JP2007121896A - Focus detector and optical system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a focus detector capable of improving the focus detecting accuracy of an image-formation optical system, and to provide an optical system. <P>SOLUTION: The focus detector detects a focusing state on the scheduled image-formation surface of the image-formation optical system based on the deviation of a pair of images by a pair of luminous fluxes passing through different positions of the pupil of the image-formation optical system. It calculates a conversion coefficient for converting the deviation of a pair of images into the defocus amount of the image-formation optical system based on information showing the distribution of the luminous flux and the aperture information of the image-formation optical system. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a focus detection device that detects a focus adjustment state of an imaging optical system, and an optical system including the focus detection device.

A so-called pupil division type focus detection method is known as a TTL focus detection method for detecting a focus adjustment state of an imaging optical system using a light beam that has passed through the imaging optical system. In this pupil division type focus detection method, a relative positional deviation amount of a pair of images formed on a predetermined imaging plane by a light beam that has passed through different regions of the exit pupil of the imaging optical system is detected, and the image deviation amount. Is multiplied by a predetermined conversion coefficient to convert to a defocus amount in the optical axis direction. Therefore, it is also called a phase difference detection method or an image shift detection method.
A focus detection device is known that uses a conversion coefficient corresponding to the brightness (F value) of an imaging optical system when converting an image shift amount into a defocus amount (see, for example, Patent Document 1). . According to this focus detection apparatus, even when vignetting occurs in the focus detection light beam due to the influence of the brightness of the imaging optical system, high-precision focus detection is possible using an appropriate conversion coefficient. It is going to be.

Prior art documents related to the invention of this application include the following.
Japanese Patent Publication No. 07-062732

  However, when the focus detection position is in the vicinity of the planned imaging plane that is off the optical axis of the imaging optical system, the vignetting of the focus detection light beam is also generated by the lens opening other than the aperture opening, so that the brightness is simply increased. There is a problem that an accurate conversion coefficient cannot be obtained with only the information.

  A focus detection device that detects a focus adjustment state on a planned imaging plane of an imaging optical system based on a shift amount of a pair of images by a pair of light beams that have passed through different positions of a pupil of the imaging optical system, The conversion coefficient for converting the shift amount of the pair of images into the defocus amount of the imaging optical system is calculated based on the information indicating the distribution of the image and the aperture information of the imaging optical system.

  According to the present invention, in the pupil division type focus detection method, an accurate conversion coefficient for converting a pair of image shift amounts into a defocus amount of the imaging optical system can be obtained. Detection accuracy can be improved.

  A so-called pupil division type focus detection method is known as a TTL focus detection method for detecting a focus adjustment state of an imaging optical system using a light beam that has passed through the imaging optical system. In this pupil division type focus detection method, a relative positional deviation amount of a pair of images formed on a predetermined imaging plane by a light beam that has passed through different regions of the exit pupil of the imaging optical system is detected, and the positional deviation amount is detected. Is multiplied by a predetermined conversion coefficient to convert to a defocus amount in the optical axis direction. Therefore, it is also called a phase difference detection method or an image shift detection method.

  In the pupil division method, the defocus amount (the shift direction and the shift amount of the current imaging plane relative to the planned imaging plane) is accurately calculated as the detection result of the focus detection state. By displacing the imaging optical system accordingly, it is possible to focus the imaging optical system more quickly than other focus detection methods such as a contrast detection method.

  The pupil division type focus detection method includes a re-imaging method and a microlens method. First, the re-imaging method will be described. The re-imaging method is a diaphragm having a condenser lens, an image sensor, a pair of re-imaging lenses, and a pair of apertures arranged in the vicinity of the pair of re-imaging lenses. In this method, an image formed on a predetermined focal plane by a re-imaging lens is re-imaged as a pair of images on an image sensor, and a relative positional shift amount of the pair of images is detected. In this method, the shape of the pair of aperture mask apertures is projected by the condenser lens in the vicinity of the exit pupil plane of the imaging optical system, and the pair of light beams passing through the projected pair of aperture aperture shape regions A pair of images is re-imaged.

  FIG. 1 is a diagram showing the configuration of a re-imaging type focus detection apparatus. The distance measuring unit 18 is disposed between the condenser lens 10 disposed in the vicinity of the planned imaging plane of the imaging optical system, the image sensor 16 disposed behind the condenser lens 10, and between the condenser lens 10 and the image sensor 16, and the planned imaging plane. A pair of re-imaging lenses 14 and 15 for re-imaging the primary image formed in the vicinity on the image sensor 16, and a pair of aperture openings disposed in the vicinity (front surface in the figure) of the pair of re-imaging lenses. The aperture mask 11 has 12 and 13.

  Information corresponding to the intensity distribution of the pair of images re-imaged on the image sensor 16 is output from the image sensor 16, and known image shift detection calculation processing (correlation processing, phase difference detection processing) is performed on this information. The amount of image misalignment between the pair of images is detected. Then, the deviation (defocus amount) of the current imaging plane with respect to the scheduled imaging plane is calculated by multiplying the image shift amount by a predetermined conversion coefficient.

  The condenser lens 10 is disposed on the optical axis 4, and the aperture openings 12 and 13 of the aperture mask 11 are projected on the exit pupil 1 as regions 2 and 3 in the direction of the optical axis 4. These areas 2 and 3 are called distance measuring pupils. That is, a pair of images re-imaged on the image sensor 16 is formed by a light beam passing through the pair of distance measuring pupils 2 and 3 on the exit pupil 1. The light beams 32 and 33 passing through the pair of distance measuring pupils 2 and 3 on the exit pupil 1 are called focus detection light beams.

  The distance measuring unit 28 is disposed between the condenser lens 20 disposed in the vicinity of the planned imaging plane of the imaging optical system, the image sensor 26 disposed behind the condenser lens 20, and between the condenser lens 20 and the image sensor 26. A pair of re-imaging lenses 24 and 25 for re-imaging the primary image formed in the vicinity on the image sensor 26, and a pair of aperture openings disposed in the vicinity (front surface in the figure) of the pair of re-imaging lenses. The aperture mask 21 includes 22 and 23.

