US3556656A - Contact photography frame utilizing depressurization - Google Patents

Abstract

A RECTANGULAR FRAME HAVING MOUNTED THEREIN A FLEXIBLE TRANSPARENT AND A STRETCHABLE SHEET. THE VOLUME ENCLOSED BY THE FRAME AND SHEETS MAY BE DEPRESSURIZED BY A CONVENTIONAL VACUUM CLEANER OR OTHER HIGH-VOLUME LOW-PRESSURE FLUID PUMP FOR WHICH A SUITABLE FITTING IS PROVIDED IN THE SIDE OF THE FRAME. A NEGATIVE AND SENSITIZED SHEET WITHIN THE FRAME ARE PRESSED TOGETHER BY COLLAPSE OF THE STRETCHABLE SHEET FOR EXPOSURE IN A CONTACT PHOTOGRAPHY PROCESS. THE FRAME IS PREFERABLY HOLLOW WITH OPENINGS SURROUNDING THE TOP INTERIOR PORTION TO PERMIT RAPID DEPRESSURIZATION OF THE INTERIOR.

Description

Jan. 19, 1971 G. EVENSEN 3,556,656

CONTACT PHQTOGRAPHY FRAME UTILIZING DEPRESSURIZATIQN Filed July 2, 1968 III-A 34 v INVENTOR v GUNNAR EVENSEN ATTORNEYS Patented Jan. 19, 1971 3,556,656 CONTACT PHOTOGRAPHY FRAME UTILIZING DEPRESSURIZATION Gunnar Evensen, Englewood, N.J., assignor of thirty percent each to Haraldur Hagen and Leonard Rosensweig, and live percent each to Robert E. Delaney and Robert R. Keegan as trustee for Darby and Darby Filed July 2, 1968, Ser. No. 741,994 Int. Cl. G03b 27/20 US. Cl. 35594 9 Claims ABSTRACT OF THE DISCLOSURE A rectangular frame having mounted therein a flexible transparent and a stretchable sheet. The volume enclosed by the frame and sheets may be depressurized by a conventional vacuum cleaner or other high-volume low-pressure fluid pump for which a suitable fitting is provided in the side of the frame. A negative and sensitized sheet within the frame are pressed together by collapse of the stretchable sheet for exposure in a contact photography process. The frame is preferably hollow with openings surrounding the top interior portion to permit rapid depressurization of the interior.

In the graphic arts industries there are frequent requirements for contact photography, for example, in silk screen printing, offset or lithographic printing, producing photograph prints, etc.

Contact photography is an old and well-known process, the basic steps of which comprise placing a photographic negative or transparency over a photosensitized material, illuminating the photosensitized material through the photographic negative and developing or otherwise proc-- essing the photosensitized material. In contact photography the quality of the photographic reproduction of the negative is critically dependent upon establishment of intimate contact between the protographic negative and the sensitized material during illumination. In the absence of such intimate contact, one obtains only a blurred shadowgraph rather than a sharp reproduction.

Various expedients have been used to procure intimate contact between a negative and a photosensitized material. A common expedient has been to press the negative and photosensitive sheets between a transparent glass plate and a resilient pad of rubber or similar material. In some cases a rubber pad has been pressed against the sensitized material and negative and the glass plate by a pressure differential.

In previous apparatus the various components include a relatively thick and heavy glass plate with appropriately hinged mounting, a massive pressurizable enclosure, a support structure, a thick rubber blanket, and a vacuum pump, presenting in the aggregate, an expensive and bulky apparatus. Notwithstanding the disadvantages of such apparatus, it has been in relatively Wide use due to the importance of producing high-quality work by contact photographic processes.

According to the present invention, apparatus for contact photographic work is provided which is far lighter, less bulky, less expensive, and yet is capable of producing work of equal quality and in some cases better quality than obtainable by prior apparatus.

