JP4318024B2 - 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 using a photographing lens having a focus lens and a tracking lens.
[0002]
[Prior art]
A zoom lens for TV cameras (so-called zoom lens) has a focus lens (group) in front of the zoom lens (group) (object side) and moves the focus lens in the direction of the optical axis to autofocus. In many cases, the focus adjustment is performed. In addition, a tracking lens (group) for performing tracking adjustment (flange back adjustment) is usually disposed behind the zoom lens. Conventionally, some focus lenses and tracking lenses can be operated electrically.
[0003]
Also, in contrast to television cameras, contrast-type autofocus (AF) is generally employed. For example, a high frequency component signal is extracted from a video signal photographed by a camera, and contrast is detected based on the high frequency component signal. Then, the position of the focus lens is controlled so that the contrast becomes the highest. In this specification, a value for evaluating the level of contrast is referred to as a focus evaluation value.
[0004]
Also, a hill-climbing method is known as a focus control method in such contrast AF. In the hill-climbing method, when a direction in which the focus evaluation value increases is detected, the focus evaluation value is sequentially acquired while moving the focus lens in that direction, the peak (maximum point) of the focus evaluation value is searched, and the focus evaluation value peak is passed. When a decrease in the focus evaluation value is detected, the focus lens is reversed, and the focus lens is stopped at a position where the focus evaluation value reaches a peak (see, for example, Patent Document 1).
[0005]
[Patent Document 1]
JP-A-11-103408
[0006]
[Problems to be solved by the invention]
However, the focus lens placed on the front side of the taking lens has a large diameter and is heavy, and also has a large operating range to cover the entire shooting distance. Therefore, the focus evaluation value is searched by moving the focus lens as in the above AF. Further, when the reversing operation is performed, there is a problem that the time required for focusing becomes long. On the other hand, when the tracking lens is moved, the tracking adjustment is shifted, but the same effect as when the focus lens is moved can be obtained. Moreover, it can be operated lighter and more quickly than the focus lens, and the focus can be greatly changed with a short stroke. Also, tracking adjustment is usually a problem when zooming is performed, and even if tracking adjustment shifts during focus adjustment, it does not matter much.
[0007]
An object of the present invention is to provide an autofocus system capable of quick focusing.
[0008]
[Means for Solving the Problems]
  In order to achieve the object, the invention described in claim 1Consists of a focus lens group that can be driven electrically from the subject side, a variator lens group, a compensator lens group, and a tracking lens group that is electrically driven and arranged in a relay lens groupAn autofocus system that detects a contrast of an image formed by an optical system and performs focusing based on the detected contrast.Focus lens groupWhen,SaidTracking lens groupFocus control means that controls both the drive and focusTaoAuto focus systemThe focus control means includes: a focus evaluation value generating means for generating a focus evaluation value for evaluating the contrast level of the image; and a peak detection for detecting a peak of the focus evaluation value generated by the focus evaluation value generating means. And a peak position setting means for setting the focus lens group and the tracking lens group at a position where the focus evaluation value reaches a peak after detection of the peak by the peak detection means, and the peak detection means includes the optical system. When the variable focal length is smaller than a predetermined value, the tracking lens group is moved in a direction in which the focus evaluation value reaches a peak to detect the peak of the focus evaluation value, and when the focal length is equal to or greater than the predetermined value. Detects the peak of the focus evaluation value by moving the focus lens group in the direction in which the focus evaluation value peaks.It is characterized by that. That is,Focus lens groupWhenTracking lens groupIt is possible to operate quickly by focusing using bothLens groupThe time required for focusing can be shortened by effectively using the.
[0012]
  AlsoRushIf the point distance is greater than or equal to the specified value (telephoto side)Tracking lens groupThe focal length is less than the predetermined value (wide side)) PlaceOnlyTracking lens groupTo focus quickly and enable quick focusingThe
[0013]
  Claims2The invention described in claim1In the described invention,Focus lens groupIs a lens group dedicated to focusing,Tracking lens groupIs a lens group used for tracking adjustment.
[0014]
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.
