The object of the invention follows from the above, namely to improve a light diffuser consisting of a holding mechanism and an inflatable, at least partially air-permeable sack releasably connected thereto, in such a way that the sack can be optimized and reliably filled even by people not specially trained to do so. In addition, the whole system comprising this light diffuser should be designed in a pressure sealed way that it can be in use for a relatively long time without needing to be refilled or replenished, in particular during film and television photography.
This object is solved with the characteristics given in claim 1, whereas the dependent claims comprise at least advantageous embodiments and developments.
Accordingly, the basic idea of the invention is to provide the holding mechanism, which is designed as an adapter ring, with a compressed-gas connection as well as an electronically actuatable valve leading to the gas supply, such that a first pressure sensor determines the progressively increasing pressure within the sack, which is fixed to the ring, and sends out a switch-off signal when an adjustable or predeterminable maximal pressure has been reached, so that inflation of the sack is automatically terminated regardless of whether or not, and to what extent, a key button to actuate the valve is still active.
The key button can, as mentioned, be activated manually to fill the sack with gas or replenish its contents, in which case the invention ensures that it will be turned off automatically. Furthermore, the invention also encompasses a remote control of the key-button actuation by way of an infrared interface in combination with a commercially available, appropriately programmable infrared transmission unit.
In another preferred embodiment of the invention a second sensor is provided to determine the ambient pressure, so that a switch-off signal can be derived on the basis of a predeterminable difference between the internal pressure and the external, i.e. atmospheric pressure. This embodiment offers in particular the advantage that there is no need to correct the maximal pressure level, in particular when the photography is being done at altitudes different from sea level. That is, it has proved to be the case that even relatively low filling pressures suffice to stretch the inflated sack tight, and higher pressures bring no additional advantages, but rather involve an increased risk of accidents. Because light diffusers of the kind described here are fundamentally applicable for mobile use and are used in quite different places, the automatic valve switch-off and pressure control based on differential pressure values is particullary advantageous.
Furthermore, an additional compressed-gas connection can be provided at the adapter ring in order to connect several light diffusers in series, so that only one central gas supply is needed and the filling gas can be looped through them in analogy to the electrical supply of an associated electrical spotlight.
The compressed-gas connection or connections can be joined by way of flexible pressure tubing to a compressor or compressed gas accumulator tank situated some distance away.
So that the preferably air-filled sacks can be rapidly emptied, a compressor can be switched from pressure-generating to suction operation. By this means, when the illuminating devices are being dismantled or rearranged, time and hence expense can advantageously be saved.
As mentioned, the compressed-gas connections can also lead to a compressed-gas accumulator tank. In this case there is no need to employ an on-site compressor, especially under difficult local conditions.
To further improve the rapid emptying of the air sacks, there can be provided at or in them an exhaust valve with a large opening cross section.
To improve the sealing of the sack receptacle at the adapter ring, the adapter ring in a region towards the sack comprises circumferential beads with protrusions and recesses that serve to fix in position a profiled seal with corresponding surface structures. The profiled seal is then shifted over the free end of the adapter ring. The sack is subsequently attached with its opening side over the profiled seal and a retaining ring or strap is fixed around the adapter ring so that it produces a tight pressure seal but is nevertheless readily releasable.