JP2008020832A - Autofocus system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an autofocus system capable of reducing the divergence of focus by controlling a focus considering the divergence of focus caused by the delay of follow-up operation of the focus in advance when performing the follow-up operation of the focus to a subject moving in a front-and-rear direction (optical axis direction) relative to a camera by AF. <P>SOLUTION: In an optical path length difference system AF, the position of a pair of CCDs 14A and 14B for AF provided to have an optical path length difference in order to detect a focal state is displaced in accordance with the movement of the subject that is a focusing object. Thus, the divergence of focus caused by the delay of the follow-up operation of a focus lens FL is reduced by intentionally shifting the focal state of a photographic optical system detected in AF control and an actual focal state. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an autofocus system, and more particularly to an autofocus system employing an optical path length difference type autofocus.

  As an autofocus (AF) employed in a broadcast television camera, contrast AF is generally known. In contrast AF, a high frequency component signal is extracted from a video signal obtained by a camera, and a focus evaluation value for evaluating the height of contrast is obtained based on the extracted signal. Then, the focus (focus lens group) of the photographing lens is controlled by a method called a hill-climbing method, for example, so that the focus evaluation value becomes a peak (maximum).

  In contrast AF, generally, an operation called wobbling is performed in which the focus is slightly changed. By detecting the focus evaluation value while wobbling, for example, the focus evaluation value at the front and rear positions with respect to the current focus position is detected, and from the magnitude relationship of the focus evaluation values at the front and rear positions, Whether or not the focus evaluation value is at the peak or the direction in which the focus evaluation value is at the peak is detected. The focus is moved to an in-focus position where the focus evaluation value becomes a peak by controlling the focus while sequentially detecting the peak of the focus evaluation value by such wobbling.

  Further, when performing the wobbling as described above, there have been a problem that the fluctuation in focus caused by the wobbling is recognized on the screen and a problem that it is difficult to focus accurately on a subject moving at high speed. Therefore, for example, an optical path length difference type AF as shown in Patent Document 1 has been proposed. According to this, the optical path of the photographing lens (optical system) that forms the subject image is divided into two optical paths by the light dividing means such as a half mirror. The subject light guided to one of the optical paths forms a subject image on the imaging surface of the imaging element (imaging imaging element) of the camera body arranged to capture an image (video) for recording or reproduction. The subject light guided to the other optical path forms a subject image on the imaging surface of an imaging device (AF imaging device) arranged to capture an AF image (video).

  The imaging surface of the AF imaging element is composed of, for example, two imaging surfaces arranged at different optical path lengths by two imaging elements, and the subject light branched into the AF optical path is further divided into AF imaging The light is incident on each imaging surface of the element. An image (subject image) captured by each imaging surface of the AF image sensor corresponds to an image captured by the image surface of the image sensor when the focus is displaced from the current position by a predetermined amount. A focus evaluation value is obtained from each image captured by each imaging surface of the image pickup device for the image, and by comparing them, the focus state at the current focus position with respect to the image pickup surface of the image pickup device for the image (focus, front pin, rear Pin) can be detected.

Therefore, since it is not necessary to perform wobbling, the focus can be moved to the in-focus position without causing a focus fluctuation due to wobbling. In addition, quick focusing is possible, and it is possible to accurately focus on a subject moving at high speed.
JP 2004-212458 A

  By the way, when the above-described optical path length difference type AF is continuously operated, if the subject to be focused is moving in the front-rear direction (the optical axis direction of the camera), the subject is best focused. The focus will follow. At this time, the focus follow-up operation is actually delayed rather than the movement of the subject. Therefore, the focus state changes in a state deviating from the best focus, and the best focus state is not reached until the subject stops.

  Conventionally, the delay of the focus follow-up operation is such that the focus is shifted within the depth of focus and does not stand out as a blur in the captured image. However, it is expected that even a very high-definition camera that is currently used or will be developed in the future will be visually recognized as a blur in a photographed image. In particular, when the speed of the moving subject is fast or when it is necessary to track to a short distance, the delay of the focus follow-up operation increases, and the degree of blur may not be negligible.

  The present invention has been made in view of such circumstances, and when focusing is performed by AF on a subject moving in the front-rear direction (optical axis direction) with respect to the camera, the focus is caused by a delay in the tracking operation. An object of the present invention is to provide an autofocus system that can reduce the deviation of the movement.

