GB2324858A

GB2324858A - Flash photograph quality reducing system

Info

Publication number: GB2324858A
Application number: GB9708594A
Authority: GB
Inventors: Alwyn Philip Morris
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-04-29
Filing date: 1997-04-29
Publication date: 1998-11-04
Anticipated expiration: 2017-04-29
Also published as: GB9708594D0; GB2324858B

Abstract

In a system to adversely affect the quality of flash photgraphs of a reflective object 4, a secondary flash lamp 5 associated with and directed at the object 4 is triggered when light from the primary flash lamp 1 of the camera 1 is detected. This causes the photograph to be over exposed. The object could be a painting that an exhibitor does not want photographed or the number plate of a vehicle with the system preventing a vehicle being identified by a speed camera.

Description

DEVICE FOR AND METHOD OF ADVERSELY AFFECTING FLASH PHOTOGRAPHY OF A LIGHT-REFLECTING BODY Field of the Invention This invention relates to a device for and method of adversely affecting flash photography of a light reflective body. It has particular application in preventing unauthorised photography of, for example, pictures in galleries, and in countering the use of surveillance cameras.

Background to the invention In galleries, museums and the like flash photography is usually prohibited in order to inhibit unauthorised reproduction of works of art for commercial reasons. Although the works may no longer be protected by copyright, the gallery may derive income from selling reproductions of the works, and allowing photography would reduce this income. While photography without flash might be possible, maintenance of low light levels in the gallery makes good quality photography difficult while not significantly affecting ordinary viewing.

Automatic surveillance cameras are increasingly being put to use in detecting and recording infringements of traffic law, for example exceeding speed limits. Such cameras operate by firing a high intensity flash gun towards the vehicle while the camera shutter is open, to record on film, or electronically, the image of the vehicle, and in particular its registration plate, so that the vehicle owner can be identified and prosecuted.

The present invention provides a countermeasure against unauthorised flash photography in galleries and the like, and against the use of surveillance cameras.

The device is also usable for preventing accurate flash photography of other items which are necessarily on public display, but whose nature is such that recording of details is undesirable, for example items at an exhibition, where it is desired to prevent competitors from recording exact details at an early stage of the development of the item.

Summary of the invention The invention provides a device for adversely affecting flash photography of a light reflective body by a camera using a primary flash lamp, the device comprising a secondary flash lamp located adjacent to and directed towards the body, and means for triggering the secondary flash lamp in response to detection of light from the primary flash lamp.

The invention also provides a method of adversely affecting flash photography of a light reflective body by a camera using a primary flash lamp, the method comprising triggering a secondary flash lamp located adjacent to and directed towards the body in response to detection of light from the primary flash lamp.

Another aspect of the invention provides a method of adversely affecting flash photography of a light reflective body by a camera using a primary flash lamp, the method comprising providing on or near the body a secondary flash lamp directed towards the body and detector means for detecting light from the primary flash lamp and for triggering operation of the secondary flash lamp in response thereto.

The secondary flash lamp is conveniently chosen so as to have an intensity such that the amount of light from the flash reflected back from the body towards the camera is substantially greater than that from the primary flash, whereby the image of the body is over-exposed in the camera.

The reflective body may be, for example, a reflective sign such as a vehicle registration plate. Typically, such a sign may have a surface comprising glass beads or the like to increase the efficiency of reflection. It has been found that the method and device of the invention are especially effective with such signs.

Two or more secondary flash lamps may be used, each having its own detector means, or sharing a common detector means.

Where the body is a sign such as a vehicle registration plate, the secondary flash lamp may be mounted at all along an edge thereof. Where two or more secondary flash lamps are employed, they may be mounted at or along opposed edges of the sign.

In a preferred embodiment, the sign is mounted in a frame in which the secondary flash lamp are provided in raised sides of the frame.

The detector may be mounted on the sign or immediately adjacent thereto. In the case of a vehicle registration plate, the detector may be mounted on the head of the mounting screw for the plate.

The detector may comprise a proprietary slave flash trigger unit such as is known for use in photography. Typically, such a unit is selfcontained, simply providing closing of a circuit across two connecting conductors in response to detection of a flash above a predetermined intensity and/or of a duration less than a predetermined value. Such devices can be made small, for example being contained within a transparent hemispherical body of less than 10 millimetres diameter.

Where the device is for use with a vehicle registration plate, it is suitably powered by the vehicle's electrical supply.

The secondary flash lamp is conveniently a xenon arc tube, provided with a capacitor circuit which is of sufficient capacity and recharging speed to permit the lamp to be repeatedly operated in a short period of time, so as to be effective against rapidly repeated attempts to photograph the body.

While the primary flash lamp will typically produce white light, the detector is preferably sensitive to wavelengths outside the visible range, for example infra red.

Brief Description of the Drawings In the drawings, which illustrate exemplary embodiments of the invention: Figure 1 is a diagrammatic view of an automatic surveillance camera photographing a vehicle equipped with a device according to the invention; Figure 2 is an enlarged view of the rear part of the vehicle shown in Figure 1; Figure 3 is a perspective view of the device according to a second embodiment; and Figure 4 is a circuit diagram of the secondary flash lamp.

