JP2004118141A - Auto focus system - Google Patents

Abstract

Kind Code: A1 In contrast type autofocus, subject light in a wavelength region different from a visible light region used for video is used as subject light used for autofocus, so that the subject light for autofocus is branched. The present invention provides an autofocus system that prevents a problem that the amount of subject light for video is insufficient.
The infrared light of the subject light that has entered a photographic lens is split by an infrared reflection mirror (M1) from the video subject light in the visible light region as autofocus subject light. Then, the autofocus subject light is imaged on the imaging surface of the autofocus imaging element 16 by the AF master lens ML. The AF master lens ML moves in the direction of the optical axis O ′ so that the image forming position of the autofocus subject light coincides with the imaging surface of the imaging device 16.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an autofocus system, and more particularly to an autofocus system that controls the focus of a photographic lens by contrast type autofocus.
[0002]
[Prior art]
Generally, an autofocus of a video camera or the like is based on a contrast method. This contrast method acquires, for example, a focus evaluation value indicating the sharpness (contrast) of an image by integrating the high frequency components of the video signal within a certain range (focus area) among the video signals obtained from the image sensor. Then, the focus of the photographing lens is automatically adjusted so that the focus evaluation value becomes maximum (maximum). As a result, the best focus (focus) at which the sharpness of the image captured by the image sensor is maximized is obtained.
[0003]
In the above-described autofocus control, a so-called wobbling operation of detecting a change in the focus evaluation value by slightly changing the focal position of the photographing lens is performed. The current focus state (front focus, rear focus, focus) is detected by this wobbling, and it is determined whether or not focus is achieved or the direction of focus movement when focus is not achieved. However, in an autofocus of a television camera used for television broadcasting, an operation of searching for a focus state by wobbling or the like appears in a video, which is not preferable.
[0004]
Therefore, apart from an optical system that forms an image of the subject light incident on the photographing lens on the image pickup device for video used for original imaging, part of the subject light incident on the photographing lens (a part of the light amount) is reflected by a half mirror or the like. It is conceivable to provide an optical system for focus state detection that branches and forms an image of the branched subject light on an image sensor for focus state detection (for auto focus) that is different from the image sensor for video images (Japanese Patent Application Laid-Open No. H11-163873). reference). With this configuration, the same focus evaluation value as described above can be obtained from the focus state detection imaging device, and a plurality of focus state detection imaging devices having different wobbling operations or optical path lengths in the focus state detection optical system can be obtained. The focus state can be detected by the configuration using the element, and there is an advantage that the influence of the operation for detecting the focus state does not appear in the video imaged by the video imaging device.
[0005]
[Patent Document 1]
JP-A-55-76312
[Problems to be solved by the invention]
However, when a part of the subject light incident on the photographing lens is branched to the focus state detecting optical system as described above, the amount of the subject light incident on the image pickup device for image is reduced. When the subject is bright, an appropriate amount of light can be obtained 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, and based on image information obtained from the subject light by guiding a partial light amount of the subject light incident on the photographing lens to an optical system dedicated to focus state detection (for autofocus). It is an object of the present invention to provide an auto-focus system for performing auto-focusing by using a subject light used for auto-focusing and preventing a problem that the amount of subject light incident on a video imaging device is insufficient.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1, the subject light for autofocus of a predetermined wavelength region different from the visible light region from the optical path that guides the subject light incident on the imaging lens to the image pickup means for the image, An autofocus subject light branching unit that branches to an optical path different from the optical path; and an autofocus for capturing the autofocus subject light branched by the autofocus subject light branching unit and acquiring image information of the subject as an electric signal. And a focus control unit that controls the focus of the photographic lens to be at a focus position based on the image information of the subject acquired by the autofocus imaging unit.
[0009]
According to a second aspect of the present invention, in the first aspect, the wavelength region of the subject light for autofocus is an infrared region.