[0015]
FIG. 1 is a diagram showing a schematic configuration of an optical system (photographing lens) in a lens device for a television camera to which the present invention is applied. The photographing lens 2 shown in the figure is an inner focus type so-called zoom lens, and is used by being mounted on the mount of the camera body 4. When the movable constituent lens groups arranged in the lens barrel are shown in order from the front group, the tracking lens arranged in the focus lens (group) FL, the variator lens (group) VL, the compensator lens (group) CL, and the relay system R. There is a lens (group) TL. Further, an iris I is disposed between the zoom lens ZL and the lens group of the relay system R.
[0016]
Here, the focus lens FL is driven in the optical axis direction in order to focus on the subject, and changes the position of the best image plane. The variator lens VL is driven in the direction of the optical axis in order to change the size of the image, and changes the focal length of the photographing lens 2. The compensator lens CL is driven in the optical axis direction in conjunction with the variator lens VL, and corrects the focus shift. Since the variator lens (group) VL and the compensator lens (group) CL are linked, the zoom lens (group) ZL including both of these lenses (group) is referred to. The tracking lens TL is originally driven in the optical axis direction during tracking adjustment (flange back adjustment) and its position is adjusted in order to prevent fluctuations in the image plane due to zooming. Like the FL, it is used as a lens unit for focusing on the subject. Each lens FL, ZL, TL and iris I is connected to a corresponding motor FM, ZM, TM, IM, and is electrically driven.
[0017]
FIG. 2 is a block diagram showing the configuration of the control system of the lens apparatus having the optical system shown in FIG. In the figure, the focus lens FL, the zoom lens ZL, the tracking lens TL, and the iris I shown in FIG. 1 are shown, and a focus motor FM, a zoom motor ZM, a tracking motor TM, An iris motor IM is shown. Each of the motors FM, ZM, TM, and IM is driven by a focus amplifier FA, a zoom amplifier ZA, a tracking amplifier TA, and an iris amplifier IA, respectively, according to drive signals given from the CPU 14 via the D / A converter 16. It has become so.
[0018]
The CPU 14 determines the rotational speeds of the motors FM, ZM, TM, and IM so that the respective lenses FL, ZL, TL, and iris I have the desired target position and target speed, and the voltage corresponding to the rotational speed. Are output to the amplifiers FA, ZA, TA, and IA via the D / A converter 16 as described above. Here, each of the lenses FL, ZL, TL and iris I can be controlled by either position control or speed control. For example, when the positions of the lenses FL, ZL, TL and iris I are controlled, the CPU 14 Each motor FM, ZM, TM, IM is driven at a rotational speed corresponding to the difference between the desired target position and the current position. As shown in the figure, the motors FM, ZM, TM and IM are provided with potentiometers FP, ZP, TP and IP, respectively, and the CPU 14 outputs from the potentiometers FP, ZP, TP and IP. The obtained position signal is obtained as position information indicating the current position of each lens FL, ZL, TL, and iris I via an A / D converter (not shown).
[0019]
In addition, a controller such as a focus demand 30 and a zoom demand 32 for manually operating the focus and zoom of the photographing lens 2 can be connected to the lens apparatus, and command signals output from these controllers. Is supplied to the CPU 14 via the A / D converter 13. In general, a voltage value command signal indicating a target position of focus is supplied from the focus demand 30, and a voltage value command signal indicating a target speed of zoom is supplied from the zoom demand 32.
[0020]
When controlling the position or operating speed of the focus lens FL, zoom lens ZL, tracking lens TL, and iris I by the command signal from the controller, the CPU 14 is given the target position and target speed from the controller. Determine based on the command signal. A command signal for the iris I is usually given from the camera body 4.
[0021]
In addition, the present lens apparatus has an autofocus function, and the CPU 14 performs manual focus processing for controlling focus based on a command signal from the focus demand 30, and autofocus (AF) processing described below. Is switched according to the on / off state of the AF switch S1. When the AF switch S1 is turned on, AF processing is executed.
