US2981625A - Halftone camera - Google Patents

Description

April 25, 1961 A. J. POWERS, JR., ETAL 2,981,625

HALFTONE CAMERA 5 Sheets-Sheet 1 Original Filed June 16. 1953 IN VEN TORS AUGUST/N J POWERS,\IR-

ANDREW A- AMA/DER Y r4 TTO/FNfYS B Y %7M, g w

April 25, 1961 Original Filed June 16, 1953 HALFTONE CAMERA A. J. POWERS, JR., ETAL 5,. Sheets-Sheet 3 IN V EN TORS AUGUST/N J POWERS, JR. ANDREW K. ANANDER A TTOANEYS.

Apnl 25, 1961 A. J. POWERS, JR., ETAL 2,931,625

HALFTONE CAMERA Original Filed June 16, 1953 5 Sheets-Sheet 5 97 A INVENTORS OZ 1 UGZ/ST/N J P0WER5,JR. QZL ANDREW A. AMA/05R A TTORNEYS.

United rates HALFTONE CAMERA Augustin J. Powers, J12, Glen Head, and Andrew K. Auander, Glen Cove, N.Y., assignors to Powers Chemco, Inc., Glen Cove, N.Y., a corporation of New York Continuation of application Ser. No. 361,998, June 16, 1953. This application May 26, 1958, Ser. N: 737,974

4 Claims. (Cl. 96116) The present invention relates to a novel and improved halftone camera especially suited for the production of both black-and-white and color separation halftone negatives.

This application is a continuation of our prior copending application Serial No. 361,998, filed June 16, 195 3, now abandoned.

Objects and advantages of the invention will be set forth in part hereinafter and in part will be obvious herefrom, or may be learned by practice with. the invention, the same being realized and attained by means of the instrumcntalities and combinations pointed out in the appended claims.

The invention consists in the novel parts, constructions, arrangements, combinations and improvements herein shown and described.

The accompanying drawings, referred to herein and constituting a part hereof, illustrate one embodiment of the invention, and together with the description, serve to explain the principles of the invention.

Of the drawings:

Figure 1 is a side elevation, partly broken away, showing a typical and illustrative, fragmentary embodiment of a photo-mechanical camera showing, somewhat schematically, film feeding and cutting means, film backing means and mechanism for positioning same, and a halftone screen supporting device in accordance with the present invention;

Figure 2 is a fragmentary sectional view taken along line 2-2 of Figure l and showing the halftone screen supporting frame with a circular halftone screen mounted therein;

Figure 3 is a fragmentary sectional view taken along line 33 of Figure 2 and showing portions of the halftone screen supporting frame and the method whereby it is movably mounted within the camera body;

Figure 4 is a fragmentary sectional view taken along line 4-4 of Figure 2 and showing portions of the screen supporting frame which are adjustably positionable to accommodate screens of various sizes;

Figure 5 is a fragmentary sectional view, on a larger scale, taken along line 5-5 of Figure 2 and showing a conventional circular halftone screen and its frame as mounted on the screen supporting frame members;

Figure 6 is a fragmentary sectional view taken along line 6-6 of Figure 2 and showing other features of the screen supporting frame members;

Figure 7 is a fragmentary perspective view showing the method of slidably mounting certain horizontal screen supporting frame members on their vertical guides and scale means for judging their position thereon;

Figure 8 is a fragmentary view similar to Figure 2 but showing a rectangular halftone screen mounted in the screen supporting frame members; and

Figure 9 is a fragmentary sectional view, on a larger scale, taken along line 9-9 of Figure 8.

The present invention is in many respects an improvement upon a Chemco photomechanical camera shown and described in the prior patent to F. T. Powers No. 2,282,427, granted May 12, 1942, but in other respects the improvements are of more general application, and may be applied to a wide variety of photomechanical cameras utilizing photographically-sensitized paper or other forms of film which are fed from a relatively long roll of film, the proper and desired length of film being cut from the supply roll and being moved to ex posure position where the cut portion is held during exposure.

