JP2012173309A - Focus detection device and control method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focus detection device for highly accurately detect a focus by performing highly accurate correction concerning stray light, while reducing the storage capacity of information on the correction of the stray light.SOLUTION: A focus detection part (208) for detecting the focus state of an imaging lens, based on position relation of paired optical images generated by paired light fluxes passing through different areas of an exit pupil of the imaging lens includes: storage means (ROM) for storing a difference in the light amounts of the paired optical images corresponding to the position of a light source in the field of the imaging lens and the light amount of the light source as correction information for correcting one signals to be output from paired photoelectric conversion parts; and correction means (PRS) for correcting the one signals to be output from the paired photoelectric conversion parts, based on the detection result of light source detection means and the correction information of the storage means, when a defocusing amount is smaller than a predetermined value.

Description

  The present invention generally relates to a focus detection device mounted on an imaging device, and more particularly to a focus detection device that detects a focus state of an imaging optical system and a control method thereof.

  Conventionally, a so-called image shift type focus detection method is known as a focus detection method of a photographing lens. In this method, it is assumed that the two optical images to be compared are images of the same shape that are merely laterally shifted. Therefore, if the light beam used for focus detection includes a light beam (stray light) that does not need to be used originally and the optical images to be compared have different shapes, the accuracy of the focus detection result is deteriorated. Therefore, to prevent stray light from being generated in the photographic lens and the focus detection optical system, the optical components are subjected to antireflection coating on the optical components, and surface treatment (painting, etc.) is applied to the mechanical components with little reflection. To reduce stray light. However, although it is possible to reduce the reflection of the optical component and the mechanism component, it is difficult to configure the stray light generated so that it does not exist completely.

  Conventionally, there has been proposed a method for reducing the influence of stray light included in a light beam used for focus detection as described above on a focus detection result. The focus detection apparatus described in Patent Document 1 stores in advance the relationship between the stray light generation source, the position of stray light, and the amount of light. At the time of photographing, the position and light amount of a region having a large amount of light that can be a stray light generation source within the photographing range are detected, and the position and light amount of stray light are calculated from the stored relationship between the stray light generation source and stray light. And the countermeasure which reduces the influence on a focus detection result is disclosed by correct | amending the signal which photoelectrically converted each pair of optical image light in a focus detection area | region using the position and light quantity of the calculated stray light. .

JP 2006-184321 A

  However, in the conventional technique disclosed in Patent Document 1 described above, it is necessary to correct each of the signals obtained by photoelectrically converting the pair of optical image light in the focus detection region, and the correction value is also obtained by photoelectrically converting the pair of optical image light. It was necessary to memorize corresponding to the signal. Therefore, since two types of correction data for each pair of optical images are required, there is a problem that the capacity of stored data necessary for correction increases. Further, in order to perform focus detection with higher accuracy, it is necessary to perform correction including a small amount of stray light. In that case, it is necessary to increase the gradation of the correction value, leading to an increase in the capacity of stored data.

  Furthermore, when the same position contains stray light at the same position with respect to a signal obtained by photoelectrically converting a pair of optical image light from a certain stray light generation source, the influence on the focus detection result is small. In the prior art disclosed in Patent Document 1 described above, correction values are prepared for each pair of optical images, and information on stray light that has a small influence on the focus detection result is also stored. It had been.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a focus detection apparatus and a control method therefor that perform high-precision focus detection and high-precision focus detection while reducing the storage capacity of information related to stray light correction. .

  In order to achieve the above object, the technical feature of the present invention is that, based on the positional relationship between the pair of optical images generated by the pair of light beams that have passed through different regions of the exit pupil of the photographing lens, A control method of a focus detection device for detecting a focus state, which is based on a difference between a light amount of a pair of optical images corresponding to a position of a light source in a field of the photographing lens stored in advance and the light amount of the light source. Then, a correction step for correcting one signal output from the photoelectric conversion unit that photoelectrically converts the pair of optical image lights, and a defocus amount is calculated according to the output of the photoelectric conversion unit after the correction And a defocus amount calculating step.

  According to the present invention, it is possible to provide a focus detection apparatus and a control method therefor that perform high-precision focus detection and high-precision focus detection while reducing the storage capacity of information related to stray light correction.

