WO2005109071A1

WO2005109071A1 - Wide angle viewing device

Info

Publication number: WO2005109071A1
Application number: PCT/IB2005/001235
Authority: WO
Inventors: Milan Momcilo Popovich; Antoine Yvon Messiou
Original assignee: Milan Momcilo Popovich
Priority date: 2004-05-10
Filing date: 2005-05-09
Publication date: 2005-11-17

Abstract

An improved door viewer providing a large area viewable image is disclosed, comprising a wide-angle lens (1), a multiple reflection lens (2) and a diffusing screen (4). The multiple reflection lens comprises a first transmitting surface (12) operative to admit external scene light, second (24a) and third (24b) transmitting surfaces for transmitting light towards a viewer and first (21a) and second (23a) reflecting surfaces. The second reflecting surface surrounds the first transmitting surface. The first reflecting surface surrounds the second transmitting surface. The third transmitting surface surrounds both the first reflecting surface and the second transmitting surface. Low incidence angle light entering first transmitting surface passes through the second transmitting surface towards the viewer. High incidence angle light entering the first transmitting surface, is reflected at the first reflecting surface, reflected at the second reflecting surface, and passes through the third transmitting surface towards the viewer. Said ray paths traverse at least one light-refracting medium.

Description

TDE ANGLE VIEWING DEVICE

This application claims the benefit of the United States Provisional Patent Application No. 60/569,295 by the same inventors filed on 10 May 2004.

BACKGROUND OF THE INVENTION

This invention relates to a viewing device, and more particularly to a wide angle viewing apparatus for security applications.

Door viewers for home security are well known. One common approach provides a peephole incorporating a miniature wide-angle lens. Peepholes suffer from the problem that the viewer's face must be pressed against a tiny hole, which is not ideal for elderly and handicapped people and children.

United States Patent No. 4,082,434 discloses a wide-angle door viewer comprising a concave objective lens, an intermediate concave lens and a convex eyepiece lens. The eyepiece lens is positioned at a predetermined distance from the objective lens. The intermediate lens corrects the aberration of the erect virtual image formed by the objective lens. The eyepiece lens magnifies the image formed by the intermediate lens. A magnified final erect virtual image is formed on the eyepiece lens. The 4,082,434 apparatus suffers from the problem that the location of the virtual image makes it impractical to insert a diffusing screen to provide a real image. Therefore, the user's eye must be positioned close to the eyepiece lens. Further, the small effective diameter of the concave objective lens results in a dim image. Increasing the effective diameter of the concave objective lens to provide a brighter image will allow visual access from outside unless a shutter is incorporated into the viewer.

United States Patent No. 4,257,670 discloses an optical peephole device comprising three lens assemblies disposed serially along a common optical axis. The first assembly provides a doublet comprising a thick-edged meniscus and a double-concave lens. The second assembly comprises five identical plano-convex lenses equidistantly spaced from each other. The third assembly provides accommodation and comprises a plano-convex lens and an eyepiece. An erect virtual image formed by the meniscus is converted into an inverted real image by the plano-convex lens. The other plano-convex lenses correct aberrations and performs a second inversion on said inverted real image, such that the final erect real image is formed on the plano-convex lens. The disadvantage of the 4,257,670 apparatus is that although the image derived from the planoconvex lens is erect and real, the luminance of the final image suffers from the transmission losses incurred by the large number of lenses. As in the case of the 4,082,434 apparatus it is not possible to provide a real image and consequently the user's eye must be positioned close to the eyepiece. Furthermore, the device is not suitable for typical domestic door applications due to its large overall length.

United States Patent No. 4,892,399 by Ohn discloses a door viewer comprising two prisms of rectangular isosceles triangle shape in cross section whose hypotenuse surfaces abut horizontally, a front convex lens, an intermediate plano-convex lens and a plano-convex eyepiece lens. The front convex lens has a front concave surface and a rear convex surface to correct chromatic aberration. The convex surfaces of the intermediate and eyepiece lenses are positioned face to face with each other to correct barrel distortion. The door viewer casts an image onto a ground glass screen formed on or provided abutting the eyepiece lens.

