1986-05-12
1988-02-23
Henry, Jon W.
350576, 350573, G02B 702, G02B 2316, G02B 2504
Patent
active
047266708
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
This invention relates to a security viewer to be mounted through a non-transparent partition, for example a door.
Security viewers for doors are well known and one example is described in GB Patent Specification No. 1 129 121. This known viewer consists of a spy glass which is mounted in a hole drilled through the door and acts in the manner of a spy glass to permit a person on the inside of the door to observe callers at the door. A disadvantage of the known spy glass type of security viewer is that its optical system needs to provide a wide field of view and consequently the image produced is somewhat distorted so that an observer of the inside of the door may have difficulty in identifying and recognising a caller. Also, with the known viewer, the observer needs to place his or her eye against the door in order to observe the image formed by the spy glass. Usually, the spy glass is mounted approximately 2 meters from the base of the door and consequently cannot be readily used by the elderly and the infirm.
In accordance with the invention there is provided a security viewer which provides an image of reduced distortion and which can be observed without the need for the observer to place his or her eye against the door.
In accordance with the invention, the security viewer comprises a housing for extending through a partition such as a door, the housing including an inlet aperture for collecting light from a first side of the partition, a screen for being observed from a second oppossite side of the partition, and lens means for forming from the collected light a real image on the screen of the field of view on the first side of the partition.
The formation of the real image on the screen has the advantage that the image of the field is observable from positions spaced from the partition so that the observer does not need to place his or her eye against the partition as in the prior art.
In a preferred from of the invention, the housing of the security viewer includes a tubular portion to be fitted through the hole in the partition, the tubular portion having the inlet aperture at one end thereof. An outer bezel is arranged to be fitted on to the end of the tubular housing portion so as to abut the partition. Also, an inner bezel is slidably mounted on the tubular housing portion and in use is glued in an appropriate position depending on the thickness of the door.
Preferably the lens means comprises an even number of biconvex lenses e.g. four arranged coaxially within the tubular portion of the housing. The four lenses are conveniently identical and have different radii of curvature on their opposite faces. In one embodiment, the face of each lens with the greatest curvature radius is arranged facing the screen but I have also found that by turning round one of the lenses, an improved image sharpness is produced. Preferably, a protective transparent member is arranged spanning the inlet aperture. Conveniently, the protective transparent member may be held in place by means of the outer bezel.
The screen is conveniently made of ground glass. In one embodiment, the screen is 35 mm square and thus provides an image which is observable from up to 3 or 4 meters from the partition.
In order that the invention may be more fully understood and embodiment thereof will now be described by way of illustrative example with reference to the accompanying drawings in which:
FIG. 1 is a schematic perspective view of a security viewer according to the invention; and
FIG. 2 shows the viewer of FIG. 1 in transverse section mounted in a door, the door being shown in hatched outline.
The security viewer consists of an elongate housing 1 formed of cooperating moulded plastics parts 2, 3 typically made of ABS material. The housing parts 2, 3 define a tubular portion 4 and an outwardly tapered portion 5. The tubular portion 4 in use is inserted through a hole 6 in a partition 7, typically a door of the building. The tubular portion 4 contains at one end thereof an inlet aperture 8 which collects light from one s
REFERENCES:
patent: 1682139 (1928-08-01), Mitchell
patent: 2262203 (1941-11-01), Redstone et al.
patent: 2638810 (1953-05-01), Berleme
patent: 3434773 (1969-03-01), Pitchford
patent: 3973835 (1976-08-01), Miyakawa et al.
patent: 4257670 (1981-03-01), Legrand
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