A spyhole viewer

Abstract: A spyhole viewer for a door or wall, having an objective system for producing a real, inverted image and mounted in a tubular member fixedly installable in the door or wall, at least one reflector for angularly deflecting the light beams from the objective system, an erector for inverting the inverted image and located behind at least one of the elements of the objective system, an image surface upon which the real image will appear, a housing fixedly attachable to the tubular member and accommodating at least the reflector and a projection lens mounted therein in coaxiality with the optical axis as deflected by the reflector. The optical axis is angularly deflected at least once on its way from the optical system to the viewing lens.

Description: The present invention relates to a spyhole viewer mountable in doors, walls, etc. Such viewers are known, in particular from U.S. Patents 4,726,670 and 4,892,399. These viewers are superior to earlier spyhole devices inasmuch as both have optics that produce real, projectable images which can be observed from some distance, as distinct from the earlier devices that produced virtual images which required the user's eye to be close to the eyepiece. Yet both of the above prior-art viewers suffer from disadvantages that reduce their usefulness. Both devices, and in particular the device described in U.S. Patent 4,892,399, require large holes to be provided in the door, in the case of the latter even a stepped, two-diameter hole very difficult to produce and certainly unsuitable for do-it-yourself installation, with retrofitting, starting out from an existing, relatively small bore being a very tricky business even for an expert. A further disadvantage of this disclosure is the use of what is, in fact, a double Dove prism 9,9' used as an erector element at the entrance pupil of its optics, in spite of the well-known rule that Dove prisms should only be used with bundles of parallel light beams (which in this system is obviously not the case), as otherwise aberrations will be introduced. The viewer according to U.S. Patent 4,726,670 has several more disadvantages. Its optical system is clearly not a wide-angle system, very important for this sort of application, and in both disclosures the efficiency of their ground-glass screen is severely compromised by its being exposed to ambient light, which greatly reduces contrast. US Patent 4761065 discloses another example of a spyhole viewer having a focussable image surface which is exposed to external incident light. In this case the image surface is provided by a ground glass screen or a Fresnel screen. JP-A-61245125 discloses a wide angle spyhole viewer having a complex objective system comprising a diverging front lens group mounted in a door, and a converging rear lens group which is separated from the front group by a deflecting mirror and which forms a real image in the plane of a field stop, where it can be viewed with the aid of a magnifying lens system. A further drawback common to all these disclosures is that the orientation of the optical axis of the system is fixed. For closer viewing, this forces taller users to stoop, while users of smaller stature may have to stand on their toes and even when viewing the screen from a larger distance, truly satisfactory results are obtained only when the diffusing screen is viewed in a direction more or less perpendicular thereto. It is one of the objects of the present invention to provide a wide-angle spyhole viewer that fits a relatively small hole produceable by a standard spiral drill. It is a further object of the invention to provide a viewer that uses non-distorting erector elements and protects its image screen from incident light, and that preferably permits the optical axis of the viewing side of the device to be tilted to best accommodate the individual user. Having regard to the disclosure in JP-A-61245125, according to the invention there is provided a spyhole viewer for a door or wall comprising: an objective system having an optical axis for producing a real, inverted image and mounted in a tubular member fixedly installable in said door or wall; at least one reflector means for angularly deflecting the light beams from said objective system; and a housing fixedly attachable to said tubular member and accommodating at least said reflector means and a viewing lens mounted therein in coaxiality with said optical axis as deflected by said reflector means; the viewer including erector means located behind said objective system for inverting said inverted image; characterized in that said viewer includes an optical element located inside said viewer between said objective system and at least one of said reflector means and comprising an optical surface upon which the real image produced by said objective system is projected, the optical surface being such that the real image projected thereon can be viewed through said viewing lens, whereby said optical surface is protected against external light incident directly thereon. Specific embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings in which:- Figure 1 is a top view in cross section, of a first embodiment of the viewer according to the invention; Figure 1A is a cross-sectional view of a tubular body carrying a viewing lens and attachable