Door viewers based on the principles of the Ohn device are capable of providing a small real image, typically 25-60 millimeters in size, that can be viewed from a small distance. A commercially available door viewer based on the Ohn invention, known as the Ultra Vista door viewer, is distributed via the internet website www.doorviewers.ca. The Ultra Vista door viewer provides a 132 horizontal field of view and has an output image screen size of approximately 57 millimeters diameter. The image may be viewed from a range of approximately 2 meters and has the appearance of a miniature television display. The required door opening size is 56 millimeters for door thicknesses in the approximate range 20 to 45 millimeters. However, door viewers based on the Ohn invention suffer from the problem that the viewing screen size roughly determines the size of the door hole. It is therefore difficult to provide a large area screen using a viewer designed according to the principles of the Ohn invention. There are several problems to be overcome in designing a door viewer with a small door aperture and a large area screen. To achieve a high image brightness the lens system requires a numerically low F- number, where F- number is defined as the focal length of the image projection lens divided by the effective aperture of the lens.

There are trade-offs to be made between the angle of surveillance, the range of screen viewing angles available to users, screen size and door size. Basic optical theory dictates that product of the entrance pupil area multiplied by the light collection solid angle corresponding to the field of surveillance should be roughly equal to the maximum screen viewing solid angle multiplied by the screen area. Providing a door viewer with a large viewing screen, a wide field of surveillance and a wide viewing angle will tend to increase the size of the entrance pupil. This in turn will increase the overall diameter of the lens and hence the size of door hole required.

In order to minimize the thickness of the door viewer the projection screen should have a large bend angle. In other words, the screen should be capable of directing light incident at a steep angle to the screen surface into an average direction substantially normal to the screen surface. It is difficult to maximize the photometric and screen thickness requirements simultaneously.

United States Patent No. 6,511 ,186 by Burstyn et al discloses a screen in which light rays having acute incidence angles of a screen are deflected into the viewing space by Total Internal Reflection (TIR) Fresnel lens elements or by diffractive elements. However, the apparatus disclosed by Burstyn is not suitable for numerically small F-number illumination due to the small dimensions of the Fresnel lens facets.

There is a need for a low cost door viewer that offers a large viewable area, ideally around 100 to 150 millimeters diagonal. The field of view should be 130 degrees horizontal. The installation requirements should be no more demanding in terms of door alterations and installer skill than existing technologies. The screen should be viewable from a range of around 2 meters and for a representative range of viewer heights. Desirably, the door hole size should be in the range 40-60 mm. The device should have minimal projection from the front or rear surfaces of the door. Thus there exists a need for an improved door viewer that can provide a wide field of surveillance, a large area viewable image and a thin form factor requiring only a small door aperture.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved door viewer that can provide a wide field of surveillance, a large area viewable image, and a thin form factor requiring only a small door aperture.

The objects of the invention are achieved in a first embodiment comprising a multiple reflection lens system a wide-angle lens system and a diffusing screen. The wide-angle lens system is optical coupled to the multiple reflection lens system and is disposed between the multiple reflection lens and the external scene. The multiple reflection lens system comprises a first transmitting surface operative to admit light from an external scene into the door viewer, a second transmitting surface for transmitting light towards a viewer; a third transmitting surface for transmitting light towards a viewer; a first reflecting surface; and a second reflecting surface. A first multiplicity of optical paths from said external scene to the viewer passes through the first transmitting surface, traversing at least one light refracting medium and passing through the second transmitting surface towards the viewer. A second multiplicity of optical paths from said external scene to said viewer passes through the first transmitting surface, undergoing a first reflection at the first reflecting surface and a second reflection at the second reflecting surface, and passing through the third transmitting surface towards the viewer, said paths traversing at least one light refracting medium. The first multiplicity of optical paths corresponds to incident light having an angle of incidence at the first transmitting surface less than or equal to a predefined value and said second multiplicity of optical paths corresponds to incident light having an angle of incidence at the first transmitting surface greater than said predefined value.