  Information corresponding to the intensity distribution of the pair of images re-imaged on the image sensor 26 is output from the image sensor 26, and known image shift detection calculation processing (correlation processing, phase difference detection processing) is performed on this information. The amount of image misalignment between the pair of images is detected. By multiplying this image shift amount by a predetermined conversion coefficient, the deviation (defocus amount) of the current image plane with respect to the planned image plane is calculated.

  The condenser lens 20 is disposed at a position separated from the optical axis 4, and the aperture openings 22 and 23 of the aperture mask 21 are projected onto the exit pupil 1 as distance measurement pupils 2 and 3 in the direction of the projection axis 27 with respect to the exit pupil 1. is doing. That is, a pair of images re-imaged on the image sensor 26 is formed by a light beam passing through the pair of distance measuring pupils 2 and 3 on the exit pupil 1. The light beams 42 and 43 passing through the pair of distance measuring pupils 2 and 3 on the exit pupil 1 are called focus detection light beams.

  Next, the pupil division type focus detection of the microlens method will be described. In the microlens method, a pair of light-receiving elements that receive a light beam that has passed through the microlens are received by a pair of light-receiving elements consisting of an image sensor placed behind each microlens in a microlens array arranged near the planned imaging plane. This is a method for detecting the amount of deviation between the output signal of one series of elements and the output signal of the other series.

  In this method, the aperture shape of a pair of light receiving elements positioned behind each microlens is projected in the vicinity of the exit pupil plane of the imaging optical system, and passes through the projected pair of aperture shape regions. The light amounts of the pair of images formed on the microlens array by the pair of light beams are respectively detected by the pair of light receiving elements.

  FIG. 2 is a diagram illustrating a configuration of a microlens focus detection apparatus. In FIG. 2, the same elements as those shown in FIG. The microlenses 50 and 60 are disposed in the vicinity of the planned image forming surface of the image forming optical system. By the microlens 50 disposed on the optical axis 4, the shape of the light receiving portion of the pair of light receiving elements 52 and 53 disposed behind the microlens 50 is projected onto the distance measuring pupils 2 and 3 of the exit pupil 1 in the direction of the optical axis 4. Is done. Further, the distance measurement pupil 2 of the exit pupil 1 in the direction of the projection axis 67 with the shape of the light receiving portion of the pair of light receiving elements 62 and 63 disposed behind the micro lens 60 disposed away from the optical axis 4. , 3.

  The light receiving element 52 outputs information corresponding to the intensity of the image formed on the microlens 50 by the focus detection light beam 72 that has passed through the distance measuring pupil 2. The light receiving element 53 outputs information corresponding to the intensity of the image formed on the microlens 50 by the focus detection light beam 73 that has passed through the distance measuring pupil 3. On the other hand, the light receiving element 63 outputs information corresponding to the intensity of the image formed on the microlens 60 by the focus detection light beam 82 that has passed through the distance measuring pupil 2. The light receiving element 63 outputs information corresponding to the intensity of the image formed on the microlens 60 by the focus detection light beam 83 that has passed through the distance measuring pupil 3.

  A large number of microlenses as described above are arranged in an array, and the outputs of a pair of light receiving elements arranged behind the microlenses are collected, so that the focus detection light beams that pass through the distance measuring pupil 2 and the distance measuring pupil 3 can be converted into microlenses. Information about the intensity distribution of a pair of images formed on the array is obtained. By performing known image shift detection calculation processing (correlation processing, phase difference detection processing) on this information, the image shift amount of the pair of images is detected. Further, the deviation (defocus amount) of the current imaging plane with respect to the scheduled imaging plane of the imaging optical system is calculated by multiplying this image shift amount by a predetermined conversion coefficient. In the microlens system, the aperture diameter of the microlens decreases as the size of the microlens decreases, and the projection image on the exit pupil plane of the light receiving element blurs due to diffraction.

  FIG. 3 is a diagram for explaining a diffraction phenomenon in the microlens method. FIG. 3 shows an example of a light receiving element projection image (one side) on an ideal exit pupil when there is no influence of diffraction. Reference numeral 930 denotes a circle corresponding to the aperture diameter F2.8 on the exit pupil set in front of the microlens by 100 mm, and reference numeral 940 denotes a rectangular region 940 to be projected substantially inscribed in the corresponding circle 930 of F2.8 (X = 2 to 12 mm, Y = -10 to 10 mm).

  FIG. 4 is a diagram showing a diffraction image intensity distribution pattern corresponding to FIG. FIG. 4 is a diagram obtained by simulation by setting the diffraction image intensity distribution on the exit pupil of the rectangular region 940 to be projected as a wavelength of 500 nm when the aperture of the microlens is a circle having a radius of 2 μm.

  FIG. 5 is a cross-sectional view of the diffraction pattern of FIG. 4 at Y = 0. As is apparent from FIGS. 4 and 5, in the diffraction image, the edge of the projection image deviates and a considerable part of the projection image protrudes from the circle of F2.8 (the one inside the circle of F2.8 is about 81). %). Actually, when the radius of the opening circle of the microlens becomes several tens of um or less, the focus detection region on the exit pupil starts to be deformed due to the influence of diffraction. Due to the influence of diffraction, the shape of the distance measuring pupil collapses and protrudes outside the set area, so that the light beam at the protruding portion is scattered by the aperture of the imaging optical system or the lens end other than the aperture. is there. Further, as is clear from FIG. 5, the distribution of the focus detection light flux in the distance measuring pupil is not uniform.

  FIG. 6 is a diagram for explaining spherical aberration in the microlens system. When the distance measuring pupil is formed on the exit pupil 1 by the paraxial ray of the micro lens 50, for example, the paraxial ray 90 emitted from the center point 95 of the pair of light receiving elements is on the intersection 92 of the exit pupil 1 and the optical axis 4. However, the light rays passing through the periphery of the microlens 50 reach 93 and 94 apart from the point 92 on the exit pupil 1. This phenomenon is called so-called spherical aberration, and is unavoidable in manufacturing the microlens 50. Due to the spherical aberration, the edge of the projected image is deviated, and a considerable part of the projected image protrudes from the ideal distance measuring pupil, resulting in the same result as diffraction. Similarly, aberrations other than spherical aberration (chromatic aberration, coma aberration, astigmatism, distortion aberration, curvature of field) disturb the edge of the projected image and the distribution of the focus detection light beam is not uniform.