to the first housing part, replacing the second housing part in a variant of the embodiment of Figure 1; Figure 2 is a top view, in cross section, of a second embodiment of the viewer according to the invention; and Figure 3 is a similar view of yet another embodiment, in which the erector is in the form of a bundle of optical fibers. Referring now to the drawings, there is seen in Figure 1 a multilens objective system 2 mounted in a tubular member 4 which is inserted into a bore in the door 6. Due to the fact that the narrow portion of the bundle of light rays entering through, and passing, the optical system 2, is located within the thickness of the door, permits the use of a 12.7 mm (half-inch) bore that has long been the standard bore for spyholes. The advantages of such a relatively small bore, produceable with a standard spiral drill, are obvious. The first part 8 of a two-part housing is attached to the threaded end of the tubular member 4 and locked in position by a ring 10. This housing part 8 accommodates an erector prism 12 of the Amici type and a bullet-proof armour plate 14 for preventing any hard object from being forcibly introduced into the room through the tubular member 4. Inside the tubular member 4, at an appropriate distance from the objective system 2, there is mounted a contrast-improving yet non-distorting Fresnel lens 16, the rear surface 18 of which is ground to form a diffusive screen on which materializes the real, inverted image produced by the objective system 2. The second housing part 20 is attached to the collar-like edge 22 of the first housing part 8 in a way that permits it to tilt about the optical axis A (after deflection by the erector prism 12) as indicated by the double arrow B. The purpose of this tiltability will be explained further below. The second housing part 20 accommodates a reflecting mirror 24 which deflects the optical axis A for a second time and directs it towards a viewing lens 26, through which the now erect image can be viewed by the user U, who may use both eyes. The combination of the Fresnel lens 16, its diffusing back surface 18 protected from incident light and the viewing lens 26 permit the image to be usefully viewed also from a considerable distance, while also preventing the room and any person or persons present in it to be observed from the outside of the door. For best viewing, the line of sight of the user U should be perpendicular to the general plane of the viewing lens 26. This becomes more important the closer one approaches the viewing lens, e.g. to observe details. The above-mentioned tilting feature allows easy adjustment to the individual height of the user. In a variant of this embodiment, conveniently used in narrow corridors with doors located along one of the lateral walls, the second housing part 20 with its deflecting mirror 24 is replaced by a tubular body 28 (Figure 1A) attachable with its open rim 30 to the above-mentioned collar-like edge 22 of the first housing part 8 and mounting the viewing lens 26. In this embodiment, the optical axis A is deflected only once (by the erector 12), enabling the viewer to observe the corridor from the side of the door. While this embodiment does not have the tiltability feature, an embodiment can be envisaged in which the tubular body will be tiltable, too, for instance by making the housing 8 rotatable about the axis of the tubular member 4. The embodiment of Figure 2 has a more elaborate objective system, affording an even wider viewing angle (over 100°). The Fresnel lens 16 is now located after the erector 12. Otherwise, there are no essential differences between this embodiment and that of Figure 1. In the embodiment of Figure 3, the erector element is a bundle of coherent optical fibers 34 which has been given a twist of 180°. Thus the image elements entering the bundle at its front end 36 exit it at its rear end 38, producing a real, erect image which is reflected by the reflector 32 onto the reflector 24 and thence through the viewing lens 26. The optical axis A is thus deflected twice, as in the embodiments of Figures 1 and 2. For improved contrast, a Fresnel lens can be added to the rear end 38 of the fiber bundle 34. In a per se known manner, the fiber bundle 34 is used here also to enlarge the image by spreading the end points of the fibers over a larger surface - compare the two faces 36 and 38 - or by using tapering fibers. By making the bundle 34 longer and flexing it by 90°, it could also be used to deflect the optical axis A, dispensing with the reflector 32. While roof-type prisms indeed give best results as erectors, fairly satisfactory service could also be obtained from a pair of mirrors arranged in a roof-like configuration. For best results, all reflector mirrors should be first-surface mirrors. It should also be noted that at least some of the elements of the objective systems 2 could consist of aspherical lenses. It should be understood that the above-explained tiltability feature is optional only and that the embodiments represented would also give valuable service without that feature. It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrated embodiments and that the present invention may be embodied in other specific forms without departing from the scope of the invention as defined by the following claims.