[0022]
As AF, continuous AF and one-shot AF are known. Continuous AF is to continue AF processing even if focus is once achieved by AF processing, and to focus again by AF when focus is shifted. One-shot AF is once focused by AF processing. If they are correct, the AF process is terminated and the process is switched to a manual focus process or the like. The AF processing described below can be similarly applied to both continuous AF and one-shot AF. However, the AF in this embodiment is assumed to be continuous AF, and the switch is pressed when the AF switch S1 is pressed once. Is turned on and continuous AF is executed. When the AF switch S1 is pressed again, the switch is turned off and, for example, manual focus is enabled.
[0023]
The AF method in the present embodiment is a so-called contrast method, and a video signal (luminance signal) generated by capturing an image of a subject in the camera body 4 is used. The video signal from the camera body 4 is input to the focus evaluation value generation unit 26 in FIG. 2, and the focus evaluation value generation unit 26 evaluates the level of contrast of the image based on the video signal. A focus evaluation value is generated. The configuration and processing of the focus evaluation value generation unit 26 are known and will be briefly described. First, the video signal input to the focus evaluation value generation unit 26 is converted into a digital signal by the A / D converter 18. Subsequently, only a high-frequency component signal is extracted from the video signal by the high-pass filter (HPF) 20, and only a signal within a predetermined focus area set within the photographing range is extracted from the extracted high-frequency component signal. Is extracted by the gate circuit 22. The gate circuit 22 determines whether the signal input from the HPF 20 is within the focus area based on the horizontal synchronization signal and the vertical synchronization signal included in the video signal.
[0024]
The signal extracted by the gate circuit 22 is subsequently input to the adder circuit 24 and integrated by the adder circuit 24 for each image (one field in the interlaced video signal). The signal obtained by the integration of the adder circuit 24 is a value indicating the degree of focus on the subject in the focus area (contrast level), and the value obtained by the adder circuit 24 is sequentially read by the CPU 14 as a focus evaluation value. It is done. The method for generating the focus evaluation value from the video signal is not limited to the above case.
[0025]
The CPU 14 executes the AF process when the AF switch S1 is turned on, and focuses as described later in detail so that the focus evaluation value read from the focus evaluation value generation unit 26 has a peak (maximum). The lens FL or tracking lens TL is driven to automatically adjust the focus of the photographing lens 2.
[0026]
Note that data necessary for various processes in the CPU 14 is recorded in the EEPROM 15.
[0027]
Next, the AF process in the CPU 14 will be described in detail. First, the first embodiment will be described with reference to the flowchart of FIG. In the following description, the focus lens FL is referred to as a front focus portion, and the tracking lens TL is referred to as a rear focus portion. After performing the required initial settings (step S10), the CPU 14 executes processing other than AF (step S12). Next, it is determined whether or not the AF switch S1 is turned on (step S14). While it determines with NO here, the process of step S12 is repeated. On the other hand, if YES is determined, the process proceeds to AF processing.
[0028]
When the process shifts to the AF process, the CPU 14 drives the rear focus unit to perform wobbling (step S16). In this wobbling process and operation, the rear focus unit is slightly reciprocated in the optical axis direction, and focus evaluation values at different positions in the meantime are acquired from the focus evaluation value generation unit 26. Further, based on the acquired focus evaluation value, a direction in which the focus evaluation value increases, that is, a direction (focusing direction) in which a peak (focusing) is obtained is detected. The wobbling can be performed by driving the front focus unit. However, since the front focus unit is heavy, it takes time to perform the reversing operation. Therefore, it is preferable to perform the wobbling at the rear focus unit.
[0029]
Subsequently, the CPU 14 moves the rear focus unit in the in-focus direction at a predetermined speed (step S18). At this time, focus evaluation values are sequentially acquired from the focus evaluation value generation unit 26. The focus evaluation value is acquired, for example, approximately every 1/60 seconds when a video signal for one field is given from the camera body 4 and one focus evaluation value is generated by the focus evaluation value generation unit 26. .
