JP2013008043A - Autofocus device and camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a focusing position in a short time with high efficiency without reference to specifications (whether a focal length is long) of a mounted photographic lens.SOLUTION: An autofocus device includes: a lens information acquisition unit which acquires information representing a focus adjustable range of the photographic lens; a focus evaluation calculation unit which calculates a focus evaluated value when the photographic lens is driven to perform search operation; and a control unit which performs second search operation with a driving step width equal to a predetermined driving step of first search operation when the information representing the focus adjustable range acquired from the photographic lens is less than a predetermined value, or performs the second search operation with a driving step width larger than the driving step width of the first search operation when the information representing the focus adjustable range acquired from the photographic lens is equal to or larger than the predetermined value on condition that when the first search operation with the predetermined driving step width is performed, the focus evaluated value that the focus evaluation calculation unit calculates is smaller than a predetermined value.

Description

  The present invention relates to an autofocus device (automatic focusing device) mounted on a photographing (imaging) device such as a camera and a camera including the same.

  In recent years, an optical image of a subject is imaged on a solid-state image sensor such as a CCD via an imaging lens, and an image signal that is photoelectrically converted and output by the image sensor is recorded on a recording medium or the like. Digital cameras such as cameras and digital video cameras have been put into practical use. A camera in which a video shooting function is added to a camera that shoots a still image, or a video camera that adds a still image shooting function to a video is put into practical use. In such a digital camera, there is no parallax, it is possible to focus accurately on a subject with a shallow depth of field or a distant subject, and there is no need to provide a dedicated sensor. Therefore, a contrast AF (autofocus) apparatus is used.

  The contrast method is a focus evaluation value (for example, the total value of high-frequency components of an image signal obtained from a solid-state image sensor) based on each captured image while stepping the focus adjustment lens (focus lens) at a predetermined interval (pitch). Etc.) and the lens position where the focus evaluation value is maximized is determined as the in-focus position (focus position) (see, for example, JP-A-10-142488).

  In such a contrast method, since it is generally not possible to predict the in-focus position, the focus adjustment range of the photographing lens is possible (more specifically, the focus adjustment in the photographing lens in the optical axis direction of the photographing lens). This is the range in which the lens can be driven, and the search operation (step movement of the focus adjustment lens, calculation of the focus evaluation value, etc.) is repeated over the entire range of the focus adjustment range. The search operation is sometimes simply referred to as “search”).

  Here, the focus adjustable range is determined by the focal length of the lens and the shortest shooting distance. The shortest shooting distance is the shortest shooting distance that can be focused, and the shooting distance is the distance from the camera to the subject. FIG. 10A and FIG. 10B are diagrams for describing the focus adjustable range. FIG. 10A shows the state of image formation of the lens when the subject is at a position at infinity (shooting distance = ∞). In this case, the focal point is formed at a position separated from the lens by f (f is a focal length). FIG. 10B shows the state of image formation when the subject is separated by the shortest shooting distance R.

In FIG. 10B, if the thickness of the lens is ignored,
a + b = R (Formula 1)
It becomes. Here, a is the distance from the subject to the lens, and b is the distance from the lens to the focal plane. Further, in lens imaging, the following relationship is established between a and b and the focal length f.

(1 / a) + (1 / b) = (1 / f) (Formula 2)
When the subject is at an infinite distance (a = ∞), b is the same as the focal length f (b = f), but b> f is always satisfied when a is a finite value. Solving Equation 2 for b,
b = (a · f) / (af) (Formula 3)
It becomes.

  Normally, the lens can focus on a subject whose distance is between infinity and the shortest shooting distance, and the focus adjustable range in which this is converted to the focal plane side is shown in FIGS. 10 (A) and 10 (B). As shown, b−f. Therefore, when the focus adjustable range is obtained using Equations 1 to 3, the following Equation 4 is obtained.

b−f = f ² / (af)
= 2 · f ² / [R−2 · f + √ (R ² −4 · R · f)] (Formula 4)
FIG. 11 is a graph showing the photographing distance R and the focal distance f based on Equation 4. From FIG. 11, it can be seen that the longer the focal length is and the shorter the shooting distance is, the larger the focus adjustable range is. In general, since a small digital camera has a short focal length (about 5 to 20 mm), a focus adjustable range is also narrow. For example, in Formula 4, when f = 20 mm and R = 30 cm, the focus adjustable range is about 1.4 mm. If it is this level, even if the entire range of the focus adjustable range is searched, it will not take much time and there is no practical problem.

  On the other hand, in the case of a single-lens reflex camera, the focal length of the lens is abundant compared to a small digital camera, and the focal length is also wide from about 10 mm to about 600 mm. As a result, the adjustable focus range varies greatly depending on the lens. For example, when f = 30 mm and R = 60 cm, the focus adjustable range is about 1.6 mm, but when f = 200 mm and R = 1 m, the focus adjustable range is about 50 mm, which is compared with a small digital camera. The range is nearly 50 times wider. In this case, it takes too much time to search the entire focus adjustable range, which causes a problem in practical use.

