JP2005062237A - Automatic focus system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automatic focus system for improving the response performance of an automatic focus for a moving subject and preventing a fall in focusing precision. <P>SOLUTION: In the optical path length difference type automatic focus on two imaging faces, at first, a focus position is set so that it is the best image formation position at a position being an intermediate optical path length to the two imaging planes on the basis of a video signal captured from the two imaging planes having an optical path length difference. Then, the focus position is corrected so that the position of the imaging plane for a real image for reproduction is the best image formation position. In addition, CPU 30 of a lens device controls a focus lens FL by a contrast system by acquiring the video signal captured from the two imaging planes from a camera body. In this way, the lens device can focus at high precision to the imaging plane for the real image, can enlarge the optical path length difference of the two imaging planes without lowering focusing precision, and can improve the response performance of the focus to the moving subject. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an autofocus system, and more particularly, to an autofocus system that employs contrast-type autofocus and adopts optical path length difference autofocus.
[0002]
[Prior art]
A contrast method is generally used as an autofocus (AF) employed in a broadcast television camera. 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 level 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).
[0003]
In contrast AF, the focus state (front pin, rear pin, or in-focus) is detected by wobbling that fluctuates the focus slightly, and the operating direction of the focus is determined. There is a possibility that the variation in focus due to the movement may be recognized on the screen, and there is a disadvantage that is not preferable particularly in broadcasting photography such as being unable to focus accurately on a subject moving at high speed.
[0004]
As a method for solving such a drawback, for example, it is conceivable to use a system as disclosed in Patent Document 1. According to this, two imaging surfaces having a difference in optical path length with respect to incident subject light are arranged close to each other, and the contrast (focus evaluation value) of each image captured by each imaging surface is detected. By comparing these contrasts, the focus state is detected without wobbling, and based on this, the focus of the photographing lens is controlled to be the best focus.
[0005]
In Patent Document 1, two image pickup surfaces having optical path length differences can be arranged by one image pickup device by shifting the image pickup surface of one image pickup device forward and backward in the optical axis direction by a predetermined optical path length difference for each horizontal line. However, it is also possible to arrange two imaging surfaces having an optical path length difference using two separate imaging elements. In this case, means for dividing the subject light incident on the photographic lens into the imaging surface of each imaging element is disposed in the optical system of the photographic lens or in the optical system of the camera body after passing through the photographic lens. become. In Patent Document 1, the image pickup device for detecting the focus state is the same as the image pickup device for picking up an original image (video) for display or recording (hereinafter referred to as reproduction). However, they can also be separate image sensors. Furthermore, when two image pickup surfaces having optical path length differences are arranged using two image pickup devices, one is used as an image pickup device for picking up an original image, and the other is used for detecting a focus state. An imaging device can also be used.
[0006]
[Patent Document 1]
Japanese Patent Publication No. 7-60211
[0007]
[Problems to be solved by the invention]
By the way, when the contrasts of images captured on two imaging surfaces are compared as in Patent Document 1, if the focus is controlled so that the contrasts (focus evaluation values) match, the best imaging position is the two of them. Between the two imaging surfaces. On the other hand, one or both of the two imaging surfaces are not only imaging surfaces for capturing an image for detecting a focus state, but also imaging for capturing an original image for reproduction. If it is also a plane, it is necessary to obtain sufficient focusing accuracy even on the imaging plane for capturing the original image when the middle of the two imaging planes is the best imaging position. Therefore, in Patent Document 1, the two imaging surfaces are arranged so that the optical path length difference is equal to or less than the depth of focus.
[0008]
However, if the optical path length difference between the two imaging planes is less than the depth of focus, the optical path length difference between the two imaging planes becomes too small, and the focus cannot be controlled with a sufficient response speed with respect to changes in the subject. is there. That is, when the focus is automatically controlled so that the contrasts of the images obtained from the two imaging surfaces coincide with each other, by determining the operation direction and operation speed of the focus according to the difference or ratio of the contrast, A method is used in which the focus is operated in such a way that the contrast difference becomes smaller and the operation speed becomes slower as the contrast difference becomes smaller.
[0009]
On the other hand, when the focus position is changed, the change in contrast that appears in the vicinity of the focal point becomes smaller as the subject moves at a higher speed. Therefore, as the subject moves at a higher speed, a difference in contrast between images obtained by the respective imaging surfaces is less likely to occur. In particular, the smaller the difference in optical path length between the two imaging surfaces, the more difficult the difference in contrast occurs.
