GB1558839A

GB1558839A - Remote control device for photographic flash unit

Info

Publication number: GB1558839A
Application number: GB265677A
Authority: GB
Original assignee: Bron Elektronik AG
Current assignee: Bron Elektronik AG
Priority date: 1976-01-23
Filing date: 1977-01-21
Publication date: 1980-01-09
Also published as: CH614537A5; NL7700544A; DE2602411C2; FR2339181A1; DE2602411A1; FR2339181B1

Abstract

The device consists of a transmitter (Fig. 2) and a receiver (Fig. 1). The synchronous release is performed with the aid of an emitter (14) which operates in the infrared band and is switched on by the shutter (10) of a photographic camera, and of a receiver for the flash gun (B), which receiver contains a photocell (1) and an electrical selection circuit (2) which is tuned to the modulation frequency of the infrared rays. <IMAGE>

Description

(54) "REMOTE CONTROL DEVICE FOR PHOTOGRAPHIC FLASH UNIT" (71) We, BRON ELEKTRONIK AKTIEN GESELLSCHAFT, a Swiss Company of Baslerstrasse 52, 4123 Allschwil, Switzerland, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in the following statement: This invention relates to a control device for remote control of the triggering of a flash unit in synchronism with the opening of the shutter of a photographic camera using an electromagnetic wave transmitter controllable by the camera shutter and a receiver for such waves coupled to the flash unit.

Flash units are usually triggered via a synchronizing cable by means of a contact located on and operated by the camera shutter. In studio flash units, it is known, with simultaneous use of several flash units to trigger only one ofthese flash units via a synchronizing cable whilst the remaining ones undergo a secondary triggering by means of the flash light of the first unit with the aid of photo cells built into the remaining units. For special cases of use in which the cable connection between the camera and the first flash apparatus acts in a disturbing manner because, for example, the synchronizing cable would be visible in the picture, it is further known to trigger this first flash apparatus without a cable link by means of radio waves.

The transmitter required for the radiation of the radio waves is mounted as close as possible to the camera and connected to the synchronizing contact of the camera. The receiver for the radio waves is set up in the vicinity of the first flash unit and triggers this with the aid of a cable connection. Such a radio link has however the drawback that it is expensive. Further the transmitter is so large that it acts in a disturbing manner with regard to the handling of the camera, in particular when this is carried.

A further drawback of the known radio link consists in that the total transmission interval may be slow in comparison with the shortest possible exposure times aimed at. In addition, such radio installations may require operating licences. A further drawback consists in that the transmitter in comparison with the transmission distances required usually has too great a range and therefore other installations operating likewise with radio links which are used, for example, in the same building can cause considerable disturbances. An installation operating with a radio link is in addition sensitive in respect of electrical disturbances.

The conventional photo-cell switches are frequently too insensitive to flash light and may in addition be dazzled by constant surrounding light so that the remote triggering in particular the secondary release described above does not function reliably in all cases.

An object of the present invention is to achieve a high sensitivity with the use of a photo-cell with immunity against bright continuous light and provide a possibility for remote triggering without a cable link which can obviate the above mentioned drawbacks. A further object is to provide an impulse switching which renders possible these two aims and consequently renders possible the achievement of remote triggering without a cable link of a first flash unit as well as also a secondary triggering of additional flash units which are provided with the same receiving device.

