Abstract:
An image pickup apparatus includes an image pickup device for converting an optical image into an electrical image signal, a recording device for recording the electrical image signal, a first trigger device operative to carry out a predetermined step, a second trigger device operable subsequent to an operation of the first trigger device, for causing the recording device to record the electrical image signal, and an interruption device for causing the recording device in response to an operation of the second trigger device to record the electrical image signal before completion of the predetermined step.

Description:
This application is a continuation of application Ser. No. 07/868,691 filed Apr. 15, 1992, abandoned, which is a divisional of Ser. No. 07/051,458, filed May 19, 1987, now U.S. Pat. No. 5,170,069, issued Dec. 8, 1992. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image pickup apparatus capable of picking up and recording a still image at high speed without using an interruption routine. 
     2. Related Background Art 
     A method of using an interruption function of a CPU in a microprocessor has been proposed for sequence control of a camera system. With this method, as the shutter is half depressed and switch SW 1  is turned on, the microprocessor checks a disc drive and a lens, calculates photometry and automatic exposure, displays information in a finder and performs other operations. The calculated photometry and automatic exposure are temporarily stored in a provisional memory and transferred to a regular memory after an interruption is inhibited. Thereafter, the interruption is enabled to repeat an operation of checking the depression of switch SW 1 . During this loop, if an interruption occurs due to the depression of switch SW 2  triggering a shutter release, the microprocessor enters in the interruption routine to initiate the release sequence and pick up an image using the information in the regular memory. 
     With this method, however, the sequence control jumps to the interruption routine and an image is picked up, even if a lens stop value changes due to zoom adjustment during the loop operation, or without completing the photometry. In such a case, a correct exposure cannot be obtained. 
     Further, the provisional and regular memories are required because of the interruption process. Thus, the memory capacity becomes two times larger than that without the interruption process, and the program becomes complicated. 
     A method for the sequence control without the use of interruption function may be possible. With this method, however, an image pickup sequence can be carried out only after various data such as photometry and lens data are collected, thus leading to a time lag between the depression of the release switch and an actual image pickup. 
     There is known a silver salt SLR camera of a type in which automatic exposure (AE) information is produced for each frame during a single frame photographing mode, and is fixed during a high speed continuous photographing mode (e.g., refer to Japanese Patent Unexamined Publication No. 143218/1978) 
     The reason why the AE information is fixed during the high speed continuous photographing mode, is that AE sensors are generally mounted within a TTL (Through the Taking Lens) optical path and a quick-return mirror is maintained set up so that light is not incident to the AE sensors. 
     In contrast, there is also known a video camera as disclosed, for example, in Japanese Patent Unexamined Publication No. 78925/1976, wherein color sensors for detecting R and B (G) color temperatures are mounted on a video camera body. An output ratio between the color sensors is calculated to form color temperature information based on which the color balance of the color signal processing circuit of the camera is adjusted. 
     An image pickup apparatus such as an electronic still camera adopting the above video camera technique picks up one frame and stores it in a medium such as a magnetic disc. In addition to this fundamental mode, a continuous photographing mode will become necessary for some cases. 
     With the image pickup apparatus of this type, the output of the color temperature sensor can be always obtained independently from image pickup control, stop control and the like. However, during a high speed continuous photographing mode, there is a problem that the color temperature changes at the frequency two times higher than the commercial power frequency due to flicker phenomenon of a fluorescent lamp. Thus, color changes for each photographed print. This color difference is not so conspicuous for plural prints photographed at relatively low speed, but becomes conspicuous for those photographed at high speed, e.g., 10 frames per second. 
     To drive a recording or reproducing apparatus with an image pickup apparatus such as a video camera, a battery and an AC adapter have been used selectively. 
     If a battery having a capacity maintaining a sufficient voltage during large current discharge is used, e.g., if a Ni-Cd battery is used, a motor can be started rapidly. However, if an AC adapter is to be used for the purpose of long time, indoor image regeneration or recording, a large capacity of an AC adapter is needed for large current discharge, and hence it becomes expensive. If an AC adapter of small capacity is used for large current discharge, the voltage will become low and a malfunction may occur. 
     Electronic apparatus such as an electronic camera often use a battery for their power supply. In this case, the voltage will become low as large current flows for a long time, especially at the end of battery discharge and at low temperature. For this reason, several motors or the like in the electronic camera are driven in such a manner that power consumptions (or peak power consumptions) of these devices do not occur at the same time. 
     However, this drive operation is sequential in time so that there arises some problems of long time image pickup and record operation, long time release stand-by, large release time lag, long return time of a quick-turn mirror for a single-lens reflex camera, low frame speed for continuous photographing, and the like. 
     There is known an image pickup apparatus of the type in which gains of color signal passages in a signal processing circuit are automatically adjusted by photographing a white object and making the obtained color signal levels equal to each other. 
     There is also known an image pickup apparatus of the type in which a plurality of color sensors for receiving light from an object are mounted outside of a TTL optical path. The outputs of the color sensors are compared to calculate color temperature information. The gains of color signal passages from the image pickup elements are always controlled based on the color temperature information. 