It is a center sectional view of a single-lens reflex camera. 3 is a perspective view of a focus detection unit 208. FIG. FIG. 6 is a plan view of the diaphragm 212 as viewed from the field mask 210 side. FIG. 4A is a plan view of the incident surface side of the secondary imaging lens unit 213 as viewed. FIG. 4B is a plan view of the exit surface side of the secondary imaging lens unit 213 as viewed. FIG. 6 is a plan view of the light receiving element 215 as viewed from the field mask 210 side. FIG. 6A is a diagram in which each light receiving element array of the light receiving elements 215 is back projected onto the field mask 210. FIG. 6B is a diagram in which the detection range 218 of the photometric sensor 221 is overlaid on FIG. 6A. FIG. 6 is a diagram illustrating a positional relationship between a subject 301 within a photographing range of a photographing lens 201 and a back projection image of a light receiving element array. FIG. 8A shows an ideal pair of output waveforms without stray light when the subject is out of focus. FIG. 8B is a diagram illustrating an ideal pair of output waveforms without stray light in a state where the waveforms of the pair of optical images are aligned by correlation calculation. FIG. 9A is a diagram illustrating a pair of output waveforms in the presence of stray light in a state where the subject is out of focus. FIG. 9B is a diagram illustrating a pair of output waveforms in a state where stray light is present in a state where the waveforms of the paired optical images are aligned by correlation calculation. It is a block diagram of a camera. It is explanatory drawing of the lens control circuit LNSU. It is a figure of an example of the correction information used for stray light. It is a figure which shows the focus detection operation | movement of a camera.

  Embodiments of the present invention will be described below with reference to the drawings.

  Hereinafter, an example in which the focus detection apparatus of the present invention according to the first embodiment of the present invention is applied to a single-lens reflex digital camera capable of exchanging lenses will be described.

  FIG. 1 is a central sectional view of a single-lens reflex camera.

  In the figure, 200 is a single-lens reflex camera body, 201 is a photographing lens, and L is an optical axis of the photographing lens 201. An image sensor unit 204 including an optical low-pass filter, an infrared cut filter, and an image sensor is disposed in the vicinity of the planned imaging plane of the photographic lens 201. The photographic lens 201 and the image sensor unit 204 are provided with a main mirror 202 and a sub mirror 203 that are retracted out of the photographic light beam during photographing by a known quick return mechanism. The main mirror 202 is a half mirror, and the photographing light beam is separated into reflected light guided to the upper viewfinder optical system and transmitted light incident on the sub mirror 203. The reflected light forms an image on the mat surface of the focusing plate 205 having the mat surface and the Fresnel surface, and is guided to the eyes of the observer through the pentaprism 206 and the eyepiece lens group 207. Further, part of the light diffused by the focus plate 205 passes through the photometric lens 220 and reaches the photometric sensor 221. The photometric sensor 221 is divided into a plurality of pixels, and an RGB color filter is arranged in each pixel to detect the spectral intensity of the subject. On the other hand, the transmitted light changes its optical path downward by the sub mirror 203 and is guided to the focus detection unit 208. Part of the light reflected by the main mirror 202 reaches the photometric sensor 221, and part of the light that has passed through the main mirror 202 is guided to the focus detection unit 208.

  Next, the focus detection unit included in the camera described in FIG. 1 will be described. FIG. 2 is a perspective view of the focus detection unit 208 and uses phase difference focus detection as a distance measurement principle. Note that the actual focus detection unit is made compact by folding the optical path with a reflecting mirror or the like, but is a straight developed view to eliminate the complexity of the figure.

  A field mask 210 has a central portion and cross-shaped openings 210a, 210b, and 210c on the left and right sides thereof. The field mask 210 is disposed in the vicinity of a position equivalent to the planned imaging plane of the photographing lens 201 and the imaging plane of the imaging element unit 204. A field lens 211 is disposed behind the field mask 210. The field lens 211 includes a plurality of lens portions 211a, 211b, and 211c having different optical actions, and each lens portion has a different lens optical axis. The lens portions 211a, 211b, and 211c correspond to the openings 210a, 210b, and 210c of the field mask 210, respectively.

  Reference numeral 212 denotes a stop having a plurality of openings, and reference numeral 213 denotes a secondary image forming lens unit (image forming lens unit) having lens portions corresponding to the plurality of openings of the stop 212. The secondary imaging lens unit 213 re-images the object image on the planned imaging surface imaged by the photographing lens 201 on the light receiving element array of the light receiving elements 215 arranged behind the object image. An infrared cut filter that removes an infrared wavelength component unnecessary for focus detection is disposed in the vicinity of the stop 212, but is omitted.

