fig1 ( a ) and fig1 ( b ) are drawings illustrating an aperture control function according to the invention . according to the invention , a control is given , as shown in fig1 ( a ), such that the aperture is set as computed when the minimum aperture ( line a ) computed , for example , according to a distance , comes below a predetermined value ( f5 . 6 for example ), but a camera is set to an aperture ( line b ) opened further from the computed aperture by a predetermined stage number toward the open side when the minimum aperture comes over the predetermined value . consequently , enough quantity of light may be secured even in case an object is remote , and where it stands a short distance away , an open aperture is preferred rather than the computed aperture , a flash photographing can be realized on the light less than that of being emitted through the computed aperture , and thus a recycle time can be contracted . further in the invention , a control is made to have a set aperture or the aperture decided on an extraneous light luminance other than that in which the aperture ( dotted line ) computed according , for example , to a distance is opened further from aperture values ( full lines ) decided on the externally set aperture and the extraneous light luminance by 3 stages or more at bv ≦ 6 and 5 stages or more at bv & gt ; 6 . this may permit a photographer to give priority to the aperture set by himself or the aperture decided on an extraneous light luminance . fig2 represents a stroboscope circuit used for putting one example of the invention into practice . a reference character x denotes a terminal connected to x contact of a known camera side , s denotes a terminal for inputting signals indicating a state ready for luminosity at low level and luminosity stop at high level from the camera side , c denotes a terminal for inputting a constant voltage vc from the camera side , a denotes a terminal for outputting apex values of apertures to the camera side as voltage , g denotes a terminal to be grounded , all being connected to corresponding terminals of the camera . a reference numeral 1 denotes a xenon discharge tube for main light emission , 2 denotes a main capacitor charged by a dc - dc converter which is not indicated , 3 denotes a known trigger circuit , 4 denotes a commutation circuit connected in series to the xenon discharge tube for main light emission , 5 , 6 denote resistances , 7 denotes a comparator having a constant voltage vrefl generated in a stroboscope impressed on the inversion input end , and the comparator 7 outputs a high level charge completion signal whenever a charge voltage of the main capacitor 2 reaches a predetermined value . a reference numeral 8 denotes a resistance , 9 denotes a light emitting diode working as a charge completion display means , 10 denotes an and gate , 11 , 12 denote inverters , 13 , 14 denote an or gate and an and gate forming a flip - flop , 15 , 16 , 17 denote a diode , a resistance and a capacitor which form a differentiating circuit for detecting rise only of a pulse inputted to the terminal s , 18 denotes a resistance , 19 denotes a transistor turned on according to the charge completion signal , leading in a current from a camera side by way of a resistance 20 and a terminal c , thereby transferring the stroboscope being ready for light emission to the camera side , 21 denotes a resistance , 22 denotes a transistor turned on to turn the transistor 19 off , thereby transferring ring the stroboscope starting for light emission to the camera side , 23 denotes a comparator having a constant voltage vref2 (& lt ; vc ) impressed on the inversion input end , thereby detecting whether or not the constant voltage vc is inputted to the terminal c from the camera side , 24 denotes an and gate , 25 denotes a one - shot circuit for outputting a pulse having a width of constant duration which is longer than a preemitted light , 26 denotes a trigger circuit , 27 denotes a xenon discharge tube for light preemission , 28 denotes a capacitor for light preemission , 29 denotes an infrared filter , 30 denotes an inverter , 31 , 32 , 33 denote a capacitor , a diode and a resistance forming a differential circuit for detecting rise only of a pulse output from the inverter 30 ( or fall of an output pulse of the oneshot circuit 25 ), 34 denotes a lens for specifying an angle of received light , 35 denotes a silicon photodiode for receiving the light that infrared rays of the xenon discharge tube 27 for light preemission reflect on an object , 36 , 37 denote a resistance and an operational amplifier for converting a current of the silicon photodiode 35 into voltage , 38 denotes a high - pass filter , 39 , 40 , 41 , 42 denote a resistance , an integrating capacitor , an analog switch and an operational amplifier which form an integrating circuit , 43 denotes an a / d coverter , 44 denotes a latch circuit operating for clearing motion on a low level output of the and gate 24 and also for latching motion on a differential output from the resistance 33 , 45 denotes a d / a converter , and fvc denotes a constant voltage generated in the stroboscope . a flash operation will now be described with reference to the timing chart given in fig3 . upon turning on a power switch ( not indicated ) of the