JP4819930B2 - Autofocus device for taking lens - Google Patents

Description

The present invention relates to autofocus device of the photographing lens to perform focus detection in autofocus control of the autofocus device relates to, in particular taking lens of the taking lens.

  In general, autofocus for a video camera or the like is based on a contrast method. In this contrast method, a high frequency component of a video signal within a certain range (focus area) of video signals (luminance signals) obtained from an image sensor is integrated to obtain a focus evaluation value. Then, the focus adjustment is automatically performed so that the focus evaluation value is maximized. Thus, it is possible to obtain the best focus (focusing) that maximizes the sharpness (image contrast) of the image captured by the image sensor.

  Conventionally, a method for detecting the focus state (front pin, rear pin, in-focus) of a photographic lens using a plurality of image sensors having different optical path lengths has been proposed (Japanese Patent Laid-Open No. 55-76312). No. 7-60211). For example, two focus state detection image sensors that capture an image in the same shooting range with respect to an image sensor that captures an image for video (video image sensor) each have an optical path length longer than that of the image sensor for video. Place it at a position that is shorter than the position. Based on the high frequency components of the video signal obtained from these focus state detection image sensors, the focus evaluation values for the respective imaging surfaces of the focus state detection image elements are obtained and compared in the same manner as described above. As a result, the focus state on the image pickup surface of the image pickup device for the image, that is, the front pin, the rear pin, or the in-focus state is detected from the magnitude relationship between the focus evaluation values. Such a focus state detection method can be applied to focus detection for autofocusing.

JP-A-55-76312 Japanese Patent Publication No. 7-60211

  By the way, in the focus state detection in the contrast method as described above, if the luminance signal is saturated when a high-luminance subject is photographed, an accurate focus evaluation value cannot be obtained, and thus the focus state is erroneously detected. It is known to cause an autofocus malfunction. In particular, when the focus state of the photographic lens is detected using an image pickup device other than the image pickup device as described above, the ND filter can be used only for the image pickup device. Instead, the possibility that the luminance signal obtained from the focus state detection image sensor is saturated further increases. For this reason, it is necessary to provide a saturation prevention means that does not cause saturation in the video signal of the focus state detection imaging device.

The present invention has been made in view of such circumstances, and in an apparatus for detecting a focus state using a plurality of focus state detection image sensors different from an image sensor for video, the focus state at the time of shooting a high-luminance subject is detected. An object of the present invention is to provide an autofocus device for a photographing lens that can prevent erroneous detection.

In order to achieve the object, the invention according to claim 1, a light dividing unit that divides subject light incident on a photographing lens, and an image for video out of the light divided by the light dividing unit. Three image pickup devices for picking up an image for focus state detection with light different from the light incident on the image pickup device to be detected, and three focus state detections arranged at different optical path lengths from each other and use the image pickup device, a focus evaluation value detection means for detecting a focus evaluation value indicating the degree of the sharpness of the image based on the high frequency component of one screen of the luminance signal obtained from each focus state detecting device The three focus evaluation values detected by the focus evaluation value detection unit corresponding to each of the focus state detection imaging elements are set as focus evaluation values at three different points related to the focus position of the photographing lens. Focus on Based on the value, a curve indicating the relationship between the focus position of the photographing lens and the focus evaluation value is obtained using a predetermined function, and the focus position where the focus evaluation value is maximized by the curve is detected as the focus position. Position detection means, focus control means for controlling the focus lens of the photographic lens so that the focus position of the photographic lens is the focus position detected by the focus position detection means, and each focus state detection imaging A maximum level luminance signal detecting means for acquiring a luminance signal for one screen from the element and detecting a luminance signal having the largest value among the acquired three luminance signals as a maximum level luminance signal; Based on the luminance signal at the maximum level detected by the signal detection means, determine a gain at an appropriate level that does not saturate the luminance signal, The determined gain is characterized by comprising a gain setting means for setting a gain in generating the luminance signal output from each focus state detecting device.

