Manual or automatic camera and electronic flash for use therewith

Abstract

A camera has an electrical exposure-time determining structure as well as a manually adjustable electrical structure and a light-responsive electrical structure both of which are connected to the exposure-time determining structure by way of a selecting circuit which can be set to operate the exposure-time determining structure either by way of the manually adjustable electrical structure or by way of the light-responsive electrical structure. An electronic flash assembly can be connected to the camera to provide additional flash illumination if necessary. The electronic flash assembly is connected with the camera in such a way that the exposure-time determining structure thereof will be operated by way of the light-responsive electrical structure irrespective of whether the selector circuit structure is set for operating the exposure-time determining structure by way of the manually adjustable electrical structure or by way of the light-responsive electrical structure.

Description

BACKGROUND OF THE INVENTION

The present invention relates to cameras.

In particular the present invention relates to a camera which preferably is of focal plane type and which can have connected thereto a strobe or electronic flash assembly.

When operating a photographic camera, particularly of the focal plane shutter type, with an electronic flash assembly, it is usually necessary to change over from the synchro contact to the X contact X-contact, and both the natural availabee available light as well as the flash illumination reflected from the object to be photographed are measured by the photometric structure of the automatic shutter control circuit and the control manget magnet of the trailing curtain of the shutter is deenergized at the instant when a proper amount of exposure has been achieved. Simultaneously with deenergizing of this magnet a flash stopping signal is generated by the magnet driving circuit and is applied to the flash control circuit of the electronic flash means so as to terminate the flash illumination by way of the electronic flash means.

In the event that a signal is applied from the automatic shutter control circuit to the magnet driving circuit indicating that a proper exposure has been achieved with the natural available light prior to closure of the X contact, which is to say prior to provision of flash illumination by the electronic flash means, then the flash preventing signal is provided from the magnet driving circuit through the flash control circuit to the electronic flash unit or strobe device so that the latter does not provide any flash illumination even after the X contact X-contact is closed.

Referring now to FIG. 2, there is shown therein a wiring diagram which illustrates an embodiment of the invention in greater detail. The electronic flash means is shown at the upper part of FIG. 2. This electronic flash means includes a capacitor 2, a flash tube or lamp 7, and a quenching tube 16 all connected in parallel with a source 1 of high DC voltage. Series-connected resistors 3 and 4 are also connected in parallel with respect to the voltage source 1, and a junction between the resistors 3 and 4, which serve as a divider for the source 1, is electrically connected to one terminal of a neon lamp 5 the upper terminal of which is connected with a resistor 9 and a capacitor 6 which has a terminal opposite to that connected to the neon lamp 5 grounded. Trigger coils 8 and 17 serve respectively to trigger the flash tube 7 and the quenching tube 16. A resistor 13, a trigger capacitor 12, the primary winding 8a of the trigger transformer 8 and a thyristor 11 are connected in series with each other, this series circuit also being connected in parallel with the source 1. Resistor 10 is connected between the gate and cathode of the thyristor 11, and the resistor 9 is connected between the neon tube 5 and the gate of thyristor 11. A resistor 14 and the X contact X-contact 15 are connected in parallel with each other, this parallel connection being inserted between ground and a junction between the capacitor 12 and resistor 13. A thyristor 21 forms part of a control means for the electronic flash means, this thyristor 21 serving to discharge the trigger capacitor 18 which is connected with the trigger transformer 17 of the quenching tube 16. The switches 23 and 24 form a means for connecting or disconnecting the electronic flash means to or from the camera control circuit in a manner described below.

The camera circuitry includes a light-responsive electrical means corresponding to the automatic shutter control circuit shown in FIG. 1. This light-responsive electrical means includes the photosensitive means 30 in the form of a photoelectromotive element which is electrically connected in a zero-biased state to an input of an operational amplifier 33 of the light-responsive electrical means. This latter means also includes a timing switch 31 which in a known way opens in synchronism with the start of the running down of the leading shutter curtain, and the light-responsive electrical means also includes the illustrated integration capacitor 32 connected between an inversion input terminal and an output of the amplifier 33. The timing switch 31 is adapted to be opened prior to the closing of the X contact X-contact switch 15 shown in FIG. 2 and forming part of the electronic flash means by conventional means schematically illustrated in FIG. 2 by the dot-dash line designated 100.