[0010]
Therefore, if the optical path length difference between the two imaging surfaces is made too small as in Cited Document 1, even if the focus control is performed well for a stationary subject, the subject moving at a high speed Therefore, even when the focus is greatly deviated, a difference in contrast is hardly detected, and there is a problem that the focus does not follow at a sufficient response speed with respect to a change in the subject.
[0011]
In recent years, HD (High Definition) systems have come to be used. In such systems, since the depth of focus is shallow and the optical path length difference between the two imaging planes needs to be smaller, the above-described problem. Becomes prominent.
[0012]
As a method for solving such a problem, it is conceivable to increase the optical path length difference between the two imaging surfaces without being limited to the depth of focus or less. However, in this case, even when the contrasts of the images obtained from the two imaging surfaces coincide with each other and it is determined that the image is in focus, there is a problem that the best focusing image is not obtained on the imaging surface and the best focus image cannot be obtained. Occurs.
[0013]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide an autofocus system that improves the autofocus response performance with respect to a moving subject and prevents a reduction in focusing accuracy. .
[0014]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 is directed to a light splitting means for splitting the subject light incident on the photographing optical system into the first subject light and the second subject light; An image pickup surface for acquiring an image, which is a first image pickup surface for picking up the first subject light, and a second image pickup surface for picking up the second subject light, the first image pickup A second imaging surface disposed at a position having an optical path length difference with respect to the surface, a video signal obtained by imaging with the first imaging surface, and an image obtained by imaging with the second imaging surface. The imaging optical system is configured so that the position of the optical path length intermediate between the optical path length to the first imaging surface and the optical path length to the second imaging surface is the best imaging position based on the obtained video signal. A focus control means for controlling the focus position of the first imaging surface, and the position of the first imaging surface being the best imaging position Is characterized by comprising, a focus correction means for correcting the set focus position by the focus control means so that.
[0015]
According to a second aspect of the present invention, in the first aspect of the present invention, the video signal is based on the video signal obtained by the first imaging surface after the focus correction unit corrects the focus position. A first focus evaluation value for evaluating the contrast level of the image indicated by the second image is obtained, and the contrast level of the image indicated by the video signal is evaluated based on the video signal obtained by the second imaging surface. A re-execution condition is obtained by obtaining a focus evaluation value, and a re-execution condition that a ratio between the obtained first focus evaluation value and the second focus evaluation value is changed by a predetermined value or more from a value immediately after the correction of the focus position. When it is determined by the determining means and the re-execution condition is satisfied by the determining means, the focus position control by the focus control means is re-executed. It is characterized by comprising an execution instruction means.
[0016]
According to a third aspect of the present invention, in the second aspect of the present invention, when the determination unit determines that the re-execution condition is not satisfied, the first focus evaluation value and the first focus evaluation value The second focus control means is provided for controlling the focus position so that the ratio of the focus evaluation value of 2 to the value immediately after the correction of the focus position.
[0017]
According to the present invention, first, based on a video signal obtained by two imaging surfaces having an optical path length difference, the best imaging position is set at a position having an intermediate optical path length with respect to the two imaging surfaces. Set the focus position to. Thereafter, the focus position is corrected so that the position of the imaging surface that captures the original image for reproduction becomes the best imaging position. Therefore, in the autofocus of the optical path length difference method using the two image pickup surfaces, the two image pickup surfaces can be focused with high accuracy with respect to the image pickup surface for picking up the original image without reducing the focus accuracy. It is possible to increase the difference in the optical path lengths, thereby improving the focus response performance for a moving subject or the like.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of an autofocus system according to the present invention will be described in detail with reference to the accompanying drawings.
[0019]
The television camera shown in FIG. 1 includes a camera body 10 with interchangeable lenses and a lens device 12 attached to the camera body 10. The lens device 12 electrically controls a photographic lens 14 (optical system) composed of various fixed and movable lens groups and optical components such as an iris, and a movable lens (group) and iris of the photographic lens 14 by electric control. A control device (control system) (not shown) is included.
