SE1050313A1 - Filters for sight and magnification units and an assembly comprising such a filter - Google Patents

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 ?1, and a peripheral region (R2) radially outside of the central region (R1), having a second transmittance T2(?1) in said first wavelength region ?1, wherein T1(?1)>T2(?1).

Description

100331 P:\0576 GS Development\P\080\P05760080 Appl Text and Drawings ~ To be filed.doc l 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 anoptical filter for sights When combined With magnifiers, and to a magnifier providedWith such filter.

BackgroundWhen 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 somesort is reflected to the eye of a user. By superimposing the reticle image onto a target thedevice 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 presentapplicant, yet there are numerous altematives available, With and Without a batterypowered light source for the aiming reticle, of more or less open design, etc. as is Wellknown for the skilled person.

An advantage of this type of sights as compared to conventional iron sights isthat they are generally much faster to operate, i.e. the time it takes from the spotting of atarget until the reticle is superimposed onto the target is significantly shorter than thetime required to align the two components of an iron sight With the target. A similarityis 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 telescopicmagnifier 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.

SummaThe 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 amagnifying device, characterized in that the filter is designed to operate as a spatial andspectral filter in that a central region of the filter has a first transmittance TlOtl) for aselected Wave length region Äl, and the a second region, radially outside of the centralregion has a second transmittance T2(7t1)>=0 for the Wavelength region Ål , WhereinT1(7t1)>T2(?t1), Wherein Äl includes radiation emitted by a reticle of the sight. In all 100331 P:\0576 GS Development\P\080\P05760080 Appl Text and Drawings ~ To be filed.doc 2 presently foreseeable embodiments T2(?t qíkl)>0 for Visible wavelengths not includingX1 in order to transmit as much light as possible.

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

The inventive spatial/spectral filter achieves two main objectives, the firstbeing to act as a pinhole - i.e. a spatial filter - for light emitted by the reticle, whichimproves the quality of the imaging of the reticle. Simply arranging a pinhole having atransmittance of 1 in the central region and 0 in a region outside of the central regionwould achieve this goal too, yet with a massive loss of light intensity through a sight-magnifyer combination, which would affect the performance of the combination in lowlight conditions. The present filter may however have a transmittance T20tl) in thesecond region being close to zero for the interval M, yet being as close to 1 as possiblefor 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 isthat the reticle will be less prone to display parallax effects, which are increased by themagnifier. The filter may be provided as a separate component, or form a part of eitherthe magnifier or the sight, whereof the embodiment where the filter forms part of themagnifying device is considered most relevant presently. If not using any devicebetween the sight and the magnifying device parallax effects may cause the reticle toappear diffuse for the user, and may also result in the imaginary appearance of severalreticles, which obviously is a drawback for a sight or other aiming device. One reasonfor this may be that a magnifying device collects light that have passed via a peripheralregion of the reflection or lens device arranged in the beam path, and it is a well knowneffect that any imaging distortions will be more pronounced. In the case of the reticlebeing an aiming point designed to be circular, the inventive filter improve the circularappearance of the aiming point when observed through a magnifying device. Theinventive filter may be accomplished by coating an optical component, such a lens or aflat etc. which means that the filter does not necessarily have to be provided as aseparate component, rather it may be incorporated on a component that should beincluded in the optical device in any case, such as the inlet window of a telescopicmagnifier, or a lens of a telescopic magnifier. Particular embodiments will be described in the following detailed description. 100331 P:\0576 GS Development\P\080\P05760080 Appl Text and Drawings ~ To be filed.doc 3 Brief Description of the Drawings Fig. 1 is a schematic illustration of a prior art sight in accordance withUS 6 373 628.

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

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

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

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

Description of Embodiments Starting with a description of a known sight, an example of such a sight isdisclosed in the schematic cross section of Fig. 1. It should be noted that since thedisclosure the development of the disclosed type of sight has continued, and the presentinvention 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 sightmount. An inner tube 21 is mounted with one end fixed to the outer tube 20 and theother end fixed to an adjustrnent device, not shown here, for adjustment of thelongitudinal axis of the inner tube 21 relative to the longitudinal axis of the outer tube20 to the extent required to adapt the sight to the shotgun on which it is to be used. Atsaid one end of the inner tube a double lens 22 is mounted with a coating 23 betweenthe lenses reflecting red light, or whatever wavelength the light-source used forachieving the reticle is utilizing. Inside the inner tube 21 a light source 24 is providedcomprising a light emitting diode which directs a beam of red light towards the coating23 reflecting the light beam through a surface grinded glass plate 25 with anti-reflexcoating 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 reddot which he puts on the spot on the target, where he wants the impact to take place. Alight sensor 35 may be included to control the intensity emitted from the light emittingdiode.

