Self-processing film unit having an internal dark slide

Abstract

 A self-processing photographic film unit of the preregis- tered integral type includes an intemal dark slide which protects the unit from exposure prior to use. The film unit includes a photosensitive element (18) and a cover sheet (30) between which the dark slide (12,112 or 212) is removably positioned to shield one side of the photosensitive element (18) from light. Exposure from the other side (28) is prevented by an opaque layer (22) in the element (18) itself. When used with an opaque processing composition, the unit can be handled in daylight, without fogging, both before and after exposure. The film unit is adapted for use in commercially available adaptors for professional type cameras. Figure 6 is the preferred figure for the abstract

Description

[0001] The present invention relates to self-processing film units including processing composition reservoir means, a photosensitive element and a cover sheet.

[0002] Known self-processing film units (sometimes called "instant-processing" film units) have taken a wide variety of forms, two of which are considered below. One, frequently referred to as a 4 x 5"unit, because of the print dimensions produced by the present commercial product, is shdwn in U.S. Patent No. 3,053,160, issued on Septdmber 11, 1962. This first form may also be referred to ad a'post-registered, peel-apart" film unit, which term refers to the initial and final position of the respectivd elements thereof. Another is depicted in U.S. Patent No. 4,042,395, issued on August 16, 1977. This secdnd form frequently is referred to as a "pre-registered, integral" film unit, which term also refers to the initial and final positions of its elements.

[0003] Both of the above forms include a photosensitive element, a second sheet, and a pod containing processing composition. The photosensitive element has one or more layers of light-sensitive material for recording a latent image that is processable to establish a visible image. The second sheet facilitates distribution of the processing composition over the photosensitive element for initiating such processing. It also may act as a support for the final visible image, but in some integral film units, such as the one described in U.S. Patent No. 4,042,395 the final image remains with the photosensitive element. In operation, the film units are moved through a processing device, such as a pair of pressure rollers, which ruptures the pod and distributes the composition in a layer of appropriate thickness between the photosensitive element and second sheet. The distributed composition then permeates the layers to process the latent image and establish the visible image.

[0004] In the first above described form of film unit, the second sheet is separated from the photosensitive element to permit exposure of the element, thereafter brought into registered face-to-face relationship with the element for processing, and finally separated from the element for viewing of the final print. The term "post- registered" identifies the feature requiring registration after exposure, while the term "peel-apart" refers to the fact that the second sheet must be removed from the photosensitive element in order to view the final print.

[0005] In the second or pre-registered form of film unit, the photosensitive element and second sheet are registered prior to exposure, preferably at the time of manufacture, and remain in substantially the same relative positions during and after exposure and processing. Ordinarily, the second sheet is transparent to permit exposure of the photosensitive element therethrough, and the element and sheet remain permanently attached to each other in the final print.

[0006] Further pertinent features of the above-mentioned forms of film units relate to their handling in daylight. The 4 x 5 unit can be handled individually in daylight both before and after exposure because it is disposed in an opaque envelope which surrounds the photosensitive element and second sheet until the unit is loaded in appropriate exposing apparatus. Then the envelope is removed to permit exposure of the photosensitive element. After exposure, the envelope is returned to its original position which registers the second sheet over the element and again provides a light-tight environment. The envelope is removed after processing, and the second sheet is peeled-off, as described above, to reveal the final print.

[0007] Commercially available integral film units of the second above described form have not been designed for individual daylight handling prior to exposure. They are supplied in light-tight packs for loading into the corresponding apparatus. After exposure, however, the film units are ejected immediately from the camera, and processing is completed in daylight. This is made possible by providing an opaque layer in the photosensitive element on one side of the light-sensitive layers, and by the addition of an opacifier to the processing composition. Upon ejection the opaque composition is distributed over the other side of the sensitive layers and cooperates with the opaque layer to shield the sensitive layers from light. The image forming components then diffuse through one or the other of the opaque layers (the original layer or the distributed composition), whereupon the image becomes visible.

[0008] Although previously known film units, such as those described above, apparently operate satisfactorily for their intended purpose, none offer the desired convenience for instant-processing film units that can be handled in daylight on an individual basis both before and after exposure. The 4 x 5 form described above requires rather complex manipulation of the opaque envelope. Moreover, even after removal of the envelope, the final print must be stripped from the photosensitive element. The film units are intricate in construction and difficult to manufacture, generate considerable waste in use, and require relatively complex utilizing apparatus which resists automation. While integral film units do not suffer from these problems, they have not been suitable for pre-exposure daylight handling on an individual or one-shot basis.