[0010]
According to a third aspect of the present invention, in the first or the second aspect of the present invention, when the focal length of the photographic lens is changeable, the photographic distance focused on the image pickup means is adjusted. The focal length of the photographic lens so that the relative positional relationship between the image forming position of the autofocus subject light from the object and the imaging position of the autofocus imaging means does not change due to the change in the focal length. And adjusting means for adjusting the image forming position or the image pickup position on the basis of (1).
[0011]
According to the present invention, as the subject light used for autofocus, the subject light in a wavelength region different from the visible light region used for video is used. The problem that the light amount of the subject light is insufficient can be prevented. Further, by adjusting the imaging position of the autofocus subject light or the imaging position of the autofocus imaging means according to the focal length of the photographing lens, the subject light in a wavelength region other than visible light can be adjusted to the autofocus subject light. In such a case, it is possible to prevent a problem that the focusing position is reduced due to a change in the image forming position depending on the focal length of the photographing lens.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of an autofocus system according to the present invention will be described in detail with reference to the accompanying drawings.
[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, a camera body 12, and the like. The camera body 12 captures a video for television broadcasting, and outputs a video signal in a predetermined format or records the video signal on a recording medium. (Hereinafter, referred to as a video image sensor), necessary circuits, and the like.
[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. A photographic lens includes a focus lens (group) FL, a zoom lens (group) ZL, an iris I, a relay lens including a front relay lens RLA and a rear relay lens RLB (relay optical system). Etc. are arranged. An infrared reflection mirror M1 is disposed between the front relay lens RLA and the rear relay lens RLB of the relay optical system to split the subject light for focus state detection from the subject light incident on the photographing lens. ing.
[0015]
The infrared reflecting mirror M1 is installed at an angle of about 45 degrees with respect to the optical axis O of the photographing lens, and of the subject light incident on the infrared reflecting 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 the other wavelength region (mainly in the visible light region) is transmitted through the infrared reflection mirror M1 as subject light for video. It has become. As described above, since the light in the infrared region is used as the subject light for focus state detection, the problem that the subject light in the visible light region required for the image is reduced does not occur. The wavelength region branched as the subject light for focus state detection is not necessarily the infrared region, but 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 reflection 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, the subject light incident on the imaging unit 14 is separated into three colors of red light, green light, and blue light by, for example, a color separation optical system. Incident on the image pickup surface. As a result, a color image for broadcast is captured. The focus plane P in the figure indicates a position optically equivalent to the imaging plane of each imaging element on the optical axis O of the photographing lens.
[0017]
On the other hand, the focus state detection subject light reflected by the infrared reflecting mirror M1 travels along an 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, the image is picked up on an image pickup surface of an image pickup device 16 for focus state detection (for auto focus) (hereinafter, referred to as a focus state detection image pickup device 16). Incident.
[0018]
Here, the AF master lens ML is movable in the direction of the optical axis O ′, and by changing the set position of the AF master lens ML, the image forming (surface) position of the subject light for focus state detection is changed. It is being 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). The image formation position of the image subject light does not usually coincide with the image formation position of the focus state detection object light.
[0019]
Therefore, subject light from an object (surface) located at a shooting distance to be focused, that is, subject light from an object located at a distance where the imaging surface (focus plane P) of the image pickup device for imaging is an imaging position, is transmitted to 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 focusing state detection imaging element 16. Set to position. Thereby, the focus state of the image captured by the video imaging element is accurately detected by the focus state of the image captured by the focus state detection imaging element 16.
[0020]
Further, even when the position of the zoom lens ZL changes and the focal length of the photographing lens changes with respect to the image subject light in the visible light region, the image pickup of the image pickup device takes place due to the design of the photographing lens. The distance to the object whose surface is the imaging position does not change. That is, even if the focal length of the photographing lens is changed, the photographing distance to the focused object does not change, and the image forming position of the image subject light from the object coincides with the image pickup position of the image pickup device.
[0021]
On the other hand, with respect to 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 image forming position changes. For example, FIG. 3 exemplifies a shift amount of an image formation position of a focus state detection object light in an infrared region with respect to an image formation position of a video object light in a visible light region. As shown in FIG. The imaging position of the detection subject light changes depending on the focal length.
