A rolling loop motion picture projector is convertible for projecting images either from a 2-D film strip or from a 3-D film strip. The film is advanced through the same incremental amount irrespective of whether a 2-D film of a 3-D film is being projected. The projector has a single central aperture for projecting 2-D images and respective 3-D images on opposite sides of the central aperture. The images on the 3-D film strip are anamorphically compressed in the direction of film travel by a factor of two and the 3-D apertures are correspondingly sized. Projection lenses associated with the 3-D apertures decompress the images so that images of comparable size appear on the screen irrespective of whether a 2-D film or a 3-D film is being shown.

FIELD OF THE INVENTION 
This invention relates to so-called "rolling loop" motion picture film 
projectors. 
BACKGROUND OF THE INVENTION 
The principles of a rolling loop motion picture projector are well known 
and are disclosed, for example, in U.S. Pat. No. 3,494,524 (Jones) and 
U.S. Pat. No. 3,600,073 (Shaw), the disclosures of which are hereby 
incorporated by reference. Briefly, the expression "rolling loop" refers 
to a film transport mechanism which includes a stator and a rotor that 
together define a film path. The rotor is rotatable with respect to the 
stator and has gaps in which loops of film are progressively formed and 
then decay as the rotor rotates for advancing film past an aperture 
location. Rolling loop motion picture projectors are available 
commercially from Imax Corporation of Mississauga, Ontario, Canada. 
IMAX.TM. rolling loop projectors are used for showing both 2-D and 3-D 
films. Two projectors typically are used for 3-D presentations, one for 
projecting "left-eye" images and the other for projecting corresponding 
"right-eye" images. The images may be separated using mutually 
extinguishing polarizers, in which case audience members wear glasses with 
correspondingly polarized lenses so that the viewer's left eye sees only 
left-eye images and the viewer's right eye sees only right-eye images. 
An alternative method of stereo image separation is so-called "alternate 
eye" in which left eye and corresponding right eye images are projected 
alternately and viewers wear glasses having lenses that are alternately 
transmissive and non-transmissive in synchronism with the projected 
images. Again, the viewer's left eye sees only projected left-eye images 
and the viewer's right eye sees only projected right-eye images. 
Typically, electro-optic liquid crystal cells are used as the lenses in 
the glasses. 
In motion picture theatres, there is a demand for variety in programming. 
Projector installations should be capable of allowing quick interchange 
between different films and films of different formats. 
A 3-D IMAX.TM. theatre installation typically has two projectors, which are 
used together to show 3-D films or either of which can be used to show 2-D 
films. However, such an installation obviously requires the capital cost 
and maintenance cost of two projectors. 
A dual rotor rolling loop projector is disclosed in U.S. Pat. No. 4,966,454 
(Toporkiewicz) and can be run either with two filmstrips as a 3-D 
projector or a single filmstrip as a 2-D projector. However, such a 
projector is relatively complex and costly. 
An object of the present invention is to provide a less complex form of 
rolling loop projector that is convertible for showing 2-D or 3-D films. 
SUMMARY OF THE INVENTION 
The projector provided by the present invention has a rolling loop film 
transport mechanism including a stator, a rotor which is rotatable with 
respect to the stator, the rotor and stator defining a film path, and the 
rotor having gaps in which loops of film are progressively formed and the 
decay as the rotor rotates, for advancing the film in defined incremental 
amounts past an aperture location. Means is provided at the aperture 
location defining a central aperture against which successive frames of a 
2-D film can be registered as the film is advanced through said defined 
incremental amounts, and a pair of 3-D apertures on respectively opposite 
sides of the central aperture against which frames of a 3-D film carrying 
respective left- and right-eye images can be registered. The 3-D apertures 
are dimensioned and located with respect to the central aperture so that 
successive pairs of 3-D frames can be registered with the 3-D apertures as 
the 3-D film is advanced by rotation of the rotor through the same 
incremental amount as a 2-D film is advanced. Projection lens means is 
associated with the apertures and is adapted to produce projected images 
selectively either from a 2-D film projected through the central aperture 
or from a 3-D film projected through the 3-D apertures. The projector also 
includes projection lamp means convertible for projecting a single beam 
through the central aperture or two beams through the 3-D apertures. 
