GB2077936A - Extension prism for collimator gun sight - Google Patents

Abstract

An elongate prism 10 is used with a collimator 11 to provide an image of an aiming mark superimposed on a line of sight 23 displaced from the axis 15 of the collimator 11. The prism has an angled reflecting surface 18 and an angled partially reflecting surface 21 at opposite ends, acting like a periscope. Opposite longitudinal faces 16 and 17 of the prism are accurately parallel to minimise deviation of the line of sight through the surface 21 and to make aiming accuracy independent of the orientation of the prism 10 relative to the collimator 11. <IMAGE>

Description

SPECIFICATION Extension prism for collimator gun sight The present invention is concerned with an extension prism for a collimator gun sight.

Collimator gun sights are known which provide a collimated image at infinity of an aiming mark. In one arrangement, the user of a weapon fitted with such a gun sight applies one eye to the gun sight to view the collimated image of the aiming mark, and with the other eye views the target field unobstructed. Provided the weapon user's eyes maintain correct parallax when viewing objects substantially at infinity, the weapon can be aimed by placing the aiming mark image upon the desired target point. However, to avoid problems associated with incorrect alignment of the eyes of the user of a weapon, it is also common to arrange for the collimated image of the aiming mark to be superimposed optically on a substantially undeviated view of the target field so that both can be seen with a single eye of the user.

Numerous reflex collimator gun sights are known with this arrangement.

The present invention provides an extension prism enabling the collimated image of an aiming mark provided by a non-superimposing type aiming mark generator to be superimposed on the view of the target field. Also the present invention enables the weapon fitted with the extension prism to be sighted with the eye of the weapon aimer at a substantial distance away from the aiming mark generator itself.

According to the present invention, an extension prism for a collimator gun sight comprises an elongate block of light transmissive material, the block having: adjacent one end, a first plane polished side face portion substantially parallel to the longitudinal axis of the block; at said one end, a plane internally reflecting the surface angled to reflect light, entering the block through said first side face portion, substantially along the length of the block towards the other end thereof; adjacent the other end of the block, a plane polished side face portion on the opposite side of the block to and parallel to said first side face portion and a plane partially internally reflecting surface parallel to said reflecting surface at said one end, to reflect out of the block through said second side face portion light reflected along the length of the block from said reflecting surface at said one end; and, also adjacent said other end, a third plane polished side face portion parallel to said first and second portions and opposed to said second portion on the opposite side of the partially reflecting surface, so that an image formed by light reflected in said reflecting and partially reflecting surfaces can be seen superimposed on a target field viewed through said second and third face portions.

This extension prism can be fitted to a weapon having an existing collimated aiming mark generator with the first plane polished side face portion directly in front of the collimator lens or the window of the aiming mark generator. Then, light defining the collimated aiming mark from the generator enters the block of the prism through said first plane side face portion, is reflected in the reflecting and partially reflecting surface and can be viewed by the user of the weapon looking into the block of the prism through said second side face portion. In this way, the aiming mark is superimposed on the target field viewed through both the second and third side face portions of the prism. At the same time, the point of viewing of the target field can be substantially displaced from the aiming mark generator, i.e. by substantially the length of the block of the prism.Furthermore, because the prism is formed of a solid block of material, the angles of the polished faces and reflecting surfaces are fixed, and also the precise angle of the longitudinal axis of the block of the prism relative to the aiming mark generator is not critical. Any deviations and errors in the mounting of the extension prism have no substantial effect on the aiming accuracy of the weapon, provided only that the aiming mark generator itself is accurately aligned. Since the position of the extension prism is not critical, it is thus readily possible to make the extension prism movably or detachably mounted with respect to the aiming mark generator. For example, for reasons of economy and convenience in packing, the extension prism may be mounted so as to be rotatable away from its working position.

