GB2089519A - Stowable sighting instrument - Google Patents

Abstract

In armoured and fighting vehicles for example, the space available for stowing a sighting instrument is very restricted, whereas in use the instrument should be angularly moveable to cover a wide field of view. An instrument is provided comprising two complementary parts 2, 3 of a bearing, one part 3 being fixed in an aperture in the armour 1, the second part 2 being angularly moveable about a pivoting axis. The optical system comprises elongate objective (5) and ocular (5) portions extending in substantially opposite directions from the second part 2 on either side of the armour, said portions being oppositely offset from the pivoting axis to provide a stowing position for the instrument in which the two portions lie generally alongside the outer and inner sides respectively of the armour. The second part comprises means 15, 25 (e.g. prisms or fibre optics) for optically coupling the objective and ocular portions. The instrument may be a periscope or telescope. Figs. 3 and 4 (not shown) show periscopes having lenses. <IMAGE>

Description

SPECIFICATION Stowable sighting instrument The invention relates to devices for taking observations from behind a barrier which devices comprise a retractable sighting instrument projecting through the barrier. More particularly the invention relates to such sighting instruments having elongate portions on either side of the barrier and which have a bearing secured intermediate of the ends of the sighting instrument and set in said barrier to permit angular motion of the sighting instrument relative to the barrier Such devices are commonly used in armoured fighting vehicles such as tanks or submarines.In such vehicles, the observation device should be stowed or retracted when not in use so that (a) the portion extending outside the vehicle is protected from battle damage as far as possible and (b) the portion extending inside the vehicle occupies as little space as possible and offers the least obstruction to movements of personnel. Typically the sighting instrument may be a periscope which in the case of a submarine is retracted through sliding seals into a vertical well sufficiently deep to accommodate the length of the periscope. In land fighting vehicles the space available is far more restricted and the retracted length of a periscope would be objectionable.A solution to this problem is described in United States Patent Specification No. 1,151,995 in which the periscope is bodily removed from the bearing into the vehicle and stowed as a detached item, the aperture in the barrier then being closed with an armoured plate.

Such a periscope cannot be brought into operation or stowed very rapidly and the temporary loss of seal in the barrier would be a serious objection particularly in atomic or biological warfare.

It is an object of the invention to provide a stowable sighting instrument which can be brought into operation and stowed rapidly, which provides appreciable protection for the part of the device exposed to damage when stowed, which offers minimal obstruction within the vehicle when the device is stowed and which offers the possibility of preserving the integrity of the barrier.

The invention provides a sighting instrument comprising means defining two complementary parts of a bearing, a first part in use being fixedly secured in an aperture in a barrier and the second part being angularly moveable relative to said first part about a pivoting axis, an optical system comprising an objective portion and an ocular portion extending in substantially opposite directions from said second part, at least one of said portions being elongate and said portions being oppositely offset from the pivoting axis, and means in said second part for optically coupling the objective ancl ocular portions. The offsets will be chosen in relation to the thickness of said barrier to allow the sighting instrument to be rotated in said bearing about said axis into a stowage position in which the elongate portion lies along one side of the barrier.

To enable the sighting instrument to be panned and tilted at will, in one embodiment of the invention the bearing is a ball swivel, both portions being elongate and entering the ball of the swivel in directions which pass one each on opposite sides of the centre of the ball to provide said offset.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a sectional view of a unity magnification periscope set in a ball swivel, Figure 2 shows a part-sectional view of the periscope of Figure 1 seen from the observer's position, Figure 3 shows a sectional view of a narrow field high magnification periscope, and Figure 4 shows a sectional view of a wide angle periscope.

Referring to Figures 1 and 2 an observer takes observations through a sighting instrument 4, in this case a simple mirror periscope, from beneath a barrier 1 for example the roof of an armoured vehicle. The periscope has elongate portions 5 and 6, one on either side of the barrier 1. A bearing 2, 3 comprises a ball swivel. For assembly, the outer annular fixed part 3 of the bearing is in two halves divided by the plane of the drawing in Figure 1 bolted and dowelled together (details not shown) and is fixed to the barrier 1 by bolts some of which are shown at 7 in Figure 2. A sealing '0' ring 8 is provided in an internal annular groove 9 in the annular part 3. The ball part 2 of the swivel bearing is assembled from two hemispherical parts 10 and 11 bolted together by the bolts 12 some of which are shown in Figure 1.

The upper extended portion 5 comprises a plane input window 13 and a plane frontmetallized mirror 14 set at 450 to the axis 1 6 of portion 5. A solid transparent element 1 5 has an upper face 1 7 normal to axis 16 and a lower face 1 8 set at 450 to axis 1 6 providing deflection of the downward light from mirror 14 through 900 by total internal reflection. Element 1 8 is set in an offset tubular aperture 19 integrai with the upper hemisphere 1 0. The reflection of the axis 1 6 in face 1 8 passes substantially through the centre of ball 2.Element 18 seals off aperture 19, allowing portion 5 to be removed and replaced in the event of battle damage without opening the interior of ball 2 to contamination. For this purpose portion 5 has an annular groove 21 in the mating face 22, which groove contains a sealing '0' ring, set screws 20 being provided for securing portion 5 tc the upper mating face of aperture 1 9.

The lower extended portion 6 has a plane frontmetallized mirror 23 set at 450 to the axis 24 of portion 6. A solid transparent element 25 has a lower face 27 normal to axis 24 and an upper face 28 set at 450 to axis 24 providing deflection of light from 18 through 900 by total internal reflection along axis 24. Element 25 is set in an offset tubular aperture 26 integral with the lower hemisphere 11. Axes 16 and 24 are offset from the centre of ball 2 in opposite directions and by a lateral separation from one another chosen in relation to the thickness of barrier 1. Portion 6, secured to hemisphere 11 by set screws 30, is provided with handles 29 to allow the observer to swivel the sighting instrument 4 in bearing 2, 3.