The invention described in Claim 2, a light dividing means which divides the subject light incident on the taking lens, of the divided light by the light splitting means, the image pickup device for capturing an image of the video Three image pickup devices for picking up an image for focus state detection with light different from incident light , the three image pickup devices for focus state detection arranged at positions having different optical path lengths ; Focus evaluation value detection means for detecting a focus evaluation value indicating the level of sharpness of an image based on a high frequency component of a luminance signal for one screen obtained from each focus state detection imaging device, and the focus evaluation value detection The three focus evaluation values detected by the means corresponding to the respective focus state detection image pickup elements are set as focus evaluation values at three different points related to the focus position of the photographing lens, and the focus evaluation values at the three points are obtained. Based on before A focus position detection unit that obtains a curve indicating a relationship between a focus position of the photographing lens and a focus evaluation value using a predetermined function, and detects a focus position at which the focus evaluation value is maximized by the curve as a focus position; Focus control means for controlling the focus lens of the photographic lens so that the focus position of the photographic lens is the in-focus position detected by the focus position detection means, and each focus state detection image sensor for one screen. A luminance signal is acquired, and a maximum level luminance signal detecting unit that detects a luminance signal having the largest value among the acquired three luminance signals as a maximum level luminance signal, and detected by the maximum level luminance signal detecting unit And determining the charge accumulation time at which the luminance signal is at an appropriate level that does not saturate based on the maximum luminance signal It is characterized in that the product time and a charge accumulation time setting means for setting a charge accumulation time in each focus state detecting device.

According to a third aspect of the present invention, in the first aspect of the present invention, the gain setting means has a maximum threshold value of the maximum level luminance signal detected by the maximum level luminance signal detection means. A maximum gain that falls within a range that does not exceed the value is determined as a gain that provides an appropriate level that does not saturate the luminance signal .

According to a fourth aspect of the present invention, in the second aspect of the present invention, the gain setting means has a maximum threshold value of the maximum level luminance signal detected by the maximum level luminance signal detection means. The longest charge accumulation time that does not exceed the value is determined as the charge accumulation time at which the luminance signal is at an appropriate level that does not saturate .
Further, in the invention described in claim 5, in the invention described in claim 1 or 2, whether or not the instantaneous value of the maximum level luminance signal detected by the maximum level luminance signal detecting means has reached a saturation level. The focus evaluation value detection means includes a focus evaluation value based on a high frequency component of a luminance signal in a range excluding pixels corresponding to an instantaneous value that has reached a saturation level by the saturation detection means. It is characterized by detecting.

  According to the present invention, the luminance signal gain obtained from each focus state detection image sensor or the charge accumulation time of each focus state detection image sensor is adjusted independently of the video image sensor to obtain the luminance signal. Is prevented from being saturated, so that erroneous detection of the focus state can be prevented even when a high-luminance subject is photographed. Also, when the focus state detection according to the present invention is used for autofocus control, It is possible to prevent a focus malfunction.

As described above, according to the autofocus device for a photographing lens according to the present invention, the gain of the luminance signal obtained from each focus state detection image sensor, or the charge accumulation time of each focus state detection image sensor, adjusted independently of the video imaging device, since the luminance signal is to be prevented from being saturated, it is possible to prevent erroneous detection of the focus state even when photographing a high-luminance subject, also malfunction Oh over autofocus Can be prevented.

FIG. 1 is a configuration diagram showing a configuration of a focus state detection device according to the present invention applied to a photographing lens used in a television camera system. FIG. 2 is a configuration diagram illustrating a configuration of an imaging unit for focus state detection. FIG. 3 is a diagram showing the image pickup devices A, B, and C for focus state detection on the same optical axis. FIG. 4 is a block diagram illustrating a configuration of a signal processing unit that performs focus state detection processing. FIG. 5 is a diagram showing the state of the luminance signal and its high frequency component in a focused state when shooting a subject whose luminance signal is not saturated. FIG. 6 is a diagram showing the state of the luminance signal and its high frequency component in the out-of-focus state when photographing a subject whose luminance signal does not saturate. FIG. 7 is a diagram illustrating the state of the luminance signal and its high frequency components in a focused state when shooting a high-luminance subject in which the luminance signal is saturated. FIG. 8 is a diagram showing the state of the luminance signal and its high frequency component in the out-of-focus state when shooting a high-luminance subject in which the luminance signal is saturated. FIG. 9 is a diagram illustrating a state of a focus evaluation value in each focus state detection image sensor with respect to a focus position when a certain subject is photographed. FIG. 10 is an explanatory diagram used for explaining processing of focus state detection by three focus state detection image sensors.

