Microfiche reader

A microfiche reader according to the present invention includes a housing consisting of a hood portion and a base portion, a screen located within the hood portion and visible through the front end of the hood, a combined microfiche carriage and index holder, a lens assembly and a projection system. The combined microfiche carriage and index holder serves to accurately locate the microfiche with respect to the index grid. By reason of the fact that there is no relative movement between the index grid and the microfiche in use, it is always possible to accurately locate the microfiche with respect to the projection system by reference to the index grid. The index grid is illuminated by an index illuminating lens carried by the housing. The illuminating lens is located in a fixed relationship with respect to the projection path which again contributes to the facility with which the microfiche may be accurately located in the projection path. The lens assembly includes a support plate mounted above the microfiche carriage and a slide member mounted in the support plate and a pair of lens members mounted in the slide members so that either one may be located in the projection path as required. The projection system includes a demountable modular unit which may be easily mounted in and removed from the housing. A prefocussed lamp is mounted on the modular unit and the position of the prefocussed lamp with respect to the modular unit may be adjusted so as to vary the length of the illuminating path between the prefocussed lamp and the condenser means whereby the optical system may be adjusted to accommodate objective lenses having different characteristics. The projection system consists of a prefocussed lamp which projects a beam of light onto a cold mirror which reflects the beam of light through an optical condenser which in turn directs the beam of light through the micromirror is mounted in the housing and reflects the beam of light emitted from the objective lens to a viewing screen mounted in the housing. The viewing screen consists of a unitary body of molded plastics material having an image receiving surface formed with a concave spherical curvature. The image receiving surface may be plated with a suitable coating to form an image reflecting coating thereon.

This invention relates to improvements in a microfiche reader. In 
particular, this invention relates to improvements in a front projection 
type of microfiche reader. 
PRIOR ART 
In the microfiche readers which are presently available, a microfiche is 
located in a movable holder for movement with respect to the illuminating 
path of the projection system and a corresponding grid pattern is located 
in a stationary position with respect to the microfiche housing. The 
microfiche holder has an indexing finger projecting outwardly therefrom to 
overlie the indexing grid. The indexing finger may be located at any 
position with respect to the indexing grid to locate the corresponding 
portion of the microfiche in the projection path. Because the microfiche 
holder and, therefore, the microfiche is movable relative to the indexing 
grid, the microfiche may be slightly misaligned with respect to the grid 
making the location of a specific area of the microfiche difficult at 
times. In addition, the clearances between the relatively moving 
components of the microfiche holder and indexing grid are such that 
difficulties can be experienced in obtaining correct alignment of the 
microfiche. 
I have overcome the above difficulties by reason of the fact that the 
indexing grid and microfiche are mounted in a unitary microfiche carriage 
and index holder so that no relative movement occurs between the indexing 
grid and the microfiche when the apparatus is in use. 
Considerable difficulty has also been experienced in attempting to provide 
an undercarriage support system for the microfiche carriage which will 
adequately support the carriage for movement with respect to the 
projection path of the reader. This difficulty has been overcome by 
providing an undercarriage which has V-shaped support rails and V-shaped 
wheels cooperating with one another and rails on the support platform of 
the microfiche reader to provide a minimum backlash in the system in 
response to movement of the microfiche carriage. 
In a microfiche reader it is important to ensure that the microfiche may be 
located in and removed from the microfiche carriage as easily as possible. 
I have achieved this desirable result by providing an upper glass flat 
which is automatically raised as the microfiche carriage is moved to a 
predetermined position forwardly of the platform of the reader to provide 
access to the microfiche for removal. 
The servicing of the projection system of a microfiche reader is generally 
limited to a requirement that the illuminating light may be readily 
replaced. This is achieved in accordance with one aspect of the present 
invention by reason of the fact that the lamp is mounted in a modular unit 
which may be removed from the reader housing. 
In many instances it is desirable to be able to change the objective lens 
of a microfiche reader so that the reader may be used for a variety of 
purposes. When the objective lens is changed in the known readers, 
considerable adjustment of the optical system is required. This difficulty 
is overcome by one aspect of the microfiche reader of the present 
invention which provides a prefocussed lamp which is mounted to be 
adjustably movable towards and away from the condenser lens of the 
projection system whereby the projection system may be adjusted to 
accommodate objective lenses having different characteristics by the 
movement of the position of the prefocussed lamp with respect to the 
condenser lens. Preferably the prefocussed lamp is mounted to be 
adjustably movable with respect to the modular unit which is removable 
from the main housing of the reader. 
