GB2154332A - Optical sight - Google Patents

Abstract

An optical device, primarily for use as an optical sight, comprising a parallel sided, flat plate (10, 30) a transparent material such as optically pure Perspex (Registered Trade Mark), the plate (10, 30) having a circular through hole (12, 32) whose axis is perpendicular to the side faces of the plate. When the hole (12) is viewed along its axis, the eye sees a circle but when the hole is viewed off-axis the eye sees a tube (16), so providing visual evidence of mis-alignment. The plate (30) can be mounted in the focal plane of an eyepiece (20) of an instrument, such as a telescope, microscope or gunsight, so that the axis of the hole (32) is coincident with the optical axis of the instrument. Alignment of the instrument with a desired target can be attained on the basis of observation of the circle/tube condition. <IMAGE>

Description

SPECIFICATION Optical sight The present invention is concerned with optical sights for use in accurately establishing alignment of optical systems with desired targets.

Optical alignment with a target in optical systems such as telescopes, microscopes and telescopic sights, is conventionally achieved by means of a sight which includes two pairs of cross-wires fixed or marked on the two sides of a transparent disc, respectively.

Alignment of the apparatus onto the target object is achieved by lining up the pairs of cross-wires in a congruent manner when viewing the object through the apparatus.

In other known devices, the cross-wires may be applied to one side only of the glass disc.

The actual configuration of the cross-wires in the known devices takes many forms but in most cases the wires or markings are disposed on a carrier medium through which the target object must be viewed. This has the effect of at least partially reducing the operator's view of the target, particularly on the optical axis.

It is an object of the present invention to provide an alternative sight for establishing alignment of an optical system with a target, which is easy and inexpensive to manufacture and which is easily used to give an accurate sighting, without affecting the view of the target along the optical axis.

An optical sight in accordance with the present invention comprises a parallel sided, flat plate of a transparent material having a through hole whose axis is perpendicular to the side faces of the plate.

Preferably, the hole is of circular section. In this event, when the hole is viewed along its axis, the eye sees a circle but when the hole is viewed off-axis the eye sees a tube, so providing visual evidence of mis-alignment. If the plate is mounted in the plane of the eyepiece focus of an instrument so that the axis of the hole is coincident with the optical axis of the instrument, then alignment of the instrument with a desired target can easily be attained by observation of the circle/tube condition.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which: Fig.1 shows an optical sight in accordance with the present invention when viewed in aligned and non-aligned positions; Fig.2 is an exploded side view of one embodiment of an optical instrument incorporating a sighting device in accordance with the invention; Fig.3 is a diagrammatic side view of the instrument of Fig.2 in its assembled condition; Fig.4 is a diagrammatic sectional side elevation of one of two similar components of another instrument incorporating the present invention; Figs. 5a, 5b, Sc show the view as seen by a person using both components of the instrument; and Figs. 6a and 6b illustrate how the instrument can be used in practice for testing eyes.

The present invention relies on the discovery that if a target object is viewed via a tubular hole in a plate of parallel sided transparent material then, when the viewer's eye is on the longitudinal axis of the hole, the hole is seen as a circle but when the eye moves off the axis the circle becomes a tube.

The eye is able to clearly distinguish the tube condition from the circle condition and so accurately enable the eye to be maintained on the axis of the hole. If then the axis of the hole is arranged to be rigidly aligned with the optical axis of the other components of an optical system, the eye can be correspondingly aligned with the optical axis onto the target.

This is illustrated in Fig.1 which shows one embodiment of a sight in accordance with this invention. In Fig.1 a parallel sided plate of optically pure Perspex 10 has a circular hole 1 2 drilled through it, the axis of the hole 1 2 being accurately perpendicular to the front and rear faces of the plate. The plate 10 must have a finite thickness for the present purposes but should not be too thick in order to avoid excessive light transmission losses in the portions around the hole.

As indicated in Fig.1a, when the hole 12 is viewed along its axis it is seen as a black circle 14. However, as shown in Fig.1b, when the hole 1 2 is viewed off-axis it is no longer seen as a simple circle but becomes a tube 1 6. This happens because the cylindrical side wall of the hole 1 2 now becomes visible to the eye. Fig. 1 b shows the situation where the eye is to one side of the axis. Fig. 1 c shows the situation when the eye is to one side and below the axis.

Figs. 2 and 3 illustrate a practical application of the aforegoing technique as applied to a telescope or microscope eye piece. The apparatus of Figs. 2 and 3 includes an optical eye piece 20 through which the eye observes a target (not shown). The eye piece 20 is rigidly clamped in one end of a tubular retainer member 22, for example made of brass, by means of a lock screw 24. The other end of the retainer member 22 is received in a recess 26 in a housing member 27 and acts to firmly clamp against a shoulder 28 of the recess 26 a disc 30 of optically pure Perspex having a centrally disposed tubular aperture 32 therein whose axis is accurately perpendicular to the faces of the disc 30 and coincident with the optical axis 29 of the remainder of the instrument.The disc 30, with the aperture 32, constitutes the sight provided by the present invention The housing 27 is itself attached to further optical elements (not shown) of the telescope or microscope but since these elements are wholly conventional they are not illustrated further herein.

Mounted on one side of the housing 27 is an illumination means comprising an L.E.D.

34 and associated circuitry. As best seen in Fig.3, the L.E.D.34 is disposed closely adjacent to the outer circumferential edge of the Perspex disc 30. This arrangement provides illumination for the sight when viewed in poor light conditions. When illuminated, the sight provides a bright red ring (or other colour depending on the L.E.D.) or a red tube, in dependence upon the alignment or nonalignment of the eye with the optical axis.