[0009] In accordance with the present invention, a self-processing film unit is provided which is suitable for pre-exposure as well as post-exposure daylight handling on an individual or one-shot basis. The film unit is relatively simple in its physical construction, is easy to use and generates minimal waste compared to prior such film units. Although intended for use in presently available apparatus, the film unit is conducive either to simplified or more fully automated apparatus.

[0010] In accordance with the present invention there is provided an integral self-processing photographic film unit including reservoir means for supplying processing composition, a photosensitive element and a cover sheet coupled together along their lateral margins, the element having on its surface towards the cover sheet a layer sensitive to actinic radiation for recording a latent image processable by the composition, and an opaque layer at the side of the sensitive layer away from the cover sheet characterised in that a dark slide is disposed between the element and the cover sheet in a first position overlying the sensitive layer and shielding the same from actinic radiation, the dark slide being slidable from the first position to uncover the sensitive layer for exposure.

[0011] Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 is a plan view of a film unit in accordance with a first embodiment of the invention, depicting its general features including a picture unit, dark slide, and leader;

Figs. 2-4 are cross-sectional views of the film unit of Fig. 1 taken along the lines 2-2; 3-3; and 4-4 as shown in Fig. 1 and illustrating internal features at the ends and edges of the film unit;

Fig. 5 is a fragmentary diagrammatic cross-sectional view of a photosensitive element illustrating certain of its layers;

Fig. 6 is an exploded perspective view of the film unit of Fig. 1;

Fig. 7 is an enlarged partial perspective view of a light seal provided in the film unit at a leading end thereof;

Fig. 8 is a perspective view of a known apparatus in which the film unit of Fig. 1 may be used;

Figs. 9-13 are partial perspective and front elevational views depicting the use of the film unit of Fig. 1 in the apparatus of Fig. 8;

Fig. 14 is a fragmentary perspective view of the film unit of Fig. 1 and the apparatus of Fig. 9 depicting the use of saddle shims of the film unit in supporting pressure-applying members of the apparatus;

Fig. 15 is an exploded persepctive view of a second embodiment of film unit of the invention;

Fig. 16 is a perspective view of the second embodiment with a cover sheet thereof removed;

Fig. 17 is a fragmentary perspective view of a third embodiment of film unit in accordance with the present invention;

. Fig. 18 is a cross-section through a light seal at the leading end of the film unit of Fig. 17; and

Fig. 19 is a view similar to Fig. 6 but illustrating the third embodiment of film unit.

[0012] Referring now to the drawings, and especially to Figs. 1-6, a photographic film unit 8 is depicted in accordance with a first embodiment of the present invention as including a picture unit 10, dark slide 12 and a leader arrangement 14.

[0013] The picture unit includes first and second sheets coupled along their lateral margins 16, as in a pre-registered integral film unit described above. One of the sheets is a photosensitive element 18 including a plurality of light-sensitive layers 20 (Fig. 5) an opaque layer 22 and an image receiving layer 24 carried on a dimensionally stable transparent support 26. These and additional respective layers of the photosensitive element are known in the prior art and will not be described in detail. The radiation sensitive layers are suitable for recording a latent image processable to establish a visible image. The opaque layer shields the radiation sensitive layers from actinic radiation striking one face 28 of the picture unit, and the image receiving layer receives the final image, image forming components of which diffuse thereto, through the opaque layer, during processing.

[0014] The other of the sheets is a transparent cover sheet 30 which serves several functions including confinement of the processing composition to facilitate its distribution during processing. As will become more apparent from the following description, the cover sheet also confines the dark slide in correct position.

[0015] Reservoir means, including a pod 32 (Fig. 2) and trap, 34 (Fig. 4) are disposed at the leading and trailing end regions respectively of the picture unit. The pod supplies processing composition for distribution between-the photosensitive element and cover sheet. The trap collects any excess of the composition from between the element and sheet.

[0016] The final print when it is formed in the image receiving layer 24, should have precisely established edges. For this purpose, an opaque mask 36 extends along the end regions and lateral margins of the picture unit to create an image frame which defines the perimeter of the final picture area. Preferably, the mask is of the internal type adhered to the photosensitive element facing the cover sheet. The mask also may be used for covering the pod and trap, e.g. a piece 38 over the pod and another piece 40 folded around the trap 34 and cover sheet 30. In such case, the mask helps prevent light entering between the sheets at the leading and trailing ends of the picture unit.

