum circle of confusion. Half the depth of focus (one side). Further, “δ” is 30 to 35 [μm] in the case of a general 135 size silver salt film. In the case of a digital camera, the amount is determined by the entire image sensor and the size of one pixel.

  First, in step S301, the focusing lens of the photographing optical system is placed in the in-focus position in the previous phase difference detection method AF, that is, from the current position to the front pin side, that is, the focal position is closer to the front side. Move quantitatively. Here, it is assumed that “−5Fδ” is moved. That is, “−” represents the driving direction of the front side, and “5Fδ” represents the amount.

  Next, in step S302, the accumulation operation of the sensor and the reading of accumulated charges are performed for focus detection. In step S303, the evaluation value in the contrast method is calculated at the current position and stored together with the lens position. Next, in step S304, the focus adjustment lens of the photographic optical system is slightly driven in a predetermined direction. In this embodiment, it is assumed that the current position is moved to the rear pin side (“+”) by half of Fδ. Therefore, this focus adjustment resolution is 1/4 of the depth of focus 2Fδ.

  In step S305, it is checked whether all evaluation value calculations have been completed at the focus position where the moving sum is 10Fδ using the contrast detection method. If not completed, the process returns to step S302 and the above-described operation is repeated.

  In step S305, if all of the evaluation value calculations at the focus position of 10Fδ are completed, the process proceeds to step S306, and the maximum contrast evaluation value and its position are searched and determined in 10Fδ. In step S307, the focus adjustment lens of the photographing optical system is driven to the position of the maximum contrast evaluation value, and the focus detection / adjustment operation in this contrast detection method is ended.

  This completes the focus detection / adjustment operation using both the phase difference detection method and the contrast detection method. As described above, in the one-shot AF mode, the adjustment result in the contrast detection method is finally adopted. However, by performing the phase difference detection method first, the entire driveable range of the focus adjustment lens of the photographing optical system is achieved. Thus, it is not necessary to calculate the contrast evaluation value at the time point, and as a result, it is possible to shorten the time until focusing as compared with the case where all the contrast detection methods are used.

  Next, the update operation of the conversion coefficient (κ [mm / bit]) from the image shift amount to the defocus amount of the photographing optical system in the phase difference method performed in step S104 shown in FIG. 9 will be described.

  As described above, the present embodiment aims to improve the accuracy step by step by updating the conversion coefficient that changes in a complicated manner by the learning effect. Basically, it is desirable that the image shift amount (α [bit]) and the defocus amount (Δ [mm]) have a linear relationship, and usually, such design is performed. However, depending on conditions such as the position of the distance measuring point, a nonlinear relationship may occur, particularly in the large blur region.

For example, as shown in FIG. 12, when a plurality of distance measuring points 601 (5 × 5 = 25 in the example shown in FIG. 12) are set in the shooting screen 600, basically,
Δn = κn × αn (n = 1-25)
However, as shown in FIG. 13, each is considered to be almost linear in the vicinity of the origin, but a change in inclination, hysteresis, and the like are added at the time of blurring. Therefore, it is desirable to manage the conversion coefficient κ by a function or a table for each distance measurement area.

  In the present embodiment, a table is created with a predetermined resolution (for example, 1 / 2Fδ) for each distance measurement area, and the detection deviation amount and contrast detection method in the phase difference detection method in the one-shot operation are compared with the initial design value. The conversion coefficient κ is obtained every time from the final in-focus position, and the average value including the design value is used as a new conversion coefficient to be learned.

FIG. 14 is a flowchart showing the operation of updating the phase difference conversion coefficient. In step S401, the defocus amount detected (calculated) by the phase difference detection method is corrected based on the result of the contrast detection method. Specifically, the detected defocus amount of the selected distance measuring point n is Δn [mm] (with a sign), and the difference between the result of the contrast detection method and the result of the phase difference detection method, that is, the phase difference detection If the difference between the stop position of the focus adjustment lens of the photographing optical system in the method and the stop position of the focus adjustment lens of the photographing optical system in the contrast detection method is dΔ [mm] (signed),
Δn ′ = Δn + dΔ [mm]
It becomes. Do this. In this embodiment, the table is created with a predetermined resolution (for example, 1/2 Fδ), and thus rounding is performed with this accuracy.

Next, in step S402, the conversion coefficient κ is updated. Similarly, if the conversion coefficient at the selected distance measuring point n is κn [mm / bit] and the shift amount detected (calculated) by the phase difference detection method is αn [bit], a new conversion coefficient κn [ mm / bit] uses the average value including the design value as a new conversion coefficient.
κn = ((Δn ′ / αn) + κn) / 2 [mm / bit]
It becomes.

  This completes the update of the conversion coefficient κn of the phase difference detection method.

  As described above, in this embodiment, the conversion coefficient in the phase difference detection method is learned and updated every time the one-shot AF operation is performed, so that the accuracy is improved as it is used. It should be noted that a region in which the value of the conversion coefficient itself is determined to be almost stable from the result of the learning operation may be omitted, and the original goodness of the phase difference detection method may be sufficiently extracted.

