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Title:
METHOD ANB UNIT FOR DISCHARGE IN ELECTRON FLASH TUBE
Document Type and Number:
WIPO Patent Application WO/2010/024765
Kind Code:
A1
Abstract:
The present Invention relates to a method and a flash unit for increasing the stability in an electron flash tube within its dynamic range. The present invention discloses that a flash discharge (F) is preceded by a pre-discharge (G) which is made with an amount of energy which preheats the gas in the electron flash tube but which does not emii any significant light, whereby the harmful effects of colour temperature shift, colour temperature variations, light quantity variations and aborted flash discharges are reduced substantially at low light quantities.

Inventors:
NICANDER JOHAN (SE)
Application Number:
PCT/SE2009/050965
Publication Date:
March 04, 2010
Filing Date:
August 27, 2009
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
PROFOTO AB (SE)
NICANDER JOHAN (SE)
International Classes:
G03B15/05; H05B41/32
Foreign References:
US5264895A1993-11-23
US5752097A1998-05-12
US20040150743A12004-08-05
Other References:
See also references of EP 2332008A4
Attorney, Agent or Firm:
GROTH & CO. KB (Stockholm, SE)
Download PDF:
Claims:
CLAIMS

1. A method of increasing the stability of an electron flash tube within its dynamic range, characterised in that, at least at low amounts of energy of a flash discharge, this discharge is preceded by a pre-discharge; and that said pre-discharge is made with an energy amount which preheats the gas in said electron flash tube but which does not emit any significant light, whereby repεatably stable discharges are obtained at low energy amounts and stable characteristics of the flash light are obtained on discharges with low energy amounts.

2. The method as claimed in Claim 1, characterised in that said pre-discharge is made between 50 and 10,000 microseconds before said flash discharge.

3. The method as claimed in Claim 1 or 2, characterised in that said pre- discharge is made with a voltage and a capacitance which are adapted to give said amount of energy,

4. The method as claimed in Claim 3, characterised in that the operating voltage for said pre-discharge is less than 500 V, preferably between 200 and 500 V.

5. The method as claimed in Claim 4, characterised in that the operating voltage of said flash discharge is greater than 400 V, preferably between 400 and 1,200 V.

6. The method as claimed in any of the preceding Claims, characterised in that said pre-discharge is made before flash discharges at a low energy level, such as for instance an energy level within the lower half of the dynamic range of said electron flash tube.

7. The method as claimed in any of Claims 1 to 5, characterised in that said pre-discharge is made before all flash discharges.

8. A flash unit disposed to fire an electron flash tube, where said flash unit comprises first capacitors adapted to be discharged through said electron flash tube and thereby give a flash discharge, that said flash unit includes a regulator device disposed to control said first capacitors to store different amounts of energy in order to be able to offer discharges of different sizes and thereby give flash discharges of different sizes within the dynamic range of said electron flash tube, characterised in that said flash unit also includes second capacitors, that said regulator device is disposed to control said second capacitors to be charged with an amount of energy which, on a discharge, preheats the gas in said electron flash tube but which does not emit any significant light from said electron flash tube, where said insignificant quantity of light is less than 1% of the maximum light quantity which said electron flash tube emits at the highest nominal energy for which the electron flash tube is rated, that said regulator device is disposed, at least at low amounts of energy in a flash discharge, to control said second capacitors to be discharged before said flash discharge, and thereby give a pre-discharge which precedes said flash discharge, and that said regulator device is disposed to control said second capacitors to give a pre- discharge of between 50 and 10,000 microseconds before said flash discharge from said first capacitors.

9. The flash unit as claimed in Claim 8, characterised in that said regulator device is adapted to control said second capacitors such that said pre-discharge is made at a voltage and capacitance which are adapted to give said amount of energy.

10. The flash unit as claimed in Claim 9, characterised in that said regulator device is disposed to control the operating voltage of said pre-discharge to be less than 500 V, preferably between 200 and 500 V,

11. The flash unit as claimed in Claim 10, characterised in that said regulator device is disposed to control the operating voltage of said flash discharge to be greater than 400 V, preferably between 400 and 1,200 V. 12, The flash unit as claimed in any of Claims 8 to 11, characterised in that said regulator device is disposed to control said pre-discharge to be made before flash discharges of a low energy level, for instance energy levels within the lower half of the dynamic range of said electron flash tube.

