WO2006040555A1

WO2006040555A1 - Viewing device

Info

Publication number: WO2006040555A1
Application number: PCT/GB2005/003928
Authority: WO
Inventors: Des Gibson; Ewan Waddell; Barry Reynolds
Original assignee: Apex Optical Technologies, Ltd.; Ogles Limited
Priority date: 2004-10-12
Filing date: 2005-10-12
Publication date: 2006-04-20

Abstract

A viewing device comprising a housing (122) containing an eyepiece lens arrangement (112) movable relative to an objective lens arrangement (128a, 128b), wherein the objective lens arrangement (128a, 128b) contains first and second lenses (128a, 128b), the first lens (128a) being disposed closer to the eyepiece lens arrangement (112) than the second lens (128b), wherein the second lens (128b) has a higher refractive index than the first lens (128a).

Description

VIEWING DEVICE

This invention relates to a viewing device, and is especially concerned with a magnifying viewer. More particularly, this invention relates to a mid-range magnifying viewer for the observation of objects or specimens, typically coral, and small plants and animals, within an observation vessel. More particularly still, this invention relates to a mid-range magnifying viewer for the observation of corals and their associated flora and fauna in a transparent-walled aquarium. In alternative embodiments, the invention relates to a mid-range magnifying viewer for the close observation or inspection of objects, where close physical access is restricted. Coral is grown within aquaria worldwide, either as a hobby or for the purposes of scientific study. Growing coral within a closed environment provides a considerably more practical opportunity to view the biology of the coral and the associated flora and fauna of the "reef than would be possible in its natural environment, in addition to avoiding the ecological problems of studying a reef in situ. However, studying small plants or animals within an aquatic environment often presents problems. The object to be viewed may be some distance (centimetres or metres) from the wall of the aquarium, such that close-proximity viewing is impossible. The feature size, growing speed and flowering cycles of the cultivated corals make it highly desirable to be able to study the minutely detailed structures "close-up", but this is made impossible by the distances between the viewer and the object being viewed.

Conventional microscopes are generally unsuitable, owing to their size and shape. In addition, they cannot cope with the light conditions, particularly the refraction caused by the light travelling through multiple media (i.e. water, glass and air). The refraction caused by the multiple phase boundaries results in distorted images and also in difficulty in focusing on a desired object. The difficulties become more acute when the light-path into the viewer is not perpendicular to the aquarium wall. Furthermore, neither microscopes nor telescopes provide the necessary combination of viewing range, magnification and field of view.

Simple magnifying glasses are also unsuitable for this purpose. In particular, conventional magnifying glasses do not have the required range of focus and focal length, and only have a limited magnifying power.

WO 01/96931 (Reynolds) provides a simple portable optical magnifying device which overcomes some of the above-described problems. The contents of this document are incorporated herein by reference. The device possesses the magnifying power and resolution of a conventional low-power microscope, and may be releasably attached to the outside of a transparent tank, where it is held firmly in a position normal to the plane of the tank wall.

WO 01/96931 is primarily concerned with providing a way of supporting a magnifying viewer adjacent the aquarium. However, significant problems still remain in this field. The optics of the device in WO 01/96931 are not described in great detail. Significant difficulties are encountered when developing a lens system to provide the best results in such a magnifying device. In particular, the following technical problems must be overcome: the device must be able to focus in water, which has a different refractive index to air and glass: the device must have a relatively large aperture in order to ensure image brightness; the device requires a wide range of focal lengths in order to view objects throughout the tank; the device must be compact in order to be readily positionable around the exterior of the tank.

These problems are not restricted to the field of viewing objects in aquaria. Magnified viewing of objects at a distance beyond that enabled by a microscope, and below the distance enabled by binoculars or telescopes, is problematic for several of the above reasons. Particular problems are ensuring image brightness, image quality, and wide range of focal lengths. It would, therefore, be highly desirable to provide a device which enables high quality magnification of objects viewed over a range of a few centimetres to a few meters (typically 10cm to 10m).

It is, of course, also known to use a "doublet" lens assembly as an objective lens in a telescope in order to reduce aberrations and provide a higher quality image. Doublets typically have a first lens (nearer the object being viewed) which is a crown glass and has a relatively "low" refractive index, and a second lens (nearer the eyepiece) which is a flint glass and has a higher refractive index. The use of the doublet lens system reduces the chromatic aberrations in the image. However, in respect of the abovementioned requirements, the numerical aperture of the objective is higher than can be obtained with a doublet using standard index optical glasses. Furthermore, there is a problem with viewing objects in an aqueous medium at an angle away from normal through glass (and air). If the conditions of normality/perpendicularity are not met then very significant optical aberrations (both chromatic and off-axis types) occur, resulting in a very blurred image (see Figures 3 and 5). The present invention overcomes or alleviates the problems associated with the prior art.

In broad terms, the present invention utilises a unique lens assembly in an objective lens of the viewer to provide a compact device, having a good image brightness and a wide range of focal lengths. For the reasons mentioned above, the device is preferably also capable of focusing in water.

This invention relates to a viewing device comprising a housing having an object end and a viewing end, and a light path extending within the interior of the housing from the object end to the viewing end; and an objective lens arrangement disposed in the light path, wherein the objective lens arrangement contains first and second lenses, the first lens being disposed closer to the viewing end than the second lens, wherein the second lens preferably has a higher refractive index than the first lens.

In one embodiment, the device comprises an eyepiece lens arrangement disposed in the light path at the viewing end of the housing, the eyepiece lens arrangement being moveable relative to the objective lens arrangement.