The light-responsive electrical means also includes a variable resistor or potentiometer 36 which can be set by the operator in accordance with the ASA sensitivity of the flim which is exposed, this light-responsive electrical means also including a constant current source 35 which forms with the variable resistor 36 a series circuit connected in parallel with a low voltage source 60 one terminal of which is grounded. The sliding contact of the potentiometer 36 is electrically connected to the negative input terminal of a comparator 34 which also forms part of the light-responsive electrical means. This comparator 34 has its positive input terminal connected to the output of the amplifier 33.

Thus, the output of the comparator 34 forms the output of the light-responsive electrical means, and this output is electrically connected through a resistor 56 to the base of a transistor 55, on the one hand, and to the collector of a transistor 48, on the other hand, these transistors 48 and 55 forming part of the electrical exposure-time determining means.

A manually adjustable electrical means, forming the manual shutter control circuit indicated in FIG. 1, includes a variable resistor 38 which can be set in accordance with a manually selected exposure time, this resistor 38 being connected in series with a capacitor 39. The series circuit formed by elements 38 and 39, and a second series circuit formed by a pair of resistors 41 and 42 are both connected in parallel across the low voltage source 60. The manually adjustable electrical means includes a second timing switch 37 which may be operated in the same way as the first timing switch 31 and which is connected in parallel across the capacitor 39. The manually adjustable electrical means also includes a comparator 40 which has a positive input terminal connected to a junction between the variable resistor 38 and the capacitor 39, the second timing switch 37 also being connected to this junction. The negative input terminal of the comparator 40 is connected to a junction between the resistors 41 and 42. The output of the comparator 40 forms the output of the manually adjustable electrical means and is electrically connected through a resistor 52 to the base of a transistor 53, on the one hand, and to a collector of a transistor 51, on the other hand. These transistors 51 and 53 also form part of the exposure time determining means.

A selector circuit means for electrically connecting either the manually adjustable means or the light-responsive means to the exposure time determining circuit includes the selecting switch 46 which forms the automatic-manual change-over switch indicated in FIG. 1 and which is closed by the operator in order to control the exposure time determining means by way of the light-responsive means, the switch 46 being opened in order to control the exposure time determining means by way of the manually adjustable means. The electronic flash means is connected to the selector circuit means by way of an electrical connecting means which includes not only the switch 23 but also the transistor 45 which, as illustrated in FIG. 2, is connected in parallel across the selector switch 46. The base of the transistor 45 is connected in series with the switch 23 through a resistor 43, the switch 23 in turn being connected to the neon lamp 5. The base-emitter circuit of transistor 45 has the resistor 44 connected thereto. The collector of the transistor 45 of the electrical connecting means is connected through a resistor 47 to the positive terminal of the source 60. The automatic-manual change-over switch 46 is thus connected across the emitter-collector circuit of the transistor 45.

The selector circuit means also includes a transistor 48 the base of which is connected to the collector of transistor 45, on the one hand, and to the base of a transistor 50 of the selector circuit means. The collector of transistor 50 is in turn connected through a resistor 49 to the positive terminal of the source 60, this collector also being connected to the base of a transistor 51 of the selector circuit means.

The transistor 53 of the exposure time determining means has its collector connected through a resistor 54 to the positive terminal of the source 60, this collector also being connected to the collector of transistor 55 of the exposure time determining means, the collectors of the transistors 53 and 55 being electrically connected to the base of a transistor 57 of the exposure time determining meaas means.

This transistor 57 has its collector connected through a control electromagnet 58 to the positive side of the source 60. The magnet 58 when energized holds the trailing curtain against running down in a known way, and when the magnet 58 is deenergized the trailing curtain is released to run down and terminate an exposure.

The quenching tube 16 of the electronic flash means and the circuitry controlling the same, this circuitry including the trigger transformer 17 and trigger capacitor 18 as well as the thyristor 21, form a control means for preventing operation of the electronic flash means in the event that the latter has not yet operated or for terminating operation thereof in the event that flash tube 7 has been energized and has started to provide flash illumination. This control means of the electronic flash means is electrically connected to the exposure time determining means by way of a series circuit which includes the switch 24 and the capacitor 59 which is connected to a junction between the collector of transistor 57 and the electromagnet 58. This latter series circuit is connected to the gate of the thyristor 21, this gate being grounded through the resistor 22 while the thyristor 21 is connected to a junction between the series circuit formed by resistors 19 and 20, this latter circuit being connected in parallel across the source 1, with the capacitor 18 being connected also to a junction between the resistors 19 and 20.

