JP4066244B2 - Auto focus system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an autofocus system, and more particularly to an autofocus system that controls focus of a photographing lens by contrast-type autofocus.
[0002]
[Prior art]
In general, autofocus for a video camera or the like is based on a contrast method. This contrast method, for example, obtains a focus evaluation value indicating the sharpness (contrast) of an image by accumulating high frequency components of a video signal within a certain range (focus area) of a video signal obtained from an image sensor. Then, the focus of the photographing lens is automatically adjusted so that the focus evaluation value becomes the maximum (maximum). As a result, the best focus (focusing) that maximizes the sharpness of the image captured by the image sensor can be obtained.
[0003]
In the autofocus control as described above, a so-called wobbling operation for detecting a change in the focus evaluation value by minutely changing the focal position of the photographing lens is performed. By this wobbling, the current focus state (front pin, rear pin, in-focus) is detected, and it is determined whether or not the focus is in focus or the focus moving direction when not in focus. However, in the autofocus of a TV camera used for TV broadcasting, an operation for searching for a focus state by wobbling or the like appears in the video, which is not preferable.
[0004]
Therefore, apart from the optical system that forms an image of the subject light incident on the photographing lens on the image pickup device used for original imaging, a part of the subject light incident on the photographing lens (a part of the light amount) is obtained by a half mirror or the like. It is conceivable to provide a focus state detection optical system that branches and forms an image of the branched subject light on a focus state detection (autofocus) image pickup device different from the image pickup device for video (Patent Document 1). reference). In this way, a focus evaluation value similar to that described above can be obtained from the focus state detection image sensor, and a plurality of focus state detection images having different wobbling operations or optical path lengths in the focus state detection optical system. There is an advantage that the focus state can be detected by the configuration using the element, and the influence of the operation for detecting the focus state does not appear in the video imaged by the video image sensor.
[0005]
[Patent Document 1]
JP-A-55-76312
[0006]
[Problems to be solved by the invention]
However, if a part of the subject light incident on the photographing lens is branched to the focus state detection optical system as described above, the amount of the subject light incident on the image pickup device is reduced. When the subject is bright, an appropriate amount of light can be acquired by adjusting the aperture. However, when the subject is dark, there is a problem that the amount of light is insufficient even when the aperture is opened.
[0007]
The present invention has been made in view of such circumstances. Based on image information obtained from the subject light by guiding a part of the amount of the subject light incident on the photographing lens to an optical system dedicated to focus state detection (for autofocus). An object of the present invention is to provide an autofocus system that prevents a problem in which the amount of subject light incident on an image pickup device due to subject light used for autofocus is insufficient.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, the autofocus subject light having a predetermined wavelength region different from the visible light region from the optical path that guides the subject light incident on the photographing lens to the image pickup means is provided. Autofocus subject light branching means for branching into an optical path different from the optical path, and autofocus subject light as an electrical signal by capturing the autofocus subject light branched by the autofocus subject light branching means An imaging unit; and a focus control unit that controls the focus of the photographing lens to be an in-focus position based on image information of the subject acquired by the autofocus imaging unit; When the focal length of the photographic lens can be changed, the imaging position of the autofocus subject light from the object at the photographic distance focused on the video imaging means and the imaging position of the autofocus imaging means The position of a predetermined lens arranged on the optical path of the subject light for autofocus is adjusted based on the focal length of the photographing lens so that the relative positional relationship with the lens does not fluctuate due to the change of the focal length Adjusting the imaging position by adjusting, or adjusting means for adjusting the imaging position; It is characterized by having.
[0009]
According to a second aspect of the present invention, in the first aspect of the present invention, the wavelength region of the autofocus subject light is an infrared region.
[0010]
The invention according to claim 3 is the invention according to claim 1 or 2, The focus control means wobbles a predetermined lens disposed on the optical path of the autofocus subject light, and the contrast obtained from the image information of the subject acquired by the autofocus imaging means at the time of the wobbling Detecting the focus movement direction that is the in-focus position based on the information, and moving the focus in the detected focus movement direction It is characterized by.
[0011]
According to the present invention, since subject light having a wavelength region different from the visible light region used for video is used as subject light used for autofocus, the subject light for autofocus is branched for video. The problem that the amount of the subject light is insufficient can be prevented. In addition, by adjusting the imaging position of the autofocus subject light or the imaging position of the autofocus imaging means in accordance with the focal length of the photographing lens, subject light in a wavelength region other than visible light is changed to autofocus subject light. In this case, it is possible to prevent the inconvenience that the imaging position is changed depending on the focal length of the photographing lens and the focusing accuracy is lowered.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
A preferred embodiment of an autofocus system according to the present invention will be described below in detail with reference to the accompanying drawings.
