Abstract:
A lens control apparatus for controlling the position of a focusing lens includes a rotary operation member, a detector, having a rotary encoder coupled with the rotary operation member, which detects the amount of rotation per unit time of the rotary operation member by counting the number of pulses per unit time outputted from the rotary encoder, and a conversion circuit for converting a detection output of the detector into a signal indicative of the position of the focusing lens. Further, the lens control apparatus is provided with a control characteristic changing circuit for changing a control characteristic of the lens.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a lens control apparatus of a television camera for servo-controlling the position of a focusing lens in accordance with the rotational angle of a rotary handle which is manually operable. 
     2. Description of Related Art 
     (1) In television cameras and so on, there have been known lens control apparatuses for servo-controlling the position of a focusing lens for a particular object distance in accordance with an absolute position which is a rotational angle from the mechanical end of a rotary handle. The absolute position of the rotary handle is detected by means of a potentiometer. Further, the lens control apparatus is provided with a sensitivity change-over switch for changing the sensitivity of a focusing-lens control voltage relative to the rotational angle of the rotary handle, and a curve mode change-over switch for changing the relationship between the absolute position of the rotary handle and the focusing-lens control voltage. These switches are disposed at arbitrary positions of the lens control apparatus. 
     When the sensitivity change-over switch is turned on, the sensitivity of the focusing-lens control voltage relative to the rotational angle of the rotary handle within a prescribed angular range from the absolute position thereof obtained at that time is changed, and, further, when the curve mode change-over switch is switched, the relationship between the absolute position of the rotary handle and the focusing-lens control voltage is changed, so that the position of the focusing lens can be controlled. 
     (2) There have been known lens control apparatuses for servo-controlling the position of a focusing lens for a particular object distance in accordance with the rotational angle of the rotary handle. 
     FIG. 20 is a sectional view of a conventional lens control apparatus, and FIG. 21 is a sectional view taken along the line X—X of FIG.  20 . In FIG. 20, a rotary handle  3  is attached to a main body  1  through a bearing  2 , and a potentiometer  4  is coupled with the rotating shaft  3   a  of the rotary handle  3 . In addition, a sensitivity change-over switch  5 , an LED  6  and a cable connector  7  are disposed at arbitrary positions of the main body  1 . 
     An Archimedean spiral groove  1   a  as shown in FIG. 21 is formed to the side of the main body  1  which is near to the rotary handle  3  in order to restrict the rotational range of the rotary handle  3 . Further, a linear groove  3   b  is formed in a radial direction to the side of the rotary handle  3  which confronts the spiral groove  1   a . A ball  1   b  is accommodated between the spiral groove  1   a  and the linear groove  3   b . The abutment of the ball  1   b  against both ends  1   c  of the spiral groove  1   a  restricts the maximum number of rotations of the rotary handle  3  to one to three times. 
     The main body  1  detects the rotational angle of the rotary handle  3  by means of the potentiometer  4  which recognizes it through the rotating shaft  3   a  of the rotary handle  3 . When the sensitivity change-over switch  5  is turned on in this instance, the relationship between the rotational angle θ of the rotary handle  3  and the output voltage V of the potentiometer  4  is changed from a normal mode to a fine-control mode, as shown in FIG.  22 . As a result, the sensitivity of the focusing-lens control voltage relative to the rotational angle of the rotary handle  3  is changed within a certain angle range “θn±a” about the rotational angle position θn of the rotary handle  3  obtained when the sensitivity change-over switch  5  is turned on. With this operation, the position of the focusing lens can be servo-controlled non-linearly. 