     With the former image pickup apparatus, initial setting for white balance is cumbersome. With the latter image pickup apparatus, an electronic camera is constructed of a shutter, a quick-return mirror, a stop and the like which devices are driven every time a trigger is initiated. Such an electronic camera is associated with a problem that too large a time is necessary for image photographing and recording after triggering operation. Particularly, a microcomputer is generally used for giving various functions to an electronic camera and controlling various devices of the camera. Complicated operations in various modes are executed after the triggering operation. Therefore, if the white balance control operation periodically reading the color sensor outputs is inserted between various sequential operations, the final image photographing and recording operation is delayed thus taking a long time for one frame image pickup. 
     SUMMARY OF THE INVENTION 
     It is a principal object of the present invention to provide an image pickup apparatus capable of photographing without a time lag. 
     It is another object of the present invention to provide an image pickup apparatus usable with a small memory capacity and capable of controlling an exposure precisely. 
     It is a further object of the present invention to provide an image pickup apparatus capable of properly controlling a white balance during a high speed continuous photographing mode. 
     It is a still further object of the present invention to provide an image pickup apparatus capable of preventing a malfunction caused by a rapid voltage drop of an AC adapter by making power consumptions not occur at the same time, and ensuring a rapid response of the apparatus if a battery is used for the power supply. 
     It is another object of the present invention to eliminate the above prior art problems and provide an electronic device capable of preventing a malfunction caused by a rapid voltage drop of a battery and reducing a time loss in operation. 
     It is a further object of the present invention to provide an image pickup apparatus capable of adjusting a white balance and photographing and recording a still image rapidly. 
     To achieve the above objects, the image pickup apparatus according to an embodiment of this invention comprises means for picking up an optical image; trigger means for initiating an image pickup by said image pickup means; and control means performing a preparation step for preparing an image pickup prior to initiation of an image pickup by said trigger means, and a judgement step responsive to said trigger means and included in said preparation step for omitting the following preparation step and initiating an image pickup. 
     Since control means carries out the preparation step for preparing an image pickup (such as photometry, white balance adjustment and the like) prior to initiation of an image pickup by trigger means, an image can always be picked up with correct exposure and other settings. Further, since the judgement step is included in the preparation step, the following preparation step is omitted when a trigger signal is generated by trigger means and an image pickup operation is carried out. Thus, without using an interruption routine, an image can be picked up quickly. 
     The image pickup apparatus according to another embodiment of the invention comprises color image pickup means for converting an optical image into an electric signal; color balance adjustment means for adjusting color balance of the output from said color image pickup means in accordance with a color temperature of an object; and control means for switching between two operations, one for fixing a color balance status adjusted by said color balance adjustment means in a first mode where said image pickup means picks up images continuously at relatively high speed, and the other for causing said color balance adjustment means to adjust a color balance for each image in a second mode where said image pickup means picks up images continuously at relatively low speed or picks up one image. 
     Since the color balance of a plurality of consecutive images picked up in a high speed continuous photographing mode often used for comparison between the images does not change, consecutive images each showing a small difference from another can be properly compared without difficulty. 
     In the image pickup apparatus according to another embodiment of the invention, the recording or reproducing apparatus having a motor for use in relative displacement of a recording medium and a head at high speed and a booster circuit for supplying power to the internal circuit comprises control means. When a first power supply capable of discharging a relatively large current is used, said control means actuates said booster circuit after said motor is supplied with a relatively large current. Whereas when a second power supply capable of discharging only a relatively small current is used, said control means causes to a relatively small current to be supplied to said motor after said booster circuit is actuated. 
     When the first power supply capable of discharging a relatively large current is used, control means causes the booster circuit to be actuated under control of the control means after the motor is supplied with a relatively large current. Therefore, the motor is started quickly with priority over the others. Further, when the second power supply capable of discharging only a relatively small current is used, control means the motor to be supplied with a relatively low current after the booster circuit is actuated. Therefore, the current through the booster circuit and the motor does not flow at the same time, thereby preventing a malfunction caused by a voltage drop. 
     The image pickup apparatus according to another embodiment of the invention comprises image pickup means for converting incident light from an object into an electric signal; color temperature detecting means for detecting color temperature information of incident light; drive means for changing the status of incident light; and control means for causing said drive means to change the status of incident light from an initial status to a predetermined status at the start of image pickup, and obtaining a white balance based on the output from said detecting means before said change is completed. 
     Control means causes drive means to change the status of incident light from the initial status to the predetermined status at the start of image pickup. A white balance is obtained before the change is completed. Therefore, a precise white balance based on the color temperature information just before an image pickup operation can be obtained without a time lag. 
     The electric device according to another embodiment of this invention comprises discrimination means for discriminating between a first status indicating that a power supply capability has been degraded and a second status indicating that a power supply capability is not degraded; and control means for switching between two operations based on an output from said discrimination means, one for supplying power to a plurality of drivers substantially at the same time, and the other for supplying power to said plurality of drivers sequentially by a predetermined interval. 