  3 to 5 are plan views of each member in the perspective view of FIG. 2, and FIG. 3 is a plan view of the diaphragm 212 as viewed from the field mask 210 side. 4A is a plan view of the secondary imaging lens unit 213 viewed from the incident surface side, and FIG. 4B is a plan view of the secondary imaging lens unit 213 viewed from the exit surface side. FIG. 5 is a plan view of the light receiving element 215 as viewed from the field mask 210 side.

  In FIG. 3, the diaphragm 212 has two pairs of openings 212a-1 and 212a-2 and 212a-3 and 212a-4 at the center. Two pairs of openings 212b-1 and 212b-2, 212b-3 and 212b-4 are on the right side, and two pairs of openings 212c-1 and 212c-2, 212c-3 are on the left side. And 212c-4, respectively.

  In FIG. 4A, a prism portion corresponding to the aperture of FIG. 3 is formed on the incident surface side of the secondary imaging lens unit 213. Therefore, like the diaphragm 212, two pairs of prism portions 213a-1 and 213a-2, 213a-3 and 213a-4 are formed in the central portion. Two pairs of openings 213b-1 and 213b-2, 213b-3 and 213b-4 are on the right side, and two pairs of openings 213c-1, 213c-2 and 213c-3 are on the left side. And 213c-4 are formed respectively.

  In FIG. 4B, a spherical lens portion is formed on the exit surface side of the secondary imaging lens unit 213 corresponding to the prism portion of FIG. Similarly, two pairs of lens portions 214a-1 and 214a-2 and 214a-3 and 214a-4 are formed in the central portion. Two pairs of openings 214b-1 and 214b-2, 214b-3 and 214b-4 are on the left side, and two pairs of openings 214c-1, 214c-2 and 214c-3 are on the right side. And 214c-4 are formed respectively.

  In FIG. 5, the light receiving element 215 is formed with a light receiving element array as a photoelectric conversion portion corresponding to the lens portion in FIG. Similarly, two pairs of light receiving element arrays 215a-1 and 215a-2, 215a-3 and 215a-4 are formed in the central portion. Two pairs of openings 215b-1 and 215b-2, 215b-3 and 215b-4 are on the right side, and two pairs of openings 215c-1, 215c-2 and 215c-3 are on the left side. And 215c-4 are formed. The light receiving element array detects the distribution of the light amount of the pair of optical images and outputs the pair of electrical signals to a PRS described later.

  3 to 5 correspond to the opening portion of the field mask 210 and the lens portion of the field lens 211, respectively. For example, the light beam that has passed through the field mask opening 210b passes through the field lens 211b, and passes through two pairs of aperture openings 212b-1 and 212b-2, and 212b-3 and 212b-4, thereby forming four light beams. To be separated. The four light beams are incident on two pairs of prism portions 213b-1 and 213b-2, 213b-3 and 213b-4 of the secondary imaging lens unit 213, respectively, and two pairs of lens portions. It injects from 214b-1 and 214b-2, 214b-3 and 214b-4. Then, four optical images corresponding to the field mask opening 210b are formed on the two pairs of light receiving element rows 215b-1, 215b-2, 215b-3, and 215b-4 of the light receiving element 215. Four crosses 216-1, 216-2, 216-3, and 216-4 indicated by dotted lines in FIG. 5 indicate respective optical images, and optical images 216-1 and 216-2, and optical images 216-3 and 216, respectively. -4 is a pair. These pairs of optical images are optical images generated by a pair of light beams that have passed through different areas of the exit pupil of the photographing lens 201.

  In the focus detection unit configured as described above, the pair of optical images move in a direction toward or away from each other with the defocusing of the photographing lens 201 with respect to the planned imaging plane.

  For example, the optical images inside the pair of optical images 216-1 and 216-2 move in the vertical direction, and this movement is detected by arranging the light receiving element rows in the vertical direction as shown in FIG. That is, the light quantity distribution relating to this optical image is detected based on the outputs of the light receiving element arrays 215b-1 and 215b-2. Then, by calculating using a well-known correlation calculating means, the amount of change of the paired optical image interval associated with the taking lens 201 with respect to the in-focus state is obtained. Here, the outputs of the light receiving element arrays 215b-1 and 215b-2 are signals obtained by receiving optical image light, performing photoelectric conversion, and outputting the light.

