Viewer assemblies and viewable material adapted thereto

A magnified viewer capable of viewing an information card or sheet supported on a support base of the viewer. The viewer includes a magnifying lens supported above the support base by means of two oppositely disposed side portions. The side portions are each attached at one end to the support base by a first set of hinges, and at their opposite ends to the magnifying lens by a second pair of hinges. Since the side portions are pivotably connected to both the support base and the viewing lens, the user of the viewer can readily scan the magnifying lens across the information card by merely tilting the side portions from one side to another.

This application is a 371 continuation of PCT/GB92/01072 filed Jun. 15, 
1992. 
BACKGROUND OF THE INVENTION 
This present invention relates to assemblies of a viewer and viewable 
material such as maps or like visually depicted information such as route 
guides. It extends further for example to viewing of handbook information, 
charts or cable-management diagrams. For convenience the invention will be 
described with reference to maps. 
It is commonplace to present maps, that is to say stylised area 
representations of a tract of terrain or complex routes, in the form of a 
large sheet of paper or like material covering a large area and containing 
a great deal of information. Typically, because of their large size these 
sheets are rolled or folded. If the maps are to be used indoors, for 
example for planning or teaching purposes, the nature of the sheet is of 
secondary importance since it is readily capable of being unrolled or 
unfolded to the extent desired to give the immediately relevant 
information, and kept in that state. However, very frequently maps are 
intended to be read out of doors as part of some sporting or other 
activity. For example, in addition to the maps and route guides e.g. 
subway guides generally utlized by tourists or other travellers, skiers 
need to consult piste maps, orienteers need maps of the topography and 
utilization of countryside, and glider pilots or partakers in like aerial 
sports need some form of map consultation. It is common, therefore, to 
provide maps at different scales and to emphasise different features. 
Indeed, some maps are provided as route indicators showing in a more or 
less elongated form the features of a desired route but not showing 
associated countryside (to any great extent) at either side of the route. 
One problem common to the consultation of maps outdoors concerns the 
convenient manipulation of the maps. Typically, for example, a skier who 
is warmly clothed against the temperature and is wearing gloves and 
carrying the usual ski poles finds it difficult to open the map and fold 
it to the relevant part. He has to remove his gloves, and having no 
suitable pockets in the suit, typically hold them under one arm or in a 
similarly inconvenient position while he attempts to unfold and refold the 
map to a suitable location. If there is any sort of wind or like condition 
this can be a very difficult feat, and must of course be carried out again 
in reverse prior to actually commencing the descent. Such problems arise 
with hikers, orienteers, mountainers, gliders, hang-gliders, and in a wide 
range of other sports. Similar problems also arise in military use of 
maps, and the problem is compounded by the fact that the back of a 
conventional map is usually white in color and thus, if held up while the 
map is perused, is visible over long distances as a target for enemy fire. 
Tourist maps also can be inconvenient for use, and their use is indicative 
of unfamiliarity with the locality, attracting fraud or theft. 
Moreover, there is often the requirement for consultation of maps at night, 
using some form of torch or the like; military uses or night emergency 
services often require such a facility. 
Other difficulties arise when using maps or charts in confined spaces e.g. 
underground or in cable ducting. 
There is thus a requirement to provide maps or like information for 
occasional consultation in a convenient fashion over a range of outdoor 
map-using activities. 
SUMMARY OF THE INVENTION 
The present invention is based in part upon the realization that the area 
of a map normally consulted in detail during active use is not large, and 
is not the whole unfolded map area of a conventional map. Typically, the 
area consulted in detail by the user, as indicated above, is that which 
can be perceived when the whole of the rest of the map is folded back. 
Such an area, for example, is typically of a size about 15 by 25 cm up to 
perhaps A4 size. Map consultation typically involves consultation and 
scrutiny within a succession of detailed regions of about this size on the 
sheet. 
The present invention sets out to provide a magnifying viewer for a 
detailed map of which the printed sheet is small enough to give a 
magnified image, for consultation of generally the size of a folded 
portion of map, as discussed above, and at a suitable apparent distance 
from the user. Most preferably, the viewer is so configured as to permit 
selective clearly and accurately magnified scrutiny of all areas of the 
printed sheet. 