The present invention has for its object the provision of a novel and improved photomechanical or photoengraving camera in which means are combined for accurately mounting variously sized halftone screens of conventional construction in precise parallelism with the film supporting plane of the film backing member and maintaining this parallelism, once it is so adjusted, during movement of the screen away from and to its proper focusing position. The invention further provides a novel and improved combination in which either rectangular halftone screens or frame mounted, rotatable, circular halftone screens, of conventional construction, may be used and, in the case of the frame mounted circular screen, the screen may be rotated without losing its parallelism with the film backing member. A further object is the provision of means on the outside of the camera for moving the adjusted halftone screen into and out of its focusing or screen separation position, locking it in any desired position and determining its position accurately by a graduated scale associated with the moving means.

in general, the camera comprises the usual lens, bellows and film supply and suction back or film supporting means, all enclosed, as is usual, in a light-tight housing so that extraneous light is excluded. The backing memher is preferably a suction type of standard construction which securely holds the flexible sheet of film against its lens-facing surface after the film has been cut from the supply and properly positioned in front of the backing member. The backing member is movable bodily to wards and away from the exposure plane of the camera and can be locked in either the rearward film receiving position, or the forward focal plane position.

A movable halftoue screen supporting frame is provided which is capable of holding either a rectangular screen or a screen frame with a rotatable, circular screen, and is further capable of being adjusted to accommodate screens of various sizes or diameters. The screen supporting frame is constructed in the form of a large rectangle haviug vertical side members which are held in spaced relation by upper and lower horizontal members secured thereto. Secondary vertical bars are provided which are parallel and closely adjacent to the vertical members of the main framework and rigidly secured, at their sides, to the horizontal members of said framework. Upper and lower cross bars are slidably mounted on the vertical secondary bars and provided at each end with a chain mechanism which serves to maintain each cross bar parallel with the other during any sliding adjustment along the vertical secondary bars.

The upper and lower cross bars serve for the direct support of the halftone screen and are provided on their rear face, or that face nearest the film backing member, with a plurality of thin aligning plates against which the rear surface of a halftone screen can be pressed. Each cross bar is provided on its front face with a screen frame holding member Which is slidably mounted on studs carried by the cross bars and spring urged towards the cross bars. The upper and lower screen frame holding members are adapted to receive the flange of a conventionalcircular screen frame and are provided with a plurality of clamp screws which serve to secure the flange on the slidable holding members, which being spring urged towards the cross bars, thus press the rear face of the circular screen against the thin aligning plates carried by the cross bars. The halftone screen is thus held in exact parallelism with the cross bars regardless of whether the screen is in exact parallelism with its frame or not.

Provision is also made on the cross bars for holding and clamping in place against the aforementioned thin aligning plates a rectangular halftone screen which, in conventional practice, is not provided with a frame. A plurality of holding lugs are secured on the front face of the lower cross bar and have their rear faces beveled so that, in conjunction with the aligning plates, a V-shaped trough is formed for receiving the lower edge of a rec- 'tangular screen. The upper margin of the screen is held against the aligning plates on the upper cross bar by a pair of swingable spring fingers pivoted on said upper cross bar. Thus a rectangular halftone screen is held in exact parallelism with the cross bars.

The halftone screen supporting frame as a whole is mounted within the camera body to have an externally controlled horizontal movement for placing the halftone screen in any desired position. The supporting frame is hung on horizontal tracks, secured to the camera body structure, by means of rollers attached to upper extensions of the vertical side members of the supporting frame. Movement of the frame is effected by an interconnected rack and gear arrangement provided adjacent each corner of the supporting frame wherein the gears are mounted on shafts which are journalled in bearings secured to the camera body structure and the racks are secured to the screen supporting frame. Of the four racks provided, one is fixed to the supporting frame while the other three are secured thereto by a spring and screw arrangement. The upper gear shaft extends to the outside of the camera body and is provided at its external end with a crank arm whose distal end cooperates with an arcuate clamping plate on which a graduated scale is provided. By rotating the crank arm the four interconnected gears are rotated a corresponding amount and hence, through their associated racks, produce a horizontal movement of the screen supporting frame. The position of the frame is accurately indicated by the position of the crank arm in relation to the scale markings on the clamping plate.

The location and proportions of the mechanism are such that when the crank arm is rotated clockwise, at least one of the thin aligning plates will come in direct contact with the front surface of the film backing member when the latter is in its focal plane position. Adjustment may then be made, if necessary, to bring all of the aligning plates into contact with the film backing mem ber by appropriate manipulation of the spring and screw arrangement provided on three of the four racks. With the aligning plates in contact with the backingmember and the halftone screen in contact with the aligning plates parallelism between the backing member and the halftone screen is assured, fixed and maintained even after the backing member and screen are moved away from each other during operation of the camera.

