referring now to fig1 and 2 , a preferred embodiment of a contact printer 10 embodying the present invention is illustrated . the contact printer comprises a platen member 12 having a planar upper surface 14 with dimensions slightly larger than the maximum dimensions of the largest original to be copied thereon . a light carriage 16 , having a length approximately equal to one dimension of the platen member 12 , is arranged to be moved across the platen transversely to the length of the carriage , thereby providing coverage of the entire platen during its movement . the upper surface of the platen member 14 forms a vacuum table for the film 18 and the original 20 which are superposed thereon for exposure of the film ( see fig2 ). a rigid chamber 22 , having a thickness of approximately one inch , is formed beneath the vacuum table . a plurality of vacuum ports 24 are formed in the film / original accepting portion of the surface 14 and communicate between the surface and the interior of the chamber . with the exception of the vacuum ports 24 , the chamber 22 is sealed so that a vacuum pump ( not shown , but normally disposed remote from the apparatus ) can pull a vacuum within the chamber which is then applied , via ports 24 , to the film and original which are placed on the surface 14 . the ports 24 have a diameter of approximately 0 . 040 inch which is sufficiently large to effectively apply the vacuum to the film / original disposed on the surface 14 , but is sufficiently small and the capacity of the vacuum pump is great enough that it will maintain the vacuum even though the size of the film / original is less than the maximum , leaving some of the vacuum ports uncovered . the vacuum ports outside of the area covered by the maximum size film / original are connected by shallow grooves 26 having a cross section of 0 . 015 inch by 0 . 015 inch which permit air trapped between the film / original and a cover sheet ( to be further described hereinbelow ) to be evacuated . it has been found that satisfactory operation can be achieved with a vacuum pump which is capable of flow rates of between 15 and 30 cfm while generating a vacuum within the chamber of between 8 and 12 inches of water . the light carriage 16 is disposed on the upper surface of the vacuum table and is arranged to be moved across the table from a home position ( the rear of the vacuum table in the example illustrated ) to the opposite edge of the table , and returned to the home position . the carriage is provided with wheels ( not shown ) at each end thereof which ride upon tracks ( not shown ) provided at the lateral edges of the platen surface 14 or within the platen . the carriage is driven by a drive screw 28 within and extending the length of the platen which engages and drives a drive - nut 30 connected to the carriage . the drive screw is driven by a variable speed , reversible motor ( not shown ) located within the platen . the light carriage 16 carries one or more high uv output fluorescent aperture lamps 32 , with an associated mechanical light collimator 34 positioned beneath each lamp , a roll of a transparent cover sheet 36 , an associated pressure roller 38 , and a pair of cleaner rolls 40 and 42 . the fluorescent lamps 32 are long tubular bulbs extending the length of the carriage . the phosphors which coat the inner walls of the bulbs are selected to generate light having a wavelength in the range of 350 nm to 460 nm , which matches the sensitivity of the film being exposed . the bulbs have an internal reflective layer between the phosphor and the envelope glass which covers a major angular portion of the envelope wall and reflects a high percentage of the radiation striking it . a clear window 44 , having an aperture of about 60 ° of the bulb circumference , is provided along the length of the bulb with no phosphor or reflective layer . this window produces an elongated , concentrated beam of high luminance uv light output along the length of the bulb because the reflective coating directs the major part of the bulb output through the uncoated window . the lamps are selectively oriented in the carriage with the windows 44 directed downwardly so that the beam of concentrated light is directed toward the sensitized film material 18 . the mechanical light collimator 34 associated with each bulb comprises a plurality of parallel , fine collimator tubes 46 which are closely spaced and which transmit parallel rays of light from the fluorescent aperture lamp to the exposure plane . inasmuch as image quality is related to the solid angle of the light incident on the original / film lamination surface , based on a given distance between the sensitized film emulsion and the image of the original , the equivalent diameter of the tubes and their length are selected to extinguish incident angles of light at the exposure plane greater than a predetermined solid angle , for example a solid angle of between about 3 ° and about 9 °. moreover , since the illumination at the film surface depends upon the light output of the lamp and the distance of the lamp from the film surface , for a given lamp output , the shorter the length of the collimator , the greater the exposure power at the film . a preferred embodiment employs hexagonal tubes having an equivalent diameter of 0 . 125 inch and a length of 0 . 5 inch , with the bottom of the tube spaced above the film plane a distance of 0 . 