[0017] On top of (as seen in Fig. 3) the mask 36, opaque side rails 42 of predetermined caliper are provided for spacing the mask 36 and cover sheet 30 to receive the dark slide 12. The cover sheet is secured with adhesive to the photosensitive element by means of. the side rails and mask.

[0018] The combined mask and side rails also prevent light from entering between the sheets at the lateral margins of the picture unit.

[0019] The leader arrangement includes a flexible but somewhat stiff leader 44 overlapped with and attached to the leading end of the photosensitive element 18 to facilitate handling of the film unit in cooperating apparatus as described more fully hereinafter.

[0020] Saddle detents or shims 46 and 48 are provided at the lateral edges of the leader for similar purposes.

[0021] Referring now more specifically to Figs. 8, 11 and 14, the saddle shims 46 and 48 are provided at opposite margins of the leader where they straddle the dark slide. The detents are located relative to the rest of the film unit so they are between the pressure-applying members 70, 71 when the film unit is correctly Positioned in a camera back adapter 60.

[0022] The saddle shims 46, 48 are made of relatively hard plastic and are concave where they engage and support the pressure-applying members. The concave shape increases the force that must be exerted on the film unit to pull the detents from under the pressure-applying member, and this shape is considered preferrable when the detends are relatively incompressible. With more compressible materials, this concavity of the saddle shims can be reduced or eliminated, so long as the force required to displace the shims from under the pressure-applying member is greater than the frictional force required to remove the dark slide 12 from between the photosensitive element 18 and cover sheet 30 without shifting the photosensitive element.

[0023] As shown in Fig. 11, the saddle shims 46, 48 have a thickness, even at the bottom of the concavity, which is greater than the thickness of the dark slide 12.

[0024] It will be noted that, within the bounds of mask 36, photosensitive layer 20 is overlayed only by transparent cover sheet 30. Therefore, should light fall upon the cover sheet, it will pass therethrough to expose the photosensitive layer and form a latent image. Of course, this would prevent handling of the film unit assembly in lighted conditions unless adequate, light-tight arrangements are made, However, in accordance with the present invention the internal dark slide 12 is positioned between the photosensitive element and cover sheet and cooperates with the opaque layer on the opposite side of the radiation sensitive layers to encase the sensitive layers and to shield them from premature exposure. Thus, a single film unit can be handled in daylight without fogging. The dark slide 12 is of sufficient length to extend from the trailing end section of the picture unit to beyond the leader 14 so that it is natural to grasp the dark slide 12 rather than the leader 44 whenever the dark slide is present, as may be seen in Fig. 1. The dark slide may be regarded as extending out of the picture unit through a passage formed between the photosensitive element and the cover sheet, as may be seen in Fig. 2. The dark slide covers the entire image frame and extends outwardly from the image frame to overlap the mask around the entire perimeter of the final-image area. The thickness of the dark slide is chosen so it will be confined and occupy the space between the mask and the cover sheet. It should not be so thick that its interference with the other elements causes undesirable frictional resistance nor so thin that it separates from the mask permitting light to reach and fog the photosensitive element. Such conditions may be met if the dark slide and side rails have substantially the same thickness. However, the objective of preventing a light leak around the edges of the dark slide may also be achieved in other ways. For example, the dark slide, if thinner than the side rails, may be lightly secured by adhesive to the mask to form a light seal. The adhesion is arranged to be easily overcome upon withdrawal of the dark slide.

[0025] At the leading end of the picture unit, where the dark slide exits from between the photosensitive element and cover sheet, additional light sealing means 49 are provided.

[0026] Referring now more specifically to Figs. 2, 6, and 7, the light seal 49 includes a flexible strip 52 of opaque material having body and flap portions, 56 and 51 (Fig. 7), respectively, of predetermined length and width dimensions. The strip 52 is coupled to the photosensitive element 18, or actually to the mask 36 on the element by adhesive, and is coupled to the dark slide by interleaving with or folding into a Z-shaped fold in the dark slide, so that pulling on the slide will straighten and release the strip from the dark slide. The length of the strip and the point of its attachment to the photosensitive element'are chosen so that the strip will lie flat against the element 18 in its straightened condition without extending beyond the leading end of the element. The width is selected to match the width of the photosensitive element and provide an adequate light seal.