13. The flash unit as claimed in any of Claims 8 to 11 , characterised in that said regulator device is adapted to control said pre-discharge to be made before all flash discharges.

Description:
METHOD AND UNIT FOR DISCHARGE IN ELECTRON FLASH TUBE

TECHNICAL FIELD

The present invention relates to a method for increasing the stability in an electron flash tube within its dynamic range, as well as a flash unit adapted to fire an electron flash tube, where the flash unit includes first capacitors adapted to be discharged through the electron flash tube and thereby give a flash discharge, as well as a regulator device adapted to control the first capacitors so as to store different amounts of energy to be able to offer discharges of different sizes and thereby give flash discharges of different sizes within the dynamic range of the electron flash tube.

BACKGROUND ART

Electric flash units employ capacitors for storing an amount of energy which can be discharged through an electron flash tube so as to generate a discharge and a flash light in connection with photography. During the discharge, a plasma is formed inside the electron flash tube where the character of the plasma also determines the character of the flash light.

There are extreme demands on being able, using one and the same equipment, to vary the flash light from an extremely low light quantity to an extremely high light quantity while maintaining the character or nature of the flash light.

An electron flash tube is dimensioned, as far as is possible, to give constant light characteristics throughout its entire dynamic range. A series of parameters, such as the physical dimensions of the flash tube, the gas pressure, the gas mixture and the composition of the electrodes is adapted in order, together with the operating voltage and capacities of the flash unit, to provide the optimal conditions for constant light characteristics within the dynamic range of the electron flash tube. BRIEF SUMMARY OF THE PRESENT INVENTION

Problems

With a view to varying the amount of energy from an electron flash tube, the flash tube is discharged with energy amounts of different sizes and at discharge cycles of different speeds, where a discharge with a low amount of energy gives a low quantity of light from the electron flash tube.

However, there resides a problem in that an electron flash tube which is adapted for discharges of high energy amounts does not give repeatably stable discharges at low energy amounts and different characteristics of the flash light vary at discharges with low energy amounts.

There resides a problem, in low energy amounts, in colour temperature variations of the flash light from one discharge to another to a considerably higher degree than those colour temperature variations which occur on discharges at higher energy amounts.

There also resides a problem in that, at low energy amounts, a shift takes place in the colour temperature in relation to that colour temperature which is obtained from the electron flash tube on discharges at higher energy amounts.

There further resides a problem, in low energy amounts in the discharge, in light quantity variations from the electron flash tube to a higher degree than takes place at high energy amounts.

There also resides a problem in that, at low energy amounts in the discharge, it occasionally happens that no firing of the electron flash tube takes place so that no flash discharge takes place at all on discharge of the capacitors.

Solution

The present invention discloses that a flash discharge is to be preceded by a pre-discharge which is made with an energy amount which preheats the gas in the electron flash tube but which is so slight that, on the discharge, it does not emit any significant light. This pre-discharge has as an effect that the nominal colour temperature of the light in a discharge with a low energy amount will be the same, or at least within an acceptable deviation from the colour temperature in a discharge with a high energy amount. Further, the pre-discharge affords the effect that both the colour temperature variations and the light quantity variations are reduced substantially at low energy amounts of the discharge. The pre-discharge also entails that the electron flash tube almost always fires even in small energy amounts in the discharge.

A flash unit according to the present invention is adapted so as, at least in small discharges, to permit a pre-discharge to take place through the electron flash tube prior to the flash discharge proper.