According to the invention therefore there is provided a control device for remote control of the triggering of a flash unit in synchronism with the opening of the shutter of a photographic camera using an electro-magnetic wave trans mitter controllable by the camera shutter and a receiver for such waves arranged to be coupled to the flash unit, characterised in that the transmitter operates in the infra-red range and the receiver has a device sensiti"e to infra-red rays, said transmitter of infra-red rays comprising a light emitting diode or a group of light emitting diodes, and said infra-red rays being modulated in their intensity with a frequency which is within the band width of an electric selection circuit connected to the infra-red sensitive device which circuit operates via an amplifier and a rectifier on an integrator and following threshold switch which switch upon reaching a predetermined threshold value is arranged to trigger the flash unit. Due to the use of amplitude modulated infra-red rays there results in conjunction with the selection circuit of the amplifier a high degree of safety against faulty triggering. The use of infra-red rays is therefore particularly favourable because in the receiver there may be provided one or several semiconductor photo diodes for the conversion of the rays into alternating current with the selected modulation frequency which practically follow in an inertialess manner the intensity variations of the infra-red rays and have in the infra-red range the best sensitivity. Because the transmitter of the infra-red rays comprises a light emitting diode or a group of light emitting diodes, there is a possibility of radiating the infra-red rays used for the remote control only during a very short period, for example, during a half milli-second and thus effect the triggering. The band width of the selection circuit provided in the receiver may extend from a few Kilohertz to a few hundred Kilohertz. Hereby it is possible to receive a large portion of the spectrum, and use same for the secondary triggering, which results when the semiconductor photo diode provided in the receiver is exposed to the flash light of an extraneous flash unit. The quality factor of the selection circuit of the receiver may be suitably approximately 20 to 30.

By means of the control device according to the invention, it is possible to provide a studio flash installation which comprises several flash units each provided with a respective one of said receivers but only one of the flash units is controlled by the infra-red rays of the transmitter whereas the remaining flash units with secondary triggering are ignited upon ignition of the first flash unit.

The invention will now be described further by way of example only and with reference to the accompanying drawings in which: Figure 1 is a circuit diagram of the receiver of one form of control device according to the invention; Figure 3 is a circuit diagram of the transmitter of the control device; and Figure 3 is a graph illustrating variation of the intensity I of an electronic flash with time t.

The control device is provided for controlling triggering of an electronic flash unit indicated in Figure 1 at B. The unit B is triggered by the receiver indicated in Figure 1 when the transmitter shown in Figure 2 is switched on and transmits an infra-red triggering signal.

In detail the transmitter comprises a switch circuit 11 which is connected to a synchronizing contact 10 connected to a camera, not shown, and prevents faulty triggering due to rebounding of the synchronizing contact. Furthermore, a timing circuit 12 is provided which limits the duration of the triggering impulses produced by the transmitter to about half a milli-second.

From the timing circuit 12, an HF-oscillator 13 is controlled which oscillates with a frequency of about 20 to 100 kHz and feeds a light emitting diode of a group of light emitting diodes 14. The infra-red light produced by such diodes 14 has a wavelength of, for example, 800 x 10-9m and is modulated in its intensity at the frequency of the oscillator 13.

For receiving the amplitude modulated infra-red light radiated by the transmitter there is provided in the receiver according to Figure 1 a semi-conductor photo diode 1, sensitive in particular to the said wavelengths, which produces an alternating current which fluctuates with the frequency of the amplitude modulation of the infra-red light. This alternating current is fed to a selection circuit 2 which contains a resonance circuit adapted to the modulation frequency which consists of a condensor 15 and a coil 16 and is damped by a resistance 17. To the selection circuit 2 is connected a linear amplifier 3 which feeds a rectifier 4. The rectified alternating current half waves are fed to an integrator 5 which, for example, may consist of a condensor with parallel switched load resistance. The equal voltage occurring on this integrator, in consequence of the considerable amplification by the amplifier 3, increases rapidly and reaches thereby a value with which the threshold circuit 6 connected to the integrator 5 corresponds and triggers the flash unit B.

In order to achieve a sufficiently wide range of the receiver, the amplification factor of the amplifier 3 is selected as great as possible, such amplification being limited by the background noise of the constructional elements used, and above all by the background noise of the photodiode 1 which background noise occurs when the photo-diode is subjected to the influence of continuous light from the surroundings.