In one aspect the invention consists in an information-carrying surface and 
a magnifying reader assembly comprising: 
(a) a surface provided with information at a relatively smaller scale but 
in sufficiently high detail to carry all the information content of a 
larger such surface on a relatively larger scale, and supported and/or 
held in a flat or curved viewing plane, 
(b) a magnifying lens supported for ready movement either generally towards 
the surface to an inner storage position close to the surface or away from 
the surface to a predetermined or selectable extent to give on viewing 
through the lens a perceived image generally at the relatively larger 
scale, as an outer viewing position, 
(c) the lens and/or its support at least in part constituting a protective 
cover for the surface when moved to the inner storage position, and/or a 
protective cover being provided to fit over the lens at the inner storage 
position. Usually the surface is a printed map, route plan or chart. 
In many forms, but not every form, of the invention the assembly carries 
attachment means which in use maintain it in an accessible position on the 
body of a wearer, and which are easily manipulable to move the lens 
between the two positions, e.g. by using a gloved hand. 
A feature of at least one embodiment of the present invention is the 
provision of a suitable map or the like for magnifying. For the 
convenience of discussion, the information to be magnified is assumed to 
be a map. It is intended that this map shall carry all of the necessary 
information so that when magnified the image is equivalent to a map of a 
larger scale. Thus, it is not a question of taking a map on the scale of 
for example 1:100,000 and magnifying it so that it looks to be on a scale 
of 1:20,000, the invention is concerned with, for example, taking a map 
already at the scale of 1:20,000, reducing it to a smaller size and 
printing or impressing it upon a background in such a way that it becomes 
a finely detailed reduced version of that larger scale map, (not 
effectively consultable by the naked eye) and thereafter magnifying that 
finely detailed reduced version so that the apparent image is back to the 
original size, or thereabouts. 
The invention extends to such assemblies whether they are capable of 
containing one sheet of printed paper or polymer, or of polymer-coated 
paper, or a roll or a magazine of such sheets (e.g. an accumulation of 
separate or interconnected sheets) which can be preselected for the area 
in question. 
In a particularly valued form of the invention the printed surface is in 
the form of a flexible sheet of polymer or polymer-faced material the size 
and shape of a standard credit card (i.e. approxisately 55 by 85 mm). Such 
a map on the one hand lends itself to easy storage in conventionally 
available wallets or similar devices and on the other hand is a shape to 
partake of a technology of high precision printing upon the polymeric 
surface, such as used for security purposes on credit cards. There is thus 
technology available for printing such material at this preferred size, 
and moreover (as discussed below) there is a ready level of magnification 
which would give an image of approximately 3.times. to 8.times. linear 
magnification, more preferably 3.times. to 6.times. linear magnification 
to resemble the size of an area of map normally consulted. 
The equipment of the present invention is often so constructed that the 
sheet of material e.g. the credit card-sized sheet of polymer, is mounted 
for viewing by incident light. However, the invention also extends to 
embodiments which use transmitted light. Such light may be provided by 
simple bulbs, by electroluminescent strips, betalights, etc. We have found 
that for consultation of a map or similar depiction incident light is 
usually sufficient even at magnifications of about, for example, 5.times.. 
For reasons discussed in more detail below, this leads to a longer 
lifetime of the high-precision printed sheet. 
The invention can also extend to the provision of relief maps in the zone 
in question. Other types of maps or similar printed articles can also be 
utilized e.g. for use underwater and at night. 
The magnifying lens is preferably a simple lens. However, the invention 
also extends to optical viewing systems with more than one lens. In a 
preferred embodiment, as discussed in more detail below, the lens is 
supported on a tilting framework above the map, and in others it is 
supported upon a slidable or other frame. 
Although the lens can be variously configured and can be simple or complex, 
we have found in most preferred embodiments that a lens can be best 
utilized within a linear magnification of between 3.times. and 8.times., 
more preferably 3.times. to 6.times., and preferably at about 5.times. . A 
typical lens diameter is about 10-30 mm. The lens moreover can be of any 
magnifying configuration but is preferably planoconvex, with the flat side 
closer to the eye of the viewer. It can however be biconvex, with a 
relatively flatter side outwards. Such a lens gives adequate magnification 
without undue distortion (especially in certain preferred embodiments of 
the invention as discussed below) and is suitable to increase the apparent 
size of any image printed in the convenient credit card-format and 
expanded to a convenient size for concentration. 
Preferably, the viewer is configured so that the map or the like is held in 
a viewing plane which is somewhat constrained as to overall vertical 
distance from the lens. Too close a plane gives a blurred image, as does 
too far a plane. For a lens of the preferred magnification and diameter 
given above, the optimum plane should be adopted within usually .+-.5 mm. 