[0020]
In the camera body 10, two image pickup devices (two-dimensional CCDs) 20 and 22 are disposed, and a light splitting optical system 24 such as a half mirror that splits incident subject light into two subject light is disposed. Yes. The subject light that has entered the camera body 10 after passing through the photographing lens 14 is divided into two subject lights by the light splitting optical system 24, and one of the divided subject lights is an imaging surface of the image sensor 20. The other is incident on the imaging surface of the image sensor 22.
[0021]
The image sensor 20 is an image sensor arranged to capture an original image (video) for reproduction, and a video signal obtained by photoelectric conversion by the image sensor 20 and processed by a signal processing circuit (not shown) For example, it is output from an external video signal output terminal to an external device. Further, the video signal obtained from the image sensor 20 is also sent to the lens device 12 as will be described later, and is used to detect the focus state. When the video signal obtained from the image sensor 20 is a color signal, for example, a luminance signal is used to detect a focus state.
[0022]
On the other hand, the image sensor 22 is an image sensor that is arranged exclusively for detecting the focus state. A video signal (for example, a luminance signal) obtained by photoelectric conversion by the image sensor 22 is obtained from the image sensor 20. Together with the received video signal, it is sent to the lens device 12 and used to detect the focus state.
[0023]
In the figure, a so-called single-plate camera that captures an original image by one image sensor 20 is shown, but three image sensors for red (R), green (G), and blue (B) are shown. 3 may be a so-called three-plate camera that captures an original image, and the image sensor 20 shown in FIG. 1 captures one image sensor for each of R, G, and B at an optically equivalent distance. You may understand that it was shown with the element. In that case, a color separation optical system that splits subject light that has passed through the photographing lens 14 and entered the camera body into R, G, and B light is disposed at the position of the light splitting optical system 24 in FIG. The subject light split into the wavelengths of the respective colors by the resolving optical system is incident on the imaging surface of the imaging device corresponding to each wavelength. At this time, for example, a means for branching subject light for focus state detection is provided in the color separation optical system, and the subject light branched thereby is made incident on the imaging surface of the image sensor 22. As will be described in detail later, two luminance signals obtained from two imaging planes arranged with a difference in optical path length are used for focus state detection in the present embodiment. The signal may be acquired from any one of the R, G, and B image sensors that capture the original image, or may be generated from signals obtained from the three R, G, and B image sensors. May be. In addition, the dedicated image sensor 22 for detecting the focus state, a unit for branching the subject light to the imaging surface of the image sensor 22, and the like may be arranged in the lens device 12 instead of the camera body 10.
[0024]
Here, FIG. 2 shows a diagram in which the imaging surface of the imaging device 20 and the imaging surface of the imaging device 22 are represented on the same optical axis. As shown in the drawing, the optical path length of the subject light incident on the imaging surface 20A of one imaging element 20 is shorter than the optical path length of the subject light incident on the imaging surface 22A of the other imaging element 22. The imaging surfaces of the imaging elements 20 and 22 are arranged with an optical path length difference. As a result, the subject light incident on the photographing lens 14 is imaged by the two imaging surfaces having the optical path length difference. However, the positions of the imaging surfaces 20A and 22A may be reversed. In addition, the image pickup surface X indicated by a broken line in the figure is located between the image pickup surface 20A and the image pickup surface 22A, and the optical path length to the image pickup surface 20A is equal to the optical path length to the image pickup surface 22A, that is, each The imaging surfaces arranged at positions where the optical path lengths to the imaging surfaces 20A and 22A are ½ of the optical path length difference between the imaging surfaces 20A and 20B are shown. This imaging plane X is not actually arranged, and shows the position of the imaging plane that becomes a reference when detecting the focus state from two video signals as will be described in detail later.
[0025]
FIG. 3 is a block diagram showing the configuration of the lens device 12. The photographic lens 14 in the lens device 12 includes a focus lens (group) FL driven in the optical axis direction for focusing as a movable lens group, and an optical axis direction for changing the image magnification (focal length). A zoom lens (group) ZL driven by the Also, an iris I that is driven to open and close to change the aperture value is arranged.
The focus lens FL, the zoom lens ZL, and the iris I are connected to the focus motor FM, the zoom motor ZM, and the iris motor IM, respectively, and are driven by the motors FM, ZM, and IM. Yes.