5 inch . the transparent cover sheet 36 has dimensions substantially equal to the width and length of the vacuum table and is supported as a roll 48 mounted in the carriage 16 parallel with and ahead of the fluorescent tubes ( as viewed with respect to the initial travel of the carriage ). the outer , free end of the cover sheet is releasably connected to the vacuum table as indicated at 50 . the cover sheet is wrapped on a core 52 which is removably held at each end by hub members , 54 and 56 , rotatably mounted in the carrier . one hub 54 is connected to one end of a constant force tension spring 58 which acts to apply tension to the roll of the cover sheet material as it is unwound and wound by movement of the carriage across the vacuum table , as will be further described hereinbelow . the other end of the tension spring is connected to and wrapped on a storage drum 60 where it remains in its idle position . through the unwinding force generated as the cover sheet is unwound , the spring is transferred onto the core hub 54 , and produces the winding torque moment to the shaft of the core to rewind the cover sheet when the carriage movement is reversed . the other hub 56 is spring loaded along the core axis by an axial compression spring 62 . the axial compression spring permits the hub 56 to be moved axially , disengaging the cover sheet roll to permit its easy replacement . thus , when the cover sheet becomes damaged , worn , scratched , dirty or translucent , and thus would adversely affect the exposure light directed therethrough , it can be replaced with a new cover sheet . the cover sheet 36 is formed of an impermeable sheet of a polymeric material which is substantially transparent to uv radiation . the material also preferably resists abrasion and possesses anti - static properties , or is treated to obtain these properties , so that it resists the accumulation of dust , dirt , and other materials which would adversely affect the transmission of exposing light therethrough , or which would adversely affect the collimation of the light . it has been found that a sheet of clear polyester sheeting having a thickness of approximately 0 . 004 inch satisfactorily meets these requirements . the sheeting may be provided with anti - static properties via coatings or other treatments to minimize the static attraction of dust and dirt to the cover sheet , to prevent the cover sheet from &# 34 ; clinging &# 34 ; to the film / original laminate , and to prevent static discharges which can impart an unwanted exposure to the film . the sheeting can also be provided with an abrasion resistant coating to minimize scratching of the cover sheet which would adversely affect its &# 34 ; clear &# 34 ; optical properties . still further , the cover sheet can be provided , on the surface thereof which contacts the film / original laminate , with an optically clear matte finish which facilitates the ready application of the vacuum to the cover sheet / original / film laminate by providing miniscule air passages for the removal of air . the cover sheet acts as a &# 34 ; vacuum lid &# 34 ; as it is unwound over the original / film laminate during vacuum drawdown as the carriage is moved across the vacuum table to expose the film . the cover sheet also protects the original / film laminate underneath from any abrasive action of the pressure roller 38 as it forces the cover sheet / original / film lamination into intimate contact to remove any air from the lamination which might otherwise distort the resulting exposure . because of its importance to the satisfactory exposure of the contact print , the cover sheet must be kept clean . as an aid to keeping the cover sheet optically clean and free from dust and lint , the cleaner rolls 40 and 42 are mounted transversely of the light carriage 16 between the cover sheet roll 48 and the pressure roller 38 in engagement with the front and rear surfaces of the cover sheet 36 . the cleaner rolls are rotatable and are driven by contact with the cover sheet as it is unwound over the film / original laminate and rewound during each exposure cycle . the cleaner rolls are formed of a single component urethane having 20 durometer shore a hardness which clean the cover sheet without scratching . initially , the light carriage 16 is parked at the rear of the vacuum table 14 . a sheet of film or paper 18 is positioned emulsion side - up on the platen . the longest sheet dimension is preferably perpendicular to carriage motion to minimize the carriage travel necessary to fully cover the sheet and thus keep the time required to a minimum . the vacuum pump is activated and applies the vacuum to the film through the ports 24 to hold the film to the platen surface . the original 20 , such as a color separation , is then placed on top of the film . the separation can be positioned by means of registration pins ( not shown ). if registration pins are used , they are located along the edge of the original / film laminate closest to the carriage home position . the type of film or paper to be exposed , or the exposure speed thereof , is entered into the machine controller . the film information and lamp intensity readings are then used to calculate the carriage traverse speed . when the &# 34 ; start &# 34 ; button is actuated , the carriage 16 moves forward toward the front edge of the platen 14 at the proper dot - for - dot exposure speed . while the carriage moves forward , the clear anti - static cover sheet 36 is unwound to cover the original / film lamination . the pressure roller 38 pushes out any remaining air from the lamination and the cover sheet is drawn into intimate contact with the lamination by the vacuum through the ports 24 . the carriage continues until the &# 34 ; end of travel &# 34 ; position is reached and reverses direction to finish exposing the film and return to the home position . as the carriage returns to the home position , the cover sheet 36 is rewound on the core 52 by the constant tension spring 58 , uncovering the original / film lamination after exposure for that area has been completed . it is apparent that with small film sizes , complete traverse of the platen by the carriage is not necessary . the &# 34 ; end of travel &# 34 ; position is selectable and can be specified by the user . when the carriage is back at home position , the vacuum and the lamps are shut off or placed on standby , and the film and separation can be removed . the invention has been described with reference to specific embodiments and variations , but it should be apparent that other modifications and variations can be made within the spirit and scope of the invention , which is defined by the following claims .