     (i) However, since the maximum number of rotations (maximum rotational angle θ) of the rotary handle  3  is predetermined in the lens control apparatus of the above-mentioned prior art (1), the focusing-lens control voltages V in all the modes must be made identical at each of a starting end and a terminating end of the entire rotating range of the rotary handle  3 , as shown in FIG.  23 . Accordingly, there is a problem that when the sensitivity of the focusing-lens control voltage is changed from the normal mode to the fine-control mode at a rotational angle θ 1  during process of operation of the focusing lens and, after an optimum position of the focusing lens is obtained at a rotational angle θ 2 , the normal mode is resumed, the focusing-lens control voltage V changes from a value Pf to a value Pn, so that the position of the focusing lens will be shifted. 
     Further, since the focusing-lens control voltage V is determined on the basis of the absolute position of the rotary handle  3 , there is a problem that when the curve mode change-over switch is switched from a straight-line mode to a curved-line mode, the focusing-lens control voltage V changes from a value Pb to a value Pa, as shown in FIG. 24, so that the position of the focusing lens will be shifted. 
     (ii) Since the maximum number of rotations of the rotary handle  3  is predetermined also in the lens control apparatus of the above-mentioned prior art (2), focusing-lens control voltages Vo at a starting end of the rotary handle  3  in all the modes or focusing-lens control voltages Ve at a terminating end of the rotary handle  3  in all the modes must be made always identical, as shown in FIG.  22 . Therefore, the lens control apparatus has a problem that when the sensitivity of the focusing-lens control voltage is switched from the normal mode to the fine-control mode at the rotational angle position θn during process of operation of the focusing lens and, after an optimum position of the focusing lens is obtained at the rotational angle “θn+a”, the normal mode is resumed, the focusing-lens control voltage changes from a value Vb to a value Va, so that the position of the focusing lens will be shifted. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the present invention is to solve the above problem (i) and provide a lens control apparatus in which, even if the mode of the sensitivity of a focusing-lens control voltage relative to the rotational angle of a rotary handle is changed over, the focusing-lens control voltage is not varied and, hence, the position of a focusing lens is not shifted. 
     Another object of the present invention is to solve the above problem (ii) and provide a lens control apparatus in which, even if the mode of the sensitivity of a focusing-lens control voltage relative to the rotational angle of a rotary handle is changed over, the position of a focusing lens is not shifted, and the sensitivity of the focusing-lens control voltage can be obtained in two types of modes. 
     To attain the above objects, in accordance with an aspect of the present invention, there is provided a focusing lens control apparatus, which comprises a rotary operation member, a measuring circuit, having a rotary encoder coupled with the rotary operation member, which counts number of pulses per unit time outputted from the rotary encoder, and a conversion circuit which converts a measurement output of the measuring circuit into a position signal indicative of a position of a focusing lens, wherein the position of the focusing lens is controlled on the basis of the position signal outputted from the conversion circuit. 
     Further, to attain the above objects, in accordance with another aspect of the present invention, there is provided a lens control apparatus, which comprises a rotary operation member, state detecting means for detecting a rotating state of the rotary operation member, a conversion circuit which converts a detection signal provided by the state detecting means into a position signal indicative of a position of a lens, the lens being driven on the basis of the position signal outputted from the conversion circuit, and conversion characteristic changing means for changing a conversion characteristic of the conversion circuit. 
     These and further objects and features of the present invention will become apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 is a view showing the arrangement of a lens control apparatus according to a first embodiment of the present invention. 
     FIG. 2 is a flowchart of the calculation sequence in the first embodiment. 
     FIG. 3 is a graph showing a relationship between pulse variation data and an amount of variation of focusing-lens control data in the first embodiment. 
     FIG. 4 is a graph showing another relationship between the pulse variation data and the amount of variation of focusing-lens control data in the first embodiment. 
     FIG. 5 is a flowchart of the calculation sequence in a second embodiment of the present invention. 
     FIG. 6 is a graph showing a relationship between pulse variation data and an amount of variation of reference data in the second embodiment. 
