EP2553378A1

EP2553378A1 - Filter for sights and magnifiers and an assembly comprising such a filter

Info

Publication number: EP2553378A1
Application number: EP11763148A
Authority: EP
Inventors: Ralf Wiklund
Original assignee: GS Development AB
Current assignee: Aimpoint AB
Priority date: 2010-04-01
Filing date: 2011-03-29
Publication date: 2013-02-06
Also published as: WO2011123035A1; SE536566C2; SE1050313A1; EP2553378A4

Abstract

A spatial-spectral filter (6) adapted to be positioned between an outlet aperture (8) of a low-magnification sight (2) and an outlet aperture (10) of a magnifying device (4), comprises a central region (R1) having a first transmittance T1 in a first wavelength interval λ1, and a peripheral region (R2) radially outside of the central region (R1), having a second transmittance T2(λ1) in said first wavelength region λ1, wherein T1(λ1)>T2(λ1).

Description

FILTER FOR SIGHTS AND MAGNIFIERS, AND AN ASSEMBLY COMPRISING SUCH A FILTER

Field of the Invention

The present invention relates to improvement of a sight, and in particular to an optical filter for sights when combined with magnifiers, and to a magnifier provided with such filter.

Background

When there are numerous non-magnifying sights available, and in particular what is often referred to as red-dot sights or reflex sights, where a reticle image of some sort is reflected to the eye of a user. By superimposing the reticle image onto a target the device that the sight is mounted on may be aimed at the target.

An example of such a sight is disclosed in US 6 373 628 by the present applicant, yet there are numerous alternatives available, with and without a battery powered light source for the aiming reticle, of more or less open design, etc. as is well known for the skilled person.

An advantage of this type of sights as compared to conventional iron sights is that they are generally much faster to operate, i.e. the time it takes from the spotting of a target until the reticle is superimposed onto the target is significantly shorter than the time required to align the two components of an iron sight with the target. A similarity is that both these types of sights are non-magnifying in their basic design.

For the reflex-type sight to be modified to a magnifying sight, a telescopic magnifier may be arranged between the reflex -type sight and the eye of the user.

The present invention aims at improving such a combination of a telescopic magnifier and a sight.

Summary

The present invention achieves the aim by providing an optical filter adapted to be positioned between the outlet aperture of a sight and an outlet aperture of a magnifying device, characterized in that the filter is designed to operate as a spatial and spectral filter in that a central region of the filter has a first transmittance Τ1(λ1) for a selected wave length region λΐ, and the a second region, radially outside of the central region has a second transmittance Τ2(λ1)>=0 for the wavelength region λΐ, wherein Τ1(λ1)>Τ2(λ1), wherein λΐ includes radiation emitted by a reticle of the sight. In all presently foreseeable embodiments Τ2(λ≠λ1)>0 for visible wavelengths not including λΐ in order to transmit as much light as possible.

The sight is preferably a non-magnifying sight or a low-magnification sight with a magnification less than two. In this context this magnification corresponds to a sight which may be used with both eyes open, while still readily allowing for the user to combine the information received via each eye.

The inventive spatial/spectral filter achieves two main objectives, the first being to act as a pinhole - i.e. a spatial filter - for light emitted by the reticle, which improves the quality of the imaging of the reticle. Simply arranging a pinhole having a transmittance of 1 in the central region and 0 in a region outside of the central region would achieve this goal too, yet with a massive loss of light intensity through a sight- magnifier combination, which would affect the performance of the combination in low light conditions. The present filter may however have a transmittance Τ2(λ1) in the second region being close to zero for the interval λΐ, yet being as close to 1 as possible for other wavelengths, thus acting as a spectral filter in this region.

The direct effect of the filter, when used 'between' a sight and a magnifier is that the reticle will be less prone to display parallax effects, which are increased by the magnifier. The filter may be provided as a separate component, or form a part of either the magnifier or the sight, whereof the embodiment where the filter forms part of the magnifying device is considered most relevant presently. If not using any device between the sight and the magnifying device parallax effects may cause the reticle to appear diffuse for the user, and may also result in the imaginary appearance of several reticles, which obviously is a drawback for a sight or other aiming device. One reason for this may be that a magnifying device collects light that have passed via a peripheral region of the reflection or lens device arranged in the beam path, and it is a well known effect that any imaging distortions will be more pronounced. In the case of the reticle being an aiming point designed to be circular, the inventive filter improve the circular appearance of the aiming point when observed through a magnifying device. The inventive filter may be accomplished by coating an optical component, such a lens or a flat etc. which means that the filter does not necessarily have to be provided as a separate component, rather it may be incorporated on a component that should be included in the optical device in any case, such as the inlet window of a telescopic magnifier, or a lens of a telescopic magnifier. Particular embodiments will be described in the following detailed description. Brief Description of the Drawings

Fig. 1 is a schematic illustration of a prior art sight in accordance with

US 6 373 628.