To adjust the magnification of the projected image in known microfiche 
readers., the objective lens is removed and replaced by another lens. This 
adjustment requires a knowledge of the structure of the microfiche reader 
assembly and can create difficulties for operators not familiar with the 
structure. This difficulty has been overcome according to one aspect of 
the microfiche reader described herein by mounting a pair of objective 
lenses in a slide member which is slidably mounted in a support plate 
above the microfiche carriage, the lenses being releasably secured in the 
illuminating path of the projector as required in use. 
The majority of microfiche readers presently in use have a projection 
system which requires a power-driven fan in order to provide adequate 
cooling. Because of the very substantial amount of heat generated by the 
conventional optical system, it has been necessary to make the housings 
relatively large and to provide a powerful fan-driven cooling system. The 
fan-driven cooling system is noisy and creates a further source of service 
difficulties. These difficulties are overcome by one aspect of the 
apparatus described herein which provides an optical system and venting 
system and housing construction which permits the microfiche reader to 
operate without the use of a forced-air cooling system. 
Considerable difficulty has also been experienced in providing a screen for 
a microfiche reader which has adequate reflective characteristics to 
function effectively as a screen in a front projection system. The screen 
of the microfiche reader according to one aspect of the present invention 
overcomes this difficulty and is formed from a unitary body of molded 
plastics material which has an image receiving surface formed with a 
concave spherical curvature and which is coated with a layer of an image 
reflecting material. 
SUMMARY OF INVENTION 
According to one aspect of the present invention, there is provided in a 
microfiche reader of the type having a housing, an image projection system 
including projector means and a screen for receiving a projected image and 
an illuminating path extending from the projector means to the screen, the 
improvement of a combination microfiche carriage and index holder which 
comprises a frame, a first window opening through said frame, means for 
locating a microfiche in a predetermined position with respect to said 
first window for the projection of light therethrough, a second window 
opening through said frame, a transparent index grid mounted in said 
second window in a predetermined position with respect to said second 
window for the projection of light therethrough, index illuminating means 
underlying said second window and located in a fixed relationship with 
respect to a portion of the illuminating path which projects through said 
first window opening, said frame being mounted for planar movement with 
respect to said housing to locate any required area of the grid in the 
beam of light emanating from the index illuminating means and thereby to 
locate the corresponding areas of the microfiche in the illuminating path 
of the projector for projection onto the screen. 
According to a further aspect of the present invention, there is provided 
in a microfiche reader of the type having a housing, an image projection 
system including projector means and a screen for receiving a projected 
image and an illuminating path extending from the projector means to the 
screen, a microfiche carriage having an upper glass flat arranged to be 
disposed above a microfiche in the carriage, the improvement of a lens 
assembly which comprises a support plate mounted above said microfiche 
carriage, passage means opening through said support plate in alignment 
with the illuminating path of said projector, a slide member mounted in 
said support plate for movement relative thereto, a pair of lens passages 
opening through said slide member, a lens holder mounted in each of said 
lens passages, a lens member releasably mounted in each of said lens 
holders, said carriage means being slidable relative to said support plate 
to locate one or other of said lens members in said illuminating path of 
said projector, and releasable lock means for releasably locking either of 
said lens members in said illuminating path in use. 
According to a further aspect of the present invention, there is provided a 
microfiche reader of the type having a housing, a viewing screen located 
within said housing and a projection system for projecting an illuminating 
beam of light along an illuminating path, said illuminating beam being 
directed through a condenser lens, a microfiche and an objective lens 
arranged in series and onto said screen, the improvement wherein said 
projection system includes a demountable modular unit which comprises a 
frame removably mounted in an operative position in said housing, mirror 
means mounted in said frame in a fixed position with respect to said 
frame, said mirror means being located in said illuminating path when said 
frame is in said operative position, a prefocussed lamp mounted in said 
frame for movement towards and away from said mirror means to vary the 
length of the illuminating path between the prefocussed lamp and the 
condenser means whereby the optical system may be adjusted to accommodate 
objective lenses having different characteristics. 