The second reflecting surface surrounds the first transmitting surface. The first reflecting surface surrounds the second transmitting surface and the third transmitting surface surrounds both first reflecting surface and the second transmitting surface. In a preferred operational configuration the second transmitting surface, the first reflecting surface and the third transmitting surface lie on a first single continuous surface and the first transmitting source and the second reflecting surface lie on a second single continuous surface. Said first and second single continuous surfaces enclose at least one refractive index medium.

At least one of the second or third transmitting surfaces of the multiple reflection lens system may have diffusing characteristics.

Each surface of the multiple reflection lens system may be characterized by one of a spherical, Fresnel, diffractive or aspheric optical surface form. Each surface of the multiple reflection lens system may have an anamorphic surface form.

At least one of the first and second reflecting surfaces of the multiple reflection lens system may function as a total internal reflection surface. At least one of the first and second reflecting surfaces of the multiple reflection lens system may have a reflective coating.

The diffusing screen is disposed between the multiple reflection lens system and the viewer. Said diffusing screen comprises a central portion disposed between the second transmitting surface of the multiple reflection lens system and the viewer and a surrounding portion disposed between the third transmitting surface and the viewer. The central portion of the diffusing screen is designed to bend rays emerging from the central portion of the multiple reflection lens into a viewing direction substantially normal to the diffusing screen surface.

All of the optical surfaces of the door viewer may have a common axis of symmetry.

In a second embodiment of the invention similar to the first embodiment a further lens system is disposed between the second transmitting surface of the multiple reflection lens system and the central portion of the diffusing screen.

In a third embodiment of the invention similar to the first embodiment the multiple reflection lens systems is divided into two air spaced portions such that the first and second multiplicity of ray paths each traverse at least one air space. The air space is enclosed by a pair of opposing optical surfaces. Said opposing surfaces may have any of the optical surface forms used in the first embodiment and may each comprise more than one type of optical surface form.

In another embodiment of the invention similar to the first embodiment the first multiplicity of optical paths corresponds to incident light having angles of incidence less than the critical angle at the first reflecting surface. The second multiplicity of optical paths corresponds to incident light having angles of incidence greater than or equal to the critical angle at the first reflecting surface.

A more complete understanding of the invention can be obtained by considering the following detailed description in conjunction with the accompanying drawings wherein like index numerals indicate like parts. For purposes of clarity details relating to technical material that is known in the technical fields related to the invention have not been described in detail.

BRIEF DESCRIPTION OF THE DRAWINGS FIG.l A is a schematic three-dimensional view of an operational configuration of then invention. FIG. IB is a schematic three-dimensional view of an operational configuration of then invention. FIG.2A is a schematic side elevation view of a first embodiment of the invention. FIG.2B is a schematic rear elevation view of a first embodiment of the invention. FIG.3 is a schematic rear elevation view showing the central and peripheral regions of the displayed image.

FIG.4 is a schematic side elevation view showing the propagation of rays in a first embodiment of the invention.

FIG.5 is a schematic side elevation view of a second embodiment of the invention. FIG.6 is a schematic side elevation view showing the propagation of rays in a second embodiment of the invention.

FIG.7 is a schematic side elevation view of a further embodiment of the invention. FIG.8 is a schematic side elevation view of a yet further embodiment of the invention. FIG.9 is a schematic side elevation view of a yet further embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION The basic concept of a door viewer according to the principles of the invention is shown in FIG.1. FIG.1 A shows a schematic three-dimensional view of a door viewer. The door viewer comprises a wide-angle lens system 10, multiple reflection lens system 20 and a viewing screen element 30. FIG1B shows a schematic side elevation showing the door viewer in a typical operational configuration. The wide-angle lens system is inserted into a cylindrical hole in the door 50. In FIG.1 A the input rays are generally indicated by 1000 and the output rays are generally indicated by 2000. It should be noted that FIG.1 is provided only for the purposes of showing the approximate appearance of the invention in a typical operational configuration. The details of the optical system are discussed in the descriptions of the embodiments of the invention given below.

