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GB2090012A - Night Sight with Injected Graticule - Google Patents

Night Sight with Injected Graticule Download PDF

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Publication number
GB2090012A
GB2090012A GB8040800A GB8040800A GB2090012A GB 2090012 A GB2090012 A GB 2090012A GB 8040800 A GB8040800 A GB 8040800A GB 8040800 A GB8040800 A GB 8040800A GB 2090012 A GB2090012 A GB 2090012A
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GB
United Kingdom
Prior art keywords
graticule
magnifier
beam splitter
intensifier
image
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB8040800A
Other versions
GB2090012B (en
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Philips Electronics UK Ltd
Original Assignee
Philips Electronic and Associated Industries Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Philips Electronic and Associated Industries Ltd filed Critical Philips Electronic and Associated Industries Ltd
Priority to GB8040800A priority Critical patent/GB2090012B/en
Publication of GB2090012A publication Critical patent/GB2090012A/en
Application granted granted Critical
Publication of GB2090012B publication Critical patent/GB2090012B/en
Expired legal-status Critical Current

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Classifications

    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B23/00Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices
    • G02B23/12Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices with means for image conversion or intensification

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  • Physics & Mathematics (AREA)
  • Astronomy & Astrophysics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Telescopes (AREA)

Abstract

An injected graticule in a night sight comprising an image intensifier 21 should be provided in a colour distinctive from that of the intensifier phosphor screen, at high resolution, and without the introduction of veiling glare or the annoying obscuration of target detail. A night sight is provided having an observer's magnifier comprising two sets of optical elements 26, 27 between which a graticule injecting beam splitter 28, embedded in a transparent plate 29, is located, occupying only a central strip of the magnifier aperture. The beam splitter may comprise a semi- reflective layer at 45 DEG to the magnifier axis, the optical powers of the two sets of elements being chosen to render the virtual images of an illuminated graticule 30 and the phosphor screen 23 coplanar. The layer may be a multi-layer interference filter having a transmission in the strip at least 90 per cent of that either side of the strip. <IMAGE>