The above-described structure of FIG. 2 operates in the following manner:

The timing switch 31 opens in synchronism with the release of the leading shutter curtain and the photoelectric current from the element 30 is integrated by way of the integration capacitor 32, the element 30 being adapted for external photometering or TTL (through-the-lens) photometering of reflected light coming from the leading curtain of the shutter and the film surface. The voltage provided by way of the slidable terminal of the potentiometer 36, set according to the film speed, namely, the voltage according to the ASA sensitivity, is compared at the comparator 34 with the voltage integrated by the capacitor 32. At the instant when the integrated voltage achieves a specified exposure level, the output of the comparator 34 varies from the negative terminal voltage L of the source 60 to the positive terminal voltage H thereof.

The voltage of capacitor 39 of the manually adjustable electrical means gradually rises in accordance with the time constants of the variable resistor 38 and the capacitor 39, upon opening of the second timing switch 37, and the output of the comparator 40 also varies from L to H at the moment of coincidence between this gradually rising voltage and the voltage at the junction point between the resistors 41 and 42.

With the transistor 45 in its OFF state and with the automatic-manual change-over switch 46 closed, both of the transistors 48 and 50 are also in their OFF state, while the transistor 51 is turned ON, so that the variation of the output of the comparator 40 from L to H can not be transmitted to the transistor 53. However, at this time the variation of the output of the comparator 34 from L to H is transmitted to the transistor 55 inasmuch as the transistor 48 is in its OFF state, while the transistor 57 is also turned OFF inasmuch as the transistor 55 is turned ON since this variation in the output of the comparator 34 is transmitted thereto. As a result, the control magnet 58 for the trailing shutter curtain is deenergized. Thus the magnet 58 has been controlled by the light-responsive electrical means while the automatic-manual change-over switch 46 remains closed, and a time which elapses from the instant of opening of the timing switch 31 to the deenergizing of the magnet 58 for the trailing shutter curtain determines the proper exposure time.

With the transistor 45 still in its OFF state but with the switch 46 placed by the operator in its open position, both of the transistors 48 and 50 are turned ON, and thus the transistor 51 is turned OFF, so that only the variation of the ouput of the comparator 40 from L to H is transmitted to the transistors 53 and 57. Thus, under these conditions the control magnet 58 for the trailing shutter curtain is controlled by the manually adjustable electrical means while the automatic-manual change-over switch 46 remain remains open, and a time which elapses from the instant when the second timing switch 37 opens to the instant of deenergizing of the magnet 58 for the trailing shutter curtain determines the manually regulated exposure time.

In order to provide independent operation of the electronic flash means, both of the switches 23 and 24 may be opened so that there is no connection between the electronic flash means and the camera. These switches 23 and 24 are both closed in order to bring about control of the electronic flash means by the photometric circuit of the camera.

When the capacitor 2 attains a specified charging voltage, the neon lamp 5 receives the voltage necessary and adequate for illuminating the same, so that the voltage of the capacitor 6 rises and the transistor 45 is turned ON. Thus in this event it will be seen that the control magnet 58 for the trailing shutter curtain is automatically controlled by way of the light-responsive electrical means when the terminal voltage of the electronic flash means reaches a specified charging voltage, irrespective of whether the camera is set by the switch 46 for automatic or manual operation. Thus the lamp 5 together with the capacitor 6 form the signal generating means for generating a signal indicating that the electronic flash means is ready for operation, and this signal is utilized also for turning the transistor 45 ON, so that irrespective of the position of the switch 46 the exposure time determining means will be controlled by the light-responsive electrical means.

Upon completion of the charging, voltage is applied through the resistors 9, 10 to the gate of the thyristor 11, so that the latter is turned ON. Upon opening of the first timing switch 31 in synchronism with the release of the leading shutter curtain, the photoelectric current from the photoelectromotive element 30 which is generated due to natural light effects integration of the integration capacitor 32. As was pointed out above, the X contact X-contact switch 15 closes subsequently to the opening of the timing switch 31. In the event that the voltage of the integrating capacitor 32 still has not achieved a specified value at the moment when the X contact X-contact or switch 15 closes, the flash tube 7 is energized since the electrical charge of the capacitor 12 is discharged through the trigger coil 8 8a, the thyristor 11 and the switch 15, so that a high voltage is generated on at the trigger electrode of the flash tube 7.