  FIG. 7 is an explanatory diagram of vignetting of the focus detection light beam. Reference numeral 5 denotes a planned imaging plane, reference numerals 6 and 7 denote focus detection light beams when vignetting occurs, reference numerals 56 and 57 denote focus detection light beams when there is no vignetting, and reference numerals 8 and 9 denote centroids of focus detection light beams 56 and 57 when there is no vignetting. Positions 78 and 79 are the gravity center positions of the focus detection light beams 6 and 7, 45 is the intersection of the planned imaging plane 5 and the optical axis 4, 36 is the opening angle when the gravity center positions 8 and 9 are viewed from the point 45, and 35 Is the opening angle when the barycentric positions 78 and 79 are viewed from the point 45, 46 is the distance from the planned imaging plane 5 to the exit pupil plane 1, and 40 is the stop of the imaging optical system that coincides with the exit pupil plane 1 The exit pupils 41 and 44 are exit pupils of the stop of the imaging optical system located at a position other than the exit pupil plane 1.

FIG. 7 shows the vignetting of the focus detection light beam when the focus detection position is on or near the optical axis, and a distance measurement pupil is formed on the exit pupil plane 1 set at a distance 46 from the planned imaging plane 5. Thus, when the aperture stop of the imaging optical system is sufficiently large, no vignetting occurs in the focus detection light beams 56 and 57. If the opening angle 36 at which the gravity centers 8 and 9 of the focus detection light beams 56 and 57 face the point 45 is Θa, the image shift amount is H, the conversion coefficient is ka, and the defocus amount is D, the defocus is expressed by the following equation. The quantity D is determined.
D = H × ka = H / (2 × Tan (Θa / 2)) (1)

When the exit pupil 40 of the imaging optical system is located at a position coincident with the exit pupil plane 1 and the brightness thereof becomes dark, a phenomenon called vignetting occurs by blocking a part of the focus detection light beams 56 and 57. The generated light flux that can be actually used for focus detection is the focus detection light fluxes 6 and 7. Assuming that the opening angle 35 facing the gravity center positions 78 and 79 of the focus detection light beams 6 and 7 where the vignetting occurs from the point 45 is Θb, the image shift amount is H, the conversion coefficient is kb, and the defocus amount is D, the following The defocus amount D is obtained by the equation.
D = H × kb = H / (2 × Tan (Θb / 2)) (2)
When the focus detection position is on or near the optical axis, the focus detection is performed if the brightness is the same even if the exit pupils 41 and 44 of the stop of the imaging optical system are located at positions other than the exit pupil plane 1. The vignetting of the luminous flux does not change significantly.

  FIG. 8 is a diagram for explaining how to obtain the center of gravity of the focus detection light beam. In FIG. 8, the exit pupil 40 of the imaging optical system blocks a part of the focus detection light beam 57. The light beam that can actually be used for focus detection is the focus detection light beam 7 inside the exit pupil 40. The center-of-gravity position 9 of the focus detection light beam 57 is the distribution center of gravity of the light beam of the focus detection light beam 57 (corresponding to the distance measuring pupil on the exit pupil plane 1). Here, the center of gravity indicates the center of gravity in the direction in which the distance measuring pupils are arranged (x direction in the figure). The centroid position 79 of the focus detection light beam 7 vignetted by the exit pupil 40 of the imaging optical system is the distribution centroid of the light beam of the focus detection light beam 7 (corresponding to the distance measurement pupil on the exit pupil plane 1). .

  The distribution information of the light beam 57 of the focus detection light beam 57 when vignetting has not occurred is previously obtained by measurement or calculation and stored as two-dimensional information or the like as distance measurement pupil information. Information on the exit pupil of the imaging optical system (brightness information = diameter and position of the exit pupil) is obtained as aperture information in advance by measurement or calculation and stored as two-dimensional information. The two-dimensional distance measurement pupil information and aperture information are overlapped, and the position of the center of gravity of the focus detection light beam existing inside the exit pupil of the imaging optical system is obtained by calculation. If the barycentric positions 78 and 79 of the pair of focus detection light beams 6 and 7 are obtained, the opening angle 35 at the point 45 can be obtained using the distance 46 between the planned imaging plane 5 and the exit pupil plane 1. .

For example, if the distance between the gravity center positions is S, the distance 46 is M, and the opening angle is Θb, the opening angle Θb can be obtained by the following equation.
Θb = 2 × ArcTan (S / (2 × M)) (3)
When the focus detection position is on or near the optical axis, the focus detection is performed if the brightness is the same even if the exit pupils 41 and 44 of the stop of the imaging optical system are located at positions other than the exit pupil plane 1. Since the vignetting of the luminous flux does not change greatly, the vignetting of the focus detecting beams 56 and 57 need only consider the brightness of the exit pupil corresponding to the optical aperture of the imaging optical system. Two-dimensional ranging pupil information and aperture information are superimposed, and the total amount (corresponding to the amount of light) of the focus detection light beam existing inside the exit pupil of the imaging optical system is obtained by calculation.

  FIG. 9 is a diagram for explaining the vignetting of the focus detection light beam. 47 is a point separated from the intersection 47 of the planned imaging plane 5 and the optical axis 4, 36 is an opening angle when the gravity center positions 8 and 9 are viewed from the point 47, and 35 is a gravity center position 78 and 79 viewed from the point 47. , 46 is the distance from the planned imaging plane 5 to the exit pupil plane 1, 48 is the exit pupil of the aperture other than the stop of the imaging optical system far from the exit pupil plane 1, and 49 is the exit pupil plane 1. The exit pupil 58 of the aperture other than the aperture of the imaging optical system closer to the aperture 58 is the projection axis of the distance measuring pupil.

