CROSS REFERENCE TO RELATED APPLICATION 
     This is a divisional of U.S. patent application Ser. No. 09/665,132, filed Sep. 19, 2000, in the name of Yet Chan and entitled “FILM ALIGNMENT MECHANISM AND FRAME COUNTER RESETTING MECHANISM”, now U.S. Pat. No. 6,587,645. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a mechanism suitable for ensuring alignment within a camera of film having pre-exposed latent images thereon, and to a camera incorporating such a mechanism, and to a film frame counter resetting mechanism. 
     It is known to provide photographic film which has been partly exposed in regions of each film frame with an image which is retained as a latent image. The user who loads the film then exposes the film in the normal manner in a specially adapted camera. The camera includes some masking arrangement to mask out the area of the film which bears the latent images, so that these are not double-exposed. When the film has been exposed by the user, it is processed and developed in the normal way, the finished pictures bearing both the pre-exposed images provided by the manufacturer (hereinafter referred to as “pre-exposed images”), and the user-exposed images thereon. For example, it can be arranged that the film is pre-exposed with a decorative strip which carries a message such as “happy birthday” or “wish you were here”, the camera including a strip-like mask in the exposure window to prevent double-exposure of the pre-exposed film region. 
     It has been previously proposed by the applicant to provide such a film in a package or assembly comprising a standard 35 mm cassette and a second spoolless film container into which the film is wound extending from there to the cassette. Such a film package is disclosed for example in applicant&#39;s U.S. patent application Ser. No. 10/141,751. In use, the assembly is fitted into the camera with the cassette and film container arranged on opposite sides of a film exposure window. As pictures are successively taken the film is progressively wound out of the film container back in the cassette, finally being wound back fully into the cassette which can then be removed by the user for developing and processing. The film container is then discarded. 
     A particular problem arises in seeking to align the film in the camera, since it is necessary that the film be precisely positioned in the camera so that the pre-exposed images align precisely with the exposure window of the camera and hence the user-exposed images. 
     In one aspect the present invention is directed to ensuring this alignment. 
     SUMMARY OF THE INVENTION 
     In a first aspect the invention provides a camera for use with film bearing a series of latent pre-exposed images for subsequent user-exposure, comprising a film sprocket mechanism extending into a film passageway, the sprocket mechanism having a plurality of equidistantly-spaced teeth including an alignment tooth which is visually distinguishable from the other tooth, and comprising a main wheel part on which said other teeth are formed, and a separate part securable to the main wheel part which carries the alignment tooth. 
     The alignment tooth may be formed of a different colour to the other teeth, either by painting the alignment tooth or moulding it of a different coloured plastics material. 
     These parts may be formed of moulded plastics where the plastics are of contrasting colours. The main wheel part may define a part-annular recess, and the alignment tooth extends from a part-annular insert receivable in said recess. The sprocket wheel may be operatively commented to a shutter mechanism and wind-on mechanism where rotation of the sprocket wheel is arranged to effect re-cocking of the shutter mechanism. The wind-on mechanism prevents rotation of the sprocket wheel when the shutter is re-cocked. In the re-cocked state of the shutter mechanism the alignment tooth extends rearwardly within the camera towards the film passageway. 
     In a further aspect the invention resides in a sprocket wheel as defined above. 
     In a further aspect the invention resides in a method of loading film bearing a series of pre-exposed latent images for subsequent user-exposure into a camera having a film sprocket wheel operatively connected to a shutter mechanism and provided with a film alignment tooth, comprising the steps of: a) opening the camera back; b) rotating the film sprocket wheel until the film alignment tooth thereof extends towards the film passageway, and until the shutter mechanism is re-cocked; c) inserting film into the camera so that an alignment mark on the film is aligned with the alignment tooth; and d)closing the camera back. 
     A further problem with simple cameras of this type where the user reloads the film is in re-setting of the film frame counter, and a second aspect of the invention is directed to a mechanism for carrying out this resetting. 