In other words, the invention provides what is essentially a "standard" 2-D 
rolling loop film projector that can run either a standard 2-D filmstrip 
or a 3-D filmstrip. Since the rolling loop mechanism of the projector will 
advance the film through the same incremental amount irrespective of the 
images on the filmstrip, a specially prepared filmstrip must be used for 
3-D image presentation. Preferably, the 3-D images are anamorphically 
compressed by a factor of two in the direction of film travel as compared 
with a standard 2-D image. In other words, two 3-D images fit into the 
same area of the film as a single 2-D image. The images must also be 
separated in the direction of film travel by a distance equal to the 
length of a normal 2-D format image. 
For example, in the art, the length of the film image (in the direction of 
film travel) is normally referred to in terms of the number of marginal 
perforations in the film that correspond to the length of one image, e.g. 
"15 perf". Accordingly, if 15 perf is the normal length of a 2-D image, 
the 3-D images will be anamorphically compressed to occupy a space of 7.5 
perf and the images will be separated from one another by 15 perf. As the 
film is advanced at each increment, successive images on the filmstrip 
will be brought into register with the relevant aperture or apertures, 
whether the film is a 2-D film or a 3-D film. 
The projection lens means of the projector will then be optically designed 
to decompress the 3-D images so that the projected images will be of 
comparable size whether 2-D or 3-D images are being projected. 
Anamorphic compression of the 3-D images can be accomplished using optical 
printing techniques in preparing the film. Some re-arrangement of the 
sequence of the images on the filmstrip will also have to be undertaken 
during printing, as compared with the "natural" sequence in which the 
images will be captured in shooting a film.

DESCRIPTION OF PREFERRED EMBODIMENT 
Central to this embodiment of the present invention is the technique 
illustrated in FIG. 1 for producing successive pairs of alternating 
left-eye and right-eye stereoscopic images on a single filmstrip. The 
image format on the filmstrip is shown in FIG. 1(c) where the filmstrip 
itself is denoted by reference numeral 20. FIG. 2 shows a comparable 2-D 
filmstrip 22 for use in the projector of the invention. Before describing 
to FIGS. 1 and 2, however, it may be helpful to briefly refer to FIGS. 3 
and 4 which show diagrammatically and in plan, the principal components of 
the projector for projecting filmstrip 20 or 22. FIG. 3 shows the 
projector configured for 3-D image presentation while FIG. 4 shows the 
projector configured to project 2-D images. 
The projector has a rolling loop film transport mechanism of the general 
type described in the Jones and Shaw patents referred to supra. The 
mechanism includes a stator 24 and a rotor 26 which is rotatable with 
respect to the stator. The rotor and stator co-operate to define a film 
path. In FIG. 3, the 3-D filmstrip 20 is shown in the film path while in 
FIG. 4 the 2-D filmstrip 22 is shown in the path. The rotor has gaps 28 in 
which loops of film are progressively formed and then decay as the rotor 
rotates for advancing film in defined increments past an aperture location 
generally denoted 30. Input and output sprockets for feeding the film into 
the film path and withdrawing it from the film path respectively are 
indicated at 32 and 34. 
For clarity of illustration, film loops have not been shown in the gaps in 
the rotor; reference may be had to the Jones and Shaw patents for a 
detailed description of the rotor structure. Suffice it to say that light 
can pass outwardly through the rotor as generally indicated by the arrows 
36 in FIG. 3 and 38 in FIG. 4 in the areas between the rotor gaps 28. 
