Patent Abstract:
A lens drive control device includes a zoom lens, a drive mechanism for driving at least one lens unit which constitutes the zoom lens, a control circuit for controlling the drive mechanism, and a switch for switching between a shooting state and a non-shooting state of the zoom lens, wherein, when the zoom lens is switched from the non-shooting state to the shooting state by the switch, the control circuit causes the drive mechanism to drive the zoom lens to a zoom position other than a wide-angle end.

Full Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a lens drive control device and an image pickup apparatus using the lens drive control device and, more particularly, to a lens drive control device and an image pickup apparatus suited for use in small-sized electronic still cameras (e.g., digital cameras) having an image pickup element such as a CCD (charge-coupled device).  
           [0003]    2. Description of Related Art  
           [0004]    In recent years, the image pickup apparatus using an image pickup element such as a CCD have been widespread in the form of video cameras or electronic still cameras. These image pickup apparatus are capable of taking and storing a video image with ease. The stored video image can be viewed on the CRT (cathode-ray tube) or like display device or printed out as photographs.  
           [0005]    However, the conventional video camera and electronic still camera trend to take over the system of the silver-halide film camera without any considerable alternation. For the electronic still camera, some disadvantages arise in employing all the features of that system.  
           [0006]    For example, lens drive systems which prevail in the lens-shutter-type silver-halide cameras have a common feature that, when switched from the non-shooting mode where the lens barrel is retracted into the camera body to the shooting mode, the zoom lens is driven to the wide-angle end in response to turning-on of the electric power supply. On the contrary, for the small-sized electronic still camera, there are occasions that such an initial setting is unfavorable.  
           [0007]    An appropriate type of optical system to the small-sized electronic still camera is the negative lead type of zoom lens in which the front lens unit is negative in refractive power and the rear lens unit is positive in refractive power. In some cases, the physical length for the wide-angle end of the negative lead type of zoom lens becomes longer than for the telephoto end. With the zoom lens of such a form, when the electric power supply is turned on, it results that the initial setting process of the zoom lens goes to the wide-angle end after having once passed across the telephoto end. On the contrary, the electronic still camera has a feature that the telephoto end is rather more often enjoyed than the wide-angle end. This is because, when the electronic still camera is used as a document camera to read documents into the computer or to shoot personal name cards, the telephoto end is usually used at which the distortion is lesser than at the wide-angle end.  
           [0008]    On consideration of such a usage of the electronic still camera, it is not always necessary to take the initial setting in the wide-angle end in response to turning-on of the power supply. Also, in the lens configuration described above, the initial setting process overruns the telephoto end which is rather high in the frequency of use. Therefore, the zoom lens is apt to be driven wastefully, thereby causing the premature consumption of the battery.  
         BRIEF SUMMARY OF THE INVENTION  
         [0009]    An object of the present invention is to provide a lens drive control device which prevents the lens from being driven wastefully when the electric power supply is turned on, and an image pickup apparatus using the lens drive control device.  
           [0010]    To attain the above object, in accordance with an aspect of the invention, there is provided a lens drive control device, which comprises a zoom lens, drive means for driving at least one lens unit which constitutes the zoom lens, control means for controlling the drive means, and a switch for switching between a shooting state and a non-shooting state of the zoom lens, wherein, when the zoom lens is switched from the non-shooting state to the shooting state by the switch, the control means causes the drive means to drive the zoom lens to a zoom position other than a wide-angle end.  
           [0011]    In accordance with another aspect of the invention, there is provided a lens drive control device, which comprises a zoom lens in which a distance between a lens surface closest to an object side and a lens surface closest to an image side becomes minimum in a predetermined zoom position other than a wide-angle end, drive means for driving at least one lens unit which constitutes the zoom lens, control means for controlling the drive means, and a switch for switching between a shooting state and a non-shooting state of the zoom lens, wherein, when the zoom lens is switched from the non-shooting state to the shooting state by the switch, the control means causes the drive means to drive the zoom lens to the predetermined zoom position.  
