Lens control apparatus

A video camera having a variator lens and focus lens which calculates in-focus positions varying with the drive of the variator lens based on previously stored in-focus position data, and performs the calculation a plurality of times during a period of a vertical-synchronizing signal in an image signal.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a lens control apparatus to be preferably
 used in a video camera.
 2. Description of the Related Art
 Recently, video cameras or camcorders have become remarkably widespread,
 and many improvements have been made in performance, function, and
 operability thereof. Particularly, miniaturization thereof and increase in
 magnification of zooming are strongly demanded, and many attempts have
 been made to achieve them.
 The reason why miniaturization of the video cameras is realized in these
 circumstances is that lenses of an internal focusing type which are small
 and capable of high-magnification zooming are adopted.
 FIG. 1 schematically illustrates a configuration of a commonly used lens
 system of the internal focusing type.
 Referring to FIG. 1, there are provided the first fixed lenses 101; the
 second lenses for varying magnification (hereinafter, referred to as a
 variator lens); a diaphragm 103, the third fixed lenses 104; the fourth
 lenses 105 (hereinafter, referred to as a focus lens) having both a
 focusing function and a so-called compensator (focus compensation)
 function of compensating for a shifting of a focal plane due to a
 magnification varying, and an image pick-up surface 106.
 According to the lens system constructed as shown in FIG. 1, since the
 focus lens 105 has both the compensator function and focusing function,
 the position of the focus lens 105 for focusing on the image pick-up
 surface 106 varies with object distances even if focal lengths are equal.
 And, it is needless to say that the position of the focus lens 105 varies
 with the focal lengths even if the object distances are equal.
 FIG. 2 is the plot of the position of the focus lens 105 for focusing on
 the image pick-up surface when the object distances are varied in each of
 the focal lengths. If a locus shown in FIG. 2 is selected in accordance
 with the object distance during magnification varying, and the focus lens
 105 is shifted in accordance with the locus, a zooming without defocus
 becomes possible.
 According to a lens system of a for-element focusing type, a compensator
 lens is provided separately from the focus lens with respect to the
 variator lens, and the variator lens and compensator lens are coupled by
 means of a mechanical cam ring. Therefore, when a knob for manual zooming
 is provided to vary the focal length manually, the cam ring follows the
 knob to rotate however fast the knob may be actuated, so that the variator
 lens and compensator lens shift along a groove of the cam ring. Thus,
 defocus is not caused by the zooming when the focus lens is in focus.
 In a zoom control of the lens system of the internal focusing type having
 characteristics as described above, it is popular that a plurality of
 locus data shown in FIG. 2 are stored in a lens control microcomputer in
 one form or another, the locus of the focus lens is selected in accordance
 with the positions of the focus lens and variator lens, and the zooming is
 performed by tracing the selected locus.
 Further, since the position of the focus lens with respect to the variator
 lens is read out from a memory device so as to be utilized for controlling
 the positions of the lenses, the position of each lens must be read out
 accurately to some extent. Particularly, as is also apparent from FIG. 2,
 the inclination of the locus of the focus lens varies every moment with
 the change of the focal length when the variator lens shifts with constant
 or nearly constant speed. This shows that the shifting speed and shifting
 direction of the focus lens change every moment. In other words, an
 actuator of the focus lens must perform accurate speed response from 1 Hz
 to several hundred Hz.
 As an actuator which satisfies the above-described requirement, the use of
 a stepping motor in the focus lens of the internal-focusing lens system is
 becoming popular. Since the stepping motor rotates in complete synchronism
 with stepping pulses output from the lens control microcomputer or the
 like, and a stepping angle per pulse is constant, it is possible to obtain
 a high speed response and, stopping accuracy and position accuracy can be
 obtained.
 In addition, the use of the stepping motor offers the following advantage.
 Since a rotation angle of the motor with respect to the number of stepping
 pulses is constant, the stepping pulse can be used as an incremental
 encoder, and there is no need to provide additionally a specific position
 encoder.