In another embodiment, the device comprises a camera (e.g. SLR, webcam or digital camera), attachment means disposed at the viewing end of the housing. The attachment means may be an SLR adapter. The attachment means may comprise a field flattener lens arrangement. The first lens of the objective lens arrangement is disposed closer to the viewing end (or the eyepiece lens arrangement or camera attachment means), than the second lens.

The first and second lenses may comprise a doublet. The first and second lenses of the may be cemented together. Alternatively, the first and second lenses of the may be separated by a gap, which may be air-filled. In one embodiment, there are no further lenses disposed first and second lenses. In another embodiment, the first and second lenses of the are separated by a gap, which may be up to 10mm, optionally up to 5mm. In another embodiment, the first and second lenses are arranged in contact, but are not cemented together.

The first lens and second lenses of the objective lens arrangement preferably both have high refractive indices. More preferably, the first lens has a refractive index of between 1.60 and

1.75 and Abbe V number of between 52 and 100, and the second lens has a refractive index of between 1.65 and 2.0 and Abbe V number of between 53 and 58. The use of a double-lens system wherein both lenses have "high" refractive indices, and wherein the second lens has a higher refractive index than the first lens, results in significant improvements in terms of reduced image aberration when viewing objects within a tank.

The effective viewing range of the viewing device may be in the region of 270mm to infinity. More preferably, the effective viewing range is in the region of 230mm to infinity. If the viewing device further comprises a macro lens arrangement (as described below), the effective viewing range may include the region of 90mm to 300mm, and preferably the viewing range extends from 90mm, more preferably 70mm, to 300mm. The viewing range means the distance between the object being viewed and the objective lens arrangement, while the effective viewing range means the distance over which the object can be maintained in focus by the magnifying viewer.

More preferably, the first lens has a refractive index of between 1.65 and 1.70 and Abbe V number of between 52 and 100. Still more preferably, the first lens has a refractive index of between 1.675 and 1.70 and Abbe V number of between 53 and 58.

More preferably, the second lens has a refractive index of between 1.70 and 1.90 and Abbe V number of between 30 and 50. Still more preferably, the second lens has a refractive index of between 1.75 and 1.85 and Abbe V number of between 31 and 37. Most preferably still, the second lens has a refractive index of between 1.82 and 1.86 and Abbe V number of between 31 and 33. In one specific embodiment of the present invention, the first lens has a refractive index of 1.6968 and an Abbe number of 55.41, and the second lens has a refractive index of 1.85 and an Abbe number of 32.17.

In an alternative to the first preferred embodiment, the objective lens arrangement contains first, second and third lenses, the first lens being disposed closer to the viewing end that the second lens, and the second lens being disposed closer to the viewing end arrangement than the third lens, wherein the second lens has a lower refractive index than the first lens, and wherein the third lens is bent away from the first and second lenses, towards the object end. The term "bent" as used in relation to this embodiment has its standard meaning in the field of lens design, i.e. an equiconvex lens bent toward the object is a concave convex lens, concave toward the object.

In this alternative embodiment, the first lens preferably has a refractive index within the range of between 1.55 and 2, and an Abbe V number of between 2 and 40, the second lens preferably has a refractive index within the range of between 1.55 and 2, and Abbe V number of between 20 and 80, and the third lens preferably has a refractive index of between 1.5 and 2, and Abbe V number of between 20 and 80.

In a second preferred embodiment, the viewing device further comprises an illumination source. The viewing device has a viewing direction along the axis of the light path, and the illumination source is preferably adapted to provide illumination along the viewing direction of the viewer. The illumination source is preferably adapted to illuminate at least part of a field of view of the viewing device. Enhancement in viewed object colour and/ or contrast can be achieved through use of the light source in conjunction with the viewing device. The light source may be standard filament bulbs or light emitting diodes, although it is preferred to use LEDs in view of their small size, brightness and low power requirements. LEDs provide a means of varying colour and illumination level independently. This can be achieved using a combination of three LED colours combined to provide white or coloured light.

When viewing objects within an aquarium, the "reef keeper" wants to observe features within the marine tank environment using a high and controlled magnification. In addition, the reef keeper wants to observe the environment at variable illumination and colour to simulate night and day cycles and also to enhance the colour contrast to provide best viewing conditions.

In a preferred embodiment, the illumination source comprises at least one LED, arranged to provide illumination along the viewing direction of the viewer.

In a more preferred embodiment, the illumination source comprises a ring of LEDs positioned substantially circumferentially around a longitudinal axis of the viewing device, and arranged to provide illumination along the viewing direction of the viewer.

The illumination source may be controllable such that it illuminates a specific focal point of the viewing device as the viewing device is focused.

The illumination source may comprise at least one LED.

The LEDs provide a means to vary colour and illumination level independently. This can be achieved by using a combination of three LED colours in combination, to provide white or coloured light. Therefore, in one preferred embodiment, the illumination source comprises a plurality of LEDs, wherein the LEDs individually produce at least three different wavelengths of light.

The illumination source may comprise a means to vary brightness of the illumination provided by the illumination source. In one embodiment, the brightness of the light produced by the plurality of LEDs may be adjusted as a whole.

In one embodiment, the illumination source will comprise a plurality of LEDs, wherein the at least two of the plurality of LEDs produce light of a different wavelength. In this embodiment, the wavelength of light produced by the illumination source may be adjusted. In one embodiment, the illumination source comprises at least three LEDs, wherein the at least three LEDs produce light of at least three differing wavelengths. In one embodiment, at least one LED produces red light, at least one LED produces blue light, and at least one LED produces green light. The brightness of the LED(s) producing each wavelength of light can be adjusted independently, in one embodiment. The illumination source may be releasably mounted directly onto the viewing device. Alternatively the illumination source may be releasably attachable to the wall of the tank.