     Discrimination means judges if the power supply capability has been degraded or not. Based on this judgement, control means switches between the two operations, one for supplying power to the plurality of motors substantially at the same time and the other for supplying sequentially by the predetermined interval. Therefore, the overall system operates quickly if the power supply capability is sufficient, whereas it operates slowly if the capability has been degraded. Thus, a rapid voltage drop is avoided to accordingly extend the service life of the power supply. 
     The other objects and aspects of the present invention will become apparent from the following detailed description and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing an example of an image pickup apparatus embodying the present invention; 
     FIG. 2 is a block diagram showing the main part of the circuit included in the apparatus of FIG. 1; 
     FIG. 3 is a block diagram showing the main part of the circuit shown in FIG. 2; 
     FIGS. 4A and 4B are flow charts respectively showing first and second embodiments of the programs used by the image pickup apparatus according to this invention; 
     FIGS. 5A to  5 F are flow charts showing the main part of the flow charts of FIGS. 4A and 4B; 
     FIGS. 6A and 6B are views respectively showing an AC adapter package and a battery package; 
     FIGS. 7A and 7B are timing charts respectively when an AC adapter is used and when a battery is used; 
     FIG. 8 is a block diagram showing a third embodiment of the image pickup apparatus according to the present invention; 
     FIGS. 9A and 9B are flow charts illustrating the operation of the apparatus shown in FIG. 8; 
     FIG. 10 is a flow chart of a fourth embodiment according to the invention; and 
     FIG. 11 is a flow chart of a fifth embodiment according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a perspective view showing an example of the construction of the image pickup apparatus according to an embodiment of the present invention. The apparatus shown in FIG. 1 is constructed of a body  1 , a lens barrel  2 , a stop or aperture  3 , a quick-return mirror  4 , a shutter unit  5 , an image pickup element  6 , an LCD display  7 , a two-stroke release switch  8 , a magnetic disk drive unit  9 , a continuous photographing mode switching control unit  10 , a color temperature detecting sensor window  11 , and a battery package or an AC adapter package  25  which can be replaced within the body  1 . SW 3 , as will be described later discriminates between the battery package and the AC adapter package. 
     A battery is a first power supply capable of discharging a relatively large current, whereas an AC adapter is a second power supply capable of discharging only a relatively small current. 
     FIG. 2 is a block diagram showing an example of the circuit used in the image pickup apparatus according to the embodiment of the present invention. The circuit is constructed of a stop driving apparatus  12 , a mirror driving apparatus  13 , a shutter driving apparatus  14 , a signal processing circuit  15  for processing the output from the image pickup element  6 , a recording apparatus  16 , and other elements. A color temperature sensor  116  detects a color temperature of light incident from the sensor window  11 . A photometry apparatus  19  measures an object brightness by receiving a part of light guided to a finder optical system (not shown) via the quick-return mirror  4 . 
     A control circuit  17  includes a microcomputer. A disk motor control circuit  18  is used for controlling the rotation of a magnetic disc within the recording apparatus. As the recording medium, a magnetic tape may be used instead of a magnetic disc. Also a head may be driven at high speed instead of rotating a disc at high speed. 
     The release switch  8  includes switch SW 1  turning on at a first stroke, and switch SW 2  turning on at a second stroke. 
     The continuous photographing mode switching control unit  10  can select one of three modes, i.e., a single shot mode S, a low speed continuous photographing mode L (2 frames/sec) and a high speed continuous photographing mode H (10 frames/sec). 
     The packages for a battery  120  and an AC adapter  121  have, as shown in FIGS. 6A and 6B, a recess A for an AC adapter but have no recess for a battery. Therefore switch SW 3  turns off when an AC adapter is used, whereas it turns on when a battery is used. A regulator  122  supplies power to the disk motor and the like. A DC/DC converter  123  serving as a booster supplies power to the image pick up elements and others. Q 1  and Q 2  denote switching transistors. The battery  120  and the AC adapter  121  are selectively connected between terminals  24   a  and  24   b.  When SW 1 ′ is actuated in cooperation with the first release switch SW 1 , or transistor Q 2  is turned on, transistor Q 1  is turned on to feed the output of the battery  120  or the AC adapter  121  to the regulator  122  whereat the power is stabilized and supplied to necessary circuits (such as a disk motor in the disk motor control circuit). Power is also supplied to the DC/DC converter  123  when SW 1 ′ is turned on whereat the power is boosted and supplied to the image pickup element  6  and the like for driving the same. 
     The battery  20  may be chargeable or not so long as it can discharge a large current. The AC adapter  121  is of the type that can discharge only a small current. 
     FIG. 3 is a block diagram showing the main part of the circuit shown in FIG.  2 . Sample/hold circuits  20   a  to  20   c  in the signal processing circuit  15  are controlled by sample/hold pulses shifted in phase by  120  degrees. R, G and B stripe filters (not shown) are attached on the front surface of the image pickup element  6  in the vertical scan direction. The width of each stripe filter equals to that of a pixel. Since the horizontal line signal for the image pickup element  6  is constructed of R, G and B point sequential signals, each R, G and B signal is separated by the sample/hold circuits  20   a  to  20   c.    