 As described above, when the magnification varying is performed while
 maintaining in-focus with the use of the stepping motor, it is necessary
 to store the locus data of FIG. 2 in the lens control microcomputer or the
 like in one form or another (either the locus itself or a function having
 a variable of the lens position will do), read out the locus data in
 accordance with the position or the shifting speed of the variator lens,
 and then move the focus lens based on the data.
 FIGS. 3A and 3B illustrate an example of the already proposed locus
 follow-up method.
 FIG. 3B shows a memory table in the lens control microcomputer in which the
 locus data of FIG. 3A are stored. As apparent from FIG. 3B, shifting
 ranges of the variator lens and focus lens are split into a plurality of
 areas, and focus lens data a0, a1, . . . , b0, b1, . . . determined by the
 variator lens positions z0, z1, . . . and the object distance are stored
 in order. In FIG. 3B, v represents the variator lens position, n
 represents the object distance and each of the data Anv (n=0, 1 . . . m;
 v=0, 1 . . . s) are focus lens position data which are unitarily
 determined by the variator lens position and object distance.
 In FIG. 3A, each of z0, z1, z2 . . . z6 represents the variator lens
 position; each of a0, a1, a2 . . . a6 and each of b0, b1, b2 . . . b6
 represent typical loci of the focus lens stored in the lens control
 microcomputer. And, each of p0, p1, p2 . . . p6 represent the locus of the
 focus lens calculated from the above-described two loci. The locus is
 calculated by the following expression:
EQU p(n+1)=.vertline.p(n)-a(n).vertline./
 .vertline.b(n)-a(n).vertline..multidot..vertline.b(n+1)-a(n+1).vertline.+a
 (n+1) (1)
 The expression (1) shows that when the focus lens is on p0, a ratio of a
 line segment b0-a0 divided internally by p0 is determined and a point
 which divides internally a line segment b1-a1 in accordance with the above
 ratio is taken as p1. A standard shifting speed of the focus lens for
 maintaining in-focus can be found from the position difference between p1
 and p0, and the time involved in shifting of the variator lens from z0 to
 z1.
 A case will now be described where there is no restriction such that the
 variator lens should stop only on the border having the stored typical
 locus data. FIG. 4 is a view for explaining an interpolation method of the
 variator lens position in which a part of FIG. 3A is extracted and the
 variator lens is at the voluntary position.
 In FIG. 4, the vertical axis represents the focus lens position and the
 horizontal axis represents the variator lens position, respectively, and
 the typical locus positions (the focus lens position with respect to the
 variator lens position) stored in the lens control microcomputer are
 represented by a0, a1 . . . ak-1, ak . . . an and b0, b1 . . . bk-1, bk .
 . . bn according to the object positions when the variator lens positions
 are Z0, Z1 . . . Zk-1, Zk . . . Zn, respectively.
 When the variator lens is on Zx which is not the zoom border and the focus
 lens position is px, ax and bx are determined by the following
 expressions:
EQU ax=ak-(Zk-Zx)(ak-ak-1)/(Zk-Zk-1) (2)
EQU bx=bk-(Zk-Zx)(bk-bk-1)/(Zk-Zk-1) (3)
 That is, ax and bx can be determined by internally dividing one of the four
 stored typical locus data (ak, ak-1, bk, and bk-1 in FIG. 4) of the same
 object distance by the internal division ratio obtained from the present
 variator lens position and two zoom border positions (for example, Zk and
 Zk-1 of FIG. 4) which sandwich the present variator lens position. And, pk
 and pk-1 can be determined by internally dividing one of the four stored
 typical locus data (ak, ak-1, bk, and bk-1 in FIG. 4) of the same object
 distance by the internal division ratio obtained from ax, px and bx of
 expression (1). When zooming from a telephoto side to a wide view side, a
 shifting speed of the focus lens for maintaining in-focus can be found
 from the difference between the follow-up position pk of the focus lens
 and the present position px of the focus lens, and the time involved in
 shifting of the variator lens from Zx to Zk. When zooming from a wide view
 side to a telephoto side, the standard shifting speed of the focus lens
 for maintaining in-focus can be found from the difference between the
 follow-up position pk-1 of the focus lens and the present position px of
 the focus lens, and the time involved in shifting of the variator lens
 from Zx to Zk-1. The locus follow-up method as described above already has
 been proposed.