Shutters 40 are provided across the gaps so that light is obstructed when 
the shutters pass through the projected light beams. Similar so-called 
"flicker" shutters can be provided between the gaps to provide an 
acceptable flicker rate. Again for ease of illustration, only four rotor 
gaps are shown in FIGS. 3 and 4 although in practice a larger number of 
gaps normally will be provided (e.g. 12). A cam unit for decelerating the 
film as it approaches the aperture location is indicated at 42. 
Outwardly of the rotor at the aperture location 30 is an aperture block 
assembly generally denoted 44. The aperture block assembly is shown in 
detail in FIGS. 11 to 16 which will be described later. The aperture block 
assembly provides a single central aperture indicated at 46 in FIG. 4 at 
which successive frames of 2-D film 22 can be registered as the film is 
advanced by rotation of the rotor. A light beam projected from a 
projection lamp 48 (FIGS. 5 and 6) is shown in FIG. 4 at 50 and is 
directed through aperture 46 and film 22. 
On opposite sides of aperture 46 are a pair of 3-D apertures 52, 54 (FIG. 
3), against which frames of a 3-D film carrying respective left- and 
right-eye images can be registered. The 3-D apertures 52, 54 are located 
with respect to the central aperture so that successive pairs of 3-D 
frames can be registered with the 3-D apertures as the film is advanced by 
rotation of the rotor 26. As noted previously, the rotor advances the film 
through the same incremental amount whether a 2-D film or a 3-D film is 
being projected. Accordingly, the images must be appropriately arranged on 
the filmstrip 20 (FIG. 1(c)) to ensure proper registration with the 
apertures 52, 54 and the spacing between successive pairs of apertures 
must be equal to the film advance increment, i.e. the length of a single 
normal 2-D image. 
As will be described in more detail in connection with FIGS. 1 and 2, in 
order to achieve the required image format on the film, the 3-D images are 
anamorphically compressed in the direction of film travel by a factor of 2 
as compared with the 2-D images. 
Respective light beams 56 and 58 for the two 3-D images are shown in FIG. 3 
emanating from the projection lamp 48 (FIGS. 5 and 6). Outwardly of the 
aperture block assembly 44 is a projection lens assembly 60 that includes 
a single central lens 62 for the 2-D images (see FIG. 4) and two outer 
lenses 64 and 66 for the 3-D images. These lenses are optically designed 
to decompress the anamorphically compressed images on the filmstrip 20 so 
that the images that appear on the screen are normal uncompressed images 
of comparable size to the images that are projected through the central 
lens 62. from the 2-D filmstrip 22. 
Reverting to FIG. 1, the 3-D filmstrip 20 and the method by which it made 
will now be described. FIG. 1(a) shows diagrammatically at 70 a 3-D camera 
that is used to record successive left-eye and right-eye images of an 
object 72. The camera has left-eye and right-eye lenses 74 and 76 through 
which left-eye and right-eye views respectively of the object are recorded 
on a filmstrip 78. FIG. 1(b) shows the images as they appear on the 
filmstrip 78. The first pair of images L.sub.1 and R.sub.1 appear adjacent 
to one another and are followed by a second pair of images L.sub.2 and 
R.sub.2, and so on. Typically, each image will occupy a length of the 
filmstrip (in the direction of film advance) equal to 15 of the marginal 
perforations P on the filmstrip. FIG. 2 shows a typical 2-D filmstrip with 
normal sequential "15 perf" images numbered 1, 2, 3 and 4. 
FIG. 1(c) shows the final 3-D filmstrip 20 that is used in the projector. 
The images that are recorded in the camera 70 on filmstrip 78 (FIG. 1(b)) 
are converted into the format shown in FIG. 1(c) by an optical printing 
technique performed in a conventional optical printer fitted with an 
anamorphic lens assembly that horizontally compresses the images by a 
factor of 2 so that each of the images on filmstrip 20 occupies a length 
of only 7.5 perfs. In order to provide for proper sequencing of the images 
on the filmstrip, the images must also be interlaced to produce the 
sequence shown in FIG. 1(c). The printer has a film movement which is set 
to produce the required interlacing. The movement involves two sequential 
operations, a 22.5 perf advance (to record the second image of the image 
pair after the first image of that pair has been recorded) followed by a 
7.5 perf retreat (to record the first eye image of the next image pair). 