           [0012]    In accordance with a further aspect of the invention, there is provided a lens drive control device, which comprises a zoom lens, drive means for driving at least one lens unit which constitutes the zoom lens, control means for controlling the drive means, a switch for switching between a shooting state and a non-shooting state of the zoom lens, storage means for storing a zoom position taken when the zoom lens has been switched from the shooting state to the non-shooting state by the switch, and command means for issuing a command to read out the zoom position stored in the storage means, wherein, when the zoom lens is switched from the non-shooting state to the shooting state by the switch, if the command to read out the zoom position stored in the storage means is issued by the command means, the control means causes the drive means to drive the zoom lens to the zoom position stored in the storage means.  
           [0013]    In accordance with a still further aspect of the invention, there is provided an image pickup apparatus having the lens drive control device described above.  
           [0014]    These and further aspects and features of the invention will become apparent from the following description of preferred embodiments thereof taken in conjunction with the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0015]    [0015]FIG. 1 is a block diagram of an image pickup apparatus having a lens drive control device according to an embodiment of the invention.  
         [0016]    [0016]FIG. 2 is a flow chart for explaining an operation of the image pickup apparatus.  
         [0017]    [0017]FIG. 3 is a flow chart for explaining the operation of the image pickup apparatus.  
         [0018]    [0018]FIG. 4 is a sectional side view of a lens part of the image pickup apparatus.  
         [0019]    [0019]FIG. 5 is a front view of the lens part of the image pickup apparatus.  
         [0020]    [0020]FIG. 6 is a diagram showing the zooming movements of lens units of a numerical example 1 of an optical system in the embodiment of the invention.  
         [0021]    FIGS.  7 (A),  7 (B) and  7 (C) are longitudinal section views of the numerical example 1 of the optical system in three operative positions.  
         [0022]    FIGS.  8 ( 1 ),  8 ( 2 ),  8 ( 3 ) and  8 ( 4 ) are graphic representations of the aberrations of the numerical example 1 of the optical system in the wide-angle end.  
         [0023]    FIGS.  9 ( 1 ),  9 ( 2 ),  9 ( 3 ) and  9 ( 4 ) are graphic representations of the aberrations of the numerical example 1 of the optical system in a middle focal length position.  
         [0024]    FIGS.  10 ( 1 ),  10 ( 2 ),  10 ( 3 ) and  10 ( 4 ) are graphic representations of the aberrations of the numerical example 1 of the optical system in the telephoto end.  
         [0025]    [0025]FIG. 11 is a diagram showing the zooming movements of lens units of a numerical example 2 of an optical system in the embodiment of the invention.  
         [0026]    FIGS.  12 (A),  12 (B) and  12 (C) are longitudinal section views of the numerical example 2 of the optical system in three operative positions.  
         [0027]    FIGS.  13 ( 1 ),  13 ( 2 ),  13 ( 3 ) and  13 ( 4 ) are graphic representations of the aberrations of the numerical example 2 of the optical system in the wide-angle end.  
         [0028]    FIGS.  14 ( 1 ),  14 ( 2 ),  14 ( 3 ) and  14 ( 4 ) are graphic representations of the aberrations of the numerical example 2 of the optical system in a middle focal length position.  
         [0029]    FIGS.  15 ( 1 ),  15 ( 2 ),  15 ( 3 ) and  15 ( 4 ) are graphic representations of the aberrations of the numerical example 2 of the optical system in the telephoto end.  
         [0030]    [0030]FIG. 16 is a diagram showing the zooming movements of lens units of a numerical example 3 of an optical system in the embodiment of the invention.  
         [0031]    FIGS.  17 (A),  17 (B) and  17 (C) are longitudinal section views of the numerical example 3 of the optical system in three operative positions.  
