Color temperature control of flash units

Abstract

A flash unit that includes a flash generator having at least one energy storage element and at least two light source channels as well as having at least two flash tubes, the flash tubes being supplied with energy by the energy storage element by means of the light source channels. The flash unit further includes an energy quantity control device, by means of which it is possible to provide for each light source channel any desired energy quantity from a minimum charge to a maximum charge of the at least one energy storage element, and a color temperature control device, by means of which it is possible to set a color temperature for each light source channel independently of the energy quantity provided therefor. The functions of all light source channels are fully equivalent.

Claims

1. A flash unit comprising: a flash generator having at least one energy storage element and at least two light source channels as well as having at least two flash tubes, the at least two flash tubes being supplied with energy by the at least one energy storage element via the light source channels; an energy quantity control device configured to supply said each light source channel any desired energy quantity from a minimum charge to a maximum charge of the at least one energy storage element; and a color temperature control device configured to vary an average emitted color temperature for said each light source channel independently of the energy quantity supplied for said each light source channel by independently controlling times of flash discharges of the at least two flash tubes, wherein functions of the at least two light source channels being fully equivalent.

2. The flash unit according to claim 1, wherein the at least two light source channels are equivalent in respect of their function and their setting.

3. The flash unit according to claim 1, wherein the average emitted color temperature is identical for the at least two light source channels.

4. The flash unit according to claim 1, wherein the at least two light source channels are at least one of independent of one another with respect to their function and the energy quantity supplied therefor can be set separately from one another.

5. The flash unit according to claim 1, wherein the at least two light source channels are freely selectable.

6. The flash unit according to claim 1, further comprising a trigger device which at a preset timepoint supplies a first light source channel with energy and which at a further number of predetermined timepoints, which are defined by a voltage present at the first light source channel, supplies a respective predetermined number of light source channels with energy.

7. The flash unit according to claim 6, further comprising a cut-off device which switches off respective light source when at least one of a predetermined target energy quantity and a target color temperature has been reached for the respective predetermined number of light source channels.

8. The flash unit according to claim 1, wherein the at least one energy storage element includes a plurality of rechargeable energy storage elements.

9. The flash unit according to claim 8, wherein the plurality of rechargeable energy storage elements connect to the at least two flash tubes in at least one of in parallel for the emission of more charge for a flash and sequentially for a plurality of successive flashes of the flash unit.

10. The flash unit according to claim 8, further comprising a charging device for the energy storage element which has a charging control means for introducing a preset charge into one or more of the plurality of rechargeable energy storage elements.

11. The flash unit according to claim 10, wherein the charging device is configured to set charging time, charging current and charging voltage in such a way that a discharge of the plurality of rechargeable energy storage elements by means of the at least two flash tubes produces a preset amount of light in a preset discharge time at a preset color temperature.

12. The flash unit according to claim 1, wherein the energy storage element is housed in a generator and the at least two flash tubes in a light source.

13. The flash unit according to claim 12, further comprising a time control means and a charging control means, wherein the time control means and the charging control means are housed in at least one of respective modules and a common module and wherein at least one of the generator and the light source includes a connection for the at least one of the respective modules and the common module.

14. The flash unit according to claim 1, further comprising a flash control that is affected by means of a cut-off means.

15. The flash unit according to claim 14, wherein the flash control is affected by means of a combination of an ignition delay means and the cut-off means.

16. The flash unit according to claim 1, wherein flashes produced are caused to be at least one of centered, superimposed and generated in series.

17. A method of controlling a flash unit having at least one energy storage element and at least two light source channels as well as having at least two flash tubes, each associated with a respective light source channel, the method comprising: discharging the at least one energy storage element; exciting the at least two flash tubes to emit light to generate a respective flash discharge of each of the at least two flash tubes; setting any desired energy quantity for each of the respective flash discharges of the at least two flash tubes; and varying an average emitted color temperature for each flash discharge independently of an energy quantity supplied for said each of the respective flash discharges by independently controlling times of the respective flash discharges, wherein functions of the at least two light source channels being fully equivalent.

18. The method according to claim 17, further comprising, providing a third flash tube; delaying the respective flash discharge of the third flash tube in time with respect to that of at least one of the at least two flash tubes; and setting a cut-off timepoint for the respective flash discharge of the third flash tube independently of that of the at least two flash tubes.

19. The method according to claim 18, further comprising, setting ignition and the cut-off timepoint of each flash tube so that each flash tube emits light of a preset color temperature averaged over a time of the respective flash discharge.

20. The method according to claim 19, wherein the preset color temperatures are identical.

21. The method according to claim 17, further comprising, producing a preset amount of light in a preset discharge time at a preset color temperature with the respective flash discharges of the at least two flash tubes.