The extension prism is especially useful for use with a mass produced weapon in which the aiming mark generator or collimator itself is moulded into the barrel of the weapon on manufacture. The extension prism can then be used to provide a line of sight for the user of the weapon at a substantial distance from the barrel and collimator. Because the angle between the extension prism and the collimator is not critical, the prism may be arranged to be removable from the barrel or may be adjustable in position to suit the user of the weapon. Furthermore, the mechanical arrangements for mounting the prism or for adjusting its position may be made relativaly cheaply.

Preferably, said block has a uniform rectangular cross-section. Said first and third side face portions may be constituted by respective portions of one elongate side face of the block, and said second side face portion may then be constituted by a portion of the opposite elongate side face.

Said reflecting surface at said one end of the block may be formed by the end face of the block which is then at an acute angle to said one elongate side face and perpendicular to the two elongate side faces adjacent to said one side face.

Conveniently, said block has a first major portion comprising said first and second side face portions, said reflecting surface at said one end and an opposite end face in the plane of said partially reflecting surface, and a second minor portion, comprising said third side face portion, which is cemented to said opposite end face of the major portion with a partially reflecting layer at the interface between the portions. Preferably, this arrangement of prism is formed by working said one side face of the block accurately parallel to the opposite side face after cementing the block portions together.

The present invention also comprises a collimator gun sight having an aiming mark generator providing a collimated image of an aiming mark, in combination with an extension prism as described above, arranged to reflect said collimated image in the reflecting and partially reflecting surfaces of the prism to superimpose the image on the target field.

An example of the invention will now be described with reference to the accompanying drawing which is a schematic illustration of an extension prism embodying the present invention.

In the drawing, an extension prism 10 is shown in combination with an aiming mark generator or collimator 11. In use, both the prism 10 and aiming mark generator 11 are mounted on a weapon or other device to be aimed. In the drawing, the body of the weapon or device is represented by the hatching 12. The manner by which the prism 10 and collimator 11 are fastened or mounted upon the body 12, typically the barrel of a weapon, is not important to the present invention and no details are shown in the drawing.

It is sufficient that the collimator 11 itself is firmly and accurately aligned with the line of fire of the weapon so that the collimated aiming mark seen through a collimator lens 13 would correctly identify the aiming point of the weapon. The collimator 11 may be mounted to be adjustable, e.g. for windage and elevation in the usual way.

The prism 10 can be detachably mounted and its positioning relative to the collimator 11 is not critical provided that it can be located substantially with the position and orientation shown in the drawing. The prism 10 may also be mounted adjustably by any suitable means so that it can be moved or rotated about various axes as desired.

The collimator 11 itself may be of any suitable sort adapted to generate a collimated image at infinity of an aiming mark. For example, a suitable form of collimator is that described and claimed in the specification of Patent No. 8015979.

The prism 10 is formed of a solid block of optically transparent material, typically glass of a suitable quality. The block is elongate having a longitudinal axis 14 which is arranged to be substantially perpendicular to the optical axis 1 5 of the collimator 11. The block has a rectangular cross-section with opposite elongate side faces 1 6 and 1 7 which are accurately parallel to each other over the entire length of the block. In the illustrated example, both of faces 1 6 and 1 7 are polished, whereas the adjacent pair of longitudinal faces of the block can be milled or etched to produce a dispersive grey finish. A lower end face 18 of the block is angled at substantially 450 to the longitudinal axis 14 of the block as shown providing an acute angle with the side face 1 6.

The end face 1 8 is perpendicular to the elongate side faces which are adjacent to the indicated side faces 16 and 17. The end face 18 is totally internally reflective to light rays entering the block 1 0 through the lower portion of the side face 1 6 immediately opposite the collimator lens 13 of the collimator 11 and substantially parallel to the optical axis 15 of the collimator. To ensure total internal reflection, the surface 18 can be silvered if necessary.

The block 10 is formed of the major portion 1 9 and a minor portion 20. The end of the major portion 1 9 opposite to the end face 1 8 is in a plane accurately parallel to the face 1 8. The minor portion 20 is cemented to the major portion 1 9 as shown with a partially reflecting layer at the interface between the two portions so as to form a partially reflecting surface 21 as shown. The partially reflecting layer may be formed by an aluminium or dichroic coating on the end face of the major portion 1 9 of the block. Preferably, the partially reflecting layer 21 is arranged to provide between fifteen to twenty per cent transmission.