In one embodiment, the present invention comprises a first frame portion provided with a fitting for a hose of a vacuum cleaner which may be of the conventional household type, the frame being covered on the bottom side with a very stretchable sheet material of rubber or the like. A second lighter frame portion of the same shape as the first frame portion is provided to fit on top of the first frame portion and has mounted therein a sheet of thin flexible transparent material which is relatively less stretchable than the rubber material covering the bottom frame portion. A sealing strip is provided around the (preferably bottom) frame portion so that the two fit together in substantially sealed relationship.

In use, the top frame portion, which is preferably of light construction, is lifted to place a photosensitized material within the lower frame portion and to place a negative in the desired position over the photosensitized material. The photosensitized material may be simply a sheet of photographic paper or it may be a silk screen and frame or it may be a photo-offset plate for use in lithographic or other printing processes. The top frame is then placed on the bottom frame and the vacuum cleaner started to depressurize the interior of the frame. In a matter of seconds the stretchable bottom sheet presses the negative and photosensitive material against the top transparent sheet in very intimate contact so that the photosensitized material can be exposed through the negative to produce a clear, sharp photographic reproduction. The above steps are simply reversed to remove the exposed sensitized material and negative and to ready the apparatus for a repetition of the process.

From the foregoing explanation, it will be seen that the present apparatus does not involve heavy glass plates, bulky supporting structures or vacuum pumps, and is ideally light, simple and inexpensive.

In addition to providing the above-described advantages, it is an object of the present invention to provide a frame for contact photographic processing which is light, portable and inexpensive and which incorporates a light flexible transparent window through which materials may be exposed.

It is another object of the present invention to provide an inexpensive frame for contact photography in which the force for pressing negative and photosensitive material together is provided by a pressure differential created by an ordinary vacuum cleaner.

Other objects and advantages of the present invention will be apparent from a consideration of the following description in conjunction with the appended drawing, in which:

FIG. 1 is a perspective view of contact photography apparatus according to the present invention;

FIG. 2 is a sectional view of a portion of the apparatus of FIG. 1 taken along the line 2-2 of FIG. 1 and illustrating the aparatus in the unoperated position; and

FIG. 3 is a vertical sectional view of a portion of the apparatus of FIG. 1 along the line 3-3 in FIG. 1 and illustrating the apparatus in the operative (depressurized) condition.

Referring to FIGS. 1 through 3, a frame 11 for contact photography is illustrated which is formed of four side members 13. The side members 13 are illustrated to be of equal length so that the frame is in the form of a square, but the frame may obviously be formed as a more or less elongated rectangle or in another shape. Each of the frame Walls 13 is preferably of hollow construction with an outer wall 15, an inner wall 17, a top wall 19, and a bottom 21.

Bottom 21 is provided with a channel 23 for purposes later to be described. Inner wall 17 of frame side 13 is provided with openings 25 which may, for example, be three in number and approximately equally spaced along the top of said inner wall.

Frame sides 13 may be secured together in any suitable fashion and may be rendered more rigid and rugged by internal corner braces 27 as illustrated in FIGS. 2 and 3. Frame sides 13 may be further secured together by welding, soldering or by appropriate fasteners. Frame sides 13, and in fact the entire frame structure, may conveniently be formed of extruded or otherwise preformed aluminum stock. Alternatively, the frame 13 maybe formed of wood, synthetic resin materials, other metals, or any other suitable structural material. Although certain advantages accrue from forming the frame 11, and in particular the sides 13 of hollow stock, this is not essential.

One of the frame sides 13 is provided with a fitting 29, adapted to receive the hose of a conventional vacuum cleaner as will later be described.

The central Opening in frame 11 is covered at the bottom with a highly stretchable sheet 31. Sheet 31 may be formed, for example, of rubber, of either natural or synthetic type, or of a synthetic resin. A particularly suitable material has been found to be a rubber sheet sold as dental dam of approximately .02 inch thickness. While other thicknesses may be used, the sheet is preferably less than 0.1 inch thick.

The sheet 31 is conveniently secured in place in channel 23 by means of a resilient tube 33 dimensioned to be a press fit into channel 23. This method of fastening is known, for example, in securing screens to window screen frames and in fact the stock for formation of frame sides 13 may conveniently be procured from manufacturers of window screen and storm Iwindow stock.