  In order to achieve the object, the autofocus system according to claim 1 is detected by a focus state detection unit that detects a focus state of the photographing optical system with respect to a subject to be focused, and a focus state detection unit. The focus of the photographic optical system is controlled by controlling the focus of the photographic optical system so that the focus state is in focus, and performs automatic focus adjustment, and the focus of the photographic optical system is adjusted by the auto focus control means following the subject. When the subject is moving, the actual focus state when the focus state detected by the focus state detection means indicates the in-focus state is the front pin when the subject is moving to the closest side. The focus state detected by the focus state detection means so as to become a rear focus when the subject is moving to the infinity side. It is characterized by comprising a, and adjustment means for adjusting the.

  According to the present invention, during autofocus control, focus shift due to a delay in the focus tracking operation with respect to a moving subject is reduced by adjusting the focus state detected by the focus state detection means.

  The autofocus system according to a second aspect is the invention according to the first aspect, wherein the focus state detecting means includes a plurality of subject images formed by the photographing optical system arranged at positions of different optical path lengths. An AF imaging means for imaging on the imaging surface; a focus evaluation value detecting means for detecting a focus evaluation value indicating the height of contrast of each video signal obtained by imaging on each imaging surface of the AF imaging means; Comparing means for detecting a focus state by comparing the focus evaluation values for the respective imaging surfaces detected by the focus evaluation value detecting means, and the adjusting means moves the position of each imaging surface of the AF imaging means Means for changing the optical path length of a dedicated optical path for guiding subject light to each imaging surface of the AF imaging means, or disposed on a dedicated optical path for guiding subject light to each imaging surface of the AF imaging means. The It is characterized in that Utsushitai a means for moving the position of the lens for forming an image. The present invention shows a specific mode of adjusting means for adjusting the focus state detected by the focus state detecting means in the so-called optical path length difference type autofocus.

  According to a third aspect of the present invention, in the autofocus system according to the second aspect, the adjustment unit may apply a shift amount of the focus state detected by the focus state detection unit to each imaging surface of the AF imaging unit. It is characterized in that it is determined based on the focus evaluation value obtained for the focus or based on the moving speed of the focus. The present invention shows a specific mode for determining the shift amount of the focus state.

  According to the autofocus system of the present invention, when the focus is moved to follow the subject moving in the front-rear direction with respect to the camera, the focus shift due to the delay of the follow-up operation can be reduced.

  Hereinafter, the best mode for carrying out an autofocus system according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a side view showing an appearance and a partial internal configuration of a photographic lens used in an autofocus system according to the present invention. The photographic lens 10 shown in the figure is used as an interchangeable lens in, for example, a broadcast or commercial television camera. Various optical system members constituting the photographic optical system are provided in a lens barrel having an appearance as shown in the figure. Is retained. A mount is formed at the rear end of the lens barrel, and the mount is detachably attached to the camera body (camera head) 12 of the television camera.

  In addition, a half mirror 14 is disposed in the photographing optical system of the photographing lens 10 in the figure, and light is emitted from a normal main light path along the optical axis O that guides subject light to the camera body 12 by the half mirror 14. An optical path for AF along the axis O ′ is branched and provided. The AF optical path is provided with AF CCDs 16A and 16B used for optical path length difference autofocus (AF), which will be described in detail later, and the subject light incident on the photographing lens 10 passes through the AF optical path. It is guided to the AF CCDs 16A and 16B.

  The overall configuration of the photographing optical system arranged in the lens barrel is as shown in FIG. A part of it is shown in FIG. As shown in these drawings, the photographing optical system includes a main-line optical path along the optical axis O for guiding subject light to the camera body, and the AF optical path along the optical axis O ′ branched from the optical path of the optical axis O. The focus lens (group) FL, zoom lens (group) ZL, aperture I, front relay lens (group) RA, half mirror 14 and rear side are arranged on the main optical path in order from the front side (subject side). A relay lens (group) RB is arranged.