[0022]
For this reason, the set position of the AF master lens ML is corrected based on the focal length of the photographing lens (the set position of the zoom lens ZL), and even if the focal length of the photographing lens changes. The imaging position of the object light for focus state detection from the object at the focusing distance to be focused matches the imaging position of the image sensor for focus state detection.
[0023]
Incidentally, the wavelength region used as the subject light for focus state detection may be limited by an optical filter, a lens material, a lens coat, or the like so that the image forming position does not greatly vary depending on the subject condition. A focus state detecting image sensor having a characteristic of low sensitivity to light in a wavelength region may be used.
[0024]
FIG. 4 is a block diagram showing a configuration of a control system of the lens device 10. In this figure, a focus lens FL, a zoom lens ZL, an iris I, and an AF master lens ML shown in FIG. 1 are shown, and each of the lenses FL, ZL, ML and the iris I is a corresponding focus motor FM, The motors FM, ZM, MM, and IM are 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 I changes its opening amount). Each of them is driven by a focus amplifier FA, a zoom amplifier ZA, an AF master amplifier MA, and an iris amplifier IA in accordance with drive signals supplied from the CPU 26 via a D / A converter 28, respectively.
[0025]
For example, a command such as a position (target position) and a speed (target speed) to be set for the focus lens FL and the zoom lens ZL is sent from the controller such as the zoom demand 20 or the focus demand 22 via the A / D converter 24 to the CPU 26. Command signal to be given, and based on the command signal given from the controller, the CPU 26 controls the focus lens FL and the zoom lens ZL to reach the target position or target speed commanded by the command signal. The rotation speed of each motor FM, ZM is determined, and a drive signal of a voltage corresponding to the rotation speed is output to each amplifier FA, ZA via the D / A converter 28 as described above.
[0026]
The CPU 26 detects the rotational position of the focus motor FM by the focus potentiometer FP as information on the current position of the focus lens FL, and determines the rotational position of the zoom motor ZM as information on the current position of the zoom lens ZL. It is detected by the pontension meter ZP. When the command signal for the focus lens FL or the zoom lens ZL instructs movement to a target position, the target position is sequentially compared with the current position of the focus lens FL or the zoom lens ZL for focusing. The rotation speed of the motor FM or the zoom motor ZM is determined.
[0027]
For the iris I, a command signal for instructing the set position (aperture value) of the iris I is generally given from the camera body (not shown) to the CPU 26, and the CPU 26 sets the iris I set as the iris I While the rotational position of the iris is detected by the iris potentiometer IM, a drive signal for driving the iris motor IM is output to the iris amplifier IA such that the aperture value is instructed by the instruction signal.
[0028]
On the other hand, the CPU 26 performs a drive signal for correcting the position of the AF master lens ML based on the set position of the zoom lens ZL (focal length of the photographing lens) as described above, and a signal for wobbling at the time of auto-focusing described later. A drive signal is generated, and the drive signal is output to the AF master amplifier MA to drive the AF master motor MM so that the AF master lens ML is at a target position or a target speed. Further, the CPU 26 detects the rotation position of the AF master motor MM as the set 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 at a desired target position.
[0029]
Here, the position correction of the AF master lens ML based on the set position (focal length of the photographing lens) of the zoom lens ZL will be described. The ROM 30 shown in FIG. And correction position data indicating an appropriate setting position (correction position) of the AF master lens ML. 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 the autofocus processing as described later. Then, the read correction position is set as the target position, and the AF master motor MM is driven to move the AF master lens ML to the correction position as described above.
[0030]
Next, the auto focus will be described. In this system, an automatic reset AF switch S1 which is normally turned off is provided, and when the AF switch S1 is turned off, manual focus (hereinafter, MF) is selected. The cameraman can adjust the focus by the MF by operating a predetermined operation member provided on the focus demand 22. That is, when the AF switch S1 is off, the CPU 26 drives the focus lens FL (focusing 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 mode is switched from MF to auto focus (hereinafter, AF), the 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 in-focus position. The fact that AF is executed only once means that once the focus lens FL is set to the focus position by AF, AF is not executed even if the focus position changes thereafter. In the embodiment, if AF is executed only once, the AF switch S1 returns to MF if it has returned to OFF.