Detailed Description of the Illustrated Embodiments Referring first to Figure 1, the surveillance camera 1 is typically mounted at the roadside and carries a flash gun 2 directed towards the receding vehicle 3. A speed detecting device within the camera housing detects the speed of a passing vehicle and activates the camera when the detected speed exceeds the limit for the particular road. As with other cameras using flash, the camera shutter opens first, and when it is fully open, the flash gun is operated to emit a high speed flash which illuminates the vehicle and permit an image of the vehicle, and in particular the registration plate, to be recorded on film in the camera 1.

Mounted adjacent to the registration plate 4 of the vehicle 3 is a secondary flash device including a flash detector directed rearwardly of the film. As may be seen from figure 2, the secondary flash device is positioned relative to the registration plate so as to direct its flash towards the surface of the registration plate 4 so that light is reflected back from the registration plate towards the camera 1. The speed of response of the detector and the secondary flash is such that it can operate while the camera shutter is still open. The intensity of the light from the secondary flash device, being located close to the reflective surface of the registration plate 4, is such as to over-expose the film in the camera at least in so far as the image of the registration plate is concerned.

Figure 3 shows an alternative embodiment of the device, suitable for mounting on the rear of a vehicle. The device 6 comprises a rectangular frame which takes the place of the registration plate on the rear of the vehicle, the registration plate then being mounted within the frame. At each side of the frame a secondary flash tube 7 is mounted within the structure of the frame so as to be directed towards the surface of the registration plate, whereby light from the flash tube is reflected rearwardly from the plate 4 towards the camera 1. The detector 8 is mounted on the surface of the registration plate 4 and is directed rearwardly so as to receive the light from the flash gun 2 on the surveillance camera 1. The detector device is linked to the trigger circuit for the flash tubes 7, while power is supplied to the device by means of a connection to the vehicle's power supply inside the boot of the vehicle, installation requiring only the passage of a pair of wires from the device in to the vehicle boot or other convenient connection point.

Referring to Figure 4, the device incorporates a conventional flash control circuit in which a capacitor 9 is charged up at high voltage by means of a high frequency transformer supplied from the direct current supply of the vehicle through an inverter (not shown). A diode 10 provides half wave rectification. The xenon arc tube 11 is connected across the capacitor 9 and is triggered by a high voltage pulse from a trigger capacitor 12 through a transformer 13 when external switch 14 is momentarily closed. The switch 14 is provided in the present invention by an electronic detector, such as is used for example in photography to control slave flash units.

The detector may be arranged to trigger both flash tubes 7 simultaneously.

It will be appreciated that additional flash tubes may be mounted on or in the other sides of the frame, and that each flash tube may be provided with its own detector as a fail safe arrangement, so that if one flash fails to be triggered, at least one other flash tube will be independently triggered, thus avoiding total failure of the device.

Claims

1. A device for adversely affecting flash photography of a light reflective body by a camera using a primary flash lamp, the device comprising a secondary flash lamp located adjacent to and directed towards the body, and means for triggering the secondary flash lamp in response to detection of light from the primary flash lamp.

2. A device according to Claim 1, wherein the secondary flash lamp has an intensity such that the amount of light from the flash reflected back from the body towards the camera is substantially greater than that from the primary flash, whereby the image of the body is over-exposed in the camera.

3. A device according to Claim 1 or 2, wherein two or more secondary flash lamps are used.

4. A device according to Claim 3, wherein each secondary flash lamp has its own detector means.

5. A device according to Claim 3, wherein the secondary flash lamps share a common detector means.

6. A device according to any preceding claim, wherein the body is a sign such as a vehicle registration plate, and the secondary flash lamp is mounted at or along an edge thereof.

7. A device according to Claim 6, wherein two or more secondary flash lamps are mounted at or along opposed edges of the sign.

8. A device according to Claim 7, wherein the sign is mounted in a frame in which the secondary flash lamps are provided in raised sides of the frame.

9. A device according to any preceding claim, wherein the detector is mounted on the sign or immediately adjacent thereto.

10. A device according to any preceding claim, wherein the or each secondary flash lamp is a xenon arc tube, provided with a capacitor circuit which is of sufficient capacity and recharging speed to permit the lamp to be repeatedly operated in a short period of time.

11. A device according to any preceding claim, wherein the detector is sensitive to wavelengths outside the visible range.

12. A method of adversely affecting flash photography of a light reflective body by a camera using a primary flash lamp, the method comprising triggering a secondary flash lamp located adjacent to and directed towards the body in response to detection of light from the primary flash lamp.

13. A method of adversely affecting flash photography of a light reflective body by a camera using a primary flash lamp, the method comprising providing on or near the body a secondary flash lamp directed towards the body and detector means for detecting light from the primary flash lamp and for triggering operation of the secondary flash lamp in response thereto.

14. A device for adversely affecting flash photography of a light reflective body by a camera using a primary flash lamp, substantially as described with reference to, or as shown in, the drawings.

15. A method of adversely affecting flash photography of a light reflective body by a camera using a primary flash lamp, substantially as described with reference to the drawings.