FIG. 9 shows the vignetting of the focus detection light beam when the focus detection position is away from the optical axis, and the distance measurement pupil is formed on the exit pupil plane 1 set at a distance 46 from the planned imaging plane 5. If the aperture stop of the imaging optical system is sufficiently large, no vignetting occurs in the focus detection light beams 56 and 57. If the opening angle 36 facing the gravity center positions 8 and 9 of the focus detection light beams 56 and 57 from the point 47 is Θc, the image shift amount is H, the conversion coefficient is kc, and the defocus amount is D, the defocus is expressed by the following equation. The quantity D is determined.
D = H × kc = H / (2 × Tan (Θc / 2)) (4)
When the exit pupil 40 of the imaging optical system is located at a position coincident with the exit pupil plane 1 and the brightness thereof becomes dark, a phenomenon called vignetting occurs by blocking a part of the focus detection light beams 56 and 57. appear.

Further, when the focus detection position is not in the vicinity of the optical axis, focus detection is also performed by the exit pupils 48 and 49 (even when the F value is brighter than the exit pupil of the stop) by the lens end other than the stop of the imaging optical system. The vignetting of the light flux for use occurs, and the light flux that can actually be used for focus detection becomes the focus detection light fluxes 6 and 7. Assuming that the opening angle 35 facing the gravity center positions 78 and 79 of the focus detection light beams 6 and 7 where the vignetting occurs from the point 47 is Θd, the image shift amount is H, the conversion coefficient is kd, and the defocus amount is D, the following The defocus amount D is obtained by the equation.
D = H × kd = H / (2 × Tan (Θd / 2)) (5)
When the focus detection position is not in the vicinity of the optical axis, the exit pupil of the stop located at a position other than the exit pupil plane 1 or other than the stop of the imaging optical system even if the F value is brighter than the exit pupil of the stop Vignetting of the focus detection light beam is also generated by the exit pupils 48 and 49 corresponding to the lens end portions.

  FIG. 10 is a diagram for explaining how to obtain the center of gravity of the focus detection light beam. On the exit pupil plane 1, a part of the focus detection light beam 57 is shielded by the exit pupils 48 and 49 as shown in FIG. That is, for the point 47 which is the focus detection position, the exit pupil of the imaging optical system has a shape defined by the exit pupil 48 on the left side and the exit pupil 49 on the right side as shown in FIG. When the exit pupil having the above shape is called a peripheral exit pupil, a light beam that can actually be used for focus detection is a focus detection light beam 7 inside the peripheral exit pupil. The center-of-gravity position 9 of the focus detection light beam 57 is the distribution center of gravity of the light beam of the focus detection light beam 57 (corresponding to the distance measuring pupil on the exit pupil plane 1). Here, the center of gravity indicates the center of gravity in the direction in which the distance measuring pupils are arranged (x direction in the figure). The center-of-gravity position 79 of the focus detection light beam 7 vignetted by the peripheral exit pupil of the imaging optical system is the distribution centroid of the light beam of the focus detection light beam 7 (corresponding to the vignetting distance measuring pupil on the exit pupil plane 1). .

  The distribution information of the light beam 57 of the focus detection light beam 57 when vignetting has not occurred is previously obtained by measurement or calculation as distance measurement pupil information and stored as two-dimensional information or the like. Information on the exit pupil corresponding to the stop of the imaging optical system and the lens end other than the stop (brightness information = diameter and position of the exit pupil) is obtained in advance by measurement or calculation and stored as two-dimensional information. Keep it. The shape of the peripheral exit pupil when the exit pupil plane is viewed from the focus detection position is obtained from the aperture information of the imaging optical system. The two-dimensional distance measurement pupil information and the peripheral exit pupil shape are overlapped, and the center of gravity position of the focus detection light beam existing inside the peripheral exit pupil is obtained by calculation.

If the barycentric positions 78 and 79 of the pair of focus detection light beams 6 and 7 are obtained, the opening angle 35 at the point 45 can be obtained using the distance 46 between the planned imaging plane 5 and the exit pupil plane 1. . For example, if the distance between the gravity center positions is S, the distance 46 is M, and the opening angle is Θd, the opening angle Θd can be obtained by the following equation.
Θd = 2 × ArcTan (S / (2 × M)) (6)
The two-dimensional distance measurement pupil information and the peripheral exit pupil shape are superimposed, and the total amount (corresponding to the amount of light) of the focus detection light beam existing inside the peripheral exit pupil is obtained by calculation.

  FIG. 11 shows a block diagram of the optical system. The digital still camera 201 includes a camera body 203 and an interchangeable lens 202 and is coupled by a mount unit 204. The interchangeable lens 202 includes a lens 209 for forming a subject image, a focusing lens 210, an aperture 211, and a lens CPU 206 that controls driving of the focusing lens 210 and driving of the aperture 211.

  The camera body 203 has an image sensor 212 disposed on the planned imaging plane of the interchangeable lens 202, a body CPU 214 that reads out image signals from the image sensor 212 and controls the operation of the entire digital still camera, and an image signal from the body CPU 214. For detecting a focus adjustment state of the interchangeable lens 202, a liquid crystal display finder (EVF) 216, and a liquid crystal display 216. Eyepiece lens 217 and a liquid crystal display element driving circuit 215 for driving the liquid crystal display element 216 of the liquid crystal viewfinder in accordance with the control of the body CPU 214. The focus detection unit 213 and the lens CPU 206 transmit various types of information (aperture information necessary for calculating the conversion coefficient, a defocus amount for driving the lens, and the like) through an electrical contact unit 218 provided in the mount unit 204.

  The image sensor 212 incorporates microlens focus detection image sensors in a plurality of portions corresponding to a plurality of focus detection positions. The subject image formed on the image sensor 212 through the interchangeable lens 202 is photoelectrically converted by the image sensor 212, and the output is sent to the body CPU 214. The output of the microlens focus detection image sensor is the focus detector. Sent to the department. The focus detection unit 213 communicates with the lens CPU 206 to read the aperture information of the mounted lens, and converts the aperture information, the distance measurement pupil information held by the focus detection unit 213, and information on a plurality of focus detection positions. Based on this, a conversion coefficient and ranging light quantity information are calculated for each of the plurality of focus detection positions.