[0013]
FIG. 1 is a diagram showing a configuration of an optical system of a television camera system to which the present invention is applied. The television camera system includes, for example, a lens device 10 and a camera body 12, and the camera body 12 captures a video for television broadcasting and outputs or records a video signal in a predetermined format on a recording medium. Image pickup device (hereinafter referred to as an image pickup device for video), required circuits, and the like are mounted.
[0014]
The lens device 10 is detachably attached to the camera body 12 and includes an optical system (photographing lens) shown in FIG. 1 and a control system described later. The configuration of the optical system will be described. The photographing lens includes a focus lens (group) FL, a zoom lens (group) ZL, an iris I, a relay lens (relay optical system) including a front relay lens RLA and a rear relay lens RLB. Etc. are arranged. Between the front relay lens RLA and the rear relay lens RLB of the relay optical system, an infrared reflection mirror M1 for branching the subject light for focus state detection from the subject light incident on the photographing lens is disposed. ing.
[0015]
The infrared reflection mirror M1 is installed with an inclination of about 45 degrees with respect to the optical axis O of the photographic lens. Of the subject light incident on the infrared reflection mirror M1, a predetermined wavelength region (for example, about (800 nm to 1000 nm) is reflected at right angles as subject light for focus state detection, and light in other wavelength regions (mainly visible light region) is transmitted through the infrared reflection mirror M1 as subject light for video. It has become. In this way, since light in the infrared region is used as subject light for focus state detection, there is no problem that subject light in the visible light region necessary for video is reduced. It should be noted that the wavelength region branched as the subject light for focus state detection is not necessarily the infrared region, and may be another wavelength region as long as it is a wavelength region other than the visible light region.
[0016]
The image subject light transmitted through the infrared reflecting mirror M1 is emitted from the rear end side of the photographing lens 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. As a result, 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.
[0017]
On the other hand, the focus state detection subject light reflected by the infrared reflecting mirror M1 travels along the optical axis O ′ perpendicular to the optical axis O, and enters the AF master lens (group) ML. Then, after being condensed by the AF master lens ML and reflected by the total reflection mirror M2, it is applied to the imaging surface of the imaging device 16 for focus state detection (autofocus) (hereinafter referred to as the imaging device 16 for focus state detection). Incident.
[0018]
Here, the AF master lens ML is movable in the direction of the optical axis O ′. By changing the setting position of the AF master lens ML, the imaging (surface) position of the focus state detection subject light is changed. It has come to be adjusted. FIG. 2 shows the imaging (surface) positions of the image subject light in the visible light region and the focus state detection subject light in the infrared region emitted from the same object (surface), as shown in FIG. The image formation position of the image subject light and the image formation position of the focus state detection object light are usually not the same.
[0019]
Therefore, subject light from an object (surface) at a shooting distance to be focused, that is, subject light from an object at a distance with the imaging surface (focus plane P) of the image pickup device for image formation as an imaging position, enters the photographing lens. When it is assumed that the light is incident, the AF master lens ML is configured such that the imaging position of the focus state detection subject light matches the imaging position (the position of the imaging surface) of the focus state detection imaging element 16. Set to position. Thus, the focus state of the image captured by the video image sensor is accurately detected by the focus state of the image captured by the focus state detection image sensor 16.
[0020]
In addition, for image subject light in the visible light region, even when the position of the zoom lens ZL changes and the focal length of the photographic lens changes, the photographic lens is designed to capture the image of the image sensor. The distance to the object whose surface is the imaging position is not changed. That is, even if the focal length of the photographing lens is changed, the photographing distance to the object to be focused does not change, and the imaging position of the subject light for video from the object coincides with the imaging position of the imaging element for video.
[0021]
On the other hand, for the focus state detection subject light in the infrared region, when the position of the zoom lens ZL changes and the focal length of the photographing lens changes, the imaging position changes. For example, FIG. 3 exemplifies the shift amount of the imaging position of the focus state detection subject light in the infrared region with respect to the imaging position of the image subject light in the visible light region. As shown in FIG. The imaging position of the detection subject light varies depending on the focal length.
[0022]
For this reason, the setting position of the AF master lens ML is corrected based on the focal length of the photographing lens (setting position of the zoom lens ZL), and even if the focal length of the photographing lens changes. The image formation position of the focus state detection subject light from the object at the in-focus shooting distance coincides with the image pickup position of the focus state detection image sensor.