stroboscope , the main capacitor 2 and the capacitor 28 for light preemission are charged . when a charging voltage of the main capacitor 2 develops to the voltage ready for light emission of the xenon discharge tube 1 for main light emission , the comparator 7 outputs a high level charge completion signal , and thus the light emitting diode 9 is actuated to indicate a charge completion . the transistor 19 is turned on concurrently . then , from depressing a first stroke of a release button of the camera , the constant voltage vc is impressed on the terminal c from a camera side , and from leading in a current through the terminal c , a state ready for light emission is transferred to the camera side . then , an output of the comparator 23 gets high in level , an output of the and gate 24 also gets high in level , and the one - shot circuit 25 operates . thus the xenon discharge tube 27 for light preemission is actuated to radiate infrared rays on an object . the reflected light is then incident on the silicon photodiode 35 , and a voltage according to a brightness of the object is obtained from the operational amplifier 37 . the high - pass filter 38 removes a natural light almost not changing as compared with a waveform of the preemitted light and passes only the preemitted light waveform . the voltage is proportional naturally to the inverse square of the distance . the analog switch 41 is kept off while an output of the one - shot circuit 25 is high in level , therefore an output voltage of the high - pass filter 38 is integrated by the current flowing through the resistance 39 and the integrating capacitor 40 and then output from the operational amplifier 42 . the integrated output is converted into a digital value through a / d converter 43 and stored by the latch circuit 44 at a fall time of an output pulse of the one - shot circuit 25 . the stored digital value is converted into a voltage easy to handle as ( 11 + dv - pv ( max ))× vc / 16 through the d / a converter 45 according to the constant voltage vc of the terminal c and transferred to the camera side as analog distance information vef . one example of the analog distance information vef , pv = 5 [ gno = 32 ( iso 100 )] is shown in fig4 . the camera side processes the analog distance information vef to obtain av value and thus controls the camera apertures . from depressing a second stroke of the release button thereafter , a voltage of the terminal s comes first to a low level , a synchro switch is then turned on according to a running shutter , and a voltage of the terminal x gets low in level . thus , an output of the and gate 10 becomes high in level , the trigger circuit 3 operates , and the xenon discharge tube 1 for main light emission is actuated . an output of the and gate 14 gets high in level at the same time , and the transistor 19 is turned off while the transistor 22 is turned on . the current is stopped from flowing into the terminal c , consequently . on the other hand , the camera comes to operate for ttl and diming of reflection on the film surface . then , whenever reaching a proper level , the voltage of the terminal s comes to a high level , a differential pulse arising on the resistance 16 at the rise is inputted to the commutation circuit 4 , and the xenon discharge tube 1 for main light emission is stopped from emission . fig3 represents the case where a charge completion state is maintained while the first flash emission is over , and the charge completion state is cleared by the second flash emission . then , it goes without saying that a distance information ( pv ( max )- dv ) transferred from the terminal a to the camera side may be given in a digital value instead of the analog . fig5 shows a circuit on the camera side for putting one example of the invention into practice . a reference numeral 50 denotes a single - chip microprocessor having rom , ram in a chip , which is provided with 24 separate input / output ports , a reset terminal rs and 8 - bit parallel data bus terminal db . a hexadecimal number is used for internal arithmetic operation of the microprocessor 50 , and the hexadecimal numbers given in fig1 are made to coordinate with various apex values of the camera . for example , f 1 . 4 corresponds to apex 1 and is 08h ( h indicating hexadecimal number ) accordingly . the shutter speed 1 / 4000 is apex 13 and 68h . for easy understanding , the lens open aperture is set at f 1 . 4 , the lens minimum aperture is set at f 32 , the highest shutter speed is set at 1 / 4000 sec ., the synchronizing speed is set at 1 / 250 to 1 / 00 sec . and the lowest speed is set at 1 sec ., however , it goes without saying that these values are not necessarily imperative . a reference numeral 51 denotes a power - up clear circuit for outputting a power - up clear signal for a certain period of time when a power is closed from a supply circuit which is not indicated therein , 52 denotes an a / d converter for converting analog voltages 0 to vc into 256 stages of digital values shown in fig1 , 53 denotes a d / a converter for converting a digital value from the microprocessor 50 into analog voltage shown in fig1 , 54 , 55 denote analog switches , 56 denotes a silicon photodiode for measuring brightness of an object , 57 denotes a diode for logarithmic compacting , 58 denotes an operational amplifier , 59 to 62 denote resistances , 63 denotes an operational amplifier , 64 denotes a silicon photodiode for measuring a film reflected light of the stroboscope , 65 denotes a diode for logarithmic compacting , 66 denotes an operational amplifier , 67 denotes an expanding transistor , 68 denotes an inverter , 69 denotes an analog switch , 70 denotes an integrating capacitor for strobodimming , 71 denotes an operational amplifier , 72 denotes a constant voltage source , outputting a reference voltage of a dimming comparator . for convenience &# 39 ; sake , the reference voltage is specified at vc + 1 . 