Thus, at this time the photoelectromotive element 30 is exposed to the light provided by the flash illumination and reflected from the object to be photographed, so that in this way the integration capacitor 32 performs an additional integration. When the integrated value achieves a specified exposure level, the control manget magnet for the trailing curtain is deenergized as described above.

Simultaneously with the deenergizing of the electromagnet 58, a flash stopping signal is generated at the collector of the transistor 57 and is applied through the capacitor 59 and switch 24 to the gate of transistor thyristor 21, causing the latter to be turned ON, and as a result the capacitor 18 is discharged so that an induction voltage is generated by the trigger coil 17, thus rendering the quenching tube 16 conductive. Now the electrical charge of the capacitor 2 is rapidly discharged and flashing of the flash tube 7 is terminated.

In the event that the voltage of the integration capacitor 32 which is generated due to the natural available light has already achieved the specified value prior to closing of the X contact X-contact or switch 15, the quenching tube 16 is triggered before triggering of the flash tube 7 and the electrical charge of the capacitor 2 is discharged so that the flash tube 7 does not become energized even when the X contact X-contact or switch 15 is subsequently closed.

If the condition of the electronic flash means is such that the capacitor 2 does not achieve the required charging voltage, then the neon lamp 5 remains nonconductive and unenergized, and thus the transistor 45 remains in its OFF state, so that under these conditions the shutter of the camera is controlled in accordance with the selected position of the switch 46 and no voltage will be applied to the gate of thyristor 11, so that the latter remains OFF. Thus, under these conditions, when the switch 15 closes or the thyristor 21 is turned ON, nevertheless the capacitors 12 and 18 cannot be discharged inasmuch as these capacitors have not been charged, with the result that the flash tube 7 and the quenching tube 16 are not triggered. Therefore, there will be no creation of flash illumination by discharge of the capacitor 2.

The structure of the present invention which is described above and shown in the drawings and which operates as set forth above provides remarkably advantageous results.

Thus, with the structure of the present invention the shutter of the camera is capable of being selectively controlled either by the light-responsive electrical means in a fully automatic manner or by way of the manually adjustable electrical means to provide a manually selected exposure time, with the latter operations under proper conditions taking place prior to complete charging of the electronic flash means, while upon completion of the charging of the electronic flash means the camera shutter is of necessity automatically controlled by way of the light-responsive electrical means irrespective of the setting of the switch 46 to provide automatic or manual shutter regulation. As a result it is completely unnecessary for the operator to preliminarily set the exposure time at a given value in order to carry out flash photography. In this way it is possible to eliminate the inconvenience encountered with conventional cameras where in order to carry out flash photography it is essential that the operator preset the exposure time to a given value.

The light-responsive electrical means is a photometric circuit of the external measuring type or of the TTL type which is incorporated within the camera, the latter utilizing reflection from the leading curtain of the shutter or from the film, and this light-responsive electrical means is used during flash photography in order to facilitate the making of exposures properly. This feature enables the electronic flash means to have an exceedingly compact construction, since the control of the electronic flash means is derived from the light-responsive electrical means of the camera itself, and thus such controls need not be incorporated into the electronic flash means while at the same time an increased usefulness is achieved for the photometric circuit which is incorporated into the camera.

Furthermore, with the structure of the invention creation of flash illumination by the electronic flash means is prevented in the event that the exposure which can be achieved from the natural available light is already at the required level prior to actuation of the electronic flash means. The latter will provide flash illumination only when the required exposure level has not been achieved by the time the X contact X-contact switch 15 closes to carry out operation with flash illumination, so that it is possible to achieve a correct exposure irrespective of the particular object which is to be photographed. Erroneous flash operation is avoided inasmuch as there will be no creation of flash illumination prior to complete charging of the electronic flash means.

In order to bring about a manually regulated operation of the electronic flash means, it is only necessary to open the switches 23 and 24 so that transmission of the charge completion signal from the electronic flash means to the camera is prevented and of course control of the electronic flash means from the camera also is prevented.

It is thus clear from the above that by way of the present invention it is indeed possible to achieve certain remarkable results.