According to a further aspect of the present invention, there is provided a 
microfiche reader of the front projection type having a housing, a 
microfiche carrier mounted in said housing and a projection system for 
projecting an illuminated image from a microfiche, the improvement wherein 
said projection system comprises a prefocussed lamp mounted in said 
housing providing a source of a beam of light, a cold mirror mounted in 
said housing in the path of the beam of light emitted from said 
prefocussed lamp for reflecting said beam, an optical condenser mounted in 
said housing in the path of the beam of light reflected by said cold 
mirror, said optical condenser directing the beam of light through the 
microfiche carrier, an objective lens mounted in said housing for 
receiving the beam of light transmitted through said microfiche carrier, a 
first surface mirror mounted in said housing in the path of the beam of 
light emitted from said objective lens, a viewing screen mounted in said 
housing for receiving the illuminated beam of light reflected from said 
first surface mirror, said prefocussed lamp being adjustable towards and 
away from said optical condenser whereby the projection system may be 
adjusted to accommodate objective lenses having different characteristics. 
According to a further aspect of the present invention, there is provided a 
microfiche viewer having a housing, a screen mounted in said housing and a 
front projection system for projecting images from a microfiche onto a 
screen, the improvement wherein said screen comprises a unitary body of 
molded plastics material having an image receiving surface formed with a 
concave spherical curvature, said image receiving surface being coated 
with a layer of image reflecting material. 
According to a further aspect of the present invention, there is provided a 
microfiche viewer having a housing, wherein the screen has an upper edge 
and a lower edge, and a pair of side edges, said side edges converging 
with respect to one another whereby the screen has an image receiving 
surface which is narrower at said upper edge than it is at said lower edge 
to conform to the configuration of the projected image.

A microfiche reader according to an embodiment of the present invention is 
illustrated in FIG. 1 of the drawings. In FIG. 1 of the drawings, the 
reference numeral 10 refers generally to the microfiche reader housing 
which consists of a hood portion 12 and a base portion 14. A screen 16 is 
located within the hood 12 and is visible through the front end of the 
hood. A combined microfiche carriage and index holder 18 is supported on 
the base portion 14 and is mounted for movement with respect to the base 
portion. A lens assembly 20 is mounted in the hood 12 and disposed above 
the carriage 18. 
MICROFICHE CARRIAGE 
The structure of the combined microfiche carriage and index holder 18 and 
its support structure is illustrated in FIGS. 2, 8 and 9 of the drawings. 
The combined microfiche carriage and index holder 18 consists of a frame 
22 which has a first window 24 opening therethrough and a second window 26 
opening therethrough. The lower glass flat 28 (FIG. 8) is located in the 
first window 24 and an upper glass flat holder 30 is pivotally mounted by 
means of lugs 32 in recesses 34. The lugs 32 form hinges about which the 
upper glass flat 30 may pivot so as to be raised out of engagement with 
the lower glass flat 28. An actuator extension 36 extends rearwardly and 
upwardly from the back edge of the upper glass flat holder. The actuator 
extension 36 engages the lug 38 located on the underside of the lens 
support plate 40 (FIG. 3) so that when the carriage 18 is moved outwardly 
towards the operator, the actuator extension will at a predetermined 
location cause the upper glass flat to pivot upwardly to facilitate the 
location of a microfiche 44 between the lower glass flat 28 and the upper 
glass flat 30. An index grid 46 is located in the second window 26. Two 
sets of ribs 48 extend across the underside of the carriage 18 in a spaced 
parallel relationship. 