Hereinafter, preferred embodiments of an autofocus device for a taking lens according to the present invention will be described in detail according to the accompanying drawings.

  FIG. 1 is a configuration diagram showing a configuration of a focus state detection apparatus according to the present invention applied to a photographic lens used in a television camera system, for example. The TV camera system shown in FIG. 1 includes a photographic lens 12 that can be exchanged with a camera body 10, and the camera body 10 shoots a video for broadcasting and outputs a video signal in a predetermined format or records it on a recording medium. For this purpose, an image pickup device (image pickup device for video) and necessary circuits are incorporated. On the other hand, the photographic lens 12 is detachably attached to the front side of the camera body 10, and the optical system of the photographic lens 12 has a fixed focus lens F ′, a movable focus lens F, a variable focus lens F from the front end side as is well known. A zoom lens Z composed of a magnification system and a correction system, an iris I, a relay lens (relay optical system) composed of a front relay lens R1 and a rear relay lens R2, and the like are disposed. Note that the configuration of each lens in the drawing is simplified, and there is a lens group including a plurality of lenses shown as one lens.

  Further, as shown in the figure, the optical path of the subject light between the front relay lens R1 and the rear relay lens R2 of the relay optical system is inclined at about 45 degrees with respect to the optical axis O of the photographing lens 12, A half mirror 24 that divides subject light (light beam) into transmitted light and reflected light is disposed.

  Of the subject light incident from the front end side of the photographing lens 12, the transmitted light that has passed through the half mirror 24, that is, the subject light for video, is emitted from the rear end side of the photographing lens 12 and is applied to the imaging unit 20 of the camera body 10. Incident. Although the configuration of the imaging unit 20 is omitted, the subject light incident on the imaging unit 20 is separated into, for example, three colors of red light, green light, and blue light by a color separation optical system, and an image sensor (video) for each color. Is incident on the imaging surface of the imaging device. As a result, a color image for broadcasting is taken. In addition, the focus surface 22 in the drawing shows the optically equivalent position on the optical axis O of the photographing lens 12 with respect to the image pickup surface of each image pickup device.

  On the other hand, the reflected light reflected by the half mirror 24, that is, the subject light for focus state detection, is an image pickup unit 26 for focus state detection along an optical axis O ′ substantially perpendicular to the optical axis O of the photographing lens 12. Led to. Here, between the front relay lens R1 and the rear relay lens R2, the subject light is in a substantially parallel light state, and the subject light reflected by the half mirror 24 is condensed with the same character as the rear relay lens R2. Is incident on the imaging unit 26 for detecting the focus state.

  FIG. 2 is a configuration diagram illustrating the configuration of the imaging unit 26. As shown in the figure, the image pickup unit 26 includes three prisms P1, P2, and P3 constituting a light splitting optical system and three image pickup elements (two-dimensional CCDs) A, B, and C for detecting a focus state. . As described above, the subject light reflected by the half mirror 24 and traveling along the optical axis O ′ first enters the first prism P1, and is reflected and transmitted by the half mirror surface 40 of the first prism P1. Divided. Of these, the reflected light is incident on the imaging surface of the imaging device C. On the other hand, the transmitted light then enters the second prism P2, and is further divided into reflected light and transmitted light by the half mirror surface 42 of the second prism P2. Of these, the reflected light is incident on the image sensor B. On the other hand, the transmitted light passes through the third prism P3 and enters the image sensor A. The subject light is divided by the half mirror surface 40 of the first prism P1 and the half mirror surface 42 of the second prism P2 so that the amount of subject light incident on each of the image sensors A, B, and C is equal. Further, these image pickup devices A, B, and C for detecting the focus state are CCDs that pick up black and white images in the present embodiment.