     Low pass filters (LPF)  21   a  to  21   c  have a cut-off frequency of 0.5 MHz. An LPF  23  has a cut-off frequency of 3 MHz and forms a high band luminance signal Y. Gain control amplifiers  22   a  and  22   b  are provided for R and B channels. A matrix circuit  27  forms Y, R-Y and B-Y signals from Y, R, G and B signals. An encoder  28  generates composite video signals which are recorded on the disc  30  through the head  29  one-field signal per one track. A disc motor  31  rotates at 3600 rpm and generates fifteen periodic FG (Frequency Generating) pulses per one rotation at equal intervals. A stepping motor  301  drives the disc motor  31  to shift the head by means of a head carriage  300  on which the head  29  is mounted. 
     A white diffusion plate  32  fitted into the window  11  formed in the camera body receives environmental light (light source). R and B filters  33  and  34  applies red and blue light to light receiving elements  35  and  36 , respectively. The outputs IR and IB from the light receiving elements  35  and  36  are amplified and subjected to logarithmic compression by logarithmic amplifiers  37  and  38  to obtain logIR and logIB. 
     An subtracter  39  operates to obtain logIR−logIB=logIR/IB. IR/IB corresponds to a color temperature. An A/D converter  40  samples the output of logIR/IB from the subtracter  39  in response to the FG pulses and converts it into a color temperature digital signal which is inputted to the control circuit  17 . 
     The control circuit  17  controls the gains of the gain control amplifiers  22   a  and  22   b  in accordance with the color temperature signal. Namely, as IR/IB becomes large, i.e., as the color temperature becomes low, the gain of the gain control amplifier  22   a  is lowered, whereas the gain of the gain control amplifier  22   b  is made high. 
     FIG. 4A is a flow chart showing an example of a control sequence of the control circuit  17 . FIGS. 5A to  5 F are flow charts showing sub-routines of the flow chart of FIG.  4 A. 
     The program starts at step S 50 . At step S 501 , information on the lens  2  (e.g., stop value, zoom ratio, F number and so on) is fetched. Next, photometry is performed at step S 502  and a white balance control is performed at step S 503 . In particular, at the photometry step, light incident via the stop  3  and the mirror  4  is received by a light receiving element (not shown) and integrated to detect an object brightness level Bv. A stop value Av is then determined using an algorithm Av=Bv−Tv, Tv being a preset shutter time. At the white balance routine as shown in FIG. 5D, digital values of color temperature information inputted to the control circuit  17  in response to FG pulses are integrated for  25  msec at step S 541 . The integrated value CA is stored in a memory MA (not shown) in the control circuit  17  at step S 542 . At step S 543 , the data in the memory MA and the data in a memory MB (to be described later) are added together to form a color temperature data Co for 50 msec. The gains of the amplifiers  22   a  and  22   b  are controlled in accordance with the data Co. 
     Next, the sampled values are integrated again for 25 msec. The integrated value CB is newly stored in the memory MB (step S 545 ). Next, the data in the memory MA and the renewed data in the memory MB are added together to form a new color temperature data Co for 50 msec which is about 25 msec later than the data Co at step S 543 . The gains of the amplifiers  22   a  and  22   b  are again controlled in accordance with this new data Co (step S 546 ). 
     To obtain the color temperature data Co, an integrated value for 50 msec is used. The reason for this is to eliminate flicker of a fluorescent lamp. 
     Particularly, the frequency of the commercial power supply is 50 Hz or 60 Hz and the energy of flicker of a fluorescent lamp has a frequency two times higher than that of the power supply frequency. A color temperature changes with the flicker energy frequency. Therefore, a color temperature data at least for one period of flicker must be integrated so as to obtain a stable color temperature data. On the other hand, if the integration time becomes long, a response of white balance is degraded. 
     Thus, to integrate flicker light at the commercial power supply frequencies of 50 Hz and 60 Hz and hence at the flicker energy frequencies of 100 Hz and 120 Hz, at least {fraction (1/100)} sec and {fraction (1/120)} sec are respectively required. As a result, a minimum integration time for avoiding the influence of flicker becomes 50 msec which is a least common multiple of both integration times. 
     If the gains of the amplifiers  22   a  and  22   b  are controlled at each 50 msec, the response of white balance becomes poor. Therefore, in this embodiment a new color temperature data is fetched at each 25 msec to control the gains. 
     After the white balance routine S 503 , step S 51  stands by until the release switch SW 1  is turned on. If the switch is turned on, the disc motor  31  starts moving at a disc motor drive routine S 52  shown in FIG.  5 F. 