A first embodiment of the door viewer is illustrated schematically in FIG.2. According to FIG.2 A the door viewer comprises a wide-angle lens system 1 a multiple reflection lens system 2 and a diffusing screen 4. The wide-angle lens system comprises at least a front refracting surface 11 and a surface 12 that provides the entrance surface to the multiple reflection lens system. Surface 12 may be an internal surface of the wide-angle lens. Alternatively, surface 12 may be the rear surface of the wide-angle lens, said rear surface being either in contact with or air- separated from the multiple reflection lens system. Alternatively, the wide-angle lens may form part of the multiple reflection lens system, with surface 12 corresponding to a virtual surface separating the wide-angle and multiple reflection lens systems.

The multiple reflection lens system comprises the entrance surface 12, the curved reflecting surfaces 21a, 21b, a central curved surface portion 22, the curved reflective surface portions 23a, 23 b and the curved transmitting surface portions 24a, 24b. In a preferred embodiment of the invention surfaces 21a, 12, 21b form a first single continuous surface and surfaces 24a, 23a, 22, 23b, 24b form a second single continuous surface. Said first and second surfaces enclose at least one refracting medium. Desirably the refracting medium is an optical plastic. Alternatively the refracting medium many be an optical glass. For the purposes of describing the invention the lenses will be assumed to be axi-symmetric and the invention will be discussed in terms of rays confined to the meridional plane intersecting the points AA'. It will also be understood that that curved reflecting surfaces 21a, 21b and 23a, 23b and curved transmitting surface portions 24a, 24b represent intersection of annular surface areas with said meridional plane. Hence, the multiple reflection lens system comprises the entrance surface 12, the curved reflecting surfaces 21a, 21b, a central curved surface portion 22, the curved reflective surface portions 23a, 23b and the curved transmitting surface portions 24a, 24b. FIG.2B provides a rear elevation vide view of the rear surface of the multiple reflection lens system showing the disposition of the actual surface portions corresponding to meridional section surfaces 24a, 23a, 22, 23b, 24b.

For the purposes of the invention a wide angle lens means a lens element or system of lenses capable of collecting light with incidence angles from 0 degrees to greater than ±60 degrees. The wide-angle lens system may be a multi element wide-angle lens with an internal aperture stop. Alternatively the lens may be designed to have an external stop as, for example, in a landscape lens. The wide-angle lens system may be comprised of spherical, aspherical, diffractive and other surface forms known to those skilled in the art. The invention is not limited to any particular type of wide-angle lens configuration. In a practical implementation of the invention the wide-angle lens will also include optical elements to reverse the orientation of the image in one or both of the vertical and horizontal directions. Methods for inverting and erecting images are known to those skilled in the art. For example, the image inverting elements comprise a system of lens. Alternatively, the image inverting elements may comprise prisms as used in US Patent No. 4,892,399 by Ohn, for example. The apparatus for inverting and erecting the image does not form part of the present invention.

The reflecting surfaces of the multiple reflection lens system may rely on total internal reflection. Alternatively, the reflecting surface may use mirror coatings.

The screen 4 is fabricated from a rear projection screen material having a suitable diffusion angle. The diffusion angle will be determined from consideration of the required range of viewing distances and viewer heights. As shown in FIG.2 the screen comprises a central portion 41 and outer annular portion represented by 42a, 42 according to the earlier defined geometrical convention. The central portion 41 and the outer portions 42a, 42b of the screen may be designed to provide different diffusion characteristics. For example, the central and outer positions may be fabricated from different materials. Alternatively, the central and outer portions may have different structures. One or both of the screen portions may incorporate diffractive structures, which are designed to have combined light bending and diffusing properties. The screens may be based on Fresnel surfaces. One or more portions of the screen may employ holographic light shaping diffusers. The screen may be physically separated from the surfaces of the lens 3 and the multiple reflection lens 2. Alternatively the screen may abut the surfaces the lens 3 and the multiple reflection lens 2. The screen may be curved. The screen may be implemented on one or both of the outer surfaces of the multiple reflection lens 2 as a thin layer of scattering material deposited onto said outer surfaces or a surface relief structure formed in said outer surface.