The stretchability of sheet material 31 is such that a pressure differential of about one pound per square inch will cause it to be deformed to substantially fill the volume of the frame (the frame may be of dimensions 2" x 12" x 18 or larger). More specifically, the stretchability of the sheet should be such that a one-foot square is elongatable by one inch by a force of less than pounds applied on one side.

In some cases it may be desirable to rigidify and ruggedize the structure of FIGS. 1-3 with a rigid panel secured under the stretchable sheet 31. Such a panel may be formed of metal, synthetic resin, fiber board, or wood and should be generously perforated with holes (e.g. several hundred A inch holes as in standard peg-board stock) to permit free collapse of sheet 31 into the frame. The panel may be screwed, riveted or otherwise secured to the bottom of frame 11.

The contact photography frame is provided with a top portion 35 formed of four sides 37 which may also conveniently be formed from aluminum stock.

Frame portion 35 may also be reinforced-with corner braces 39 in a manner similar to that previously described for the bottom frame portion. Top frame sides 37 are provided with a channel 41 so that a flexible but relatively unstretchable sheet 45 may be mounted in frame portion 35 by means of tubing 43 fitting snugly in channel 41 in a manner similar to that by which sheet 31 is mounted in frame 11.

While top frame portion 35 could be hinged or otherwise secured as a cover for frame 11, it is preferable that it remain as a separate portion held in place only by the pressure differential.

A resilient sealing strip 47 is provided around the top of the bottom frame portion by suitable adhesive so that a reasonably air-tight seal is provided between top frame sides 37 and bottom frame sides 13- when a pressure differential exists within the frame relative to the atmospheric pressure. It will be appreciated that the frames themselves and the seal between frame portions need not be perfectly air-tight, but only sufficiently air-tight to permit the frame to be depressurized at least to the extent of about one pound per square inch by a conventional vacuum cleaner.

The sealing strip 47 may be formed of foam rubber or foam synthetic resin, in particular, available stock material used for weather stripping purposes is suitable.

As previously explained, the depressnrization of the frame 11 may be accomplished by a conventional vacuum cleaner illustrated at 49 having a hose 51 with an end fitting 53 with which the fitting 29 is adapted to mate.

The normal On-Off switch 55 for the vacuum cleaner 49 may be utilized in the operation of the contact photography frame or alternatively a more conveniently placed switch may be arranged by connecting it in the power line to the vacuum cleaner 49.

Customarily in contact photography a light source 57 is provided specifically to illuminate the work in a substantially uniform manner. Obviously, this is not a requirement as ordinary room illumination or even sunlight may be used for contact photography.

For purposes of illustration, a sheet of photosensitive material 59 and a partially transparent negative 61 are shown appropriately positioned in the frame 11.

The operation of the apparatus in a typical case will be as follows. Frame 11 is placed on a convenient table or other work surface. Top frame portion 35 is removed and the materials involved in the exposure step of the contact photographic process are placed inside frame 11. In the simplest case the materials will consist of a photosensitized sheet 59 and a photographic negative 61, or the equivalent. It should be noted however that the frame is deep enough to accommodate a silk screen frame or virtually any material one might 'wish to use in contact photography.

In some cases it Will be desired to produce a composite print from more than one negative, and in such cases the thicknesses of the negative portions will not be uniform. As will later be described, the present apparatus provides highly unobvious and unexpected advantages in the case of this difiicult type of contact photography.

Once the proper arrangement of the contact photography materials is made, the top frame portion 35 is placed on top of the bottom portion 11 and the frame is depressurized by actuation of the vacuum cleaner 49 or other fluid pump. Immediately the stretchable sheet 31 collapses upward, firmly pressing the photographic materials against the transparent sheet 45. This takes, at the most, a few seconds. It will be noted that the sheet 31 will balloon upward first contacting the center of the Window 45 and thereafter the contact will spread outwardly with a motion tending to smooth out the contact photography materials.