For this reason a preferred viewing plane is curved. Moreover, some 
expedient such as selective moveability of the card or (preferably) 
selective tiltability of the lens is much to be preferred since then all 
parts of the map or the surface of e.g. credit-card size can be 
scrutinised with optimum clarity and uniform magnification. 
The assembly can be embodied in a number of different wearable forms. For 
example, it can be located on the back of a glove or mitten in a folded 
down position, and can be lifted into a viewing position with the other 
hand. 
However, since gloves or mittens are themselves specialised articles of 
commerce, it may be easier to provide the map as part of a detachable unit 
upon or around the arm of a wearer. 
One form of this envisages a form of detachable resilient cuff made for 
example of synthetic polymeric material and providing in its structure 
slideways whereby an upper and magnifying portion of the cuff can be slid 
upwards to the requisite distance above an underlying printed map. Such a 
device can be incorporate other features such as a digital watch in a 
suitable location in the cuff. Indeed, the combination of a map and other 
usable items, such as clocks, thermometers, barometers, alarms, compasses 
and the like is a feature of the present invention. 
The assembly can be otherwise applied to elements of a user's protective 
clothing, provided that however it is arrange so that it is readily 
accessible for viewing. For example, if it is not located on the arm or 
the hand it could be embodied as a smooth wallet or container to be worn 
dependent upon a neck chain or in a pocket. This is not absolutely fixed 
in relation to the body but is regularly reachable and accessible for 
viewing without the necessity of removing it from the head of the wearer 
and over any protective headgear. 
It is envisaged according to some embodiments of the invention that the 
structure shall be such as to be readily operable by a gloved hand. In 
many outdoor sports protective clothing of more or less cumbersome nature 
is worn, and in particular gloves or mittens are worn for skiing. As 
indicated above, it is not always practicable to remove these and 
manipulate a conventional map, and it is envisaged therefore that in some 
of the detailed embodiments, the invention can, by simple movement of a 
gloved hand, be placed in a viewing condition. 
Three specific embodiments of the invention which present themselves 
particularly for consideration are as follows. 
In one preferred embodiment there is provided a resilient cuff containing 
on an upper face the assembly, in which the magnifying lens is formed of 
transparent rigid synthetic polymeric material and possesses two 
downwardly extending legs slidable in sides of the cuff so as to be 
movable from a lower to an upper position in relation to the map plane. 
The "legs" may provide a modicum of protection in use, again rain or snow, 
on the detailed map. 
In another particuarly preferred embodiment the invention is embodied as a 
synthetic polymeric structure having a support plane which is flat or 
arcuate e.g. part-cylindrical in contour, and two upwardly foldable 
portions hinged to either side edge of the support plane and carrying at 
their free ends a lens spaced from the support plane and from any map 
supported thereon. Preferably the foldable portions are hinged both where 
they meet the support plane and the lens, so that the lens can be tilted 
to focus upon any portion of the support plane, thus avoiding distortion, 
of scale or otherwise. The foldable portions again provide a modicum of 
protection against weather. 
The support plane may be defined by the respective upper edges of parallel 
ribs on a base structure, and be continued into a wall portion of the said 
base as a retaining groove. Such a base structure may possess a transverse 
rib at one end including an entry slot to locate the area of surface to be 
examined. One of the upwardly foldable side portions can itself possess a 
transverse slot to accept the area and position it for rib entry slot. 
In a third embodiment the invention is embodied as a smoothly contoured 
wallet or like container having a lid which is readily manipulable to an 
outward position and carrying a viewing lens, optionally biased to move 
out to a viewing position spaced above the case, the body of the case 
carrying a support for a suitable high detail map. Within the volume there 
can possibly be electrical circuitry selectively operable to provide 
indication of time, temperature, barometric pressure, elapsed time, alarm 
situations, compass bearing or the like. The wallet is preferably smoothly 
contoured with a large operating button for opening purposes and an 
equivalently large operating button for selection of the desired displayed 
parameter. 
The preferred embodiments, as discussed in detail above are conveniently 
such that the detailed depiction of the map or the like is provided in a 
credit card size and format. The technology of printing in high precision 
upon credit card-sized polymer coated substrates is already known and can 
be utilized in the production of the equipment according to the invention. 
