IMPROVEMENTS IN OPTICAL DEVICES

Abstract: A device for deflecting a field of view comprises a rectangular portion (10) of a quadrant of a Fresnel lens having its optical centre (11) at a corner of the rectangular portion (10). Mounting means in the form of an adhesive pad (13) and a deformable strip (14) allow the rectangular lens portion (10) to be secured to the rear windscreen of a vehicle.

Description: IMPROVEMENTS IN OPTICAL DEVICES The invention relates to optical devices of the type for deflecting fields of view, and more particulary but not exclusively to optical devices for deflecting the field of view of a person in a vehicle to allow that person to view areas, notably the rear of the vehicle, normally obscured. British Patent Specification No. 1418045 shows exampl of devices for expanding and deflecting fields of view usin a complete Fresnel lens combined with a Fresnel prism, the lens expanding the field of view and the prism carrying out deflection of the field of view. According to the invention there is provided a device for deflecting a field of view comprising part only of a Fresnel lens having a negative focal length, the optical centre of the Fresnel lens lying at or adjacent an edge of the part of the lens. The device preferably comprises a quadrant or -a portion of a quadrant of the Fresnel lens. The portion of the quadrant may be a rectangle having the optical centre of the lens at one corner. The device preferably comprises mounting means for mounting the device, for example, in the region of the back window of a vehicle. The mounting means are preferably adjustable and may comprise a bendable element which has sufficient rigidity to support the device in a desired position, or a stiff hinge, or a hinge and means to clamp the hinge in a desired position. The clamping means may comprise an adjustable clarnp arm. The device may be incorporated directly in a vehicle. The device may comprise more than one Fresnel lens of negative focal length lying one on top of another. In this way, for example, two lenses which individually pro¬ duce a deviation of a particular angle would produce a combined deviation of double that particular angle. The invention further provides a vehicle having a device according to the invention located in the region of a corner of the rear window of the vehicle and arranged to allow the driver to view that part of the rear of the vehicle on the side opposite to that on which the device is located. By way of example, one embodiment of a view deflecting device and a modification thereto according to the inven¬ tion will now be described with reference to the accompany¬ ing drawings, in which:- Fig. 1 is a view illustrating an embodiment of a view deflecting device; Fig. 2 is a schematic side view of a vehicle illustra¬ ting the positioning of the view deflecting device of Fig.1 Fig. 3 is a schematic plan view of part of the vehicle of Fig. 2; • * _ Fig.s 4A, 4B, and 4C are three views showing how the device of Fig. 1 is to be fitted to vehicle rear windscreen of different rakes; and Figs. 5A and 5B show schematically a modified adjust¬ able support fot the view deflecting device. Fig. 1 shows a view deflecting device 10 which is rectangular in overall shape. The rectangle is part of a quadrant of a Fresnel lens having an angle of deviation of up to 50°. The centre 11 of the Fresnel lens is at one corner of the rectangle and concentric groove formations 12 which give the Fresnel lens its optical properties cover the surface of the rectangle. The rectangular portion 10 of the Fresnel lens is of plastics material, although it will be appreciated that other materials could be used. It will be appreciated that, although the optical centre 11 is shown at a corner of the rectangular lens portion 10, the centre could be at other positions adjacent the edge. For example, the rectangle defined by the chain lines in Figure 1 would operate effectively as a view deflecting device and the term "adjacent" the edge is intended to cover such a configuration. The device 10 was described above as being formed from part of a single Fresnel lens. It will be appreciated that - 3 - a device of a particular angle of deviation could also b made by taking two Fresnel lens parts each of which would deviate by half the desired angle and laying the two lens parts one on the other. Superimposition of lens parts in this way can, however, reduce the clarity of image formed. Mounting means in the form of an adhesive pad 13 is attached to the lens portion 10 by a bendable metal strip 14. The strip 14 has sufficient rigidity to retain a desired configuration once deformed. Figs. 4A, 4B and 4C show different configurations of the view deflecting d.evice when mounted on vehicle rear windscreens of different rake. To work satisfactorily, the Fresn.el lens portion 10 must be perpendicular to the line of sight, and in Fig. 4A the device is shown mounted on a vertical rear windscreen, in Fig. 4B the device is shown mounted on a steeply raked rear windscreen and in Fig. 4C the de¬ vice is. shown mounted on a gently raked rear windscreen. It will be appreciated that there axe alternatives to - adhesive pads for mounting the device; for example, a suction pad could be used. There are various alternatives to the bendable metal strip 14 for allowing adjustment of the position of the Fresnel lens portion. For example, a stiff hinge of plastics material or a hinge having high friction resistance could be used. A further alternative is shown in Figs. 5A and 5B where a three part clip supports the lens portion. The three part clip has a first element 15 attached rigidly to the lens portion, a -second element 16 which in use is attached to the rear windscreen 17 and freely hinged to the first element 15 and a third lock¬ ing element 17 edgedly attached to the second element 16 for clamping the first element 15 in a desired con¬ figuration. Figs. 5A and 5B show, two alternative configurations of the three part clip. It will be appreciated that it would be possible to build a view deflecting device directly " into a' vehicle, in which case separate mounting means would not be re¬ quired . Figs. 2 and 3 illustrate where the device should be positioned in a vehicle and also how the line of sight of the driver is deflected. It will be appreciated that Figs. 2 and 3 are schematic views. The Fresnel lens portion must be large enough to enable the driver to see clearly large sections of objects he is reversing towards, otherwise the image becomes difficult to interpret. The most convenient position for the optical device is in the top -corner of the rear windscreen . on the side opposite that to which the field of view is being deflected. Thus a Fresnel lens quadrant which diverts the field of view towards the right hand side of a vehicle would be positioned in the top left hand corner of the rear windscreen. Conversely, if a driver wishes to be able to see the rear left hand side of his vehicle and what is being approached by it, the device would be one which deflects the field of view to the right and would be positioned in the top right hand corner of the rear windscreen. It may be advantageous to position two devices, one in each top corner of the rear windscreen. To make use of the device or devices, the driver can conveniently adjust his angle of vision in the rear view mirror 20 until he can see the device. The line of sight 21 in side view and plan view is shown in Figs. 2 and 3 respectively. The effect of the device is to enable a driver to reverse a vehicle as if he was kneeling on the vehicle back seat looking out of the rear window. Even if a whole Fresnel lens were located in " the above position or portions in a vehicle rear window, only the selected quadrant would be used by a driver to achieve the desired deflection of view. The advantage of this embodiment of the invention is that a device is provided which is simple and easy to manufacture and enables the driver of a motor vehicle with a rear window to reverse up to an object, such as another car, without fear of hitting it. The device is small enough to leave the driver's normal rear vision unimpaired a typical size for the device being 4"x3" and is suitable for use on any motor vehicle irrespective of the rake of the rear windscreen. \