  When the optical axes of the subject light incident on the image sensors A, B, and C (optical axes of the respective image sensors) are shown on the same straight line, as shown in FIG. 3, until the light enters the image sensors A, B, and C. The optical path length of the image sensor B is the shortest, the optical path length of the image sensor C is the longest, and the optical path length of the image sensor A is an intermediate length between the optical path lengths of the image sensor B and the image sensor C. It has become. In other words, the imaging surfaces of the imaging device B and the imaging device C are arranged in parallel at positions equidistant from the imaging surface of the imaging device A. The image pickup surface of the image pickup device A has a conjugate relationship with the focus surface 22 (see FIG. 1) of the camera body 10, and the optical path length with respect to the subject light incident on the photographing lens 12 is that of the image pickup device for the image of the camera body 10. It matches the imaging surface. The light splitting optical system that splits the subject light into the image sensors A, B, and C is not limited to the configuration using the prisms P1 to P3 as described above.

  With the optical system configured as described above, the subject light incident on the photographic lens 12 is arranged in the vicinity of the position conjugate with the focus surface 22 of the camera body 10 and is used for imaging for detecting three focus states having different optical path lengths. Images are taken by the elements A, B, and C.

  Next, the outline of the auto focus control based on the focus state detection will be described. As shown in FIG. 1, the images captured by the three image sensors A, B, and C of the image capturing unit 26 for the focus state detection are signals. The data is taken into the processing unit 28. As will be described later, the signal processing unit 28 determines that the focus state of the photographic lens 12 is in focus with respect to the focus surface 22 of the camera body 10 based on the high frequency components of the images acquired from the image sensors A, B, and C. The position (focus position) of the focus lens F is obtained. Then, a control signal for instructing movement of the focus lens F to the focus position is output to the focus motor drive circuit 30. The focus motor drive circuit 30 drives a focus motor (not shown), moves the focus lens F via a power transmission mechanism 32 such as a gear, and sets the focus lens F to a focus position instructed by the signal processing unit 28. . By performing such processing continuously, autofocus control is performed.

  Next, the configuration of the signal processing unit 28 and the focus state detection process will be described. FIG. 4 is a block diagram showing the configuration of the signal processing unit 28. As shown in the figure, the image of the subject imaged by each of the image pickup devices A, B, and C for focus state detection is output as a video signal of a predetermined format, and the image pickup devices A, B, and C are similarly configured. High-pass filters 50, 60, 70, A / D converters 52, 62, 72, gate circuits 54, 64, 74, and adders 56, 66, 76 indicate image sharpness (image contrast). It is converted into a focus evaluation value signal and input to the CPU 86. The processing up to obtaining the focus evaluation value will be described with a circuit provided for the image sensor A. Since the image sensor A in the present embodiment is a CCD that captures a black and white image, the video output from the image sensor A is displayed. The signal is output as a luminance signal indicating the luminance of each pixel constituting the screen. The luminance signal output from the image sensor A is first input to a high pass filter (HPF) 50, and a high frequency component of the luminance signal is extracted. The high frequency component signal extracted by the HPF 50 is converted into a digital signal by the A / D converter 52. The gate circuit 54 extracts only the digital signal corresponding to the pixels in a predetermined focus area (for example, the central portion of the screen) from the digital signals for one screen (one field) of the image captured by the image sensor A. After that, the value of the digital signal in the extracted range is added by the adder 56. Thereby, the sum total of the values of the high frequency components of the luminance signal in the focus area is obtained. The value obtained by the adder 56 is a focus evaluation value indicating the level of image sharpness in the focus area.

  Further, the signal processing unit 28 includes a maximum level detection circuit 80 and an auto gain control (AGC) circuit 82 for preventing saturation of luminance signals from the image sensors A, B, and C as shown in FIG. A saturation detection circuit 84 is installed. Here, the problem in the case where the luminance signal is saturated will be described. FIGS. 5 and 6 show the state of the luminance signal and the high-frequency component when photographing a subject whose luminance signal does not saturate. FIG. 7 and FIG. 8 are diagrams showing the state of the luminance signal and its high frequency components when shooting a high luminance subject in which the luminance signal is saturated. As shown in FIGS. 5A and 6A, when there is a subject whose focus state is to be detected in the screen, the subject is in focus with respect to the image sensor (eg, image sensor A). Sometimes, the luminance signal output from the image sensor sharply changes in the contour portion of the subject as shown in FIG. And the high frequency component (absolute value) shows a high value as shown in FIG. On the other hand, when in the out-of-focus state, the luminance signal changes more slowly than in the in-focus state at the contour portion of the subject as shown in FIG. A low value is shown as in FIG. Therefore, the focus evaluation value obtained in this case is appropriate because it shows the maximum value in the focused state.