As shown in FIG. 9 of the drawings, a V-shaped wheel 50 is mounted for 
rotation on a shaft 52 which is supported by the ribs 48. A plurality of 
wheels 50 are located in this manner in a channel 54 formed between the 
ribs 48 at spaced intervals along the length of the ribs. A rectangular 
shaped undercarriage 56 is formed with a pair of support rails 58 
extending transversely thereof and a pair of U-shaped channel members 60 
extending longitudinally thereof. As shown in FIG. 9 of the drawings, each 
of the rail members 58 has a V-shaped rail portion 62 which is 
proportioned to support the V-shaped wheels 50. A plurality of additional 
wheel members 50 are located in the U-shaped channel members 60 at spaced 
intervals along the length thereof. Channels 64 are formed in the surface 
of the platform 66 of the base member 14. Support rails 68 of the same 
contour as the rails 62 extend longitudinally of the channels 64. A narrow 
lip portion 70 projects outwardly from an outer side edge of each channel 
64. In use, the lip 70 overlies the ledge 72 which projects outwardly from 
the side of the U-shaped channel members 60 and serves to retain the 
undercarriage 56 in engagement with the rail member 58. 
To mount the undercarriage 56 on the platform 64, it is located towards the 
front end of the platform and lowered to a position in which the wheel 
members 50 carried by the undercarriage rest on the support rails 64. The 
carriage 22 is mounted on the undercarriage 56 by locating the wheel 
members 50 on the guide rails 62. Longitudinal movement of the carriage 18 
with respect to the reader is achieved by the movement of the 
undercarriage 56 along the support rails 68 and transverse movement is 
achieved by transverse movement of the carriage 26 with respect to the 
undercarriage 58 by the movement of the support wheels 50 along the guide 
rails 62. 
As shown in FIGS. 2 and 2a of the drawings, an index illuminating passage 
74 opens through the wall of the platform 66 centrally of the width 
thereof. An index illuminating lens 76 is located in the passage 74 and 
serves to concentrate the light emitted through the passage 74. As will be 
described hereinafter, light emitted from the lens 76 passes through the 
indexing grid 46 and serves to provide a method of locating a required 
location on the microfiche by reference to the illuminated grid. 
THE BASE MEMBER 
The base member 14 has a bottom wall 80 (FIG. 2a) extending from the back 
face thereof towards the front face. An angularly inclined bottom wall 82 
extends upwardly and forwardly from the bottom wall 80 to a front wall 86 
which extends vertically upwardly to the platform 66. An inner wall 88 
extends upwardly from the platform and a top wall 90 extends rearwardly 
from the inner wall 88 to the back wall 93. A pair of guide rails 92 are 
located on the inner face of the bottom wall 80. A plurality of vent 
openings 94 are located in the bottom wall 80 and in the inclined bottom 
wall 82. An operating switch 95 is mounted in the front wall 86. Vent 
passages 96 are located in the platform 66. A condenser passage 98 opens 
through the platform 66. Air circulation passages 100 and 101 open through 
the top wall 90 and back wall 93 respectively. A lamp mounting passage 102 
opens through the back wall 93 of the base. 
A removable drawer 104 is proportioned to extend through the passage 102 in 
the back wall so as to be located within the base 14 with the back plate 
106 thereof closing the passage 102. The drawer 104 has a bottom wall 108, 
the opposite side edges of which are adapted to fit within the track 
formed by the guide rails 92. An electrical plug member 110 is located at 
the inner end of the drawer 104 and is adapted to fit within a socket 112 
located in the base 14 when the drawer is located in an opposite position 
within the base. A prefocussed lamp 114 is adjustably mounted on the 
bottom wall 108 by means of a mounting bolt 115 which is threaded and 
which extends through a passage 116 in the bottom wall 108 and is clamped 
by means of a nut 118 and a spring washer 120. 
The lamp 114 and its associated housing may be moved longitudinally of the 
bottom wall 108 to any required position. The lamp 114 is electrically 
connected to the plug member 110 by wires 122 such that when the drawer 
104 is located in an operative position within the base, electrical power 
is supplied to the prefocussed lamp 14. 
The electrical power is supplied to the microfiche reader as a whole by 
means of cable 126. The electrical power is supplied to the transformer 
128 which is located in the housing and the transformer 128 is 
electrically connected to ON/OFF switch 95 by lines 130. 