In FIG. 1(c) the dotted outlines denoted 52 and 54 represent the two 3-D 
apertures 52 and 54 referred to previously in connection with FIG. 3 and 
outline 46 represents the central 2-D image aperture. It will be seen that 
the image sequence on the filmstrip allows the left-eye image of the first 
pair to be in register with aperture 52 at the same time as the right-eye 
image of that pair is in register with aperture 54. Also, the area between 
the L.sub.1 and R.sub.1 images is of a length equal to the length of a 
normal 15 perf 2-D image. The film advance mechanism of the projector 
moves the film through the length of one normal 2-D image (15 perfs) at 
each increment. When the film advances (to the left) from the position 
shown in FIG. 1(c), the left-eye image L.sub.2 of the second pair is 
brought into register with aperture 52 and the right-eye image R.sub.2 of 
that pair into register with aperture 54. Subsequent frame pairs similarly 
register with the respective apertures as the film is advanced. 
FIGS. 5 and 6 show diagrammatically the projection lamp means of the 
projector of FIGS. 3 and 4 and, in conjunction with FIGS. 7 and 8, 
illustrate how the projection lamp means is convertible for projecting a 
single beam through the central aperture 46 or two beams through the 3-D 
apertures 52 and 54. 
FIG. 5 shows the projection lamp 48 and illustrates the fact that the lamp 
is positioned to project a light beam 80 upwardly towards a mirror 82 by 
which the beam is then reflected forwardly to the projection lens assembly 
60. For clarity of illustration, only these components have been shown. 
As seen in FIGS. 7 and 8, mirror 82 is circular and has two distinct 
semi-circular surface portions 84 and 86, one (84) of which is plane, 
while the other (86) is defined by a series of parallel ridges 88 that 
extend normal to the diametral line 90 at which the two surface portions 
84 and 86 meet. Reverting to FIG. 5, it will be seen that the mirror is 
designed to be turned about its centrepoint by an electric servo-motor 92 
so that either the plane surface portion 84 of the mirror or the ridged 
surface portion 86 can be moved into the path of the light beam 80 from 
lamp 48. 
When a 2-D film is to be projected, the plane surface portion 84 of the 
mirror is positioned in light beam 80 so that a single beam of light is 
reflected from mirror 82 to the 2-D projection lens 62 as shown in FIG. 7. 
When a 3-D film is to be projected, mirror 82 is turned to bring its 
ridged surface portion 86 into the path of light beam 80. Referring to 
FIG. 8, each of the ridges 88 is precision formed in surface portion 86 of 
mirror 82 so that the light beam 80 that is incident on the mirror from 
projection lamp 48 is split into two distinct beams 94 and 96 as the light 
is reflected off the mirror, and the respective beams are directed to the 
left and right hand projection lenses 64 and 66 of the projector, for 
projecting the left- and right-hand image pair on film 20. As mentioned 
previously, the lenses 64 and 66 are different from lens 62 in that they 
are engineered to anamorphically decompress the images so that the images 
appear at normal size on the projection screen. Alternate projection of 
the images is achieved by appropriate timing of the shutters 40 of the 
projector, in known manner. 
Since the 3-D images on film 20 (FIG. 1(c)) are narrower than the 
corresponding 2-D images on film 22 (FIG. 2), it is desirable to use a 
narrower light beam for projecting the 3-D images, in order to maximize 
transmission of available light. Accordingly, the projector also includes 
provision for vertical movement of the projection lamp 48 as illustrated 
in FIG. 6, between an upper position for 2-D projection, and a lower 
position for 3-D projection. FIG. 6 shows the projection lamp in full 
lines in its lower position for 3-D projection and in chain-dotted lines 
in an upper position for 2-D projection. Reference numeral 98 denotes the 
larger beam that is achieved in the upper position for 2-D projection, 
while reference numeral 94 indicates one of the two narrower beams 
required for 3-D projection. 