     FIG. 7 is a graph showing another relationship between the pulse variation data and the amount of variation of reference data in the second embodiment. 
     FIG. 8 is a graph showing a relationship between the reference data and focusing-lens control data in the second embodiment. 
     FIG. 9 is a view showing the arrangement of a lens control apparatus according to a third embodiment of the present invention. 
     FIG. 10 is a flowchart of the calculation sequence in the third embodiment. 
     FIG. 11 is a flowchart of the calculation sequence in a fourth embodiment of the present invention. 
     FIG. 12 is a sectional view of a lens control apparatus according to a fifth embodiment of the present invention. 
     FIG. 13 is a block diagram of a control circuit in the fifth embodiment. 
     FIG. 14 is a flowchart of the calculation sequence in the fifth embodiment. 
     FIG. 15 is a graph showing a relationship between a rotational angle of a handle and an output voltage in the fifth embodiment. 
     FIG. 16 is a sectional view of a lens control apparatus according to a sixth embodiment of the present invention. 
     FIG. 17 is a side elevational view of the lens control apparatus in the sixth embodiment when the lens control apparatus is in operation. 
     FIG. 18 is a sectional view of a lens control apparatus according to a seventh embodiment of the present invention. 
     FIG. 19 is a side elevational view of the lens control apparatus in the seventh embodiment when the lens control apparatus is in operation. 
     FIG. 20 is a sectional view of a conventional lens control apparatus. 
     FIG. 21 is a sectional view taken along the line X—X of FIG.  20 . 
     FIG. 22 is a graph showing a relationship between a rotational angle of a handle and an output voltage. 
     FIG. 23 is a graph showing another relationship between the rotational angle of the handle and the output voltage. 
     FIG. 24 is a graph showing a further relationship between the rotational angle of the handle and the output voltage. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. 
     FIG. 1 is a view showing the arrangement of an endless focusing lens control apparatus according to a first embodiment of the present invention. In FIG. 1, a rotary encoder  11 , which is mounted on a rotary handle  10  provided for operating a focusing lens, is arranged to detect the rotational angle of the rotary handle  10  and output pulses proportional to the rotational angle. The output of the rotary encoder  11  is supplied to a counter  12  for counting the pulses and, then, to a CPU  13  for calculating focusing-lens control data. The CPU  13  is connected to a memory  14  for storing calculation coefficients and initial data to be used in the calculation of the focusing-lens control data, and to a D/A converter  15  for digital-to-analog converting the focusing-lens control data outputted from the CPU  13  into a focusing-lens control voltage and supplying the focusing-lens control voltage to a focusing motor control circuit  19 . 
     Although the lower portion of FIG. 1 illustrates the arrangement of a well-known zoom lens, the detailed description thereof is omitted here. 
     Further, connected to the CPU  13 , respectively are the output of a sensitivity change-over switch  16  for changing over the sensitivity of the focusing-lens control data relative to the rotational angle of the rotary handle  10 , and the output of a curve mode change-over switch  17  for changing over the relationship between the rotational angle of the rotary handle  10  and the amount of variation of the focusing-lens control data. 
     FIG. 2 shows a flowchart of the calculation sequence of the CPU  13 . First, after a power supply for the lens control apparatus is turned on, an initial value Xo which can be arbitrarily set is inputted from the memory  14  and, then, is set to a focusing-lens control data buffer Y′, at step S 1 . The number of pulses per unit time which corresponds to the rotational angle of the rotary handle  10  is inputted from the counter  12  and, then, is set to pulse variation data P, at step S 2 . The counter  12  is cleared at step S 3 . A state of the sensitivity change-over switch  16  is inputted and determined at step S 4 . 
     When the sensitivity change-over switch  16  is in a fine-control mode, a fine-control mode coefficient A is inputted from the memory  14  at step S 5   a , and a state of the curve mode change-over switch  17  is inputted and determined at step S 6   a . When the curve mode change-over switch  17  is in a straight-line mode, an amount of variation dY of focusing-lens control data Y is obtained by calculation using the following calculation formula at step S 7   a . In the calculation formula, “A” represents the fine-control mode coefficient, “P” represents the pulse variation data. 
     