0v . a reference numeral 73 denotes a dimming comparator , 74 denotes an inverter , 75 denotes an or gate , 76 denotes a film photosensitivity iso input circuit , 77 denotes a set point input circuit for inputting a set point of the shutter speed at the time of shutter priority mode and a set point of the aperture at the time of aperture priority mode , 78 denotes a first tension magnet for releasing a first tension of the camera and actuating a mechanical release sequence , 79 denotes an aperture control magnet for controlling automatically an aperture of the camera , 80 denotes a leading curtain magnet for running a shutter leading curtain , 81 denotes a trailing curtain magnet for running a shutter trailing curtain , 82 to 85 denote transistors . a reference numeral 86 denotes a first stroke switch getting on at the first stroke of the release button , which is ready for starting photometry on the camera . a reference numeral 87 denotes a second stroke switch getting on at the second stroke of the release button , which is ready for starting shutter release of the camera . a reference numeral 88 denotes an aperture switch interlocking with the automatic diaphragm , getting on / off once whenever the camera is stopped down at 1 / 8 stage . a reference numeral 89 denotes a mirror - up switch getting on at holding up a mirror , 90 denotes a trailing curtain switch getting on when the trailing curtain has run , 91 denotes a first mode setting switch for setting a shutter priority mode from being off and an aperture priority mode from being on , 92 denotes a second mode setting switch for setting a program mode prior to the mode set by the first mode setting switch from its being off , 93 to 99 denote pull - up resistances , 100 to 102 denote resistances , 103 denotes an operational amplifier , 104 denotes an analog switch , 105 denotes a comparator , 106 denotes a shutter speed display circuit , latching data of a data bus at rise of the port p04 , thereby carrying out a display corresponding to the data . then , when a signal level of the port p16 is high , the display is blinked to provide warning . a reference numeral 107 denotes an aperture display circuit , latching data of the data bus at rise of the port p05 , thereby carrying out a display corresponding to the data . then , when a signal level of the port p17 is high , the display is blinked to provide warning . a reference numeral 108 denotes an x contact . vc , vcc , 2xvc denote constant voltages fed from a power circuit which is not indicated therein . the shutter speed display circuit 106 and the aperture display circuit 107 are of a circuit configuration , therefore one example of the shutter speed display circuit 106 will be shown in fig6 . a reference numeral 200 denotes a latch circuit , latching data of the data bus at rise of the port p05 of the microprocessor 50 . the output terminals t 0 to t 3 represent a first digit of the hexadecimal number , and those t 4 to t 7 represent a second digit of the hexadecimal number . reference numerals 201 to 204 denote inverters , 205 denotes a nand gate , outputting a high level when the port p16 of the microprocessor 50 is low in level but inverting and outputting a clock pulse when it is high in level . a reference numeral 206 denotes a clock pulse generator circuit for blinking display , 207 , 208 , 209 , 210 denote an and gate , a nand gate , a resistance and a light emitting diode for indicating 1 / 4000 sec . when an output of the latch circuit 200 is 68h to 6fh , and when the output port p16 comes to a high level , the light emitting diode 210 blinks to warning . reference numerals 211 to 214 denote a set of like elements indicating 1 / 2000 sec . when an output of the latch circuit 200 is 60h to 67h , 215 to 218 denote a set of like elements indicating 1 / 1000 sec . when the output of the latch circuit 200 is 58h to 5fh , 219 to 223 denote a set of elements indicating 1 sec . when the output of the latch circuit 200 is 08h to 0fh . an operation of the microprocessor 50 will be described with reference to the flowcharts given in fig7 to fig9 . in describing the flowcharts , the ports p00 to p07 will be called &# 34 ; port0 &# 34 ; collectively . then , the ports p10 to p17 will be called &# 34 ; portl &# 34 ;. when the ports are operated one by one or , for example , the port p01 is made to be a high level , the notation will be p01 ← 1 . when made to be a low level , the notation will be p01 ← 0 likewise . when operating port0 including the eight ports collectively or , for example , p17 , p16 , p15 , . . . p10 of port1 are to read 10100101 , the notation will be such port1 ← a5h . in case data is inputted from the a / d converter 52 , a necessary operation may be such that a photometry is selected with p00 ← 1 first , an 8 - bit data is read from a data bus terminal db after a / d conversion of the photometry information is over , and then a / d conversion selection is cleared with p00 ← 0 therefor , however , the above will be omitted to the following notation : where acc indicates an accumulator . when an analog distance information is subjected to a / d conversion at p01 : in case a data is output to the shutter speed display circuit 106 and others , an 8 - bit data is output , with p04 ← 1 therefor , to the data bus terminal db from the accumulator acc , and then latched with p04 ← 0 , thus the notation being as : likewise , an output to the aperture display circuit 107 will be notational as : when a power is closed from a power circuit which is not indicated therein , the power - up clear circuit 51 outputs a low level for a certain period of time , and the microprocessor 50 is thus reset . the reset microprocessor 50 then executes programs in sequence from a of the flowchart of fig7 . outputs of the ports p00 to p07 and p10 to p17 are all turned to low level . thus the a / d converter 52 , the film photosensitivity iso input circuit 76 , the set point input circuit 77 , the shutter speed display circuit 106 , the aperture display circuit 107 and the d / a converter 53 are kept from selection , the magnets 78 to 81 are all turned off , the strobodimming integrating capacitor 70 is discharged , a voltage on the terminal s is made to a high level , and flickering of the shutter speed display circuit 106 and the aperture display circuit 107 is transferred to lighting . the display is put out by outputting 00h to the shutter speed display circuit 106 and the aperture display circuit 107 . the port p20 is sensitized . if the first stroke switch 86 is kept off , then # 1 , # 2 and # 3 loops are repeated to await the first stroke switch 86 getting on . let it be assumed , now , the camera has been charged already , the trailing curtain switch 90 is turned off , and the main capacitor 2 ( fig2 ) of the stroboscope has completed charging . further , the assumption is such that the second mode setting switch 92 is kept off , and the program mode has been set . the photographer catches an object through finder , and when the first stroke of the release button is depressed , the first stroke switch 86 is turned on , and the camera is ready for photometry . it branches to # 4 according to a branch instruction # 3 in fig7 . a brightness bv of the extraneous light is measured on the silicon photodiode 56 . assuming a current ispd flowing through the silicon photodiode 56 when bv = 0 is i o , ispd = 2 bv × i o at the brightness bv . assuming an output voltage of the operational amplifier 58 is v 58 : ## equ4 ## where k : boltzmann constant then , if values of the resistances 59 , 62 , 60 , 61 be r 1 , r 2 , r 3 , r 4 respectively , an output v 63 of the operational amplifier 63 can be expressed as : ## equ5 ## from selecting resistance values r 1 , r 2 , r 3 , r 4 so as to have : ## equ6 ## the brightness bv of the extraneous light is inverted by the operational amplifier 63 , therefore it is returned to what it stands originally by taking a hexadecimal negative number . for example , a / d converted value is f8h when bv = 1 but when the hexadecimal negative number is taken , it becomes 08h or apex value bv = 1 . the a / d converted value becomes c0h when bv = 8 , and the negative number is 40h . the value is then loaded in the register bv . apex code of iso is inputted from the film photosensitivity iso input circuit 76 and loaded in the register sv . ev value is computed from the extraneous light brightness bv and the film photosensitivity sv and loaded in a register ev . the analog switch 104 is turned on with the port p07 kept at high level . then , an output of the operational amplifier 103 is fed back by way of the resistance 100 , therefore a voltage on the terminal c rises . now , if the stroboscope is charged , then a constant current is sucked in through the terminal c , therefore an output voltage of the operational amplifier 103 gets higher than vc . accordingly , a voltage on non - turnover input end of the comparator 105 also exceeds vc , and thus an output of the comparator 105 is turned over to a high level . in this case , the stroboscope preemits infrared rays on a rise of the voltage on the terminal c , a distance to the object is thus measured , converted into an analog voltage and output from the terminal a as analog distance information vef . when the stroboscope has been charged , the output of the comparator 105 is on a high level as described at # 8 , therefore it branches to # 10 of fig8 by way of b . the analog distance information vef from the stroboscope is converted into a digital value and loaded in the accumulator . a minimum aperture ( apex value ) is computed according to the digital distance information and loaded in a register avef . in this case , 58h is a constant . the reason why acc is halved is that the first stage vc / 16 on the stroboscope side is to be converted into the first stage vc / 32 on the camera side . for example , the aperture will be 32 ÷ 8 = f4 to the object