JP2005156736A - Auto focus system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a focus evaluation value of appropriate property and to increase AF accuracy and rapidness by changing a low-pass side cut off frequency of an HPF for extracting a signal of high frequency components from a video signal based on the focal distance and the diaphragm value of a photographic lens, in an auto focus system for automatically focusing the photographic lens by introducing a contrast system automatic focusing method. <P>SOLUTION: In the optical path length difference system auto focus system, the HPFs 82A and 82B for extracting the signal of high frequency components from the video signal are arranged in a focus evaluation value forming part 58 for forming the focus evaluation value showing the height of contrast from the video signals obtained from two imaging elements 32A and 32B. The cut off frequency of the HPFs is changed by an instruction signal from a CPU 54, and then, the focus evaluation value of appropriate property can be formed in accordance with the set state of the photographic lens. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an autofocus system, and in particular, contrast type autofocus (hereinafter referred to as AF) that performs automatic focus adjustment of a photographing lens based on a high frequency component of a video signal in contrast type autofocus (hereinafter referred to as AF). ).

  A contrast method is generally used as an AF method employed in a television camera or a video camera. In contrast AF, for example, a high frequency component signal is extracted from a video signal obtained by photographing a subject by a filter (electrical filter), and the contrast of the subject image is increased or decreased based on the high frequency component signal. (Sharpness) is evaluated. Then, the focus (focus lens) position of the photographing lens is controlled so that the evaluation value (referred to as a focus evaluation value in the present specification) is maximized (maximum).

  Further, the focus evaluation value indicates a mountain-shaped distribution in the vicinity of the peak point in a graph (focus position-focus evaluation value graph) representing the relationship with the focus position, and the focus is set as the peak point. A so-called hill-climbing method is generally known in which the focus is moved in a direction in which the evaluation value indicates an increase, and the focus is stopped when the focus evaluation value is switched from an increase to a decrease.

For example, Patent Documents 1 and 2 describe a contrast type AF.
JP 63-74273 A JP-A-3-297282

  By the way, the rate of change in the focus evaluation value with respect to the amount of change in the focus (focus lens) position (referred to as focus sensitivity in this specification) differs depending not only on the subject condition but also on the optical setting state of the photographing lens. For example, a rear focus type photographing lens differs depending on an aperture value, and a front focus type photographing lens with a zoom function differs depending on a focal length and an aperture value. If the aperture value is fixed with the latter photographic lens and the focus is moved in the whole area, the graph curve in the focus position-focus evaluation value graph becomes flatter when the zoom is at the wide side (focal length is shorter). Nearly, the focus sensitivity is low. On the other hand, the closer the telephoto side is (the longer the focal length side), the more the graph curve in the focus position-focus evaluation value graph draws a steep mountain near the peak point, and the focus sensitivity increases. Assuming that the focal length is constant and the focus is moved over the entire area, the graph curve in the focus position-focus evaluation value graph peaks as the aperture becomes closer to the open side (the side where the aperture value (F number) becomes the minimum value). It becomes a curve that draws a steep mountain near the point.

  In general, when the graph curve in the focus position-focus evaluation value graph is almost flat, that is, when the focus sensitivity is low, it is difficult to detect the true best focus position, and the focusing accuracy is low. On the other hand, when the graph curve is steep, that is, when the focus sensitivity is high, when the focus is adjusted to the best focus position, i.e., the peak point of the graph curve, the peak point passes through unless it is slowed down considerably. There is a possibility that the possibility of being too large becomes unstable. If the problem is solved only by slowing down the focus operation speed in order to avoid this, it takes time to focus, and there arises a problem that the tracking performance of AF with respect to a moving object is lowered.

  The present invention has been made in view of such circumstances, and it is possible to acquire a focus evaluation value having a suitable characteristic in accordance with the optical setting state of the photographing lens, thereby improving the accuracy and speed of AF. An object is to provide an auto orcus system.

  In order to achieve the above object, according to the first aspect of the present invention, an image formed by a photographing lens is picked up by an image pickup means, and a high frequency is obtained from an image signal obtained by the image pickup means by an electric filter means. The component signal is extracted, a focus evaluation value for evaluating the contrast level of the image is obtained based on the high frequency component signal, and the focus position of the photographing lens is controlled automatically based on the focus evaluation value. In the auto-focus system that performs focusing with the electric filter means based on the setting state of the photographing lens so that the focus sensitivity indicating the ratio of the change in the focus evaluation value with respect to the change amount in the focus position is appropriate. A filter characteristic adjusting means for changing the cutoff frequency on the low frequency side is provided.