     In a further aspect directed to resetting of the film frame counter, the invention resides in a camera having a pair of film-receiving chambers arranged on opposite sides of an exposure window between which, in use, film extends through a film passageway: a film sprocket wheel having a plurality of teeth which, in use, engage a film extending within the film passageway; a film counter drive wheel operatively connected to the film sprocket wheel driven by rotation of the sprocket wheel; a pivotably mounted film frame counter wheel mounted on a displaceable pivot engageable with the drive wheel; and resilient means which urge the film frame counter wheel to a reset position in which the film frame counter wheel adopts a predefined orientation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention are now described, by way of example only, with reference to the following drawings in which: 
     FIG. 1 shows a camera in accordance with an embodiment of the invention with a back cover opened and a film door removed; 
     FIG. 2 shows the insertion of a film package into the camera; 
     FIG. 3 shows the film fitted into the camera and correctly aligned with an alignment sprocket; 
     FIG. 4 shows the camera with the back fitted thereon; 
     FIG. 5 shows the shutter and wind-on mechanisms of the camera; 
     FIG. 6 shows a mechanism for re-setting a film frame counter when the counter is at a “start” position; 
     FIG. 7 shows the mechanism of FIG. 6 at a position corresponding to part exposure of a film; and 
     FIG. 8 shows the mechanism of FIG. 6 on re-setting. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As seen in FIG. 1, the camera, indicated generally by numeral  2 , includes a main body part  4  which carries the majority of the operative components of the camera  2 , and a front cover part  6  and rear or back cover part  8  which together enclose the main body  4 . The main body  4  supports a shutter mechanism  9  provided with a lens assembly  11  (FIG.  5 ), a front portion of which extends through an aperture in the front cover part  6 . The main body  4  defines part of a first film-cassette receiving chamber  12  which receives a film-containing cassette or patrone  13  of a film package or assembly described further below. Other standard film formats can equally be accommodated with appropriate modification. A second film receiving chamber  14  is arranged at the opposite side of the camera. Between the film chambers  12  and  14  is arranged an exposure window  18  located between upper and lower film guides  20 ,  22  which support the film at its edges as it extends between the film chambers. A film passageway for the film to travel between the film chambers  12  and  14  is defined between the back cover  8  and opposed region of the main body  4  and film guides  20 ,  22 . The main body  4 , and front and rear cover parts  6 ,  8  define an opening at the lower end of the film cassette chamber  12 , which is closed in use by a removable film door  24 , allowing removal of the film cassette  13  through the opening once the film has been exposed. As is known in the art, the film door  24  and adjacent parts of the main body  4  are provided with appropriate adaptations in the form of co-operating grooves on the cover plate  24  and flanges on the main body  4  which together ensure light-tight closure of the opening. 
     The rear cover part  8  is removably fitted to the main body  4 . This is achieved by providing at opposite edges a pair of protrusions  25  on the main body  4  which snap-fit into apertures  27  on the back cover  8 . Alternatively, the back cover  8  can be hingedly secured to the main body  4  or the front cover  6  and a releasable latch provided to allow opening and closing of the back cover  8 . These arrangements allow the user to readily open and close the camera for reloading films therein. 
     As is conventional, the camera is provided with a wind-on mechanism including a rotatable film advance wheel or thumb wheel  30  having a plurality of teeth held on top of the main body  4  beneath a plate  31 , and lower shaped drive shaft  32  which extends into and engages the central spool of the conventional film patrone or cassette  13 . The mechanism includes a film sprocket wheel  34  located just above the film exposure window  18 , and a film counter. The film sprocket wheel  34  is operatively connected to the re-cocking mechanism of the shutter, so that each time the film is wound on one frame by the user (by turning the film advance wheel), the film sprocket wheel is rotated one turn, which primes the shutter, and in addition prevents further rotation of the film advance wheel  30 , as is further described below. 
     The film is provided in the form of a film assembly comprising a first film cassette  13  which is a conventional 35 mm cassette or patrone, and a second film container  15  preferably of a smaller dimension than a conventional cassette, into which the majority of the film is pre-wound before the assembly is supplied to the user. A flexible backing strip  17  is joined to both cassette  13  and container  15  to prevent separation of the cassette  13  and container  15  which could result in inadvertent withdrawal of film. A cut-out portion  19  is provided in the backing strip  17  exposing a portion of the film edge. As can be seen more clearly in FIG. 3 the film is provided with an alignment notch  21  adjacent an alignment perforation  23 . 