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 100331 P:\0576 GS Development\P\080\P05760080 Appl Text and Drawings ~ To be filed.doc 4 next to impossible to fabricate, and it is also well known that imaging distortionsincrease with the distance from the centerline, which implies that light from the lightsource 24 reflected from the peripheral region of the double lens 22 and coating 23 willappear more distorted to an individual using the sight.

A first embodiment of the present invention is illustrated in the assembly ofFig. 2. To the right a low-magnification sight or a non-magnifying sight 2, e. g. of thetype disclosed in US 6 373 628 (Fig. 1) may be arranged. In such a sight an aimingreticle 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 areflective surface. The thus generated aiming reticle will be essentially parallax free, yetwhen the light source is reflected via the peripheral region of the reflective surface anyimaging distortions may be more pronounced, as previously discussed referring toFig. 1. This is rarely a problem since the double lens 22 (see Fig. 1) changes the point ofimpact very little, as compared to a solution using a single-lens system, where parallaxand other distortion effects may be significantly more pronounced.

In the present embodiment, however, a magnifying device 4 is arranged in thebeam path between the sight and the user. A magnifying device 4 may be beneficialwhen f1ring at targets located at longer distances. Another reason may be when usingthe aiming device in low-light conditions, since the magnifying device 4 willconcentrate the light available and thus improve the light-conditions for a user. Theseeffects are well-known, and further explanation is considered obsolete, yet slightlysimplif1ed, the magnifying device collects all light entering through its inlet window,and concentrates it before it exits the outlet window, hence the improvement of thelight-conditions. However, the magnifier increases the distortion and parallax effectswhen the aiming dot, or reticle, is placed at the border of the lens. For this reason a usermay 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 beampath. The filter 6 will block peripheral beams - beams of light from the light sourcebeing reflected from the peripheral region of the reflective surface - while transmittingcentral beams from the light source. “Central beams” essentially corresponds to beamspassing through the sight, parallel to an optical axis thereof and in a central regionthereof, and “peripheral beams” are interpreted in an analogous way. The same filterwill transmit radiation of most other visual wavelengths entering into the system. This means that detrimental image distortions will be minimized while benef1cial light 100331 P:\0576 GS Development\P\080\P05760080 Appl Text and Drawings ~ To be filed.doc 5 concentration Will remain essentially unchanged. This is possible since the light sourceemits light in a narroW Wavelength interval. If a laser diode is used as a light sourceonly a single Wavelength is used. Blocking this narroW Wavelength interval on a portionof the surface of the filter 6 Will not affect the total light collected significantly, and thenarroW spectrum of a light-emitting diode may also accomplish a beneficial result.

An inventive filter according to one embodiment is illustrated in the front viewof Fig. 3. In the central region R1 as much as possible of the light emitted by the lightsource should be transmitted, and in the peripheral region R2 as little as possible of thesame light should not be transmitted. In both regions R1 and R2 as much as possible oflight of other Wavelengths should be transmitted. In some cases it is desired to blocklight or radiation of other Well defined Wavelengths too, Which obviously may beapplied in the present invention as Well.

The size of the filter 6 is matched (essentially equal) to the size of the outletWindow of the sight, and may thus be adapted to various sights. The size of the centralregion R1 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.

DataCentral region R1:Ideal transmittance in the Wavelength of the reticle: TlOtl) = 100%Practical transmittance in the Wavelength of the reticle: TlOtl) = 95-98%Ideal transmittance for other Wavelengths: TlOqíkl) = 100%Practical transmittance for other Wavelengths: TlOqíkl) = 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: T2(7t1) = 0% Practical transmittance in the Wavelength of the reticle: T2(7t1) = 2-20% Ideal transmittance for other Wavelengths: T20qí7t1) = 100% Practical transmittance for other Wavelengths: T20qí7t1) = 80-98% Diameter: Will vary With application, yet the same diameter as the inletaperture 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). 100331 P:\0576 GS Development\P\080\P05760080 Appl Text and Drawings ~ To be filed.doc 6 Generalizing the above information gives the estimation that the peripheralregion R2 preferably has a diameter corresponding to about 100% of the diameter of theoutlet aperture of the sight it is used in combination with, and that the central region R1has a diameter of about 20-60 % of said aperture, preferably of about 30-40%. Thediameter of the inlet aperture of the magnifier preferably corresponds to the diameter ofthe outlet aperture of the sight.