[0023]
Note that the wavelength region used as the focus state detection subject light may be limited by an optical filter, a lens material, a lens coat, or the like so that the imaging position does not vary greatly depending on subject conditions. You may make it use the imaging element for a focus state detection of a characteristic with low sensitivity with respect to the light of a wavelength range.
[0024]
FIG. 4 is a block diagram showing the configuration of the control system of the lens apparatus 10. In the figure, the focus lens FL, the zoom lens ZL, the iris I, and the AF master lens ML shown in FIG. 1 are shown. The lenses FL, ZL, ML, and iris I respectively correspond to the corresponding focus motors FM, It is driven by a zoom motor ZM, an AF master motor MM, and an iris motor IM (each lens moves in the optical axis direction, and the iris amount of the iris I changes), and each motor FM, ZM, MM, IM is Each is driven by a focus amplifier FA, a zoom amplifier ZA, an AF master amplifier MA, and an iris amplifier IA according to drive signals given from the CPU 26 via the D / A converter 28, respectively.
[0025]
The CPU 26 is instructed, for example, from the controller such as the zoom demand 20 and the focus demand 22 via the A / D converter 24 to the position (target position) and speed (target speed) to be set for the focus lens FL and the zoom lens ZL. Based on the command signal given from the controller, the CPU 26 makes the focus lens FL and the zoom lens ZL have the target position or target speed commanded by the command signal. The rotational speeds of the motors FM and ZM are determined, and a voltage drive signal corresponding to the rotational speed is output to the amplifiers FA and ZA via the D / A converter 28 as described above.
[0026]
The CPU 26 uses the focus potentiometer FP to detect the rotation position of the focus motor FM as information on the current position of the focus lens FL, and also uses the rotation position of the zoom motor ZM as information on the current position of the zoom lens ZL. It is detected by a pontensometer ZP. When the command signal for the focus lens FL or the zoom lens ZL instructs to move to the target position, the target position and the current position of the focus lens FL or the zoom lens ZL are sequentially compared for focusing. The rotational speed of the motor FM or the zoom motor ZM is determined.
[0027]
For the iris I, generally, a command signal for instructing the setting position (aperture value) of the iris I is given to the CPU 26 from a camera body (not shown), and the CPU 26 uses the iris motor IM as the setting position of the iris I as described above. Is detected by the iris potentiometer IM, and a drive signal for driving the iris motor IM is output to the iris amplifier IA so as to obtain the aperture value commanded by the command signal.
[0028]
On the other hand, the CPU 26, as described above, for driving signals for correcting the position of the AF master lens ML based on the setting position of the zoom lens ZL (focal length of the photographing lens) and for wobbling during autofocus described later. A drive signal is generated, the drive signal is output to the AF master amplifier MA, and the AF master motor MM is driven so that the AF master lens ML has a target position or target speed. Further, the CPU 26 detects the rotational position of the AF master motor MM as the setting position of the AF master lens ML by the AF master potentiometer MP, and drives the AF master motor MM while comparing the current position with the target position. By doing so, the AF master lens ML is set to a desired target position.
[0029]
Here, the position correction of the AF master lens ML based on the setting position of the zoom lens ZL (focal length of the photographing lens) will be described. The ROM 30 shown in FIG. 1 stores the correction position (zoom position) of the zoom lens ZL. Correction position data indicating the set position (correction position) of the appropriate AF master lens ML is stored. The CPU 26 detects the current zoom position and reads the correction position of the AF master lens ML corresponding to the zoom position from the correction position data in the ROM 30 during autofocus processing as will be described later. Then, the read correction position is set as the target position, and the AF master motor MM is driven as described above to move the AF master lens ML to the correction position.
[0030]
Next, auto focus will be described. In this system, an auto-return type AF switch S1 that is normally turned off is provided. When the AF switch S1 is turned off, manual focus (hereinafter referred to as MF) is selected. The cameraman can adjust the focus by MF by operating a predetermined operation member provided in the focus demand 22. That is, when the AF switch S1 is OFF, the CPU 26 drives the focus lens FL (focus motor FM) based on the command signal given from the focus demand 22 as described above.
[0031]
On the other hand, once the AF switch S1 is turned on, the focus mode is switched from MF to auto focus (hereinafter referred to as AF), AF is executed only once by the processing of the CPU 26, and the position of the focus lens FL is automatically set to the focus position. The meaning that AF is executed only once means that once the focus lens FL is set to the in-focus position by AF, AF is not executed even if the in-focus position changes thereafter. In this form, when AF is executed only once, the AF switch S1 returns to MF if the AF switch S1 returns to OFF.