It will be understood that the foregoing general description and the following detailed description as well are exemplary and explanatory of the invention but are not restrictive thereof.

Referring now in detail to the present preferred and illustrated embodiment of the present invention as shown in the accompanying drawings, the invention is shown as embodied in a photo-engraving camera which substantially corresponds in its principal parts to a Chemco camera, many of the parts of which will not be described as they do not relate to, nor assist in the understanding of the present invention.

The illustrated camera includes the camera body 10, on the forward portion of which are supported the camera bellows l2, and at the extreme forward portion of which is supported the camera lens 14 which may be moved back and forth to proper exposure position so that the image to be photographed is properly focused on the sensitized material. Within the camera body 10 is supported one or more film supply units, such as the film roll 16 from which the deisred length of photographically sensitized film or paper may be fed to be severed by conventional knife mechanism 13, actuated by external lever 19, so that the desired size of sheet film may be supported on the forward face of a backing member 20- in a position normal to the axis of the camera lens 14. Between the forward surface of the backing member 20 and the camera lens there is provided a halftone screen supporting frame 21 in which is mounted the halftone screen 22. In Figures 1 through 7 halftone screen 22 is shown as a conventional circular screen which is rotatably mounted on a frame 23 having a generally rectangular outline. In Figures 8 and 9 a conventional, unframed, rectangular halftone screen 22' is shown mounted in supporting frame 21. The camera body and bellows are so constructed, as is usual, that the film to be exposed is shielded from extraneous light and receives only that light which is admitted through the shutter associated with the camera lens 14.

The film backing member 20- preferably is of the vacuum type which is relatively rigid and provided with a foraminated surface towards the lens by which suction may be applied to a sheet of sensized film to hold it flat and accurately in the focal plane of the camera. At the rear the vacuum backing member 20 is provided with a suction hose 24 which is connected to a suction pump of suflicient capacity to develop a suction of several inches of mercury over the entire front surface of the backing member.

Backing member 29 is also mounted to be moved forwardly and rearwardly with respect to the focal plane of the camera lens, always maintaining its front surface normal to the axis of the lens, and is preferably mounted so that this movement may be controlled from an exterior manipulative handle, such as the crank arm 26 which moves over a track member 28 to give an external indication of the position of the backing member with reference to the focal plane, and may also be provided with conventional means for locking the crank arm 26 in its adjusted position for exposure. The backing member is conveniently mounted for this forward and rearward movement by means of the depending legs 30 provided with rollers 32 which run in horizontally extending tracks 34 fixed to any adjacent part of the camera body structure. The backing member is moved by means of the parallel link motion parts comprising the links 36 which are pivoted on the top and bottom of the backing memher and at either side thereof and have their rear ends pivoted to rotatably mounted segments 38. Segments 38 are linked together for simultaneous equal movement by means of a pivotally attached vertical link 40. Segments 38 are rotatably mounted by means of shafts which extend across the camera and are supported in the sides of the camera body. The upper ones of the segments 38 are rigidly fixed to the shaft on the external end of which is secured the crank arm 26 so as to be moved thereby, thus moving all four of the segments 38 and causing a uniform movement of the backing member 20.