In a third preferred embodiment, the viewing device further a means for adjusting the viewing orientation of the housing relative to the object being viewed. The adjusting means preferably comprises a spacer secured to the object end of the housing, the spacer permitting light to pass therethough to the objective lens arrangement, wherein the connection between the housing and spacer permits the housing to pivot relative to the spacer. In the preferred embodiment, the spacer is adapted to be fixed to a surface, such as a transparent wall of an aquarium, whereby the housing can pivot relative to the spacer to alter the viewing orientation of the housing, by altering the angle between the longitudinal axis of the housing and the surface. The housing may be pivotable relative to the spacer about an axis, or about a point. It is preferred that the housing is pivotable relative to the housing about a point, as this provides allows for the greatest variation in viewing orientation. Preferably, the spacer is releasably connected to the housing. Preferably also, the spacer is adapted to be releasably connected to the transparent surface. It is preferred that at least part of the spacer is flexible to permit the pivoting of the housing relative to the spacer.

Preferably, the spacer includes a fluid chamber arranged such that the light path from the external environment to the objective lens arrangement passes through the fluid chamber. The fluid chamber is preferably filled with a fluid which is selected to be substantially the same as the refractive index of the medium surrounding the object to be viewed. Thus, when the object to be viewed is in an aquarium, then the fluid may be selected to be water. In other circumstances, the fluid may be air or a liquid other than water. The matching of the fluid in the fluid chamber to the fluid medium surrounding the object to be viewed helps to reduce or eliminate the optical aberrations caused by viewing at an angle non-perpendicular to the wall of the tank.

Desirably, the spacer is formed of a resiliently deformable material. In one preferred construction, the spacer comprises a flexible bellows to which the housing may be attached.

Desirably, the fluid chamber includes a transparent end wall through which light can enter the chamber from the environment. The end wall preferably comprises a material having substantially the same refractive index as the surface (eg the aquarium wall). The end wall is preferably arranged such that it engages the surface, when the spacer has been secured thereto. The viewing device may comprise any combination of the first (or alternative first), second and third embodiments, including any combination of the preferred features of each embodiment. Preferably, the viewing device includes the first embodiment (or the alternative first embodiment) in combination with one or, most preferably, both of the second and third embodiments. The viewing device may be utilised in combination with other lens arrangements, and optionally other attachments. hi one preferred embodiment, the viewing device further comprises a macro lens system. The macro lens system may be attached to the existing objective; the macro lens reduces the effective viewing range, and enables fine detail to be observed at close focus. In a preferred embodiment, the device further comprises an eyepiece lens arrangement disposed in the light path within the viewing end of the housing, and moveable relative to the objective lens assembly.

Focussing of the device is typically provided by means to enable movement of the an eyepiece lens assembly with respect to the housing of the device. In one preferred embodiment, the housing comprises a main focus barrel, operable to provide primary movement of the eyepiece. The housing may further comprise a fine adjustment focus ring, which may be integral with the eyepiece lens assembly.

In another preferred embodiment, the viewing device further comprises means to attach a camera or camcorder thereto. The means may comprise a relay lens assembly for the attachment of a camera. Alternatively a camera may be attached directly to the viewing device. The camera may be a web cam. The eyepiece lens assembly may not be present when the camera attachment means is installed. Alternatively, the eyepiece lens assembly is a photographic eyepiece, and may contain a field flattener therein.

Various problems arise when using a digital camera or the like. In particular, the exit pupil of the current 11.2 mm effective focal length (EFL) eyepiece is 10.3mm behind the last optical surface, i.e. the eye relief is 10.3mm. To utilise the image from the eyepiece the entrance pupil of the eye (or lens) should be located in this plane. The entrance pupil of the human eye is approximately 3mm behind the cornea's surface leaving a gap around 7.3mm between the last surface of the eyepiece and the first surface of the eye. A typical web camera also has its entrance pupil approximately 3mm behind the front surface, to make it possible to get the camera close enough to the eyepiece to image the entire field. Figure 20 shows this set-up, in which a fixed focus 4.8mm web cam lens is imaging through the standard eyepiece. Modern digital cameras tend to have x3, x6 or even xl O zoom lenses. Furthermore, they can be quite fast. Such lenses are much larger than a fixed focus web cam lens and crucially have an entrance pupil farther behind their front surface. For example, a digital camera may have a F2.8 to F3.0 f =6.0mm to 36mm lens, with an entrance pupil about 20mm behind the front surface. Clearly a very restricted field would result if these cameras were used with the standard eyepiece.

Thus, in one embodiment, the device further comprises a long eye relief eyepiece, for use with a digital camera.

Preferably the viewing device is releasably attachable to a surface, such as the wall of an aquarium. The attachment of the viewing device or the housing to the tank may be achieved by means of a partial vacuum system, as described in detail in WO 01/96931. In an alternative embodiment, the attachment may be by means of adhesive, a clamp system, or any other way.

In another aspect of the invention, there is provided the use of a viewing device as described above for the observation of objects through a transparent wall. The wall may be an aquarium wall. The objects may be in an aqueous medium.

In another aspect of the invention, there is provided the use of a viewing device as described above for the observation of objects within the range of 70mm to 10m from the object end of the viewing device.