22. The method of claim 17, further comprising, producing the respective flash discharges such that the respective flash discharges are at least one of centered, superimposed and generated in series.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an embodiment of the flash unit according to the invention;

(2) FIG. 2 shows an embodiment of the method according to the invention for controlling a flash unit, for example in accordance with FIG. 1;

(3) FIG. 2a shows the variation with time of the output energy of the flash unit according to the invention for different light source channels;

(4) FIG. 3 shows the variation with time of the color temperature of a flash discharge in a flash unit according to the invention in an especially simple configuration of the ignition and cut-off timepoints;

(5) FIG. 4 shows the variation with time of the color temperature of a flash discharge in a flash unit according to the invention in which the color temperatures of the individual flash tubes are identical to one another;

(6) FIG. 5 shows the variation with time of the color temperature of a flash discharge in a flash unit according to the invention in which the color temperature of one flash tube is deliberately selected to be different from that of the other flash tube;

(7) FIG. 6 is a general diagram illustrating the variation with time of the color temperature in the case of a flash discharge;

(8) FIG. 7 shows, superimposed, the variation with time of the color temperature of two flash discharges which result in different average color temperatures; and

(9) FIG. 8 is a diagram in accordance with FIG. 7, in which the average color temperature of one flash discharge has been compensated using a conventional method.

(10) FIG. 9 is a diagram showing the energy curve at the energy store during a flash operation.

DETAILED DESCRIPTION

(11) FIG. 1 shows an embodiment of the flash unit 1 according to the invention. In a light source 10 of the flash apparatus 1 there are arranged a first, a second and a third flash tube 11-13 which can be, for example, xenon tubes. A generator 20 of the flash unit 1 has an energy store 21 in which energy store elements 23 can be charged with electrical energy by means of a charging device 22.

(12) The flash unit 1 according to the invention also has an energy quantity control device 14 and a color temperature control device 15. By means of the energy quantity control device 14, any desired energy quantity from the minimum charge to the maximum charge of the energy store 21 can be provided individually for each light source channel, i.e. for each flash tube 11-13. By means of the color temperature control device 15, it is possible to set a color temperature for each light source channel, i.e. for each flash tube 11 to 13, independently of the energy quantity provided for the respective flash tube 11-13. An exemplary curve of the energy output quantities of the flash unit 1, i.e. of the flash generator 20, is shown in FIG. 2a. It should be mentioned at this point that all light source channels, that is to say therefore all channels for the flash tubes 11-13, are equivalent in respect of their function and their setting. Furthermore, they can be set independently of one another and, especially in respect of their function or the energy quantity provided therefor, separately from one another.

(13) As energy store elements 23 there are used capacitors, the total capacity of an energy store element possibly being multiplied by parallel connection of a plurality of capacitors. The energy store 21 is connected to the flash tubes 11-13 in order to supply them with electrical energy for a flash discharge. The charging device 22 is capable of charging the energy store elements 23 with a preset charge, the charge in the energy store elements 23 being controllable by means of charging current, charging voltage and charging time. Handling is simplest when, at a preset charging voltage, the charging time is selected to be such that an equilibrium is able to develop.

(14) The energy store 21 can be connected to the flash tubes 11-13 in such a way that only some of the energy store elements 23 feed the flash discharge. As a result, immediately after a flash discharge it is possible to trigger a further flash discharge with the aid of energy store elements not previously used. At the same time it is possible for discharged energy store elements 23 to be re-charged during a flash discharge that is being fed by other energy store elements 23.

(15) In a control means 30 of the flash unit 1, the times of the flash discharge in the flash tubes 11-13 can be fixed by means of a time control means 31. For that purpose, the time control means 31 is provided with an ignition circuit 32 and a cut-off device in the form of an interruption device 33 which are each able to actuate each of the flash tubes 11-13 individually. The ignition circuit 32 can therefore make the connection between the energy store 21 and each individual flash tube 11-23, while the interruption device 33 interrupts that connection in order to extinguish the flash, the time control means 31 being arranged to calculate suitable ignition and cut-off timepoints for preset amounts of light and color temperatures.

(16) A charging control means 34 of the control means 30 is connected to the charging device 22 of the generator 20. The charging control means 34 is capable of calculating the above-mentioned charging parameters of the charging device 22 for the desired maximum amount of light.

(17) The function of the described flash unit 1 will now be explained on the basis of a description of the method according to the invention, as shown in FIG. 2. If, first of all, the flash parameters are to be set, in a first step S1 the desired energy quantities or amounts of light are fixed individually for each flash tube 11-13. That can be effected by a user, but also automatically, for example, taking into account the external light conditions detected by sensors. In a next step S2, the desired color temperatures for each individual flash tube 11-13 are set by the user or automatically in a corresponding way.

(18) In a third step S3, the charging control means 34 calculates the charging parameters for the charging device 22 on the basis of the desired amounts of light and color temperatures. In steps S4 and S5, the time control means 31 calculates the individual ignition and cut-off timepoints of each individual flash tube 11-13, the cut-off timepoints of the second and third flash tubes being calculated as a delay with respect to the first flash tube. The first flash tube therefore forms the time reference point which is determined, for example, by the triggering of a photograph.