     First at step S 410 , line p of the control circuit is set at high level to turn on the transistor Q 2  so that power is supplied to the regulator  122 . Next, at step S 420  it in (FIG. 2) is checked if the switch SW 3  is turned on or not. The switch SW 3  is made to turn on if a battery package is used. In this case, a motor servo control is initiated at step S 430  by the disc motor control circuit  18 . A relatively large first current I 2  (FIG. 7A) is fed to the motor to drive it rapidly (current I 1  is a current flowing through the control circuit  17  after the switch SW 1  is turned on). 
     The current is reduced to I 3  at step S 431  to conduct a servo control. At the next step S 440  the current I 3  is maintained as it is and thereafter, at step S 450  line q is set at high level to drive the DC/DC converter. A maximum of I 1 +I 3 +I 4  instantaneous current flows at this time instant. Then at step S 460  after a constant time T 2  the routine returns to the main flow program. 
     If an AC adapter is connected, the step S 420  is negated. Therefore, at step S 470  the line q is set at high level to drive the DC/DC converter. A maximum of I 1 +I 4  instantaneous current flows at this time instant as shown in FIG.  7 B. 
     After a constant time T 3  (step S 480 ), the disc motor is driven by the disc motor control circuit  18 . In this case, a second current I 5  smaller than the first current is fed to the motor. The reason for this is that since an AC adapter is used in a home, the disc motor is not needed to be driven rapidly, and a small current should be used. As an example of switching the first and second currents, a switch may be used in such a way that the first current is directly fed to the motor from the power supply, whereas the second current is fed to the motor via an attenuator. After supplying the current I 5  for a certain time at step S 490 , the current I 5  is reduced to I 3  at step S 491  to switch to a servo control. After a constant time T 4  at step S 500 , the routine returns to the main flow. 
     As seen from the above embodiment of this invention, if a battery is used, the disc motor is driven first and then the DC/DC converter is initiated. Therefore, only a short time is required for image photographing and recording. On the other hand, if an AC adapter is used, the DC/DC converter is first initiated and the motor is driven slowly. Therefore, although it takes a long time for driving the disc motor and the DC/DC converter, a maximum current is suppressed so that a compact and simple AC adapter can be used. 
     After the sub-routine S 52 , it is checked if the motor rotation has become stable based on a FG (Frequency Generating) signal and a PG (Pulse Generating) signal, both well known in the art, supplied from the disc motor control circuit. If stable, “1” is set at flag F 1  at step S 522 , whereas if not, “0” is set at flag F 1  at step S 523 . Thereafter, an AE (Automatic Exposure) and AWB (Automatic White Balance) routine is executed at step S 524 . This routine executes automatic exposure control and automatic white balance control, an example of which is shown in FIGS. 5A to  5 C. 
     In the AE and AWB routine, it is checked at step S 200  if the release switch SW 2  is turned on and if the flag F 1  is “1” (i.e., if a trigger for image photographing and recording has been issued and if the recording is possible). If not, information on the lens is read at step S 201  to execute an exposure calculation and a white balance control using the newest data. 
     Thereafter, the flow advances to an photometry routine S 202 , an automatic white balance routine (AWB) S 203 , and an AE operation step S 204 . At the AE operation step S 204 , an AV value determined based on the photometry data is corrected using the newest lens data read at step S 201 . If affirmative at step S 200 , the steps  201  to  204  are skipped. 
     Thus, without waiting for the end of all the sequential steps, the photographing sequence to be described later can be followed. 
     The photometry routine S 202  in FIG. 5A which is detailed as shown in FIG. 5B has step S 205  similar to step S 200 . Therefore, although a photometry process is again executed at photometry step S 206  if NO at step S 205 , the photometry process is not executed if YES and the flow advances to step S 203 . 
     Similarly, in the automatic white balance routine S 203  detailed in FIG. 5C, step S 207  similar to steps S 200  and  203  is provided. Therefore, if YES at step S 207 , a display routine S 525  follows without executing the white balance routine S 208 . The white balance routine S 208  is detailed in FIG. 5D as described previously. 
     Also, in a display routine detailed in FIG. 5E, step S 209  similar to steps S 200 ,  205  and  207  is provided. Therefore, if YES at step S 209 , step S 55  follows by skipping a display step S 210 . 
     After the display routine S 525 , it is checked at step S 55  if the release switch SW 1  is turned on or not. If not, the flow jumps to step S 67  whereat the line p is set at low level to turn off the transistor Q 2 , stop the disc motor, and complete the program. 
     If YES at step S 55 , it is checked at step S 56  if the release switch SW 2  is turned on and if the flag F 1  is “1”, i.e., if a trigger for image photographing and recording has been issued and if the recording is possible. If NO, the flow resumes step S 524  to repeat the photometry operation, white balance adjustment, display operation and so on. 
     If the release switch SW 2  is turned on and if the flag F 1  is “1” at steps S 56 ,  200 ,  205 ,  207  and  209 , then a photographing and recording sequential control starts. At step S 57  the mirror is retracted or set up from the photographing optical path by the mirror driving apparatus. At step S 58 , the stop is moved down by the stop driving apparatus  14  from an open state to the stop-down value Av determined by the photometry data obtained at steps S 502  and  206  and the preset shutter time. 