       
         
           dY=A*P 
         
       
     
     When the curve mode change-over switch  17  is in a curved-line mode, the following calculation formula is used at step S 7   b , wherein “C”, “D” and “E” represent constants. 
     
       
           dY=C* ( A*P ) 2   +D* ( A*P ) +E   
       
     
     When the sensitivity change-over switch  16  is in a normal mode at step S 4 , a normal mode coefficient B is inputted from the memory  14  at step S 5   b , and the state of the curve mode change-over switch  17  is inputted and determined at step S 6   b . When the curve mode change-over switch  17  is in the straight-line mode, the amount of variation dY of the focusing-lens control data Y is obtained from the following calculation formula at step S 7   c.   
     
       
         
           dY=B*P 
         
       
     
     On the other hand, when the curve mode change-over switch  17  is in the curved-line mode, the following calculation formula is used at step S 7   d.   
     
       
           dY=C* ( B*P ) 2   +D* ( B*P ) +E   
       
     
     FIG.  3  and FIG. 4 are graphs showing the relationships between the pulse variation data P and the amount of variation dY of the focusing-lens control data Y in the straight-line mode and the curved-line mode, respectively. 
     At step S 8 , the focusing-lens control data Y is calculated by adding the amount of variation dY determined at step S 7   a , S 7   b , S 7   c  or S 7   d  to the focusing-lens control data Y′ which was outputted to the D/A converter  15  in the previous sampling. At step S 9 , the focusing-lens control data Y is outputted to the D/A converter  15  to thereby control the focusing lens. The focusing lens control data Y corresponds to a position signal indicative of the position of the focusing lens. At step S 10 , the focusing-lens control data Y is transferred to the focusing-lens control data buffer Y′, and after that, step S 2  to step S 10  are repeated again. 
     FIG. 5 shows a flowchart of the calculation sequence of the CPU  13  according to a second embodiment of the present invention. The arrangement of the lens control apparatus according to the second embodiment is the same as that shown in FIG.  1 . First, after a power supply for the lens control apparatus is turned on, an initial value Xo which can be arbitrarily set is inputted from the memory  14  and, then, is set to reference data Xs, at step T 1 . When the curved-line mode shown in FIG. 24 is employed, the reference data Xs is arranged as a curve whose inclination is different depending upon the value of a focusing-lens control voltage. That is, since the relationship between the difference of the rotational angles of the rotary handle  10  and the amount of variation of the focusing-lens control voltage is different depending upon a value of the focusing-lens control voltage, the conversion into the amount of variation of the focusing-lens control voltage cannot be unconditionally executed only by using pulse data corresponding to the difference of the rotational angles of the rotary handle  10 . Therefore, the reference data Xs which corresponds to the focusing-lens control voltage in the relationship of 1:1 is introduced in the second embodiment. 
     The number of pulses corresponding to the rotational angle of the rotary handle  10  is inputted from the counter  12  and, then, is set to pulse variation data P, at step T 2 . The counter  12  is cleared at step T 3 . A state of the sensitivity change-over switch  16  is inputted and determined at step T 4 . When the sensitivity change-over switch  16  is in the fine-control mode, a fine-control mode coefficient A is inputted from the memory  14  at step T 5   a . Then, the data P inputted from the counter  12  is converted into an amount of variation Xf of the reference data Xs, using the following calculation formula at step T 6   a.   
     
       
         
           Xf=A*P 
         
       
     
     On the other hand, when the sensitivity change-over switch  16  is in the normal mode at step T 4 , a normal mode coefficient B is inputted from the memory  14  at step TS b . Then, the pulse variation data P is converted into an amount of variation Xn of the reference data Xs, using the following calculation formula at step T 6   b.   
     
       
         
           Xn=B*P 
         
       
     
     FIG.  6  and FIG. 7 are graphs showing the relationships between the pulse variation data P and the amount of variation X of the reference data in the straight-line mode and the curved-line mode, respectively. 
     At step T 7 , a state of the curve mode change-over switch  17  is inputted and determined. When the curve mode change-over switch  17  is in the curved-line mode, the data mode set to the curve mode change-over switch  17  in the previous sampling is compared with the data mode set thereto at this time, at step T 8   a . When the former data mode is equal to the current data mode, reference data Xs′ which was used in the previous sampling is set as the reference data Xs at this time as it is, at step T 9   a   2 , as shown in the following formula. 
     