Description

SPECIFICATION Night Sight with Injected Graticule This invention relates to image intensifier night sights and more particularly to providing such sights with an injected graticule.
Image intensifier night sights typically comprise an objective lens, an image intensifier tube and a magnifier. The objective lens focusses a real inverted image of an external scene on the input window of the intensifier tube. The tube increases the brightness of this image and also provides a further image inversion, an erect intensified image being presented to the magnifier on the output window of the tube. The magnifier presents an erect magnified virtual image to the observer's eye and, where necessary sufficient eye-relief between the outermost optical element of the magnifier and the observer's eye to allow for rearward movement of the sight when attached to a weapon having recoil.
Since the magnifier cannot form a real image of the objective aperture, there is no exit pupil as in a conventional daylight telescopic sight. Hence the magnifier is designed to provide a full view of the virtual image by a dark adapted eye pupil when set back from the magnifier by the desired eye relief with adequate tolerance for transverse pupil position.
Image intensifier tubes suitable for such sights may be the so-called "wafer" or proximity focussed tube, for example Philips type XX 0. Such tubes typically comprise a planar fibre optic input window with the photocathode on the inside surface of this window. In sequence, there follows in close proximity a channel plate intensifier section, a phosphor screen and a fibre-optic output window having a 1 80 degree twist in image orientation to provide the further inversion. Alternatively, in another type of tube, for example, Philips type Xxi 501, an electron optical image inversion is provided immediately following the fibre optic input window, foilowed by a channel plate intensifier section, phosphor screen and conventional fibre-optic output window.With either type of tube the input scene real image is focussed onto the usually flat outside surface of the input window and the output image for the magnifier is presented on the outer surface of the output window.
The injection of a graticule for aiming or measuring purposes into the output image of an intensifier sight using the above types of intensifier tube may, in principle, be accomplished in one of several ways. In one way, the graticule is prepared as an opaque pattern on one surface of a transparent plate. The pattern side of this plate is placed in contact with the input window and casts a dark shadow graticule onto the scene details. However, if the target is in a generally dark area of the scene, the graticule may be difficult to discern, especially since it does not differ in colour from the scene details in the intensifier output.
A bright-line graticule of adjustable brightness may be provided by preparing the graticule as a transparent pattern on an otherwise opaque substrate and by injecting this graticule pattern as a collimated beam into the objective lens parallel to the latter's optical axis. The graticule pattern is then imaged on the centre of the intensifier tube input window. The disadvantages with this method are that again the graticule is not distinctive in colour and that resolution degradation as the graticule image passes through the tube produces glare adjacent to the graticule which may obscure target details.
A bright-line graticule may be provided by using an edge-illuminated transparent plate on which the graticule is etched as a light-scattering pattern. This plate may be placed in contact with either the input or output windows, but with the disadvantage that scattering within the plate will produce veiling glare across the whole scene.
It is desirable, then, to provide graticule injection after the intensifier, in a colour distinctive from that of the phosphor screen of the tube and at variable brightness, and at high resolution without the introduction of veiling glare or obscuration of target details. In particular, the injection means should not produce any noticeable diminution of picture brightness in the area adjacent to the target as compared to more remote areas, which diminution would otherwise be of considerable annoyance to the user.
The invention provides a night sight with injected graticule, comprising an objective lens for forming a real image of a scene upon the input window of an image intensifier tube, and a magnifier allowing an observer to view the output window of the intensifier tube, said magnifier comprising two axially separated sets of optical elements between which a beam splitter is arranged across a central part of the magnifier aperture and is inclined to the magnifier axis to reflect light from an illuminated graticule pattern into the line of sight of the observer, wherein the power of the set of optical elements between the beam splitter and the observer is chosen to place the virtual image of the graticule seen in the beam splitter in coincidence with the virtual image of the intensifier output window provided by both sets of optical elements, and wherein the transmission of the beam splitter over the range of wavelengths emitted by the intensifier is at least 90 per cent of the transmission outside said central part.
The beam splitter may comprise a semi-reflective layer embedded in a transparent plate transverse to the magnifier optical axis. To reduce the separation between the two sets of optical elements, the thickness of the transparent plate may be such that the layer extends across only the centre portion of the magnifier aperture.
The layer may comprise a multilayer interference filter which is semi-reflective over a first band of light wavelengths used to illuminate the graticule and is substantially transparent over a second band of light wavelengths in which the intensifier tube phosphor emits, which second band is substantially separate from said first band.
An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a plan view of a night sight, Figure 2 shows a sectional plan view of the image intensifier and magnifier sections of the sight of Figure 1, Figure 3 shows the spectral emissions of the intensifier phosphor P and the graticule light source L, Figure 4 shows the spectral transmission of the transparent plate and of its dichroic layer at a range of angles of incidence of light on the layer, Figure 5 shows ray paths in the magnifier when viewing the phosphor screen, Figure 6 shows the transverse ray aberrations of the magnifier of Figure 5 as a function of distance across the magnifier aperture for three positions in the image field, Figure 7 shows ray paths in the magnifier for light from the graticule, and Figure 8 shows the transverse ray aberrations of the magnifier portion of Figure 7.