The required vertical movement of lamp 48 can be achieved by any convenient 
mechanical means. For example, the projection lamp could be supported by a 
carriage that is mounted for vertical movement in guides by means of a 
rack and pinion arrangement under the control of an electric servo-motor. 
FIGS. 9 and 10 show timing diagrams respectively for 3-D image projection 
and 2-D image projection. The horizontal (X) axis represents time while 
the vertical (Y) axis indicates the intensity of the projected light. The 
respective axes are shown to the same scale in both views. In FIG. 9, the 
diagram denoted (a) shows the left-eye light while the diagram indicated 
(b) shows the right-eye light. 
While it would be possible to operate the projector of the invention using 
polarizers for separating the left-eye and right-eye images, the preferred 
approach is to use the alternate eye technique referred to previously. 
This is illustrated by comparing FIGS. 9(a) and (b). It will be seen, for 
example, that the light intensity for the left-eye image (FIG. 9(a)) rises 
to a maximum level at which it continues before falling off rapidly, at 
the same time as the intensity of light for the corresponding right-eye 
image begins to increase from zero. In other words, only one image is on 
the screen at any one time. This is achieved by the timing of the shutters 
40 carried by the rotor of the projector. 
FIG. 10 shows a single and similar but more elongated profile for the light 
that passes through the central aperture 46 during 2-D projection and 
occurs because the 2-D aperture 46 is longer in the direction of film 
travel than the 3-D apertures 52 and 54. 
FIGS. 11 to 16 show in some detail the aperture block assembly 44 referred 
to in connection with FIGS. 3 and 4, as seen from the rotor side, i.e. 
looking towards the screen. The film path is denoted F (film 20 or 22), 
and the projection lenses are indicated at 62 (2-D lens) and 64 and 66 
(3-D lenses). The path of the film F remains the same whichever film is 
projected but the projection lenses move vertically depending on which 
film is being used, as will be described. 
The aperture block assembly has a fixed base or frame 100 and includes a 
carriage 102 that is vertically movable in the frame 100 under the control 
of an air cylinder 104. The projection lenses 62, 64 and 66 are secured to 
and move with carriage 102. 
Sets of register pins for engaging the perforations in the film are shown 
on frame 100 on opposite sides of the carriage in the film path and are 
denoted 106 and 108 respectively. As shown in FIG. 11, the carriage 102 is 
in a position for projecting 3-D images and the left and right 3-D 
apertures are represented at 52 and 54 respectively. The apertures are in 
fact defined laterally (in the direction of film travel) by two guideways 
110 and 112 respectively in the carriage, each of which receives a 
so-called "field flattener" lens element, the two elements being denoted 
respectively 114 and 116. As successive image pairs are brought into 
position for projection by rotation of the rotor, the image portions of 
the film are laid onto the inner surfaces of the lens elements 114, 116. 
The vertical limits of the respective apertures are defined by the cone of 
light from projection lamp 48. 
Each of the field flattener lens elements 114, 116 is vertically slidable 
in its respective guideway 110, 112 under the control of an associated air 
cylinder, 118 or 120, so that "clean" portions of the lens element surface 
can periodically be brought into position for engagement by the film, and 
any debris that has accumulated on the lens element is moved aside. 
Reference may be made to U.S. Pat. Nos. 4,365,877 and 4,441,796 (Shaw) for 
a detailed description of displaceable field flattener lens elements of 
this type. The disclosures of the Shaw patents are incorporated herein by 
reference. 
