Electronic flash units

Claim 2

An electronic flash unit which is capable of obtaining flash characteristics substantially equivalent to a continuous flash by permitting a flash discharge tube to repeatedly emit a pulse flash during an exposure of camera shutter; comprising: a series circuit combining said flash discharge tube and a main switching element which are interposed in a discharge loop of a main capacitor; a trigger circuit for permitting said discharge tube to inititate flash emission in response to a synchronized signal from said camera; a flash control circuit which produces a flash termination signal by detecting the fact that a value associated with pulse flashes reaches a predetermined level and further produces a flash resumption signal within a period of time less than the deionization time of said discharge tube after generation of said flash termination signal; a flash termination circuit which forcibly turns said main switching element off in response to said flash termination signal to terminate said flash emissions; and a flash resumption circuit which turns said main switching element on again in response to said flash resumption signal to resume said flash emissions of said discharge tube prior to the flash discharge tube de-ionization time.

Claim 3

An electronic flash unit according to claim 1, in which said flash control circuit includes a monitor circuit which detects a charged voltage on said main capacitor and produces said flash termination signal.

Claim 4

An electronic flash unit according to claim 2, in which said monitor circuit includes means for switching detection levels of said charged voltage.

Claim 5

An electronic flash unit according to claim 2, in which said monitor circuit includes means for switching the capacity of a capacitor to be charged in response to said charged voltage.

Claim 6

An electronic flash unit according to claim 1, in which said flash control circuit includes a monitor circuit which detects a quantity of flashlight of said discharge tube and produces said flash termination signal.

Claim 7

An electronic flash unit according to claim 5, in which said monitor circuit includes means for switching a detection level of said quantity of flashlight.

Claim 8

An electronic flash unit according to claim 1, in which said flash control circuit includes a flash interval setting circuit which produces said flash resumption signal by counting a flash interval from initiation of the previous pulse flash to initiation of the next pulse flash.

Claim 9

An electronic flash unit according to claim 7, in which said flash interval setting circuit includes means for switching said flash interval.

Claim 10

An electronic flash unit according to claim 7, in which said flash interval setting circuit produces a rapid charging signal for rapidly charging a commutation capacitor simultaneously with said flash resumption signal.

Claim 11

An electronic flash unit according to claim 7, in which said flash interval setting circuit produces a rapid charging signal for rapidly charging a commutation capacitor later than said flash resumption signal.

Claim 12

An electronic flash unit according to claim 1, in which said flash control circuit includes a flash interval setting circuit which produces said flash resumption signal by counting a flash interval from termination of the previous pulse flash to initiation of the next pulse flash.

Claim 13

An electronic flash unit according to claim 11, in which said flash interval setting circuit includes means for switching said flash interval.

Claim 14

An electronic flash unit according to claim 11, in which said flash interval setting circuit produces a rapid charging signal for rapidly charging a commutation capacitor simultaneously with said flash resumption signal.

Claim 15

An electronic flash unit according to claim 11, in which said flash interval setting circuit produces a rapid charging signal for rapidly charging a commutation capacitor later than said flash resumption signal.

Claim 16

An electronic flash unit according to claim 1, in which said main switching element is formed by a thyristor of the electrostatic induction type.

Claim 17

An electronic flash unit according to claim 15, in which said main switching element has a control circuit which is formed by a transistor circuit without a commutation capacitor.

Claim 18

An electronic flash unit according to claim 1, further including means for counting a total flash time during which said pulse flash is intermittently repeated.

Claim 19

An electronic flash unit according to claim 1, further including a mode changeover switch which selectively switches a flat flash mode which permits said discharge tube to intermittently emit pulse flashes and a continuous flash mode which permits said discharge tube to emit a continuous flash only one time.

Claim 20

An electronic flash unit according to claim 18, further including a photometric circuit for said continuous flash mode and operating as an automatic flash control type electronic flash unit in said continuous flash mode.

Claim 21

An electronic flash unit according to claim 1, further including switching means which is in cooperation with a manual setting member which is manually present prior to taking a picture so that a substantial guide number can be made variable by operating said member; and means responsive to said switching means for altering the time occurrence of the flash termination signal depending upon the setting of the manual setting member.

Claim 22

An electronic flash unit according to claim 1, in which said flash control circuit includes a time setting circuit which automatically changes a quantity of light per pulse flash and/or a flash interval by detecting a charged voltage on said main capacitor and changing a time point of issuing said flash termination signal and/or said flash resumption signal in accordance with said charged voltage so that a quantity of flash per unit time is maintained constant irrespective of the magnitude of said charged voltage.