[0030]
Next, the CPU 14 determines whether or not the rear focus unit has passed the peak of the focus evaluation value (step S20). That is, it is determined whether or not the latest focus evaluation value obtained from the focus evaluation value generation unit 26 is smaller than the focus evaluation value acquired before that. If NO is determined, it is then determined whether or not the rear focus unit has moved a predetermined amount d described later (step S22). If NO is determined again, the processing from step S18 is repeated.
[0031]
On the other hand, if YES in step S20, that is, if it is determined that the peak of the focus evaluation value has passed, the process proceeds to step S28. If YES in step S22, that is, if it is determined that the rear focus unit has moved the predetermined amount d, then the front focus unit is moved in the in-focus direction (step S24). At this time, focus evaluation values are sequentially acquired from the focus evaluation value generation unit 26. Then, it is determined whether or not the front focus portion has passed the peak of the focus evaluation value (step S26). When it determines with NO, the process from step S24 is repeated. On the other hand, when it determines with YES, it transfers to step S28.
[0032]
Here, the effect | action by the process from step S16 to step S26 is demonstrated using FIG. 4, FIG. First, the state quantity related to the focus of the entire optical system of the photographing lens 2 that changes with the movement of the front focus unit and the rear focus unit is referred to as a focus position in this specification. For example, the focus position can be expressed by the shooting distance of the shooting lens 2.
[0033]
4 and 5, the focus position (shooting distance) is taken on the horizontal axis and the focus evaluation value is taken on the vertical axis, and graphs of focus evaluation values obtained at respective focus positions when a certain subject is photographed are illustrated. Yes. First, it is assumed that the focus position is set to a position corresponding to the point P1 on the graph of FIG. 4 (position close to the focal point P0) before moving the front focus section and the rear focus section. It is assumed that the rear focus unit is set to a tracking adjusted position (reference position). At this time, the increasing direction of the focus evaluation value is detected by the wobbling process in step S16, and the in-focus direction is determined to be the infinity direction. Then, the rear focus unit is driven in the direction of infinity by the process of step S18, and the focus position changes from the position of the point P1 on the graph toward the position of the focal point P0.
[0034]
Subsequently, it is assumed that the focus position has passed the position of the in-focus point P0 before the rear focus unit moves by the predetermined amount d. The amount of change d ′ when the predetermined amount d is converted into the value of the focus position is shown in FIG. If the first focus evaluation value is acquired at the position where the focus position is the point P2 after passing through the in-focus point P0, the focus evaluation value decreases from the focus evaluation value acquired once before, and the process of step S20 Thus, it is determined that the focus evaluation value has passed the peak. Thereby, the process proceeds to step S28. At this time, the driving of the rear focus unit is stopped. Even when the process of stopping the driving of the rear focus unit is performed when the focus position reaches the point P2, it actually takes time until the rear focus unit stops due to inertia or the like. . For this reason, it stops at a position where the focus position is slightly shifted to the infinity side from the position of the point P2.
[0035]
According to this, as shown in FIG. 4, the change amount d ′ is larger than the change amount x of the focus position from the position of the point P1, which is the initial position, to the position of the point P2, where the decrease in the focus evaluation value is confirmed. If it is larger, YES is not determined in the process of step S22. Therefore, only the rear focus unit is driven to a position that passes through the focal point P0.
[0036]
On the other hand, it is assumed that the focus position is set to a position corresponding to the point P1 on the graph of FIG. 5 (a position far from the focal point P0) before moving the front focus section and the rear focus section. At this time, the increasing direction of the focus evaluation value is detected by the wobbling process in step S16, and the in-focus direction is determined to be the infinity direction. Then, the rear focus unit is driven in the direction of infinity by the process of step S18, and the focus position changes from the position of the point P1 on the graph toward the position of the focal point P0.
[0037]
Subsequently, it is assumed that the amount of movement of the rear focus portion reaches the predetermined amount d when the position of the point P2 is reached without passing through the position of the focal point P0. That is, assume that when the position of the point P2 is reached, the change amount of the focus position reaches the change amount d ′ (the change amount when the predetermined amount d is converted into the value of the focus position). At this time, YES is determined in the process of step S22, and the driving of the rear focus unit is stopped.