FIG. 12 shows the carriage 102 and the lens elements 114 and 116 in the 
positions in which they are shown in FIG. 11, for projecting a 3-D film 
20. FIG. 13 is a similar view but showing the two lens elements 114 and 
116 having been moved down to bring a "clean" portion of the lens element 
surface into position for contact by the film. FIG. 16 shows corresponding 
sectional views on lines A--A of FIGS. 12 and 13. Wiper blade elements 122 
and 124 are shown above and below the film respectively for cleaning the 
lens element surfaces in accordance with the teachings of the '877 and 
'796 Shaw patents. 
FIGS. 12 and 13 also show that the carriage includes, between the two 
apertures (represented in this view by outlines of the projection lenses 
64 and 66), a fixed plate 126 (see also FIG. 11) which forms part of the 
carriage and across which the film is laid during projection. Formed in 
the plate are a series of vertical slots 128 comprising vacuum ports, for 
holding the film flat against the lens elements 114, 116 during 
projection. 
FIG. 12 also shows T slots 130 and 132 that are provided in the bottom 
faces of the respective lens elements 114 and 116 and are engaged by 
complimentary formations on the respective air cylinders 118 and 120 so 
that the lens elements can readily be disconnected from the air cylinders 
and changed (when the film is not present). 
FIGS. 14 and 15 show carriage 102 as having been moved to an upper position 
as compared with the position shown in FIGS. 11, 12 and 13 so that the 2-D 
projection lens 62 is positioned in the film path, for projecting 2-D 
images. In other words, FIGS. 14 and 15 show the position of the carriage 
102 for projecting a 2-D film. Again, a field flattener lens element 
assembly (denoted 134) is mounted in a guideway 136 in carriage 102 so 
that the film is laid onto the inner surface of the lens element during 
projection. This lens element is also vertically movable for cleaning and 
may have associated wipers (not shown). In this case, an air cylinder 138 
is mounted above the lens element and the lens element is coupled to the 
air cylinder by a T-shaped coupling arrangement similar to that described 
in connection with the lens elements 114 and 116. FIG. 15 shows the lens 
element 134 as having been moved up with respect to its position in FIG. 
14, for cleaning. 
Respective series of vacuum ports 140, 142 are provided in carriage 102 on 
opposite sides of lens element 134, for holding the film flat against the 
inner surface of that element during projection. 
In summary, the invention provides a projector that is quickly and easily 
convertible for showing either a 2-D film or a 3-D film without the cost, 
complexity or maintenance requirements for using two projectors for 3-D 
projection, or of a double-rotor projector. 
It will of course be appreciated that the preceding description relates to 
a particular preferred embodiment of the invention and that many 
modifications are possible. 
In most applications, anamorphic compression of the 3-D images, and 
subsequent decompression during projection will be required. The projected 
images will then appear as of comparable size to an audience, whethe 2-D 
or 3-D. However, it is conceivable that such anamorphic compression and 
decompression may not be essential, for example, if a special effect is 
required. 
Similarly, it would be possible to use separate light sources for 2-D and 
3-D image projection, although it is preferred to use a single light 
source and a special mirror to produce either a single beam of light for 
2-D image projection or two beams of light for 3-D projection. The mirror 
that is used to achieve this effect could be designed as in the preferred 
embodiment, although different mirror surface configurations are possible. 
For example, individual mirror facets could be used to split the incident 
light into two beams, rather than the ridged arrangement described. The 
mirror could be moved linearly rather than rotationally to bring different 
surface portions of the mirror into the path of the light. 
Similarly, movement of the lamp towards and away from the mirror, while 
preferred, is not essential. 
Finally, the particular design of the aperture block assembly shown in 
FIGS. 11 to 16 is preferred but not essential. A simple fixed assembly 
with immoveable field flattener lens elements could be used where 
accumulation of debris is not a concern. The arrangement described is, 
however, preferred because it not only provides for cleaning of the lens 
element assemblies but also allows for incorporation into the aperture 
block assembly of suction ports for holding the film against the lens 
elements.