All surfaces are preferably provided with an anti-reflection coating, and mayalso be provided with coatings blocking the transmittance of other selectedwavelengths, e.g. such as to block harrnful laser radiation from rangefinders, not already included in the previous data on transmittance T1 and T2..

Light source The light source used for the reticle may vary, yet one practical exampleincludes a light source emitting light at a peak of 650 nm. When reflected in the frontlens towards the user the wavelength of the peak will be shifted to 657 nm, and in thisparticular example 657 nm will thus constitute kl. A typical light emitting diode usedhas a half width of 10-20 nm. If a laser diode is used the wavelength region kl collapsesto a single wavelength.

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

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

Fig. 4 illustrates an assembly where the inventive filter 6” forms part of amagnifying device, which is one of several attractive embodiments for a product basedon the present invention.

Fig. 5 illustrates transmission curves for the central and the peripheral region ofthe filter, respectively. The full line represents the ideal curve, and the dashed lineillustrates a more practical curve, though the skilled person realizes that the practicalcurve does not represent a true transmission curve, which usually has a smootherappearance. For illustrative purposes, however, these curves are considered satisfactory.

For all embodiments of the present invention the relation T2>=0 for kl may be valid. 100331 P:\0576 GS Development\P\080\P05760080 Appl Text and Drawings ~ To be filed.doc 7 In yet another embodiment of the present invention the filter is manufacturedby coating a lens or a flat of suitable material, and by drilling, cutting or in any otherWay removing the material of the lens/ flat and coating in the central region. Thismethod of manufacture may instead be the other Way around; i.e. that the material isremoved before the coating is applied. Yet another method includes an initial step ofcoating a lens or flat, Whereafter the coating is removed in the central region by meansof an abrasive or chemical process. A further method includes covering the centralregion With a mask during the coating process. The coating referred to in these methodscomprises a bandpass coating, reducing the transmittance of the Wavelength interval ofthe 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 forrning part of this description.

Claims (12)

1.A spatial-spectral filter (6) adapted to be positioned between an outletaperture (8) of a low-magnification sight or a non-magnification sight (2) and an outletaperture (10) of a magnifying device (4), said filter (6) comprising a central region (R1)having a first transmittance T1(7t1) in a first Wavelength interval X1 , and a peripheralregion (R2) radially outside of the central region (R1), having a second transmittanceT2(7t1) in said first Wavelength region kl , Wherein T2(7t1)

2. The filter of claim 1, Wherein T2(?t1) is less than 50%, preferably less than 20%, and even more preferred less than 10%.

3. The filter of claim 2, Wherein T2(7t1) is between 2% and 20%.

4. The filter of any preceding claim, Wherein T1(7t1) 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

6. The filter of any preceding claim, Wherein the transmittance for visibleWavelengths outside of the Wavelength region kl exceeds 80%, e.g. 95-98% for both regions of the filter.

7. The filter device of any preceding claim comprising a coating blockingWavelengths in selected from the group comprising: 1550 nm selected Wavelengthsbetween 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. An assembly comprising a filter of any preceding claim and a magnifying device.

10. The assembly of claim 9, Wherein the magnifying device have an inlet aperture of diameter D, preferably matched to the outlet aperture of a sight, the 100331 P:\0576 GS Development\P\080\P05760080 Appl Text and Drawings ~ To be filed.doc 9 peripheral region (R2) has a diameter of about lxD and the central region (R2) has adiameter of about 0,2-0,6xD, more preferred of about 0,3-0,4xD.

11. The assembly of claim 9 or 10, Wherein the diameter of the peripheralregion is about 20 mm and the diameter of the central region is about 4-15 mm, more preferred about 4-5 mm.

12. The assembly of claim 9, Wherein the magnification M = 3, the diameter ofR1 is 3-15 mm, preferably 8-10 mm, the diameter of R2 is 18-22 mm, preferably about20 mm and kl has a peak at 657 nm.