       
         
           Xs=Xs′ 
         
       
     
     On the other hand, when the data mode set at this time is different from the data mode set in the previous sampling, that is, when the data mode has been switched from the straight-line mode to the curved-line mode, the reference data Xs′ is corrected at step T 9   a   1  using the following calculation formula based on the focusing-lens control data Y which was outputted to the D/A converter  15  in the previous sampling. In the following calculation formula, “Fa −1 (Y)” is the inverse function of a function “Fa(X)=C*Xs 2 +D*Xs+E”, which is to be used in the curved-line mode. 
     
       
           Xs′=Fa   −1 ( Y ) 
       
     
     At step T 10   a , the reference data Xs is calculated from the following formula by adding the amount of variation Xaf of the reference data obtained at step T 6   a  in the fine-control mode to the reference data Xs′. 
     
       
         
           Xs=Xs′+Xaf 
         
       
     
     In the normal mode, the reference data Xs is calculated likewise by adding the amount of variation Xan obtained at step T 6 b to the reference data Xs′. 
     At step T 11   a , coefficients C, D and E to be used in the function for the curved-line mode is read out from the memory  14 . At step T 12   a , a focusing-lens control data Y is calculated by substituting the reference data Xs obtained at step T 10   a  into the following function for the curved-line mode. 
     
       
         
           Y=C*Xs 
           2 
           +D*Xs+E 
         
       
     
     The focusing lens is controlled at step T 13  by outputting the focusing-lens control data Y to the D/A converter  15 . At step T 14 , the reference data Xs is transferred to the reference data buffer Xs′. Thereafter, step T 2  to step T 14  are repeated again. 
     While the quadratic function is used as the function for the curved-line mode in the second embodiment, any arbitrary function such as a cubic function, an exponential function and so on may be used. 
     The processes executed at step T 2  to step T 12   a  or T 12   b  will be described with reference to FIG. 8, FIG.  6  and FIG.  7 . When the pulse variation data P inputted from the counter  12  at step T 2  is Pn (P=Pn), the amount of variation of the reference data is Xaf in the curved-line mode and the fine-control mode, is Xan in the curve-line mode and the normal mode, is Xbf in the straight-line mode and the fine-control mode, and is Xbn in the straight-line mode and the normal mode, at step T 5   a  or T 5   b  and step T 6   a  or T 6   b , as shown in FIG.  6  and FIG.  7 . When the data mode being set is not changed from the data mode in the previous sampling at step T 8   a  or T 8   b , the reference data Xs is obtained by adding the amount of variation Xaf, Xan, Xbf or Xbn in the respective modes to the reference data Xs′ obtained in the previous sampling. For example, the reference data Xs is obtained by adding Xaf to Xs′ (Xs=Xs′+Xaf) in the curve-line mode and the fine-control mode. 
     The focusing-lens control data Y which corresponds to the reference data Xs in each mode is determined as described above. Here, in a case where the data mode being set has not changed, a point Qa shifts to a point Qaf in the curve-line mode and the fine-control mode, the point Qa shifts to a point Qan in the curve-line mode and the normal mode, a point Qb shifts to a point Qbf in the straight-line mode and the fine-control mode, and the point Qb shifts to a point Qbn in the straight-line mode and the normal mode. 
     On the other hand, in a case where the data mode being set has changed, the reference data Xs′ is corrected to reference data Xs″ at step T 9   a   1  or T 9   b   1 , using the focusing-lens control data Y at the previous sampling, so as to prevent the focusing-lens control data Y from being changed due to the change-over of the modes. Accordingly, the reference point shifts from the point Qb to a point Qa′ in FIG. 8 at step T 10   a  or T 10   b . Then, the point Qa′ shifts to a point Qaf′ in the fine-control mode and shifts to a point Qan′ in the normal mode. 
     When the curve mode change-over switch  17  is in the straight-line mode at step T 7 , the situation of the curved-line mode is also applied thereto. However, when the data mode set previously is different from the data mode set at this time, the reference data Xs′ which is the internal data of the CPU  13  is corrected on the basis of the focusing-lens control data Y outputted in the previous sampling at step T 9   b   1 , using the following calculation formula. In the following calculation formula, “Fb −1 (Y)” is the inverse function of a function “Fb(X)=G*Xs”, which is to be used in the straight-line mode. 
     