  On the other hand, as shown in FIGS. 7 (A) and 8 (A), when there is a high-intensity subject to be detected in focus on the screen, the luminance signal at the contour of the subject is shown in FIGS. The state of the change hardly changes between the in-focus state and the out-of-focus state as shown in FIG. 8B, and the high frequency of the luminance signal as shown in FIGS. 7C and 8C. There is almost no difference in the size of the components. Rather, in the out-of-focus state, the area of the image becomes larger, so the high frequency component may become larger. In such a case, the focus evaluation value is not maximized in the focused state, which is not appropriate.

  Therefore, in the present invention, the following processing is performed by the maximum level detection circuit 80, the auto gain control (AGC) circuit 82, and the saturation detection circuit 84. First, the maximum level detection circuit 80 acquires the luminance signal output from each of the image sensors A, B, and C, and detects which image sensor output the luminance signal is the maximum level. For example, the luminance signal for one screen output from each image sensor is acquired, and the maximum value is detected for each luminance signal. Then, the luminance signal showing the largest maximum value among the maximum values for each luminance signal is set as the luminance signal of the maximum level. The maximum level luminance signal detected by the maximum level detection circuit 80 is then input to the AGC circuit 82. The AGC circuit 82 obtains an appropriate gain of the luminance signal based on the input luminance signal, and sets a gain for generating the luminance signal in each of the image sensors A, B, and C so as to obtain the gain. Here, as an appropriate gain, for example, the maximum gain within a range in which the maximum value of the luminance signal for one screen input from the maximum level detection circuit 80 does not exceed a predetermined threshold (for example, does not become saturated). Set. This prevents saturation of luminance signals output from the image sensors A, B, and C.

  Further, since the saturation of the luminance signal may be detected even if such an auto gain control function is used, the saturation detection circuit 84 instantaneously outputs the luminance signal output from the maximum level detection circuit 80 to the AGC circuit 82. The value level is monitored, and when the saturation level is reached at a certain instantaneous value, the pixel indicating the instantaneous value is excluded from the focus evaluation value calculation target. That is, the saturation detection circuit 84 designates the range of pixels in which the instantaneous value of the luminance signal has reached the saturation level to each gate circuit 54, 64, 74, and the gate circuit 54, 64, 74 outputs a signal within that range. Do not extract. As a result, the focus evaluation value is not added to the pixel range in which the instantaneous value of the luminance signal reaches the saturation level without adding the values of the high frequency components of the luminance signal in the adders 56, 66, and 76. It will be required.

  In the above configuration, the gain of the luminance signal is adjusted in order to prevent the luminance signal from being saturated. However, the present invention is not limited to this, and adjustment of the charge accumulation time of each of the image sensors A, B, and C, so-called The level of the luminance signal can be appropriately adjusted by the function of the electronic shutter. For example, in FIG. 4, an electronic shutter control circuit is installed instead of the AGC circuit 82. Similarly to the above, based on the luminance signal output from the maximum level detection circuit 80, an appropriate charge accumulation time for each of the image sensors A, B, and C is obtained, and each image sensor A is set to have the charge accumulation time. , B, and C are set. As in the case of the above gain adjustment, for example, the appropriate charge accumulation time is such that the maximum value of the luminance signals for one screen input from the maximum level detection circuit 80 does not exceed a predetermined threshold value (for example, Set the longest accumulation time within a range that does not become saturated. This prevents saturation of luminance signals output from the image sensors A, B, and C.

  The above-described auto gain control function and electronic shutter function are executed regardless of the processing such as the auto gain control function and electronic shutter function for the image pickup device for video. Naturally, there may be a situation in which the luminance signal gain and charge accumulation time for the image pickup devices A, B, and C differ from the luminance signal gain and charge accumulation time for the image pickup device.