[0027] The strip and dark slide are maintained in their interfolded condition by pinching pressure from the photosensitive element 18 and cover sheet 30; or, if a more secure device is desired, the strip can be strippably sealed to the element 18 and sheet 30 in their lateral margins 53, 55.

[0028] Notches 54 and 57 (Fig. 6) also may be provided in the flap portion of the strip for facilitating the proper unfolding progression of the strip and dark slide as the latter is pulled from the film unit. The notches also may interact with the side rails 42 for improving the light seal 49 in the corners.

[0029] Referring now more specifically to Figs. 8-14, the operation of the film unit is depicted with known apparatus. The apparatus comprises a camera-back adapter 60 of a type available commercially, including a body portion 62, and a processing section 64. The body portion bounds a cavity for receiving individual ones of the film units and an exposure aperture a through which film units in the cavity may be exposed. The processing section 64 includes the pair of pressure-applying members 70, 71 (Fig. 9) and a passageway 72 which passes between light blocking means 74. A latch 76 partially shown in Figs. 9 and 10 is movable from an open (loading) position (Fig. 9) where the pressure-applying members 70, 71 are spaced- apart, and a closed (processing) position (Fig. 10) where the members are urged together prior to initiating processing.

[0030] In operation, and referring first to Fig. 9, the latch 76 is moved to the open position, and the film unit is inserted through the passageway 72 between the pressure-applying members 70, 71 and into the cavity behind the exposure aperture 68. Means, not shown, support the film unit in a substantially flat condition suitable for exposure. The latch 76 is closed and releases the pressure-applying members 70, 71 the upper of which drops onto the saddle shims 46 and 48 to hold the film unit in its correct operative position. The shims 46, 48 also act as lifters and support the pressure-applying members 70, 71 and thereby provide for easy removal of the dark slide and also hold the picture unit in position on subsequent withdrawal of the dark slide. The dark slide 12 is then removed by grasping its leading end and pulling the slide (Fig. 12) entirely from the remainder of the film unit and the apparatus. During such motion, the Z-shaped fold and the flap portion 51 of the light seal 49 unfold. Removal of the dark slide 12 uncovers the photosensitive element 18 and its light-sensitive layers 20 for exposure. After exposure of the picture unit 10, the leader 14, made readily accessible by removal of the longer dark slide 12, is pulled to initiate processing and to remove the picture unit 10 from the apparatus (Fig. 13). The saddle shims move with the leader 14. from between the members 70, 71 allowing the members to move towards each other. As the picture unit 10 passes between the members 70, 71, the pod 32 is ruptured and continued pulling distributes the processing composition from the pod between the photosensitive element and cover sheet. Assuming the composition includes an opacifier, as is common in integral film units, distribution of the composition establishes another opaque layer which cooperates with the first opaque layer 22 to shield the light sensitive layers 20 from further exposure and permit daylight processing. During processing, image-wise distribution of dyes diffuse through the first opaque layer 22 to the image-receiving layer 24, where the transferred image is visible at face 28 of the picture unit. Finally, if desired, the leader can be stripped from the picture unit which then becomes the final print.

[0031] A second embodiment of the invention, depicted in Figs. 15 and 16, includes a dark slide 112 that is suited for being repositioned between the photosensitive element 18 and cover sheet 30 after exposure of the photosensitive element. In most respects including the provision of a leader 44 and saddle shims 46 and 48 (not shown in Figs. 15 and 16)this second embodiment is the same as the first embodiment, except the dark slide is notched or otherwise formed to define ears 133 at its trailing end; and the side rails 142 define abutments 143 at their leading ends. The ears 133 on the slide 112 and the abutments 143 on the rails cooperate to arrest movement of the dark slide 112 after it clears the image frame, defined by the mask 36, but before it is removed beyond a position at which it is aligned for re-insertion between the photosensitive element and cover sheet after exposure of the photosensitive element, which position is depicted in Fig. 16.

[0032] Thus, the dark slide 112 is movable between the photosensitive element 18 and the cover sheet 30 between a first position where it shields the photosensitive element from exposure through image frame defined by mask 36 and a second position (Fig. 16) where it uncovers the photosensitive element 18 for exposure through the cover sheet 30.

