US1490669A - Film-developing rack - Google Patents

Description

April 15 1924..

P. HIGGINSON FILM DEVELOPING RACK Filed Dec'. 6, 1922l [m/vrai; PE/Pcy Maw/wam.

l TToF/YEYJ' Patented Apr. l5, 1924.

PERCX HIGGINSONfOF LOS ANGELES, CALIFORNIA.

FILM-DEVELOEING RACK.

Application led December 6, 1922. Serial No. 605,172.

To all whom t may concern:

Be it known that I, Pintor HIGGINsoN, a subject of the King of Great Britain, resid ing at Los Angeles, in the county of Los Angeles and State of California, have invented a new and useful Film-Developing Rack, of which the following is a specifica-v tion. y

This invention relates to the art of photography and relates particularly to the production of motion pictures.

Of the many devices employed in the development of motion picture film, the simple fihn rack is most extensively used, owing to the simplicitythereof and the fact that with its use valuable film is more nearly under perfect control throughout the development process than where complicated continuous development apparatus is employed.

A. further advantage of the use of these film racks is that the space required for their manipulation is comparatively small and that they may be immersed in narrow tanks, thus making it possible to employ a minimum quantity of developing solution. These racks consist of a rectangular frame having a pair of parallel bars placed at two opposing edges of the frame over which bars the film is disposed. The ease with which such racks may be handled and the small space and small tanksfrequired with their use make them extremely valuable in film laboratory work.

There is, however, an objection to the use of these racks which film laboratories throughout the country have endeavored to overcome, this objection being the formation of rack spots which are portions of the film receiving a greater development than the remainder of the film and so called from the fact that they occur at the points where the film bends over the aforementioned par allel bars of the rack. Positive films printed from negatives having these rack spots consequently have corresponding light spots which, if very pronounced, cause a flicker in the projection of the film. This overdevelopment of the negative film at those points at which it bends over the bars is ascribed to various causes, one of the large film manufacturing laboratories advancing the theory' thatit is due to eonvectioncurrents in the developing solution. This convection explanation of the cause of rack spots is substantially as follows:

When an exposed film wound upon a developing rack of the character described is placed in the developing solution, a chemical reaction occurs between the silver compound of the exposedemulsion coating of the film and the chemical elements of the developer with the result that the development of the image voccurs and a film of developing solution of reduced strength is disposed over the face of the film due to the fact that a portion of the strength of the developing solution coming in contact with the exposed film surface is expended in the chemical action between the developing solution andthe exposed emulsion coating. This film or layer of reduced strength developer being heavier than the full strength developer displaces, by gravitation, downwardly across the face of the film. This movement, of course, is very slow owing to the very slight difference in the densities of the full strength developer and the reaction product. Naturally, as the reaction product moves downwardly across the face of the film full strength developer fiows downwardly to take the place of the reaction product and comes in contact with the uppermost portion of the film, which is that portion bending over the top aforementioned bars. At the lower edge of the rack where the downwardly fiowing reaction product leaves the film aslight agitation of the developer is produced which causes full strength solution to be brought into contact with those portions of the film which bend over the lower bar. Therefore, it is assumed that owing to the portions of the film which bend over the bars being subjected to stronger developing solution than the remainder of the film, a more extensive deposit `of silver will occur at these points of bending.

Another theory as to the formation of rack spots, and one which seems to be supported by the practice and experiment, is that where a `film is bent around a small diameter, the pores of the emulsion are opened, thus permitting greater rapidity of chemical action at those points. The actual cause of rack spots may be a combination of the two above mentioned explanations, but from the inventors experience it has been found that the definition of the rack spot is very nearly proportionate to the curvature of the film which extent of curvature controls the opening of the pores. In other words, where the film is bent over a rod of half inch diameter a certain degree of over development or a certain excess of silver deposit takes place over a given area which is, controlled by the diameter ot the rod. When a portion of the same lilm is turned over a rod oitl three inch diameter, the actua-l over-deposit or silver is substantially the same as the deposit of the smaller area resulting from the use of the half inch diameter` rod, but owing to the tact that this silver deposit is spread over a greater area of film, the spot produced thereby is not as evident as the spot produced by the small diameter bar.

By using a curved surface or cylinder O' live or sir; inch diameter over which to eX- tend the lilm, it is possible to make this rack spot entirely imperceptible to the human eye, and the actual difference in the opacity ol the different portions of the film can only be detected by the use ot sensitive instruments. A reason why racks having large diameter surfaces over which to place the film are not employed is that they are not easily handled, and require larger developing tanks and greater' amounts of developing solution than the standard racks.

It is the principal object of my invention to provide a lilm developing rack which does not cause rack spots in a iilm developed thereupon, and by the use oi which a very even development of the iilm may be accomplished.

The especial advantages ot my invention and further objects thereof will be made evident hereinafter.

Referring to the drawing which is for illustrative purposes only,

Fig. 1 is an elevational view of my in vention having a length of motion picture film wound thereupon.

Fig. 2 is a fragmentary enlarged section taken upon a plane represented by the line 2-2 of Fig. 1.

Fig. 3 is a fragmentary section taken substantially upon a plane represented by the line 3-3 of Fig. 2.