  In order to deal with such a problem, for example, a technique for limiting the search range to a part of the focus adjustable range has been proposed (for example, Japanese Patent Application Laid-Open No. 2004-94130). However, simply narrowing the focus adjustment range is effective when the in-focus position is within the limited range. However, if the in-focus position is outside the limited range, the in-focus position is effective. There is a problem in that the autofocus operation ends without being performed.

  To improve this point, if the in-focus position cannot be detected within the limited range, increase the step interval (interval of step movement of the focus adjustment lens) and re-search the entire focus adjustable range. A technique has been proposed (for example, JP-A-2005-24984). However, if the lens has a long focal length (ie, a large adjustable range), this method is considered effective, but if the focal length is short (ie, the adjustable focal range is small), Before a sufficient number of focus evaluation values are accumulated to determine the in-focus position, the search of the entire focus adjustable range is completed (for example, where five focus evaluation values are desired to be obtained) In the case where only three steps can be driven within the adjustable range and only three focus evaluation values can be obtained), the focus position may not be detected as a result.

  In Japanese Patent Laid-Open No. 2001-343581, when the movement range of the focus adjustment lens is large, the entire range is searched at a relatively large step interval to obtain a rough focus position, and then the rough focus is obtained. There has been disclosed a technique in which the focus position is obtained by re-searching around the position at a relatively small step interval. However, with this technique, if the lens movement range is too large in the first search and the step interval becomes large, there is a case where the peak of the focus evaluation value (rough focus position) may not be detected. There is. In addition, since the entire castle is searched first and then the detailed search is performed thereafter, there is a problem that the time required for detecting the in-focus position may not be reduced so much.

The present invention has been made in view of the above-described points, and an object of the present invention is to be able to detect the in-focus position in a short time with high efficiency regardless of the specifications of the mounted photographing lens. It is to be.
Japanese Patent Laid-Open No. 10-142488 JP 2004-94130 A JP 2005-24984 A JP 2001-343581 A

  An autofocus device according to the present invention includes a lens information acquisition unit that acquires information indicating a focus adjustable range from a photographing lens, and a focus evaluation calculation that calculates a focus evaluation value when a search operation is performed by driving the photographing lens. And when the focus evaluation value calculated by the focus evaluation calculation unit is smaller than a predetermined value when a first search operation with a predetermined driving step width is performed, the focus adjustable range acquired from the photographing lens Is less than a predetermined value, the second search operation is executed in the same manner as the drive step width during the first search operation, and the information indicating the focus adjustable range acquired from the photographing lens is A control unit that executes the second search operation with a driving step width larger than the driving step width at the time of the first search operation when it is equal to or greater than a predetermined value; And features.

  In the present invention, since the second search operation is controlled based on the lens information of the photographic lens mounted when the focus detection fails in the first search operation, the photographic lens based on the lens information is controlled. Conditions (eg, search range, step interval, etc.) for performing the second search operation can be appropriately selected according to specifications (eg, focal length, focus adjustment range length, etc.). There is an effect that the focal position can be detected efficiently in a short time.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a cross-sectional view schematically showing a schematic configuration of a camera system including an autofocus device according to an embodiment of the present invention. This camera system is a digital single-lens reflex camera system and also has a video shooting function.

  In FIG. 1, the camera system CM includes a camera body CB and a photographic lens CL that is interchangeably attached to the camera body CB. A finder portion FD is integrally fixed to the upper portion of the camera body CB. However, the photographing lens CL may be integrally fixed to the camera body CB.

  In the specification of the present application, the photographic lens is a lens system including a single lens, a plurality of lenses, other optical elements, or the like, or in addition to the lens system, a lens barrel and some lenses are driven. The whole lens assembly including a mechanism unit, and a control unit for controlling the mechanism unit and the like, a memory, and the like as the case may be. The photographing lens CL in the present embodiment means such an entire lens assembly.

  An imaging element 20 such as a high-resolution CCD is attached inside the camera body CB. The image sensor 20 converts an image of a subject formed on the light receiving surface into an image signal and outputs the image signal. Note that the imaging device 20 includes an infrared cut filter for cutting infrared light, an optical low-pass filter for preventing image aliasing noise, and the like on the front surface (on the photographing lens CL side). The image sensor 20 includes an electronic shutter (function) for adjusting the exposure time of an image of a subject projected by electrical control. Although not shown, a mechanical shutter for adjusting the exposure time by mechanically driving the oblique member is provided on the front surface of the image sensor 20.

  The viewfinder unit FD is an optical viewfinder for observing an optical image of a subject formed through the photographing lens CL, a quick return mirror 70 described later, and the like. The focusing screen 25, the pentaprism 30, the photometric element 40, A relay lens 50, an eyepiece 60, and the like are provided. The photometric element 40 is an element that measures the brightness of an image formed on the light to determine the shutter speed and the aperture value.