  Based on the focus evaluation values obtained from the image sensors A, B, and C as described above, the CPU 86 detects the current focus state of the photographic lens 12 with respect to the focus surface 22 of the camera body 10. FIG. 9 is a diagram showing the state of the focus evaluation value with respect to the focus position when a certain subject is imaged, with the focus position of the taking lens 12 on the horizontal axis and the focus evaluation value on the vertical axis. A curve a indicated by a solid line in the figure indicates a focus evaluation value obtained from the image sensor A at a position conjugate with the focus surface 22 of the camera body 10 with respect to the focus position, and a curve b indicated by a dotted line in the figure. , C show the focus evaluation values obtained from the image sensors B and C, respectively, with respect to the focus position.

  In the figure, the focus position F3 at which the focus evaluation value of the curve a is maximum (maximum) is the in-focus position, but it is assumed that the focus position of the taking lens 12 is now set to the position F1 in the figure. At this time, the focus evaluation values obtained from the image sensors A, B, and C are values corresponding to the focus position F1 by the curves a, b, and c. At this time, since the focus evaluation value obtained from at least the image sensor B is larger than the focus evaluation value obtained from the image sensor C, the focus position is set closer to the focus position F3, which is the focus position. That is, it can be seen that this is the state of the front pin.

  On the other hand, if the focus position of the photographic lens 12 is set to the position F2 in the figure, the focus evaluation values obtained from the image sensors A, B, and C are respectively set to the focus position F2 by the curves a, b, and c. Corresponding value. At this time, since at least the focus evaluation value obtained from the image sensor C is larger than the focus evaluation value obtained from the image sensor B, the focus position is set to infinity from the focus position F3 which is the focus position. It can be seen that the state is the state of the rear pin.

  Assuming that the focus position of the photographic lens 12 is set to the in-focus position F3 in the figure, the focus evaluation values obtained from the image sensors A, B, and C are respectively set to the focus position F3 by the curves a, b, and c. Corresponding value. At this time, since the focus evaluation value obtained from the image sensor B and the focus evaluation value obtained from the image sensor C are equal, the focus position may be set to the focus position F3, that is, the focus state. I understand.

  In this way, based on the focus evaluation values obtained from the image sensors A, B, and C, the focus state at the current focus position of the photographic lens 12 is detected as either the front pin, the rear pin, or the in-focus state. Can do. On the other hand, in such a focus state determination method, only the focus evaluation value obtained from the image sensors B and C is sufficient, and the focus evaluation value obtained from the image sensor A is unnecessary. Therefore, it is possible to directly detect the focus position at which the in-focus state is obtained by effectively using the focus evaluation values obtained from the three image sensors A, B, and C as follows.

In FIG. 9 above, the curves a, b, and c for the focus evaluation values obtained from the image sensors A, B, and C have substantially the same shape. Therefore, the focus obtained from the image sensors B and C at a certain focus position. The evaluation value can be regarded as a focus evaluation value of the image sensor A at a focus position displaced by a predetermined shift amount from the focus position. For example, it is assumed that the focus position is set to F4 in the drawing in the curve a of the focus evaluation value of the image sensor A shown in FIG. In this case, the focus evaluation value obtained from the imaging element A, shows the values of the points P _A on the curve a. On the other hand, the focus evaluation value obtained from the image sensor B indicates the value of the point P _B on the curve a at the focus position F5 displaced by a predetermined shift amount to the infinity side from the focus position F4. obtained focus evaluation value indicates a value of a point P _C on the curve a in the focus position F6 which is displaced by a predetermined shift amount to the near side than the focus position F4. Note that the difference between the focus position F4 and the focus position F5, that is, the shift amount for the focus evaluation value obtained from the image sensor B is, for example, in FIG. The difference between the focus positions F4 and F6, that is, the shift amount for the focus evaluation value obtained from the image sensor C is equal to the maximum point of the curve c in FIG. It is equal to the difference between the focus position, the curve a and the focus position of the maximum point.

On the other hand, the curve a can be approximated by a predetermined function (for example, a quadratic curve). Therefore, the curve a can be specifically identified from the focus evaluation values at the three points P _A , P _B , and P _C obtained from the image sensors A, B, and C, and the focus evaluation value is the maximum in the curve a. An in-focus position F3 can be obtained.