       
           Xs′=Fb   −1 ( Y ) 
       
     
     Then, the coefficient G for the function for the straight-line mode is read out from the memory  14  at step T 11   b , and the focusing-lens control data Y is calculated using the following function at step T 12   b.   
     
       
         
           Y=G*Xs 
         
       
     
     FIG. 9 shows a view showing the arrangement of an endless focusing lens control apparatus according to a third embodiment of the present invention. Although in FIG. 1 the D/A converter  15  is interposed between the CPU  13  and a zoom lens in which the focusing lens is operated, the third embodiment is provided with a serial driver  18  for outputting focusing-lens control data Y from the CPU  13  as serial data. The other components of the third embodiment are the same as those shown in FIG.  1  and denoted by the same numerals as those shown in FIG.  1 . 
     FIG. 10 shows a flowchart of the calculation sequence of the CPU  13  in the third embodiment, wherein step S 1  to Step S 8  are the same as those in FIG.  2 . The focusing-lens control data Y is outputted to the serial driver  18  to thereby transmit the data to the zoom lens, at step S 9   a . The focusing-lens control data Y is transferred to the focusing-lens control data buffer Y′ at step S 10 , and step S 2  to step S 10  are repeated again. 
     FIG. 11 shows a flowchart of the calculation sequence according to a fourth embodiment of the present invention, wherein step T 1  to step T 12  are the same as those in FIG.  5 . Focusing-lens control data Y is outputted to the serial driver  18  at step T 13   a  to thereby transmit the data to the zoom lens. The reference data Xs is transferred to the reference data buffer Xs′ at step T 14 , and step T 2  to step T 14  are repeated again. 
     FIG. 12 shows a sectional view of a lens control apparatus according to a fifth embodiment of the present invention. A rotary handle  22  is attached to a focus demand main body  20  through a bearing  21  and a rotary encoder  23  is coupled with a rotating shaft  22   a  of the rotary handle  22 . At arbitrary positions of the focus demand main body  20 , there are disposed a mode change-over switch  24  for changing over modes of a sensitivity of operation of the focusing lens relative to the rotational angle of the rotary handle  22  and an LED  25  for indicating the change-over of modes, and a cable connector  26  for connecting the focus demand main body  20  to a lens main body (not shown) is provided. In addition, a control circuit  27  is disposed inside the focus demand main body  20 . The outputs of the rotary encoder  23  and the mode change-over switch  24  are connected to the control circuit  27 , and the output of the control circuit  27  is connected to the LED  25  and the cable connector  26 . 
     FIG. 13 is a diagram showing the block circuit arrangement of the interior of the control circuit  27 . In FIG. 13, the output of a counter  29  is connected to a CPU  28 , and the output of the CPU  28  is connected to a storage part  30 . Further, the output of the rotary encoder  23  is connected to the counter  29 , and the output of the CPU  28  is connected to the mode change-over switch  24  and the LED  25 . 
     Various switches (not shown) permit the rotary encoder  23  to recognize the rotational angle of the rotary handle  22  through the rotating shaft  22   a  which is rotatably supported by the bearing  21 . The rotational angle is detected by the counter  29 , which is beforehand initialized. The rotary handle  22  can infinitely rotate because the focus demand main body  20  does not have a means for restricting the rotating range of the rotary handle  22 . The control circuit  27  receives a rotational angle signal which is produced by the rotary encoder  23  in accordance with the rotational angle of the rotary handle  22 , and supplies the rotational angle signal to the lens main body (not shown) through the cable connector  26 , as a position control signal for the focusing lens. 
     FIG. 14 shows a flowchart of the calculation sequence of the CPU  28 . The CPU  28  inputs a current counter value Xn from the counter  29  at step S 21 . The CPU  28  calculates the difference between the current counter value Xn and a counter value Xn- 1  which was obtained at the previous sampling, at step S 22 . A state of the mode change-over switch  24  is inputted at step S 23 , and the inputted switch data is determined at step S 24 . When the switch data is off, that is, in the normal mode, the calculation coefficients A 1 , A 2 , . . . An for an output signal in the normal mode are inputted from the storage part  30  at step S 25 , and the amount of change Y of the output signal is obtained using the inputted coefficients at step S 26 . 