  A liquid crystal panel capable of displaying an image formed on the image sensor 20 is provided on the back surface of the camera body CB. Therefore, the image of the subject can be viewed through either the eyepiece 60 of the finder unit FD or the liquid crystal panel.

  In the camera body CB, a quick return mirror 70 is pivotally supported on the front side of the image sensor 20 so as to be rotatable. A sub mirror 80 is integrally attached to the back side (image sensor 20 side) of the main mirror of the quick return mirror 70. The quick return mirror 70 has a posture (first posture / mirror down state) in which the front surface of the image pickup device 20 is blocked at about 45 degrees with respect to the image pickup surface of the image pickup device 20 as shown in FIG. Can be selectively operated at high speed in a posture (second posture / mirror-up state) that is rotated clockwise and substantially orthogonal to the light receiving surface of the image sensor 20 (substantially parallel below the focusing screen 25). It is a mirror.

  A part of the main mirror of the quick return mirror 70 (near the central part) is a half mirror (the other part is a total reflection mirror), and the quick return mirror 70 is in the first posture, and the photographing lens CL Most of the light from the mirror is reflected by the main mirror toward the finder section FD (focusing screen 25), and a part of the light transmitted through the half mirror section of the main mirror is reflected by the sub mirror 80. Yes. The light reflected by the sub mirror 80 is further reflected by the mirror 90 and is incident on the phase difference detection AF detection element 100.

  When the quick return mirror 70 is switched to the second posture, the light from the photographing lens CL is incident on the image sensor 20 via the mechanical shutter (not shown) described above. The phase difference detection AF detection element 100 includes two line sensors and a mask or the like that divides incident light into two and makes each incident on the line sensor. The light divided into two by the mask is re-imaged on the two line sensors, respectively, and the difference between the image plane positions is detected. This difference corresponds to the amount of focus shift (defocus amount).

  A phase difference AF switch (AF_SW) 92 and a contrast AF switch (AF_SW) 95 are provided on the upper or rear surface of the camera body CB. These switches are switches operated by the photographer. While the phase difference AF switch 92 is pressed, the phase difference AF is executed based on the detection value of the phase difference detection AF detection element 100 while the quick return mirror 70 is in the first posture. When the contrast AF switch 95 is pressed, the quick return mirror 70 is switched to the second posture, and while the contrast AF switch 95 is pressed, the contrast AF is executed based on the image signal detected by the image sensor 20. Is done.

  The photographing lens CL is an optical system for forming an image of a subject on the light receiving surface of the image sensor 20. In FIG. 1, the photographic lens CL is exemplified by a zoom lens whose focal length can be changed, but may be a single focal lens. A fish eye lens, a wide-angle lens, a telephoto lens, a micro lens, and the like can be arbitrarily exchanged and mounted.

  The photographing lens CL includes a fixed lens 210a, a focal length adjustment lens 210b, a focus adjustment lens 210c, and a fixed lens 210d inside the lens barrel 200. Each lens 210a, 210b, 210c, 210d is a lens system composed of a single lens or a plurality of lenses. The fixed lenses 210a and 210d are fixed to the lens barrel 200, and the focal length adjustment lens 210b and the focus adjustment lens 210c are attached to be movable in the direction along the optical axis AX of the photographing lens CL.

  In general, the focal length adjusting lens 210b changes the position in the direction of the optical axis AX when the photographer manually rotates a zoom ring (not shown) or the like, and changes the focal length of the photographing lens CL accordingly. It can be done. The position of the focal length adjustment lens 210b is detected (monitored) by the zoom encoder 220. The detection value of the zoom encoder 220 is supplied to the focal length detection unit 340.

  The position of the focus adjustment lens 210c in the direction along the optical axis AX is changed by the focus adjustment lens drive motor (actuator) 240 based on the lens drive signal from the lens drive amount setting unit 370, and the change in the position is the focus adjustment. It is detected (monitored) by the lens position encoder 230.

  The diaphragm 250 is a variable aperture diaphragm for adjusting the amount of light incident on the image sensor 20, and the diaphragm setting may be performed automatically by the camera or manually by the photographer. The aperture value is determined based on the output of the photometric element 40 in the program mode or the shutter speed priority mode. In the aperture priority mode or the manual mode, it is manually set by the photographer. The operation of the diaphragm 250 is controlled by an unillustrated diaphragm control motor or the like based on the diaphragm value set automatically or manually.

  The contrast AF control unit CNT forms a control system in cooperation with the focus evaluation value calculation unit 330, the focal length detection unit 340, the lens drive amount setting unit 370, and the like, and performs the main part of the contrast AF control process described later. A processing device to be executed.