         [0032]    FIGS.  18 ( 1 ),  18 ( 2 ),  18 ( 3 ) and  18 ( 4 ) are graphic representations of the aberrations of the numerical example 3 of the optical system in the wide-angle end.  
         [0033]    FIGS.  19 ( 1 ),  19 ( 2 ),  19 ( 3 ) and  19 ( 4 ) are graphic representations of the aberrations of the numerical example 3 of the optical system in a middle focal length position.  
         [0034]    FIGS.  20 ( 1 ),  20 ( 2 ),  20 ( 3 ) and  20 ( 4 ) are graphic representations of the aberrations of the numerical example 3 of the optical system in the telephoto end.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]    Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings.  
         [0036]    [0036]FIG. 1 is a block diagram showing an image pickup apparatus having a lens drive control device according to an embodiment of the invention.  
         [0037]    Referring to FIG. 1, a first lens unit  1  has a negative refractive power. A second lens unit  2  has a positive refractive power. The first lens unit  1  acts as the compensator, while the second lens unit  2  acts as the variator. The first and second lens units  1  and  2  constitute a zoom lens. Incidentally, for the zoom lens configuration, many other types may be considered. So, it is to be understood that the zoom lens in the invention is not confined to the type shown in FIG. 1.  
         [0038]    A stop SP, an optical low-pass filter  3  and an image sensor  4  such as interline-type CCD are included in the optical system. Light entering through the first lens unit  1  is adjusted in the intensity by the stop SP and passes through the second lens unit  2  and the low-pass filter  3  to form an image on the image sensor  4 .  
         [0039]    An amplifier  5  amplifies an output signal of the image sensor  4  and outputs the amplified output signal. A camera processing circuit  6  processes the output signal of the amplifier  5  as a video signal. The video signal outputted from the camera processing circuit  6  is supplied to a recording part  7 , where the video signal is recorded on a recording medium. As the recording medium, a magnetic disc, a magnetic tape, a PC card, or a magneto-optical disc may be considered.  
         [0040]    An electric motor  8  drives the stop SP, and is controlled by a CPU  14 . An auto-focus (AF) circuit  9  determines a focusing state of the zoom lens at the present time on the basis of the video signal from the camera processing circuit  6  and outputs information on the focusing state to the CPU  14 . In the image pickup apparatus in the present embodiment, the AF method to be used is assumed to take it as the in-focus position when a frequency component of the luminance component of the video signal reaches a peak, or the so-called the “TV signal” AF. Instead of this, the TCL type, or the infrared type may be used.  
         [0041]    A focusing lens is driven to axially move in such a way as to make minute excursions on the basis of the information on the focusing state sent from the AF circuit  9 . In the case of the embodiment, the focusing lens may be either the first lens unit  1  or the second lens unit  2 . Otherwise, both of the lens units  1  and  2  may be used as the focusing lens. As the focusing lens is driven to minutely oscillate, the luminance signal of video signal obtained by the image sensor  4  oscillates in synchronism with the oscillation of the focusing lens. Such a luminance signal is transferred from the image sensor  4  through the camera processing circuit  6  and the AF circuit  9  to the CPU  14 . When the luminance signal exceeds a certain value, the CPU  14  determines that an in-focus state has been attained and, then, stops the focusing lens from further excursion.  
         [0042]    A reset switch  10  is provided for the first lens unit  1 . When a counter disposed in the CPU  14  is used to measure the moving amount of the first lens unit  1 , the reset switch  10  functions as a sensor for the reference position. Another reset switch  11  is provided for the second lens unit  2 . When another counter disposed in the CPU  14  is used to measure the moving amount of the second lens unit  2 , the reset switch  11  functions as a sensor for the reference position.  
         [0043]    Stepping motors  12  and  13  function as drive means for moving the lens units  1  and  2 , respectively. When the lens units  1  and  2  are moved to effect zooming, focusing, or retracting, the stepping motors  12  and  13  are energized through respective drivers  20  and  21 .  
