GB2187353A - Rifle sight - Google Patents

Abstract

A rifle sight comprises a casing 10, a telescope 13 having an objective lens 16, an eyepiece 16, a fixed graticule 20 and an adjustable graticule 21. The rifle sight also includes a range finder comprising a laser 26, a detector 27 and an LED display 28 visible from outside the sight. In use, the sight is mounted on a sniper's rifle. The sniper aligns the fixed graticule on a target. A button is pressed and the laser emits a laser pulse towards the target. The reflected pulse is received by objective lens 16 and reflected by a beam splitter 30 to detector 27 which calculates the range of the target and the range is displayed on display 28. The sniper then uses the range information to adjust the horizontal cross wire of graticule 21 and graticule 21 is aligned on the target when firing the rifle. <IMAGE>

Description

SPECIFICATION Rifle sight This invention relates to a telesscopic rifle sight for mounting on a sniper rifle.

A conventional telescopic rifle sight is essentially a telescope having an objective lens unit, an eye piece lens unit and a graticule mounted in the focal plane of the eye lens unit. The graticule has horizontal and vertical cross wires the positions of which can be adjusted by associated adjustment knobs mounted on the casing of the rifle sight. The vertical cross wire is associated with a scale calibrated in wind speed and the position of this cross wire is adjusted to take account of the wind speed. The horizontal cross wire is associated with a distance scale and the position of this cross wire is adjusted in accordance with the range of the target from the rifle to take account of bullet drop.

With such a conventional rifle sight, the sniper adjusts the horizontal cross wire on the basis of his own estimate of the range of the target from the rifle. However, it is difficult to judge the range accurately and so this adjustment is liable to be inaccurate. In an attempt to overcome this problem, a range finder has been proposed which can be mounted on top of the rifle sight. However, this combination of a separate range finder and rifle sight results in a buiky structure. Moreover, unless the range finder is connected to the rifle sight with great accuracy, the range finder and rifle sight may not be properly aligned.

It is accordingly an object of this invention to provide a new or improved rifle sight in which the above mentioned problems are overcome or reduced.

According to this invention there is provided a rifle sight comprising an elongate casing, a telescope mounted in said casing and arranged for viewing a target area, said telescope comprising an objective lens unit, an eye piece lens unit, and an adjustable graticule, and a range finder mounted in said casing and directed towards said target area.

By mounting the telescope and range finder in a single casing, a rifle sight is obtained which is of a relatively compact design and in which the range finder may be accurately aligned with the telescope during manufacture of the rifle sight.

Preferably, said range finder comprises a laser arranged to transmit laser pulses towards said target area, and a detector responsive to laser pulses reflected from said target area and arranged to calculate range by measuring the time period between the transmission of a pulse from said laser and its reception by the detector.

Conveniently, the range finder includes a beam splitter positioned to deflect part of the light received by the objective lens unit to said detector.

By using a beam splitter to deflect part of the light recevied by the objective lens to the detector, there is no need to provide a separate objective lens unit for the detector and this helps to reduce the overall dimensions of the rifle sight.

Said beam spliter may be a reflector which reflects light at the wave length of the laser pulses.

The telescope may include a fixed graticule.

The fixed graticule is used when making range measurements and the adjustable graticule is used when firing the rifle. When only an adjustable graticule is provided, there is danger that the range finder will not be accurately directed towards the target during range measurements with the resulting possiblity of a false reading.

This invention will now be described in more detail, by way of example, with reference to the drawings in which: Figure 1 is a diagrammatic plan view of a rifle sight embodying this invention; Figure 2 is a diagrammatic side view of the rifle sight; Figure 3 is a diagrammatic front view; Figure 4 is a diagrammatic rear view; Figure 5 is a block diagram of the electronic circuitry of the rifle sight; and Figure 6 shows a modification to the rifle sight.

Referring now to the drawings, the rifle sight comprises an elongate casing 10 which may be formed, for example, from steel or plastics material and which has a rear face 11 and front face 12. The shape of the casing 10 will be described in more detail below.