Most preferably, the map or chart information is printed on one face only, 
with indexing or other information on the obverse, either at normal size 
or for magnification, or in a mixture. Moreover, and as already indicated 
in general terms, the lens is preferably from 3.times. to 8.times. e.g. 
about 5.times. in linear magnification, and is preferably planoconvex with 
the curved side inward to the depiction. A lens of 5.times. magnification 
would imply a focal length, in accordance with the formula 
##EQU1## 
or about 62 mm. 
Certain further advantages, not hitherto achieved, flow from the choice of 
parameters proposed above, and lead to improved use and working lifetime 
of the assembly. As any user of maps will be aware, there is a tendency 
for maps to deteriorate in use, whether this is due to mechanical folding 
and unfolding or whether it is due to the incidence of rain-and snow upon 
the surface. The maps as utilized in the present invention are 
individually of small printed size, so that the problems of folding and 
unfolding are overcome. Moreover, although finely printed they are 
typically protected both in periods of use and in periods of non-use. In 
periods of use, the sides of the viewer, extending up to either side of 
the map, provide a modicum of protection. If the map is viewed in incident 
light the viewers head, more or less vertically over the map, gives 
further practical protection. The case or structure is then only opened to 
view the map in a location relative to the user such that the map and its 
fine detail printing are effectively protected. Even if the map is viewed 
in incident light the finger overlap with the top side edges, especially 
with a gloved hand, provides useful weather protection. Moreover, such 
protection in use is united with suitable protection in periods of 
non-use; the problem of loss of detailed depiction on the map is still 
present if the map were allowed to abrade against the inner surface of, 
for example, a pocket of a garment. In accordance with the invention the 
structure of the viewer is such as to fold over and protect the surface of 
the map and the fine printing upon its surface. 
It is moreover a general advantage that, by providing maps in readily 
consultable form, the tendency to check on the map is increased and the 
safety of the user is thus enhanced.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 shows in opened and exploded form the essential components of a 
first embodiment of the equipment in accordance with the present 
invention. 
Integral molding 1 comprises a base or mounting 2, side walls 3, and a pair 
of lens mounting components 4 and 5. The base mounting 2 includes 
retaining lips or clips 6, and is in a preferred embodiment of the general 
size and shape of a conventional credit card. 
Other features of the assembly are a stack of printed maps 7, each of which 
is of credit card size and shape, which are intended to be held jointly 
under the clips with the depiction of the uppermost map visible. 
As explained above, the depiction on the map is printed in high precision 
so that when magnified it gives an image which is that of a portion of a 
conventional map of the usual scale for some outdoor activity, such as 
walking, skiing, cycling, etc. 
In the embodiments shown the assembly is completed by a planoconvex lens 8. 
Other magnifying lenses are however also possible, especially biconvex 
lenses with a relatively flatter outer face. 
FIG. 2 shows the assembled elements of FIG. 1. 
The lens 8 is installed with its flat side outwards. There is thus 
constituted a viewer with a curved base and with protective side walls 3 
such that if the viewer is used in outdoor conditions and in incident 
light upon the map 7, the combination of the protective side walls 3 and 
general protective environment occasioned by the user looking downwards 
through the lens is such that the exposed map is sheltered to some extent 
against the effect of weather. 
FIGS. 3a and 3b show diagrammatically an important modification of the 
viewer as shown in FIG. 2. In the viewer of FIGS. 3a and 3b the lens mount 
is so arranged as to be hinged at its side edges 9. Because of this it can 
be manipulated in use so that it always perceives the map, upon the curved 
base, essentially at right angles. By this configuration two sources of 
potential error are removed. Firstly, spherical aberration, by which areas 
seen obliquely through a lens have different and distorted appearance from 
areas seen orthogonally through a lens, is avoided. Secondly, difference 
of effective distance of the lens from the map is also avoided, which can 
lead to difference in magnification and thus difference in the apparent 
scale or distance as perceived by the user. 
For a map depiction of the size of a credit card a 25 mm diameter lens can 
be fabricated with a 5.times. linear magnification so that, without 
spherical or other distortions of scale, a detailed map can be viewed of 
an apparent size of approximately 25 by 40 cm, and at an apparent distance 
of inspection of about 30 cm or thereabouts. 
This in itself is probably somewhat larger than necessary for detailed 
one-off connection. However, if the viewer is itself used by someone 
wearing goggles or spectacles, who cannot therefor move his eye to be 
closely adjacent to the lens then (even though the field of view may be 
constrained by e.g. the lens surround) the effective patch viewed is still 
of adequate size. 