The halftone screen supporting frame 21 is a relatively large, rectangular, slightly resilient framework consisting of vertically extending side members 46 and 48 connected together near their top and bottom ends and in widely spaced parallel relation by horizontal members 55') and 52. The top end of each side member 46 and 48 is provided with a laterally extending roller 54 adapted to roll in a trackway 55 which may be secured to the camera body structure 10. Adjacent to and parallel with the side members 46 and 48 there is provided a pair of secondary side bars 56 and 58 the ends of which are rigidly secured on the horizontal frame members 50 and 52. Side bars 56 and 58 may be conveniently formed from strap shaped material and arranged so that their broad surfaces face each other. An upper, screen sup porting cross bar 60 and a lower screen supporting cross bar 62 are slidably connected at their ends to secondary side bars 56 and 58. Each of the four slidable connections is similar to the others but, as constructed, is formed as right or left hand as its position may require. The left hand slidable connection between the upper cross bar 60 and the secondary side bar 56 as shown in Figure 2, is illustrated in detail in Figure 7. As embodied the side bars 56 and 58 are each provided with inwardly projecting lip portions 64 behind which the ends of cross, bars 60 and 62 extend. The base of an angle bracket 65 is secured on the forward face of each bar 60 and 62 near the ends thereof but is spaced therefrom by a plate 66 so as to provide a recess into which the lip 64 projects. The flanges 67 of angle brackets 65 lie against the broad inner face of its associate secondary side bars 56, 58 and are each provided with a hole 68 through which the threaded shank of a clamp screw 69 (Figure 2) extends. A series of threaded holes 70 provided in the secondary side bars 56, 58 and holes 68 permit each cross bar 60, 62 to be clamped in with one of the holes 70. Thus, cross bars 60 and 62, which directly support the halftone screen 22 or 22', may be moved relative to each other so as to accommodate screens of various sizes and to center the screen with respect to the focal axis of the camera lens.

Means are provided to insure that during adjusting movement of the cross bars 66 and 62 each end of a bar moves the same distance no matter where the operator may grasp the bar. As embodied such means comprise a cross shaft 72 which is journalled at one end in the secondary side bar 56 and at the other end in secondary side bar 58. This shaft is positioned somewhat above the uppermost position to which cross bar 66 may be set. A sprocket '73 is fixed on each end of shaft 72 against the inside face of the adjacent secondary bar. In vertical alignment with each sprocket 73 there is an idler sprocket 74 which is located somewhat below the lowermost position to which cross bar 60 may be set and each sprocket 74 is rotatably mounted on a stud 75 carried by the secondary sidebar 56 or 58. Trained snugly around each pair of sprockets 73, 74 is a sprocket chain '76 and the rear reach of each chain is anchored, as by screws 76', to the base leg of its respective angle bracket 65. Thus, movement of one end of cross bar 60 is imparted equally to the other end through chain 76, sprocket 73 and shaft 72.

A similar movement-equalizing arrangement of sprockets and chains is provided for the lower cross bar 62 and comprises shaft 77, sprockets 78 and 79, studs 80 and chains 81, but shaft 77 and idler sprockets 79 are located below and above the cross bar 62, respectively.

Means are provided for easily selecting the proper position of either cross bar 60 or 62 for holding a halftone screen of a particular size. As embodied, each of the four angle brackets 65 is provided with a pointer 85 which is secured on the flange 67 of the bracket at a point adjacent the hole 68. A graduated scale 86 is provided for each pointer 85 and mounted on the outer side of each secondary side bar 56 and 58 in a position corresponding to that occupied by each of the four series of threaded holes 7t) in said side bars. Numbered graduations on the scales 86 indicate to an operator the level at which cross bars 60 and 62 are to be set to accommodate a particular size screen and when the pointers 85 are brought to the desired point the clamp screws 69 are inserted through bracket holes 6% into a threaded hole 76 to lock the cross bars in the selected position.

Both upper and lower cross bars 60 and 62 are provided with clamping and aligning devices to accommodate either a conventional, unframed, rectangular halftone screen or a conventional, frame supported, rotatable,

circular halftone screen. In Figures 1 to 7 of the drawings the use of a framed, circular screen is shown and will now be described.

The conventional circular screen 22 is usually held in a rigidly constructed frame 23 which is generally rectangular in shape and provided with grooved rollers 91 at the corners for rotatably supporting the screen. The screen itself is mounted on the rearward face of the frame 23 and hence the screens back face extends rearwardly of the frame a distance equivalent to its thickness and it is this feature which is utilized by the present invention for accurately aligning the planar surfaces of the screen in parallelism "with the plane occupied by the screen supporting frame 21.

Referring now to the lower cross bar 62, a screen frame holding member 95 is s-lidably mounted thereon by means of a pair of studs 96 (see Figure 6) which are fixed in the cross bar and project forwardly through suitable apertures in holding member and thence termimate in a reduced and threaded end on which a hand nut 97 is screwed. A spring 98, between the hand nut 97 and the forward face of the holding member 95 serves to urge the latter rearwardly towards the cross bar 62. The upper edge of holding member 95 is formed as a stop to receive and support the lower edge of screen frame 23 and the latter is held in this stop by a plurality of spaced clamp screws 99 carried in plates 100 which are fixed on the front face of holding member 95. Welded, or otherwise secured to the rear face of cross bar 62 are a plurality of relatively thin aligning plates 101 which project above the top edge of cross bar 62 a sufiicient distance so that at least two or more of the plates 161 are in the path of the marginal periphery of the rear face of the halftone screen 22 as the latter is urged rearwardly by springs 98.