[0032]
Here, the lens apparatus 10 includes a focus evaluation value generation circuit that generates a focus evaluation value for evaluating the degree of focusing based on the video signal (luminance signal) obtained from the focus state detection imaging element 16. It is installed. The focus evaluation value is a value indicating the level of contrast (sharpness) of an image, and the detection method is conventionally known in contrast AF.
[0033]
FIG. 1 shows a focus evaluation value generation circuit. From a video signal acquired from the focus state detection image sensor 16, only a high-frequency component is first extracted by a high-pass filter (HPF) 32 and A / D converted. The digital signal is converted by the device 34. Of the high-frequency components converted into digital signals, a signal only within a predetermined focus area set within the photographing range is extracted by the gate circuit 36. In addition to the signal from the A / D converter 34, a video signal is directly input to the gate circuit 36, and a signal only in the focus area is extracted using a synchronization signal in the video signal. The high-frequency component signals extracted by the gate circuit 36 are integrated for each field by the adder circuit 38, and the signal obtained by the integration indicates the degree of focus on the subject in the focus area (contrast level). The CPU 26 reads the focus evaluation value. The method for detecting the focus evaluation value from the video signal is not limited to the above case.
[0034]
When the AF switch S1 is turned on, the CPU 26 generates a drive signal for driving the focus motor FM based on the focus evaluation value, and the drive signal is sent to the focus amplifier FA as in the case of MF. The focus lens FL is output and moved to the in-focus position. Specifically, the CPU 26 appropriately outputs a drive signal for driving the AF master lens ML to the AF master amplifier MA via the D / A converter 28, and moves the AF master lens ML back and forth in the optical axis direction. The focus evaluation value is acquired from the store evaluation value generation circuit (addition circuit 38) while being (wobbled) (for example, acquired for each field). Thereby, a focus evaluation value equal to that when the focus lens FL is moved back and forth from the current set position is detected. Based on the focus evaluation value acquired during the wobbling, the CPU 26 determines whether or not the focus evaluation value is maximum at the current position of the focus lens FL. If the focus evaluation value is the maximum, focus is obtained, and the focus lens FL is stopped at the focus position. Also, the process returns to MF processing. On the other hand, if the focus evaluation value is not maximal, it is determined from the magnitude relationship between the focus evaluation values acquired during wobbling whether the in-focus position is in an infinite direction or a close direction from the current position. Then, a drive signal is output to the amplifier FA, and the focus lens FL is moved in the determined direction. In this way, the focus lens FL is automatically set to the in-focus position by repeating the wobbling of the wobbling lens WL and the movement of the focus lens FL.
[0035]
Next, the processing procedure during AF in the CPU 26 will be described with reference to the flowchart of FIG.
[0036]
First, after performing required initial settings (step S10), the CPU 26 executes processes other than AF (step S12). Note that processing other than AF includes processing related to driving of the focus lens FL by MF. Next, it is determined whether or not the AF switch S1 is turned on (step S14). When it determines with NO, it returns to said step S12. On the other hand, if YES is determined, the process proceeds to AF processing. First, the current position (zoom position) of the zoom lens ZL is read from the zoom potentiometer ZP (step S16). Next, correction position data indicating the setting position (correction position) of the AF master lens ML corresponding to the current zoom position is read from the ROM 30 (step S18). Then, using the read correction position as a target position, the AF master lens ML is moved to the target position (step S20). Subsequently, it is determined whether or not the AF master lens ML has reached the target position (step S22). While it is determined NO, the processes of step S20 and step S22 are repeated.
[0037]
If it is determined as YES in step S22, the CPU 26 performs wobbling by moving the AF master lens ML back and forth around the correction position moved as described above (step S24). At this time, the focus evaluation value is acquired from the focus evaluation value generation circuit, for example, for each field. Then, based on the focus evaluation value acquired during wobbling, it is determined whether or not the focus evaluation value is maximum at the current position of the focus lens FL, that is, whether or not it is in focus (step S26). Here, when it determines with YES, it returns to said step S12. That is, switching to MF. On the other hand, if NO is determined, it is determined whether or not the focus position is in an infinite direction with respect to the current position of the focus lens FL based on the focus evaluation value acquired during wobbling (step S28). If YES is determined, the focus motor FM is driven to move the focus lens FL in an infinite direction (step S30). On the other hand, if NO is determined, the focus lens FL is moved in the closest direction (step S32).
[0038]
Then, after executing processing other than AF (step S34), the processing from the above step S16 is repeated until it is determined that the in-focus state is obtained in step S28.