FIG. 4 shows a further configuration of the map shown in FIGS. 1, 2 and 3. 
As described above, when the map is in use there is a modicum of 
protection of the finely printed surface against the weather. Likewise, 
when the map is folded up as shown in FIG. 4 the hinges 9 can permit the 
lens to lie between the two sides walls, and the side walls jointly cover 
at least a major proportion of the map surface. Thus, the viewer when put 
away into a garment pocket is still protected both as to the lens and in 
terms of map degradation. 
The essential features of the present invention can however be embodied in 
a totally different shape. Thus, FIG. 5 shows in exploded form a totally 
different embodiment of the invention in the form of a bracelet or cuff. 
In this embodiment, a relatively broad bracelet or cuff 10 defines an 
upper mounting surface 11 to receive, as before, a small map printed in 
high precision, preferably of the general size of a credit card. The cuff 
continues around the wearer's arm, in a conventional form for uniting by a 
buckle or clip. If desired it can be a simple resilient gripping cuff. The 
uppermost surface of the cuff is constituted as a lens 12 with side 
members 13 which can be recessed at 13a to form suitable finger and thumb 
grips. This element slides within suitable recesses in the sides of the 
cuff, by by virtue of tongues 14 which cooperate with recesses 15. It will 
be appreciated that the effective width of the tongues 14 can be if 
desired the same as that of the map, e.g. by extending the width of the 
cuff to either side of the map. 
The device as shown operates as a viewer under incident light by the user 
pulling the lens 12 up away from the map and looking down through the lens 
onto the map surface. As before, the side walls of the viewer sub-assembly 
provides some form of protection against the weather, and the fact that 
the user looks down through the lens is again a further protection in use 
of the precision-printed map surface. 
Configuration of the invention in the form of a cuff as shown in FIG. 5 
allows further elaboration of the device. For example, it is possible to 
incorporate in a recess in the cuff, for example beneath the holder for 
the maps, a conventional small battery and to recover this battery with a 
simple removable lid. Such a battery can then be utilized to run a digital 
timer 18 covered with a suitable transparent face 19. If desired, other 
electronic functions can be incorporated. The general nature of the cuff 
lends itself to the provision of operating buttons on either edge face, 
e.g. as shown at 20 and 21 in exploded form to operate microswitches 22 
and 23 within the cuff. A suitable design of buttons will permit use even 
with the encumbrance of gloves or mittens when engaged in outdoor 
activity. 
A yet further embodiment of the invention is shown in FIG. 6. This has a 
totally different appearance, but possesses the essential features of the 
embodiments as set forth in earlier figures. It is provided in the form of 
a wallet 30 with a lid 31 hinged together at 32 and enclosing, in a major 
part of its interior volume, a stack of suitable precision-printed maps 33 
of the general nature as discussed above, held in place by clips 34. The 
lid is recessed at 35 to hold a suitably configured polymeric lens 36, 37 
under biasing conditions such that, when the box is opened, the lens 
biases outwards to locate at a suitable viewing distance over the maps. 
The minor portion of the container, at 37, could be empty but can 
alternatively include a printed circuit board 38, programmed to operate 
upon a liquid crystal display 39, driven by a battery 40. The battery is 
held in a suitable holder unit 41, within recess 42 covered by a lid 43. 
The whole unit provides a window for viewing the liquid crystal display, 
by means of a membrane 44 of transparent polymer. As is known in the 
electronic art, suitable sensors may be provided responsive to 
temperature, humidity, and other meteorological qualities in addition to a 
conventional time display and possibly compass reading. 
The features listed as locating in the minor portion 37 of the wallet are 
of course ancillary to the general nature of the invention as discussed 
above, which is again concerned with the provision of a polymeric or like 
card substrate of the size of a credit card held in a relatively protected 
environment in period of non-use and viewable by incident light under 
relatively protected conditions in a period of use to give an image of a 
conventional usable size. 
The embodiment of FIG. 6 could be modified by including within the wallet 
an erectable framework as in FIG. 1, using the inside of the lid as a 
suitable storage space for a supply of maps. If desired, a translucent 
screen could be provided in the wallet for use with transmitted light. The 
wallet cover, if uppermost when the viewer is in use, protects against 
rain or snow. 