[0038]
Next, the front focus unit is driven in the direction of infinity by the process of step S24, and the focus position changes from the position of the point P2 toward the position of the focal point P0. If the first focus evaluation value is acquired at a position where the focus position passes through the position of the in-focus point P0 and the focus position becomes the point P3 after passing through the in-focus point P0, the focus evaluation value is acquired once before. It is determined that the focus evaluation value has passed the peak of the focus evaluation value by the process of step S26. Thereby, the process proceeds to step S28. At this time, the driving of the front focus unit is stopped.
[0039]
According to this, first, when the rear focus unit is driven from the reference position and the change amount of the focus position reaches the change amount d ′ as shown in FIG. 5 before confirming the decrease in the focus evaluation value, The front focus unit is driven instead of the focus unit. Then, the front focus unit is driven to a position that passes through the focal point P0.
[0040]
By the way, the predetermined amount d is set to a value such that the variation d ′ is larger than the variation s from the focal point P0 to the point P3 as shown in FIG. However, in the above description, the point P3 is a position where the focus evaluation value is first acquired after passing the in-focus P0 and the decrease in the focus evaluation value is confirmed. A point where the front focus portion actually stops when the process of stopping the drive of the focus portion is performed is defined as a point P3.
[0041]
That is, when the rear focus unit is returned to the reference position (that is, the position set by tracking adjustment) after the front focus unit stops at the point P3, the focus position P4 at that time is as shown in FIG. The movement amount d is set so as to be closer to the focal point P0, that is, at a position shifted in the same direction as the initial position P1 with respect to the focal point P0. Although the effect of this is related to the processing described later and is omitted here, the amount of change in the focus position per unit movement amount of the front focus unit and the rear focus unit differs depending on the focal length. The change amount s varies depending on the moving speed of the front focus unit. Accordingly, the moving amount d also varies depending on the focal length and the moving speed of the front focus unit. Therefore, the moving amount d is determined based on the focal length (the setting position of the zoom lens ZL) and the moving speed of the front focus unit.
[0042]
Next, a description will be given of a case where YES is determined in step S20 or step S26 of FIG. 3 and the process proceeds to step S28. First, the CPU 14 returns the focus from the focus evaluation value generation unit 26 while returning the rear focus unit to the reference position. An evaluation value is acquired and the in-focus position is confirmed (step S28). The reference position is an initial position before the rear focus unit is moved, and indicates a position set by tracking adjustment. The confirmation of the in-focus position is a process for accurately determining the position at which the focus evaluation value reaches a peak. For this purpose, the speed at which the rear focus unit is returned to the reference position is made slower than the movement speed in step S18.
[0043]
Subsequently, the CPU 14 calculates the in-focus position of the front focus unit when the rear focus unit is returned to the reference position based on the in-focus position of the rear focus unit confirmed in step 28 (step S30). Then, the rear focus unit is moved to the reference position (step S32), and the front focus unit is moved to the in-focus position (step S34). At this time, as described with reference to FIG. 5, the movement amount d of the rear focus unit is the same as the reference position with respect to the in-focus point when the rear focus unit is returned to the reference position. Since the position is set so as to be shifted in the direction, the moving direction of the front focus portion in step S34 always coincides with the moving direction in step S24. That is, normally, since the weight is heavy and the reversing operation does not require a reversing operation of the front focus portion, it is possible to focus quickly. When the above process ends, the process from step S14 is repeated.
[0044]
Note that the processing from step S28 to step S34 can take various forms. For example, the confirmation of the in-focus position in step S28 is not always performed by driving the rear focus unit. If the front focus unit is driven in step S24, the focus evaluation value is passed after the peak. The in-focus position may be confirmed by reversing the front focus unit. However, since the front focus unit is heavy and takes time to reverse, it is advantageous to check the in-focus position by driving the rear focus unit.