Fig. 2 is a sight-magnifier assembly comprising a filter according a first embodiment of the present invention.

Fig. 3 is a schematic front view of a filter according to the first embodiment of the present invention.

Fig. 4 is a schematic view of an assembly where a filter according to the first embodiment is arranged in a magnifier.

Figs. 5a and 5b illustrate idealized transmission curves for a filter according to one embodiment of the present invention.

Fig. 6 illustrates various filters configured for attachment to a magnifier or sight.

Fig. 7 illustrates presently preferred filter arrangements.

Fig. 8 is a schematic illustration, partly transparent, of a filter arrangement of

Fig. 7 arranged in a sight/magnifier combination.

Description of Embodiments

Starting with a description of a known sight, an example of such a sight is disclosed in the schematic cross section of Fig. 1. It should be noted that since the disclosure the development of the disclosed type of sight has continued, and the present invention should not be limited in this respect.

The sight 2 comprises a light tunnel which is formed by an outer tube 20, which may be mounted to the barrel of the shotgun by using a conventional sight mount. An inner tube 21 is mounted with one end fixed to the outer tube 20 and the other end fixed to an adjustment device, not shown here, for adjustment of the longitudinal axis of the inner tube 21 relative to the longitudinal axis of the outer tube 20 to the extent required to adapt the sight to the shotgun on which it is to be used. At said one end of the inner tube a double lens 22 is mounted with a coating 23 between the lenses reflecting red light, or whatever wavelength the light- source used for achieving the reticle is utilizing. Inside the inner tube 21 a light source 24 is provided comprising a light emitting diode which directs a beam of red light towards the coating 23 reflecting the light beam through a surface grinded glass plate 25 with anti -reflex coating facing the left end of the light tube, as indicated by dot and dash lines in Fig. 1. When the shooter looks at the target through the light tunnel from this end, he sees a red dot which he puts on the spot on the target, where he wants the impact to take place. A light sensor 35 may be included to control the intensity emitted from the light emitting diode.

Imaging of the reticle is thus performed by reflecting the light emitted by the light source 24 via the double lens 22 and coating 23. As is well known, an ideal lens is next to impossible to fabricate, and it is also well known that imaging distortions increase with the distance from the centerline, which implies that light from the light source 24 reflected from the peripheral region of the double lens 22 and coating 23 will appear more distorted to an individual using the sight.

A first embodiment of the present invention is illustrated in the assembly of

Fig. 2. To the right a low-magnification sight or a non-magnifying sight 2, e.g. of the type disclosed in US 6 373 628 (Fig. 1) may be arranged. In such a sight an aiming reticle created by the projection of a light-source arranged to one side (upper, lower, left, right, or anywhere there between) of the sight is reflected to the eye of a user via a reflective surface. The thus generated aiming reticle will be essentially parallax free, yet when the light source is reflected via the peripheral region of the reflective surface any imaging distortions may be more pronounced, as previously discussed referring to Fig. 1. This is rarely a problem since the double lens 22 (see Fig. 1) changes the point of impact very little, as compared to a solution using a single-lens system, where parallax and other distortion effects may be significantly more pronounced.

In the present embodiment, however, a magnifying device 4 is arranged in the beam path between the sight and the user. A magnifying device 4 may be beneficial when firing at targets located at longer distances. Another reason may be when using the aiming device in low-light conditions, since the magnifying device 4 will concentrate the light available and thus improve the light-conditions for a user. These effects are well-known, and further explanation is considered obsolete, yet slightly simplified, the magnifying device collects all light entering through its inlet window, and concentrates it before it exits the outlet window, hence the improvement of the light-conditions. However, the magnifier increases the distortion and parallax effects when the aiming dot, or reticle, is placed at the border of the lens. For this reason a user may be more troubled by image distortions than what is the case when a non- magnifying sight is used on its own.