     On the other hand, when the switch data is on, that is, in the fine-control mode, the calculation coefficients B 1 , B 2 , . . . Bn for an output signal in the fine-control mode are inputted from the storage part  30  at step S 27 , and the amount of change Y of the output signal is obtained using the inputted coefficients at step S 28 . 
     Next, output data Yn is obtained at step S 29  by adding the output data Yn−1 obtained at the previous sampling to the amount of change Y of the output signal obtained at steps S 25 -S 28 . The output data Yn is compared with mode-end limit data Ym at step S 30 . When Ym&gt;Yn, the output data Yn is made equal to the mode-end limit data Ym (Yn=Ym) at step S 31 , whereas when Ym≦Yn, the output data Yn is compared with infinitely far end limit data YI at step S 32 . When YI&lt;Yn, the output data Yn is made equal to the infinitely far end limit data YI (Yn=YI) at step S 33 , so that the output data Yn is restricted by the maximum value YI and the minimum value Ym. On the other hand, when YI&gt;Yn, the output data Yn is outputted to the zoom lens at step S 34 . 
     Thus, the output signal of the rotary encoder  23  is outputted to the zoom lens through the control circuit  27  as described above. If, after the sensitivity of operation of the focusing lens relative to the rotational angle θ is changed from the normal mode to the fine-control mode by turning on the mode change-over switch  24  on the focus demand main body  20  during outputting of the signal for the normal mode, the mode change-over switch  24  is turned off again during outputting of the signal for the fine-control mode to thereby return the fine-control mode to the original normal mode, the relationship between the rotational angle θ and the output voltage V of the rotary encoder  23  varies as shown in FIG.  15 . 
     FIG. 15 shows three types of mode change-over combinations. When the rotational angles of the rotary handle  22  at the starting end and terminating end of the focusing lens are represented by θo and θe, respectively, and the rotational angles at the time of the mode change-over are represented by θa and θb, the rotational angle θe changes to angles θe 1  to θe 3  depending upon the three types of the mode combinations. 
     Since the restriction to the rotation of the rotary handle  22  is abolished as described above, the rotational angle θe up to the output voltage Ve at the terminating end of the focusing lens can be arbitrarily changed depending upon a prestored mode. As a result, even if the sensitivity of operation of the focusing lens is returned to the original normal mode, the position of the focusing lens is never shifted. 
     When the mode of the sensitivity of operation of the focusing lens is changed, the LED  25  on the focus demand main body  20  is made to light up or blink in response to the command signal from the control circuit  27 , so that the operator can externally confirm the mode change-over. Further, a means for generating sound, a means for partially or totally vibrating the focus demand main body  20 , and so on, for example, may be employed, in addition to the display by the LED  25 . The turning-off of the mode change-over switch  24  may be controlled on the basis of the number of times the mode change-over switch  24  is opened and closed, or may be controlled by an additional external switch provided separately. 
     With this arrangement, even if, after obtaining an optimum sensitivity by switching the sensitivity mode of the focusing lens operation at an arbitrary zooming position, the operator returns the switched sensitivity mode to an original sensitivity mode, the position of the focusing lens is not shifted. Further, when two or more types of a rotational angle signal to be switched are prestored in the control circuit  27 , the sensitivity of the focusing lens operation can be changed to the modes as many as the number of the types of the rotational angle signal. In this case, a particular mode of sensitivity which is employed to the focusing lens operation can be discriminated by the number of times the mode change-over switch  24  is turned on or by increasing the number of mode change-over switches  24 . 