  If the change amount (image shift amount) of the optical image interval of the pair can be known, the relationship between the change amount and the defocus amount of the photographing lens 201 is approximated by a polynomial having the change amount as a variable in advance. The defocus amount of the photographing lens 201 can be predicted. Thereby, it is possible to detect the focus of the photographing lens 201. In the case of the light receiving element arrays 215b-3 and 215b-4, the basic operation is the same except that the vertical direction described above is changed to the horizontal direction.

  The pair of light receiving element arrays 215b-1 and 215b-2 are suitable for focus detection of a subject having a contrast component in the vertical direction because the light receiving elements are arranged in the vertical direction. On the other hand, the light receiving element arrays 215b-3 and 215b-4 are suitable for focus detection of a subject having a contrast component in the left and right direction because the light receiving elements are arranged in the left and right direction. When both are combined, so-called cross-type focus detection is performed that is not affected by the direction of the contrast component of the subject.

  In the above description, only the part relating to the subscript b has been described, but the same applies to the subscripts a and c.

  FIG. 6A is a diagram in which each light receiving element array of the light receiving elements 215 is back projected onto the field mask 210. Since the field mask 210 is disposed in the vicinity of the planned imaging plane of the photographic lens 201, there is no problem even if FIG. 6A is considered to be the planned imaging plane. In the figure, a rectangle 217 indicated by a dotted line that is slightly larger than the field mask 210 is an imaging range by the imaging lens 201. In addition, back projection images 218a, 218b, 218c, 219a, 219b, and 219c of the light receiving element arrays shown in a cross shape are formed in the three field mask openings. Since the pair of light receiving element arrays coincide on the planned imaging plane, they are displayed in an overlapping manner. Since the back-projected images 218a, 218b, 218c, 219a, 219b, and 219c are light receiving element arrays, the light amount distribution of the subject can be detected in this cross area. That is, these back-projected images become a so-called cross-type focus detection region. In this embodiment, the cross-type focus detection area is provided with a total of three places, that is, the central portion and the peripheral portion of the photographing range 217 as shown in FIG. 6, and the focus detection of the subject in the focus detection region can be performed. The cross-type focus detection area has two directions in which the spreading directions are orthogonal to each other, so that focus detection can be performed on most subjects regardless of the contrast component direction of the subject.

  FIG. 6B displays the detection range 218 of the photometric sensor 221 in an overlapping manner with respect to FIG. The detection range 218 of the photometric sensor 221 is divided into 3 parts vertically and 5 parts horizontally, and has a total of 15 areas. Each region is composed of a plurality of pixels provided with the above-described RGB color filters, and a light amount distribution within the photographing range can be obtained. Three locations near the center are arranged corresponding to the focus detection areas 210a to 210c.

  FIG. 7 shows a state where the subject 301 exists in the photographing range of the photographing lens 201 shown in FIG. The subject 301 is a subject composed of a white portion on the upper side and a shaded portion on the lower side in the drawing. In the backprojected image of the light receiving element array described with reference to FIG. 6, 218a is suitable for detecting the light amount distribution of the subject. In FIG. 7, the back-projected image 218 a is shown superimposed on the subject 301. FIG. 8A shows output signals of the light receiving element arrays 215a-1 and 215a-2 corresponding to the backprojected image 218a in the state shown in FIG. In a state where the subject 301 is out of focus, the output signal 302-1 of the light receiving element array 215a-1 and the output signal 302-2 of the light receiving element array 215a-2 are paired as shown in FIG. There is a deviation in the waveform position of the optical image. FIG. 8B shows a state in which the waveforms of the paired optical images are aligned by a known correlation calculation means in such a state. In an ideal state where there is no stray light in the light flux reaching the focus detection unit from the subject, the pair of output signals 302-1 and 302-2 are substantially coincident as shown in FIG. 8B. In this case, since the correlation between the pair of optical images is very high, the defocus amount can be detected with high accuracy.

  However, in actuality, various stray light may be generated when the light flux from the subject passes through the photographing lens and reaches the light receiving element of the focus detection unit. The main factors are minute reflection on the surface of an optical component such as a lens and surface reflection of a mechanical component that holds the optical component.

  FIG. 9A shows an output waveform in the case where stray light generated at some point from the same subject as in FIG. 7 through the photographing lens to the light receiving element of the focus detection unit is included. Similarly to FIG. 8A, the output signal 303-1 of the light receiving element array 215a-1 and the output signal 303-2 of the light receiving element array 215a-2 are obtained. In contrast to the ideal state without stray light in FIG. 8A, the output signal 303-1 indicates a state in which the outputs 304 and 306 are increased due to stray light, and the output signal 303-2 is due to stray light. The state where the output of 305 is increasing is shown. As described above, the stray light can be generated at various places. Depending on the place where the stray light is generated, there are those that occur in both the pair of optical images and those that occur only in one of the optical images. In FIG. 9A, the stray light 304, 305 having the same light amount is generated at the same position in both of the pair of output signals 303-1 and 303-2, and the stray light 306 is generated only in the output signal 303-1. Shows the state.