iso 100 , gno = 32 and 8 m in distance , therefore a voltage on the terminal a is 3 vc / 4 from fig4 and the a / d converted value is c0h , ## equ7 ## that s , a code of f4 aperture . a status of the second mode setting switch 92 will be discriminated . since the program mode is selected now , it is kept off , and the program is branched to # 13 . in # 13 to # 19 , a shutter speed and an aperture conforming to the stroboprogram line sp shown in fig1 will be decided according to the ev value computed at # 7 . the ev value is compared with apex 19 ( 98h in hexadecimal number ), and where it is greater , the program goes forward to # 14 . the shutter speed is synchronized at 1 / 250 sec . and the aperture is minimized at f32 on the camera , but the extraneous light is nevertheless overwhelming , therefore the aperture display circuit 107 is operated to flicker for warning . the ev value is compared with apex 14 ( 70h in hexadecimal number ), and where it is greater , the program is branched to # 16 . the shutter speed is synchronized at 1 / 250 sec . and the aperture is obtained through arithmetic operation . in this case , the aperture comes within f5 . 6 to f32 . the ev value is compared with apex 12 ( 60h in hexadecimal number ), and where it is greater , the program is branched to # 18 . the aperture is set at f5 . 6 , and the shutter speed is obtained through arithmetic operation . in this case , the shutter speed comes within 1 / 60 to 1 / 250 . the shutter speed is set at 1 / 60 sec ., and the aperture is obtained through arithmetic operation . in this case , the aperture comes within f . 1 . 4 to f5 . 6 . in the operations # 13 to # 19 , a combination of the shutter speed and the aperture appropriate to the extraneous light is obtained . then , the shutter speed in this case will not lead to a slit exposure by synchronizing it selectively at 1 / 250 to 1 / 60 sec . the program branches to # 21 when the bv value is apex 6 ( cloudy weather ) or over but to # 24 when it is less than 6 . when the extraneous light brightness bv is valued at 6 or over , a daylight synchronous photographing is prevailing , so decided , to give the extraneous light priority , and a control is carried out according to the shutter speed and the aperture appropriate to the extraneous light which are obtained through # 13 to # 19 . accordingly , the stroboscope emits the light as auxiliary to the extraneous light in this case . however , in case the minimum aperture avef computed according to a distance information from the stroboscope comes below f1 . 4 , that is , a distance to the object at the time of iso 100 exceeds 32 m , the flash light emission is not effective , and hence the program branches to # 23 . in case , further , the aperture av appropriate to the extraneous light comes on the side 5 stages or more stopped down from the computed minimum aperture avef , that is , a full light emission of the stroboscope is still under 5 stages or more , the flash light emission is also not effective , and thus the program branches to # 23 . for the stroboscope low luminance warning , the shutter speed display circuit 106 and the aperture display circuit 107 are operated to flickering simultaneously . where bv ≦ 6 at # 20 , the program branches to # 24 . the camera aperture will be decided according to the minimum aperture avef computed on the distance information from the stroboscope at # 24 to # 31 . when avef is greater than f64 , the program branches to # 25 . a stopped - down side of avef is limited by f22 . # 26 avef : f16 when avef is greater than f16 , the program branches to # 27 . where f16 ≦ avef & lt ; f64 , avef is decreased by 3 stages ( 18h ). the reason is that when the distance is shorter than 2 m ( iso 100 , gno = 30 ), the control is effective on an aperture 3 stages opened from the aperture through which the stroboscope emits the light full , the light emission on the guide number 3 stages less is to shorten a cycle time , thus permitting a continuous light emission . then , since an aperture shift comes in 3 stages , the light emission can be stopped at an attenuated portion of the flash waveform even in a short distance photographing , thereby ensuring a proper exposure . where avef is greater than f5 . 6 , the program branches to # 29 . where avef comes below f5 . 6 , the minimum aperture computed on the distance information from the stroboscope will be used as it stands . the reason is that when the object stands away from 5 . 6 m , an aperture , so selected , for full light emission is powerful enough to get the light full reaching a remote object . further , an out - of - focus condition can be prevented as much as possible rather than fixed at open aperture f1 . 4 . the aperture avef according to the distance information from the stroboscope which is obtained at # 24 to # 29 is compared with the aperture av according to the extraneous light which is obtained at # 13 to # 19 . when the aperture avef comes on a stopped - down side from the aperture av , that is , when the strobe light becomes a main light , the aperture avef according to a distance from the stroboscope is decided to be an aperture of the camera by substituting av with avef . apertures decided according to # 24 to # 31 are as shown in fig1 ( a ). loops # 24 to # 31 relate to a feature of the invention . then , when the aperture avef comes on an open side from the aperture av , that is , the extraneous light becomes a main light , the aperture av according to the extraneous light is decided to be an aperture of the camera . when the aperture av comes on an open side from the open aperture f1 . 