     FIG. 16 is a view showing the arrangement of a lens control apparatus according to a sixth embodiment of the present invention. In FIG. 16, a focus demand  31  is connected to a zoom demand  32  through a connecting means  33  such as a connector cable, and a mode change-over switch  34  for selecting the sensitivity mode of a focusing lens operation is mounted on the zoom demand  32 . The other components of the sixth embodiment are the same as those of the fifth embodiment, and the same numerals denote the same components. 
     FIG. 17 is a view showing the operating state of an ordinary servo type television lens. The cameraman M operates the focus demand  31  with one hand Ma and the zoom demand  32  with the other hand Mb. Then, the cameraman M changes over the sensitivity of a focusing lens operation by the mode change-over switch  34  on the zoom demand  32 . 
     When the cameraman M turns on the mode change-over switch  34  on the zoom demand  32 , information on the turning-on of the mode change-over switch  34  is transmitted to the control circuit  27  through the connecting means  33 . The control circuit  27  converts the mode of the rotational angle signal produced by the rotary encoder  23  to thereby change over the sensitivity of the focusing lens operation relative to the rotational angle of the rotary handle  22 . 
     Since the cameraman M can switch the mode change-over switch  34  while holding the focus demand  31  and the zoom demand  32  with both the hands Ma and Mb, he or she can change over the sensitivity of the focusing lens operation at any desired position without interrupting the focusing lens operation. Incidentally, an optical transmission through space by an LD or LED or ultrasonic waves may be used as the connecting means  33 . 
     FIG. 18 is a view showing the arrangement of a lens control apparatus according to a seventh embodiment of the present invention, wherein a mode change-over switch  35  for changing over a mode of the sensitivity of a focusing lens operation is arranged as a foot-operating type and connected to the focus demand  31  through a connecting means  36  such as a connector cable. 
     FIG. 19 shows a state where the cameraman M is changing over the sensitivity mode by operating, with his or her foot, the mode change-over switch  35  located at his or her feet. When the cameraman M turns on the mode change-over switch  35  with any one of his or her feet Mc, information on the turning-on of the mode change-over switch  35  is transmitted to the control circuit  27  through the connecting means  36 . The control circuit  27  converts the mode of the rotational angle signal produced by the rotary encoder  23 , likewise the fifth and sixth embodiments, to thereby change over the sensitivity of the focusing lens operation relative to the rotational angle of the rotary handle  22 . 
     As described above, since the cameraman M can switch the mode change-over switch  35  at a desired zoom position with any one of his or her feet Mc while holding the focus demand  31  and the zoom demand  32  with both the hands Ma and Mb, respectively, he or she can change over the sensitivity of the focusing lens operation without interrupting the focusing and zooming operations. 
     As described above, a lens control apparatus according to the present invention can optionally change over the sensitivity of a focusing lens operation and returns the sensitivity to its original state again at any optional position by converting the rotational angle of the rotation input means which represents the difference of the positions of the focus demand into the position signal of the focusing lens by the focus control means and calculating the focus converting characteristics of the control means on the basis of the reference data. Further, when a curve mode is switched, the lens control apparatus can change over the relationship between a focus demand position and a focusing-lens control voltage at any optional position. Accordingly, the degree of freedom of the focusing lens operation can be increased. 
     In addition, since a lens control apparatus according to the present invention abolishes the restriction to the rotational angle at both the ends of the rotation input means in the focus demand, the cameraman can arbitrary change over the sensitivity of the focusing lens operation at any desired position or returns the sensitivity to its original state again. As a result, the degree of freedom of the focusing lens operation can be increased.