  FIG. 9B shows a state in which the waveforms of the paired optical images are aligned by a well-known correlation calculation means, as in FIG. 8B. Since there is a difference in the shape of the pair of output waveforms due to stray light, the accuracy in calculating the amount of deviation of the waveform position deteriorates. In the subject 301, it is ideal that a waveform alignment result obtained by the correlation calculation unit means that a pair of output signals coincide with each other in a portion corresponding to a boundary portion between a white portion and a black portion having the highest contrast. In FIG. 9B, a slight deviation occurs due to the influence of stray light. The interval between the arrows 307 in the figure indicates a deviation. The main cause of this shift is stray light 306 generated only in the output signal 303-1, and stray light 304, 305 generated in the same position and the same amount of light in both the output signals 303-1, 303-2. Is less affected. This is also clear from the fact that the output signals 303-1 and 303-2 completely match when the stray light 306 is not present. In general, the influence of stray light is more easily received by a subject having a low spatial frequency, and the detection accuracy of the defocus amount is deteriorated even by very minute stray light. In this embodiment, the difference in the shape of the paired optical images due to the stray light can be reduced by correcting the output signal. The correction method will be described in detail later.

  Hereinafter, a method for correcting the output signal based on the difference in the shape of the pair of optical images caused by stray light will be described.

  FIG. 10 is a block diagram of the camera.

  In the figure, PRS is a central processing circuit of the camera, which is a one-chip microcomputer in which, for example, a CPU, RAM, ROM, ADC (A / D converter), input / output ports and the like are arranged. The PRS has a function as means for calculating the defocus amount from the output of the pair of light receiving element arrays. The PRS also has a function of correcting one electric signal output from the pair of light receiving element arrays as will be described later. In addition, a series of camera control software and parameters including AF control are stored in the ROM. The ROM also stores correction information for correcting one electric signal output from a pair of light receiving element arrays described later, and has a function of storing the correction information.

  DBUS is a data bus. The MDR is a motor control circuit that receives data input via the data bus DBUS while the control signal CMTR is input from the central processing circuit PRS, and controls a motor (not shown) based on the data. The SHT receives data input via the data bus DBUS while the control signal CSHT is input from the central processing circuit PRS, and based on the data, a shutter control circuit that performs travel control of a shutter front curtain and a rear curtain (not shown) It is. APR is an aperture control circuit that receives data input via the data bus DBUS while the control signal CAPR is input, and controls an aperture control mechanism (not shown) based on the data. SWS is a switch group such as release switches SW1 and SW2, continuous shooting mode switches, and various information setting switches. LCOM is a lens communication circuit that receives data input via the data bus DBUS while the control signal CLCOM is input, and performs serial communication with the lens control circuit LNSU based on the data. The lens communication circuit LCOM transmits lens driving data DCL to the lens control circuit in synchronization with the clock signal LCK, and at the same time, lens information DLC is serially input. The lens driving data DCL includes the type information of the mounted camera, the type of the focus detection unit of the camera, information on the lens driving amount at the time of shooting, and the like.

  BSY is a signal for informing the camera side that a focus adjustment lens (not shown) is moving. When this signal is generated, serial communication is not performed. SPC is a photometry circuit, and when it receives a control signal CSPC from the central processing circuit PRS, it sends the photometry output SSPC of the photometry sensor 221 to the central processing circuit PRS. The photometric output SSPC is A / D converted by the ADC in the central processing circuit PRS and used as data for controlling the shutter control circuit SHT and the aperture control circuit APR.

  Reference numeral 400 denotes a light projection circuit for projecting auxiliary light for focus detection, which drives the LED to emit light by the control signal ACT and the synchronous clock CK from the central processing circuit PRS.