  According to a second aspect of the present invention, in the first aspect of the present invention, the photographing lens includes a zoom function and a diaphragm function, and the filter characteristic adjusting unit is configured to set the photographing lens as a setting state of the photographing lens. A zoom position and an aperture position are detected, and a cutoff frequency on the low frequency side in the electrical filter means is changed based on the detected zoom position and aperture position.

  According to a third aspect of the present invention, in the first aspect of the present invention, the imaging unit includes a plurality of imaging surfaces having different optical path lengths, and the autofocus system is an image formed by the imaging lens. Are picked up by the plurality of image pickup surfaces, a signal of a high frequency component is extracted by the electric filter means from each video signal obtained by picking up the images from each image pickup surface, a focus evaluation value is obtained, and the focus evaluation is performed. It is characterized in that focusing is performed automatically by controlling the focus position of the photographing lens based on the value.

  According to the autofocus system of the present invention, it is preferable that the low-frequency cutoff frequency of the electrical filter means for extracting the high-frequency component signal from the video signal is changed based on the setting state of the photographing lens. Get the focus evaluation value of the characteristic and optimize the focus sensitivity. As a result, the accuracy and speed of AF can be improved.

  Hereinafter, preferred embodiments of an autofocus system according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a block diagram of a television camera system to which an autofocus system according to the present invention is applied. In the figure, a contrast method is used as the AF method, and based on the contrast of a plurality of images (video signals) imaged on a plurality of imaging surfaces (two imaging surfaces in the present embodiment) having different optical path lengths. The configuration in the case of adopting a so-called optical path length difference method for focusing is shown. As shown in the figure, this television camera system is composed of a lens device 10 and a camera main body 12 and the like. The camera main body 12 shoots a broadcast video and outputs or records a predetermined format video signal. An image sensor for recording on a medium (hereinafter referred to as an image sensor for video), a required circuit, and the like are mounted.

  The lens device 10 is detachably attached to the camera body 12 and mainly includes an optical system (photographing lens) and a control system. First, the configuration of the photographing lens will be described. The photographing lens includes a focus lens (group) 16, a zoom lens (group) 18, a diaphragm 20, a relay lens (relay optical) including a front relay lens 22A and a rear relay lens 22B. System) etc. are arranged. A half mirror 24 is arranged between the front relay lens 22A and the rear relay lens 22B of the relay optical system to branch the subject light incident on the photographing lens to the focus state detection optical path.

  The half mirror 24 is installed with an inclination of approximately 45 degrees with respect to the optical axis O of the photographing lens, and a part of the subject light (for example, 1/3 light amount) that has passed through the front relay lens 22A is used for focus state detection. Reflected at right angles as subject light for focus state detection in the optical path.

  The subject light transmitted through the half mirror 24 is emitted from the rear end side of the photographing lens as subject light for video (for subject image acquisition) and then enters the imaging unit 14 of the camera body 12. Although the configuration of the imaging unit 14 is omitted, subject light incident on the imaging unit 14 is separated into, for example, three colors of red light, green light, and blue light by a color separation optical system, and an image pickup device for video for each color. Is incident on the imaging surface. Thereby, a color image for broadcasting is taken. In addition, the focus surface P in the figure indicates the optically equivalent position on the optical axis O of the imaging lens with respect to the imaging surface of each image pickup device.

  On the other hand, the subject light reflected by the half mirror 24 travels along the optical path for focus state detection along the optical axis O ′ perpendicular to the optical axis O as subject light for focus state detection (for AF), and relays. The light is condensed by the lens 26 and enters the focus state detection unit 28.

  The focus state detection unit 28 includes two prisms 30A and 30B constituting a light splitting optical system and a pair of image pickup devices 32A and 32B for focus state detection (hereinafter referred to as focus state detection image pickup devices 32A and 32B). It is configured.

  As described above, the subject light reflected by the half mirror 24 travels along the optical axis O ′ and first enters the first prism 30A. Then, the light is equally divided into reflected light and transmitted light by the half mirror surface M of the first prism 30A. Of these, the reflected light is incident on the imaging surface of one focus state detection image sensor 32A, and the transmitted light is incident on the other focus state detection image sensor 32B. Note that, for example, 1/6 of the total object light incident on the photographing lens is incident on the respective imaging surfaces of the focus state detection imaging elements 32A and 32B.