[0033] It is possible in some envisaged embodiments to use the dark slide 112 as a leader for the film unit. If the dark slide 112 or its ears 133 and the abutments 143 of the side rails are formed of a material strong enough to resist deformation, and to transmit the appropriate tensional forces to the picture units, the latter could be withdrawn after exposure of the photosensitive element 18, by means of the dark slide 112 through processing rollers or other pressure applying members to rupture the pod and distribute the processing composition over the exposed photosensitive element 18. A leader, similar to the leader 14, would not be necessary in such embodiments.

[0034] It also may be desirable in this second embodiment to provide a thicker material for the dark slide, to increase its rigidity, and to provide a corresponding increase in the thickness of the side rails 142, to accommodate the thicker dark slide. In such case, the mask can be used to establish the thickness of the distributed layer of processing composition by utilizing rollers which are of form such as to run on the mask and not on the side rails. The rollers may be of reduced diameter in the region of the side rails or may be of length less than the distance between the side rails. In either instance, the rollers may be of reduced diameter in the image region to provide a predetermined thickness of spread processing composition over that determined by the thickness of the mask. The increased thickness of the side rails will not then adversely affect the processing of the film unit. This is because the side rails do not play a role in spacing the rollers when the film unit is used with such rollers.

[0035] The embodiment of Figs. 15 and 16, whether or not provided with a light seal as illustrated in and described with reference to either Figs. 1 to 7 above or Figs. 17 to 19 hereinafter or some other form, and whether or not provided with a leader such as leader 12, may be exposed in an apparatus lacking pressure-applying members. In such case the dark slide would be reinserted after photographic exposure so that the film unit could be transferred in ambient light to a device which has pressure-applying members. In this latter device, the dark slide is withdrawn to the maximum extent and thereafter the film unit is drawn through the pressure-applying members.

[0036] Figs. 17 to 19 illustrate a third embodiment of a film unit according to the present invention. This embodiment differs from the first described embodiment only in the form taken by the light seal present between the dark slide and the picture unit. Parts of the film unit 108 of identical construction to those in the first embodiment have been given like reference numerals.

[0037] In this embodiment, the light seal 149 comprises two opaque flaps 151 and 156 secured in register by their leading edges to respective sides of a dark slide 212. The flaps 151 and 156 are of a thin material, for example 0.005 cms thick and of length greater than the width of the dark slide and at least equal to the width of the film unit. The flaps are secured to each other along the leading edges of those portions 158 and 159 thereof which extend beyond the lateral edges of the dark slide 212. The secured leading edges of the extending portions 158, 159 are swept back. In this way, the light seal 149 forms a cowl. The dark slide 212 of this embodiment extends between the photosensitive element 18 and the cover sheet 30 in the same way as in the two previous embodiments. The light seal 149, caps the leading end of the picture unit 10 formed of the sheets 18 and 30, one flap 151 lying on top of the leading edge of the cover sheet 30 and partly over the pod 32 and its cover 38 and the other flap 156 extends beneath the leading end of the photosensitive element 18 and between the element 18 and the stiff leader 44 thereof as shown most clearly in Fig. 18.

[0038] In this way, no light can enter the picture unit 10 at the leading end thereof whilst the dark slide 212 with its light seal 149 is in position. As in the previous embodiments, no light can reach the photosensitive element 18 through the cover sheet 30 because of the cooperation between the dark slide 212, the side rails 42 and the mask 36 which provide therebetween a labyrinthine light trap. The film unit 108 can thus be handled in daylight prior to insertion into a camera back adapter 60 of the kind above described.

[0039] In use, the latch 76 of an adaptor 60 is moved to the loading position and the film unit 108 is inserted thereinto as described in relation to the first: embodiment. The latch 76 is moved to the closed position and the adaptor 60 mounted on a camera (not shown) if it has not already been so mounted. This causes the pressure applying members 70, 71 to be urged together and the member 70 to sit on the saddle shims 46, 48.

[0040] The dark slide 212 can then be grasped and pulled to withdraw the dark slide from the picture unit 10. On such movement, the flaps 151,156 uncover the leading end of the picture unit and the portions 153 and 159 are deflected towards the dark slide 212 as they pass between the saddle shims 46, 48. As the material from which the light seal 149 is made is so thin, the dark slide together with the two thicknesses of the light seal can pass between the pressure applying members 70, 71 without lifting the member 70 from the saddle shims 46, 48 even at the lateral edges of the dark slide where, for example, due to deformation of the portions 158 and 159, four thicknesses of light seal 149 will be present. The photosensitive element may then be photographically exposed and thereafter the stiff leader 44 grasped and pulled to initiate processing of the picture unit 10 as described in relation to the first embodiment.