Referring to Figure 1, a plan view of a night sight with an injected graticule is shown comprising an objective lens housing 15, an image intensifier and magnifier housing 1 6 having a battery compartment 1 7 and up/down left/right graticule adjusting screws 1 8 and 19, and a rubber eye shield 20. Figure 2 shows housing 1 6 in plan section with the lens housing 1 5 removed. The image intensifier tube 21, a so-called "wafer" or proximity focussed tube, for example a Philips type XX1410, in use receives the real, inverted, image of the scene formed by the objective lens in housing 1 5 on the flat outer surface 22 of its fibre optic input window 24.The intensified output image is presented on the concave outer surface 23 of a fibre optic window which incorporates an image twister to re-erect the scene image. Intensification is provided by a channel electron multiplier plate within the tube, the whole intensifier being energised by a battery in compartment 1 7. Details of the tube operation are not given here, but may be obtained from published literature, since this is not relevant to the invention.
The magnifier 25, so-called to distinguish it from the eyepiece of a conventional telescope which views directly the image formed by the objective lens, comprises two axially separated sets of optical elements 26 and -27 between which is arranged a beam splitter 28 embedded in a transparent plate 29 transverse to the magnifier optical axis.
The graticule details are prepared as a transparency in an otherwise opaque layer 30 embedded in a transparent plate 31. This affords mechanical protection and places surface dust, etc out of focus.
A light source 32 is typically a light emitting diode (LED), for example a CQY 24A, emitting light in a spectral band from 590 nm to 670 nm and having a peak output from 630 nm to 650 nm. The forward current in the LED is controlled by means not shown to adjust the graticule brightness relative to that of the output image of the image intensifier tube. The LED 32 and the graticule plate 30 are mounted in a housing 33 which is square in a cross-section normal to the plane of Figure 2 and is free to slide across surface 34 against which it is spring-loaded by spring 35. A spring loaded plunger 36 urges housing 33 against a stop 37 whose axial position is adjustable by screw 1 9 to provide controlled axial adjustment of the graticule which is viewed as a transverse motion in the beam splitter 28.Up and down adjustment of the graticule is provided by a similar plunger and a stop adjusted by screw 18 (Figure 1).
Figure 3 shows the relative spectral outputs of the intensifier phosphor screen P and the LED L, these being a substantial degree of separation in the bands of light wavelengths emitted.
The beam splitting layer 28 is embedded in plate 29 to provide support and protection, in view of the acceleration forces to which it may be subjected when the sight is attached to a weapon. However, it is desirable to reduce the thickness of plate 29 as far as possible to reduce weight and overall length and to give adequate design latitude for the magnifier. In consequence, the layer 28, which is inclined at 450 to the magnifier axis, extends only over a central part of the magnifier aperture in the form-of a band. Any absorption of phosphor light in this central band would show as a darkened band in the image which would fall across the target area and would give rise to doubt and annoyance of the observer.
The edges of the darkened band are out of focus, assisting to some degree in reducing the visibility of the band. But the annoyance can only be removed if the transmission of the beam splitting layer is not less than 90% of that of the clear regions on either side of the band. The reflectivity of the layer in the band of wavelengths of LED 32 is of less importance since the LED brightness can be adjusted accordingly. To achieve such a transmission factor, advantage is taken of the spectral separation of phosphor and LED outputs, a dichroic layer comprising a multi-layer interference filter being selected for the beam splitter. For example, a 6 layer filter comprising alternating layers of high refractive index (2.40+0.2) and low refractive index (1.70iso.2) materials may be used on a glass substrate, the filter being designed to be cemented between glass plates of refractive index 1.52. The transmission spectrum of such a beam splitter is shown in Figure 4. The curve N shows the transmission of that portion of plate 29 outside the beam splitting area. Three transmission curves for the layer are given covering the range of angles of incidence of phosphor light which occur in the magnifier. In Figure 5 the range of angles of rays in the cones of rays from various points on the image may be seen as they pass through the splitter plate shown between surfaces 7 and 8.In the region of peak phosphor output at 525 nm the plate transmission N is 93%, the best and worst splitter transmissions being 95% and 91%.
Figure 5 shows both sets of optical elements 26, 27 the beam splitter plate 29 and the concave fibre optic output window 23 of a Philips XX1410 intensifier. The parameters of a typical design are given in the following table, all dimensions being in millimetres, V being convex, C being concave.
Surface Radius Central Thickness Separation Nd Vd Aperture stop 20.0 1 28.954V 1.6204 60.33 8.0 2 54.568V 1.75 3 28.654C 2.5 1.7847 25.76 4 185.22V 0.34 5 44.283V 7.0 1.5168 64.17 6 44.283V 0.42 7 PLANO 7.0(19.0) 1.5168 64.17 8 PLANO 9 25.277V 7.9 1.5168 64.17 10 25.277V/C 2.0 1.7847 25.76 11 68.582V 5.83 12 40.00C (Intensifier output window) The effective focal length of the whole magnifier of Figure 5 is 24.38 mm.
Figure 7 shows the set of optical elements 27 between the beam splitter 29 and the observer and the effective thickness, 1 9.0 mm, of the beam splitter 29 to the graticule 30. The separation between the plane input surface on the side of plate 29 and the graticule is 9.18 mm. The effective focal length of this part of the magnifier is 33.10 mm.
The plate 29 is constructed as two separate plates, each having one side bevelled at 450. The layers of the filter are evaporated onto one bevelled side, the two bevelled edges then being cemented together.
Figures 6 and 8 show the transverse ray aberrations for the magnifiers of Figures 5 and 7 respectively. The abberrations are given as a function of ray distance from the centre of the input aperture stop S (eye side) for three field positions, at three values of wavelength, 500 nm, 550 nm, and 600 nm in Figure 6 and 600 nm, 625 nm and 650 nm in Figure 8.
The aperture stop S shown in Figures 5 and 7 is set 20.0 mm from the surface 1 to give adequate eye relief. The diameter of the aperture stop is 14 mm affording adequate iateral tolerance of eye position for a fully dark adapted eye pupil of 7 mm.
In use, the magnifier is focussed at -1.0 to -1.5 dioptres to cope with the field curvature usually present in magnifiers. At the edge of the image, field curvature will reduce this focusing to about -0.5 dioptres. This variation of focus can be accommodated by the eye.