  SNS is a ranging light receiving circuit having a plurality of pairs of light receiving element arrays 215a-1 / 215a-2, 215a-3 / 215a-4,... 215c-3 / 215c-4. Each distance measuring light receiving circuit is configured to receive an image at a position corresponding to the backprojected images 218 and 219 in FIG. SDR is a sensor drive circuit that controls each light receiving circuit in accordance with signals STR and CK input from the central processing circuit PRS. The sensor driving circuit SDR controls each light receiving circuit by the control signals φ1, φ2, CL, SH, selects any one of the light receiving circuits by the selection signals SEL1 to SEL6, and an image signal obtained from the selected light receiving circuit. SSNS is transmitted to the central processing circuit PRS.

  FIG. 11 shows how the lens control circuit LNSU obtains focal length information and distance ring information of a lens. The memory unit 401 stores the lens type, the position of the distance ring, the position of the zoom ring, the coefficient of the defocus amount versus the focus adjustment lens extension amount, and the like. The stored information is converted into a signal, calculated by the control unit 403 in the lens control circuit LNSU, and input as lens information DLC to the central processing circuit PRS via the lens communication circuit LCOM. The focal length information of a photographing lens having a plurality of focal lengths, that is, a so-called zoom lens, is a representative value of each range obtained by dividing a continuously changing focal length into a plurality of ranges. Further, since the position information of the distance ring in this case is not directly used for the focus calculation, so much accuracy is not required. The lens driving unit 402 adjusts the focus state (focus position) by moving the lens constituting the photographing lens 201. A control unit 403 controls the entire photographing lens 201.

  Hereinafter, a method for calculating the position and the amount of stray light included in the light beam reaching the light receiving element of the focus detection unit from the subject, that is, stray light correction will be described.

  In this embodiment, the ROM stores, as correction information, the relationship between the position of the light source that is the source of stray light and the position of the stray light in the light receiving element corresponding to the light amount of the light source and the amount of light. On the other hand, using the light receiving element array of the light receiving elements 215, the position and light amount of the light source that is the source of stray light are detected. In this embodiment, the light receiving element 215 has a function of detecting the position of the light source that is the source of stray light in the object field of the photographing lens and the light amount of the light source. The correction amount is calculated using the correction information stored in advance and the position and light amount of the light source that is the source of the detected stray light. Details will be described below.

  FIG. 12 shows an example of correction information stored in the ROM of FIG. On the vertical axis, the position of the light source that is the source of stray light is indicated by the number (m) of the pixels constituting the light receiving element array. Similarly, the horizontal axis indicates the generation position of stray light by the number (n) of the pixels constituting the light receiving element array. In the table, the light amount difference (difference) between a pair of optical images generated by stray light is shown as a ratio (K (m, n)). For example, when the light source that is the source of stray light is present at the sixth pixel in the light receiving element array, the difference in the output of the paired optical image is caused by the stray light at the fifth to ninth pixels in the light receiving element array. Will occur. Further, it is shown that 3% (K (6, 7)) of the output of the sixth pixel in the light receiving element array is generated as the difference between the outputs of the paired optical images at the seventh pixel. The ratio of the light amount difference between the paired optical images stored here is the light amount difference when there is no positional shift in the positional relationship between the paired optical images, that is, when the defocus amount is almost zero. When defocusing occurs and there is a deviation in the position of the pair of optical images, the position of the light source that is the source of stray light during the output of the pair of light receiving element arrays is different. The generation factor is not limited to stray light. Therefore, in this embodiment, correction information focusing on the light amount difference between the pair of optical images in a state where there is no positional deviation between the pair of optical images is stored. By storing such correction information, it is not necessary to have correction information for each pair of optical images, and the capacity of correction information to be stored in the ROM can be reduced. Further, when the same amount of stray light is generated at the same position in both the pair of optical images as in the stray light 304 and 305 described with reference to FIG. 9, the corresponding correction information is 0%. Concerning stray light that does not adversely affect the accuracy of focus detection, the correction information capacity is reduced. Further, by using the difference between the light amounts of the paired optical images as the correction information, it is possible to treat a smaller amount of stray light as a correction target than to handle the stray light of one optical image. For example, when measuring the position and light amount of stray light based on actual measurement to create correction information, it is difficult to separate the luminance unevenness and stray light of the subject if only one optical image is measured. . For this reason, the threshold of the amount of light that can be recognized as stray light becomes large, and a very small amount of stray light is excluded from the correction target. As in this embodiment, by using the difference between the pair of optical images, stray light can be detected with high accuracy, and correction information can be configured with a small information capacity.