The formation of the viewed image using the apparatus of FIG.2 is now explained with reference to FIG.3 and FIG.4. FIG3 illustrates the geometrical characteristics of the image displayed on the screen. A central circular image portion 300 is formed as a result of low incidence angle light propagating through surface 11 of the wide-angle lens system element, the virtual interface 13, surface 22 of the multiple reflection lens system, lens 3 and screen element 41. An annular image region 400 substantially abutting the circular region is formed as a result of high incidence angle light propagating through surface 11 of the wide angle lens system and the virtual interface 13, undergoing reflections at surfaces 23a, 23b and 21a, 21b, and propagating through transmitting surfaces 24a, 24b and screen elements 42a, 42b. The effect of any visible join between the central and annular regions 300,400 can be minimized by careful optical design. However, a visible boundary is likely to acceptable for most applications. The formation of the image regions 300 and 400 will now be explained in more detail with reference to FIG.4.

FIG.4 shows the propagation of incident light rays in the meridional plane. We consider a low incidence angle ray 100 and a high incidence angle ray 200. The ray 100 is the limiting ray that corresponds to the edge of the circular region 300. In other words rays with incidence angles equal to or less than that of the ray 100 will be imaged in the circular region 300. The ray 200 is the limiting ray that defines the inner edge of the outer annular region 400. In other words rays with incidence angles equal to or greater than that of the ray 200 will be imaged in the annular image region 400. The paths of the rays inside the wide-angle lens systems are represented by the dashed lines 101 , 201. In practice the precise ray paths will depend on the type of wide- angle lens and the type of image rotation mechanism incorporated within the lens. Since the details of the wide angle lens and the image rotator, in particular, do not form part of the present invention the ray paths have not been shown in detail. After propagation through the wide-angle lens the rays 101, 201 enter the multiple reflection lens as the rays 102 and 202 respectively.

We first consider the propagation of the incident ray 200 after propagation through the wide- angle lens and into the multiple reflection lens system 2. The ray 202 intercepts the first reflective surface 23a and is reflected in the direction 203 towards the second reflective surface 21a where it is reflected into the direction 204. The reflected ray 204 impinges on the refracting surface 24a where it is refracted into the direction 205 towards the screen element 42a. The ray is scattered at the screen element 42a into the diffuse ray directions generally indicated by 206.

We now consider the propagation of the incident ray 100 after propagation through the wide- angle lens and into the multiple reflection lens system 2. The ray 102 intercepts the central refracting surface 22 where it is refracted into the ray direction 103 towards the diffusing screen element 41. The screen element 41 is designed to bend rays emerging from the central portion of the multiple reflection lens into a viewing direction substantially normal to the screen surface. Finally the ray 1034 is scattered by the screen element 41 into the diffuse directions generally indicated by 104.

A second embodiment of the proposed wide angle-viewing device is illustrated schematically in FIG.5. The viewing device comprises the wide-angle lens system 1 and multiple reflection lens system 2 and the diffusing screen 5 and a further lens system 3. Since the characteristics of the wide-angle and multiple reflection lens systems are similar to those of the embodiment shown in FIGS.2-4 the same labels have been used to describe the surface elements. The screen 5 may be based on any of the surface types discussed in relation to the embodiments shown in FIGS.2- 4. The screen comprises a central portion 51 and an outer surrounding portion represented by 51a, 51b. Said inner and outer portions may have substantially different scattering properties. FIG.6 shows the propagation of incident rays in the meridional plane. The rays are defined in a similar fashion to the rays 100,200 of FIG.4. We consider a low incidence angle ray 110 and a high incidence angle ray 210. The paths of the rays inside the wide-angle lens systems are represented by the dashed lines 111, 211 where once again the illustration of the light propagation inside said lens has been simplified for the purposes of explaining the invention. After propagation through the wide-angle lens the rays 111, 211 enter the multiple reflection lens as the rays 112 and 212 respectively.

We first consider the propagation of the incident ray 210 after propagation through the wide- angle lens and into the multiple reflection lens system 2. The ray 212 intercepts the first reflection surface 23 a and is reflected in the direction 213 towards the second reflection surface 21a where it is reflected into the direction 214. The reflected ray 214 impinges on the refracting surface 24a where it is refracted into the direction 215 towards the screen element 52a. The ray 215 is scattered by the screen element 52a into diffuse ray directions generally indicated by 216.