[0041] It may be possible, in this third embodiment, if it is desired not to use an opacifier in the processing composition contained in the pod 32, to have the dark slide 212 of the form shown in the second embodiment above described. In such form, the dark slide would not be totally removed from the picture unit during exposure and would be returned to the fully inserted position after exposure. Thereafter, the film unit could be removed from the exposing apparatus and transferred to a suitable processing apparatus.

Claims

1. An integral self-processing photographic film unit including reservoir means for supplying processing composition, a photoesnsitive element and a cover sheet coupled together along their lateral margins, the element having on its surface towards the cover sheet a layer sensitive to actinic vadiation for recording a latent image processable by the composition, and an opaque layer at the side of the sensitive layer away from the cover sheet characterised in that a dark slide is disposed between the element and the cover sheet in a first position overlying the sensitive layer and shielding the same from actinic radiation, the dark slile being slidable from the first position to uncover the seisitive layer for exposure.

2. A film unit as claimed in claim 1 characterised in that the dark slide includes a potion accessible, when the dark slide is in the first position, exteriorily of the coupled element and cover sheet .'or sliding the dark slide from the passageway formed between the element and the sheet, a light seal being provided for preventing actinic radiation from entering the passageway and reaching the photosensitive element,

3. A film unit according to claim 1 0 2, characterized in that the dark is slidable from its first position to a second position wherefrom it is returnable to the first position after exposure, and in that cooperating means on the dark slide and the film unit define such second position.

4. A film unit according to claim 2 or claims 2 and 3, characterized in that the light seal include a strip of flexible, opaque sheet material, first means fo coupling the sheet material to the dark slide, and secon means for coupling the sheet material to the photosensitive element, at least one of the first and second coupling means being releasable by movement of the dark slide from its first position.

5. A film unit according to claim 4, characterized in that the strip of flexible, opaque sheet material is folded back upon itself between its coupling to uhe dark slide and its coupling to the photosensitive element.

6. A film unit according to claim 5, characterized in that the means coupling the strip to the dark slide includes a Z-shaped fold in the dark slide, a portion of the strip being interleaved with the Z-shaped fold.

7. A film unit according to claim 2 or any claim appendant thereto, characterized in that the light seal is carried by the dark slide and encloses the portion of the photosensitive element and of the cover sheet at the mouth of the passageway.

8. A film unit according to claim 7, characterized in that the light seal includes first and second opaque flaps disposed one at each side of the dark slide and extending beyond the edges of the dark slide and, in the extending regions, being sealed to one another along their leading edges.

9. A film unit according to claim 3 or any claim appendant thereto, characterized in that the dark slide and the cooperating means are so formed that tensile forces may be transmitted from the dark slide to the other portions of the film unit when the dark slide is in its second position.

10. A film unit according to any one of the preceding claims for use in apparatus for exposing and processing the film unit, the apparatus having means for locating the film unit in position for exposure and a pair of pressure-applying members - through which the film unit is passed for initiating processing of the film unit, the film unit being characterized in that the element or the sheet includes a leader for use in drawing the unit from the apparatus between the pressure-applying members, ia that the dark slide extends from between the element and sheet in superposition with the leader, and that shims are provided on the leader, said shims being so formed and disposed as to be located between the pressure-applying means when the film unit is in position for exposure and serving to space the pressure-applying means apart to facilitate removal of the dark slide and to resist shifting of the photosensitive element upon withdrawal of the dark slide.

11. A film unit according to any one of the preceding claims, characterized in that the reservoir means contains a processing composition which is opaque.

12. A film unit according to any one of the preceding claims, characterized in that an opaque mask is secured to the photosensitive element and the cover sheet between the element and the sheet, the mask serving to bound an image frame, and that said dark slide when in its first position extends adjacent the cover sheet, outwardly beyond the image frame in all directions.

13. A film unit according to claim 12, characterized in that side rails are interposed between the mask and the cover sheet, the dark slide being disposed between the rails.

14. A film unit according to claim 13, characterized in that the rails and the dark slide have substantially the same thickness.

Drawing