     Next, a white balance routine is again executed at step S 581 . This white balance routine is the same as that described in steps S 541  to  546  shown in FIG.  5 D. 
     Since it takes about 60 msec from the start of the mirror set-up and stopping-down operations at steps S 57  and  58  to the end of the operations, the white balance operation can be executed within this time period. 
     After a lapse of a short time from the end of the white balance routine at step S 581 , the end of mirror set-up and stopping-down are detected by sensors (not shown) to thereafter follow proceed to step S 60 . 
     At step S 60  the shutter is opened by the shutter driving apparatus  14 . After a lapse of the shutter time Tv, the shutter is closed at step S 61 . Then at step S 62 , the output from the image pickup element is recorded in the disc. At step S 621  the head  29  is shifted to the next empty track of the disc. 
     Thereafter, it is again checked at step S 63  if the release switch SW 2  is turned on and if the flag F 1  is “1”. If YES, it is checked at step S 64  based on the reading from the control unit  10  if a high speed continuous photographing mode is adopted. In case of a high speed continuous photographing mode, the flow returns to step S 60  to repeat the photographing and recording operation such as the next step shutter opening and closing and the head shift to the next empty track. In this case, not only the photometry value and the stop value (Av) but also the white balance status are maintained unchanged. Therefore, the color does not change and images continuously photographed have a correct color balance. Further, as seen in the prior art, with the photometry data fixed because of the mirror set-up, if the color balance changes irrespective of a constant brightness level, a difference between continuously photographed images becomes more conspicuous. However, the embodiment of this invention does not have such a problem. 
     If the release switch SW 2  is turned off at step S 63 , or if it is turned on and the flag F 1  is “1” but a high speed continuous photographing mode is not adopted, the flow advances to step S 65  whereat the mirror is returned to the optical path and the stop is again opened. 
     Then at step  66  it is checked, based on the reading from the control unit  10 , if a low speed continuous photographing mode is adopted. If YES, the flow again begins with step S 524  to execute photometry and white balance operations. 
     If NO, the flow advances to step S 67  whereat the disc motor is stopped and the program terminates. As such, the photometry and white balance operations are effected for each frame in the low speed continuous photographing mode. This mode, with the finder being used, is usually adopted not for the case where high speed continuously photographed images are desired but for the case where a failure in photographing is serious and a fine change of an object must be taken account of. Thus, it is desirable that each frame has correct exposure and white balance. 
     In the above embodiment, the outputs of the color temperature sensors are sampled in response to FG pulses to convert them into a digital value for use in a white balance control. Therefore, dedicated sampling pulses are not required to be generated by a synchro signal oscillator for example. Further, it is advantageous in that the motor speed control by the control circuit and other controls can be easily performed in synchronization with the white balance control using the program. 
     In the embodiment, if the release switch is fully depressed at once, the flow may advance to the stopping-down step S 58  without the photometry operation. To avoid such a case, steps S 502  and S 503  are provided to first execute the photometry and white balance operations. The steps are also provided to avoid a possibility that the white balance operation is executed only once for 50 msec at step S 581 , and hence results in an unstable white balance value. 
     As seen from the above embodiment, the photographing and recording operations can be executed immediately after the initiation of a photographing and recording trigger without employing an interruption function, thereby reducing a release time lag. 
     Further, according to the embodiment, a white balance adjustment is executed during the time while the incident light status to the image pickup element is controlled to change from the initial status to the predetermined status. The initial status means, for example, that the mirror is set down to the photographing optical axis to guide the light to the optical finder and the photometry apparatus  19 , or means an initial lens focus position in case of an AF mechanism. The predetermined status means, for example, that the mirror is set up to a predetermined fixed position and the stop value is set at a calculated one, or that an in-focus state is achieved in case of an AF mechanism. Thus, without increasing a time lag between the initiation of a photographing and recording trigger and the end of the recording, the incident light control such as exposure and white balance control, and AF control can be executed precisely and at a short time. Incident light control means may include a shutter as well as a stop, mirror and an AF mechanism. 
     Since the white balance control can be executed based on the white balance information obtained immediately before the exposure by the shutter, a precise white balance control properly following a change in light can be ensured. 
     Furthermore, even if the release switch is fully depressed at once, a correct white balance is assured without a significant release time lag. This can be realized using software. The software itself becomes idle and has no burden during the time while the driving apparatus is controlled to change the incident light from the initial status to the predetermined status. 
     The description of the embodiment has been directed to an electronic camera, but it is obvious that the invention can advantageously be applied to a camera using a silver salt film. 
     As seen from the description of the first embodiment of the present invention, the photographing and recording can be initiated without using an interruption function. Therefore, the program can be simplified with a small capacity of memory. In addition, the photographing and recording can be executed smoothly as if an interruption routine is used. 