HOOD STRUCTURE 
The structure of the hood 12 is illustrated in FIGS. 1 and 3 of the 
drawings. As shown in FIG. 3 of the drawings, the hood 12 has a pair of 
side walls 132, a top wall 134, an upper back wall 136, a lower back wall 
138 and a bottom wall 140. A passage 142 opens between the lower back wall 
138 and the bottom wall 140. A screen support shoulder is formed about the 
inner edge of the passage 142 and consists of side shoulder portions 144, 
top shoulder portion 146 and bottom shoulder portion 148. A pair of 
support lugs 150 (only one shown) are located at the lower edge of each 
side wall 132 and serve to support the lens support plate 40 as will be 
described hereinafter. The bottom wall 140 is formed with a plurality of 
air circulating vent passages 152. The hood 12 is mounted on the base 14 
with the bottom wall 140 supported by the top wall 90 of the base. 
Mounting screws 154 secure the hood with respect to the base. A window 
mounting lip 156 is located at the front edge of the hood to secure a 
window 158 therein. The screen 16 has mounting passages 160 (FIG. 6) in 
the back face thereof which are threadably engaged by mounting screws 162 
(FIG. 3) which extend through passages 164 formed in the upper screen 
mounting shoulder 146 to secure the screen with respect to the housing in 
the position shown in chain lines in FIG. 3. A highly reflective mirror 
165 is mounted on the inner face of the top wall 134 of the hood to 
reflect images projected thereon onto the screen 16. 
SCREEN 
The screen 16 is made from a unitary body of molded plastics material such 
as A.B.S. The image receiving surface 166 of the screen has a concave 
spherical curvature. The side edges 168 of the screen converge with 
respect to one another in a direction towards the upper edge of the 
screen. It has been found that the configuration of the image receiving 
surface achieved by providing a concave curvature both longitudinally and 
transversely of the screen and by reducing the width of the screen towards 
the upper end is most suitable for receiving images projected by the 
projection system described hereinafter. The unitary body of the screen 16 
includes side walls 170, top wall 172, bottom wall 174 and a pair of 
diagonally extending reinforcing webs 176. The inner edge of the side 
walls is shaped to follow the configuration of the hood in which it is 
mounted. The image receiving surface 166 of the screen is plated with a 
layer of silver or the like to form an image reflecting coating thereon. 
LENS ASSEMBLY 
The lens assembly 20 is illustrated in FIGS. 3, 4 and 5 of the drawings. 
The lens assembly 20 consists of a support plate 40 which is mounted on 
support lugs 150 of the hood 14 by means of mounting screws 180. The 
support plate 40 has a passage 182 opening therethrough. As shown in FIGS. 
3 and 4 of the drawings, a support rail 184 is located below the side 
edges of the passage 182 in a spaced relationship with respect to the 
support plate 40. A slide member 186 has a central portion 188 which is 
substantially shorter in length than the passage 182. The slide member 186 
also has a pair of end portions 190 which are thinner than the central 
portion 188. The slide member 186 is mounted in the support plate 40 and 
is supported therein by support rails 184. The central portion 188 of the 
slide member projects into the passage 182 and the end portions 190 
underlie the support plate 40 at opposite ends of the passage 182. By 
reason of the fact that the central portion 188 is shorter than the 
passage 182, the slide member 186 may be moved back and forth in the 
passage 182. The front support rail 184 has a notch 192 opening 
therethrough which serves to operably locate the required objective lens 
in the projection path as will be described hereinafter. The slide member 
186 has a pair of tubular sleeve projections 194 projecting downwardly 
therefrom. The sleeve projections 194 have passages 196 opening 
therethrough. A longitudinal slot 198 also opens through each sleeve 
projection at the front end thereof, a portion of the slot 198 also 
opening through the central portion 188 of the slide into the passage 196. 
A pair of lens holders 200 are adapted to fit within the passages 196. 
Each of the lens holders 200 has a key projection 202 extending 
longitudinally thereof. The key 202 has a lip portion 204 at the upper end 
thereof which projects outwardly from the main body. The main body of the 
key 202 is adapted to fit in a close fitting relationship within the slot 
198 so that the lens holder member 200 may drop downwardly through the 
passage 196 when the key portion 202 is aligned with the notch 192 in the 
support rails 184 of the support plate 40. When the key 202 is cut of 
alignment with the notch 192, the lip portion 204 rides along the support 
rail 184 and holds the lens holder in a raised position. Objective lenses 
206 and 207 are threadably mounted in the lens holders 200. The objective 
lenses 206 and 207 have a housing 208 which has a greater diameter than 
the diameter of the passage 196 in the slide member 186 so that the 
housings 208 limit the extent to which the lenses may drop relative to the 
slide member 186. 