         [0044]    The CPU  14  functions as a control means, and, in response to the respective input signals, controls the movements of the motor  8  for the stop SP, the stepping motors  12  and  13 , an electronic shutter, and others. A trigger switch  15 , when pushed, renders the CPU  14  to actuate the electronic shutter and the recording part  7  so that the video image formed on the image sensor  4  is taken in and recorded on the recording medium. A memory  16  temporarily stores information on the zoom position taken when the electric power supply is turned off.  
         [0045]    A power supply switch  17 , when closed, connects the electric power supply to the CPU  14 . A zoom switch  18 , when pushed to the wide-angle end, actuates the CPU  14  to command the drivers  20  and  21  so that zooming goes to the wide-angle end, or when pushed to the telephoto side, zooming goes to the telephoto side, or when not pushed, zooming does not take place.  
         [0046]    A recovery switch  19  determines which zoom position is resumed as the zoom lens moves when the power supply switch  17  is turned on again, depending on its ON/OFF position. In the present embodiment, if the recovery switch  19  is in the ON position, setting is carried out so that the zoom lens is driven to the position stored in the memory  16  obtained when the power supply has been last turned off. If the recovery switch  19  is in the OFF position, the zoom lens is driven to a position where the overall lens length (distance from a lens surface closest to the object side to a lens surface closest to the image side) of the zoom lens becomes shortest.  
         [0047]    Next, an operation of the image pickup apparatus according to the embodiment is described with reference to flow charts shown in FIGS. 2 and 3.  
         [0048]    After the flow of operation has started at a step F 10 , the ON/OFF of the power supply switch  17  is first determined. If the power supply switch  17  is in the on-state, the flow proceeds to a step F 12 , where the ON/OFF of the recovery switch  19  is determined.  
         [0049]    If the recovery switch  19  is in the off-state, the flow proceeds to a step F 13 , where the lens units  1  and  2  are driven from the retracted position (stowage position) to the zoom positions where the overall lens length becomes shortest. Meanwhile, if the recovery switch  19  is in the on-state, the memory  19  is accessed at a step F 14  to read out the zoom position stored. Then, at a step F 15 , the lens units  1  and  2  are driven to the read-out zoom position.  
         [0050]    If the zoom switch  18  is found to be turned on (to either one of the wide-angle and telephoto sides) at a step F 16 , the flow proceeds to a step F 17 , where the lens units  1  and  2  are driven along their respective loci toward the wide-angle end or the telephoto end depending on the switched side of the zoom switch  18 . If the zoom switch  18  is found to be turned off, the flow proceeds to a step F 18 , skipping the step F 17 .  
         [0051]    If, at the step F 18 , the trigger switch  15  is found to be turned on, the flow proceeds to a step F 19 , where the AF circuit  9  is driven to effect automatic focusing. If, at a step F 20 , an in-focus state is found to be attained, the flow proceeds to a step F 21 , where the video image is taken in. At the next step F 22 , the recording part  17  carries out recording of the video image on the recording medium. If the trigger switch  15  is found to be turned off, the flow returns to the step F 16 .  
         [0052]    A step F 23 , a check is made to find the ON/OFF of the power supply switch  17 . If the power supply switch  17  is found to be turned on, the flow returns to the step F 16 . If the power supply switch  17  is found to be turned off, the flow proceeds to a step F 24 , where the current zoom position is stored in the memory  16 . At the next step F 25 , the lens units  1  and  2  are driven to the position where the overall lens length becomes shortest. Then, at a step F 26 , the zoom lens is stowed (retracted) into the camera body. Then, the power supply is turned off at a step F 27 .  
         [0053]    Next, with reference to FIGS. 4 and 5, the structural arrangement of a lens part of the image pickup apparatus in the present embodiment is described below. FIG. 4 is a longitudinal side section view of the lens part and FIG. 4 is a front end view of the same.  