Typically, the viewing device further comprises an image inverting prism assembly disposed in the light path between the eyepiece lens arrangement and the objective lens arrangement. In a preferred embodiment, the prism is a "roof penchant prism", which gives rise to a very compact instrument. However, the type of prism arrangement is not limiting on the scope of the invention. A number of prism arrangements could in principle be used. A prism may not be necessary when a camera is to be used in conjunction with the viewing device. In one embodiment, the device comprises a moveable objective lens arrangement. In this configuration, the eyepiece (if present) or the camera attachment means, is kept stationary, and the objective lens is moved with respect thereto. This is a significant advantage, as it enables a photographer to maintain a camera in a fixed position, hi this embodiment, the prism assembly may be removed, which has the advantage of moving the focal plane into a position which can be accessed by an unmodified, standard camera. Focusing may be achieved by movement of the objective lens arrangement with respect to the eyepiece or camera attachment. A focus ring disposed on the housing of the device may move the objective lens arrangement with respect to the viewing end of the housing. It will be appreciated that the device comprising the photographic eyepiece can be used visually, as well as with a camera attached.

The eyepiece may be a Standard high quality eyepiece with, for example, a focal length of ~1 lmm and field of view of -50°, although other focal lengths can be used to provide higher magnification. It is to be understood that the form of the eyepiece is not restricted to that shown in Table 1 and Figure 3. Different eyepieces of varying optical specification may be used.

In one embodiment, the device comprises a means to increase the depth of field. Said means may comprise a fixed or variable aperture. By varying the size of the aperture the depth of field of the viewing device could be adjusted. A smaller aperture could be used when illumination levels are high.

In another embodiment, variable magnification may be achieved with the use of a zoom eyepiece. For example an eyepiece with focal length variable in the range 12 to 4 mm could be used to give a variation of a factor of 3 in magnification for a fixed object distance.

Reference is now made to the accompanying drawings, in which: Figures 1 and 2 depict perspective views of a device according to the prior art

(specifically WO 01/96931);

Figure 3 depicts the aberrations in an image obtained with a device comprising a standard glass objective;

Figure 4 depicts the aberrations in an image obtained with a device according to the first embodiment of the present invention;

Figure 5 is a ray trace diagram obtained with one embodiment of a viewing device according to the present invention;

Figure 6 is a ray trace diagram obtained with the first embodiment of a viewing device according to the present invention, in which the viewing device further includes a macro lens attachment;

Figure 7 is a ray trace diagram obtained with an alternative embodiment of a viewing device according to the present invention;

Figure 8 is a plan view of an embodiment of a viewing device according to the present invention; Figure 9 is a plan view of a macro lens for attachment for use with a viewing device according to the present invention;

Figure 10 is a plan view of a relay lens system for the attachment of a Web cam for use with a viewing device according to the present invention; Figure 11 is a exploded view of a viewing device according to the present invention; Figure 12 is a ray trace diagram depicting the diffraction of water on entry into an aquarium at an angle away from normal;

Figure 13 is a plan view of an image resulting from viewing an object in an aquarium at an angle away from normal;

Figure 14 is a ray trace diagram obtained with an embodiment of a viewing device according to the third embodiment of the present invention;

Figure 15 is a plan view of an image resulting from viewing an object in an aquarium at an angle away from normal using a device according to the third embodiment of the present invention;

Figure 16 is a schematic view of a device according to the third embodiment of the present invention;

Figure 17 is a schematic view of a device according to the third embodiment of the present invention; Figure 18 is a schematic view of a device according to an embodiment of the present invention incorporating an illumination device;

Figure 19 is a schematic view of the LED array as depicted in Figure 18; Figure 20 is a ray trace diagram of a fixed focus 4.8mm webcam lens imaging through a standard eyepiece; Figure 21 is a ray trace diagram of a long eye relief eyepiece (25mm eye relief EFL =

11.2mm), according to an embodiment of the present invention;

Figure 22 depicts the performance of the long eye relief eyepiece of Figure 21; Figure 23 is a schematic view of a device according to an embodiment of the present invention, showing the layout of the device with the long relief eyepiece of Figure 21 and a zoom lens set to 30mm EFL, and with a field corresponding to a modern CCD "1/2.7" (6.6mm diagonal);

Figures 25 is a ray trace diagram of an embodiment of the invention in which the objective lens arrangement is moveable with respect to the eyepiece lens arrangement, combined with a field flattener, showing the device focused at 237mm and 1000mm in water; Figure 26 is a full ray trace diagram of the embodiment shown in Figure 23;

Figure 27 is a ray trace diagram of another embodiment of the invention in which the objective lens arrangement is moveable with respect to the eyepiece lens arrangement, and further incorporating a macro lens arrangement and a field flattener, showing the device focused at 75mm and 300mm in water;

Figure 28 is a full ray trace diagram of the embodiment shown in Figure 27;

Figure 29 is an embodiment of a field flattener lens, suitable for use in the present invention.

It is to be understood that the term "viewing end", as used herein, refers to the end of the viewing device which, in use, the operator will look into. The term "object end", as used herein, refers to the end of the viewing device which, in use, the operator will direct substantially at the object to be viewed. A distant object viewed through the viewing device in this manner will appear magnified to the operator. In use, therefore, the operator holds the viewing device with the viewing end proximate his/her eye, and the object end directed substantially toward the object being viewed.