PROJECTION SYSTEM 
The image projection system is illustrated in FIG. 7 of the drawings. As 
shown in FIG. 7 of the drawings, light emanating from the prefocussed lamp 
114 travels along the path 210 and is reflected by a first cold mirror 212 
which, as shown in FIG. 2 of the drawings, is mounted in the demountable 
drawer 104. The light is reflected by the mirror 212 along the path 214 to 
a condenser lens 216. The condenser lens 216 is mounted in the passage 98 
formed in the platform 66 of the base 14. The light beam passes through 
the condenser lens 216 and is directed along the path 218 through a 
portion of the microfiche 44. The image carried by the microfiche 44 is 
projected through the objective lens 206 along the path 220 onto the first 
surface mirror 165. The image is reflected from the mirror 165 along the 
path 222 onto the image receiving surface 166 of the screen 16. The lamp 
114 illuminates the interior of the base 14 and the light from within the 
base is emitted through the index illuminating lens 76 along the path 224 
which projects through the index grid 46. By reason of the fact that the 
index grid 46 and microfiche 44 are mounted in the combined microfiche 
carriage and index holder 18 in a fixed relationship with respect to one 
another and the fact that the index illuminating beam of light travels 
along a path 224 which is located in a fixed relationship with respect to 
the path 218 of the microfiche illuminating light beam, it is possible to 
locate any required portion of the microfiche in the projection path by 
locating the corresponding portion of the index grid in the index 
illuminating path. The slide member 190 is movable so as to permit either 
one of the objective lenses 208 to be located in the path 218. In use, the 
objective lenses 208 may have different magnifications so that the 
magnification of the microfiche reader may be adjusted by the simple act 
of moving the slide 190 to and fro to align the required objective lens 
with the image projecting path 218. Similarly, the carriage 18 is movable 
relative to the condenser lens 216 in the direction of the X-axis and in 
the direction of the Y-axis shown in FIG. 7. This mobility of the carriage 
18 permits any portion of the microfiche 44 and index grid 46 to be 
located in the paths 218 and 224 respectively so that any portion of the 
microfiche 46 may be projected onto the image receiving surface 166 of the 
screen 16. 
OPERATION 
Prior to operation of the microfiche reader, the required objective lenses 
are selected. The optical characteristics of the objective lenses may be 
such that it is necessary to adjust the position of the prefocussed lamp 
114 with respect to the condense lens 216 in order to focus the beam 
emitted from the condenser lens 216 on the objective lens 207. As 
previously indicated, the prefocussed lamp 114 is adjustable with respect 
to the drawer 104. The position of the prefocussed lamp 114 is, therefore, 
adjusted by releasing the clamping nut 118 and moving the lamp 114 
longitudinally of the bottom wall 108 of the drawer. 
In order to locate the microfiche 44 in the microfiche holder 18, the 
microfiche holder 18 is moved in the direction of the X-axis (FIG. 7) 
until the upper glass flat 30 is elevated by engagement of the actuator 
lip 36 with the tongue 38 which projects downwardly from the support plate 
40. The microfiche 44 is then located between the upper and lower glass 
flats 28 and 30 and the carriage 18 is moved inwardly, as a result of 
which the upper glass flat 30 is lowered into a face-to-face relationship 
with the microfiche 44. 
As previously indicated, one of the objective lens members 208 is aligned 
with the path 218. The lens holder 200 of the aligned objective lens rests 
on the upper glass flat 32 while the lens holder of the non-aligned 
objective lens is held in a spaced relationship above the upper glass flat 
32. When the lens holder 200 is aligned with the projection path, the key 
202 and lug 204 are free to slide in the notch 192 in the support rails 
184. By reason of the fact that the lower end of the aligned lens holder 
rests on the upper glass flat, the distance between the objective lens and 
the microfiche 44 is a constant and consequently the objective lens can be 
accurately located with respect to the microfiche and with respect to the 
image receiving surface 166 of the screen 16. 