  Next, a correction method using the correction information described above will be described. In this embodiment, since the information stored as the correction information is the difference between the outputs of the pair of optical images, correction for stray light can be performed by correcting only one of the pair of output signals. It can be carried out. Assume that the output of each pixel of the pair of output signals 303-1 and 303-2 described in FIG. 9A is X (n) and Y (n). n indicates a pixel number, and in FIG. 9A, the pixel number increases in order from 1 as it proceeds to the right on the horizontal axis. In this embodiment, when correction is performed on the output waveform of X (n) and the corrected signal is X2 (n), the corrected signal X2 (n) is written as follows. .

  M is a pixel number indicating a light source position where stray light may be generated. In FIG. 12, the number of pixels constituting the output signal 303-1 is the same as the number N of pixels (15 pixels in the table), but the present invention is not limited to this. If stray light may be generated over a wider range, M may have a larger value.

  When correction is performed as described above, the correction information K (m, n) may be set with the amount of stray light based on the information of X (n) -Y (n). After the correction is completed, the defocus amount can be calculated by calculating using X2 (n) and Y (n) using a well-known correlation calculating means.

  The focus detection operation of the camera having the above configuration will be described with reference to the flowchart of FIG.

  In the camera shooting flow, when a first stroke operation (so-called half-pressing operation) of the release switch of the camera or a dedicated focus detection operation start switch is detected, the focus detection operation is started.

  In step 1 (abbreviated as “S” in the figure), the light receiving element is exposed with respect to a focus detection region designated in advance. The exposure amount adjusting means provided in the light receiving element 215 is controlled so as not to saturate the amount of light received, and the exposure ends. Thereafter, the image signal SSNS obtained from the light receiving circuit corresponding to the designated focus detection area is transmitted to the central processing circuit PRS.

  In step 2, the focus detection result of the designated focus detection region, that is, the defocus amount is calculated based on the image signal from the light receiving element array. Here, a phase difference is detected using a known method using correlation calculation, for example, a method disclosed in Japanese Patent Publication No. 5-88445, using image signals obtained from a pair of light receiving element arrays. Thus, the defocus amount including the defocus direction can be calculated. Also, it is determined whether or not each focus can be detected by a known method based on the contrast of the image signal.

  In step 3, the central processing circuit PRS determines whether the calculated defocus amount is equal to or less than a predetermined value. As described above, since the correction information is calculated from the difference between the outputs of the pair of optical images, it is assumed that the defocus amount is small to some extent, that is, the output waveforms of the pair of optical images are almost overlapped. . Therefore, in step 3, it is determined whether or not the defocus amount is correctable. If NO is selected in step 3, since the defocus amount is large and is not suitable for correction, the process proceeds to step 7, and the photographic lens is driven based on the defocus amount calculated in step 2, and from step 1 again. Performs focus detection.

  If YES is selected in step 3, the process proceeds to step 4 and correction is performed on one of the output waveforms of the pair of optical images in order to reduce the influence of stray light by the method described above.

  In step 5, the defocus amount is calculated using the corrected output waveform calculated in step 4. The calculation method is the same as in step 2.

  In step 6, it is determined from the calculated defocus amount whether the in-focus state is achieved. If NO in step 6, that is, if it is determined that the in-focus state is not obtained, driving of the photographing lens is started according to the defocus amount calculated from the focus detection processing result, and the focus detection operation is performed again from step 1. Perform (Step 7). If YES in step 6, that is, if it is determined that the subject is in focus, the second switch operation (so-called full press operation) of the release switch for starting the photographing operation is waited for, and the focus detection process is terminated. If the standby state continues for a certain period of time, the focus detection situation may have changed, so the focus detection operation is started again.

  With the configuration described above, it is possible to correct the stray light with high accuracy and perform focus detection with high accuracy while reducing the storage capacity of the information related to the correction of stray light.

  In the above-described example, the example in which the light receiving element 215 is used as the light source detection unit that detects the position of the light source that is the generation source of the stray light is shown, but the light source detection unit is not limited thereto. For example, the photometric sensor 221 can be used to detect the position and light amount of a light source that is a source of stray light. In this case, the influence of the stray light generation source outside the focus detection area can be reduced, and the stray light can be corrected with higher accuracy.