  The focus evaluation value calculation unit 330 calculates a focus evaluation value of a portion corresponding to a predetermined distance measurement area in the image signal output from the image sensor 20, and supplies the calculation result to the contrast AF control unit CNT. As a method of calculating the focus evaluation value in the focus evaluation value calculation unit 330, a method of performing high frequency emphasis filter processing on an image and integrating the results can be used. However, the focus evaluation value calculation method may of course be another method. The focal length detection unit 340 detects the current focal length of the photographing lens CL from the output of the focus adjustment lens position encoder 220 and supplies it to the contrast AF control unit CNT.

  The lens drive amount setting unit 370 sets the lens drive amount based on the control signal from the contrast AF control unit CNT and sends a drive signal to the focus adjustment drive motor 240 to move the focus adjustment lens 210c along the optical axis AX. Move to.

  The contrast AF control unit CNT drives the focus adjustment lens drive motor 240 via the lens drive amount setting unit 370 according to various control processes that will be described in detail later, and moves the focus adjustment lens 210c step by step. The focus evaluation value calculated by the focus evaluation value calculation unit 330 based on the image signal from the imaging element 20 is accumulated and held. Next, the lens drive is performed so that the position where the focus evaluation value is maximized is calculated using a predetermined mathematical interpolation formula, and this is used as a focus position, and the focus adjustment lens 210c is positioned at the focus position. The focus adjustment lens drive motor 240 is controlled via the amount setting unit 370.

  Next, control of the AF (autofocus) apparatus according to the first embodiment of the present invention will be described. The contrast AF of this embodiment is roughly composed of the following four processes (first to third searches, focusing drive). The search (search operation) is a series of processes for detecting the in-focus position by performing repeated operations such as step movement of the focus adjustment lens in the lens optical axis AX direction and calculation of the focus evaluation value. This is a process for searching for the focal position.

  In the first search (first search operation), the in-focus position is detected with a predetermined step width in a predetermined search range (first search range) narrower than the focus adjustable range of the photographing lens CL. The step width in the first search is also set to a relatively small value so that the in-focus position can be calculated with necessary accuracy. The step width in the first search is, for example, about 100 μm to 200 μm. These first search parameters (first search range and step width) are stored in advance in a memory in the camera (memory in the control unit CNT) regardless of the type of lens.

  In the second search (second search operation), the in-focus position cannot be detected in the first search (such as when the in-focus position is not within the first search range), and the focal length of the photographing lens CL is preset. This is performed when the value is equal to or greater than a predetermined threshold. The search range in the second search (second search range) is set in a range wider than the first search range, and the step width is larger than that of the first search, that is, based on the collected focus evaluation value. Thus, the focus position is set to a relatively large value that does not allow the focus position to be calculated with a required accuracy, but that can detect a rough position of the focus position. The second search range may be completely different in position from the first search range (it may not overlap with the first search range), or may partially overlap with the first search range. . That is, the position of the second search range may be partly different from the first search range. The step width in the second search is, for example, about 1 mm to 1.2 mm.

  The third search is performed when a rough position of the in-focus position is detected by the second search. In the third search, the in-focus position is searched with the same step width as the first search, with the in-focus position in the second search as the center. The focus drive is a process of moving the focus adjustment lens 210c to the focus position when the focus position is detected in the first or third search.

  Next, the above process will be described in more detail with reference to FIG. FIG. 2 is a flowchart showing the processing of the control system including the contrast AF control unit CNT of the autofocus device according to the first embodiment of the present invention. When the process is started, first, in S100, it is determined whether or not the phase difference AF switch 92 is OFF. If No (if ON), the process proceeds to S200, and the above-described phase difference AF is executed. In S100, if Yes (OFF), the process proceeds to S300, and it is determined whether or not the contrast AF switch 95 is ON. In S300, this determination is repeated if No (if OFF), and the process proceeds to S400 if Yes (if ON).

  In S400, the quick return mirror 70 is raised (set to the second posture), the light through the photographing lens CL is guided to the image sensor 20, and the image sensor 20 starts capturing and outputting the image signal from here, and evaluates the focus. The value calculation unit 330 starts calculating the focus evaluation value. Next, in S500, the position of the focus adjustment lens 210c immediately before executing the first search is acquired as an initial position, and in S600, the first search is executed.

  In the first search, as described above, the focus evaluation value calculation unit 330 calculates the focus evaluation value while step-moving the focus adjustment lens 210c with a relatively small step width, and the calculated focus evaluation value is the contrast AF control. Are sequentially supplied to the unit CNT. The contrast AF control unit CNT performs a predetermined interpolation operation based on each supplied focus evaluation value, and calculates a focus position. If the focus position cannot be detected here, the focus detection fails.

  Next, in S700, the contrast AF control unit CNT determines whether or not the in-focus position has been found in the first search (whether the in-focus detection has succeeded or failed), and if it is found (in the case of Yes). The process proceeds to S800, and the focus drive for moving the focus adjustment lens 210c to the detected focus position is executed via the lens drive amount setting unit 370 and the focus adjustment lens drive motor 240. If the in-focus position is not found in S700 (No), the process proceeds to S900.