  FIG. 2 shows the optical axis of the subject light incident on the video image sensor of the camera body 12 and the optical axis of the subject light incident on the pair of focus state detection image sensors 32A and 32B on the same straight line. . As shown in the figure, the optical path length of the subject light incident on one focus state detection image pickup device 32A is set shorter than the optical path length of the subject light incident on the other focus state detection image pickup device 32B. The optical path length of the subject light incident on the image pickup surface (focus plane P) of the image pickup device is set to be an intermediate length. That is, the pair of focus state detection image pickup devices 32A and 32B (the image pickup surfaces thereof) are respectively disposed at positions equidistant (d) in the front-rear direction from the image pickup surface (focus surface P) of the image pickup device.

  Therefore, the subject light for focus state detection branched by the half mirror 24 is equidistant from the image pickup surface (focus surface P) of the image pickup device for video by the pair of focus state detection image pickup devices 32A and 32B. Imaged at position. The focus state detection imaging elements 32A and 32B acquire a video signal for focus state detection (autofocus control) as will be described later, and do not need to capture a color image. In this embodiment, it is assumed that the CCD is for capturing a black and white image.

  Next, a control system related to AF control in the lens apparatus 10 will be described. FIG. 3 is a block diagram showing a configuration of a control system related to focus control. The focus lens 16 is connected to a focus motor 50 as shown in FIG. 3, and when the focus motor 50 is driven, the focus lens 16 moves in the optical axis direction and the focus of the photographing lens is changed. The focus motor 50 is supplied with a drive voltage from the focus motor drive circuit 52, and the focus motor drive circuit 52 is supplied with a control signal from the CPU 54.

  The control signal from the CPU 54 indicates, for example, a voltage value corresponding to the rotational speed of the focus motor 50, that is, the moving speed (focus instruction speed) of the focus lens 16, and the voltage value is given to the focus motor drive circuit 52. Then, the voltage is applied to the focus motor 50 as a drive voltage by the focus motor drive circuit 52. Thereby, the rotation speed of the focus motor 50 is controlled by the CPU 54.

  Further, a focus position signal having a value corresponding to the current position of the focus lens 16 is supplied from the focus lens position detector 56 to the CPU 54. Therefore, in the process of the CPU 54, the moving speed of the focus lens 16 can be controlled to a desired speed by controlling the rotation speed of the focus motor 50 as described above. By controlling the rotational speed of the focus motor 50 while acquiring the focus position signal, the set position of the focus lens 16 can be controlled to a desired position.

  The focus control can be switched to manual focus control by a predetermined switch (not shown). In the case of manual focus control, a command signal from a focus demand or the like is given to the CPU 54 in accordance with the manual operation of the operator. Based on the command signal, the position of the focus lens 16 is controlled as described above.

  On the other hand, an image (video) captured by the pair of focus state detection imaging elements 32A and 32B is a video signal for sequentially transmitting pixel values along a plurality of scanning lines (horizontal lines) constituting one screen. And output to the focus evaluation value generation unit 58. The configuration and processing of the focus evaluation value generation unit 58 will be described later. In the focus evaluation value generation unit 58, each focus state detection image pickup device 32A is obtained from the video signals obtained by the focus state detection image pickup devices 32A and 32B. , 32B, a focus evaluation value indicating the level of contrast (sharpness) of each image is generated, and the generated focus evaluation value is given to the CPU. The focus evaluation value generated based on the video signal from the focus state detection image sensor 32A is referred to as a focus evaluation value of channel A (chA), and is based on the video signal from the focus state detection image sensor 32B. The generated focus evaluation value is referred to as a focus evaluation value of channel B (chB).

  As will be described in detail later, the CPU 54 acquires the chA and chB focus evaluation values from the focus evaluation value generation unit 58, and focuses the focus state of the photographing lens based on the acquired focus evaluation values. The lens 16 is controlled.

  Here, the configuration and processing of the focus evaluation value generation unit 58 will be described. As shown in FIG. 4, the video signals output from the focus state detection imaging devices 32A and 32B are respectively input to the A / D converters 80A and 80B of the focus evaluation value generation unit 58 and converted into digital signals. The The focus state detection image pickup devices 32A and 32B are both CCDs that capture black and white images, and the video signals output from the focus state detection image pickup devices 32A and 32B correspond to the respective pixels constituting each screen. This is a luminance signal indicating the luminance value.