We next consider the propagation of the incident ray 110 after propagation through the wide- angle lens and into the multiple reflection lens system 2. The ray 112 intercepts the central refracting surface22 where it is refracted in the ray direction 113 towards the lens element 3. The lens element 3 directs the ray 113 into a direction 114 towards the diffusing screen region 51. Desirably the ray 114 is substantially normal to the screen region 51. Finally, the ray 114 is scattered by the screen element 51 into the diffused directions generally indicated by 115.

In a further embodiment of the invention, similar to the first embodiment, the wide-angle lens system and the multiple reflection lens system may be separated as shown in FIGS.7. The wideangle lens system 6 comprises at least a front refracting surface 61 and a rear surface 62. The wide-angle lens may also incorporate an image rotator as discussed earlier. One advantage of having a separation between the wide-angle lens and the multiple reflection lens is that two curved surfaces are available for optimization. The basic imaging properties of the embodiment of FIG.7 are similar to those of the embodiment shown in FIG.2-4. In a yet further embodiment of the invention similar to the first embodiment, shown in FIG.8, the multiple reflection lens system may be divided into two elements having opposing separated surfaces 25 and 26 as shown in FIG.8. Such an arrangement would provide a further two surfaces separated by an air gap for design optimization. Said surfaces may have any of the surface forms discussed earlier. Surfaces 25 and 26 may each be continuous composite surfaces comprising more than one surface form. For example, said composite surfaces may have central circular portions and outer annular portions. Alternatively, surfaces 25 and 26 may have identical but opposite curvatures such that there is no air gap between the two elements. Surfaces 25 and 26 may be planar as shown in FIG.8. Dividing the multiple reflection lens into two thinner elements may offer cost benefits if moulding processes are used to fabricate the lens elements. The basic imaging properties of the embodiment of FIG.8 are similar to those of the embodiment shown in FIG.2.

FIG.9 shows a further embodiment of the invention in which the multiple reflection lens system is divided into two elements having the opposing separated curved surfaces 27 and 28. Said surfaces may have any of the surface forms discussed earlier. For example, 27 and 28 may each be continuous composite surfaces comprising more than one surface form. Said composite surfaces may have central circular portions and outer annular portions.

The basic invention is not restricted to door security viewers. Possible applications include viewers for use in vehicles and process monitoring. The invention could be used to provide visual access in many application domains where cost factors, hazardous environments or privacy requirements preclude the use of windows.

Image formation by the door viewer has been described in terms of rotationally symmetric optical surfaces. However, the viewer may also use optical elements on based other forms such as cylindrical elements or anamorphic optical elements. The optical elements discussed in FIGS2-8 may be fashioned to provide elliptical cross sections. Alternatively, portions of the optical elements may be removed to provide rectangular cross sections. In a typical door viewer application the subject being viewed is likely to be in line with or below the optical axis of the viewer. Hence, the emergent rays corresponding to the centre of the subject will typically be along the optical axis or at some angle above the optical axis. It is therefore desirable that the viewing screen should have asymmetrical diffusion properties such that light hitting the screen is bent towards the nominal viewing position.

The design of the door viewer will require careful optimization to maximize light throughput and minimize aberrations and distortions. For example, chromatic aberration may be traded off against image distortion.

The refracting and reflecting surfaces of the door viewer may employ spherical, aspherical, diffractive and other optical surface forms known to those skilled in the art. Diffractive optical surfaces in particular may play a key role in optimizing the performance. The use of diffractive optical surfaces will offer considerable form factor benefits, including reducing the required door hole size and minimizing the distance of the viewer screen from the door surface. Any of the optical surfaces used in the viewer may incorporate diffractive forms for the purposes of color correction. Further benefits of using diffractive surface forms include improving the image resolution of the image and compensating for chromatic aberrations. Other benefits of using diffractive surfaces will be familiar to those skilled in the art of optical design.

The viewer may incorporate an ancillary light source for viewing in poor lighting conditions.

It will be clear to those skilled in the art that the invention could also be applied with the directions of the ray paths reversed.

Although the invention has been described in relation to what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not limited to the disclosed arrangements, but rather is intended to cover various modifications and equivalent constructions included within the spirit and scope of the invention.