  The lens CPU 206 changes the aperture information according to the focusing state, zooming state, and aperture setting state. Specifically, the lens CPU 206 monitors the positions of the lenses 209 and 210 and the aperture position of the aperture 211, calculates aperture information according to the monitor information, or apertures according to the monitor information from a lookup table prepared in advance. Select information. The focus detection unit 213 corrects the pair of image signals for each focus detection position according to the distance measurement light amount information, and then performs a known focus detection calculation process to calculate the image shift amount of the pair of images for each focus detection position. To do.

  The focus detection unit 213 multiplies the image shift amount calculated for each focus detection position by the conversion coefficient obtained for each focus detection position, and calculates the defocus amount at each focus detection position. The focus detection unit 213 determines a final defocus amount based on a plurality of defocus amounts. For example, the defocus amount indicating the closest distance among the plurality of defocus amounts is set as the final defocus amount. Alternatively, an average value of a plurality of defocus amounts is set as a final defocus amount. When the focus detection unit 213 determines that lens driving is necessary based on the final defocus amount (when it is determined that the image is out of focus), the focus detection unit 213 transmits the final defocus amount to the lens CPU. The lens CPU 206 calculates a lens driving amount based on the received defocus amount, and drives the focusing lens 210 to a focal point based on the lens driving amount. The body CPU 214 generates an image signal for display based on the output signal from the image sensor 212 and causes the liquid crystal display element 216 to display the image signal via the liquid crystal display element driving circuit 215.

  FIG. 12 shows a specific example of the focus detection position in the digital still camera shown in FIG. As shown in FIG. 12, for example, the focus detection position 301 is the center of the screen, the focus detection positions 302 and 303 are the top and bottom of the screen, and the focus detection positions 304 and 305 are as shown in FIG. It is arranged on the left and right of the screen.

  FIG. 13 is a detailed configuration diagram of the image sensor 212 corresponding to FIGS. 11 and 12. In the image sensor 212, imaging pixels 310 are two-dimensionally arranged, and focus detection pixels 311 (microlens systems) are arranged as shown in portions corresponding to the five focus detection positions in FIG. ing.

  FIG. 14 is a flowchart showing the operation of the digital still camera (optical system, see FIG. 11) (operation of the body CPU 214 and the focus detection unit 213). When the power is turned on in step 100, the process is started, and the process proceeds to step 110. In step 110, aperture information is received from the lens CPU. In the following step 120, a conversion coefficient and distance measurement light quantity information for each focus detection position are calculated based on the aperture information, distance measurement pupil information, and focus detection position information. In step 130, a pair of image signals are read from the focus detection pixels of the image sensor for each focus detection position, and corrected with distance measurement light quantity information. Details of this correction will be described later.

  In step 140, an image shift amount of the pair of image signals corrected for each focus detection position is calculated. In step 150, a defocus amount is calculated by multiplying the image shift amount by a conversion coefficient for each focus detection position, and a final defocus amount is determined based on the plurality of defocus amounts. In step 160, based on the final defocus amount, it is determined whether or not the imaging optical system is in a focused state. If it is determined in step 160 that the in-focus state is not achieved, the process proceeds to step 170, the defocus amount is transmitted to the lens CPU, the imaging optical system is driven to the in-focus position, and the process returns to step 110 to repeat the above operation.

  If it is determined in step 160 that the in-focus state has been reached, the process proceeds to step 180, where it is determined whether or not a shutter release has been performed. If it is determined that no shutter release has been performed, the process returns to step 110 and the above operation is performed. repeat. On the other hand, if it is determined that the shutter release has been performed, the process proceeds to step 190 to execute the photographing operation, and then returns to step 110 to repeat the above operation.

  FIG. 15 is a diagram for explaining correction of an image signal based on distance measurement light quantity information. In FIG. 15, the vertical axis represents the intensity distribution (light quantity) of the image signal at one focus detection position, and the horizontal axis represents the position deviation within the focus detection position. Here, the position deviation in the focus detection position corresponds to the positions of a plurality of focus detection pixels belonging to one focus detection position on the image sensor shown in FIG. 13, for example. As shown in FIG. 15A, the pair of image signals 400 and 401 in the case where no vignetting is generated in the focus detection light beam is obtained by simply shifting the same image signal function horizontally. By performing a known image shift detection operation on such a pair of image signals, an accurate image shift amount of the pair of image signals 400 and 401 can be calculated.

  When vignetting occurs in the focus detection light beam, the amount of the focus detection light beam passing through the distance measuring pupil changes depending on the focus detection position and the position deviation within the focus detection position, for example, an object having uniform brightness is imaged. Even in this case, it is not uniform like the pair of image signals 402 and 403 as shown in FIG. As described with reference to FIGS. 7 to 10, the pair of image signals 402 and 403 for the uniform luminance object as shown in FIG. 15B are the aperture information, the distance measurement pupil information, the focus detection position, and the focus detection position. Based on the positional deviation, it can be calculated as the amount of focus detection light beam that can actually be used for focus detection, that is, the distance measurement light quantity information.

  A pair of image signals 404 and 405 in the case where vignetting is generated in the focus detection light beam is as shown in FIG. 15C, and the same signal is not relatively shifted. Therefore, even if the image shift detection calculation is performed as it is, an error occurs in the image shift amount. A pair of image signals 404 and 405 is a pair of image signals 400 and 401 in the case where no vignetting occurs in the focus detection light beam shown in FIG. This is an image signal multiplied by (distance light quantity information) 402 and 403. On the other hand, when a pair of image signals 404 and 405 in the case where vignetting is generated in the focus detection light beam, distance measurement light quantity information 402 and 403 are obtained by calculation, and the pair of distance measurement light quantity information is used as a pair. By removing the image signals 404 and 405, it is possible to obtain a pair of image signals 400 and 401 when no vignetting occurs in the focus detection light beam.

  In this way, by correcting the signal in which vignetting has occurred with the distance measurement light quantity information, the degree of coincidence between the pair of images is increased, and the image shift amount can be accurately calculated.

  FIG. 16 shows another embodiment of the optical system. The optical system shown in FIG. 11 has a configuration in which pixels for focus detection are embedded in the image sensor. In the optical system shown in FIG. 16, focus detection is performed by a focus detection unit (focus detection device) separate from the image sensor. It is configured to do. In FIG. 16, description of devices similar to those shown in FIG. 11 is omitted. 320 is a focus detection unit (re-imaging method), 321 is a main mirror (half mirror), 322 is a sub mirror, and 323 is a folding mirror. The image sensor 212 is an image sensor dedicated to imaging.