[0026]
The motors FM, ZM, and IM are connected to the focus amplifier FA, the zoom amplifier ZA, and the iris amplifier IA, respectively, and each amplifier is connected from the CPU 30 mounted on the lens device 12 via the D / A converter 32. When a drive signal is given to FA, ZA, IA, a voltage corresponding to the drive signal is applied to each motor FM, ZM, IM, and each motor FM, ZM, IM is driven at a speed corresponding to the applied voltage. It is like that.
[0027]
Therefore, the CPU 30 can control the focus lens FL, the zoom lens ZL, and the iris I at a desired operation speed based on the voltage values of the drive signals output to the amplifiers FA, ZA, and IA. Position information indicating the current position of the focus lens FL, the zoom lens ZL, and the iris I is supplied from the potentiometers FP, ZP, and IP to the CPU 30 via the A / D converter 34, respectively. By controlling the operation speed while referring to these current positions, the positions of the focus lens FL, zoom lens ZL, and iris I can also be controlled.
[0028]
On the other hand, a lens controller such as a focus demand 36 for manually operating the focus and a zoom demand 38 for manually operating the zoom can be connected to the lens device 12 as a lens accessory (attached device). The focus demand 36 shown in the figure is a digital lens controller. When the focus demand 36 is connected to the lens device 12, the SCI (serial communication interface) 40, 42 is connected between the focus demand 36 and the CPU 30 of the lens device 12. And various signals are exchanged by serial communication. Thereby, for example, a command signal indicating the target position of the focus is given from the focus demand 36 to the CPU 30 based on a manual operation of a predetermined focus operation member (for example, a focus ring). In the manual focus mode, the CPU 30 controls the position of the focus lens FL based on the command signal, and sets the focus to the target position given by the command signal.
[0029]
A zoom demand 38 shown in the figure is an analog lens controller. When the zoom demand 38 is connected to the lens device 12, for example, a command signal indicating a zoom target speed based on a manual operation of a zoom operation member is A / It is given to the CPU 30 via the D converter 34. The CPU 30 controls the operating speed of the zoom lens ZL based on the command signal, and moves the zoom at the target speed given by the command signal.
[0030]
In addition, the lens device 12 is provided with an AF switch S1 for switching between a manual focus mode and an autofocus mode. The CPU 30 executes a manual focus mode process when the AF switch S1 is off, and executes an autofocus mode process when the AF switch S1 is on. In the manual focus mode process, the focus lens FL is controlled based on the command signal from the focus demand 36 as described above.
[0031]
On the other hand, in the auto focus mode process, the focus lens FL is controlled based on the focus information acquired by the processing circuits 50A to 56A and the processing circuits 50B to 56B to perform automatic focus adjustment.
[0032]
The processing circuits 50A to 56A are circuits that generate focus evaluation values indicating the level of contrast of the image from the video signal (luminance signal) obtained from the image sensor 20 of the camera body 10, and the processing circuits 50B to 56B are This is a circuit that generates a focus evaluation value indicating the level of contrast of an image from a video signal (luminance signal) obtained from the image sensor 22 of the camera body 10. Since the processing contents of the processing circuits 50A to 56A and the processing circuits 50B to 56B match each video signal, only the processing circuits 50A to 56A will be described below.
[0033]
As shown in the figure, when a video signal obtained by the imaging device 20 of the camera body 10 is given from the camera body 10 to the lens device 12, the video signal is first converted into a digital signal by the A / D converter 50A. . Subsequently, only the signal of the high frequency component is extracted from the video signal by the digital filter 52A, and only the signal within a predetermined focus range set within the shooting range (on the screen) from the extracted signal of the high frequency component is extracted. Is extracted by the gate circuit 54A. The signal extracted by the gate circuit 54A is then integrated for each image (for one field in the interlaced video signal) by the adder circuit 56A. The signal obtained by the integration of the adder circuit 56A is a value indicating the degree of focus on the subject within the focus range (contrast level), and this value is sequentially read by the CPU 30 as a focus evaluation value. The focus evaluation value obtained from the video signal from the image sensor 20 in this way is referred to as the focus evaluation value of the channel (ch) A. Similarly, the processing circuits 50B to 56B process the video signal from the image sensor 22. The obtained focus evaluation value is referred to as a chB focus evaluation value.
[0034]
All the processing units of the lens device 12 shown in FIG. 3 are not necessarily arranged in the lens device 12, and may be arranged in any part of the entire system including the camera body 10. For example, the processing circuits 50A to 56A and 50B to 56B may be arranged in the camera body 10, or a focus lens based on the focus evaluation values obtained from the processing circuits 50A to 56A and 50B to 56B as will be described later. The processing of the CPU 30 that controls the position of the FL may be performed on the camera body 10 side.