Figures 1 and 2 depict a prior art device 1, having a telescopic housing 2, a conventional objective lens 3, and an eyepiece 4. Seal member 7 will, in use, contact a flat surface (depicted "a" in Figure 2), which is typically a glass wall of an aquarium. Chamber 8, defined by the seal member 7 and the flat surface, can be partially evacuated by the use of a piston device, in order to secure the viewer to the flat surface. The piston device comprises a lever 9 connected via pivot 10 to the cylinder 17 and by pin 11 to piston rod 12. Movement of lever 9 from position B to position A will draw plunger 13 from position B' to position A' within piston cylinder 14. Movement of the plunger 13 from position B' to position A' draws air into the piston-cylinder

14 from chamber 8 via opening 15, thereby evacuating chamber 8, and sealing seal member 7 and against the flat surface, thereby affixing the device 1 to the flat surface.

An observer (represented by the eye 16) views along the length of the device 1 through eyepiece 4. Focus may be adjusted by means of adjustable cylinder 17, which may be rotated within housing 2 to either extend or reduce the distance between eyepiece 4 and objective 3, by virtue of screw thread 18 and 19.

The prior art device further comprises optional lenses or prisms 6. With reference now to figures 3 and 4, the aberrations of a normal glass objective are compared to the aberrations produced by a viewing device according to the present invention. These example exclude any effects from eyepiece lenses. Both devices were evaluated against the wall of a tank containing water, where the object being viewed was 304mm away from the objective lens, immersed in the water. The normal glass objective comprises a doublet lens, in which the outer lens (i.e. object side) of the doublet is made from BK7 glass (having a refractive index of 1.51 and an Abbe number of 64.17), and the inner lens (i.e. the eyepiece side) of the doublet is made from SF5 glass (having a refractive index of 1.67 and an Abbe number of 32.2). The objective of the example according to the present invention comprised an outer lens having a refractive index of 1.85 and an Abbe number of 32.17, and an inner lens having a refractive index of 1.6968 and an Abbe number of 55.41.

It is clear that the aberrations produced by the device according to the present invention are much reduced. In particular, the spherical aberration of the image is dramatically better when viewed through the device of the present invention. Table Ia

Table Ib

Table Ia above is a prescription of an exemplary device according to the present invention, including an optional macro lens. Column 1 gives the surface number in the device: surface 0 is the exit pupil of the system in this case. Column 2 gives the spherical radius of curvature of this surface (positive if centre to right). Column 3 gives the centre thickness to the next surface. Column 4 gives half the diameter of the surface, i.e. the radius measured from the optic axis to the component's edge. Column 5 gives the name of the glass or other optical material, Column 6 gives an indication of what part of the optical system the surfaces are in.

Table Ib indicates the refractive indices and Abbe number of the glasses used in Table Ia.

Figure 5 shows a ray trace for a viewing device according to the present invention

(distances in mm).

Figure 6 shows a ray trace for a viewing device according to the present invention and including a macro lens attachment. The configuration shown actually corresponds closely to the furthest distance that the instrument can focus with the macro attached. The macro lens is the three elements immediately to the left of the glass plate.

The arrangement of a high index glass next to the window of an aquarium and the water within the aquarium permits the necessary refraction from the water into the objective's first element without the use of a high curvature. High curvature is to be avoided in objectives as it introduces various high order aberrations.

With reference now to figure 7, a ray trace produced by a viewing device according to the alternative embodiment is shown. This device is able to achieve a similar performance to the first embodiment, through the use of "lower index" lenses. However, this device does require an extra lens, which is positioned in front of the doublet and is "bent" toward the object. The use of three lenses in this way allows for good colour correction. Table 2 below gives the prescription for this alternative objective type.

Table 2a

Table 2b

With reference now to figure 8, a viewing device 100 according to a first embodiment of the present invention is depicted schematically. Primary focus ring 102 outwardly circumscribes the eyepiece/prism assembly tube 104, and is rotatably fixed so as to allow movement of the assembly tube 104, thereby permitting extension or reduction of the distance between the eyepiece lens assembly 112 (which comprises eyepiece lenses 110, 114) and the prism assembly 120 in relation to the objective lens 128a, 128b in a standard manner. Adjustment of this distance provides a change in the focus distance.

Locking flange 106 prevents overextension of the primary focus ring 102. The eyepiece lens assembly 106 terminates, at its outer end, in a rubber eyepiece cup 108.

Internal extension piece 122 comprises a press mounting thread 1 18 into which the eyepiece assembly 112 threadedly connects proximate the eyepiece flange 116, thereby enabling interchanging of the eyepiece lens assembly 112 to provide various magnification levels. Prism assembly 120 comprises prism 124 and prism flanges 126.

The objective lens 128a, 128b is a doublet lens in which the outer lens 128b has a higher refractive index than the inner lens 128a. It is affixed to the viewing device 100 via flange 130. In the depicted embodiment, eyepiece 112/prism 120 adjustment in relation to the objective lens 128a, 128b of around 50mm provides focus range adjustment from typically 280mm to infinity. Additional fine focus control can be achieved via a second focus barrel allowing movement of the eyepiece assembly 112 with respect to the objective [not shown].

The device 100 provides enhanced resolution, and can cover a wide range of object distances. The length of such the device 100 is approximately 97mm to 175mm. Short range focus can be achieved by adding a macro lens, as shown in figure 9. Macro lens assembly 200 comprises a macro lens tube 210, containing a triplet lens system 240, affixed by a lens mounting flange 220 and a stop 230. The macro lens assembly 200 can be screw fitted to the objective end of the viewing device 100. Eyepiece/prism adjustment of 50mm provides a focus range of typically 90 to 300mm (i.e. movement of both the eyepiece and prism 50mm with respect to the objective lens arrangement 128).

It should be noted that the prior art device 1 could be modified, in accordance with the invention, to replace the objective lens 3 with the objective lens 128a, 128b shown in figure 8.