Claims: A spyhole viewer for a door or wall (6), comprising: an objective system (2) having an optical axis (A) for producing a real, inverted image and mounted in a tubular member (4) fixedly installable in said door or wall (6); at least one reflector means (12,24; 32,24) for angularly deflecting the light beams from said objective system (2); and a housing (8,20;8,28) fixedly attachable to said tubular member (4) and accommodating at least said reflector means (12,24; 32,24) and a viewing lens (26) mounted therein in coaxiality with said optical axis (A) as deflected by said reflector means (12,24; 32,24); the viewer including erector means (12; 34), located behind said objective system (2), for inverting said inverted image; characterized in that said viewer includes an optical element (16; 34) located inside said viewer between said objective system (2) and at least one of said reflector means (12,24; 32,24) and comprising an optical surface (18; 38) upon which the real image produced by said objective system (2) is projected, the optical surface (18; 38) being such that the real image projected thereon can be viewed through said viewing lens (26), whereby said optical surface (18; 38) is protected against external light incident directly thereon. The spyhole viewer as claimed in claim 1, wherein said objective system (2) is a multi-element wide-angle system. The spyhole viewer as claimed in claim 1, wherein at least one element of said objective system (2) is an aspherical element. The spyhole viewer as claimed in claim 1, wherein said at least one reflector means comprises a plane mirror (24) which is arranged to deflect said optical axis (A) by at least approximately 90° and is mounted in said housing (8) in proximity to said viewing lens (26). The spyhole viewer as claimed in claim 1, wherein said erector means is a prism-type erector (12) mounted in said housing (8). The spyhole viewer as claimed in claim 5, wherein said prism-type erector (12) is an Amici roof prism. The spyhole viewer as claimed in claim 1, wherein said erector means is a mirror-type erector mounted in said housing (8). The spyhole viewer as claimed in claim 1, wherein said erector means is a coherent bundle of optical fibers (34), twisted by 180° and at least partly located and mounted in said tubular member (4). The spyhole viewer as claimed in claim 1, wherein said optical element is a Fresnel lens (16), and said optical surface is constituted by the ground rear surface (18) of said Fresnel lens (16). The spyhole viewer as claimed in claim 8, wherein said bundle of optical fibers constitutes said optical element, and said optical surface is constituted by the end face (38), remote from said objective system (2), of said bundle of optical fibers (34). The spyhole viewer as claimed in claim 9, wherein said Fresnel lens (16) is mounted in said tubular member (4). The spyhole viewer as claimed in claim 9, wherein said Fresnel lens (16) is mounted in said housing (8). The spyhole viewer as claimed in claim 4, wherein said reflector means comprises an additional reflector (32) mounted in said housing (8) in proximity to said tubular member (4). The spyhole viewer as claimed in claim 4, wherein said housing is a two-part housing, the first part (8) whereof is fixedly attachable to said tubular member (4) and the second part (20) whereof, accommodating said plane mirror (24) and said viewing lens (26), is capable of being swivelled about an axis (B) perpendicular to the axis of said tubular member (8). The spyhole viewer as claimed in claim 14, wherein said second housing part (20) is replaced by a tubular body (28) attached at one of its ends to said first housing part (8) and comprising at its other end an image-intensifying viewing lens (26). The spyhole viewer as claimed in claim 1, further comprising an armour plate (14) mounted inside said housing (8) behind said tubular member (4).

Inventors: GOLDSTEIN PINCHAS, GOLDSTEIN, PINCHAS
Applicants: GOLDSTEIN PINCHAS, GOLDSTEIN, PINCHAS
Application year: 1992
Main classification: G02B25
IPC codes: G02B23, G02B25