FIG. 7a shows a case 50 which comprises two upwardly foldable portions 51 
and 52 journalled at 53 and 54 respectively. The shorter portion 52 is 
provided with a ribbed regions as at 55 to assist gripping and pivotal 
opening. At the upper face of the closed case 50 is the parting line 56 
between the two portions 51 and 52 and, a domed region 57 and slit 58 both 
from portion 51. 
FIG. 7b shows the same device when opened ready for use. No viewing member 
is shown in order that the structure of the device can be more readily 
understood. The device comprises a tray or base 60 with side walls 61 and 
internal ribs 62 parallel to the walls. Each rib has an upper surface 62a 
and these upper surfaces are curved to define a common curved support 
plane. The inner faces of the sidewalls 61 are grooved at 61a in 
continuation of the same support plane. 
The portion 52 is continued forward by a planar support leg 63, terminating 
in a hinge structure at 63a, discussed in more detail below. The planar 
support leg 63 joins the upper surface of end portion 52 over steps 64 and 
65 respectively. In this embodiment the viewing support or mounting 
consists of a plate 66, hinged at 63a and similarly hinged at 67 to the 
respective foldable portion 51 and 52. The plate 66 carries planoconvex 
lens 68 with, as shown in FIG. 7b the flat side 68a uppermost. As 
discussed above, other types of lens can also be used. 
FIG. 8 shows base 60 with side walls 61 internally grooved at 61a and ribs 
62 with curved upper edges 62a. Transverse end rib 75, described in more 
detail below, includes transverse feed slot 77. 
The exact nature of the mounting of the lens and the plate is more apparent 
from FIG. 9a. The plate 66 is rectangular in nature and carries at each 
side a hinge pin 69 and 70 respectively, for cooperation with hinges 63a 
and 67. 
FIG. 9b shows in more detail the configuration of the hinge structures. 
Hinge member 63a clasps pin 69 and is mounted at the end of a terminal 
region 71 lying in a plane at a slight angle to that of the support leg 
63. On the other support member 51 the hinge structure 67 is located at 
the end a wall 72 extending from the outer surface of the support 51. 
While details of the invention such as the hinge structure can obviously be 
varied within the scope of the claims of this application, the hinge 
structures as shown provide an example for ready use as shown in FIGS. 
10a, b and c and in FIGS. 11a and 11b. 
FIGS. 10a, 10b and 10c show diagrammatically the orientation of the 
equipment firstly when the center of the viewing surface is being 
examined; secondly when one of the two end regions is being examined; and 
thirdly when the other of the two end regions is being examined. In each 
case the distance from the lens to the viewing surface is essentially the 
same so that accurate magnification, without the blurred images that come 
from the viewing surface being either too close or too distant, is 
achieved. Thus a planoconvex lens of a size suitable for use by a lay user 
can be used for accurate inspection of a field of view larger than the 
static field of view as would he obtained, for example, in FIG. 10a if no 
hinges 63a, 67 were provided. 
FIGS. 11a and 11b show how the structure shown in FIGS. 10a, 10b and 10c 
can be folded up for transport or storage. The shorter portion 51 is 
pushed downwards. The hinge structure 63a thereon is of such a nature that 
the plate can invert and arrive with its convex surface within the domed 
portion 57 and the flat surface of the lens lying safely within the case. 
In practice this latter is spaced above the plane of leg 63 of the 
foldable portion 52. 
FIG. 12 shows in more detail the folding arrangements in the region of the 
lens, whereby the lens is protected during periods of non-use and 
transport. 
As indicated above, the planar leg 63 terminates in steps 64 and 65 before 
it joins the level of the foldable portion 52. Au the device is folded, 
hinges 63a and 67 jointly operate so that the lens 68 becomes accommodated 
within the domed region 57. When the device is fully closed, the endmost 
edge 51a of the end member 51 locates on step 65. The hinge 67 and its 
support rib 72 locate on step 64. Thus, the flat surface at 68a of the 
planoconvex lens is spaced above the surface 73 of the planar support 
extension 63 so as to preserve it from scratching and contamination. It 
can equally well be arranged that the curved surface 68b of the lens is 
similarly spaced by a small amount from the inside of the domed portion 
57. 
FIG. 13 shows in detail a medial section of the end region of the tray, 
with the portion 51 shown diagramatically. As also shown in FIG. 8, the 
end regions of the tray are recessed at 74 and the end wall of the tray is 
provided, adjacent to the hinge 53 with an upstanding transverse rib 75, 
slightly chamfered at its upper corners 76 (see FIG. 13) and slotted at 
77. The slot 77 lies in continuation of the curved plane defined by the 
upper faces 62a of ribs 62 and by the groove 61a in the side walls 61. The 
configuration is such so that the slot opens both into vertical face 79 
and into horizontal face 80 of rib. 