[0035]
Next, auto focus (AF) processing in the CPU 30 of the lens apparatus 12 will be described. When the focus evaluation values of chA and chB are acquired as described above, the current focus state of the photographic lens 14 can be known based on the focus evaluation values. First, the principle will be described. FIG. 4 is a diagram illustrating the state of the focus evaluation value with respect to the focus position when a certain subject is imaged, with the horizontal axis indicating the position (focus position) of the focus lens FL of the photographing lens 14 and the vertical axis indicating the focus evaluation value. is there. Curves A and B indicated by solid lines in the figure indicate the chA and chB focus evaluation values obtained from the image sensors 20 and 22, respectively, with respect to the focus position. On the other hand, a curved line C indicated by a dotted line in the figure indicates that the imaging surface X is assumed when the imaging surface X is arranged between the imaging surfaces 20A and 22A of the imaging device 20 and the imaging device 22 (see FIG. 2). The graph when a focus evaluation value is calculated | required with the obtained video signal is shown.
[0036]
First, the focus state with respect to the imaging surface X is detected with the position F0 where the focus evaluation value of the curve C is maximized (maximum) as the in-focus position. When the focus position of the photographic lens 14 is set to F1 in the figure, the chA focus evaluation value V _A1 Is a value corresponding to the position F1 of the curve A, and the focus evaluation value V of chB _B1 Is a value corresponding to the position F1 of the curve B. In this case, the chA focus evaluation value V _A1 Is the focus evaluation value V of chB _B1 Bigger than. From this, it can be seen that the focus position is set closer to the in-focus position (F0), that is, the state of the front pin.
[0037]
On the other hand, when the focus position of the photographic lens 14 is set to F2 in FIG. _A2 Is a value corresponding to the position F2 of the curve A, and the focus evaluation value V of chB _B2 Is a value corresponding to the position F2 of the curve B. In this case, the chA focus evaluation value V _A2 Is the focus evaluation value V of chB _B2 Smaller than. From this, it can be seen that the focus position is set to the infinity side from the focus position (F0), that is, the state of the rear pin.
[0038]
On the other hand, when the focus position of the photographic lens 14 is set to F0, that is, the in-focus position, the chA focus evaluation value V _A0 Is a value corresponding to the position F0 of the curve A, and the focus evaluation value V of chB _B0 Is a value corresponding to the position F0 of the curve B. At this time, the focus evaluation value V of chA _A0 And chB focus evaluation value V _B0 Are equal. From this, it can be seen that the in-focus state is set to the in-focus position (F0).
[0039]
In this way, it is possible to detect whether the current focus state of the photographic lens 14 is a front pin, a rear pin, or an in-focus state with respect to the imaging plane X, based on the chA and chB focus evaluation values. Note that the focus state detected here is not a focus state with respect to the imaging surface 20A of the imaging element 20 that captures an image for reproduction. For example, when the focus state is detected as described above based on the focus evaluation values of chA and chB, and the focus state is determined, the best imaging positions at that time are the imaging surface 20A and the imaging element 22 of the imaging element 20. This is the position of the imaging plane X in the middle of the imaging plane 22A.
[0040]
Next, an outline of AF processing in the CPU 30 of the lens apparatus 12 will be described.
When the focus evaluation values of chA and chB do not match, the CPU 30 controls the position of the focus lens FL based on the focus evaluation values of chA and chB, and the focus lens FL is first focused on the imaging plane X. Move to the position. In other words, when the state is determined to be the front pin with respect to the imaging surface X, the focus lens FL is moved in the infinity direction, and when the state is determined to be the rear pin, the focus lens FL Move in the close direction. When the focus evaluation values of chA and chB match to determine that the imaging surface X is in focus, the focus lens FL is stopped at that position. As a result, the focus of the photographing lens 14 is brought into focus with respect to the imaging surface X. After the focus lens FL is set to the in-focus position in this way, the above process is repeated when the in-focus state, that is, the state where the chA and chB focus evaluation values match does not continue for a predetermined time or longer. Thereby, for example, when the in-focus position fluctuates when the subject is moving, the focus lens FL moves following the focus position.