To this end an inventive spatial-spectral filter 6 may be arranged in the beam path. The filter 6 will block peripheral beams - beams of light from the light source being reflected from the peripheral region of the reflective surface - while transmitting central beams from the light source. "Central beams" essentially corresponds to beams passing through the sight, parallel to an optical axis thereof and in a central region thereof, and "peripheral beams" are interpreted in an analogous way. The same filter will transmit radiation of most other visual wavelengths entering into the system. This means that detrimental image distortions will be minimized while beneficial light concentration will remain essentially unchanged. This is possible since the light source emits light in a narrow wavelength interval. If a laser diode is used as a light source only a single wavelength is used. Blocking this narrow wavelength interval on a portion of the surface of the filter 6 will not affect the total light collected significantly, and the narrow spectrum of a light-emitting diode may also accomplish a beneficial result.

An inventive filter according to one embodiment is illustrated in the front view of Fig. 3. In the central region Rl as much as possible of the light emitted by the light source should be transmitted, and in the peripheral region R2 as little as possible of the same light should not be transmitted. In both regions Rl and R2 as much as possible of light of other wavelengths should be transmitted. In some cases it is desired to block light or radiation of other well defined wavelengths too, which obviously may be applied in the present invention as well.

The size of the filter 6 is matched (essentially equal) to the size of the outlet window of the sight, and may thus be adapted to various sights. The size of the central region Rl may also vary in order to remove an adequate amount of the distorted reticle while still making the reticle visible when viewing through the magnifier.

Data

Central region Rl:

Ideal transmittance in the wavelength of the reticle: Τ1(λ1) = 100%

Practical transmittance in the wavelength of the reticle: Τ1(λ1) = 95-98% Ideal transmittance for other wavelengths: Τ1(λ≠λ1) = 100%

Practical transmittance for other wavelengths: Τ1(λ≠λ1) = 95-98%

Diameter: Will vary with application, yet 3-10 mm, in some cases up to

12-15 mm when used in front of a sight with 20 mm outlet aperture may give an indication. Peripheral region R2:

Ideal transmittance in the wavelength of the reticle: Τ2(λ1) = 0%

Practical transmittance in the wavelength of the reticle: Τ2(λ1) = 2-20%

Ideal transmittance for other wavelengths: Τ2(λ≠λ1) = 100%

Practical transmittance for other wavelengths: Τ2(λ≠λ1) = 80-98%

Diameter: Will vary with application, yet the same diameter as the inlet aperture of the magnifying device or the outlet aperture of the sight is preferable (that is, the diameter of the filter should not limit the performance of a sight/magnifier assembly).

Generalizing the above information gives the estimation that the peripheral region R2 preferably has a diameter corresponding to about 100% of the diameter of the outlet aperture of the sight it is used in combination with, and that the central region Rl has a diameter of about 20-60 % of said aperture, preferably of about 30-40%. The diameter of the inlet aperture of the magnifier preferably corresponds to the diameter of the outlet aperture of the sight.

All surfaces are preferably provided with an anti-reflection coating, and may also be provided with coatings blocking the transmittance of other selected

wavelengths, e.g. such as to block harmful laser radiation from rangefmders, not already included in the previous data on transmittance Tl and T2.