  Next, in S900, the contrast AF control unit CNT determines whether the focal length of the photographing lens CL is less than a predetermined value (whether it is short). This determination is based on the current focal length (lens information) of the photographic lens CL detected by the focal length detection unit 340 and a predetermined value (threshold value) set in advance in a memory included in the contrast AF control unit CNT. This is done by comparing. If the focal length is less than the predetermined value (Yes), the process proceeds to S1000, and if the focal length is greater than the predetermined value (No), the process proceeds to S1200. Such a predetermined value is set to an appropriate value in advance in relation to the focal length of the photographing lens CL.

  In S900, when the focal length is less than the predetermined value (in the case of Yes), since the focus adjustable range is also small, it is estimated that a considerable amount of search within the focus adjustable range is being performed by the first search. Therefore, there is a high possibility that the in-focus position does not exist. Therefore, in S1000, the focus adjustment lens 210c is driven to the initial position, and in S1100, the contrast AF operation is stopped. In this embodiment, when the in-focus position is not found, the driving is performed to the intended position. However, the present invention is not limited to this, and for example, the lens position at the time when it is determined that the detection is impossible is held. Also good. In S1100, when the operation of contrast AF is stopped, it is preferable to notify the photographer that the in-focus position has not been found (that the subject cannot be detected by AF). This notification may be displayed, for example, on a liquid crystal screen or in a finder as a document or a graphic, or by a warning sound.

  In S900, when the focal length is equal to or larger than the predetermined value (in the case of No), the focus adjustable range is also large, so that even if the in-focus position is not found within the first search range, the focus is outside the first search range. There is a high possibility that a focal position exists. Therefore, in this case, the process proceeds to S1200, where the second search range wider than the first search range is set, and the step width is set larger than the first search, and the second search is executed. Although it is efficient to set the second search range so as not to overlap the first search range, a part of the second search range may overlap.

  Next, in S1300, it is determined whether or not an in-focus position has been found in the second search. If not found, the process proceeds to S1000, and if found, the process proceeds to S1400 to execute the third search. In the second search, even if the in-focus position is found, the required accuracy cannot be guaranteed because the step width is large. Therefore, a third search is performed in which the vicinity of the in-focus position found by the second search is searched with a fine step width comparable to that of the first search.

  Next, in S1500, it is determined whether or not the in-focus position has been found in the third search. If found (Yes), the process proceeds to S800 to execute the in-focus drive, and if not found (No In the case), the process proceeds to S1000.

  FIGS. 3A and 3B show an example in which a lens with a short focal length is used and the in-focus position is found in the first search. FIG. 3A is a graph showing the relationship between the lens position and the focus evaluation value, where the horizontal axis represents the lens position and the vertical axis represents the focus evaluation value. P1 to P5 indicated by black circles in FIG. 3A are focus evaluation values acquired by the contrast AF control unit CNT. P0 indicates the lens position at the time of starting the AF operation. FIG. 3B is a graph showing the relationship between the lens position and time corresponding to FIG. 3A. The horizontal axis represents the lens position, and the vertical axis represents time.

  At the start of execution of contrast AF, the lens is positioned at P0, and after driving the lens to P1, the focus evaluation value is acquired as P2-> P3-> P4-> P5. At the time of P5, it is determined that the focus evaluation value has become a mountain shape, and a focus position is obtained, and focus drive is performed.

  FIGS. 4A and 4B show an example in which a lens with a long focal length is used and the in-focus position is found in the first search. The horizontal and vertical axes in FIGS. 4A and 4B are the same as those in FIGS. 3A and 3B. As shown in FIG. 4A, the base of the focus evaluation value curve is wider than that in FIG. The basic operation is the same as in FIGS. 3A and 3B. If the in-focus position is found in the first search, the in-focus drive is performed as it is to complete the autofocus operation. As described above, when the in-focus position is found in the first search, the auto-focus operation using the contrast AF according to the present embodiment is the same regardless of the focal length, and the in-focus position is detected at high speed regardless of the length of the focal length. can do.

  FIGS. 5A and 5B show an example in which a lens having a short focal length is used and the in-focus position is not found in the first search. The horizontal and vertical axes in FIGS. 5A and 5B are the same as those in FIGS. 3A and 3B. The operation of contrast AF is the same as in the case of FIGS. 3A and 3B, but the focus evaluation value does not become a mountain shape even if the focus evaluation values are acquired from P1 to P5. Also, if the focal length is short, the focus adjustable range is also narrowed, so the first search range can cover most of the focus adjustable range. Therefore, if the in-focus position is not found in the first search, the possibility of finding the in-focus position is low even if the entire focus adjustable range is searched. Therefore, when the focal length is short and the in-focus position cannot be found in the first search, it is impossible to detect and the lens is returned to the position (initial position) where P0 is acquired.