     FIG. 1 shows in the inset a sprocket gear  34  comprising eight sprocket teeth, the gear being precisely dimensioned so the circumference is the dimension of one film frame so that the teeth fit into the sprocket holes of a 35 mm film and so that advance of the film by a single film frame causes precisely a single rotation of the gear. 
     The sprocket gear  34  comprises two separate parts, namely a main gear  38  having seven spaced teeth and which defines an annular or a part-annular recess  40 , and a slot at the position of the eighth tooth, and a separate alignment tooth part  42  formed on a part-annular portion  44  which constitutes an insert fitting into the recess  40 . This allows the alignment tooth  42  to be moulded out of a different coloured plastics material; for example, the majority of the camera components are usually of black moulded plastics; alignment tooth  42  may be of a contrasting colour such as white. 
     The shutter mechanism  9  contains a spring-loaded shutter plate which has an exposed end S arranged to be stroked by a striker  50  (further discussed below) of a trigger mechanism  140  for momentarily flicking the shutter plate (shutter release) and thus opening an exposure aperture behind the lens to permit photographic exposure on the film through the exposure chamber  18 . 
     The trigger mechanism  140  is formed by the striker  50  which is horizontally pivotable and an assembly of the sprocket  34  and an upper cam  70  which are axially inter-engaged for simultaneous horizontal rotation. The striker  50  has first, second and third side projections  51 ,  52  and  53  and is spring-loaded by spring  90  to, on release, turn in the anti-clockwise sense (viewed from above) and also to move upwards, thereby urging the second projection  52  to stroke the shutter plate end S and urging the third projection  53  against the cam  70 . 
     The sprocket  34  is keyed to the cam  70  so that upon movement by the film-advancing wheel  30 , the film rotates the sprocket  34  and in turn the cam  70  above in the same direction. 
     The cam  70  has an upper circular disc portion  71  (shown in dotted lines to allow the features below to be seen) having a side cutout  72  and a lower radially expanding cam portion  73  having a radial step  74 , the cutout  72  being formed immediately in front of the step  74  below. The cam portion  73  is arranged to be in side contact with the third projection  53  of the striker  50  for, upon rotation by the sprocket  34  and through a cam action, turning the striker  50  in the opposite clockwise direction against the action of a spring  90 . The striker  50  will stop turning when its third projection  53  reaches and interlocks from below with the cutout  72 , the striker moving upwards under the continual upward action of the same spring  90 . At this time, all the aforesaid rotating and turning actions stop and the film advancement is just completed. At this position a lug  80  on the first projection  51  is urged up to engage the film advance wheel  30  from below preventing it from being rotated. The sprocket wheel  34  also cannot be rotated as the cam  70  is prevented from rotating by the third projection  53 . 
     At such time, the film strip has just been advanced for one frame and the trigger mechanism  140  is primed or re-cocked ready for action to permit photographic exposure on the film strip. For this purpose, the user is required to depress a trigger button (not shown) which engages the top  92  of the striker&#39;s axle for moving the striker  50  downwards to release the third projection  53  is urged to turn back quickly under the action of the spring to have its second projection  52  stroking the shutter plate end S as described above. The projection  80  is then clear of the film advance wheel  30  which can then be rotated to wind on the film. 
     It is arranged that the sprocket gear  34  is positioned on the cam  70  so that at the position in which the alignment tooth  42  is extending exactly rearwardly towards the film, the shutter mechanism is re-cocked and the sprocket  34  cannot be moved any further. Thus, the position of the alignment tooth  42  is precisely defined and cannot be varied by the person installing the film, whereby precise alignment of the film bearing pre-exposed images with the film frame can be readily achieved. 
     In use, the user opens the camera back as shown in FIG.  1 . The film door  24  will have been previously removed to remove the exposed film, or in the case of a new camera, is detached. 
     The sprocket gear  34  must be rotated manually in an anti-clockwise sense (viewed from above) or rightward direction (viewed towards the rear of the camera) until it can be rotated no further at which position the alignment tooth  42  will point exactly rearwardly towards the film. 
     As shown in FIGS. 2 and 3 a film package is fitted into the film chambers with the alignment notch  21  aligned with the alignment tooth  42 . The film door is fitted and camera back closed. In this position the film counter will show the number of exposures remaining eg 27 exposures, as shown in FIG.  4 . The camera is then ready for use by the user with the film precisely aligned therein. 