[0032]
Here, the lens device 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 device 16. It is installed. Note that the focus evaluation value is a value indicating the level of contrast (sharpness) of an image, and the method of detecting the focus evaluation value is conventionally known in AF of a contrast method.
[0033]
FIG. 1 shows a focus evaluation value generation circuit. In a video signal acquired from the focus state detection imaging device 16, first, only a high frequency component is extracted by a high-pass filter (HPF) 32 and A / D conversion is performed. The signal is converted into a digital signal by the device 34. Then, of the high-frequency components converted into digital signals, signals only in a predetermined focus area set in the photographing range are extracted by the gate circuit 36. Note that a video signal other than the signal from the A / D converter 34 is directly input to the gate circuit 36, and a signal only in the focus area is extracted by using a synchronization signal in the video signal. The signal of the high-frequency component extracted by the gate circuit 36 is integrated by the adding circuit 38 for each field, and the signal obtained by the integration indicates the degree of focusing on the subject in the focus area (the level of contrast). The CPU 26 reads the focus evaluation value. Note that the method of detecting the focus evaluation value from the video signal is not limited to the above-described case.
[0034]
When the AF switch S1 is turned on, a drive signal for driving the focus motor FM is generated by the CPU 26 based on the focus evaluation value, and the drive signal is transmitted to the focus amplifier FA as in the case of the MF. The focus lens FL is output and moves to the 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. While wobbling, the focus evaluation value is obtained from the store evaluation value generation circuit (addition circuit 38) (for example, obtained for each field). As a result, a focus evaluation value equal to that obtained when the focus lens FL is moved back and forth from the current set position is detected. The CPU 26 determines whether or not the focus evaluation value is the maximum at the current position of the focus lens FL based on the focus evaluation value acquired during the wobbling. If the focus evaluation value is maximal, focus has been obtained, and the focus lens FL is stopped at that focus position. Further, the process returns to the MF process. On the other hand, if the focus evaluation value is not the local maximum, it is determined from the magnitude relationship of the focus evaluation values acquired during wobbling whether the focus position is in the infinite direction or the 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. By repeating the wobbling of the wobbling lens WL and the movement of the focus lens FL in this manner, the focus lens FL is automatically set to the in-focus position.
[0035]
Next, a processing procedure at the time of AF in the CPU 26 will be described with reference to a flowchart of FIG.
[0036]
First, the CPU 26 performs necessary initialization (step S10), and then executes processing other than AF (step S12). It should be noted that the processing other than the AF includes processing related to driving of the focus lens FL by the MF. Next, it is determined whether the AF switch S1 has been turned on (step S14). If the determination is NO, the process returns to step S12. On the other hand, if the determination is YES, the process proceeds to AF processing, and 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 set position (correction position) of the AF master lens ML corresponding to the current zoom position is read from the ROM 30 (step S18). Then, the AF master lens ML is moved to the target position using the read correction position as the target position (step S20). Subsequently, it is determined whether or not the AF master lens ML has reached the target position (Step S22), and the processes of Step S20 and Step S22 are repeated while determining NO.
[0037]
If YES is determined in the step S22, the CPU 26 moves the AF master lens ML back and forth about the correction position moved as described above to perform wobbling (step S24). At this time, the focus evaluation value is obtained from the focus evaluation value generation circuit, for example, for each field. Then, based on the focus evaluation value acquired during the wobbling, it is determined whether or not the focus evaluation value is the maximum at the current position of the focus lens FL, that is, whether or not the lens is in focus (step S26). Here, if the determination is YES, the process returns to step S12. That is, the mode is switched to MF. On the other hand, if NO is determined, it is determined whether or not the in-focus position is in the infinite direction from the current position of the focus lens FL based on the focus evaluation value acquired during wobbling (step S28). When the determination is YES, the focus motor FM is driven to move the focus lens FL in the infinite direction (step S30). On the other hand, if NO is determined, the focus lens FL is moved in the close direction (step S32).