Mounted in casing 10, there is provided a telescope 13 having a optical axis 14, a lens mounting tube 15, an objective lens unit at the front of the casing and comprising a single convex lens 16, and an eye piece lens unit 17 positioned at the rear of the casing 10 and comprising a pair of convex lenses 18 and 19. The telescope 13 further includes a fixed graticule 20 and an adjustable gr6ticule 21 both of which are positioned approximately in the focal plane of the eye piece lens unit 17.

The fixed graticule 20 has fixed horizontal and vertical cross wires. The adjustable graticule 21 has a horizontal cross wire whose position can be adjusted by a knob 22 mounted on the exterior of casing 10 and which is associated with a scale graduated in distance. The adjustable graticule 21 also has a vertical cross wire which may be adjusted by a knob 23 also mounted on the exterior of the casing 10 and which is associated with a scale graduated in wind speed.

Also mounted in casing 10, there is provided a range finder comprising a Q-switched Nd-YAG laser 26, a detector 27, and 'an LED display 28.

Referring now to Figure 5, there is shown a block diagram of the electronic circuitry of the range finder. The laser 26 is provided with a trigger circuit 26a operated by a push-button switch 26b, a pulse forming network 26c, and a power supply 26d. The detector 27 includes a photo-sensor 27a in the form of an avalanche photodiode, a counter 27b, and a clock pulse generator 27c. The display 28 is provided with a display driver 28b. The various components receive power from a battery pack 40. In order to minimize the space requirements the counter 27b, the clock pulse generator 27c and the display driver 28b are formed as a surface mounted assembly and the output of display driver 28b is multiplexed to the individual digits of display 28.

On depressing buttom 26b, trigger circuit 26a applies a 30kV pulse to a flash lamp forming part of laser 26, a trigger pulse to the power supply 26d, and a reset pulse to counter 27b. On receiving a trigger pulse, the power supply 26d changes the voltage which it applies to pulse forming network 26c from 2kV to 5kV and simultaneously establishes a bias voltage for avalanche diode 27a.

On receiving the 30kV pulse, the flash lamp fires and laser 26, which is passively 0switched, emits a 14ns laser pulse at a wavelength of 1.06/zm through a window 29 in the front face 12 of casing 10 towards the target area viewed by telescope 13. More specifically, the laser 26 is accurately aligned with the fixed graticule 20 so the laser pulse is incident on the target area at the position defined by the intersection of the cross wires of graticule 20. Laser 26 includes an internal photo-sensor which detects the laser pulse and transmits a signal to cause counter 27b to commence counting clock pulses.

The laser pulse is reflected back from the target towards the range finder and is collected by the objective lens 16. A reflector 30 inclined at 45 to the optical path 14 reflects the laser pulse received by objective lens 16 onto photodiode 27a. The reflector 30 is of the type known as a pericle and comprises a thin membrane of optical material which reflects light at a wavelength of 1.06,cm and which is transparent to light at other wavelengths.

When the laser pulse is incident on photodiode 27a, it transmits a pulse to counter 27b which stops counting the clock pulses. Thus, the counter 27b measures the time which elapses between the transmission of the laser pulse from laser 26 to its reception by photodiode 27a. This time represents the range and the output of counter 27b is supplied to display driver 28b and the range is displayed on a face 28a of display 28.

A compensator 31 of identical construction to reflector 30 is mounted in the tube 15 at 45 to the optical axis 14 but in the opposite sense to reflector 30 and at a position optically behind reflector 30. The compensator 31 compensates for the small displacement caused by reflector 30 to the light rays passing therethrough. As both reflector 30 and compensator 31 reflect light at the wave lengths of the laser pulses, these pulses are prevented from reaching the eye of the sniper and thereby eliminating the risk of any damage which such pulses might otherwise cause.

Conveniently, the battery 40 may be located inside the sniper's clothing so that the battery will operate efficiently even in very cold conditions. The button 26b for operating the laser 26 may conveniently be located on the rifle on which the rifle sight is mounted. The cables from the battery 40 and from the button 26b are connected through the casing via a connector 32.