[0041]
Here, an example of a specific control method for moving the focus lens FL to the in-focus position will be described. When the focus evaluation values of chA and chB obtained sequentially from the camera body 10 are AFV_A and AFV_B, the CPU 30 first obtains the ratio AFV = AFV_A / AFV_B. As can be seen from FIG. 4, when the focus evaluation value ratio AFV is 1, the imaging surface X is in focus, and the focus evaluation value ratio AFV is greater than 1. In this case, the focus state with respect to the imaging surface X is the front pin state. In this case, the moving direction of the focus lens FL is set to the infinity side. Further, the moving speed of the focus lens FL at this time is set to C · (AFV−1), for example. The coefficient C is a constant. Then, an instruction (drive signal) for executing the operation set as described above is output to the focus amplifier FA shown in FIG.
As a result, the focus lens FL moves faster as the AFV becomes larger in the direction in which AFV = 1, and when the AFV approaches 1, it decelerates and stops at the in-focus position where AFV = 1.
[0042]
On the other hand, when the value of the focus evaluation value ratio AFV is smaller than 1, the focus state is the rear focus state with respect to the imaging surface X. In this case, the moving direction of the focus lens FL is set to the close side. Further, the moving speed of the focus lens FL at this time is set to, for example, C · (1 / AFV−1). Thus, the focus lens FL moves faster as 1 / AFV becomes larger in the direction of 1 / AFV = 1 (AFV = 1), and decelerates when 1 / AFV approaches 1, and 1 / AFV = 1. Stop at the in-focus position.
[0043]
By the way, when the focus lens FL is stopped at the in-focus position while adjusting the moving speed of the focus lens FL using the ratio or difference between the focus evaluation values of chA and chB as a parameter, the imaging surface 20A of the image sensor 20 is If the difference in optical path length from the imaging surface 22A of the imaging element 22 is small, there arises a problem that the focus lens FL does not follow the subject moving at a high speed with a sufficient response speed. FIG. 5 shows a graph of the focus evaluation value when the subject is moving at high speed when the optical path length difference between the imaging surface 20A and the imaging surface 22A is reduced so as to be equal to or less than the focal depth of the photographing lens 14, for example. It is a figure. On the other hand, FIG. 6 is a graph of the focus evaluation value when the subject is moving at high speed in the case of the present embodiment and when the difference between the optical path lengths of the imaging surface 20A and the imaging surface 22A in FIG. FIG. As shown in these figures, when the subject is moving at a high speed, the contrast is low and the inclination near the peak point of the focus evaluation value is also gentle. Therefore, as can be seen from the graph of FIG. 5, if the difference in optical path length between the imaging surface 20A and the imaging surface 22A is too small, a difference in the focus evaluation values of chA and chB hardly occurs. The moving speed of the focus lens FL obtained by the above equation such as C · (AFV-1) is extremely slow even if it is greatly deviated from the distance to the close side. If the coefficient C is set to a large value, the moving speed of the focus lens FL can be generally increased. However, when the moving subject stops or the subject is stationary from the beginning. In some cases, the moving speed of the focus lens FL is too fast, which causes a problem that the stopping operation at the in-focus position becomes unstable. Therefore, the focus lens FL cannot follow the subject moving at a high speed at a sufficient speed.
[0044]
On the other hand, as can be seen from the graph of FIG. 6, if the optical path length difference between the imaging surface 20A and the imaging surface 22A is increased as in the present embodiment, the chA even when the subject is moving at high speed. And the focus evaluation value of chB are sufficiently large, and the focus lens FL can follow the subject moving at high speed at a sufficient speed.
[0045]
On the other hand, reducing the optical path length difference between the imaging surface 20A and the imaging surface 22A and limiting it to the focal depth or less controls the position of the focus lens FL so as to be in focus with respect to the imaging surface X as described above. By doing so, there is an advantage in that an in-focus state can be obtained also on the image pickup surface 20A for picking up an original image. When the optical path length difference between the imaging surface 20A and the imaging surface 22A is increased in order to improve the response performance of the focus lens FL as in the present embodiment, the focus is set so that the imaging surface X is in focus. Even if the lens FL is controlled, the image pickup surface 20A of the image pickup device 20 that picks up the original image is not brought into focus. However, since the contrast of the subject moving at high speed is low, when the subject is moving at high speed, even if the subject is not in focus with respect to the imaging surface 20A of the imaging device 20, the reproduced image is displayed. There is almost no sense of incongruity. On the other hand, a stationary subject needs to be brought into focus with respect to the imaging surface 20A of the imaging device 20, but this point is solved by the control described below.