  In this way, when the CPU 86 in FIG. 4 detects the focus position that is in focus based on the focus evaluation values obtained from the image sensors A, B, and C, the focus motor drive circuit is configured so that the focus position is obtained. A control signal is transmitted to 30 and the focus lens F is moved. Thereby, autofocus control is performed.

  As described above, in the above-described embodiment, the image pickup device is positioned at a position before and after the image pickup surface is optically equidistant with respect to the image pickup device A for detecting the focus state arranged at a position conjugate to the focus surface 22 of the camera body 10. B and the image sensor C are arranged, but the image sensors A, B, and C are arranged so that the optical path lengths are different, and the optical path length is longer than the position conjugate to the focus surface 22 of the camera body 10. It is sufficient that at least one of the image pickup devices A, B, and C is arranged at each of the positions where the distance becomes shorter. That is, as described above, when the focus evaluation value obtained from the image sensors B and C at a certain focus position is regarded as the focus evaluation value of the image sensor A at the focus position displaced by a predetermined shift amount from the focus position. The shift amount may be set based on the distance between the image sensors B and C with respect to the image sensor A. As a method for obtaining the shift amount, for example, the focus position is changed while photographing a fixed subject, and the focus position at which the focus evaluation value obtained from each of the image sensors A, B, and C is maximized is detected. Then, with respect to the focus position where the focus evaluation value obtained from the image sensor A is maximized, the displacement amount of each focus position where the focus evaluation value obtained from each image sensor B, C is maximized is detected. The displacement amount is set as the shift amount.

  In the above-described embodiment, the imaging surface of the imaging device A for detecting the focus state is arranged at a conjugate position with the focusing surface 22 of the camera body 10, but it is not always necessary to do so. That is, the above-described method for detecting the displacement amount of each focus position at which the focus evaluation value obtained from each of the image sensors B and C is maximum with respect to the focus position at which the focus evaluation value obtained from the image sensor A is maximum. Similarly, the amount of displacement of the focus position at which the focus evaluation value obtained from the image sensor A is maximum is detected with respect to the focus position at which focusing is obtained on the focus surface 22 of the camera body 10, and the amount of displacement is imaged. The shift amount for the focus evaluation value obtained from the element A is used. That is, the focus evaluation value obtained from the image sensor A is regarded as the focus evaluation value at the focus position displaced from the actual focus position by the shift amount. Note that the shift amount of the focus evaluation value obtained from the image sensors B and C is similarly detected. Thus, a focus evaluation value curve for the focusing surface 22 of the camera body 10 can be obtained based on the focus evaluation values of the image pickup devices A, B, and C obtained at a certain focus position. The focus position can be obtained.

  In the above embodiment, the image pickup unit 26 includes the three image pickup devices A, B, and C for focus state detection. However, only the two image pickup devices B and C for focus state detection are arranged in the camera body. By placing the lens 10 before and after the position conjugate to the ten focus surfaces 22, it is detected whether the focus state is the front pin, the rear pin, or the in-focus state, and the autofocus control is performed based on the detection result. You may make it perform. Conversely, using four or more imaging devices for detecting the focus state with different optical path lengths, at least one of the positions where the optical path length becomes longer and shorter than the position conjugate to the focus surface 22 of the camera body 10. An in-focus position may be detected with higher accuracy by arranging an image sensor.

  In the above embodiment, the case where the focus state detection by the focus state detection device according to the present invention is applied to autofocus has been described. However, the present invention is not limited to this, and is used for other purposes, for example, the display of the focus state. You can also

  DESCRIPTION OF SYMBOLS 10 ... Camera body, 12 ... Shooting lens, F ... Focus lens, R1 ... Front side relay lens, R2 ... Rear side relay lens, R3 ... Relay lens, 24 ... Half mirror, 26 ... Imaging part, A, B, C ... Imaging Elements 28... Signal processor 30. Focus motor drive circuit 50 60 60 70 High pass filter 54 64 64 74 Gate circuit 56 66 76 Adder 80 Maximum level detection circuit 82 ... Auto gain control circuit, 84 ... Saturation detection circuit, 86 ... CPU