  FIGS. 6A and 6B show an example in which a lens having a long focal length is used and the in-focus position is not found in the first search. The horizontal and vertical axes in FIGS. 6A and 6B are the same as those in FIGS. 3A and 3B. Also in this example, since the focus evaluation values of the first search (P1 to P5) did not become a mountain shape, the in-focus position cannot be found within the first search range. However, a lens having a long focal length has a wide focus adjustment range, and there is a possibility that a focus position exists at a position away from the first search range. Therefore, even if the in-focus position is not found in the first search range like a lens having a short focal length, the in-focus position does not necessarily exist within the focus adjustable range.

  For this reason, when the focal length is long and the in-focus position is not found in the first search, the second search is executed. The second search has a search range wider than the first search range, and is set, for example, in the entire focus adjustable range. Also, the step width is set wider than that of the first search so that the search does not take much time. After setting the search range and step width in this manner, the lens is driven to the end of the focus adjustable range, and the search is started from there toward the other end. Q1 to Q7 indicated by black triangles in FIG. 6A are focus evaluation values acquired by the contrast AF control unit CNT in the second search. Similarly to the first search, it is assumed that the in-focus position is found in the second search when the focus evaluation value has a mountain shape.

  However, in the second search having a wide step width, there is a possibility that the accuracy is not sufficiently obtained even if the in-focus position is found. Therefore, if the in-focus position is found in the second search, the in-focus position is detected by executing the third search with substantially the same step width (narrow step width) as in the first search. R1 to R4 indicated by black circles in FIG. 6A are focus evaluation values acquired by the contrast AF control unit CNT in the third search.

  As described above, in the first embodiment, the operation is performed in accordance with the focal length of the mounted photographic lens (when the focal length of the zoom lens is changed, or when the photographic lens is replaced with a different focal length). By changing it, the photographer can promptly respond to the photographer by promptly informing the photographer that the lens with a short focal length cannot be detected. In addition, a lens with a long focal length can increase the probability of detecting the in-focus position.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In the first embodiment described above, the second search is executed only when the in-focus position is not found in the first search and the focal length is long. On the other hand, in the second embodiment, when the in-focus position is not found in the first search, the second search is executed regardless of the length of the focal length, and according to the length of the focal length, The step width of the second search is changed. That is, when the focal length is short, the focus adjustment range is narrow, so the step width is reduced. When the focal length is long, the focus adjustment range is wide, and conversely, the step width is widened.

  FIG. 7 is a flowchart showing the processing of the control system including the contrast AF control unit CNT of the autofocus device according to the second embodiment of the present invention. Steps substantially the same as those in FIG. 2 are denoted by the same reference numerals, and a part of the description is omitted. In S700, when the in-focus position is not found by the first search, it is the same as in the first embodiment that the length of the focal length is determined in S900. If it is determined in S900 that the focal length is less than the predetermined value (Yes), the process proceeds to S910, the step width of the second search is set to the same step width as that of the first search, and the focal length is predetermined. If it is determined that the value is greater than or equal to the value (No), the process proceeds to S920, and the step width of the second search is set wider than that of the first search.

  Next, in S1200, the second search is executed with the step width set in S910 or S920, and in S1300, it is determined whether or not an in-focus position has been found. The second search range is the same as that in the first embodiment. If the in-focus position is not found in S1300 (No), the process proceeds to S1000. In S1300, when the in-focus position is found (in the case of Yes), the process proceeds to S1340, and the length of the focal length is compared with a predetermined value in the same manner as in S900, and when the focal length is less than the predetermined value (Yes) In the case), the process proceeds to S800. If the focal length is equal to or greater than the predetermined value (in the case of No), the process proceeds to S1400 and the third search is executed.

  As described above, in the second search, when the focal length is short, the step width is the same as that of the first search (that is, a narrow width), and thus the accuracy of the found focus position can be sufficiently guaranteed. Therefore, when the focal length is short, the focus driving may be directly performed. On the other hand, when the focal length is long, the step width of the second search is wide, so the accuracy of the found focus position cannot be guaranteed. For this reason, when the focal length is long, the third search is executed to finely search the vicinity of the in-focus position found in the second search.

  FIGS. 8A and 8B show an example in which a lens with a short focal length is used and the in-focus position is not found in the first search. The horizontal and vertical axes in FIGS. 8A and 8B are the same as those in FIGS. 3A and 3B. In FIG. 8A, since the focus evaluation value does not become a mountain shape in P1 to P5, the focus position is not detected. Therefore, the lens is driven to the end of the focus adjustable range, and the second search is started from there. However, since the focus adjustment range is narrow, the step width is set to the same value as the first search and the search is performed. Then, the in-focus position is detected soon, and the operation is shifted to the in-focus drive to complete the operation. Further, when the focal length is long, the same operation as that in FIGS. 6A and 6B is performed.

  As described above, when the focal length is short, by setting the step width of the second search to the same value as that of the first search, it is not necessary to execute the third search, so that the focusing time can be shortened. In addition, the number of focus evaluation values necessary for determining whether or not there is a focus position can be acquired even within a narrow focus detectable range, and the focus position can be reliably detected.

