GB2162654A

GB2162654A - Weapons sighting apparatus having image enhancer and graticule injection

Info

Publication number: GB2162654A
Application number: GB08415080A
Authority: GB
Inventors: Roger Brian Huxford
Original assignee: LASERGAGE Ltd
Current assignee: LASERGAGE Ltd
Priority date: 1984-06-13
Filing date: 1984-06-13
Publication date: 1986-02-05

Abstract

In a weapons sighting apparatus such as a rifle night-sight, a magnifier lens system 6 is pivoted about the centre of curvature X of the curved output screen, S, of a proximity image intensifier 4. Adjusting pins 20,22 provide the necessary degrees of freedom to pivot the graticule image so that it remains coincident with the curved scene image at any position in the field of view. This arrangement avoids parallax errors between scene image and the graticule image. <IMAGE>

Description

SPECIFICATION Weapons sighting apparatus This invention relates to weapons sighting apparatus, particularly to devices incorporating image enhancers such as image intensifiers having a curved real image plane. The invention is specifically concerned with the injection of a graticule into the line of sight of such apparatus.

Some known weapons sighting apparatus, especially those incorporating image intensifiers, have an objective lens system focussing the scene onto the input side of the image enhancer and a magnifier lens system focussed on the enhancer output (in the case of an image intensifier, on the phosphor viewing screen).

Of the types of image intensifiers commonly in use, those of the second generation and in particular the channel inverter tube, have a curved input window for the photo-cathode and various electrodes are used to focus the electron beam on to a plain surface, i.e. the channel plate. In the case of proximity image intensifiers, these have a flat input window for the photocathode followed closely by the channel plate and output phosphor; they have no intermediate focussing electrodes but the image is inverted by means of a fibre optic bundle or "conduit" following the phosphor screen. It is customary to have a curved output window on the optical fibres. This simplifies the magnifier design as the correction of field curvature is less stringent.

Any residual field curvature is then easily accommodated by the ability of the eye to re-focus at various object distances. The magnifier presents the operator with a distant virtual image of the field of view.

For aiming purposes the graticule information can be generated in a number of ways, either by injection into the objective or magnifier to provide a bright pattern or as a shadow graticule positioned at the focal plane of the objective or magnifier. This invention is concerned with graticules injected into the magnifier. This is normally accomplished at the magnifier by generating the graticule image visually off-axis, e.g. by illuminating a screen marked with the graticule. The graticule image is injected into the field of view of the weapons sighting apparatus typically by a prism or mirror system. A means of adjusting the position of the graticule image in the field of view is provided to enable the weapon to be calibrated and enable the operator to use the graticule image as an accurate aiming mark, aligned with the barrel of the weapon.The optical path length from the graticule generation position to the magnifier lens system is arranged such that the graticule image is thus viewed (at least on the optical axis of the instrument) at a position coincident with and in focus with on-axis images from the image intensifier.

Known position adjusting means for the graticule image cause the latter to move in a flat plane transverse to the optical axis. When the magnifier is not highly corrected for field curvature, this causes the off-axis image of the viewed scene and the off- axis graticule image no longer to coincide.

This introduces a parallax error for the viewer movement of the eye across the exit pupil causes the virtual images of the scene and the graticule to move with respect to one another, which can result in an aiming error. The problem is particularly marked where two groups of optical components are used to provide the field of curvature correction for the overall system and the graticule is injected between these components. This invention is concerned with avoiding this problem.

According to the invention there is provided a weapons sighting apparatus having an image enhancing device provided with a curved output screen, a lens system viewing said screen to provide an image thereof, means for injecting a graticule image onto the screen image, and means for adjusting the position of the graticule image relative to the screen by pivoting the graticule image about the centre of curvature of the screen.

The adjusting means can take a variety of forms.

The lens system can be fixed relative to the optical axis of the apparatus and the graticule image adjusted in an arcuate manner so as to maintain coincidence of the virtual graticule and scene images.