In order that influence of this backgound noise may be kept as small as possible there is provided for the selection circuit 2 a quality factor of, for example, 20 to 30. If the quality factor is selected too small, then the background noise occurs as a disturbing phenomenon. It is recommended, however, not ot increase the quality factor beyond the said value, otherwise the transmission time is lengthened unneces warily The quality of the selection circuit 2 is in addition determined by the desired double function which consists in that with the same receiving circuit there is received the infra-red signals of the transmitter according to Figure 2 and also the flash light of other flash units so that for secondary triggering further flash units may be used. Thereby the photo cell hitherto usually built into the generator of the flash unit is superfluous.

This double function is achieved in that the transmitting frequency and the band width of the receiver (that is the circuit quality of the selection circuit 2) are selected such that as large a portion of the light spectrum as possible can be received which results when the receiving diode 1 its exposed to the flash light of an extraneous flash unit. For the explanation there is shown in Figure 3 a typical variation of the light intensity 1 of an electronic flash with time t. The very steep ascending curve 20 contains frequency components each in the range of a few kilohertz to a few hundred Kilohertz. The selection circuit 2 and the modulation frequency of the transmitter and of its oscillator 13 are so selected that as large a portion as possible of this spectrum can pass the selection circuit.

In order to reduce as far as possible the influence of the background noise which is produced by constant continuous light on the photo-diode 1 of the receiver, the photo diode 1 may be connected in series with a filter, not shown, in the drawing allowing passage only of infra-red rays.

The actuation of the receiver by the transmitter may take place in two ways, namely: a) By diffuse radiation in a room bounded by walls in which the transmitter emits the infra-red rays which are reflected diffusely by the walls. This gives the possibility that the receiver can be set up at any place in the room and is actuated in a certain manner by the infrared radiation reflected by the walls.

b) In very large rooms in which the surface of the walls is too great for a uniform radiation with infra-red light, or in the open, the actuation may be effected by directing the infra-red rays ofthe transmitter directly onto the photo-diode 1 of the receiver.

Moreover, in consequence ofthe above described function there is the possibility with the aid of the receiver of switching additional flash units with secondary triggering with the aid of the flash light which emerges from a first remote controlled flash unit and in the photo-diode of the receiver or the additional receiver releases alternating currents with frequency components which are within the band width of the selection circuit 2.

In studio flash installations frequently also flash exposure measuring apparatus is used which is provided with a release knob for a camera and is connected to the camera via a synchronizing cable. Such a synchronizing cable may be replaced with advantage by an infra-red channel as described above when the infra-red transmitter is accommodated in the exposure measuring apparatus and the flash unit or the flash units which are provided with the said receiver are triggered without cable links.

The control device described above is also suitable for remote controlling, apart from the remote control function described, further functions of the flash unit and the quality of the light, the power diestribution and so on.

For controlling such further functions several selection circuits could be provided with respective following valuation switching.

WHAT WE CLAIM IS: 1. A control device for remote control of the triggering of a flash unit in synchronism with the opening of the shutter of a photographic camera using an electro-magnetic wave transmitter controllable by the camera shutter and a receiver for such waves arranged to be coupled to the flash unit, characterised in that the transmitter operates in the infra-red range and the receiver has a device sensitive to infrared rays, said transmitter of infra-red rays comprising a light emitting diode or a group of light emitting diodes and said infra-red rays being modulated in their intensity with a frequency which is within the band width of an electric selection circuit connected to the infra-red sensitive device which circuit operates via an amplifier and a rectifier on an integrater and following threshold switch which switch upon reaching a predetermined threshold value is arranged to trigger the flash unit.

2. A control device according to claim 1, characterised in that the infra-red sensitive device comprises a semi-conductor photodiode.

3. A control device according to claim 1 or 2, characterised in that the transmitter is arranged to transmit a signal of continuous duration for a half milli-second.

4. A control device according to any one of claims 1 to 3, characterised in that the band width of the selection circuit extends from a few Kilohertz to a few hundred Kilohertz.