[Third Embodiment]
Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 9 is a sectional view showing a schematic configuration of a camera according to the third embodiment of the present invention. Components substantially the same as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

  As shown in FIG. 9, the photographing lens CL includes a memory MEM in which various pieces of lens information related to the photographing lens CL are stored in advance. Here, as the lens information stored in the memory MEM, it is assumed here that information on the shortest shooting distance of the shooting lens CL is stored in advance. When the photographing lens CL is attached to the camera body CB, the lens information in the memory MEM can be read by the contrast AF control unit CNT built in the camera body CB via a connection electrode (not shown). Yes. The contrast AF control unit CNT calculates a focus adjustable range based on the shortest shooting distance as lens information read from the memory MEM and the focal length as lens information from the focal length detection unit 340.

  In the first or second embodiment described above, it is estimated whether or not the focus adjustable range is long due to the length of the focal length, and whether or not the second search is executed and the step width of the second search are determined according to the focal length. Was. However, as shown in FIG. 11, the focus adjustable range depends not only on the focal length of the lens but also on the shortest shooting distance. Therefore, depending on the specifications of the lens, there is a possibility that a lens that does not need to execute the second search even at the same focal length or does not need to widen the step width of the second search may appear.

  Therefore, in the third embodiment, in order to drive the lens more efficiently, the shortest shooting distance is used in addition to the focal length. In this way, since the focus adjustable range can be calculated from the focal length and the shortest shooting distance according to Equation 4, the search operation may be determined based on the range. The basic operation is the same as that in the flowcharts shown in FIGS. 2 and 7, and the step of determining the length of the focal length (S900, S1340) is performed in the focus adjustable range calculated from the shortest shooting distance and the focal length. It becomes a step to judge the length. The predetermined value used for this determination also corresponds to the focus adjustable range.

  In addition, as the lens information stored in the memory MEM, not the shortest shooting distance but the focus adjustable range itself may be stored. By storing the focus adjustable range itself, it is not necessary to calculate the focus adjustable range using the focal length and the shortest shooting distance, and a faster AF operation and a more accurate AF operation are possible.

  In the first or second embodiment described above, the contrast AF control unit CNT receives the focal length as the lens information of the photographic lens CL mounted from the focal length detection unit 340, and in S900, The comparison is made by comparing the length with a predetermined value. In the memory MEM of the photographic lens CL of the third embodiment described above, information on the focal length is stored as lens information (in the case of a single focus lens, it is In the case of a focal length and a zoom lens, a representative value or an average value or a variable range of the focal length is stored in advance, information on the focal length is read from the memory MEM, and the length thereof is determined. Good.

  Further, in the case where the focus adjustable range can be acquired as in the third embodiment described above, in S900 of FIG. 2 according to the first embodiment, the length of the focal length is not compared with a predetermined value. The ratio of the first search range with respect to the focus adjustable range is compared with a predetermined ratio set in advance. If the ratio is equal to or greater than the predetermined ratio, the process proceeds to S1000 and the second search is not executed. If it is finished and the ratio is less than the predetermined ratio, the process may advance to S1200 to execute the second search. The predetermined ratio can be set to 50 to 70% of the focus adjustable range. Even if the search for about 50 to 70% of the focus adjustable range is completed, if the in-focus position cannot be detected, it is highly possible that the in-focus position does not exist even if the entire range is searched. This is because it is considered that it is more efficient to finish without searching for the part.

  Similarly, in S900 of FIG. 7 according to the second embodiment, the ratio of the first search range with respect to the focus adjustable range is not determined by comparing the focal length with the predetermined value. If the ratio is equal to or greater than the predetermined ratio, the process proceeds to S910, where the step width of the second search is set to be the same as the step width of the first search and is less than the predetermined ratio. In S920, the step width of the second search may be set wider than the step width of the first search, and the second search may be executed in S1200. The predetermined ratio can be set to 50 to 70% of the focus adjustable range.

  When a search of 50 to 70% or more of the focus adjustable range has been completed, the remaining range where the search has not been completed is small, and focusing is performed with a narrow step width without setting a wide step width. It can be considered that the in-focus position can be detected in a shorter time when the detection is continued. On the other hand, if the search has been completed for less than about 50 to 70% of the focus adjustable range, the remaining range for which the search has not been completed is large. This is because, after detecting the focal position, it is considered more efficient to perform a fine search around the approximate focal position with the required accuracy.

  Further, the above-described parameters (search range, step width) of the first search are stored in the memory MEM, and the parameters are transmitted to the control unit CNT on the camera side before the first search operation (at the time of the first search) As a parameter to be used, the first search operation can be performed using an optimum search parameter for each lens.

  The embodiment described above is described for facilitating the understanding of the present invention, and is not described for limiting the present invention. Therefore, each element disclosed in the above embodiment includes all design changes and equivalents belonging to the technical scope of the present invention.