In order to prevent operation of laser 26 interfering with operation of photo-sensor 27a, counter 27b, clock pulse generator 27c, and display driver 28b, these latter components are encased in a shield which comprises two or three layers of aluminium foil. The individual layers are connected to the earth of these components and they are separated from each other by insulating material.

The casing 10 will now be described in more detail. Viewing the casing from the rear, it may be seen that the rear part is of rectangular cross section of sufficient dimensions to accommodate eye piece unit 17. Moving away from rear face 11, the width of the left side of the casing increases at a surface 34 so as to accommodate the laser 26. Moving further forward, to a surface 35, the width of the right side of the casing increases so as to accommodate detector 27. As may be seen in Figures 3 and 4, the right hand side is of stepped configuration. Finally, at the front of the laser, the depth of the bottom surface of the casing increases at a surface 36 so that the front face 12 is of sufficient depth to accommodate the objective lens 16.

In operation, a sniper aligns the intersection of the horizontal and vertical cross wires of the fixed graticule 20 with the target and presses the button 26b mentioned above so as to make a range measurement. The range measurement is then displayed on display 28 and the sniper adjusts knob 22 in accordance with this range. He will also adjust knob 23 in accordance with wind speed. The sniper now directs the intersection of the vertical and horizontal cross wires of graticule 21 on the target for firing.

Referring now to Figure 6, there is shown a modification to the rifle sight. As before, the rifle sight includes an objective lens 16, an eyepiece 1 7 comprising lenses 18, 19 and a detector 27. Beam splitter 30 is replaced by a beam splitter 41, fixed graticule 20 is replaced by a fixed graticule 42, and the adjustable graticule 21 is replaced by a planar/convex lens 43 and a graticule 44 in the form of a liquid crystal display backlit by a radioactive flourescent device 45. The components 42, 43, 44, 45 are located on a axis 46 perpendicular to axis 14 and passing through the middle of beam splitter 41. The beam splitter reflects reflected laser pulses to detector 27 and also the images of graticules 42 and 44 to eyepiece 17. The graticule 44 has a pair of cross wires which are controlled electronically.

The vertical cross wire is controlled by a potentionmeter mounted on the outside of casing 10. The horizontal cross wire is controlled directly by the range finder and display device 28 may be removed or retained as desired.

The remaining components are substantially as described with reference to Figures 1 to 5.

In another modification, the range information is displayed in the field of view of telescope 13.

In a further modification, an optical device is placed in front of laser 26 to change the wavelength of the laser pulses to 1.5 m. Such a device may use a technique such as Raman shifting. At 1.5,am, there is no danger of the laser pulse causing damage either to the eyes of the sniper or to the eyes of others.

Claims (8)

1. A rifle sight comprising an elongate casing, a telescope mounted in said casing and arranged for viewing a target area, said telescope comprising an objective lens unit, an eye piece lens unit, and an adjustable graticule, and a range finder mounted in said casing and directed towards said target area.

2. A rifle sight as claimed in claim 1, in which said range finder comprises a laser arranged to transmit laser pulses towards said target area, and a detector responsive to laser pulses reflected from said target area and arranged to calculate range by measuring the time period between the transmission of a pulse from said laser and its reception by the detector.

3. A rifle sight as claimed in claim 2, in which the range finder includes a beam splitter positioned to deflect part of the light received by the objective lens unit to said detector.

4. A rifle sight as claimed in claim 3, in which said beam splitter comprises a reflector which reflects light at the wavelength of the laser pulses.

5. A rifle sight as claimed in any one of the preceding claims in which the telescope includes a fixed graticule.

6. A rifle sight as claimed in any one of the preceding claims, in which the adjustable graticule comprises an electronic display device having a cross-wire whose position is con trolledby the range finder.

7. A rifle sight as claimed in any one of the preceding claims including means for optically changing the wavelength of light emitted by the laser.

8. A rifle sight substantially as hereinbefore described with reference to, and as shown in, Figures 1 to 5, or Figure 1 to 5 as modified by Figure 6, of the accompanying drawings.