1n the practice ol my invention l employ a frame 11y comprised of vertical members 12, a central cross bar 111 and cross bars 15 placed near the extremities oit' the vertical members 11. Near each end vertical member 11 an inwardly faced recess 18 is formed in which is placed a bearing block 19 which receives and rotatably supports a pin 20 provided in the end of a roller 21.

rllhe pin 2O is integrally formed with a knurled thumb wheel 23, one of which is placed at each of the ends of the rollers 21, as shown in Fig. 1. The roller 21 is preferably formedof a wooden core 25 having celluloid spacing collars 26 and sleeves 27 mounted thereupon. Spring members 30 mounted upon the cross bars 15 are employed to hold the bearing members 19 in rper roller 21 as indicated at 41.

outward positions and holes 32 and 33 are drilled through the ends of the members 11, as shown, through which pins may be inserted to provide variations in the limits of the outward travel of the bearing blocks under the action of the spring 30. A film 35 is placed upon the rack in the following manner: n

The rollers are first forced inwardly and pins placed through the holes 32. A film 35 having an elastic member 37 attached to the end 38 thereof is then wound upon the rack by first hooking the free end of the elastic member over a hook 39 on the upper cross bar 15. rhe elastic member is then stretched to a considerable emtent and the winding ont the nlm` upon the rack accomplished by placing itlirst between the first two collars 26 on the lower roller 21 as indicated at 110, then passing the film across the outside of the rack to the space between the second and third spacing collars on the up- This winding action is continued until the entire strip of ilm is wound upon the rack; whereupon an elastic member 43 is attached to the end la of the iilin strip 35, and the elastic 43 stretched and hooked over a hook i5 in the lower cross bar 15. The pins are then removed frein the holes 32 and the springs 30 allowed to torce the rollers outwardly, thus stretching the film tightly over the rollers 21.

The rack upon which the is now wound is placed in the developing tank. The length of time required for developing 4 of film is controlled by many different conditions, among those being the exposure of the film and the activity of the develop ing solution, into which activity of the solution temperature conditions enter. The average length of time equired for the development of iilm may be assumed as being from live to ten minutes. After the film has been in the solution for a short time, for example one minute, the roller 21 at the top of the rack is slightly turned my manipulating one et the narrow thumb wheels 23, thus causing the film to advance a short distance upon the rollers 21. lt the turning of the rollery 21 is in a lett hand direction, those portions 50 of the film upon the front of the rack would move downwardly while the portions 51 upon the back of the rack would be carried upwardly, thus removing from the rollers those portions of the film which have previously been bent thereover and bringing the adjacent pontions of the iilm into this bent position. The turning of the upper roller 21 as hereinbetore described is continued at regular intervals until the tilm is entirely developed.

The length of the rack commonly employed for this purpose is, for convenience lil() in handling, about four feet. It will be perceived that it is a very simple matter to obtain a movement of the film thereupon through a considerable distance, owing to the attachment of the ends of the film by means of elastic members 37 and 43, as hereinbefore described. As hereinbefore stated, the amount of surplus silver deposit upOn film due to bending of the film over the rollers is substantially the same whether or not the film is bent over a small'dianieter or large diameter, it will be understood that by employing a large diameter bend, the intensity of the silver deposit, may be made imperceptible owing to the distribution of the silver deposit of a very large area. By moving the film upon the rollers 2l of the development raelr shown in the drawing, I obtain the same effect as where a large diameter bar is employed. With my in.- vention this deposit may be distributed, if desired, over an area having a length of from two to four feet; therefore, making the presence of surplus silver deposit upon the film entirely imperceptible. For practical purposes the movement of the film need not he more than five or six inches, and therefore, where the diameter of the roller is substantially one and one-fourth inches one revolution thereof will acffomplish this desired movement. i

lifter the film has been developed, fixed,

and washed, and is ready for drying, the i rollers are forced all the way in against the action of the springs and pins placed through the holes 33 thus allowing the film 35 to rest loosely upon the rack so that the contraction thereof during drying will be unhampered.

I claim as my invention:

l. In a film developing rack, the combination ofi: a fiat frame; and a roller turnably mounted at each end of said frame over which a film strip may he wound upon said rack, each of said rollers comprising a shaft having collars held in spaced 4relationship thereupon by sleeves, and having a thumb wheel at each end thereof whereby said rollers may be rotated.

2. In a film developing rack, the combination of: afi-at frame; four bearing blocks, one mounted to slide in each corner of said frame; and two rollers, each being mounted to have each end turnl freely in one of said bearing blocks.

3. In a film developing rack, the combination of: a flat frame; four bearing blocks, one mounted to slide in each corner of said frame; elastic means for forcing said blocks outwardly in said frame; and two rollers, each being mounted to have each end turn freely in one of said bearing blocks.

4. In a film rack, the combination of: a frame; two roller-s mounted in opposite ends of said frame and adapted to have a film wound therearound; and means for securing the ends of said film so that it may be shifted on said rollers during development.

5. In a film rack, the combination of: a frame; two rollers mounted in opposite ends of said frame and adapted to have a film wound therearound; and means for securA ing the ends of said film so that it may be shifted on said rollers duringdevelop ment by turning one of said rollers.

6. In a film rack, the combination ofi a frame; two rollers mounted in opposite ends of said fra-me and adapted to have a film wound therearound; and elastic means for securing the ends of said film so that it may be shifted on said rollers during development.

In testimony whereof, I have hereunto set my hand at Los Angeles, California this 29th day of November 1922.

PERCY HIGGINSO'N.

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