The filter as such is intimately coupled to the use of the magnification device (magnifier), even if it very well may be provided as a separate piece configured to be included in a an assembly comprising the magnifier. Such a filter may be configured to be releasably mounted to a magnifier. The filter may e.g. comprise an outer thread to be combined with an inside thread of the magnifier. The filter may also comprise projections projecting radially and being configured to engage corresponding cutouts in the magnifier. According to another alternative the filter is dimensioned to be inserted in a tubular, or other, fitting of the magnifier device, in which fitting the filter may be releasably held in place by any suitable means. The filter may also comprise a tubular socket or means extending from its outer perimeter, essentially in the direction of a normal to its surface. Such a tubular socket or extending means may be configured (dimensioned) to engage a radially outer surface of the magnifier (or the sight) in order to position the filter correctly. In an embodiment where the magnifier and the filter are provided as an aggregate the filter may constitute the entrance window of the magnifying device. The filter may also be arranged behind another entrance window in order for the filter to be adequately protected. According to such an alternative the filter and magnifier does not have to be configured to be releasable in relation to eachother, yet they still may be. The above features for making the filter releasably attachable to a magnifying device may also be used to make the filter releasably attachable to a non- magnification sight (or low-magnification sight), since such an attachment may also be an alternative for the person using the filter in a sight/magnifier combination. The portion of the filter provided the threads, projections etc preferably is a separate part, such as a fitting in which the active filter portion is arranged. A few examples of filters configured for releasable attachment to a magnifier or a sight is presented in Fig. 6, in which; 6 represents a filter of the type being clamped or held into place by an arrangement on the magnifier or the sight; 106 a filter provided with an external thread for cooperation with an inside thread of the magnifier or sight, the thread preferably being arranged on a fitting in which the filter is arranged; 206 a filter provided with a sleeve preferably of material having some resilience, such us natural or synthetic rubber, which may fit over one end of the magnifier or the sight, the sleeve may also be dimensioned to cooperated with an inner perimeter of the magnifier or sight and may have inwardly or outwardly extending ridges for increasing friction, and the bead indicated at one end of the sleeve (the same end in which the filter is arranged) may have larger dimensions such as to provide a grip when attaching or removing the filter unit; 306 a filter provided with radial projections, preferably arranged on a fitting in which the filter is arranged, which projections cooperate with corresponding grooves of the magnifier or the sight. From these examples the skilled person realizes that there are several alternatives for releasable attachment of the filter to the magnifier or the sight. The use of a fitting having an outer thread or the use of a resilient sleeve adapted for engagement with an inner perimeter of the sight or magnifier are the solutions being most preferred presently, such as the embodiments exemplified in Fig. 7. The fitting 40 to the left is preferably manufactured from a metal such as aluminum or stainless steel or from a rigid plastic composite and comprises an engagement end 42 provided with threads and a grip end 44 having a larger diameter than the engagement end. The material used should be adequate for its purpose and it should be understood that the examples given above should not be construed as limiting. The grip end 44 may be provided with axial grooves or undulations/corrugations for increasing the grippability, i.e. in practice facilitating for the user to obtain a firm grip of the filter device, which is beneficial when the device is to be handled. The actual filter 6 is arranged in the area of the grip end, yet it may be located elsewhere along the axial length of the fitting. Having it slightly countersunk into the fitting should reduce wear and should make the filter less sensitive for impacts. The resilient-sleeve fitting 50, to the right, has a design which is similar to the rigid fitting 40 to the left. Instead of threads the sleeve may have outwardly extending ridges for increasing the strength of its engagement with an inner perimeter of the sight or the magnifier at its engagement end 52. If the sleeve is dimensioned for engagement with an outer perimeter of the sight or magnifier it may instead be provided with inwardly extending ridges. The grip end 54 of the sleeve may also have a design which improves the grippability. Projections configured to fit in grooves of the sight or magnifier may be used as operational feature of the engagement end, instead of threads or ridges. The sleeve 50 may be quite rigid, yet resilient enough to allow for such deformation that it may be inserted in a cylindrical receiving area of the magnifier or the sight. The resilience of the sleeve 50 may also be of such nature that the filter may be inserted into a socket in the grip end of the sleeve 50. In a preferred embodiment the sleeve 50 is manufactured in one piece, yet in other embodiments the sleeve 50 may be manufactured from more than one type of plastic, e.g. by co-moulding. In such an embodiment the ridges may be formed from a more resilient plastic and the rest of the sleeve may be formed in a less resilient material. The ridges may also be arranged in circumferential grooves of the engagement end, e.g. in the form of o-rings.

A schematic drawing, partly transparent, of a filter arrangement of Fig. 7 arranged in a sight/magnifier combination is illustrated in Fig. 8. Here a resilient sleeve 50 carrying a filter 6 according to one embodiment of the present invention is arranged in a cylindrical inlet end of a magnifier 4 downstream a sight 2. Only one

circumferential ridge engaging the cylindrical inlet is shown, yet there may be two or more if considered adequate. The use of the same reference

Light source

The light source used for the reticle may vary, yet one practical example includes a light source emitting light at a peak of 650 nm. When reflected in the front lens towards the user the wavelength of the peak will be shifted to 657 nm, and in this particular example 657 nm will thus constitute λΐ . A typical light emitting diode used has a half width of 10-20 nm. If a laser diode is used the wavelength region λΐ collapses to a single wavelength.