While the transparent sheet 45 is not nearly so stretchable as the sheet 31, it is somewhat deformable and assumes the shape illustrated in FIG. 3. The preferred placement of holes 25 assures that they will not be blocked by collapse of sheet 31. The photographic materials are now pressed together with a pressure of many pounds and may be exposed by energizing the lamp 57 for the desired time interval in accordance with standard techniques.

Due to the thinness and clarity of transparent sheet 45, virtually no diminution or distortion of the light from lamp 57 takes place.

As will be seen in FIG. 3, the transparent sheet 45 assumes a generally fiat shape in its central area, but it is by no means critical that that the contact photographic materials be maintained in a flat configuration, since the photographic process is a contact process rather than a projection process. The primary consideration is equal illumination over the area of the frame and this is achievable to a satisfactory degree by proper selection of illuminating lamps, the lamp illustrated in FIG. 1 being intended only as a schematic representation.

A very important feature of the apparatus is the flexibility of sheet 45. This becomes particularly important when more than one negative is utilized in a single exposure, as is often desirable to accomplish a desired layout. In prior devices utilizing a glass plate rather than flexible sheet 45, different thicknesses of negative in a single exposure almost inevitably resulted in shadows along the line of demarcation between different negative thicknesses. Such shadows obviously will be reproduced on the photosensitive material, creating a difficult if not insurmountable problem. It has been found with the apparatus as illustrated in FIGS. l3, that the flexibility of transparent sheet 45 renders possible easy contact photography processing for different negative thickness in a single exposure. This is believed due to the fact that the flexible transparent sheet 45 curves smoothly around the edge of the discontinuity between different negative thicknesses and prevents the formation of shadows. Whatever the reason may be, work with layouts having different negative thicknesses has been found to be greatly facilitated with the present apparatus, as compared with apparatus employing a rigid plate of glass or other rigid transparent material.

Of course, following the exposure of the contact photographic materials 'within frame 11, it is a simple matter to turn off the fluid pump, whereupon air rapidly leaks into the frame, causing it to be depressurized and permitting the top frame portion 35 and the contact photographic materials to be removed. It has been found unnecessary to provide any valve or opening for the purpose of depressurizing the frame, but such an opening could readily be provided if found desirable.

It should be noted that upon both pressurization and depressurization, the feet 34 lift frame 11 from its supporting surface adequately to permit the flow of air occasioned by the collapse and restoration of the stretchable sheet 31.

Numerous variations may be devised to the apparatus of FIGS. 1-3, but several such variations are worthy of particular note. In one variation the function of the stretchable sheet and of the transparent sheet are fulfilled by a single transparent stretchable sheet (e.g. polyvinyl chloride sheet). By the use of a stretchable transparent sheet material, it is possible to dispense with upper frame portion 35, and the sheet 31 is replaced with a stretchable transparent polyvinyl chloride sheet. The stretchability of such a sheet is not as great as the preferred material for sheet 31 but it is nevertheless sufficient to stretch into and substantially fill a frame of dimensions approximately two feet by three feet by two inches under not more than a few pounds per sq. in. pressure differential.

Such an alternative form of frame would be utilized in an inverted position, as compared with the apparatus shown in FIGS. 1, 2 and 3. In other words, the contact photography materials would be placed on a flat table or other work surface and the bottom frame portion 11 would be inverted and placed over the contact photography materials. Upon depressurization, the flexible transparent sheet would collapse and impart the required pressure to the contact photography materials to maintain them in intimate contact. The frame illustrated in FIGS. 1, 2 and 3 may also be used in an inverted position in conjunction with alight table for illuminating from below.

It is noteworthy that with such an alternative form of apparatus, the work surface does not have to be horizontal and, in fact, the frame can be placed at any angle or on a vertical wall where the depressurization will hold it and the materials inside securely in place.

From the foregoing description it will be seen that a particularly simple but at the same time highly effective contact photography frame is provided, having a number of advantages over prior devices.

In addition to those modifications and variations of the invention which have been described and suggested, other variations and modifications will be apparent to those of skill in the art, and the scope of the invention is accordingly not to be construed to be limited to the particular embodiments illustrated or suggested, but is to be defined by reference to the appended claims.