         [0054]    In FIGS. 4 and 5, an axially movable first lens unit  101 , an axially movable diaphragm unit  102  and an axially movable second lens unit  103  correspond to the first lens unit  1 , the stop SP and the second lens unit  2 , respectively, shown in FIG. 1. A holding frame  104  holds the first lens unit  101 . As the holding frame  104  moves axially, the holding frame  104  is restrained from rotation by a guide bar  105 . The guide bar  105  has such a stroke as to cause the overall lens length of the zoom lens to become shorter in the non-shooting state than in the shooting state. Another guide bar  106  guides the diaphragm unit  102  to move along the optical axis, and has such a stroke as to cause the overall lens length of the zoom lens to become shorter in the non-shooting state than in the shooting state. A holding frame  107  holds the second lens unit  103 . As the holding frame  107  moves axially, the holding frame  107  is restrained from rotation by a guide bar  108 . The guide bar  105  has such a stroke as to cause the overall lens length of the zoom lens to become shorter in the non-shooting state than in the shooting state. A U bar  109  restrains the first holding frame  104 , the diaphragm unit  102  and the second holding frame  107  from turning about the respective guide bars  105 ,  106  and  108  in the direction perpendicular to the optical axis, and has such a stroke as to cause the overall lens length of the zoom lens to become shorter in the non-shooting state than in the shooting state.  
         [0055]    A stepping motor  110  is arranged to drive the holding frame  104  axially. A rack  111  transmits the driving force of the stepping motor  110  to the holding frame  104 . A sensor  112  is arranged to detect the initial position of the first lens unit  101 . Another stepping motor  113  is arranged to drive the second lens unit  103  axially. Another rack  114  transmits the driving force of the stepping motor  113  to the holding frame  107 . Another sensor  115  is arranged to detect the initial position of the second lens unit  103 . The stepping motors  110  and  113  correspond to the stepping motors  12  and  13  shown in FIG. 1, respectively, and the sensors  112  and  115  correspond to the reset switches  10  and  11  shown in FIG. 1, respectively.  
         [0056]    A spring  116  urges the diaphragm unit  102  always toward the object side. A main tube  117  holds the guide bars  105 ,  106  and  108  and the bar  109  at their one ends, and fixedly carries the stepping motors  110  and  113  and the sensors  112  and  115 .  
         [0057]    A CCD unit  118  is integrally composed of a low-pass filter  118   a  and a chip  118   c  and has an image receiving surface  118   b . The CCD unit  118  corresponds to a combination of the low-pass filter  3  and the image sensor  4  shown in FIG. 1.  
         [0058]    A rear tube  119  holds the guide bars  105 ,  106  and  108  and the U bar  109  at their opposite ends and fixedly carries the CCD unit  118 . The stepping motors  110  and  113  are mounted on a motor holding plate  120 .  
         [0059]    The upper half of FIG. 4 shows the state of the lens part in which the first lens unit  101  is in the most forward position. The lower half of FIG. 4 shows the state in which the lens part is in the retracted position. In moving the first lens unit  101  forward, the stepping motor  110  is energized to transmit its driving force to the rack  111 . The driving force transmitted to the rack  111  causes the holding frame  104  to axially move forward. Along with the forward movement of the holding frame  111 , the diaphragm unit  102  which is urged by the spring  116  toward the object side, too, is moved forward. The diaphragm unit  102 , which is being moved forward, eventually abuts on a stopper  117   a  provided on the main tube  117  and stops from further moving forward, thus reaching the position of the upper half of FIG. 4. On the other hand, in moving the first lens unit  101  backward, the stepping motor  110  is energized in the reversed direction. So, the reverse driving force of the stepping motor  110  is transmitted to the rack  111  to move the holding frame  104  toward the image side. After a projection  104   a  of the holding frame  104 , which is being moved backward, abuts on the diaphragm unit  102 , the diaphragm unit  102 , too, is moved backward together with the holding frame  104 , thus reaching the position of the lower half of FIG. 4.  