4 , the aperture of the camera is set to f1 . 4 , while the shutter speed display circuit 106 and the aperture display circuit 107 are operated to flicker . thus , it is warned that a proper exposure is not obtainable even through the extraneous light and the strobe light . apertures decided at # 13 to # 33 are shown in fig1 ( a ), fig1 ( b ) and fig1 ( c ). fig1 ( a ) indicates the case of is06 , fig1 ( b ) indicates the case of is0100 , and fig1 ( c ) indicates the case of is01600 . in fig1 ( a ), fig1 ( b ) and fig1 ( c ), the lower side from a dotted line is a warning area . from # 33 the program goes forward to # 34 of fig7 by way of c . the second stroke switch 87 is sensitized . unless the second stroke switch 87 is turned on , the program returns to # 3 and repeats the loops # 3 to # 34 , thus repeating photometry and operation display . from depressing the release button as far as the second stroke , the second stroke switch 87 gets on , and the program branches to # 36 . the trailing curtain switch 90 is sensitized . unless charging is over , the program branches to # 3 . if charging is completed , then the program goes forward to a release control shown in fig9 by way of e . a high level is output to the port p10 . thus the transistor 82 is turned on to excite the first tension magnet 78 . a first tension of the camera is released , and a mechanical release sequence which is not indicated is actuated . the transistor 83 is turned on by outputting a high level to the port p11 , and excites the aperture control magnet 79 to commence an aperture control . waiting for 10 ms long enough to clear the first tension . a difference in level between the decided camera aperture av and the open aperture f1 . 4 is obtained and loaded in the accumulator . loops # 42 to # 44 are routines for stopping - down control . the mechanical release sequence actuated at # 37 drives a stopping - down mechanism , and the aperture is stopped down from open . whenever the aperture is stopped down 1 / 8 stages according thereto , the aperture switch 88 is turned on / off once , generating one pulse . if the stage number to be stopped down is 0 , the program branches to # 45 . waiting for generation of 1 pulse according to on / off operation of the aperture switch 88 . when pulses for the stopping - down stage number obtained at # 41 are counted through the loops # 42 to # 44 , the program goes forward to # 45 . the stopping - down mechanism is stopped by stopping the excitation of the aperture control magnet 78 . thus , a camera aperture can be coordinated with the aperture av . whether or not the stroboscope has been charged is discriminated . if not , then the program goes forward to # 55 . however , the charging is over currently , and hence the program goes forward to # 47 . when bv value is greater than apex 5 , the program goes forward to # 49 , but when it is less , the program goes forward to # 48 . a film photosensitivity is output to the d / a converter 53 . the d / a converter 53 outputs a voltage shown in fig1 to an emitter of the expanding transistor 67 . for example , a voltage vc -( 4 kt / q ) 1n 2 is output at the time of iso 100 . a high level is output from the ports p14 , p15 . thus a short circuit of the strobodimming integrating capacitor 70 is released , and an integration is commenced . since a charge on the strobodimming integrating capacitor 70 is 0 at first , an output of the operational amplifier 71 is vc , therefore an output of the dimming comparator 73 is kept low in level . two inputs of the or gate 74 become low in level both , therefore a voltage on the terminal s also becomes low in level , thus permitting a light emission of the stroboscope . the leading curtain magnet 83 is excited , and the shutter leading curtain begins to run . the leading curtain magnet 83 is stopped from being excited . whenever the shutter leading curtain has run , the x contact 108 gets on and the stroboscope emits the light . the strobe light reflects on an object and is exposed to the film through a photographing lens . the quantity of light irradiated on the film is indicated by lf . then , a part of the light irradiated on the film reflects on the film surface and is incident on the silicon photodiode 64 . the quantity of light in this case is indicated by lspd . lspd is then specified to be 2 - 4 times as much as the quantity of light on the film surface . if a photoelectric current of the silicon photodiode 64 be ispd , an output voltage v 66 of the operational amplifier 66 will be expressed as : ## equ8 ## a base - emitter voltage vbe of the transistor is expressed by the following equation at the time of iso 100 : ## equ9 ## accordingly , a collector current ice of the expanding transistor 67 will be : that is , it is amplified 2 4 times . likewise , it becomes 2 0 times at the time of iso 6 and 2 8 at the time of iso 1600 . when the collector current ice is stored in the strobodimming integrating capacitor 70 , an output voltage v 71 of the operational amplifier 71 will be : ## equ10 ## the output voltage v 71 rises from vc according to a light emission of the stroboscope and when it equalizes to a voltage of the constant voltage source 72 , an output of the dimming comparator 73 turns over to a high level from low , and raises a voltage on the terminal s to a high level . thus , as mentioned above , the commutation circuit 4 ( fig2 ) stops the light emission of the stroboscope . if a film exposure by the stroboscope in this case be p , then : ## equ11 ## assuming that a conversion efficiency δ of the silicon photodiode 64 is 4 na per lux : ## equ12 ## if c = 400 pf , δv = 1 . 