  The light beam incident on the body 203 from the interchangeable lens 202 is divided by the main mirror 321 and one is reflected in the direction of the folding mirror 323, and is reflected in the direction of the eyepiece lens 217 by the folding mirror 323, and is observed as a viewfinder image. The light beam that has passed through the main mirror 321 is reflected by the sub mirror 322, received by the refocusing focus detection unit 320, and the focus detection unit 320 outputs a pair of image signals. The focus detection unit is configured as shown in FIG. 1, and a plurality of re-imaging optical systems and image sensors are arranged corresponding to a plurality of focus detection positions on the screen.

  At the time of shooting, the main mirror 321 and the sub mirror 322 are retracted from the shooting optical path, and the image pickup device 212 picks up an image. A pair of image signals output from the focus detection unit 320 is processed by the focus detection unit 213. The focus detection unit 213 and the lens CPU 206 transmit various types of information (aperture information necessary for calculating a conversion coefficient, a defocus amount for driving the lens, and the like) through an electrical contact unit 218 provided in the mount unit 204. The focus detection unit 213 communicates with the lens CPU 206 to read the aperture information of the mounted lens, and based on the aperture information, the distance measurement pupil information held by the focus detection unit 213, and information on a plurality of focus detection positions. Thus, the conversion coefficient and the distance measurement light quantity information are calculated for each of the plurality of focus detection positions.

  The focus detection unit 213 corrects the pair of image signals for each focus detection position according to the distance measurement light amount information, and then performs a known focus detection calculation process to calculate the image shift amount of the pair of images for each focus detection position. To do. The focus detection unit 213 calculates the defocus amount at each focus detection position by multiplying the image shift amount calculated for each focus detection position by the conversion coefficient obtained for each focus detection position, and obtains a plurality of defocus amounts. Based on this, the final defocus amount is determined. Further, when the focus detection unit 213 determines that lens driving is necessary based on the final defocus amount (when it is determined that the lens is out of focus), the focus detection unit 213 transmits the final defocus amount to the lens CPU.

  The lens CPU 206 calculates a lens driving amount based on the received defocus amount, and drives the focusing lens 210 to a focal point based on the lens driving amount.

  The optical system is not limited to the digital still camera described above. The present invention can also be applied to a small camera module built in a mobile phone or the like. In the above description, the re-imaging method and the microlens method have been described as examples of the pupil division type focus detection method. However, the present invention is not limited to these methods, and the exit pupil is divided by some method and divided. Any method may be used as long as it detects the amount of image misalignment between a pair of images formed using a light beam passing through the pupil.

  Thus, according to one embodiment, the focal point on the planned imaging plane of the imaging optical system based on the amount of deviation of the pair of images formed by the pair of focus detection light beams that have passed through the imaging optical system. When detecting the adjustment state, a pair of focus detection pupil information indicating the distribution of the focus detection light beam used for focus detection and a pair of aperture information defining the light beam emitted from the imaging optical system to the focus detection device. Since the conversion coefficient for converting the image shift amount to the defocus amount of the imaging optical system is calculated, the pair of image shift amounts are defocused by the imaging optical system in the pupil division type focus detection method. An accurate conversion coefficient for conversion into a quantity can be obtained, and the focus detection accuracy of the imaging optical system can be improved.

  According to one embodiment, based on the above-mentioned distance measurement pupil information and aperture information, the light beams that can be used for focus detection are separated from the pair of focus detection light beams, and Since the opening angle of the center of gravity of the light flux distribution is calculated and the conversion coefficient is calculated based on the opening angle of the center of gravity, vignetting occurs in the focus detection light beam, and the vignetting method is further applied to the imaging optical system. Even when changing due to exchange, focusing, or zooming, an accurate conversion coefficient can be quickly obtained, and the accuracy and responsiveness in focus detection can be improved.

  According to one embodiment, the two light beams that can be used for focus detection are separated from the pair of focus detection light beams on the exit pupil plane of the imaging optical system, and the center of gravity of the two separated light beam distributions is separated. Since the interval was calculated, and the opening angle of the center of gravity was calculated based on the distance between the planned imaging surface and exit pupil plane of the imaging optical system and the center of gravity interval, the opening angle of the center of gravity was accurately and It can be obtained quickly, and the accuracy and responsiveness in focus detection can be further improved.

  Furthermore, according to the embodiment, since the distance measurement pupil information includes information on the direction of the focus detection light beam according to the focus detection position, the vignetting method of the focus detection light beam according to the focus detection position. Even if they are different, an accurate conversion coefficient can be quickly obtained, and the accuracy and responsiveness in focus detection can be improved.

  According to one embodiment, since the aperture information is information according to the focus detection position, an accurate conversion coefficient can be quickly obtained even when the vignetting method of the focus detection light beam differs depending on the focus detection position. The accuracy and responsiveness in focus detection can be improved.

  According to the embodiment, since the conversion coefficient is calculated based on the focus detection position information, the distance measurement pupil information, and the aperture information, the vignetting method of the focus detection light beam varies depending on the focus detection position. However, an accurate conversion coefficient can be quickly obtained, and the accuracy and responsiveness in focus detection can be improved.

  Furthermore, the distance measurement light amount information regarding the light amount of the pair of focus detection light beams that can be used for focus detection is calculated based on the focus detection position information, the distance measurement pupil information, and the aperture information, and the pair of focus detection light beams Since the pair of images formed by the correction is corrected based on the distance measurement light quantity information, it is possible to detect the amount of image shift with high accuracy, thereby enabling highly accurate focus detection.