A dimmer means is provided in the lighting circuitry to control the current through the L.E.D. and thereby control the amount of light emitted by the L.E.D. Thus, ring brightness can be controlled so that for example, an astrophotographer could use a dim star as a target without the illuminated ring blocking out the star's light.

By the use of the sight, the optical axis of the instrument can be accuratley aligned in relation to a desired target. The user is thereby able to fix accurately the visual axis through any optical system such as a telescope, microscope, telescopic sight etc., so enabling the user to align the optical system and associated equipment with ease and great accuracy whilst still allowing a clear view of the target.

Theoretically the plate containing the hole can be made of any optically pure transparent medium but in practice it is preferred to use a plastics material such as Perspex since this is easier to machine. The actual dimensions of the aperture and thickness of the plate are capable of wide variation but a typical embodiment might employ a plate having a thickness of 1.4 mm and a hole of 0.8 mm diameter.

In the case of a gunsight, the device can be used without any other optical elements, and may comprise simply a block of perspex mounted on top of the barrel and having a tubular aperture whose axis is generally parallel to the bore of the barrel, the precise orientation of the aperture being finely variable by fine set screws or micrometers.

Strictly speaking, the hole in the plate need not be of circular section and any shape could be used. However, in practice, a circularly sectioned hole would normally be used for ease of machining.

Figs. 4 to 6 illustrate another application of the present invention for use in testing certain defects of the human eyes.

Fig.4 shows a first component of such an instrument which comprises a transparent plastics plate 40 having a through-bore 42 in accordance with the basic invention. The plate 40 is mounted in front of a ground plastics screen 44 and in the focal plane of an eyepiece lens 46, with the centre of the bore 42 on the optical axis of the lens 46. The parts 44,42 and 46 are mounted in a convenient box-like housing 48, for example of opaque plastics material. In the embodiment shown, the housing 48 is mounted on a base 50 by way of a universal joint 52. The component shown is, say, for use with the left eye. A similar component is provided for the right eye, its housing being mounted on the base 50 by means of a respective universal joint 52.The two components are mounted on the base 50 so that a person whose eyes are to be tested can look into the two eye pieces with his/her left and right eyes, respectively.

As indicated in Fig.Sa, the plate 40 of one component (say the left-hand one) is provided with a relatively large bore 42 and also with a vertical line 54a produced by, for example, scoring of the plate surface or by marking it in some other way. As indicated in Fig.Sb, the plate 40 of the other (right-hand) component is provided with a bore 42', which is somewhat smaller in diameter than the bore 42, and also with a horizontal line 54b.

In use, the viewer is asked to look into the two eye pieces at the same time and to adjust the relative positions of the housings 48 until the configuration of Fig.Sc is obtained, i.e with the smaller bore 42' positioned centrally within the larger bore 42 and with the lines 54a, 54b as far as possible mutually perpendicular.

Certain eye defects, such as squint, can be quantified using this apparatus. For example, as shown in Fig.6, for a person with good eye control the perpendicularly oriented crosswires would be achieved without relative tilting of the housings 48 (Fig.6a). However, in order for a person with a given level of squint to see the cross-wires at right angles to each other, one of the housing would have to be tilted by a specific amount in relation to the other housing (see Fig.6b). By examining and measuring the angle of tilt, as set by the user using one or both of the universal joints 52, the degree of squint can be quantified.

In some tests, it may not be necessary to mount the housings 48 on a common base and they could simply be held, one in each hand, facing the person conducting the test.

The relative angle of tilt could then be judged roughly by visual inspection by that person.

It is possible in other embodiments for one of the plates 40, say the plate associated with the left eye, to have a horizontal line in addition to the vertical line 54a. In some circumstances this may help the user to align the crossed lines perpendicularly in the two housings.

Claims (11)

1. An optical device for use as an optical sight comprising a parallel sided, flat plate of a transparent material having a through hole whose axis is perpendicular to the side faces of the plate.

2. An optical device as claimed in claim 1 wherein the hole is of circular section.

3. An optical device as claimed in claim 1 or 2 wherein the flat plate is made of a plastics material.

4. An optical device as claimed in claim 3, wherein the plastics material is optically pure Perspex.

5. An optical device as claimed in claim 1, 2, 3 or 4 including a means for illuminating an edge region of the flat plate whereby to enhance the visibility of the hole.

6. An optical sight as claimed in claim 5 wherein the illuminating means comprises an LED.

7. An optical sight as claimed in claim 5 or 6, wherein the illumination is of variable intensity.

8. An optical device as claimed in any of claims 1 to 7, wherein the flat plate is mounted in the focal plane of an eyepiece of an optical instrument, such as a telescope or microscope, with the axis of the hole coincident with the optical axis of the eyepiece.

9. An optical device for use in testing human eyes, comprising a pair of units each of which includes a flat plate of a transparent material having a through hole whose axis is perpendicular to the side faces of the plate, the flat plate being mounted in the focal plane of an eyepiece lens, between the latter lens and a ground screen and with the axis of the hole on the axis of the eyepiece, the hole of the plate in one of said units being larger than the hole of the plate in the other unit, the flate plates of both units each carrying a straight line mark positioned so as to pass through the axis of the hole in that plate.

10. An optical device as claimed in claim 9, wherein the two units are adapted to be hand held.

11. An optical device as claimed in claim 9 wherein the two units are mounted on a common base by means of respective universal joints.

1 2. An optical device substantially as herinbefore described with reference to and as illustrated in the accompanying drawings.