0v , then : that is , the stroboscope can be stopped from emitting the light on a proper film exposure of iso 100 . then , a current amplification factor of the expanding transistor 67 changes by varying iso , therefore a flash exposure appropriate to cope with iso can be secured . the trailing curtain magnet 81 is excited to start the shutter trailing curtain going . a charge stored in the strobodimming integrating capacitor 70 is discharged . further , with the voltage on the terminal s retained at high level , the stroboscope is prohibited from emitting the light . the program then returns to # 3 of fig7 by way of d . as described above , the film can be exposed properly on the stroboscope when the extraneous light brightness bv is apex 5 or below . when the extraneous light brightness bv exceeds apex 5 at # 47 , the situation is decided to apply to a daylight synchronous photographing , and the program branches to # 49 accordingly . the daylight synchronous photographing uses the stroboscope as an auxiliary light when there is a big difference in luminance between the main object and the background , thereby exposing both appropriately . however , an appropriate exposure of the background and the main object on the stroboscope is capable of providing an unnatural photograph like composite one . consequently , the background is exposed appropriately , and the stroboscope is dimmed 1 to 2 stages under , thereby obtaining a natural daylight synchronized photograph . when bv is 9 or over , a strobodimming 5 stages ( och ) under will be applied . in # 51 to # 53 , the strobodimming is adjusted bit by bit under where bv comes within apex 5 to 9 . for example , it is adjusted 3 / 8 stages under at bv = 6 , and 3 / 4 stages under at bv = 7 . dimming levels obtained through arithmetic operation at # 48 to # 53 are as shown in fig1 . according to what has been described above , optimal shutter speed , aperture and dimming level can be decided from the extraneous light brightness and the main object distance in a stroboprogram mode . next , a description refers to an aperture priority mode wherein a photographer sets an aperture and a shutter priority mode wherein a shutter speed is set in the flash mode . loops # 1 to # 11 are similar to the stroboprogram mode , therefore a description will be omitted , and hence the description will be given to # 12 and onward in fig8 . if the port p26 is low in level , then the mode is aperture priority or shutter priority , therefore the program goes forward to # 64 . discriminating whether the first mode setting switch 91 is turned on or off . if off , then the mode is shutter priority , and hence the program branches to # 71 , but if on , the mode is aperture priority , and the program branches to # 65 . a hexadecimal number corresponding to the aperture set by a photographer is inputted from the set point input circuit 77 . if the computed shutter speed is faster than the synchronous 1 / 250 sec ., then the shutter speed is set at 1 / 250 sec ., and the shutter speed display circuit 106 is operated to flicker for warning . if the computed shutter speed is slower than the longest 1 sec ., the shutter speed is set at 1 sec ., and the shutter speed display circuit 106 is operated to flicker for warning . thus , a shutter speed appropriate to the extraneous light is computed to the set aperture . a hexadecimal number corresponding to the shutter speed set by a photographer is inputted from the set point input circuit 77 . when a shutter speed faster than the synchronous 1 / 250 sec . is set , a slit exposure may result , therefore the shutter speed is set at 1 / 250 sec . the aperture av appropriate to the extraneous light is obtained through arithmetic operation . if the computed aperture comes on the side stopped down from f32 , the aperture is set at f32 , and the aperture display circuit 107 is operated to flicker for warning . if the computed aperture comes on the side open from f1 . 4 , the aperture is set at f1 . 4 , and the aperture display circuit 107 is operated to flicker for warning . if a distance information from the stroboscope is away from f1 . 