When the microfiche is operably located in the microfiche holder 18, as 
described above, the microfiche holder 18 may be moved to align any 
required portion of the index grid with respect to the index illuminating 
lens 74. The beam of light emitted through the illuminating lens 74 will 
illuminate the section of the grid corresponding to the portion of the 
microfiche which projected onto the screen. In this manner, any required 
portion of the microfiche may be projected onto the screen by reference to 
the illuminated section of the index grid. 
SUMMARY 
From the foregoing it will be apparent that the microfiche reader described 
above provides a number of improvements over the known structures. In one 
such improvement, the microfiche reader provides a combined microfiche 
carriage and index holder 18. By reason of the fact that both the 
microfiche 44 and the index grid 46 are mounted in a fixed relationship 
with respect to one another, it is easier to accurately locate the 
required section of the microfiche with respect to the illuminating path. 
In addition, the undercarriage support structure for the combined 
microfiche carrier and index holder is designed to provide free movement 
of the carriage 18 with respect to the projection path. The V-shaped 
profile of the guide rails and support wheels is such that there will be a 
minimum backlash in the guide track system. It will also be noted that by 
reason of the fact that the microfiche is retained in a stationary 
relationship with respect to the index grid, any backlash in the 
undercarriage support system does not contribute to any misalignment of 
the microfiche with respect to the grid as would be the case in a 
structure where the microfiche is moved relative to the grid. The fact 
that the upper glass flat is elevated automatically when the carriage 18 
is moved to a predetermined forward position greatly facilitates the 
removal and placement of the microfiche between the upper and lower glass 
flats. 
A further improvement is provided in the structure of the lens assembly in 
that the assembly provides two lens members, either one of which may be 
moved into the projection path as required. Furthermore, the lens assembly 
is designed to permit the objective lens holder to rest on the upper 
surface of the upper glass flat thereby positively locating the objective 
lens in a set position with respect to the microfiche. 
A still further improvement provided by the microfiche reader of the 
preferred embodiment is in the structure of the projection system which 
includes a demountable modular unit 104 which supports a prefocussed lamp 
for movement thereon so that the lamp may be moved towards and away from 
the condenser lens whereby the optical system may be adjusted to 
accommodate objective lenses having different characteristics. This 
provides for a very simple adjustment of the optical system which is not 
available in existing microfiche reader devices. 
A still further improvement provided by further features of the microfiche 
reader is in the projection system which includes a prefocussed lamp, a 
first cold mirror, an optical condenser, an objective lens, first surface 
mirror, and a viewing screen, all of which are mounted in series along the 
projection path. The viewing screen is formed from a unitary body of 
molded plastics material and has an image receiving surface formed with a 
concave spherical curvature. The concave spherical curvature of the image 
receiving surface provides for the minimum distortion of the projected 
image. 
Yet another advantage of the structure of the microfiche reader of the 
preferred embodiment is in the fact that it is not necessary to provide a 
forced air cooling system in order to cool the projection system. The 
prefocussed lamp is preferably a ninety watt lamp. The base member is 
formed with a plurality of ventilating passages 94. The base member 14 is 
supported on feet 81 so that it is spaced above its support surface in use 
so that air may be admitted through all of the ventilating passages 94. 
The air passes upwardly through the base and a portion of the cooling air 
may be discharged from the base through ventilating passages 36 in the 
upper wall of the platform 66. The remaining portion of the cooled air, 
which is the major portion of the air, is discharged from the base through 
the passages 100 in the upper wall 90 to pass through the passages 152 in 
the bottom wall 140 of the hood and to be directed rearwardly from the 
hood through the passage 142 in the back wall of the hood and thus to 
atmosphere. It has been found that this air circulating system provides 
adequate cooling for a ninety watt rated prefocussed lamp 114. 
Furthermore, it has been found that this cooling system sufficiently cools 
the entire housing of the microfiche viewer to an extent that the viewer 
may be made entirely from an injection molded plastics material such as 
Merlon SF600 structured foam plastic. By reason of the fact that all of 
the various components of the viewer housing and carriage may be made from 
injection molded plastic material, the overall cost of production of the 
microfiche viewer can be minimized in a mass production process. 
These and other advantages of the microfiche viewer of the present 
invention will be apparent to those skilled in the art.