  The video signals converted into digital signals by the A / D converters 80A and 80B are then input to high-pass filters (HPF) 82A and 82B, and high-frequency components included in the video signals are extracted by the HPFs 82A and 82B. Is done. The high frequency component signals extracted by the HPFs 82A and 82B are input to the gate circuits 84A and 84B.

  From the signals of the high frequency components input to the gate circuits 84A and 84B, only signals in a range corresponding to pixels in a predetermined focus area (for example, the center of the screen) on the screen are extracted. 86B. Then, one field (or one frame) is added by the addition circuits 86A and 86B. As a result, the sum of the signal values in the focus area among the signals of the high frequency components extracted from the video signals by the HPFs 82A and 82B is obtained. The values obtained by the adder circuits 86A and 86B are focus evaluation values indicating the level of image contrast (sharpness) in the focus area, and the focus evaluation value obtained by the adder circuit 86A is the channel A (chA). As the focus evaluation value, the focus evaluation value obtained by the adding circuit 86B is given to the CPU 54 as the focus evaluation value of channel B (chB).

  Next, focus state detection and focus (focus lens 16) control based on the focus evaluation value will be described. By acquiring the chA and chB focus evaluation values from the focus evaluation value generation unit 58 as described above, it is possible to detect the current focus state of the photographic lens with respect to the image pickup surface (focus surface P) of the image pickup device for video. .

  FIG. 5 shows the position of the focus lens 16 (focus position) on the horizontal axis and the focus evaluation value on the vertical axis, and the focus position showing the relationship between the focus position and the focus evaluation value when a certain subject is photographed. -Focus evaluation value graph. A curve C indicated by a dotted line in the figure indicates a focus evaluation value when it is assumed that a focus evaluation value is obtained from a video signal from a video image sensor (or an image sensor arranged at a conjugate position with the video image sensor). The curves A and B indicated by the solid line in the figure indicate the focus evaluation values of chA and chB obtained from the focus state detection imaging elements 32A and 32B, respectively, with respect to the focus position. Is. In the figure, the position F3 at which the focus evaluation value of the curve C is maximum (maximum) is the in-focus position.

  When the focus position of the photographing lens is set to F1 in the figure, the chA focus evaluation value FVA1 corresponds to the position F1 of the curve A, and the chB focus evaluation value FVB1 corresponds to the position F1 of the curve B. The value to be In this case, the chA focus evaluation value FVA1 is larger than the chB focus evaluation value FVB1, and accordingly, the focus position is set closer to the in-focus position (F3), that is, It can be seen that this is the state of the front pin.

  On the other hand, when the focus position of the photographing lens is set to F2 in the figure, the chA focus evaluation value FVA2 is a value corresponding to the position F2 of the curve A, and the chB focus evaluation value FVB2 is the position F2 of the curve B. The value corresponding to. In this case, the chA focus evaluation value FVA2 is smaller than the chB focus evaluation value FVB2, and therefore, the focus position is set to the infinity side from the in-focus position (F3). That is, it can be seen that the rear pin is in the state.

  On the other hand, when the focus position of the photographing lens is set to F3, that is, the in-focus position, the chA focus evaluation value FVA3 is a value corresponding to the position F3 of the curve A, and the chB focus evaluation value FVB3 is The value corresponds to the position F3 of the curve B. At this time, the chA focus evaluation value FVA3 and the chB focus evaluation value FVB3 are equal to each other, which indicates that the focus position is set to the in-focus position (F3).

  As described above, it is possible to detect whether the current focus state of the photographing lens is the front pin, the rear pin, or the in-focus state based on the focus evaluation values of chA and chB obtained from the focus evaluation value generation unit 58. it can.

  Therefore, the focus lens 16 can be moved to the in-focus position by controlling the position of the focus lens 16 based on the chA and chB focus evaluation values obtained from the focus evaluation value generation unit 58. That is, when the focus evaluation values of chA and chB are determined to be the front pins, the focus lens 16 is moved in the infinity direction, and when the focus evaluation values are determined to be the rear pins, When the focus lens 16 is moved in the closest direction and the focus lens 16 is determined to be in focus, the focus lens 16 can be moved to the focus position by stopping the focus lens 16 at that position. it can.