  Subject light incident on the photographing lens 10 from the subject passes through the focus lens FL, the zoom lens ZL, the aperture I, the front relay lens RA, the half mirror 14, and the rear relay lens RB in this order, and the optical in the camera body 12 is obtained. Incident into the system. The optical system of the camera body 12 includes a color separation optical system 30 that separates incident subject light into wavelengths of three colors of red (R), green (G), and blue (B), and subjects of each color separated. Video CCDs for each of R, G, and B for picking up an image of light are arranged. Incidentally, R, G, and B image CCDs arranged at optically equivalent optical path length positions are represented by one image CCD 32 as shown in FIG. The subject light incident on the imaging surface of the video CCD 32 is photoelectrically converted by the video CCD 32. Then, a video signal for recording or reproduction is generated by a predetermined signal processing circuit in the camera body 12.

  As shown in FIG. 1, a focus ring 22, a zoom ring 24, and an iris ring 26 are rotatably disposed on the outer periphery of the lens barrel. When the focus ring 22 and the zoom ring 24 are respectively rotated. When the focus lens FL and the zoom lens ZL move back and forth in the direction of the optical axis O and the iris ring 26 is rotated, the aperture I opens and closes. As a result, when the position of the focus lens FL changes, the focus position (focus position) changes, and when the position of the zoom lens ZL changes, the zoom magnification (focal distance) changes and the position of the aperture I (aperture) Changes, the amount of subject light passing through the photographing optical system changes. Although omitted in FIG. 1, a drive unit for rotating these operation rings 22, 24, and 26 by a motor is mounted on the side of the lens barrel. The focus lens FL, the zoom lens ZL, and the aperture I can be electrically driven by being rotated by a motor.

  On the other hand, the AF optical path includes an AF relay lens RB ′ equivalent to the rear relay lens RB, a mirror 18, a light splitting optical system 20 including two prisms 20A and 20B, and the AF CCD 16A, 16B is arranged. In the half mirror 14, the subject light incident through the front relay lens RA is divided into two. Of the incident subject light, the subject light transmitted through the half mirror 14 is guided to the camera body 12 along the main optical path of the optical axis O as described above. The subject light reflected by the half mirror 14 is guided to an AF optical path having an optical axis O ′ substantially perpendicular to the optical axis O. For example, about 50% of the subject light is transmitted through the half mirror 14 with respect to the subject light incident on the half mirror 14. However, as the half mirror 14, one having arbitrary transmittance and reflectance characteristics can be used.

  The subject light reflected by the half mirror 14 and guided to the AF optical path passes through the AF relay lens RB ′ and then totally reflected by the mirror 18 and enters the light splitting optical system 20. The subject light incident on the light splitting optical system 20 is split into two subject lights having equivalent amounts of light at the half mirror surface M where the first prism 20A and the second prism 20B are joined. The subject light reflected by the half mirror surface M enters the imaging surface of one AF CCD 16A, and the subject light transmitted through the half mirror surface M enters the imaging surface of the other AF CCD 14B.

  Video signals obtained by photographing with the AF CCDs 14A and 14B are used in an optical path length difference AF as described later. Details of the optical path length difference AF will be described later.

  Further, the AF relay lens RB ′ is movable in the direction of the optical axis O ′, and is driven by a motor (not shown) installed in the lens barrel. When the position of the AF relay lens RB ′ changes, the position at which the subject light branched into the AF optical path changes, and the relative position between the position at which the subject light forms an image and the imaging surface of the AF CCD is changed. The positional relationship changes. As a result, an effect equivalent to the case where the position where the imaging surfaces of the AF CCDs 14A and 14B are arranged is changed.

  FIG. 3 is a configuration diagram showing a configuration of a control system related to AF control using the photographing lens 10. Note that the control system components in the photographic lens 10 are mounted on a drive unit (not shown) that is mounted mainly on the side of the lens barrel.

  The control system related to the AF control controls the focus lens FL and the AF relay lens RB ′ of the photographic lens 10. The CPU 40 controls the entire system, and the focus lens FL and the AF relay lens RB ′. Based on video signals obtained from the motors FM, RM and position sensors FP, RP connected to each of the motors, amplifiers FD, RD connected to the motors FM, RM, and the pair of AF CCDs 14A, 14B. It is composed of an AF circuit 50 and the like that acquire information necessary for control.

