Photography – Camera support – Surveillance type
Patent
1997-06-06
1999-10-26
Mathews, Alan A.
Photography
Camera support
Surveillance type
396351, 348143, 352242, G03B 1700, H04N 718
Patent
active
059716312
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to transparent or partly transparent windows or similar components for optical systems, which cannot be formed as a single, flat plate owing to the wide viewing angle required. For example, the window may constitute transparent protection for a long-range camera.
BACKGROUND TO THE INVENTION
It is known to make clear and colored lens covers for warning lights in the form of cylinders, hemispheres and cones. In these contexts the precise behavior of an optical ray passing through the window is seldom significant, slight distortions are easily tolerated and indeed, some diffusion may be required or deliberately introduced.
For a device such as a long range camera, however, curvature in the window introduces progressively varying refractional effects across the field of view. This impairs the geometry of the incident beam at the camera by disturbing the notional parallelism and distribution of the incoming beam, and the resulting degradation of the image can become intolerable.
SUMMARY OF THE INVENTION
The invention is based on an improved enclosure window for use with an omni-directional optical system, which is preferably a long-range surveillance camera but might be an optical projector. The window is constituted as a number of angled, discrete plates or segmented areas with localised bends or narrow joints, rather than as a continuously curving surface. In this way, for example, a 360.degree. window can be formed from, for example, seven or eight flat segments. A camera located within the window area and directed outwards will then, for most conditions, be operating through a single flat window region. When the line-of sight does include an interface between two such flat segments or panes, the resulting distortion of the image is relatively less pronounced to the eye, since unlike the situation with a continuously curved window, it then approximates to two distinct images almost super-imposed.
Any reasonable number of flat or substantially flat segments or panes of which the broad faces are flat and mutually parallel may be disposed about a curved profile to accommodate a desired viewing region, but for the most satisfactory performance the angle which each effectively subtends should be large in relation to the beam width of the optical device. Indeed, too many segments would cause the window to approximate a continuous curve and become subject to more complex image distortions. Preferably there are more than six and fewer than thirteen segments. Any solid angle subtended by a local bend or joint should be minimized to preserve the useful area of the window
Various possible manufacturing methods exist. For example, an omni-directional window may be formed form a suitably shaped single sheet of semi-flexible transparent material by the machining of grooves on an inside surface to delineate the joints between the segments or panes and then folding the sheet along the length of each machined groove. A suitable adhesive may be applied sparingly at the machined grooves to improve the mechanical strength of the assembly. This method of manufacture provides a continuous external seal to the window without reliance on adhesive or other sealant.
Alternatively, separate plates may be cut to profiles and angles determined by the number of plates to be used, and chamfered at their abutting edges to provide mating surfaces at assembly. Adhesive or other sealant may be used for assembly if required, or to maintain an environmental protection.
A similar assembly may be obtained by injection molding, provided the flat surfaces are maintained over a sufficiently wide area of each window segment.
BRIEF DESCRIPTION OF THE DRAWING
Further features of the invention will be apparent from the following description, with reference to a preferred but non-limiting example shown in the accompanying drawings wherein:
FIG. 1 illustrates in section a camera head assembly incorporating the present invention;
FIG. 2 is a cut-away sectional view of the assembly shown in FIG. 1, the
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Poole Neal John
Urwin Jonathan
Farley Walter C.
Mathews Alan A.
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