Therefore, the CPU 54 controls the focus lens 16 as follows based on the focus evaluation values of chA and chB. First, assuming that the focus evaluation value of chA acquired from the focus evaluation value generation unit 58 is FVA, and the focus evaluation value of chB is FVB, the state of the front pin when FVA> FVB (when FVA / FVB> 1). Therefore, the drive direction of the focus lens 16 is set to infinity, and the moving speed (focus instruction speed) CV of the focus lens 16 is expressed by the following equation (1):
CV = k * (FVA / FVB-1) (1)
Set by. However, the coefficient k is a predetermined constant described later. On the other hand, in the case of FVA <FVB (in the case of FVA / FVB <1), the rear pin is in the state, so that the driving direction of the focus lens 16 is set to the closest direction, and the moving speed CV of the focus lens 16 is set to the following. Formula (2),
CV = k * (FVB / FVA-1) (2)
Set by. However, the coefficient k in the equation (2) shows the same value as the coefficient k in the equation (1). When FVA = FVB (FVA / FVB = 1), the focus lens 16 is set to 0 (stop) because it is in focus.

In this embodiment, the specific method for obtaining the moving speed CV of the focus lens 16 is first to obtain the ratio R = FVA / FVB of the focus evaluation values of chA and chB, and the ratio R is smaller than 1 (R < 1) Determine whether or not. If this condition is satisfied, the reciprocal of the focus evaluation value ratio R is reset to the value of R (that is, R = 1 / R). If the above condition is not satisfied, the value R of the focus evaluation value is left as it is. Using the focus evaluation value ratio R, the moving speed CV of the focus lens 16 is expressed by the following equation (3):
CV = k * (R-1) (3)
Ask for. Note that when FVA = FVB, R = 1, so CV = 0 according to the above equation.

  The CPU 54 acquires the focus evaluation values FVA and FVB for chA and chB, and sets the movement direction and the movement speed CV of the focus lens 16 as described above based on the focus evaluation values FVA and FVB. A control signal for driving the focus lens 16 at the moving speed CV is output to the focus motor drive circuit 52 of FIG. Then, by repeatedly executing this process, the focus of the taking lens is set to the in-focus state.

  Next, switching of the cutoff frequency of the HPFs 82A and 82B (see FIG. 4) for extracting high frequency components from the video signals obtained by the focus state detection imaging elements 32A and 32B in the focus evaluation value generation unit 58. explain. Each of the HPFs 82A and 82B has a frequency characteristic as shown in FIG. 6, and among the video signals passing through the HPFs 82A and 82B, a signal having a lower frequency component than the cutoff frequency fc is cut off (cut-off frequency). The characteristic is such that a signal having a frequency component higher than fc passes.

  The HPFs 82A and 82B are electrical filters whose frequency characteristics can be changed by changing setting parameters, such as digital filters, for example. The cutoff frequency fc of these HPFs 82A and 82B is an instruction signal (parameter of the parameter). It can be set and changed to a desired value by an instruction or the like). The CPU 54 switches the cutoff frequency fc of the HPFs 82A and 82B among, for example, three values of fc0, fc1, and fc2 (fc1 <fc0 <fc2). Further, the CPU 54 obtains detection signals from the zoom lens position detector 100 and the aperture position detector 102 for detecting the positions of the zoom lens and the diaphragm of the photographing lens shown in FIG. 3, and based on these detection signals. It is determined which value of fc0, fc1, and fc2 is set as the cutoff frequency fc of the HPFs 82A and 82B. That is, the value of the cut-off frequency fc is switched among the above three values according to the focal length (zoom magnification) and the aperture value (F number) of the photographing lens determined by the position of the zoom lens and the aperture (the value of the detection signal). . Of the three values fc0, fc1, and fc2 set as the value of the cut-off frequency fc, fc0 is a reference value indicating a standard value.