Figure 10 is a plan view of a relay lens system 300 for the fitment of a webcam. The relay lens system can be screw-fitted to the viewing device 100 in place of the eyepiece 104. Primary focus is achieved, as previously described, by rotation of primary focus ring 102. Fine focus control is provided by focus ring 314 on the relay lens system 300.

The lens system 300 can be fitted to a standard webcam (not shown) by means of CS adapter 302. A locking screw 308 is provided to enable the relay lens system 300 to be secured to the CS mount. The lens system 300 additionally comprises relay barrel 304 and relay housing 318, retaining rings 306, 310, 320 and 322, focus ring 314, pin 316 and focus retaining ring 312. The outer surface of focus ring 314 is provided with a grip 324 for ease of use.

As shown schematically in Figure 11 , a viewing device 100 is shown in exploded form and further comprises suction device 400 for attachment of the device 100 to a flat surface, macro lens assembly 200, and eyepiece lens assembly 112. Suction device 380 can be of any design suitable for the releasable attachment of the viewing device 100 (and any additional attachments) to the flat surface and which will enable light to pass from the flat surface to the viewing device 100. One such suitable suction device is described in EP 1940721.2. The additional attachments for the viewing device 100 can be simply attached to the viewing device 100, for instance by threaded engagement, or by friction fitting.

With reference now to figures 12 and 13, the difficulties in angled viewing of an object through a range of media having differing refractive indices are examined. The following specific description, by way of example, relates to an object disposed in an aqueous medium within an aquarium. Figure 12 is a ray trace diagram showing the effect of the multiple media refraction on the light path. The light travels from an object 400 disposed in water 410 in an aquarium, through the water 410 and the wall of the aquarium 420 (which will typically be made of glass), and then through air 430 on the outside of the aquarium before reaching an observer's eye. When using a viewing device 100 along this optical light path, a stationary spot in the water appears as a roughly triangular image of multiple spots, as shown in figure 13. In these spot diagrams a whole series of rays are traced and a point is plotted for each ray. As the imaging system is not perfect the rays gives rise to points which do not overlap. The law of refraction (Snell's law) is non linear therefore the result is a blurred spot which is represented by the multiple points. The spot refers to the collection of multiple points not the individual points. Figures 14 and 15 show the corrective effect produced by a viewing device 100 according to the third embodiment of the present invention, which utilises a "water wedge system" (indicated A) between the glass 420 and the viewing device 100 to reduce the above- described refractive aberrations. The "water wedge system" results in the light path travelling through water 410, 410' on both sides of the glass 420, rather than travelling through air 430 on the external side and water 410 on the internal side.

As shown in figure 14, the light path, travelling from an object 400 in water 410 within the aquarium, is refracted by the glass pane 420 but the refraction is "corrected" as the light path re-enters the water 410', as the refractive index of the water 410' in the "water wedge system" external to the aquarium is substantially identical with the refractive index of the water 410 within the aquarium.

Figures 16 and 17 show schematically two differing devices which both accord to the third embodiment of the invention. With reference to Figure 16, the angled viewing device 500 is shown with removable viewing device 100 including eyepiece lens assembly 112 attached. Viewing device 500 comprises a base stand 510 having a flat surface suitable for resting against the wall of the aquarium. The base stand 510 may contain an integral suction mechanism (not shown) to releasably affix the device to the aquarium wall. The base stand 510 comprises domed refraction chamber 550, which comprises a transparent outer wall, containing within an aqueous medium having a substantially identical refractive index with the aqueous medium within the aquarium to be viewed. The flat base of the domed refraction chamber (not shown) is placed in use in close proximity to the wall of the aquarium, substantially excluding any air between the two surfaces. The base stand 510 further comprises two upstanding arms 520, which are rotatably coupled with universal joint mechanism 540 via pins 530.

Universal joint mechanism 540 comprises inner and outer concentric rings 542, 544. Outer concentric ring 544 is rotatably coupled via pins 530 to the upstanding arms 520 of the base stand 510 at 0 degree and 180 degree orientations, and is rotatably coupled by pins 546 to the inner concentric ring 544 at 90 degree and 270 degree orientations.

Inner concentric ring 542 has a central viewing aperture (not shown) which, through the universal joint mechanism 540, is maintained in close proximity to the "outer" domed surface of the domed refraction chamber 550 irrespective of the angle of the inner concentric ring 542 in relation to the flat surface of the base stand 510. Viewing device 100 is releasably attachable to the viewing aperture of the inner concentric ring 542, preferably threadedly attached.

The angled viewing device 600 shown in figure 17 comprises base plate 610 which is releasably attachable to the wall of an aquarium, preferably by a partial vacuum means (not shown). Base plate 610 also comprises a central viewing aperture (not shown) to allow the light path to enter the viewing device 100. The central viewing aperture is placed, in use, in close proximity to the wall of the aquarium, such that air is substantially excluded from affecting (by refraction) the path of light from the object being viewed to the viewing device 100.

Rotatably and sealably attached to base plate 610 is substantially hemispherical chamber member 620, which contains within an aqueous medium having substantially the same refractive index as the aqueous medium within the aquarium. The hemispherical chamber member 620 is in turn rotatably and sealably attached to eyepiece attachment member 630. Eyepiece attachment member 630 comprises an asymmetrical viewing aperture 640, into which a viewing device 100 can be releasably attached.