     Further, the entire system including a motor is started at a short time with somewhat a large maximum current of a battery, whereas in case of an AC adapter a reduced maximum current is set irrespective of a slow start of the system. Thus, unnecessary burden on the AC adapter and a malfunction caused by a voltage drop can be avoided. A proper shutter chance of an image shot can be ensured in case of a battery. 
     FIG. 4B is a flow chart of a second embodiment of the control sequence of the control circuit  17 . The flow chart of FIG. 4B is a simplified version of that shown in FIG. 4A, wherein similar steps are represented by identical numbers. 
     The program starts from step S 50  and waits at step S 51  until the release switch SW 1  is turned on. When the switch turns on, the disc motor  31  is driven at step S 52  and is followed the photometry step (step S 53 ) and the white balance routine step S 54 ). At the photometry step, light incident from the stop  3  and the mirror  4  is received by a light receiving element (not shown) and integrated to detect an object brightness level Bv. The stop value Av is calculated using an algorithm Av=Bv−Tv, where Tv is a preset shutter time. At the white balance routine S 54 , the gains of the amplifiers  22   a  and  22   b  are controlled at the steps shown in FIG. 5 as described previously. 
     After the white balance sub-routine S 54 , it is checked at step S 55  if the release switch SW 1  is turned on. If NO, the flow skips to step S 67  whereat the disc motor is stopped and the program terminates. 
     If YES at step S 55 , it is checked at step S 56  if the release switch SW 2  is turned on, i.e., if a photographing and recording trigger is issued. 
     If the switch SW 2  is not turned on, the flow resumes step S 53  to repeat the photometry and white balance operations. In this case, as described previously, the output of the light receiving element is integrated for each 50 msec by a loop including steps S 53 ,  54 ,  55  and  56  to control the gains at each 25 msec. 
     If the release switch SW 2  is turned on, the mirror is retracted from the photographing optical path by the mirror driving apparatus  13  at step S 57 . The stop is moved down by the stop driving apparatus  14  from a stop open status to the stop value Av determined by the photometry data obtained at step S 53  and the preset shutter time. 
     Next, the head  29  is shifted at step S 621  to the next empty track of the disc. The shutter is opened by the shutter driving apparatus  14  (step S 60 ) and closed at step S 61  after a lapse of the shutter time Tv. The output of the image pickup element is recorded in the disc at step S 62 . 
     The following steps S 63  to  68  operate in a same manner as described with FIG.  4 A. According to the embodiment shown in FIG. 4B, the white balance control can be achieved using a simplified flow control, with a fixed white balance during high speed continuous photographing. 
     FIG. 8 is a block diagram showing a third embodiment of the image pickup apparatus according to the present invention, wherein a drop in power supply level is detected to change a control sequence for driving the system. 
     Elements having similar function to those shown in FIGS. 1 to  7  are represented by identical reference numbers. 
     In this embodiment, the stop driving apparatus outputs a signal U upon completion of opening the stop, and the mirror driving apparatus  13  outputs a signal V upon completion of mirror set-down. The control circuit  17  outputs a head shift signal Hs to drive a stepping motor described later and shift the head. Upon completion of the head shift, a signal HC is outputted from the motor and inputted to the control circuit  17 . 
     Divider resistors R 1  and R 2  divide the power supply level to be supplied to the regulator. A comparator COMP outputs a low level signal BE when the power supply level is larger than a reference voltage Vref, and a high level signal BE when smaller than Vref. 
     FIGS. 9A and 9B are flow charts illustrating the operation of the apparatus shown in FIG.  8 . Identical reference numbers to those in FIGS. 1 to  8  represent similar steps. 
     Step S 52  shown in FIG. 4B advances to reference character A in FIG.  9 A. Steps S 53  to  58  in FIG. 9A are identical to those in FIG.  4 B. Thereafter, without moving the head, the shutter is opened at step S 60  and closed at step S 61  to execute the recording at step S 62 . 
     The flow advances to step S 651  shown in FIG. 9B whereat an output BE from the comparator COMP is read. If the signal BE is not at high level at step S 652  because of a power supply voltage drop, then a motor  301  in the recording apparatus is driven to move a head carriage  300  and shift the head by one track. 
     If a head shift end signal HC is outputted from the motor  301  after completion of one track shift (step S 654 ), the mirror is returned (set down) to the original position at step S 655 . Thereafter, if a mirror set-down end signal V is obtained from the mirror driving apparatus  13  at step S 656 , the stop is opened by the stop driving apparatus  12  at step S 657 . At step S 658 , if a stop open end signal U is obtained from the stop driving apparatus, the flow advances to step S 665 . 
     As seen from the above, if the power supply level drops, the operations such as head motion, mirror set-down, stop opening are sequentially performed so that power supply consumptions do not occur at the same time, to thereby eliminate a voltage drop caused by a rapid current discharge and a malfunction. 
     If the output of the comparator COMP is at low level at step S 652  because the power supply level does not drop, then the three operations including the mirror set-down, head motion and stop opening are executed substantially at a same time at steps S 659  to  661 . 