[0039]
As described above, in the above embodiment, whether or not the focus evaluation value is maximum at the current position of the focus lens FL (whether in-focus is obtained) or the in-focus position by wobbling the AF master lens ML. Is infinite or close to the current position of the focus lens FL, but it does not perform wobbling, but multiple focus state detection images arranged at different optical path lengths The present invention can also be applied to a contrast method using an element. In this method, a focus evaluation value is obtained for each video signal based on a plurality of video signals obtained from a plurality of focus state detection imaging elements having different optical path lengths in the same manner as in the above embodiment, and those focus evaluation values are obtained. Whether the focus lens FL is in focus at the current position of the focus lens FL, and if not in focus, the focus position is infinite or close to the current position of the focus lens FL. Is judged. In this case, when light in a wavelength region other than the visible light region, for example, in the infrared region, is used as the focus state detection subject light, for example, the focus state detection from the object at the photographing distance to be focused. Adjust the focusing position detection subject light imaging position so that the positional relationship between the imaging position of the subject light and each of the imaging positions of the multiple focus state detection imaging elements does not vary depending on the focal length of the photographic lens. To do.
[0040]
In the above-described embodiment, the case where the imaging position of the focus state detection subject light fluctuates depending on the focal length of the photographing lens is described. However, the present invention is not limited to this. The correction position of the AF master lens ML may be determined in consideration of the aperture value and the focus position.
[0041]
In the above embodiment, the relative position relationship between the imaging position of the focus state detection subject light and the imaging position of the focus state detection image sensor is adjusted by adjusting the setting position of the AF master lens ML. However, the present invention is not limited to this, and the imaging position of the focus state detection imaging element may be adjusted.
[0042]
【The invention's effect】
As described above, according to the autofocus system of the present invention, subject light having a wavelength region different from the visible light region used for video is used as subject light used for autofocus. By branching the subject light, it is possible to prevent a problem that the amount of the subject light for video is insufficient. In addition, by adjusting the imaging position of the autofocus subject light or the imaging position of the autofocus imaging means in accordance with the focal length of the photographing lens, subject light in a wavelength region other than visible light is changed to autofocus subject light. In this case, it is possible to prevent the inconvenience that the imaging position is changed depending on the focal length of the photographing lens and the focusing accuracy is lowered.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an optical system of a television camera system to which the present invention is applied.
FIG. 2 is a diagram illustrating a difference in image formation position between image subject light in a visible light region and focus state detection subject light in an infrared region.
FIG. 3 is a diagram exemplifying a shift amount of an imaging position of focus state detection subject light in an infrared region with respect to an imaging position of image subject light in a visible light region.
FIG. 4 is a block diagram illustrating a configuration of a control system of the lens apparatus.
FIG. 5 is a flowchart showing a processing procedure at the time of AF in the CPU 26;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Lens apparatus, 12 ... Camera body, 16 ... Imaging device for focus state detection, 26 ... CPU, ZL ... Zoom lens, FL ... Focus lens, ML ... AF master lens, I ... Iris, M1 ... Infrared reflecting mirror, M2 ... Total reflection mirror, ZM ... Zoom motor, FM ... Focus motor, MM ... AF master motor, IM ... Iris motor, ZA ... Zoom amplifier, FA ... Focus amplifier, MA ... AF master amplifier, IA ... Iris amplifier, S1 ... Auto focus (AF) switch

Claims (3)

Autofocus subject light branching means for branching autofocus subject light in a predetermined wavelength region different from the visible light region into an optical path different from the optical path from the optical path for guiding the subject light incident on the photographing lens to the image pickup means;
Imaging means for autofocus that captures the subject light for autofocus branched by the subject light branching means for autofocus and acquires image information of the subject as an electrical signal;
Focus control means for controlling the focus of the photographing lens to be a focus position based on image information of the subject acquired by the autofocus imaging means;
When the focal length of the photographic lens can be changed, the imaging position of the autofocus subject light from the object at the photographic distance focused on the video imaging means and the imaging position of the autofocus imaging means The position of a predetermined lens arranged on the optical path of the subject light for autofocus is adjusted based on the focal length of the photographing lens so that the relative positional relationship with the lens does not fluctuate due to the change of the focal length Adjusting the imaging position by adjusting, or adjusting means for adjusting the imaging position;
Autofocus system comprising the.   2. The autofocus system according to claim 1, wherein a wavelength region of the autofocus subject light is an infrared region. The focus control unit wobbles a predetermined lens arranged on the optical path of the autofocus subject light, and the contrast obtained from the image information of the subject acquired by the autofocus imaging unit at the time of the wobbling 3. The autofocus system according to claim 1 or 2, wherein a focus movement direction as a focus position is detected based on the information, and the focus is moved in the detected focus movement direction .

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