Angled viewing devices 500 and 600 enable the user to view through a flat glass wall of an aquarium at a wide range of angles, whilst avoiding substantially the refractive effect of light passing at an angle from water to air through the glass wall. The user can therefore attach the device 500 or 600 to the aquarium wall at a fixed point and readily vary the viewing angle and orientation to scan the aquarium, without experiencing the disorientating effects which would normally be caused by refraction.

Figure 18 is a schematic depiction of a device according to the present invention, incorporating an LED illumination device, which is depicted in greater detail in Figure 19. The device as shown in Figures 18 and 19 comprises a ring of LED" s of three colours, inclined to provide illumination along the viewing direction of the viewer. Variation in relative brightness of each of the three different colour output LED's provides a means of colour control whilst uniform change in power output of the three LED's provides a means of controlling illumination level. The control means for brightness and colour control (not shown) can be housed within the viewing device, or provided as a separate unit, optionally remotely controlled. The illumination source shown in Figure 19 can be mounted either on the viewer direct or a device to secure the viewer to a viewing window as shown in Figure 18.

As mentioned above, typical digital cameras cannot generally be used in conjunction with a standard eyepiece as it results in a very restricted field (the entrance pupil is often some distance behind the front of the camera's lens). An adapted eyepiece should therefore be used, which has a lengthened eye relief in comparison to the standard eyepiece. Figure 21 shows an eyepiece according to an embodiment of the present invention in which the eyepiece provides 25mm of eye relief. The performance of this eyepiece is shown in Figure 22. The long eye relief of this lens allows it to be used with the relatively large zoom lenses used in digital cameras.

With reference to Figure 23, a lens system incorporates the long eye relief lens of Figure 21, with a zoom lens set to 30mm EFL, and with a field corresponding to a modern CCD "1/2.7" format i.e. (6.6mm diagonal). The Modulation Transfer Fuction (MTF) of this lens is shown in Figure 24 (imaging 1000mm into water). The linear magnification of the set up in Figure 23 is 0.3561 compared to that at the focal lane of -0.1047 i.e. it is some 3.4 times higher (and erect). Of course, there is the magnification of the CCD to image.

Further lens data for the exemplary embodiment shown in Figure 23 is set out below.

Surfaces : 8 Stop : 1

System Aperture : Image Space F/# = 6

Glass Catalogs : schott MISC

Ray Aiming : Off

Apodization :Uniform, factor = O.OOOOOE+000 Effective Focal Length : 11.20185 (in air)

Effective Focal Length : 1 1.20185 (in image space) Back Focal Length : 1.5047

Total Track : 43.32303

Image Space F/# 6

Paraxial Working F/# : 6 Working F/# : 5.999377

Image Space NA : 0.08304548

Object Space NA : 9.334875e-011

Stop Radius : 0.9334875

Paraxial Image Height : 3.424749 Paraxial Magnification : 0

Entrance Pupil Diameter 1.866975

Entrance Pupil Position : 0

Exit Pupil Diameter : 94.19859

Exit Pupil Position : -565.1718 Field Type : Angle in degrees

Maximum Field : 17

Primary Wave : 0.588

Lens Units : Millimeters

Angular Magnification : 0.01981956

SURFACE DATA SUMMARY:

Surf Type Comment Radius Thickness Glass Diameter Conic

OBJSTANDARD Infinity Infinity 0

0

STOSTANDARD Infinity 22.98489 1.866975 0 2 STANDARD 28.3213 1.499155 LAK8 18.4

0

3 STANDARD 41.33726 3.588727 LAKlO 18.4 0

4STANDARD -26.27828 0.09975933 18.4 0

5 STANDARD 9.268877 5.672846 SSK2 15.6 0

6STANDARD -457.5937 7.992722 TEO2 15.6 0 7 STANDARD 7.633779 1.484931 6.6 0

IMA STANDARD Infinity 6.071785 0

INDEX OF REFRACTION DATA:

Surf Glass Temp Pres 0.486000 0.588000 0.656000 0 20.00 1.00 1.00000000 1.00000000 1.00000000 1 20.00 1.00 1.000000001.000000001.00000000

2 LAK8 20.00 1.00 1.72223495 1.71297323 1.70898761

3 LAKlO 20.00 1.00 1.72998112 1.719967941.71569552

4 20.00 1.00 1.000000001.000000001.00000000 5 SSK2 20.00 1.00 1.63049723 1.622274641.61878753

6 TEO2 20.00 1.00 2.331858432.274765652.25323278

7 20.00 1.00 1.000000001.000000001.00000000

8 20.00 1.00 1.000000001.000000001.00000000

With reference now to Figures 25 and 26, an embodiment is described in which the objective lens is moveable, enabling the eyepiece or camera attachment to be kept stationary. The prism has been removed from the device. The device comprises a "field flattener/corrector lens" mounted outwardly (i.e. toward the object end) of the objective lens arrangement. The field corrector lens ensures minimal blurring at the image edge, and enhances the depth of focus of the device. A typical specification for a field corrector lens is shown in Figure 29.

The field corrector lens may be used in conjunction with any of the above-described embodiments. Typically, the field corrector lens will be positioned within an adapter suitable for attachment of a camera to the device. Refractive indices and Abbe V numbers were determined at the same wavelength throughout the application, namely 587.5nm.

Whilst the present invention has been described in relation with particular emphasis towards viewing objects positioned within an aquarium, it will be appreciated that the invention is not restricted to this use. The viewing device could find use in any circumstances where, for safety reasons or because of physical restraints, the viewer cannot themselves get complete visual access to the object due to the distance between the object and the viewer. One such use could be in medical practice, where the viewer is a doctor or surgeon who wishes to view internal aspects of a patient, for instance during a surgical procedure. The viewer is useful in all instances where it is necessary to view an object, magnified and in focus, over a distance of around 90cm to 10 metres, in particular around 3 to 5 meters. Another potential use is in viewing artwork, for example in observing for deterioration or defects while the artwork is hanging or difficult to view close-up for other reasons. Known magnification devices do not make this possible. Another potential use is in viewing solar arrays, where it is difficult to access the array "close-up". It will be appreciated that the invention described above may be modified.

