Optical: systems and elements – Prism – With reflecting surface
Patent
1998-03-17
1999-09-14
Spyrou, Cassandra
Optical: systems and elements
Prism
With reflecting surface
33245, G02B 504
Patent
active
059531657
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to optical aiming devices generally.
BACKGROUND OF THE INVENTION
Aiming devices, such as weapon sights, are well known in the art. Conventional non-optical aiming devices generally include two sights mounted on the weapon, a rear sight and a front sight. Both sights and the target, a total of three points, must be aligned with the user's eye in a straight line for accurate shooting. Aligning three points with the eye is a task which can be cumbersome and tiring.
Optical sights which overcome the problem of aligning three points are known, such as sights manufactured by C-More, Manassas, Va. USA, which are described in U.S. Pat. Nos. 5,369,888 and 5,383,278. Many laser sights are also known.
Another optical sight is the one manufactured by InterAims of Sweden under the tradename One V. Such a sight employs a laser diode which produces a red light which passes through a dichroic beam splitter. Red light is reflected towards the target and perceived by the user as a red dot. Rays in the rest of the visible light spectrum pass to the user's eye. The user only has to line up two points with his eye: the red dot and the target.
The red dot system has some drawbacks. It requires an electrical power source, and is relatively expensive, large in size and weight. A bright light source near the target makes it difficult to discern the red dot. It is extremely difficult to discern the red dot when aiming on a red background, and in any case there is color transmission distortion.
SUMMARY OF THE INVENTION
The present invention seeks to provide an improved, simple, effective and inexpensive optical aiming device which requires no external source of power, is compact in size and weight and causes minimum color distortion.
The aiming device includes two optical elements, such as prism assemblies, positioned one in front of the other along the length of the weapon. The user sights through the prism assemblies in the direction of the target.
With each prism assembly is associated a total internal reflection plane oriented at a critical angle with respect to an axis pointing to the target. Any portion of visible light emanating from the target and impinging on each prism assembly at an angle greater than the critical angle is reflected by the prism assembly, while any other portion of the visible light passes therethrough. In the reflected portion, light is reflected in a direction away from the user's eye and the reflected portion is perceived as being dark. Thus associated with each prism assembly is a clear region adjacent a dark region with a common demarcation arc therebetween.
When pointed at a target, the demarcation arc corresponds to a locus of points passing through the target. The clear region of each prism is caused by light coming from the target at angles with respect to the demarcation arc less than the critical angle, while the dark region is caused by light coming from the target at angles with respect to the demarcation arc greater than or equal to the critical angle.
The two prism assemblies are oriented such that their dark regions form an angle with respect to each other. This means that the demarcation arcs of each prism assembly are also oriented at an angle with respect to each other, intersecting at a common point. Since both demarcation arcs are aimed at the target, their common point of intersection lies on the line which points exactly to the target.
Thus the optical device is properly aimed by aligning two points: the intersection point of the demarcation arcs and the bull's eye of the target. The two demarcation arcs are analogous to longitudinal and latitudinal arcs which define the desired targeted point.
The view through a prism may be somewhat distorted due to the shape of the prism, as is known in the art. The present invention compensates for this effect by making each prism assembly with two optically identical prisms positioned such that their total internal reflection planes are located symmetrically with respect to each other.
REFERENCES:
patent: 3511556 (1970-05-01), Ammann
patent: 4806007 (1989-02-01), Bindon
patent: 5002364 (1991-03-01), Steenblik
patent: 5369888 (1994-12-01), Kay et al.
patent: 5383278 (1995-01-01), Kay
patent: 5440424 (1995-08-01), Wu et al.
patent: 5579159 (1996-11-01), Ito
Cherny Euncha
Ophir Optronics Ltd.
Spyrou Cassandra
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