 FIG. 5 is a flowchart showing a control of the above-described system which
 is usually processed in a lens control AF (automatic focusing)
 microcomputer. The processing is started from S1. A reset routine S2
 resets RAM and various ports in the AF microcomputer. A communication
 routine S3 exchanges data of a zoom switch instructing the zooming and
 data of magnification varying, such as a variator lens position, with a
 system control microcomputer (hereinafter, referred to as a system
 controller). An AF processing routine S4 processes a sharpness signal of
 an AF evaluation signal to perform automatic focusing in accordance with a
 change in the evaluation signal. A zoom processing routine S5 is a routine
 for processing an operation of a compensator lens to maintain in-focus
 during the zooming. In this routine, a standard drive direction and a
 standard drive speed of the focus lens which traces the locus shown in
 FIG. 3 are calculated.
 A drive direction/speed select routine S6 selects the drive directions and
 drive speeds of the variator lens and focus lens calculated in S4 and S5
 in accordance with the automatic focusing and magnification varying. This
 routine prevents the lenses from being driven beyond the telephoto end,
 beyond the wide view end, beyond the closest end and beyond the infinity
 end which are specified on the programs so that the lenses do not butt
 against mechanical ends. S7 outputs a control signal to a motor driver in
 accordance with the data of the drive directions and drive directions of
 the variator lens and focus lens determined in the routine S6, so as to
 control drive/stop of the lenses. After completion of processing in S7,
 the procedure returns to the routine S3. A series of processing in FIG. 5
 are performed in synchronization with a vertical-synchronizing signal (the
 processing in S3 waits for the next vertical-synchronizing signal to
 come). That is, in a video camera, since focus data for automatic focusing
 is detected in a field cycle (a cycle of the vertical-synchronizing
 signal), a flow of the control also synchronizes to the
 vertical-synchronizing signal and is repeatedly performed in the cycle.
 However, because zoom speed has increased in recent years so the variator
 lens shifts, for example, from Z4 to Z6 in FIG. 3A during the
 vertical-synchronizing period. Thus, when the above-described operation is
 performed once during the vertical-synchronizing period, the focus lens
 shifts from p4 to p6' to defocus by p6'-p6, whereby the locus can not be
 traced exactly during the zooming. The term "vertical-synchronizing
 period" means a cycle of the vertical-synchronizing signal, i.e. a field
 period.
 SUMMARY OF THE INVENTION
 It is an object of the present invention to provide a video camera which
 enables the focus lens to follow exactly zooming even if zoom speed is
 high.
 It is another object of the present invention to allow the compensator lens
 to follow the zooming with high accuracy.
 According to a preferred embodiment of the invention, there is provided a
 video camera comprising a variator lens; a focus lens; drive means for
 shifting the variator lens and focus lens separately toward the optical
 axis; storage means for storing in-focus position data in each object
 distance of the focus lens with respect to the variator lens; calculation
 means for calculating a shifting speed of the focus lens when shifting the
 variator lens based on the in-focus position stored in the storage means;
 and control means for controlling the drive means based on outputs of the
 calculation means, wherein the calculation means and control means are
 actuated a plurality of times in one vertical-synchronizing period.
 According to another preferred embodiment of the invention, there is
 provided a video camera wherein the number of times calculation and
 control is performed during the vertical-synchronizing period is
 determined in accordance with the shifting speed of the variator lens.
 According to a further preferred embodiment of the invention, there is
 provided a lens control apparatus, such as that of a video camera, wherein
 the calculation of the shifting speed of the focus lens when there is
 shifting of the variator lens, and control of shifting of the focus lens
 by the calculation results, are performed a plurality of times in one
 vertical-synchronizing period.
 Further objects, features and advantages of the present invention will
 become apparent from the following description of the preferred
 embodiments with reference to the attached drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The preferred embodiments of the video camera system according to the
 present invention will now be described in detail.