     The mirror set-down end signal V, head shift end signal HC, and stop open end signal U are waited for respectively at steps S 662  to  664 . Thereafter, the flow advances to step S 665 . As seen from the above, when the power supply voltage is sufficiently high, the three operations including the mirror set-down, head motion and stop opening are executed substantially at the same time. Therefore, preparation for the next photographing can be completed quickly. 
     At step S 665  it is checked if the switch SW 1  is turned on. If not, the output P of the control circuit  17  is set at low level to turn off the transistor Q 2  (step S 57 ) and stop supplying the power, to thus terminate the program. 
     If the switch SW 1  is turned on at step S 665 , it can be considered that the operator still wants to take a photograph so that the flow resumes at step S 53 . 
     In the above embodiment, after the photographing, the three operations including the mirror set-down, head motion and stop opening are sequentially executed one after another. Similarly, in steps S 57  and  58  immediately before photographing, the control operations for the stop, mirror and others may be executed sequentially when the power supply drops, or substantially at a same time when the power supply does not drop. 
     Further in the above embodiment, the timings for supplying power to a plurality of driving apparatuses are changed in accordance with the first and second conditions of the power supply. However, the timings may be changed in accordance with a plurality of finely divided conditions of the power supply. 
     According to the third embodiment of the present invention, discrimination means judges if the power supply capability has been degraded or not. Based on this judgement, control means switches between the two operations, one for supplying power to the plurality of motors substantially at a same time and a other for supplying sequentially with the predetermined interval. Therefore, the overall system operates quickly if the power supply capability is sufficient, whereas it operates slowly if the capability has been degraded. Thus, a rapid voltage drop is avoided to accordingly extend a service life of a power supply. 
     FIG. 10 is a flow chart showing the fourth embodiment of the control sequence of the control circuit  17  according of the present invention. Similar steps to those in FIGS. 1 to  9  are represented by identical reference numbers. 
     The control sequence to step S 58  after the program starts at step S 50  is identical to that described with reference to FIG. 4B, so the description therefor is omitted. 
     The white balance routine is executed at step S 581 . This routine is identical with that described with reference to steps S 541  to  546  in FIG.  5 D. 
     It takes about 60 msec for the operation starting from the mirror set-up and stopping-down at steps S 57  and  58  to the end thereof. Thus, the white balance operation can be sufficiently executed within this time. 
     After a short time lapse from the end of the white balance routine at step S 581 , if it is detected by sensors (not shown) that the mirror set-up and stopping-down have been completed, the flow advances to step S 60  whereat the shutter is opened by the shutter driving apparatus  14 . After a lapse of the shutter time Tv, the shutter is closed at step S 61 . The output of the image pickup element is recorded in the disc at step S 62  and thereafter, the head  29  is shifted to the next empty track of the disc at step S 621 . 
     The following steps S 63  to  68  are identical with those shown in FIG. 4B, so the description therefor is omitted. 
     A flow chart of the fifth embodiment of the control sequence of the control circuit is shown in FIG.  11 . 
     Steps having identical functions as those shown in FIGS. 1 to  10  are represented by the same reference numerals. 
     In this embodiment, the operation of the switch SW 2  is executed using an interrupt processing, which is different from the fourth embodiment. 
     If the release switch SW 1  is turned on at step S 55 , an interruption of the switch SW 2  is permitted at step S 43  and the flow returns to step S 53 . Whereas if the release switch SW 1  is turned off at step S 55 , the interruption of the switch SW 2  is inhibited at step  101  to stop the disc motor at step S 67 . Then the flow returns to step S 51 . 
     In the SW 2  interrupt processing, the interruption of the SW 2  is temporarily stopped at step S 103  and thereafter, the processes at steps S 57  to  66  as described previously are executed. In case of a low speed continuous photographing mode at step S 66 , the flow returns to step S 53  in the same manner as the fourth embodiment. If not, the flow returns to step S 67  to stop the motor and resume step S 51 . 
     As described above, a white balance adjustment is executed during the time while the incident light status to the image pickup element is controlled to change from the initial status to the predetermined status. The initial status means, for example, that the mirror is set down to the photographing optical axis to guide the light to the optical finder and the photometry apparatus  19 , or means an initial lens focus position in case of an AF mechanism. The predetermined status means, for example, that the mirror is retracted to a predetermined fixed position and the stop value is set at a calculated one, or that an in-focus state is achieved in case of an AF mechanism. Thus, without increasing a time lag between the initiation of a photographing and recording trigger and the end of the recording, the incident light control such as exposure and white balance control, and AF control can be executed precisely and in a short time. Incident light control means may include a shutter as well as a stop, mirror and AF mechanism. 
     Since the white balance control can be executed based on the white balance information obtained immediately before the exposure by the shutter, a precise white balance control properly following a change in light can be ensured. 
     Furthermore, even if the release switch is fully depressed at once, a correct white balance is assured without a significant release time lag. This can be realized using software. The software itself becomes idle and has no burden during the time while the driving apparatus is controlled to change the incident light from the initial status to the predetermined status.