0 in an aperture conversion , then the stroboscope is not capable of giving the light sufficient in quantity to a proper exposure , therefore the program branches to # 80 . both shutter speed display circuit 106 and aperture display circuit 107 are operated to flicker , thereby warning that the strobe light is not powerful enough to reach before photographing . if bv & gt ; 6 , the program branches to # 83 , and if bv ≦ 6 , then it branches to # 82 . the situation that the minimum aperture avef computed at # 11 is greater ( coming on a stopped - down side ) than the camera aperture av to be controlled actually indicates that the stroboscope guide number is capable of giving enough quantity of light to the main object to dimming . where the minimum aperture avef is less ( coming on an open side ), to the contrary , than the camera aperture av , a proper quantity of light cannot be given even by the full emission of light of the stroboscope , of which a warning must be given . however , a warning will not be given at # 82 before the minimum aperture avef comes less than the camera aperture av by 3 stages or over . accordingly , at bv ≦ 6 , a warning will be kept from going as long as an exposure value permissible to a certain degree as photograph even though it is somewhat under in consideration of an error to arise at the time of measurement . when bv & gt ; 6 , the situation may apply to a daylight synchronous photographing , and the exposure will come somewhat under as described at # 49 to # 53 , therefore the warning is given only when the minimum aperture avef is less than the camera aperture av by 5 stages or over . in case the stroboscope is not connected , or the main capacitor 2 ( fig2 ) of the stroboscope has not yet been charged , a control of ae mode will be carried out on the camera . loops # 1 to # 9 are similar to the flash mode . the analog switch 104 is turned on at # 8 , however , since the terminal c is kept open , an output of the operational amplifier 103 becomes vc , and an output of the comparator 105 becomes low in level . accordingly , the program branches to # 84 at # 9 . a state of the second mode setting switch 92 is discriminated , and if it stands in the program mode , the program branches to # 98 . a state of the first mode setting switch 91 is discriminated . if it stands in the shutter priority mode , the program branches to # 92 , but if in the aperture priority mode , then the program branches to # 86 . loops # 86 to # 91 refer to an arithmetic operation in aperture priority , and operate , almost similarly to # 65 to # 70 , the shutter speed appropriate to the extraneous light to the set aperture av . those # 92 to # 97 refer to an arithmetic operation in shutter priority , and operates , almost similarly to # 71 to # 78 , the aperture appropriate to the extraneous light to the set shutter speed . loops # 98 to # 107 refer to an arithmetic operation in ae program mode . when the computed aperture comes on the side stopped down from f32 , the aperture is set at f32 . when the computed aperture comes on the side open from f1 . 4 , the aperture is set at f1 . 4 . the proper shutter speed tv is computed according to the computed aperture value . if the computed shutter speed is faster than 1 / 4000 sec ., then , with the shutter speed set at 1 / 4000 sec ., the shutter speed display circuit 106 and the aperture display circuit 107 are operated to flicker for warning . if the computed shutter speed is slower than 1 sec ., the shutter speed is set at 1 sec ., and the shutter speed display circuit 106 and the aperture display circuit 107 are operated to flicker for warning . thus , shutter speeds and apertures of the program at the time of ae mode , the shutter priority and the aperture priority are computed . these values are as shown in the program line ae of fig1 . then , while the first stroke switch 86 is kept on , a photometry through # 3 to # 9 , an arithmetic operation through # 84 to # 107 and a display routine through # 34 to # 36 are executed repeatedly in order as in the case of flash mode . further , when the second stroke switch 87 is turned on , the program goes forward to a release control routine of fig9 thus controlling automatic diaphragm and shutter . then , in the illustrative example , the distance information is obtained from the stroboscope , however , it can be obtained otherwise from a distance detector of the camera or from a distance ring . as described above , according to the invention , in case the minimum aperture ready for strobodimming which is obtained from a distance to the object , a stroboscope guide number and a film photosensitivity come below a predetermined value , a camera diaphragm is adjusted to the minimum aperture , but where the minimum aperture exceeds the predetermined value , the camera diaphragm is controlled to an aperture opened further than the minimum aperture , thus enhancing a continuous light emitting performance of the stroboscope . according to the invention , furthermore , in case the minimum aperture ready for strobodimming which is computed from a distance to the object , a stroboscope guide number and a film photosensitivity is opened further by a constant stage number or greater than the aperture set by a photographer or the aperture computed from a brightness of the extraneous light , a warning is given that the situation is not to cope with a flash photographing , but where it does not come on the side open by a constant stage number or over , the camera diaphragm is controlled to the aperture set by a photographer or the aperture computed from a brightness of the extraneous light , therefore the photographer &# 39 ; s intention can be esteemed so much , and a daylight synchronous photographing can be facilitated .