The lens system may be coated so as to act as a bandpass filter, transmitting all visible wavelengths between 420 and 1100 nm but for a narrow wavelength interval including the wavelength emitted by the light-source, which itself is reflected. The longer wavelength is used for Night Vision Device (NVD).

Since the light from the light source has a wavelength of e.g. 650 nm, most light from entering the inlet aperture of the sight will be transmitted, and in particular light in a wavelength range where the human eye is most sensitive.

Fig. 4 illustrates an assembly where the inventive filter 6' forms part of a magnifying device, which is one of several attractive embodiments for a product based on the present invention.

Fig. 5 illustrates transmission curves for the central and the peripheral region of the filter, respectively. The full line represents the ideal curve, and the dashed line illustrates a more practical curve, though the skilled person realizes that the practical curve does not represent a true transmission curve, which usually has a smoother appearance. For illustrative purposes, however, these curves are considered satisfactory. For all embodiments of the present invention the relation T2>=0 for λΐ may be valid.

In yet another embodiment of the present invention the filter is manufactured by coating a lens or a flat of suitable material, and by drilling, cutting or in any other way removing the material of the lens/flat and coating in the central region. This method of manufacture may instead be the other way around; i.e. that the material is removed before the coating is applied. Yet another method includes an initial step of coating a lens or flat, after which the coating is removed in the central region by means of an abrasive or chemical process. A further method includes covering the central region with a mask during the coating process. The coating referred to in these methods comprises a bandpass coating, reducing the transmittance of the wavelength interval of the aiming reticle.

The skilled person also realizes that the above description is exemplifying only, and that the inventive idea has a significantly larger scope, as defined by the appended claims forming part of this description.

Claims

1.A spatial-spectral filter (6) configured to be positioned between an outlet aperture (8) of a low-magnification sight or a non-magnification sight (2) and an outlet aperture (10) of a magnifying device (4), said filter (6) comprising a central region (Rl) having a first transmittance Τ1(λ1) in a first wavelength interval λΐ, and a peripheral region (R2) radially outside of the central region (Rl), having a second transmittance Τ2(λ1) in said first wavelength region λΐ, wherein Τ2(λ1)<Τ1(λ1).

2. The filter of claim 1, wherein Τ2(λ1) is less than 50%, preferably less than

20%), and even more preferred less than 10%>.

3. The filter of claim 2, wherein Τ2(λ1) is between 2% and 20%.

4. The filter of any preceding claim, wherein Τ1(λ1) is higher than 90%, preferably higher than 95%, and even more preferably higher than 98%.

5. The filter of any preceding claim wherein 0.02<Τ2(λ1)/Τ1(λ1)<0.25

6. The filter of any preceding claim, wherein the transmittance for visible wavelengths outside of the wavelength region λΐ exceeds 80%>, e.g. 95-98%> for both regions of the filter.

7. The filter device of any preceding claim comprising a coating blocking wavelengths in selected from the group comprising: 1550 nm selected wavelengths between 800-1000 nm, for both regions of the filter.

8. The filter of any preceding claim, further comprising a broadband anti- reflection coating for both regions of the filter.

9. The filter of any preceding claim, wherein the filter is configured to be releasably attached to an inlet end of a magnifying device or an outlet end of a non- magnification sight.

10. The filter of claim 9, wherein an outer perimeter comprises outwardly extending projections or threads for cooperation with corresponding means of the magnifying device or the non-magnification sight.

11. The filter of any preceding claim, wherein the diameter of Rl is 3-15 mm, preferably 4-10 mm.

12. An assembly comprising a filter of any preceding claim and a magnifying device or a sight, wherein the filter is releasably attached to the magnifying device or the sight.

13. The assembly of claim 12, wherein the magnifying device have an inlet aperture of diameter D, preferably matched to the outlet aperture of a sight, the peripheral region (R2) has a diameter of about IxD and the central region (R2) has a diameter of about 0,2-0,6xD, more preferred of about 0,3-0,4xD.

14. The assembly of claim 12 or 13, wherein the diameter of the peripheral region is about 20 mm and the diameter of the central region is about 4-15 mm, more preferred about 4-5 mm.

15. The assembly of claim 12, wherein the magnification M = 3, the diameter of Rl is 3-15 mm, preferably 8-10 mm, the diameter of R2 is 18-22 mm, preferably about 20 mm and λΐ has a peak at 657 nm.