Claims

1. In a camera, electrical exposure-time determining means, light-responsive electrical means, manually adjustable electrical means, and selector circuit means electrically connecting said light-responsive electrical means and said manually adjustable electrical means to said exposure-time determining means for selectively controlling the latter either by way of said light-responsive electrical means for automatically determining the exposure time in accordance with lighting conditions or by way of said manually adjustable electrical means for providing a manually determined exposure time, electronic flash means for providing, if necessary, additional flash illumination to be utilized for exposure, and electrical connecting means connecting said electronic flash means to said selector circuit means for rendering the latter operable to control said exposure-time determining means by way of said light-responsive electrical means irrespective of whether said selector circuit means is set for controlling said exposure-time determining means by way of said light-responsive electrical means or said manually adjustable electrical means when additional flash illumination is required from said electronic flash means.

2. The combination of claim 1 and wherein said electronic flash means includes a control means for preventing operation of said electronic flash means in the event that the latter has not yet operated to produce flash illumination and for terminating operation of said electronic flash means after the latter has started to provide flash illumination, said exposure-time determining means being electrically connected with said control means for operating the latter upon termination of an exposure either to prevent operation of said electronic flash means in the event that the latter has not yet provided any flash illumination or to terminate operation of said electronic flash means in the event that the latter has started to provide flash illumination.

3. The combination of claim 2 and wherein a means is operatively connected with said electronic flash means for selectively disconnecting said control means thereof from said exposure-time determining means and for selectively disconnecting said electronic flash means from said selector circuit means by way of said electrical connecting means, so that if desired the electronic flash means can be operated independently of the camera while said exposure-time determining means can be selectively operated either by way of said light-responsive means or by way of said manually adjustable means.

4. The combination of claim 2 and wherein said electronic flash means includes a signal-generating means for generating a signal indicating that said electronic flash means is ready for operation, said electrical connecting means connecting said signal-generating means to said selector circuit means for rendering said exposure-time determining means operable only by way of said light-responsive means irrespective of whether said selector circuit means is set for operation by said light-responsive means or by said manually adjustable means, only when said signal is generated by said signal-generating means, whereby after said signal is generated if sufficient light is available for exposure without flash illumination said exposure-time determining means will operate said control means to prevent operation of said electronic flash means while if additional flash illumination is required, said additional flash illumination will be detected by said light-responsive means and said exposure-time determining means will operate said control means to terminate operation of said electronic flash means when the light from the latter and the available light are sufficient for exposure.

5. The combination of claim 4 and wherein said selector circuit means includes a selecting switch capable of being manually placed in open or closed positions and connecting said light-responsive means to said exposure-time determining means in one of said positions and said manually adjustable means to said exposure-time determining means in the other of said positions, said electrical connecting means including a transistor connected in parallel across said switch and rendered operable upon receiving said signal for connecting said light-responsive means to said exposure-time determining means irrespective of the position of said switch.

6. The combination of claim 4 and wherein said electronic flash means includes a flash lamp and a trigger circuit electrically connected therewith for rendering said lamp operable to provide flash illumination, said trigger circuit including a trigger capacitor and a thyristor connected in series therewith and having a gate, said signal generating means being electrically connected with said gate to prevent charging of said trigger capacitor unless said signal is generated, so that without generation of said signal said electronic flash means cannot operate and said exposure-time determining means will be operated either by said light-responsive means or by said manually adjustable means in accordance with the condition of said selector circuit means.

7. The combination of claim 4 and wherein said light-responsive electrical means includes a timing switch adapted to be closed opened in synchronism with opening of a shutter of a camera for rendering said light-responsive electrical means operative, and said electronic flash means including an X-contact switch adapted to close subsequent to the closing opening of said timing switch for rendering said electronic flash means operative, whereby if said light-responsive electrical means receives an amount of light sufficient for exposure prior to closing of said X-contact switch said exposure-time determining means will terminate the exposure and will operate said control means to prevent operation of said electronic flash means even if said X-contact switch should subsequently close. 8. Electronic flash apparatus for a camera having a shutter, electrical exposure-time determining means, light-responsive means for supplying information on light intensity to said electrical exposure-time determining means, a timing switch in said camera included in said light-responsive means and adapted to be opened in synchronism with opening of said shutter for rendering said light-responsive means operative and an X-contact switch coupled to said timing switch by means for closing said X-contact switch subsequent to the opening of said timing switch, said flash apparatus comprising:

flash means for illumination; and

control means electrically connected to said flash means and adapted to be electrically connected to said X-contact switch and to said electrical exposure-time determining means of the camera when said camera and flash apparatus are connected for preventing operation of said flash means when said flash means has not yet operated to provide flash illumination and for terminating operation of said flash means after said flash means has started to provide flash illumination.