Claims (5)

A light splitting means for splitting the subject light incident on the taking lens ;
Of the light split by the light splitting means, there are three image pickup devices that pick up an image for focus state detection using light different from the light incident on the image pickup device for picking up images for video. Three focus state detecting image sensors arranged at positions where the optical path lengths are different from each other ;
A focus evaluation value detection means for detecting a focus evaluation value indicating the degree of the sharpness of the image based on the high frequency component of one screen of the luminance signal obtained from each focus state detecting device,
The three focus evaluation values detected by the focus evaluation value detection unit corresponding to each of the focus state detection imaging elements are set as focus evaluation values at three different points related to the focus position of the photographing lens. Based on the focus evaluation value, a curve indicating the relationship between the focus position of the photographing lens and the focus evaluation value is obtained using a predetermined function, and the focus position at which the focus evaluation value is maximum is detected as the in-focus position by the curve. In-focus position detecting means,
Focus control means for controlling the focus lens of the photographic lens so that the focus position of the photographic lens becomes the focus position detected by the focus position detection means;
A maximum level luminance signal detection that acquires a luminance signal for one screen from each of the focus state detection imaging devices, and detects a luminance signal having the largest value among the acquired three luminance signals as a maximum level luminance signal. Means,
Based on the luminance signal at the maximum level detected by the maximum level luminance signal detecting means, a gain is set to an appropriate level that does not saturate the luminance signal, and the determined gain is output from each of the focus state detection imaging devices. Gain setting means for setting as a gain when generating a luminance signal to be generated,
An autofocus device for a taking lens, comprising: A light splitting means for splitting the subject light incident on the taking lens ;
Of the light split by the light splitting means, there are three image pickup devices that pick up an image for focus state detection using light different from the light incident on the image pickup device for picking up images for video. Three focus state detecting image sensors arranged at positions where the optical path lengths are different from each other ;
A focus evaluation value detection means for detecting a focus evaluation value indicating the degree of the sharpness of the image based on the high frequency component of one screen of the luminance signal obtained from each focus state detecting device,
The three focus evaluation values detected by the focus evaluation value detection unit corresponding to each of the focus state detection imaging elements are set as focus evaluation values at three different points related to the focus position of the photographing lens. Based on the focus evaluation value, a curve indicating the relationship between the focus position of the photographing lens and the focus evaluation value is obtained using a predetermined function, and the focus position at which the focus evaluation value is maximum is detected as the in-focus position by the curve. In-focus position detecting means,
Focus control means for controlling the focus lens of the photographic lens so that the focus position of the photographic lens becomes the focus position detected by the focus position detection means;
A maximum level luminance signal detection that acquires a luminance signal for one screen from each of the focus state detection imaging devices, and detects a luminance signal having the largest value among the acquired three luminance signals as a maximum level luminance signal. Means,
Based on the luminance signal at the maximum level detected by the maximum level luminance signal detection means, a charge accumulation time at which the luminance signal becomes an appropriate level that does not saturate is determined, and the determined charge accumulation time is used for detecting each focus state Charge storage time setting means for setting the charge storage time in the image sensor;
An autofocus device for a taking lens, comprising: The gain setting means has a maximum gain within a range in which the maximum value of the maximum level luminance signal detected by the maximum level luminance signal detection means does not exceed a predetermined threshold value. 2. The photographing lens autofocus device according to claim 1, wherein the gain is determined as a level gain. The gain setting means does not saturate the luminance signal for the longest charge accumulation time in which the maximum value of the luminance signal at the maximum level detected by the maximum level luminance signal detection means does not exceed a predetermined threshold. 3. The photographic lens autofocus device according to claim 2, wherein the charge accumulation time is set to an appropriate level. Saturation detection means for detecting whether or not the instantaneous value of the maximum level luminance signal detected by the maximum level luminance signal detection means has reached a saturation level, and the focus evaluation value detection means is provided by the saturation detection means. 3. The autofocus device for a photographing lens according to claim 1, wherein the focus evaluation value is detected based on a high frequency component of a luminance signal in a range excluding a pixel corresponding to an instantaneous value reaching a saturation level. .

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