Claim 23

An electronic flash unit according to claim 1, in which said flash control circuit includes means connected to intended exposure time information setting means, which automatically changes a quantity of light per pulse flash and/or a flash interval by changing a time point of issuing said flash termination signal and/or said flash resumption signal in accordance with said exposure time information so that an effective guide number can be maintained constant irrespective of the magnitude of an exposure time.

Claim 24

An electronic flash unit according to claim 22, in which said setting means comprises manual setting means such as a rotary switch and a changeover switch.

Claim 25

An electronic flash unit according to claim 1, in which said flash control circuit includes means connected to intended exposure time information detecting means, which automatically changes a quantity of light per pulse flash and/or a flash interval by changing a time point of issuing said flash termination signal and/or said flash resumption signal in accordance with said exposure time information so that an effective guide number can be maintained constant irrespective of the magnitude of an exposure time.

Claim 26

An electronic flash unit according to claim 24, in which said detecting means includes a photometric circuit for measuring brightness of an object to be photographed and a calculation circuit which calculates exposure time information based on information concerning brightness of an object to be photographed, a film speed and a diaphragm which are derived from said photometric circuit.

Claim 27

An electronic flash unit according to claim 24, in which said flash control circuit further includes a correction circuit which automatically changes a quantity of light per pulse flash and/or a flash interval by detecting a charged voltage on said main capacitor and changing a time point of issuing said flash termination signal and/or said flash resumption signal in accordance with said charged voltage so that a quantity of flashlight per unit time can be maintained constant irrespective of the magnitude of said charged voltage.

Claim 28

An electronic flash unit according to claim 20 further including a voltage reference circuit coupled to said switching means for changing the voltage reference level depending upon the setting of the manual setting member.

Claim 29

An electronic flash unit according to claim 27 further including means for comparing the voltage on said main capacitor with said voltage reference level for controlling the time point of occurrence of said flash termination signal.

Claim 30

An electronic flash unit according to claim 20 further comprising means for coupling the voltage on said main capacitor to a selected one of a plurality of chargeable members with the chargeable members selected being dependent upon the setting of the manual setting member.

Claim 31

An electronic flash unit according to claim 29 further comprising means for comparing the output of the selected charging member with a predetermined reference level for controlling the time point of occurrence of said flash termination signal when the voltage level of the selected chargeable member reaches the reference level.

Claim 32

An electronic flash unit according to claim 20 further comprising a counter and means for setting the count in said counter according to the setting of said manual setting member.

Claim 33

An electronic flash unit according to claim 31 wherein said means for setting the count further comprises oscillator means; means for converting the output of said oscillator means into a plurality of different output frequencies and means for coupling one of said output frequencies to said counter depending upon the setting of said manual setting member.

Claim 34

An electronic flash unit according to claim 32 further comprising second counter means for receiving a count from said first counter means for generating a flash termination signal whose length is a function of the output frequency set into said second counter means.

Claim 35

An electronic flash unit according to claim 20 further comprising oscillator means; means for converting the output of said oscillator means into a plurality of different output frequencies; a plurality of operational amplifiers each having an output and inverting and non-inverting inputs respectively coupled through first resistance means to ground and through second resistance means to the slider arm of a potentiometer which is set according to the setting of said manual setting member; each of said operational amplifiers having their outputs coupled to the inverting inputs of the next adjacent operational amplifier wherein only one of said operational amplifiers is maintained in a first state while the remaining operational amplifiers are maintained in the opposite state, dependent upon the setting of said manual setting member; the plurality of gating means each having one input coupled to receive one of said different frequency signals and a second input coupled to the output of an associated one of said operational amplifiers for passing the signal frequency applied to the gate when the gate is enabled by its associated operational amplifier; first counter means for receiving the signal frequency pass for developing a predetermined count.

Claim 36

An electronic flash unit according to claim 34 further comprising second counter means for receiving a count in said first counter means; said flash control circuit producing the flash termination signal as a function of the count in said second counter means.

Claim 37

An electronic flash unit according to claim 1 in which said flash control circuit includes a monitor circuit comprised of first and second capacitor means for selectively detecting a charge voltage on said main capacitor to produce said flash termination signal; means for alternately enabling one of said charging capacitor means while discharging the other of said capacitor means; said enabling and discharging means comprising means for generating a count signal when the capacitor means being charged reaches a predetermined level; said count pulse discharging the capacitor means being charged and enabling the remaining capacitor means which was discharged on the previous operation to be charged.