What is claimed is:

1. Apparatus for contact photography or the like comprising a substantially rigid and generally air-tight hollow rectangular frame surrounding a central opening having means including a large aperture in one outer side thereof for connecting said frame to fluid exhaust pumping means and a plurality of smaller apertures on the top inner sides communicating to said central opening, fluid exhaust pumping means connected to said large aperture, a resiliently stretchable substantially air impervious sheet smoothly secured in air-tight manner over the opening on one face of said frame, a sealing surface extending around the opening on the other face of said frame to cooperate with a covering surface to enclose the interior of said frame in a generally air-tight manner except for said aperture, said stretchable sheet being stretchable at a pressure differential of less than 5 pounds per square inch sufliciently to substantially fill the interior volume of said frame, a covering surface comprising a second frame adapted to cooperate with said sealing surface and having secured smoothly in the central opening thereof a flexible relatively less stretchable transparent sheet of thickness less than 0.1 inch, and a light source for uniformly illuminating said interior volume of said frame through said transparent sheet, whereby contact photography materials comprising a transparency and a photo-sensitive article may be placed in said rectangular frame, pressed together between said transparent sheet and said stretchable sheet by a pressure differential, and exposed through said transparent sheet.

2. A frame for contact photography or the like comprising a high volume, low pressure fluid exhaust pumpings means, a substantially rigid and generally air-tight hollow rectangular frame surrounding a central opening having means including a large aperture in one outer side thereof for connecting said frame to said fluid exhaust pumping means, and said frame having a plurality of smaller openings on the inner sides communicating to said central opeing, a resiliently stretchable substantially air impervious sheet smoothly secured in air-tight manner over the opening on one face of said frame, and a sealing surface extending around the opening on the other face of said frame to cooperate with a covering surface to enclose the interior of said frame in a generally air-tight manner except for said aperture, said stretchable sheet being stretchable at a pressure differential of less than 10 pounds per square inch sufliciently to substantially fill the interior volume of said frame.

3. A frame for contact photography or the like comprising a high volume, low' pressure fluid exhaust pumping means, a substantially rigid and generally air-tight frame with a central opening and having an aperture in one side thereof connected to said fluid exhaust pumping means, a stretchable substantially air impervious sheet secured over the opening on one face of said frame, and sealing means around the opening on the other face of said frame to cooperate with a covering surface to enclose the interior of said frame in a generally air-tight manner except for said aperture, said stretchable sheet being stretchable at a pressure differential of less than 10 pounds per square inch sufliciently to substantially fill the interior volume of said frame.

4. Apparatus for contact photography or the like comprising a substantially rigid and generally air-tight frame with a central opening and having means including an aperture in one side thereof for connecting said frame to fluid exhaust pumping means, and a transparent stretchable substantially air impervious sheet secured over the opening of said frame.

5. Apparatus as claimed in claim 4, wherein said sheet is less than 0.1 inch thick.

6. Apparatus as claimed in claim 4 wherein said frame is hollow and has a plurality of further apertures communicating from the interior of the hollow frame to its central opening.

7. Apparatus as claimed in claim 4, wherein said frame is rectangular with sides of at least one foot dimension and has a depth of approximately 2 inches.

8. Apparatus as claimed in claim 4 further including a cover frame and means for producing a substantially airtight seal between said cover frame and the first said frame, said cover frame having secured in substantially air-tight manner in the central opening thereof a flexible transparent sheet material.

9. Apparatus as claimed in claim 8, wherein said stretchable sheet is stretchable at a pressure differential of 8 less than 5 pounds per square inch sufiiciently to substan- FOREIGN PATENTS th interior volume Of the first said frame. Great Britain References Cited JOHN M. HORAN, Primary Examiner UNITED STATES PATENTS 5 R. A. WINTERCORN, Assistant Examiner 3,385,193 5/1968 Dougherty et a1 355-93 U.S. Cl. X.R.

3,463,587 8/1969 Oltra et a1 35594X 355-120

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