It is sectional drawing which shows schematic structure of the camera of 1st Embodiment of this invention. It is a flowchart which shows the operation | movement of contrast AF of the camera of 1st Embodiment of this invention. It is a graph for demonstrating the case where the focal distance of 1st Embodiment of this invention is short, Comprising: Focus detection was successful by 1st search, (A) is the relationship between a lens position and a focus evaluation value. (B) shows the relationship between the lens position and time. It is a graph for demonstrating the case where the focal distance of 1st Embodiment of this invention is long, Comprising: Focus detection was successful by 1st search, (A) is a relationship between a lens position and a focus evaluation value. (B) shows the relationship between the lens position and time. It is a graph for demonstrating the case where the focal distance of 1st Embodiment of this invention is short, Comprising: Focus detection fails by 1st search, (A) is the relationship between a lens position and a focus evaluation value. (B) shows the relationship between the lens position and time. FIG. 6 is a graph for explaining a case where the focal length of the first embodiment of the present invention is long, the focus detection fails by the first search, and the second and third searches are executed, (A) Indicates the relationship between the lens position and the focus evaluation value, and (B) indicates the relationship between the lens position and time. It is a flowchart which shows the operation | movement of contrast AF of the camera of 2nd Embodiment of this invention. FIG. 10 is a graph for explaining a case where the focal length of the second embodiment of the present invention is short, the focus detection fails by the first search, and the second search is executed, and FIG. (B) shows the relationship between the lens position and time. It is sectional drawing which shows schematic structure of the camera of 3rd Embodiment of this invention. It is a figure for demonstrating the focus adjustable range, (A) shows the mode of image formation of a lens when a to-be-photographed object is infinite, and (B) is a case where a to-be-photographed object is in the position away from the shortest imaging distance This shows how the lens of the lens is imaged. It is a figure which shows the relationship between the focal distance in an ideal lens system, the shortest imaging distance, and the focus adjustable range.

  CM ... Camera, CB ... Camera body, CL ... Shooting lens, FD ... Finder section, CNT ... Contrast AF control section, MEM ... Memory, 20 ... Image sensor, 70 ... Quick return mirror, 210c ... Focus adjustment lens, 330 ... Focus Evaluation value calculation unit, 340... Focal length detection unit, 370... Lens drive amount setting unit.

Claims (8)

A lens information acquisition unit for acquiring information indicating a focus adjustable range from the photographing lens;
A focus evaluation calculation unit that calculates a focus evaluation value when driving the photographing lens and performing a search operation;
If the focus evaluation value calculated by the focus evaluation calculation unit is smaller than a predetermined value when performing a first search operation with a predetermined drive step width, information indicating the focus adjustable range acquired from the photographing lens Is less than a predetermined value, the second search operation is executed in the same manner as the driving step width at the time of the first search operation, and the information indicating the focus adjustable range acquired from the photographing lens is equal to or greater than the predetermined value. In this case, the autofocus device includes: a control unit that executes the second search operation with a drive step width larger than the drive step width at the time of the first search operation. An autofocus device according to claim 1,
When the control unit executes the second search operation and detects that the focus evaluation value is equal to or greater than a predetermined value, the control unit sets a drive step width smaller than the drive step width in the second search operation to the third step. An autofocus device characterized by executing a search operation. The autofocus device according to claim 1 or 2, wherein
When the focus evaluation value calculated by the focus evaluation calculation unit is smaller than a predetermined value when performing the first search operation within a predetermined first search range, the control unit starts from the first search range. An autofocus device characterized in that the second search operation is executed within a wide second search range. An autofocus device according to any one of claims 1 to 3, wherein
The information indicating the focus adjustable range is focal length information of the photographing lens. A lens information acquisition unit for acquiring information indicating a focus adjustable range from the photographing lens;
A focus evaluation calculation unit that calculates a focus evaluation value when driving the photographing lens and performing a search operation;
If the focus evaluation value calculated by the focus evaluation calculation unit is smaller than a predetermined value when a first search operation with a predetermined drive step width is performed within a predetermined first search range, the focus adjustment is performed. When the ratio of the first search range to the possible range is equal to or greater than a predetermined ratio, the second search operation is performed with the drive step width set during the first search operation, and the focus adjustment possible range is set. When the ratio of the first search range to the predetermined ratio is less than the predetermined ratio, the second step is set to a step width larger than the driving step width in the first search operation. An autofocus device comprising: a control unit that executes a search operation. An autofocus device according to claim 5,
When the focus evaluation value calculated by the focus evaluation calculation unit is smaller than a predetermined value when performing the first search operation within the first search range, the control unit is wider than the first search range. The second search operation is executed within a second search range of the autofocus device. The autofocus device according to any one of claims 1 to 6, wherein
The autofocus device, wherein the second search range is set to a range that does not overlap with the first search range. A camera comprising the autofocus device according to any one of claims 1 to 7.

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