To stow the lower end 6 of the sighting instrument within the vehicle and to protect the upper portion 5, the sighting instrument can be rotated in the ball swivel about an axis normal to the plane of Figure 1 into a stowage position 31 shown dotted. The lateral offset of axis 24 relative to the centre of ball 2 allows portion 6 to lie substantially adjacent to and along the underside of barrier 1. To improve the stowing a recess 32 is provided in portion 6 to cooperate with a cutaway portion 33 of barrier 1. On the top side of the barrier a cut-away portion 34 is similarly provided in bearing 3 to allow the upper portion 5, offset to the opposite side of the ball centre from portion 6, to lie substantially adjacent to and along the topside of the barrier 1 and maybe to nest in an armoured shield thereon.

The opposed offsets of the portions 5 and 6 have an incidentai benefit in that there is no straight line path for missiles such as small arms bullets through the optical elements of the periscope.

The static field of view of the periscope of Figure 1 is comparatively small since the size of the face 1 7 of element 1 5 defines the field of view of the instrument, due allowance being made for the effective shortening of the distance from the observer's eye, considered stationary relative to mirror 23, to face 1 7 by the refraction effect of the elements 15 and 25. The dynamic field of view is defined by the field of view which the observer can scan by moving his eye up or down, left or right relative to the mirror 23, effectively moving a projection of the face 1 7 across the face of mirror 14. Static and dynamic fields of view of, for example, 40 and 9" respectively may be obtained. The total field of view in the horizontal plane will be 3600 since the ball is freely rotatable about a vertical axis.In the vertical plane the total field of view may be, for example, 100 in elevation and 500 in depression.

Figure 3 shows a variation of the periscope of Figure 1 in which a relatively narrow field view with substantial magnification is provided by adding a telescope to the optical components of the periscope of Figure 1 said telescope comprising objective lens 35 and eyepiece 36. For stowage, provision may be made for removing the eyepiece 36 from portion 6 to allow the latter to lie along the underside of barrier 1.

Figure 4 shows a unity magnification wide angle periscope in which portion 5 is provided with a wide angle objective 37 optically in front of mirror 14. The optical elements 1 5 and 25 are absent, their place being taken for the purpose of the lateral separation of axes 1 6 and 24 by the 450 total internal reflection prisms 40 and 42. The optical system is symmetrical either side of the lens 41 which is part of the image relay optics comprising lenses 38, 39, 41,43 and 44 which relay the first real image formed in the back focal plane lens 37 into the focal plane of lens 45 with unity magnification. Lens 45 has the same focal length as lens 37 and hence the observer views the original scene at a total magnification of unity.

As with the periscope of Figure 3, the objective 45 may be removable for periscope stowage.

The three embodiments of the invention described above are related to periscopes. However the sighting instrument may be a telescope set, for example, in a vertical barrier. The telescope may then be rotated so that the longitudinally extending portions on either side of the barrier lie in any desired direction along their respective sides of the barrier. Clearly the optical system of the sighting instrument need not be restricted to any particular wavelength range and accordingly near infra-red or thermal infra-red instruments may take advantage of the invention. Image conversion or intensification devices may also be incorporated.

Conventional total internal reflection prisms have been shown to effect the lateral separation of the optical axes of the parts of the instrument on either side of the barrier. Alternatively a coherent bundle of optical fibres bent to follow the cranked optical path through the bearing may be used, an objective lens being used to form an image of the scene on one end of the bundle and an eyepiece being used to view the relayed image available at the other end of the bundle.

The invention has been described using a ball swivel as the bearing in which the sighting instrument is set. A cylindrical bearing may be used, the offset of the optical axes taking place across the diameter of the cylinder. The cylindrical bearing may then, in turn, be set in an annular bearing In the barrier having a rotation axis normal to the barrier to allow 3600 viewing in the horizontal plane.

The objective or ocular portions need not be elongate, either optical component being, for example, recessed into the second part of the bearing so that when stowed the component is shielded within the first part of the bearing.

Claims (7)

1. A sighting instrument comprising means defining two complementary parts of a bearing, a first part in use being fixedly secured in an aperture in a barrier and the second part being angularly moveable relative to said first part about a pivoting axis, an optical system comprising an objective portion and an ocular portion extending in substantially opposite directions from said second part, at least one of said portions being elongate and said portions being oppositely offset from the pivoting axis, and means in said second part for optically coupling the objective and ocular portions.

2. A sighting instrument as claimed in Claim 1, wherein the bearing is a ball swivel, both portions being elongate and entering the ball of the swivel in directions which pass one each on opposite sides of the centre of the ball to provide said offset.

3. A sighting instrument as claimed in Claim 1, wherein the bearing comprises a cylindrical bearing having its cylinder axis substantially parallel to said barrier, the elongate portions entering the cylinder of the bearing in directions which pass one each on opposite sides of said cylinder axis to provide said offset.

4. A sighting instrument as claimed in any of Claims 1, 2 or 3, wherein the sighting instrument is a periscope.

5. A sighting instrument as claimed in any one of Claims 1 to 4 inclusive, wherein said objective portion comprises a removeable outer member and an inner member fixed within and sealing the entrance to said second part of the bearing.

6. A sighting instrument as claimed in any preceding claim in which said objective and ocular portions are coupled by a coherent bundle of optical fibres.

7. A sighting instrument for taking observations from behind a barrier substantially as described with reference to Figures 1 and 2 or Figure 3 or Figure 4 of the accompanying drawings.