The means which injects the image from its offaxis generation position onto the field of view (e.g.

the prism system or dichroic mirror) may also be adjusted in position curvedly. Preferably, however, the graticule image generator is fixed to a housing for the lens system and the housing is pivoted about the centre of curvature of the screen. In such a case, the graticule image remains on the optical axis of the lens system but this axis pivots relative to the optical axis of the remainder of the instrument. The pivoting mechanism may take the form of a universal joint e.g. a gimbal or a low friction bearing.

Preferably, the lens system is a magnifier having at least two spaced-apart lenses or groups of lenses and the injection means injects the graticule image into the field of view at a position between the spaced-apart lenses or groups.

A preferred embodiment of the invention in the form of a rifle night-sight will now be described with reference to the accompanying drawings, given by way of example, in which: Figure 1 is a vertical cross-section through the night-sight parallel to the optical axis; Figure 2 is an end elevation of the magnifier section of the night-sight (i.e. with the image intensifier and objective lens system removed) partially sectioned along axis A-A; and Figures 3 and 4 are, respectively, vertical crosssections through the relevant parts of two alternative night sights according to the invention.

Referring to Figures 1 and 2, the night-sight comprises an objective lens system 2 (shown partially), a proximity image intensifier 4, and a magnifier lens system 6. The objective lens system 2 and image intensifier 4 are conventional and require no further description. The monochromatic (green) image is displayed on a curved screen S, of the image intensifier 4, and the magnifier lens system 6 is focussed on this curved screen.

The magnifier lens system comprises spacedapart lenses 8 and a dichroic mirror 10, transmissive to green light and reflective to red light, and supported firmly in a housing 12. The housing 12 is itself supported relative to a casing 14 for the apparatus by means of a gimbal 16, support plunger 18 and horizontal and vertical adjusting pins 20 and 22 respectively. The gimbal comprises a pair of vertical trunnions 24 set in the casing 14, a gimbal ring 26 encircling the housing 12, and a pair of horizontal trunnions 28 extending from the gimbal ring 26 into the housing 12 (and shown in phantom in Figure 1). The centre of pivoting of the gimbal 16 (the intersection of the axes of the vertical and horizontal trunnions 24,28) is at position X, which is on the optical axis of the instrument and coincides with the centre of curvature of the screen of the image intensifier.

Each adjusting pin 20,22 is supported on threads by a domed nut 30 capable of rotation within casing 14. Each nut 30 comprises a slot 32 to receive a screw-driver or coin for adjusting purposes and is provided with teeth 34 which engage a springbiassed ball 36. An O-ring seal 38 prevents ingress of foreign materials in the region where the nut 30 rotates in casing 14. Each adjusting pin 20,22 bears onto a bearing surface 40 of housing 12, and has a flat cutaway surface 21 to abut a plate 23 to prevent rotation of the adjusting pin.

The axis of the support plunger 18 is disposed at an angle of 45- to the axes of the adjusting pins 20,22 and comprises a spring-loaded pin 42 urged against a bearing surface 44 of housing 12.

A graticule injection system supported by housing 12 comprises a red LED 45, prism 46 and screen 48 having an opening in the shape of the desired graticule image. The optical path length from screen 48 to dichroic mirror 10 is arranged such that the graticule image and the image of the screen of the image intensifier coincide.

In use, the graticule injection system injects a red graticule image onto the surface of dichroic mirror 10, which is reflected to the eye of the observer superimposed on the transmitted green image of the field of view.

To calibrate the instrument so that the graticule coincides with the aiming point of the weapon, it may be necessary to inject the graticule at various positions across the field of view. This is accomplished by rotation of domed nuts 30 which in turn cause adjusting pins 20 and 22 to move horizontally and vertically, respectively, towards or away from housing 12. Since the support plunger 18 is biassed against bearing surface 44, the action of rotation of either or both of the domed nuts 30 causes the housing 12 to pivot about position X.