Since the weight of the hal-ftone screen and its frame is carried by the holding member 95 the strain on its supporting studs 96 may be relieved by rollers 162 one of which is rotatably mounted in a transverse slot near each end of the holding member 95. Rollers 102 are adapted to roll on a ledge 103 which may be for-med as part of the lower edge of cross bar 62. Ledge 103 also serves to add rigidity to cross bar 62.

Upper cross bar 60 is provided with a slidably mounted, screen frame holding member 104 carried by studs 105 which are fixed in cross bar 6i), extend through suitable apertures in holdingmember 104 and terminate in reduced and threaded shanks on which are screwed hand nuts 106. A coiled spring 107 is placed about each stud shank and has one end bearing against the hand nut 106 and the other end against the holding member 104 thus urging the latter towards the cross bar 66. A vertically depending lip 108, formed along the lower edge of holding member 104 and in vertical alignment with the riser of stepped recess formed onthe upper edge of lower cross bar 62, provides a surface against which the rear upper margin of screen frame 23 can be clamped. Clamping means comprise a pair of fingers 109 which are pivotally attached to the holding member 104, in spaced relation, by knurled hand screws 110. The distal end of each finger 199' is provided with a thumb screw 111, which, when the finger is vertically disposed, can serve to clamp the screen frame 23 against the lip 138 on holding member 104. A ledge 112, formed along the top edge of cross bar 60, provides rigidity to the cross bar and an undersurface of a guide for the holding member 104. A plurality of relatively thin aligning plates 113 are welded or otherwise secured to the rear face of cross bar 60 and project below the lower edge of the bar a sutficient distance so that at least two or more of the plates 113 are in the path of the marginal periphery of the rear face of the halftone screen 22 as the latter is urged rearwardly by springs 107. The plates 113 cor- 101 on the lower cross bar 62.

The mounting of screen 22 and its frame 23 is accomplished by first partially unscrewing clamp screws 99, associated with the lower cross bar 62, loosening hand screws 110 and thumb screws 111 which are mounted in fingers 109, associated with the upper cross bar 6i), and then swinging the fingers 1119 to a horizontal position. The lower edge of screen frame 23 is then canted into position on the stop provided on the upper edge of holding member 95 and the frame and screen then swung into a vertical position. The screen is then pressed rearwardly until it rests against the upper and lower aligning plates 113 and 191 after which the fingers 16 9 are dropped to their vertical position and clamped by screws 110. Thumb screws 111 and clamp screws 99 are then manipulated so that as their ends press against the screen frame 23 the upper and lower holding members 194 and 95 are forced away from the cross bars, against the urging of springs 107 and 98, until the lip 103 on the upper cross bar 60 and the riser of the stop on the lower cross bar 62 are clamped against the rearwardface of the screen frame 23. Thus, the screen 22 is firmly pressed against the aligning plates 101 and 113 and thereby held in accurate parallelism wtih the plane occupied by the screen supporting frame 21 as a whole.

Movement of the halftone screen supporting frame 21 between its forward, or screen loading position, and its rearward, or screen focusing position, is accomplished by means of a gear and rack arrangement which is interconnected so =as to produce a parallel motion of the supporting frame 21. As embodied, a pair of upper gears 12% are provided and fixed on a shaft 121 which is journailed in the camera body structure, one gear being to the rear and in line with the upper portion of frame side member 46 and the other similarly arranged with respect to frame side member 48. A pair of lower gears 122, rotatably mounted on a cross shaft 123, are in vertical alignment with upper gears 129' and to the rear of the lower portions of side members 46 and 48. Each upper gear 120 is connected to its corresponding lower gear 122 by a link 124. Thus, any rotation of upper shaft 121 imparts a corresponding rotation to all four of the gears. Attached near each corner of the screen supporting frame 21 and projecting rearwardly therefrom there is provided a rack 125 which is adapted to mesh with one of the gears 120 or 122, and to eliminate lost motion between the gear and rack a pressure roller 126 is rotatably mounted on an adjustable bracket 127 which may be attached to a convenient portion of the camera body structure by belt and slot connections 128. A jack screw 129 beneath each of the brackets 128 provides means for the accurate positioning of the rollers 126.