  On the other hand, in the so-called servo mode in which focus detection / adjustment operations are performed continuously, accuracy is of course important, but the demand for speed is also high. Therefore, in the present embodiment, only the one-shot AF is used for the operation of updating the conversion coefficient of the phase difference detection method as described above. Therefore, the focus adjustment operation (servo AF operation) in the servo mode in which the photographer continuously performs photographing is as shown in FIG.

  The photographer sets the servo AF mode with the switch 45 shown in FIG. 1, and the servo AF operation is started and continued while the distance metering switch is turned on by the first stroke of the release button 41.

  First, in step S501, the accumulation operation of the sensor and the reading of accumulated charges are performed for focus detection. In step S502, a phase difference detection calculation is performed to obtain an image shift amount between the two images.

  In step S503, the image shift amount is converted into a defocus amount of the photographing optical system. The current conversion coefficient is used as it is for this conversion. In step S504, the focus adjustment lens of the photographing optical system is driven by a necessary amount in a direction in which the detected defocus amount is eliminated.

  Note that while the distance metering switch is ON, the servo AF operation is resumed from step S501.

[Modification]
In the embodiment described above, the image sensor for focus detection, particularly for focus detection in the phase difference detection method and for imaging is used in combination. However, when the number of pixels for shooting is extremely large and one pixel is miniaturized, it is difficult to divide the photoelectric conversion unit. Therefore, it is desirable that the image pickup device for photographing has a normal structure, focus detection is performed only by the contrast detection method, and focus detection by the phase difference detection method is used in combination with an image pickup device for other purposes or used alone.

  FIG. 16 is a diagram illustrating an example of an optical arrangement in the case where an image sensor for an electronic view finder (EVF) and an image sensor for focus detection using a phase difference detection method are combined. Since the image sensor used for the EVF may have a relatively small number of pixels, it can be easily realized with an image sensor in which the light receiving unit is divided as in this embodiment.

  FIG. 16 shows an example of a TTL (through the lens) finder, in which 900 is a photographing optical axis, 901 is a photographing optical system, 902 is a quick return half mirror, 903 is an image sensor for focus detection and photographing in a contrast detection system, and 904 Is a low-pass filter of the image sensor for photographing, 905 is an image sensor for focus detection and EVF using a phase difference detection method, and 906 is a low-pass filter of the image sensor for EVF.

  In this modification, the state shown by the solid line is maintained in the photometry and distance measurement state before the photographing operation, focus detection by the EVF output and the phase difference detection method is performed at the output of the image sensor 905, and contrast detection is performed at the output of the image sensor 903. The focus detection is performed by the method, and the quick return half mirror 902 jumps up as indicated by the arrow as the photographing operation starts, and the photographing total light flux is guided to the photographing image sensor 903.

  FIG. 17 is a diagram illustrating an example of an optical arrangement in the case where the EVF image sensor and the focus detection image sensor using the phase difference detection method are dedicated to each other. FIG. 17 is also an example of a TTL (through the lens) finder, similar to FIG. 16, and a focus detection sub-mirror 907 using the phase difference detection method and a secondary optical for focus detection using the phase difference detection method with respect to the components shown in FIG. A system 908, a focus detection image sensor 909 using a phase difference detection method, and an infrared cut filter 910 for a focus detection image sensor using a phase difference detection method are added. Instead, the image sensor 905 is a normal image sensor dedicated to EVF and having no division structure.

  In the range-finding state before the photographing operation in this modification, the state illustrated by the solid line is maintained at the focus detection stage by the phase difference detection method, and the phase difference detection by the EVF output by the output of the image sensor 905 and the output of the image sensor 909 is performed. The focus detection is performed by the method. Then, in the focus detection stage using the contrast detection method, the sub mirror 907 rises like an arrow, and focus detection is performed using the contrast detection method based on the output of the image sensor 903.

  Then, with the start of the photographing operation, the quick return half mirror 902 rises as indicated by an arrow in a state where the sub mirror 907 is raised, and the photographing total light flux is guided to the photographing image sensor 903.

  Note that the focus detection image pickup device 909 is provided with an infrared cut filter 910 because it is assumed to be a monochrome line sensor having no color filter, which is widely implemented in a single-lens reflex camera for a silver salt film.

  In the embodiments described above, the photographic lens is described as being fixed, but the same is true for the interchangeable lens.

  Even if the present invention is applied to a system composed of a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), it is applied to an apparatus (for example, a copier, a facsimile machine, etc.) composed of a single device. It may be applied.

  Another object of the present invention is to supply a recording medium in which a program code of software realizing the functions of the above-described embodiments is recorded to a system or apparatus, and the computer (CPU or MPU) of the system or apparatus stores the recording medium in the recording medium. Needless to say, this can also be achieved by reading and executing the programmed program code.

  In this case, the program code itself read from the recording medium realizes the functions of the above-described embodiment, and the recording medium storing the program code constitutes the present invention.

  As a recording medium for supplying the program code, for example, a floppy (registered trademark) disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like is used. be able to.

  Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an OS (operating system) operating on the computer based on the instruction of the program code. It goes without saying that a case where the function of the above-described embodiment is realized by performing part or all of the actual processing and the processing is included.

  Further, after the program code read from the recording medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. It goes without saying that the CPU or the like provided in the board or the function expansion unit performs part or all of the actual processing and the functions of the above-described embodiments are realized by the processing.

It is a block diagram which shows the structure of the electronic still camera in an Example. It is a figure which shows the circuit structure of the area sensor part in an image sensor. It is sectional drawing which shows the structure of the light-receiving part (for example, 130-11) shown in FIG. It is a top view which shows arrangement | positioning of the pixel of an image pick-up element, a photoelectric conversion part, and a color filter. It is a timing chart which shows read-out operation of an image sensor. It is a timing chart in the case of adding the signal of a 1st, 2nd photoelectric conversion part. It is a figure which shows separately the light beam which injects into a 1st photoelectric conversion part, and the light beam which injects into a 2nd photoelectric conversion part, respectively. It is a figure which shows the division | segmentation of the exit pupil of an imaging optical system. 6 is a flowchart showing a one-shot AF operation. It is a flowchart which shows AF operation | movement by a phase difference detection system. It is a flowchart which shows AF operation by a contrast detection system. It is a figure which shows an example of the ranging point arrangement | positioning in an imaging | photography screen. It is a figure showing the conversion coefficient in a phase difference detection system. It is a flowchart which shows the operation | movement of the conversion coefficient update of a phase difference system. It is a flowchart which shows servo AF operation | movement. It is a figure which shows an example of an optical arrangement | positioning at the time of combining the image pick-up element for electronic viewfinders (EVF), and the image pick-up element for focus detection by a phase difference detection system. It is a figure which shows an example of an optical arrangement | positioning at the time of dedicating the image sensor for EVF, and the image sensor for focus detection by a phase difference detection system, respectively. It is a figure for demonstrating the focus detection by a shift | offset | difference system. It is a figure which shows an example of the calculating method which calculates | requires deviation | shift amount. It is a figure showing the state of the light beam for focus detection in the exit pupil of an imaging optical system. It is a figure which shows the vignetting condition of the focus detection light beam.

Explanation of symbols

LNS lens
PUP pupil lens pupil area
SNS Photoelectric conversion element array for focus detection
MSK focus detection field mask
FLDL focus detection field lens
DP Aperture for focus detection
Secondary optical system for AFL focus detection

Claims (9)

A photoelectric conversion step of photoelectrically converting a pair of light images emitted from the same part of the subject and input via different paths;
First focus adjustment for adjusting the objective lens to the in-focus position based on the relative shift amount detected from the pair of photoelectrically converted light images and the conversion coefficient for converting the relative shift amount into the focus shift amount of the objective lens. Process,
A second focus adjustment step of adjusting the objective lens to a focus position based on contrast information detected from a pair of photoelectrically converted light images;
And a updating step of updating the conversion coefficient based on the in-focus positions adjusted in the first and second focus adjustment steps, respectively.   The focus detection and adjustment method according to claim 1, wherein the photoelectric conversion step is used for both imaging and focus detection.   The focus detection and adjustment method according to claim 1, wherein the photoelectric conversion step is used for both a finder and a focus detection.   The focus detection and adjustment method according to claim 1, wherein the photoelectric conversion step is dedicated to focus detection.   2. The focus detection and adjustment method according to claim 1, wherein the updating step is performed in a one-shot mode in which focus adjustment is performed once. A photoelectric conversion step of photoelectrically converting a pair of light images emitted from the same part of the subject and input via different paths;
First focus adjustment for adjusting the objective lens to the in-focus position based on the relative shift amount detected from the pair of photoelectrically converted light images and the conversion coefficient for converting the relative shift amount into the focus shift amount of the objective lens. Process,
A second focus adjustment step of adjusting the objective lens to a focus position based on contrast information detected from a pair of photoelectrically converted light images,
When the one-shot mode in which the focus adjustment is performed once is selected, the focus adjustment is performed in the second focus adjustment step after the first focus adjustment step, and the servo mode in which the focus adjustment is continuously performed is selected. A focus detection and adjustment method, wherein focus adjustment is performed in the first focus adjustment step. Photoelectric conversion means for photoelectrically converting a pair of light images emitted from the same part of the subject and input through different paths;
First focus adjustment for adjusting the objective lens to the in-focus position based on the relative shift amount detected from the pair of photoelectrically converted light images and the conversion coefficient for converting the relative shift amount into the focus shift amount of the objective lens. Means,
Second focus adjusting means for adjusting the objective lens to a focus position based on contrast information detected from a pair of photoelectrically converted light images;
A focus detection and adjustment device, comprising: update means for updating the conversion coefficient based on the in-focus positions respectively adjusted by the first and second focus adjustment means.   A program for causing a computer to execute each procedure of the focus detection and adjustment method according to claim 1.   A computer-readable recording medium on which the program according to claim 8 is recorded.

Images