[0046]
As described above, when the focus lens FL is set to the in-focus position at which the imaging surface X is in focus, when the focus state continues for a specified time or longer without moving the focus lens FL, the subject Can be determined to be stationary. In this case, the CPU 30 moves the focus lens FL to displace the best imaging position from the imaging surface X to the imaging surface 20A of the imaging element 20. That is, the focus lens FL is moved in the closest direction by an amount corresponding to one half of the optical path length difference between the imaging surface 20A of the imaging device 20 and the imaging surface 22A of the imaging device 22. As a result, when high focusing accuracy is required, for example, when the subject is stationary or when the moving subject is stopped, the imaging surface 20A of the imaging element 20 that captures the original image is aligned. The position of the focus lens FL is corrected so as to be in focus. Therefore, when the optical path length difference between the imaging surface 20A of the imaging device 20 and the imaging surface 22A of the imaging device 22 is increased in order to improve the response performance of the focus lens FL as described above, the focusing is performed with respect to the imaging surface X. By simply controlling the focus lens FL so as to be in the state, the problem that the imaging surface 20A is not brought into focus is solved.
[0047]
Next, a specific processing procedure of the CPU 30 will be described using the flowchart of FIG. First, the CPU 30 sets the parameter COUNT to 0 (step S10). Next, the chA focus evaluation value AFV_A and the chB focus evaluation value AFV_B are acquired (steps S12 and S14). Then, the ratio between the focus evaluation value AFV_A for chA and the focus evaluation value AFV_B for chB is obtained, and this value is set as AFV (step S16). That is, AFV = AFV_A / AFV_B.
[0048]
Subsequently, the CPU 30 determines whether or not the condition of AFV = 1 is satisfied (step S18). That is, it is determined whether or not the chA focus evaluation value AFV_A and the chB focus evaluation value AFV_B match, and it is determined whether or not the imaging surface X is in focus. If NO is determined, it is determined whether or not the condition of AFV <1 is satisfied (step S20).
If YES is determined, the focus lens FL is moved in the closest direction because it is in the rear pin state with respect to the imaging surface X (step S22). On the other hand, if NO is determined, the focus lens FL is moved in the direction of infinity because it is in the state of the front pin with respect to the imaging surface X (step S24). After the process of step S22 or step S24, the process returns to step S10 and the above process is repeated.
[0049]
If YES in step S18, that is, if it is determined that the imaging surface X is in focus, the value of the parameter COUNT is increased by 1 (step S26). That is, COUNT = COUNT + 1. Then, it is determined whether or not a condition of COUNT <n is satisfied for a predetermined value n (integer) (step S28). When it determines with YES, it returns to step S12. If YES is determined n times consecutively in step S18, NO is determined in step S28. That is, the in-focus state is maintained for a predetermined time required to determine “YES” in step S18 continuously n times after setting the focus lens FL at a position where the in-focus state with respect to the imaging surface X is set. In that case, NO is determined in step S28. This determination process determines whether the subject is stationary.
[0050]
If NO is determined in step S28, the CPU 30 instructs the focus lens FL to move in the closest direction by an amount corresponding to ½ of the optical path length difference between the imaging surface 20A of the imaging device 20 and the imaging surface 22A of the imaging device 22. (Step S30). Then, it is determined whether or not the movement has ended (step S32). When the focus lens FL moves to a position where it is in focus with respect to the imaging surface 20A, it is determined YES in step S32, and the focus lens FL stops at that position.
[0051]
If YES is determined in step S32, the CPU 30 acquires the chA focus evaluation value AFV_A and the chB focus evaluation value AFV_B (steps S34 and S36). Then, a focus evaluation value ratio AFVR = AFV_A / AFV_B is obtained, and the ratio AFVR is stored (step S38).
[0052]
Subsequently, the CPU 30 acquires the focus evaluation value AFV_A for chA and the focus evaluation value AFV_B for chB (steps S40 and S42), and obtains the ratio AFV = AFV_A / AFV_B (step S44). Then, it is determined whether or not the focus evaluation value ratio AFV obtained in step S44 matches the focus evaluation value ratio AFVR obtained in step S38 (step S46). Thus, it is detected whether or not the subject has changed. When it determines with YES, ie, when it determines with there being no change in a to-be-photographed object, the process from step S40 is repeated. On the other hand, if it is determined NO, that is, if a change occurs in the subject, the process returns to step S10 and is executed again from the first process.