Advantages

As a result of the method according to the present invention, or a flash unit according to the present invention, a possibility will be afforded to work with the entire dynamic range of an electron flash tube without the harmful effects of colour temperature shift, colour temperature variations, light quantity variations and aborted flash discharges. This makes it possible to work also with flash discharges which display extremely low light quantities and then also obtain the same repeatability and predictability as is obtained in flash discharges with high light quantities.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS A method and a flash unit displaying the properties associated with the present invention will now be described in greater detail hereinbelow for purposes of exemplification, with reference to the accompanying Drawings where:

Fig. 1 schematically represents a graph which illustrates both a colour temperature shift and high colour temperature variations for flash discharges with a low energy level in relation to flash discharges with a high energy level;

Fig. 2 schematically represents a graph which illustrates both light quantity variations and sporadically aborted flash discharges for flash discharges with a low energy level in relation to flash discharges with a high energy level; Fig. 3 schematically represents a diagram with a pre-discharge according to the present invention which is carried out prior to the flash discharge proper;

Fig. 4 schematically represents a graph which illustrates how shifts, variations and aborted flash discharges have been reduced by means of the employment of a pre-discharge according to the present invention; and

Fig. 5 schematically and highly simplified illustrates a flash unit according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following disclosures, the present invention will be described in detail and it should be understood that a practical application of the present invention requires adaption to the specific electron flash tube which is employed, since the physical dimension of the electron flash tube, as well as the gas pressure, the gas mixture and the composition of the electrodes in the electron flash tube entail that energy levels, operating voltages, time disclosures and other specifications for the present invention need to be adapted to each respective electron flash tube. However, the skilled person, taking the following description as the point of departure, will be able to understand and apply the present invention to different electron flash tubes. Thus, disclosures are given below, by way of illustrated examples, of operating voltages, energy levels and time disclosures in order to show possible embodiments of the present invention.

Fig. 1 shows how large colour temperature variations may occur in a flash discharge when low energy amounts are used in accordance with the prior art technology. Here, it is possible to see that flash discharges with low energy amounts A give a distribution in colour temperature of +/- 270 K, while the colour temperature variations for flash discharges with normal or high energy amounts B lie at +/- 40 K. The same figure also shows that, at a low energy amount A, there will be obtained a colour temperature of around 6,200 K, while a high energy amount B gives a colour temperature of around 6,000 K, which demonstrates that the low energy amount gives a colour temperature shift on the order of 200 K.

Fig. 2 shows how great light quantity variations occur for flash discharges with a small energy amount C. Here, it is schematically shown how large variations occur for flash discharges with an energy amount on the order of 10 Ws, while the light quantity variations are considerably lower for flash discharges with a large energy amount D, in the figure shown with an energy amount on the order of 2,000 Ws. Another problem which is shown in Fig. 2 is that the electron flash tube does not fire at all E in certain discharges at the low energy level C. In the figure, the scale for the energy amount is logarithmic, which implies that the light quantity variations at the high energy amount D may in absolute figures be equal to, or even greater than the light quantity variations at low energy amounts C. However, it is more critical with these variations at low energy amounts C, since the relative variations in relation to the absolute energy amount will be so much greater in low energy amounts C, while they will be negligible in high energy amounts D.

The present invention relates to a method whereby the stability of an electron flash tube increases within its dynamic range. Fig. 3 schematically illustrates that a flash discharge F is to be preceded by a pre-discharge G, and that this pre-discharge G is made with an energy amount which preheats the gas in the electron flash tube but does not necessarily emit any significant light. The term significant light is taken to signify light which does not harmfully affect the total light quantity which emanates from the pre-discharge G and the flash discharge F together. Thus, a pre- discharge G may take place without the electron flash tube actually firing and giving light, but it may also emit a low light which in total does not affect the result from the flash discharge F.

The pre-discharge G has the effect that repeatably stable discharges and that stable characteristics in the flash light may be obtained on discharges with low energy amounts.

Depending upon the operating voltage for the flash discharge, the operating voltage for the pre-discharge, the capacitance for the pre-discharge and the time delay between the pre-discharge and the flash discharge must be adapted. Thus, the pre-discharge G must be made with a voltage and a capacitance which are adapted to give a desired low energy amount.

The pre-discharge G must be made within a certain time before the flash discharge, and, according to one exemplifying embodiment of the present invention, the pre-discharge is made between 50 and 10,000 microseconds before the flash discharge F.