(19) The control means 30 has now been set ready for the use of the flash unit 1. It will be understood that the setting of the parameters need not be carried out afresh for each flash. Instead, the flash unit can be used with the parameters now calculated for as long as desired and for any desired number of flashes. It would also be possible for the control means 30 to be of substantially simpler construction and to have no capability at all for actually calculating the flash parameters on the basis of the total amount of light and the color temperature. In that case, there are simply provided a plurality of schemes for charging voltage and ignition and cut-off timepoints. The user can then make a selection from those fixed schemes, which can also be selected by more illustrative names (for example daylight, bright) than by fixing the physical parameters of amount of light and color temperature.

(20) In a further step S6, which in the case of the fixed preset parameter scheme can also be the first step, the energy store elements 23 in the energy store 21 are charged by the charging device 22. From that moment on, the flash unit is ready for use and when a flash is triggered, the first flash tube is ignited, step S7.

(21) From that timepoint on, the time control means 31 simultaneously monitors whether the delay interval for the ignition of a further flash tube 11, 12 has elapsed since the ignition of the first flash tube. In that case, the further flash tube 11, 12 is also ignited. At the same time, all flash tubes are monitored as to whether the cut-off timepoint has been reached and therefore the connection to the energy store 21 of the flash tube 11-13 in question has to be interrupted in order to extinguish the flash.

(22) For further use of the flash unit 1, the cycle is repeated either using the same flash parameters in step S6 with the charging of the energy store elements 23 and possibly with the use of other, still charged store elements 23, or using modified flash parameters with the amounts of light and color temperatures being set afresh.

(23) FIGS. 3 to 5 show, in diagrammatic form, various application scenarios of the flash unit 1 according to the invention. The Figures show, superimposed, the variation with time of the color temperatures of two flash tubes, only two flash tubes being shown here for the purpose of simplification. FIG. 3 shows the simplest case, in which the flash tube 2 is merely switched off with a delay with respect to the flash tube 1. This has the result that the flash tube 2 emits a larger amount of light but that at the same time, on account of the higher yellow components, the flash tube 2 has a lower color temperature than the flash tube 1.

(24) In FIG. 4, however, the ignition timepoint of the flash tube 2 is delayed with respect to the flash tube 1 and at the same time the cut-off timepoint is selected to be early so that the average of the color temperature of the two flash tubes over time is identical, the flash tube 2, in accordance with the substantially smaller area in FIG. 4, emitting a smaller amount of light.

(25) FIG. 5 shows that according to the invention it is also possible, with a delayed ignition timepoint of the flash tube 2, deliberately to select a different average color temperature with respect to the flash tube 1.

(26) The flash unit according to the invention therefore enables the brightness and color temperature of a plurality of flash tubes to be selected individually.

(27) In summary, it can be stated that the flash unit according to the invention is capable of delivering any desired energy level to any desired light source channel, i.e. to any desired flash tube. With this unit structure it is possible to deliver the total energy of the energy store 21 by means of any light source channel. It is also possible to set for the respective light source channels an energy quantity between 0 and 100 percent of the energy available in the energy store 21 or the flash generator 20, independently of the values set in the secondary channels, it being understood that the sum of the values set over the channels may not be greater than the energy available in the energy store 21. In addition, the energies are so controlled (current curve, voltage curve and variation with time) that the resultant flashes have the same color temperature from channel to channel. At the same time, for each light source channel the color temperature can be regulated and set independently of the energy quantity selected for the flash. This has the advantage inter alia that the light source connectors no longer have to be exchanged when an asymmetry is to be, for example, reversed or inverted. This saves time and difficult handling for the user. A further advantage is that the operation of such a flash generator 20, i.e. such a flash unit 1, does not require specific knowledge or understanding of the generator structure. That is especially of advantage in the case of hire businesses where the simplicity allows easy initial set-up and where the hire time is being paid for. With this structure there are no limitations or internal conditions which have to be taken into consideration during setting. Because the functions of all light source channels are fully equivalent, any channel can be connected without other light sources or flash tubes being connected.

(28) Asymmetries can be simply inverted by means of pushbutton selection, without the need to manipulate light source cables or to operate a plurality of operating elements. That flexibility can be achieved by selecting the voltage ranges of the flashes to be generated in such a way that the energy quantity supplied to the flash tube at those voltages produces a color temperature that is constant or has a selected value. To implement the method it is necessary that, during the first flash (blue when the precalculated voltage Ub2 has been reached (see in this connection FIG. 2a)), the second flash be triggered voltage-shifted. Accordingly, the third flash is likewise triggered when the voltage Ub3 has been reached. When Ub3 has been reached, the flash operation is active on three channels. That operation or that method can also be used for a higher number of channels.

(29) The end of the flash is controlled in accordance with a flash cut-off operation, it being necessary to note that that alone does not allow the same color temperature to be reached. The method according to the invention has the advantage of theoretically unlimited asymmetry. The prior art of three stops becomes theoretically unlimited and depends only upon the implementation quality or accuracy. The color temperature can be regulated channel-specifically. At the same time, the energy quantity can be freely determined for each channel.

(30) With the multi-channel flash units according to the invention it is therefore possible for a plurality of flashes to be produced simultaneously, that is to say with at least one superimposition of the flashes (in a photographic sense).

(31) Although the invention has been described on the basis of the above-mentioned exemplary embodiments, it also comprises further advantageous combinations of the mentioned features.