Optical: systems and elements – Compound lens system – Telescope
Patent
1995-10-27
1997-04-01
Dzierzynski, Paul M.
Optical: systems and elements
Compound lens system
Telescope
359833, 359837, 359838, B60R 106
Patent
active
056172451
DESCRIPTION:
BRIEF SUMMARY
The present invention relates generally to a rear view mirror unit, and particularly to a rear view mirror unit suitable for a vehicle such as a motor vehicle, although the rear view mirror unit of the present invention may also be used for other vehicles, such as aircraft and railway vehicles.
Mirrors in general are used to deflect light from its incident direction to a reflected direction and in so doing, according to the laws of geometric optics, to direct the light towards an observer's eye in such a way as to create a virtual image which appears in front of the observer. In this way an observer whose attention must not be diverted from forward vision, such as the driver of the vehicle, can nevertheless observe the positions and movements of objects behind him by quickly glancing towards the rear view mirror.
Conventionally rear view mirrors used for vehicles comprises a single flat or spherically curved reflector positioned forwardly of -he observer at a location enabling it to deflect light from a region behind the observer with a single reflection towards the observer's eyes. The lateral field of view available to the observer is dependent on the lateral width of the mirror, its radius of curvature and its proximity. The closer the mirror to the observer's eye the wider the field of view. Internally fitted rear view mirrors having a considerable width are frequently fitted to vehicles at or near the upper part of the windscreen so as to gather light entering the vehicle from the region behind it through a rear window. It is not possible, however, to extend the field of view over the whole region of interest, because of view-obstructing parts of the vehicle, and in order to cover a wider field, wing or door mirrors have been utilized. Wing mirrors, mounted on the front wings of the vehicle have in more recent times been superseded by door-mounted mirrors because of their greater proximity to the observer, giving a wider and more satisfactory field of view.
Unfortunately, however, door-mounted external rear view mirrors, which by definition must extend beyond the lateral boundaries of the vehicle, have two major disadvantages, the first of which is the increased air resistance due to their cross-sectional area and projection from the body, and the second (due to the same factors) is the potential hazard they offer to other road users. To cope with this latter the majority of external rear view mirrors are mounted on snap-release or spring biased mountings which enable the mirror to be folded back in the event of an impact. This arrangement, however, is inadequate at higher speeds and only really satisfactory at extremely low speeds where the mass of the external mirror can be neglected in determining the impact force.
German Offenlegungsschrift DE 3146486 A1 discloses a rear view mirror in which an attempt to reduce the lateral extent of the mirror is made by the provision of a refracting element on the outside of a side window for directing light from the outside of the vehicle towards a reflector on the interior of the vehicle so as the produce a virtual image in the same position as it would be formed by a plane reflector in a conventional position outside the window. This device suffers from a number of disadvantages, not least of which is that, in one embodiment total internal reflection destroys the image and in another the size of the refractors required for an adequate field of view would be excessive.
Another attempt to produce a wide angle rear view mirror which does not have a great lateral extent is described in German Patentschrift DE 3335981 C2. The device includes a plurality of refractors for deflecting the light as well as a plurality of reflectors for bending the light through 180.degree. in a system similar to binocular prisms. This system suffers from complexity and, consequently, from great expense, particularly in the production of an adequate number of high quality optical components. The practical implementation of such a highly complex system would be extremely difficult and f
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Dzierzynski Paul M.
Jr. John Juba
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