  In the above-described example, the correction is always performed when the calculated defocus amount is equal to or smaller than the predetermined value. However, the focus detection processing method is not limited thereto. That is, it may be determined whether or not to perform correction based on the spatial frequency information (subject contrast) of the optical image obtained from the pair of light receiving element arrays. In general, the amount of stray light is very small compared to the amount of light obtained from the original subject. Therefore, when the contrast of the subject is high, the adverse effect on the focus detection result is small. Therefore, for example, after step 3 in FIG. 13, it is determined whether the contrast of the subject is large or small with respect to a predetermined value. If it is large, it is determined that the influence of stray light is small, and stray light correction and defocus amount are performed. It is also possible to omit the calculation. In other words, it is determined that the output from the light receiving element array is corrected when the contrast of the subject is equal to or less than a predetermined value, and it is determined that the output from the light receiving element array is not corrected when the contrast of the subject is greater than the predetermined value. . In this case, since unnecessary correction processing is not performed, the speed of focus detection processing can be increased.

  Further, in the above-described example, correction execution determination, defocus amount determination, and stray light correction are performed based on the result of one exposure (step 1 in FIG. 13). However, the focus detection processing method is not limited thereto. Absent. When determining whether or not to perform correction based on information such as the spatial frequency information (subject contrast) of the pair of optical images, the determination can be made even when the defocus amount is large to some extent. Therefore, for example, after step 1 in FIG. 13 before determining whether the defocus amount is equal to or smaller than a predetermined value, it is determined whether the contrast of the subject is larger or smaller than the predetermined value. It is possible to determine that the influence of stray light is small and to omit the correction. That is, whether or not stray light correction is performed is determined from the output of the pair of photoelectric conversion units before the output of the pair of photoelectric conversion units to be corrected is obtained. In this case, since the necessity for the correction process can be determined in an earlier step of the focus detection operation, the speed of the focus detection process can be increased.

  In this embodiment, a focus detection unit having an optical system that performs re-imaging has been described as a focus detection method. However, the focus detection method is not limited to this, and various other focus detection methods can be used. The method can also be applied. For example, a phase difference type focus detection using a pair of pixels arranged on the planned imaging plane 210 of the photographing lens as disclosed in Japanese Patent Laid-Open No. 2000-156823 using light beams passing through different portions of the photographing lens 201 It is also effective when performing.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

  According to the present invention, it is possible to provide a high-accuracy focus detection device that can realize accurate correction for stray light.

200 SLR Camera Body 201 Shooting Lens 208 Focus Detection Unit 210 Field Mask 211 Field Lens 212 Diaphragm 215 Light-Receiving Element (Row)
216 Optical image 221 Photometric sensor LCOM Lens communication circuit PRS Central processing circuit ROM Information storage means

Claims (5)

A focus detection device that detects a focus state of the photographing lens based on a positional relationship between a pair of optical images generated by a pair of light beams that have passed through different regions of the exit pupil of the photographing lens,
A pair of photoelectric conversion units that photoelectrically convert the pair of optical image lights and output a signal;
Defocus amount calculating means for calculating a defocus amount according to the output of the pair of photoelectric conversion units;
Light source detection means for detecting the position of the light source in the field of view of the photographing lens and the light quantity of the light source;
For correcting one of the signals output from the pair of photoelectric conversion units, the difference between the light amount of the pair of optical image light according to the position of the light source in the object field of the photographing lens and the light amount of the light source Storage means for storing correction information;
A focus detection apparatus comprising: a correction unit that corrects one signal output from the pair of photoelectric conversion units based on a detection result of the light source detection unit and correction information of the storage unit. A determination means for determining whether to perform the correction;
The focus detection apparatus according to claim 1, wherein whether or not to perform correction by the determination unit is determined based on spatial frequency information of optical image light obtained from outputs of the pair of photoelectric conversion units. A determination means for determining whether to perform the correction;
The determination as to whether or not to perform correction by the determination means is performed from the output of the pair of photoelectric conversion units before the output of the pair of photoelectric conversion units to be corrected is obtained. The focus detection apparatus described.   When the defocus amount is smaller than a predetermined value, the correction unit determines one signal output from the pair of photoelectric conversion units based on the detection result of the light source detection unit and the correction information of the storage unit. The focus detection apparatus according to claim 1, wherein correction is performed. A control method of a focus detection device that detects a focus state of the photographing lens based on a positional relationship between a pair of optical images generated by a pair of light beams that have passed through different regions of the exit pupil of the photographing lens,
Photoelectrics for photoelectrically converting the pair of optical image lights based on the difference between the light source position in the field of the photographing lens stored in advance and the light quantity of the pair of optical image lights according to the light quantity of the light source. A correction step for correcting one of the signals output from the conversion unit;
And a defocus amount calculation step of calculating a defocus amount according to the output of the pair of photoelectric conversion units after the correction.