  When a drive signal having a predetermined value is output from the CPU 40 to each amplifier FD, RD, each motor FM, RM rotates at a speed corresponding to the value of the drive signal, and the rotation speed of each motor FM, RM is set. The focus lens FL and the AF relay lens RB ′ move at a corresponding speed. Further, position signals indicating the current positions of the focus lens FL and the AF relay lens RB ′ are given to the CPU 40 from the position sensors FP and RP. Thereby, the CPU 40 can control the focus lens FL and the relay lens RB ′ so as to have a desired moving speed or a desired position.

  At the time of AF control, the CPU 40 controls the focus lens FL based on the AF information obtained from the AF circuit 50 so that a predetermined subject is in focus in the video imaged by the video CCD 32 of the camera body 12. .

  Here, basic control contents of AF control in the present autofocus system will be described. FIG. 4 is a diagram showing the image CCD 32 of the camera body 12 and the pair of AF CCDs 16A and 16B on the same optical axis. As shown in the figure, the optical path length of the subject light incident on the imaging surface of one AF CCD 16A is set shorter than the optical path length of the subject light incident on the imaging surface of the other AF CCD 16B. The optical path length of subject light incident on the imaging surface of the image CCD 32 is set to be an intermediate length. In other words, the image pickup surfaces of the pair of AF CCDs 16A and 16B are arranged so as to be positioned at an equal distance d in the front-rear direction with respect to the image pickup surface of the image CCD 32. As will be described later, the positional relationship between the imaging surface of the image CCD 32 and the imaging surfaces of the AF CCDs 16A and 16B changes as the position of the AF relay lens RB ′ moves. The position of the AF relay lens RB ′ at this time is set as a reference position.

  According to the pair of AF CCDs 16A and 16B arranged on the photographing lens 10 in this way, the imaging surfaces of the subject light incident on the photographing lens 10 are placed at equidistant positions before and after the imaging surface of the imaging CCD 32, respectively. A video signal equivalent to the arrangement is obtained. The AF CCDs 16A and 16B do not need to capture color images, and in the present embodiment, it is assumed that black and white video signals (luminance signals) are acquired from the AF CCDs 16A and 16B.

  In the AF circuit 50 of FIG. 3, the video signals obtained by the AF CCDs 16A and 16B are converted into digital signals by the A / D converter 52, and then input to the high-pass filter (HPF) 54. Only the signal of the frequency component is extracted. The video signal from which the signal of only the high frequency component is extracted is subsequently input to the gate circuit 56, and the gate circuit 56 sets a predetermined AF area (for example, a rectangular area at the center of the screen) set within the photographing range (screen). ) Is extracted within the range corresponding to.

  The range of the AF area is set by an instruction signal from the CPU 40, and the operator can specify a desired range using a predetermined controller.

  The video signal extracted by the gate circuit 56 is integrated for each field by the addition circuit 58A when it is obtained from the AF CCD 16A, and by the addition circuit 58B when it is obtained from the AF CCD 16B. It is output from the AF circuit 50 for each field.

  The integrated values obtained from the adder circuits 58A and 58B in this way indicate values for evaluating the contrast height of the subject images captured by the AF CCDs 16A and 16B, respectively. In this specification, this integrated value is referred to as a focus evaluation value. The focus evaluation value obtained from the video signal of the AF CCD 16A is referred to as the chA focus evaluation value, and the focus evaluation value obtained from the AF CCD 16B video signal is referred to as the chB focus evaluation value.

  The CPU 40 detects the focus state of the taking lens 10 (shooting optical system) with respect to the image CCD 32 based on the focus evaluation values of chA and chB obtained in this way. The focus state is detected based on the following principle. FIG. 5 is a diagram illustrating the relationship between the focus position and the focus evaluation value when a certain subject is photographed, with the horizontal axis indicating the position (focus position) of the focus lens FL of the photographing lens 60 and the vertical axis indicating the focus evaluation value. It is. Curves A and B indicated by solid lines in the figure indicate the focus evaluation values of chA and chB obtained from the AF CCDs 16A and 16B, respectively, with respect to the focus position. On the other hand, a curved line C indicated by a dotted line in the figure indicates the focus evaluation value with respect to the focus position when it is assumed that the focus evaluation value is obtained from the video signal obtained from the video CCD 32.