5. A control device according to claim 3 or 4, characterised in that the quality factor of the selection circuit of the receiver is about 20 to 30.

6. A studio flash installation with several flash units and with at least one control device according to any one of claims 1 to 5, characterised in that each flash unit is provided with a respective said receiver but only one of the flash units is controlled by means of the infra-red rays of the transmitter whereas the remaining flash units with secondary triggering are switched on upon ignition of said one flash unit.

7. A control device according to any one of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. function which consists in that with the same receiving circuit there is received the infra-red signals of the transmitter according to Figure 2 and also the flash light of other flash units so that for secondary triggering further flash units may be used. Thereby the photo cell hitherto usually built into the generator of the flash unit is superfluous. This double function is achieved in that the transmitting frequency and the band width of the receiver (that is the circuit quality of the selection circuit 2) are selected such that as large a portion of the light spectrum as possible can be received which results when the receiving diode 1 its exposed to the flash light of an extraneous flash unit. For the explanation there is shown in Figure 3 a typical variation of the light intensity 1 of an electronic flash with time t. The very steep ascending curve 20 contains frequency components each in the range of a few kilohertz to a few hundred Kilohertz. The selection circuit 2 and the modulation frequency of the transmitter and of its oscillator 13 are so selected that as large a portion as possible of this spectrum can pass the selection circuit. In order to reduce as far as possible the influence of the background noise which is produced by constant continuous light on the photo-diode 1 of the receiver, the photo diode 1 may be connected in series with a filter, not shown, in the drawing allowing passage only of infra-red rays. The actuation of the receiver by the transmitter may take place in two ways, namely: a) By diffuse radiation in a room bounded by walls in which the transmitter emits the infra-red rays which are reflected diffusely by the walls. This gives the possibility that the receiver can be set up at any place in the room and is actuated in a certain manner by the infrared radiation reflected by the walls. b) In very large rooms in which the surface of the walls is too great for a uniform radiation with infra-red light, or in the open, the actuation may be effected by directing the infra-red rays ofthe transmitter directly onto the photo-diode 1 of the receiver. Moreover, in consequence ofthe above described function there is the possibility with the aid of the receiver of switching additional flash units with secondary triggering with the aid of the flash light which emerges from a first remote controlled flash unit and in the photo-diode of the receiver or the additional receiver releases alternating currents with frequency components which are within the band width of the selection circuit 2. In studio flash installations frequently also flash exposure measuring apparatus is used which is provided with a release knob for a camera and is connected to the camera via a synchronizing cable. Such a synchronizing cable may be replaced with advantage by an infra-red channel as described above when the infra-red transmitter is accommodated in the exposure measuring apparatus and the flash unit or the flash units which are provided with the said receiver are triggered without cable links. The control device described above is also suitable for remote controlling, apart from the remote control function described, further functions of the flash unit and the quality of the light, the power diestribution and so on. For controlling such further functions several selection circuits could be provided with respective following valuation switching. WHAT WE CLAIM IS:

1. A control device for remote control of the triggering of a flash unit in synchronism with the opening of the shutter of a photographic camera using an electro-magnetic wave transmitter controllable by the camera shutter and a receiver for such waves arranged to be coupled to the flash unit, characterised in that the transmitter operates in the infra-red range and the receiver has a device sensitive to infrared rays, said transmitter of infra-red rays comprising a light emitting diode or a group of light emitting diodes and said infra-red rays being modulated in their intensity with a frequency which is within the band width of an electric selection circuit connected to the infra-red sensitive device which circuit operates via an amplifier and a rectifier on an integrater and following threshold switch which switch upon reaching a predetermined threshold value is arranged to trigger the flash unit.

7. A control device according to any one of

claims 1 to 5, characterised in that the receiver is arranged to perform one or more functions other than the triggering of the flash unit.

8. A control device substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.