The presence of two adjusting pins 20,22 provides the necessary degrees of freedom to enable the graticule image to be moved off-axis to any position within the field of view subject of course to the limit of movement of housing 12 within casing 14. Since the pivoting movement of housing 12 is about the centre of curvature X of the image intensifier screen S, the graticule image coincides not only with the on-axis virtual image of the screen, but also with the off-axis images if it is so moved to such positions during calibration. The graticule image follows the curvature of the scene image and this coincidence of images avoids any parallax errors. The engagement of teeth 34 of nuts 30 with the spring- biassed balls 36 provide a "click-stop" form of adjustment and assist to prevent the apparatus going out of calibration during use.

Figure 3 illustrates an alternative embodiment identical to that of Figures 1 and 2 except that the gimbal 16 (i.e. gimbal ring 26 and trunnions 24,28) is replaced by a low friction bearing having curved bearing surfaces 52,54 providing a ball-joint action enabling the housing 12 to pivot about position X.

An O-ring 55 is provided at the outer edge of the bearing surfaces for sealing purposes.

Figure 4 illustrates a further embodiment. In this example the housing 12 and graticule injection system are fixedly supported on casing 14. The dichroic mirror 10 is supported in a cylindrical ring member 56. The latter has a curved bearing surface 58 which abuts a complementary bearing surface 60 of a mounting ring 62 which fixedly supports the frontmost lens 64 of the magnifier lens system. Bearing surface 58 is supported for movement across and against surface 60 by the horizontal and vertical adjusting pins 20 and 22 and support plunger 18 (only the vertical adjusting pin 22 is seen in Figure 4). The cylindrical ring member 56 has flats (e.g. at 66) to bear against the adjusting pins 20,22 and support plunger 18. The apparatus operates as with Figures 1 to 3 except that the magnifier lens system remains aligned with the optical axis of the remainder of the instrument. Pivoting of the dichroic mirror 10 gives the appearance of pivoting the graticule image about the centre of curvature of the screen of the image intensifier.

Claims

1. A weapons sighting apparatus having an image enhancing device provided with a curved output screen, a lens system viewing said screen to provide an image thereof, means for injecting a graticule image onto the screen image, and means for adjusting the position of the graticule image relative to the screen by pivoting the graticule image about the centre of curvature of. the screen.

2. An apparatus according to claim 1 comprising a housing fixedly supporting the lens system and the injection means, and said adjusting means comprising means for pivoting said housing about the centre of curvature of the screen.

3. An apparatus according to claim 2 wherein said adjusting means comprises pivot support means enabling the housing to pivot only about said centre of curvature and means for restraining said pivot action.

4. An apparatus according to claim 3 wherein the pivot support means comprises a universal joint.

5. An apparatus according to claim 4 wherein said pivot support means comprises a gimbal or a low friction bearing extending between said hous ing and a casing of the apparatus which fixedly supports said image enhancing device.

6. An apparatus according to claim 4 or 5, wherein said restraining means comprises at least a pair of adjustable pins in contact with the housing and spaced- apart in a plane transverse to the optical axis of the apparatus.

7. An apparatus according to claim 6 which additionally comprises means for biassing the housing against said pins.

8. An apparatus according to claim 1 wherein said adjusting means comprises means for moving the injecting means relative to said lens system.

9. An apparatus according to any of claims 1 to 8 wherein the lens system comprises a magnifier having at least two spaced-apart lenses or groups of lenses and wherein the injection means injects the graticule image onto the screen image at a position between said spaced-apart lenses or groups.

10. An apparatus according to any of claims 1 to 9 wherein the image enhancing device is an image intensifier.

11. An apparatus according to claim 10 wherein the injection means includes a dichroic mirror transmissive to the light from the image intensifier but positioned to reflect the graticule image to the eye of the observer.

12. A weapons sighting apparatus substantially as herein described with reference to Figures 1 to 3, or 4, or 5 of the accompanying drawings.