         [0060]    The driving force generated by the stepping motor  113  is transmitted through the rack  114  to the holding frame  107 , thus axially moving the holding frame  107  backward and forward. The sensor  112  is arranged to detect the initial position of the holding frame  104  and the sensor  115  is arranged to detect the initial position of the holding frame  107 . The sensors  112  and  115  send detection signals to a CPU (not shown in FIGS. 4 and 5), which corresponds to the CPU  14  shown in FIG. 1. The CPU controls the energization of the stepping motors  110  and  113  in accordance with the detection signals received.  
         [0061]    Next, numerical examples 1 to 3 of optical systems suited for use in the lens drive control device in the present embodiment are shown. In the numerical data for the examples 1 to 3, ri is the radius of curvature of the i-th lens surface, when counted from the object side, di is the i-th lens thickness or air separation, when counted from the object side, ni is the refractive index of the material of the i-th lens element, when counted from the object side, and υi is the Abbe number of the material of the i-th lens element, when counted from the object side. The lens surface indicated by * is an aspheric surface, and in the numerical data there are also the values of the radius of the osculating sphere and the aspheric coefficients in the following polynomial:  
       X   =           h   2     /   R       1   +       1   -       (     1   +   K     )            (     h   /   R     )     2               +     Bh   2     +     Ch   6     +     Dh   8                             
 
         [0062]    where X is the coordinate in the direction of the optical axis and h is the coordinate in the direction perpendicular to the optical axis, the direction in which light advances being taken as positive. R is the radius of the osculating sphere, and K, B, C and D are the aspheric coefficients. Also, the notation D-0X means 10 −x .  
                                                                                                                                                                                                                                                                                                     Numerical Example 1:            f = 3.74849   Fno = 1:2.8   2ω = 64.8°            r1 = 205.814   d1 = 1.00   n1 = 1.74330   ν1 = 49.2       *r2 = 3.621   d2 = 1.35       r3 = 6.370   d3 = 2.10   n2 = 1.64769   ν2 = 33.8       r4 = 46.696   d4 = Variable       r5 = ∞(Stop)   d5 = Variable       r6 = 4.880   d6 = 2.20   n3 = 1.83400   ν3 = 37.2       r7 = −76.972   d7 = 0.18       r8 =−20.357   d8 = 1.60   n4 = 1.84666   ν4 = 23.8       r9 = 3.588   d9 = 0.11       r10 = 3.929   d10 = 1.90   n5 = 1.73077   ν5 = 40.6       *r11 = −84.003   d11 = Variable       r12 = ∞   d12 = 3.10   n6 = 1.51633   ν6 = 64.2       r13 = ∞                        Variable   Focal Length                Separation   3.75   8.55   11.02                       d4   11.74   2.17   1.20           d5   6.69   2.61   1.20            d11   2.00   5.62   7.49                        Aspheric Coefficients:               For r2:   R = 3.62053D + 00   K = −1.06318D + 00           B = 1.10799D − 03   C = −3.27073D − 06       For r11:   R = 8.40029D + 01   K = −2.06156D + 02           B = 2.51718D − 03   C = 1.50000D − 04            Numerical Example 2:            f = 3.75003   Fno = 1:2.8   2ω =63.6°            r1 = 60.170   d1 = 1.00   n1 = 1.74330   ν1 = 49.2       *r2 = 3.472   d2 = 2.78       r3 = 8.363   d3 = 4.13   n2 = 1.84666   ν2 = 23.8       r4 = 17.062   d4 = Variable       r5 = ∞(Stop)   d5 = 1.10       r6 = 6.211   d6 = 4.78   