 First Embodiment
 FIG. 6 is a block diagram showing a configuration of a video camera to
 which a first embodiment of the present invention is applied.
 Referring to FIG. 6, there are provided components of an internal focusing
 type lens system such as first fixed for-element lenses 101, second lenses
 102 for varying magnification (variator lens), a diaphragm 103, third
 fixed lenses 104, and fourth lenses (focus lens) 105 having both a
 compensation function and a focusing function. An image light passed
 through the lens system is subject to an image formation on the surface of
 an image pick-up element 106, and is converted into an image signal by a
 photoelectric conversion. There are also provided an amplifier (or an
 impedance converter) 107 and a camera signal processing circuit 108. The
 image signal processed therein is amplified by the amplifier 109 to a
 prescribed level, processed by a LCD (liquid crystal display) display
 circuit 110 and then, displayed as a pick-up image by an LED 111.
 On the other hand, the image signal amplified by the amplifier 107 is
 transmitted to a diaphragm control circuit 112 and an AF evaluation value
 processing circuit 115. The diaphragm control circuit 112 drives an IG
 driver 113 and an IG meter 114 in accordance with an input level of the
 image signal to control the diaphragm 103, thereby adjusting the quantity
 of light.
 The AF evaluation value processing circuit 115 extracts and processes only
 a high frequency component of the image signal within a focusing frame in
 a screen in accordance with a gate signal from a focusing frame producing
 circuit 117. An AF microcomputer 116 controls a focusing frame for driving
 and controlling a lens and for varying a focusing area in accordance with
 the strength of an AF evaluation signal. In addition, the AF microcomputer
 116 communicates with a system controller 122, and the system controller
 122 reads in operation data from various operating portions by means of an
 A/D converter and the like. For example, the AF microcomputer 116 and the
 system controller 122 exchange data of a zoom switch 123 (a unit zoom
 switch from which a voltage corresponding to a rotation angle of an
 operating member is output, thereby performing a variable-speed zooming)
 and data of a zoom operation, such as a direction of magnification varying
 and a focal length when zooming is controlled by the AF microcomputer 116.
 A timing generator 124 generates a vertical-synchronizing signal and
 inputs it into the AF microcomputer 116. A variator driver 118 and a focus
 lens driver 120 output, respectively, a drive energy to lens drive motors
 in accordance with instructions for driving the variator lens 102 and
 focus lens 105 output from the AF microcomputer 116. A variator lens motor
 119 drives the variator lens 102, and a focus lens motor 121 drives the
 focus lens 105, respectively.
 A method of driving the variator lens motor and focus lens motor will now
 be described when the variator lens motor 119 and focus lens motor 121 are
 stepping motors.
 The AF microcomputer 116 determines drive speeds of each of the variator
 lens motor 119 and focus lens motor 121 by means of program manipulation,
 and sends the drive speeds as rotation speed signals of each of the
 stepping motors 119 and 121 to the variator lens driver 118 and focus lens
 driver 120. In addition, the AF microcomputer 116 sends drive/stop
 instruction signals and rotation direction instruction signals of each of
 the motors 119 and 121 to the drivers 118 and 120, respectively. With
 respect to the variator lens motor 119, the drive/stop and rotation
 direction signals are output to the driver 118 mainly in accordance with a
 state of the zoom switch 123. With respect to the focus lens motor 121,
 these signals are output to the driver 120 in accordance with drive
 instruction determined by processing in the microcomputer 116 when there
 is automatic focusing and zooming. Each of the drivers 118 and 120 set
 excitation phases of the 4-phase motor for forward or backward rotations
 in accordance with the rotation direction signals, and output frequencies
 of pulse signals and voltages (or currents) to be applied to four
 excitation phases while varying them, thereby on/off controlling the
 outputs to the motors 119 and 121 in accordance with drive/stop
 instruction while controlling the rotation directions and rotation speeds
 of the motors.