[0053]
In the processing of the above flowchart, when the AFV value obtained in step S44 changes with respect to the AFVR value obtained in step S38, the processing from step S10, that is, the in-focus state with respect to the imaging surface X is performed. The process for controlling the position of the focus lens FL is performed so that the process from step 10 may be performed when the AFV value changes by a predetermined value or more with respect to the AFVR value. If the change amount of the AFV value with respect to the AFVR value is smaller than the predetermined value, the focus lens FL is moved while detecting the AFV value, instead of performing the processing from step S10, and the AFV value is changed. The position of the focus lens FL may be controlled so as to match the value of AFVR.
[0054]
In the above embodiment, the case where the present invention is applied to a television camera system has been described. However, the present invention is not limited to this and can be applied to a system equipped with an autofocus function such as a consumer movie camera.
[0055]
【The invention's effect】
As described above, according to the autofocus system of the present invention, the two imaging surfaces can be focused with high accuracy on the imaging surface that captures the original image without reducing the focusing accuracy. It is possible to increase the difference in the optical path lengths, thereby improving the focus response performance for a moving subject or the like.
[Brief description of the drawings]
FIG. 1 is a diagram showing an overall configuration of a television camera system to which the present invention is applied.
FIG. 2 is a diagram showing imaging surfaces of two imaging elements arranged to acquire a video signal for focus state detection on the same optical axis.
FIG. 3 is a block diagram showing an internal configuration of the lens apparatus.
FIG. 4 is an explanatory diagram used for explaining the principle of detecting a focus state.
FIG. 5 is a graph showing a focus evaluation value when the optical path length difference between two imaging surfaces is small.
6 is a graph showing a focus evaluation value graph when the optical path length difference between two imaging surfaces is larger than that in FIG. 5;
FIG. 7 is a flowchart showing the processing procedure of the CPU of the lens apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Camera body, 12 ... Lens apparatus, 14 ... Shooting lens, 20, 22 ... Imaging element, 24 ... Light splitting optical system, 20A, 22A ... Imaging surface, FL ... Focus lens (group), FM ... Focusing motor, FA: Focus amplifier, 30: CPU, FP: Potentiometer, 50A, 50B ... A / D converter, 52A, 52B ... Digital filter, 54A, 54B ... Gate circuit, 56A, 56B ... Adder circuit

Claims (3)

Light dividing means for dividing subject light incident on the photographing optical system into first subject light and second subject light;
A first imaging surface for capturing an image for reproduction, the first imaging surface capturing the first subject light;
A second imaging surface that images the second subject light, the second imaging surface disposed at a position having an optical path length difference with respect to the first imaging surface;
Based on the video signal obtained by imaging with the first imaging surface and the video signal obtained by imaging with the second imaging surface, the optical path length to the first imaging surface and the first Focus control means for controlling the focus position of the photographing optical system so that the position of the optical path length intermediate to the optical path length to the imaging surface of 2 is the best imaging position;
An autofocus system, comprising: a focus correction unit that corrects a focus position set by the focus control unit so that the position of the first imaging surface is the best imaging position. After the focus correction unit corrects the focus position, a first focus evaluation value for evaluating the contrast level of the image indicated by the video signal is obtained based on the video signal obtained by the first imaging surface; Based on the video signal obtained by the second imaging surface, a second focus evaluation value for evaluating the level of contrast of the image indicated by the video signal is obtained, and the obtained first focus evaluation value and second focus are obtained. A determination means for determining whether or not the re-execution condition is satisfied with a re-execution condition that a ratio with the evaluation value has changed by a predetermined value or more from a value immediately after the correction of the focus position;
The re-execution instructing unit that re-executes control of the focus position by the focus control unit when the determination unit determines that the re-execution condition is satisfied. Autofocus system. When the determination unit determines that the re-execution condition is not satisfied, the ratio between the first focus evaluation value and the second focus evaluation value becomes a value immediately after the correction of the focus position. 3. The autofocus system according to claim 2, further comprising second focus control means for controlling the focus position.

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