[0038]
Then, after executing processing other than AF (step S34), the processing from step S16 is repeated until it is determined in step S28 that focusing has been achieved.
[0039]
As described above, in the above embodiment, the AF master lens ML is wobbled to determine whether or not the focus evaluation value is the maximum at the current position of the focus lens FL (whether or not the focus has been obtained) or the in-focus position. Is determined to be in an infinite direction or a close direction from the current position of the focus lens FL. However, without performing wobbling, a plurality of focus state detection imaging devices arranged at positions having different optical path lengths are used. The present invention can 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 the focus evaluation values are calculated. From the magnitude relationship, it is determined whether the focus is obtained at the current position of the focus lens FL. If not, the focus position is in the infinite direction or closer to the current position of the focus lens FL. Is determined. In this case, when light in a wavelength region other than the visible light region, such as the infrared region, is used as the focus state detection subject light as in the above-described embodiment, the focus state detection from the object at the focusing distance to be focused is performed. Adjust the focus position detection subject light imaging position so that the positional relationship between the subject light image formation position and the respective imaging positions of the plurality of focus state detection image sensors does not fluctuate due to the focal length of the imaging lens. I do.
[0040]
Further, in the above-described embodiment, the case where the image forming position of the focus state detection subject light fluctuates according to the focal length of the photographing lens is described. The correction position and the like 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 positional 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 set position of the AF master lens ML. However, the invention is not limited to this, and the imaging position of the imaging device for focus state detection may be adjusted.
[0042]
【The invention's effect】
As described above, according to the autofocus system according to the present invention, as the subject light used for autofocus, the subject light in a wavelength region different from the visible light region used for video is used. By dividing the subject light, it is possible to prevent a problem that the quantity of the subject light for video is insufficient. Further, by adjusting the imaging position of the autofocus subject light or the imaging position of the autofocus imaging means according to the focal length of the photographing lens, the subject light in a wavelength region other than visible light can be adjusted to the autofocus subject light. In such a case, it is possible to prevent a problem that the focusing position is reduced due to a change in the image forming position depending on the focal length of the photographing lens.
[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 between an image forming position of a subject light for video in a visible light region and a subject light for focus state detection in an infrared region.
FIG. 3 is a diagram exemplifying a shift amount of an imaging position of a focus state detection subject light in an infrared region with respect to an imaging position of a video subject light in a visible light region;
FIG. 4 is a block diagram showing a configuration of a control system of the lens device.
FIG. 5 is a flowchart illustrating a processing procedure at the time of AF in the CPU 26;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Lens device, 12 ... Camera body, 16 ... Focus state detection imaging element, 26 ... CPU, ZL ... Zoom lens, FL ... Focus lens, ML ... AF master lens, I ... Iris, M1 ... Infrared reflection 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 the autofocus subject light of a predetermined wavelength region different from the visible light region to a light path different from the optical path from the optical path for guiding the subject light incident on the imaging lens to the image pickup means,
An auto-focus imaging unit that captures auto-focus subject light branched by the auto-focus subject light branch unit and acquires image information of the subject as an electric signal;
Focus control means for controlling the focus of the photographic lens to be at a focus position based on image information of a subject obtained by the autofocus imaging means,
An auto focus system comprising: 2. The autofocus system according to claim 1, wherein the wavelength region of the subject light for autofocus is an infrared region. When the focal length of the photographing lens can be changed, an image forming position of the autofocus subject light from an object at a photographing distance focused on the video image pickup unit and an image pickup position of the autofocus image pickup unit Adjusting means for adjusting the imaging position or the imaging position based on the focal length of the photographing lens so that the relative positional relationship with the focal length does not change due to the change in the focal length. Item 1. The autofocus system according to item 1 or 2.

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