 FIG. 7 is a flowchart showing an operation of the first embodiment which is
 processed in the AF microcomputer 116 performing a lens control. The
 processing is started from S201. A reset routine S202 resets RAM and
 various ports in the AF microcomputer 116. A communication routine S203
 exchanges data of zoom switch 123 and data of magnification varying, such
 as a position of the variator lens 102 with the system controller 122. An
 AF processing routine S204 extracts high frequency components and the like
 from the image signal to generate a sharpness signal, obtains peak values
 and internal values of the sharpness signal, to generate an evaluation
 signal and further, performs automatic focusing in accordance with a
 change in the evaluation signal. A zoom processing routine S205 is a
 routine for processing an operation of a compensator lens for maintaining
 in-focus during the zooming. In this routine, a drive direction and a
 drive speed of the focus lens 105, which traces the locus shown in FIGS. 3
 and 4 and maintains in-focus, are calculated.
 A drive direction/speed select routine S206 selects the drive directions
 and drive speeds of the variator lens and focus lens calculated in the
 routines S204 and S205 in accordance with the automatic focusing and
 zooming. This routine prevents the lenses from being driven beyond the
 telephoto end, beyond the wide view end, beyond the closest end, and
 beyond the infinity end, which are specified on the program so that the
 lenses do not butt against mechanical ends. S207 outputs a control signal
 to the lens drivers 118 and 120 in accordance with the data of the drive
 directions and drive speeds of the variator lens and focus lens determined
 in the routine S206 so as to control drive/stop of the lenses. S208 waits
 for the fixed time to elapse, corresponding to the period required to
 reach the middle point of the vertical-synchronizing period. Since the
 position of the variator lens is renewed when the zooming is being
 performed in S209, a zoom processing is performed in a routine S210 to
 calculate the drive direction and the drive speed of the focus lens 105 as
 shown in FIGS. 3 and 4. A routine S211 prevents the lenses from being
 driven beyond the telephoto end, beyond the wide view end, beyond the
 closest end, and beyond the infinity end, which are specified on the
 program so that the lenses do not butt against mechanical ends by the
 drive directions and drive speeds of the variator lens and focus lens
 calculated in the routine S210. A routine S212 outputs control signals to
 the lens drivers 118 and 120 in accordance with data of the drive
 directions and drive speeds of the variator lens and focus lens to control
 drive/stop of the lenses. After completion of processing in S212, the
 procedure returns to S203. A series of processing in FIG. 7 are performed
 in synchronization with the vertical-synchronizing signal (the processing
 in S203 waits for the next vertical-synchronizing signal to come).
 If a follow-up speed of the focus lens is calculated once during the
 vertical-synchronizing period while zooming so as to drive the focus lens,
 the focus lens speed shows inclinations p4 and p5 when the variator lens
 shifts from the position Z4 to the position Z6 during the
 vertical-synchronizing period in FIG. 3A, and the focus lens shifts to the
 position p6' after one vertical-synchronizing period, thereby making it
 difficult to trace the locus of the focus lens. However, when the
 follow-up speed of the focus lens is calculated two times as described in
 this embodiment, the focus lens speed shows inclinations p4 and p5 in the
 first half of the vertical-synchronizing period, passes p5 and shows the
 inclinations p5 and p6 and then, reaches p6. Thus, the locus of the focus
 lens can be exactly traced, and the compensator lens can follow the
 zooming to compensate with high accuracy for the in-focus positions
 varying with the drive of the variator lens, so that in-focus can be
 securely maintained.
 Second Embodiment
 It is described in the first embodiment that the zoom processing routine,
 drive direction/speed select routine and motor drive control of the
 variator lens and focus lens are performed two times within the
 vertical-synchronizing period, so as to allow the focus lens to follow
 exactly the zooming. However, according to a method of the first
 embodiment, it is difficult for the focus lens to follow the zooming
 exactly in the case where the zoom speed is faster and, for example, the
 variator lens shifts from the position Z3 to the position Z6 during the
 vertical-synchronizing period in FIG. 3A. Thus, a method for allowing the
 focus lens to follow the zooming exactly in the case of higher speed
 zooming will now be described in the second embodiment.