9. Electronic flash apparatus as claimed in claim 8, further comprising a souce of voltage electrically connected to said flash means and signal generating means electrically connected to said source of voltage and connectable to said electrical exposure-time determining means of said camera for generating a signal indicating that said flash means is ready for operation.

10. Electronic flash apparatus as claimed in claim 9, wherein said camera has manually adjustable electrical means and settable selector circuit means electrically connecting said light-responsive means in said flash manually adjustable means to said exposure-time determining means, said apparatus further comprising electrical connecting means electrically connecting said signal-generating means to the selector circuit means of the camera for rendering said exposure-time determining means operable only by way of said light-responsive means irrespective of the setting of said selector circuit means for operation by said light-responsive means or by said manually adjustable means, only when said signal is generated by said signal-generating means, whereby after said signal is generated if sufficient light is available for exposure without flash illumination said exposure-time determining means will operate said control means to prevent operation of said flash means while if additional flash illumination is required, said additional flash illumination will be detected by said light-responsive means and said exposure-time determining means will operate said control means to terminate operation of said flash means when the light from the latter and the available light are sufficient for exposure.

11. Electronic flash apparatus as claimed in claim 10, wherein said flash means consists of a flash lamp and said electronic flash apparatus further comprises a trigger circuit electrically connected to said flash lamp for rendering said lamp operable to provide flash illumination, said trigger circuit including a trigger capacitor and a thyristor connected in series therewith and having a gate, said signal-generating means being electrically connected to said gate to prevent charging of said trigger capacitor unless said signal is generated, so that without generation of said signal said electronic flash apparatus cannot operate and said exposure-time determining means of said camera will be operated either by said light-responsive means or by said manually adjustable means in accordance with the condition of said selector circuit means.

12. Electronic flash apparatus as claimed in claim 10, wherein if said light-responsive means receives an amount of light sufficient for exposure prior to closing of said X-contact switch, said exposure-time determining means of said camera will terminate the exposure and will operate said control means to prevent operation of said electronic flash apparatus even if said X-contact switch should subsequently close.

13. Electronic flash apparatus as claimed in claim 8, further comprising switch means electrically connected to said flash means for selectively disconnecting said control means from said exposure-time determining means of said camera, to permit said flash means to be operated independently of said camera. 14. Electronic flash apparatus for a camera having a shutter, electrical exposure-time determining means, light-responsive means for supplying information on light intensity to said electrical exposure-time determining means, a timing switch in said camera included in said light-responsive means adapted to be opened in synchronism with opening of said shutter for rendering said light-responsive means operative and an X-contact switch coupled to said timing switch by means for closing said X-contact switch subsequent to the opening of said timing switch, said flash apparatus comprising:

a source of potential;

a main capacitor electrically connected to said source of potential;

flash means for providing flash illumination; and

flash control means adapted to be electrically connected to said X-contact switch and to said electrical exposure-time determining means of said camera when said camera and flash apparatus are connected, said control means including,

a first trigger circuit including a first trigger transformer for triggering said flash means and a first thyristor electrically connecting said first transformer to said source of potential and which becomes conductive in response to a signal representing completion of charging of said main capacitor;

quenching means electrically connected in parallel with said flash means for terminating energization thereof; and

a second trigger circuit including a second trigger transformer for triggering said quenching means and a second thyristor electrically coupled to said second transformer and electrically connected to said source of potential, said second thyristor becoming conductive in response to exposure-time information from said electrical exposure-time determining means of the camera, said second trigger transformer being electrically connected to said source of potential through said first thyristor, said second trigger circuit being caused to operate before said first trigger circuit to prevent said flash means from flashing when the exposure-time information from said electrical exposure-time determining means indicates that flash illumination from said flash means is not required and when said exposure-time information indicates a requirement for flash illumination and exposure-time information turning on said second thyristor upon reaching a proper exposure value after said flash means has started providing flash illumination thereby automatically adjusting the duration of said flash illumination.