Claims (4)

Claims
1. A night sight with injected graticule, comprising an objective lens for forming a real image of a scene upon the input window of an image intensifier tube, and a magnifier allowing an observer to view the output window of the intensifier tube, said magnifier comprising two axially separated sets of optical elements between which a beam splitter is arranged across a central part of the magnifier aperture and is inclined to the magnifier axis to reflect light from an illuminated graticule pattern into the line of sight of the observer, wherein the power of the set of optical elements between the beam splitter and the observer is chosen to place the virtual image of the graticule seen in the beam splitter in coincidence with the virtual image of the intensifier output window provided by both sets of optical elements, and wherein the transmission of the beam splitter over the range of wavelengths emitted by the intensifier is at least 90 per cent of the transmission outside said central part.
2. A night sight is claimed in Claim 1, wherein said beam splitter comprises a semi-reflective layer embedded in a transparent plate transverse to the magnifier optical axis.
3. A night sight as claimed in Claim 2, wherein said layer comprises a multilayer interference filter which is semi-reflective over a first band of light wavelengths used to illuminate the graticule and is substantially transparent over a second band of light wavelengths in which the intensifier tube phosphor emits, which second band is substantially separate from said first band.
4. A night sight having an injected graticule substantially as described with reference to the accompanying drawings.
GB8040800A 1980-12-19 1980-12-19 Night sight with injected graticule Expired GB2090012B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB8040800A GB2090012B (en) 1980-12-19 1980-12-19 Night sight with injected graticule

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB8040800A GB2090012B (en) 1980-12-19 1980-12-19 Night sight with injected graticule

Publications (2)

Publication Number Publication Date
GB2090012A true GB2090012A (en) 1982-06-30
GB2090012B GB2090012B (en) 1984-04-11

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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0133729A1 (en) * 1983-08-10 1985-03-06 Philips Electronics Uk Limited Graticule illuminator for an image intensifier
EP0156436A2 (en) * 1984-03-23 1985-10-02 Philips Electronics Uk Limited Power supply for an intensified night sight
GB2162654A (en) * 1984-06-13 1986-02-05 Lasergage Ltd Weapons sighting apparatus having image enhancer and graticule injection
EP0181124A2 (en) * 1984-10-25 1986-05-14 Schlumberger Electronics (U.K.) Limited Imaging system
US4721374A (en) * 1985-02-22 1988-01-26 U.S. Philips Corporation Combined night/day viewing apparatus having a large field
US4794246A (en) * 1987-07-10 1988-12-27 Varo, Inc. Universal passive night vision system
GB2211626A (en) * 1987-10-23 1989-07-05 Messerschmitt Boelkow Blohm A reflex sight with night sighting provision

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2144872A (en) * 1983-08-10 1985-03-13 Philips Electronic Associated Graticule illumination system for an image intensifier
EP0133729A1 (en) * 1983-08-10 1985-03-06 Philips Electronics Uk Limited Graticule illuminator for an image intensifier
US4792673A (en) * 1983-08-10 1988-12-20 U.S. Philips Corporation Graticule illuminator for an image intensifier
EP0156436A3 (en) * 1984-03-23 1987-04-08 Philips Electronic And Associated Industries Limited Power supply for an intensified night sight
EP0156436A2 (en) * 1984-03-23 1985-10-02 Philips Electronics Uk Limited Power supply for an intensified night sight
US4629881A (en) * 1984-03-23 1986-12-16 U.S. Philips Corp. Power supply for an intensified night sight
GB2162654A (en) * 1984-06-13 1986-02-05 Lasergage Ltd Weapons sighting apparatus having image enhancer and graticule injection
EP0181124A2 (en) * 1984-10-25 1986-05-14 Schlumberger Electronics (U.K.) Limited Imaging system
EP0181124A3 (en) * 1984-10-25 1989-03-01 Schlumberger Electronics (U.K.) Limited Imaging system
US4721374A (en) * 1985-02-22 1988-01-26 U.S. Philips Corporation Combined night/day viewing apparatus having a large field
US4794246A (en) * 1987-07-10 1988-12-27 Varo, Inc. Universal passive night vision system
GB2211626A (en) * 1987-10-23 1989-07-05 Messerschmitt Boelkow Blohm A reflex sight with night sighting provision
GB2211626B (en) * 1987-10-23 1992-03-04 Messerschmitt Boelkow Blohm A reflex sight with night sighting provision

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Publication number Publication date
GB2090012B (en) 1984-04-11

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PCNP Patent ceased through non-payment of renewal fee