[0045]
Further, although the rear focus unit is returned to the reference position after the in-focus position is confirmed, the rear focus unit is not necessarily returned to the reference position. If the rear focus part is not returned to the reference position, tracking adjustment will be out of order, and zooming may occur if zooming is performed in this state. Since it is not performed on air or during recording, there are few problems. Thus, for example, when the rear focus unit is driven and the focus position is confirmed in step S28, the rear focus unit may be stopped at that position. In addition, the operator may be able to select whether or not to return the rear focus unit to the reference position with a switch or the like. Furthermore, the rear focus unit may be returned to the reference position at the start of manual focus by the focus demand 30, or the rear focus unit may be gradually returned to the reference position along with the focus operation.
[0046]
In the first embodiment, the movement amount of the rear focus unit is limited by the predetermined amount d, but it is not necessarily limited by the predetermined amount d. For example, the rear focus unit can be moved within the entire movable range reaching the mechanical end.If the rear focus unit does not pass the peak focus evaluation value even when it reaches the mechanical end, the front focus unit is You may make it drive.
[0047]
Further, in the first embodiment, when the rear focus unit moves by a predetermined amount d and does not pass the peak of the focus evaluation value, the driving of the rear focus unit is stopped and the front focus unit is moved. However, the present invention is not limited to this, and if the rear focus unit does not pass the peak of the focus evaluation value even if the rear focus unit moves by a predetermined amount d, the rear focus unit is continuously driven without stopping. In addition, the front focus unit may be driven.
[0048]
Next, the AF processing in the CPU 14 will be described with reference to the flowchart of FIG. Generally, when the zoom of the photographic lens 2 is on the wide side (when the focal length is short), it is possible to focus on a subject at a desired distance only by driving the tracking lens TL (rear focus portion). On the other hand, when the zoom of the taking lens 2 is on the telephoto side (when the focal length is long), the amount of change in the focus position per unit movement amount of the tracking lens TL is extremely small, so that only the tracking lens TL can be used for focusing. There are cases where it is not possible. That is, the entire range of the required shooting distance cannot be covered with the stroke of the tracking lens TL. Therefore, in the second embodiment, driving of the front focus unit and the rear focus unit is switched according to the focal length.
[0049]
As shown in FIG. 7, the CPU 14 performs processing other than AF (step S52) after performing required initial settings (step S50). Next, it is determined whether or not the AF switch S1 is turned on (step S54). While the determination is NO here, the process of step S52 is repeated. On the other hand, if YES is determined, the process proceeds to AF processing.
[0050]
When the process proceeds to AF processing, the CPU 14 first reads the current focal length (step S56). That is, the current position of the zoom lens ZL is read. Then, it is determined whether or not the read focal length is wider than the predetermined focal length (step S58). When it determines with YES, it transfers to step S60, and when it determines with NO, it transfers to step S66.
[0051]
If YES is determined and the process proceeds to step S60, the rear focus unit is first driven to perform wobbling to detect the in-focus direction (step S60). Then, the rear focus unit is moved in the in-focus direction at a predetermined speed (step S62). At this time, focus evaluation values are sequentially acquired from the focus evaluation value generation unit 26. Subsequently, the CPU 14 determines whether or not the rear focus unit has passed the peak focus evaluation value (step S64). When it determines with NO, the process from step S62 is repeated. On the other hand, when it determines with YES, it transfers to step S72.
[0052]
If NO is determined in step S58 and the process proceeds to step S66, first, the rear focus unit is driven and wobbling is performed to detect the in-focus direction (step S66). Then, the front focus unit is moved at a predetermined speed in the in-focus direction (step S68). At this time, focus evaluation values are sequentially acquired from the focus evaluation value generation unit 26. Subsequently, the CPU 14 determines whether or not the rear focus unit has passed the peak focus evaluation value (step S70). When it determines with NO, the process from step S68 is repeated. On the other hand, when it determines with YES, it transfers to step S72.
[0053]
In step S72, the CPU 72 finely adjusts the rear focus unit and confirms the in-focus position (step S72). Subsequently, based on the in-focus position of the rear focus unit confirmed in step S72, the in-focus position of the front focus unit when the rear focus unit is returned to the reference position is calculated (step S74). Then, the rear focus unit is moved to the reference position (step S76), and the front focus unit is moved to the in-focus position (step S78). When the above process ends, the process from step S55 is repeated.