n3 = 1.69680   ν3 = 55.5       r7 = −10.395   d7 = 0.31       r8 = −6.817   d8 = 2.00   n4 = 1.84666   ν4 = 23.8       r9 = −2163.195   d9 = 1.20       r10 = 10.043   d10 = 1.60   n5 = 1.73077   ν5 = 40.6       *r11 = 21.256   d11 = Variable       r12 = 154.453   d12 = 1.00   n6 = 1.80400   ν6 = 46.6       r13 = −23.948   d13 = 3.10       r14 = ∞   d14 = 3.10   n7 = 1.51633   ν7 = 64.2       r15 = ∞                        Variable   Focal Length                Separation   3.75   8.60   11.10                       d4    11.85   2.69   1.10           d11   1.12   9.04   13.12                        Aspheric Coefficients:               For r2:   R = 3.47155D + 00   K = −1.52122D + 00           B = 2.11152D − 03   C = −1.34125D − 05       For r11:   R = 2.12556D + 01   K = 6.49763D + 01           B = 3.59566D − 04   C = −5.36520D − 05            Numerical Example 3:            f = 3.75000   Fno = 1:2.8   2ω = 64.6°            r1 = −1580.189   d1 = 1.00   n1 = 1.58313   ν1 = 59.4       *r2 = 2.786   d2 = 1.85       r3 = 5.844   d3 = 1.50   n2 = 1.84666   v2 = 23.8       r4 = 10.648   d4 = Variable       r5 = ∞(Stop)   d5 = 1.10       r6 = 5.328   d6 = 2.10   n3 = 1.58313   ν3 = 59.4       r7 = −11.129   d7 = 0.30       r8 = −44.181   d8 = 1.00   n4 = 1.84666   ν4 = 23.8       r9 = 6.765   d9 = 0.38       *r10 = −17.497   d10 = 1.50   n5 = 1.80610   ν5 = 40.9       r11 = −6.978   d11 = Variable       r12 = 12.184   d12 = 1.50   n6 = 1.51633   ν6 = 64.1       r13 = −51.853   d13 = 3.10       r14 = ∞   d14 = 3.10   n7 = 1.51633   ν7 = 64.2       r15 = ∞                        Variable   Focal Length                Separation   3.75   8.60   11.10                       d4   11.85   2.69   1.10            d11   1.12   9.04   13.12                        Aspheric Coefficients:               For r2:   R = 2.78636D + 00   K = −6.97078D − 01           B = −4.78910D − 04   C = 1.77019D − 05           D = −1.64098D − 06       For r10:   R = 5.32776D + 00   K = −9.08473D − 01           B = −7.94778D − 04   C = −1.82429D − 06           D = −1.44616D − 06                  
 
         [0063]    [0063]FIG. 6 shows the total zooming movement of each of the lens units in the paraxial zone of the numerical example 1. The optical system of the numerical example 1 is of the 2-unit type with the minus-plus refractive power arrangement. The negative first lens unit as the compensator and the positive second lens unit as the variator are moved in differential relation to vary the focal length.  
         [0064]    As is apparent from FIG. 6, in the numerical example 1, the overall lens length (a distance between a lens surface closest to the object side and a lens surface closest to the image side) of the zoom lens is shortest in the telephoto end. In application of the invention to the optical system of the numerical example 1, it is, therefore, desirable that the retraction starts from the telephoto end and, when the power supply is turned on, the zoom lens first moves to the telephoto end.  
         [0065]    FIGS.  7 (A),  7 (B) and  7 (C) are longitudinal section views of the numerical example 1 of the optical system in three zoom positions. The overall lens length of the zoom lens is shortest in the telephoto end as shown in FIG. 6. FIGS.  8 ( 1 ),  8 ( 2 ),  8 ( 3 ) and  8 ( 4 ) to FIGS.  10 ( 1 ),  10 ( 2 ),  10 ( 3 ) and  10 ( 4 ) are graphic representations of the aberrations of the numerical example 1 of the optical system in the respective zoom positions indicated in FIGS.  7 (A),  7 (B) and  7 (C). FIGS.  8 ( 1 ) to  8 ( 4 ) are in the wide-angle end, FIGS.  9 ( 1 ) to  9 ( 4 ) are in a middle focal length position, and FIGS.  10 ( 1 ) to  10 ( 4 ) are in the telephoto end.  