  According to an embodiment, an optical system is configured by the camera body 203 including the focus detection device of the above-described embodiment and the interchangeable lens 202 including an imaging optical system that can be attached to and detached from the camera body 203. Then, a CPU 214 for calculating a conversion coefficient is installed on the camera body 203 side, and distance measuring pupil information is stored in the memory thereof, while aperture information is stored in a memory of the lens CPU 206 of the interchangeable lens 202, and the camera body 203 is stored. Since the aperture information is read from the interchangeable lens 202 and the conversion coefficient is calculated based on the aperture information and the distance measurement pupil information, the main body including the above-described focus detection device, Even in an optical system consisting of a lens groove body that can be attached and detached, vignetting may occur in the light beam for focus detection. Who vignetting can also be determined quickly and accurately transform coefficients even vary by the exchange and focusing and zooming of the imaging optical system, it is possible to improve the accuracy and responsiveness in the focus detection.

<< Variation of center of gravity calculation of focus detection beam >>
In FIG. 8 and FIG. 9 described above, the distribution information of the same focus detection light beam is obtained when obtaining the center of gravity of the focus detection light beam at the center (intersection of the planned image formation surface and the optical axis) and the periphery on the planned image formation surface. However, if the distance measurement pupil information indicating the distribution of the light beam for focus detection differs according to the position on the planned imaging plane, the distance measurement pupil information corresponding to each position is stored, When obtaining the center of gravity of the focus detection light beam, distance measurement pupil information corresponding to a position on the planned imaging plane (focus detection position) may be used.

  If there are many focus detection positions and a large amount of storage capacity is required to store the distance measurement pupil information corresponding to the focus detection position, the distance measurement pupil information corresponding to a small number of specific positions as shown in FIG. Is stored, and distance measurement pupil information at an arbitrary focus detection position is obtained by interpolation from distance measurement pupil information at a specific position near the focus detection position. In this way, the storage capacity for storing the distance measuring pupil information can be reduced.

  In FIG. 17 (a), distance measurement pupil information (see FIGS. (B) and (d)) indicating the distribution of the light beam for focus detection is stored for specific positions 401 and 402 on the scheduled imaging plane 400. It is assumed that Here, in the case of obtaining distance measurement pupil information at an arbitrary focus detection position 403, a specific position existing in the vicinity of the position 403, which is a specific position in which distance measurement pupil information is stored in advance, in this case, the position 401 The distance measurement pupil information of the focus detection position 403 (see FIG. 4C) is obtained by interpolation using the distance measurement pupil information 402 and 402. In this interpolation calculation, the distance measurement pupil information of the specific position 401 and the specific position 402 are determined according to the distance between the focus detection position 403 and the specific position 401 and the distance between the focus detection position 403 and the specific position 402. Apportions the distance measurement pupil information.

<< Other Modifications of Center of Gravity Position of Focus Detection Beam >>
In FIG. 8 and FIG. 9 described above, the distribution information of the focus detection light beam on the exit pupil plane 1 is used when obtaining the center of gravity of the focus detection light beam, but depending on the distance in the optical axis direction from the planned imaging plane. If the distance measurement pupil information indicating the distribution of the focus detection light beam is different, the distance measurement pupil information corresponding to the distance in the optical axis direction from the planned imaging plane is stored, and the center of gravity of the focus detection light beam is calculated. When obtaining, distance measurement pupil information corresponding to the exit pupil position of the optical system (distance in the optical axis direction from the planned imaging plane) may be used.

  When enormous storage capacity is required to store distance measurement pupil information corresponding to the distance in the optical axis direction from the planned imaging plane, distance measurement corresponding to a small number of specific distances as shown in FIG. The pupil information is stored, and the distance measurement pupil information at an arbitrary distance is obtained by interpolation from the distance measurement pupil information at a specific distance in the vicinity. In this way, the storage capacity for storing the distance measuring pupil information can be reduced.

  In FIG. 18, distance measurement pupil information (see FIGS. (B) and (d)) indicating the distribution of the light beam for focus detection is stored at positions 411 and 412 that are apart from the planned imaging plane 400 by a specific distance. It is assumed that Here, when obtaining the distance measuring pupil information at the exit pupil position 413 of the imaging optical system, a specific position existing in the vicinity of the position 413, where the distance measuring pupil information is stored in advance, Then, using the distance measurement pupil information at the positions 411 and 412, distance measurement pupil information (see FIG. 7C) at the exit pupil position 413 is obtained by interpolation calculation. In this interpolation calculation, the distance measurement pupil information at the specific position 411 and the distance measurement pupil information at the specific position 412 according to the distance between the position 413 and the specific position 411 and the distance between the position 413 and the specific position 412. Apportion.

  In the above description, the example in which the distribution information (ranging pupil information) of the focus detection light beam used for obtaining the center of gravity of the focus detection light beam is stored in advance, but the focus detection device can perform high-speed calculation processing. When equipped with a microcomputer, the light beam directly from the configuration parameters of the focus detection system (photoelectric conversion unit size, microlens curvature, microlens refractive index, distance between microlens and photoelectric conversion unit, microlens aperture diameter, etc.) By performing tracking calculation and diffraction calculation, distance measurement pupil information corresponding to an arbitrary position on the planned imaging plane or an arbitrary distance in the optical axis direction from the planned imaging plane may be obtained.

  If the ray tracing calculation or diffraction calculation takes too much time, a point spread function corresponding to an arbitrary position on the planned imaging plane or an arbitrary distance in the optical axis direction from the planned imaging plane is calculated in advance. The distance measurement pupil information (design distance measurement pupil information) when there is no diffraction or aberration is stored, and when the center of gravity of the focus detection light beam is obtained, the focus detection position and the imaging optical system By reading out the point spread function corresponding to the exit pupil position and the design ranging pupil information, and performing the convolution calculation of this point spread function and the design ranging pupil information, the focus detection position and the exit of the imaging optical system are obtained. The distance measuring pupil information corresponding to the pupil position is obtained by calculation and used.

  If a large storage capacity is required to store a point spread function corresponding to an arbitrary position on the planned imaging plane or an arbitrary distance in the optical axis direction from the planned imaging plane, Stores a point spread function corresponding to a specific position above or a specific distance in the optical axis direction from the planned imaging plane, and a point spread function corresponding to the focus detection position or the exit pupil position of the imaging optical system Is interpolated using a point spread function corresponding to a specific position near the focus detection position or a specific distance near the exit pupil distance of the imaging optical system. In this way, the storage capacity for storing the point spread function can be reduced.