  In the figure, the focus state is in focus when the focus is set at the focus position F0 when the focus evaluation value of the image CCD 32 indicated by the curve C is maximized (maximum). If the focus of the taking lens 10 is set to the focus position F1 closer to the focus position F0, the focus evaluation value of chA is the value VA1 of the curve A corresponding to the focus position F1, The focus evaluation value of chB is the value VB1 of the curve B corresponding to the focus position F1. In this case, as can be seen from the figure, the chA focus evaluation value VA1 is larger than the chB focus evaluation value VB1. From this, when the focus evaluation value VA1 of chA is larger than the focus evaluation value VB1 of chB, the focus is set closer to the focus position F0, that is, the state of the front pin It turns out that it is.

  On the other hand, when the photographing lens 10 is set to the focus position F2 on the infinity side of the focus position F0, the focus evaluation value of chA is the value VA2 of the curve A corresponding to the focus position F2, The focus evaluation value of chB is the value VB2 of the curve B corresponding to the focus position F2. In this case, the chA focus evaluation value VA2 is smaller than the chB focus evaluation value VB2. From this, when the focus evaluation value VA2 for chA is smaller than the focus evaluation value VB2 for chB, the focus is set to the infinity side from the focus position F0, that is, the rear pin It turns out that it is in a state.

  On the other hand, when the focus of the photographing lens 10 is set to the focus position F0, that is, the focus position, the focus evaluation value of chA is the value VA0 of the curve A corresponding to the focus position F0, and chB Is the value VB0 of the curve B corresponding to the focus position F0. In this case, the chA focus evaluation value VA0 is equal to the chB focus evaluation value VB0. From this, it can be seen that when the focus evaluation value VA0 for chA and the focus evaluation value VB0 for chB are equal, the focus is set at the focus position F0, that is, the focus state.

  In this way, it is possible to detect whether the current focus state of the photographing lens 10 is a front pin, a rear pin, or an in-focus state with respect to the image CCD 32 based on the focus evaluation values of chA and chB.

  In the AF control, the CPU 40 in FIG. 3 performs focusing so that the focus state of the photographing lens 10 with respect to the image CCD 32 is sequentially detected based on the focus evaluation values of chA and chB as described above. The lens FL is controlled. For example, when the focus state is the front pin, the focus lens FL is moved in the infinity direction, and when the focus state is the rear pin, the focus lens FL is moved in the closest direction. When the focus state is in focus, the focus lens FL is stopped. As a result, the focus lens FL moves to a position where the focus state of the photographing lens is in focus and stops. An AF method in which automatic focus adjustment is performed using a plurality of AF CCDs having optical path length differences is referred to as an optical path length difference method.

  Note that the CPU 40 does not simply detect the focus state, but also detects the amount of focus deviation from the difference or ratio of the focus evaluation values of chA and chB, and reflects them in the speed at which the CPU 40 moves the focus lens FL. It is also possible.

  Next, focus follow-up control in the case where the CPU 40 continuously executes AF control by the optical path length difference type AF as described above to cause the focus to always follow a predetermined subject will be described. When the subject to be focused by AF moves in the front-rear direction with respect to the television camera, that is, in the direction of the optical axis O in the photographing lens 10, the distance of the subject changes and follows it. The focus lens FL also moves. At this time, the focus position (in-focus position) at which the in-focus state is achieved changes, and the subject is stopped because the focus position follows in a state where the focus position is shifted to the near side or the infinity side. It will be an image that has been blurred.

  For example, a case where the target subject is moving to the close side will be described below. In this case, as shown in FIG. 6, the focus lens FL moves forward so that the focus is closer to the close side than the current position. is doing. At this time, due to the delay in the follow-up operation of the focus lens FL, the image formation position S where the image of the subject is formed with respect to the current position of the focus lens FL is a distance behind the imaging surface of the video CCD 32. The state is shifted by f. This state indicates the state of the rear pin, and the positional relationship with the imaging surfaces of the AF CCDs 14A and 14B also indicates the state of the rear pin as shown in FIG. When this state is shown by a graph showing the relationship between the focus position and the focus evaluation value similar to FIG. 5, the focus position is set to the focus position F2 on the infinity side with respect to the focus position F0 as shown in FIG. It will be in the state. At this time, the CPU 40 moves the focus lens FL to the close side in order to move the focus lens FL to the focus position F0. However, since the subject itself has moved to the close side and the focus position F0 has moved to the close side, While the lens is moving, the focus lens FL does not coincide with the in-focus position F0 and is maintained in a state in which the focus position F2 is set at the infinity side of the in-focus position F0.