[0054]
In the second embodiment as well, the processing from step S72 to step S78 can take various forms as in the first embodiment. For example, the confirmation of the in-focus position in step S72 is not always performed by driving the rear focus unit. If the front focus unit is driven in step S64, the focus evaluation value peak is passed. The in-focus position may be confirmed by reversing the front focus unit. However, since the front focus unit is heavy and takes time to reverse, it is advantageous to check the in-focus position by driving the rear focus unit.
[0055]
Further, although the rear focus unit is returned to the reference position after the in-focus position is confirmed, the rear focus unit is not necessarily returned to the reference position. In addition, the operator may be able to select whether or not to return the rear focus unit to the reference position with a switch or the like. Furthermore, the rear focus unit may be returned to the reference position at the start of manual focus by the focus demand 30, or the rear focus unit may be gradually returned to the reference position along with the focus operation.
[0056]
In the above embodiment, the autofocus system used for the television camera has been described. However, the present invention can also be applied to an autofocus system other than the television camera.
[0057]
【The invention's effect】
As described above, according to the autofocus system of the present invention, since both the front focus unit and the rear focus unit are driven to perform focusing, the focus unit that can operate quickly can be used effectively. Thus, the time required for focusing can be shortened.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of an optical system (photographing lens) in a lens device for a television camera to which the present invention is applied.
FIG. 2 is a block diagram showing a configuration of a control system of a lens apparatus having the optical system shown in FIG.
FIG. 3 is a flowchart showing a first embodiment of AF processing in a CPU.
FIG. 4 is a diagram used for explaining the effect of the processing from step S16 to step S26 in the flowchart of FIG. 3;
FIG. 5 is a diagram used for explaining the action of the processing from step S16 to step S26 in the flowchart of FIG. 3;
FIG. 6 is a diagram used for explaining a predetermined amount d for limiting the amount of movement of the rear focus unit (tracking lens).
FIG. 7 is a flowchart illustrating a second embodiment of AF processing in the CPU.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 2 ... Shooting lens, 4 ... Camera body, 13 ... A / D converter, 14 ... CPU, 16 ... D / A converter, 18 ... A / D converter, 20 ... High pass filter, 22 ... Gate circuit, 24 ... Addition circuit, 26 ... focus evaluation value generation unit, 30 ... focus demand, 32 ... zoom demand, FL ... focus lens (front focus unit), ZL ... zoom lens, TL ... tracking lens (rear focus unit), FM ... focus Motor, ZM ... zoom motor, TM ... tracking motor, FA ... focus amplifier, ZA ... zoom amplifier, TA ... tracking amplifier, S1 ... AF switch

Claims (2)

The contrast of an image formed by an optical system consisting of a focus lens group, a variator lens group, a compensator lens group, and a relay lens group that can be driven electrically from the subject side. detecting, a autofocus system for focusing based on the contrast the detected, O over said with a focus lens group, the focus control means to focus drives and controls both the tracking lens group In the focus system ,
The focus control means includes a focus evaluation value generation means for generating a focus evaluation value for evaluating the contrast level of the image, a peak detection means for detecting a peak of the focus evaluation value generated by the focus evaluation value generation means, A peak position setting means for setting the focus lens group and the tracking lens group at a position where the focus evaluation value reaches a peak after detection of the peak by the peak detection means,
When the variable focal length of the optical system is smaller than a predetermined value, the peak detection means detects the peak of the focus evaluation value by moving the tracking lens group in a direction in which the focus evaluation value reaches a peak, When the distance is equal to or greater than the predetermined value, the focus lens group is moved in a direction in which the focus evaluation value reaches a peak, and the peak of the focus evaluation value is detected . 2. The autofocus system according to claim 1, wherein the focus lens group is a lens group dedicated to focusing, and the tracking lens group is a lens group used for tracking adjustment.

Images