As shown in FIG. 13, when the foldable portion 51 is erected to support the 
lens the slot 58 therein lies in a continuation of the general curved 
plane defined by the edges 62a and the groove 61a. Thus, a 
credit-card-sized sheet to be examined can be fed through the slot 58, 
thence in through the opening to the slot 77, and onto the curved plan 
defined by the edges 62a. The marginal edges of such a card are held at 
61a. Since slot 77 opens into both the horizontal face 80 and the vertical 
face 79 the leading edge of the card being inserted is guided into the 
slot 77 for easy loading. Exact positioning for this can if desired be 
achieved by a `click` fastening at the correct opening position. 
Slot 58 is moreover so positioned that when the portion 51 is closed the 
slot accommodates the transverse rib 75 (being led thereto by the chamfers 
76) whereby the closed container is again safeguarded against ingress of 
dust or other potentially damaging material. 
While the Applicant does not intend to be bound by any theory as to the 
operation of his invention he has established as a matter of 
experimentation that there are design constraints on an optical viewer as 
shown in FIGS. 7 to 12, to be used for examination of a map or the like. 
A large conventional handheld magnifying glass of say 100 mm diameter gives 
a large clear field of view but not particularly high magnification. It is 
suitable for scanning large areas, for example of print, but it is not 
suitable for higher magnification over a smaller area. 
On the other hand, the use of a small eyepiece lens, such as a microscope 
eyepiece of 3 mm diameter, for example, is not always acceptable to lay 
users and needs a modicum of experience. 
However, simple use of a lens of intermediate dimensions between about 15 
and 40 mm diameter, while convenient to the eye is again difficult for 
many purposes. 
Firstly, the depth of clear magnification is not great. That is to say, the 
article to be examined must lie within a relatively small range of 
distances from the lens. In the case of the present invention, using a 
lens of about 20 cm diameter with a magnification of about 5.times. a 
variation of a few millimetres in the distance from the lens to the object 
gives not only a difference in magnification but a significant loss of 
clarity, whether because the lens is too close (so that the loss of 
clarity is due to the non-optimum distance of the image from the eye,) or 
whether it is too far. Thus there is a constraint upon the distance from 
the lens. 
There is also a related constraint upon the useable field of view. In 
particular, using such a lens as described by way of example, the clearest 
field of view is not much greater than a circle of 50-60 diameter on the 
card or other viewing surface. 
Hitherto this has been no problem. For a conventional slide viewer the 35 
mm maximum slide dimension fits comfortably within the area of accurate 
viewing of a simple lens system. Larger film formats indeed use 
differently constituted viewers. 
Similar considerations arise with postage stamp viewing. For simple lens 
systems such as jewellers loops, or small botanical magnifying glasses, 
the desired field of view is similarly small. However, when closely 
viewing precision-printed maps (for example) a magnification of 3, 4 or 
5.times. would only be sufficient to give a clear field of view equivalent 
to an area which would be up to a maximum of 250 mm or so in diameter on a 
full sized map after magnification and might be less. This in itself would 
carry only a small amount of total information and not be practical as a 
separate viewing card. 
The present invention therefore provides constraint on the viewing distance 
and provides some means enabling a zone of accurate magnification to be 
selectively inspected from a somewhat larger, but still readily 
handleable, unit. Typically, it allows all parts of a credit-card sized 
map or plan e.g. a subway plan to be inspected and accurately read even by 
a lay user. In the preferred embodiment this is done by a tilting 
arrangement of the lens and by holding the viewing card in for example a 
suitable curved constrained plane correspondingly, but other expedients 
could be adopted which involve a stationary lens and selectively movable 
map areas of small overall physical dimension but nonetheless larger than 
the field of accurate magnification for a static lens of magnification 3 
to 8.times. and diameter say 10 to 40 mm. 
The invention has its origins in upon a careful selection of 
characteristics of (a) user-friendly simple optics, (b) small scale 
viewing areas with high precision printing or otherwise imparted 
information upon them, and (c) means for constraining the areas both as to 
distance from the lens and as to selective inspection of the different 
parts of the viewing areas for a maximum accuracy and clarity of 
magnification.