  In such a case, when the focus evaluation values of chA and chB are in the focus state indicating the rear focus, the positions of the imaging surfaces of the AF CCDs 16A and 16B are intentionally set so that the actual focus state is in focus. By shifting the focus lens, it is possible to reduce the focus shift when the focus lens FL is operated to follow. For example, as shown in FIG. 8, it is assumed that the positions of the imaging surfaces of the AF CCDs 16A and 16B are shifted to the front side with respect to the imaging surface of the image CCD 32. At this time, at the focus position where the chA and chB focus evaluation values indicate the rear pin, the imaging surface of the video CCD 32 is in focus. That is, at the focus position (focus position) where the focus evaluation values of chA and chB obtained from the AF CCDs 16A and 16B indicate the in-focus state, the actual focus state with respect to the imaging surface of the image CCD 32 becomes the front pin. By doing so, the shift of the focus that becomes the rear pin due to the delay of the follow-up operation of the focus lens FL is reduced.

  The above description is for the case where the target subject is moving to the closest side. However, when the target subject is moving to the infinity side, the direction in which the AF CCDs 14A and 14B are shifted is opposite to the above. Become.

  Next, a method of shifting the AF CCDs 14A and 14B as shown in FIG. 8 will be described. As a direct method, the AF CCDs 14A and 14B can be moved by a motor or the like. In FIGS. 1 and 2, the light splitting optical system 20 and the AF CCDs 14A and 14B are unitized, and these are integrated. It is conceivable that the optical axis can be moved by a motor or the like. In the photographic lens 10 of the present embodiment, as shown in the block diagram of the control system in FIG. 3, the AF relay lens RB ′ is moved in the direction of the optical axis by the motor RM, so that the object light is connected in the AF optical path. Control equivalent to shifting the position of the imaging surface of the AF CCDs 14A and 14B by moving the image position is performed.

  Further, it is desirable that the amount of shifting the AF CCDs 16A and 16B (shift amount) coincides with a focus shift amount (f in FIG. 6) caused by a delay in the follow-up operation of the focus lens FL, and the focus shift amount is It is substantially determined by the moving speed of the focus lens FL that follows the movement of the subject. Therefore, the AF relay lens RB ′ is displaced from the reference position (the position in the reference state as shown in FIG. 6) by a predetermined amount with respect to the moving speed of the focus lens FL, thereby adjusting the moving speed of the focus lens FL. On the other hand, the AF CCDs 16A and 16B are shifted by a predetermined amount. For example, if the movement of the subject is gradually delayed and stopped, the AF relay lens RB ′ gradually approaches the reference position and stops at the reference position, and the shift amounts of the AF CCDs 16A and 16B gradually decrease to 0. Stop in the state.

  The shift amounts of the AF CCDs 16A and 16B may be determined from the focus evaluation values of chA and chB, and may be determined according to, for example, the ratio or difference between the focus evaluation values of chA and chB.

  As described above, in the above-described embodiment, the AF relay lens RB ′ is moved as a method of shifting the AF CCDs 16A and 16B. However, a plate glass that changes the optical path length to the AF optical path (or air other than glass) A method of inserting and removing plate-like transparent members having different refractive indexes may be used. Further, as shown in FIG. 9, wedge-shaped glass members (or transparent members having a refractive index different from air other than glass) 100 and 102 are opposed to each other, and subject light passes through the overlapping portions, and these glass members are also passed. The optical path length of the AF optical path may be changed by changing the thickness of the overlapping part by sliding the motor with a motor or the like.