  Here, if the focus lens is moved from the closest end to the infinity end with the cutoff frequency fc of the HPFs 82A and 82B set to the reference value fc0, the chA and chB generated by the focus evaluation value generation unit 58 The focus evaluation value is generally represented by a graph curve having a shape as shown in the focus position-focus evaluation value graphs of FIGS. FIGS. 7A and 7B show only one of the graphs of the focus evaluation values of chA and chB having substantially the same shape (the same applies to FIG. 8 described below). FIG. 7A shows a case where the focal length of the taking lens is long (in the case of a long focal length), and the graph curve becomes a steep mountain-shaped curve near the peak point, and the focal point with respect to the change amount of the focus lens. Focus sensitivity indicating the rate of change of the evaluation value is increased. On the other hand, FIG. 7B shows a case where the focal length of the photographing lens is short (in the case of a short focal length), the graph curve becomes nearly flat, and the focus sensitivity becomes low. Similarly, when the aperture value (F number) is different from the focal length, the smaller the F number, the sharper the graph curve becomes as shown in FIG. 7A, and the focus sensitivity becomes higher. As the value increases, the graph curve becomes almost flat as shown in FIG. 7B, and the focus sensitivity decreases.

The focus sensitivity (slope of the graph curve) near the peak point (best focus position) of the graph curve is generally proportional to the square of the focal length (zoom magnification) and increases in inverse proportion to the F number,
(Focus sensitivity) = C * (Zoom magnification) ^ 2 / (F number): (C is a constant) (4)
The focus sensitivity can be expressed quantitatively by the following formula. Although the focus sensitivity varies depending on the subject conditions, the constant C is fixed to an appropriate value assuming that the subject conditions are constant, and the focus sensitivity is evaluated by the above equation (4). It is possible to determine whether the focus sensitivity is likely to be high or low.

  On the other hand, if the cut-off frequency fc of the HPFs 82A and 82B is switched between, for example, fc1 and fc2 and the focus lens is moved from the closest end to the infinity end with the focal length of the photographing lens constant, the focal points of chA and chB The evaluation value is generally represented by a graph curve having a shape as shown in the focus position-focus evaluation value graphs of FIGS. FIG. 8A shows a case where the cutoff frequency of the HPFs 82A and 82B is a high frequency fc2, and the graph curve becomes a steep mountain-shaped curve near the peak point, and the focus sensitivity is increased. On the other hand, FIG. 8B shows a case where the cutoff frequency of the HPFs 82A and 82B is a low frequency fc1, and the graph curve becomes nearly flat and the focus sensitivity is low.

  Therefore, the CPU 54 is set on the condition that the focus sensitivity tends to be high at the current focal length or (zoom magnification) and aperture value (F number) of the photographing lens when the cutoff frequency fc of the HPFs 82A and 82B is set to the reference value fc0. When it is determined that there is, for example, when the value of the above equation (4) is larger than the predetermined threshold value SH, the cutoff frequency fc of the HPFs 82A and 82B is set to fc1 having a value smaller than the reference value fc0. This prevents a problem that the focus sensitivity becomes too high.

  On the other hand, when the cutoff frequency fc of the HPFs 82A and 82B is set to the reference value fc0, it is determined that the focus sensitivity or the aperture value (F number) of the current photographing lens tends to be low. In this case, for example, when the value of the above equation (4) is smaller than the predetermined threshold value SL (<SH), the cutoff frequency fc of the HPFs 82A and 82B is set to fc2 having a value larger than the reference value fc0. This prevents a problem that the focus sensitivity is too low.

  When none of the above conditions is satisfied, for example, when the value of the above equation (4) is not less than the threshold value SL and not more than the threshold value SH, the cutoff frequencies fc of the HPFs 82A and 82B are set. The reference value is fc0.

  As described above, by changing the cutoff frequency fc of the HPFs 82A and 82B, an appropriate focus sensitivity can be obtained.

  In the above embodiment, the cutoff frequencies fc of the HPFs 82A and 82B are switched at three levels. However, the cutoff frequency fc is further set according to the focus sensitivity value calculated by the above equation (4). It may be switched at many levels (or continuous values), or may be switched at two levels.

  In the above embodiment, the focus sensitivity is calculated by the above formula (4) as an example, but the focus sensitivity may be calculated by using another formula, or the focus sensitivity is calculated. Instead of setting the value of the cut-off frequency fc, the cut-off frequency fc is referred to by referring to table data stored in advance in the memory as the value of the cut-off frequency fc to be set for the positions of the zoom lens and the stop. May be set.

  In the above embodiment, the high pass filter (HPF 82A, 82B) is used as an electrical filter for extracting high frequency components from the video signals obtained by the focus state detection image pickup devices 32A, 32B. A filter (BPF) may be used, and even in this case, appropriate focus sensitivity can be obtained by changing the low-frequency cutoff frequency of the BPF as in the above embodiment.