It is a figure which shows the structure of the focus detection apparatus of a re-imaging system. It is a figure which shows the structure of the focus detection apparatus of a micro lens system. It is a figure explaining the diffraction phenomenon in a micro lens system. It is a figure which shows the diffraction image intensity distribution pattern corresponding to FIG. 5 is a cross-sectional view of Y = 0 of the diffraction image intensity distribution pattern of FIG. It is a figure explaining the spherical aberration in a micro lens system. It is explanatory drawing of the vignetting of the light beam for focus detection. It is a figure explaining how to obtain | require the gravity center of the light beam for focus detection. It is a figure explaining the vignetting of the light beam for focus detection. It is a figure explaining how to obtain | require the gravity center of the light beam for focus detection. It is a block diagram of an optical system. It is a figure which shows the specific example of the focus detection position in the digital still camera shown in FIG. It is a detailed block diagram of the image pick-up element corresponding to FIG. 11, FIG. It is a flowchart which shows operation | movement of a digital still camera. It is a figure explaining correction | amendment of the image signal by ranging light quantity information. It is a figure which shows the other Example of an optical system. It is a figure explaining the modification of the gravity center position calculation of the focus detection light beam. It is a figure explaining the other modification of calculation of the gravity center position of the light beam for focus detection.

Explanation of symbols

1 Exit pupil 2, 3 Distance pupil 4 Optical axis 6, 7 Focus detection light beam 8, 9 Center of gravity position 12, 13, 22, 23 Aperture aperture 16, 26 Image sensor 18, 28 Distance unit 32, 33, 42, 43, 56, 57, 72, 73, 82, 83 Focus detection light beam 41, 44 Exit pupil 50, 60 of imaging optical system Micro lens 52, 53, 62, 63 Light receiving element 67 Projection axis 78, 79 Center of gravity Position 201 Digital still camera 203 Camera body 206 Lens CPU
211 Diaphragm 212 Image Sensor 210 Digital Still Camera 212 Image Sensor 213 Focus Detection Unit 214 Body CPU
310 Imaging Pixel 311 Focus Detection Pixel (Microlens System)

Claims (11)

A focus detection device that detects a focus adjustment state on a planned imaging plane of the imaging optical system based on a shift amount of a pair of images by a pair of light beams that have passed through different positions of a pupil of the imaging optical system,
A conversion coefficient for calculating a conversion coefficient for converting a shift amount of the pair of images into a defocus amount of the imaging optical system based on information indicating the distribution of the light flux and aperture information of the imaging optical system A focus detection apparatus comprising a calculation means. The focus detection apparatus according to claim 1,
The conversion coefficient calculation means calculates an opening angle of the center of gravity of two light flux distributions that can be used for focus detection among the pair of light fluxes based on the information indicating the distribution of the light fluxes and the aperture information, A focus detection apparatus that calculates a conversion coefficient based on an opening angle of the center of gravity. The focus detection apparatus according to claim 2,
The conversion coefficient calculation means calculates a center-of-gravity interval on the exit pupil plane of the imaging optical system of two light beam distributions that can be used for focus detection in the pair of light beams, and schedules the imaging optical system A focus detection apparatus that calculates an opening angle of the center of gravity based on a distance between an imaging plane and the exit pupil plane and the center-of-gravity interval. The focus detection apparatus according to any one of claims 1 to 3,
It detects a focus adjustment state of the imaging optical system at a predetermined focus detection position on a predetermined imaging surface of the imaging optical system, and information indicating the distribution of the luminous flux corresponds to the focus detection position. A focus detection apparatus characterized in that information on the direction of a focus detection light beam is included. In the focus detection apparatus according to any one of claims 1 to 4,
A focus adjustment state of the imaging optical system at a predetermined focus detection position on a predetermined imaging surface of the imaging optical system; and the aperture information is information corresponding to the focus detection position. Feature focus detection device. The focus detection apparatus according to any one of claims 1 to 3,
Detecting a focus adjustment state of the imaging optical system at a predetermined focus detection position on a predetermined imaging surface of the imaging optical system, and the conversion coefficient calculating means includes information on the focus detection position, the light flux The conversion coefficient is calculated based on the information indicating the distribution of the aperture and the aperture information. The focus detection apparatus according to any one of claims 1 to 3,
Detecting a focus adjustment state of the imaging optical system at a predetermined focus detection position on a predetermined imaging surface of the imaging optical system, the focus detection position information, information indicating the distribution of the luminous flux, and the aperture Distance measurement light quantity information calculating means for calculating information on the light quantity of the pair of focus detection light fluxes available for focus detection based on the information, and a pair of images of the pair of focus detection light fluxes on the light quantity information A focus detection apparatus, further comprising: an image correction unit that corrects the image by the correction. The focus detection apparatus according to any one of claims 1 to 3,
Pupil information storage means for storing information indicating a plurality of light flux distributions corresponding to a plurality of positions on the planned imaging plane;
Interpolation calculation means for obtaining information indicating the distribution of the luminous flux corresponding to the focus detection position on the planned imaging plane by interpolation based on information indicating the distribution of the plurality of luminous fluxes stored in the pupil information storage means A focus detection device comprising: The focus detection apparatus according to any one of claims 1 to 3,
Pupil information storage means for storing information indicating a plurality of distributions of the luminous fluxes corresponding to a plurality of distances in the optical axis direction from the planned imaging plane;
Based on the information indicating the distribution of the plurality of light beams stored in the storage means, the information indicating the distribution of the light beams corresponding to the distance from the planned imaging surface of the exit pupil of the imaging optical system is obtained by interpolation calculation. A focus detection apparatus comprising: an interpolation calculation means to be obtained.   An optical system comprising the focus detection apparatus according to claim 1 and an imaging optical system. The optical system according to claim 10.
The optical system includes a main body including the focus detection device, and a lens structure including the imaging optical system that can be attached to and detached from the main body.
The conversion coefficient calculating means installed on the main body side and holding information indicating the distribution of the luminous flux, holding the aperture information on the lens structure side, and the conversion coefficient calculating means installed on the main body side, An optical system, wherein the aperture information is read from the lens structure, and the conversion coefficient is calculated based on the aperture information and information indicating the distribution of the luminous flux.

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