  In the above embodiment, the positions of both of the imaging surfaces are shifted without changing the optical path length difference between the imaging surfaces of the AF CCD 16A and the AF CCD 16B. The focus state indicated by the focus evaluation values of chA and chB may be shifted to the opposite side to the moving direction of the subject from the actual focus state. That is, according to the present invention, the actual focus state when the focus state detection means for detecting the current focus state determines that the in-focus state is the front focus when the moving direction of the subject is the closest side. The focus state determined by the focus state detection means may be adjusted by some method so that the rearward focus is obtained when the movement direction is at infinity. For example, not only the method of shifting the positions of the imaging surfaces of the AF CCDs 16A and 16B, but also adjusting the focus state determined by the focus state detection means by adjusting the gain for one of the focus evaluation values of chA and chB. Is possible. Further, when adjusting (shifting) the focus state determined by the focus state detection means, the shift amount is determined by the focus position when the focus state detection means determines that it is in focus and the actual focus state is in focus. The focus position of the subject image, the subject image image formation position when the focus state detection means determines that it is in focus, and the subject image image formation position when the actual focus state is in focus It can be expressed quantitatively by the difference between and the like. In this way, when it is grasped that the shift amount in the focus state can be varied by a continuous value, the shift amount is determined based on the moving speed of the focus lens FL in the same manner as described in the above embodiment. Alternatively, it may be determined from the focus evaluation values of chA and chB.

  In the above embodiment, focus tracking control such as shifting the positions of the imaging surfaces of the AF CCDs 16A and 16B is performed only when the focus lens FL is continuously moving for a certain time or more following the subject. It may be.

  In the above-described embodiment, it is assumed that AF control is continuously performed. However, once the focus state is reached, AF is stopped until an AF execution instruction is issued again. The present invention can also be applied to AF control until focusing on a moving subject.

FIG. 1 is a side view showing an appearance and a partial internal configuration of a photographic lens used in an autofocus system according to the present invention. FIG. 2 is a diagram illustrating the overall configuration of the photographing optical system. FIG. 3 is a configuration diagram showing a configuration of a control system related to AF control using the photographing lens of FIGS. 1 and 2. FIG. 4 is a diagram showing the image CCD and the pair of AF CCDs on the camera body on the same optical axis. FIG. 5 is an explanatory diagram used for explaining the principle of detecting the focus state. FIG. 6 is an explanatory diagram used for explaining the focus tracking control. FIG. 7 is an explanatory diagram used for explaining the focus tracking control. FIG. 8 is an explanatory diagram used for explaining the focus tracking control. FIG. 9 is a diagram showing another embodiment for shifting the position of the imaging surface of the AF CCD.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Shooting lens, 12 ... Camera body, 14 ... Half mirror, 16A, 16B ... AF CCD, 18 ... Mirror, 20 ... Light splitting optical system, 32 ... Image CCD, 40 ... CPU, 50 ... AF circuit, 52 ... A / D converter, 54 ... High-pass filter, 56 ... Gate circuit, 58A, 58B ... Adder circuit, FL ... Focus lens, ZL ... Zoom lens, I ... Aperture, RA ... Front relay lens, RB ... Rear relay lens , MF, RM ... Motor, FP, RP ... Position sensor

Claims (3)

A focus state detecting means for detecting a focus state of the photographing optical system with respect to a subject to be focused;
Auto focus control means for controlling the focus of the photographing optical system so that the focus state detected by the focus state detection means is in focus and performing automatic focus adjustment;
When the focus of the photographing optical system is moved by the autofocus control unit following the subject, an actual focus state when the focus state detected by the focus state detection unit indicates an in-focus state. The focus state detected by the focus state detection means so that it becomes a front pin when the subject moves to the close side, and a rear pin when the subject moves to the infinity side. Adjusting means for adjusting
An autofocus system characterized by comprising   The focus state detection unit includes an AF imaging unit that captures a subject image formed by the imaging optical system on a plurality of imaging surfaces arranged at different optical path lengths, and each imaging surface of the AF imaging unit. The focus evaluation value detecting means for detecting the focus evaluation value indicating the contrast height of each video signal obtained by imaging with the focus evaluation value for each imaging surface detected by the focus evaluation value detecting means is compared. Comparing means for detecting the focus state, the adjusting means moving the position of each imaging surface of the AF imaging means, and a dedicated optical path for guiding subject light to each imaging surface of the AF imaging means Means for changing the optical path length of the lens, or means for moving the position of a lens for forming a subject image arranged in a dedicated optical path for guiding subject light to each imaging surface of the AF imaging means. Characterize Motomeko 1 of the auto-focus system.   The adjusting means determines the amount of focus state shift detected by the focus state detecting means based on the focus evaluation value obtained for each imaging surface of the AF imaging means or based on the moving speed of the focus. 3. The autofocus system according to claim 2, wherein

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