Claims

CLAIMS:

1. A viewing device comprising a housing having an object end and a viewing end, and a light path extending within the interior of the housing from the object end to the viewing end; and an objective lens arrangement disposed in the light path, wherein the objective lens arrangement contains first and second lenses, the first lens being disposed closer to the viewing end than the second lens, wherein the second lens has a higher refractive index than the first lens.

2. A device according to claim 1, wherein the refractive index of the first lens is at least 1.65 and the refractive index of the second lens is at least 1.70.

3. A device according to claim 1 or 2, where the first lens has an Abbe V number of between 52 and 100, and the second lens has an Abbe V number of between 53 and 58.

4. A device according to claim 1, 2 or 3, wherein the effective viewing range of the device is from 90mm to infinity.

5. A device according to claim 1, 2, 3 or 4, further comprising means to releasably attach the viewing device to a flat transparent surface.

6. A device according to claim 5, wherein the flat transparent surface is a wall of an aquarium.

7. A device according to any preceding claim, further comprising an illumination source, wherein the illumination source provides illumination substantially along a viewing direction of the viewer.

8. A device according to claim 7, wherein the illumination source comprises at least one LED, arranged to provide illumination substantially along the viewing direction of the viewer.

9. A device according to claim 7 or 8, wherein the illumination source comprises a ring of LEDs positioned circumferentially around a longitudinal axis of the viewing device, and arranged to provide illumination along the viewing direction of the viewer.

10. A device according to claim 7, 8 or 9, wherein the illumination source further comprises control means to vary the colour of light produced by the illumination source.

11. A device according to claim 10, wherein the illumination source comprises at least three LEDs each producing light of at differing wavelengths.

12. A device according to any one of claims 7 to 11, wherein the illumination source further comprises means for varying brightness of the illumination provided by the illumination source.

13. A device according to any preceding claim, further a means for adjusting the viewing orientation of the housing relative to the object being viewed.

14. A device according to claim 13, wherein the adjusting means comprises a spacer secured to the object end of the housing, the spacer permitting light to pass therethough to the objective lens arrangement, wherein the connection between the housing and spacer permits the housing to pivot relative to the spacer.

15. A device according to claim 14, wherein the spacer is adapted to be fixed to a surface, such as a transparent wall of an aquarium, whereby the housing can pivot relative to the spacer to alter the viewing orientation of the housing, by altering the angle between the longitudinal axis of the housing and the surface.

16. A device according to claim 14 or 15, wherein the housing is pivotable relative to the spacer about an axis.

17. A device according to claim 15 or 16, wherein the housing is pivotable relative to the spacer about a point.

18. A device according to any one of claims 14 to 17, wherein the spacer is releasably connected to the housing.

19. A device according to any one of claims 14 to 17, wherein the spacer is adapted to be 5 releasably connected to the surface.

20. A device according to any one of claims 14 to 19, wherein at least part of the spacer is flexible to permit the pivoting of the housing relative to the spacer.

10 21. A device according to any one of claims 14 to 20, wherein the spacer includes a fluid chamber arranged such that the light path from the external environment to the objective lens arrangement passes through the fluid chamber.

22. A device according to claim 21, wherein the fluid chamber is filled with a fluid which is 15 selected to be substantially the same as the refractive index of the medium surrounding the object to be viewed.

23. A device according to claim 22, wherein the fluid is water.

20 24. A device according to any one of claims 14 to 23, wherein the spacer is a flexible bellows to which the housing is be attached.

25. A device according to any one of claims 14 to 24, wherein the fluid chamber includes a transparent end wall through which light can enter the chamber from the environment.

25

26. A device according to claim 25, wherein the end wall is arranged such that it can engage the surface, when the spacer has been secured thereto.

27. A device according to any preceding claim, further comprising a macro lens secured to 30 the object end of the housing.

28. A device according to any preceding claim, further comprising means to attach a camera thereto or camcorder thereto.

29. A device according to any preceding claim, further comprising a relay lens assembly disposed in the light path at the viewing end of the housing.

30. A device according to any one of claims 1 to 28, further comprising an eyepiece lens 5 arrangement disposed in the light path at the viewing end of the housing, the eyepiece lens arrangement being movable relative to the objective lens arrangement.

31. A device according to claim 30, wherein the eyepiece lens arrangement is a long relief eyepiece.

10

32. A device according to claim 31 , further comprising a digital camera.

33. A device according to any preceding claim, further comprising a field corrector lens.

15 34. Use of a device according to any preceding claim to observe objects through a transparent surface.

35. Use according to claim 34, wherein the transparent surface is the wall of an aquarium, and the objects are in an aqueous medium. 0

36. Use of a device according to any of claims 1 to 33 for viewing objects separated from the viewing device by a distance of between 70mm to 10 metres.

37. Use according to claim 36, wherein the object is between 270mm and 5 metres from the 5 viewing device.

38. Use according to claim 36 or 37, wherein the object is artwork.

39. A viewing device substantially as herein described, with reference to and as shown in the 0 accompanying drawings.

40. Use of a viewing device substantially as herein described with reference to and as shown in the accompanying drawings to observe objects within an aquarium.