     In an alternative modification, instead of forming the alignment tooth  42  as a separate part, the sprocket wheel can instead have all eight teeth formed unitarily, and the alignment tooth can be painted a separate colour or coated in some other way to give a contrasting colour to the other seven teeth. 
     In a still further alternative the alignment tooth is distinguished by some other indicating means such as use of a marking, indicia or symbol or letters or similar. 
     In a still further alternative the alignment tooth may have a different shape to distinguish it from the other seven teeth. 
     FIG. 5 also shows a film frame counter  100 . The counter  100  has a plurality of peripheral teeth, and markings indicative of the number of film frames remaining and is supported on the top plate  31 . It is driven for rotation by a drive wheel  102  formed unitarily with the top of the cam  70 . Thus, as the cam  70  rotates as film is wound on the counter  100  rotates, by a single tooth for each film frame. 
     Unlike a conventional film frame counter wheel which is mounted to rotate about a fixed pivot point, the counter wheel  100  is mounted on a movable axis. 
     More particularly, a lever  104  is provided which is itself mounted on the top plate  31  and beneath the counter  100  (note that the overlying portion of the counter is cutaway in the drawings to show this) to pivot about point P. At one end  105  the lever  104  supports the film frame counter wheel in a manner to allow rotation. At the other end  106  the lever  104  is provided with an actuating surface which bears against the inside of the camera back  8  when the back is closed, as discussed further below. 
     The film counter wheel  100  is provided with resilient means in the form of a coil spring  108  which extends between a claw  110  on the top plate and a short finger  112  depending on the underside of the film frame counter wheel  100  adjacent to the pivot. 
     When the camera back is open the lever  104  is unconstrained by the back and the force of the spring  108  (FIG. 8) urges the lever  104  in the direction of the arrow A in FIG.  1  and pulls the axis of the film frame counter wheel  100  away from the counter wheel drive gear  102  so the periphery is disengaged therefrom. The film frame counter wheel  100  is thereby unconstrained by the drive gear  102  and will rotate to adopt the position shown in FIG. 8 where the lever abuts a stop  114  on the underside of the top plate  31 . 
     After insertion of film into the camera, the camera back is closed so that the back bears against the actuating end  106  of the lever  104  urging this to pivot through a small angle in the direction of the arrow B in FIG.  6 . In this position the edge of the film frame counter wheel  100  bears against the counter wheel advancing drive gear  102 . In this position a “start” or S mark on the film frame counter  100  will be aligned with the frame counter window  116  on the top of the outer camera housing. 
     As can be seen in FIGS. 6 to  8 , the actuating end  106  of the lever  104  is joined to the portion which is pivotably mounted on the top plate through a narrowed region which accords a degree of resilience. This gives the bearing of the film frame counter wheel  100  against the drive gear  102  a degree of resilience so that a continuos bearing force is supplied to the gear wheel and means that excessive force is not imparted to the drive gear  102 . 
     As pictures are successively taken and the film is advanced, the drive gear rotates  102  once for each film frame advanced, and for each rotation of the drive gear  102  the film frame counter wheel  110  is rotated in a clockwise sense by a distance corresponding to one tooth. As the film is advanced and the counter wheel  100  progressively rotates the spring  108  becomes increasingly extended, and becomes increasingly wrapped around the pivot. FIG. 7 shows the end of the spring  108  in a position corresponding to 12 exposures remaining on the film. 
     When the end of the film is recorded the film is removed by the user through the film door. In order to reload the camera, the camera door is opened, and when this occurs the pivoting of the lever to the position described above and shown in FIG. 8 is allowed and the rotation of the counter wheel  100  also allowed, thereby automatically resetting the film counter so the start mark S appears in the counter window  116 . 
     The mechanism described allows for automatic re-setting of the frame counter.
A camera for use with film bearing a series of latent pre-exposed images for subsequent user-exposure, comprises a film sprocket wheel ( 34) extending into a film passageway, the sprocket wheel comprising a wheel having a plurality of equidistantly-spaced teeth one ( 42) of which is visually distinguishable from other teeth, for example being formed of a contrasting color.