Light reflected in the end face 1 8 up the length of the block 10 is partially reflected again in the layer 21 and emerges through the side face 1 7 of the block. Thus, an eye 22 of a user of the weapon fitted with the prism and collimator can view the collimated image of the aiming mark reflected in the partially reflecting layer 21 and superimposed on a view of the target field seen by the eye along a line of sight 23. Since the faces 16 and 17 of the complete block 10, including both the major and minor portions 1 9 and 20, are accurately parallel, there is substantially no deflection or-deviation of the target field as seen along the line of sight 23.

Furthermore, because the surfaces 1 6 and 1 7 are parallel and also the reflecting surface 1 8 and partially reflecting surface 21 are also parallel, the line of sight 23 defined by the image of the aiming mark reflected in the surface 21 is constantly accurately parallel to the optical axis 1 5 of the collimator 11. Thus, the weapon can be accurately aimed in accordance with the collimator 11 substantially unaffected by the prism 10. Because the position of the prism 10 is not critical, it can readily be made detachable or movable, e.g.

foldable with respect to the collimator 11. This facilitates for example packing of the weapon.

When manufacturing the prism 10 it is convenient first to form accurately the end faces, 18 and 21 of the portion 1 9 of the prism, apply -the partially reflecting coating to the end face 21 and then cement on the minor portion 20. Then, the entire side face 1 6 including that part provided by the minor portion 20 is worked accurately parallel to the opposite side face 17. 7.

Claims (9)

1. An extension prism for a collimator gun sight comprising an elongate block of light transmissive material, the block having: adjacent one end, a first plane polished side face portion substantially parallel to the longitudinal axis of the block; at said one end, a plane internally reflecting surface angled to reflect light, entering the block through said first side face portion, substantially along the length of the block towards the other end thereof; adjacent the other end of the block, a second plane polished side face portion on the opposite side of the block to and parallel to said first side face portion and a plane partially internally reflecting surface parallel to said reflecting surface at said one end, to reflect out of the block through said second side face portion light reflected along the length of the block from said reflecting surface at said one end; and, also adjacent said other end, a third plane polished side face portion parallel to said first and second portions and opposed to said second portion on the opposite side of the partially reflecting surface, so that an image formed by light reflected in said reflecting and partially reflecting surfaces can be seen superimposed on a target field viewed through said second and third face portions.

2. An extension prism as claimed in claim 1, wherein said block has a uniform rectangular cross-section.

3. An extension prism as claimed in claim 2, wherein said first and third side face portions are constituted by respective portions of one elongate side face of the block, and said second side face portion is constituted by a portion of the opposite elongate side face.

4. An extension prism as claimed in claim 3, wherein said reflecting surface at said one end of the block is formed by the end face of the block which is at an acute angle to said one elongate side face and perpendicular to the two elongate side faces adjacent to said one side face.

5. An extension prism as claimed in claim 3 or claim 4, wherein said block has a first major portion comprising said first and second side face portions, said reflecting surface at said one end and an opposite end face in the plane of said partially reflecting surface, and a second minor portion, comprising said third side face portion, which is cemented to said opposite end face of the major portion with a partially reflecting layer at the interface between the block portions.

6. An extension prism as claimed in claim 5 and formed by working said one side face of the block accurately parallel to the opposite side face after cementing the block portions together.

7. A collimator gun sight having an aiming mark generator providing a collimated image of an aiming mark, in combination with an extension prism as claimed in any preceding claim arranged to reflect said collimated image in the reflecting and partially reflecting surfaces of the prism to superimpose the image on the target field.

8. A collimator gun sight as claimed in claim 7 wherein the extension prism is movably or detachably mounted with respect to the aiming mark generator.

9. An extension prism for a collimator gun sight substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.