Claims: CLAIMS 1. A device for deflecting a field of view, comprising part only of a Fresnel lens having a negative focal length, the optical centre of the Fresnel lens lying at or adjacent an edge of the part of the lens. 2. A device as claimed in claim 1 comprising a quadrant of the Fresnel lens. 3. A device as claimed in claim 2 comprising part of a quadrant of the Fresnel lens. 4. A device as claimed in claim 3 wherein the portion of the quadrant is a rectangle having the optical centre of the lens at one corner thereof. 5. ' A device as claimed in any preceding claim comprising mounting means for mounting the device. 6. A device as claimed in ' in claim 5 wherein the mounting means are adjustable. 7. A device as claimed in claim 6 wherein the adjustable mounting means comprise a bendable element having sufficien rigidity to support the device in a desired position. 8. A device as claimed in claim 6 wherein the adjustable mounting means comprises a stiff hinge. 9. A device as claimed in claim 6 wherein the adjustable mounting means comprise a hinge and means to clamp the hinge in a desired position. 10. A device as claimed in any one of claims 5 to 9 wherei the mounting means comprises an adhesive pad. 11. A device as claimed in any one of claims 5 to 9 wherei the mounting means comprises a suction pad. 12. A device as claimed in any one of claims 1 to 4 mounte directly in a vehicle. 13. A device as claimed in any preceding claims comprising more than one Fresnel lens of negative focal length lying one on top of another. 14. A device for deflecting a field of view substantially as hereinbefore described with reference to an as shown in Figs. 1 to 4 or in Figs. 1 to 4 as modified by Fig. 5 of the accompanying drawings. 15. A vehicle having a device as claimed in any preceding claim located in the region of a corner of the rear window of the vehicle and arranged to allow the driver to view that part of the rear of the vehicle on the side opposite to that on which the device is located. ■ a

Inventors: FOX ARNOLD JEFFREY
Applicants: FOX ARNOLD JEFFREY
Application year: 1982
Main classification: B60R1
IPC codes: B60R1