The present invention further discloses as one possible embodiment that the operating voltage for the pre-discharge G is less than 500 V, preferably between 200 and 500 V, for en electron flash tube which has a dynamic working range where the operating voltage for a flash discharge F is greater than 400 V, for instance between 400 and 1,200 V, These operating voltages afford the possibility of reducing the energy amount from a normal flash discharge of 2,400 Ws to as low as nine times halving of the energy amount, i.e. an energy quantity as low as 4.7 Ws, and this with a repeatability and stability in respect of colour temperature shift, colour temperature variations and light quantity, and also without aborted flash discharges.

In the upper span of the range disclosed by way of example for the operating voltage of the pre-discharge G, i.e. at 500 V, it may occur that the pre-discharge G itself results in light emanating from the electron flash tube, but this light will be so slight or weak that it does not harmfully affect the total flash discharge. How great such an effect will be naturally depends on the desired amount of energy in the flash discharge proper. If it were the case that the flash discharge F proper has an operating voltage in the lower range, which in this embodiment is 400 V, and if it were the case that a pre-discharge G is employed which has an operating voltage of the same order of magnitude as the flash discharge F, the pre-discharge G will result in a discharge with a first light quantity and the flash discharge F will result in a second light quantity of the same order of magnitude as the first light quantity. However, it should be understood that in such an event, the total light quantity will be an aggregate of the two discharged light quantities, where the first light quantity will vary in accordance with prior art technology, but where the second light quantity will be stable according to the present invention, which also in this case results in a light quantity which is sufficiently stable for certain practical applications. The higher the energy amount which the flash discharge F has, the lesser will be the effect of a possible light quantity from the pre-discharge G, and it is also possible to set the amount of energy in the pre-discharge G at a level which does not result in any light quantity, i.e. where only a heating of the electron flash tube takes place without firing of the electron flash tube. It should be understood that a pre-discharge G according to the present invention may either be made exclusively before flash discharges F at a low energy level, such as for example an energy level within the lower half of the dynamic range of the electron flash tube, or be made before all flash discharges F regardless of energy level. The present invention also relates to a flash unit 1, schematically illustrated in

Fig. 5, the flash unit 1 being disposed to fire an electron flash tube 2. The flash unit 1 comprises first capacitors 11 adapted to be discharged through the electron flash tube 2 and thereby give a flash discharge. The flash unit 1 also comprises a regulator device 12 disposed to control the first capacitors 11 to store different amounts of energy in order to be able to offer discharges of different sizes and thereby give flash discharges of different sizes within the dynamic range of the electron flash tube 2.

The present invention specifically discloses that the flash unit 1 also includes second capacitors 13 where the regulator device 12 is disposed to control the second capacitors 13 to be charged with an amount of energy which, on a discharge, preheats the gas in the electron flash tube 2 but which does not result in the electron flash tube 2 emitting any significant light. Further, the present invention discloses that the regulator device 12 is disposed to control the second capacitors 13 to be discharged prior to a flash discharge, and thereby give a pre-discharge which precedes the flash discharge. The regulator device 12 is disposed to control the second capacitors to a pre- discharge between 50 and 10,000 microseconds before a flash discharge from the first capacitors 11.

Further, the regulator device 12 is disposed to control the second capacitors 11 such that a pre-discharge is made at a voltage and capacitance which are adapted to give the requisite amount of energy.

As one exemplifying embodiment, the regulator device 12 may be disposed to control the operating voltage for the pre-discharge to be less than 500 V, preferably between 200 and 500 V, and to control the operating voltage for the flash discharge to be greater than 400 V, preferably between 400 and 1,200 V,

According to one conceivable embodiment, the regulator device 12 is adapted to control the pre-discharge so as to be made before flash discharges at a low energy level, such as for instance energy levels within the lower half of the dynamic range of the electron flash tube 2.

According to a further conceivable embodiment, the regulator device 12 is disposed to control the pre-discharge to be made before all flash discharges.

The present invention is naturally not restricted to the embodiments disclosed above by way of example, but may undergo modifications without departing from the scope of the inventive concept as disclosed in the appended Claims.