  In the above embodiment, the cutoff frequency is changed using an electrical filter that can change the cutoff frequency by changing the value of the setting parameter in the HPFs 82A and 82B, such as a digital filter. Not limited to this, a plurality of HPFs having different cutoff frequencies may be combined, and the weighting of the filter processing of each HPF may be changed.

  In the above-described embodiment, the case where the front focus type photographing lens in which the focus lens 16 is disposed on the front side of the optical system is used has been described. For example, the rear focus type in which the focus lens is disposed on the rear side of the optical system. When the photographic lens is used, the focus sensitivity is not significantly affected by the position of the zoom lens and changes only to the aperture value. Therefore, the cutoff frequencies of the HPFs 82A and 82B may be changed based only on the aperture value. .

  In the above-described embodiment, the case where the present invention is applied to the so-called optical path length difference type autofocus has been described. However, the contrast type autofocus (for example, one optical path length difference method) is generally used instead of the optical path length difference method. The present invention can also be applied to an AF method in which a focus evaluation value is acquired from a video signal imaged on an imaging surface and the focus is controlled so that the focus evaluation value is maximized (maximum).

  Further, although cases have been described with the above embodiment as examples where the present invention is applied to a television camera system, the present invention is not limited thereto, and can also be applied to a video camera and a still camera for capturing a still image. .

FIG. 1 is a block diagram of a television camera system to which an autofocus system according to the present invention is applied. FIG. 2 is a diagram in which the optical axis of the subject light incident on the image pickup device for the image and the optical axis of the subject light incident on the pair of focus state detection image pickup devices are displayed on the same straight line. FIG. 3 is a block diagram illustrating a configuration of a control system of the lens apparatus related to the focus control. FIG. 4 is a block diagram illustrating a configuration of the focus evaluation value generation unit. FIG. 5 is a diagram illustrating the state of the focus evaluation value with respect to the focus position when a certain subject is photographed, with the focus position of the photographing lens on the horizontal axis and the focus evaluation value on the vertical axis. FIG. 6 is a diagram showing frequency characteristics of HPF. FIGS. 7A and 7B are views showing differences in focus evaluation values due to differences in focal length (or aperture value) of the photographing lens. FIGS. 8A and 8B are diagrams showing differences in focus evaluation values due to differences in the cutoff frequency of HPF.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Lens apparatus, 12 ... Camera body, 14 ... Imaging part, 16 ... Focus lens (group), 18 ... Zoom lens (group), 20 ... Aperture, 22A ... Front side relay lens, 22B ... Rear side relay lens, 24 ... Half mirror, 26 ... relay lens, 28 ... focus state detection unit, 32A, 32B ... focus state detection imaging device, 50 ... focus motor, 52 ... focus motor drive circuit, 54 ... CPU, 56 ... focus lens position detector, 58: Focus evaluation value generator, 80A, 80B ... A / D converter, 82A, 82B ... High pass filter (HPF), 84A, 84B ... Gate circuit, 86A, 86B ... Adder circuit, 100 ... Zoom lens position detector, 102: Aperture position detector

Claims (3)

An image formed by the photographing lens is picked up by the image pickup means, a high frequency component signal is extracted from the video signal obtained by the image pickup means by an electric filter means, and based on the high frequency component signal In an autofocus system that obtains a focus evaluation value for evaluating the level of contrast of the image and automatically adjusts the focus position of the photographing lens based on the focus evaluation value,
The cut-off frequency on the low frequency side in the electrical filter means is changed based on the setting state of the photographing lens so that the focus sensitivity indicating the ratio of the change in the focus evaluation value to the change amount in the focus position is appropriate. An autofocus system comprising a filter characteristic adjusting means. The photographing lens has a zoom function and a diaphragm function, and the filter characteristic adjusting unit detects a zoom position and a diaphragm position of the photographing lens as a setting state of the photographing lens, and based on the detected zoom position and diaphragm position. 2. The autofocus system according to claim 1, wherein a cutoff frequency on a low frequency side in the electrical filter means is changed. The imaging means includes a plurality of imaging surfaces having different optical path lengths, and the autofocus system is obtained by imaging an image formed by the imaging lens with the plurality of imaging surfaces and imaging with each imaging surface. A focus evaluation value is obtained by extracting a signal of a high frequency component from each video signal by the electric filter means, and the focus position of the photographing lens is controlled based on the focus evaluation value to automatically focus. The autofocus system according to claim 1.

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