Of the four racks 125 three are adjustably attached to the frame sidemembers 46, 48 while the fourth, shown as the one at the upper left corner of the frame 21 in Figure 2, is fixed to the side member 46 as by nut 130. The adjustable connections each comprise a reduced shank portion 131, on the racks 125, which projects through an aperture in the side members and has a hand not 132 screwed on its threaded end. Interposed between the frame side members and the body portion of the rack is a compression spring 133. Manipulation of hand nuts 132 thus permits the screen supporting frame 21 as a whole to be adjusted into parallelism with a reference plane such as the lens-facing surface of the film backing member 20.

Provision is made on the outside of the camera body for moving the screen supporting frame 21 into a desired position by extending one end of the upper shaft 121, on which gears 12% are fixed,.through a side wall of the camera body and clamping thereon a hand lever 1 12 which is provided at its extremity with a locking screw 143. Screw 143 cooperates with a slot 144- in an arcuate plate 145 which is secured to the camera body. Graduations 146 on arcuate plate 1.4- provide means for setting the hand lever 142 in such position as to obtain a particularly desired position of the screen supporting frame 21.

. Referring now to Figures 8 and 9 the means for supporting a conventional, unframed, rectangular screen 22' will be described. A plurality of holding lugs 136 are fixed at spaced intervals along the upper front margin and edge of the lower cross bar 62. That portion of the lugs 136 which projects above cross bar 62 has its rear face sharply beveled so that in conjunction with the adjacent aligning plate 191 there is formed a V-shaped trough in which the lower edge of a halftone screen 22 may rest with the bevel forcing the rear lower margin of the screen 22' into contact with aligning plate 101. The upper cross bar '60 is so adjusted that it is above the upper edge of screen 22 but still in such position that the rear upper margin of screen 22 may be laid against two or more of the aligning plates 113. Spring fingers 137 are pivotally attached to the front face of cross bar 69, as by a screw 138, and provided at their distal end with a screen contacting stud 139 and knob 140. Thus, when the screen 22' is brought against the aligning plates 113 the pivoted fingers 137 may be swung from their horizontal, non-use position in which they are placed during use of a circular screen, to a vertical position to press the screen 22 against the aligning plates.

Adjustments and operation A halftone screen 22 or 22 of the proper size and mesh for a particular photographing operation having been selected and brought to camera site, the bellows 12 is detached from the camera body and moved away a sufficient distance to permit an operator to have complete access to the interior front of the camera body. The operating hand lever 142 is then swung to its upper position and locked by clamp screw 143 thereby moving the screen supporting frame 21 to its forward or screen loading position as shown in solid lines in Figure 1. Upper and lower cross bars 60 and 62 are then moved to the correct positions, as indicated by their pointers and graduated scales 86, so as to properly receive and center the selected halftone screen, and clamped in such position by screws 69. Assuming a circular screen is to be used, the lower edge of the screen frame 23 is centrally placed on the lower holding member and swung to a vertical position, thus bringing the rear upper and lower margins of the screen against aligning plates 101 and 113. The screen frame is then clamped into position by upper and lower clamp screws 111 and 99.

At this point the film backing member 20 is moved to its focal plane position by manipulating lever 26. This position is indicated in dot and dash lines in Figure 1. Hand lever 142 is now rotated clockwise to move the screen supporting frame 21 rearwardly until some one of the aligning plates 101 or 113 come to rest against forward surface of the film backing member. This will happen if the supporting frame 21 is not in accurate parallelism with the backing member. By inspection the operator then determines which of the aligning plates are not in contact with the backing member and by manipulation of one or more of the three hand nuts 132, which are associated with the adjustable racks 125, shifts the screen supporting frame 21 until all the aligning plates are in contact with the backing member. Since the screen is already in contact with the aligning plates and the plates are in contact with the backing member the parallelism between screen and backing member is substantially perfect. The operator then loosens the conventional clamping means between the hand lever 142 and the shaft 121 and sets and clamps the hand lever at the graduation on the arcuate plate 145. The graduations of scale 145 indicate varying distances of screen separation from the backing member, allowance being made in the graduations for the thickness of the aligning plates which is less than the minimum screen separation required for the photoengraving work to be performed by a camera of the type described herein.