 FIG. 8 is a flowchart showing an operation of the second embodiment.
 The second embodiment is different from the first embodiment in that the
 processing from S308 to S312 is included in the flowchart which perform
 calculations shown in FIGS. 3 and 4 at the specified number of times m in
 the zoom processing routine S305 to obtain the focus lens follow-up speed,
 set the drive directions and speeds of the variator lens and focus lens,
 and drive the variator lens motor and the focus lens motor. The specified
 number of times m may be the number of times falling within the
 vertical-synchronizing period. S308 counts the specified number of times,
 and whether or not the specified number of times is n times is judged in
 S309. If not n times, the procedure advances to S310 to wait for the fixed
 time to elapse. The fixed time is determined by the vertical-synchronizing
 period, specified number of times m, and processing times from the routine
 S305 to S307.
 As described above, the performance of the processing S305 to S307 at m=n
 times during the vertical-synchronizing period enables the focus lens to
 follow exactly the zooming, even in higher speed zooming.
 Third Embodiment
 In the second embodiment, it is described that the zoom processing routine,
 drive direction/speed select routine and motor drive control of the
 variator lens and focus lens are performed m=n times during the
 vertical-synchronizing period, in order to allow the focus lens to follow
 exactly the zooming even during high speed zooming. Recently, however, the
 zoom speed has become variable. For example, the zoom switch 123 consists
 of a variable resistance as shown in FIG. 9A, and a voltage value thereof
 is input to the system controller to perform A/D conversion, thereby
 determining the zoom speed. As shown in FIG. 9B, the zooming is stopped at
 the intermediate value of the voltage of about 2.5 V. When the voltage
 value is smaller than the intermediate value, a wide-view zooming is
 effected. Wide view zooming is performed at higher speeds when the voltage
 value is smaller. When the voltage value is larger than the
 above-described intermediate value, telephoto zooming is effected.
 Telephoto zooming is performed at higher speeds when the voltage value is
 larger. Although the zoom speed is divided into three steps of low speed,
 medium speed and high speed in this embodiment, it can be subdivided into
 steps. In case there are any kinds of zoom speed, if the specified number
 of times m is fixed to n times, the condition arises in which n times are
 not required during low speed zooming, and n times are insufficient during
 the high speed zooming. Thus, setting of the specified number of times m
 matched with the zoom speed allows the focus lens to follow the zooming at
 any zoom speed. An example thereof will be described as a third
 embodiment.
 FIG. 10 is a flowchart showing an operation of the third embodiment.
 The third embodiment is different from the second embodiment in that S510
 and S512 are included in the flowchart. In S512, the specified number of
 times m is set to n' determined by the zoom speed. During low speed
 zooming, n' is reduced, and during high speed zooming, n' is increased. In
 S510, a fixed time is determined by the specified number of times m,
 determined by the vertical-synchronizing period and zoom speed.
 As described above, the number of times for carrying out processing from
 S505 to S507 during the vertical-synchronizing period is changed by the
 zoom speed to set an optimum specified number of times for the zoom speed
 at that time, thereby allowing the focus lens to follow exactly the
 zooming at any zoom speed.
 Modification
 In each of the above-described embodiments, the zooming is performed by
 operating members of the video camera itself. However, a video camera
 system according to the present invention can also be implemented in
 performing the zooming by a remote controller and the like. In addition,
 in each of the embodiments, a vertical-synchronizing signal is generated
 in the video camera. However, a video camera system according to the
 present invention can also be implemented by inputting the
 vertical-synchronizing signal from outside.
 As described above, according to the embodiments, it is possible to allow
 the focus lens to follow the zooming, even if the zoom speed is high.
 In addition, according to other embodiments, the focus lens follow-up speed
 and direction are calculated and controlled a plurality of times in one
 cycle of the vertical-synchronizing signal of the video camera during the
 zooming. Thus, it is possible to allow the focus lens to follow the
 zooming with high accuracy, regardless of the zoom speed.
 Furthermore, generation of defocus due to follow-up delay of the focus lens
 during the zooming can be prevented, thereby obtaining excellent image
 quality.