Firearms – Implements – Sight devices
Reexamination Certificate
1999-03-25
2001-12-11
Johnson, Stephen M. (Department: 3641)
Firearms
Implements
Sight devices
C042S130000, C042S131000, C042S137000, C042S143000
Reexamination Certificate
active
06327806
ABSTRACT:
DESCRIPTION
1. Technical Field
This invention relates to optical devices for sighting at a target to be aimed at, and more particularly, but not exclusively, to an electro-optical sighting device for a hand gun.
2. Background Art
Optical sights can be mounted on a hand gun, rifle, shotgun or other small arm which includes bow, cross bows, paint guns and air guns. In sights of this type, a graticule is illuminated using incident light either from the target area, from the sky above, or from an adjacent artificial light source such as a Tritium Phosphor, or a light emitting diode (LED). The graticule may either reflect the incident light or transmit the incident light to form a sighting image.
The target is viewed through the sight usually by means of a planar doublet reflector, or a similar combination of spherical lenses, or a thin meniscus lens, which forms a sighting image of the graticule superimposed on an image of the target. With a spherical lens set, it is necessary to ensure that the angle formed between the light rays from the graticule which are reflected from a surface within the spherical lens set, and the optical axis of the lens set, is relatively small. This gives rise to relatively long focal lengths or small viewing apertures, otherwise spherical aberration will occur causing the graticule image to become blurred and parallax errors to become large.
Typically focal length to aperture ratios of up to 4:1 or more, are used. This requirement causes the optical arrangement to become long compared to its aperture, and it is difficult to make compact designs. It is possible to avoid the problem of spherical aberration by using aspherical lens sets, but these have been difficult and expensive to produce.
Battery life is a fundamental problem when these systems are considered for use in arduous conditions such as military or law enforcement applications. Even high performance types of LED have high current consumptions when maximum brightness is required in bright sunlit conditions. Reducing the brightness of the LED would enhance the battery life but to the detriment of useability. Alternatively, larger batteries add to the bulk of the system.
Mounting optical sights, which have circular optical apertures principally derived from rifle telescopic sights where this is suitable, low on to the top of a hand gun, means that the optical area immediately above the gun is at its narrowest, i.e. at the edge of the optic. The area on either side of this is usually taken up by the optical housing and mount system. In effect the conventional shape is entirely wrong for mounting onto a hand gun, where a wide aperture is desirable close to the top of the gun.
Moreover, known optical systems used particularly in competition shooting, have the system mounted onto the frame of the hand gun using an additional bracket or an integral bracket arrangement which causes the sight to be mounted above the gun in such a manner that the profile of the gun is greatly increased. Any increase in profile causes the gun to become more cumbersome, especially if the sight weights several once, (1 oz.≈28 gm). It also has the disadvantage that the top of the gun, which can be used by the eye to quickly align the gun with the target, can no longer be seen by the shooter.
A further disadvantage of such a system is that the gun has to be specifically modified to accept the mounting bracket. This means that retro-fitting to a standard gun is expensive, and the gun is permanently marred if the sight is subsequently removed. Furthermore, most integral mount systems are specific to one type of hand gun and cannot be fitted to rifles and/or revolvers and/or semi-auto pistols without further specialised brackets.
Most electro-optical sights suffer from the violent vibration and shock that is produced by hand guns when they are fired. This is most noticeable in some types of competition shooting where large numbers of relatively high power cartridges are fired. The mount system is often designed to try to isolate this vibration from the sight. These mount systems are usually fastened to the frame of the hand gun since, when the gun is fired, the frame is subject to a much smaller movement and lower vibration than, for example, the slide of the gun. Thus, for ideal sighting purposes, the sight should be mounted in a position directly onto or set into the rear part of the slide of a semi-automatic hand gun. However, the vibration and high acceleration would then be passed directly to the sight. Known sights are not constructed in a manner which could be suitably adapted to this type of mounting on the gun's slide or could withstand the forces imposed on it.
When an electronic failure occurs it is seldom likely to be the electronic components themselves but their mechanical/electrical connection to other components, such as switches, battery connections, circuit board contacts, solder contacts, etc. Usually, in known sight designs, some or all of these components are mounted permanently within the sight, which means that the sight has to be replaced or repaired by the manufacturer, should failure occur.
Known electro-optical sights, which employ an LED, use an electro-mechanical system to switch the LED on and control its intensity. Using a switch system has several disadvantages; primarily the user may neglect or not have time to actuate the switch and adjust, e.g. for light intensity, the device when required, or may neglect to switch the system off. If left switched on, on full brightness, the battery will be exhausted in a few hours and the system becomes useless. Switches also are prone to failure due to vibration, shock and physical damage.
These systems would have to be especially rugged to survive day-to-day service life in a military environment and be able to withstand severe impact and drop tests. Known systems cannot fulfil this criteria of compactness and ruggedness.
Another problem with electro-optical sights is the spherical aberration of the optical element. An attempt to address this problem is made in U.S. Pat. No. 5,189,555 where the element, which has a long focal length (apparently of the order of 9 cm), has its surface facing away from the LED of an indeterminate shape and its surface towards the LED parabolically shaped—as is well known for avoidance of parallax and spherical aberration problems. However, the long focal length makes the overall length of the sight too long for weapons requiring a short length for the sight, and also seems likely to produce an aperture ratio no better than about f.3 or f.4. If the focal length of the lens of U.S. Pat. No. 5,189,555 were to be reduced and, to reduce costs, the lens were to be molded of plastics material, then to ensure molding accuracy it would of necessity result in a thin lens. However, due to its thinness, such a thin lens would be liable to relaxation and/or movement in use and provide for inaccurate focussing and/or imaging aberrations of the electro-optical sight incorporating such a lens.
The present invention aims to overcome one or more of the above-mentioned and/or other disadvantages of the prior art.
According to one aspect of the invention there is provided an optical device for sighting a target to be aimed at in the line of sight of a user, comprising an optical element of transparent material having a front surface for facing the target and a back surface in which the the user views an image of the target, and a source of light directed at and reflected back from the back surface to create a sighting image for the user to align with the image of the target as viewed in the optical element, characterized in that the optical element is a thick meniscus optical element as hereinbelow defined and is composed of a base element which (a) is provided on one face thereof with a mold-replicated parabolic aspherical surface that constitutes said back surface and defines it as one of short focal length, namely less than 5 cm (2 inches), and which (b) is provided on the other face thereof with an aspherical correcting surface that
Firearms Research Limited
Freiburger Thomas M.
Johnson Stephen M.
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