Claims

What is claimed is: 1. An apparatus for displaying an image comprising: a first light transmitting surface operative to admit light from an external scene; a second light transmitting surface operative to transmit light towards a viewer; a third light transmitting surface operative to transmit light towards a viewer; a first light reflecting surface; and a second light reflecting surface; wherein a first multiplicity of optical paths from said external scene to said viewer passes through said first transmitting surface, traverses at least one light refracting medium and passes through said second transmitting surface; and wherein a second multiplicity of optical paths from said extemal scene to said viewer passes through said first transmitting surface, undergoes a first reflection at said first reflecting surface and a second reflection at said second reflecting surface, and passes through said third transmitting surface; said optical paths traversing at least one light refracting medium.

2. The apparatus of claim 1 wherein said first multiplicity of optical paths corresponds to incident light having an angle of incidence at said first transmitting surface less than or equal to a predefined value, and wherein said second multiplicity of optical paths corresponds to incident light having an angle of incidence at said first transmitting surface greater than said predefined value.

3. The apparatus of claim 1 wherein said first multiplicity of optical paths corresponds to incident light having angle of incidence less than the critical angle at said first reflecting surface, and wherein said second multiplicity of optical paths corresponds to incident light having high angle of incidence greater than or equal to the critical angle at said first reflecting surface.

4. The apparatus of claim 1 further comprising a diffusing screen wherein a first portion of said diffusing screen is substantially disposed between said second transmitting surface and said viewer and wherein a second portion of said diffusing screen is substantially disposed between said third transmitting surface and said viewer.

5. The apparatus of claim 1 wherein said second reflecting surface surrounds said first transmitting surface, wherein said first reflecting surface surrounds said second transmitting surface and wherein said third transmitting surface surrounds both said first reflecting surface and said second transmitting surface.

6. The apparatus of claim 5 wherein said second transmitting surface, said first reflecting surface and said third transmitting surface lie on a first continuous surface and said first transmitting surface and said second reflecting surface lie on a second continuous surface.

7. The apparatus of claim 5 wherein said first second and third transmitting surfaces and said first and second reflecting surfaces have a common axis of rotational symmetry.

8. The apparatus of claim 5 wherein said first and second reflecting surface and said third transmitting surface are annular surfaces.

9. The apparatus of claim 1 wherein at least one of said second and third transmitting surfaces has diffusing characteristics

10. The apparatus of claim 1 wherein said first multiplicity of ray paths and said second multiplicity of ray paths traverses at least one air space.

11. The apparatus of claim 1 wherein said second multiplicity of ray paths traverses at least one air space.

12. The apparatus of claim 1 further comprising a wide-angle lens system optically coupled to said apparatus and disposed between said apparatus and said external scene.

13. The apparatus of claim 1 wherein said first light transmitting surface is one of a front, rear or internal surface of said wide angle lens system.

14. The apparatus of claim 1 wherein said second transmitting surface, said first reflecting surface and said third transmitting surface lie on a first continuous surface, and wherein said first transmitting surface and said second reflecting surface lie on a second continuous surface, and wherein the space between said first and second continuous surfaces contains at least one refractive index medium.

15. The apparatus of claim 1 wherein said second transmitting surface, said first reflecting surface and said third transmitting surface lie on a first continuous surface, and wherein said first transmitting surface and said second reflecting surface lie on a second continuous surface, and wherein said the space between said first and second continuous surfaces contains at least one air space.

16. The apparatus of claim 1 wherein each of said first, second and third transmitting surfaces and said first and second reflecting surfaces is characterised by one of an axisymmetric Fresnel, diffractive, aspheric, or spherical optical surface form.

17. The apparatus of claim 1 wherein each of said first second and third transmitting surfaces and said first and second reflecting surfaces is characterised by an anamorphic surface form.

18. The apparatus of claim 1 wherein at least one of said first or second reflecting surfaces functions as a total internal reflection surface.

19. The apparatus of claim 1 wherein a reflective coating is applied to at least one of said first or second reflecting surfaces.

0. The apparatus of claim 1 further comprising at least one lens disposed between said second transmitting surface and said diffusing screen.