         [0066]    [0066]FIG. 11 shows the total zooming movement of each of the lens units of the numerical example 2. The optical system of the numerical example 2 is of the 3-unit type with the minus-plus-plus refractive power arrangement. The negative first lens unit and the positive second lens unit are moved in differential relation to vary the focal length.  
         [0067]    As is apparent from FIG. 11, in the numerical example 2, the overall lens length of the zoom lens is shortest in a zoom position indicated by A. In application of the invention to the numerical example 2, it is, therefore, desirable that the retraction starts from the zoom position A, and when the power supply is turned on, the zoom lens first moves to the zoom position A.  
         [0068]    FIGS.  12 (A),  12 (B) and  12 (C) are longitudinal section views of the numerical example 2 of the optical system in three zoom positions. The overall lens length of the zoom lens is shortest neither in the wide-angle end nor in the telephoto end, but in a certain zoom position for the middle focal length. FIGS.  13 ( 1 ),  13 ( 2 ),  13 ( 3 ) and  13 ( 4 ) to FIGS.  15 ( 1 ),  15 ( 2 ),  15 ( 3 ) and  15 ( 4 ) are graphic representations of the aberrations in the respective zoom positions shown in FIGS.  12 (A),  12 (B) and  12 (C). FIGS.  13 ( 1 ) to  13 ( 4 ) are in the wide-angle end, FIGS.  14 ( 1 ) to  14 ( 4 ) are in the middle focal length position, and FIGS.  15 ( 1 ) to  15 ( 4 ) are in the telephoto end.  
         [0069]    [0069]FIG. 16 shows the total zooming movement of each of the lens units of the numerical example 3. The optical system of the numerical example 3 is of the 3-unit type with the minus-plus-plus refractive power arrangement. The negative first lens unit and the positive second lens unit are moved in differential relation to vary the focal length.  
         [0070]    As is apparent from FIG. 16, in the numerical example 3, the overall lens length of the zoom lens is shortest in a zoom position indicated by B. In application of the invention to the numerical example 3, it is, therefore, desirable that the retraction starts from the zoom position B, and when the power supply is turned on, the zoom lens first moves to the zoom position B.  
         [0071]    FIGS.  17 (A),  17 (B) and  17 (C) are longitudinal section views of the numerical example 3 of the optical system in three zoom positions. The overall lens length of the zoom lens is shortest neither in the wide-angle end nor in the telephoto end, but in a certain zoom position for the middle focal length. FIGS.  18 ( 1 ),  18 ( 2 ),  18 ( 3 ) and  18 ( 4 ) to FIGS.  20 ( 1 ),  20 ( 2 ),  20 ( 3 ) and  20 ( 4 ) are graphic representations of the aberrations in the respective zoom positions indicated by FIGS.  17 (A),  17 (B) and  17 (C). FIGS.  18 ( 1 ) to  18 ( 4 ) are in the wide-angle end, FIGS.  19 ( 1 ) to  19 ( 4 ) are in a middle focal length position, and FIGS.  20 ( 1 ) to  20 ( 4 ) are in the telephoto end.  
         [0072]    The image pickup apparatus in the present embodiment, when the power supply is turned on, moves the lens from the retracted position to that zoom position which compromises the minimum distance and the high frequency of use. Therefore, the shooting state can be quickly made up. Also, since the zoom position taken when the power supply has been turned off at the last time is stored, the zoom lens can be moved to the stored zoom position, if necessary, when the power supply is turned on again. Therefore, the wasteful driving of the zoom lens can be reduced. So, the consumption of the battery in the image pickup apparatus can be reduced.  
         [0073]    As has been described above, in the lens drive control device and the image pickup apparatus according to the embodiment of the invention, the wasteful lens driving can be reduced when the power supply is turned on.

Technology Classification (CPC): 6