If desired the screen 22 may now be rotated to any position which the work involved requires without destroying the parallelism between it and the backing member. Since the screen is in contact at all times with the aligning plates any variations in the parallelism between the screen 22 and its frame 23 are taken up, during rotation of the screen, by the holding members 104 and 95 shifting their positions on their supporting studs.

The bellows may now be rejoined to the camera body and conventional practice followed in unrolling a strip of sensitized material or film, cutting it to the required size, securing it in place on the backing member by suction means, moving the backing member from film receiving position to exposure position, setting the screen supporting frame by means of hand lever 142 and graduations 146 so as to obtain the proper screen separation and, finally, completing the operation by exposing the film.

The invention in its broader aspects is not limited to the specific mechanisms shown and described but departure may be made therefrom within the scope of the accompanying claims without departing from the principles of the invention and without sacrificing its chief advantages.

We claim:

1. In a halftone camera the combination of a halftone screen having a central portion and an outer peripheral screen, movable means on the frame for urging the align ing members into engagement with the screen, said screen clamped in position between said aligning members and said frame, means for moving said planar surface and said aligning members into contact, means for angularly orienting said frame to move any aligning members not in contact with said planar surface into engagement therewith, said aligning members being constructed and arranged to' each contact said planar surface when said screen and said surface are parallel, and means for moving said screen and said planar surface away from each other a pre-determined distance to focus and exposure position respectively.

2. The invention as set forth in claim 1 wherein said halftone screen comprises a holder and a circular rotatable halftone screen and wherein the urging means on the frame comprise rotatable clamping elements mounted on the face of the frame farthest from the rigid planar surface, said clamping members being movable relatively toward and away from the supporting frame, moving said aligning members into and out of engagement with said screen.

3. The invention as defined in claim 1 wherein said movable means on said frame is adapted to urge said aligning members into engagement with a rotatable circular halftone screen, and including additional means adapted to co-act with said aligning members for accommodating a non-rotatable rectangular halftone screen.

4. The invention as defined in claim 1 wherein said edge portion of less thickness than said central portion movable means includes Springs for resiliently urging Said whereby the face of said central portion lies in a plane extending beyond the plane of said edge portion, a rigid planar surface for supporting photo-sensitive material in the focal plane of the camera, a supporting means for the screen, said supporting means comprising a frame defining an opening to accommodate the half tone screen, a plurality of aligning members fixed to the face of the frame nearest the rigid planar surface and extending inwardly of the opening at spaced intervals and directly engaging the face of the central portion of the halftone aligning members into engagement with said screen.

References Cited in the file of this patent UNITED STATES PATENTS 851,593 Hatt Apr. 23, 1907 1,187,045 De Bouzek June 13, 1916 1,535,225 Hayes et a1. Apr. 28, 1925 2,044,184 Powers June 16, 1936 2,115,233 Powers Apr. 26, 1938 2,653,510 Huebner Sept. 29, 1953

Claims (1)

1. IN A HALFTONE CAMERA THE COMBINATION OF A HALFTONE SCREEN HAVING A CENTRAL PORTION AND AN OUTER PERIPHERIAL EDGE PORTION OF LESS THICKNESS THAN SAID CENTRAL PORTION WHEREBY THE FACE OF SAID CENTRAL PORTION LIES IN A PLANE EXTENDING BEYOND THE PLANE OF SAID EDGE PORTION, A RIGID PLANAR SURFACE FOR SUPPORTING PHOTO-SENSITIVE MATERIAL IN THE FOCAL PLANE OF THE CAMERA, A SUPPORTING MEANS FOR THE SCREEN, SAID SUPPORTING MEANS COMPRISING A FRAME DEFINING AN OPENING TO ACCOMODATE THE HALF TONE SCREEN, A PLURALITY OF ALIGNING MEMBERS FIXED TO THE FACE OF THE FRAME NEAREST THE RIGID PLANAR SURFACE AND EXTENDING INWARDLY OF THE OPENING AT SPACED INTERVALS AND DIRECTLY ENGAGING THE FACE OF THE CENTRAL PORTION OF THE HALFTONE

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